Synergistic effect of high-dose mizoribine and low-dose tacrolimus on renal allograft survival in nonhuman primates

Genetic and clinical determinants of mizoribine pharmacokinetics in renal transplant recipients

AIM

Mizoribine (MZR) is an immunosuppressant for the prevention of allograft rejection in Asian countries, but the great variability in pharmacokinetics (PK) limits its clinical use. This study was to explore genetic and clinical factors that affect the MZR PK process.

METHODS

Blood samples and clinical data were collected from 60 Chinese renal transplant recipients. MZR plasma concentration was measured at pre-dose (0 h) and 0.5, 1, 2, 3, 4, 5, 6, 8, and 12 h post-dose by high performance liquid chromatography with an ultraviolet detector. PK parameters were calculated by non-compartmental analysis. High-throughput sequenced single nucleotide polymorphism was applied screening possible genetic factors.

RESULTS

Extensive inter-individual MZR PK differences were reflected in the process of elimination (k_e, CL/F, MRT and t_1/2) and intestinal absorption (C_max and T_max), as well as in the dose-normalized exposure (AUC_0-12h/D). From 146 SNPs within 39 genes screened, AUC_0-12h/D was found higher in recipients with CREB1 rs11904814 TT than with G allele carriers (3.135 ± 0.928 versus 2.084 ± 0.379 μg h ml^-1 mg^-1, p = 0.007). Recipients with SLC28A3 rs10868138 TT had lower t_1/2 as compared to C allele carriers (0.728 ± 0.189 versus 0.951 ± 0.196 h, p = 0.001). Serum creatinine (SCr) explained 35.5% of C₀/D variability (p < 0.001). Pure effects of genotypes CREB1 and SLC28A3 were 13.7% (p = 0.004) and 17.5% (p = 0.001) for AUC_0-12h/D and t_1/2, respectively. When additionally taking SCr into models, CREB1 and SLC28A3 genotypes explained 20.0% (p = 0.038) and 46.5% (p < 0.001) of AUC_0-12h/D and t_1/2 variability, respectively.

CONCLUSION

CREB1 and SLC28A3 genotypes, as well as SCr, are identified as determinants in predicting inter-individual MZR PK differences in renal transplant recipients.

Reduced variability in tacrolimus pharmacokinetics following intramuscular injection compared to oral administration in cynomolgus monkeys: Investigating optimal dosing regimens

Tacrolimus is one of the most commonly used immunosuppressive agents in animal models of transplantation. However, in these models, oral administration is often problematic due to the lowered compliance associated with highly invasive surgery and due to malabsorption in the intestinal tract. Therefore, we carried out a study to determine the pharmacokinetics of tacrolimus after intramuscular (IM) injection and to determine the optimal IM dosing regimens in primate models. Six male cynomolgus monkeys (Macaca fascicularis) were used in the study. Doses of 0.1 mg/kg and 5 mg were administered via IM injection and oral administration, respectively, once to determine single-dose pharmacokinetics and once daily for 5 days to determine multiple-dose pharmacokinetics. According to pharmacokinetic model estimates, the inter- and intra-individual variabilities in bioavailability following IM injection were remarkably reduced compared with those following oral administration. Monte Carlo simulations revealed that C_peak, C_trough and AUC would also have less variability following IM injection compared with oral administration. In this study, we found that the pharmacokinetic characteristics of tacrolimus were more constant following IM injection compared with oral administration. These results suggest that IM injection can be an alternative route of administration fin non-human primate model studies.

Combination effect of mycophenolate mofetil with mizoribine on cell proliferation assays and in a mouse heart transplantation model

BACKGROUND

Mycophenolate mofetil (MMF) is a highly potent immunosuppressant that suppresses the proliferation of T and B cells by the uncompetitive inhibition of inosine monophosphate dehydrogenase (IMPDH). Consequently, under MMF immunosuppression, good graft survival has been achieved in clinical organ transplantation, although MMF shows adverse gastrointestinal effects. Mizoribine (MZ) also inhibits IMPDH in a competitive manner and is used clinically for organ transplantation in Japan as an immunosuppressant with fewer adverse gastrointestinal effects. Therefore, in this study we investigated the synergistic effects on in vitro and in vivo assays of mice of a combination of MMF with MZ immunosuppression.

METHODS

Mixed lymphocyte reaction (MLR) assay and a mouse heart transplantation model were used to evaluate the immunosuppressive effect of MMF with MZ. The median-effect principle and a combination index (CI) were employed to determine synergism, an additive effect, or antagonism.

RESULTS

Combination of MMF with MZ resulted in mild synergistic effects in the inhibition of MLR (CI = 0.854-1.143). In the mouse heart transplantation model, C57BL/6 recipients who received a BALB/c heart under the combination of MMF and MZ at 40 + 40 or 80 + 80 mg/kg/day showed a strong synergistic prolongation of graft survival with 19.7 +/- 18.9 (P = 0.0012, CI = 0.438) and 78.4 +/- 36.9 days (P = 0.0002, CI = 0.317), respectively, compared with recipients treated with MMF or MZ monotherapy. CONCLUSIONS.: The combination of MMF and MZ showed mild synergistic effects in the inhibition of MLR and strong synergistic effects in a mouse heart transplantation model.