Abstract 1963: Analysis of aryl substitution and intramolecular ligand H-bonding in selective inhibitors of the MEK5/ERK5 cascade

Abstract

Abstract Mitogen Activated Protein Kinase (MAPK) pathways initiate with external signaling, proceed through a sequence of protein kinases, and alter cell proliferation, growth, and survival. MAPK pathways proceed through a well-ordered sequence but are interconnected and modified by the cell's internal needs. The MEK-catalyzed phosphorylation of its target ERK represents the most selective interaction of MAPK signaling cascades. The type III MEK1/2 inhibitor, Mekinist, was recently approved by the FDA for the treatment of unresectable or metastatic melanoma with BRAF V600E or V600K mutations. This success suggests inhibitors of other MEK/ERK cascades may be reasonable strategies for anti-cancer therapeutic strategies. Despite the likely involvement of MEK5 phosphorylation of ERK5 in early and triple negative breast cancers, prostate cancer, and renal cancer, little work has been focused on developing selective MEK5 inhibitors. We have previously described an initial series of anthranilic acid derivatives structurally derived from the known non-selective MEK inhibitor PD0325901. To explore structural requirements for selective inhibition of MEK5 versus MEK1/2, aryl substitution and the role of proposed internal hydrogen bonding of the ligand were examined with novel compounds. These were tested at 10 μM in MDB-MB-213 cells subsequently treated with EGF to induce MEK1/2 and MEK5 phosphorylation. Western blot analysis following electrophoresis using IR-tagged antibodies raised against pERK1/2, pERK5, ERK1/2, or ERK5 permitted determination of total and relative inhibition of MEK-mediated generation of pERK. Incubation with PD0325901 resulted in full suppression of both pERK1/2 and pERK5. For the aryl substitutions examined, omission of the halogens on the pendant phenyl group (SC-1-181) abolished MEK1/2 inhibition(0% decrease in pERK1/2) yet retained good MEK5 inhibition (82% decrease in pERK5). Disruption of an internal nitrogen-acyl hydrogen bond preferentially decreased MEK5 inhibition (SC-2-32: 40% and 16% decrease in pERK5 and pERK1/2 respectively). This establishes early evidence of significant variation in specificity of MEK type III binding sites that may be exploited as pharmacological tools and possibly as therapeutic agents for cancers overexpressing MEK5. Citation Format: Patrick T. Flaherty, Jane C. Cavanaugh, Mohit Gupta, Colin Vechery, Suravi Chakrabarty, Darlene Monlish, Thomas Wright. Analysis of aryl substitution and intramolecular ligand H-bonding in selective inhibitors of the MEK5/ERK5 cascade. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1963. doi:10.1158/1538-7445.AM2015-1963