Abstract 74: Targeting nuclear export for triple-negative breast cancer therapy

Abstract

Abstract Triple-negative breast cancers (TNBC) comprise the most aggressive subtype of breast cancer. They rapidly acquire resistance to chemotherapy and are also refractory to endocrine therapy and HER2 inhibitors. In fact, no targeted therapies are currently available against these tumors. Genome sequencing studies have shown that TNBCs are exceedingly heterogeneous in genetic mutations as well as copy number variations. Yet, TNBC almost invariably harbor inactivating mutations in TP53, which seems to be a crucial event in the pathogenesis of these tumors. We recently performed a series of siRNA lethality screens in vitro (N = 11 cell lines) to identify, in an unbiased way, recurrent vulnerabilities that could be harnessed as novel targets for TNBC therapy. Hits were genes whose silencing triggered massive cell death in ≥ 30% of TNBC lines tested. The screens re-discovered mitosis as a frequent Achilles’ heel of these tumors (antimitotic drugs are currently a mainstay of TNBC therapy), supporting the validity of the approach. The nuclear transport gene RAN also scored among the most frequent TNBC selective dependencies. Moreover, TNBC cell lines were exquisitely sensitive to selinexor (KPT-330), a first-in-class inhibitor of exportin 1 (XPO-1) currently in phase 2 trials, both in vitro and in vivo. TNBC cells treated with selinexor died of apoptosis. In contrast, normal human primary breast epithelial progenitors (BPE) underwent cell cycle arrest (but not death) upon selinexor treatment, and were able to resume proliferation upon drug removal. The efficacy of selinexor across different TNBC models varied, suggesting that additional factors, beside the TNBC status, are at play. Preliminary data based on a genome-wide CRISPR screen for genes and networks conferring sensitivity to selinexor using a p53-mutant TNBC cell line (MDA-MB-231) implicated a number of TP53-related genes as key mediators of response. Together, these data support the notion that p53-mutant TNBC coopt nuclear export function to silence TP53-associated networks and that XPO-1 inhibitors could be a viable strategy to tackle TNBC in the clinic. Citation Format: Fabio Petrocca. Targeting nuclear export for triple-negative breast cancer therapy. [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 74.