Augmenting focused ultrasound-mediated drug delivery to brain tumors with vascular normalization

The blood-tumor barrier (BTB) hinders the delivery and penetration of systemically administered therapeutic agents into the brain tumor microenvironment. The BTB is created by dilated and leaky microvessels that cause regional perfusion variability and poor convective delivery gradients, often while still retaining

enhanced efflux transporter expression and tight-junction integrity. To enhance therapeutic delivery across the BTB, we and others have deployed non-invasive, MR image-guided, transcranial pulsed focused ultrasound (FUS), in combination with microbubbles (MBs). MBs oscillate upon exposure to FUS, exert mechanical stresses

on the microvasculature, and open the BTB for augmented payload delivery. Yet, despite the promise of this

approach, there is still room for significant improvement. Indeed, spatial perfusion variability still limits MB access, dilated tumor vessels have diminished contact with oscillating intravascular MBs, and high interstitial tumor pressure still limits transport when the BTB is opened. Here, we aim to overcome these obstacles to more

effective FUS+MBs-mediated drug delivery by “pre-normalizing” brain tumor microvasculature via VEGF-R2 blockade, a pharmacological approach not limited by the BTB because VEGFR2+ endothelium is in direct contact with the bloodstream. We posit that vascular normalization will improve FUS+MB drug delivery because it

reduces interstitial tumor pressure, improves tumor perfusion and oxygenation, and reverses tumor endothelial cell anergy that limits immune cell infiltration and function. In this proposal, for models of both primary and metastatic brain tumors, we will develop FUS+MB based approaches that leverage vascular normalization to improve drug delivery across the BTB. Aim 1 will be to

identify vascular normalization timing window(s) that provide optimal conditions for focused ultrasound-mediated drug delivery to brain tumors. We will identify such optimal windows for delivery of 2 different sized MRI contrast agents [MultiHance (~1 kDa; simulating small molecule drugs) and Gad-IgG (~150 kDa; simulating mAb

immunotherapy)]. T1 MRI mapping will be used to precisely quantify the spatiotemporal distribution of contrast agent after FUS+MB-mediated delivery. Aim 2 will use this information and leverage vascular normalization to augment therapeutic efficacy of focused ultrasound-mediated immunotherapy delivery to brain tumors. Here, we

will deliver promising immunotherapies (αCD47 and αPD-1) that we hypothesize may best benefit from FUS+MB delivery in the setting of vascular normalization and may also be rapidly translated into clinical trials at our institution. Studies will include longitudinal assessment of tumor growth by MRI, generation of Kaplan-Meier

curves for animal survival, and histological analysis of tumor response. Because vascular normalization offers opportunities for enhanced immune cell infiltration via augmented endothelial cell adhesion molecule expression, we will also test whether tumor control occurs through CD4 and/or CD8 T cell-dependent mechanisms.