Therapeutic drug measurement of mycophenolic acid derivatives in transplant patients

Production of Mycophenolic Acid by a Newly Isolated Indigenous Penicillium glabrum

Soil-occupant fungi produce a variety of mycotoxins as secondary metabolites, one of which is mycophenolic acid (MPA), an antibiotic and immunosuppressive agent. MPA is mainly produced by several species of Penicillium, especially Penicillium brevicompactum. Here, we present the first report of MPA production by a local strain belonging to Penicillium glabrum species. We screened ascomycete cultures isolated from moldy food and fruits, as well as soils, collected from different parts of Iran. MPA production of one hundred and forty Penicillium isolates was analyzed using HPLC. Three MPA producer isolates were identified, among which the most producer was subjected to further characterization, based on morphological and microscopic analysis, as well as molecular approach (ITS, rDNA and beta-tubulin gene sequences). The results revealed that the best MPA producer belongs to P. glabrum IBRC-M 30518, and can produce 1079 mg/L MPA in Czapek-Dox medium.

MRP4 is responsible for the efflux transport of mycophenolic acid β-d glucuronide (MPAG) from hepatocytes to blood

Mycophenolic acid (MPA) has become a cornerstone of immunosuppressive therapy, in particular for transplant patients. In the gastrointestinal tract, the liver and the kidney, MPA is mainly metabolized into phenyl-β-d glucuronide (MPAG). Knowledge about the interactions between MPA/MPAG and membrane transporters is still fragmented. The aim of the present study was to explore these interactions with the basolateral hepatic MRP4 transporter. The inhibition of the MRP4-driven transport by various drugs which can be concomitantly prescribed was also evaluated. In vitro experiments using vesicles overexpressing MRP4 showed an ATP-dependent transport of MPAG driven by MRP4 (Michaelis-Menten constant of 233.9 ± 32.8 µM). MPA was not effluxed by MRP4. MRP4-mediated transport of MPAG was inhibited (from -43% to -84%) by ibuprofen, cefazolin, cefotaxime and micafungin. An in silico approach based on molecular docking and molecular dynamics simulations rationalized the mode of binding of MPAG to MRP4. The presence of the glucuronide moiety in MPAG was highlighted as key, being prone to make electrostatic and H-bond interactions with specific residues of the MRP4 protein chamber. This explains why MPAG is a substrate of MRP4 whereas MPA is not.

Ex vivo binding of the immunosuppressant mycophenolic acid to dog and cat plasma proteins and the effect of co-incubated dexamethasone and prednisolone

Mycophenolic acid (MPA) has been shown to be promising for the treatment of autoimmune diseases in dogs and cats. In humans, MPA is highly bound to plasma proteins (~97%). It has been recommended to monitor free drug plasma concentrations because the free MPA correlates with its immunosuppressive effect. However, it is unknown if MPA is highly bound to plasma proteins in dogs and cats. The objectives of this study were to determine the extent of plasma protein binding of MPA and evaluate the effect of prednisolone and dexamethasone on the extent of protein binding of MPA in dogs and cats. The extent of plasma protein binding of MPA was determined in plasma collected from clinically healthy adult cats (n = 13) and dogs (n = 14) by combining high-throughput dialysis and ultra-high-liquid chromatography. This study reveals that MPA is highly bound to plasma proteins (>90%) in dogs and cats, mean extent of binding of MPA at 15 μg/ml to plasma proteins being 96% (range, 95%-97%) and 92% (range, 90%-93%) for dogs and cats, respectively. In dog plasma, MPA is primarily bound to albumin. In vitro, prednisolone increased the unbound MPA in dogs (p < .01) but not in cats (p = .07) while dexamethasone had no effect on MPA plasma binding in either species (p > .05). Results of this study provide valuable information for designing future pharmacokinetic and pharmacodynamic studies and also therapeutic monitoring programs for dogs and cats.

Utilization of Multi-Immunization and Multiple Selection Strategies for Isolation of Hapten-Specific Antibodies from Recombinant Antibody Phage Display Libraries

Phage display technology provides a powerful tool for the development of novel recombinant antibodies. In this work, we optimized and streamlined the recombinant antibody discovery process for haptens as an example. A multi-immunization approach was used in order to avoid the need for construction of multiple antibody libraries. Selection methods were developed to utilize the full potential of the recombinant antibody library by applying four different elution conditions simultaneously. High-throughput immunoassays were used to analyse the binding properties of the individual antibody clones. Different carrier proteins were used in the immunization, selection, and screening phases to avoid enrichment of the antibodies for the carrier protein epitopes. Novel recombinant antibodies against mycophenolic acid and ochratoxin A, with affinities up to 39 nM and 34 nM, respectively, were isolated from a multi-immunized fragment antigen-binding (Fab) library.

Simultaneous determination of mycophenolate and its metabolite mycophenolate-7-o-glucuronide with an isocratic HPLC-UV-based method in human plasma and stability evaluation

OBJECTIVES

Mycophenolic acid (MPA) is an immunosuppressive agent which is commonly used in a fixed dose regime in solid organ transplantation. For clinical trials and therapeutic drug monitoring measuring plasma concentrations is necessary. Also, stability issues have to be addressed.

METHODS

We describe an isocratic, RP-based HPLC-UV method for simultaneous determination of MPA and its major metabolite Mycophenolic acid 7-o Glucuronide (MPAG) in human plasma. Pre-analytics included protein precipitation with acetonitrile. The method was validated according to EMA/FDA guidelines. Patient lithium-heparin plasma and blood was used for evaluation of short-term (72 hours at room temperature = RT) and long-term stability (2 years at -80 °C) without acidification.

RESULTS

Linearity was assessed in the concentration range of 0.5-40.0 μg/mL for MPA and 5.0-350.0 μg/mL for MPAG, respectively. For MPA coefficient of variation was <7.0% (lower limit of quantification = LLOQ: 10.8%), for MPAG <9.6% (LLOQ: 10.6%). Bias ranged between -1.9 and +1.5% for MPA and for MPAG between -4.3 and -0.3%. The method showed agreement with a reference method for both analytes. MPA remained stable for 7 h (-1.6 to +8.4% change to the initial concentration) and MPAG for 24 h (-1.8 to -11.5% change) at RT in lithium heparin blood. After 2 years of storage at -80 °C MPA, MPAG concentrations and 95% CIs remained within ±15% of the initial value.

CONCLUSION

The presented assay is applicable for clinical studies. Blood samples were stable for 7 hours at RT and plasma for 2 years stored at -80 °C.

Renal glucuronidation and multidrug resistance protein 2-/ multidrug resistance protein 4-mediated efflux of mycophenolic acid: interaction with cyclosporine and tacrolimus

Mycophenolic acid (MPA) is an immunosuppressant used in transplant rejection, often in combination with cyclosporine (CsA) and tacrolimus (Tac). The drug is cleared predominantly via the kidneys, and 95% of the administered dose appears in urine as 7-hydroxy mycophenolic acid glucuronide (MPAG). The current study was designed to unravel the renal excretory pathway of MPA and MPAG, and their potential drug-drug interactions. The role of multidrug resistance protein (MRP) 2 and MRP4 in MPA disposition was studied using human embryonic kidney 293 (HEK293) cells overexpressing the human transporters, and in isolated, perfused kidneys of Mrp2-deficient rats and Mrp4-deficient mice. Using these models, we identified MPA as substrate of MRP2 and MRP4, whereas its MPAG appeared to be a substrate of MRP2 only. CsA inhibited MPAG transport via MRP2 for 50% at 8 μM (P < 0.05), whereas Tac had no effect. This was confirmed by cell survival assays, showing a 10-fold increase in MPA cytotoxicity (50% reduction in cell survival changed from 12.2 ± 0.3 μM to 1.33 ± 0.01 μM by MPA + CsA; P < 0.001) and in perfused kidneys, showing a 50% reduction in MPAG excretion (P < 0.05). The latter effect was observed in Mrp2-deficient animals as well, supporting the importance of Mrp2 in MPAG excretion. CsA, but not Tac, inhibited MPA glucuronidation by rat kidney homogenate and human uridine 5'-diphospho-glucuronosyltransferase-glucuronosyltransferase 1A9 (P < 0.05 and P < 0.01, respectively). We conclude that MPA is a substrate of both MRP2 and MRP4, but MRP2 is the main transporter involved in renal MPAG excretion. In conclusion, CsA, but not Tac, influences MPA clearance by inhibiting renal MPA glucuronidation and MRP2-mediated MPAG secretion.

Virtual high-throughput screening identifies mycophenolic acid as a novel RNA capping inhibitor

The RNA guanylyltransferase (GTase) is involved in the synthesis of the ^m7Gppp-RNA cap structure found at the 5′ end of eukaryotic mRNAs. GTases are members of the covalent nucleotidyl transferase superfamily, which also includes DNA and RNA ligases. GTases catalyze a two-step reaction in which they initially utilize GTP as a substrate to form a covalent enzyme-GMP intermediate. The GMP moiety is then transferred to the diphosphate end of the RNA transcript in the second step of the reaction to form the Gppp-RNA structure. In the current study, we used a combination of virtual database screening, homology modeling, and biochemical assays to search for novel GTase inhibitors. Using this approach, we demonstrate that mycophenolic acid (MPA) can inhibit the GTase reaction by preventing the catalytic transfer of the GMP moiety onto an acceptor RNA. As such, MPA represents a novel type of inhibitor against RNA guanylyltransferases that inhibits the second step of the catalytic reaction. Moreover, we show that the addition of MPA to S. cerevisiae cells leads to a reduction of capped mRNAs. Finally, biochemical assays also demonstrate that MPA can inhibit DNA ligases through inhibition of the second step of the reaction. The biological implications of these findings for the MPA-mediated inhibition of members of the covalent nucleotidyl superfamily are discussed.

Recipient-based approach to tailoring immunosuppression in liver transplantation

Improvements in the field of transplant immunosuppression (IS) have led to significant advances in long-term survival of liver transplant recipients. Despite this progress, survival rates vary depending on recipient, donor and/or perioperative factors. Tailoring IS based on recipient factors is of growing interest among health care providers involved in the care of organ transplant recipients. To date there is no consensus document addressing individualized IS therapy for liver transplant recipients. This review will discuss the information available on the effect of the various IS drugs on recipient-based factors such as age, ethnicity, and liver disease etiology.

Determination of total, free and saliva mycophenolic acid with a LC-MS/MS method: application to pharmacokinetic study in healthy volunteers and renal transplant patients

Mycophenolic acid (MPA) is the active moiety of mycophenoate mofetil (MMF), an ester prodrug widely used as an immunosuppressant. Therapeutic drug monitoring (TDM) of MPA is becoming mandatory for transplant patients received MMF therapy in the routine clinical practice because of large individual variability, dose-related toxicity and the risk of acute rejection. In this study, a rapid, sensitive and selective LC-MS/MS method was developed and validated for the quantitative analysis of total and free MPA in plasma and in saliva that uses one identical liquid chromatographic and mass spectrometric condition. Following protein precipitation for total and saliva MPA, and ultrafiltration for free MPA, chromatographic separation was performed on an Allure PFP Propyl analytical column (100 x 2.1 mm, 5 microm, RESTEK Co., Bellefonte, PA, USA) with 0.1% formic acid in acetonitrile and 0.1% formic acid in water (45:55, v/v) as the mobile phases. The compounds were quantified by positive electrospray ionization tandem mass spectrometry. Selectivity, linearity, accuracy, precision, recovery, matrix effect, and saliva stability were evaluated during method validation. The validated method was applied to a pharmacokinetic study of MPA after an oral administration of a single 1000 mg of MMF to eight healthy male volunteers and 750 mg bid of MMF to nine renal transplant patients.

Multicenter evaluation of a new inosine monophosphate dehydrogenase inhibition assay for quantification of total mycophenolic acid in plasma

The performance characteristics of a new inosine monophosphate dehydrogenase inhibition assay for the quantification of total mycophenolic acid (MPA) in plasma (Roche Diagnostics) were assessed in a multicenter evaluation. Validation data were collected from four institutions. Within-run and total imprecision were acceptable (n = 21 for each of 7 materials, coefficients of variation ranging 0.7-9.6%). The lower limit of quantification was 0.31 mg/L. The assay was linear from 0.31 to 15.0 mg/L. Method comparison with validated high-performance liquid chromatography with ultraviolet light or liquid chromatography tandem mass spectrometry methods showed good agreement (coefficients of correlation 0.974-0.994, slopes 1.01-1.17, intercepts -0.17 to 0.06). There was no difference found between results from different transplant types (cardiac vs. renal) or comedications (cyclosporine vs. tacrolimus). The recovery of samples from a proficiency testing scheme was acceptable. The cross-reactivity of AcMPAG, an in vitro active metabolite of MPA, was examined by adding AcMPAG to a pool of patient samples and subsequent quantification. MPA overestimation by AcMPAG cross-reactivity was found to be low (<5%). Thus, this interference is expected to be clinically irrelevant. In conclusion, the Roche Total MPA assay is a promising alternative for MPA quantification where chromatographic methods are not available.

Measurement of mycophenolic acid in plasma or serum by a commercial enzyme inhibition technique in comparison with a high performance liquid chromatography method

: Mycophenolic acid (MPA) is the primary active metabolite of the immunosuppressant mycophenolate mofetil. High performance liquid chromatography (HPLC) is commonly used for therapeutic drug monitoring (TDM) of MPA but requires batched runs. Recently, an enzyme inhibition assay (EIA) was approved for MPA TDM on random-access platforms using either serum or EDTA plasma. We evaluated the EIA on a Roche Integra 400 using serum and heparinized plasma in comparison with a validated HPLC method.

: Heparinized plasma from leftover clinical samples on which MPA was ordered along with paired serum samples, drawn at the same time for other clinical tests, were used for the method comparison.

: The EIA was linear from 3.1 to 44.0 μmol/L with an accuracy of 93.9%–107.1%. The intra- and inter-day variations were 0.5%–2.7% and 1.6%–2.1%, respectively. The limit of detection was 0.8 μmol/L and the limit of quantification was 3.1 μmol/L. The method showed a mean bias of 0.6 μmol/L (7.6%) in serum samples (3.1–34.1 μmol/L) vs. the HPLC method using paired plasma (n=229). Heparinized plasma (n=114) vs. serum showed a mean bias of –0.1 μmol/L (–1.6%) by the EIA.

: The random-access EIA on Integra 400 is acceptable for clinical MPA TDM in either serum or heparinized plasma.

Clin Chem Lab Med 2008;46:1281–4.

Liquid chromatographic determination of mycophenolic acid and its metabolites in human kidney transplant plasma: pharmacokinetic application

BACKGROUND AND OBJECTIVE

Difference in the hydrophilic properties of mycophenolic acid metabolites makes it technically difficult to simultaneously determine their plasma levels in one analytical run. Therapeutic drug monitoring (TDM) for MPA ensures adequate MPA exposure levels to both prevent rejection and avoid related toxicity. One measure limitation for TDM for MPA is the availability of simple, rapid and reproducible method for determination of MPA derivatives.

METHOD

Herein we report a single method to measure MPA and its metabolites using a gradient elution system in less than 10 min. We further tested applicability of our method in both stable and unstable renal transplant recipients with a wide range of levels.

RESULTS

Intra- and inter-day imprecision were less than 8% and 10%, respectively. Accuracy of the estimated concentrations ranges from 90% to 108%.

CONCLUSION

Collectively these data show that the new method is reasonably accurate and precise for the simultaneous determination of MPA and its metabolites in human plasma.