Abstract
In general, hemopoietic and solid tumor cells are cultured in an atmospheric concentration of O2±5% CO2 although most cells proliferate and differentiate in vivo at lower oxgen tension. Regarding cancer therapy, in vitro culture cell systems still have unsolved technical problems such as unsuccessful colony formation in tumor clonogenic assay. It has also been reported that hypoxia-resistant cells may be the cause of poor respons to chemo-different degrees and radio-therapy. In this study therefore, the effect of different degrees of reduced ambient oxygen tension (1, 5, 10%) on in vitro colony growth was investigated in a double soft agar layer system (modified HTCA method) and in conventional liquid monolayer culture for chemosensitivity testing using 4 cell lines of human oral squamous cell carcinoma. Light and ultrastructural microscopic features were also examined. All cell lines had an optimal oxygen concentration of 5% O2 in colony forming assay, but the optimal value was not clear in liquid mass culture.In regard to colony formation, external growth was observed in 5, 10 and 20% 02 and internal capsular formation including cannibalization-like features was seen in 1% O2. Concerning phase-contrast features, spindle-shaped changes and an increase in degenerated granules were observed at 1% O2. Ultrastructurally, conspicuous degeneration of mitochondria (swollen changes) were seen at 1% O2 and the elongation of many microfilaments were mainly observed at 5 and 10% O2.These findings support the assumption that different oxygen supply processes exist between double soft agar layer colony formation and monolayer liquid cell culture. Therefore, it may be useful to apply low oxygen tension for double soft agar layer colony formation, particularly for clinical specimens of the oral cavity.
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