Fig. 4. Cardiac glycosides inhibit MB cell growth in vitro and prolong survival in vivo.
(A) Dose-response curve for the cardiac glycosides (proscillaridin A, digoxin, lanatoside C, digitoxigenin, and digoxigenin) on MB-derived cell lines (MED8A and D283) and the control glioblastoma line (U87). Cell viability was assessed at 72 hours. (B) IC50 values for the dose titration experiment. (C) Schematic of orthotopic PDX model treatment with digoxin. Twenty-four days after tumor cell implantation, mice received digoxin (2 mg/kg ip daily) for 14 days, followed by 21 days without treatment, and followed by another 14 days of treatment. (D) Hematoxylin and eosin (H&E) staining examples of untreated tumors from orthotopic PDX models of group 3 (ICb-2555MB) and group 4 (ICb-1078MB) MB. (E and F) Kaplan-Meier curves showing digoxin-treated mice compared to untreated controls. (E) Digoxin treatment prolonged survival in an orthotopic PDX model of group 4 MB (ICb-1078MB) to 113 days (n = 7) versus 92 days (n = 6) for untreated controls (log-rank test, P = 0.001). Two long-surviving mice were euthanized at 219 days while asymptomatic. Gross-scale image of one long-surviving mouse with large tumor and H&E staining demonstrating no evidence of tumor in the two long-surviving mice, one with a tumor and one without is shown. (F) Digoxin treatment prolonged survival in an orthotopic PDX model of group 3 MB (ICb-2555MB) to 180 days (n = 10) versus 102 days (n = 8) for untreated controls (log-rank test, P < 0.001). H&E comparison of two long-term surviving mice, one with a microscopic tumor and one without is shown. Scale bars, 1 mm (black) and 0.1 mm (white).