The goal of this proposal is to synthesize and evaluate analogues of cambinol, a small molecule inhibitor of human NAD-dependent deacetylases SIRT1 and SIRT2, and to validate SIRT1 and/or SIRT2 as therapeutic targets in germinal center lymphomas. SIRT1, SIRT2 and other NAD- dependent deacetylases have been implicated in control of cellular responses to stress and in tumorigenesis through deacetylation of important regulatory proteins including p53 and the BCL6 oncoprotein. We have identified a compound we named cambinol that inhibits NAD-dependent deacetylase activity of human SIRT1 and SIRT2. Consistent with the role of SIRT1 in promoting cell survival during stress, inhibition of SIRT1 activity with cambinol during genotoxic stress leads to hyperacetylation of key stress response proteins and promotes cell cycle arrest. Treatment of BCL6- expressing Burkitt's lymphoma (BL) and diffuse large B-cell lymphoma (DLBCL) cells with cambinol as a single agent induces apoptosis and is accompanied by hyperacetylation of BCL6 and p53. Because acetylation inactivates BCL6 and activates p53 and other checkpoint pathways, the antitumor activity of cambinol in BL cells may be due to a combined effect of BCL6 inactivation and checkpoint activation. In preliminary studies, cambinol was well tolerated in mice and inhibited growth of BL xenografts. Germinal center is a developmental stage when B-cells proliferate rapidly while undergoing somatic hypermutation and class switch recombination. Rapid proliferation of germinal center cells in spite of genomic instability is accomplished in part through suppression of DNA-damage checkpoints through BCL6-dependent and other transcriptional repression mechanisms. Based on the known roles of SIRT1 and SIRT2 (SIRT1/2) as protein deacetylases that act on a number of targets, we hypothesize that SIRT1 and/or SIRT2 controls essential transcriptional programs in germinal center B-cells that can be exploited for treatment of lymphoma. We will test this hypothesis in a convergent research program. We will: 1) Develop isoform specific analogues of cambinol and assemble an SAR for SIRT1 and SIRT2 isoform specific inhibitors;2). Validate SIRT1 and/or SIRT2 as anticancer drug targets for germinal center-derived lymphomas. Germinal center formation will serve as a surrogate for B-cell lymphomagenesis;3). Determine the role of SIRT1/2- mediated deacetylation of BCL6 in cambinol's antilymphoma activity, and;4). Determine the activity of optimized SIRT1/2 inhibitors in vivo using human lymphoma xenografts in mice and in the transgenic mouse model of DLBC lymphomas. These interdisciplinary studies will provide critical validation for NAD-dependent deacetylases as viable anticancer drug targets.
We propose to develop new anti-lymphoma drugs that target SIRT1, an enzyme involved in regulating cells'response to stress as well as cellular differentiation. Deregulation of cellular differentiation leads to the development of almost all lymphomas. Our preliminary data suggest that inhibition of SIRT1 and perhaps SIRT2 is lethal to B- cell lymphoma cells and sensitizes many other cancer cell types to conditions of stress such as standard cytotoxic chemotherapy. Our goal is to use the tools of medicinal chemistry, protein crystallography, biochemistry and cell biology to develop potent and selective inhibitors of SIRT1 as anti-lymphoma drugs.
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