Abstract 3800: Targeting PI3K signaling pathway for therapeutic enhancement of verteporfin-mediated photodynamic therapy

Abstract

Abstract Photodynamic therapy (PDT) induces cell injury and death through generation of reactive oxygen species (ROS) after light activation. Verteporfin is a photosensitizer that has been approved for the treatment of age-related macular degeneration and is under investigation for targeting tumor vasculature for therapy. Being primarily localized in mitochondria, verteporfin-mediated PDT induced a rapid apoptotic cell death in SVEC mouse endothelial cells by activating mitochondria-initiated cell death pathways. However, activation of phosphatidylinositol 3-kinase (PI3K) signaling pathway was also observed after verteporfin-PDT, especially at a sub-lethal dose. Furthermore, activation of PI3K signaling was correlated with cell growth after PDT. Thus, the goal of this study is to test the hypothesis that therapeutic outcome of verteporfin-PDT can be enhanced by targeting PDT-induced pro-survival PI3K signaling pathway. We found that PI3K-mTOR pathway inhibitor NVP-BEZ235 (BEZ235) significantly inhibited PDT-induced PI3K signaling activation and combination of BEZ235 and verteporfin-PDT resulted in more cell apoptosis and greater inhibition in cell proliferation in SVEC cells. The combination therapy led to significantly more tumor growth inhibition than each individual treatment in the PC-3 prostate tumor model. Examination of tumor samples for PI3K signaling activity and functional vasculature revealed that the combination treatment caused more inhibition in PI3K signaling and reduction in functional blood vessels than verteporfin-PDT or BEZ235 treatment alone. These results indicate that targeting pro-survival PI3K signaling pathway is an effective approach for enhancing tumor response to verteporfin-PDT. Citation Format: Daniel E. Kraus, Pratheeba Palasuberniam, Bin Chen. Targeting PI3K signaling pathway for therapeutic enhancement of verteporfin-mediated photodynamic therapy. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3800. doi:10.1158/1538-7445.AM2015-3800