Friedrich Koch-Nolte

Sirolimus and FK778: a comparison of two anti‐proliferative immunosuppressants for prevention of experimental obliterative airway disease

This study examined the efficacies of sirolimus and the novel immunosuppressive agent FK778 to prevent obliterative airway disease (OAD). Tracheae from Brown–Norway donors were heterotopically transplanted in the greater omentum of Lewis rats. Recipients were treated for 28u2003days with sirolimus (0.5 or 2u2003mg/kg), FK778 (5 or 20u2003mg/kg), or combination regimens (0.5u2003+u20035u2003mg/kg, 2u2003+u200320u2003mg/kg). Tracheal segments were evaluated for degree of luminal obliteration, percentage of luminal epithelial cell coverage, and peritracheal infiltration. In vitro smooth muscle cell (SMC) proliferation and migration assays were performed to assess direct nonimmune‐related effects of the drugs. Sirolimus 2u2003mg/kg and FK778 20u2003mg/kg effectively reduced graft infiltration and prevented airway obliteration, whereas FK778 5u2003mg/kg was insufficient. Sirolimus 0.5u2003mg/kg at least showed moderate inhibitory effects on luminal obliteration and graft infiltration. Combination regimens revealed no significant beneficial effects. Both sirolimus and FK778 barely showed preserved epithelial coverage. Within the range of relevant concentrations, FK778 showed more potent anti‐proliferative and anti‐migratory effects on SMC in vitro than sirolimus. Both agents proved effective to prevent OAD development without preserving relevant amounts of epithelium. The anti‐proliferative potency on SMCs seems to be an especially important mechanism for FK778. De novo combination regimens revealed no beneficial interaction and thus remain doubtful.

139: FK778: New cellular and molecular mechanisms of action

PURPOSEnThe new malononitrilamide FK778 is currently being evaluated as an immunosuppressant for organ transplantation. Its main mechanism is inhibition of a pivotal enzyme of pyrimidine biosynthesis. This report revealed new mechanisms of action on different cell types involved in acute and chronic allograft rejection.nnnMETHODSnPurified Brown-Norway rat aortic endothelial cell (EC) cultures were pretreated with several concentrations of FK778. Endothelial adhesion molecule expression (ICAM-1/VCAM-1) stimulated with TNF-alpha was quantified by immunofluorescence. Purified Lewis rat lymphocytes (LC) incubated with FK778 were stimulated via TCR/CD28 signals, and CD25 expression was quantified using FACS analysis. Uridine addition was used in all assays to reverse the pyrimidine synthesis blockade. Lymphocyte-EC interaction was assessed by micromanipulator-assisted single-cell adhesion assays. Finally, smooth muscle cell (SMC) proliferation and migration was analyzed. Uridine addition was used in all assays to reverse the pyrimidine synthesis blockade.nnnRESULTSnTNF-alpha stimulation and TCR/CD28 co-stimulation significantly increased EC ICAM-1/VCAM-1-expression and LC CD25 surface expression, respectively. These effects were dose-dependently inhibited by FK778 and were not reversed by the addition of uridine. FK778 dose-dependently attenuated LC adhesion to allogeneic EC. The dose-dependent inhibition of SMC proliferation by FK778 was abolished by uridine addition, whereas the inhibitory effect on SMC migration was not affected by uridine supplementation.nnnCONCLUSIONSnFK778 directly reduced endothelial adhesion molecule up-regulation, inhibited lymphocyte activation, and attenuated lymphocyte-endothelium interactions, critical early steps in graft rejection. These effects were separate from the blockade of pyrimidine synthesis. The antiproliferative potency of FK778 on SMC may be an important mechanism to inhibit the fibroproliferative lesions of chronic organ rejection.