Abstract 3735: Regulation of HPV gene expression by 5-azacytidine treatment in head and neck cancer

Abstract

Abstract Human papillomavirus (HPV) causes approximately 80% of head and neck squamous cell carcinoma (HNSCC) in the oropharynx, and its incidence is now higher than uterine cervical cancer in the US. The CDC estimates that this common sexually transmitted disease accounts for nearly 13,000 HPV+ HNSCC patients per year in the United States. Despite having a higher cure rate than HPV- HNSCC, the recurrence rate is approximately 30%. These patients have few therapeutic options since resistance to treatment arises from all known therapeutic modalities. Initial therapy for HPV+ HNSCC is aggressive and often results in negative lifelong side effects. The substantial recurrence rate and high morbidity of primary therapy suggest the need for new treatments. Global genome hypermethylation in HPV+ HNSCC, compared to HPV-, prompted our lab to explore demethylation as a therapeutic option. 5-azacytidine (5-aza) and 5-aza-2′-deoxycytidine (decitabine) are synthetic cytidine analogs that cause DNA demethylation by trapping methyltransferases to chromatin. These demethylating agents are FDA approved for the treatment of myelodysplasia and acute myeloid leukemia. Recently, we found that HPV+ HNSCC cells are more sensitive than HPV- cells to 5-aza, that low doses of 5-aza delayed HPV+ xenograft tumor growth, and that HPV+ tumor samples from patients treated with 5-aza in a window trial had increased apoptosis. We also observed a marked downregulation of HPV gene expression after 5-aza. Decreased HPV E6 expression, followed by reactivation of tumor suppressor p53, induced p53-dependent apoptosis in HPV+ HNSCC. Thus, decreased expression of HPV genes is an important component of 5-aza-associated toxicity toward HPV+ HNSCC; therefore, we further explored mechanisms through which demethylation negatively regulates the expression of HPV genes. First, we determined that 5-aza regulates transcription of HPV genes, but not the stability of HPV transcripts. Second, we found that transcriptional regulation of HPV genes after 5-aza depends on the proto-oncogene JunB, a component of the transcription factor Activator Protein 1 (AP-1). Moreover, our experiments revealed that clonogenic survival of HPV+ head and neck cancer cells is dependent on JunB expression. In summary, our study provides an improved mechanistic understanding of the regulation of HPV gene transcription in HNSCC and identifies a novel HPV+ HNSCC dependency on JunB, potentially providing a basis for a new rational targeted therapy. Citation Format: Hina Rehmani, Natalia Isaeva, Wendell G. Yarbrough. Regulation of HPV gene expression by 5-azacytidine treatment in head and neck cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 3735.