Misregulation of DNA damage repair pathways in HPV-positive head and neck squamous cell carcinoma contributes to cellular radiosensitivity

Abstract

Patients with human papillomavirus type 16 (HPV)-associated oropharyngeal squamous cell carcinomas (OPSCC) display increased sensitivity to radiotherapy and improved survival rates in comparison to HPV-negative forms of the disease. However the cellular mechanisms responsible for this characteristic difference are unclear. Here, we have investigated the contribution of DNA damage repair pathways to the in vitro radiosensitivity of OPSCC cell lines. We demonstrate that two HPV-positive OPSCC cells are indeed more radiosensitive than two HPV-negative OPSCC cells, which correlates with reduced efficiency for the repair of ionising radiation (IR)-induced DNA double strand breaks (DSB). Interestingly, we show that HPV-positive OPSCC cells consequently have upregulated levels of the proteins XRCC1, DNA polymerase β, PNKP and PARP-1 which are involved in base excision repair (BER) and single strand break (SSB) repair. This translates to an increased capacity and efficiency for the repair of DNA base damage and SSBs in these cells. In addition, we demonstrate that HPV-positive but interestingly more so HPV-negative OPSCC display increased radiosensitivity in combination with the PARP inhibitor olaparib. This suggests that PARP inhibition in combination with radiotherapy may be an effective treatment for both forms of OPSCC, particularly for HPV-negative OPSCC which is relatively radioresistant.

Radiosensitization approaches for HPV‐positive and HPV‐negative head and neck squamous carcinomas

“…Here, we show that the enhanced sensitivity to PARP inhibition could be linked to higher activity of the BER pathway in HPV‐positive HNSCCs. High expression of selected BER and single‐strand break (SSB) related genes in HPV‐positive HNSCC cells was previously reported by Nickson et al . In contrast to their report, only LIG1 was significantly upregulated in all our HPV‐positive cell lines.…”

“…Although no profound investigations on differences in DNA repair pathways between both groups of HNSCC was performed, several preclinical studies—ours included—ascribed increased RT response in HPV‐positive cancers due to defects in DDR pathways . Several studies showed that HPV‐positive HNSCC are characterized by decreased double‐strand break (DSB) repair capacity probably because of malfunctions in nonhomologous end‐joining (NHEJ) and homologous recombination repair (HRR) pathways . These observations strongly suggest that different approaches should be employed for radiosensitization of different groups of HNSCC patients.…”

The p97–Ataxin 3 complex regulates homeostasis of the DNA damage response E3 ubiquitin ligase RNF 8

“…We performed neutral DNA comet assays to directly quantify amounts of genomic DSBs (Fig A; Nickson et al , ; Carter et al , ). Depletion of ATX3 with two different siRNAs significantly increased the level of DSBs even in unchallenged conditions.…”

The relevance of the lymph node ratio as predictor of prognosis is higher in HPV‐negative than in HPV‐positive oropharyngeal squamous cell carcinoma

“…HPV‐negative OPSCC are frequently associated with consumption of tobacco and alcohol, cause less lymphatic metastasis, and were shown to have a worse prognosis in comparison with HPV‐positive OPSCC . The worse response of HPV‐negative OPSCC to radiotherapy and chemotherapy was assumed to be the reason . LNR was shown to be a significant prognostic factor in OPSCC patients …”

“…Many studies could demonstrate that the prognosis is superior in HPV‐positive OPSCC compared to HPV‐negative OPSCC. The explanation for better outcome in HPV‐positive OPSCC patients—even amongst patients with more advanced stage of disease—may be the better response to radiotherapy and chemotherapy …”