No abstract

E-ISA247 (voclosporin) is a cyclosporin A analogue that is in late-stage clinical development for the treatment of autoimmune diseases and the prevention of organ graft rejection. The X-ray crystal structures of E-ISA247 and its stereoisomer Z-ISA247 bound to cyclophilin A have been determined and their binding affinities were measured to be 15 and 61 nM, respectively, by fluorescence spectroscopy. The higher affinity of E-ISA247 can be explained by superior van der Waals contacts between its unique side chain and cyclophilin A. Comparison with the known ternary structure including calcineurin suggests that the higher immunosuppressive efficacy of E-ISA247 relative to cyclosporin A could be a consequence of structural changes in calcineurin induced by the modified E-ISA247 side chain.

Voclosporin (VCS) is a novel calcineurin (CN) inhibitor intended for prevention of organ graft rejection and treatment of lupus nephritis. These studies evaluated the single ascending dose pharmacokinetics (PK) and pharmacodynamics (PD, CN activity) of VCS and the effect of food. VCS was administered orally in single doses of 0.25 through 4.5 mg/kg in 62 subjects in the single ascending dose study and as a single oral 1.5 mg/kg dose to 18 subjects after fasting, consumption of a low-fat and high-fat meal. Non-compartmental PK, PD, and PKPD correlation were evaluated. Following single oral doses, systemic exposure increased in a linear manner and demonstrated 1:1 dose-proportional, first-order linear PK above 1.5 mg/kg. VCS inhibited CN activity in a dose-related fashion with maximal inhibition peaking at 3.0 mg/kg. PKPD correlation indicated an EC50 of 78.3 ± 6.8 ng/mL. Administration of VCS with a low-fat and high-fat meal decreased C(max) by 29% and 53%, respectively, and AUC(inf) by 15% and 25%, respectively. Following ascending single doses of VCS, exposure increased in a linear fashion. A food effect on exposure was demonstrated, with a more pronounced effect following a high-fat meal. VCS concentrations were also found to correlate with CN activity.

Sirolimus (rapamycin, Rapamune) is a potent immunosuppressive drug that received marketing approval from the US Food and Drug Administration on September 15, 1999. Research into defining its pharmacokinetic (PK) behavior, interaction with other agents, and metabolism is ongoing. It has been established that oral doses of both liquid and solid formulation are rapidly, though incompletely and variably, absorbed. Metabolism by the intestinal and hepatic CYP3A family of enzymes likely contributes to variability in absorption and low bioavailability. Sirolimus has a long terminal half-life, the AUC correlates well with trough and peak concentrations, and it exhibits a moderate degree of dose proportionality. There is significant interpatient variability in PK parameters of sirolimus, though it exhibits predictable PK behavior when used with prednisone and cyclosporine neoral. There is a decreased rejection risk with higher doses and target level attainment. Several species of sirolimus metabolites have been characterized, and are measurable in whole blood and tissue specimens. Many more species of sirolimus metabolites are detectable, but they are not quantifiable at this time. The total concentration of metabolites appears to be less than that of the parent drug when examined through the PK profile. A reference method for the quantitation of metabolites remains elusive because of a lack of proper standardization. The clinical significance of sirolimus metabolites remains to be proven.

ISA247 is a novel cyclosporine analog. In this study we compare, in vitro, the effects of ISA247 on immune function with those of cyclosporine. Whole blood from cynomolgus monkeys (n = 5) was incubated with different concentrations of ISA247 or cyclosporine and stimulated with different mitogens in culture medium. Lymphocyte proliferation was assessed by [3H]-TdR incorporation assay and by flow cytometry. Flow cytometry was also used to assess production of intracellular cytokines by T cells and expression of T cell activation surface antigens. The concentration of drug necessary to attain 50% of the maximum effect (EC50) was subsequently calculated. EC50 values for ISA247 were lower than for cyclosporine, and the differences were statistically significant for lymphocyte proliferation, T cell cytokine production, and expression of all T cell activation surface antigens but one. We conclude that ISA247 suppresses diverse immune functions more potently than cyclosporine in vitro.