Mechanisms involved in hydroxycamptothecin-induced apoptosis of gastric cancer cells.

OBJECTIVE: Hydroxycamptothecin (HCPT) is a unique antitumor drug that acts directly on topoisomerase I and inhibits its activity. However, the mechanism of HCPT-induced apoptosis is unclear. In the present study, the mechanism of HCPT-induced apoptosis in gastric cancer cells was investigated by detecting the expression of p53 , c -myc , bcl-2 , bcl-xl and bcl-xs genes in gastric cancer cells. METHODS: Apoptosis of gastric cancer cells (SGC-7901, MKN-45) was determined by terminal deoxyribonucleotidyl transferase-mediated dUTP– digoxigenin nick-end labeling (TUNEL) and flow cytometry. The mRNA and protein levels of the p53 , c-myc , bcl-2 , bcl-xl and bcl-xs genes were tested by reverse transcription–polymerase chain reaction analysis and immunocytochemical stain, respectively. RESULTS: Hydroxycamptothecin may induce apoptosis in different differentiated gastric cancer cells. The effect of HCPT-induced apoptosis on gastric cancer cells was dependent on the dose of HCPT used and the time of exposure to HCPT. Both SGC-7901 and MKN-45 cells manifested some morphological features of apoptosis after 12 h exposure to HCPT, including cell shrinkage, nuclear condensation, DNA fragmentation and formation of apoptotic bodies. Some typical subdiploid peaks before the G0 /G1 phase were observed. The apoptotic rates induced by 10 μg/mL HCPT in SGC-7901 and MKN-45 cells were 21.88 and 12.34%, respectively. The mRNA and protein levels of p53 and bcl-2 were downregulated after treatment with HCPT in SGC-7901 cells. However, the c-myc, bcl-xl and bcl-xs protein levels were unchanged in SGC-7901 cells. In MKN-45 cells, the mRNA and protein levels of p53 increased after treatment with HCPT, whereas the protein levels of bcl-2, c-myc, bcl-xl and bcl-xs remained unchanged. CONCLUSIONS: Our results indicate that HCPT-induced apoptosis in gastric cancer cells may be regulated through modulation of the expression of p53 and bcl-2 genes. [ABSTRACT FROM AUTHOR]