Urinary coproporphyrin I/(I + III) ratio as a surrogate for MRP2 or other transporter activities involved in methotrexate clearance

Factors influencing methotrexate pharmacokinetics highlight the need for individualized dose adjustment: a systematic review

PURPOSE

To develop a population pharmacokinetic (PPK) model for methotrexate (MTX) dosage for all ages, assess the association between concentration and clearance, and determine covariates affecting MTX disposition.

METHODS

We compared MTX PK profiles among neonates, children, and adults by performing a systematic literature search for published population MTX models and conducted a Monte Carlo-based meta-analysis. Subsequently, we evaluated study quality and covariates significantly affecting dosage regimens and compared LDMTX and HDMTX PK profiles.

RESULTS

Of the total 40 studies included, 34 were HDMTX, and six were LDMTX studies. For HDMTX, three studies involving neonates reported estimated apparent clearances (median, range) of 0.53 (0.27-0.77) L/kg/h; for 14 studies involving children, 0.23 (0.07-0.23) L/kg/h; and for 13 involving adults, 0.11 (0.03-0.22) L/kg/h. Neonates had a higher volume of distribution than children and adults. For LDMTX studies, apparent clearance was 0.085 (0.05-1.68) L/kg/h, and volume of distribution was 0.25 (0.018-0.47) L/kg, lower than those of HDMTX studies, with large between-subject variability. Bodyweight significantly influenced apparent clearance and volume of distribution, whereas renal function mainly influenced clearance. Mutations in certain genes reduced MTX clearance by 8-35.3%, whereas those in others increased it by 15-48%. Body surface area (BSA) significantly influenced apparent clearance with a median reduction of 51% when BSA increased in pediatric patients.

CONCLUSIONS

Methotrexate dosage regimens were primarily based on body surface area and renal function. Further studies are needed to evaluate MTX pharmacokinetics and pharmacodynamics in both children (especially infants) and adults.

External evaluation and systematic review of population pharmacokinetic models for high-dose methotrexate in cancer patients

Several population pharmacokinetic (PPK) models have been established to optimize the therapeutic regimen and reduce the toxicity of high-dose methotrexate (HDMTX) in patients with cancer. However, their predictive performance when extrapolated to different clinical centers was unknown. In this study, we aimed to externally evaluate the predictive ability of HDMTX PPK models and determine the potential influencing factors. We searched the literature and determined the predictive performance of the selected models using methotrexate concentrations in 721 samples from 60 patients in the First Affiliated Hospital of the Navy Medical University. Prediction-based diagnostics and simulation-based normalized prediction distribution errors (NPDE) were used to evaluate the predictive performance of the models. The influence of prior information was also assessed using Bayesian forecasting, and the potential factors affecting model predictability were investigated. Thirty models extracted from published PPK studies were assessed. Prediction-based diagnostics showed that the number of compartments potentially influenced model transferability, and simulation-based NPDE indicated model misspecification. Bayesian forecasting significantly improved the predictive performance of the models. Various factors, including bioassays, covariates, and population diagnosis, influence model extrapolation. The published models were unsatisfactory for all prediction-based diagnostics, except for the 24 h methotrexate concentration monitoring and simulation-based diagnostics, making them inappropriate for direct extrapolation. Moreover, Bayesian forecasting combined therapeutic drug monitoring could improve the predictive performance of the models.

Evaluation and Application of Population Pharmacokinetic Models for Identifying Delayed Methotrexate Elimination in Patients With Primary Central Nervous System Lymphoma

Objective: Several population pharmacokinetic (popPK) models have been developed to determine the sources of methotrexate (MTX) PK variability. It remains unknown if these published models are precise enough for use or if a new model needs to be built. The aims of this study were to 1) assess the predictability of published models and 2) analyze the potential risk factors for delayed MTX elimination.

Methods: A total of 1458 MTX plasma concentrations, including 377 courses (1–17 per patient), were collected from 77 patients who were receiving high-dose MTX for the treatment of primary central nervous system lymphoma in Huashan Hospital. PopPK analysis was performed using the NONMEM® software package. Previously published popPK models were selected and rebuilt. A new popPK model was then constructed to screen potential covariates using a stepwise approach. The covariates were included based on the combination of theoretical mechanisms and data properties. Goodness-of-fit plots, bootstrap, and prediction- and simulation-based diagnostics were used to determine the stability and predictive performance of both the published and newly built models. Monte Carlo simulations were conducted to qualify the influence of risk factors on the incidence of delayed elimination.

Results: Among the eight evaluated published models, none presented acceptable values of bias or inaccuracy. A two-compartment model was employed in the newly built model to describe the PK of MTX. The estimated mean clearance (CL/F) was 4.91 L h⁻¹ (relative standard error: 3.7%). Creatinine clearance, albumin, and age were identified as covariates of MTX CL/F. The median and median absolute prediction errors of the final model were -10.2 and 36.4%, respectively. Results of goodness-of-fit plots, bootstrap, and prediction-corrected visual predictive checks indicated the high predictability of the final model.

Conclusions: Current published models are not sufficiently reliable for cross-center use. The elderly patients and those with renal dysfunction, hypoalbuminemia are at higher risk of delayed elimination.

Body Surface Area Dosing of High-Dose Methotrexate Should Be Reconsidered, Particularly in Overweight, Adult Patients

BACKGROUND

High-dose methotrexate is used for treating several types of cancer. However, it is associated with a high risk of acute kidney injury (AKI), especially in patients with high MTX concentrations. Although therapeutic drug monitoring is performed to monitor MTX concentrations, it is unclear what concentration should be considered critical, thus requiring rescue protocols to prevent nephrotoxicity.

METHODS

Patients treated with high-dose methotrexate for lymphoma or acute lymphoblastic leukemia and those benefited from therapeutic drug monitoring were included. The relationship between MTX concentrations and the presence or absence of AKI was assessed. MTX concentrations were analyzed using a population pharmacokinetic approach. Specific attention was given to morphological covariates because MTX doses are individualized according to body surface area (BSA).

RESULTS

In total, 328 patients and 657 cycles of treatment were analyzed. Higher MTX concentrations were observed in the AKI+ group. For cycle 1, all patients showing an MTX concentration >6 µM at 36 hours or >2 µM at 48 hours after infusion developed nephrotoxicity. The final pharmacokinetic model had 2 compartments and included the effect of age on clearance (CL) and of body weight on peripheral distribution volume. None of the morphological covariates tested on CL led to significant improvement in the model. Higher MTX concentrations were observed in patients with extreme BSA values (≥2 m2) or body mass index (≥25 kg/m2). Patients with AKI who received at least 1 cycle had higher BSA and BMI.

CONCLUSIONS

The results from this study provide additional information on the relationship between MTX concentration and nephrotoxicity. Patients with a plasma MTX concentration >6 µM at 36 hours were more likely to manifest AKI. In addition, the results suggest that overweight patients have a high AKI risk and that BSA-based adjustment of MTX dose is not appropriate.

Transporter Activity Changes in Nonalcoholic Steatohepatitis: Assessment with Plasma Coproporphyrin I and III

Expression and functional changes in the organic anion transporting polypeptide (OATP)-multidrug resistance-associated protein (MRP) axis of transporters are well reported in patients with nonalcoholic steatohepatitis (NASH). These changes can impact plasma and tissue disposition of endo- and exogenous compounds. The transporter alterations are often assessed by administration of a xenobiotic or by transporter proteomic analysis from liver biopsies. Using gene expression, proteomics, and endogenous biomarkers, we show that the gene expression and activity of OATP and MRP transporters are associated with disease progression and recovery in humans and in preclinical animal models of NASH. Decreased OATP and increased MRP3/4 gene expression in two cohorts of patients with steatosis and NASH, as well as gene and protein expression in multiple NASH rodent models, have been established. Coproporphyrin I and III (CP I and III) were established as substrates of MRP4. CP I plasma concentration increased significantly in four animal models of NASH, indicating the transporter changes. Up to a 60-fold increase in CP I plasma concentration was observed in the mouse bile duct-ligated model compared with sham controls. In the choline-deficient amino acid-defined high-fat diet (CDAHFD) model, CP I plasma concentrations increased by >3-fold compared with chow diet-fed mice. In contrast, CP III plasma concentrations remain unaltered in the CDAHFD model, although they increased in the other three NASH models. These results suggest that tracking CP I plasma concentrations can provide transporter modulation information at a functional level in NASH animal models and in patients. SIGNIFICANCE STATEMENT: Our analysis demonstrates that multidrug resistance-associated protein 4 (MRP4) transporter gene expression tracks with nonalcoholic steatohepatitis (NASH) progression and intervention in patients. Additionally, we show that coproporphyrin I and III (CP I and III) are substrates of MRP4. CP I plasma and liver concentrations increase in different diet- and surgery-induced rodent NASH models, likely explained by both gene- and protein-level changes in transporters. CP I and III are therefore potential plasma-based biomarkers that can track NASH progression in preclinical models and in humans.

A rare case of methotrexate and primaquine co-administration in a mantle cell lymphoma patient

WHAT IS KNOWN AND OBJECTIVE

High-dose methotrexate (HD-MTX) is associated with a plethora of adverse drug reactions and potential drug interactions (DIs). But there is a paucity of information regarding the safety of co-administering primaquine with HD-MTX.

CASE SUMMARY

A 65-year-old male patient was diagnosed with mantle cell lymphoma (MCL) with CNS involvement and treated with three cycles of IV HD-MTX. His case was further complicated by fungal pneumonia treated with primaquine during cycle-2. Serial blood sampling and subsequent population pharmacokinetics (PK) modelling suggests a possible distribution-mediated DI between the two drugs.

WHAT IS NEW AND CONCLUSION

This is the first case report to highlight the safe co-administration of MTX and primaquine, despite a possible PK interaction.

[Renal toxicity of high-dose methotrexate]

INTRODUCTION

High-dose methotrexate (at least 1g/m²) is used to treat haematologic malignancies and osteosarcomas. Acute kidney injury is a well-known adverse-event after high-dose methotrexate and may lead to delayed drug elimination. Besides usual therapeutics (hyperhydration, urine alkalinisation, leucovorin rescue, renal replacement therapy), a costly specific enzymatic treatment (glucarpidase) is now available but its clinical impact remains elusive.

PATIENTS AND METHODS

We analysed high-dose methotrexate prescription charts in 11 clinical centres during the last 15 years to identify and describe adult patients who developed acute kidney injury (according to KDIGO classification). Glucarpidase use was recorded (French temporary regulatory approval criteria: methotrexate at least 10μmol/L at 48h or at least 3μmol/L at 48h associated with acute kidney injury).

RESULTS

Seventy-six acute kidney injury cases have been studied. Mean peak creatinine was 206μmol/L after a mean delay of 5.6 days, with 19 cases of stage 1 acute kidney injury (25%), 29 cases of stage 2 (38%) and 27 cases of stage 3 (36%). Anuria (one case) and need for renal replacement therapy (four cases) were unusual whereas fluid overload was often observed (29%). Three months after high-dose methotrexate treatment, mortality-rate was 17%, and 12% of surviving patients developed renal sequelae.

CONCLUSION

Sixty-one percent of patients received a glucarpidase perfusion during acute kidney injury. Despite a dramatic decrease of methotrexate serum levels, glucarpidase as compared with conservative treatment did not modify acute kidney injury stage, recovery delay, need for renal replacement therapy or the incidence of extrarenal toxicities. Net clinical benefit was not observed even after stratification according to eligibility criteria for glucarpidase use. Glucarpidase has probably no or little effects on methotrexate localized into tubular lumen or proximal tubular cells and that may account for the absence of nephroprotective effect for enzymatic treatment.

In Vitro Stimulation of Multidrug Resistance-Associated Protein 2 Function Is Not Reproduced In Vivo in Rats

Previously we reported that coproporphyrin-I (CP-I) is an optimal probe substrate for multidrug resistance-associated protein 2 (MRP2), and stimulation of MRP2-mediated transport is probe substrate-dependent. In the present investigation, we assessed if the in vitro stimulation is physiologically relevant. Similar to human MRP2 transport, CP-I was transported by rat Mrp2 in a typical Michaelis-Menten kinetics with apparent K_m and V_max values of 15 ± 6 µM and 161 ± 20 pmol/min/mg protein, respectively. In vivo Mrp2 functions were monitored by biliary and renal secretion of CP-I and its isomer CP-III, in bile-duct cannulated rats before and after treatment with mitoxantrone, progesterone, and verapamil. These compounds stimulated Mrp2-mediated CP-I transport in vitro. No significant increase in biliary or renal clearances, as well as in the cumulative amount of CP-I or CP-III eliminated in bile, were detected following treatment with the in vitro stimulators, indicating an in vitro to in vivo disconnect. In presence of 10 µM bilirubin, the in vitro stimulation was suppressed. We concluded that the in vitro stimulation of CP-I transport mediated by Mrp2 is not translatable in vivo, and proposed that the presence of endogenous compounds such as bilirubin in the liver may contribute to the in vitro to in vivo disconnect.

Endogenous Metabolites-Mediated Communication Between OAT1/OAT3 and OATP1B1 May Explain the Association Between SLCO1B1 SNPs and Methotrexate Toxicity

Although OATP1B1 is not expressed in the kidney, polymorphisms in SLCO1B1 have been associated with methotrexate clearance or toxicity. This unexpected pharmacogenetic association may reflect remote communication between liver and kidney transporters. This study confirms the pharmacogenetic association with methotrexate toxicity in adult patients with hematological malignancies. Using a targeted urinary metabolomics approach, we identified 38 and 34 metabolites which were differentially excreted between wildtype and carriers of the c.388A>G or c.521T>C variant alleles, respectively, half of them being associated with methotrexate toxicity. These metabolites mainly consisted of fatty acid derivatives and microbiota catabolites, including glycine conjugates and other uremic toxins, all known OATs substrates. These results suggest that dysfunction of a transporter affects the excretion profile of endogenous or exogenous substrates, possibly through metabolite-mediated interactions involving other transport systems, even in distant organs. This opens the way for better comprehension of complex pharmacokinetics and transporter-mediated drug-drug or nutrient-drug interactions.