Abstract 3833: Ceramide/tamoxifen nanoliposomal combination - A promising strategy for treatment of chemoresistant breast cancer

Abstract

Abstract Drug resistance in breast and other cancers results from multiple gene interactions. Ceramide, a key intermediate in the sphingolipid pathway, can act as a powerful tumor suppressor. The employ of ceramide-based agents as opposed to the administration of ceramide generators such as daunorubicin, could be a smart strategy for cancer therapy. Polychemotherapy remains the best option for treatment of breast cancer at the aggressive, metastatic stage. The aim of our study was to investigate the cytotoxic and antiproliferative effects of ceramide (short-chain C6-ceramide) administered in combination with tamoxifen, used here as an inhibitor of ceramide glycosylation. We previously demonstrated the cytotoxicity of this combination in MDA-MB-231 cells; however, little regarding mechanism was established. The present study employs nanoliposomal formulations of both agents, a strategy to enhance efficacy. Four triple-negative chemoresistant breast cancer cell lines, MDA-MB-231, MDA-MB-468, BT-20 and Hs578T were used. Cytotoxicity assays revealed that C6-ceramide/tamoxifen synergistically reduced viability, compared to single agents in all four cell lines. For example, in MDA-MB-468 cells, nanoliposomal C6-ceramide (2.5 µM), tamoxifen (5 µM), and the combination reduced cell viability to 70, 85, and 10% of control, respectively (96 hr). A hallmark of cancer, implicated in tumor growth as well as metastasis, is resistance to induction of apoptosis. Assessment of cellular apoptosis showed that C6-ceramide/tamoxifen treatment promoted DNA fragmentation in a dose-dependant manner, attaining a value that was 36% over control at 24 hr. Introduction of the pan-caspase inhibitor, z-VAD-fmk, completely reversed DNA fragmentation, showing that apoptosis was mediated by caspase activation. The aggressive and metastatic behavior of any tumor is dependent on the ability of the cells to proliferate. Interestingly, the lower concentrations of our drug combination (2.5 µM) induced cell cycle arrest at G1, the first growth phase. In summary, this approach has potential to circumvent limitations of ceramide-based therapies, such as rapid ceramide clearance due to metabolism, the inability to attain therapeutic levels when ceramide-generating agents are employed, and inherent insolubility that is encountered. These findings demonstrate the in vitro efficacy of combination C6-ceramide/tamoxifen nanoliposomal formulations for suppressing growth of breast cancer cells, and suggest that tamoxifen may be an effective adjuvant for enhancing ceramide-driven cell death cascades. Supported by NIGMS 77391 and ABC's, Los Angeles. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3833. doi:1538-7445.AM2012-3833