Triptolide as a potentially promising therapy for diffuse midline glioma

Abstract Diffuse Midline Gliomas (DMG) are amongst the most lethal pediatric brain tumors. Children diagnosed with DMG face a grim prognosis of 9-11 months from diagnosis. Over 85% of DMG patients harbor mutation affecting histone-encoding genes (H3.1K27M, H3.3K27M) leading to genome hypomethylation and transcriptional disruption. Despite decades of clinical studies, the development of an effective therapy remains a challenge. Triptolide is a diterpenoid triepoxide compound inhibiting cell growth and exhibiting preclinical antitumor activity. A large drug screen conducted by the NCI using DMG cell lines identified triptolide as a candidate for reducing DMG cell viability. To further investigate triptolide and its potential for clinical intervention, we used DMG preclinical in vitro and in vivo models. In vitro viability assays with triptolide alone and in combination with other therapeutic drugs (ONC201 and ONC206), were carried out using seven DMG cell lines. Single treatment with triptolide resulted in a significant decrease in DMG cell viability and combination with both ONC201 and ONC206 showed additivity. Triptolide’s toxicity was assessed in vivo through direct injections into the yolk sac of zebrafish. Preliminary data demonstrated how triptolide has higher toxicity compared to un-injected and DMSO control groups. However, a major limitation of triptolide’s clinical utility is its low solubility. Therefore, for in vivo studies, we used minnelide, a water-soluble analog of triptolide, with potent antitumor properties. Studies were performed in eleven RAG2 female mice. PDX tumor-bearing mice were treated with minnelide and ONC201 for three weeks as single or in combination. Survival studies showed no significance in minnelide monotherapy. However, minnelide + ONC201 combination therapy resulted in significant (p=0.01) survival of PDX models. Our current studies investigate the efficacy of a higher dose of minnelide in vivo. Our goal is to establish minnelide potential as a combination strategy for the treatment of children diagnosed with DMG.