Phase I Study of an AKT Inhibitor (MK-2206) Combined with Lapatinib in Adult Solid Tumors Followed by Dose Expansion in Advanced HER2+ Breast Cancer

Purpose: Preclinical data support combining AKT inhibitors with HER2-targeted therapies to overcome resistance to treatment. This phase I study combined the investigational AKT inhibitor, MK-2206, with lapatinib to determine the MTD. Experimental Design: The dose escalation cohort enrolled adults with advanced solid tumors, who received MK-2206 dosed 30 to 60 mg every other day and lapatinib 1,000 to 1,500 mg daily continuously, escalated using a 3+3 design. Cycles were 28 days except cycle 1 (35 pharmacokinetic interactions). The dose expansion cohort enrolled adults with advanced HER2(+) breast cancer. Results: Twenty-three participants enrolled in the dose escalation cohort. Dose-limiting toxicities were hyponatremia, fatigue, rash, hypocalcemia, and mucositis. Common toxicities included diarrhea, nausea, and rash. The MTD was reached at MK-2206 45 mg orally every other day and lapatinib 1,500 mg orally daily. Two participants maintained stable disease for > 4 months, including a colorectal cancer participant with substantial carcinoembryonic antigen decrease. Of 5 participants in the dose expansion cohort, 2 maintained stable disease for > 6 months, including one with prior progression on single-agent lapatinib. Plasma MK-2206 concentrations decreased after addition of lapatinib, but in vitro studies indicate lapatinib increases the intracellular levels of MK-2206. Conclusions: MK-2206 combined with lapatinib can be tolerated with both drugs above biologically active single-agent doses. Overlapping toxicities result in significant diarrhea and rash, which can be managed medically. Antitumor activity was promising and supports evaluation of AKT inhibitors combined with HER2-targeted therapies.