[Synergism of antitumor effects on ovarian carcinoma using autocatalytic caspase-3 combined with flavopiridol].

OBJECTIVE

to investigate the antitumor effects on ovarian cancer using recombinant adenoviruses expressing autocatalytic caspase-3 driven by amplified human telomerase reverse transcriptase promoter (AdHTVP2G5-rev-casp3) combined with flavopiridol.

METHODS

following the treatment with AdHTVP2G5-rev-casp3 combined with flavopiridol, cell survival rate was measured by cell counting kit 8; cell apoptotic rate and cell cycle distribution were detected by flow cytometry. Western blot was performed to observe the expression of p17, the active subunit of caspase-3, and p85, the cleavage segment of substrate of caspase-3, in AO cells. The mice survival rates were measured for abdominally metastatic tumor models and the volume of tumor nodules were determined for subcutaneous tumor models following the treatments of AdHTVP2G5-rev-casp3 combined with flavopiridol. HE staining was used to detect the histopathological changes of various organs, and the serum level of alanine transaminase (ALT) and aspartate aminotransferase (AST) were measured to monitor liver damages following the intraperitoneal administration of AdHTVP2G5-rev-casp3 and flavopiridol.

RESULTS

there was no significant cell-killing effects or apoptosis in AO cells following treatments with AdHTVP2G5-rev-casp3 or flavopiridol at low dosage alone (apoptotic rate all < 11%), whereas significant synergism of their sequential combination was observed in AO cells. This sequential treatment of AdHTVP2G5-rev-casp3 [multiplicity of infection (MOI) was 20] infection for 72 hours, followed by flavopiridol (300 nmol/L) for 48 hours, could result in the most substantial cell death, and AO cells survival rate and apoptotic rate were 73.5% and 11.6%, respectively. Following treatments with AdHTVP2G5-rev-casp3 at low doses (MOI = 10), there was a significant increase in cell number with S-phase content (62.5%), which resulted in the most marked apoptosis induced by sequential treatments with flavopiridol. The sequential combination could induce significantly higher levels of p17 and p85 expression than that when their applications alone. Combined AdHTVP2G5-rev-casp3 and flavopiridol treatment prolonged mouse survival [mean survival time of (286 ± 6) days] and suppressed tumor growth significantly (tumor growth suppression rate of 81%), when compared with treatment using either alone. The levels of serum ALT and AST were not significantly elevated and no obvious lesions were found in any organs in treatments with AdHTVP2G5-rev-casp3 of low doses combined with flavopiridol.

CONCLUSIONS

AdHTVP2G5-rev-casp3 at low doses results in a significant increase in cell number with S-phase content, which significantly enhanced the sensitivity of cells to flavopiridol. Treatments of autocatalytic caspase-3 combined at low doses with flavopiridol result in significant synergistic antitumor effects, significant tumor growth suppression and prolonged survival of mice. When compared with normal dose flavopiridol alone, the combination could resulted in minimal liver toxicity.