Convergent Therapeutic Strategies to Overcome the Heterogeneity of Acquired Resistance in &ITBRAF&ITV600E Colorectal Cancer

Clonal heterogeneity associated with acquired resistance presents a critical therapeutic challenge. Whole-exome sequencing of paired tumor biopsies and targeted sequencing of cell-free DNA (cfDNA) from patients with BRAF(V600E) colorectal cancer receiving BRAF inhibitor combinations identified 14 distinct alterations in MAPK pathway components driving acquired resistance, with as many as eight alterations in a single patient. We developed a pooled clone system to study clonal outgrowth during acquired resistance, in vitro and in vivo. In vitro, the dynamics of individual resistant clones could be monitored in real time in cfDNA isolated from culture media during therapy. Outgrowth of multiple resistant clones was observed during therapy with BRAF, EGFR, and MEK inhibitor combinations. However, ERK inhibition, particularly in combination with BRAF and EGFR inhibition, markedly abrogated clonal outgrowth in vitro and in vivo. Thus, convergent, up-front therapy may suppress outgrowth of heterogeneous clones harboring clinically observed resistance alterations, which may improve clinical outcome. SIGNIFICANCE: We observed heterogeneous, recurrent alterations in the MAPK pathway as key drivers of acquired resistance in BRAF(V600E) colorectal cancer, with multiple concurrent resistance alterations detectable in individual patients. Using a novel pooled clone system, we identify convergent up-front therapeutic strategies capable of intercepting multiple resistance mechanisms as potential approaches to suppress emergence of acquired resistance. (C) 2018 AACR.