Caspase-dependent and -independent panc-1 cell death due to actinomycin D and MK 886 are additive but increase clonogenic survival

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

Preclinical Research & Development 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 (NFκB) 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 NFκB would enhance induction of apoptosis by ActD, via phosphorylation of c-Jun, by minimizing NFκB 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 18/0.015 μM, respectively.

Tumor-associated protein SPIK/TATI suppresses serine protease dependent cell apoptosis

Serine protease dependent cell apoptosis (SPDCA) is a recently described caspase independent innate apoptotic pathway. It differs from the traditional caspase dependent apoptotic pathway in that serine proteases, not caspases, are critical to the apoptotic process. The mechanism of SPDCA is still unclear and further investigation is needed to determine any role it may play in maintaining cellular homeostasis and development of disease. The current knowledge about this pathway is limited only to the inhibitory effects of some serine protease inhibitors. Synthetic agents such as pefabloc, AEBSF and TPCK can inhibit this apoptotic process in cultured cells. There is little known, however, about biologically active agents available in the cell which can inhibit SPDCA. Here, we show that over-expression of a cellular protein called serine protease inhibitor Kazal (SPIK/TATI/PSTI) results in a significant decrease in cell susceptibility to SPDCA, suggesting that SPIK is an apoptosis inhibitor suppressing this pathway of apoptosis. Previous work has associated SPIK and cancer development, indicating that this finding will help to open the doorway for further study on the mechanism of SPDCA and the role it may play in cancer development.

Unknotting the roles of Bcl-2 and Bcl-xL in cell death

The antiapoptotic Bcl-2 family proteins Bcl-2 and Bcl-xL play important roles in inhibiting mitochondria-dependent extrinsic and intrinsic cell death pathways. It seems that these two proteins have distinct functions for inhibiting extrinsic and intrinsic cell death pathways. The overexpression of Bcl-2 is able to inhibit not only apoptotic cell death but also in part nonapoptotic cell death, which has the role of cell cycle arrest in the G1 phase, which may promote cellular senescence. The overexpression of Bcl-2 may also have the ability to enhance cell death in the interaction of Bcl-xL with other factors. The overexpression of Bcl-xL enhances autophagic cell death when apoptotic cell death is inhibited in Bax(-/-)/Bak(-/-) double knockout cells. This review discusses the previously unexplained aspects of Bcl-2 and Bcl-xL functions associated with cell death, for better understanding of their functions in the regulation.

Involvement of the cGMP signalling pathway in the regulation of viability in insulin-secreting BRIN-BD11 cells

We have evaluated the hypothesis that cGMP may serve as an intracellular messenger regulating the viability of pancreatic beta-cells. A direct activator of soluble guanylyl cyclase, YC-1, caused a time- and dose-dependent loss of viability in clonal BRIN-BD11 beta-cells. This was accompanied by a rise in cGMP and was antagonised by Rp-8-pCPT-cGMPS, a selective inhibitor of protein kinase G (PKG). Reverse transcription polymerase chain reaction analysis confirmed that BRIN-BD11 cells (and human islets) express all three known isoforms of PKG (PKG-Ialpha, -Ibeta and II). Cell death induced by YC-1 was not sensitive to cell-permeable caspase inhibitors and was not accompanied by oligonucleosomal DNA fragmentation. The response was, however, inhibited by actinomycin D, suggesting that a transcription-dependent pathway of programmed cell death is involved in the actions of cGMP.