Abstract 1287: The dual IAP antagonist, ASTX660, increases the anti-tumor activity of paclitaxel in preclinical models of triple-negative breast cancer in vivo

Abstract

Abstract Background: Paclitaxel-mediated secretion of inflammatory mediators, including TNFα, potentially creates paracrine and autocrine signaling loops that can reduce paclitaxel-induced apoptosis with resultant cancer cell survival (paclitaxel resistance). One mechanism of cancer cell survival is the expression of inhibitor of apoptosis proteins (IAPs): Cellular IAP (cIAP) is involved in inflammatory pro-survival NF-κB activation, blocking the activation of effector caspases 3 and 7, while X-linked IAP (XIAP) directly binds the effector caspases 3, 7 and 9, inhibiting the full activation of the apoptotic pathway. Antagonism of IAPs in the setting of paclitaxel treatment may enhance the cancer cell death by switching the chemotherapy-induced inflammatory TNFα signaling from pro-survival to apoptosis. ASTX660 is an orally bioavailable dual antagonist of cIAP and XIAP, currently being investigated in a single-agent Phase 1/2 clinical trial in patients with advanced solid tumors and lymphomas (NCT02503423). Here, we characterize the activity of ASTX660 in triple-negative breast cancer (TNBC) preclinical models as a single agent and in combination with paclitaxel. Results: We first investigated the viability of 21 TNBC cell lines treated with ASTX660 in vitro and found that 43% were sensitive either to ASTX660 alone (MDA-MB-231 and HCC38) or in the presence of exogenous TNFα (HCC1806, Hs578T, BT549, HCC1395, DU4475, MDA-MB-453 and mouse EMT6). In HCC1806 xenografts in mice, both ASTX660 (daily oral treatment) and paclitaxel (weekly intravenous treatment) as single agents caused moderate tumor growth inhibition but not regression. ASTX660 and paclitaxel combination treatment, however, caused regression and all tumors achieved a partial response by Day 19 of treatment. An increase in circulating acute-phase-proteins in animals was also observed on paclitaxel treatment. Conclusions: Our study suggests that paclitaxel treatment causes an inflammatory response which could qualitatively change the tumor environment. Inhibition of IAPs in such inflammatory environment induced by paclitaxel may lead to rapid apoptotic cell death. Thus, addition of IAP antagonist may be a promising approach to enhance the TNBC response to paclitaxel therapy. Citation Format: Tomoko Smyth, Yoko Nakatsuru, Ryoto Fujita, George Ward, Luke Bevan, Jon Lewis, Nicola Wallis, John Lyons. The dual IAP antagonist, ASTX660, increases the anti-tumor activity of paclitaxel in preclinical models of triple-negative breast cancer in vivo. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1287.