The association of the UGT1A8, SLCO1B3 and ABCC2/ABCG2 genetic polymorphisms with the pharmacokinetics of mycophenolic acid and its phenolic glucuronide metabolite in Chinese individuals

A joint population pharmacokinetic model to assess the high variability of whole-blood and intracellular tacrolimus in early adult renal transplant recipients

Tacrolimus (TAC) has high pharmacokinetic (PK) variability during the early transplantation period. The relationships between whole-blood and intracellular TAC concentrations and clinical outcomes remain controversial. This study identifies the factors affecting the PK variability of TAC and characterizes the relationships between whole-blood and intracellular TAC concentrations. Data regarding whole-blood TAC concentrations of 1,787 samples from 215 renal transplant recipients (<90 days postoperative) across two centers and intracellular TAC concentrations (648 samples) digitized from previous studies were analyzed using nonlinear mixed-effects modeling. The effects of potential covariates were screened, and the distribution of whole-blood to intracellular TAC concentration ratios (RWB:IC) was estimated. The final model was evaluated using bootstrap, goodness of fit, and prediction-corrected visual predictive checks. The optimal dosing regimens and target ranges for each type of immune cell subsets were determined using Monte Carlo simulations. A two-compartment model adequately described the data, and the estimated mean TAC CL/F was 23.6 L·h-1 (relative standard error: 11.5 %). The hematocrit level, CYP3A5*3 carrier status, co-administration with Wuzhi capsules, and tapering prednisolone dose may contribute to the high variability of TAC PK variability during the early post-transplant period. The estimated RWB:IC of all TAC concentrations in peripheral blood mononuclear cells (PBMCs) was 4940, and inter-center variability of PBMCs was observed. The simulated TAC target range in PBMCs was 20.2-85.9 pg·million cells-1. Inter-center variability in intracellular concentrations should be taken into account in further analyses. TAC dosage adjustments can be guided based on PK/PD variability and simulated intracellular concentrations.

Influence of genetic polymorphisms on pharmacokinetics and treatment response of mycophenolic acid: a scoping review

This scoping review explores the impact of genetic polymorphisms on the pharmacokinetics and treatment responses of mycophenolic acid (MPA), an immunosuppressant. The study includes 83 articles from 1226 original studies, focusing on transplantation (n = 80) and autoimmune disorders (n = 3). Genetic variants in uridine 5'-diphospho-glucuronosyltransferase (UGT1A9, UGT1A8 and UGT2B7) and transmembrane transporters (ABCC2, SLCO1B1, SLCO1B3 and ABCB1) significantly affected MPA's pharmacokinetics and susceptibility to its adverse effect. Whereas variants in several genes including UGT1A9, UGT2B7, IMPDH1 and IMPDH2 have been associated with a higher risk of transplant rejection. However, there is a lack of studies on MPA's impact on autoimmune disorders and limited research on the Asian population. The findings underscore the need for further research on MPA's impact across different populations and diseases, particularly among other Asian ethnic groups, to advance personalized medicine in MPA therapy.

Influence of Calcineurin Inhibitors and Genetic Polymorphism of Transporters on Enterohepatic Circulation and Exposure of Mycophenolic Acid in Chinese Adult Renal Allograft Recipients

There is significant enterohepatic circulation (EHC) during the disposition of mycophenolic acid (MPA). The aim of this study was to elucidate factors influencing the EHC of MPA in Chinese adult renal allograft recipients. After 2 weeks of therapy with mycophenolate mofetil or enteric-coated mycophenolate sodium, blood samples were collected from 125 patients at 0 to 12 hours post-administration and MPA concentrations were determined. The influence of calcineurin inhibitors (CNIs) and genetic polymorphisms on MPA exposure and EHC was studied. The Shapley additive explanations method was used to estimate the impact of various factors on the area under the plasma drug concentration-time curve (AUC_0-12h ) for MPA. An extreme gradient boosting (XGboost) machine learning-based model was established to predict AUC_0-12h . Results showed that the dose-normalized AUC_6-12h (dn-AUC_6-12h ) of MPA was significantly lower in patients co-administered with cyclosporine (CsA) than in patients co-administered with tacrolimus (TAC) (P < .05). For patients co-administered with TAC, patients with ABCC2 C-24T CC or SLCO1B1 T521C TT genotypes had significantly higher values of dn-AUC_6-12h (P < .05). Patients with SLCO1B3 334T/699G alleles had significantly lower dn-AUC_6-12h values than homozygotes (P < .05). By introducing body weight, age, and EHC-related factors, including co-administered CNIs and genetic polymorphism of drug transporters, as covariates in the XGboost machine learning model, the prediction performance of AUC_0-12h for MPA in Chinese adult renal allograft recipients can be improved.

SLCO1B3 T334G polymorphisms and mycophenolate mofetil-related adverse reactions in kidney transplant recipients

Background: The correlation between SLCO1B3 T334G polymorphisms and mycophenolate mofetil (MMF) adverse reactions in kidney recipients is unknown. Methods: A single-center, retrospective study was performed in which 111 patients were divided into four groups according to the type of adverse effect experienced. The clinical data and concentrations of MMF at different months after transplantation were statistically analyzed. Results: The G allele in the gastrointestinal reaction group was significantly higher than that in the no adverse effects group (p < 0.05). Logistic regression model showed that the SLCO1B3 T334G genotype was an independent risk factor for gastrointestinal reactions caused by MMF. Conclusion: Patients with the SLCO1B3 T334G GG genotype were more likely to experience gastrointestinal reactions.

Recent lessons learned from population pharmacokinetic studies of mycophenolic acid: physiological, genomic, and drug interactions leading to the prediction of drug effects

INTRODUCTION

Mycophenolic acid (MPA) is a widely used immunosuppressant in transplantation and autoimmune disease. Highly variable pharmacokinetics have been observed with MPA, but the exact mechanisms remain largely unknown.

AREAS COVERED

The current review provided a critical, comprehensive update of recently published population pharmacokinetic/dynamic models of MPA (n=16 papers identified from PubMed and Embase, inclusive from January 2017 to August 2021), with specific emphases on the intrinsic and extrinsic factors influencing the pharmacology of MPA. The significance of the identified covariates, potential mechanisms, and comparisons to historical literature have been provided.

EXPERT OPINION

While select covariates affecting the population pharmacokinetics of MPA are consistently observed and mechanistically supported, some variables have not been regularly reported and/or lacked mechanistic explanation. Very few pharmacodynamic models were available, pointing to the need to extrapolate pharmacokinetic findings. Ideal models of MPA should consist of: i) utilizing optimal sampling points to allow the characterizations of absorption, re-absorption, and elimination phases; ii) characterizing unbound/total MPA, MPA metabolites, plasma/urinary concentrations, and genetic polymorphisms to facilitate mechanistic interpretations; and iii) incorporating actual outcomes and pharmacodynamic data to establish clinical relevance. We anticipate the field will continue to expand in the next 5 to 10 years.

Factors Affecting Time-Varying Clearance of Cyclosporine in Adult Renal Transplant Recipients: A Population Pharmacokinetic Perspective

AIM

The pharmacokinetic (PK) properties of cyclosporine (CsA) in renal transplant recipients are patient- and time-dependent. Knowledge of this time-related variability is necessary to maintain or achieve CsA target exposure. Here, we aimed to identify factors explaining variabilities in CsA PK properties and characterize time-varying clearance (CL/F) by performing a comprehensive analysis of CsA PK factors using population PK (popPK) modeling of long-term follow-up data from our institution.

METHODS

In total, 3674 whole-blood CsA concentrations from 183 patients who underwent initial renal transplantation were analyzed using nonlinear mixed-effects modeling. The effects of potential covariates were selected according to a previous study and well-accepted theoretical mechanisms. Model-informed individualized therapeutic regimens were also evaluated.

RESULTS

A two-compartment model adequately described the data and the estimated mean CsA CL/F was 32.6 L h^-1 (relative standard error: 5%). Allometrically scaled body size, hematocrit (HCT) level, CGC haplotype carrier status, and postoperative time may contribute to CsA PK variability. The CsA bioavailability in patients receiving a prednisolone dose (PD) of 80 mg was 20.6% lower than that in patients receiving 20 mg. A significant decrease (52.6%) in CL/F was observed as the HCT increased from 10.5% to 60.5%. The CL/F of the non-CGC haplotype carrier was 14.4% lower than that of the CGC haplotype carrier at 3 months post operation.

CONCLUSIONS

By monitoring body size, HCT, PD, and CGC haplotype, changes in CsA CL/F over time could be predicted. Such information could be used to optimize CsA therapy. CsA dose adjustments should be considered in different postoperative periods.

SLCO1B3 polymorphisms and clinical outcomes in kidney transplant recipients receiving mycophenolate

Aim: Determine the influence of SLCO1B3 polymorphisms on outcomes in kidney transplant recipients. Materials & methods: We retrospectively evaluated 181 adult kidney transplant recipients receiving mycophenolate. Outcomes included treated biopsy-proven acute rejection (tBPAR), de novo donor-specific antibody (dnDSA) formation, graft survival, patient survival and mycophenolate-related adverse effects among SLCO1B3 genotypes. Results: The presence of SLCO1B3 variants was not associated with increased risk of tBPAR (HR: 1.45, 95% CI: 0.76-2.74), dnDSA (HR: 0.46, 95% CI: 0.16-1.36) or composite of tBPAR or dnDSA (HR: 1.14, 95% CI: 0.64-2.03). Graft and patient survival were reduced among variant carriers; however, inconsistent findings with the primary analysis suggest these associations were not due to genotype. Adverse effects were similar between groups. Conclusion: Presence of SLCO1B3 polymorphisms were not predictive of rejection or dnDSA in kidney transplant recipients.

Effect of UGT polymorphisms on pharmacokinetics and adverse reactions of mycophenolic acid in kidney transplant patients

Mycophenolic acid (MPA) is a common immunosuppressive drug for kidney transplantation patients, and is characterized by a narrow therapeutic index and significant individual variability. UGTs are the main enzymes responsible for the metabolism of MPA. Although, many studies have focused on the relationship between UGT polymorphisms and pharmacokinetics and adverse reactions of MPA, the conclusion are controversial. We reviewed the relevant literature and summarized the significant influences of UGT polymorphisms, such as UGT1A8 (rs1042597, rs17863762), UGT1A9 (rs72551330, rs6714486, rs17868320, rs2741045, rs2741045) and UGT2B7 (rs7438135, rs7439366, rs7662029), on the pharmacokinetics of MPA and its metabolites and adverse reactions. The review provides a reference for guiding the individualized administration of MPA and reducing adverse reactions to MPA.

Genetic polymorphisms in metabolic enzymes and transporters have no impact on mycophenolic acid pharmacokinetics in adult kidney transplant patients co-treated with tacrolimus: A population analysis

WHAT IS KNOWN AND OBJECTIVE

Mycophenolate mofetil, an ester prodrug of mycophenolic acid (MPA), is widely used to prevent graft rejection after kidney transplantation. The pharmacokinetic (PK) of MPA has been extensively studied, which revealed a high degree of variability. An integrated population PK (PopPK) model of MPA and its main metabolite mycophenolic acid glucuronide (MPAG) was developed using the adult patients who underwent kidney transplant and were administered oral mycophenolate mofetil combined with tacrolimus.

METHODS

In total, 917 MPA and 740 MPAG concentrations in191 adult patients were analysed via nonlinear mixed-effects modelling. The concentration-time data were adequately described using a chain compartment model, including central and peripheral compartments for MPA and a central compartment for MPAG. Stepwise forward inclusion and backward elimination procedures were used to investigate the effects of genetic polymorphisms, including in UGT1A8, UGT1A9, UGT2B7, ABCB1, ABCC2, ABCG2, SLCO1B1, SLCO1B3, and HNF1α.

RESULTS AND DISCUSSION

These genetic polymorphisms in metabolic enzymes and transporters have no obvious impact on the PK of MPA in adult patients who underwent kidney transplant and were co-treated with tacrolimus. The post-transplant time, serum albumin, and creatinine clearance were identified as significant covariates affecting the PK of MPA and MPAG, which should be considered in the clinical use of mycophenolate mofetil.

WHAT IS NEW AND CONCLUSION

We established a PopPK model of MPA and MPAG in Chinese adult patients who underwent kidney transplant and were co-treated with tacrolimus. Genetic polymorphisms in metabolic enzymes and transporters showed no obvious impact on MMF PK. A model-informed dosing strategy was proposed by the established model, and MMF dose adjustment should be based on ALB levels and the post-transplantation time.

The Impact of Genetic Polymorphisms on the Pharmacokinetics and Pharmacodynamics of Mycophenolic Acid: Systematic Review and Meta-analysis

BACKGROUND

Mycophenolic acid (MPA) is among the most commonly prescribed medications for immunosuppression following organ transplantation. Highly variable MPA exposure and drug response are observed among individuals receiving the same dosage of the drug. Identification of candidate genes whose polymorphisms could be used to predict MPA exposure and clinical outcome is of clinical value.

OBJECTIVES

This study aimed to determine the impact of genetic polymorphisms on the pharmacokinetics and pharmacodynamics of MPA in humans by means of a systematic review and meta-analysis.

METHODS

A systematic search was conducted on PubMed, EMBASE, Web of Sciences, Scopus, and the Cochrane Library databases. A meta-analysis was conducted to determine any associations between genetic polymorphisms and pharmacokinetic or pharmacodynamic parameters of MPA. Pooled-effect estimates were calculated by means of the random-effects model.

RESULTS

A total of 37 studies involving 3844 individuals were included in the meta-analysis. Heterozygous carriers of the UGT1A9 -275T>A polymorphism were observed to have a significantly lower MPA exposure than wild-type individuals. Four single nucleotide polymorphisms (SNPs), namely UGT1A9 -2152C>T, UGT1A8 518C>G, UGT2B7 211G>T, and SLCO1B1 521T>C, were also significantly associated with altered MPA pharmacokinetics. However, none of the investigated SNPs, including SNPs in the IMPDH gene, were found to be associated with the clinical efficacy of MPA. The only SNP that was associated with adverse outcomes was SLCO1B3 344T>G.

CONCLUSIONS

The present systematic review and meta-analysis identified six SNPs that were significantly associated with pharmacokinetic variability or adverse effects of MPA. Our findings represent the basis for future research and clinical implications with regard to the role of pharmacogenetics in MPA pharmacokinetics and drug response.

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.

ABCB1, ABCG2, ABCC1, ABCC2, and ABCC3 drug transporter polymorphisms and their impact on drug bioavailability: what is our current understanding?

INTRODUCTION

Interindividual differences in drug response are a frequent clinical challenge partly due to variation in pharmacokinetics. ATP-binding cassette (ABC) transporters are crucial determinants of drug disposition. They are subject of gene regulation and drug-interaction; however, it is still under debate to which extend genetic variants in these transporters contribute to interindividual variability of a wide range of drugs.

AREAS COVERED

This review discusses the current literature on the impact of genetic variants in ABCB1, ABCG2 as well as ABCC1, ABCC2, and ABCC3 on pharmacokinetics and drug response. The aim was to evaluate if results from recent studies would increase the evidence for potential clinically relevant pharmacogenetic effects.

EXPERT OPINION

Although enormous efforts have been made to investigate effects of ABC transporter genotypes on drug pharmacokinetics and response, the majority of studies showed only weak if any associations. Despite few unique results, studies mostly failed to confirm earlier findings or still remained inconsistent. The impact of genetic variants on drug bioavailability is only minor and other factors regulating the transporter expression and function seem to be more critical. In our opinion, the findings on the so far investigated genetic variants in ABC efflux transporters are not suitable as predictive biomarkers.

Racial Disparity in Drug Disposition in the Digestive Tract

The major determinants of drug or, al bioavailability are absorption and metabolism in the digestive tract. Genetic variations can cause significant differences in transporter and enzyme protein expression and function. The racial distribution of selected efflux transporter (i.e., Pgp, BCRP, MRP2) and metabolism enzyme (i.e., UGT1A1, UGT1A8) single nucleotide polymorphisms (SNPs) that are highly expressed in the digestive tract are reviewed in this paper with emphasis on the allele frequency and the impact on drug absorption, metabolism, and in vivo drug exposure. Additionally, preclinical and clinical models used to study the impact of transporter/enzyme SNPs on protein expression and function are also reviewed. The results showed that allele frequency of the major drug efflux transporters and the major intestinal metabolic enzymes are highly different in different races, leading to different drug disposition and exposure. The conclusion is that genetic polymorphism is frequently observed in different races and the related protein expression and drug absorption/metabolism function and drug in vivo exposure can be significantly affected, resulting in variations in drug response. Basic research on race-dependent drug absorption/metabolism is expected, and FDA regulations of drug dosing adjustment based on racial disparity are suggested.

Effect of Protein Binding on Exposure of Unbound and Total Mycophenolic Acid: A Population Pharmacokinetic Analysis in Chinese Adult Kidney Transplant Recipients

OBJECTIVES

The population pharmacokinetic (popPK) characteristics of total mycophenolic acid (tMPA) have been investigated in various ethnic populations. However, investigations of popPK of unbound MPA (uMPA) are few. Thus, a popPK analysis was performed to: (1) characterize the PK of uMPA and tMPA and its 7-O-mycophenolic acid glucuronide (MPAG) metabolite in kidney transplant patients cotreated with cyclosporine (CsA), and (2) identify the clinically significant covariates that explain variability in the dose-exposure relationship.

METHODS

A total of 740 uMPA, 741 tMPA, and 734 total MPAG (tMPAG) concentration-time data from 58 Chinese kidney transplant patients receiving MPA in combination with CsA were analyzed using NONMEM® software with the stochastic approximation expectation maximization (SAEM) followed by the important sampling (IMP) method. The influence of covariates was tested using a stepwise procedure.

RESULTS

The PK of uMPA and unbound MPAG (uMPAG) were characterized by a two- and one-compartment model with first-order elimination, respectively. A linear protein binding model was used to link uMPA and tMPA. Apparent clearance (CL/F) and central volume of distribution (VC/F) of uMPA (CLuMPA/F and VCuMPA/F, respectively) and protein binding rate constant (k B) were estimated to be 851 L/h [relative standard error (RSE), 7.1%], 718 L (18.5%) and 53.4/h (2.3%), respectively. For uMPAG, the population values (RSE) of CL/F (CLuMPAG) and VC/F (VCuMPAG/F) were 5.71 L/h (4.4%) and 29.9 L (7.7%), respectively. Between-subject variability (BSVs) on CLuMPA/F, VCuMPA/F, CLuMPAG/F, and VCuMPAG/F were 51.0, 80.0, 31.8 and 48.4%, respectively, whereas residual unexplained variability (RUVs) for uMPA, tMPA, and uMPAG were 47.0, 45.9, and 22.0%, respectively. Significant relationships were found between k B and serum albumin (ALB) and between CLuMPAG/F and glomerular filtration rate (GFR). Additionally, model-based simulation showed that changes in ALB concentrations substantially affected tMPA but not uMPA exposure.

CONCLUSIONS

The established model adequately described the popPK characteristics of the uMPA, tMPA, and MPAG. The estimated CLuMPA/F and unbound fraction of MPA (FUMPA) in Chinese kidney transplant recipients cotreated with CsA were comparable to those published previously in Caucasians. We recommend monitoring uMPA instead of tMPA to optimize mycophenolate mofetil (MMF) dosing for patients with lower ALB levels.

Impact of SLCO1B3 polymorphisms on clinical outcomes in lung allograft recipients receiving mycophenolic acid

Single-nucleotide polymorphisms (SNPs) in genes involved in mycophenolic acid (MPA) metabolism have been shown to contribute to variable MPA exposure, but their clinical effects are unclear. We aimed to determine if SNPs in key genes in MPA metabolism affect outcomes after lung transplantation. We performed a retrospective cohort study of 275 lung transplant recipients, 228 receiving mycophenolic acid and a control group of 47 receiving azathioprine. Six SNPs known to regulate MPA exposure from the SLCO, UGT and MRP2 families were genotyped. Primary outcome was 1-year survival. Secondary outcomes were 3-year survival, nonminimal (≥A2 or B2) acute rejection, and chronic lung allograft dysfunction (CLAD). Statistical analyses included time-to-event Kaplan-Meier with log-rank test and Cox regression modeling. We found that SLCO1B3 SNPs rs4149117 and rs7311358 were associated with decreased 1-year survival [rs7311358 HR 7.76 (1.37-44.04), p = 0.021; rs4149117 HR 7.28 (1.27-41.78), p = 0.026], increased risk for nonminimal acute rejection [rs4149117 TT334/T334G: OR 2.01 (1.06-3.81), p = 0.031; rs7311358 GG699/G699A: OR 2.18 (1.13-4.21) p = 0.019] and lower survival through 3 years for MPA patients but not for azathioprine patients. MPA carriers of either SLCO1B3 SNP had shorter survival after CLAD diagnosis (rs4149117 p = 0.048, rs7311358 p = 0.023). For the MPA patients, Cox regression modeling demonstrated that both SNPs remained independent risk factors for death. We conclude that hypofunctional SNPs in the SLCO1B3 gene are associated with an increased risk for acute rejection and allograft failure in lung transplant recipients treated with MPA.

Impact of UGT2B7 and ABCC2 genetic polymorphisms on mycophenolic acid metabolism in Chinese renal transplant recipients

AIM

To evaluate genetic variants affecting mycophenolic acid (MPA) metabolism in Chinese renal transplant recipients.

METHODS

Total 11 SNPs of UGT1A9, UGT1A8, UGT2B7, ABCC2, ABCG2 and SLCO1B3 were genotyped in 408 Chinese renal transplant recipients. Associations between SNPs and MPA concentration/dose ratio (C₀/D) were analyzed using different genetic models. Multivariate linear regression was used to analyze associations between log (C₀/D) and clinical factors. Results: After adjustment by clinical factors, UGT2B7 rs7662029 was associated with log (C₀/D) using a dominant (p = 0.041) and an additive (p = 0.038) model, ABCC2 rs717620 was associated with log (C₀/D) using a recessive model (p = 0.019). Using additive model, SNP-SNP interactions were identified (p = 0.002) between ABCC2 rs717620 and UGT1A9 rs2741049, with interactions (p = 0.002) between ABCC2 rs717620 and UGT1A8 rs1042597. Age, albumin and serum creatinine were associated with log (C₀/D).

CONCLUSION

rs7662029 and rs717620 may affect MPA pharmacokinetics. SNP-SNP interactions and clinical factors may have significant effects on MPA metabolism.

Polymorphisms of the Multidrug Pump ABCG2: A Systematic Review of Their Effect on Protein Expression, Function, and Drug Pharmacokinetics

The widespread expression and polyspecificity of the multidrug ABCG2 efflux transporter make it an important determinant of the pharmacokinetics of a variety of substrate drugs. Null ABCG2 expression has been linked to the Junior blood group. Polymorphisms affecting the expression or function of ABCG2 may have clinically important roles in drug disposition and efficacy. The most well-studied single nucleotide polymorphism (SNP), Q141K (421C>A), is shown to decrease ABCG2 expression and activity, resulting in increased total drug exposure and decreased resistance to various substrates. The effect of Q141K can be rationalized by inspection of the ABCG2 structure, and the effects of this SNP on protein processing may make it a target for pharmacological intervention. The V12M SNP (34G>A) appears to improve outcomes in cancer patients treated with tyrosine kinase inhibitors, but the reasons for this are yet to be established, and this residue's role in the mechanism of the protein is unexplored by current biochemical and structural approaches. Research into the less-common polymorphisms is confined to in vitro studies, with several polymorphisms shown to decrease resistance to anticancer agents such as SN-38 and mitoxantrone. In this review, we present a systematic analysis of the effects of ABCG2 polymorphisms on ABCG2 function and drug pharmacokinetics. Where possible, we use recent structural advances to present a molecular interpretation of the effects of SNPs and indicate where we need further in vitro experiments to fully resolve how SNPs impact ABCG2 function.

Comparison of Pfannenstiel or Extended Iliac Port Site Kidney Extraction in Laparoscopic Donor Nephrectomy: Do We Have Consensus?

OBJECTIVES

Our objective was to compare the outcomes of the different extraction sites between extended iliac port site incision and Pfannenstiel incision during laparoscopic donor nephrectomy.

MATERIALS AND METHODS

We prospectively evaluated patients who underwent laparoscopic donor nephrectomy from June 2014 to March 2015 at our institution. Perioperative parameters were included, with particular reference to warm ischemic time. The other parameters recorded included operative time, blood loss, hospital stay, analgesic requirement, and cosmetic results.

RESULTS

We analyzed a total of 41 patients. Kidney retrieval site of each patient was made randomly. Extraction sites were done by using extended iliac port site incisions in 23 patients and by Pfannenstiel incision in 18 patients. Mean warm ischemic time was 4.09 minutes with extended iliac port site incision versus 4.94 minutes with Pfannenstiel incision (P = .04). Mean operative time, blood loss, hospital stay, and analgesic requirements were comparable between the 2 groups. Mean cosmetic score was 10.39 with extended iliac port site versus 12.06 with Pfannenstiel incision.

CONCLUSIONS

Extraction with extended iliac port site incision had significantly less warm ischemic time than Pfannenstiel incision in laparoscopic donor nephrectomy. It was also not inferior to Pfannenstiel incision regarding the other.

External evaluation of published population pharmacokinetic models of tacrolimus in adult renal transplant recipients

AIM

Several tacrolimus population pharmacokinetic models in adult renal transplant recipients have been established to facilitate dose individualization. However, their applicability when extrapolated to other clinical centres is not clear. This study aimed to (1) evaluate model external predictability and (2) analyze potential influencing factors.

METHODS

Published models were screened from the literature and were evaluated using an external dataset with 52 patients (609 trough samples) collected by postoperative day 90 via methods that included (1) prediction-based prediction error (PE%), (2) simulation-based prediction- and variability-corrected visual predictive check (pvcVPC) and normalized prediction distribution error (NPDE) tests and (3) Bayesian forecasting to assess the influence of prior observations on model predictability. The factors influencing model predictability, particularly the impact of structural models, were evaluated.

RESULTS

Sixteen published models were evaluated. In prediction-based diagnostics, the PE% within ±30% was less than 50% in all models, indicating unsatisfactory predictability. In simulation-based diagnostics, both the pvcVPC and the NPDE indicated model misspecification. Bayesian forecasting improved model predictability significantly with prior 2-3 observations. The various factors influencing model extrapolation included bioassays, the covariates involved (CYP3A5*3 polymorphism, postoperative time and haematocrit) and whether non-linear kinetics were used.

CONCLUSIONS

The published models were unsatisfactory in prediction- and simulation-based diagnostics, thus inappropriate for direct extrapolation correspondingly. However Bayesian forecasting could improve the predictability considerably with priors. The incorporation of non-linear pharmacokinetics in modelling might be a promising approach to improving model predictability.

The role of glucuronidation in drug resistance

The final therapeutic effect of a drug candidate, which is directed to a specific molecular target strongly depends on its absorption, distribution, metabolism and excretion (ADME). The disruption of at least one element of ADME may result in serious drug resistance. In this work we described the role of one element of this resistance: phase II metabolism with UDP-glucuronosyltransferases (UGTs). UGT function is the transformation of their substrates into more polar metabolites, which are better substrates for the ABC transporters, MDR1, MRP and BCRP, than the native drug. UGT-mediated drug resistance can be associated with (i) inherent overexpression of the enzyme, named intrinsic drug resistance or (ii) induced expression of the enzyme, named acquired drug resistance observed when enzyme expression is induced by the drug or other factors, as food-derived compounds. Very often this induction occurs via ligand binding receptors including AhR (aryl hydrocarbon receptor) PXR (pregnane X receptor), or other transcription factors. The effect of UGT dependent resistance is strengthened by coordinate action and also a coordinate regulation of the expression of UGTs and ABC transporters. This coupling of UGT and multidrug resistance proteins has been intensively studied, particularly in the case of antitumor treatment, when this resistance is "improved" by differences in UGT expression between tumor and healthy tissue. Multidrug resistance coordinated with glucuronidation has also been described here for drugs used in the management of epilepsy, psychiatric diseases, HIV infections, hypertension and hypercholesterolemia. Proposals to reverse UGT-mediated drug resistance should consider the endogenous functions of UGT.

Associations of UDP-glucuronosyltransferases polymorphisms with mycophenolate mofetil pharmacokinetics in Chinese renal transplant patients

AIM

To evaluate the effects of UDP-glucuronosyltransferases (UGTs) polymorphisms on the pharmacokinetics of the immunosuppressant mycophenolate mofetil (MMF) in Chinese renal transplant recipients.

METHODS

A total of 127 renal transplant patients receiving MMF were genotyped for polymorphisms in UGT1A9 -1818T>C, I399C>T, -118T9/10, -440C>T, -331T>C, UGT2B7 IVS1+985A>G, 211G>T, -900A>G, UGT1A8 518C>G and UGT1A7 622T>C. The plasma concentrations of the MMF active moiety mycophenolic acid (MPA) and main metabolite 7-O-MPA-glucuronide (MPAG) were analyzed using HPLC. Univariate and multivariate analyses were used to assess the effects of UGT-related gene polymorphisms on MPA pharmacokinetics.

RESULTS

The dose-adjusted MPA AUC0-12 h of the patients with the UGT2B7 IVS1+985AG genotype was 48% higher than that of the patients with the IVS1+985AA genotype, which could explain 11.2% of the inter-individual variation in MPA pharmacokinetics. The dose-adjusted MPAG AUC0-12 h of the patients with the UGT1A7 622CC and UGT1A9 -440CT/-331TC genotypes, respectively, was significantly higher than that of the patients with 622T homozygotes and -440C/-331T homozygotes. Furthermore, the genotypes UGT1A9 -1818T>C and UGT1A8 518C>G were associated with a low dose-adjusted MPAG AUC0-12 h.

CONCLUSION

The UGT2B7 11+985A>G genotype is associated with the pharmacokinetics of MPA in Chinese renal transplant patients, which demonstrates the usefulness of this SNP for individualizing MMF dosing.

Genotype and allele frequencies of drug-metabolizing enzymes and drug transporter genes affecting immunosuppressants in the Spanish white population

Interpatient variability in drug response can be widely explained by genetically determined differences in metabolizing enzymes, drug transporters, and drug targets, leading to different pharmacokinetic and/or pharmacodynamic behaviors of drugs. Genetic variations affect or do not affect drug responses depending on their influence on protein activity and the relevance of such proteins in the pathway of the drug. Also, the frequency of such genetic variations differs among populations, so the clinical relevance of a specific variation is not the same in all of them. In this study, a panel of 33 single nucleotide polymorphisms in 14 different genes (ABCB1, ABCC2, ABCG2, CYP2B6, CYP2C19, CYP2C9, CYP3A4, CYP3A5, MTHFR, NOD2/CARD15, SLCO1A2, SLCO1B1, TPMT, and UGT1A9), encoding for the most relevant metabolizing enzymes and drug transporters relating to immunosuppressant agents, was analyzed to determine the genotype profile and allele frequencies in comparison with HapMap data. A total of 570 Spanish white recipients and donors of solid organ transplants were included. In 24 single nucleotide polymorphisms, statistically significant differences in allele frequency were observed. The largest differences (>100%) occurred in ABCB1 rs2229109, ABCG2 rs2231137, CYP3A5 rs776746, NOD2/CARD15 rs2066844, TPMT rs1800462, and UGT1A9 rs72551330. In conclusion, differences were recorded between the Spanish and other white populations in terms of allele frequency and genotypic distribution. Such differences may have implications in relation to dose requirements and drug-induced toxicity. These data are important for further research to help explain interindividual pharmacokinetic and pharmacodynamic variability in response to drug therapy.

How accurate and precise are limited sampling strategies in estimating exposure to mycophenolic acid in people with autoimmune disease?

Mycophenolic acid (MPA) is a potent immunosuppressant agent, which is increasingly being used in the treatment of patients with various autoimmune diseases. Dosing to achieve a specific target MPA area under the concentration-time curve from 0 to 12 h post-dose (AUC12) is likely to lead to better treatment outcomes in patients with autoimmune disease than a standard fixed-dose strategy. This review summarizes the available published data around concentration monitoring strategies for MPA in patients with autoimmune disease and examines the accuracy and precision of methods reported to date using limited concentration-time points to estimate MPA AUC12. A total of 13 studies were identified that assessed the correlation between single time points and MPA AUC12 and/or examined the predictive performance of limited sampling strategies in estimating MPA AUC12. The majority of studies investigated mycophenolate mofetil (MMF) rather than the enteric-coated mycophenolate sodium (EC-MPS) formulation of MPA. Correlations between MPA trough concentrations and MPA AUC12 estimated by full concentration-time profiling ranged from 0.13 to 0.94 across ten studies, with the highest associations (r (2) = 0.90-0.94) observed in lupus nephritis patients. Correlations were generally higher in autoimmune disease patients compared with renal allograft recipients and higher after MMF compared with EC-MPS intake. Four studies investigated use of a limited sampling strategy to predict MPA AUC12 determined by full concentration-time profiling. Three studies used a limited sampling strategy consisting of a maximum combination of three sampling time points with the latest sample drawn 3-6 h after MMF intake, whereas the remaining study tested all combinations of sampling times. MPA AUC12 was best predicted when three samples were taken at pre-dose and at 1 and 3 h post-dose with a mean bias and imprecision of 0.8 and 22.6 % for multiple linear regression analysis and of -5.5 and 23.0 % for maximum a posteriori (MAP) Bayesian analysis. Although mean bias was less when data were analysed using multiple linear regression, MAP Bayesian analysis is preferable because of its flexibility with respect to sample timing. Estimation of MPA AUC12 following EC-MPS administration using a limited sampling strategy with samples drawn within 3 h post-dose resulted in biased and imprecise results, likely due to a longer time to reach a peak MPA concentration (t max) with this formulation and more variable pharmacokinetic profiles. Inclusion of later sampling time points that capture enterohepatic recirculation and t max improved the predictive performance of strategies to predict EC-MPS exposure. Given the considerable pharmacokinetic variability associated with mycophenolate therapy, limited sampling strategies may potentially help in individualizing patient dosing. However, a compromise needs to be made between the predictive performance of the strategy and its clinical feasibility. An opportunity exists to combine research efforts globally to create an open-source database for MPA (AUC, concentrations and outcomes) that can be used and prospectively evaluated for AUC target-controlled dosing of MPA in autoimmune diseases.

Population pharmacokinetics of mycophenolic acid and its main glucuronide metabolite: a comparison between healthy Chinese and Caucasian subjects receiving mycophenolate mofetil

PURPOSE

Mycophenolate mofetil (MMF), a prodrug of the immunosuppressive agent mycophenolic acid (MPA), is widely used for prophylaxis of solid organ transplant rejection. MPA is primarily metabolized to 7-O-mycophenolic acid glucuronide (MPAG), an inactive metabolite that undergoes enterohepatic recirculation (EHC). This study assessed ethnic differences in the pharmacokinetics (PK) of MPA and MPAG between healthy Chinese and Caucasian subjects using population PK analysis.

METHODS

Data were pooled from 132 healthy subjects (80 Chinese, 52 Caucasians) in eight clinical studies in which MMF was administered in a single oral dose. Population PK analysis was performed using NONMEM®.

RESULTS

The PK of MPA and MPAG were best described by a five-chain compartment model, including a gallbladder compartment for EHC and a transit absorption model. Ethnicity was significantly correlated with the apparent clearance (CL/F) and volume of distribution (V/F) of MPAG but not those of MPA. Weight was identified as a covariate and was correlated with the PK of MPA and MPAG. MPA CL/F was 11.5 L/h for a 70-kg healthy subject, and the MPAG CL/F values were 1.36 and 1.90 L/h for 70-kg Chinese and Caucasian individuals, respectively. Internal and external evaluation indicated model validity.

CONCLUSIONS

This is the first population PK analysis to evaluate ethnic differences in the PK of MPA and MPAG in healthy Chinese and Caucasian subjects. No differences were observed in the PK of MPA between healthy Chinese and Caucasian subjects. Although, the MPAG CL/F was approximately 40 % higher in Caucasians, this finding may not be clinically relevant.

Relevance of UDP-glucuronosyltransferase polymorphisms for drug dosing: A quantitative systematic review

UDP-glucuronosyltransferases (UGT) catalyze the biotransformation of many endobiotics and xenobiotics, and are coded by polymorphic genes. However, knowledge about the effects of these polymorphisms is rarely used for the individualization of drug therapy. Here, we present a quantitative systematic review of clinical studies on the impact of UGT variants on drug metabolism to clarify the potential for genotype-adjusted therapy recommendations. Data on UGT polymorphisms and dose-related pharmacokinetic parameters in man were retrieved by a systematic search in public databases. Mean estimates of pharmacokinetic parameters were extracted for each group of carriers of UGT variants to assess their effect size. Pooled estimates and relative confidence bounds were computed with a random-effects meta-analytic approach whenever multiple studies on the same variant, ethnic group, and substrate were available. Information was retrieved on 30 polymorphic metabolic pathways involving 10 UGT enzymes. For irinotecan and mycophenolic acid a wealth of data was available for assessing the impact of genetic polymorphisms on pharmacokinetics under different dosages, between ethnicities, under comedication, and under toxicity. Evidence for effects of potential clinical relevance exists for 19 drugs, but the data are not sufficient to assess effect size with the precision required to issue dose recommendations. In conclusion, compared to other drug metabolizing enzymes much less systematic research has been conducted on the polymorphisms of UGT enzymes. However, there is evidence of the existence of large monogenetic functional polymorphisms affecting pharmacokinetics and suggesting a potential use of UGT polymorphisms for the individualization of drug therapy.

Association of CYP2C9*2 with bosentan-induced liver injury

Bosentan (Tracleer) is an endothelin receptor antagonist prescribed for the treatment of pulmonary arterial hypertension (PAH). Its use is limited by drug-induced liver injury (DILI). To identify genetic markers of DILI, association analyses were performed on 56 Caucasian PAH patients receiving bosentan. Twelve functional polymorphisms in five genes (ABCB11, ABCC2, CYP2C9, SLCO1B1, and SLCO1B3) implicated in bosentan pharmacokinetics were tested for associations with alanine aminotransferase (ALT), aspartate aminotransferase (AST), and DILI. After adjusting for body mass index, CYP2C9*2 was the only polymorphism associated with ALT, AST, and DILI (β = 2.16, P = 0.024; β = 1.92, P = 0.016; odds ratio 95% CI = 2.29-∞, P = 0.003, respectively). Bosentan metabolism by CYP2C9*2 in vitro was significantly reduced compared with CYP2C9*1 and was comparable to that by CYP2C9*3. These results suggest that CYP2C9*2 is a potential genetic marker for prediction of bosentan-induced liver injury and warrants investigation for the optimization of bosentan treatment.

Establishment of recombinant lentiviral vector with ABCG2 overexpression and effects of the recombinant on human breast cancer MCF-7 cells' biological characteristics

Aim of the study

ATP-binding cassette super family G2 (ABCG2) is recognized as the key point of the cancer cells’ resistance to chemotherapy drugs. But there have been rare reports about the relationship between ABCG2 and the invasion, migration and animal tumor formation abilities of cancer cells. We want to establish a recombinant lentiviral vector with ABCG2 overexpression, and study the vector's effect on human breast cancer MCF-7 cells’ biological abilities above to improve our understanding about ABCG2.

Material and methods

The recombinant lentiviral vector with ABCG2 overexpression was transfected into human breast cancer MCF-7 cells. The cells’ abilities of migration and invasion were tested by wound healing assay, and transwell invasive assay. The MCF-7 cells infected were injected in the left back of the nude mice. In the meantime the MCF-7 cells without anything were injected in the right back of same nude mice as the control group. Western blotting was used to detect the expression of ABCG2 in MCF-7 cells infected, the transplantation tumor tissue and the control group MCF-7 cells.

Results

The recombinant lentiviral vector with ABCG2 overexpression infected human breast cancer MCF-7 cells successfully, and the transfection efficiency was 95.4 ±2.8%. The wound line of MCF-7 cells infected healed after 48 hours, but the line of control group MCF-7 cells still existed. The number of the cells going through the membrane in infected MCF-7 cells was 78.34 ±0.25, and the number in control group MCF-7 cells was 15.28 ±0.12, p < 0.05. A much bigger transplantation tumor appeared in the MCF-7 cell infected nude mice. The expression of ABCG2 in infected MCF-7 cells and the transplantation tumor tissue was significantly higher than that in control group MCF-7 cells, p < 0.05.

Conclusions

We obtained ABCG2 overexpression in human breast cancer MCF-7 cells which showed the increasing migration, invasion and animal tumor formation abilities. Therefore, the results revealed that there might be a relationship between overexpression of ABCG2 and MCF-7 cells with increasing invasion, migration and animal tumor abilities.