title: Neutron radiation enhances cisplatin cytotoxicity independently of apoptosis in human head and neck carcinoma cells.
abstract: Recent advances in combined modality treatment of locally advanced head and neck cancer have improved local and regional disease control and survival with better functional outcome. However, the local and regional failure rate after radiation therapy is still high for tumors that respond poorly to cisplatin-based neoadjuvant chemotherapy. This clinical observation suggests a common biological mechanism for resistance to cisplatin and photon irradiation. In this report, we investigated the molecular basis underlying cisplatin resistance in head and neck squamous carcinoma (HNSCC) cells and asked if fast neutron radiation enhances cisplatin cytotoxicity in cisplatin-resistant cells. We found that cisplatin sensitivity correlates with caspase induction, a cysteine proteinase family known to initiate the apoptotic cell death pathway, suggesting that apoptosis may be a critical determinant for cisplatin cytotoxicity. Neutron radiation effectively enhanced cisplatin cytotoxicity in HNSCCs including cisplatin-resistant cells, whereas photon radiation had little effect on cisplatin cytotoxicity. Interestingly, neutron-enhanced cisplatin cytotoxicity was associated neither with apoptosis nor with cell cycle regulation, as determined by caspase activity assay, annexin V staining, and flow cytometric analysis. Taken together, the present study provides a molecular insight into cisplatin resistance and may also provide a basis for more effective multimodality protocols involving neutron radiation for patients with locally advanced head and neck cancer.
authors.affiliation: Department of Radiation Oncology, Wayne State University School of Medicine, Barbara Ann Karmanos Cancer Institute, Detroit, Michigan 48201, USA.
authors.forename: H E
authors.initials: HE
authors.lastname: Kim
authors.forename: M A
authors.initials: MA
authors.lastname: Krug
authors.forename: I
authors.initials: I
authors.lastname: Han
authors.forename: J
authors.initials: J
authors.lastname: Ensley
authors.forename: G H
authors.initials: GH
authors.lastname: Yoo
authors.forename: J D
authors.initials: JD
authors.lastname: Forman
authors.forename: H R
authors.initials: HR
authors.lastname: Kim
mesh_terms: D017304:Annexin A5 / Q000378:metabolism; D017209:Apoptosis; D002277:Carcinoma / Q000188:drug therapy*; D020169:Caspases / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects / Q000528:radiation effects; D002945:Cisplatin / Q000627:therapeutic use*; D003131:Combined Modality Therapy; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D019008:Drug Resistance, Neoplasm; D005214:Fast Neutrons / Q000627:therapeutic use*; D005434:Flow Cytometry; D006258:Head and Neck Neoplasms / Q000188:drug therapy*; D006801:Humans; D017785:Photons / Q000627:therapeutic use; D013997:Time Factors; D014407:Tumor Cells, Cultured
chemical_list: D017304:Annexin A5; D020169:Caspases; D002945:Cisplatin