PROJECT SUMMARY/ABSTRACT Patients diagnosed with advanced stage KRAS mutant colorectal cancer have an overall survival of roughly one year. Despite the emergence of an increased number of molecular targeted agents, the prognosis for patients with these cancers remains poor with 5-year survival rates of <10%. Recently, progress has been made in the clinical advancement of therapeutics directed specifically against KRASG12C mutations, which are present in roughly five percent of colorectal tumors. However, monotherapy trials conducted with KRASG12C targeted agents, while encouraging, have met with disappointing lack of durable responses, dictating the need for combination approaches. EGFR is known to reactivate MAPK kinase signaling in response to downstream intervention, an event that is further complicated by the role of the PI3K/mTOR pathway in mediating resistance. The central hypothesis of this proposal is that a dual small molecule inhibitor that potently and selectively targets both EGFR and PI3 kinase represents a viable treatment strategy in combination with the KRASG12C inhibitor clinical candidate AMG-510. To test this hypothesis, we have designed small molecules that exhibit potent and selective dual inhibition of EGFR and PI3K family members. We propose to carry out a mouse trial of our dual EGFR/PI3K lead molecule MTX-531 in combination with AMG-510 in xenograft models established from patients diagnosed with KRASG12C mutant colorectal cancer. Molecular profiling will be carried out to elucidate markers that correlate with inherent sensitivity as well as the adaptive signaling changes that lead to progression. Responder models will be re-evaluated in confirmatory testing in head-to- head comparison with the combination of cetuximab and AMG-510. The overall objective of this proposal is to demonstrate preclinical proof of concept for pursuit of this development path to optimize the therapeutic potential of MTX-531 as a precision medicine approach for the treatment of KRASG12C mutant colorectal cancer.