NOVEL MODE OF ACTION OF THE CALCIUM-ANTAGONIST MIBEFRADIL (RO-40-5967) - POTENT IMMUNOSUPPRESSION BY INHIBITION OF T-CELL INFILTRATION THROUGH ALLOGENEIC ENDOTHELIUM

Cyclosporin A reduces the mitotic activity of allosensitized lymphocyt es, but fails to limit emigration of these cells into the donor organ. However, the modulation of both lymphocyte proliferation and infiltra tion are desirable characteristics of immunosuppressive therapy. The c alcium-channel blocker, verapamil, has recently been shown to effectiv ely prevent the trans-migration of CD4(+) and CD8(+) T cells through a llogeneic endothelium. Mibefradil (Ro 40-5967) represents a new genera tion of calcium antagonists with high potency and long-term activity. To evaluate the immunosuppressive potential of this drug, the influenc e of mibefradil on lymphocyte adhesion to, horizontal locomotion along , and penetration through allogeneic endothelium (HUVEC) was performed . When lymphocytes were prestimulated for 24hr with mibefradil, adhesi on and penetration were dose-dependently reduced. The adhesion ID50 va lues were 3.4 mu M (CD4(+) T cells) versus 9.2 mu M (CD8(+) T cells) a nd 2.1 mu M (CD4(+) T cells) versus 3.9 mu M (CD8(+) T cells) with reg ard to penetration. Mibefradil also effectively blocked horizontal loc omotion. Specific down-regulation of T-cell binding to the P-selectin receptor (ID50: CD4(+) T cells, 0.8 mu M; CD8(+) T cells, 1.2 mu M) an d to the intracellular adhesion molecule-1 (ICAM-1) receptor (ID50: CD 4(+) T cells, 1.9 mu M; CD8(+) T cells, 1.5 mu M) by mibefradil seems to be responsible for the decreased adhesion and penetration rates. Re duction of intracellular F-actin in T lymphocytes could diminish cell locomotion. In conclusion, the potent suppressive properties of mibefr adil support its use as a co-medication in cyclosporin A-based immunos uppressive therapy.