Focused Ultrasound-Mediated Blood Brain Barrier Opening is Safe and Feasible in Diffuse Intrinsic Pontine Glioma after Radiation Treatment

Abstract

Diffuse intrinsic pontine glioma (DIPG), also known as diffuse midline glioma, is a fatal disease in children. Unlike glioblastoma for adults, there are no effective systemic therapies and radiotherapy is the only modality of treatment. With radiation, overall survival improves as compared to supportive care; however, all patients succumb to disease recurrence and ultimately die. The challenge is that the disease is heterogeneous with extensive infiltrative microscopic disease that extends to regions in which the blood brain barrier (BBB) remains relatively intact. Focused ultrasound (FUS) is a novel technology that allows for non-invasive opening of the BBB that is reversible. The question remains whether this can be performed safely in the brainstem after standard radiation. The purpose of this study is to examine the safety and feasibility of BBB-opening with FUS following radiation in a mouse model. A mouse syngeneic DIPG cell line harboring H3.3K27M, PDGF-B (+), and p53 (-/-) was used to factor the potential inflammatory effects of radiation and ultrasound that may contribute to harm. 10,000 cells in 1 μl was injected into the brainstem. At 3 weeks after implantation, magnetic resonance imaging (MRI) T1-post contrast and T2 sequences were obtained to confirm tumor growth. Using the small animal radiation research platform (SARRP), 9 Gy in 3 fractions was delivered to the brainstem. FUS-mediated BBB-opening with microbubbles was performed within 5 day of completion of radiation. Vitals were continuously monitored during FUS. MRI was obtained to confirm BBB-opening. An additional MRI was obtained at 48 hours to show BBB-closure. Mice were observed daily for neurological deficits, including motor dysfunction, seizure, irregular breathing and death. Daily weights were recorded. Kondziela’s inverted screen test was performed before and after FUS to assess for motor strength. Kaplan Meier methods were used to assess survival. Using MRI guidance, radiation to the brainstem was tolerated by mice harboring DIPG. FUS-mediated BBB-opening in the brainstem was feasible and confirmed on MRI. BBB closure was seen by 48-hours after BBB-opening. Compared to radiation alone, FUS did not alter vitals, motor function, weight change, neurological deficit and survival. This is the first study to demonstrate that FUS-guided BBB-opening in the brainstem to target DIPG is safe and feasible after radiation. These results are currently being translated into the clinic to assess the safety and feasibility of FUS in children with DIPG.