Abstract 3325: Combination of DNMT and HDAC inhibitors reprogram cancer stem cell signaling to overcome drug resistance

Abstract

Abstract In recent years, impressive technical advancements have been made in the isolation and validation of the mammary stem cells (MaSCs) and cancer stem cells (CSCs). However, the signaling pathways that regulate stem cell self-renewal are largely unknown. Further, CSCs are believed to contribute to resistance to chemotherapy and radiation therapy. However, an effective therapeutic strategy to overcome this resistance is yet to be identified. We have recently discovered that the DNA methyltransferases, especially DNMT1, play critical role in MaSCs and CSCs self-renewal and targeted deletion of this gene impaired mammary tumor formation by inhibiting CSCs formation. However, the molecular mechanism(s) by which DNMTs control CSCs and the therapeutic relevance of DNMTs inhibitors in regulation of CSCs and overcome drug resistance are also largely unknown. In this study, using MMTV-Neu-Tg mouse mammary tumor model, we found that both luminal progenitor and basal stem cells are susceptible to genetic and epigenetic modifications, which leads to activation of un-activated Neu-Tg into transformed tumor forming phenotype. Combination of 5-Azacytidine, a DNMT inhibitor, and butyrate, a HDAC inhibitor, markedly reduces CSCs and consequently increases the overall survival of the animal. RNA-seq analysis of the CSCs treated with 5-AzaC+butyrate provides evidence that combined inhibition of DNMTs and HDACs reduces CSCs pool in the mammary gland by blocking growth-promoting signaling molecules like RAD51AP1 and SPC25. RAD51AP1 and SPC25, which are known to play a key role in DNA damage repair and kinetochore assembly, are significantly overexpressed in breast tumor tissues and associated with decreased overall patients’ survival. Further, these two genes are overexpressed in Tamoxifen and Taxol resistant human breast cancer cell lines. Functional inactivation of these genes in breast caner cells facilitates chemotherapy-induced apoptosis and reduces tumor growth. Overall, our studies provide strong evidence that breast CSCs (both basal stem cells and luminal progenitor cells) are susceptible for genetic and epigenetic modifications and associated with resistance to chemo- and radiotherapy. Thus, combination of DNMT and HDAC inhibitors can serve as an effective therapeutic strategy to block mammary tumor growth and to overcome drug resistance by inhibiting CSCs. Citation Format: Rajneesh Pathania, Ravindra B. Kolhe, Sabarish Ramachandran, Gurusamy Mariappan, Priyanka Thakur, Puttur D. Prasad, Vadivel Ganapathy, Muthusamy Thangaraju. Combination of DNMT and HDAC inhibitors reprogram cancer stem cell signaling to overcome drug resistance. [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 3325.