# Comparing and combining xevinapant with ATR and PARP inhibition for the radiosensitization of HPV-negative HNSCC cells

## TL;DR

This study compares xevinapant with ATR and PARP inhibitors to improve radiation treatment in HPV-negative head and neck cancer cells.

## Contribution

The study reveals that ATR and PARP inhibition may be more effective than xevinapant for radiosensitization in HPV-negative HNSCC.

## Key findings

- Xevinapant showed moderate radiosensitization in some but not all HPV-negative HNSCC cell lines.
- ATR and PARP inhibitors (tuvusertib and olaparib) induced stronger radiosensitization than xevinapant.
- Combining ATR and PARP inhibitors was especially effective in three out of four cell lines tested.

## Abstract

Radiochemotherapy with the apoptosis stimulator xevinapant demonstrated superiority over radiochemotherapy in a randomized phase 2 trial in head and neck squamous cell carcinoma (HNSCC) but the subsequent phase 3 trial failed. Here, we compared the radiosensitization through xevinapant with two other emerging approaches, the inhibition of ATR and PARP through tuvusertib and olaparib, in a panel of four radioresistant HPV-negative HNSCC cell lines (HSC4, UT-SCC-60A, SAS, SAT). Without irradiation the analyses of proliferation and colony formation showed varying sensitivities of the cell lines towards the different agents and their combinations. When combined with radiation in colony formation assays, we observed moderate radiosensitization through xevinapant in individual cell lines but not in general. Both tuvusertib and olaparib induced stronger radiosensitization than xevinapant and combining both agents resulted in especially profound radiosensitization in three out of the four cell lines tested, whereas their combination with xevinapant or the combination of xevinapant with cisplatin was less effective. Assessment of cell death induction via annexin V/DAPI staining failed to generally predict cytotoxicity or radiosensitization of these approaches. Overall, our data are in line with the recent failure of the phase 3 TrilynX trial and suggest further investigation of ATR and PARP inhibition for the curative treatment of HPV-negative HNSCC.

The online version contains supplementary material available at 10.1038/s41598-026-38550-3.