# Motion-based tissue ex vivo (MOTEX) assay to assess proton and X-ray irradiation responses in head and neck squamous cell carcinoma

## TL;DR

A new ex vivo assay shows some head and neck tumors respond better to proton than X-ray radiation, linked to DNA repair issues or low immune cell presence.

## Contribution

Introduces MOTEX, an ex vivo assay to assess proton and X-ray irradiation responses in HNSCC with novel insights into tumor heterogeneity.

## Key findings

- Three out of nine tumors showed increased sensitivity to proton irradiation.
- Proton-sensitive tumors were either HR-deficient or had low immune infiltration.
- Not all immune-deserted tumors exhibited X-ray resistance.

## Abstract

•Proton-sensitive HNSCC tumors were identified with an ex vivo irradiation.•One of the proton-sensitive tumors was homologous recombination (HR) deficient.•Two X rays-resistant but proton-sensitive tumors had low immune cell infiltration.

Proton-sensitive HNSCC tumors were identified with an ex vivo irradiation.

One of the proton-sensitive tumors was homologous recombination (HR) deficient.

Two X rays-resistant but proton-sensitive tumors had low immune cell infiltration.

Proton radiotherapy is applied for various tumor sites, offering better dose distribution resulting in decreased excess radiation of healthy tissue. Furthermore, the biological effects of proton irradiation may be different from X-ray irradiation, depending on tumor characteristics. This is particularly relevant for head and neck squamous cell carcinoma (HNSCC), which displays high biological heterogeneity. However, this heterogeneous response to various radiation modalities is currently not included in clinical decision making due to lack of response prediction models.

Nine oral cavity tumor specimens were obtained after surgical resection, cut into thin slices, irradiated with both X-ray and protons, and cultured ex vivo for up to five days. We subsequently analyzed proliferation, apoptosis, DNA repair and immune cell infiltration.

Most tumors (five out of nine) showed similar response to proton and X-ray irradiation. However, in three tumors a significantly larger decrease in viability was measured upon proton irradiation. One of those tumors was homologous recombination deficient (HRD). The other two proton-sensitive tumors showed low numbers of infiltrating immune cells, including tumor infiltrating lymphocytes, while the most X-ray sensitive tumor had a particularly high immune cell infiltration.

The ex vivo assay revealed heterogeneous response of HNSCC tumors to proton and X-ray irradiation. The tumors with increased sensitivity to proton irradiation either showed HR deficiency or low immune cell infiltration. However, not all immune-deserted tumors showed this skewing towards X-ray resistance. These findings require validation in a larger cohort of patients.