Intravital Imaging of Rapid Short-pulse Ultrasound-Induced Blood-Tumor Barrier Opening with Two-photon Microscopy

Rapid short-pulse (RaSP) ultrasound with microbubbles is a novel modality for blood-brain barrier (BBB) opening and intracranial drug delivery, which has less energy and thus probably safer compared with the widely used long-pulse sequence. While previous work developing RaSP has focused on assessing the efficiency and safety profile of BBB opening in healthy mouse brain mainly through in vitro fluorescence microscopy and histological staining, the real-time process of RaSP-induced BBB opening and blood-tumor barrier (BTB) opening in mouse tumor model has yet to be investigated. In this study we watched the dynamic process of BTB opening and drug delivery mediated by RaSP ultrasound utilizing intravital two-photon imaging. Mice with cranial window chamber were implanted with GL261-GFP glioma cells to establish tumor model. With a house-made fluorescent drug, two-photon microscopy revealed enhanced drug delivery across the BTB and drug uptake by tumor cells, providing the first evidence of RaSP ultrasound-induced BTB opening and intravital images of drug extravasation.