Are extracellular vesicles mediators of chemotherapy resistance in head and neck cancer?

Abstract

Head and neck cancer (HNC) is a term that describes malignancies that arise in areas such as the mouth and lips, larynx, pharynx, salivary glands, nose, paranasal sinus, and nasopharynx. HNC usually occurs after exposure to carcinogenic factors such as alcohol, tobacco, and human papilloma virus (HPV). Moreover, this type of cancer has a high recurrence rate at the primary site after treatment. Cisplatin is a cornerstone in the chemotherapeutic treatment of HNC, utilized for its ability to induce cancer cell death. However, resistance to cisplatin remains a significant challenge, reducing its efficacy. There is evidence that extracellular particles (EPs) such as extracellular vesicles (EVs) and vault particles mediate resistance to chemotherapy in some cancer types. However, little is known of their relative contribution, especially in HNC. Given the pivotal role of cisplatin in HNC treatment, it was hypothesized that EPs released from HNC cells exposed to cisplatin facilitate chemotherapy resistance by exporting cisplatin or by mediating intercellular communication with neighbouring cells. To test this hypothesis, MTT assay was used to determine the concentration of cisplatin required to reduce cell viability by 50% (IC50) in H357 and FaDu HNC cell lines. EV deficient (H357△HGS) and vault particle deficient (H357△MVP) were utilised to explore their contribution to cisplatin resistance. A cisplatin-resistant H357 cell line (cisplatinR) was generated by prolonged exposure to increasing concentrations of cisplatin, and putative proteins involved in resistance were quantified by western blotting. The proportion of cells undergoing apoptosis in response to cisplatin treatment was determined by flow cytometry. The concentration of EPs in cell line conditioned medium and ultracentrifugation pellets were determined by nanoparticle tracking analysis (NTA). EPs pellets were characterised by western blotting to detect EV (CD63 and TSG101) and vault particle (MVP) markers. Apoptosis was triggered in the H357 cell line following treatment with cisplatin, but not in the FaDu cell line. Treatment of H357 with cisplatin also resulted in increased release of EPs, which included EV and vault particles. Despite releasing fewer EPs in response to cisplatin treatment, the EV deficient cell line (H357△HGS) showed no significant difference in cisplatin sensitivity, whereas the vault particle deficient cell line (H357△MVP) was more resistant to cisplatin treatment. The cisplatinR 2 cell line showed increased viability and reduced apoptosis but released fewer EPs following cisplatin treatment. The findings suggest that the differential release of EPs in response to cisplatin treatment might contribute to the variability in chemotherapy resistance among HNC cell lines. Specifically, vault particles may play a more crucial role than previously understood in mediating resistance to cisplatin. This insight into the mechanistic underpinnings of cisplatin resistance in HNC cells could guide the development of novel therapeutic strategies aimed at enhancing cisplatin sensitivity by targeting the release or function of specific EPs.