Hi, this is Zach Englander. I'm a second-year resident in neurosurgery at NYP Columbia, and my talk today is titled, Safety and Feasibility of Focus Ultrasound Mediated Blood-Brain Barrier Opening in a Murine Model of Brainstem Glioma. I have no disclosures. DIPG makes up 10 percent of all pediatric central nervous system tumors and is a devastating cancer. It is highly aggressive and particularly infiltrative. This along with the eloquent nature of the brainstem makes surgical resection impossible. The current standard of care is radiation followed by systemic therapy. However, median survival remains poor at around nine months. While we have begun to learn a lot about the molecular characteristics of these tumors within the last decade, the blood-brain barrier is thought to limit the penetrance of systemic therapies. Focus ultrasound in combination with intravenous microbubbles has been developed over the last several years to facilitate the delivery of drugs across the blood-brain barrier. The gaseous microbubbles expand and contract while being sonicated and mechanically open the tight junctions within the cerebral vasculature. Unlike systemic osmotic agents like mannitol, focus ultrasound can target regions of interest. This figure on the right depicts our setup with mice anesthetized below a single element transducer powered by a function generator through a power amplifier. Given that the application of focus ultrasound in brainstem tumors has yet to be studied, we set out to test the safety and feasibility of focus ultrasound in a murine pontine tumor model. We used a PDGFB amplified P10, P53 knockout cell line developed by our lab by viral injection into the mouse cerebrum. We implanted the cell line by injection into the brainstem of B6 albino mice, and confirmed their growth on post-injection day 13 on MRI. We then randomized mice to either control single focus ultrasound or double focus ultrasound groups. Mice in the one-time treatment group were sonicated on post-injection day 14, and those in the double treatment group were treated on post-injection day 14 and 19. A select group of mice were then sacrificed immediately after treatment for histology. The remaining mice were serially monitored for weight loss and survival. Once mice underwent ultrasound treatment, blood-brain barrier opening was confirmed on contrast-enhanced T1-weighted imaging. One mouse subsequently underwent Evans blue dye injection, perfusion, and brain harvesting. Gross histology revealed blood-brain barrier opening in the pattern of contrast enhancement. We also obtained serial T2 imaging which showed no evidence of ultrasound-related hemorrhage. Repeat imaging at 72 hours demonstrated reclosure of the blood-brain barrier. Mice that underwent a second round of ultrasound had successful reopening of the blood-brain barrier. To further assess the safety of the treatment, we monitored cardiopulmonary vitals before, during, and after treatment. We did not see any apneic events or cardiac pauses. We did observe a slight physiological drop in heart rate from baseline after each injection of microbubbles shown with the red arrows. However, heart rate returned to baseline. Motor testing was also completed with sequential weightlifting before and after treatment. There was no change in motor testing after the first treatment. We did actually see an improvement in the mice that underwent two rounds of treatment, but that was likely related to increased test exposure and less likely any neuromodulatory effect. Mice did not show any evidence of post-procedural weight loss within the five-day period after treatment as shown in this figure. Furthermore, survival was similar in all three groups. Lastly, on review by two blinded neuropathologists, there was no difference seen between focus ultrasound and control groups. In conclusion, focus ultrasound blood-brain barrier opening is a safe method in a preclinical Ponting glioma model. Future work will need to look at testing focus ultrasound enhanced delivery of systemic therapy. Here are my acknowledgments. Thank you very much.

Zach Englander

neurosurgery

focused ultrasound

blood-brain barrier

brainstem glioma