Combination of the mTOR Inhibitor Ridaforolimus and the Anti-IGF1R Monoclonal Antibody Dalotuzumab: Preclinical Characterization and Phase I Clinical Trial

Purpose: mTOR inhibition activates compensatory IGFR signaling. We evaluated the ridaforolimus (mTOR inhibitor) and dalotuzumab (anti-IGF1R antibody) combination. Experimental design: In vitro and in vivo models, and a phase I study where advanced cancer patients received ridaforolimus (10-40 mg/day QD×5/week) and dalotuzumab (10 mg/kg/week or 7.5 mg/kg QOW) were explored. Results: Preclinical studies demonstrated enhanced pathway inhibition with ridaforolimus and dalotuzumab. With 87 patients treated in the phase I study, main DLTs of the combination were primarily mTOR-related stomatitis and asthenia at doses of ridaforolimus lower than expected, suggesting blockade of compensatory pathways in normal tissues. Six confirmed partial responses were reported (3 breast cancer patients); 10/23 breast cancer patients and 6/11 ER+/high proliferative breast cancer patients showed antitumor activity. Conclusions: Our study provides proof-of-concept that inhibiting the IGF1R compensatory response to mTOR inhibition is feasible with promising clinical activity in heavily pretreated advanced cancer, particularly in ER+/high proliferative breast cancer.