Abstract Pacritinib is a clinically-approved JAK2/IRAK1/ACVR1 inhibitor for the treatment of myelofibrosis. As JAK2 inhibition has shown utility against a range of tumors, including glioblastoma (GBM), we aimed to investigate its role in the treatment of diffuse midline glioma, a still universally fatal disease of childhood. Against GBM, the JAK2 inhibitor AZD1480 demonstrated a significant cytotoxic effect against cell lines with elevated levels of phospho-STAT3, an important JAK2-modified transcriptional regulator. Here, we utilized our patient-derived diffuse intrinsic pontine glioma (DIPG) models, including two with H3.3 mutations (PBT-22FH, PBT-29FH), one with a H3.1 mutation (PBT-27FH), and one that is histone wildtype (PBT-24FH). To assess preclinical utility of this agent, we performed assays defining viability, apoptosis, and signaling analysis as a prelude to in vivo analyses. Across our models, the IC50 was found to be 1.47 (range: 1.18-2.02 uM) at 96 hours. We also observed robust apoptotic responses using a caspase 3/7 assay. Notably, apoptosis was swift, peaking at 34 hours (range: 20-44) across our models at 10 uM drug. To confirm on-target effect we analyzed signaling of the JAK/STAT pathway via multiple markers in western blot analysis and found reduced pSTAT3, pSTAT5, and pJAK2 levels, indicative of JAK2 inhibition. As this is a CNS-penetrant and clinically available inhibitor, this work supports further investigation of pacritinib against DIPG/DMG.
Biery et al. (Fri,) studied this question.