Actinomycin-D and dimethylamino-parthenolide synergism in treating human pancreatic cancer cells.

Pancreatic cancer is the third leading cause of death in the US with a poor 5-year survival rate of 8.5%. A novel anti-cancer drug, dimethylamino parthenolide (DMAPT), is the water-soluble analog of the natural sesquiterpene lactone, parthenolide. The putative modes of action of DMAPT are inhibition of the Nuclear chain factor kappa-light-chain enhancer of activated B cells (NFB) pathway and depletion of glutathione levels; the latter causing cancer cells to be more susceptible to oxidative stress-induced cell death. Actinomycin-D (ActD) is a polypeptide antibiotic that binds to DNA, and inhibits RNA and protein synthesis by inhibiting RNA polymerase II. A phase 2 clinical trial indicated that ActD could be a potent drug against pancreatic cancer; however, it was not a favored drug due to toxicity issues. New drug entities and methods of drug delivery, used alone or in combination, are needed to treat pancreatic cancer more effectively. Thus, it was postulated that combining DMAPT and ActD would result in synergistic inhibition of Panc-1 pancreatic cancer cell growth because DMAPT's inhibition of NFB would enhance induction of apoptosis by ActD, via phosphorylation of c-Jun, by minimizing NFB inhibition of c-Jun phosphorylation. Combining these two drugs induced a higher level of cell death than each drug alone. A fixed drug ratio of DMAPT: ActD (1,200:1) was used. Data from metabolic (MTT) and colony formation assays were analyzed for synergism with CompuSyn software, which utilizes the Chou-Talalay equation. The analyses indicated synergism and moderate synergism at combination concentrations of DMAPT/ActD of 12/0.01 and 18/0.015M, respectively.