Optimization and application of an HPLC method for quantification of inosine-5'-monophosphate dehydrogenase activity as a pharmacodynamic biomarker of mycophenolic acid in Chinese renal transplant patients

BACKGROUND

The immunosuppressive agent mycophenolic acid (MPA) is a non-competitive, reversible inhibitor of inosine-5'-monophosphate dehydrogenase (IMPDH). Thus, IMPDH activity can serve as a potential pharmacodynamic biomarker to optimize dosing of MPA.

METHODS

Peripheral blood mononuclear cells were isolated from 2 mL blood samples and an in vitro enzymatic reaction was subsequently performed for 120 min. To determine IMPDH activity in Chinese healthy volunteers and renal transplant patients, a high performance liquid chromatography assay was established and validated by subtracting adenosine monophosphate (AMP) from blank samples for eliminating exogenous AMP interference.

RESULTS

The accuracy of our method ranged between -0.8% and 12.5%, and the precision ranged between 0.7% and 6.3%. The mean value of IMPDH activity across 11 healthy volunteers was 46.60 ± 14.28 μmol/s/mol AMP. A negative relationship between MPA concentration and IMPDH activity was observed in four renal transplant patients treated with MPA 13 days post-transplantation, while the inhibitory rate of IMPDH activity ranged from 24% to 42%.

CONCLUSION

A bioanalytical assay for IMPDH quantification was optimized and evaluated. The differences in the pharmacodynamics of MPA between Asians and Caucasians may provide some evidence for dosing differences among ethnicities.

Mycophenolic Acid-Induced Developmental Defects in Zebrafish Embryos

With the increasing use of mycophenolic acid (MPA) in solid organ transplantation, some clinical studies indicate that it is also a human teratogen. However, it is unknown by which mechanism MPA acts as a teratogen. Mycophenolic acid was a selective blocker of de novo purine synthesis, and its immunosuppressive effect is mediated by the inhibition of inosine monophosphate dehydrogenase, which could be a target for MPA-induced toxicity as well. The aim of our study was to examine the direct influence of MPA exposure on zebrafish ( Danio rerio) embryos. Morphological defects including tail curvature and severe pericardial edema in zebrafish embryos caused by MPA (3.7-11.1 µmol/L) were found in a dose-dependent manner. The teratogenic index (25% lethal concentration value (LC25)/no observed adverse effect level ratio) was 16, which indicated MPA as a teratogen. Quantitative polymerase chain reaction analysis revealed that the expression level of impdh1b and impdh2 was significantly reduced by MPA treatment at 8 µmol/L (equals to LC25 level). All the toxic effects could be partially reversed by the addition of 33.3 µmol/L guanosine. Our results indicated that MPA impairs the development of zebrafish embryos via inhibition of impdh activity, which subsequently caused a guanosine nucleotide depletion in vivo.

Clinical Pharmacokinetic and Pharmacodynamic Monitoring for Mycophenolate Mofetil

The use of mycophenolate mofetil (MMF), in combination with cyclosporine (CsA) or tacrolimus (FK) and corticosteroids, has been shown to improve clinical outcomes through significant reduction in the incidence of acute rejection in solid organ transplant patients. A fixed oral dosing regimen of 1 or 1.5 g MMF twice daily received Food and Drug Administration approval in 1995 with no recommendations for concentration monitoring at that time. Subsequent evidence has generated substantial debate on the need of clinical monitoring for MMF. This article summarizes the rationale, evidence, and approaches of clinical monitoring for MMF. Mycophenolic acid (MPA), the active moiety of MMF, noncompetitively inhibits the enzyme inosine monophosphate dehydrogenase (IMPDH), which is the target enzyme for MPA. Pharmacokinetic monitoring, by use of MPA predose or MPA area under the concentration-time curve (AUC) values, and pharmacodynamic monitoring by analysis of inhibition of IMPDH have been evaluated in organ transplant patients. The possibility of drug interactions between other immunosuppressive agents has also received attention recently. The clinical implications of drug interactions are discussed in this article.

Role of FK778 Alone or in Combination with Tacrolimus or mTOR Inhibitors as an Immunomodulator of Immunofunctions: In Vitro Evaluation of T Cell Proliferation and the Expression of Lymphocyte Surface Antigens

We evaluated the in vitro capacity of FK778, alone or in combination with other immunosuppressive drugs: Tacrolimus (TRL); Sirolimus (SRL), Everolimus (EVL), to inhibit clonal expansion of T-lymphocytes and expression of lymphocyte-activation surface antigens; secondly, we compared the immunosuppressive potential of FK778 combined with TRL, SRL and EVL with the same combinations using Mycophenolic acid (MPA) as antimetabolite. Lymphocyte proliferation was assessed by 3H-Thymidine incorporation, in whole blood cultures stimulated with ConA. The effect of FK778 on alloresponse was evaluated by MLC and the expression of lymphocyte surface antigens by cytometry. FK778, TRL, SRL and EVL showed a high in vitro capacity to inhibit lymphocyte proliferation in a concentration-dependent way. Combinations of FK778 with TRL, SRL, or EVL presented an additive effect, especially FK778+TRL. Similar inhibition capacity of the clonal expansion was observed, when FK778 was combined with TRL, SRL or EVL, respecting the same combinations but using MPA instead of FK778. In addition, FK778 inhibited the expression of lymphocyte surface antigens involved in activation, co-stimulatory and apoptosis signals. In conclusion, FK778 inhibits the proliferative response induced by mitogeneic and allogeneic stimuli and the expression of surface antigens. Combinations of FK778 with TRL or mTOR inhibitors presented an additive effect and their action on T cell proliferation was similar to that of combinations with MPA. Since FK778, TRL and mTOR inhibitors present different action mechanisms and involve different cellular targets, these combinations may help prevent episodes of allorejection in organ transplants. FK778 and mTOR inhibitors may represent an alternative treatment for patients with renal failure.

Influence of mTOR-inhibitors and mycophenolic acid on human cholangiocellular carcinoma and cancer associated fibroblasts

Background

The incidence of Cholangiocellular Carcinoma (CCA) is increasing in the western world. The tumour has a high proportion of desmoplastic stroma and is correlated with a worse prognosis when cancer associated myofibroblasts (CAFs) are present. Recent studies showed promising results after liver transplantation (LTx) in non-resectable early stage CCA. Mycophenolic acid (MPA) and the mTor inhibitor Everolimus are used to prevent organ rejection but recently were shown to exhibit an antiproliferative effect on CCA-cells. Little is known about the influence of immunosuppressive drugs on tumour cell proliferation and migration after paracrine stimulation by CAFs. Moreover, it is still unknown, which signaling pathways are activated following these specific cell-cell interactions.

Methods

CCA cell lines HuCCT1 and TFK1 were utilized for the study. CAFs were derived from resected CCA cancer tissue. Cell viability was measured by the crystal violet assay and tumour cell invasion was quantified using a modified co-culture transmigration assay. Semiquantitative cytokine-expression was measured using a cytokine-array. Protein expression and phosphorylation of ERK, STAT3 and AKT was determined by Western-blot analysis.

Results

CCA cells treated with MPA exhibited a dose related decrease in cell viability in contrast to Cyclosporine A (CSA) treatment which had no effect on cell viability. Everolimus significantly inhibited proliferation at very low concentrations. The pro-invasive effect of CAFs in co-culture transmigration assay was significantly reduced by Everolimus at a concentration of 1nM (p = 0.047). In contrast, MPA and CSA showed no effect on tumour cell invasion. Treatment of CAFs with 1nM Everolimus showed a significant reduction in the expression of IL 8, IL 13, MCP1, MIF and Serpin E1. CCA-cells showed significant increases in phosphorylation of ERK, STAT3 and AKT under the influence of conditioned CAF-media. This effect was suppressed by Everolimus.

Conclusions

The secretion of proinflammatory cytokines by CAFs may lead to increased activation of JAK/STAT3-, ERK- and AKT-signaling and increased migration of CCA-cells. Everolimus abrogates this effect and inhibits proliferation of CCA-cells even at low concentrations.

LTx for non-resectable early stage CCA is currently performed in several clinical studies. Consistent with a role for common immunosuppressants in inhibiting tumour cell-proliferation and -invasion, our study indicates that a combination of standard therapies with Everolimus and MPA is a promising therapy option to treat CCA following LTx.

Derivatives containing both coumarin and benzimidazole potently induce caspase-dependent apoptosis of cancer cells through inhibition of PI3K-AKT-mTOR signaling

Coumarins are a large family of compounds derived from a wide range of plants, fungi, and bacteria, and coumarin derivatives can have extremely variable structures and consequently diverse biological properties including antitumor activity. Compounds that bear a benzimidazole moiety are known to possess antitumor activity and a variety of other biological activities. High-throughput screening of a compound library identified a coumarin-containing and a benzimidazole-containing compound [#32, 7-(diethylamino)-3-(1-methyl-1H-benzimidazol-2-yl)-2H-chromen-2-one] that has potent anticancer activity. Evaluation of 17 additional analogs further identified three compounds with anticancer activity in 14 different human cancer cell lines. Fluorescence-activated cell sorting and western blotting analyses suggested that these compounds can induce caspase-dependent apoptosis. Real-time reverse transcriptase PCR analyses of 26 cancer-related genes revealed that seven genes (NPPB, ATF3, DDIT4, CDH10, TSPAN14, TXNIP, and AXL) were significantly upregulated and nine genes (PAGE4, LRP8, SNCAIP, IGFBP5, SLCO2A1, CLDN2, ESRRG, D2HGDH, and PDGFRA) were significantly downregulated. The most upregulated gene is natriuretic peptide precursor B (NPPB) or brain natriuretic peptide, which is increased by 7-, 27-, and 197-fold at 12, 24, and 48 h, respectively. The second most upregulated gene is ATF3, which is increased by 23-fold at the 48 h timepoint. PAGE4 and IGFBP5 are the two most downregulated genes, with a 17-fold reduction in both genes. The expression of several genes (DDIT4, PDGFRA, LRP8, IGFBP5) and western blotting data on key signaling proteins indicate that compound #32 significantly inhibits the PI3K-AKT-mTOR pathway, an intracellular signaling pathway critical in cell proliferation and apoptosis.

Connectivity mapping using a combined gene signature from multiple colorectal cancer datasets identified candidate drugs including existing chemotherapies

BACKGROUND

While the discovery of new drugs is a complex, lengthy and costly process, identifying new uses for existing drugs is a cost-effective approach to therapeutic discovery. Connectivity mapping integrates gene expression profiling with advanced algorithms to connect genes, diseases and small molecule compounds and has been applied in a large number of studies to identify potential drugs, particularly to facilitate drug repurposing. Colorectal cancer (CRC) is a commonly diagnosed cancer with high mortality rates, presenting a worldwide health problem. With the advancement of high throughput omics technologies, a number of large scale gene expression profiling studies have been conducted on CRCs, providing multiple datasets in gene expression data repositories. In this work, we systematically apply gene expression connectivity mapping to multiple CRC datasets to identify candidate therapeutics to this disease.

RESULTS

We developed a robust method to compile a combined gene signature for colorectal cancer across multiple datasets. Connectivity mapping analysis with this signature of 148 genes identified 10 candidate compounds, including irinotecan and etoposide, which are chemotherapy drugs currently used to treat CRCs. These results indicate that we have discovered high quality connections between the CRC disease state and the candidate compounds, and that the gene signature we created may be used as a potential therapeutic target in treating the disease. The method we proposed is highly effective in generating quality gene signature through multiple datasets; the publication of the combined CRC gene signature and the list of candidate compounds from this work will benefit both cancer and systems biology research communities for further development and investigations.

Mycophenolic acid inhibits migration and invasion of gastric cancer cells via multiple molecular pathways

Mycophenolic acid (MPA) is the metabolized product and active element of mycophenolate mofetil (MMF) that has been widely used for the prevention of acute graft rejection. MPA potently inhibits inosine monophosphate dehydrogenase (IMPDH) that is up-regulated in many tumors and MPA is known to inhibit cancer cell proliferation as well as fibroblast and endothelial cell migration. In this study, we demonstrated for the first time MPA’s antimigratory and anti-invasion abilities of MPA-sensitive AGS (gastric cancer) cells. Genome-wide expression analyses using Illumina whole genome microarrays identified 50 genes with ≥2 fold changes and 15 genes with > 4 fold alterations and multiple molecular pathways implicated in cell migration. Real-time RT-PCR analyses of selected genes also confirmed the expression differences. Furthermore, targeted proteomic analyses identified several proteins altered by MPA treatment. Our results indicate that MPA modulates gastric cancer cell migration through down-regulation of a large number of genes (PRKCA, DOCK1, INF2, HSPA5, LRP8 and PDGFRA) and proteins (PRKCA, AKT, SRC, CD147 and MMP1) with promigratory functions as well as up-regulation of a number of genes with antimigratory functions (ATF3, SMAD3, CITED2 and CEAMCAM1). However, a few genes that may promote migration (CYR61 and NOS3) were up-regulated. Therefore, MPA’s overall antimigratory role on cancer cells reflects a balance between promigratory and antimigratory signals influenced by MPA treatment.

Correlation of IMPDH1 gene polymorphisms with subclinical acute rejection and mycophenolic acid exposure parameters on day 28 after renal transplantation

The risk of acute rejection in patients with higher exposure to mycophenolic acid (MPA), the active metabolite of mycophenolate mofetil (MMF), might be due to inosine 5'-monophosphate dehydrogenase (IMPDH) polymorphisms. The correlations with subclinical acute rejection, IMPDH1 polymorphisms and MPA exposure on day 28 post-transplantation were investigated in 82 Japanese recipients. Renal transplant recipients were given combination immunosuppressive therapy consisting of tacrolimus and 1.0, 1.5 or 2.0 g/day of MMF in equally divided doses every 12 hr at designated times. There were no significant differences in the incidence of subclinical acute rejection between IMPDH1 rs2278293 or rs2278294 polymorphisms (p = 0.243 and 0.735, respectively). However, in the high MPA night-time exposure range (AUC > 60 microg x h/ml and C(0 )> or = 1.9 microg/ml), there was a significant difference in the incidence of subclinical acute rejection between IMPDH1 rs2278293 A/A, A/G and G/G genotypes (each p = 0.019), but not the IMPDH1 rs2278294 genotype. In the higher daytime MPA exposure range, patients with the IMPDH1 rs2278293 G/G genotype also tended to develop subclinical acute rejection. In patients with the IMPDH rs2278293 A/A genotype, the risk of subclinical acute rejection episode tends to be low and the administration of MMF was effective. The risk of subclinical acute rejection for recipients who cannot adapt in therapeutic drug monitoring (TDM) of MPA seems to be influenced by IMPDH1 rs2278293 polymorphism. The prospective analysis of IMPDH1 rs2278293 polymorphism as well as monitoring of MPA plasma concentration after transplantation might help to improve MMF therapy.

Pharmacokinetics and pharmacodynamics in renal transplant recipients under treatment with cyclosporine and Myfortic

INTRODUCTION

Efficacious prophylaxis of acute rejection episodes (ARE) requires adequate exposure to each component of the immunosuppressive treatment from the first days after renal transplantation. The aim of the present study was to evaluate the correlation between cyclosporine (CsA) and mycophenolic acid (MPA) exposure based upon pharmacokinetics (PK) and pharmacodynamics (PD) and 6-month biopsy-proven acute rejection (BPAR) episodes and chronic allograft nephropathy on 6 month protocol biopsies.

PATIENTS AND METHODS

We examined twenty-two first or second de novo renal transplant recipients treated with steroids, Sandimmune Neoral (CsA) and Myfortic (720 mg twice a day). PK (C0, C2, and AUC(0-12h)) for both drugs were determined on days 7, 90, and 180. Calcineurin activity, interleukin-2 and interferon-gamma synthesis as well as %CEM were tested at days 7 and 180. CsA dosages were adjusted by C2 monitoring. Collected data included: BPAR during the first 6 months and Banff histological parameters on the 6-month protocol biopsies.

RESULTS

Eighteen of 22 patients completed 1 year follow-up under treatment. The 6-month BPAR was 18% (4/22). Six-month protocol biopsies in 50% of 14 recipients showed chronic allograft nephropathy 1. At day 7, CsA C2 and AUC median values were 138 ng/mL and 6377 ng x h/mL, while C0 MPA was 1.0 microg/mL and AUC = 23.9 microg x h/mL. CsA C2 medians at 3 and 6 months were 1468 and 1720 ng/mL. MPA-AUC reached therapeutic targets at 3 months (32.3 microg x h/mL) and was 48.3 microg x h/mL at 6 months. Patients with BPAR showed lower CsA AUC (P = .06) and a significantly lower baseline inhibition of calcineurin activity (P < .005) than patients with no BPAR. An increase in mesangial matrix in 6-month protocol biopsies correlated with higher CsA C2 (P = .01). All biomarkers evaluated were significantly inhibited compared with the standard population.

CONCLUSIONS

When Myfortic is administered together with CsA, it is advisable to begin with higher doses (720 mg x 3 days) to reach adequate PK targets and improve BPAR rates. To prevent chronic allograft nephropathy, lower CsA C2 should be targeted from 3 months.

T-cell function monitoring in stable renal transplant patients treated with sirolimus monotherapy

BACKGROUND

Sirolimus is an agent with lymphocyte-specific features similar to those of calcineurin inhibitors but with a different mechanism of action and safety profile. To optimize the use of sirolimus-based immunosuppression, further investigation of appropriate pharmacokinetic (sirolimus exposure) and pharmacodynamic (sirolimus T-cell immunomodulator effect) monitoring is required to determine personalized target concentrations.

AIM

The main objective of the study was to evaluate the feasibility and reproducibility of combined pharmacokinetic and pharmacodynamic monitoring and to apply biomarkers of immunosuppression in stable kidney transplant recipients receiving sirolimus monotherapy.

METHODS

Fourteen renal transplant patients treated with sirolimus monotherapy (median 2 years) were included in this study. Pharmacokinetic and pharmacodynamic parameters were evaluated in each patient three times: at inclusion in the study (day 1), then again at 3 and 6 months.

RESULTS

The median sirolimus concentration was 11.5 ng/mL. CD4+ T-cell adenosine triphosphate (ATP) concentrations (150 ng/mL) and interleukin (IL)-10 production (50.9 ng/mL) were significantly lower in treated patients than in healthy controls (n = 95) [301 ng/mL; 278 ng/mL, respectively]. Median inhibition of T-cell proliferation was 60% (31-96%) in treated patients. Interferon-gamma and transforming growth factor-beta production was found to be similar to those in the healthy controls. Our results suggest an association between low ATP and IL-10 concentrations and the presence of infection.

CONCLUSIONS

The sequential measurement of these biomarkers in stable renal transplant recipients treated with monotherapy could be useful to evaluate the biological effect of sirolimus in each patient and to establish personalized therapy taking into account the individual response to the drug.

Individualization of mycophenolate mofetil dose in renal transplant recipients

The immunosuppressive agent mycophenolate mofetil has been successfully used over the past 10 years to prevent acute allograft rejection after renal transplantation. It has mainly been administered as a fixed dose of mycophenolate mofetil 1000 mg b.i.d. The pharmacokinetics of mycophenolic acid, the active moiety of the prodrug mycophenolate mofetil, show large between-patient variability, and exposure to mycophenolic acid correlates with the risk for acute rejection. This suggests that already excellent clinical results can be further improved by mycophenolate mofetil dose individualization. This review discusses different arguments in favour of individualization of mycophenolate mofetil dose, as well as strategies for managing mycophenolate mofetil therapy individualization, including pharmacokinetic and pharmacodynamic monitoring and dose individualization based on pharmacogenetic information. It is expected that pharmacokinetic monitoring of mycophenolic acid will offer the most effective and feasible tool for mycophenolate mofetil dose individualization.

Therapeutic drug monitoring of mycophenolic acid: does it improve patient outcome?

Treatment with the immunosuppressive agent mycophenolate mofetil (MMF) decreases the risk of rejection after renal transplantation and improves graft survival compared with azathioprine. The exposure to the active metabolite mycophenolic acid (MPA) is correlated to the risk of developing acute rejection. The interpatient variability in exposure of MPA is wide relative to the proposed therapeutic window of the MPA AUC(0 12) (30 - 60 mg.h/l). The pharmacokinetics of MPA are influenced by patient characteristics such as gender, time after transplantation, serum albumin concentration, renal function, comedication and pharmacogenetic factors. Therapeutic drug monitoring is likely to reduce inter-patient variability. Limited sampling strategies are used to predict the full AUC(0 12). Three prospective randomised studies compared concentration controlled MMF therapy to a fixed-dose regimen. Preliminary outcomes of these studies showed conflicting results and longer follow up is needed to further clarify the role of therapeutic drug monitoring in increasing the therapeutic potential of MMF.

Conversion From Mycophenolate Mofetil to Enteric-Coated Mycophenolate Sodium in Maintenance Renal Transplant Recipients Receiving Tacrolimus: Clinical, Pharmacokinetic, and Pharmacodynamic Outcomes

BACKGROUND

Mycophenolic acid (MPA) pharmacokinetics using the mycophenolate mofetil (MMF) formulation are known to differ between patients receiving tacrolimus or cyclosporine, but only limited data exist concerning concomitant use of tacrolimus and enteric-coated mycophenolate sodium (EC-MPS).

METHODS

In this six-month, multicenter, open-label, single-arm trial, 63 maintenance renal transplant patients receiving tacrolimus were converted from mycophenolate mofetil (MMF) to EC-MPS.

RESULTS

MPA concentration-time profiles in 21 patients showed that MPA exposure was similar with MMF or EC-MPS (mean area under the curve 39.9+/-11.6 microg x h/mL versus 43.7+/-17.4 microg x h/mL at day 14 post-conversion). Median time to peak concentration was 0.5 hr with MMF and 1.5 hr with EC-MPS. Inosine monophosphate dehydrogenase (IMPDH) activity was almost identical: area under the enzyme activity time curve (AEC) was 124.2+/-32.0 nmol x h/mg prot/h with MMF and 130.3+/-36.6 nmol x h/mg prot/h with EC-MPS at 14 days post-conversion; average daytime IMPDH activity was 10.3+/-2.7 nmol/h/mg protein and 10.9+/-2.7 nmol/h/mg protein, respectively. Maximal daytime inhibition of IMPDH activity was 67% with MMF and 62% with EC-MPS at day 14. One patient (1.6%) experienced mild biopsy-proven acute rejection. No graft losses or deaths occurred. Renal function remained stable (mean calculated creatinine clearance 70.6+/-26.8 mL/min with MMF and 68.8+/-25.4 mL/min six months post-conversion). Adverse events or infections with a suspected relation to EC-MPS occurred in 12 patients (19%). Four patients discontinued EC-MPS due to adverse events or infections.

CONCLUSIONS

MMF and EC-MPS are associated with similar MPA exposure and equivalent pharmacodynamic effect. Conversion of tacrolimus-treated maintenance renal transplant patients from MMF to EC-MPS is safe and well-tolerated and does not compromise therapeutic efficacy.

Mycophenolic acid trough level monitoring in solid organ transplant recipients treated with mycophenolate mofetil: association with clinical outcome

BACKGROUND

Mycophenolate mofetil (MMF) is widely and successfully used in immunosuppressive regimens for the prophylaxis of organ rejection following transplantation. Conventionally, it is administered at a fixed dose without serial measurements of plasma concentrations of mycophenolic acid (MPA), the active metabolite. Recently, there has been an increased interest in therapeutic drug monitoring (TDM) of MMF therapy to optimize the benefit/risk index of the drug. Predose trough samples of MPA are considered most convenient and economic, thereby allowing an increased use of TDM in the transplant setting. However, the added value of TDM for MMF therapy is still under debate.

OBJECTIVE

This paper reviews (based on a systematic PubMed and EMBASE search, 1995-June 2006) the current evidence of the usefulness and clinical relevance of MPA trough level monitoring during MMF therapy in solid organ transplantation.

FINDINGS AND CONCLUSIONS

Based on data available in the public domain, the contribution of MPA trough level monitoring during MMF therapy in solid organ transplant recipients remains unproven. Available studies have limitations and report conflicting results. There is a lack of prospective randomized trials, particularly in pediatric renal transplant recipients and in cardiac and liver transplantation. While there is a suggestion that there may be a relationship between efficacy and MPA trough levels, the majority of studies showed no correlation between MPA plasma concentrations and adverse effects. Based on current evidence, the adherence to presently recommended target ranges for MPA troughs in solid organ transplantation cannot assure an improved clinical outcome with MMF therapy. Whether MPA trough level monitoring leads to improved efficacy and less toxicity is currently subject to a large randomized trial; final results are eagerly awaited.

Activation of the purine salvage pathway in mononuclear cells of cardiac recipients treated with mycophenolate mofetil

BACKGROUND

The objective of this study was to investigate purine nucleotide metabolism in peripheral blood mononuclear cells (PBMC) of cardiac transplant recipients switched from azathioprine to mycophenolate mofetil (MMF).

METHODS

Concentrations of guanosine 5'triphosphate (GTP) and adenosine 5'triphosphate (ATP), the activities of inosine monophosphate dehydrogenase (IMPDH), guanine phosphoribosyltransferase (GPRT), and hypoxanthine phosphoribosyltransferase (HPRT) were determined in PBMC of 27 cardiac transplant recipients before switch to MMF and 3, 6, and 12 months thereafter.

RESULTS

There was no difference in the activities of IMPDH and salvage pathway enzymes GPRT and HRPT as well as in intracellular GTP and ATP concentrations between the patients before switch to MMF and healthy controls. The GTP and ATP concentrations in PBMC of cardiac recipients did not change during the entire observation period. Although the MPA trough level remained similar, IMPDH activity declined from 897 to 316 pmol/10(6)PBMC/h 3 months after MMF onset, was almost completely inhibited after 6 months, and partially restored to 143 pmol/10(6)PBMC/h 12 months after switch to MMF. In contrast, GPRT activity increased after 3, 6, and 12 months of MMF therapy and HPRT activity 3 and 6 months after switch to MMF.

CONCLUSIONS

We demonstrated for the first time an induction of salvage pathway enzyme activities in PBMC under MMF therapy. This probably accounts for the maintenance of intracellular purine nucleotide pools and prevents the GTP depletion.

ZNRD1 mediates resistance of gastric cancer cells to methotrexate by regulation of IMPDH2 and Bcl-2

We previously showed that downregulation of a transcription-associated gene (ZNRD1) could reverse the resistant phenotype of gastric cancer cells through regulation of the transcription of multidrug resistance gene 1 (MDR1). In the present study, we determined both known and novel differentially expressed genes in VCR-induced multidrug resistant gastric cancer cell SGC7901/VCR transfected with ZNRD1 siRNA or empty vector control. Screening was performed using the Human Cancer Xpro(tm) HC-III plus arrays, containing 3072 cancer-related cDNAs. Ten genes, involved in cell cycle control, nucleic acid binding, and protein phosphorylation, among other functions, underwent more than 5-fold change. Of the downregulated genes we chose Inosine monophosphate dehydrogenase 2 (IMPDH2) for further validation by quantitative RT-PCR. In vitro and in vivo drug sensitivity analyses revealed that inhibition of ZNRD1 and IMPDH2 activity sensitized SGC7901/VCR cells to methotrexate. Additionally, inhibition of ZNRD1 could suppress adriamycin-induced apoptosis and significantly downregulate the expression of Bcl-2, but it did not alter the expression of the glutathione-S-transferase, or intracellular glutathione content. Taken together, the findings suggest that ZNRD1 could act as a modulator of methotrexate chemotherapy in gastric cancer cells through the regulation of IMPDH2 and Bcl-2.Key words: ZNRD1, IMPDH2, multidrug resistance, apoptosis, gastric cancer.

Sequential Determination of Pharmacokinetics and Pharmacodynamics of Mycophenolic Acid in Liver Transplant Patients Treated with Mycophenolate Mofetil

BACKGROUND

In liver transplantation, mycophenolate mofetil (MMF) is habitually administered using fixed doses. We assessed whether mycophenolic acid (MPA) monitoring could be advisable in liver transplant patients.

METHODS

In 15 liver transplant patients receiving tacrolimus, daclizumab and MMF (1 g bid, orally), we determined the 12-hour plasma MPA pharmacokinetic profile after one dose of MMF at days 6, 10, and 16, and months 3 and 6. The inhibitory capacity of serum MPA on proliferation of CEM cells, a cell line insensitive to other immunosuppressants, was also determined.

RESULTS

A large interindividual variability in MPA profiles was observed at any time. Regardless of a gradual increase in individual MPA AUC and C(0) over time following transplantation, a substantial proportion of patients had these parameters below the ranges recommended in other organ transplantations throughout the study. When MPA AUC and C(0) were within the recommended ranges, CEM proliferation was inhibited by almost all serum samples, but when these pharmacokinetic parameters were below the recommended ranges, CEM proliferation was very variable and, therefore, unpredictable. No relationship between MPA pharmacokinetics and the efficacy of MMF could be established (only one patient developed rejection), probably due to the concomitant administration of tacrolimus and daclizumab. Gastrointestinal symptoms were the only adverse events with a significant relationship with MPA levels.

CONCLUSIONS

During the first postoperative months, exposure to MPA is low in a considerable proportion of liver transplant patients receiving MMF at a fixed dose of 1 g bid. MPA monitoring appears necessary in these patients.

Effect of mycophenolate mofetil on immune response and plasma and lymphatic tissue viral load during and after interruption of highly active antiretroviral therapy for patients with chronic HIV infection: a randomized pilot study

The main goal of this study was to assess the role of mycophenolate mofetil (MMF) during interruption of highly active antiretroviral therapy (HAART). Seventeen patients with early-stage chronic HIV type 1 infection were treated with HAART for 12 months. They were then randomized (day 0) to receive MMF (HAART-MMF group, n = 9) or to continue the regimen (HAART group, n = 6) for 120 additional days. At day 120 in the HAART-MMF group, HAART was discontinued, and MMF administration was continued. The primary end point of the study was the number of individuals maintaining a plasma viral load (VL) set point of <200 copies/mL after at least 6 months off HAART. At day 120, all patients in both groups had undetectable plasma VLs. After 6 months off HAART, 5 of 9 patients in the HAART-MMF group versus 1 of 6 patients in the HAART group maintained a plasma VL of <200 copies/mL (P = 0.28). According to the ability of their plasma to inhibit cellular proliferation, patients were reclassified and divided into an inhibition group (n = 6) and a no inhibition group (n = 9). The doubling time of VL rebound was significantly higher in the inhibition group (mean +/- SE, 10.22 +/- 1.3) than in the no inhibition group (mean +/- SE, 4.6 +/- 1.6; P = 0.03). Moreover, 5 of 6 patients in the inhibition group maintained a plasma VL of <200 copies/mL versus 1 of 9 patients in the no inhibition group (P = 0.005) after 6 months off HAART. We found that combining MMF and HAART delayed VL rebound and improved control of viral replication without HAART but only when inhibition of lymphocyte proliferation was achieved.

Pharmacokinetics and Pharmacodynamics of Low Dose Mycophenolate Mofetil in HIV-Infected Patients Treated with Abacavir, Efavirenz and Nelfinavir

BACKGROUND

The use of mycophenolate mofetil in combination with highly active antiretroviral therapy (HAART) has been proposed in order to inhibit HIV replication. Due to the low doses involved, pharmacokinetic-pharmacodynamic monitoring is recommended.

OBJECTIVE

The aim of this study was to characterise the pharmacokinetic and pharmacodynamic monitoring of low doses of mycophenolate mofetil (0.25 g twice daily) in HIV-infected patients treated with HAART and after programmed discontinuation of HAART, in order to assess whether low doses of this immunosuppressive agent provide a biological effect.

METHODS

Mycophenolic acid (MPA) plasma levels (assessed by high-performance liquid chromatography) and the capacity of patients' sera to inhibit CEM cell line proliferation (assessed by (3)H-thymidine uptake) were measured post-dose at 0, 20, 40 minutes and 1, 2, 4, 6, 8, 10 and 12 hours in nine HIV-infected patients treated with a combination of abacavir, nelfinavir and efavirenz (HAART) and mycophenolate mofetil 0.25 g twice daily at days 7, 28, 120 and 150 (30 days without HAART) after the treatment initiation. A control group of eight patients was treated with HAART alone.

RESULTS

In the 35 post-dose curves analysed, no differences were found in MPA levels between days 7, 28, 120 and 150: area under the plasma concentration-time curve - mean value 15.3 mg . h/L, range 10.4-24.4 mg . h/L; minimum plasma concentration - mean value 0.60 mg/L, range 0.20-4.67 mg/L; maximum plasma concentration mean value 2.60 mg/L, range 0.94-7.98 mg/L. Pretreatment patients' sera did not inhibit CEM proliferation. Post-treatment patients' sera inhibited CEM proliferation to <40% in 25 of 35 curves at 0 hours (six of nine patients), in 34 of 35 curves at 1 hour, in 32 of 35 curves at 2 hours, in 22 of 35 curves at 4 hours, and in 8 of 35 curves at 12 hours. The MPA level versus CEM proliferation inhibition had a concentration that produces 50% of the maximum drug effect (EC(50)) of 0.33 mg/L. Viral load at day 150 was >200 copies/mL in all control patients and in three of nine patients receiving mycophenolate mofetil. These three patients were the only ones repeatedly unable to inhibit pre-dose CEM proliferation to <40%.

CONCLUSIONS

Mycophenolate mofetil pharmacokinetic profiles in HIV patients under HAART are not significantly different from those found in transplant patients. Sera from the majority of patients receiving low doses of mycophenolate mofetil inhibited lymphocyte proliferation during most of the inter-dose interval, despite low MPA plasma levels. For some patients, higher doses may be necessary: the capacity of sera to inhibit CEM proliferation may help to identify these patients.

An exploratory study on pharmacogenetics of inosine-monophosphate dehydrogenase II in peripheral mononuclear cells from liver-transplant recipients

Mycophenolate mofetil (MMF) is an immunosuppressant used for the prophylaxis of rejection in renal, pancreas, and liver transplantation. It inhibits the inducible isoform of the enzyme inosine-monophosphate dehydrogenase (IMPDH II) via its active metabolite mycophenolic acid (MPA). IMPDH II is necessary for de novo purine synthesis in activated lymphocytes. The aims of the present study were to evaluate the feasibility of a real-time polymerase chain reaction (PCR) quantitative assessment of IMPDH II gene expression in liver transplant recipients as well as to provide a preliminary evaluation of possible correlations with drug tolerability. RNA was extracted from peripheral blood mononuclear cells of liver recipients after at least 6 months of MMF administration. IMPDH II gene expression was assessed using quantitative, real-time PCR and normalized using glyceraldheyde-3-phosphate dehydrogenase (GAPDH). Finally, adverse events associated with MMF administration were recorded. Real-time PCR quantitation of IMPDH II gene expression was reliable, sensitive, and specific. The intrapatient variability for both IMPDH II and GAPDH assays was lower than 0.6% in all patients. The results demonstrated a wide interpatient variability, with the mean value +/- standard deviation of 0.949 +/- 0.525 (95% confidence interval, 0.669-1.229) and a median value of 0.797. Patients with treatment-related toxicities displayed a trend to a higher level of IMPDH II expression than those without toxicity (mean, 1.126 vs 0.771). In conclusion, pharmacogenetic analysis of IMPDH II may represent a novel approach to MMF therapeutic monitoring.

Pharmacodynamic approach to immunosuppressive therapies using calcineurin inhibitors and mycophenolate mofetil

BACKGROUND

Graft survival depends on adequate immunosuppression. To evaluate the effect on the immune system of immunosuppressive therapies using calcineurin inhibitors (CNIs), several pharmacodynamic indices have been proposed to complement pharmacokinetic data. In this preliminary study we compared some of these parameters during combined immunosuppressant therapies.

METHODS

We treated 65 stable renal transplant recipients with cyclosporin A (CsA; n = 16), tacrolimus (TRL; n = 10); CsA + mycophenolate mofetil (MMF; n = 14); TRL + MMF (n = 13), and MMF (n = 12). Twelve nontreated healthy controls were also included. Calcineurin activity (CNA) in peripheral blood mononuclear cells was measured using (32)P-labeled peptide. Interleukin-2 (IL-2) and interferon-gamma production in phytohemagglutinin-activated whole blood were measured at 0 and 2 h postdose. The areas under the curves, c(min), c(max), and concentration at 2 h (c(2 h)) were also measured.

RESULTS

We found no differences in CNA between groups receiving CNIs alone or combined with MMF [median (25th-75th percentiles)]: CsA(2 h), 3.87 (3.00-6.85)% alkaline phosphatase (AP); CsA+MMF(2 h), 3.90 (1.78-5.19)% AP; TRL(2 h), 5.68 (3.02-16.00)% AP; TRL+MMF(2 h), 11.80 (4.05-14.63)% AP. In vitro IL-2 production was significantly lower in the groups receiving combined therapy than in groups receiving CNIs alone [median (25th-75th percentiles)]: CsA(2 h), 276.52 (190.41-385.25) ng/L; CsA+MMF(2 h), 166.48 (81.06-377.01) ng/L (P <0.001); TRL(2 h), 249.34 (127.48-363.50) ng/L; TRL+ MMF(2 h), 122.13 (51.02-180.00) ng/L (P <0.001). The correlations (r) between c(2 h) and CNA 2 h postdose were as follows: CsA, r = -0.74; CsA+MMF, r = -0.84; TRL, r = -0.70; TRL+ MMF, r = -0.70 (P <0.001 in all cases).

CONCLUSIONS

The measurement of CNA may be of help in following the effect on the immune system of CNI treatments, even in combined therapies, but does not reflect the additional effect of MMF. In contrast, IL-2 in vitro production reflects the effect of both MMF and CNIs.

Mycophenolate mofetil for solid organ transplantation: does the evidence support the need for clinical pharmacokinetic monitoring?

The need for clinical pharmacokinetic monitoring (CPM) of the immunosuppressant mycophenolate mofetil (MMF) has been debated. Using a previously developed algorithm, the authors reviewed the evidence to support or refute the utility of CPM of MMF. First, MMF has proven efficacy for prevention of organ rejection in renal and cardiac transplant populations. In addition, the pharmacologically active form of MMF, mycophenolic acid (MPA), can be measured readily in plasma, and relationships between the incidence of rejection and MPA predose concentrations and MPA area under the curve (AUC) have been reported. A lower limit of the therapeutic range (MPA predose concentrations >1.55 microg/mL, as measured by enzyme multiplied immunoassay technique [EMIT], or MPA AUC >30 or 40 microg. h/mL, as measured by high-performance liquid chromatography [HPLC]) has been suggested to prevent rejection in renal allograft patients. Similarly, in cardiac transplant patients, decreased incidences of organ rejection have been reported in patients with MPA concentrations >2 or 3 microg/mL (using EMIT) and total AUC values >42.8 microg. h/mL (using HPLC). However, the relationship between pharmacokinetic parameters and adverse events in renal and cardiac transplant patients remains unclear. Due to the nature of antirejection therapy, the pharmacologic response of MMF is not readily assessable, and therapy is life-long. MPA pharmacokinetics exhibit large inter- and intrapatient variability and may be altered in specific patient populations due to changes in protein binding, concomitant disease states, or interactions with concurrent immunosuppressants. Therefore, on the basis of current evidence, CPM can provide more information regarding efficacy of MMF than clinical judgment alone in select patient populations. However, further randomized, prospective trials are required to clarify unresolved issues. Specifically, an upper limit of the therapeutic range, above which the risk of side effects is increased, needs to be elucidated for MMF therapy. Other future directions for research include determining a practical limited sampling strategy for MPA AUC; clarifying the relationship between free MPA concentrations, efficacy, and toxicity; and defining the pharmacodynamic relationship between activity of inosine monophosphate dehydrogenase (the enzyme inhibited by MPA) and risk of rejection or adverse effects.

Therapeutic monitoring of mycophenolate mofetil in organ transplant recipients: is it necessary?

Adequate immunosuppression minimising the risk of organ rejection with acceptable tolerability of the used drugs is a crucial step in organ transplantation. The primary goal is to maintain a consistent time-dependent target concentration by tailoring individual dosage leading to the best efficacy and tolerability combination. The use of therapeutic drug monitoring (TDM) to optimise immunosuppressive therapy is routinely employed for maintenance drugs such as cyclosporin and tacrolimus. The question whether therapeutic monitoring of mycophenolic acid (MPA) in organ transplant recipients treated with mycophenolate mofetil is necessary is not definitely answered. The correlation of mycophenolic acid pharmacokinetic parameters with efficacy and toxicity makes the therapeutic monitoring of this drug promising. However, further studies are mandatory to draw the best guidelines in order to achieve higher levels of evidence that MPA-TDM may improve patient outcome.

Therapeutic drug monitoring for immunosuppressants

BACKGROUND

Immunosuppressants have significantly increased patient survival, e.g. in renal transplant up to 90% for the first year.

METHODS

Four immunosuppressants are used for clinical applications in the United States: cyclosporine (CsA) (Sandimmune and Neoral), FK 506-tacrolimus (ProGraf), mycophenolic mofetil (CellCept)--the prodrug for the mycophenolic acid (MPA), and rapamycin (RAPA) (Sirolimus). For CsA and FK 506, the rationale for monitoring is due to the variable pharmacokinetics, acute infection, dosage adjustment, non-compliance check, and for long-term maintenance therapy. Targeted whole blood concentrations ranges are: for CsA, 100-400 ng/ml depending on the methods, therapy and organs; and for FK 506, 5-20 ng/ml. For MPA, drug bioavailability--the plasma area-under-curve up to 12 h of 32.2-60.6 mg h/l was correlated to the biopsy-proven rejection rate of <10%. Monitoring is advocated for liver and renal transplants, for pediatrics, and for checking for non-compliance. RAPA monitoring is useful to check for variable pharmacokinetics, for non-compliance and others. The therapeutic range is tentatively targeted for 5-15 ng/ml. Monitoring methodologies are: for CsA, immunoassays such as fluorescence polarization immunoassay, and liquid chromatography (LC); for FK 506, microparticle enzyme immunoassay (MEIA); for MPA, enzyme multiplied immunoassay and LC; and for RAPA, MEIA, LC and LC-mass spectrometry. Proficiency survey programs for CsA and FK 506 are available from the US and Europe.

CONCLUSIONS

Monitoring of immunosuppressants has become an essential adjunct to the drug therapy for organ transplant patients.

Non-radioactive determination of inosine 5'-monophosphate dehydro-genase (IMPDH) in peripheral mononuclear cells

BACKGROUND

The immunosuppressive activity of mycophenolate mofetil (MMF) is based on the reversible inhibition of inosine 5'-monophosphate dehydrogenase (IMPDH) by mycophenolic acid (MPA). It was the aim of this study to develop a nonradioactive method for specific measurement of IMPDH activity in isolated peripheral mononuclear cells (MNC).

METHODS

The procedure is based on the incubation of lysed MNC with inosine 5'-monophosphate (IMP) followed by direct chromatographic determination of produced xanthosine 5'-monophosphate (XMP). IMPDH activity was measured in MNC of MMF-treated patients and nontreated volunteers.

RESULTS

The within-run (n = 10) and between-run (n = 20) coefficients of variation (CV) for IMPDH activity were < 8% and < 10%, respectively. IMPDH activity in 60 healthy volunteers (19-63 yr) ranged from 4.72 to 32.92 nmol/h/mg protein (mean = 18.39 +/- 6.24). The IC(50) for in vitro inhibition of IMPDH activity was about 2 to 3 microg/L. Application of a single dose of 1 g MMF in dialysis patients resulted in a significant inhibition (by 47-95%; p < 0.05) of IMPDH activity in lysed MNC.

CONCLUSIONS

The proposed assay specifically and reliably measures IMPDH activity in MNC. The procedure is applicable to evaluate pharmacodynamic activity in MMF-treated patients. The observed interindividual variability of IMPDH activity may reflect pharmacodynamic differences in MMF-treated patients.