Additive Growth Inhibition after Combined Treatment of 2-Methoxyestradiol and Conventional Chemotherapeutic Agents in Human Pancreatic Cancer Cells

Objective: Most chemotherapeutic regimens for pancreatic cancer (PC) use combination therapy. 2-Methoxyestradiol (2-ME2) is a natural estrogen metabolite with proven tumor-inhibiting effect as a single agent. The aim of this study was to determine whether a combination of 2-ME2 with other established chemotherapeutic compounds increases its tumor-inhibiting effect on human PC cells. Materials and Methods: The human PC cell lines AsPC-1 and MiaPaCa-2 were treated with 2-ME2 alone or in combination with different doses of gemcitabine, cisplatin, cetuximab, 5-fluorouracil and paclitaxel in vitro (range: 0.5-5 mu M). FACS analysis and nuclear staining were used to reveal apoptotic cells and cell-cycle changes after treatment. Subsequent in vivo experiments were performed on a subcutaneous tumor model in nude mice using AsPC-1 cells. Results: A tumor-reductive effect of 2-ME2 was found in both human PC cell lines. The combination of 2-ME2 with other agents resulted in additive growth inhibition of both cell lines through the induction of apoptosis and cell-cycle arrest. The growth inhibition was confirmed in vivo. After 32 days' treatment, gemcitabine alone showed no effect on tumor growth at a dose of 75 mg/kg body-weight. However, 2-ME2 at a daily dose of 2 mg per animal led to a growth inhibition of 63% with no evident toxicity. The combination of 2-ME2 and gemcitabine caused a growth-inhibition of 83%. Major toxicity was observed in the combination group, with six deaths out of eight animals in this group. Conclusion: 2-ME2 can be successfully combined with other chemotherapeutic agents. However, toxicity in the in vivo experiment is strong and requires further investigation.