Validation of an LC-MS/MS method for the quantification of mycophenolic acid in human kidney transplant biopsies

Development of a novel UPLC-MS/MS method for the simultaneous quantification of mycophenolic mofetil, mycophenolic acid, and its major metabolites: Application to pharmacokinetic and tissue distribution study in rats

Mycophenolate mofetil (MMF) is a prodrug of mycophenolic acid (MPA) used to prevent rejection in organ transplant patients. The purpose of this study is to develop a sensitive LC-MS/MS method to simultaneously quantify MMF, MPA, and two major metabolites, mycophenolic acid-glucuronide (MPAG) and Acyl-mycophenolic acid-glucuronide (AcMPAG) and applied this method in a pharmacokinetic (PK) and tissue distribution study. A Shimadzu UHPLC system coupled to an AB Sciex QTrap 4000 mass spectrometer was used for the analysis. Protein precipitation with a mixture of methanol: acetonitrile (2:1, v:v) was used to process the plasma samples and tissue samples. Separation was achieved using an Ultra Biphenyl 5 µm column (100 × 2.1 mm) with 0.1% formic acid in water (A) and acetonitrile (B) as the mobile phases. Quantification analysis was performed under positive ionization mode using the multiple reaction monitoring (MRM) approach. The method was linear in the range of 1.22 - 1250.00 nM for all four analytes with correlation coefficient values > 0.99. The method was reproducible, with intra- and inter-day accuracy ranging from 85.0 ± 11.2-108.3 ± 6.50 for all analytes in both plasma, liver and intestine homogenates. The extraction recovery and matrix effect of plasma sample using a mixture methanol/acetonitrile (2:1, V:V) can achieve an acceptable range (<20%), but extraction recovery and matrix effect of AcMPAG decreased to 64.10 ± 15.42 in the liver and intestine homogenates. The analytes in plasma were found to be stable under bench-top, freeze-thaw, and storage conditions. The validated method was successfully applied to quantify MMF, MPA, MPAG, and AcMPAG in a rat PK study. The PK results showed MPA was the major form exposed in the plasma in rats after oral administration of MMF, but the major metabolites in the rat's tissue disposition were MPAG.

Kidney and Liver Tissue Tacrolimus Concentrations in Adult Transplant Recipients-The Influence of the Whole Blood and Tissue Concentrations on Efficiency of Treatment during Immunosuppressive Therapy

Tacrolimus (TAC) has a narrow therapeutic index and highly variable pharmacokinetic characteristics. Close monitoring of the TAC concentrations is required in order to avoid the risk of acute rejection or adverse drug reaction. The results in some studies indicate that inter-tissue TAC concentrations can be a better predictor with regards to acute rejection episode than TAC concentration in whole blood. Therefore, the aim of the study was to assess the correlation between dosage, blood, hepatic and kidney tissue concentration of TAC measured by a validated liquid chromatography tandem mass spectrometry (LC-MS/MS) and clinical outcomes in a larger cohort of 100 liver and renal adult transplant recipients. Dried biopsies were weighed, mechanically homogenized and then the samples were treated with a mixture of zinc sulfate—acetonitrile to perform protein precipitation. After centrifugation, the extraction with tert-butyl methyl ether was performed. The analytical range was proven for TAC tissue concentrations of 10–400 pg/mg. The accuracy and precision fell within the acceptance criteria for intraday as well as interday assay. There was no correlation between dosage, blood (C₀) and tissue TAC concentrations. TAC concentrations determined in liver and kidney biopsies ranged from 8.5 pg/mg up to 160.0 pg/mg and from 7.1 pg/mg up to 215.7 pg/mg, respectively. To the best of our knowledge, this is the first LC-MS/MS method for kidney and liver tissue TAC monitoring using Tac¹³C,D₂ as the internal standard, which permits measuring tissue TAC concentrations as low as 10 pg/mg.

Overview of therapeutic drug monitoring of immunosuppressive drugs: Analytical and clinical practices

Immunosuppressant drugs (ISDs) play a key role in short-term patient survival together with very low acute allograft rejection rates in transplant recipients. Due to the narrow therapeutic index and large inter-patient pharmacokinetic variability of ISDs, therapeutic drug monitoring (TDM) is needed to dose adjustment for each patient (personalized medicine approach) to avoid treatment failure or side effects of the therapy. To achieve this, TDM needs to be done effectively. However, it would not be possible without the proper clinical practice and analytical tools. The purpose of this review is to provide a guide to establish reliable TDM, followed by a critical overview of the current analytical methods and clinical practices for the TDM of ISDs, and to discuss some of the main practical aspects of the TDM.

Personalized Therapy for Mycophenolate: Consensus Report by the International Association of Therapeutic Drug Monitoring and Clinical Toxicology

ABSTRACT

When mycophenolic acid (MPA) was originally marketed for immunosuppressive therapy, fixed doses were recommended by the manufacturer. Awareness of the potential for a more personalized dosing has led to development of methods to estimate MPA area under the curve based on the measurement of drug concentrations in only a few samples. This approach is feasible in the clinical routine and has proven successful in terms of correlation with outcome. However, the search for superior correlates has continued, and numerous studies in search of biomarkers that could better predict the perfect dosage for the individual patient have been published. As it was considered timely for an updated and comprehensive presentation of consensus on the status for personalized treatment with MPA, this report was prepared following an initiative from members of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology (IATDMCT). Topics included are the criteria for analytics, methods to estimate exposure including pharmacometrics, the potential influence of pharmacogenetics, development of biomarkers, and the practical aspects of implementation of target concentration intervention. For selected topics with sufficient evidence, such as the application of limited sampling strategies for MPA area under the curve, graded recommendations on target ranges are presented. To provide a comprehensive review, this report also includes updates on the status of potential biomarkers including those which may be promising but with a low level of evidence. In view of the fact that there are very few new immunosuppressive drugs under development for the transplant field, it is likely that MPA will continue to be prescribed on a large scale in the upcoming years. Discontinuation of therapy due to adverse effects is relatively common, increasing the risk for late rejections, which may contribute to graft loss. Therefore, the continued search for innovative methods to better personalize MPA dosage is warranted.

Mycophenolic acid concentrations in peripheral blood mononuclear cells are associated with the incidence of rejection in renal transplant recipients

AIMS

Although therapeutic drug monitoring of plasma mycophenolic acid (MPA) concentrations has been recommended to individualize dosage in transplant recipients, little is known regarding lymphocyte concentrations of MPA, where MPA inhibits inosine monophosphate dehydrogenase (IMPDH). This study investigated the utility of measuring predose MPA concentrations in peripheral blood mononuclear cells (C_0C ) and predose IMPDH activity, as predictors of graft rejection in renal transplant recipients.

METHODS

Forty-eight patients commencing mycophenolate mofetil (1 g twice daily) in combination with tacrolimus and prednisolone were recruited. Blood was collected for determination of trough total (C_0P ) and unbound (C_0u ) plasma MPA concentrations. Peripheral blood mononuclear cells were isolated for determination of C_0C and IMPDH activity. The incidence of rejection within 2 days of sample collection was determined histologically and classified according to the Banff 2007 criteria.

RESULTS

There was no association between MPA C_0C and C_0P (r_s  = 0.28, P = 0.06), however, MPA C_0C were weakly correlated with MPA C_0u (r_s  = 0.42, P = 0.013). Multivariate analysis indicated that MPA C_0C was the only covariate independently associated with rejection (FDR-adjusted P = 0.033). The receiver operating characteristic area under the curve (AUC) for the prediction of severe rejection using MPA C_0C was 0.75 (P = 0.013), with 73% sensitivity and specificity at a C_0C threshold of 0.5 ng 10^-7 cells. However, predose IMPDH activity was not a predictor of rejection (P > 0.15).

CONCLUSIONS

MPA C_0C measurement within the early post-transplant period may be useful to facilitate early titration of MPA dosing to significantly reduce rejection.

Comparison of PETINIA and LC-MS/MS for determining plasma mycophenolic acid concentrations in Japanese lung transplant recipients

Background

Mycophenolic acid (MPA) treatment requires therapeutic drug monitoring to improve the outcome after organ transplantation. The aim of this study was to compare two methods, a particle enhanced turbidimetric inhibition immunoassay (PETINIA) and a reference liquid chromatography tandem mass spectrometry (LC-MS/MS) for determining plasma MPA concentrations from Japanese lung transplant recipients.

Methods

Plasma MPA concentrations were determined from 20 Japanese lung transplant recipients using LC-MS/MS and the PETINIA on the Dimension Xpand Plus-HM analyzer.

Results

The mean MPA concentration measured by PETINIA was significantly higher than that measured by LC-MS/MS (3.26 ± 2.73 μg/mL versus 2.82 ± 2.71 μg/mL, P < 0.0001). The result of the Passing Bablok analysis was a slope of 1.104 (95% confidence interval [CI], 1.036–1.150) and an intercept of 0.229 (95%CI, 0.144–0.315). Bland–Altman analysis revealed PETINIA overestimates plasma MPA concentration by 26.25% and 95%CI from 21.43 to 31.07%.

Conclusion

The measurement of MPA by the PETINIA in Japanese lung transplant patients should evaluate the result with attention to positive bias.

A novel freeze-dried storage and preparation method for the determination of mycophenolic acid in plasma by high-performance liquid chromatography

Plasma samples were conventionally stored at freezing conditions until the time of detection. Such a technique, when carried out over an extended period, is energy consuming; in addition, preparation and transportation of stored samples is inconvenient. In this study, a freeze-dried storage and preparation method was proposed to determine the presence of mycophenolic acid (MPA) in plasma. Fresh plasma samples were freeze-dried using a device, and then stored at ambient temperature. After the stored samples were soaked with methanol spiked with the internal standard, high-performance liquid chromatography was conducted to detect MPA. The proposed method was demonstrated to be precise and accurate over the linear range of 0.5-50 μg mL^-1 , with both intra- and inter-day precision being <7% and biases <10%. The freeze-dried samples were stable at ambient temperature for at least 40 days. This method was also successfully applied to the pharmacokinetic study of MPA in healthy volunteers. Pharmacokinetic parameters, such as maximum plasma concentration, time point of maximum plasma concentration and elimination half-life, among others, were consistent with the results in the published study. This proposed technique was proved to be simple, reproducible and energy saving. This approach could also simplify the storage and analysis of samples in clinical and scientific drug research.

Intra-cellular immunosuppressive drugs monitoring: A step forward towards better therapeutic efficacy after organ transplantation?

Immunosuppressive drugs (IS) used in solid organ transplantation are critical dose drugs with high intra- and inter-subject variability. Therefore, IS therapeutic drug monitoring (TDM), mainly as trough levels analysis, is a major support to patient management, mandatory to optimize clinical outcome. Even though transplant patients undoubtedly benefited by this pre-dose (C0) monitoring, the relationship between these C0 concentrations and the incidence of graft rejections remains hardly predictable. Identification and validation of additional biomarkers of efficacy are therefore very much needed. As the main IS effects are mediated through the inhibition of lymphocyte proliferation pathways, direct drug quantification within this target compartment would appear meaningful, providing hopefully more consistent information on drug efficacy. Due to the analytical performances improvement, these intracellular concentrations became accessible for comprehensive studies regarding clinical benefit of intracellular IS TDM after solid organ transplantation. Over the last ten years, number of studies investigated the potential relationship between IS blood and intracellular pharmacokinetics, genetic variability, and clinical efficacy after solid organ transplantation. A recent literature review suggests that calcineurin inhibitors (tacrolimus and cyclosporine) intracellular concentrations appear more closely related to drug efficacy than blood levels. This closer association has however not been described for the m-TOR inhibitors (sirolimus, everolimus) and the antimetabolite (mycophenolic acid). Additional larger and multicenter clinical trials are needed to confirm these observations.

Current methods of the analysis of immunosuppressive agents in clinical materials: A review

More than 100000 solid organ transplantations are performed every year worldwide. Calcineurin (cyclosporine A, tacrolimus), serine/threonine kinase (sirolimus, everolimus) and inosine monophosphate dehydrogenase inhibitor (mycophenolate mofetil), are the most common drugs used as immunosuppressive agents after solid organ transplantation. Immunosuppressive therapy, although necessary after transplantation, is associated with many adverse consequences, including the formation of secondary metabolites of drugs and the induction of their side effects. Calcineurin inhibitors are associated with nephrotoxicity, cardiotoxicity and neurotoxicity; moreover, they increase the risk of many diseases after transplantation. The review presents a study of the movement of drugs in the body, including the processes of absorption, distribution, localisation in tissues, biotransformation and excretion, and also their accompanying side effects. Therefore, there is a necessity to monitor immunosuppressants, especially because these drugs are characterised by narrow therapeutic ranges. Their incorrect concentrations in a patient's blood could result in transplant rejection or in the accumulation of toxic effects. Immunosuppressive pharmaceuticals are macrolide lactones, peptides, and high molecular weight molecules that can be metabolised to several metabolites. Therefore the two main analytical methods used for their determination are high performance liquid chromatography with various detection methods and immunoassay methods. Despite the rapid development of new analytical methods of analysing immunosuppressive agents, the application of the latest generation of detectors and increasing sensitivity of such methods, there is still a great demand for the development of highly selective, sensitive, specific, rapid and relatively simple methods of immunosuppressive drugs analysis.

Do cytostatic drugs reach drinking water? The case of mycophenolic acid

Mycophenolic acid (MPA) has been identified as a new river contaminant according to its wide use and high predicted concentration. The aim of this study was to monitor the impact of MPA in a drinking water treatment plant (DWTP) that collects water downstream Llobregat River (NE Spain) in a highly densified urban area. During a one week survey MPA was recurrently detected in the DWTP intake (17-56.2 ng L(-1)). The presence of this compound in river water was associated to its widespread consumption (>2 tons in 2012 in Catalonia), high excretion rates and low degradability. The fate of MPA in waters at each treatment step of the DWTP was analyzed and complete removal was observed after pretreatment with chlorine dioxide. So far, MPA has not been described as water contaminant and its presence associated with its consumption in anticancer treatments is of relevance to highlight the importance of monitoring this compound.