Photodynamic therapy-induced angiogenic signaling: consequences and solutions to improve therapeutic response.

Photodynamic therapy (PDT) can be a highly effective treatment for diseases ranging from actinic keratosis to cancer. While use of this therapy shows great promise in preclinical and clinical studies, understanding the molecular consequences of PDT is critical to designing better treatment protocols. A number of publications have documented alteration in angiogenic factors and growth factor receptors following PDT, which could abrogate treatment effect by inducing angiogenesis and re-establishment of the tumor vasculature. In response to these findings, work over the past decade has examined the efficacy of combining PDT with molecular targeting drugs, such as anti-angiogenic compounds, in an effort to combat these PDT-induced molecular changes. These combinatorial approaches increase rates of apoptosis, impair pro-tumorigenic signaling, and enhance tumor response. This report will examine the current understanding of PDT-induced angiogenic signaling and address molecular-based approaches to abrogate this signaling or its consequences thereby enhancing PDT efficacy.