Evaluation of hypericin-mediated photodynamic therapy in combination with angiogenesis inhibitor bevacizumab using in vivo fluorescence confocal endomicroscopy.

Photodynamic therapy (PDT) is an alternative cancer treatment modality that offers localized treatment using a photosensitizer and light. However, tumor angiogenesis is a major concern following PDT-induced hypoxia as it promotes recurrence. Bevacizumab is a monoclonal antibody that targets vascular endothelial growth factor (VEGF), thus preventing angiogenesis. The combination of PDT with antiangiogenic agents such as bevacizumab has shown promise in preclinical studies. We use confocal endomicroscopy to study the antiangiogenic effects of PDT in combination with bevacizumab. This technique offers in vivo surface and subsurface fluorescence imaging of tissue. Mice bearing xenograft bladder carcinoma tumors were treated with PDT, bevacizumab, or PDT and bevacizumab combination therapy. In tumor regression experiments, combination therapy treated tumors show the most regression. Confocal fluorescence endomicroscopy enables visualization of tumor blood vessels following treatment. Combination therapy treated tumors show the most posttreatment damage with reduced cross-sectional area of vessels. Immunohistochemistry and immunofluorescence studies show that VEGF expression is significantly downregulated in the tumors treated by combination therapy. Overall, combining PDT and bevacizumab is a promising cancer treatment approach. We also demonstrate that confocal endomicroscopy is useful for visualization of vasculature and evaluation of angiogenic response following therapeutic intervention.