Abstract 4129: Chloroquine and romidepsin: combination therapy for treatment of breast cancer metastases

Abstract

Abstract Cancer metastasis is favored through dynamic regulation of gene expression and comprehensive cellular processes including epigenetic regulation. Aberrant gene expression by altered epigenetic regulation plays a fundamental role in the maintenance of breast cancer stem cell (BCSC) and drug resistance. Additionally, intrinsic tumor heterogeneity in primary tumors and the presence of the breast cancer stem cells complicates treatment options even further. Thus, it is hypothesized that the breast cancer metastasis can be cured by an effective treatment, targeting both the bulk and the BCSCs at the same time. Previously, chloroquine (CQ), inhibited spontaneous breast cancer metastasis to lungs very effectively through inhibition of autophagy as well as DNA hypomethylation. Romidepsin (RO), a highly potent and FDA-approved histone deacetylases inhibitor, is known to exert outstanding anti-cancer effects on numerous cancer types. Thus, we propose a combination therapy of chloroquine and romidepsin to target the breast cancer metastasis. The goal of this study is to test if the combined therapy will effectively inhibit breast cancer metastasis by targeting both bulk tumors and BCSCs compared to each single agent treatment. We evaluated in vitro anti-tumor effects of the combination therapy of chloroquine and romidepsin by measuring mammosphere forming efficiency (MSFE) and by analyzing apoptosis through Annexin V staining in paclitaxel sensitive and resistant Hs578t cells. Secondly, we investigated anti-tumor effects of vehicle (Con), CQ, RO, or their combination (RO-CQ) using a cell line and a patient-derived orthotopic xenograft models. Thirdly, we assessed BCSC populations and tumor initiation ability by FACS analysis, MSFE measurement, and limiting dilution assays (LDA). Finally, we evaluated the metastatic potential of tumors after the each treatment using an in vivo MDA-MB-231 lung metastasis model. We observed that the RO-CQ treatment resulted in the most significant reduction of MSFE and induction of apoptosis in BCSCs and bulk tumors compared to other treatment groups in both paclitaxel sensitive and resistant Hs578t cells. Secondly, only the RO-CQ treatment caused significant inhibition of tumor growth in vivo with substantial decrease in the CD44+/CD24- or Aldefluor+ BCSCs. The reduction of BCSCs by the RO-CQ treatment was well correlated with the severely reduced primary and the secondary MSFE. Also, the reduction of BCSCs was well reflected in the LDA, in which the RO-CQ treatment impaired tumor initiating ability. Finally, we confirmed in vivo that CQ alone and the RO-CQ treatments substantially abolished the metastatic potential of highly metastatic MDA-MB-231 cells. Our data suggest that the two FDA-approved drugs on breast cancer metastases will facilitate the rapid translation of basic discoveries into clinical approaches which can lead to improved survival for breast cancer patients with refractory metastases. Citation Format: Dong Soon Choi, Jenny C. Chang. Chloroquine and romidepsin: combination therapy for treatment of breast cancer metastases. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 4129. doi:10.1158/1538-7445.AM2015-4129