Individualizing combination of two antiproliferative immunosuppressants with pharmacodynamic modeling of stimulated lymphocyte responses.

BACKGROUND: Unpredictable serious adverse events (SAE) of immunosuppression, e.g. nephrotoxicity, with the nephrotoxic immunosuppressants have fostered interest in alternative regimens, which contain two antiproliferative agents, and individualized therapy. However, titration of such combinations to individual needs is not understood. SPECIFIC AIM: To determine concentration (C) mixtures of mycophenolate mofetil (MMF) and sirolimus (SRL), which produce half-maximal inhibitory effect (EC(50)) on human lymphocytes from individual subjects. METHODS: Concentration mixtures of MMF (0-5 mug/ml) and SRL (0-30 ng/ml) were incubated with whole blood from each of five healthy human subjects. The intracellular cytokines IL-2, TNF-alpha, and IFN-gamma were measured in PMA-ionomycin-stimulated T-cells (CD4+), while CD54, CD95, CD86, CD25, CD69, and CD71 were measured in pokeweed mitogen-stimulated B-cells, by flow cytometry. Pharmacodynamic (PD) relationships were evaluated using Hill equations modified for single and multidrug regimens, and expressed as EC(50) for each target receptor. RESULTS: No change was seen in the expression of the T-cell cytokines with either MMF or SRL. Each B-cell receptor was inhibited with increasing concentrations of either MMF or SRL. Each B-cell receptor was also inhibited half-maximally at lower concentrations of MMF in the presence of SRL, than with either agent alone, for the test population of five subjects together, and for each of five individual subjects. However, each subject showed distinctly different amounts of MMF and SRL that needed to be present together, in order to produce an identical inhibitory effect on lymphocyte function. CONCLUSIONS: PD analysis of biological effect can potentially predict optimal concentration mixtures of two immunosuppressants for individual recipients, and enhance rejection prophylaxis and safety. While this holds promise for drug development efforts, clinical application must await correlation of lymphocyte markers with post-transplant clinical outcomes.

Multiparametric effect: concentration analyses.

Immunosuppressant drug toxicity currently competes with acute rejection, as the major cause of efficacy failure of potent new agents in clinical transplantation. The development of mechanistic drug targets as surrogate endpoints for use in the clinic has been facilitated by fluorescent imaging techniques which measure multiple cytokines and cell surface receptors on stimulated (peripheral blood) lymphocyte responses. However, the promise of delivering customized drug therapy to the transplant recipient remains unfulfilled. In this brief review, computational algorithms that can relate multiparametric effects to clinical drug concentrations of immunosuppressants are discussed. Based on Hill equations, these pharmacodynamic modeling techniques have been used to simulate single-agent effects, combination regimen effects, as well as the individual response to combination regimens. The potential implications of these models crystallize the clinical challenges confronting practitioners of clinical, post-transplant immunosuppression.