Perifosine synergistically enhances TRAIL-induced myeloma cell apoptosis via up-regulation of death receptors

Purpose: The aim of this study is to investigate the efficacy of a novel Akt inhibitor, perifosine, in combination with tumor necrosis factor - related apoptosis-inducing ligand (TRAIL) in human myeloma cells and primary patient samples. Experimental Design: The activity of perifosine in combination with TRAIL was evaluated with experiments testing the effect of perifosine on DR4/DR5 expression by the use of chimeric blocking antibodies, as well as si RNA. Results: DR4 and DR5 expression was induced by exposure to single-agent perifosine. After exposure of human myeloma cell lines or primary patient samples to increasing doses of perifosine with exogenous TRAIL, we identified synergistically enhanced apoptosis when compared with the perifosine alone, which was achieved with levels well below clinically achievable concentrations for both agents. Transfection with siRNA against DR4, and DR5 reduced the level of apoptosis induced by the combination but did not result in total abrogation of the combination effect. Overexpression of activated Akt, the proposed target for perifosine, did not inhibit the combination effect. Anti-DR4 and DR5 chimeric proteins blocked the cytotoxicity induced by the combination, and the use of c-FLICE-like interleukin protein (FLIP) siRNA enhanced the efficacy at the combination, further supporting the importance of the DR4/DR5 axis in the effect of perifosine. Conclusion: Our observation seems to be independent of the effects of perifosine on Akt signaling, and may represent an additional mechanism of action for this agent, and supports future clinical trials combining these two agents.