Improvements in PDT tumor responsiveness may be achieved by employing combined modality regimens targeting malignant cells as well as treatment-induced angiogenesis and/or inflammation.

No 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 PDTmediated cancer therapy. [Cancer Res 2007;67(10):4989-95]

Photodynamic therapy (PDT) elicits both apoptotic and necrotic responses within treated tumors and produces microvascular injury leading to inflammation and hypoxia. PDT also induces expression of angiogenic and survival molecules including vascular endothelial growth factor, cyclooxygenase-2 (COX-2), and matrix metalloproteinases. Adjunctive administration of inhibitors to these molecules improves PDT responsiveness. In the current study, we examined how the combination of PDT and COX-2 inhibitors improve treatment responsiveness. Photofrin-mediated PDT combined with either celecoxib or NS-398 increased cytotoxicity and apoptosis in mouse BA mammary carcinoma cells. Immunoblot analysis of protein extracts from PDT-treated cells also showed poly(ADP-ribose) polymerase cleavage and Bcl-2 degradation, which were further enhanced following combined therapy. Tumor-bearing mice treated with PDT and either celecoxib or NS-398 exhibited significant improvement in long-term tumor-free survival when compared with PDT or COX-2 inhibitor treatments alone. The combined procedures did not increase in vivo tumor-associated apoptosis. Administration of celecoxib or NS-398 attenuated tissue levels of prostaglandin E 2 and vascular endothelial growth factor induced by PDT in treated tumors and also decreased the expression of proinflammatory mediators interleukin-1B and tumor necrosis factor-A. Increased tumor levels of the antiinflammatory cytokine, interleukin 10, were also observed following combined treatment. This study documents for the first time that adjunctive use of celecoxib enhances PDTmediated tumoricidal action in an in vivo tumor model. Our results also show that administration of COX-2 inhibitors enhance in vitro photosensitization by increasing apoptosis and improve in vivo PDT responsiveness by decreasing expression of angiogenic and inflammatory molecules. (Cancer Res 2005; 65(20): 9473-8)