Creating a Chemical Probe to Identify the Target of a Novel Immune Suppressing Compound

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Immunosuppressants are absolutely essential for successful organ transplantation and are useful in the treatment of autoimmune disorders. Analyzing their mechanism of action can, as in the case of cyclosporine and calcineurin, yield important insights into basic features of T cell biology. We recently embarked upon an ambitious three-step project intended to use chemical biology approaches to identify unknown pathways involved in lymphocyte function. The over-arching rationale underlying the project was that compounds that inhibit T cell activation and work via unknown molecular mechanism (MMOA) could be developed into chemical probes that could be used to identify novel cellular targets, which would reveal currently-unknown aspects of basic T cell biology and might become the basis for new classes of immunosuppressant agents. The first step of the project- screening the NIH's Molecular Libraries Small Molecule Repository of ~375,000 compounds and identifying compounds with unknown MMOA- succeeded. We monitored lytic granule exocytosis using TALL-104 human cytotoxic T lymphocytes as a model, measuring externalization of LAMP-1/ CD107a using flow cytometry. Among hits with unknown MMOA was 2-N-[(2-methoxyphenyl)methyl]-4-N-[(4- propan-2-ylphenyl)methyl]thieno[3,2-d]pyrimidine-2,4-diamine, CID 49792547, which is the subject of this application. This compound inhibits lytic granule exocytosis with potency in the micromolar range, but does not work via any of the mechanisms we tested. It inhibits IL-2 production by Jurkat human leukemic T cells, confirming that has broad immunosuppressive activity. It is a drug-like molecule that is amenable to synthesis and the generation of diverse analogs. The project's intended second step was to generate analogs for structure-activity analysis, then use that information to design chemical probes to use in the third and final step, applying affinity-based and/or photo- crosslinking approaches to identify the unknown target that underlies the compound's activity. However, Chemistry Center support was withdrawn when the NIH MLPCN program ended. This application for an R03 is intended to allow us to continue to pursue the overall goals of the project by creating probes for target identification. We will create analogs of CID 49792547, then test their effects on lytic granule exocytosis, IL-2 secretion and toxicity. This information will allow us to identify the highest possible affinity analogs and will reveal sites that can be used to attach linkers which will allow the compound to be coupled to biotin for creation of an affinity matrix and to bifunctional photo-crosslinking/ click-chemistry groups that can be used to label target proteins. Future efforts will be directed towards target identification using probes developed in this application and in a companion application submitted previously focused on another compound.