David Richard

Hydroxyquinoline-derived compounds and analoguing of selective Mcl-1 inhibitors using a functional biomarker

Anti-apoptotic Bcl-2 family proteins are important oncology therapeutic targets. To date, BH3 mimetics that abrogate anti-apoptotic activity have largely been directed at Bcl-2 and/or Bcl-xL. One observed mechanism of resistance to these inhibitors is increased Mcl-1 levels in cells exposed to such therapeutics. For this reason, and because Mcl-1 is important in the onset of lymphoid, myeloid, and other cancers, it has become a target of great interest. However, small molecule inhibitors displaying potency and selectivity for Mcl-1 are lacking. Identifying such compounds has been challenging due to difficulties in translating the target selectivity observed at the biochemical level to the cellular level. Herein we report the results of an HTS strategy coupled with directed hit optimization. Compounds identified have selective Mcl-1 inhibitory activity with greater than 100-fold reduced affinity for Bcl-xL. The selectivity of these compounds at the cellular level was validated using BH3 profiling, a novel personalized diagnostic approach. This assay provides an important functional biomarker that allows for the characterization of cells based upon their dependencies on various anti-apoptotic Bcl-2 proteins. We demonstrate that cells dependent on Mcl-1 or Bcl-2/Bcl-xL for survival are commensurately responsive to compounds that genuinely target those proteins. The identification of compound 9 with uniquely validated and selective Mcl-1 inhibitory activity provides a valuable tool to those studying the intrinsic apoptosis pathway and highlights an important approach in the development of a first-in-class cancer therapeutic.

Abstract 2466: Characterization and development of on-target Mcl-1 inhibitors; BH3 profiling provides a valuable drug discovery tool.

Anti-apoptotic Bcl-2 family proteins are central to the regulation of the intrinsic apoptotic pathway, and as such constitute an important group of targets with great potential as oncology therapeutics. The Bcl-2 family protein Mcl-1 has been demonstrated to facilitate survival and chemoresistance in multiple myeloma, AML, and other cancers, and agents which affect this pathway have become highly sought after. Currently, however, no therapies exist which directly target Mcl-1. We have identified compounds that target Mcl-1 which may be characterized as both Mcl-1-selective and pan-Mcl-1/Bcl-2 inhibitors. This effort has been facilitated by utilization of the BH3 profiling technology to guide SAR. This assay allows for determination of the mitochondrial priming state of both cell culture samples and primary patient samples. We have demonstrated a correlation between myeloma and leukemia cell line response to treatment with our inhibitors and the mitochondrial priming state of such cell lines. Such correlations have also been shown with respect to the extent of cytochrome C release. In the case of the selective Mcl-1 inhibitor, we have shown that cytochrome C release occurs preferentially in leukemia cell lines which are highly primed for Mcl-1 rather than Bcl-2. In addition, our Mcl-1 selective inhibitor demonstrates enhanced cell killing ability in leukemia cells which have been engineered to selectively express Mcl-1, Bcl-2, and Bcl-xL. Our current lead candidate possesses excellent drug-like properties and displays impressive efficacy in a multiple myeloma disseminated xenograft model. This work demonstrates the utility of the BH3 profiling assay as providing a functional biomarker for drug discovery tool and its ability to validate the on-target activity of Mcl-1 and Bcl-2 inhibitors. Citation Format: David J. Richard, Nicole Carlson, William Pierceall, Ryan Lena, Thomas Bannister, Peter Hodder, Timothy Spicer, Michael Andreeff, Joseph Opferman, Brian Koss, Andrew Kung, Michael Cardone. Characterization and development of on-target Mcl-1 inhibitors; BH3 profiling provides a valuable drug discovery tool. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2466. doi:10.1158/1538-7445.AM2013-2466