Abstract 353: Vorinostat enhances anti-tumor effects of cisplatin in head and neck cancer cells by targeting cancer stem cells
Authors: Kumar Bhavna , Yadav Arti , Teknos Theodoros N. , Kumar Pawan 
Published: August 2015

Abstract
Objective: Head and neck squamous cell carcinoma (HNSCC) remains a major health care problem worldwide, comprising almost 50% of all malignancies in some developing nations. Even with extensive surgery and full course chemoradiation treatment the survival rates of HNSCC patients have not significantly improved over the last two decades. Acquisition of chemoresistance, locoregional recurrence and metastatic phenotype are the major causes of treatment failure and mortality in these patients. It is therefore imperative that we gain a better understanding of the molecular mechanisms that contribute to the aggressive tumor phenotype in order to develop novel and effective strategies for the treatment of head and neck cancer patients. Recent studies have highlighted the role of histone deacetylases (HDACs) in regulating a number of genes that are involved in cell cycle control, proliferation, survival, DNA repair and differentiation. In this study, we examined if treatment with a HDAC inhibitor, Vorinostat could reverse chemoresistance in head and neck cancer cells and enhance the therapeutic efficacy of cisplatin treatment.
Methodology: HDACs expression in tumor samples from HNSCC patients was examined by real time PCR. Cell growth was examined by MTT assay and colony formation assay. Western blot analysis was used to measure changes in protein levels. Cancer stem cell phenotype was assessed by tumorsphere formation. A SCID mouse xenograft model was used to access the in vivo efficacy of Vorinostat.
Results: Our results show that HDAC1, 2, and 6 levels are markedly increased in the head and neck cancer cell lines as compared to normal human oral keratinocytes. We took two cisplatin sensitive cell lines and grew them in increasing concentrations of cisplatin to mimic acquired resistance in patients. Both of these cisplatin resistant cell lines (cisR) showed further increase in HDAC1 and 2 expressions as compared to the cispaltin sensitive parental cells. Depletion of HDAC1 and 2 in these cisR cell lines by siRNA significantly enhanced cisplatin sensitivity. Next, we used an HDAC inhibitor, Vorinostat on these cell lines and observed a dose dependent inhibition of cell proliferation (MTT). In addition, Vorinostat treatment significantly decreased tumorsphere formation and the expression of stem cell marker, Nanog. Vorinostat in combination with cisplatin showed a synergistic effect on the inhibition of cell proliferation and tumorsphere formation. We then assessed the efficacy of Vorinostat treatment as a single agent or in combination with cispaltin in SCID mouse xenograft model. Similar to the in vitro results, combination treatment was most effective in reducing the tumor burden in the mice.
Conclusions: Taken together, our results suggest that targeting of HDACs with Vorinostat could be an effective treatment strategy for the treatment of HNSCC patients that do not respond to currently used treatment regimens.
Citation Format: Bhavna Kumar, Arti Yadav, Theodoros N. Teknos, Pawan Kumar. Vorinostat enhances anti-tumor effects of cisplatin in head and neck cancer cells by targeting cancer stem cells. [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 353. doi:10.1158/1538-7445.AM2015-353