OpenSourceMalaria:Story so far
This is a human-readable summary of the open source drug discovery for malaria project. A less readable collection of all the relevant data can be found here.
The story so far in the open source drug discovery for malaria project
Last year the Todd lab at The University of Sydney received funding for a pilot project in open source drug discovery from the Medicines for Malaria Venture (MMV). The project champion at the outset was Tim Wells. Jeremy Burrows came on board and led the suggestion to go after a few of the actives that had been placed in the public domain in 2010 by GlaxoSmithKline and others. Work got underway in the lab in August 2011. The team were successful in securing further funding from an Australian Research Council Linkage grant - a scheme where funds from an external agency are matched by the Australian Government. This has generated funding from May 2012 for three years.
The scientific idea behind the project is familiar medicinal chemistry methodology - the aim is to find a small molecule that is effective for the treatment of malaria, and that involves generating molecules (the Todd lab's primary responsibility) and evaluating them (with other members of the project). Based on the biological results, analogs are made, or the series might be ditched and another one selected. The first series to be tried is based on an arylpyrrole that was one of the most attractive hits in the original GSK dataset, but there are plenty of other series that are also very attractive from a medchem perspective.
The difference with this project though (as described in the 6 Laws) is that everything is open, meaning all the experiments go on the web (including the ones that did not turn out well). All the data are available. Anyone can do anything they wish with the compounds, with the proviso the project is cited (see licence conditions below). The main difference is that anyone can take part - people may make molecules, offer guidance and input in other ways that change the direction of the project as it is happening, i.e. rather than the release of all data at the end of the project, data are released as the project is happening so that people can become genuinely involved in the research. Thus the iterative cycle of analog synthesis in response to biological data that is normally guided by luck and medchem intuition is now guided by the intuition of the collective. Similarly, since the biological data are all open too, it should be easier to form an objective assessment of a molecule's performance divorced from the judgement of those closest to the compounds. In the same way that in software development "with enough eyeballs all bugs are shallow" the open nature of the research makes the science better and faster. This was found to be the case in a previous synthetic chemistry project involving the drug praziquantel.
Rounds of Synthesis and Evaluation Completed to Date
Paul Ylioja started by resynthesising the two known active compounds from the GSK set (OSM-S-5 and OSM-S-6 - structures below), plus a few simple derivatives, and confirming that they were active. The current list of all the compounds made thus far in this part of the project is kept in this spreadsheet. The biological evaluation was carried out by three separate labs (Vicky Avery, Stuart Ralph and the original GSK Tres Cantos Lab led by Javier Gamo) to ensure a solid footing of repeatability. The original compounds contained an ester which was thought likely to hydrolyze in vivo, so various versions of the "lower half" of these leads were also evaluated to check whether the original hits were prodrugs, but all these compounds were found to be inactive. The project champion from MMV, Paul Willis, recommended a few "near neighbor" compounds that also looked interesting, and a number of these were made too and evaluated in this first round. One compound, OSM-S-9, was found to be more active than the original GSK hits. Sanjay Batra came on board the project and his student Soumya made (and is making) some analogs varying in the position of the fluorine atom, though the activity of those tested to date is low. (Sanjay works at the CDRI in Lucknow, India, where Saman Habib also works - Saman is leading the Indian OSDDm project which will hopefully get started soon). The outcome was that the original hits remained interesting (because of their reasonable potency and logP values) but that highly potent novel antimalarials were also being generated in this class. Thus a second set of compounds was synthesized and evaluated, giving rise to several new highly potent compounds, one of which (OSM-S-39) displayed a picomolar IC50 value. This is impressive given the small number of compounds made to date, and is testament to the quality of the hits contained in the original GSK set.
At this point the decision was taken to take the most promising compounds on to advanced biological evaluation, to see what the promise of this class really is (rather than continue to increase potency through analog synthesis). Evaluations to date are as follows.
- Metabolic and solubility assays: The two original GSK compounds (OSM-S-5 and OSM-S-6) and six other compounds made in this project were evaluated by Sue Charman's lab at Monash for their stability in phosphate buffer. The raw data are here and can be discussed here. The GSK originals displayed good solubility but moderate degradation rates. The other compounds were degraded more slowly but at a cost of low solubility. Subsequently the original GSK compound OSM-S-5 was evaluated for stability in human and mouse plasma. The compound was stable in human plasma but susceptible to hydrolysis in mouse plasma. Esterase activity is known to be higher in rodents than in other species which was confirmed using a control compound in this assay (p-nitrophenol acetate) so the results are not too surprising. Lab book page here.
- hERG: One of the original GSK compounds (OSM-S-5) plus one of the most potent novel compounds identified to date (OSM-S-35) were subjected to the hERG assay and passed, perhaps implying that this class of compounds should not exhibit undesirable cardiac side effects. Discussion page here.
- Late Stage Gametocyte Assay: Four of the compounds have also been evaluated in a late stage gametocyte assay with very interesting results indicating unusually high activity in blocking the transmission of the parasite. The original GSK compound OSM-S-5 was inactive. Discussion page here.
- In vivo: However, the two original GSK compounds as well as one of the most promising near neighbor compounds (OSM-S-35) were evaluated in mice and found to possess zero oral efficacy (Results available here). Subsequent analysis of the plasma samples from the trial with one of the GSK compounds (OSM-S-5) showed that the compound was indeed orally available, but levels in the blood were not being maintained. Raw data here.
Other discussions of the biological results described above can be found here. The biological data requires careful consideration about whether to change the focus of the project to another series or whether to continue to alter the structures of the best compounds to overcome the in vivo roadblock.
A decision was taken to carry out a third round of analog synthesis and evaluation on the arylpyrrole series, with an emphasis on analogs a) with low logP and b) that lack the thiazolidinone heterocycle. A consultation occurred asking for suggestions for the ten most appropriate compounds to make, and the ten most interesting for commercial procurement. The final stage of the consultation took place live on the web. As a result the lists were finalised; commercial compounds were ordered and synthesis commenced. In early November, the team received results from the biological evaluation of the commercial compounds and the the synthetic compounds that had been completed, along with some analogues. This set of compounds were found to possess low to negligible levels of activity. This surprised the team but also provided some interesting insights. For example, a forked series, the pyrazoles, looked attractive but so far, all examples tested (e.g., OSM-S-92) were found to be inactive. The next batch of 'third round compounds were synthesised and evaluated in December 2012. As with the first batch, all of the compounds were essentially inactive (OSM-S-103 showed mild activity).
At the end of 2012, there remained a few compounds which needed synthetic input from any labs interested in contributing. Patrick Thompson, a collaborator from the University of Edinburgh built on Matin Dean's work on the sulfonamide whilst Murray Robertson and Alice Williamson focused on synthesising further analogues of the near-neighbours, in order to find potent molecules with increased solubility. The near-neighbours were evaluated and a number of potent compounds were discovered, some with lower LogP than the first set of near-neighbour compounds. An open consultation is set to take place on Tuesday 26th February in order to discuss the latest biology results and to decide the next steps for the project.
The project has to date had no luck in securing donations of the compounds from commercial suppliers. On considering some structurally 'similar' active compounds from the TCAMS set, the team have also decided to synthesise a few extra compounds plus hybrids, in order to assess their biological activity.
What Are the Compounds Doing?
What might this series of compounds be doing to the parasite to kill it so effectively? It's not clear. The original screens were whole-cell assays, so while it is known that the compounds are effective, it's not known what they are doing in any detail. Iain Wallace from ChEMBL has performed a prediction of the biological role of these compounds (as well as predictions for the whole "Malaria Box", which is a set of compounds MMV are providing to people for antimalarial screening and which are the focus of a current round of Gates requests for proposals). Iain clustered the compounds as a similarity map, allowing visualization of the correlation between structure and predicted activity. Discussed also here. One of the predictions was that the compounds hit an enzyme known as DHODH, and GSK are at the time of writing screening some of the project's compounds against this enzyme. These predictions are made using informatics - a comparison of the structures of our compounds with other known compounds that have known activities. The argument is based on extrapolation. To evaluate whether the prediction is correct, a subset of compounds has been sent to Corey Nislow at the University of Toronto for screening in a yeast-based assay that does not identify for sure what the compounds are doing (which is very difficult) but provides harder biological evidence for a role.
How to Obtain Other Compounds
The original compounds from the GSK assay were commercially available, arising from libraries that are provided to larger companies by smaller specialised companies. In a medicinal chemistry project like this one starts with a set of compounds, then one sources further compounds that are similar. Novel compounds need to be made. Other compounds may be available by other means, however. Typically in academia required compounds are made in-house because academia works as a closed system, which is inefficient if relevant compounds exist elsewhere on the planet and can be sourced by other means more quickly. In this project organic synthesis of novel compounds is currently being performed in Sydney and Lucknow. But for known compounds the following needs to be done.
1) Identification of Commercial Compounds: What if some compounds we require are already commercially available? How can these be found? Iain Wallace was able to do a search of databases such as eMolecules for relevant compounds above a certain threshold of similarity and filter compounds by supplier, generating the "hitlist" quickly and with no manual human input. These can be converted into spreadhseets for quick visualisation - see here for examples on Jimmy Cronshaw's series (see below for these).
2) Obtaining Commercial Compounds: With the compounds identified, the relevant suppliers need to be contacted to ask for donations. That will probably not be trivial since it needs a human interaction. Failing that the compounds can just be bought.
3) Identification of Other/academic Compounds: What about compounds that could be useful to the project but which are not commercially available, e.g. compounds sitting in academic lab fridges? Some can be found using resources like SciFinder, though these require expensive subscriptions. Many compounds that might be perfect for the project may not even be in the published literature, which is another argument for openness in science.
4) Get Other/academic Compounds: This will be a case of manual contact with interested groups. One such enquiry has already been submitted, to see what happens. Naturally contributions are rewarded by possible authorship on resulting papers.
Ultimately, as a species, we are not very efficient at sharing valuable chemical resources. A user-driven list would be helpful - "I need compound X. I can buy it from you, or you can give it to me, or you can make it for me or with me, but I need the compound in timeframe Y." This is like a Molecular Craigslist, and would reduce some of the supply-demand barriers in chemical research.
The arypyrrole series was the first to be examined. Two other interesting-looking starting points from the GSK set, based on a triazolourea and a thienopyrimidine, were the focus of James Cronshaw's honours thesis at Sydney University. The triazolourea (OSM-S-56) was found to be even more active than the original GSK hit (TCMDS 134395). James has synthesised the thienopyrimidine series lead, and we are awaiting confirmation of the compounds antimalarial activity. If the lead compound is confirmed as active then it will be necessary to decide which, if either, of the series are to be taken on further. In general a strategy for the project is to decide as early as possible which series are looking attractive biologically, because there are still a lot of leads to pursue. If any of these structures look synthetically attractive to you based on your previous experience, please consider joining the project. Some of these molecules are quite straightforward to make and would be suitable for undergraduate lab classes.
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