Abstract 3354: HDAC inhibitor SAHA suppressed beast cancer stem cells in vitro and in vivo

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Although conventional chemotherapies eliminate differentiated cancer cells in the bulk of tumors, they are ineffective against cancer stem cells (CSCs), which initiate tumors and result in cancer recurrence. The purpose of this study is to investigate the efficacy of HDAC inhibition by SAHA on breast CSCs through epigenetic modifications in cancer stem cells. Two different breast cancer cell lines with basal (SUM159) and luminal (MCF7) subtypes were used in this study. In order to examine HDAC mediated CSC regulation, we utilized a number of in vitro and in vivo CSC assays including tumorsphere formation, Aldefluor assay, CD44+/CD24- phenotype and mouse xenografts. Breast cancer stem cells (CSC) were monitored after treatment of different concentrations of SAHA (0.5-2µM). The ability of HDAC inhibitor to suppress the self-renewal capability of CSCs was evaluated by tumorsphere assay from a single Aldefluor-positive cell in a 96-well Ultra-low attachment plate under the suspension condition. The tumorsphere formation rate was used to evaluate the self-renewal capability of CSCs. The mouse xenograft model bearing with SUM159 cells and primary breast tumors (MC1) was used to test the inhibition of SAHA on CSCs and impairment of their self renewal in vivo. Microarray gene expression analysis was performed to elucidate molecular mechanisms of HDAC underlying the CSC inhibition, following the treatment of SAHA. SAHA reduced SUM159 Aldefluor-positive cells in a concentration-dependent manner with significant reduction (>50%) at 1µM. SAHA dramatically reduced the CSC population (CD44+/CD24 low) by 90% in MCF7 cells. Since CSCs are able to expand its population through the self-renewal, a CSC-targeting drug to inhibit both self-renewal and to eliminate CSCs is highly desired. Tumorsphere formation assay showed that SAHA (0.5µM) reduced the tumorsphere formation rate by 77%. In addition, the sustaining tumorsphere reductions (∼80%) in second and third passages in the absence of SAHA suggest the the impaired self-renewal capability of breast CSCs by SAHA is not repairable. Furthermore, the size of SAHA-treated tumorspheres was substantially smaller than that of the control, suggesting that SAHA also inhibited the proliferation of progenitor cells. In SUM159 tumor xenograft model, SAHA significantly inhibited the tumor growth by 45% and 84% in SUM159 and MC1 tumor xenografts, respectively, compared to the vehicle-treated group. SAHA reduced Aldefluor-positive cells in SUM159 and MC1 tumors by 50-90% following 2-week treatment. Tumor reimplantation showed that SAHA was able to abolish the tumor engraftment ability of cells derived from drug-treated mice in secondary mice. These data suggest that SAHA was able to target breast CSCs in vitro and in vivo. SAHA not only diminished the CSC population but also attenuated their self-renewal ability of the residual CSCs. 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 3354. doi:10.1158/1538-7445.AM2011-3354