Efficacy of a Covalent ERK1/2 Inhibitor, CC-90003, in KRAS-Mutant Cancer Models Reveals Novel Mechanisms of Response and Resistance

As a critical signaling node, ERK1/2 are attractive drug targets, particularly in tumors driven by activation of the MAPK pathway. Utility of targeting the MAPK pathway has been demonstrated by clinical responses to inhibitors of MEK1/2 or RAF kinases in some mutant BRAF-activated malignancies. Unlike tumors with mutations in BRAF, those with mutations in KRAS (> 30% of all cancers and > 90% of certain cancer types) are generally not responsive to inhibitors of MEK1/2 or RAF. Here, a covalent ERK1/2 inhibitor, CC90003, was characterized and shown to be active in preclinical models of KRAS-mutant tumors. A unique occupancy assay was used to understand the mechanism of resistance in a KRAS-mutant patient-derived xenograft (PDX) model of colorectal cancer. Finally, combination of CC-90003 with docetaxel achieved full tumor regression and prevented tumor regrowth after cessation of treatment in a PDX model of lung cancer. This effect corresponded to changes in a stemness gene network, revealing a potential effect on tumor stem cell reprograming. Implications: Here, a covalent ERK1/2 inhibitor (CC90003) is demonstrated to have preclinical efficacy in models of KRAS-mutant tumors, which present a therapeutic challenge for currently available therapies.