Interaction of sirolimus and everolimus with hepatic and intestinal organic anion-transporting polypeptide transporters

Role of Drug Transporters in Elucidating Inter-Individual Variability in Pediatric Chemotherapy-Related Toxicities and Response

Pediatric cancer treatment has evolved significantly in recent decades. The implementation of risk stratification strategies and the selection of evidence-based chemotherapy combinations have improved survival outcomes. However, there is large interindividual variability in terms of chemotherapy-related toxicities and, sometimes, the response among this population. This variability is partly attributed to the functional variability of drug-metabolizing enzymes (DME) and drug transporters (DTS) involved in the process of absorption, distribution, metabolism and excretion (ADME). The DTS, being ubiquitous, affects drug disposition across membranes and has relevance in determining chemotherapy response in pediatric cancer patients. Among the factors affecting DTS function, ontogeny or maturation is important in the pediatric population. In this narrative review, we describe the role of drug uptake/efflux transporters in defining pediatric chemotherapy-treatment-related toxicities and responses. Developmental differences in DTS and the consequent implications are also briefly discussed for the most commonly used chemotherapeutic drugs in the pediatric population.

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.

Is It Time to Use Modeling of Cellular Transporter Homeostasis to Inform Drug-Drug Interaction Studies: Theoretical Considerations

Mathematical modeling has been an important tool in pharmaceutical research for 50 + years and there is increased emphasis over the last decade on using modeling to improve the efficiency and effectiveness of drug development. In an earlier commentary, we applied a multiscale model linking 6 scales (whole body, tumor, vasculature, cell, spatial location, time), together with literature data on nanoparticle and tumor properties, to demonstrate the effects of nanoparticle particles on systemic disposition. The current commentary used a 4-scale model (cell membrane, intracellular organelles, spatial location, time) together with literature data on the intracellular processing of membrane receptors and transporters to demonstrate disruption of transporter homeostasis can lead to drug-drug interaction (DDI) between victim drug (VD) and perpetrator drug (PD), including changes in the area-under-concentration-time-curve of VD in cells that are considered significant by the US Food and Drug Administration (FDA). The model comprised 3 computational components: (a) intracellular transporter homeostasis, (b) pharmacokinetics of extracellular and intracellular VD/PD concentrations, and (c) pharmacodynamics of PD-induced stimulation or inhibition of an intracellular kinetic process. Model-based simulations showed that (a) among the five major endocytic processes, perturbation of transporter internalization or recycling led to the highest incidence and most extensive DDI, with minor DDI for perturbing transporter synthesis and early-to-late endosome and no DDI for perturbing transporter degradation and (b) three experimental conditions (spatial transporter distribution in cells, VD/PD co-incubation time, extracellular PD concentrations) were determinants of DDI detection. We propose modeling is a useful tool for hypothesis generation and for designing experiments to identify potential DDI; its application further aligns with the model-informed drug development paradigm advocated by FDA.

Preincubation With Everolimus and Sirolimus Reduces Organic Anion-Transporting Polypeptide (OATP)1B1- and 1B3-Mediated Transport Independently of mTOR Kinase Inhibition: Implication in Assessing OATP1B1- and OATP1B3-Mediated Drug-Drug Interactions

Organic anion transporting polypeptides (OATP)1B1 and OATP1B3 mediate hepatic uptake of many drugs including lipid-lowering statins. Current studies determined the OATP1B1/1B3-mediated drug-drug interaction (DDI) potential of mammalian target of rapamycin (mTOR) inhibitors, everolimus and sirolimus, using R-value and physiologically based pharmacokinetic models. Preincubation with everolimus and sirolimus significantly decreased OATP1B1/1B3-mediated transport even after washing and decreased inhibition constant values up to 8.3- and 2.9-fold for OATP1B1 and both 2.7-fold for OATP1B3, respectively. R-values of everolimus, but not sirolimus, were greater than the FDA-recommended cutoff value of 1.1. Physiologically based pharmacokinetic models predict that everolimus and sirolimus have low OATP1B1/1B3-mediated DDI potential against pravastatin. OATP1B1/1B3-mediated transport was not affected by preincubation with INK-128 (10 μM, 1 h), which does however abolish mTOR kinase activity. The preincubation effects of everolimus and sirolimus on OATP1B1/1B3-mediated transport were similar in cells before preincubation with vehicle control or INK-128, suggesting that inhibition of mTOR activity is not a prerequisite for the preincubation effects observed for everolimus and sirolimus. Nine potential phosphorylation sites of OATP1B1 were identified by phosphoproteomics; none of these are the predicted mTOR phosphorylation sites. We report the everolimus/sirolimus-preincubation-induced inhibitory effects on OATP1B1/1B3 and relatively low OATP1B1/1B3-mediated DDI potential of everolimus and sirolimus.

Evidence that decreased expression of sinusoidal bile acid transporters accounts for the inhibition by rapamycin of bile flow recovery following liver ischemia

Rapamycin is employed as an immunosuppressant following organ transplant and, in patients with hepatocellular carcinoma, to inhibit cancer cell regrowth following liver surgery. Preconditioning the liver with rapamycin to induce the expression of antioxidant enzymes is a potential strategy to reduce ischemia reperfusion (IR) injury. However, pre-treatment with rapamycin inhibits bile flow, especially following ischemia. The aim was to investigate the mechanisms involved in this inhibition. In a rat model of segmental hepatic ischemia and reperfusion, acute administration of rapamycin by intravenous injection did not inhibit the basal rate of bile flow. Pre-treatment of rats with rapamycin for 24 h by intraperitoneal injection inhibited the expression of mRNA encoding the sinusoidal influx transporters Ntcp, Oatp1 and 2 and the canalicular efflux transporter Bsep, and increased expression of canalicular Mrp2. Dose-response curves for the actions of rapamycin on the expression of Bsep and Ntcp in cultured rat hepatocytes were biphasic, and monophasic for effects on Oatp1. In cultured tumorigenic H4IIE liver cells, several bile acid transporters were not expressed, or were expressed at very low levels compared to hepatocytes. In H4IIE cells, rapamycin increased expression of Ntcp, Oatp1 and Mrp2, but decreased expression of Oatp2. It is concluded that the inhibition of bile flow recovery following ischemia observed in rapamycin-treated livers is principally due to inhibition of the expression of sinusoidal bile acid transporters. Moreover, in tumorigenic liver tissue the contribution of tumorigenic hepatocytes to total liver bile flow is likely to be small and is unlikely to be greatly affected by rapamycin.

Sirolimus and mirabegron interaction in a hematopoietic cell transplant patient

PURPOSE

Hematopoietic cell transplant patients are exposed to numerous classes of medications. Transplant practitioners must vigilantly monitor for drug interactions especially involving immunosuppressants. We report a hematopoietic cell transplant patient receiving sirolimus who developed supratherapeutic serum concentrations after initiating mirabegron.

SUMMARY

A 31-year-old, 98 kg female received a second umbilical cord blood transplant four years after the first transplant for relapsed acute myeloid leukemia. Mycophenolate mofetil and sirolimus were utilized for graft versus host disease prophylaxis. The patient was receiving sirolimus 2 mg daily and the serum concentration on day 26 post-transplant (day + 26) was within therapeutic range (6.7 μg/L, goal range 3-12 μg/L). Her post-transplant course was complicated by BK viruria-associated cystitis for which she was started on mirabegron. Six days after starting the new medication (day + 33), the sirolimus serum concentration increased to 19.2 μg/L. Thus mirabegron was discontinued and sirolimus was held. Sirolimus was restarted once the serum concentration was within goal and subsequently stabilized with a combination of 1 mg and 2 mg daily for a total weekly dose of 10 mg. The proposed mechanisms of interaction include: (1) sirolimus inhibition of organic anion transporting polypeptide leading to increased mirabegron in the intestinal lumen; (2) mirabegron inhibition of P-glycoprotein leading to increased absorption of sirolimus and; (3) increased sirolimus absorption leading to increased sirolimus serum concentrations.

CONCLUSION

To our knowledge, this is the first report of a potential drug interaction between sirolimus and mirabegron. Transplant specialists should be aware of this potential interaction when considering the concurrent use of these medications.

Therapeutic Drug Monitoring of Everolimus: A Consensus Report

In 2014, the Immunosuppressive Drugs Scientific Committee of the International Association of Therapeutic Drug Monitoring and Clinical Toxicology called a meeting of international experts to provide recommendations to guide therapeutic drug monitoring (TDM) of everolimus (EVR) and its optimal use in clinical practice. EVR is a potent inhibitor of the mammalian target of rapamycin, approved for the prevention of organ transplant rejection and for the treatment of various types of cancer and tuberous sclerosis complex. EVR fulfills the prerequisites for TDM, having a narrow therapeutic range, high interindividual pharmacokinetic variability, and established drug exposure-response relationships. EVR trough concentrations (C0) demonstrate a good relationship with overall exposure, providing a simple and reliable index for TDM. Whole-blood samples should be used for measurement of EVR C0, and sampling times should be standardized to occur within 1 hour before the next dose, which should be taken at the same time everyday and preferably without food. In transplantation settings, EVR should be generally targeted to a C0 of 3-8 ng/mL when used in combination with other immunosuppressive drugs (calcineurin inhibitors and glucocorticoids); in calcineurin inhibitor-free regimens, the EVR target C0 range should be 6-10 ng/mL. Further studies are required to determine the clinical utility of TDM in nontransplantation settings. The choice of analytical method and differences between methods should be carefully considered when determining EVR concentrations, and when comparing and interpreting clinical trial outcomes. At present, a fully validated liquid chromatography tandem mass spectrometry assay is the preferred method for determination of EVR C0, with a lower limit of quantification close to 1 ng/mL. Use of certified commercially available whole-blood calibrators to avoid calibration bias and participation in external proficiency-testing programs to allow continuous cross-validation and proof of analytical quality are highly recommended. Development of alternative assays to facilitate on-site measurement of EVR C0 is encouraged.

Cell permeability beyond the rule of 5

Drug discovery for difficult targets that have large and flat binding sites is often better suited to compounds beyond the "rule of 5" (bRo5). However, such compounds carry higher pharmacokinetic risks, such as low solubility and permeability, and increased efflux and metabolism. Interestingly, recent drug approvals and studies suggest that cell permeable and orally bioavailable drugs can be discovered far into bRo5 space. Tactics such as reduction or shielding of polarity by N-methylation, bulky side chains and intramolecular hydrogen bonds may be used to increase cell permeability in this space, but often results in decreased solubility. Conformationally flexible compounds can, however, combine high permeability and solubility, properties that are keys for cell permeability and intestinal absorption. Recent developments in computational conformational analysis will aid design of such compounds and hence prediction of cell permeability. Transporter mediated efflux occurs for most investigated drugs in bRo5 space, however it is commonly overcome by high local intestinal concentrations on oral administration. In contrast, there is little data to support significant impact of transporter-mediated intestinal absorption in bRo5 space. Current knowledge of compound properties that govern transporter effects of bRo5 drugs is limited and requires further fundamental and comprehensive studies.

Insights into solute carriers: physiological functions and implications in disease and pharmacokinetics

SLCs transport many endogenous and exogenous compounds including drugs; SLCs dysfunction has implications in pharmacokinetics, drug toxicity or lack of efficacy.

Role of Organic Anion-Transporting Polypeptides (OATPs) in Cancer Therapy

The superfamily of organic anion-transporting polypeptides (OATPs, gene symbol SLCO) includes important transporters handling a variety of endogenous and xenobiotic substrates. Currently, 11 human OATPs are known and their substrates include endogenous hormones and their conjugates, anticancer drugs, and imaging agents. The contribution of OATPs to the in vivo disposition of these substrates has been extensively investigated. An accumulating body of evidence also indicates that the expression of some OATPs may be up- or downregulated in several types of cancers, suggesting potential pathogenic roles during the development and progression of cancer. Given that the role of OATPs in handling cancer therapeutics has been already covered by several excellent reviews, this review will focus on the recent progresses on the topic, in particular the role of OATPs in the disposition of anticancer drugs, the impact of OATP genetic variations on the function of OATPs, and the OATPs differentially expressed in cancer and their potential roles in cancer development, progression, and treatment.

Cyclosporine-inhibitable cerebral drug transport does not influence clinical methadone pharmacodynamics

BACKGROUND

Interindividual variability and drug interaction studies suggest that blood-brain barrier drug transporters mediate human methadone brain biodistribution. In vitro and animal studies suggest that methadone is a substrate for the efflux transporter P-glycoprotein, and that P-glycoprotein-mediated transport influences brain access and pharmacologic effect. This investigation tested whether methadone is a transporter substrate in humans [corrected].

METHODS

Healthy volunteers received oral (N=16) or IV (N=12) methadone in different crossover protocols after nothing (control) or the validated P-glycoprotein inhibitor cyclosporine (4.5 mg/kg orally twice daily for 4 days, or 5 mg/kg IV over 2 h). Plasma and urine methadone and metabolite concentrations were measured by mass spectrometry. Methadone effects were measured by miosis and thermal analgesia (maximally tolerated temperature and verbal analog scale rating of discreet temperatures).

RESULTS

Cyclosporine marginally but significantly decreased methadone plasma concentrations and apparent oral clearance, but had no effect on methadone renal clearance or on hepatic N-demethylation. Cyclosporine had no effect on miosis or on R-methadone concentration-miosis relationships after either oral or IV methadone. Peak miosis was similar in controls and cyclosporine-treated subjects after oral methadone (1.4±0.4 and 1.3±0.5 mm/mg, respectively) and IV methadone (3.1±1.0 and 3.2±0.8 mm, respectively). Methadone increased maximally tolerated temperature, but analgesia testing was confounded by cyclosporine-related pain.

CONCLUSIONS

Cyclosporine did not affect methadone pharmacodynamics. This result does not support a role for cyclosporine-inhibitable transporters mediating methadone brain access and biodistribution.

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

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

Intestinal drug transporters: an overview

The importance of drug transporters as one of the determinants of pharmacokinetics has become increasingly evident. While much research has been conducted focusing the role of drug transporters in the liver and kidney less is known about the importance of uptake and efflux transporters identified in the intestine. Over the past years the effects of intestinal transporters have been studied using in vivo models, in situ organ perfusions, in vitro tissue preparations and cell lines. This review aims to describe up to date findings regarding the importance of intestinal transporters on drug absorption and bioavailability, highlighting areas in need of further research. Wu and Benet proposed a Biopharmaceutics Drug Disposition Classification System (BDDCS) that allows the prediction of transporter effects on the drug disposition of orally administered drugs. This review also discusses BDDCS predictions with respect to the role of intestinal transporters and intestinal transporter-metabolizing enzyme interplay on oral drug pharmacokinetics.

Effects of selected OATP and/or ABC transporter inhibitors on the brain and whole-body distribution of glyburide

Glyburide (glibenclamide, GLB) is a widely prescribed antidiabetic with potential beneficial effects in central nervous system injury and diseases. In vitro studies show that GLB is a substrate of organic anion transporting polypeptide (OATP) and ATP-binding cassette (ABC) transporter families, which may influence GLB distribution and pharmacokinetics in vivo. In the present study, we used [(11)C]GLB positron emission tomography (PET) imaging to non-invasively observe the distribution of GLB at a non-saturating tracer dose in baboons. The role of OATP and P-glycoprotein (P-gp) in [(11)C]GLB whole-body distribution, plasma kinetics, and metabolism was assessed using the OATP inhibitor rifampicin and the dual OATP/P-gp inhibitor cyclosporine. Finally, we used in situ brain perfusion in mice to pinpoint the effect of ABC transporters on GLB transport at the blood-brain barrier (BBB). PET revealed the critical role of OATP on liver [(11)C]GLB uptake and its subsequent impact on [(11)C]GLB metabolism and plasma clearance. OATP-mediated uptake also occurred in the myocardium and kidney parenchyma but not the brain. The inhibition of P-gp in addition to OATP did not further influence [(11)C]GLB tissue and plasma kinetics. At the BBB, the inhibition of both P-gp and breast cancer resistance protein (BCRP) was necessary to demonstrate the role of ABC transporters in limiting GLB brain uptake. This study demonstrates that GLB distribution, metabolism, and elimination are greatly dependent on OATP activity, the first step in GLB hepatic clearance. Conversely, P-gp, BCRP, and probably multidrug resistance protein 4 work in synergy to limit GLB brain uptake.

A drug safety evaluation of everolimus in kidney transplantation

INTRODUCTION

Calcineurin inhibitors (CNI) have greatly reduced the rate of acute rejection and improved short-term graft survival after organ transplantation, however, long-term survival has hardly changed since their introduction. CNIs are believed to contribute to graft fibrosis, have side effects that adversely affect cardiovascular risk, and are associated with an increased rate of post-transplant malignancies. Everolimus, a mammalian target of rapamycin (mTOR) inhibitor, is not associated with graft fibrosis, has a superior cardiovascular risk profile to CNI therapy and has shown potential for the prevention and treatment of diverse forms of cancer.

AREAS COVERED

This review summarizes key aspects of everolimus, including its mechanism of action, pharmacokinetics, pharmacodynamics, drug-drug interactions and pivotal clinical studies with a focus on safety and efficacy.

EXPERT OPINION

Everolimus is effective in improving graft function in selected kidney transplant patients. Most adverse events are present for a short time after the introduction of everolimus, and are manageable. Everolimus has the potential to become an important agent in de novo and maintenance immunotherapy in kidney transplant recipients.

Mycophenolic acid glucuronide is transported by multidrug resistance-associated protein 2 and this transport is not inhibited by cyclosporine, tacrolimus or sirolimus

1. The purpose of this study was to investigate the contribution of MRP2 to the efflux of mycophenolic acid (MPA), and its phenyl glucuronide (MPAG) and acyl glucuronide (AcMPAG) metabolites, using Madin-Darby canine kidney II cells stably transfected with human MRP2 gene (MDCKII/MRP2 cells). 2. Compared to parental MDCKII cells, MPAG was significantly translocated from basolateral (BL) to apical (AP) side in MDCKII/MRP2 cells, indicating MPAG is a substrate for MRP2. AcMPAG is highly translocated from BL to AP side in both cells, suggesting that AcMPAG is actively secreted possibly through an efflux transporter other than MRP2. Appreciable translocation of MPA was not observed in MDCKII/MRP2 cells. 3. Furthermore, using MRP2-expressing Sf9 membrane vesicles, the Michaelis-Menten constant (Km) value for MRP2-mediated MPAG transport was calculated at 224.2 ± 42.7 µM. In the vesicle system, cyclosporine, tacrolimus and sirolimus did not inhibit the uptake of MPAG via MRP2. 4. These findings indicate that only MPAG not MPA and AcMPAG is a substrate for MRP2 and that the interaction between MPAG and concomitantly administered immunosuppressive agents does not occur at MRP2 level.

Interaction of innovative small molecule drugs used for cancer therapy with drug transporters

Multiple new small molecules such as tyrosine kinase, mammalian target of rapamycin (mTOR) and proteasome inhibitors have been approved in the last decade and are a considerable progress for cancer therapy. Drug transporters are important determinants of drug concentrations in the systemic circulation. Moreover, expression of drug transporters in blood-tissue barriers (e.g. blood-brain barrier) can limit access of small molecules to the tumour (e.g. brain tumour). Finally, transporter expression and (up)regulation in the tumour itself is known to affect local drug concentrations in the tumour tissue contributing to multidrug resistance observed for multiple anticancer agents. This review summarizes the current knowledge on: (i) small molecules as substrates of uptake and efflux transporters; (ii) the impact of transporter deficiency in knockout mouse models on plasma and tissue concentrations; (iii) small molecules as inhibitors of uptake and efflux transporters with possible consequences for drug-drug interactions and the reversal of multidrug resistance; and (iv) on clinical studies investigating the association of polymorphisms in genes encoding drug transporters with pharmacokinetics, outcome and toxicity during treatment with the small molecules.