Malononitrilamides 715 and 279 prolong rat cardiac allograft survival, reverse ongoing rejection, inhibit allospecific antibody production and interact positively with cyclosporin

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.

Liver regeneration is impaired by FK778 in partially hepatectomized rats, while supplemental uridine restores both liver growth and hepatocyte proliferation

AIM

The impact of mandatory immunosuppression on liver regeneration after segmental liver transplantation is of clinical importance. FK778, a novel immunosuppressant, inhibits pyrimidine biosynthesis and prevents rejection after organ transplantation in a dose-dependent manner. We investigated the effect of FK778 at a highly effective dose on liver regeneration in a small animal model.

METHODS

Inbred Lewis rats were subjected to 70% partial hepatectomy (PH) and treated with saline (n = 28), uridine (n = 16), FK778 alone (n = 28) or in combination with uridine (n = 16). FK778 was given intravenously daily at a dose of 25 mg/kg bodyweight (bw) and uridine was given daily intraperitoneally at a dose of 250 mg/kg bw. Liver bodyweight ratio (LBR), hepatocyte proliferation index (PI), blood chemistry and morphological analysis were incorporated. PI was determined by Ki-67 immunostaining. De Ritis ratio was calculated to assess the extent of liver damage.

RESULTS

In FK778-treated animals PI was decreased at 24 h and 72 h and LBR was lower at 48 h and 72 h (P < 0.05) after the PH. In addition, morphological analysis showed confluent central lobular necrosis at 72 h in four of seven animals. Uridine supplementation restored PI, LBR and the de Ritis ratio in FK778-treated animals and no confluent necroses were observed.

CONCLUSION

FK778 is antihepatotrophic as well as antiproliferative during rat liver regeneration. Both liver growth and hepatocyte proliferation are completely restored by supplementation with uridine. In addition, supplemental uridine markedly reduces the severity of morphological abnormalities consistent with FK778 toxicity.

Is the Malononitrilamide FK778 Better for the Prevention of Acute or Chronic Rejection?

OBJECTIVE

The aim of this study was to assess the efficacy of FK778 to prevent acute and chronic allograft rejection compared with other immunosuppressive agents.

MATERIALS AND METHODS

Heterotopic Brown-Norway (BN)-to-Lewis rat cardiac transplantations and heterotopic BN-to-Lewis tracheal transplantations were performed to study acute heart rejection and the development of chronic obliterative airway disease (OAD), respectively. Recipients were treated with FK778, tacrolimus, MMF, or sirolimus for 10 days (acute rejection study) or 28 days (chronic OAD study) at varying doses.

RESULTS

In untreated recipients, cardiac allograft survival was 6.2 +/- 0.4 days. FK778 (20 mg/kg), tacrolimus (2 or 8 mg/kg), mycophenolate mofetil (MMF; 40 mg/kg), or sirolimus (0.5 or 2 mg/kg) significantly prolonged graft survival to 17.0 +/- 2.8, 18.5 +/- 2.7, 25.0 +/- 2.5, 20.7 +/- 3.8, 14.5 +/- 2.2, and 23.2 +/- 1.5 days, respectively (P < .05). Tracheal grafts in untreated recipients showed intense infiltration and complete luminal obliteration by day 28. FK778 (20 mg/kg), tacrolimus (1 or 4 mg/kg), MMF (10 or 40 mg/kg), or sirolimus (0.5 or 2 mg/kg) significantly inhibited tracheal luminal obliteration (19.5% +/- 16.4%, 44.2% +/- 33.6%, 12.3% +/- 3.3%, 61.7% +/- 18.6%, 18.3% +/- 11.3%, 55.0% +/- 30.9%, and 8.5% +/- 3.5% (P < .05). All 4 high-dose groups showed similar efficacy.

CONCLUSIONS

When used in therapeutic doses, tacrolimus and sirolimus were more effective than FK778 to prolong cardiac allograft survival. However, with its antiproliferative effects on smooth muscle cells, its good tolerability, and its blockade of cytomegalovirus replication, FK778 proved effective to prevent chronic OAD development. Thus, FK778 may acquire an important role in maintenance therapy for the prevention of long-term fibroproliferative complications.

Pharmacologic approaches to composite tissue allograft

This article discusses the pharmacologic approaches and the most promising new compounds for composite tissue allograft tolerance. Although some approaches rely on a combination of immunosuppressive agents that act synergistically against rejection, other strategies use immunologic manipulation, including major histocompatibility complex matching, induction of chimerism, and use of monoclonal antibodies to abrogate the immune response. There is still a need, however, to reproduce these findings in species phylogenetically closer to humans. This may be the target of future research efforts, which may overcome the challenge of limb and face transplant rejection.

FK778 does not impair intestinal allograft absorption in a preclinical model of total small bowel transplantation

Malononitrilamide 715 (FK778), a new low-molecular weight immunosuppressant, inhibits both T-cell and B-cell function by acting on the pathway for de novo pyrimidine biosynthesis. Pyrimidines are important for intestinal trophism; their inhibition may predispose to metabolic and functional impairments, such as diarrhea and malabsorption. In this study we assessed the absorptive capacity of intestinal allografts in a large-animal model of small bowel transplantation (SBTx) in pigs chronically treated with FK778. Ten outbred pigs underwent total orthotopic SBTx. Immunosuppression consisted of oral tacrolimus (trough levels 5-15 ng/mL) and oral FK778 (4 mg/kg per day) administered for 60 days. The D-xylose absorption test was performed at day 60 to evaluate carbohydrate absorption. Results were compared to normal controls. Eight of the 10 animals were alive and in good condition at day 60. All of their allografts were free of rejection. The animals had a mean maximal weight loss of 6.4% during the study period; the final weight was comparable to the initial weight (P > .05). Diarrhea was present in all animals (mean 16% of postoperative days). The D-xylose curves showed that absorption in the transplanted animals at day 60 was similar to that in the untreated controls (P > .05). The absence of differences was confirmed by the statistical analysis. In conclusion, our preclinical study in pigs showed that chronic treatment with FK778 in combination with tacrolimus did not impair carbohydrate absorption by the allograft after SBTx.

Assessment of an LC-MS method for plasma quantification of the new immunosuppressant FK778 through comparison with HPLC-UV

FK778 is a new immunosuppressive agent, derived from the leflunomide-active metabolite A77 1726. It inhibits de novo pyrimidine nucleotide synthesis showing efficacy in the prevention and treatment of rejection in experimental transplant models. The aim of this work was to develop an HPLC-MS method to measure FK778 in plasma for pharmacokinetic studies. The equipment used for mass evaluation was an HLPC coupled to an ion trap analyzer through an electrospray source. After precipitation of plasma proteins with acetonitrile, the supernatant was injected onto an analytical RP-C18 column. Chromatographic separation was performed under isocratic conditions, using a mobile phase consisting of ammonium acetate buffer and acetonitrile (55:45. vol/vol). MS detection was performed in the negative ionization mode by monitoring the molecular ion of FK778 (m/z 307) and IS (m/z 269), using selected ion monitoring for both. However, we observed peaks corresponding to dimers, trimers, and tetramers of FK778 (m/z 637, m/z 945, m/z 1274). The HPLC-MS method was applied to pharmacokinetics in animal models showing comparable results to those obtained by an HPLC-UV assay at 290 nm. Good agreement was observed in the plasma FK778 concentration versus time curves. The rapid preparation of samples and the short run-time make this method attractive for use in clinical practice.

Mechanistic Study of Malononitrileamide FK778 in Cardiac Transplantation and CMV Infection in Rats

BACKGROUND

FK778 is a malononitrilamide, a class of immune suppressive compounds with antiviral features and experimental activity in chronic rejection, a potentially interesting combination for organ transplantation. The goal of this project was to study the tolerability, immune suppressive efficacy, and anti-cytomegalovirus (CMV) activity of FK778 and to assess the in vivo relevance of its previously described inhibition of de novo pyrimidine synthesis.

METHODS

Heart transplants were performed in rats (Brown Norway [BN] to Lewis) and treated with varying doses of FK778 or leflunomide for 28 days. At 28 days, at the time of rejection or at the death of the animal, the allograft and other vital organs were obtained for study by light microscopy and immunohistochemistry. In separate experiments, Lewis rats were given sublethal irradiation, inoculated with rat CMV (Maastricht strain), and treated with varying doses of FK778 and leflunomide. In both the transplant and CMV studies, IP uridine was given at 250 mg/kg to cohorts or animals receiving FK778 and leflunomide.

RESULTS

FK778 controls acute rejection and inhibits CMV replication at 20 mg/kg but is toxic at 25 mg/kg. Toxicity is manifested as anemia, changes in hepatic and intestinal histology, and mortality. The toxicity but not the immune suppressive or antiviral efficacy, is reduced significantly by exogenous uridine administration.

CONCLUSION

FK778 has both immune suppressive and antiviral activities, neither of which is entirely dependent on inhibition of pyrimidine synthesis. These, and other published observations, suggest that the antiviral activity and a considerable part of the efficacy of the malononitrilamide family of drugs is attributable to activities other than drug induced pyrimidine deficiency.

FK778 and FK506 Combination Therapy to Control Acute Rejection after Rat Liver Allotransplantation

BACKGROUND

In organ transplantation, several immunosuppressants are currently used to control graft rejection. Clinically, no single immunosuppressive agent can completely prevent posttransplantation immunoreaction; thus, combination therapy is usually performed. Novel agents with more powerful immunosuppressive activity and less toxicity need to be developed.

METHODS

Lewis rat livers were orthotopically transplanted into Brown-Norway recipients. FK778 was administered orally from day 0 to day 6 to prevent acute rejection and from day 7 to day 13 to rescue ongoing rejection. To assess the combined effects, recipients were treated with intramuscular injection of FK506 and oral administration of FK778 from day 0 to day 6. Blood chemistry and histopathologic findings were measured to determine the patient's general condition and the graft condition. Allospecific antibodies were measured using enzyme-linked immunosorbent assays. The FK778 trough concentration was examined by using high-performance liquid chromatography.

RESULTS

The acute immune response was suppressed by FK778 alone in a dose-dependent manner. The optimal FK778 dosage was determined to be 20 mg/kg per day, because adverse effects (weight loss and intestinal bleeding) occurred at 30 mg/kg per day. FK778 treatment from day 7 to day 13 rescued liver grafts from ongoing rejection. The intramuscular FK506 (0.125 mg/kg per day) injection and the oral FK778 (20 mg/kg per day) gavages suppressed acute liver graft rejection effectively and maintained better graft condition compared with monotherapy. CONCLUSIONS.: FK778 treatment effectively prevented acute rejection and rescued ongoing rejection after liver transplantation. The optimal dosage was determined to be 20 mg/kg per day. Combination therapy with FK506 was more beneficial than FK778 monotherapy.

NEW DRUGS TO IMPROVE TRANSPLANT OUTCOMES

Fujisawa is committed to improving the outcomes of transplant patients worldwide. Research and development programs are underway for a new modified release dosage form of tacrolimus (MR-4), a new analog of leflunomide (FK 778), and several novel compounds (PG 490-88, AGI 1096) in collaboration with other companies. These programs are targeted to address many of the unmet medical needs in transplantation including (1) improving compliance, (2) reducing chronic rejection, and (3) improving long-term safety by reducing infectious and cardiovascular risk.

The interaction between FK778 and tacrolimus in the prevention of rat cardiac allograft rejection is dose dependent

OBJECTIVE

The synthetic malononitrilamide FK778 inhibits T- and B-cell responsiveness, phagocyte effector function, exerts inhibitory activity against cytomegalovirus, and is thus one of the most promising new immunosuppressive drugs. The aim of this study was to evaluate the combination of FK778 and tacrolimus in a high-responder rat cardiac transplantation model.

METHODS

The Brown Norway-Lewis rat strain combination was used to investigate graft survival after 10 days of posttransplant oral therapy with FK778 (5 or 20 mg/kg), tacrolimus (2 or 8 mg/kg), or combination regimens at varying doses (5+2 mg/kg, 10+1 mg/kg, or 20+8 mg/kg). Grafts were harvested after cessation of cardiac contractions. Combination indices (CI) were calculated for drug combinations.

RESULTS

In untreated recipients, allograft survival was 6.2+/-0.4 days. FK778 at 20 mg/kg and tacrolimus at 2 or 8 mg/kg significantly prolonged graft survival to a mean survival time (MST) of 17.0+/-2.8, 18.5+/-2.7, and 25.0+/-2.5 days, respectively. The two low-dose drug combinations achieved a graft survival of 23.2+/-2.9 and 25.2+/-3.1 days, which was significantly longer compared with FK778 at 5 mg/kg, FK778 at 20 mg/kg, and tacrolimus at 2 mg/kg (P </=0.003) and was similar to that of high-dose tacrolimus therapy (8 mg/kg). The drugs showed synergistic interactions (CI values of 0.62 and 0.52, respectively). With the high-dose drug combination, MST was 30.0+/-4.1 days, which was significantly longer compared with all other groups (P </=0.012). However, drugs showed only additive interaction (CI=0.95), and recipients suffered enhanced toxic side effects.

CONCLUSIONS

This study provides evidence that FK778 and tacrolimus show supportive interaction in their immunosuppressive potency that is synergistic in low-dose combinations and additive in higher doses.

Additive Effects of Leflunomide and Tacrolimus in Prevention of Islet Xenograft Rejection

Leflunomide is a low molecular weight immunosuppressive drug which inhibits the enzymes dehydroorotate dehydrogenase and protein tyrosine kinase, both of which are important components in the immune response. As the mechanisms of action of leflunomide and tacrolimus are different, we postulated an additive or synergistic effect of the two drugs and investigated the effects of leflunomide alone, or in combination with a suboptimal dose of tacrolimus, on xenogeneic islet transplantation in a rat-to-mouse model. A total of 1200-1500 rat islets were transplanted under the left kidney capsule of streptozotocin-induced diabetic BALB/c mice. The median survival time (MST) of the untreated group was 6 days. Leflunomide at 5, 10 and 20 mg/kg/d administrated for 10 days significantly prolonged MST to 10, 16 and 20 days. A dose of tacrolimus (2 mg/kg/d) was associated with a graft survival of 9 (range 6-12) days; most grafts rejected during ongoing therapy. When tacrolimus (2 mg/kg/d) was combined with leflunomide (10 mg/kg/d), the survival time of the islet xenografts was increased further to 22 days, significantly longer than with leflunomide or tacrolimus alone. In summary, our findings demonstrate that leflunomide prolonged xenogeneic islet graft survival, and that its immunosuppressive effect was improved when combined with tacrolimus.

Immunosuppression with FK778 and mycophenolate mofetil in a rat cardiac transplantation model

FK778 blocks the dihydro-orotate dehydrogenase, necessary for pyrimidine synthesis, and mycophenolate mofetil (MMF) inhibits the inosine monophosphate dehydrogenase, a crucial enzyme for purine biosynthesis. Beneficial immunosuppressive effects have been suggested for the combination of both drugs. The Brown Norway-Lewis rat heterotopic heart transplantation model was used. FK778 (5 and 20 mg/kg/day), MMF (10 and 40 mg/kg/day), or a combination of both drugs for 10 days was used for prevention of acute graft rejection. Grafts of untreated animals were rejected after 6.2 +/- 0.4 days. Low-dose FK778 and low-dose MMF administration did not result in a significantly prolonged graft survival (6.7 +/- 0.8 and 8.7 +/- 1.4 days; P=not significant). Grafts of rats treated with high-dose FK778 or high-dose MMF survived significantly longer (17.0 +/- 2.8 and 20.7 +/- 3.8 days; P<0.01). Concomitant use of low-dose FK778 with low-dose MMF produced synergistic interactions (mean survival time 12.3 +/- 2.9 days; P<0.01; combination index=0.85). High-dose drug combination (mean survival time 24.0 +/- 1.4 days) showed antagonistic drug interaction (combination index=1.55) with increased toxic side effects.

Synergistic effects of malononitrilamides (FK778, FK779) with tacrolimus (FK506) in prevention of acute heart and kidney allograft rejection and reversal of ongoing heart allograft rejection in the rat

BACKGROUND

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.

METHODS

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.

RESULTS

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.

CONCLUSIONS

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.

Combination therapy of malononitrilamide FK778 with tacrolimus on cell proliferation assays and in rats receiving renal allografts

BACKGROUND

Malononitrilamide FK778, an analogue of leflunomide's active metabolite, is a promising novel small molecule with immunosuppressive and immunomodulatory properties. In this study, we evaluated the ability of combination therapy of FK778 with tacrolimus to inhibit lymphocyte proliferation and to prevent acute allograft rejection.

METHODS

Proliferation assay was used to evaluate the effect of FK778 plus tacrolimus on murine splenocytes, monkey lymphocytes, and human peripheral blood mononuclear cells, after activation with T or B cell-specific mitogens. A rat kidney transplantation model was used to evaluate the ability of FK778 combined with tacrolimus to prolong allograft survival. Median-effect principle and combination index (CI) were used to determine synergism, summation, or antagonism.

RESULTS

A total of 58 combinations of FK778 plus tacrolimus were evaluated. Of the combinations tested, 82.8% (24/29) produced additive to synergistic effects in B cells, whereas 79.3% (23/29) produced moderate antagonistic effects in T cells. A concomitant 14-day therapy of FK778 (10 mg/kg/day) and tacrolimus (1 mg/kg/day) synergistically prolonged renal allograft survival to 25.5+/-5.9 days (CI=0.458). However, when addition of FK778 to tacrolimus therapy was delayed to day 7 after transplantation, a strong synergism was obtained (mean survival time=74.9+/-14.8 days, CI<0.001).

CONCLUSIONS

This study demonstrates that the combination of FK778 with tacrolimus in vitro produces synergistic inhibition on B-cell proliferation but not on T cell proliferation in mice, nonhuman primates, and humans. When the addition of FK778 treatment was delayed to day 7 after transplantation, a strong synergism was produced in prolongation of renal allograft survival in the rat.

Significant prolongation of renal allograft survival by delayed combination therapy of FK778 with tacrolimus in nonhuman primates

BACKGROUND

Malononitrilamide 715 (FK778) is a new class of low-molecular-weight immunosuppressant that is a derivative of the active metabolite of leflunomide, A77 1726. In this study, the authors evaluated the combined effect of FK778 with tacrolimus in prevention of renal allograft rejection in Vervet monkeys.

METHODS

Male Vervet monkeys were obtained from Caribbean Primates Ltd. Donor and recipient monkeys were from different breeding colonies. Eleven groups (n>or=4 per group) were involved in this study. FK778 and tacrolimus were administered orally for 60 days according to protocol.

RESULTS

Naive controls rejected renal grafts, with a median survival time (MST) of 8.0 days in group 1. When recipient monkeys were treated with tacrolimus 1.0 mg/kg/day in group 2 or FK778 2.5 mg/kg/day in group 3, the MST was 16.0 days (P=0.001) and 11.0 days (P=0.266), respectively. Combination therapy of these two agents at the same doses immediately after transplantation resulted in an MST of 25.0 days (P=0.016) in group 4. When tacrolimus was initiated immediately after transplantation and FK778 treatment was delayed until day 7 after surgery in group 5, recipient survivals were significantly prolonged to 38.0 days (P=0.02). These results were repeatable when FK778 5.0 mg/kg/day (9.0 days, P=0.544 in group 6) was combined with tacrolimus 1.0 mg/kg/day immediately after transplantation (8.0 days, P=0.339) in group 7, or when FK778 was delayed 7 days (60.0 days, P=0.002) in group 8. Furthermore, it was also repeatable when FK778 10 mg/kg/day was combined with tacrolimus 1.0 mg/kg/day with a 7-day delay.

CONCLUSIONS

A significant prolongation of renal allograft survival was produced when FK778 administration was delayed by 7 days combined with tacrolimus in Vervet monkeys.

FK778, a powerful new immunosuppressant, effectively reduces functional and histologic changes of chronic rejection in rat renal allografts

BACKGROUND

FK778 is a new derivative of the active leflunomide metabolite A77 1726. It effectively prevented acute allograft rejection in several experimental transplant models, and it is currently in phase II trials in human transplant recipients. In this study, we examined the effects of FK778 in a well-established model of chronic renal allograft rejection in the rat.

METHODS

Kidneys of Lewis (LEW) and F344 rats were orthotopically transplanted into bilaterally nephrectomized LEW recipients as the isograft and allograft control, respectively. Allograft recipients were orally administered FK778 at doses of 3 mg/kg per day, 10 mg/kg per day, and 20 mg/kg per day for 10 days. Blood and 24-hr urine samples were collected once a week after grafting for plasma creatinine, allo-specific antibodies, and proteinuria determination. Kidney grafts were harvested on the 90th day after transplantation and subjected to histologic, immunohistologic, and reverse transcriptase-polymerase chain reaction analysis. Histologic sections were semiquantitatively scored using criteria adapted from the Banff' classification for transplant pathologic conditions.

RESULTS

Recipients treated with FK778 for 10 days exhibited a dose-dependent decrease in proteinuria and plasma creatinine for the entire 90-day period after transplantation when compared with the allograft control. FK778, at doses of 10 mg/kg per day and 20 mg/kg per day, remarkably reduced chronic histologic changes, including tubular atrophy, glomerulosclerosis, fibrointimal hyperplasia, and transplant glomerulopathy. In addition, FK778 treatment was associated with decreased intragraft mononuclear cell infiltration, serum allo-specific immunoglobulin (Ig)M and IgG antibody production, and intragraft transforming growth factor beta messenger RNA expression in those recipients surviving 90 days after transplantation when compared with the allograft control.

CONCLUSION

FK778 effectively reduces functional and histologic chronic kidney allograft rejection in the rat.

A novel leflunomide derivative, FK778, for immunosuppression after kidney transplantation in dogs

BACKGROUND

Leflunomide and its metabolite, A77 1726, interfere with pyrimidine metabolism and exert potent immunosuppression in experimental organ transplantation. However, clinical use of the agents has been restrained because of an extended half-life. FK778, one synthetic malononitrilamide derived from A77 1726, is synthesized to overcome this problem while maintaining similar therapeutic efficacy.

METHODS

Immunosuppressive effect, pharmacokinetics, and adverse events of FK778, as a single drug treatment or combination with tacrolimus or cyclosporine, were determined in a canine kidney transplantation model. The agents were daily administered orally to the animals for 90 days after surgery. Animal survival, pharmacokinetics, biochemistry, hematology, and histopathology were evaluated.

RESULTS

FK778 at 4 mg/kg prolonged median survival of the control animals from 10 days to 30.5 days. Administration of 4 mg/kg FK778 with 0.3 mg/kg tacrolimus or 10 mg/kg cyclosporine increased median survival to 75.5 days and 50.5 days, respectively. In combined treatments, trough levels of FK778 at 4 mg/kg ranged between 40 microg/mL and 100 microg/mL after 1 month. Vomiting and diarrhea were common in animals given FK778. Bone marrow suppression was seen at higher doses.

CONCLUSIONS

FK778 is a promising new immunosuppressant that may be used in combination with current standard drugs in organ transplantation.

Tolerance or rejection: A delicate balance as judged by exposure of heart-transplanted rats to the immunomodulator Linomide

When applied in rodent transplant models most immunosuppressive drugs yield adequate graft protection for as long as the drug is given, and permanent graft survival is often induced. The immunomodulator, Linomide, previously shown to stimulate T cells and prevent apoptosis, usually reduces or abolishes both tolerance induction and the graft-protective effect of the immunosuppressive drug. By chance, we observed that Linomide alone exerted a modest but unequivocal graft-protective effect in the BN to WF strain combination. This finding was analysed by simple genetic mapping of rat strains. Untreated WF recipients kept BN grafts for a median of 8 days, whereas Linomide treatment prolonged graft survival to 12. 5 days (P = 0.0001). In control groups (DA to LEW, BN to LEW, DA to WF and WF to BN), median graft survival was 5.5-7 days irrespective of whether Linomide was given. However, the BN to F1 (LEW x WF) combination also manifested slightly longer graft survival in the presence of Linomide. F1 (BN x WF) to WF grafts survived a median of 15 days without Linomide and 46 days with Linomide treatment. Both in the presence and absence of Linomide, two of the control graft combinations [F1 (BN x DA) to WF and F1 (BN x WF) to BN] manifested 6-7-day graft survival. Taken together, our results suggest a delicate balance between unresponsiveness and rejection, while a single agent (Linomide) may either cause on its own long-term survival of allografts in one setting or rejection despite optimal immunosuppression in another setting.

Malononitrilamides and tacrolimus additively prevent acute rejection in rat cardiac allografts

The novel immunosuppressive agents malononitrilamides (MNA) 279 and 715 are derivatives of A77 1726, the primary metabolite of leflunomide. The effects of these agents have been previously demonstrated in rat skin and cardiac allo- and xenotransplant models. The aim of this study was to evaluate the combination of MNA and tacrolimus in a high-responder rat cardiac allotransplant model. Graft survival was evaluated following 10 days of post-transplant oral therapy of MNA or tacrolimus alone and the drugs combined in PVG recipients of DA grafts. An iso-effect curve of single and combined drugs was constructed. Histological changes in grafts were evaluated at 10 days. MNA (20 mg/kg) or tacrolimus (2.4 mg/kg) alone prolonged graft survival with median survival of 14 and 13.5 days, respectively. Combined therapy of MNA (10 mg/kg) and tacrolimus 1.6 mg/kg likewise resulted in a median survival of 13.25 days and an iso-effect curve for these doses was constructed. Another iso-effect curve for median graft survival of 18-19 days, including MNA (10 mg/kg) + tacrolimus (3.2 mg/kg) in combination, MNA (30 mg/kg) alone and tacrolimus (4.8 mg/kg) alone, was constructed and both isoboles showed a straight line, demonstrating additive effects (zero interaction). In addition, histological analysis of grafts confirmed the benefit of the drug combination. No additional toxicity was noted with combined therapy. Optimal doses of MNA or tacrolimus had comparative effects on graft survival and histological changes, and a combination of the two drugs was beneficial with respect to both these parameters. The iso-effect curves verified additive effects of the drug combination.

Malononitrilamides 715 and 279 prevent accelerated cardiac allograft rejection synergistically with cyclosporin A in presensitized rats

A77 1726 is a malononitrilarnide (MNA) and the active metabolite of leflunomide. Leflunomide has been extensively investigated and shown to be a potent immunosuppressive drug. However, the half-life of A77 1726 is about 15-18 days in humans and the leflunomide is, therefore, currently being evaluated for the treatment of autoimmune disease and not for transplantation. The search for analogues has led to the development of MNA 715 and 279, derivatives of A77 1726. Previous limited experimental experience has shown these MNAs to prevent skin allograft and xenograft rejection and graft-versus-host disease in rodents, and to reverse ongoing allograft rejection. The aim of the present study was to verify the efficacy of these MNAs in a cardiac retransplant model of sensitized rats, concerning prevention of accelerated rejection, inhibition of antibody production and interaction with cyclosporin A (CsA). Heterotopic cardiac transplantation and retransplantation in Dark Agouti (DA) to Piebald Virol Glaxo (PVG) rats was used. Subgroups of rats were given either CsA, MNA 715, MNA 279 or combined CsA/MNA for 10 days starting either day 0 or day -1, as of regrafting or no treatment. Titres of allospecific IgM and IgG were quantitated by flow cytometry. Ten days of MNA 715 or 279 from day -1 prevented accelerated rejection of the retransplant, as did CsA. Neither treatment given from day 0 prevented rejection within 24 h. However, a combination of MNA 715 or 279 and CsA from day 0 effectively prevented accelerated regraft rejection. Production of specific alloantibodies was reduced in all immunosuppressed subgroups, IgG titres at day 7 in MNA-treated subgroups being significantly lower compared with those in the CsA-treated subgroup. In conclusion, MNA 715 and 279 were shown to be potent immunosuppressants with the capacity to prevent accelerated regraft rejection in rat cardiac transplants, most efficiently in combination with CsA, and to suppress specific alloantibody production.