Synergistic effects of mycophenolate mofetil and sirolimus in prevention of acute heart, pancreas, and kidney allograft rejection and in reversal of ongoing heart allograft rejection in the rat

Background. The effect of mycophenolate mofetil (MMF) and sirolimus (rapamycin, RAPA) mono- and combination-therapy was examined in prevention of acute heart, pancreas, and kidney allograft rejection and in reversal of ongoing heart allograft rejection in the rat, Methods. Both drugs were administered orally for up to 30 days. Eleven groups (n=6) were involved in the first part of the heart allografting model. Brown Norway (RT1(n)) to Lewis (RT1(l)) combination was used in the heart and pancreas transplantation models, whereas Buffalo (RT1(b)) to Wistar Furth (RT1(u)) was used in the kidney transplantation model. Results. The naive control group showed a mean survival time of 6.5+/-0.6 days. There were graded dose-responses to monotherapy of MMF 10 and 20 mg/kg/day (12.5+/-2.6 days; 19.3+/-9.0 days) and RAPA 0.2, 0.4, 0.8, and 1.8 mg/kg/day (19.2+/-2.0 days; 30.0+/-7.3 days; 50.8+/-12.5 days; 51.2+/-2.6 days), respectively (P=0.001). Results with the combined use of drugs indicate that a synergistic or very strong synergistic interaction was produced when compared with monotherapy of MMF or RAPA: MMF 10 mg/kg/day+RAPA 0.2 mg/kg/day (52.7+/-5.7 days, combination index [CI]=0.189), MMF 20 mg/kg/day+RAPA 0.2 mg/kg/day (57.7+/-5.7 days, CI=0.084), MMF 10 mg/kg/day+RAPA 0.4 mg/kg/day (50.2+/-13.5 days, CI=0.453), and MMF 20 mg/kg/day+ RAPA 0.4 mg/kg/day (51.5+/-6.8 days, CI=0.439), respectively. These results were repeatable in the prevention of acute pancreas and kidney allograft rejection in the rat. In the second part of the study of reversal of ongoing acute heart allograft rejection model, the combined treatment of MMF 10 mg/kg/day+RAPA 0.2 mg/kg/day (35.5+/-16.0 days, CI=0.794) and MMF 20 mg/kg/day+RAPA 0.2 mg/kg/day (57.2+/-4.7 days, CI=0.310) represented synergistic interaction compared with monotherapy of MMF or RAPA. Conclusions. Concomitant therapy of MMF and RAPA produces a synergistic effect in prevention of heart, pancreas, and kidney allograft rejection and in reversal of ongoing heart allograft rejection in the rat.