Testing of the Akt/PKB inhibitor MK-2206 by the pediatric preclinical testing program

Background: MK-2206 is a small molecule allosteric inhibitor of Akt/PKB that is undergoing clinical trials for treatment of cancer. Procedures: MK-2206 was tested against the PPTP in vitro panel using a 96-hour exposure (1.0nM-10μM), and in vivo using thrice weekly dosing for a planned 4 weeks at its maximum tolerated dose (MTD) of 180mg/kg. Results: In vitro, the median relative IC ₅₀ value for MK-2206 was 2.2μM. Four cell lines with IC ₅₀ values<200nM included two ALL cell lines (COG-LL-317 and RS4;11), an AML cell line with an activating KIT mutation (Kasumi-1), and a Ewing sarcoma cell line (CHLA-10). In vivo, MK-2206 induced significant differences in EFS distribution compared to control in 12 of 29 (41%) of the evaluable solid tumor xenografts and in 2 of 8 (25%) of the evaluable ALL xenografts. Significant differences in EFS distribution were most frequently noted in the osteosarcoma panel (6 of 6). A single solid tumor xenograft (OS-31) had a greater than twofold increase in time to event compared to control animals, with all other solid tumor xenografts showing lesser degrees of tumor growth inhibition. Objective responses were not observed for either the solid tumor or ALL xenografts. Conclusions: MK-2206 showed its most consistent activity in vitro against ALL cell lines and in vivo against osteosarcoma xenografts. However, no objective responses were observed in solid tumor or ALL xenografts. Further preclinical work evaluating MK-2206 in pediatric models in the combination therapy setting may contribute to its pediatric development.