80. RNAPII stimulates Topoisomerase I activity to promote efficient transcription
Cell, 2015, submitted
Negative and positive supercoiling is generated in “twin domains” in the template DNA respectively upstream and downstream of the translocating RNA polymerase II (RNAPII) . The accumulation of this torsional stress may facilitate or impede transcription [2-4]. By transiently breaking one strand, allowing axial rotation of the DNA and resealing the nick, Topoisomerase I (Top1) removes torsional stress . Besides the relaxation of the excess torsional stress generated during transcription elongation, Top1 has been also linked to early events during transcription initiation in vitro [6-9]. However the mechanisms coordinating Top1 activity with RNA synthesis throughout the different stages of the transcription cycle remain obscure. To interrogate the coupling between transcription and Top1 function, we generated high-resolution maps of both Top1 occupancy and activity in vivo. The genomic distribution patterns of Top1 and RNAPII were overlaid to reveal the dynamics of Top1 at transcribed loci. Here we show that a positive feedback loop develops between Top1 and RNAPII during pause-release. As the carboxyl-terminal domain (CTD) of RNAPII is progressively phosphorylated, Top1 is stimulated above its intrinsic relaxation rate. This activation is strongly dependent on the kinase activity of BRD4 that phosphorylates serine 2 of CTD  and participates in the regulation of the early events of transcription elongation. Our results demonstrate that phosphorylated RNAPII is required for maximal Top1 activity and activated Top1 is needed for efficient elongation. The coupling between the generation and removal of transcriptionally generated supercoils allows tuning of DNA topology to spur elongation while preserving the negative torsional stress at start sites that assists promoter melting . Considering the importance of Top1 inhibitors as anti-neoplastic agents  and the compelling interest in the anti-cancer activity of BRD4/BET-inhibitors [13, 14], we anticipate that our work will illuminate a new rational for drug discovery and new approaches for combinatorial treatments.
79. Chemical Genetic Screens Identify Candidate Drugs that Enhance and Mitigate Cellular Response to Immunotoxin Therapy
ACS Chem. Biol., 2015, submitted
78. Large Scale Pharmacological Profiling of 3D Tumor Models of Cancer Cells
J. Biomol. Screen., 2015, submitted
The discovery of chemotherapeutic agents for the treatment of cancer mostly uses cell proliferation assays on plastic surfaces, referred to as 2D monolayer growth assays. Compounds identified using 2D cell proliferation assays do often fail to advance during clinical development because these assays do not reproduce the cellular complexity of tumors and their microenvironment in vivo. The use of three dimensional (3D) cellular systems has been explored as more predictive in vitro tumor models for drug discovery. Small scale screens have shown that pharmacological responses tend to differ between 2D and 3D cancer cell growth models. However, the limited scope of screens using 3D models has not provided a clear delineation of the cellular pathways and processes that differentially regulate cell survival and death in the different in vitro tumor models. Here we sought to further understand the differences in pharmacological responses between cancer tumor cells grown in different conditions by profiling a large collection of 1912 chemotherapeutic agents. We compared pharmacological responses obtained from traditional 2D monolayer to the effects see in cells that were forming spheres and cells in preformed 3D spheres. The target annotation of the compound library screened enabled the identification of those key cellular pathways and processes that when modulated by drugs induced cell death in all growth conditions or selectively in the different cell growth models. In addition, we also show that many of the compounds targeting these key cellular functions can be combined to produce synergistic cytotoxic effects, which in many cases differ in the magnitude of the synergism depending on the cellular model and cell type. The results from this work provide a high throughput screening framework to profile the responses of drugs both as single agents and in pairwise combinations in the 3D sphere models of cancer cells.
77. Actinoramide A stereoisomer identified as potent anti-malarial from titration-based screening of marine natural product extracts
J. Nat. Prod., 2015, 78, 2411-2422
[ Abstract ]
[DOI 10.1021/acs.jnatprod.5b00489 ]
Methods to facilitate the rapid identification and prioritization of active natural product extracts derived from diverse marine microorganisms continues to evolve. Here we describe the discovery of potent anti-malarial activity from two marine Streptomyces sp. extracts identified from thousands tested using a pharmacologically-driven, quantitative high throughput screening approach. Seven compounds were isolated from two phylogenetically related marine Streptomyces species; Streptomyces ballenaensis collected from Costa Rica and Streptomyces bangulaensis collected from Papua New Guinea. Among them, actinoramides A and B belong to an unusually elaborated tetrapeptide series of natural products, including the actinoramides/padanamides. In addition, we characterized of series of new compounds, including actinoramides D, E, epi-actinoramide A and uvitamycins A and B, which are closely related biosynthetic congeners of the previously reported metabolites.
76. Synergy Maps: Exploring compound combinations using network-based visualization
J. Cheminf., 2015, 7,
[ Abstract ]
[ Link ]
The phenomenon of super-additivity of biological response to compounds applied jointly, termed synergy, has the potential to provide many therapeutic benefits. Therefore, high throughput screening of compound combinations has recently received a great deal of attention. Large compound libraries and the feasibility of all-pairs screening can easily generate large, information-rich datasets. Previously, these datasets have been visualized using either a heat-map or a network approach—however these visualizations only partially represent the information encoded in the dataset.
A new visualization technique for pairwise combination screening data, termed “Synergy Maps”, is presented. In a Synergy Map, information about the synergistic interactions of compounds is integrated with information about their properties (chemical structure, physicochemical properties, bioactivity profiles) to produce a single visualization. As a result the relationships between compound and combination properties may be investigated simultaneously, and thus may afford insight into the synergy observed in the screen. An interactive web app implementation, available at http://richlewis42.github.io/synergy-maps, has been developed for public use, which may find use in navigating and filtering larger scale combination datasets. This tool is applied to a recent all-pairs dataset of anti-malarials, tested against Plasmodium falciparum, and a preliminary analysis is given as an example, illustrating the disproportionate synergism of histone deacetylase inhibitors previously described in literature, as well as suggesting new hypotheses for future investigation.
Synergy Maps improve the state of the art in compound combination visualization, by simultaneously representing individual compound properties and their interactions. The web-based tool allows straightforward exploration of combination data, and easier identification of correlations between compound properties and interactions.
75. Aurora B Kinase is a Potent and Selective Target in MYCN-driven Neuroblastoma
Oncotarget, 2015, 6, 35247-35262
[ Abstract ]
[DOI 10.18632/oncotarget.6208 ]
Despite advances in multimodal treatment, neuroblastoma (NB) is often fatal for children with high-risk disease and many survivors need to cope with long-term side effects from high-dose chemotherapy and radiation. To identify new therapeutic targets, we performed an siRNA screen of the druggable genome combined with a small molecule screen of 465 compounds targeting 39 different mechanisms of actions in four NB cell lines. We identified 58 genes as targets, including AURKB, in at least one cell line. In the drug screen, aurora kinase inhibitors (nine molecules) and in particular the AURKB-selective compound, barasertib, were the most discriminatory with regard to sensitivity for MYCN-amplified cell lines. In an expanded panel of ten NB cell lines, those with MYCN-amplification and wild-type TP53 were the most sensitive to low nanomolar concentrations of barasertib. Inhibition of the AURKB kinase activity resulted in decreased phosphorylation of the known target, histone H3, and upregulation of TP53 in MYCN-amplified, TP53 wild-type cells. However, both wild-type and TP53 mutant MYCN-amplified cell lines arrested in G2/M phase upon AURKB inhibition. Additionally, barasertib induced endoreduplication and apoptosis. Treatment of MYCN- amplified/TP53 wild-type neuroblastoma xenografts resulted in profound growth inhibition and tumor regression. Therefore, aurora B kinase inhibition is highly effective in aggressive neuroblastoma and warrants further investigation in clinical trials.
74. High-throughput matrix screening identifies synergistic and antagonistic antimalarial drug combinations
Scientific Reports, 2015, 5,
73. MP68-17 Novel Intravesical Therapies Identified from High Throughput Screening
J. Urology, 2015, 193, e864-e865
INTRODUCTION AND OBJECTIVES
Since the approval of BCG, no new therapies have been introduced for bladder cancer. We utilized high throughput screening (HTS) to screen bladder cancer cell lines against oncology drugs. From these, we identified eight novel drugs as potential intravesical agents.
We screened 8 bladder cancer cell lines against 1,912 oncology drugs using a 48 hr cell proliferation assay with an ATP?based readout (CellTiterGlo) to determine activity and potency of compounds in a dose response manner. From the most active compounds, we identified favorable compounds for intravesical therapy: molecular size of 700-1000 g/mol and lipophilicity measured by Topographical Polar Surface Area < 90 (TPSA). These compounds were analyzed for cytotoxicity in an MTS cell proliferation assay to determine the IC50s of these drugs in 6 cell lines (3 not used in the original screen).
The initial screen identified 95 compounds active in 8 cell lines. The top 50 compounds were further analyzed for molecular size of 700-1000 g/mol and TPSA<90. This identified mitomycin C and 8 novel compounds (Table 1) that were further tested by MTS in 6 bladder cancer cell lines. The top 3 agents were: YM-155, flavopiridol, and bardoxolone methyl with IC 50s that ranged from 1-30 nm, 0.2-12 nm, and 0.8-2 nm respectively in the 6 cell lines. The MTS curves are included in Figures 1-3.
HTS is an efficient way to elicit novel targets and therapies for cancer. We identified novel candidates for intravesical therapy and are currently elucidating the mechanism of action of these drugs.
72. Selective targeting of JAK/STAT signaling is potentiated by Bcl-xL blockade in IL-2-dependent adult T-cell leukemia
Proc. Nat. Acad. Sci., 2015, 112, 12480-12485
[ Abstract ]
[DOI 10.1073/pnas.1516208112 ]
Adult T-cell leukemia (ATL) develops in individuals infected with human T-cell lymphotropic virus-1 (HTLV-1). Presently there is no curative therapy for ATL. HTLV-1-encoded protein Tax up-regulates Bcl-xL expression and activates interleukin-2 (IL-2), IL-9, and IL-15 autocrine/paracrine systems resulting in amplified JAK/STAT signaling. Inhibition of JAK signaling reduces cytokine-dependent ex vivo proliferation of PBMCs from ATL patients in smoldering/chronic stages. Currently, two JAK inhibitors are approved for human use. In this study, we examined activity of multiple JAK inhibitors in ATL cell lines. The selective JAK inhibitor ruxolitinib was examined in a high-throughput matrix screen combined with >450 potential therapeutic agents and Bcl-2/Bcl-xL inhibitor navitoclax was identified as a strong candidate for multicomponent therapy. The combination was noted to strongly activate BAX, effect mitochondrial depolarization and increase caspase 3/7 activity that lead to PARP and Mcl-1 cleavage. Ruxolitinib and navitoclax independently demonstrated modest antitumor efficacy while the combination dramatically lowered tumor burden and prolonged survival in an ATL murine model. This combination strongly blocked ex vivo proliferation of five ATL patients’ PBMCs. These studies provide support for a therapeutic trial in patients with smoldering/chronic ATL using a drug combination that inhibits JAK signaling and anti-apoptotic protein Bcl-xL.
71. A whole genome RNAi screen highlights components of the ER/Golgi as a source of resistance to immunotoxin-mediated cytotoxicity
Proc. Nat. Acad. Sci., 2015, 112, 1135-1142
[ Abstract ]
[DOI 10.1073/pnas.1501958112 ]
Immunotoxins (antibody-toxin fusion proteins) target surface antigens on cancer cells and kill these cells via toxin-mediated inhibition of protein synthesis. To identify genes controlling this process, an RNAi whole-genome screen (? 22,000 genes at three siRNAs per gene) was conducted via monitoring the cytotoxicity of the mesothelin-directed immunotoxin SS1P. SS1P, a Pseudomonas exotoxin-based immunotoxin, was chosen because it is now in clinical trials and has produced objective tumor regressions in patients. High and low concentrations of SS1P were chosen to allow for the identification of both mitigators and sensitizers. As expected, silencing known essential genes in the immunotoxin pathway, such as mesothelin, furin, KDEL receptor 2, or members of the diphthamide pathway, protected cells. Of greater interest was the observation that many RNAi targets increased immunotoxin sensitivity, indicating that these gene products normally contribute to inefficiencies in the killing pathway. Of the top sensitizers, many genes encode proteins that locate to either the endoplasmic reticulum (ER) or Golgi and are annotated as part of the secretory system. Genes related to the ER-associated degradation system were not among high-ranking mitigator or sensitizer candidates. However, the p97 inhibitor eeyarestatin 1 enhanced immunotoxin killing. Our results highlight potential targets for chemical intervention that could increase immunotoxin killing of cancer cells and enhance our understanding of toxin trafficking.
70. Novel Phenotypic Outcomes Identified for a Public Collection of Approved Drugs from a Publicly Accessible Panel of Assays
PLoS ONE, 2015, 10, e0130796 EP –
[ Abstract ]
[DOI 10.1371%2Fjournal.pone.0130796 ]
Phenotypic assays have a proven track record for generating leads that become first-in-class therapies. Whole cell assays that inform on a phenotype or mechanism also possess great potential in drug repositioning studies by illuminating new activities for the existing pharmacopeia. The National Center for Advancing Translational Sciences (NCATS) pharmaceutical collection (NPC) is the largest reported collection of approved small molecule therapeutics that is available for screening in a high-throughput setting. Via a wide-ranging collaborative effort, this library was analyzed in the Open Innovation Drug Discovery (OIDD) phenotypic assay modules publicly offered by Lilly. The results of these tests are publically available online at www.ncats.nih.gov/expertise/preclinical/pd2 and via the PubChem Database (https://pubchem.ncbi.nlm.nih.gov/) (AID 1117321). Phenotypic outcomes for numerous drugs were confirmed, including sulfonylureas as insulin secretagogues and the anti-angiogenesis actions of multikinase inhibitors sorafenib, axitinib and pazopanib. Several novel outcomes were also noted including the Wnt potentiating activities of rotenone and the antifolate class of drugs, and the anti-angiogenic activity of cetaben.
69. Chemogenomic profiling of endogenous PARK2 expression using a genome-edited coincidence reporter
ACS Chem. Biol., 2015, 10, 1188-1197
[ Abstract ]
[DOI 10.1021/cb5010417 ]
Parkin, an E3 ubiquitin ligase, is a central mediator of mitochondrial quality control and is linked to familial forms of Parkinson’s disease (PD). Removal of dysfunctional mitochondria from the cell by Parkin is thought to be neuroprotective, and pharmacologically increasing Parkin levels may be a novel therapeutic approach. We used genome-editing to integrate a coincidence reporter into the PARK2 gene locus of a neuroblastoma-derived cell line and developed a quantitative high-throughput screening (qHTS) assay capable of accurately detecting subtle compound-mediated increases in endogenous PARK2 expression. Interrogation of a chemogenomic library revealed diverse chemical classes that up-regulate the PARK2 transcript, including epigenetic agents, drugs controlling cholesterol biosynthesis, and JNK inhibitors. Use of the coincidence reporter eliminated wasted time pursuing reporter-biased false positives accounting for ?2/3 of the actives and, coupled with titration-based screening, greatly improves the efficiency of compound selection. This approach represents a strategy to revitalize reporter-gene assays for drug discovery.
68. A high-throughput assay for small molecule destabilizers of the KRAS oncoprotein
PLoS One, 2014, 9, e103836
67. Genome editing-enabled HTS assays expand drug target pathways for Charcot-Marie-Tooth disease
ACS Chem. Biol., 2014, 9, 2594-2602
[ Abstract ]
[DOI 10.1021/cb5005492 ]
Copy number variation resulting in excess PMP22 protein causes the peripheral neuropathy, Charcot-Marie-Tooth Disease, type 1A. To broadly interrogate chemically sensitive transcriptional pathways controlling PMP22 protein level, we used the targeting precision of TALEN-mediated genome editing to embed reporters within the genetic locus harboring the Peripheral Myelin Protein 22 (Pmp22) gene. Using a Schwann cell line with constitutively high endogenous levels of Pmp22 we obtained monoallelic insertion of secreted bioluminescent reporters with sufficient signal to enable a 1536-well assay. Our findings from the quantitative high-throughput screening (qHTS) of several thousand drugs and clinically investigated compounds using this assay design both overlapped and expanded results from a previous assay using a randomly inserted reporter gene controlled by a single regulatory element of the Pmp22 gene. A key difference was the identification of a kinase-controlled inhibitory pathway of Pmp22 transcription revealed by the activity of the Protein kinase C (PKC)-modulator bryostatin
66. ATR inhibitors VE-821 and VX-970 sensitize cancer cells to topoisomerase I inhibitors by disabling DNA replication initiation and fork elongation responses
Cancer. Res., 2014, 74, 6968-6979
[ Abstract ]
[DOI 10.1158/0008-5472.CAN-13-3369 ]
Camptothecin, a specific topoisomerase I inhibitor is a potent anticancer drug, especially against solid tumors. This agent produces well-characterized double-strand breaks upon collision of replication forks with topoisomerase I cleavage complexes. In an attempt to improve its efficacy, we conducted a synthetic lethal siRNA screening using a library that targets nearly 7000 human genes. Depletion of ATR, the main transducer of replication stress-induced DNA damage response exacerbated cytotoxic response to both camptothecin and the indenoisoquinoline LMP-400, a novel class of topoisomerase inhibitors in clinical trial. Inhibition of ATR by the recently developed specific inhibitor VE-821 induced synergistic antiproliferative activity when combined with either topoisomerase inhibitor. Cytotoxicity induced by the combination with LMP-400 was greater than with camptothecin. Using single cell analysis and DNA fiber spread, we show that VE-821 abrogated the S-phase checkpoint, restored origin firing and replication fork progression. Moreover, the combination of a topoisomerase inhibitor with VE-821 inhibited the phosphorylation of ATR and ATR-mediated Chk1 phosphorylation but strongly induced ?H2AX. Single cell analysis revealed that ?H2AX pattern changed overtime from well-defined focus to a pan-nuclear staining. The change in ?H2AX pattern can be useful as a predictive biomarker to evaluate the efficacy of therapy. The key implication of our work is the clinical rationale it provides to evaluate the combination of indenoisoquinoline topoisomerase I inhibitors with ATR inhibitors.
65. On the Validity versus Utility of Activity Landscapes: Are All Activity Cliffs Statistically Significant?
J. Cheminf., 2014, 6,
[ Abstract ]
[DOI 10.1186/1758-2946-6-11 ]
Most work on the topic of activity landscapes has focused on their quantitative description and visual representation, with the aim of aiding navigation of SAR. Recent developments have addressed applications such as quantifying the proportion of activity cliffs, investigating the predictive abilities of activity landscape methods and so on. However, all these publications have worked under the assumption that the activity landscape models are “real” (i.e., statistically significant).
The current study addresses for the first time, in a quantitative manner, the significance of a landscape or individual cliffs in the landscape. In particular, we question whether the activity landscape derived from observed (experimental) activity data is different from a randomly generated landscape. To address this we used the SALI measure with six different data sets tested against one or more molecular targets. We also assessed the significance of the landscapes for single and multiple representations.
We find that non-random landscapes are data set and molecular representation dependent. For the data sets and representations used in this work, our results suggest that not all representations lead to non-random landscapes. This indicates that not all molecular representations should be used to a) interpret the SAR and b) combined to generate consensus models. Our results suggest that significance testing of activity landscape models and in particular, activity cliffs, is key, prior to the use of such models
64. BioAssay Research Database (BARD): Chemical biology and probe-development enabled by structured metadata and result types
Nucl. Acids Res., 2014, 43, D1163-D1170
[ Abstract ]
[DOI 10.1093/nar/gku1244 ]
BARD, the BioAssay Research Database (https://bard.nih.gov/) is a public database and suite of tools developed to provide access to bioassay data produced by the NIH Molecular Libraries Program (MLP). Data from 631 MLP projects were migrated to a new structured vocabulary designed to capture bioassay data in a formalized manner, with particular emphasis placed on the description of assay protocols. New data can be submitted to BARD with a user-friendly set of tools that assist in the creation of appropriately formatted datasets and assay definitions. Data published through the BARD application program interface (API) can be accessed by researchers using web-based query tools or a desktop client. Third-party developers wishing to create new tools can use the API to produce stand-alone tools or new plug-ins that can be integrated into BARD. The entire BARD suite of tools therefore supports three classes of researcher: those who wish to publish data, those who wish to mine data for testable hypotheses, and those in the developer community who wish to build tools that leverage this carefully curated chemical biology resource.
63. An overview of the challenges in designing, integrating, and delivering BARD: A public chemical-biology resource and query portal for multiple organizations, locations, and disciplines
J. Biomol. Screen., 2014, 19, 614-627
[ Abstract ]
[DOI 10.1177/1087057113517139 ]
Recent industry-academic partnerships involve collaboration among disciplines, locations, and organizations using publicly funded “open-access” and proprietary commercial data sources. These require the effective integration of chemical and biological information from diverse data sources, which presents key informatics, personnel, and organizational challenges. The BioAssay Research Database (BARD) was conceived to address these challenges and serve as a community-wide resource and intuitive web portal for public-sector chemical-biology data. Its initial focus is to enable scientists to more effectively use the National Institutes of Health Roadmap Molecular Libraries Program (MLP) data generated from the 3-year pilot and 6-year production phases of the Molecular Libraries Probe Production Centers Network (MLPCN), which is currently in its final year. BARD evolves the current data standards through structured assay and result annotations that leverage BioAssay Ontology and other industry-standard ontologies, and a core hierarchy of assay definition terms and data standards defined specifically for small-molecule assay data. We initially focused on migrating the highest-value MLP data into BARD and bringing it up to this new standard. We review the technical and organizational challenges overcome by the interdisciplinary BARD team, veterans of public- and private-sector data-integration projects, who are collaborating to describe (functional specifications), design (technical specifications), and implement this next-generation software solution.
62. Blockade of oncogenic I$\kappa$B kinase activity in ABC DLBCL by small molecule BET protein inhibitors
Proc. Natl. Acad. Sci., 2014, 111, 11365-11370
[ Abstract ]
[DOI 10.1073/pnas.1411701111 ]
The activated B-cell–like (ABC) subtype of diffuse large B-cell lymphoma (DLBCL) is an aggressive cancer that can only be cured in roughly 40% of cases. These malignant cells rely on the NF-?B signaling pathway for survival. Here, we report that genetic or pharmacologic interference with bromodomain and extraterminal domain (BET) chromatin proteins reduces NF-?B activity and ABC DLBCL viability. Unexpectedly, the mechanism involves inhibition of I?B kinase, the key cytoplasmic enzyme that activates the NF-?B pathway. The NF-?B pathway in ABC DLBCL is activated by B-cell receptor signaling, which can be blocked by the BTK kinase inhibitor ibrutinib. BET inhibitors synergized with ibrutinib to decrease growth of ABC DLBCL tumors in mouse models. BET inhibitors should be evaluated in ABC DLBCL clinical trials.
61. High-throughput combinatorial screening identifies drugs that cooperate with Ibrutinib to kill ABC Diffuse Large B Cell Lymphoma cells
Proc. Nat. Acad. Sci., 2014, 111, 2349-2354
[ Abstract ]
[DOI 10.1073/pnas.1311846111 ]
The clinical development of drug combinations is typically achieved through trial-and-error or via insight gained through a detailed molecular understanding of dysregulated signaling pathways in a specific cancer type. Unbiased small molecule combination (matrix) screening represents a high-throughput means to explore hundreds and even thousands of drug-drug pairs for potential investigation and translation. Here, we describe a high-throughput screening platform capable of testing compounds in pair-wise matrix blocks for the rapid and systematic identification of synergistic, additive and antagonistic drug combinations. Experimental details are provided for this platform including the software codes for a novel compound dispensing methodology and a web-based data interface. We utilize this platform to conduct a combination screen to determine drug-drug combinations for the Bruton’s tyrosine kinase (BTK) inhibitor ibrutinib (PCI-32765) against the activated B-cell-like subtype of diffuse large B-cell lymphoma (ABC DLBCL). The results of this study highlight a striking level of synergy/additivity between ibrutinib and inhibitors of the PI3K-AKT-mTOR signaling cascade including the PI3K inhibitor BKM-120, the AKT inhibitor MK-2206 and the mTOR inhibitor everolimus. We also found that ibrutinib had strong combination responses with chemotherapeutic components of the current standards of care for DLBCL including doxorubicin, gemcitabine and docetaxel.
60. Inhibition of Ceramide Metabolism Sensitizes Human Leukemia Cells to Inhibition of BCL2-like Proteins
PLoS One, 2013, 8, e54525
[ Abstract ]
[ Link ]
The identification of novel combinations of effective cancer drugs is required for the successful treatment of cancer patients for a number of reasons. First, many “cancer specific” therapeutics display detrimental patient side-effects and second, there are almost no examples of single agent therapeutics that lead to cures. One strategy to decrease both the effective dose of individual drugs and the potential for therapeutic resistance is to combine drugs that regulate independent pathways that converge on cell death. BCL2-like family members are key proteins that regulate apoptosis. We conducted a screen to identify drugs that could be combined with an inhibitor of anti-apoptotic BCL2-like proteins, ABT-263, to kill human leukemia cells lines. We found that the combination of D,L-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP) hydrochloride, an inhibitor of glucosylceramide synthase, potently synergized with ABT-263 in the killing of multiple human leukemia cell lines. Treatment of cells with PDMP and ABT-263 led to dramatic elevation of two pro-apoptotic sphingolipids, namely ceramide and sphingosine. Furthermore, treatment of cells with the sphingosine kinase inhibitor, SKi-II, also dramatically synergized with ABT-263 to kill leukemia cells and similarly increased ceramides and sphingosine. Data suggest that synergism with ABT-263 requires accumulation of ceramides and sphingosine, as AMP-deoxynojirimycin, (an inhibitor of the glycosphingolipid pathway) did not elevate ceramides or sphingosine and importantly did not sensitize cells to ABT-263 treatment. Taken together, our data suggest that combining inhibitors of anti-apoptotic BCL2-like proteins with drugs that alter the balance of bioactive sphingolipids will be a powerful combination for the treatment of human cancers.
59. Profile of the GSK published protein kinase inhibitor set across ATP-dependent and-independent luciferases: Implications for reporter-gene assays
58. Genome-wide high-content RNAi screens identify regulators of Parkin upstream of mitophagy
Nature, 2013, 504, 291-295
[ Abstract ]
[DOI 10.1038/nature12748 ]
An increasing body of evidence points to mitochondrial dysfunction as a contributor to the molecular pathogenesis of neurodegenerative diseases such as Parkinson’s. Recent studies of the PD-associated genes PINK1 and Parkin suggest that they may act in a quality control pathway preventing the accumulation of dysfunctional mitochondria. Here we elucidate regulators impacting Parkin translocation to damaged mitochondria with genome-wide siRNA screens coupled to high-content microscopy. Screening yielded gene candidates involved in diverse cellular processes that were subsequently validated in confirmatory assays. This led to characterization of TOMM7, as essential for stabilizing Pink1 on the outer mitochondrial membrane following mitochondrial damage. Additionally, we discovered HSPA1L (HSP70 family member) and BAG4 play mutually opposing roles in the regulation of Parkin translocation. The screens also revealed that SIAH3, found to localize to mitochondria, inhibits Pink1 accumulation after mitochondrial insult, reducing Parkin translocation. Overall, our screens provide a rich resource to understand mitochondrial quality control.
57. What are we “tweeting” About Obesity? Mapping Tweets with Topic Modeling and Geographic Information System
Cartography and GIS, 2013, 4, 90-102
[ Abstract ]
[DOI 10.1080/15230406.2013.776210 ]
Public health related tweets are difficult to identify in large conversational datasets like Twitter.com. Even more challenging is the visualization and analyses of the spatial patterns encoded in tweets. This study has the following objectives: how can topic modeling be used to identify relevant public health topics such as obesity on Twitter.com? What are the common obesity related themes? What is the spatial pattern of the themes? What are the research challenges of using large conversational datasets from social networking sites? Obesity is chosen as a test theme to demonstrate the effectiveness of topic modeling using Latent Dirichlet Allocation (LDA) and spatial analysis using Geographic Information System (GIS). The dataset is constructed from tweets (originating from the United States) extracted from Twitter.com on obesity-related queries. Examples of such queries are `food deserts’, `fast food’, and `childhood obesity’. The tweets are also georeferenced and time stamped. Three cohesive and meaningful themes such as `childhood obesity and schools’, `obesity prevention’, and `obesity and food habits’ are extracted from the LDA model. The GIS analysis of the extracted themes show distinct spatial pattern between rural and urban areas, northern and southern states, and between coasts and inland states. Further, relating the themes with ancillary datasets such as US census and locations of fast food restaurants based upon the location of the tweets in a GIS environment opened new avenues for spatial analyses and mapping. Therefore the techniques used in this study provide a possible toolset for computational social scientists in general, and health researchers in specific, to better understand health problems from large conversational datasets.
56. RNAi Screen Reveals Candidate miRNAs Associated with the NF-kappaB Pathway
FASEB J., 2013, 27, 780-781
55. Targeting IRAK1 as a Novel Therapeutic Approach for Myelodysplastic Syndrome
Cancer Cell, 2013, 24, 90-104
[ Abstract ]
[DOI 10.1016/j.ccr.2013.05.006 ]
Myelodysplastic syndromes (MDSs) arise from a defective hematopoietic stem/progenitor cell. Consequently, there is an urgent need to develop targeted therapies capable of eliminating the MDS-initiating clones. We identified that IRAK1, an immune-modulating kinase, is overexpressed and hyperactivated in MDSs. MDS clones treated with a small molecule IRAK1 inhibitor (IRAK1/4-Inh) exhibited impaired expansion and increased apoptosis, which coincided with TRAF6/NF-?B inhibition. Suppression of IRAK1, either by RNAi or with IRAK1/4-Inh, is detrimental to MDS cells, while sparing normal CD34+ cells. Based on an integrative gene expression analysis, we combined IRAK1 and BCL2 inhibitors and found that cotreatment more effectively eliminated MDS clones. In summary, these findings implicate IRAK1 as a drugable target in MDSs.
54. Large-Scale Screening Identifies a Novel microRNA, miR-15a-3p, which Induces Apoptosis in Human Cancer Cell Lines
RNAi Biology, 2013, 10, 1-14
[ Abstract ]
[DOI 10.4161/rna.23339 ]
MicroRNAs (miRNAs) have been found to be involved in cancer initiation, progression and metastasis and, as such, have
been suggested as tools for cancer detection and therapy. In this work, a large-scale screening of the complete miRNA
mimics library demonstrated that hsa-miR-15a-3p had a pro-apoptotic role in the following human cancer cells: heLa,
Aspc-1, MDA-MB-231, KB3, Me180, hcT-116 and A549. MiR-15a-3p is a novel member of the pro-apoptotic miRNA cluster,
miR-15a/16, which was found to activate caspase-3/7 and to cause viability loss in B/cMBA.Ov cells during preliminary
screening. subsequent microarrays and bioinformatics analyses identified the following four anti-apoptotic genes: bcl2l1,
naip5, fgfr2 and mybl2 as possible targets for the mmu-miR-15a-3p in B/cMBA.Ov cells. Follow-up studies confirmed the
pro-apoptotic role of hsa-miR-15a-3p in human cells by its ability to activate caspase-3/7, to reduce cell viability and to
inhibit the expression of bcl2l1 (bcl-x
) in heLa and Aspc-1 cells. MiR-15-3p was also found to reduce viability in heK293,
MDA-MB-231, KB3, Me180, hcT-116 and A549 cell lines and, therefore, may be considered for apoptosis modulating
therapies in cancers associated with high Bcl-x
expression (cervical, pancreatic, breast, lung and colorectal carcinomas).
The capability of hsa-miR-15a-3p to induce apoptosis in these carcinomas may be dependent on the levels of Bcl-x
expression. The use of endogenous inhibitors of bcl-x
and other anti-apoptotic genes such as hsa-miR-15a-3p may
provide improved options for apoptosis-modulating therapies in cancer treatment compared with the use of artificial
53. Cisplatin Sensitivity Mediated by WEE1 and CHK1 is Mediated by miR-155 and the miR-15 Family
Cancer Cell, 2012, 72, 5945-5955
52. Identification of Mammalian Protein Quality Control Factors by High-throughput Cellular Imaging
PLoS One, 2012, 7, e31684
[ Abstract ]
[DOI 10.1371/journal.pone.0031684 ]
Protein Quality Control (PQC) pathways are essential to maintain the equilibrium between protein folding and the clearance of misfolded proteins. In order to discover novel human PQC factors, we developed a high-content, high-throughput cell-based assay to assess PQC activity. The assay is based on a fluorescently tagged, temperature sensitive PQC substrate and measures its degradation relative to a temperature insensitive internal control. In a targeted screen of 1591 siRNA genes involved in the Ubiquitin-Proteasome System (UPS) we identified 25 of the 33 genes encoding for 26S proteasome subunits and discovered several novel PQC factors. An unbiased genome-wide siRNA screen revealed the protein translation machinery, and in particular the EIF3 translation initiation complex, as a novel key modulator of misfolded protein stability. These results represent a comprehensive unbiased survey of human PQC components and establish an experimental tool for the discovery of genes that are required for the degradation of misfolded proteins under conditions of proteotoxic stress.
51. High-Throughput Screening For Genes That Prevent Excess DNA Replication In Human Cells And For Molecules That Inhibit Them
Methods, 2012, 57, 234-248
[ Abstract ]
[DOI 10.1016/j.ymeth.2012.03.031 ]
High-throughput screening (HTS) provides a rapid and comprehensive approach to identifying compounds that target specific biological processes as well as genes that are essential to those processes. Here we describe a HTS assay for small molecules that induce either DNA re-replication or endoreduplication (i.e. excess DNA replication) selectively in cells derived from human cancers. Such molecules will be useful not only to investigate cell division and differentiation, but they may provide a novel approach to cancer chemotherapy. Since induction of DNA re-replication results in apoptosis, compounds that selectively induce DNA re-replication in cancer cells without doing so in normal cells could kill cancers in vivo without preventing normal cell proliferation. Furthermore, the same HTS assay can be adapted to screen siRNA molecules to identify genes whose products restrict genome duplication to once per cell division. Some of these genes might regulate the formation of terminally differentiated polyploid cells during normal human development, whereas others will prevent DNA re-replication during each cell division. Based on previous studies, we anticipate that one or more of the latter genes will prove to be essential for proliferation of cancer cells but not for normal cells, since many cancer cells are deficient in mechanisms that maintain genome stability.
50. Cheminformatics, the Computer Science of Chemical Discovery Turning Open Source
Comm. ACM, 2012, 55, 65-75
[ Abstract ]
[DOI 10.1145/2366316.2366334 ]
One of the most prominent success stories in all the sciences over
the last decade has been the advance of bioinformatics: the
interdisciplinary collaboration between computer scientists and
molecular biologists that led to the
sequencing of the human genome and other accomplishments. However,
few computer scientists are familiar
with a related discipline: cheminformatics, the use of computers to
represent the structures of small molecules and analyze their
properties. Cheminformatics has wide applicability, from the
drug discovery to agrochemicals and materials design.
While researchers in both academia and industry have made important
contributions to this field for decades, new and
exciting collaborative opportunities have arisen from an “opening” of
data and software as an effect of changing mindsets,
and chemists volunteering time
for “Open Science”. Researchers have gained access to
freely available open source software packages and open databases of tens of millions
of chemicals, allowing academic chemists to confront a variety of
algorithmic problems whose solutions will be critical to address
current challenges ranging from
determining the behavior of small molecules in biological pathways,
to finding therapies for rare and neglected diseases.
In this paper, we give a broad overview of the field of cheminformatics with a
focus on open questions and challenges.
49. Exploring Uncharted Territories — Predicting Activty Cliffs in Structure-Activity Landscapes
J. Chem. Inf. Model., 2012, 52, 2181-2191
[ Abstract ]
[DOI 10.1021/ci300047k ]
The notion of activity cliffs is an intuitive approach to characterizing structural features that
play a key role in modulating biological activity of a molecule. A variety of methods have been
described to quantitatively characterize activity cliffs, such as SALI and SARI. However, these
methods are primarily retrospective in nature; highlighting cliffs that are already present in the
dataset. The current study focuses on employing a pairwise characterization of a dataset to train
a model to predict whether a new molecule will exhibit an activity cliff with one or more members
of the dataset. The approach is based on predicting a value for pairs of objects rather than the
individual objects themselves (and thus allows for robust models even for small structure-activity
relationship datasets). We extracted structure-activity data for several ChEMBL assays and
developed random forest models to predict SALI values, from pairwise combinations of molecular
descriptors. The models exhibited reasonable RMSE’s though, surprisingly, performance on the more
significant cliffs tended to be better than on the lesser ones. While the models do not exhibit
very high levels of accuracy, our results indicate that they are able to prioritize molecules in
terms of their ability to activity cliffs, thus serving as a tool to prospectively identify
48. Dealing with the Data Deluge: Handling the Multitude of Chemical Biology Data Sources
Curr. Protocols Chem. Biol., 2012, 4, 193-209
[ Abstract ]
[DOI 10.1002/9780470559277.ch110262 ]
Over the last 20 years, there has been an explosion in the amount and type of biological and chemical data that has been made publicly available in a variety of online databases. While this means that vast amounts of information can be found online, there is no guarantee that it can be found easily (or at all). A scientist searching for a specific piece of information is faced with a daunting task—many databases have overlapping content, use their own identifiers and, in some cases, have arcane and unintuitive user interfaces. In this overview, a variety of well-known data sources for chemical and biological information are highlighted, focusing on those most useful for chemical biology research. The issue of using data from multiple sources and the associated problems such as identifier disambiguation are highlighted. A brief discussion is then provided on Tripod, a recently developed platform that supports the integration of arbitrary data sources, providing users a simple interface to search across a federated collection of resources.
47. A Furoxan-Amodiaquine Hybrid as a Potential Therapeutic for Three Parasitic Diseases
Med. Chem. Comm., 2012, 3, 1505-1511
[ Abstract ]
[DOI 10.1039/C2MD20238G ]
Parasitic diseases continue to have a devastating impact on human populations worldwide. Lack of effective treatments, the high cost of existing ones, and frequent emergence of resistance to these agents provide a strong argument for the development of novel therapies. Here we report the results of a hybrid approach designed to obtain a dual acting molecule that would demonstrate activity against a variety of parasitic targets. The antimalarial drug amodiaquine has been covalently joined with a nitric oxide-releasing furoxan to achieve multiple mechanisms of action. Using in vitro and ex vivo assays, the hybrid molecule shows activity against three parasites — Plasmodium falciparum, Schistosoma mansoni, and Ancylostoma ceylanicum.
46. Diversity-Oriented Synthesis Yields a Novel Lead for the Treatment of Malaria
ACS Med. Chem. Lett., 2012, 3, 112-117
[ Abstract ]
[ Link ]
Here, we describe the discovery of a novel antimalarial agent using phenotypic screening of Plasmodium falciparum asexual blood-stage parasites. Screening a novel compound collection created using diversity-oriented synthesis (DOS) led to the initial hit. Structure–activity relationships guided the synthesis of compounds having improved potency and water solubility, yielding a subnanomolar inhibitor of parasite asexual blood-stage growth. Optimized compound 27 has an excellent off-target activity profile in erythrocyte lysis and HepG2 assays and is stable in human plasma. This compound is available via the molecular libraries probe production centers network (MLPCN) and is designated ML238.
45. Exploiting Synthetic Lethality for the Therapy of ABC Diffuse Large B Cell Lymphoma
Cancer Cell, 2012, 21, 723-737
44. Exploring Structure-Activity Data Using the Landscape Paradigm
WIREs Comput. Mol. Sci., 2012, 2, 829-841
[ Abstract ]
[DOI 10.1002/wcms.1087 ]
In this article, we present an overview of the origin and applications of the activity landscape view of structure–activity relationship (SAR) data as conceived by Shanmugasundaram and Maggiora. Within this landscape, different regions exemplify different aspects of SAR trends—ranging from smoothly varying trends to discontinuous trends (also termed activity cliffs). We discuss the various definitions of landscapes and cliffs that have been proposed as well as different approaches to the numerical quantification of a landscape. We then highlight some of the landscape visualization approaches that have been developed, followed by a review of the various applications of activity landscapes and cliffs to topics in medicinal chemistry and SAR analysis.
43. A 1536-well Quantitative High Throughput Screen to Identify Compounds Targeting Cancer Stem Cells
J. Biomol. Screen., 2012, 17, 1231-1242
[ Abstract ]
[DOI 10.1177/1087057112458152 ]
Tumor cell subpopulations called cancer stem cells (CSCs) or tumor-initiating cells (TICs) have self-renewal potential and are thought to drive metastasis and tumor formation. Data suggest that these cells are resistant to current chemotherapy and radiation therapy treatments, leading to cancer recurrence. Therefore, finding new drugs and/or drug combinations that cause death of both the differentiated tumor cells as well as CSC populations is a critical unmet medical need. Here, we describe how cancer-derived CSCs are generated from cancer cell lines using stem cell growth media and nonadherent conditions in quantities that enable high-throughput screening (HTS). A cell growth assay in a 1536-well microplate format was developed with these CSCs and used to screen a focused collection of oncology drugs and clinical candidates to find compounds that are cytotoxic against these highly aggressive cells. A hit selection process that included potency and efficacy measurements during the primary screen allowed us to efficiently identify compounds with potent cytotoxic effects against spheroid-derived CSCs. Overall, this research demonstrates one of the first miniaturized HTS assays using CSCs. The procedures described here should enable further testing of the effect of compounds on CSCs and help determine which pathways need to be targeted to kill them.
42. A Survey of Quantitative Descriptions of Molecular Structure
Curr. Topics Med. Chem., 2012, 12, 1946-1956
[ Abstract ]
[DOI 10.2174/156802612804910278 ]
Numerical characterization of molecular structure is a first step in
many computational analysis of chemical structure data. These numerical
representations, termed descriptors, come in many forms, ranging
from simple atom counts and invariants of the molecular graph to
distribution of properties, such as charge, across a molecular
surface. In this article we first present a broad categorization of
descriptors and then describe applications and toolkits that can be
employed to evaluate them. We highlight a number of issues
surrounding molecular descriptor calculations such as versioning and
reproducibility and describe how some toolkits have attempted to
address these problems.
41. Genome-Wide RNAi Screen For Lysosomal Storage Disorders
Molecular Genetics and Metabolism, 2012, 105, S63
40. Chemical Genomic Profiling for Antimalarial Therapies, Response Signatures, and Molecular Targets
Science, 2011, 333, 724-729
[ Abstract ]
[DOI 10.1021/ci200081k ]
Malaria remains a devastating disease largely because of widespread drug resistance. New drugs and a better understanding of the mechanisms of drug action and resistance are essential for fulfilling the promise of eradicating malaria. Using high-throughput chemical screening and genome-wide association analysis, we identified 32 highly active compounds and genetic loci associated with differential chemical phenotypes (DCPs), defined as greater than or equal to fivefold differences in half-maximum inhibitor concentration (IC(50)) between parasite lines. Chromosomal loci associated with 49 DCPs were confirmed by linkage analysis and tests of genetically modified parasites, including three genes that were linked to 96\% of the DCPs. Drugs whose responses mapped to wild-type or mutant pfcrt alleles were tested in combination in vitro and in vivo, which yielded promising new leads for antimalarial treatments.
39. KNIME workflow to assess PAINS filters in SMARTS format. Comparison of RDKit and Indigo cheminformatics libraries
Mol. Inf., 2011, 30, 847-850
38. Open Data, Open Source and Open Standards in Chemistry: The Blue Obelisk Five Years On
J. Cheminf., 2011, 3,
[ Abstract ]
[DOI 10.1186/1758-2946-3-37 ]
The Blue Obelisk movement was established in 2005 as a response to the lack of Open Data, Open Standards and Open Source (ODOSOS) in chemistry. It aims to make it easier to carry out chemistry research by promoting interoperability between chemistry software, encouraging cooperation between Open Source developers, and developing community resources and Open Standards.
This contribution looks back on the work carried out by the Blue Obelisk in the past 5 years and surveys progress and remaining challenges in the areas of Open Data, Open Standards, and Open Source in chemistry.
We show that the Blue Obelisk has been very successful in bringing together researchers and developers with common interests in ODOSOS, leading to development of many useful resources freely available to the chemistry community.
37. Exploratory analysis of kinetic solubility measurements of a small molecule library
Bioorg. Med. Chem., 2011, 19, 4127-4134
[ Abstract ]
[DOI 10.1016/j.bmc.2011.05.005 ]
Kinetic solubility measurements using prototypical assay buffer conditions are presented for a ?58,000 member library of small molecules. Analyses of the data based upon physical and calculated properties of each individual molecule were performed and resulting trends were considered in the context of commonly held opinions of how physicochemical properties influence aqueous solubility. We further analyze the data using a decision tree model for solubility prediction and via a multi-dimensional assessment of physicochemical relationships to solubility in the context of specific ‘rule-breakers’ relative to common dogma. The role of solubility as a determinant of assay outcome is also considered based upon each compound’s cross-assay activity score for a collection of publicly available screening results. Further, the role of solubility as a governing factor for colloidal aggregation formation within a specified assay setting is examined and considered as a possible cause of a high cross-assay activity score. The results of this solubility profile should aid chemists during library design and optimization efforts and represent a useful training set for computational solubility prediction.
36. RNAi Screening Identifies TAK1 as a Potential Target for the Enhanced Efficacy of Topoisomerase Inhibitors
Curr. Cancer Drug Targets, 2011, 11, 976-986
[ Abstract ]
[DOI 10.1002/cmdc.201100179 ]
In an effort to develop strategies that improve the efficacy of existing anticancer agents, we have conducted a siRNA-based RNAi screen to identify genes that, when targeted by siRNA, improve the activity of the topoisomerase I (Top1) poison camptothecin (CPT). Screening was conducted using a set of siRNAs corresponding to over 400 apoptosis-related genes in MDA-MB-231 breast cancer cells. During the course of these studies, we identified the silencing of MAP3K7 as a significant enhancer of CPT activity. Follow-up analysis of caspase activity and caspase-dependent phosphorylation of histone H2AX demonstrated that the silencing of MAP3K7 enhanced CPT-associated apoptosis. Silencing MAP3K7 also sensitized cells to additional compounds, including CPT clinical analogs. This activity was not restricted to MDA-MB-231 cells, as the silencing of MAP3K7 also sensitized the breast cancer cell line MDA-MB-468 and HCT-116 colon cancer cells. However, MAP3K7 silencing did not affect compound activity in the comparatively normal mammary epithelial cell line MCF10A, as well as some additional tumorigenic lines. MAP3K7 encodes the TAK1 kinase, an enzyme that is central to the regulation of many processes associated with the growth of cancer cells (e.g. NF-kB, JNK, and p38 signaling). An analysis of TAK1 signaling pathway members revealed that the silencing of TAB2 also sensitizes MDA-MB-231 and HCT-116 cells towards CPT. These findings may offer avenues towards lowering the effective doses of Top1 inhibitors in cancer cells and, in doing so, broaden their application.
35. Improving Usability and Accessibility of Cheminformatics Tools for Chemists Through Cyberinfrastructure and Education
In Silico Biol., 2011, 11, 41-60
34. Discovery of New Antimalarial Chemotypes Through Chemical Methodology and Library Development
Proc. Nat. Acad. Sci., 2011, 108, 6775-6780
[ Abstract ]
[DOI 10.1073/pnas.1017666108 ]
In an effort to expand the stereochemical and structural complexity of chemical libraries used in drug discovery, the Center for Chemical Methodology and Library Development at Boston University has established an infrastructure to translate methodologies accessing diverse chemotypes into arrayed libraries for biological evaluation. In a collaborative effort, the NIH Chemical Genomics Center determined IC(50)’s for Plasmodium falciparum viability for each of 2,070 members of the CMLD-BU compound collection using quantitative high-throughput screening across five parasite lines of distinct geographic origin. Three compound classes displaying either differential or comprehensive antimalarial activity across the lines were identified, and the nascent structure activity relationships (SAR) from this experiment used to initiate optimization of these chemotypes for further development.
33. Advances in Cheminformatics Methodologies and Infrastructure to Support the Data Mining of Large, Heterogeneous Chemical Datasets
Curr. Comp. Aid. Drug Des., 2010, 6, 50-67
In recent years, there has been an explosion in the availability of publicly accessible chemical information, including chemical structures of small molecules, structure-derived properties and associated biological activities in a variety of assays. These data sources present us with a significant opportunity to develop and apply computational tools to extract and understand the underlying structure-activity relationships. Furthermore, by integrating chemical data sources with biological information (protein structure, gene expression and so on), we can attempt to build up a holistic view of the effects of small molecules in biological systems. Equally important is the ability for non-experts to access and utilize state of the art cheminformatics method and models. In this review we present recent developments in cheminformatics methodologies and infrastructure that provide a robust, distributed approach to mining large and complex chemical datasets. In the area of methodology development, we highlight recent work on characterizing structure-activity landscapes, QSAR model domain applicability and the use of chemical similarity in text mining. In the area of infrastructure, we discuss a distributed web services framework that allows easy deployment and uniform access to
computational (statistics, cheminformatics and computational chemistry) methods, data and models. We also discuss the development of PubChem derived databases and highlight techniques that allow us to scale the infrastructure to extremely large compound collections, by use of distributed processing on Grids. Given that the above work is applicable to arbitrary types of cheminformatics problems, we also present some case studies related to virtual screening for anti-malarials and predictions of anti- cancer activity.
32. Use of Genetic Algorithm and Neural Network Approaches for Risk Factor Selection: A Case Study of West Nile Virus Dynamics in an Urban Environment
Computers, Environment and Urban Systems, 2010, 34, 189-203
[ Abstract ]
[DOI 10.1016/j.compenvurbsys.2010.02.007 ]
The West Nile virus (WNV) is an infectious disease spreading rapidly throughout the United States, causing illness among thousands of birds, animals, and humans. Yet, we only have a rudimentary understanding of how the mosquito-borne virus operates in complex avian–human environmental systems coupled with risk factors. The large array of multidimensional risk factors underlying WNV incidences is environmental, built-environment, socioeconomic, and existing mosquito abatement policies. Therefore it is essential to identify an optimal number of risk factors whose management would result in effective disease prevention and containment. Previous models built to select important risk factors assumed a priori that there is a linear relationship between these risk factors and disease incidences. However, it is difficult for linear models to incorporate the complexity of the WNV transmission network and hence identify an optimal number of risk factors objectively.
There are two objectives of this paper, first, use combination of genetic algorithm (GA) and computational neural network (CNN) approaches to build a model incorporating the non-linearity between incidences and hypothesized risk factors. Here GA is used for risk factor (variable) selection and CNN for model building mainly because of their ability to capture complex relationships with higher accuracy than linear models. The second objective is to propose a method to measure the relative importance of the selected risk factors included in the model. The study is situated in the metropolitan area of Minnesota, which had experienced significant outbreaks from 2002 till present.
31. Towards interoperable and reproducible QSAR analyses: Exchange of datasets.
Journal of Cheminformatics, 2010, 2,
[ Abstract ]
[DOI 10.1186/1758-2946-2-5 ]
ABSTRACT: BACKGROUND: QSAR is a widely used method to relate chemical structures to responses or properties based on experimental observations. Much effo
rt has been made to evaluate and validate the statistical modeling in QSAR, but these analyses treat the dataset as fixed. An overlooked but highly important issue i
s the validation of the setup of the dataset, which comprises addition of chemical structures as well as selection of descriptors and software implementations prior
to calculations. This process is hampered by the lack of standards and exchange formats in the field, making it virtually impossible to reproduce and validate analys
es and drastically constrain collaborations and re-use of data. RESULTS: We present a step towards standardizing QSAR analyses by defining interoperable and reproduc
ible QSAR datasets, consisting of an open XML format (QSAR-ML) which builds on an open and extensible descriptor ontology. The ontology provides an extensible way of
uniquely defining descriptors for use in QSAR experiments, and the exchange format supports multiple versioned implementations of these descriptors. Hence, a datase
t described by QSAR-ML makes its setup completely reproducible. We also provide a reference implementation as a set of plugins for Bioclipse which simplifies setup o
f QSAR datasets, and allows for exporting in QSAR-ML as well as old-fashioned CSV formats. The implementation facilitates addition of new descriptor implementations
from locally installed software and remote Web services; the latter is demonstrated with REST and XMPP Web services. CONCLUSIONS: Standardized QSAR datasets open up
new ways to store, query, and exchange data for subsequent analyses. QSAR-ML supports completely reproducible creation of datasets, solving the problems of defining
which software components were used and their versions, and the descriptor ontology eliminates confusions regarding descriptors by defining them crisply. This makes
it easy to join, extend, combine datasets and hence work collectively, but also allows for analyzing the effect descriptors have on the statistical model’s performan
ce. The presented Bioclipse plugins equip scientists with graphical tools that make QSAR-ML easily accessible for the community.
30. PubChem as a Source of Polypharmacology
J. Chem. Inf. Model., 2009, 49, 2044-2055
[ Abstract ]
[DOI 10.1021/ci9001876 ]
Polypharmacology provides a new way to address the issue of high
attrition rates arising from lack of efficacy and toxicity. However,
the development of polypharmacology is hampered by the incomplete
SAR data and limited resources for validating target
combinations. The PubChem bioassay collection, reporting the activity of
compounds in multiple assays, allows us to study polypharmacological
behavior in the PubChem collection via cross-assay analysis. In this
paper, we developed a network representation of the assay collection
and then applied a bipartite mapping between this network and
various biological networks (i.e., PPI, pathway) as well as
artificial networks (i.e., drug-target network). Mapping to a
drug-target network allows us to prioritize new selective
compounds, while mapping to other biological networks enable us to
observe interesting target pairs and their associated compounds
in the context of biological systems. Our results indicate this
approach could be a useful way to investigate polypharmacology in
the PubChem bioassay collection.
29. Chemoinformatic Analysis of Drugs, Natural Products, Molecular Libraries Small Molecule Repository and Combinatorial Libraries
J. Chem. Inf. Model., 2009, 49, 1010-1024
[ Abstract ]
[DOI 10.1021/ci800426u ]
A multiple criteria approach is presented, that is used to perform a comparative analysis of four recently developed combinatorial libraries to drugs, Molecular Libraries Small Molecule Repository (MLSMR) and natural products. The compound databases were assessed in terms of physicochemical properties, scaffolds, and fingerprints. The approach enables the analysis of property space coverage, degree of overlap between collections, scaffold and structural diversity, and overall structural novelty. The degree of overlap between combinatorial libraries and drugs was assessed using the R-NN curve methodology, which measures the density of chemical space around a query molecule embedded in the chemical space of a target collection. The combinatorial libraries studied in this work exhibit scaffolds that were not observed in the drug, MLSMR, and natural products databases. The fingerprint-based comparisons indicate that these combinatorial libraries are structurally different than current drugs. The R-NN curve methodology revealed that a proportion of molecules in the combinatorial libraries is located within the property space of the drugs. However, the R-NN analysis also showed that there are a significant number of molecules in several combinatorial libraries that are located in sparse regions of the drug space.
28. Navigating Structure Activity Landscapes
Drug Discov. Today, 2009, 14, 698-705
[ Abstract ]
[DOI 10.1016/j.drudis.2009.04.003 ]
The problem of how to systematically explore structure-activity relationships (SARs) is still largely unsolved in medicinal chemistry. Recently, data analysis tools have been introduced to navigate activity landscapes and assess structure-activity relationships on a large scale. Initial investigations reveal a surprising heterogeneity among SARs and shed light on the relationship between `global’ and `local’ SAR features. Moreover, insights are provided into the fundamental issue of why modeling tools work well in some cases, but not in others.
27. Pharmacophore Representation and Searching
CDK News, 2008, ASAP
[ Abstract ]
[ Link ]
In this article we describe the design and use of a set of Java classes to represent pharmacophores and use such representations in pharmacophore searching applications.
26. Assessing how well a modeling protocol captures a structure-activity landscape
J. Chem. Inf. Model., 2008, 48, 1716-1728
[ Abstract ]
[DOI 10.1021/ci8001414 ]
We introduce the notion of structure-activity landscape index (SALI) curves as a way to assess a model and a modeling protocol, applied to structure-activity relationships. We start from our earlier work [J. Chem. Inf. Model., 2008, 48, 646-658], where we show how to study a structure-activity relationship pairwise, based on the notion of “activity cliffs” – pairs of molecules that are structurally similar but have large differences in activity. There, we also introduced the SALI parameter, which allows one to identify cliffs easily, and which allows one to represent a structure-activity relationship as a graph. This graph orders every pair of molecules by their activity. Here, we introduce the new idea of a SALI curve, which tallies how many of these orderings a model is able to predict. Empirically, testing these SALI curves against a variety of models, ranging over two-dimensional quantitative structure-activity relationship (2D-QSAR), three-dimensional quantitative structure-activity relationship (3D-QSAR), and structure-based design models, the utility of a model seems to correspond to characteristics of these curves. In particular, the integral of these curves, denoted as SCI and being a number ranging from -1.0 to 1.0, approaches a value of 1.0 for two literature models, which are both known to be prospectively useful.
25. The Structure-Activity Landscape Index: Identifying and Quantifying Activity-Cliffs
J. Chem. Inf. Model., 2008, 48, 646-658
[ Abstract ]
[DOI 10.1021/ci7004093 ]
A new method for analyzing a structure-activity relationship is proposed. By use of a simple quantitative index, one can readily identify “structure-activity cliffs”: pairs of molecules which are most similar but have the largest change in activity. We show how this provides a graphical representation of the entire SAR, in a way that allows the salient features of the SAR to be quickly grasped. In addition, the approach allows us view the SARs in a data set at different levels of detail. The method is tested on two data sets that highlight its ability to easily extract SAR information. Finally, we demonstrate that this method is robust using a variety of computational control experiments and discuss possible applications of this technique to QSAR model evaluation.
24. A Flexible Web Service Infrastructure for the Development and Deployment of Predictive Models
J. Chem. Inf. Model., 2008, 48, 456-464
[ Abstract ]
[DOI 10.1021/ci700188u ]
The development of predictive statistical models is a common task in
the field of drug design. The process of developing such models
involves two main steps: building the model and then deploying the
model. Traditionally such models have been deployed using web page
interfaces. This approach restricts the user to using the specified
web page and using the model in other ways can be cumbersome. In
this paper we present a flexible and generalizable approach to the
deployment of predictive models, based on a web service
infrastructure using R. The infrastructure described allows one to
access the functionality of these models using a variety of approach
ranging from web pages to workflow tools. We highlight the
advantages of this infrastructure by developing and subsequently
deploying random forest models for two datasets.
23. On the Interpretation and Interpretability of QSAR Models
J. Comp. Aid. Molec. Des., 2008, 22, 857-871
[ Abstract ]
[DOI 10.1007/s10822-008-9240-5 ]
The goal of a quantitative structure–activity relationship (QSAR) model is to encode the relationship between molecular structure and biological activity or physical property. Based on this encoding, such models can be used for predictive purposes. Assuming the use of relevant and meaningful descriptors, and a statistically significant model, extraction of the encoded structure–activity relationships (SARs) can provide insight into what makes a molecule active or inactive. Such analyses by QSAR models are useful in a number of scenarios, such as suggesting structural modifications to enhance activity, explanation of outliers and exploratory analysis of novel SARs. In this paper we discuss the need for interpretation and an overview of the factors that affect interpretability of QSAR models. We then describe interpretation protocols for different types of models, highlighting the different types of interpretations, ranging from very broad, global, trends to very specific, case-by-case, descriptions of the SAR, using examples from the training set. Finally, we discuss a number of case studies where workers have provide some form of interpretation of a QSAR model.
22. Utilizing high throughput screening data for predictive toxicology models: Protocols and application to MLSCN assays
J. Comp. Aid. Molec. Des., 2008, 22, 367-384
[ Abstract ]
[DOI 10.1007/s10822-008-9192-9 ]
Computational toxicology is emerging as an encouraging alternative to experimental testing. The Molecular Libraries Screening Center Network (MLSCN) as part of the NIH Molecular Libraries Roadmap has recently started generating large and diverse screening datasets, which are publicly available in PubChem. In this report, we investigate various aspects of developing computational models to predict cell toxicity based on cell proliferation screening data generated in the MLSCN. By capturing feature-based information in those datasets, such predictive models would be useful in evaluating cell-based screening results in general (for example from reporter assays) and could be used as an aid to identify and eliminate potentially undesired compounds. Specifically we present the results of random forest ensemble models developed using different cell proliferation datasets and highlight protocols to take into account their extremely imbalanced nature. Depending on the nature of the datasets and the descriptors employed we were able to achieve percentage correct classification rates between 70% and 85% on the prediction set, though the accuracy rate dropped significantly when the models were applied to in vivo data. In this context we also compare the MLSCN cell proliferation results with animal acute toxicity data to investigate to what extent animal toxicity can be correlated and potentially predicted by proliferation results. Finally, we present a visualization technique that allows one to compare a new dataset to the training set of the models to decide whether the new dataset may be reliably predicted.
21. Userscripts for the Life Sciences
BMC Bioinformatics, 2007, 8, 487
[ Abstract ]
[DOI 10.1186/1471-2105-8-487 ]
The web has seen an explosion of chemistry
and biology related resources in the last 15 years: thousands of
scientific journals, databases, wikis, blogs and resources are available with
a wide variety of types of information. There is a huge need to aggregate
and organise this information. However, the sheer number of resources makes it
unrealistic to link them all in a centralised manner. Instead,
search engines to find information in those resources flourish, and formal
languages like Resource Description Framework and Web Ontology Language
are increasingly used to allow linking of resources.
A recent development is the use of userscripts to change the appearance of
web pages, by on-the-fly modification of the web content. This opens
possibilities to aggregate information and computational results from
different web resources into the web page of one of those resources.
20. Chemical Data Mining of the NCI Human Tumor Cell Line Database
J. Chem. Inf. Model., 2007, 47, 2063-2076
[ Abstract ]
[DOI 10.1021/ci700141x ]
The NCI Developmental Therapeutics Program Human Tumor cell line data set is a publicly available database that contains cellular assay screening data for over 40 000 compounds tested in 60 human tumor cell lines. The database also contains microarray assay gene expression data for the cell lines, and so it provides an excellent information resource particularly for testing data mining methods that bridge chemical, biological, and genomic information. In this paper we describe a formal knowledge discovery approach to characterizing and data mining this set and report the results of some of our initial experiments in mining the set from a chemoinformatics perspective.
19. Counting Clusters Using R-NN Curves
J. Chem. Inf. Model., 2007, 47, 1308-1318
[ Abstract ]
[DOI 10.1021/ci600541f ]
Clustering is a common task in the field of cheminformatics. A key parameter that needs to be set for non-hierarchical clustering methods, such as $k$-means, is the number of clusters, k. Traditionally the value of $k$ is obtained by performing the clustering with different values of $k$ and selecting that value that leads to the optimal clustering. In this study we describe an approach to selecting k, a priori, based on the R-NN curve algorithm described by Guha et al. (J.~Chem.~Inf.~Model., 2006, 46, 1713-1722) which uses a nearest neighbor technique to characterize the spatial location of compounds in arbitrary descriptor spaces. The algorithm generates a set of curves for the dataset which are then analyzed to estimate the natural number of clusters. We then performed k-means clustering with the predicted value of k as well as with similar values to check that the correct number of clusters was obtained. In addition we compared the predicted value to the number indicated by the average silhouette width as a cluster quality measure. We tested the algorithm on simulated data as well as on two chemical datasets. Our results indicate the the R-NN curve algorithm is able to determine the natural number of clusters and is in general agreement the average silhouette width in identifying the optimal number of clusters
18. A Web Service Infrastructure for Chemoinformatics
J. Chem. Inf. Model., 2007, 47, 1303-1307
[ Abstract ]
[DOI 10.1021/ci6004349 ]
The vast increase of pertinent information available to drug discovery scientists means that there is strong demand for tools and techniques for organizing and intelligently mining this information for manageable human consumption. At Indiana University, we have developed an infrastructure of chemoinformatics web services that simplify the access to this information and the computational techniques that can be applied to it. In this paper, we describe this infrastructure, give some examples of its use, and then discuss our plans to use it as a platform for chemoinformatics application development in the future.
17. Ensemble Feature Selection: Consistent Descriptor Subsets for Multiple QSAR Models
J. Chem. Inf. Model., 2007, 47, 989-997
[ Abstract ]
[DOI 10.1021/ci600563w ]
Selecting a small subset of descriptors from a large pool to build a predictive QSAR model is an important step in the QSAR modeling process. In general subset selection is very hard to solve, even approximately, with guaranteed performance bounds. Traditional approaches employ deterministic or stochastic methods to obtain a descriptor subset that leads to an optimal model of a single type (such as linear regression or a neural network). With the development of ensemble modeling approaches, multiple models of differing types are individually developed resulting in different descriptor subsets for each model type. However it is advantageous, from the point of view of developing interpretable QSAR models, to have a single set of descriptors that can be used for different model types. In this paper, we describe an approach to the selection of a single, optimal, subset of descriptors for multiple model types. We apply this approach to three datasets, covering both regression and classification, and show that the constraint of forcing different model types to use the same set of descriptors does not lead to a significant loss in predictive ability for the individual models considered. In addition, interpretations of the individual models developed using this approach indicate that they encode similar structure-activity trends.
16. Chemical Informatics Functionality in R
J. Stat. Soft., 2007, 18,
[ Abstract ]
[ Link ]
The flexibility and scope of the R programming environment has made it a popular choice for statistical modeling and scientific prototyping in a number of fields. In the field of chemistry, R provides several tools for a variety of problems related to statistical modeling of chemical information. However, one aspect common to these tools is that they do not have direct access to the information that is available from chemical structures, such as contained in molecular descriptors.
We describe the rcdk package that provides the R user with access to the CDK, a Java framework for cheminformatics. As a result, it is possible to read in a variety of molecular formats, calculate molecular descriptors and evaluate fingerprints. In addition, we describe the rpubchem that will allow access to the data in PubChem, a public repository of molecular structures and associated assay data for approximately 8 million compounds. Currently the package allows access to structural information as well as some simple molecular properties from PubChem. In addition the package allows access to bio-assay data from the PubChem FTP servers.
15. Local Lazy Regression: Making Use of the Neighborhood to Improve QSAR Predictions.
J. Chem. Inf. Model., 2006, 46, 1836-1847
[ Abstract ]
[DOI 10.1021/ci060064e ]
Traditional quantitative structure-activity relationship (QSAR) models aim to capture global structure-activity trends present in a data set. In many situations, there may be groups of molecules which exhibit a specific set of features which relate to their activity or inactivity. Such a group of features can be said to represent a local structure-activity relationship. Traditional QSAR models may not recognize such local relationships. In this work, we investigate the use of local lazy regression (LLR), which obtains a prediction for a query molecule using its local neighborhood, rather than considering the whole data set. This modeling approach is especially useful for very large data sets because no a priori model need be built. We applied the technique to three biological data sets. In the first case, the root-mean-square error (RMSE) for an external prediction set was 0.94 log units versus 0.92 log units for the global model. However, LLR was able to characterize a specific group of anomalous molecules with much better accuracy (0.64 log units versus 0.70 log units for the global model). For the second data set, the LLR technique resulted in a decrease in RMSE from 0.36 log units to 0.31 log units for the external prediction set. In the third case, we obtained an RMSE of 2.01 log units versus 2.16 log units for the global model. In all cases, LLR led to a few observations being poorly predicted compared to the global model. We present an analysis of why this was observed and possible improvements to the local regression approach.
14. R-NN Curves: An Intuitive Approach to Outlier Detection Using a Distance Based Method
J. Chem. Inf. Model., 2006, 46, 1713-1722
[ Abstract ]
[DOI 10.1021/ci060013h ]
Libraries of chemical structures are used in a variety of cheminformatics tasks such as virtual screening and QSAR modeling and are generally characterized using molecular descriptors. When working with libraries it is useful to understand the distribution of compounds in the space defined by a set of descriptors. We present a simple approach to the analysis of the spatial distribution of the compounds in a library in general and outlier detection in particular based on counts of neighbors within a series of increasing radii. The resultant curves, termed R-NN curves, appear to follow a logistic model for any given descriptor space, which we justify theoretically for the 2D case. The method can be applied to data sets of arbitrary dimensions. The R-NN curves provide a visual method to easily detect compounds lying in a sparse region of a given descriptor space. We also present a method to numerically characterize the R-NN curves thus allowing identification of outliers in a single plot.
13. The Blue Obelisk–Interoperability in Chemical Informatics.
J. Chem. Inf. Model., 2006, 46, 991-998
[ Abstract ]
[DOI 10.1021/ci050400b ]
The Blue Obelisk Movement (http://www.blueobelisk.org/) is the name used by a diverse Internet group promoting reusable chemistry via open source software development, consistent and complimentary chemoinformatics research, open data, and open standards. We outline recent examples of cooperation in the Blue Obelisk group: a shared dictionary of algorithms and implementations in chemoinformatics algorithms drawing from our various software projects; a shared repository of chemoinformatics data including elemental properties, atomic radii, isotopes, atom typing rules, and so forth; and Web services for the platform-independent use of chemoinformatics programs.
12. Scalable Partitioning and Exploration of Chemical Spaces using Geometric Hashing
J. Chem. Inf. Model., 2006, 46, 321-333
[ Abstract ]
[DOI 10.1021/ci050403o ]
Virtual screening (VS) has become a preferred tool to augment high-throughput screening1 and determine new leads in the drug discovery process. The core of a VS informatics pipeline includes several data mining algorithms that work on huge databases of chemical compounds containing millions of molecular structures and their associated data. Thus, scaling traditional applications such as classification, partitioning, and outlier detection for huge chemical data sets without a significant loss in accuracy is very important. In this paper, we introduce a data mining framework built on top of a recently developed fast approximate nearest-neighbor-finding algorithm called locality-sensitive hashing (LSH) that can be used to mine huge chemical spaces in a scalable fashion using very modest computational resources. The core LSH algorithm hashes chemical descriptors so that points close to each other in the descriptor space are also close to each other in the hashed space. Using this data structure, one can perform approximate nearest-neighbor searches very quickly, in sublinear time. We validate the accuracy and performance of our framework on three real data sets of sizes ranging from 4337 to 249,071 molecules. Results indicate that the identification of nearest neighbors using the LSH algorithm is at least 2 orders of magnitude faster than the traditional k-nearest-neighbor method and is over 94% accurate for most query parameters. Furthermore, when viewed as a data-partitioning procedure, the LSH algorithm lends itself to easy parallelization of nearest-neighbor classification or regression. We also apply our framework to detect outlying (diverse) compounds in a given chemical space; this algorithm is extremely rapid in determining whether a compound is located in a sparse region of chemical space or not, and it is quite accurate when compared to results obtained using principal-component-analysis-based heuristics.
11. Generating, Using and Visualizing Molecular Information in R
10. Validation of the CDK Surface Area Routine
9. Recent Developments of the Chemistry Development Kit (CDK) – An Open-Source Java Library for Chemo- and Bioinformatics
Curr. Pharm. Des., 2006, 12, 2110-2120
[ Abstract ]
[DOI 10.2174/138161206777585274 ]
The Chemistry Development Kit (CDK) provides methods for common tasks in molecular informatics, including 2D and 3D rendering of chemical structures, I/O routines, SMILES parsing and generation, ring searches, isomorphism checking, structure diagram generation, etc. Implemented in Java, it is used both for server-side computational services, possibly equipped with a web interface, as well as for applications and client-side applets. This article introduces the CDK’s new QSAR capabilities and the recently introduced interface to statistical software.
8. Interpreting Computational Neural Network QSAR Models: A Detailed Interpretation of the Weights and Biases
J. Chem. Inf. Model., 2005, 45, 1109-1121
7. Interpreting Computational Neural Network QSAR Models: A Measure of Descriptor Importance
J. Chem. Inf. Model., 2005, 45, 800-806
[ Abstract ]
[DOI 10.1021/ci050022a ]
We present a method to measure the relative importance of the descriptors present in a QSAR model developed with a computational neural network (CNN). The approach is based on a sensitivity analysis of the descriptors. We tested the method on three published data sets for which linear and CNN models were previously built. The original work reported interpretations for the linear models, and we compare the results of the new method to the importance of descriptors in the linear models as described by a PLS technique. The results indicate that the proposed method is able to rank descriptors such that important descriptors in the CNN model correspond to the important descriptors in the linear model.
6. Determining the Validity of a QSAR Model–A Classification Approach
J. Chem. Inf. Model., 2005, 45, 65-73
[ Abstract ]
[DOI 10.1021/ci0497511 ]
The determination of the validity of a QSAR model when applied to new compounds is an important concern in the field of QSAR and QSPR modeling. Various scoring techniques can be applied to specific types of models. We present a technique with which we can state whether a new compound will be well predicted by a previously built QSAR model. In this study we focus on linear regression models only, though the technique is general and could also be applied to other types of quantitative models. Our technique is based on a classification method that divides regression residuals from a previously generated model into a good class and bad class and then builds a classifier based on this division. The trained classifier is then used to determine the class of the residual for a new compound. We investigated the performance of a variety of classifiers, both linear and nonlinear. The technique was tested on two data sets from the literature and a hand built data set. The data sets selected covered both physical and biological properties and also presented the methodology with quantitative regression models of varying quality. The results indicate that this technique can determine whether a new compound will be well or poorly predicted with weighted success rates ranging from 73% to 94% for the best classifier.
5. Using R to Provide Statistical Functionality for QSAR Modeling in CDK to Provide Statistical Functionality for QSAR Modeling in CDK
4. Using the CDK as a Backend to R
3. Development of Linear, Ensemble, and Nonlinear Models for the Prediction and Interpretation of the Biological Activity of a Set of PDGFR Inhibitors.
J. Chem. Inf. Comput. Sci., 2004, 44, 2179-2189
[ Abstract ]
[DOI 10.1021/ci049849f ]
A QSAR modeling study has been done with a set of 79 piperazyinylquinazoline analogues which exhibit PDGFR inhibition. Linear regression and nonlinear computational neural network models were developed. The regression model was developed with a focus on interpretative ability using a PLS technique. However, it also exhibits a good predictive ability after outlier removal. The nonlinear CNN model had superior predictive ability compared to the linear model with a training set error of 0.22 log(IC50) units (R2 = 0.93) and a prediction set error of 0.32 log(IC50) units (R2 = 0.61). A random forest model was also developed to provide an alternate measure of descriptor importance. This approach ranks descriptors, and its results confirm the importance of specific descriptors as characterized by the PLS technique. In addition the neural network model contains the two most important descriptors indicated by the random forest model.
2. The Development of QSAR Models To Predict and Interpret the Biological Activity of Artemisinin Analogues
J. Chem. Inf. Comput. Sci., 2004, 44, 1440-1449
[ Abstract ]
[DOI 10.1021/ci0499469 ]
This work presents the development of Quantitative Structure-Activity Relationship (QSAR) models to predict the biological activity of 179 artemisinin analogues. The structures of the molecules are represented by chemical descriptors that encode topological, geometric, and electronic structure features. Both linear (multiple linear regression) and nonlinear (computational neural network) models are developed to link the structures to their reported biological activity. The best linear model was subjected to a PLS analysis to provide model interpretability. While the best linear model does not perform as well as the nonlinear model in terms of predictive ability, the application of PLS analysis allows for a sound physical interpretation of the structure-activity trend captured by the model. On the other hand, the best nonlinear model is superior in terms of pure predictive ability, having a training error of 0.47 log RA units (R2 = 0.96) and a prediction error of 0.76 log RA units (R2 = 0.88).
1. Generation of QSAR Sets with a Self-Organizing Map.
J. Mol. Graph. Model., 2004, 23, 1-14
[ Abstract ]
[DOI 10.1016/j.jmgm.2004.03.003 ]
A Kohonen self-organizing map (SOM) is used to classify a data set consisting of dihydrofolate reductase inhibitors with the help of an external set of Dragon descriptors. The resultant classification is used to generate training, cross-validation (CV) and prediction sets for QSAR modeling using the ADAPT methodology. The results are compared to those of QSAR models generated using sets created by activity binning and a sphere exclusion method. The results indicate that the SOM is able to generate QSAR sets that are representative of the composition of the overall data set in terms of similarity. The resulting QSAR models are half the size of those published and have comparable RMS errors. Furthermore, the RMS errors of the QSAR sets are consistent, indicating good predictive capabilities as well as generalizability.