Development of brain-penetrant, histone evicting anthracycline drugs for treatment of diffuse midline glioma

Johns Hopkins University, Baltimore MD

Investigators

Abstract

PROJECT SUMMARY The pediatric brain tumor diffuse midline glioma (DMG) has a dismal prognosis and no curative therapies. Despite many clinical trials, DMG remains an incurable, uniformly fatal diagnosis with median survival under one year. A breakthrough in our understanding of DMG biology was the discovery of oncogenic histone H3 K27M mutation as the defining molecular driver of DMG. Genetic studies have confirmed that DMG cells are critically dependent on the mutant histone, such that deletion of H3-K27M abolishes the ability of these cells to form tumors. Further, the dominant negative effect of H3-K27M on gene regulation requires its deposition into chromatin. Therefore, drugs that interfere with H3-K27M mutant histone incorporation into chromatin could revolutionize DMG therapy by directly targeting the root cause of oncogenic transformation. Anthracycline drugs are cornerstones of chemotherapy due to their ability to intercalate into DNA, trap topoisomerases, and induce DNA damage. Recently, a novel mechanism of action for anthracycline derivatives was discovered. By intercalating into DNA, these drugs can 'evict' or displace histones from chromatin. N-alkylated derivatives (such as the natural product aclarubicin) have been shown to selectively induce histone eviction in regions marked by H3-K27 trimethylation at concentrations that do not induce DNA breaks. We found that aclarubicin is selectively toxic to H3-K27M DMG cells and causes specific gene expression changes at targets of H3K27 trimethylation that are dysregulated by H3-K27M mutation. We subsequently developed novel anthracycline derivatives, exemplified by lead compound JHU-5287, that act predominantly by the mechanism of histone eviction, rather than by induction of DNA damage. Importantly, JHU-5287 exhibits excellent brain penetration, in contrast to the poor brain distribution of current anthracycline drugs. To capitalize on this discovery, we will now focus on further characterization and optimization of the lead compound for desirable pharmacological properties (R61 Phase), thus enabling in vivo efficacy studies in mouse orthotopic xenograft models of DMG (R33 Phase). In vivo efficacy achieved at the R33 phase would allow us to fulfill entry criteria for the Blueprint Neurotherapeutics Network and advance to the translational phase. This proposal involves a collaborative effort with investigators of Johns Hopkins Drug Discovery (JHDD), who supply broad expertise in medicinal chemistry, drug metabolism and pharmacokinetics, and animal pharmacology.