Abstract LB-386: Targeting of induced cancer stem cells with iniparib in combination with carboplatin and gemcitabine

BACKGROUND: Mounting evidence exists that human breast cancers include a stem-like cell population with self-renewing, tumorigenic properties. This population of cells, known as cancer stem cells (CSCs) or tumor-initiating cells, shares phenotypic characteristics with embryonic stem cells (ESCs), including activation of certain developmental pathways, and is resistant to many anticancer therapies. Distinguishing features of stem cells include active DNA repair and resistance to apoptosis, which enable their survival in the presence of conventional cytotoxic and cytostatic therapies that target actively proliferating cells. Identification of pharmaceuticals that preferentially target CSCs represents a novel strategy in modern drug discovery and development. We investigated whether treatment with iniparib (BSI-201) can potentiate the anti-proliferative effects of gemcitabine and carboplatin in CSCs. METHODS: A multi-stage stem cell carcinogenesis model that mirrors the natural progression of carcinogenesis was previously developed using in vitro and in vivo selection of mutated ESCs, which exhibit specific tumor-initiating and cancer stem cell-associated behaviors (SLL Sciences). These induced CSCs (iCSCs) were treated with iniparib (3.7, 11, 33, or 100 μM), gemcitabine (1.5 nM), carboplatin (10 μM), or gemcitabine + carboplatin for 72 hours, and effects on iCSC proliferation were evaluated using an ELISA-based bromodeoxyuridine (BrdU) assay and an ATP-based detection assay for measuring cellular metabolism. Effects of iniparib and/or gemcitabine on DNA damage were evaluated by immunofluorescence staining of iCSC using antibodies against γH2AX (a marker of double strand DNA breaks) at 24 hours after treatment. RESULTS: Treatment with iniparib alone resulted in a dose-dependent decrease in cellular proliferation and metabolism, with the IC50 established at 60 μM. Iniparib (60 μM), gemcitabine (1.5 nM), and carboplatin (10 μM) each induced >50% reduction in iCSC proliferation; addition of iniparib to gemcitabine resulted in an 80% reduction in BrdU incorporation compared with gemcitabine alone (P = 0.027). To assess iniparib-associated DNA damage, γH2AX foci were quantified in > 300 cells for each treatment combination. Cells treated with iniparib, gemcitabine, or iniparib + gemcitabine demonstrated 3.7-, 6.8-, and 8.8-fold increases in γH2AX foci, respectively, compared with untreated control (P CONCLUSIONS: These findings demonstrate that iniparib increases the effects of gemcitabine in terms of antiproliferative activity and DNA damage in this CSC model. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-386. doi:10.1158/1538-7445.AM2011-LB-386