Survivin, a Member of the Inhibitor of Apoptosis Family, Is Induced by Photodynamic Therapy and Is a Target for Improving Treatment Response

Abstract

We observed that photodynamic therapy (PDT) induces the expression and phosphorylation of the inhibitor of apoptosis (IAP) protein survivin in murine and human cancer cells and tumors. Survivin inhibits caspase-9, blocks apoptosis, and is associated with resistance to chemotherapy and radiation. Survivin is a client protein for the 90-kDa heat shock protein (Hsp-90), and the binding of survivin to Hsp-90 assists in the maturation, proper folding, assembly, and transport of this IAP protein. A derivative of the antibiotic geldanamycin, 17-allylamino-17-demethoxygeldanamycin (17-AAG), interferes with proper binding of client proteins, such as survivin, to Hsp-90 and leads to misfolding of client proteins, ubiquination, and proteasome degradation. We hypothesized that PDT efficacy may be reduced by treatment-mediated expression and phosphorylation of survivin, and therefore, targeting the survivin pathway could increase PDT responsiveness. To address this hypothesis, we examined cellular and molecular responses following exposure to PDT, 17-AAG, and the combination of PDT plus 17-AAG in human BT-474 breast cancer cells using Photofrin and NPe6 as photosensitizers. Cells treated with the combination of PDT and 17-AAG exhibited decreased expression of the Hsp-90 client proteins phosphorylated survivin, phosphorylated Akt, and Bcl-2. The decreased expression of these client proteins was accompanied by higher apoptotic indexes and increased cytotoxicity. To confirm a specific role for survivin in modulating PDT, we used a human melanoma cell line, YUSAC2/T34A-C4, stably transfected with an inducible dominant-negative survivin gene under the control of a tetracycline-regulated (tet-off) promoter. PDT treatment of melanoma cells expressing the dominant-negative survivin resulted in increased cleavage of the caspase substrate poly(ADP-ribose) polymerase, apoptosis, and cytotoxicity when compared with results following PDT of the same melanoma cell line expressing wild-type survivin. These results show for the first time that targeting survivin and possibly other Hsp-90 client proteins improves in vitro PDT responsiveness and suggest that manipulation of the antiapoptotic pathway maintained by survivin may enhance PDT-mediated cancer therapy.