SYNERGISM BETWEEN SIROLIMUS AND 1,25-DIHYDROXYVITAMIN D-3 IN-VITRO AND IN-VIVO

The active form of vitamin D, 1 alpha,25-(OH)(2)D-3, displays immunomo dulatory effects in vitro and in vivo at pharmacological levels. We ev aluated the dose-effect relationship of 1,25(OH)(2)D-3 and sirolimus ( rapamycin, RAP) in vitro, on the inhibition of PHA-srimulated PBMC pro liferation, by using the median effect analysis. Pharmacological conce ntrations of 1,25(OH)(2)D-3 (between 10(-9) and 3 x 10(-6) M) interact ed synergistically with RAP (combination index value of 0.01 for 50% s uppression of PBMC proliferation). In vivo, the effect of 1,25(OH),D, and RAP combinations on the evolution of experimental allergic encepha lomyelitis in SJL mice was analyzed. 1,25(OH)(2)D-3, given ip, in mono therapy, at a dose of 2 mu g/kg every two days, from day -3 until day +19 after disease induction, or RAP, injected daily at a dose of 0.3 m g/kg for the same period, decreased EAE incidence (paralysis in 70 and 55% of the animals, respectively, versus 98% in the placebo treated g roup, p < 0.001). The combination treatment using the two drugs in the se subtherapeutical doses provided near-total clinical (8% paralysis, p < 0.001 compared to monotherapy with 1,25(OH),D, or RAP) and histolo gical protection, comparable to that obtained with RAP in monotherapy at a threefold higher dose (1 mg/kg/d). When the two drugs were given using an alternate day administration schedule (RAP at 0.6 mg/kg and 1 ,25(OH)(2)D-3 at 2 mu g/kg. each given on alternate days from day -3 t o 19), near total protection was again obtained (13% paralysis, p < 0. 001 versus control). These in vitro and in vivo data support the exist ence of synergistic interactions between 1,25(OH)(2)D-3 and RAP. Consi dering the narrow therapeutic windows of both RAP and vitamin D-relate d compounds in autoimmune disease models, combinations of these drugs could find clinical application in reducing their individual therapeut ically efficient doses to non-toxic levels. (C) 1997 Elsevier Science B.V.