Inhibition of carboplatin-induced DNA interstrand cross-link repair by gemcitabine in patients receiving these drugs for platinum-resistant ovarian cancer

Background: The potential of gemcitabine to interact with carboplatin was explored in a phase II trial in platinum-resistant ovarian cancer. Peripheral blood lymphocytes were sampled after drug administration to measure DNA interstrand cross-link formation and repair. Patients and Methods: Forty patients received carboplatin target area under concentration-time curve (AUC 4) followed by gemcitabine 1,000 mg/m2 with a second dose of gemcitabine on day 8. Peripheral blood lymphocytes were obtained in 12 patients before and at intervals during the first cycle of chemotherapy. DNA cross-link formation and repair (unhooking) were measured by the single-cell gel electrophoresis (comet) assay following ex vivo incubation. Results: The global response rate was 47% (Response Evaluation Criteria in Solid Tumors rate, 29%; CA125 rate, 63%). Delays in treatment were seen in 24% of cycles largely due to myelosuppression; 15% of day 8 administration was omitted. Peak carboplatin-induced DNA cross-linking was seen by 24 hours. Significant reduction was seen in the repair of in vivo carboplatin-induced DNA cross-links following administration of gemcitabine. Conclusion: An enhanced activity of carboplatin in platinum-resistant ovarian cancer may be due to synergy with gemcitabine through inhibition of repair of DNA cross-links. Future studies should explore coadministration of these drugs, as this may be a more effective schedule. ©2010 AACR.