title: Hypoxia induces resistance to 5-fluorouracil in oral cancer cells via G(1) phase cell cycle arrest.
abstract: Malignant tumors are exposed to various levels of hypoxic condition in vivo. It has been known that tumor cells under hypoxia are resistant to chemotherapies. To clarify the mechanism of the hypoxia-induced chemoresistance, we evaluated the effects of hypoxia on the resistance of oral squamous cell carcinoma (OSCC) cell lines to 5-fluorouracil (5-FU). OSCC cells were divided to two groups by the proliferation activity under hypoxic condition; hypoxia-resistant (HR) and hypoxia-sensitive (HS) cells. Growth of HS cells were inhibited by hypoxia and introduced to G(1) arrest in cell cycle. 5-FU effect on HS cell viability was markedly reduced in hypoxic condition without an induction of chemoresistant related protein, P-glycoprotein. However, proliferation, cell cycle, and 5-FU sensitivity of HR cells were not affected by hypoxia. Hypoxia-inducible factor (HIF)-1alpha was induced by hypoxia in all OSCC cell lines, but diminished in HS cells within 48h. Expression of p21 and p27 was strongly augmented and CyclinD expression was reduced by hypoxia in HS cells. However, the expression of these proteins was constitutive in HR cells during 48h hypoxic culture. Phosphorylation of mammalian target of rapamycin (mTOR) was reduced by hypoxia in HS cells. From these findings, we concluded that HS OSCC cells acquire 5-FU resistance under hypoxia by G(1)/S transition through an upregulation of cell cycle inhibitors.
authors: Department of Oral and Maxillofacial Surgery, School of Dentistry, Showa University, Kitasenzoku 2-1-1, Ohta-ku, Tokyo 145-8515, Japan. yoshiba@senzoku.showa-u.ac.jp
authors: Sayaka
authors: S
authors: Yoshiba
authors: Daisuke
authors: D
authors: Ito
authors: Tatsuhito
authors: T
authors: Nagumo
authors: Tatsuo
authors: T
authors: Shirota
authors: Masashi
authors: M
authors: Hatori
authors: Satoru
authors: S
authors: Shintani
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D015153:Blotting, Western; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy* / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects / Q000502:physiology; D015687:Cell Hypoxia / Q000502:physiology*; D045744:Cell Line, Tumor / Q000187:drug effects / Q000378:metabolism; D049109:Cell Proliferation / Q000187:drug effects; D056741:Cyclin D / Q000378:metabolism; D019008:Drug Resistance, Neoplasm / Q000502:physiology*; D005472:Fluorouracil / Q000494:pharmacology*; D016193:G1 Phase / Q000187:drug effects / Q000502:physiology; D006801:Humans; D009062:Mouth Neoplasms / Q000188:drug therapy* / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D056741:Cyclin D; D014157:Transcription Factors; D005472:Fluorouracil