Biomarkers of response to Akt inhibitor MK-2206 in breast cancer.

Abstract

1054 Background: Akt significantly contributes to cancer pathogenesis. PTEN, a negative regulator of PI3K/Akt signaling, is mutated or decreased, and PIK3CA is frequently mutated in multiple cancer lineages. We hypothesized that MK-2206, an allosteric Akt inhibitor, would inhibit Akt signaling thus blocking cancer cell growth, and PTEN and/or PIK3CA mutations may confer MK-2206 sensitivity in breast cancer. Methods: After determining sensitivity to MK-2206 in16 cell lines, the effect on Akt signaling was tested by reverse-phase protein array analysis and western blotting. The effect to cell cycle progression and cell death were analyzed by flow cytometry. Using RNA knockdown technique, the effect of PTEN, PIK3CA and Akt on MK2206 sensitivity was tested. Anti-tumor effect in vivo with or without paclitaxel was tested using PTEN-mutant ZR75-1 breast cancer xenografts. Results: MK-2206 inhibited Akt signaling and cell cycle progression, and increased apoptosis in a dose-dependent manner in breast cancer cell lines. Cell lines with PTEN or PIK3CA mutations were more sensitive to MK-2206 (P=0.0337), however, a number of lines with PTEN/PIK3CA mutations were MK-2206-resistant. Small interfering RNA (siRNA) knockdown of PTEN in breast cancer cells increased Akt phosphorylation concordant with increased MK-2206 sensitivity. Stable transfection of PIK3CA E545K or H1047R mutant plasmids into normal-like MCF10A breast cells enhanced MK-2206 sensitivity. Cell lines that were less sensitive to MK-2206 had lower ratios of Akt1/Akt2 and had less growth inhibition with Akt siRNA knockdown. In ZR75-1 xenografts, MK-2206 treatment inhibited Akt signaling, cell proliferation, and tumor growth. In vitro, MK-2206 showed a synergistic interaction with paclitaxel in MK-2206-sensitive cell lines, and this combination had significantly greater antitumor efficacy than either agent alone in vivo. Conclusions: MK-2206 has antitumor activity alone and in combination with chemotherapy. This activity may be greater in tumors with PTEN loss or PIK3CA mutation, providing a strategy for patient enrichment in clinical trials. However, not all tumors with PIK3CA/PTEN aberrations are MK-2206-sensitive, emphasizing the need for additional markers of response.