Targeting the MET Receptor Tyrosine Kinase as a Strategy for Radiosensitization in Preclinical Head and Neck Cancer Models

Purpose: The MET receptor participates in acquisition and maintenance of an aggressive phenotype in head and neck squamous cell carcinoma (HNSCC) and modulates the DNA damage response following ionizing radiation (IR). Here we investigate the radiosensitization potential of the novel MET tyrosine kinase inhibitor tepotinib in HNSCC models.

Experimental design: MET expression and mutation status was assessed in a cohort of patients with advanced HNSCC and in a panel of cell lines. Radiosensitization was evaluated by clonogenic assays, DNA damage by immunoblotting, cell death induction by caspase-3 cleavage and live-dead assays, and cell cycle distribution by FACS. Organotypic tissue cultures (OTCs) from freshly resected HNSCCs were established, and radiosensitization was evaluated by specific immunohistochemical markers. Single-cell proteomics by means of mass cytometry was used to elucidate the molecular basis of tepotinib-mediated radiosensitization in a MET-inhibition sensitive and a resistant cell lines.

Results: In our cohort of HNSCC, MET was highly expressed in 62.4% of primary tumors and 53.63% of lymph node metastases (LNMs), and in 6 out of 9 evaluated cell lines. MET expression in LNMs was an independent predictor of regional disease recurrence following neck dissection and radiotherapy (HR=4.84, 95% CI 1.26-18.57, p=0.0217). Tepotinib effectively abrogated MET phosphorylation and to different extents MET downstream signaling in cell lines. Moreover, pretreatment with tepotinib resulted in variable radiosensitization, enhanced DNA damage, cell death, and G2/M-phase arrest, especially in MET-expressing cells. OTCs revealed differential patterns of response towards tepotinib, irradiation, and combination of both, leading to effective radiosensitization in 10/24 of the tested OTCs. Mass cytometry revealed that radiosensitization through tepotinib seemed to be dependent on modulation of PI3K activity and crosstalk with other tyrosine kinases, especially the EphA2 receptor.

Conclusions: Our results show that MET is a potential target for radiosensitization in HNSCC, warranting further evaluation in clinical trials. Pre-therapeutic stratification and evaluation of responses in ex vivo OTCs could be important tools for optimal patient selection.