Abstract 5787: Ipatasertib impairs tumor growth in androgen sensitive and castrate resistant prostate cancer: Evidence in preclinical models

Abstract

Abstract Introduction: Therapeutic targeting the PI3K/AKT signaling pathway is an attractive strategy to combat solid tumors that exhibit hyper-AKT activity. Ipatasertib, a potent pan-AKT inhibitor, has exhibited significant inhibitory effects on tumor growth in preclinical studies, including models of Androgen Receptor (AR)-independent prostate cancer (PCa) that lack PTEN, a negative regulator of the PI3K/AKT pathway. It is currently being investigated in several ongoing clinical trials, including evaluating its efficacy in combination with abiraterone in castrate resistant PCa (CRPC) (NCT01485861). There is cross-talk between androgen signaling and PI3K/AKT pathway activation, however the optimal setting for AKT inhibition in PCa is not clear. Here we seek to determine the benefit of ipatasertib for androgen sensitive (AS) PCa alone or in combination with androgen deprivation (AD), as well as the benefit of ipatasertib alone or in combination with the antiandrogen enzalutamide in CRPC. Methods: In vitro studies utilized human androgen sensitive PCa cell lines LAPC, LAPC4shPTEN, and LNCAP, as well as two LNCaP-derived, castrate resistant cell lines. Cell viability was determined using CellTitre Glo assay and apoptosis by flow cytometry. Inhibitory effects of AKT signaling pathway was determined by western blot assays against AKT phosphorylation sites and downstream targets as well as detection for hormone receptor expression. In vivo studies utilized LuCaP 136 and LuCaP 136-derived castrate resistant (LuCaP 136CR) patient derived xenograft (PDX) models. Cells were injected into athymic mice and grouped into 4 arms. Intact mice bearing AS tumors were treated with vehicle, ipatasertib (100mg/Kg), AD, or ipatasertib + AD. Castrated mice bearing castrate-resistant tumors were treated with vehicle, ipatasertib, enzalutamide (10mg/Kg), or ipatasertib + enzalutamide. Tumor growth was determined twice/week via blinded caliper measurements. Results: Ipatasertib effectively inhibited AKT signaling, as indicated by significant decrease in phosphorylation of the downstream targets P70S6K and 4E-BP1. Our in vitro data indicate significant anti-proliferation effects of ipatasertib across all PCa models, both androgen sensitive and castrate resistant. Interestingly, this was irrespective of PTEN status. In addition, we observed a decrease in glucocorticoid receptor (GR) expression in enzalutamide resistant lines, although AR expression was not significantly altered. Preclinical animal studies showed significant response to tumor growth inhibition with ipatasertib monotherapy, which was enhanced with combination treatment. Conclusion: Ipatasertib is beneficial in models of androgen sensitive and castrate resistant PCa and can be effective in the treatment of PCa alone or in combination with current standard therapies targeting the androgen receptor. Citation Format: Remi M. Adelaiye-Ogala, Yen T. Nguyen, Jose A. Rodriguez-Nieves, Aian Neil Alilin, Supreet Agarwal, David Vanderweele. Ipatasertib impairs tumor growth in androgen sensitive and castrate resistant prostate cancer: Evidence in preclinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5787.