Ipatasertib, an oral AKT inhibitor, in combination with carboplatin exhibits anti-proliferative effects in serous endometrial cancer: Endometrial Cancer Molecularly Targeted Therapy Consortium (238)

Abstract

<b>Objectives:</b> Ipatasertib (IPAT) is an investigational, orally-administered, ATP-competitive, highly selective inhibitor of protein kinase B (AKT) that has demonstrated antitumor activity in metastatic prostate cancer and longer progression-free survival in triple-negative breast cancer. Hyperactivation of the PI3K/AKT signaling pathway is frequently seen in endometrial cancer (EC), including serous histology tumors. Thus, we evaluated the antiproliferative efficacy of IPAT in combination with standard-of-care carboplatin in human serous EC cell lines. <b>Methods:</b> The human serous EC cell lines, ARK-1 and SPEC-2, were exposed to varying concentrations of IPAT (Genetech) and carboplatin. Cell proliferation was assessed by MTT assay. To assess the synergy of IPAT and carboplatin, the combination index (CI) was calculated by the method of Chou and Talalay. Apoptosis was assessed by cleaved caspase-3 assay. Cellular stress was measured by DCFDA assay. Western immunoblotting determined the effects of IPAT and carboplatin on apoptotic (MCL-1 and BCL-2) and cellular stress (Bip and PERK) pathways in the ARK-1 and SPEC-2 cell lines. <b>Results:</b> IPAT and carboplatin significantly inhibited cell proliferation in a dose-dependent manner after 72 hours of treatment. The median IC₅₀ for IPAT was 8µM in the ARK-1 and 5µM in SPEC-2. The median IC₅₀ for carboplatin was 50µM in the ARK-1 and 65µM in SPEC-2. Simultaneous exposure of cells to various doses of carboplatin in combination with IPAT resulted in a significant synergistic antiproliferative effect (CI<1). IPAT and carboplatin induced the activity of cleaved-caspase-3 by 2.3-fold in ARK-1 and 3.8-fold in SPEC-2 (p<0.05) while simultaneously reducing expression of the apoptotic proteins MCL-1 and BCL-2. DCFDA assay analysis demonstrated that IPAT and carboplatin induced ROS products by 1.39-fold and 1.17-fold in the ARK-1 and SPEC-2 cell lines (p<0.05), respectively, and increased Bip and PERK protein expression. The effects of IPAT combined with carboplatin on apoptosis and cellular stress were greater when compared to IPAT or carboplatin alone in both cell lines (p<0.05). <b>Conclusions:</b> The combination of IPAT and carboplatin showed synergistic antiproliferative activity in human serous EC cell lines. Thus, IPAT plus carboplatin may be a promising combination in the treatment of serous EC. Studies in transgenic and patient-derived xenograft EC mouse models are underway to assess the in vivo efficacy of IPAT +/- carboplatin.