Therapeutic opportunities for diffuse midline glioma identified from high-throughput combination drug screening

Diffuse midline gliomas (DMG) are a group of molecularly related malignancies occurring in midline structures of the childhood central nervous system, including thalamus, pons, and spinal cord. These cancers are characterized by high prevalence of the histone-3K27M mutation and are universally lethal, with median survival of only 9-11 months for pontine DMG (a.k.a. DIPG). In search of novel therapeutic options, we examined multiple cell models in sequential, quantitative high-throughput screens of approved and investigational drugs. This effort generated a total of 17,456 single-agent dose responses that inspired a subsequent series of HTS-enabled drug combination assessments encompassing a total of 8883 drug-drug examinations. Top combinations were validated across a panel of patient-derived cell lines representing the major DMG genotypes. In vivo testing in patient-derived xenograft models validated the combination of the multi-HDAC inhibitor panobinostat and the proteasome inhibitor marizomib as a promising therapeutic approach. Transcriptional and metabolomic surveys revealed substantial alterations to the cellular unfolded protein response and key metabolic processes following treatment with panobinostat and marizomib. Rescue of drug induced cytotoxicity and basal mitochondrial respiration with exogenous application of nicotinamide mononucleotide (NMN) or exacerbation of these phenotypes when blocking NAD+ production via NAMPT inhibition demonstrated that metabolic catastrophe drives the combination-induced cytotoxicity. This study represents the most comprehensive single-agent and combinatorial drug screen for DIPG reported to date and identifies concomitant HDAC and proteasome inhibition as a promising therapeutic strategy that underscores under-recognized metabolic vulnerabilities in DIPG. The combined screening outcomes represent a public resource for the DMG community. RNA-seq in patient-derived DIPG cell cultures in two replicates. Libraries were sequenced on Illumina NextSeq 500, 1x75.