Abstract C259: pVHL function is involved in cell death induced by YC-1 in renal cell carcinoma

Abstract

Abstract Renal cell carcinoma (RCC) is quite resistant to chemotherapy, whereas immunotherapeutic agents, including IL-2 and IFN-α, are only modestly effective with response rates of 10–20%. Novel and more effective therapeutic agents are aspired to alter the natural history of advanced RCCs. Since the protein level of von Hippel-Lindau tumor suppressor (pVHL) was extremely low in 75% of RCCs, importance of small molecules that selectively target pVHL-deficient RCC has been highlighted recently. In this study, we evaluated several known anti-cancer agents to find small molecules that induce growth inhibition according to pVHL level in RCC cells. Our screening efforts identified YC-1, known as an anti-cancer agent that has two distinct biological actions, elevation of intracellular cGMP and inhibition of transcription factor HIF-α. In RCC cell lines we examined, YC-1 showed more effective growth inhibition to pVHL-positive RCC cells as compared to RCC cells expressing reduced level of pVHL. Cell cycle analyses revealed that YC-1 caused delay of S-phase progression and subsequent induction of apoptosis more effectively in pVHL-positive RCC cells. Under the treatment of YC-1, phosphorylation of S-phase checkpoint proteins ATM and CHK2 were elevated dramatically, and cleavages of caspase-3/9 and PARP-1, molecular hallmarks of cells undergoing apoptotic events, were promoted. However, no obvious DNA damage was observed when the cells were exposed to YC-1 at the sufficiently high concentration. This YC-1-induced preferential apoptotic cell death in pVHL-positive RCC cells did not result from its known effects, assessed by sensitivity to the other soluble guanylate cyclase activators and by HIF-1α level. No difference was observed in growth rates of RCC cells in spite of pVHL level when the cells were exposed to BAY41-2272, a YC-1 analog, at the concentration enough to up-regulate intracellular cGMP level. In addition, as pVHL plays a key role in down-regulation of HIF-1α protein, pVHL-deficient RCC cells usually showed less sensitivity to YC-1, even though they contain remarkably higher expression of HIF-1α. Our findings demonstrated that VHL expression sensitizes RCC cells to YC-1. Taken together with the previous report that pVHL functions as an inhibitor to RCC cell apoptosis induced by cellular stress, the results imply that YC-1 targets the pVHL-dependent survival pathway by unknown mechanisms. Thus, YC-1 is considered as a new lead compound of anticancer agents for target therapy of pVHL-positive RCCs. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C259.