(A) Schematic showing Minnelide hydrolyzation into active triptolide. (B) Mice were implanted with HD:MB03 cells 15 days before being treated with either vehicle or Minnelide (0.4 mg/kg, i.p., daily) for 4 days (n = 4). (C) HD:MB03 cells were allowed to form orthotopic tumors for 3 days before similarly dosing mice for 7 days. Tumor size was quantified by IVIS imaging (vehicle n = 9, Minnelide n = 10). (D) HD:MB03 cells were allowed to form orthotopic tumors for 15 days before similarly dosing mice for 4 days. MYC expression in harvested brains was determined by RT-qPCR (vehicle n = 4, Minnelide n = 5). (E) Immunostaining for indicated proteins in brain tumors from similar mice (n = 3). (F) Measurement of metastatic lesions located outside of the posterior fossa of similar mice (vehicle n = 4, Minnelide n = 5). (G) Tumors located in the spinal cord of mice similarly dosed for 21 days were measured (n = 5). (H) mG3-2929 cells were implanted 3 days before similar dosing, and symptom-free survival was determined using log-rank (Mantel-Cox) tests (vehicle n = 9, Minnelide n = 10). (I) Symptom-free survival was determined using log-rank (Mantel-Cox) tests in similarly dosed mice but harboring HD:MB03 tumors (vehicle n = 8, Minnelide n = 15). (J) Mice were similarly treated for 21 days before examining cerebellar tissues (n = 5). (K) Displayed are body weights of 2-week-old wild-type mice similarly dosed for 10 days (vehicle n = 5, Minnelide n = 6). All tumor area measurements were performed in ×2.5-magnified H&E-stained slides. All images are representative. Arrows indicate tumor presence. All tissues were harvested 6 hours after the last injection. Results are presented as mean ± SEM of data normalized to 1 vehicle-treated animal. Scale bars: 400 μm (B, F, G, and J) and 50 μm (E). Statistical significance was assessed using unpaired, 1-tailed Student’s t test. *P < 0.05; **P < 0.01; ***P < 0.001.