Combined treatment with tamoxifen and a fusicoccin derivative (ISIR-042) to overcome resistance to therapy and to enhance the antitumor activity of 5-fluorouracil and gemcitabine in pancreatic cancer cells

Although progress has been made in chemotherapeutic strategies against pancreatic cancer, overall survival has not significantly improved over the past decade. Thus, the development of better therapeutic regimens remains a high priority. Pancreatic cancer cell lines were treated with tamoxifen, a novel antitumor fusicoccin derivative (ISIR-042), and anticancer drugs, and their effects on cell growth, signaling and gene expression were determined. Xenografts of Panc-1 cells were treated with tamoxifen, ISIR-042 and 5-fluorouracil (5FU) to determine the effects on tumor growth. The inhibition of the growth of pancreatic cancer cells induced by tamoxifen was effectively reduced by α-tocopherol, a membrane stabilizer. ISIR-042 produced synergistic effects with tamoxifen in inhibiting cell growth. Tamoxifen elevated lipid peroxidation and the release of cytochrome c, and these effects of tamoxifen were reduced by α-tocopherol. ISIR-042 significantly inhibited colony formation and the expression of stemness-related genes of pancreatic cancer cells. The triple combination of tamoxifen, ISIR-042, and 5FU or gemcitabine was effective at inhibiting cell growth and the appearance of drug-resistant cells. This combined treatment significantly inhibited the growth of Panc-1 cells as xenografts without apparent adverse effects. The triple combination of tamoxifen and ISIR-042 with 5FU or gemcitabine may be highly effective against pancreatic cancer by overcoming resistance to therapy.