ERK mutations and amplification confer resistance to ERK-inhibitor therapy

Purpose:MAPK pathway inhibitors targeting BRAF and MEK have shown clinical efficacy in patients with RAF and/or RAS mutated tumors. However, acquired resistance to these agents has been an impediment to improved long-term survival in the clinic. In such cases, targeting ERK downstream of BRAF/MEK has been proposed as a potential strategy for overcoming acquired resistance. Preclinical studies suggest that ERK inhibitors are effective at inhibiting BRAF/RAS mutated tumor growth and overcome BRAF or/and MEK inhibitor resistance. However, as with other MAPK pathway inhibitors, treatment with ERK inhibitors is likely to cause resistance in the clinic. Here, we aimed to model mechanism of resistance to ERK inhibitors. Experimental Design:We tested five structurally different ATP-competitive ERK inhibitors representing three different scaffolds on BRAF/RAS mutant cancer cell lines of different tissue types to generate resistant lines. We have used in vitro modeling, structural biology and genomic analysis to understand development of resistance to ERK inhibitors and the mechanisms leading to it. Results:We have identified mutations in ERK1/2, amplification and overexpression of ERK2, and overexpression of EGFR/ERBB2 as mechanisms of acquired resistance. Structural analysis of ERK showed that specific compounds that induced on-target ERK mutations were impaired in their ability to bind mutant ERK. We show that in addition to MEK inhibitor, ERBB-receptor and PI3K/mTOR pathway inhibitors are effective in overcoming ERK-inhibitor resistance. Conclusions:These findings suggest that combination therapy with MEK or ERBB-receptor or PI3K/mTOR and ERK inhibitors may be an effective strategy for managing the emergence of resistance in the clinic.

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