Effects of prexasertib, a CHK1 inhibitor, in the immune microenvironment of head and neck squamous cell carcinoma (HNSCC).

Abstract

e18541 Background: Despite considerable advancements in the standard therapies including surgery, chemotherapy and radiotherapy, the clinical outcome for head and neck squamous cell carcinoma (HNSCC) remains poor due to tumor recurrence and metastasis. Molecular-targeted therapies have evolved as novel and promising treatment for HNSCC patients. Herein, we identified a CHK1 inhibitor, prexasertib, as a therapeutic target that enhanced the infiltration of innate and adaptive immune markers in the mice tumor immune microenvironment (TIME) and subsequently sensitizes the tumors. Methods: For this study we used syngeneic mouse model of HNSCC developed using mouse tonsil epithelial cells transformed with HRAS expression and PTPN13 knockdown to represent tobacco-induced HNSCC (MTE-Ras). In vitro drug activity of prexasertib was determined using immunoblotting, flow cytometry, cell proliferation and colony formation assays. The effect of prexasertib on TIME was quantified by Quantigene Plex panel and multiplex immunohistochemistry (mIHC). Results: We found that in vitro treatment with prexasertib increased the amount of DNA damage in the cancer cells and eventually lead to their death. Similarly, our in vivo data showed that treatment with prexasertib resulted in significant tumor regression and increased mice survival. At the molecular level, prexasertib treatment resulted in an upregulation of transcripts associated with T-cell activation, cytokines, chemokines and macrophages indicating an upregulation of inflammatory gene signature. This was further supported by our findings from mIHC staining of mice tumors showing increased infiltration of natural killer cells, natural killer T cells and dendritic cells, following prexasertib treatment. Interestingly, we also saw an increase in the Tregs after prexasertib treatment, which is indicative of an immunosuppressive environment, and we speculate this could be as a result of negative feedback following immune activation by prexasertib treatment. Conclusions: Our results uncover a previously unidentified role of prexasertib in regulating the innate and adaptive immune response in HNSCC, and therefore further corroborate CHK1 as a promising therapeutic target in HNSCC.