Abstract 914: COX-2 expression is associated with chemoresistance through cancer stemness property in head and neck squamous cell carcinoma

Introduction: COX-2 is one of the two isoforms of cyclooxygenase, an enzyme that catalyzes the conversion of arachidonic acid to prostaglandins. COX-2 is considered to be associated with progression in various cancers, and its expression has been reported to have an impact on poor prognosis in head and neck squamous cell carcinomas (HNSCCs). Furthermore, COX-2 expression has been shown to be associated with resistance to anticancer drugs. However, the precise mechanism of COX-2 for chemoresistance in HNSCC is not fully elucidated. The aim of the present study was to investigate the impact of COX-2 on cancer stem cell property, and to reveal its effect on chemoresistance by in vitro and clinicopathological assays. Methods: We examined the chemoresistance to docetaxel with or without COX-2 inhibitor (celecoxib) in HNSCC cell lines (FaDu, Detroit512) by MTS assays. To evaluate the association of COX-2 expression with stemness property, we assessed alteration of expression levels of the genes related to cancer stem cell (CSC) property after exposure to celecoxib by quantitative real-time PCR. We also performed a sphere formation assay using ultra low attachment dishes and microscopic imaging. Moreover, we analyzed immunohistochemical expressions of COX-2 and clinicopathological factors by using matched samples of pre-treatment biopsy and surgical specimens from hypopharyngeal carcinoma patients who had undergone trans-oral tumor resection with preoperative induction chemotherapy including docetaxel. Results: Cell survival rate under exposure to docetaxel was decreased by addition of celecoxib. COX-2 inhibitor downregulated the expression of Oct3/4 and Nanog. Sphere formation was inhibited by co-culture with COX-2 inhibitor, especially in FaDu cells. Immunohistochemical study in biopsy specimens revealed a negative correlation between COX-2 expression in biopsy specimens and pathological effect of induction chemotherapy in surgical specimens. Conclusion: The present study suggests that COX-2 expression is associated with cancer stemness property, and inhibition of COX-2 has a possibility to enhance chemosensitivity in HNSCCs. Furthermore, initial COX-2 expression in biopsy specimens may predict the effect of chemotherapy in HNSCCs. These results indicate that COX-2 can be an attractive target for the treatment of HNSCC. Citation Format: Shin Saito, Hiroyuki Ozawa, Yorihisa Imanishi, Mariko Sekimizu, Yoshihiro Watanabe, Fumihiro Ito, Yuichi Ikari, Nana Nakahara, Kaori Kameyama, Kaoru Ogawa. COX-2 expression is associated with chemoresistance through cancer stemness property in head and neck squamous cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 914.