FK-779

The effects of tacrolimus (FK506) and malononitrilamides (MNA) (FK778 and FK779) monotherapy and combination therapy were examined in prevention of acute heart and kidney allograft rejection and reversal of ongoing acute heart allograft rejection in the rat.

Brown Norway (RT1n)-to-Lewis (RT11) and ACI (RT1a)-to-Lewis (RT11) combinations were used, respectively, for heart and kidney transplantation models. Immunosuppressants were administered orally from day 1 to day 14 for preventing acute rejection and from day 4 to day 34 after transplantation for the reversal of ongoing acute rejection.

In the prevention of acute heart rejection model, recipient rats treated with monotherapy of tacrolimus or MNA (FK778, FK779) showed a dose-related prolongation of mean survival time (MST) compared with naive control rats (P<0.01). The mean survival time in combination therapy of tacrolimus (FK506) and FK778 indicated that an additive to synergistic interaction was produced when compared with the respective monotherapies (combination index [CI]=0.631-1.022). These results were reproducible with tacrolimus and FK779 combination therapy (CI=0.572-0.846). Furthermore, similar results were also found in the prevention of acute kidney allograft rejection in the rat (CI=0.137-0.516). In the reversal of ongoing acute heart allograft rejection, combination therapy of tacrolimus and FK778 demonstrated a strong synergistic interaction (CI=0.166-0.970) compared with monotherapy of tacrolimus or FK778.

Combination therapy of tacrolimus and MNA (FK778, FK779) produces synergistic effects in prevention of acute heart and kidney rejection and reversal of ongoing heart allograft rejection in the rat.

Chemical immunosuppression developed at the beginning of clinical transplantation remains the basis of immunosuppressive protocols used today. Clinical trials of new agents focus on the incremental improvement in one of four areas of immunotherapy: induction, basic maintenance, adjuvant and steroid therapy. Induction immunotherapy developments include the use of humanized antibodies, specific targets (basiliximab, daclizumab) and lymphocyte depletion (anti-thymocyte globulin, campath-1H). Promising results from pilot trials allow for subsequent low dose maintenance monotherapy. New inhibitors of calcineurin isoforms (ISATx247) may disassociate the anti-rejection effect from the toxicity of conventional calcineurin inhibitors. Revived investigation of older anti-proliferative or anti-metabolite drugs (rapamycin, mycophenolic acid, leflunomide) show promise in preventing B-cell responses and reducing chronic rejection but development of derivatives (everolimus, mycophenolate mofetil, ERL 080, MNA 279, MNA 715) may have a stronger commercial than experimental basis. Trials of steroid immunotherapy have focused on steroid elimination but trial of newer locally active steroids may be beneficial.