Enhancing efficacy of the MEK inhibitor trametinib with paclitaxel inKRAS-mutated colorectal cancer

Abstract

ABSTRACTBackgroundKRASis frequently mutated in the tumors of patients with metastatic colorectal cancer (mCRC) and thus represents a valid target for therapy. However, the strategies of targeting KRAS directly and targeting the downstream effector mitogen-activated protein kinase kinase (MEK) via monotherapies have shown limited efficacy. Thus, there is a strong need for novel, effective combination therapies to improve MEK-inhibitor efficacy in patients withKRAS-mutated mCRC.ObjectiveOur objective was to identify novel drug combinations that enhance MEK-inhibitor efficacy in patients withKRAS-mutated mCRC.DesignIn this study, we performed unbiased high-throughput screening (HTS) to identify drugs that enhance the efficacy of MEK inhibitorsin vitro, and we validated the efficacy of the drugsin vivo.MethodsHTS was performed using 3-dimensional CRC spheroids. Trametinib, the anchor drug, was probed with 2 clinically ready libraries of 252 drugs to identify effective drug combinations. The effects of the drug combinations on CRC cell proliferation and apoptosis were further validated using cell growth assays, flow cytometry, and biochemical assays. Proteomic and immunostaining studies were performed to determine the effects of the drugs on molecular signaling and cell division. The effects of the drug combinations were examinedin vivousing CRC patient-derived xenografts.ResultsHTS identified paclitaxel as being synergistic with trametinib.In vitrovalidation showed that, compared with monotherapies, this drug combination demonstrated strong inhibition of cell growth, reduced colony formation, and enhanced apoptosis in multipleKRAS-mutated CRC cell lines. Mechanistically, combining trametinib with paclitaxel led to alterations in signaling mediators that block cell cycle progression and increases in microtubule stability that resulted in significantly higher defects in the mitosis. Finally, the combination of trametinib with paclitaxel exhibited significant inhibition of tumor growth in severalKRAS-mutant patient-derived xenograft mouse models.ConclusionOur data provide evidence supporting clinical trials of trametinib with paclitaxel as a novel therapeutic option for patients withKRAS-mutated, metastatic CRC.