Background: Diffuse intrinsic pontine glioma (DIPG) is a devastating pediatric brain tumor with poor prognosis. Sonodynamic therapy (SDT) with ALA is a non-invasive strategy that sensitizes target tissues with a non-toxic chemical agent followed by exposure to low intensity MR-guided focused ultrasound (MRgFUS). Preclinical studies have shown that ALA is preferentially taken up by glioma cells and metabolized to protoporphyrin IX (PpIX). SDT activates protoporphyrin IX and induces tumor cell death via photodynamic effect (lipoperoxidation, apoptosis). Suheiro et al and Wu et al demonstrated that SDT killed tumors via apoptosis and lipoperoxidation in rodent glioma models with minimal damage to surrounding normal brain.^1,2 ALA SDT was well-tolerated in an ongoing first-in-human trial in adults with recurrent high-grade gliomas and demonstrated biomarker evidence of the photodynamic effect³. Methods: A Phase 1/2, multicenter, open label study (NCT05123534) is enrolling patients at Children’s National Hospital. The study employs the Bayesian optimal interval (BOIN) algorithm to evaluate safety and tolerability of treatment with SDT in newly diagnosed DIPG subjects to determine the maximum tolerated dose (MTD) or recommended phase 2 dose (RP2D) of MRgFUS energy in combination with ALA. The study will evaluate 3 ALA doses and 3 acoustic energy doses. ALA is administered IV six to nine hours prior to MRgFUS with the Exablate type-2 device. The first cohort, B1C1, evaluates the lowest drug-device dose combination and if no dose-limiting toxicity (DLT) is encountered after 3 patients, ascending dose-escalation will proceed to the second cohort, B2C1, treated with lowest dose of ALA with the second level of MRgFUS energy. Again, if no DLT is experienced, the next cohort will receive a higher dose combination. The initial patient in each cohort is treated in 2 sessions 21 to 28 days apart, each covering one-half of the pons. Subsequent patients are treated in 1 session to the whole pons. The primary objective is to evaluate the safety and tolerability of SDT in DIPG subjects. Secondary outcomes include preliminary efficacy assessments, pharmacokinetics of ALA and PpIX, mechanical performance of the Exablate Type-2 device, and radiographic evidence of tumor physiological changes associated with SDT. All patients at least 5 years of age with newly diagnosed, radiographically typical DIPG between 4-24 weeks after completion of standard radiotherapy are eligible for the trial. Patients with evidence of disease progression, diagnosis of porphyria, or prior or concurrent therapy with any other anticancer or investigational intervention will be excluded. Cohort 1 has been completed without DLT. References: 1. Suheiro et al. J Neurosurg 2018;129:1416-1428. 2. Wu et al. Sci Rep 2019;9:10465. 3. Sanai et al. NeuroOnco 2022;24(&):vii72-vii73. Clinical trial information: NCT05123534.