(F-208) MR-Guided Focused Ultrasound Blood-Brain Barrier Disruption Increases Drug Delivery and Efficacy in a Diffuse Midline Glioma Mouse Model

Introduction:: Diffuse midline glioma, specifically pontine and H3 K27M-altered, is the most common and unfortunately the deadliest brainstem tumor in children [1]. Current clinical treatment methods only involve palliative radiotherapy that does not significantly improve survival beyond its poor mean survival of 9 months [2]. These tumors remain difficult to treat with chemotherapy as they maintain an intact blood-brain barrier (BBB). Although a technique using focused ultrasound (FUS) and microbubbles (MBs) has been shown to disrupt the blood-brain barrier (BBBD) allowing larger chemotherapeutics to enter the parenchyma [3]. Panobinostat is one of the chemotherapeutics that has difficulty crossing the BBB although it has promising effects in vitro [4]. Therefore, in this study, we hypothesized that using FUS we could disrupt the BBB allowing a higher concentration of Panobinostat to enter the tumor region and provide a therapeutic effect.


Materials and Methods:: Mice were injected with BT-245 (DIPG tumor cell line) orthotopically into the pons, 1 mm laterally to the right hemisphere. The initial set of mice (n=12) had two weeks of growth then MR images were taken and used to guide FUS targeting to the center of the tumor location. In-house microbubbles were size isolated to 3 um and half of the mice (n=6) were injected via tail vein at 25 ul/kg. Right before (10-20 seconds) sonication was started with parameters as follows: center frequency: 1.515 MHz, peak negative pressure: 0.615 MPa, pulse length: 1 ms, pulse repetition frequency: 1 Hz. Sonication lasted for 3 minutes, and passive cavitation data was collected and analyzed as previously described [5]. Directly after FUS Panobinostat (LBH-589) was given (10 mg/kg) intraperitoneal (IP) and MR images were taken to determine the extent of BBBD. After 1.5 hours mouse serum and brains were extracted and split at the midbrain and cerebellum. All three samples were sent in for liquid chromatography and mass spectrometry to determine the concentration of Panobinostat at each location.

The second set of mice (n=20) were treated weekly for three weeks. Half of them were treated with both FUS and Panobinostat with the same parameters as the first set, the other half was only given Panobinostat. After 3 weeks no treatment was done on either set. MR images were taken, and body weight was examined weekly before treatment and after the treatment period ended to evaluate the extent of BBBD and tumor progression.


Results, Conclusions, and Discussions:: We have demonstrated that FUS-mediated BBBD can successfully deliver Panobinostat (LBH-589) to the pons with DMG tumors over 3-fold (Fig.1a) while only slightly increasing the concentration of the forebrain 51% (Fig. 1b). Passive cavitation detection during treatments showed ideal harmonic cavitation throughout the 3 minutes while not having any significant broadband cavitation (Fig. 2). The combination of both Panobinostat and FUS showed major decreases in tumor growth by ~71% by the end of the treatment weeks when compared to Panobinostat without FUS (Fig. 3a). A significant survival benefit was also demonstrated when treated with both Panobinostat and FUS improving the mean survival from 21 to 31.5 days (Fig. 3b).
In conclusion, our group has shown that MR-guided FUS/MB is a non-invasive, safe, and effective way to temporarily disrupt the BBB and increase drug delivery of panobinostat in a clinically relevant DIPG orthotopic xenograft mouse model. We showed the potential to treat this model weekly for 3 weeks while maintaining safe and similar BBB opening volumes. This is a critical pre-clinical step to inform the use of this technology for DIPG patients in human clinical trials.


Acknowledgements (Optional): :

References (Optional): : [1]. Veldhuijzen van Zanten, Sophie EM, et al. "A twenty-year review of diagnosing and treating children with diffuse intrinsic pontine glioma in The Netherlands." Expert review of anticancer therapy 15.2 (2015): 157-164.

[2]. Packer, Roger J., et al. "Outcome of children with brain stem gliomas after treatment with 7800 cGy of hyperfractionated radiotherapy. A childrens cancer group phase 1/11 trial." Cancer 74.6 (1994): 1827-1834.

[3]. Woodworth, Graeme F., et al. "Emerging insights into barriers to effective brain tumor therapeutics." Frontiers in oncology 4 (2014): 126.

[4]. Grasso, Catherine S., et al. "Functionally defined therapeutic targets in diffuse intrinsic pontine glioma." Nature medicine 21.6 (2015): 555-559.

[5]. Martinez, Payton, Nick Bottenus, and Mark Borden. "Cavitation Characterization of Size-Isolated Microbubbles in a Vessel Phantom Using Focused Ultrasound." Pharmaceutics 14.9 (2022): 1925.