ABCB1 1199G>A genetic polymorphism (Rs2229109) influences the intracellular accumulation of tacrolimus in HEK293 and K562 recombinant cell lines

Impact of CYP3A4 and ABCB1 genetic variants on tacrolimus dosing in Greek kidney transplant recipients

Background

Tacrolimus, an approved first-line calcineurin inhibitor, is widely prescribed in organ transplantation to prevent allograft rejection. Its narrow therapeutic index requires precise management to achieve optimal dosing and to minimize adverse drug events (ADEs) while ensuring its therapeutic efficacy. Among several factors, genetic differences contribute significantly to the inter-individual and inter-ethnic variability in pharmacokinetics (PK) of tacrolimus in kidney transplant recipients. As a result, investigating the role of genetic variation in Greek transplant recipients becomes crucial to optimizing therapeutic strategies and enhancing the efficacy of immunosuppressive treatment.

Hypothesis

Genetic variants which are known to influence the activity of enzymes or drug-transporters critical to tacrolimus pharmacokinetics, may significantly affect the required kidney post-transplant tacrolimus daily dose.

Aim

To assess the correlation of ABCB1 genetic variants (rs1128503, rs2229109) and CYP3A4 (rs2242480, rs4986910) with tacrolimus dose-adjusted trough concentration (C0/D), in Greek kidney transplant recipients.

Methods

Ninety-four unrelated Greek kidney transplant recipients were included in this study from the Department of Nephrology and Kidney Transplantation of the University General Hospital of Patras. Patients' dose-adjusted trough levels were measured at five distinct time points after transplantation and analyzed in relation to the possible influence of CYP3A4 and correlated with the abovementioned ABCB1 genetic variants using standard genotyping analysis and Sanger sequencing.

Results

The genetic variants rs1128503, rs2229109, rs2242480, rs4986910 did not show any significant association with the daily dosing requirements of tacrolimus for at least 1 year, in Greek patients who have undergone kidney transplant.

Conclusion

It remains uncertain whether these genetic variants influence the assessment of the appropriate tacrolimus dosing 1 year after transplantation in Greek kidney transplant recipients.

In vitro assessment of ATP-binding cassette transporters and their functional genetic polymorphisms on fluoroquinolone accumulation in human embryonic kidney 293 recombinant cell lines

Fluoroquinolone tissue distribution and cellular accumulation are hindered by efflux transporters, including ATP-binding cassette subfamily B member 1 (ABCB1), ATP-binding cassette subfamily G member 2 (ABCG2), and ATP-binding cassette subfamily C member 4 (ABCC4). Genetic polymorphisms (single-nucleotide polymorphisms) can impact transporter activity, leading to interindividual variability in the systemic and cellular pharmacokinetics of their substrates. This study assesses the impact of these transporters on moxifloxacin and ciprofloxacin (CIP) cellular accumulation in vitro, and the effect of common single-nucleotide polymorphisms in ABCB1 [c.1199G>A (rs2229109); common haplotype c.1236C>T (rs1128503), c.2677G>T/A (rs2032582), and c.3435C>T (rs1045642)] and ABCG2 [c.421C>A (rs2231142)]. Recombinant human embryonic kidney (HEK) cell lines overexpressing wild-type or variant transporters were generated via stable plasmid transfection. The impact of transporter overexpression on fluoroquinolone cell disposition was assessed through accumulation experiments in the presence of specific inhibitors to establish the link between transporter expression and differential accumulation. Results indicated that ABCB1 overexpression reduced moxifloxacin cellular concentration by 30% but inconsistently with that of CIP and that zosuquidar or elacridar reversed these effects. ABCG2 had no impact. ABCC4 markedly reduced CIP accumulation by 25%, even at the basal level, an effect reversed by MK517. Contrarily to the wild-type and the c.1199A carriers, ABCB1 CGT and TTT variants did not reduce antibiotic accumulation. In conclusion, moxifloxacin and CIP are substrates of the wild-type and 1199G>A ABCB1, while CGT and TTT haplotypes had a marginal impact on fluoroquinolone transport by ABCB1. CIP is a preferential ABCC4 substrate. Because of the large body distribution of these transporters, our findings may help rationalize their role and the impact of their polymorphisms in fluoroquinolone disposition in tissues and cells. SIGNIFICANCE STATEMENT: This study demonstrates that moxifloxacin and ciprofloxacin are substrates of ABCB1, with ciprofloxacin also transported by ABCC4. Specific ABCB1 polymorphisms (CGT and TTT haplotypes) reduce the ABCB1 transport capacity toward fluoroquinolones. These findings highlight the importance of considering ABCB1 and ABCC4 inducers or inhibitors, which may affect fluoroquinolone disposition in tissues and cells, as well as ABCB1 polymorphisms that could explain interindividual variability in pharmacokinetic profiles.

Whole-Exome Sequencing Followed by dPCR-Based Personalized Genetic Approach in Solid Organ Transplantation: A Study Protocol and Preliminary Results

Genetic profiling and molecular biology methods have made it possible to study the etiology of the end-stage organ disease that led to transplantation, the genetic factors of compatibility and tolerance of the transplant, and the pharmacogenetics of immunosuppressive drugs and allowed for the development of monitoring methods for the early assessment of allograft rejection. This study aims to report the design and baseline characteristics of an integrated personalized genetic approach in solid organ transplantation, including whole-exome sequencing (WES) and the monitoring of dd-cfDNA by dPCR. Preliminary results reported female recipients with male donors undergoing two pediatric and five adult kidney and three heart transplantations. WES revealed a pathogenic mutation in RBM20 and VUS in TTN and PKP2 in heart recipients, while kidney donors presented mutations in UMOD and APOL1 associated with autosomal-dominant kidney diseases, highlighting the risks requiring the long-term monitoring of recipients, donors, and their family members. %dd-cfDNA levels were generally stable but elevated in cadaveric kidney recipient and one pediatric patient with infectious complications and genetic variants in the ABCB1 and ABCC2 genes. These findings highlight the potential of combining genetic and molecular biomarker-based approaches to improve donor-recipient matching, predict complications, and personalize post-transplant care, paving the way for precision medicine in transplantation.

Population pharmacokinetics of tacrolimus whole blood and peripheral blood mononuclear cell concentrations in stable kidney-transplanted patients

AIM

Therapeutic drug monitoring of tacrolimus based on whole blood drug concentrations is routinely performed. The concentration of tacrolimus in peripheral blood mononuclear cells (PMBCs) is likely to better reflect drug exposure at the treatment target site. We aimed to describe the relationship between tacrolimus whole blood and PBMC concentrations, and the influence of patient characteristics on this relationship by developing a population pharmacokinetic model.

METHODS

We prospectively enrolled 63 stable adult kidney-transplanted patients and collected dense (12-h, n = 18) or sparse (4-h, n = 45) pharmacokinetic profiles of tacrolimus. PBMCs were isolated from whole blood (Ficoll density gradient centrifugation), and drug concentrations in whole blood and PBMCs were analysed using liquid chromatography-mass spectrometry. Patient genotype (CYP3A4/5, ABCB1, NR1I2) was assessed with PCR. Population pharmacokinetic modelling and statistical evaluation was performed using NONMEM.

RESULTS

Tacrolimus whole blood concentrations were well described using a two-compartment pharmacokinetic model with a lag-time and first-order absorption and elimination. Tacrolimus PBMC concentrations were best estimated from whole blood concentrations with the use of a scaling factor, the ratio of whole blood to PBMC concentrations (RC:PBMC), which was the extent of tacrolimus distribution into PBMC. CYP3A5*1 non-expressors and NR1I2-25 385T allele expressors demonstrated higher RC:PBMC ratios of 42.4% and 60.7%, respectively.

CONCLUSION

Tacrolimus PBMC concentration could not be accurately predicted from whole blood concentrations and covariates because of significant residual unexplained variability in the distribution of tacrolimus into PBMCs and may need to be measured directly if required for future studies.

Effect of ABCB1 most frequent polymorphisms on the accumulation of bictegravir in recombinant HEK293 cell lines

Bictegravir, a key second-generation integrase strand transfer inhibitor in the treatment of HIV, is subject to active efflux transport mediated by ABCB1 (P-glycoprotein). Several coding variants of ABCB1 have been described and associated with variable effects on substrate drugs pharmacokinetics. Here, we investigated the effect of the four most common coding ABCB1 single nucleotide polymorphisms (i.e., c.1199G > A, c.1236C > T, c.2677G > T and c.3435C > T) on the intracellular accumulation of bictegravir. Using a previously validated HEK293 recombinant cell line model, we found decreased bictegravir intracellular concentrations in cell lines overexpressing ABCB1 as compared to control cell lines, in line with the known role of ABCB1 in bictegravir transport. However, we were unable to demonstrate any significant difference in bictegravir intracellular accumulation when comparing HEK293 cells overexpressing the wild type (1236C-2677G-3435C, 1199G) or the variant (1236C-2677G-3435T, 1236T-2677T-3435T or 1199A) proteins. These findings suggest that the ABCB1 c.1199G > A and c.1236C > T-c.2677G > T-c.3435C > T variants have no or at least limited impact on the active transport of bictegravir by ABCB1.

In vitro assessment of the risk of ABCB1-mediated drug-drug interaction between rivaroxaban and tacrolimus in human embryonic kidney 293 recombinant cell lines

Background

In lung transplant patients, direct oral anticoagulants are often taken in combination with immunosuppressive drugs such as tacrolimus. Since tacrolimus is a substrate and inhibitor of the efflux protein ABCB1, also transporting direct oral anticoagulants, a possible drug-drug interaction mediated by competition for this transporter needs to be investigated.

Objectives

To determine the in vitro effect of tacrolimus on ABCB1-mediated rivaroxaban transport in order to support clinician practice.

Methods

Recombinant cell line models, based on human embryonic kidney 293 cells, were generated by a stable transfection process to overexpress ABCB1 or not (control cells). The impact of tacrolimus on ABCB1-mediated rivaroxaban transport was assessed by accumulation experiments.

Results

ABCB1 expression decreased the cellular accumulation of rivaroxaban and tacrolimus at their respective clinically relevant concentrations when compared with control cells. This confirms the involvement of ABCB1 in the active transport of tacrolimus and rivaroxaban. However, tacrolimus had no significant influence on rivaroxaban disposition at those clinically relevant concentrations.

Conclusion

Our study does not provide evidence for a possible interaction between tacrolimus and rivaroxaban when used together in practice.

A review of fetal cell lines used during drug development: Focus on COVID-19 vaccines, transplant medications, and biologics

PURPOSE

The recent coronavirus disease 2019 (COVID-19) pandemic and vaccine mandates have increased the number of patient questions related to how fetal cell lines are used during drug development and final manufacturing. This article describes our literature search and review of COVID-19 vaccines, transplant medications, and biologics whose development included use of fetal cell lines.

SUMMARY

A detailed literature search was conducted to identify the common fetal cell lines used in COVID-19 vaccine development; the two most prevalent fetal cell lines identified were HEK-293 and PER.C6. Subsequent literatures searches were conducted to identify transplant medications and biologics whose development included use of the HEK-293 or PER.C6 cell lines. For the COVID-19 vaccines, only the viral vector vaccine by Janssen was found to contain proteins produced by PER.C6 in the final preparation administered to patients, and Novavax is the only vaccine for which fetal cell lines were not directly involved in any portion of drug development. For transplant medications, many medications were studied in fetal cell lines in postmarketing studies after Food and Drug Administration approval; however, none of these medications contained fetal cells or would expose a patient to a fetal cell line. Many new biologics and cellular therapies for genetic diseases and malignancies have been directly developed from HEK-293 fetal cells or contain proteins produced directly from fetal cell lines.

CONCLUSION

There were very few drugs reviewed that were found to contain HEK-293 or PER.C6 fetal cells or proteins derived directly from fetal cell lines; however, use of fetal cell lines in biologics and gene therapies will continue to increase. Healthcare providers should be mindful of patients' beliefs while also correcting common misconceptions about how these fetal cell lines are used throughout drug development and manufacturing.

Gut microbiome modulates tacrolimus pharmacokinetics through the transcriptional regulation of ABCB1

BACKGROUND

Following solid organ transplantation, tacrolimus (TAC) is an essential drug in the immunosuppressive strategy. Its use constitutes a challenge due to its narrow therapeutic index and its high inter- and intra-pharmacokinetic (PK) variability. As the contribution of the gut microbiota to drug metabolism is now emerging, it might be explored as one of the factors explaining TAC PK variability. Herein, we explored the consequences of TAC administration on the gut microbiota composition. Reciprocally, we studied the contribution of the gut microbiota to TAC PK, using a combination of in vivo and in vitro models.

RESULTS

TAC oral administration in mice resulted in compositional alterations of the gut microbiota, namely lower evenness and disturbance in the relative abundance of specific bacterial taxa. Compared to controls, mice with a lower intestinal microbial load due to antibiotics administration exhibit a 33% reduction in TAC whole blood exposure and a lower inter-individual variability. This reduction in TAC levels was strongly correlated with higher expression of the efflux transporter ABCB1 (also known as the p-glycoprotein (P-gp) or the multidrug resistance protein 1 (MDR1)) in the small intestine. Conventionalization of germ-free mice confirmed the ability of the gut microbiota to downregulate ABCB1 expression in a site-specific fashion. The functional inhibition of ABCB1 in vivo by zosuquidar formally established the implication of this efflux transporter in the modulation of TAC PK by the gut microbiota. Furthermore, we showed that polar bacterial metabolites could recapitulate the transcriptional regulation of ABCB1 by the gut microbiota, without affecting its functionality. Finally, whole transcriptome analyses pinpointed, among others, the Constitutive Androstane Receptor (CAR) as a transcription factor likely to mediate the impact of the gut microbiota on ABCB1 transcriptional regulation.

CONCLUSIONS

We highlight for the first time how the modulation of ABCB1 expression by bacterial metabolites results in changes in TAC PK, affecting not only blood levels but also the inter-individual variability. More broadly, considering the high number of drugs with unexplained PK variability transported by ABCB1, our work is of clinical importance and paves the way for incorporating the gut microbiota in prediction algorithms for dosage of such drugs. Video Abstract.

Insights into the Pharmacogenetics of Tacrolimus Pharmacokinetics and Pharmacodynamics

The influence of pharmacogenetics in tacrolimus pharmacokinetics and pharmacodynamics needs further investigation, considering its potential in assisting clinicians to predict the optimal starting dosage and the need for a personalized adjustment of the dose, as well as to identify patients at a high risk of rejection, drug-related adverse effects, or poor outcomes. In the past decade, new pharmacokinetic strategies have been developed to improve personalized tacrolimus treatment. Several studies have shown that patients with tacrolimus doses C0/D < 1 ng/mL/mg may demonstrate a greater incidence of drug-related adverse events and infections. In addition, C0 tacrolimus intrapatient variability (IPV) has been identified as a potential biomarker to predict poor outcomes related to drug over- and under-exposure. With regard to tacrolimus pharmacodynamics, inconsistent genotype-phenotype relationships have been identified. The aim of this review is to provide a concise summary of currently available data regarding the influence of pharmacogenetics on the clinical outcome of patients with high intrapatient variability and/or a fast metabolizer phenotype. Moreover, the role of membrane transporters in the interindividual variability of responses to tacrolimus is critically discussed from a transporter scientist’s perspective. Indeed, the relationship between transporter polymorphisms and intracellular tacrolimus concentrations will help to elucidate the interplay between the biological mechanisms underlying genetic variations impacting drug concentrations and clinical effects.

Monitoring intracellular tacrolimus concentrations and its relationship with rejection in the early phase after renal transplantation

INTRODUCTION

After kidney transplantation, rejection and drug-related toxicity occur despite tacrolimus whole-blood pre-dose concentrations ([Tac]_blood) being within the target range. The tacrolimus concentration within peripheral blood mononuclear cells ([Tac]_cells) might correlate better with clinical outcomes. The aim of this study was to investigate the correlation between [Tac]_blood and [Tac]_cells, the evolution of [Tac]_cells and the [Tac]_cells/[Tac]_blood ratio, and to assess the relationship between tacrolimus concentrations and the occurrence of rejection.

METHODS

In this prospective study, samples for the measurement of [Tac]_blood and [Tac]_cells were collected on days 3 and 10 after kidney transplantation, and on the morning of a for-cause kidney transplant biopsy. Biopsies were reviewed according to the Banff 2019 update.

RESULTS

Eighty-three [Tac]_cells samples were measured of 44 kidney transplant recipients. The correlation between [Tac]_cells and [Tac]_blood was poor (Pearson's r = 0.56 (day 3); r = 0.20 (day 10)). Both the dose-corrected [Tac]_cells and the [Tac]_cells/[Tac]_blood ratio were not significantly different between days 3 and 10, and the median inter-occasion variability of the dose-corrected [Tac]_cells and the [Tac]_cells/[Tac]_blood ratio were 19.4% and 23.4%, respectively (n = 24). Neither [Tac]_cells, [Tac]_blood, nor the [Tac]_cells/[Tac]_blood ratio were significantly different between patients with biopsy-proven acute rejection (n = 4) and patients with acute tubular necrosis (n = 4) or a cancelled biopsy (n = 9; p > 0.05).

CONCLUSION

Tacrolimus exposure and distribution appeared stable in the early phase after transplantation. [Tac]_cells was not significantly associated with the occurrence of rejection. A possible explanation for these results might be related to the low number of patients included in this study and also due to the fact that PBMCs are not a specific enough matrix to monitor tacrolimus concentrations.

Monitoring Intra-cellular Tacrolimus Concentrations in Solid Organ Transplantation: Use of Peripheral Blood Mononuclear Cells and Graft Biopsy Tissue

Tacrolimus is an essential immunosuppressant for the prevention of rejection in solid organ transplantation. Its low therapeutic index and high pharmacokinetic variability necessitates therapeutic drug monitoring (TDM) to individualise dose. However, rejection and toxicity still occur in transplant recipients with blood tacrolimus trough concentrations (C₀) within the target ranges. Peripheral blood mononuclear cells (PBMC) have been investigated as surrogates for tacrolimus's site of action (lymphocytes) and measuring allograft tacrolimus concentrations has also been explored for predicting rejection or nephrotoxicity. There are relatively weak correlations between blood and PBMC or graft tacrolimus concentrations. Haematocrit is the only consistent significant (albeit weak) determinant of tacrolimus distribution between blood and PBMC in both liver and renal transplant recipients. In contrast, the role of ABCB1 pharmacogenetics is contradictory. With respect to distribution into allograft tissue, studies report no, or poor, correlations between blood and graft tacrolimus concentrations. Two studies observed no effect of donor ABCB1 or CYP3A5 pharmacogenetics on the relationship between blood and renal graft tacrolimus concentrations and only one group has reported an association between donor ABCB1 polymorphisms and hepatic graft tacrolimus concentrations. Several studies describe significant correlations between in vivo PBMC tacrolimus concentrations and ex vivo T-cell activation or calcineurin activity. Older studies provide evidence of a strong predictive value of PBMC C₀ and allograft tacrolimus C₀ (but not blood C₀) with respect to rejection in liver transplant recipients administered tacrolimus with/without a steroid. However, these results have not been independently replicated in liver or other transplants using current triple maintenance immunosuppression. Only one study has reported a possible association between renal graft tacrolimus concentrations and acute tacrolimus nephrotoxicity. Thus, well-designed and powered prospective clinical studies are still required to determine whether measuring tacrolimus PBMC or graft concentrations offers a significant benefit compared to current TDM.

Effect of four ABCB1 genetic polymorphisms on the accumulation of darunavir in HEK293 recombinant cell lines

The intracellular penetration of darunavir, a second-generation HIV protease inhibitor, is limited by the activity of the efflux P-glycoprotein (ABCB1). ABCB1 expression and/or activity levels can vary between individuals due to genetic polymorphisms including the c.1199G>A, c.1236C>T, c.2677G>T and c.3435C>T variants, which could in part explain why the pharmacokinetics of darunavir are so variable from one individual to another. While a few clinical studies have failed to demonstrate an influence of these polymorphisms on darunavir pharmacokinetics, drug-drug interactions and methodological limitations may have prevented them from revealing the true influence of ABCB1 variants. In this work, we report on the intracellular accumulation of darunavir in recombinant HEK293 cell lines expressing wild-type ABCB1 or one of several variants: ABCB1 1199A, ABCB1 3435T, and ABCB1 1236T/2677T/3435T. We demonstrate that while ABCB1 expression limits intracellular accumulation of darunavir, there is no significant difference in efflux activity between cells expressing wild-type ABCB1 and those that express any of the studied variants.

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.

Pharmacogenomics with red cells: a model to study protein variants of drug transporter genes

The PharmacoScan pharmacogenomics platform screens for variation in genes that affect drug absorption, distribution, metabolism, elimination, immune adverse reactions and targets. Among the 1,191 genes tested on the platform, 12 genes are expressed in the red cell membrane: ABCC1, ABCC4, ABCC5, ABCG2, CFTR, SLC16A1, SLC19A1, SLC29A1, ATP7A, CYP4F3, EPHX1 and FLOT1. These genes represent 5 ATP-binding cassette proteins, 3 solute carrier proteins, 1 ATP transport protein and 3 genes associated with drug metabolism and adverse drug reactions. Only ABCG2 and SLC29A1 encode blood group systems, JR and AUG, respectively. We propose red cells as an ex vivo model system to study the effect of heritable variants in genes encoding the transport proteins on the pharmacokinetics of drugs. Altered pharmacodynamics in red cells could also cause adverse reactions, such as haemolysis, hitherto unexplained by other mechanisms.

Monitoring the tacrolimus concentration in peripheral blood mononuclear cells of kidney transplant recipients

Aims

Tacrolimus is a critical dose drug and to avoid under‐ and overexposure, therapeutic drug monitoring is standard practice. However, rejection and drug‐related toxicity occur despite whole‐blood tacrolimus pre‐dose concentrations ([Tac]_blood) being on target. Monitoring tacrolimus concentrations at the target site (within peripheral blood mononuclear cells; [Tac]_cells) may better correlate with drug‐efficacy. The aim of this study was to (1) investigate the relationship between [Tac]_blood and [Tac]_cells, (2) identify factors affecting the tacrolimus distribution in cells and whole‐blood, and (3) study the relationship between [Tac]_cells and clinical outcomes after kidney transplantation.

Methods

A total of 175 renal transplant recipients were prospectively followed. [Tac]_blood and [Tac]_cells were determined at Months 3, 6 and 12 post‐transplantation. Patients were genotyped for ABCB1 1199G>A and 3435C>T, CYP3A4 15389C>T, and CYP3A5 6986G>A. Data on rejection and tacrolimus‐related nephrotoxicity and post‐transplant diabetes mellitus were collected.

Results

Correlations between [Tac]_blood and [Tac]_cells were moderate to poor (Spearman's r = 0.31; r = 0.41; r = 0.61 at Months 3, 6 and 12, respectively). The [Tac]_cells/[Tac]_blood ratio was stable over time in most patients (median intra‐patient variability 39.0%; range 3.5%–173.2%). Age, albumin and haematocrit correlated with the [Tac]_cells/[Tac]_blood ratio. CYP3A5 and CYP3A4 genotype combined affected both dose‐corrected [Tac]_blood and [Tac]_cells. ABCB1 was not significantly related to tacrolimus distribution. Neither [Tac]_blood nor [Tac]_cells correlated with clinical outcomes.

Conclusions

The correlation between [Tac]_blood and [Tac]_cells is poor. Age, albumin and haematocrit correlate with the [Tac]_cells/[Tac]_blood ratio, whereas genetic variation in ABCB1, CYP3A4 and CYP3A5 do not. Neither [Tac]_blood nor [Tac]_cells correlated with clinical outcomes.

Predictors of tacrolimus pharmacokinetic variability: current evidences and future perspectives

INTRODUCTION

In kidney transplantation, tacrolimus (TAC) is at the cornerstone of current immunosuppressive strategies. Though because of its narrow therapeutic index, it is critical to ensure that TAC levels are maintained within this sharp window through reactive adjustments. This would allow maximizing efficiency while limiting drug-associated toxicity. However, TAC high intra- and inter-patient pharmacokinetic (PK) variability makes it more laborious to accurately predict the appropriate dosage required for a given patient.

AREAS COVERED

This review summarizes the state-of-the-art knowledge regarding drug interactions, demographic and pharmacogenetics factors as predictors of TAC PK. We provide a scoring index for each association to grade its relevance and we present practical recommendations, when possible for clinical practice.

EXPERT OPINION

The management of TAC concentration in transplanted kidney patients is as critical as it is challenging. Recommendations based on rigorous scientific evidences are lacking as knowledge of potential predictors remains limited outside of DDIs. Awareness of these limitations should pave the way for studies looking at demographic and pharmacogenetic factors as well as gut microbiota composition in order to promote tailored treatment plans. Therapeutic approaches considering patients' clinical singularities may help allowing to maintain appropriate concentration of TAC.

Donor CYP3A5 Gene Polymorphism Alone Cannot Predict Tacrolimus Intrarenal Concentration in Renal Transplant Recipients

CYP3A5 gene polymorphism in recipients plays an important role in tacrolimus blood pharmacokinetics after renal transplantation. Even though CYP3A5 protein is expressed in renal tubular cells, little is known about the influence on the tacrolimus intrarenal exposure and hence graft outcome. The aim of our study was to investigate how the tacrolimus intrarenal concentration (C_tissue) could be predicted based on donor CYP3A5 gene polymorphism in renal transplant recipients. A total of 52 Japanese renal transplant patients receiving tacrolimus were enrolled in this study. Seventy-four renal biopsy specimens were obtained at 3 months and 1 year after transplantation to determine the donor CYP3A5 polymorphism and measure the C_tissue by liquid chromatography-tandem mass spectrometry (LC-MS-MS). The tacrolimus C_tissue ranged from 52 to 399 pg/mg tissue (n = 74) and was weak but significantly correlated with tacrolimus trough concentration (C₀) at 3 months after transplantation (Spearman, r = 0.3560, p = 0.0096). No significant relationship was observed between the donor CYP3A5 gene polymorphism and C_tissue or C_tissue/C₀. These data showed that the tacrolimus systemic level has an impact on tacrolimus renal accumulation after renal transplantation. However, donor CYP3A5 gene polymorphism alone cannot be used to predict tacrolimus intrarenal exposure_. This study may be valuable for exploring tacrolimus renal metabolism and toxicology mechanism in renal transplant recipients.

Pharmacogenetic-Whole blood and intracellular pharmacokinetic-Pharmacodynamic (PG-PK2-PD) relationship of tacrolimus in liver transplant recipients

Tacrolimus (TAC) is the cornerstone of immunosuppressive therapy in liver transplantation. This study aimed at elucidating the interplay between pharmacogenetic determinants of TAC whole blood and intracellular exposures as well as the pharmacokinetic-pharmacodynamic relationship of TAC in both compartments. Complete pharmacokinetic profiles (Predose, and 20 min, 40 min, 1h, 2h, 3h, 4h, 6h, 8h, 12h post drug intake) of twice daily TAC in whole blood and peripheral blood mononuclear cells (PBMC) were collected in 32 liver transplanted patients in the first ten days post transplantation. A non-parametric population pharmacokinetic model was applied to explore TAC pharmacokinetics in blood and PBMC. Concurrently, calcineurin activity was measured in PBMC. Influence of donor and recipient genetic polymorphisms of ABCB1, CYP3A4 and CYP3A5 on TAC exposure was assessed. Recipient ABCB1 polymorphisms 1199G>A could influence TAC whole blood and intracellular exposure (p<0.05). No association was found between CYP3A4 or CYP3A5 genotypes and TAC whole blood or intracellular concentrations. Finally, intra-PBMC calcineurin activity appeared incompletely inhibited by TAC and less than 50% of patients were expected to achieve intracellular IC₅₀ concentration (100 pg/millions of cells) at therapeutic whole blood concentration (i.e.: 4–10 ng/mL). Together, these data suggest that personalized medicine regarding TAC therapy might be optimized by ABCB1 pharmacogenetic biomarkers and by monitoring intracellular concentration whereas the relationship between intracellular TAC exposure and pharmacodynamics biomarkers more specific than calcineurin activity should be further investigated.

Influence of ABCB1 (1236C > T, 2677G > T and 3435C > T) polymorphisms on the transport ability of P-gp-mediated sunitinib in Caco-2 cell line

P-glycoprotein (P-gp), encoded by ABCB1 gene, participants in the transmembrane transport of multiple anticancer drugs. The aim of the current research was to observe in vitro the impacts of ABCB1 (1236 C > T, 2677G > T, and 3435C > T) polymorphisms on the efflux activity of P-gp-mediated sunitinib.Stable recombinant colonic adenocarcinoma cell (Caco-2) systems transfected with ABCB1 wild-type allele and variant alleles (1236 T, 2677T and 3435T) were constructed. The resistance of each cell line to sunitinib was assessed by cell counting kit-8 (CCK8) assay. The effects of ABCB1 (1236 C > T, 2677G > T and 3435C > T) polymorphisms on the intracellular accumulation and transepithelial permeability of sunitinib were also investigated.The recombinant cell lines transfected with ABCB1 variant alleles (1236 T, 2677T, and 3435T) showed higher resistance to sunitinib compared to cells transfecting with ABCB1 wild-type allele (p < .05). The intracellular accumulation of sunitinib was significantly decreased in the three types of recombinant cell lines overexpressing ABCB1 variant alleles in comparison of their wild-type cell lines (p < .05). The transepithelial permeability of sunitinib in recombinant cell systems in transfected with variant alleles was significantly increased compared with cells overexpressing ABCB1 wild-type allele. The P-gp activity in recombinant variant cells is stronger when mediated transport of sunitinib than wild-type counterpart. P-gp encoded by ABCB1 (1236 T, 2677T, and 3435T) variant alleles may be more efficient to transport sunitinib than wild-type allele. Our observation suggests that ABCB1 (1236 C > T, 2677G > T, and 3435C > T) polymorphisms affect the transport ability of P-gp-mediated sunitinib.Collectively, ABCB1 polymorphisms may alter the P-gp-mediated sunitinib sensitivity via regulating drug transport.

A donor and recipient candidate gene association study of allograft loss in renal transplant recipients receiving a tacrolimus-based regimen

This work investigated, in two large cohorts of French renal transplants treated with tacrolimus, the influence of donor and recipient ABCB1, CYP3A4, and CYP3A5 genotypes on the risk of allograft loss. A discovery and a replication population of 330 and 369 adult renal transplant patients, each from a different transplantation center and all receiving a tacrolimus-based immunosuppressive regimen, were retrospectively genotyped. The influence of genetic factors and other known risk factors on allograft loss was investigated using multivariate Cox proportional hazard analyses. The existence of previous transplantations (per unit HR = 1.89 [1.10-3.26] P = .0216) and the donor ABCB1 c.1199GA/AA genotype (GA/AAvs GG: HR = 3.22 [1.14-9.09], P = .0288) were associated with an increased risk of allograft loss in the discovery cohort and with graft loss due to humoral rejection in the replication cohort (per unit HR = 2.26 [1.34-3.81], P = .00229; GA/AAvs GG HR = 3.42 [1.28-9.16], P = .0142). Genotyping the donor for the ABCB1 c.1199 G>A (exon 11, rs2229109) allele may be of interest before prescribing tacrolimus to the recipient, although this polymorphism is rather rare and its effect may be limited to certain mechanisms of graft loss.

Tacrolimus diffusion across the peripheral mononuclear blood cell membrane: impact of drug transporters

Measuring tacrolimus (TAC) concentration in peripheral blood mononuclear cells (PBMCs) could better reflect the drug effect on its target (calcineurin (CaN) in lymphocytes) than whole blood concentrations. Mechanisms influencing TAC diffusion into PBMC are not well characterized. This work aimed at describing, ex vivo, TAC diffusion kinetics into PBMC and investigating the contribution of membrane transporters to regulate TAC intracellular concentration as well as the impact on CaN activity. PBMCs were incubated with TAC for 5 min to 4 h and under several experimental conditions: 37 °C (physiological conditions), 4 °C (inhibition of influx and efflux active transport), 37 °C + transporter inhibitors (verapamil, carvedilol, and probenecid and bromosulfophthalein, respectively, inhibitors of P-gp, OAT, and OATP). TAC concentration and CaN activity were measured in PBMC using liquid chromatography coupled with mass spectrometry. TAC intra-PBMC concentration was maximal after 1 h of incubation. Mean TAC PMBC concentrations were significantly lower in samples incubated at 4 °C compared to the 37 °C groups. Addition of verapamil slightly increased TAC accumulation in PBMC while other inhibitors had no effect. A significant correlation was found between TAC intra-PBMC concentration and the level of inhibition of CaN. Using an ex vivo cellular model, these results suggest that P-gp is involved in the drug efflux from PBMC while influx active transporters likely to regulate TAC intra-PBMC disposition remain to be identified. TAC concentration in PBMC is correlated with its pharmacodynamic effect. Then, TAC intra-PBMC concentration appears to be a promising biomarker to refine TAC therapeutic drug monitoring.

Effect of ABCB1 genetic polymorphisms on the transport of rivaroxaban in HEK293 recombinant cell lines

Direct oral anticoagulants (DOAC) are substrates for the ABCB1 transporter (also called P-glycoprotein), an active efflux pump. ABCB1 polymorphisms have been previously reported to influence the pharmacokinetics of several drugs such as immunosuppressants and tyrosine kinase inhibitors. Recently, in vivo studies have suggested that genetic variants might contribute to the inter-individual variability in DOAC plasma concentrations. Therefore, we evaluated the in vitro effect of the most common coding ABCB1 single nucleotide polymorphisms (SNP), 1236 C > T-2677G > T-3435C > T, and the coding ABCB1 1199 G > A SNP on the transport activity towards rivaroxaban. HEK293 cells were transfected to overexpress the ABCB1 wild-type (1236C-2677G-3435C, 1199 G) or variant proteins (1236C-2677G-3435T, 1236T-2677T-3435T or 1199 A). ABCB1 expression decreased the intracellular accumulation of rivaroxaban, when compared to control cells. This confirms the involvement of ABCB1 in the active transport of rivaroxaban. However, the ABCB1 1236 C > T-2677G > T-3435C > T and 1199 G > A SNPs had no significant influence on the intracellular accumulation of rivaroxaban when compared to the wild-type protein. These results suggest that the ABCB1 coding SNPs investigated in the present study are unlikely to contribute to the inter-individual variability in rivaroxaban plasma concentrations.

SNPs affecting the clinical outcomes of regularly used immunosuppressants

Recent studies have suggested that genomic diversity may play a key role in different clinical outcomes, and the importance of SNPs is becoming increasingly clear. In this article, we summarize the bioactivity of SNPs that may affect the sensitivity to or possibility of drug reactions that occur among the signaling pathways of regularly used immunosuppressants, such as glucocorticoids, azathioprine, tacrolimus, mycophenolate mofetil, cyclophosphamide and methotrexate. The development of bioinformatics, including machine learning models, has enabled prediction of the proper immunosuppressant dosage with minimal adverse drug reactions for patients after organ transplantation or for those with autoimmune diseases. This article provides a theoretical basis for the personalized use of immunosuppressants in the future.

Attempted validation of 44 reported SNPs associated with tacrolimus troughs in a cohort of kidney allograft recipients

AIM

Multiple genetic variants have been associated with variation in tacrolimus (TAC) trough concentrations. Unfortunately, additional studies do not confirm these associations, leading one to question if a reported association is accurate and reliable. We attempted to validate 44 published variants associated with TAC trough concentrations.

MATERIALS & METHODS

Genotypes of the variants in our cohort of 1923 kidney allograft recipients were associated with TAC trough concentrations.

RESULTS

Only variants in CYP3A4 and CYP3A5 were significantly associated with variation in TAC trough concentrations in our validation.

CONCLUSION

There is no evidence that common variants outside the CYP3A4 and CYP3A5 loci are associated with variation in TAC trough concentrations. In the future rare variants may be important and identified using DNA sequencing.

Pharmacogenetic study of the impact of ABCB1 single-nucleotide polymorphisms on lenalidomide treatment outcomes in patients with multiple myeloma: results from a phase IV observational study and subsequent phase II clinical trial

PURPOSE

Despite therapeutic advances, patients with multiple myeloma (MM) continue to experience disease relapse and treatment resistance. The gene ABCB1 encodes the drug transporter P-glycoprotein, which confers resistance through drug extrusion across the cell membrane. Lenalidomide (Len) is excreted mainly via the kidneys, and, given the expression of P-gp in the renal tubuli, single-nucleotide polymorphisms (SNPs) in the ABCB1 gene may influence Len plasma concentrations and, subsequently, the outcome of treatment. We, therefore, investigated the influence of ABCB1 genetic variants on Len treatment outcomes and adverse events (AEs).

METHODS

Ninety patients with relapsed or refractory MM, who received the second-line Len plus dexamethasone in the Rev II trial, were genotyped for the ABCB1 SNPs 1199G>A (Ser400Asn, rs2229109), 1236C>T (silent, rs1128503), 2677G>T/A (Ala893Ser, rs2032582), and 3435C>T (silent, rs1045642) using pyrosequencing, and correlations to response parameters, outcomes, and AEs were investigated.

RESULTS

No significant associations were found between genotype and either best response rates or hematological AEs, and 1236C>T, 2677G>T or 3435C>T genotypes had no impact on survival. There was a trend towards increased time to progression (TTP) in patients carrying the 1199A variant, and a significant difference in TTP between genotypes in patients with standard-risk cytogenetics.

CONCLUSIONS

Our findings show a limited influence of ABCB1 genotype on lenalidomide treatment efficacy and safety. The results suggest that 1199G>A may be a marker of TTP following Len treatment in standard-risk patients; however, larger studies are needed to validate and clarify the relationship.

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.

Impact of ABCB1 1236C > T-2677G > T-3435C > T polymorphisms on the anti-proliferative activity of imatinib, nilotinib, dasatinib and ponatinib

Overexpression of ABCB1 (also called P-glycoprotein) confers resistance to multiple anticancer drugs, including tyrosine kinase inhibitors (TKIs). Several ABCB1 single nucleotide polymorphisms affect the transporter activity. The most common ABCB1 variants are 1236C > T, 2677G > T, 3435C > T and have been associated with clinical response to imatinib in chronic myelogenous leukaemia (CML) in some studies. We evaluated the impact of these polymorphisms on the anti-proliferative effect and the intracellular accumulation of TKIs (imatinib, nilotinib, dasatinib and ponatinib) in transfected HEK293 and K562 cells. ABCB1 overexpression increased the resistance of cells to doxorubicin, vinblastine and TKIs. Imatinib anti-proliferative effect and accumulation were decreased to a larger extent in cells expressing the ABCB1 wild-type protein compared with the 1236T-2677T-3435T variant relatively to control cells. By contrast, ABCB1 polymorphisms influenced the activity of nilotinib, dasatinib and ponatinib to a much lesser extent. In conclusion, our data suggest that wild-type ABCB1 exports imatinib more efficiently than the 1236T-2677T-3435T variant protein, providing a molecular basis for the reported association between ABCB1 polymorphisms and the response to imatinib in CML. Our results also point to a weaker impact of ABCB1 polymorphisms on the activity of nilotinib, dasatinib and ponatinib.

Multidrug resistance-associated protein 4 (MRP4) controls ganciclovir intracellular accumulation and contributes to ganciclovir-induced neutropenia in renal transplant patients

Ganciclovir (GCV) is the cornerstone of cytomegalovirus prevention and treatment in transplant patients. It is associated with problematic adverse hematological effects in this population of immunosuppressed patients, which may lead to dose reduction thus favoring resistance. GCV crosses the membranes of cells, is activated by phosphorylation, and then stops the replication of viral DNA. Its intracellular accumulation might favor host DNA polymerase inhibition, hence toxicity. Following this hypothesis, we investigated the association between a selected panel of membrane transporter polymorphisms and the evolution of neutrophil counts in n=174 renal transplant recipients. An independent population of n=96 renal transplants served as a replication and experiments using HEK293T-transfected cells were performed to validate the clinical findings. In both cohorts, we found a variant in ABCC4 (rs11568658) associated with decreased neutrophil counts following valganciclovir (GCV prodrug) administration (exploratory cohort: β±SD=-0.68±0.28, p=0.029; replication cohort: β±SD=-0.84±0.29, p=0.0078). MRP4-expressing cells showed decreased GCV accumulation as compared to negative control cells (transfected with an empty vector) (-61%; p<0.0001). The efflux process was almost abolished in cells expressing MRP4 rs11568658 variant protein. Molecular dynamic simulations of GCV membrane crossing showed a preferred location of the drug just beneath the polar head group region, which supports its interaction with efflux transporters.

ABCB1 1199G>A polymorphism (rs2229109) affects the transport of imatinib, nilotinib and dasatinib

AIM

ABCB1 (or P-glycoprotein) is implicated in the multidrug-resistance phenotype, including the resistance toward anticancer drugs such as tyrosine kinase inhibitors (TKIs). The purpose of this study was to evaluate in vitro the influence of the ABCB1 1199G>A SNP on ABCB1 transport activity toward selected TKIs (imatinib, nilotinib and dasatinib) that are currently used in chronic myelogenous leukemia.

MATERIAL & METHODS

Two different cell lines, HEK293 and K562, were stably transfected with ABCB1 1199G wild-type or ABCB1 1199A variant allele. The impact of this polymorphism on accumulation and antiproliferative effects of imatinib, nilotinib and dasatinib was evaluated.

RESULTS

In K562 models, the expression of Asn400 variant protein was associated with lower antiproliferative effects of imatinib, nilotinib and dasatinib compared with Ser400 wild-type protein. Moreover, in HEK293 cells, imatinib and nilotinib intracellular accumulation were lower in variant compared with wild-type models.

CONCLUSION

Imatinib, nilotinib and dasatinib are transported more efficiently by the ABCB1 variant (Asn400) compared with the wild-type (Ser400) protein. The impact of ABCB1 1199G>A SNP on TKI response should be further investigated in chronic myelogenous leukemia patients.

Drug disposition alterations in liver disease: extrahepatic effects in cholestasis and nonalcoholic steatohepatitis

INTRODUCTION

The pharmacokinetics (PK) of drugs and xenobiotics, namely pharmaceuticals, is influenced by a host of factors that include genetics, physiological factors and environmental stressors. The importance of disease on the disposition of xenobiotics has been increasingly recognized among medical professionals for alterations in key enzymes and membrane transporters that influence drug disposition and contribute to the development of adverse drug reactions.

AREAS COVERED

This review will survey pertinent literature of how liver disease alters the PKs of drugs and other xenobiotics. The focus will be on nonalcoholic steatohepatitis as well as cholestatic liver diseases. A review of basic pharmacokinetic principles, with a special emphasis on xenobiotic metabolizing enzymes and membrane transporters, will be provided. Specifically, examples of how genetic alterations affect metabolism and excretion, respectively, will be highlighted. Lastly, the idea of 'extrahepatic' regulation will be explored, citing examples of how disease manifestation in the liver may affect drug disposition in distal sites, such as the kidney.

EXPERT OPINION

An expert opinion will be provided highlighting the definite need for data in understanding extrahepatic regulation of membrane transporters in the presence of liver disease and its potential to dramatically alter the PK and toxicokinetic profile of numerous drugs and xenobiotics.