AZD0364 Is a Potent and Selective ERK1/2 Inhibitor That Enhances Antitumor Activity in <i>KRAS</i> -Mutant Tumor Models when Combined with the MEK Inhibitor, Selumetinib

Abstract

The RAS-regulated RAF-MEK1/2-ERK1/2 (RAS/MAPK) signaling pathway is a major driver in oncogenesis and is frequently dysregulated in human cancers, primarily by mutations in <i>BRAF</i> or <i>RAS</i> genes. The clinical benefit of inhibitors of this pathway as single agents has only been realized in <i>BRAF</i>-mutant melanoma, with limited effect of single-agent pathway inhibitors in <i>KRAS</i>-mutant tumors. Combined inhibition of multiple nodes within this pathway, such as MEK1/2 and ERK1/2, may be necessary to effectively suppress pathway signaling in <i>KRAS</i>-mutant tumors and achieve meaningful clinical benefit. Here, we report the discovery and characterization of AZD0364, a novel, reversible, ATP-competitive ERK1/2 inhibitor with high potency and kinase selectivity. <i>In vitro</i>, AZD0364 treatment resulted in inhibition of proximal and distal biomarkers and reduced proliferation in sensitive <i>BRAF</i>-mutant and <i>KRAS</i>-mutant cell lines. In multiple <i>in vivo</i> xenograft models, AZD0364 showed dose- and time-dependent modulation of ERK1/2-dependent signaling biomarkers resulting in tumor regression in sensitive <i>BRAF</i>- and <i>KRAS</i>-mutant xenografts. We demonstrate that AZD0364 in combination with the MEK1/2 inhibitor, selumetinib (AZD6244 and ARRY142886), enhances efficacy in <i>KRAS</i>-mutant preclinical models that are moderately sensitive or resistant to MEK1/2 inhibition. This combination results in deeper and more durable suppression of the RAS/MAPK signaling pathway that is not achievable with single-agent treatment. The AZD0364 and selumetinib combination also results in significant tumor regressions in multiple <i>KRAS</i>-mutant xenograft models. The combination of ERK1/2 and MEK1/2 inhibition thereby represents a viable clinical approach to target <i>KRAS</i>-mutant tumors.