Abstract 3651: Deciphering immunomodulatory roles of the SMYD3 methyltransferase in HPV-negative head and neck squamous cell carcinoma

Human Papilloma virus (HPV)-negative head and neck squamous cell carcinoma (HNSCC) is a cancer with a 50% recurrence rate and poor overall survival. While immunotherapy with programmed-death-1 (PD-1) checkpoint inhibitors was recently approved in the first-line recurrent/metastatic setting, response rates are as low as 20%. A main reason for this is that a majority of these tumors have a low CD8+ T-cell intratumoral infiltrate, rendering primary resistance to T-cell based immunotherapy. We recently found that SET and MYND Domain containing 3 (SMYD3), a chromatin modifier that trimethylates histone 3 lysine 4 (H3K4me3), is overexpressed in HPV-negative HNSCC compared to normal epithelium, and that higher expression of SMYD3 is associated with lower mRNA levels of CD8A and CXCL9, 10 and 11 chemokines, which are key mediators of CD8+ T-cell trafficking, in HPV-negative HNSCC tumors (TCGA). Furthermore, SMYD3 depletion induced upregulation of CXCL9, 10, and 11 in human HNSCC cells in vitro. The purpose of this study is to evaluate whether targeting SMYD3 increases intratumoral CD8+ T-cell infiltration and enhances responses to PD-1 checkpoint inhibition, and to decipher relevant mechanisms. To investigate this hypothesis, a syngeneic, heterotopic mouse model (C57BL/6) using a doxycycline-inducible smyd3 knockdown HPV-negative mouse oral carcinoma cell line (MOC1) was generated. Experiments to assess whether smyd3 knockdown alone and in combination with PD-1 inhibition induce tumor growth restraint are planned. RT-PCR to evaluate the effects of smyd3 depletion on the expression of immune-related (type I IFN response and antigen presentation machinery) genes in the doxycycline-inducible MOC1 cell line, as well as in parental MOC1 cells using siRNA interference is being conducted. Western blotting to assess the effect of smyd3 depletion on global histone methylation marks is also being conducted. Furthermore, to assess whether smyd3 has a cell autonomous effect on the growth of MOC1 cells, cell viability assays (MTT) and cell cycle analysis are being pursued. Preliminary results have shown that smyd3 depletion in parental MOC1 cells induced significant upregulation of mouse cxcl9 and 10. Smyd3 depletion also led to significant cell death in parental MOC1 cells. Experiments to assess the effect of smyd3 depletion on CD8+ T-cell infiltration and tumor growth restraint in vivo are ongoing. This is the first study to investigate the role of SMYD3 as a regulator of antitumor immune response, and may lay the rationale to translate SMYD3 inhibitors in patients with HPV-negative HNSCC with the goal to render them susceptible to T-cell based immunotherapeutic approaches. Citation Format: Benjamin Bernard, Kyunghee Burkitt, Yvette Robbins, Nupur Nigam, Clint Allen, Lyuba Varticovski, Gordon Hager, Carter Van Waes, Vassiliki Saloura. Deciphering immunomodulatory roles of the SMYD3 methyltransferase in HPV-negative head and neck squamous cell carcinoma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 3651.