A Lack of Effectiveness in the ATM-Orchestrated DNA Damage Response Contributes to the DNA Repair Defect of HPV-Positive Head and Neck Cancer Cells

Abstract

Patients with human papillomavirus-positive squamous cell carcinoma of the head and neck (HPV+ HNSCC) have a favorable prognosis compared to those with HPV-negative (HPV−) ones. We have shown previously that HPV+ HNSCC cell lines are characterized by enhanced radiation sensitivity and impaired DNA double-strand break (DSB) repair. Since then, various publications have suggested a defect in homologous recombination (HR) and dysregulated expression of DSB repair proteins as underlying mechanisms, but conclusions were often based on very few cell lines. When comparing the expression levels of suggested proteins and other key repair factors in 6 HPV+ vs. 5 HPV− HNSCC strains, we could not confirm most of the published differences. Furthermore, HPV+ HNSCC strains did not demonstrate enhanced sensitivity towards PARP inhibition, questioning a general HR defect. Interestingly, our expression screen revealed minimal levels of the central DNA damage response kinase ATM in the two most radiosensitive HPV+ strains. We therefore tested whether insufficient ATM activity may contribute to the enhanced cellular radiosensitivity. Irrespective of their ATM expression level, radiosensitive HPV+ HNSCC cells displayed DSB repair kinetics similar to ATM-deficient cells. Upon ATM inhibition, HPV+ cell lines showed only a marginal increase in residual radiation-induced γH2AX foci and induction of G2 cell cycle arrest as compared to HPV− ones. In line with these observations, ATM inhibition sensitized HPV+ HNSCC strains less towards radiation than HPV− strains, resulting in similar levels of sensitivity. Unexpectedly, assessment of the phosphorylation kinetics of the ATM targets KAP-1 and Chk2 as well as ATM autophosphorylation after radiation did not indicate directly compromised ATM activity in HPV-positive cells. Furthermore, ATM inhibition delayed radiation induced DNA end resection in both HPV+ and HPV− cells to a similar extent, further suggesting comparable functionality. In conclusion, DNA repair kinetics and a reduced effectiveness of ATM inhibition clearly point to an impaired ATM-orchestrated DNA damage response in HPV+ HNSCC cells, but since ATM itself is apparently functional, the molecular mechanisms need to be further explored.

Impaired DNA double-strand break repair and effective radiosensitization of HPV-negative HNSCC cell lines through combined inhibition of PARP and Wee1

“…With regard to molecular targeting, the presence or lack of an increase in residual DSB levels in prostate cancer cell lines matched well between the established in vitro setting and slice cultures derived from xenograft tumors after PARP inhibition and after antiandrogen therapy [37] , [38] . Furthermore, we had recently observed a differential effect of ATM inhibition on residual DSB repair foci in HPV- and HPV+ patient-derived HNSCC slice cultures, which also corresponded well to the effects observed in HPV- and HPV+ HNSCC cell lines [24] , [39] . Together, these data clearly speak in favor of the robustness of the ex vivo approach and warrant further research into its utilization for predicting individual tumor responsiveness towards radiation and towards specific radiosensitization approaches.…”

Active Immune Phenotype in Head and Neck Cancer: Reevaluating the Iso-Effect Fractionation Based on the Linear Quadratic (LQ) Model—A Narrative Review

“…In this context, the individual determination of radio-sensitivity could be essential for improving treatment performance. In the case of HPV-positive cell lines, a resistance to cisplatin is highlighted, and the response to cetuximab and radiotherapy does not seem to differ compared to the HPV subtype according to the reports of Nagel et al [23][24][25]. Enhanced apoptosis rates and the decreased expression of E6 and E7 oncoproteins were considered the arguments for the increased sensitivity of HPV-driven HNSCC to cisplatin.…”

“…The hypoxia-related proteins CAIX or HIF-1α are considered biomarkers of radio resistance in HPV+ HNSCC. CAIX or microvascular density does not seem to be correlated with the HPV status of HNSCC, and in the case of HIF-1α, the correlation with HPV+ OPSCC and involvement in radio-sensitivity has not yet been elucidated [24][25][26][27][28][29].…”

Metastatic patterns and treatment options for head and neck cutaneous squamous cell carcinoma (Review)

“…A compromised immune system promotes mutations; therefore, subsets of cancer cells are able to evade immune detection owing to the compromised antitumor response of the immune system ( 61 ). This evasion is referred to as the escape mode, which permits unregulated tumor growth and progression ( 62 ). Cemiplimab is a monoclonal antibody that targets PD-1.…”