Abstract 101: WHSC1L1 as a therapeutic target in squamous cell carcinoma of the head and neck

Abstract

Abstract Background: Squamous cell carcinoma of the head and neck (SCCHN) is a common malignancy with high recurrence rates and poor survival, thus new therapies are eagerly awaited. Protein lysine methyltransferases (PKMTs) have recently become one of the most important targets for drug discovery efforts, but only a few studies have explored their role in the pathogenesis of SCCHN. WHSC1L1, a nuclear SET-Suppressor of variegation 3-9, Enhancer of zeste and Trithorax-domain (NSD) PKMT and chromatin modifier, was reported to be amplified (8p11.23) in 6% of SCCHN tumors. This study aims to elucidate the pathophysiological role of WHSC1L1 as an oncogenic force in SCCHN and provide rationale for the development of inhibitors targeting WHSC1L1. Methods: Cytotoxicity assays (MTTs) were conducted in one HPV-positive and one HPV-negative SCCHN cell line with WHSC1L1-specific siRNAs. Quantitative polymerase chain reaction (qPCR) and Western blotting were performed to examine WHSC1L1 expression levels in 14 SCCHN cell lines in comparison to a normal keratinocyte cell line (KGM). Immunohistochemistry (IHC) for WHSC1L1 in 115 patients with SCCHN and correlation of its expression with H3K36me2 was also performed. To identify candidate substrates that are directly methylated by WHSC1L1, in vitro methyltransferase assays using a recombinant protein library were conducted. Results: siRNA-mediated knockdown of WHSC1L1 caused significant cell death in 2 SCCHN cell lines. Approximately 30% of SCCHN cell lines overexpressed WHSC1L1 compared to normal keratinocytes. WHSC1L1 expression as evaluated by IHC was significantly stronger in SCCHN compared to normal epithelium (Kruskal-Wallis test, p = 0.002) and 24% of SCCHN sections expressed high levels of WHSC1L1, compared to 6% of dysplastic lesions and 0% of normal epithelium sections. Interestingly, no association between WHSC1L1 expression levels and H3K36me2 was observed. Conclusions: WHSC1L1 is genetically altered in multiple cancer types. In SCCHN, it is significantly overexpressed in 24% of the tumors and its knockdown caused significant growth suppression of both HPV-positive and HPV-negative SCCHN cell lines. Taken together, WHSC1L1 merits further investigation as a potential therapeutic target in SCCHN. Citation Format: Vassiliki Saloura, Theodore Vougiouklakis, Mark Lingen, Tanguy Seiwert, Everett Vokes, Yusuke Nakamura, Ryuji Hamamoto. WHSC1L1 as a therapeutic target in squamous cell carcinoma of the head and neck. [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 101. doi:10.1158/1538-7445.AM2015-101