Antisense oligonucleotide therapy for H3.3K27M diffuse midline glioma.

Diffuse midline gliomas (DMGs) are pediatric high-grade brain tumors in the thalamus, midbrain, or pons; the latter subgroup are termed diffuse intrinsic pontine gliomas (DIPG). The brain stem location of these tumors limits the clinical management of DIPG, resulting in poor outcomes for patients. A heterozygous, somatic point mutation in one of two genes coding for the noncanonical histone H3.3 is present in most DIPG tumors. This dominant mutation in the H3-3A gene results in replacement of lysine 27 with methionine (K27M) and causes a global reduction of trimethylation on K27 of all wild-type histone H3 proteins, which is thought to be a driving event in gliomagenesis. In this study, we designed and systematically screened 2′-O-methoxyethyl phosphorothioate antisense oligonucleotides (ASOs) that direct RNase H–mediated knockdown of H3-3A mRNA. We identified a lead ASO that effectively reduced H3-3A mRNA and H3.3K27M protein and restored global H3K27 trimethylation in patient-derived neurospheres. We then tested the lead ASO in two mouse models of DIPG: an immunocompetent mouse model using transduced mutant human H3-3A cDNA and an orthotopic xenograft with patient-derived cells. In both models, ASO treatment restored K27 trimethylation of histone H3 proteins and reduced tumor growth, promoted neural stem cell differentiation into astrocytes, neurons, and oligodendrocytes, and increased survival. These results demonstrate the involvement of the H3.3K27M oncohistone in tumor maintenance, confirm the reversibility of the aberrant epigenetic changes it promotes, and provide preclinical proof of concept for DMG antisense therapy. Combatting pediatric glioma: Diffuse intrinsic pontine gliomas (DIPG) are pediatric high-grade brain tumors located in the brainstem, which limits treatment options and thus leads to poor patient outcomes. These tumors often have point mutations in histone H3.3, which represents a potential target for treatment. Here, Zhang et al. have generated and screened antisense oligonucleotides (ASOs) in H3.3 mutant DIPG patient cells to directly target and inhibit glioma growth. They treated patient-derived neurospheres and two DIPG mouse models with their lead ASO, which led to reduced tumor growth, cell differentiation, and increased survival, suggesting ASOs as a promising therapy for DIPG that requires further study. —DH [ABSTRACT FROM AUTHOR]