Quantitative Monitoring and Control of Tumor Vascular Permeability In Vivo using Microbubble Contrast Agents Summary: The goal of this project is to develop a novel image-guided method of optimizing chemotherapeutic therapies in metastatic neuroblastoma patients by simultaneously monitoring and controlling tumor vascular permeability (VP) in vivo. Neuroblastomas are aggressive solid tumors responsible for 10% of childhood cancer related mortalities. Unlike many tumors, neuroblastomas exhibit poor vasculature perfusion that prevents drug extravasation and targeting of malignant tumor tissue. In order to treat metastatic neuroblastomas, high-dosage chemotherapy is used, which can have deleterious short and long-term side effects in juvenile patients. Methods of site-specific drug delivery to tumors are needed to enhance chemotherapeutic activity and lower required dosages for treatment. In this study, we propose a method of monitoring and spatially controlling drug permeability in neuroblastoma (NGP) tumors using novel microbubble contrast agents (MCA's) and ultrasound (US) imaging. MCA's are gas- filled spheres (1-10 m in diameter) that scatter US waves more effectively than surrounding blood and tissue, making them detectable with clinical US scanners. Additionally, when specific ultrasonic energy is applied, the physical response of MCA's in an US field can produce enough force to permeabilize the vasculature. This technique, known as sonoporation, is frequently utilized in laboratory testing to enhance site-specific drug delivery to tumors. Therefore, MCA's can be used to simultaneously control VP and monitor changes in blood perfusion specifically in tumor tissue. Currently, no clinical methods exist to monitor the effects of sonoporation in vivo. In this study, we will demonstrate that MCA enhanced US imaging can be used quantify vascular changes associated with sonoporation. MCA's are vascular agents that purely monitor blood perfusion. Unlike other in vivo imaging contrast agents, MCA's are too large to extravasate into tissue. However, numerous studies have demonstrated a strong correlation between VP of tissue and blood perfusion dynamics. Our preliminary data suggests that MCA perfusion dynamics correlates with qualitative indices of vascular normalization in reponse to anti-VEGF treatment (BV therapy- results in increased perfusion and VP). Therefore, we hypothesize that MCA perfusion dynamics can effectively be used to monitor changes in tumor VP associated with sonoporation as well. Next, we will apply this technique to demonstrate controlled drug uptake in neruoblastoma tumor models (NGP tumors) that exhibit varying vascular morphologies. Drug uptake in tissue is governed primarily by total blood perfusion and tumor vascular permeability, both of which can be measured using MCA enhanced US imaging. Therefore, we hypothesize that MCA perfusion dynamics can be used to maintain dose-symmetry of administered drugs. This technique would be particularly relevant for longitudinal drug therapies where the tumor vasculature is dynamically changing in response to treatment.