S-phase accumulation precedes apoptosis induced by preoperative treatment with 5-fluorouracil in human colorectal carcinoma cells

BACKGROUND. In this study, the authors examined the correlations among enhancement of apoptosis, changes in cell cycle distribution, and expression of Ki-67 in human colorectal carcinoma cells during different durations of preoperative treatment with 5-fluorouracil (5-FU). METHODS. Forty-one patients with advanced colorectal carcinoma were divided into 4 groups, which received intravenous 5-FU at 500 mg/body/day preoperatively for 3 days (n = Il), 5 days (n = 13), 7 days (n = 9), or 10 days (n = 8). Patients were further divided into two subgroups according to the DNA ploidy pattern of their tumors, i.e., diploid or aneuploid. Apoptotic cells were stained by the terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL) method. The expression of Ki-67 was examined by immunohistochemical staining. Flow cytometry was used to analyze changes in cell cycle distribution. RESULTS. Apoptosis of cancer cells was mostly increased in the 7-day group (apoptotic index [AI]: 18.3 +/- 1.7%] compared with that of the 3-day, 5-day (AI: 11.3 +/- 2.3% and 13.2 +/- 2.8%, respectively) (P < 0.01), or 10-day (AI: 16.2 +/- 2.1%) (P < 0.05) groups. The expression of Ki-67 was reduced with increasing prolongation of 5-FU administration, from 55.2 +/- 2.1% in the 3-day group to 38.1 +/- 2.7% in the 10-day group. The authors also assessed the S-phase fraction (SPF) of cancer cells to evaluate changes in cell cycle distribution caused by 5-FU. ALL tumor samples from patients treated by 5-FU showed S-phase accumulation. The ratio of SPF (after 5-FU/before 5-FU) was higher in the 5-day group (2.35 +/- 0.78) than in the 3-day (1.71 +/- 0.48), 7-day (1.68 +/- 0.55), or 10-day (1.20 +/- 0.20) groups (P < 0.05). DNA ploidy pattern of the tumor had no influence on the enhancement of apoptosis, the increased ratio of SPF, or the decrease in proliferative activity of colorectal carcinoma cells induced by 5-FU. CONCLUSIONS. S-phase accumulation preceded apoptotic cell death when intravenous 5-FU was administered continuously to human colorectal carcinoma cells. (C) 1999 American Cancer Society.