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Trying to squeeze sense out of chemical data

Archive for the ‘pubchem’ tag

A Quick Look at the GSK Malaria Dataset

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A few days ago, GSK released an approximately 13,000 member compound library (using the CC0 license) that had been tested for activity against P. falciparum. The structures and data have been deposited into ChEMBL and a paper is available, that describes the screening project and results. Following this announcement there was a thread on FriendFeed, where Jean-Claude Bradley suggested that it might be useful to compare the GSK library with a virtual library of about 117,000 Ugi compounds that he’s been using in the Open Notebook malaria project.

There are many ways to do this type of comparison – ranging from a pairwise similarity search to looking at the overlap of the distribution of compound properties in some pre-defined descriptor space. Given the size of the datasets, I decided to look at a faster, but cruder option using the idea of bit spectra, which is essentially the normalized frequency of bits in a binary fingerprint across a dataset.

I evaluated the 881-bit PubChem fingerprints for the two datasets using the CDK and then evaluated the bit spectra using the fingerprint package in R. We can then compare the datasets (at least in terms of the PubChem fingerprint features) by plotting the bit spectra. The two spectra are pretty similar, suggesting very similar distributions of functional groups. However there are a number of differences. For example, for bit positions 145 – 155, the GSK library has a higher occurrence than the Ugi library. These features focus on various types of 5-member rings. Another region of difference occurs around bit position 300 and then around positions 350-375.

The static visualization shown here is a simple summary of the similarity of the datasets, but with appropriate interactive graphics one could easily focus on the specific regions of interest. Another way would be to evaluate the difference spectrum and quickly identify features that are more prevalent in the Ugi library compared to the GSK library (i.e., positive values in the plot shown here) and vice versa.

Written by Rajarshi Guha

May 23rd, 2010 at 1:02 pm

New Version of rpubchem

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Version 1.4.3 of rpubchem is out on CRAN. There’s some minor code cleanups and also a new function called get.aid.by.cid which allows you to get assay ID’s based on whether they contain a compound (either as an active, inactive, discrepant or just tested). This uses PUG to perform the query, so can be a bit slow (and occasionally just fail).

Written by Rajarshi Guha

November 21st, 2009 at 2:11 am

Posted in software

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PubChem Bioassay Annotation Poster

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Sometime back I had described some work on the automated annotation of PubChem bioassays. The lack of annotations on the assays can make it difficult to integrate with other biological resources. Ideally, the bioassays would be manually annotated – however, it’s not a very exciting job. So, collaborating with Patrick Ruch and Julien Gobeill, we used their tool, GOCat, to automatically annotate the PubChem bioassay collection with GO terms. They recently presented a poster on this work at the 3rd International Biocuration Conference in Berlin.

Obviously, automated annotation will not be as good as expert, manual annotations. However it does a decent job and I think it’s in line with a recent post by Duncan Hull, where he quotes a paper from Google

The first lesson of Web-scale learning is to use available large-scale data rather than hoping for annotated data that isn’t available

While we’re not using the PubChem assay data directly for learning, the automated approach to annotations means that we can move on to stuff that can make use of them, rather than waiting on a full manual curation of the assay collection (which will likely supercede automated annotations, when it becomes available).

Written by Rajarshi Guha

April 21st, 2009 at 1:11 pm

Posted in cheminformatics,research

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Annotating Bioassays

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I’ve been working for some time with the PubChem Bioassay collection – a set of 1293 assays that cover a range of techniques (enzymatic, phenotypic etc.), targets and sizes (from 20 molecules to 200,000 molecules). In addition, some assays are primary, high-throughput assays whereas a number of them are smaller, confirmatory assays. While an extremely valuable collection, one of the drawbacks is the lack of curation. This has led to some people saying that the data is too noisy to be useful. Yes, the noise is a problem, but I think there’s still useful data to extract and model.

One of the problems that I have faced is that while one can perform a full text search for assays on PubChem, there is no form of annotations on the assays themselves. One effect of this is that it is difficult to link an assay to other biological resources (though for enzymatic assays, one can determine a Pubmed protein identifier). While working on my bioassay network project, I needed annotations and I didn’t want to do it manually.

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Written by Rajarshi Guha

January 25th, 2009 at 5:03 pm

Quick Comments on an Analysis of Antithrombotics

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Joerg has made a nice blog post on the use of Open Source software and data to analyse the occurence of antithrombotics. More specifically he was trying to answer the question

Which XRay ligands are closest to the Fontaine et al. structure-activity relationship data for allowing structure-based drug design?

Using Blue Obelisk tools and ChemSpider and where Fontaine et al. refers to the Fontaine Factor Xa dataset. You should read his post for a nice analysis of the problem. I just wanted to consider two points he had raised.

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Written by Rajarshi Guha

January 5th, 2009 at 1:36 am