An N-(alkylcarbonyl)anthranilic acid derivative prolongs cardiac allograft survival synergistically with cyclosporine A in a high-responder rat model

We investigated the immunosuppressive effects of the dihydroortate dehydrogenase (DHODH) inhibitor compounds ABR-222417 and ABR-224050 from Active Biotech (Sweden). We verified the inhibitory effects of these compounds on the proliferation of CD4+ and CD8+ T-cells in vivo by using superantigen staphylococcus enterotoxin A (SEA)-mediated proliferation test. To evaluate their efficacy, the compounds were screened in a low-responder heart allograft transplantation model in rats [heart from Piebald Virol Glaxo (PVG) transplanted to Dark Agouti (DA)]. The immunosuppressive effects of the compounds were then investigated in a high-responder model (DA to PVG). Treatment with ABR-222417 (30 mg/kg) was more efficient than that with ABR-224050 (10 mg/kg), and the former provided a longer graft median survival time (MST, 29.5 days) than the latter (MST, 18.5 days). Furthermore, there was a marked increase in graft survival time (53 days) when low doses of ABR-222417 and cyclosporine A (CsA) were used in combination. No sign of tolerability problems was detected using this combination or when ABR-222417 was used singly at a higher dose. Furthermore, T-cell proliferation studies in vitro support that the anti proliferative effect of ABR-222417 is caused by inhibition of de novo pyrimidine synthesis, which is the consequence of DHODH inhibition. These results show that ABR-222417 had marked immunosuppressive effects on the heart allograft transplantation and that it exerts an even more powerful inhibitory effect on graft rejection when used in combination with CsA, with good tolerability.