Imaging and Histopathological Analysis of Microvascular Angiogenesis in Photodynamic Therapy for Oral Cancer

SIMPLE SUMMARY: PDT has been recently proposed as a treatment modality for cancers. A histopathological examination of PDT showed that apparent internal hemorrhage and red blood cell (RBC) extravasation are commonly observed in malignant tumors after PDT. Tumor angiogenesis has been identified as one of the key targets in tumor treatments. In this study, in vivo chicken chorioallantoic membranes (CAMs) and a stimulated malignant oral lesions animal model were used. The velocity and structural images of in vivo microcirculation and the relation between the changes in intrinsic signal in blood components and histopathological responses during PDT were examined for more understanding. Our study demonstrated that PDT can target the microvasculatures within the tumor and cause tumor destruction. The optimization of PDT for squamous cell carcinomas of the oral cavity may depend on the ability to cause the selective destruction of only vascular-mediated events or cellular targets without the production of heat through nonthermal mechanisms. ABSTRACT: The objective of this study is to use imaging and histopathological analysis to characterize and monitor microvascular responses to photodynamic therapy (PDT). In vivo chicken chorioallantoic membranes (CAMs) and a stimulated malignant oral lesions animal model were used to determine the blood flow and the biological activities of Photofrin(®) (2.5 mg/kg) exposed to different laser power densities at 630 nm. The vascular changes, the velocity of the blood flow, the speckle flow index (SFI) of fluorescence changes, and ultrastructure damage in the microvasculature before and after PDT were recorded. The subcellular localization of Photofrin(®) revealed satisfactory uptake throughout the cytoplasm of human red blood cells at 10 s and 20 s before PDT. The mean blood-flow velocities of the veins and arteries were 500 ± 40 and 1500 ± 100 μm/s, respectively. A significant decrease in the velocities of the blood flow in the veins and arteries was detected in the CAM model after PDT. The veins and arteries of CAMs, exposed to the power densities of 80, 100, and 120 mW/cm(2), had average blood-flow velocities of 100 ± 20, 60 ± 10, and 0 μm/s and 300 ± 50, 150 ± 30, and 0 μm/s, respectively. In the stimulated malignant oral lesions animal model, the treated tumors exhibited hemorrhage and red blood cell extravasation after PDT. The oxyhemoglobin and total hemoglobin levels decreased, which resulted in a decrease in tissue oxygen saturation, while the deoxyhemoglobin levels increased. PDT using Photofrin(®) has the ability to cause the destruction of the targeted microvasculature under nonthermal mechanisms selectively.