SIRT1-Activating Compounds (STAC) Negatively Regulate Pancreatic Cancer Cell Growth and Viability Through a SIRT1 Lysosomal-Dependent Pathway.

PURPOSE: Recent studies suggest that SIRT1-activating compounds (STAC) are a promising class of anticancer drugs, although their mechanism of action remains elusive. The main goal of this study is to determine the role of STACs as a potential therapy for pancreatic cancer. In addition, we also explored the mechanism by which these compounds affect pancreatic cancer. EXPERIMENTAL DESIGN: Using in vitro (cell culture experiments) and in vivo (xenograft experiments) approaches, we studied the role of SIRT1 agonists (STAC) in human pancreatic cancer cell viability and growth. RESULTS: We show that SIRT1 is highly expressed in pancreatic cancer cells and that the STACs SRT1720, SRT1460, and SRT3025 inhibited cell growth and survival of pancreatic cancer cells. STACs enhanced the sensitivity of pancreatic cells to gemcitabine and paclitaxel, indicating that these drugs could be used in combination with other chemotherapy drugs. We also show that STACs were very effective in inhibiting tumor xenograft growth. In mechanistic studies, we observed that STACs activated a SIRT1 lysosomal-dependent cell death. Furthermore, the effect of STACs on cell viability was also dependent on the expression of the endogenous SIRT1 inhibitor DBC1. CONCLUSIONS: Taken together, our results reveal an essential role for SIRT1 and lysosomes in the death pathway regulated by STACs in pancreatic cancer cells. Clin Cancer Res; 22(10); 2496-507. ©2015 AACR.

Targeting of NAD metabolism in pancreatic cancer cells: potential novel therapy for pancreatic tumors.

PURPOSE: Here, we describe a novel interplay between NAD synthesis and degradation involved in pancreatic tumor growth. EXPERIMENTAL DESIGN: We used human pancreatic cancer cells, both in vitro (cell culture experiments) and in vivo (xenograft experiments), to demonstrate the role of NAD synthesis and degradation in tumor cell metabolism and growth. RESULTS: We demonstrated that pharmacologic and genetic targeting of Nampt, the key enzyme in the NAD salvage synthesis pathway, inhibits cell growth and survival of pancreatic cancer cells. These changes were accompanied by a reduction of NAD levels, glycolytic flux, lactate production, mitochondrial function, and levels of ATP. The massive reduction in overall metabolic activity induced by Nampt inhibition was accompanied by a dramatic decrease in pancreatic tumor growth. The results of the mechanistic experiments showed that neither the NAD-dependent enzymes PARP-1 nor SIRT1 play a significant role on the effect of Nampt inhibition on pancreatic cancer cells. However, we identified a role for the NAD degradation pathway mediated by the NADase CD38 on the sensitivity to Nampt inhibition. The responsiveness to Nampt inhibition is modulated by the expression of CD38; low levels of this enzyme decrease the sensitivity to Nampt inhibition. In contrast, its overexpression decreased cell growth in vitro and in vivo, and further increased the sensitivity to Nampt inhibition. CONCLUSIONS: Our study demonstrates that NAD metabolism is essential for pancreatic cancer cell survival and proliferation and that targeting NAD synthesis via the Nampt pathway could lead to novel therapeutic treatments for pancreatic cancer.