Cancer cells surviving hypoxia obtain hypoxia resistance and maintain anti-apoptotic potential under reoxygenation

In solid tumors hypoxia and reoxygenation may be important factors in secon dary expansion after anti-cancer therapy. Our study examined the effect of hypoxia and reoxygenation on the apoptotic potential of cancer cells, Four experimental groups were studied using a human colorectal cancer cell line (HCT116) that is apoptosis-competent in conventional culture: (1) sham, cel ls grown under conventional conditions; (2) hypoxic, cells cultured in 95% N-2 and 5% CO2 for 24 hr; (3) continued hypoxic, cells cultured for 48 hr; and (4) reoxygenation, cells grown in hypoxic conditions for 24 hr followed by another 24 hr under conventional conditions. Protein expression of p53, bcl-2 and PCNA were determined by immunohistochemistry and immunoblotting (p53), and viable cell growth rate was determined. Hypoxia for 24 hr induce d significant up-regulation of p53 and bcl-2 expression, accompanied by sig nificant decreases of cell growth rate and PCNA expression. Up-regulation o f p53 and bcl-2 expression persisted with both continued hypoxia and reoxyg enation, despite increased cell growth rate and PCNA expression. Cells esca ping hypoxia acquired sustained resistance to apoptosis and proliferate des pite an elevated p53 level, suggesting that p53 transfer to hypoxic solid t umor should be reevaluated as a cancer gene therapy approach. (C) 2001 Wile y-Liss, Inc.