Abstract 6213: Disruption of XPF function by HPV promotes alternative end joining and sensitivity to cisplatin in HNSCC

Abstract

Abstract Human papillomavirus (HPV) positive head and neck squamous cell carcinoma (HNSCC) usually show a tremendous better clinical outcome compared to their HPV-negative counterparts. Although the HPV associated survival advantage is partially explained by the enhanced cisplatin sensitivity in HNSCC (Clin Ca Res 2018, 24(23): 6001), the underlying mechanisms are still poorly elucidated. Cisplatin causes DNA interstrand crosslinks (ICLs) that requires Fanconi anemia (FA) pathway for DNA repair. Consistently, our study showed that HPV-positive HNSCC cells exhibited a FA defective cellular phenotype. In clonogenic cell survival assay, 1h treatment with 5μM cisplatin eliminated approximately 56.7% more HPV-positive HNSCC cells than HPV-negative ones. Furthermore, HPV-positive cells treated with cisplatin showed prolonged G2/M cell cycle arrest and more 53BP1 foci, indicating profound deficiency in repairing ICLs. Consistent with these findings, increased aberrant chromosome formation was observed in HPV-positive cells following Mitomycin C treatment. In order to reveal the mechanism, we further interrogated HPV-labeled HNSCC samples in TCGA database, and identified XPF, an endonuclease protein in FA pathway, was downregulated in HPV-positive HNSCC. Further analysis of cellular and clinical samples confirmed that both mRNA and protein expressions of XPF were significantly lower in HPV-positive HNSCC (P<0.001). To test the importance of XPF in HPV-induced cisplatin sensitivity, we performed a cell viability assay, and found that knock-down of XPF increased the effects of cisplatin on HPV-negative HNSCC by 39.54% (± 4.42%), while no significant change was observed in HPV-positive HNSCC (P>0.05). Notably, inhibition of XPF function by a small molecule inhibitor recapitulated the effect of HPV, resulted in enhanced error-prone DNA repair with alternative end-joining (alt-EJ). In a probe-based ddPCR assay, XPF inhibition increased 32.02% (± 5.80%, P<0.001) alt-EJ events in HPV-negative HNSCC cells, while little difference was detected in HPV-positive cells. Thus, we speculated that combined inhibition of XPF and alt-EJ may improve clinical outcome in the difficult-to-treat, HPV-negative HNSCC, which worth further research efforts. Citation Format: Qi Liu, Nan Zuo, Lin Ma, Lanlan Wei. Disruption of XPF function by HPV promotes alternative end joining and sensitivity to cisplatin in HNSCC. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6213.