The irinotecan/5-fluorouracil combination induces apoptosis and enhances manganese superoxide dismutase activity in HT-29 human colon carcinoma cells.

BACKGROUND: We examined whether induction of apoptosis and Mn-superoxide dismutase (Mn-SOD) and Cu,Zn-superoxide dismutase (Cu,Zn-SOD) activities were involved in the greater cytotoxicity of the irinotecan (CPT-11)/5-fluorouracil (5-FU) combination for human colon cancer cells when compared to both drugs alone. METHODS: HT-29 and SNU-C4 human colon carcinoma cell lines were treated with 5-FU and CPT-11, then apoptosis was evaluated by flow cytometry and SOD activities were determined by polyacrylamide gel electrophoresis. RESULTS: Enhanced apoptosis of HT-29 cells was observed with all treatments containing 5-FU in SNU-C4 cells; however, in HT-29 cells, apoptosis was enhanced only with the CPT-11/5-FU combination. In the SNU-C4 cell line, none of the treatments exerted a significant effect on Cu,Zn-SOD or Mn-SOD activity. However, in HT-29 cells, the CPT-11/5-FU combination enhanced Mn-SOD activity when compared to cells treated with CPT-11 alone. Nevertheless, the combined treatment did not interfere with Cu,Zn-SOD activity. CONCLUSION: Treatment with the CPT-11/5-FU combination may promote in HT-29 cell apoptosis by enhancing Mn-SOD activity.

Irinotecan/5-fluorouracil combination induces alterations in mitochondrial membrane potential and caspases on colon cancer cell lines.

The combination of irinotecan (CPT-11) and 5-fluorouracil (5-FU) is currently used in the treatment of advanced colorectal carcinoma. When compared to both agents alone, CPT-11 followed by 5-FU treatment demonstrated a synergistic effect. This observation can be related to increased in apoptosis induction after caspase activation. Several studies have demonstrated that changes in mitochondrial membrane potential occur earlier in apoptosis. In this study, we verified whether the collapse in mitochondrial membrane and the activation of caspases is responsible for increased apoptosis observed with CPT-11/5-FU treatment. Thus, HT-29 and SNU-C4 human colon carcinoma cell lines were exposed for 24 h to each drug alone, and to various combinations and treatment sequences, and assessed for colony formation, changes in the mitochondrial membrane potential, and the activities of caspase-3, -8, and -9. The CPT-11/5-FU treatment induced apoptosis in both cell lines; however, the most pronounced effect was observed in HT-29 cells. In these cells, both caspase-3 and -9 were involved in the activation of apoptosis after CPT-11/5-FU treatment. Moreover, in these cells, a reduction of 50% in mitochondrial membrane potential was observed with this treatment. On the other hand, in the SNU-C4 cell line in addition to caspase-3 and-9, caspase-8 seems to be important to apoptosis after CPT-11/5-FU treatment. Furthermore, in this cell line we did not observe alterations in mitochondrial membrane potential. In spite of the differences among the cell lines, these results indicated that the increase in apoptosis in HT-29 cells observed with CPT-11 followed by 5-FU treatment could be explained by a disruption in mitochondria membrane potential that induced caspases activation.