Abstract LB153: Inhibiting BRD4 as a proposed alternative therapeutic strategy for HPV16-associated head and neck squamous cell carcinoma

Abstract

Abstract Integration of Human Papilloma Virus (HPV) 16 into human genomes is an integral event for cancer progression in Head and Neck Squamous Cell Carcinoma (HNSCC). There is a need to differentiate treatment for HPV-16 integrated HNSCC from other subtypes. We hypothesize that by inhibiting Bromodomain Extra Terminal (BET) protein BRD4, a transcriptional co-regulator of host and viral genes can advance treatment in patients with the integrated subtype of HPV16 associated HNSCC. Through small molecule inhibition and knockdown of BRD4 in seven model HPV-16 integrated cell lines, we demonstrated that BRD4 down-regulates the expression of viral genes E6, E7, independent of viral E2 type of integration. Given that E6 expression is mediated by BRD4, E6-p53 interactions was abrogated as revealed through increased expression of p53. Furthermore, BRD4 inhibition caused downregulation of c-Myc. This result also suggests the function of BRD4 in the regulation of proteins in cell cycle regulation, including E2F1 and p21. BRD4 inhibition was also shown to delay DNA damage response (DDR) by reducing the expression of RAD51 in 6 out of 7 cell lines. RNA-sequencing results give further insight regarding the downregulation of genes involved in DDR – RAD51, BRCA1 and BRCA2 in all cell lines. RNA-sequencing data also gives us an understanding of the implication of BRD4-inhibition in other genes involved in cell cycle regulation. Knockdown of BRD4 done through small hairpin RNA (shRNA) constructs phenocopied the effects shown through inhibition of BRD4. Additionally, treating the above-mentioned cell lines with BRD4 inhibitor (JQ1) followed by radiation showed further downregulation of viral oncogenes E6, and E7. This suggests that combining radiation and JQ1 treatment can be a viable combination treatment. De-escalating radiation treatment with BRD4 inhibition has potential to be an effective combination treatment for HPV16 integrated HNSCC. Citation Format: Dhruthi Suresh, Chitrasen Mohanty, Albert R. Wang, Christina Kendziorski, Gopal Iyer. Inhibiting BRD4 as a proposed alternative therapeutic strategy for HPV16-associated head and neck squamous cell carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB153.