Abstract 745: A non-redox reactive allosteric inhibitor of MAPK phosphatases with selective toxicity to human cancer cells

Mitogen-activated protein kinase phosphatases (MKPs) are members of a family of dual specificity phosphatases (DUSPs) that regulate cellular signaling homeostasis by dephosphorylating mitogen-activated kinases, key mediators of cell death and survival. The archetype MKP, DUSP1 (also termed MKP-1/CL100), is overexpressed in ovarian, breast, and prostate cancers and found elevated in the “oncogenic signature” of RAS mutant tumor cells. DUSP1 mediates cancer cell migration and invasion, and protects cells from apoptosis by clinically used antineoplastic agents and gamma-irradiation. Despite the evidence that DUSP1 is a promising anticancer target, efforts to discover small molecule inhibitors have been largely unsuccessful. The MKP active site is shallow and contains a catalytic cysteine that is sensitive to oxidation. Hence, prior discovery screens have mostly identified redox-reactive structures with promiscuous biological activities. Using a zebrafish chemical screen, we recently discovered a new DUSP inhibitory chemotype that has no redox-reactive structural features and that is thought to bind to an allosteric site adjacent to the catalytic cavity. Structure-activity relationship studies in transgenic zebrafish identified an analog (VNK-215) that retained DUSP1 and DUSP6 inhibitory activity but was well tolerated by the developing embryo. Here we hypothesized that VNK-215 could be selectively cytotoxic to cancer cells due to its ability to inhibit DUSP1 and lack of redox-reactive features. We found that in MDA-MB-231 human breast cancer cells, VNK-215 had apoptotic and antimigratory activity at concentrations that inhibited DUSP1 in mammalian cells, and induced phosphorylation of the DUSP1 substrates ERK, p38, and JNK. Studies in primary rat hepatocytes and live zebrafish embryos revealed that VNK-215, unlike previously described DUSP inhibitors, did not induce reactive oxygen species, mitochondrial damage, or toxicity. Our data suggest that the promiscuous activities of existing DUSP inhibitors are the cause of redox reactivity rather than target inhibition, and posit that DUSP1 is a druggable anticancer target for small molecule allosteric inhibitors. Citation Format: Laura Vollmer, Lawrence Vernetti, Ahmet Bakan, Vasiliy Korotchenko, Ivet Bahar, Billy Day, Michael Tsang, Andreas Vogt. A non-redox reactive allosteric inhibitor of MAPK phosphatases with selective toxicity to human cancer cells. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 745. doi:10.1158/1538-7445.AM2014-745