HPV and p53 status as precision determinants of head and neck cancer response to DNA-PKcs inhibition in combination with irradiation

Abstract

Major risk factors of head and neck squamous cell carcinoma (HNSCC) are tobacco use and human papillomavirus (HPV). HPV E6 oncoprotein leads to the degradation of the p53 protein, whereas HPV-negative cancers are frequently associated with TP53 mutations. Peposertib is a potent and selective, orally administered small-molecule inhibitor of the catalytic subunit of the DNA-dependent kinase (DNA-PKcs), a key regulator of non-homologous end joining (NHEJ). NHEJ inhibition along with irradiation (IR)-induced DNA double-strand breaks has the potential to increase antitumor treatment efficacy. Here, we investigated the responses of HNSCC models with distinct HPV and p53 status to treatments with IR, DNA-PKcs inhibition, and their combination. We observed that IR-induced DNA damage combined with peposertib administration shortly before IR results in decreased cell viability and proliferation and causes DNA repair delay in all the studied HNSCC cell lines. However, our data confirm that the actual cell fate upon this treatment is strongly dependent on cellular p53/HPV status. Cells lacking functional p53 due to its degradation by HPV or due to the presence of a loss-of-function mutation are arrested in the G2 phase of the cell cycle and eliminated by apoptosis whereas p53-proficient HNSCC cell lines undergo senescence. Consequently, HPV+ cancer cell lines and xenografts display stronger and more durable responses and seem to benefit from the combined treatment more than p53-proficient HNSCCs. In conclusion, DNA-PKcs inhibitor peposertib should be further studied as a potential radiosensitizer for HNSCCs, taking into consideration the genetic background and the HPV status of a particular tumor.