Survival of colorectal cancer cell lines treated with paclitaxel, radiation, and 5-FU: Effect of TP53 or hMLH1 deficiency

Clonogenic survival and early cell death during treatment of human colon ca rcinoma cells were investigated following X-irradiation (IR) alone, IR foll owed by 5-FU for 24 h, and Taxol administered 24 h before TR and 5F-U. The investigated cell lines were: HCT116, 40-16 clonally derived from HCT116, a nd two HCT116 variants: N6CHR3 expressing hMLH1, and TP53 null cells denote d HCT116 p53-/-. The objective was to determine efficacy of the combined tr eatment and to correlate response with constitutive levels of TP53, WAF1, a nd hMLH1 proteins, as well as with mRNA levels of the apoptosis-related gen es survivin, BNIP3, and MYC. At the end of treatment with 5-FU, the proport ion of viable cells was between 0.65 and 0.70 for all cell lines. Additiona l cell loss occurred in 40-16 and HCT116 p53-/- cells following administrat ion of Taxol before IR and 5-FU. Radiation sensitivity was unaffected by co mbined treatments, except for Taxol, irradiation, and 5-FU sequence in the HCT116 p53-/- and 40-16 cell lines, where radiation sensitivity determined by clonogenic survival curve slopes was doubled or quadrupled, respectively . Under our present experimental conditions, treatment response did not cor relate with TP53 or hMLH1 status, but was associated with apoptosis-related genes, most notably BNIP3, (C) 2000 Wiley-Liss, Inc.