Population pharmacokinetics and association between A77 1726 plasma concentrations and disease activity measures following administration of leflunomide to people with rheumatoid arthritis

Serum teriflunomide concentrations in routine multiple sclerosis therapy: A cross-sectional pilot study

BACKGROUND

Teriflunomide is administered orally to treat relapsing-remitting multiple sclerosis. In this prospective pilot study, the free and total serum concentrations of teriflunomide obtained during routine health care were measured and their relationship with disease activity was evaluated.

METHODS

Eighty-nine patients were included in this study. Blood samples were collected from April 2021 to February 2022, and free and total teriflunomide serum concentrations were measured. Patient assessment involved monitoring of blood counts and potential adverse effects of teriflunomide.

RESULTS

In the steady-state group, total teriflunomide concentrations ranged from 14.7 to 144.2 mg/L, while free concentrations from 31.1 to 389.7 μg/L. In the non-steady-state group, the total concentration ranged from 2.2 to 59.3 mg/L, with free concentrations ranging from 6.8 to 143.5 μg/L. In the steady-state group, a significant inverse correlation was found between absolute peripheral blood lymphocyte count and both total and free teriflunomide serum concentrations.

CONCLUSION

Although all patients were treated with the same dose, up to a 10-fold difference in total and free teriflunomide serum concentrations, and up to a 5-fold difference in steady-state trough concentrations were observed. This vast interindividual variability can potentially lead to toxicity or, conversely, to suboptimal therapeutic concentrations of teriflunomide, with the risk of further worsening of multiple sclerosis compensation.

Association of indoor dampness indicators with rheumatic diseases/symptoms in older adults: A comparative cross-sectional study in Chongqing and Beijing

Dampness is strongly associated with rheumatic diseases, which particularly affect the older adults. Tackling dampness is therefore important, especially given that climate change is expected to exacerbate rheumatic diseases; however, limited studies have compared the risk of rheumatic diseases in older adults based on humidity levels across different regions. To explore this, a comparative cross-sectional study was conducted to collect information on the residential characteristics, lifestyles, and health outcomes of 2000 individuals aged 60-74 years from Chongqing and Beijing. From this data, we tested for an association between six indoor dampness indicators and rheumatic related diseases/symptoms. The results showed that the risk values for joint pain were higher in Chongqing than in Beijing. Moreover, the risk of joint stiffness increased more strongly in Chongqing than in Beijing as the cumulative number of dampness exposure indicators increased. The key indoor dampness indicators affecting rheumatic diseases were different for Chongqing and Beijing. Overall, this study compared the risk of rheumatic diseases in older adults in the north and south of China because of dampness exposure and, from these, provided suggestions for modifying the indoor environments to prevent or reduce rheumatic symptoms.

Leflunomide alleviates obesity via activation of the TAK1-AMPK pathway and induction of lipophagy

Lipophagy is a subset of selective autophagy that specifically degrades lipid droplets and plays an important role in obesity. Leflunomide treatment in rheumatoid arthritis (RA) patients has been associated with weight loss and decreased blood glucose levels, which cannot be attributed to its known side effects. Our prior studies showed that A77 1726, the active metabolite of leflunomide, acts as an inhibitor of S6K1 to sensitize the insulin receptor and control hyperglycemia. Whether the anti-obesity effect of leflunomide is mediated by targeting S6K1 and its underlying mechanisms remain unclear. Here, we report that A77 1726 induced LC3 lipidation and increased the formation of autophagosomes and lipoautolysosomes in 3T3-L1 adipocytes by activating TGF-β-activated kinase 1 (TAK1), AMP-activated kinase (AMPK), and Unc-51 like autophagy-activated kinase 1 (ULK1). A77 1726 reduced the content of lipid droplets in 3T3-L1 adipocytes, which was blocked by bafilomycin or by beclin-1 knockdown. Similar observations were made in murine adipocytes differentiated from S6K1-/- embryonic fibroblasts (MEFs). Leflunomide treatment restricted bodyweight gains in ob/ob mice and reduced the visceral fat deposit and the size of adipocytes. Leflunomide treatment induced autophagy in adipose and liver tissues and reduced hepatic lipid contents. Consistently, S6K1 knockout increased the levels of LC3 lipidation in the liver, muscle, and fat of S6K-/- mice. Leflunomide treatment and S6K1 deficiency both induced TAK1, AMPK, and ULK1 phosphorylation in these tissues. These observations collectively suggest that leflunomide controls obesity in part by activating AMPK and inducing lipophagy. Our study provides insights into the mechanisms of leflunomide-mediated anti-obesity activity.

Potential Anti-Mpox Virus Activity of Atovaquone, Mefloquine, and Molnupiravir, and Their Potential Use as Treatments

BACKGROUND

Mpox virus (MPXV) is a zoonotic orthopoxvirus and caused an outbreak in 2022. Although tecovirimat and brincidofovir are approved as anti-smallpox drugs, their effects in mpox patients have not been well documented. In this study, by a drug repurposing approach, we identified potential drug candidates for treating mpox and predicted their clinical impacts by mathematical modeling.

METHODS

We screened 132 approved drugs using an MPXV infection cell system. We quantified antiviral activities of potential drug candidates by measuring intracellular viral DNA and analyzed the modes of action by time-of-addition assay and electron microscopic analysis. We further predicted the efficacy of drugs under clinical concentrations by mathematical simulation and examined combination treatment.

RESULTS

Atovaquone, mefloquine, and molnupiravir exhibited anti-MPXV activity, with 50% inhibitory concentrations of 0.51-5.2 μM, which was more potent than cidofovir. Whereas mefloquine was suggested to inhibit viral entry, atovaquone and molnupiravir targeted postentry processes. Atovaquone was suggested to exert its activity through inhibiting dihydroorotate dehydrogenase. Combining atovaquone with tecovirimat enhanced the anti-MPXV effect of tecovirimat. Quantitative mathematical simulations predicted that atovaquone can promote viral clearance in patients by 7 days at clinically relevant drug concentrations.

CONCLUSIONS

These data suggest that atovaquone would be a potential candidate for treating mpox.

Therapeutic drug monitoring of disease-modifying antirheumatic drugs in circulating leukocytes in immune-mediated inflammatory diseases

The treatment of immune-mediated inflammatory diseases (IMIDs) is one of the main challenges of modern medicine. Although a number of disease-modifying antirheumatic drugs (DMARDs) are available, there is wide variability in clinical response to treatment among individuals. Therapeutic drug monitoring (TDM) has been proposed to optimize treatment; however, some patients still experience unsatisfactory outcomes, although the blood concentrations of drugs in these patients remain in the therapeutic range. One possible reason for this is that the conventional samples (e.g., whole blood or plasma) used in TDM may not accurately reflect drug concentrations or concentrations of their metabolites at the target site. Hence, more refined TDM approaches to guide clinical decisions related to dose optimization are necessary. Circulating leukocytes or white blood cells have a critical role in driving the inflammatory process. They are recruited to the site of injury, infection and inflammation, and the main target of small molecule DMARDs is within immune cells. Given this, assaying drug concentrations in leukocytes has been proposed to be of possible relevance to the interpretation of outcomes. This review focuses on the clinical implications and challenges of drug monitoring of DMARDs in peripheral blood leukocytes from therapeutic or toxicological perspectives in IMIDs.

Development of a population pharmacokinetic model and optimal dosing regimen of leflunomide in Korean population

PURPOSE

Leflunomide is an immunosuppressive drug indicated for the treatment of rheumatoid arthritis (RA). While the pharmacokinetics (PK) of its active metabolite A771726 reportedly show large interindividual variability, no efficient dose individualization strategy is currently available. The goal of this work was to develop a population PK model for A771726 and propose an optimal individualized dosing strategy.

METHODS

A771726 plasma concentration data were collected from 50 healthy male volunteers participating in two leflunomide PK studies given a single oral dose of 40 mg. Concentrations were elevated in low body weight (WT) subjects and showed multiple peaks. Thus, A771726 PK modeling was conducted incorporating allometry scaling and enterohepatic circulation (EHC). For dose optimization, simulating a set of 1000 virtual subjects from the developed model and dividing the subjects into 5 groups with WT of 50, 60, 70, 80, 90 kg, respectively, the optimal dose was explored that achieves the drug concentration most similar to the target, which was defined as the concentration for the 70 kg subject treated with the current standard dosage regimen (the loading dose of 100 mg QD for 3 days, followed by the maintenance dose of 20 mg QD).

RESULTS

The data were best described by a two compartment model with first order absorption incorporating EHC with the bile released into the intestine. None of the covariates tested was found to be significant other than WT used in allometry. Simulation showed that the optimal loading dose increased by 15 mg for every 10 kg increment in WT while the optimal maintenance dose was 15 and 25 mg for 50 and 90 kg groups, respectively, and the same (= 20 mg) for the others. Large concentration differences from the target observed in low and high WT groups disappeared when optimal doses were given.

CONCLUSIONS

This work demonstrates the importance of a population PK model-based dose optimization approach in maintaining drug therapeutic concentrations in leflunomide treatment.

Therapeutic drug monitoring of teriflunomide: do plasma concentrations predict response to leflunomide in patients with rheumatoid arthritis?

OBJECTIVES

Leflunomide is a commonly used treatment for rheumatoid arthritis. It acts by inhibiting dihydroorotate dehydrogenase through its active metabolite teriflunomide. The objective of the study was to investigate the relation between plasma-concentration of teriflunomide and disease-activity in rheumatoid arthritis.

METHODS

Data were collected from patients with rheumatoid arthritis on a stable leflunomide dose for at least 2 months. Socio-demographic data, disease characteristics and DAS28 score were recorded. Blood samples were taken for determination of teriflunomide concentration.

RESULTS

A total of 32 serum concentration-time measurements were collected. The concentration of teriflunomide was positively correlated with disease duration of RA (r²=0.2264) and the number of swollen joints (r²=0.2413). There was a trend towards a positive correlation between Health Assessment Questionnaire (HAQ) and plasma teriflunomide concentration (r²=0.1699). Weight was negatively correlated with the residual plasma concentration of teriflunomide (r²=0.2483). However, there was no significant correlation between residual-plasma-concentration of teriflunomide and the following parameters: age, sex, number of tender painful joints, patient-global-assessment, C-reactive protein (CRP) and duration of prescription of leflunomide. We did not find association between disease-activity and residual-plasma-concentration of teriflunomide (r²=0.0021) and haven't been able to define the threshold value of residual-plasma-concentration of leflunomide predictive of a good-response.

CONCLUSIONS

We did not find a concentration-effect-relationship. However, therapeutic drug monitoring of teriflunomide may be useful to ensure adherence and evaluate toxic-levels in case of adverse-events.

Pyrimidine de novo synthesis inhibition selectively blocks effector but not memory T cell development

Blocking pyrimidine de novo synthesis by inhibiting dihydroorotate dehydrogenase is used to treat autoimmunity and prevent expansion of rapidly dividing cell populations including activated T cells. Here we show memory T cell precursors are resistant to pyrimidine starvation. Although the treatment effectively blocked effector T cells, the number, function and transcriptional profile of memory T cells and their precursors were unaffected. This effect occurred in a narrow time window in the early T cell expansion phase when developing effector, but not memory precursor, T cells are vulnerable to pyrimidine starvation. This vulnerability stems from a higher proliferative rate of early effector T cells as well as lower pyrimidine synthesis capacity when compared with memory precursors. This differential sensitivity is a drug-targetable checkpoint that efficiently diminishes effector T cells without affecting the memory compartment. This cell fate checkpoint might therefore lead to new methods to safely manipulate effector T cell responses.

Saliva as Blood Alternative in Therapeutic Monitoring of Teriflunomide-Development and Validation of the Novel Analytical Method

Therapeutic drug monitoring (TDM) is extremely helpful in individualizing dosage regimen of drugs with narrow therapeutic ranges. It may also be beneficial in the case of drugs characterized by serious side effects and marked interpatient pharmacokinetic variability observed with leflunomide and its biologically active metabolite, teriflunomide. One of the most popular matrices used for TDM is blood. A more readily accessible body fluid is saliva, which can be collected in a much safer way comparing to blood. This makes it especially advantageous alternative to blood during life-threatening SARS-CoV-2 pandemic. However, drug’s saliva concentration is not always a good representation of its blood concentration. The aim of this study was to verify whether saliva can be used in TDM of teriflunomide. We also developed and validated the first reliable and robust LC-MS/MS method for quantification of teriflunomide in saliva. Additionally, the effect of salivary flow and swab absorptive material from the collector device on teriflunomide concentration in saliva was evaluated. Good linear correlation was obtained between the concentration of teriflunomide in plasma and resting saliva (p < 0.000016, r = 0.88), and even better between plasma and the stimulated saliva concentrations (p < 0.000001, r = 0.95) confirming the effectiveness of this non-invasive method of teriflunomide’s TDM. The analyzed validation criteria were fulfilled. No significant influence of salivary flow (p = 0.198) or type of swab in the Salivette device on saliva’s teriflunomide concentration was detected. However, to reduce variability the use of stimulated saliva and synthetic swabs is advised.

Therapeutic response to leflunomide in combo therapy and monotherapy is associated to serum teriflunomide (A77 1726) levels

There is a significant rate of therapeutic failure in rheumatoid arthritis (RA) patients treated with leflunomide (LEF). This study investigates the utility values of teriflunomide levels (A77 1726) in identifying RA patients who remained with moderate or severe disease activity after the treatment with LEF. In this cross-sectional study, we compared: (a) RA patients who achieved a DAS28-ESR ≤ 3.2, and (b) RA patients who maintained a DAS28-ESR > 3.2 after treatment. ROC curves determined the cut-off of A77 1726 with the better performance to identify patients achieving a DAS28-ESR ≤ 3.2. Of the 115 patients treated with LEF, 69 (60%) remained with moderate/severe disease activity and 46 (40%) achieved low disease activity/remission. Higher A77 1726 levels showed a negative correlation with DAS28-ESR (r = − 0.42, p < 0.001) and other parameters of disease activity. We obtained the following utility values with the cut-off of A77 1726 > 10 µg/mL to identify RA patients who achieved a DAS28-ESR ≤ 3.2: sensitivity of 91.31%; specificity of 73.91%; positive predictive value of 70.00%; and negative predictive value of 92.73%. Serum A77 1726 discriminated between RA patients who remained with moderate/severe disease activity despite the treatment with LEF both as monotherapy and LEF as combo therapy.

Clinical efficacy and safety of methotrexate compared with leflunomide in the treatment of rheumatoid arthritis: A protocol for systematic review and meta-analysis

BACKGROUND

Methotrexate and leflunomide are classic treatments for rheumatoid arthritis (RA), however, which is the best choice for patients of RA is still an important question clinically, and this meta-analysis is used to systematically evaluate and compare their efficacy and safety.

METHODS

We searched PubMed, Cochrance Library, Embase, SinoMed, China National Knowledge Infrastructure, China Science and Technology Journal Database, WanFang Data databases. The retrieval time was from the establishment to September 7, 2021. Literature screening, data extraction, and quality assessment were performed according to the Cochrane risk of bias tool. Meta-analysis of the included studies was performed using RevMan 5.3 software and Stata 12.0 software.

RESULTS

The clinical efficacy and safety of leflunomide and methotrexate are evaluated by American College of Rheumatology (ACR)20/50/70, DAS28, total effective rate, adverse reaction rate, morning stiffness, swollen joint count, tender joint count, erythrocyte sedimentation rate, C-reactive protein, and rheumatoid factor.

CONCLUSION

The results of this meta-analysis will provide reliable evidence clinical efficacy and safety for RA. More high-quality randomized controlled trials are still needed to provide more reliable evidence for the treatment of RA.

PROSPERO NUMBER

CRD42021270980.

Precision Medicine With Leflunomide: Consideration of the DHODH Haplotype and Plasma Teriflunomide Concentration and Modification of Outcomes in Patients With Rheumatoid Arthritis

OBJECTIVE

Leflunomide is a commonly used disease-modifying drug in the treatment of rheumatoid arthritis (RA). Its effects are mediated via inhibition of dihydroorotate dehydrogenase (DHODH) by its active metabolite teriflunomide, and the pharmacokinetics of teriflunomide are highly variable. Our objective was to examine the association between the DHODH haplotype and plasma teriflunomide concentration with response to leflunomide in patients with RA where leflunomide was added to an existing disease-modifying drug regimen after failure to achieve an adequate response with conventional triple therapy.

METHODS

Patients with RA who were taking, or were about to initiate, leflunomide were included. Participant characteristics, including the DHODH haplotype, were determined. Up to 5 plasma samples were collected after leflunomide was initiated for assays of total and free teriflunomide concentration. Disease activity was determined via the 28-joint Disease Activity Score (DAS28). The association between DAS28 scores and patient covariates was determined by linear mixed-effects modeling.

RESULTS

A total of 67 patients were included in the study. The DAS28 score after initiation of leflunomide was associated with the baseline DAS28 score (β = 0.70, P < 0.001) and was higher in those who carried the DHODH haplotype 2 (β = 0.56. P = 0.01) and did not carry the shared epitope (β = 0.56, P = 0.013). As total and free plasma teriflunomide concentration increased, the DAS28 score was significantly lower (P < 0.001 and P = 0.001, respectively). When considering threshold concentrations, teriflunomide concentrations >16 mg/liter were associated with a DAS28 score that was 0.33 lower, and when free teriflunomide concentration was >35 µg/liter, the DAS28 score was 0.32 lower.

CONCLUSION

Teriflunomide concentration and carriage of the DHODH haplotype 2 are associated with response to leflunomide in patients with RA, and a total plasma teriflunomide concentration of at least 16 mg/liter is needed to maximize the likelihood of response.

Inhibition of canine distemper virus replication by blocking pyrimidine nucleotide synthesis with A77 1726, the active metabolite of the anti-inflammatory drug leflunomide

Canine distemper virus (CDV) is the aetiological agent that causes canine distemper (CD). Currently, no antiviral drugs have been approved for CD treatment. A77 1726 is the active metabolite of the anti-rheumatoid arthritis (RA) drug leflunomide. It inhibits the activity of Janus kinases (JAKs) and dihydroorotate dehydrogenase (DHO-DHase), a rate-limiting enzyme in de novo pyrimidine nucleotide synthesis. A77 1726 also inhibits the activity of p70 S6 kinase (S6K1), a serine/threonine kinase that phosphorylates and activates carbamoyl-phosphate synthetase (CAD), a second rate-limiting enzyme in the de novo pathway of pyrimidine nucleotide synthesis. Our present study focuses on the ability of A77 1726 to inhibit CDV replication and its underlying mechanisms. Here we report that A77 1726 decreased the levels of the N and M proteins of CDV and lowered the virus titres in the conditioned media of CDV-infected Vero cells. CDV replication was not inhibited by Ruxolitinib (Rux), a JAK-specific inhibitor, but by brequinar sodium (BQR), a DHO-DHase-specific inhibitor, and PF-4708671, an S6K1-specific inhibitor. Addition of exogenous uridine, which restores intracellular pyrimidine nucleotide levels, blocked the antiviral activity of A77 1726, BQR and PF-4708671. A77 1726 and PF-4708671 inhibited the activity of S6K1 in CDV-infected Vero cells, as evidenced by the decreased levels of CAD and S6 phosphorylation. S6K1 knockdown suppressed CDV replication and enhanced the antiviral activity of A77 1726. These observations collectively suggest that the antiviral activity of A77 1726 against CDV is mediated by targeting pyrimidine nucleotide synthesis via inhibiting DHO-DHase activity and S6K1-mediated CAD activation.

Inhibition of porcine epidemic diarrhea virus (PEDV) replication by A77 1726 through targeting JAK and Src tyrosine kinases

Porcine epidemic diarrhea (PED) virus (PEDV) is a coronavirus that primarily infects porcine intestinal epithelial cells and causes severe diarrhea and high fatality in piglets. A77 1726 is the active metabolite of leflunomide, a clinically approved anti-rheumatoid arthritis (RA) drug. A77 1726 inhibits the activity of protein tyrosine kinases (PTKs), p70 S6 kinase (S6K1), and dihydroorotate dehydrogenase (DHO-DHase). Whether A77 1726 can control coronavirus infections has not been investigated. Here we report that A77 1726 effectively restricted PEDV replication by inhibiting Janus kinases (JAKs) and Src kinase activities but not by inhibiting DHO-DHase and S6K1 activities. Overexpression of Src, JAK2 or its substrate STAT3 enhanced PEDV replication and attenuated the antiviral activity of A77 1726. Our study demonstrates for the first time the ability of A77 1726 to control coronavirus replication by inhibiting PTK activities. Leflunomide has potential therapeutic value for the control of PEDV and other coronavirus infections.

Repurposing leflunomide for relapsed/refractory multiple myeloma: a phase 1 study

The inexpensive, well-tolerated, immunomodulatory agent leflunomide, used extensively for the treatment of rheumatoid arthritis, has been shown to produce significant activity against multiple myeloma (MM) in pre-clinical studies. We conducted a phase 1 study (clinicaltrials.gov: NCT02509052) of single agent leflunomide in patients with relapsed/refractory MM (≥3 prior therapies). At dose levels 1 and 2 (20 and 40 mg), no dose-limiting toxicities (DLTs) were observed. At dose level 3 (60 mg), one patient experienced elevated alanine aminotransferase; an additional three patients were enrolled at this dose level without further DLTs. Overall, toxicities were infrequent and manageable. Nine out of 11 patients achieved stable disease (SD), two subjects experiencing SD for nearly one year or longer. The tolerable safety profile of leflunomide, combined with a potential disease stabilization, is motivating future studies of leflunomide, in combination with other MM drugs, or as an approach to delay progression of smoldering MM.

The role of Chinese herbal medicine in the management of adverse drug reactions of leflunomide in treating rheumatoid arthritis

BACKGROUND

The high discontinuation rate in RA patients who use LEF might be attributed to their intolerance rather than irresponsibility. The concomitant administration of Leflunomide (LEF) with Chinese herbal medicine (CHM) provides a potential solution to preventing the adverse drug reactions (ADRs) induced by LEF during the treatment of rheumatoid arthritis (RA).

PURPOSE

To investigate whether co-administration of LEF with CHM could bring in both increased therapeutic outcomes and reduced ADRs due to the framework of treatment at the level of entire body.

STUDY DESIGN

The mechanism of LEF in RA treatment and the ADRs it induced was introduced based on recent papers. Reported clinical examples of CHM concurrent use with LEF was revealed to provide more evidence. The management of the ADRs caused by LEF was suggested by current researches on the concomitant therapy of CHM with LEF.

RESULTS

The active ingredients, compounds and medicinal herbs all demonstrated properties in relieving toxicities and reducing ADRs when used with LEF and reported in several clinical cases. The wide application of concurrent use of CHM with LEF is however hindered by the complex pathogenesis of RA which requires further scientific grounds for diagnosis and treatment.

CONCLUSION

This review introduced that the adoption of CHM is emerging as a novel strategy for the management of ADRs caused by LEF.

Clinical Pharmacokinetic Monitoring of Leflunomide in Renal Transplant Recipients with BK Virus Reactivation: A Review of the Literature

Leflunomide is an immunosuppressive drug with in vitro and initial observational evidence of antiviral activity against BK virus (BKV), a pathogen that causes opportunistic infection upon reactivation in renal transplant recipients. Leflunomide is considered an ancillary option to immunosuppression reduction in the management of BKV reactivation. Plasma or blood concentrations of teriflunomide, the active metabolite of leflunomide, are commonly monitored because of high leflunomide doses being used, known inter-individual variability in pharmacokinetics, and hepatotoxicity risk. However, the utility of clinical pharmacokinetic monitoring for leflunomide is as yet unclear. A literature search of MEDLINE (1946-December 2016), EMBASE (1974-December 2016), the CENTRAL database, and Google Scholar was performed to identify relevant English-language articles. Further articles were identified from references in relevant literature. A previously published 9-step decision-making algorithm was used to assess the available literature and determine the utility of clinical pharmacokinetic monitoring for leflunomide. Teriflunomide is readily measurable in the plasma or blood, but a clear relationship between concentration and efficacy or toxicity is lacking, and its therapeutic range is not well-established. Efficacy and toxicity endpoints such as renal function and BKV clearance can be readily assessed without measuring teriflunomide concentrations. Pharmacokinetic parameters are affected by genetic polymorphisms in cytochrome P450 CYP2C19 and ABCG2 genes. Therefore, routine clinical pharmacokinetic monitoring of leflunomide cannot be recommended based on current available evidence. However, it may provide clinical benefit in difficult situations when patients demonstrate a lack of therapeutic response or exhibit signs of drug toxicity.

Control of hyperglycemia in male mice by leflunomide: mechanisms of action

p70 S6 kinase (S6K1) is a serine/threonine kinase that phosphorylates the insulin receptor substrate-1 (IRS-1) at serine 1101 and desensitizes insulin receptor signaling. S6K1 hyperactivation due to overnutrition leads to hyperglycemia and type 2 diabetes. Our recent study showed that A77 1726, the active metabolite of the anti-rheumatoid arthritis (RA) drug leflunomide, is an inhibitor of S6K1. Whether leflunomide can control hyperglycemia and sensitize the insulin receptor has not been tested. Here we report that A77 1726 increased AKTS473/T308 and S6K1T389 phosphorylation but decreased S6S235/236 and IRS-1S1101 phosphorylation in 3T3-L1 adipocytes, C2C12 and L6 myotubes. A77 1726 increased insulin receptor tyrosine phosphorylation and binding of the p85 subunit of the PI-3 kinase to IRS-1. A77 1726 enhanced insulin-stimulated glucose uptake in L6 myotubes and 3T3-L1 adipocytes, and enhanced insulin-stimulated glucose transporter type 4 (GLUT4) translocation to the plasma membrane of L6 cells. Finally, we investigated the anti-hyperglycemic effect of leflunomide on ob/ob and high-fat diet (HFD)-induced diabetes mouse models. Leflunomide treatment normalized blood glucose levels and overcame insulin resistance in glucose and insulin tolerance tests in ob/ob and HFD-fed mice but had no effect on mice fed a normal chow diet (NCD). Leflunomide treatment increased AKTS473/T308 phosphorylation in the fat and muscle of ob/ob mice but not in normal mice. Our results suggest that leflunomide sensitizes the insulin receptor by inhibiting S6K1 activity in vitro, and that leflunomide could be potentially useful for treating patients with both RA and diabetes.

Inhibition of p70 S6 kinase activity by A77 1726 induces autophagy and enhances the degradation of superoxide dismutase 1 (SOD1) protein aggregates

Autophagy plays a central role in degrading misfolded proteins such as mutated superoxide dismutase 1 (SOD1), which forms aggregates in motor neurons and is involved in the pathogenesis of amyotrophic lateral sclerosis (ALS). Autophagy is activated when UNC-51-like kinase 1 (ULK1) is phosphorylated at S555 and activated by AMP-activated protein kinase (AMPK). Autophagy is suppressed when ULK1 is phosphorylated at S757 by the mechanistic target of rapamycin (mTOR). Whether p70 S6 kinase 1 (S6K1), a serine/threonine kinase downstream of mTOR, can also regulate autophagy remains uncertain. Here we report that inhibition of S6K1 by A77 1726, the active metabolite of an anti-inflammatory drug leflunomide, induced mTOR feedback activation and ULK1S757 phosphorylation in NSC34 cells, a hybrid mouse motoneuron cell line. Unexpectedly, A77 1726 did not suppress but rather induced autophagy by increasing AMPKT172 and ULK1S555 phosphorylation. Similar observations were made with PF-4708671, a specific S6K1 inhibitor, or with S6K1 siRNA. Further studies showed that A77 1726 induced AMPK phosphorylation by activating the TGF-β-activated kinase 1 (TAK1). Functional studies revealed that A77 1726 induced co-localization of mutant SOD1G93A protein aggregates with autophagosomes and accelerated SOD1G93A protein degradation, which was blocked by inhibition of autophagy through autophagy-related protein 7 (ATG7) siRNA. Our study suggests that S6K1 inhibition induces autophagy through TAK1-mediated AMPK activation in NSC34 cells, and that blocking S6K1 activity by a small molecule inhibitor such as leflunomide may offer a new strategy for ALS treatment.

Genetic predictors of efficacy and toxicity of iguratimod in patients with rheumatoid arthritis

Iguratimod (IGU) is a novel disease-modifying anti-rheumatic drug (DMARD) in rheumatoid arthritis (RA). Like other DMARDs, IGU exhibited significant differences in effectiveness and safety.

AIM

The aim of this study was to identify genetic predictorsof efficacyand toxicity of IGU in patients with RA.

MATERIALS & METHODS

Seven SNPs from IGU-metabolizing genes were genotyped in 272 IGU-treated patients with RA. Results: ABCG2 rs2231142 A allele conferred a higher response to IGU, while NAT2 rs1495742 G carriersconferred a lower response to IGU. CYP2C19*2 rs4244285 A carriers had higher risk for IGU-induced toxicity compared to the GG carriers.

CONCLUSION

Our study suggests that the polymorphisms of ABCG2 (rs2231142), NAT2 (rs1495741)and CYP2C19*2 (rs4244285) may help to predict thetherapeutic effectiveness and toxicity of IGU in patients with RA.

Mitochondrial dysfunction induced by leflunomide and its active metabolite

Leflunomide, an anti-inflammatory drug used for the treatment of rheumatoid arthritis, has been marked with a black box warning regarding an increased risk of liver injury. The active metabolite of leflunomide, A771726, which also carries a boxed warning about potential hepatotoxicity, has been marketed as teriflunomide for the treatment of relapsing multiple sclerosis. Thus far, however, the mechanism of liver injury associated with the two drugs has remained elusive. In this study, cytotoxicity assays showed that ATP depletion and subsequent LDH release were induced in a time- and concentration-dependent manner by leflunomide in HepG2 cells, and to a lesser extent, by A77 1726. The decline of cellular ATP levels caused by leflunomide was dramatically exacerbated when galactose was substituted for glucose as the sugar source, indicating a potential mitochondrial liability of leflunomide. By measuring the activities of immuno-captured mitochondrial oxidative phosphorylation (OXPHOS) complexes, we found that leflunomide and A77 1726 preferentially targeted complex V (F₁F_O ATP synthase), with IC₅₀ values of 35.0 and 63.7 μM, respectively. Bongkrekic acid, a mitochondrial permeability transition pore blocker that targets adenine nucleotide translocase, profoundly attenuated mitochondrial membrane depolarization, ATP depletion, and LDH leakage induced by leflunomide and A77 1726. Substantial alterations of mitochondrial function at the transcript level were observed in leflunomide-treated HepG2 cells, whereas the effects of A77 1726 on the cellular transcriptome were much less profound. Our results suggest that mitochondrial dysfunction may be implicated in the hepatotoxicity associated with leflunomide and A77 1726, with the former exhibiting higher toxicity potency.

Leflunomide for Inflammatory Arthritis in End-Stage Renal Disease on Peritoneal Dialysis: A Pharmacokinetic and Pharmacogenetic Study

OBJECTIVE

To study the pharmacokinetics and pharmacogenetics of leflunomide and document its efficacy and safety in the treatment of inflammatory arthritis in a patient with end-stage renal disease (ESRD) who was on peritoneal dialysis.

CASE SUMMARY

Therapy for a 78-year-old man with ESRD who required peritoneal dialysis was started with leflunomide 10 mg/day for psoriatic arthritis. The dosage was increased to 20 mg/day after 3 months. Monitoring was continued until the patient's unexpected death from myocardial infarction at 8 months. Total and unbound teriflunomide (the active metabolite of leflunomide) concentrations were measured by liquid-chromatography-tandem mass spectrometry. Genotyping for CYP2C19 and ABCG2 polymorphisms, both known to influence teriflunomide pharmacokinetics, was also performed.

DISCUSSION

Total concentrations of teriflunomide varied between 5.2 and 23.2 mg/L, while unbound concentrations varied between 0.0306 and 0.1468 mg/L. The unbound fraction varied between 0.367% and 0.71%. Teriflunomide was found in the dialysate at a concentration of 0.0981 mg/L. A single CYP2C19 loss of function allele was present, as was wild-type ABCG2. Leflunomide appeared to be therapeutically effective, as evidenced by a reduction in daily prednisolone dosage from 20 mg to 6mg; the Disease Activity Score in 28 joints (DAS28) was 5.46 at enrollment and 4.03 after 7 months. Health Assessment Questionnaire—Disability Index improved from 0.5 to 0.125 at 7 months. Numerous significant adverse events that were considered unrelated to leflunomide occurred.

CONCLUSIONS

Dose adjustment for leflunomide does not appear to be required in the context of ESRD requiring peritoneal dialysis. We present novel evidence that a small amount of teriflunomide is removed by peritoneal dialysis. This case suggests that leflunomide is safe to use as therapy for inflammatory arthritis despite the presence of ESRD requiring peritoneal dialysis.

Putting recommendations into practice: Australian rheumatologists' opinions on leflunomide use in rheumatoid arthritis

Leflunomide is the most recently introduced conventional disease-modifying anti-rheumatic drugs in Australia. It has several unique methods for initiation, unique monitoring recommendations and a distinctive cessation protocol in the event of serious toxicity. The aim of this study was to evaluate initiation and monitoring practices of Australian rheumatologists using leflunomide. A survey was emailed twice, approximately 3 months apart to 332 rheumatologist members of the Australian Rheumatology Association. Wave analysis was used to assess evidence of non-response bias. The response rate to the survey was 20% and there was no difference between the responses of waves 1 and 2. Fifty percent of the respondents indicated that 20 mg once daily was the initial dose of leflunomide that they most commonly prescribed, 45% indicated 10 mg once daily, whilst only 3% preferred to initiate leflunomide at 100 mg daily for 2-3 days followed by 10 mg once a day as recommended when first marketed. Of the responders, 12% had used doses above 20 mg daily and 70% had used alternate daily dosing with leflunomide. In a patient taking leflunomide with an ALT or AST >3 times the ULN on two or more blood tests, 75% of responders indicated they would stop leflunomide immediately and 20% would follow cessation by administering a cholestyramine washout. The choice of initial leflunomide dose among responding Australian rheumatologists varied considerably, although most preferred not to use the loading dose. Despite the recommendation of clinical guidelines, the use of a cholestyramine washout procedure for hepatic toxicity is not universal.

Intracellular CD3+ T Lymphocyte Teriflunomide Concentration Is Poorly Correlated with and Has Greater Variability Than Unbound Plasma Teriflunomide Concentration

Leflunomide's active metabolite teriflunomide inhibits dihydro-oroate dehydrogenase, an enzyme essential to proliferation of T lymphocytes. As teriflunomide must reach the target site to have this effect, this study assessed the distribution of teriflunomide into T lymphocytes, as intracellular concentrations may be a superior response biomarker to plasma concentrations. CD3 MicroBeads (Miltenyi Biotec, Bergisch Gladbach, Germany) were used to extract CD3⁺ T cells from the peripheral blood of patients with rheumatoid arthritis who were taking a stable dose of leflunomide. Unbound plasma and intra-CD3⁺ T cell teriflunomide concentrations were quantified using liquid chromatography-mass spectrometry. Concentration (log transformed) and partition differences were assessed through paired Student t tests. Sixteen patients provided plasma steady-state teriflunomide samples, and eight provided a sample 6-12 weeks later. At time-point one, the geometric mean teriflunomide concentration (range) in CD3⁺ T cells was 18.12 μg/L (6.15-42.26 μg/L) compared with 69.75 μg/L (32.89-263.1 μg/L) unbound in plasma (P < 0.001). The mean partition coefficient (range) for unbound plasma teriflunomide into CD3⁺ T cells was 0.295 (0.092-0.632), which was significantly different from unity (P < 0.001). The median (range) change in teriflunomide concentration between the two time points was 14% (-10% to 40%) in unbound plasma and -29% (-69 to 138%) for CD3⁺ T cells. Because teriflunomide concentrations in CD3⁺ T cells were lower and displayed a higher intraindividual variability than the unbound plasma concentrations, its applicability as a therapeutic drug-monitoring marker may be limited.

Chronic Diarrhea Associated with High Teriflunomide Blood Concentration

OBJECTIVE

To report the case of a patient treated with leflunomide that presented with chronic diarrhea associated with high teriflunomide blood concentration. An 84-year-old woman taking leflunomide 20 mg once daily for the past 2 years to treat rheumatoid arthritis (RA) was investigated for severe chronic diarrhea that had been worsening for the past 5 months. The patient's general condition progressively deteriorated and included electrolyte imbalances and a transient loss of consciousness. Therefore, hospitalization was required. Teriflunomide blood concentration was 156 mg/L. After 11 days of cholestyramine washout therapy, teriflunomide blood concentration was reduced to 6 mg/L. As the teriflunomide levels decreased, diarrhea improved. All other possible causes of diarrhea were ruled out. The patient's diarrhea finally resolved 26 days after treatment with cholestyramine.

DISCUSSION

Diarrhea is a known adverse effect of leflunomide. In this report, the severe diarrhea was associated with high blood teriflunomide concentrations. Available data suggests an association between teriflunomide concentrations greater than 50 mg/L and lower disease activity, but toxic teriflunomide levels still have to be clarified.

CONCLUSION

Further studies are needed to establish the optimal therapeutic levels of teriflunomide. However, therapeutic drug monitoring of teriflunomide blood concentrations may be helpful to improve effectiveness and to prevent toxicity in patients taking leflunomide for RA, particularly in those with suboptimal therapeutic response to leflunomide or in patients with toxicity suspected to be induced by leflunomide.

Genetic polymorphism of CYP1A2 but not total or free teriflunomide concentrations is associated with leflunomide cessation in rheumatoid arthritis

AIM

Leflunomide, via its active metabolite teriflunomide, is used in rheumatoid arthritis (RA) treatment, yet approximately 20 to 40% of patients cease due to toxicity. The aim was to develop a time-to-event model describing leflunomide cessation due to toxicity within a clinical cohort and to investigate potential predictors of cessation such as total and free teriflunomide exposure and pharmacogenetic influences.

METHODS

This study included individuals enrolled in the Early Arthritis inception cohort at the Royal Adelaide Hospital between 2000 and 2013 who received leflunomide. A time-to-event model in nonmem was used to describe the time until leflunomide cessation and the influence of teriflunomide exposure and pharmacogenetic variants. Random censoring of individuals was simultaneously described. The clinical relevance of significant covariates was visualized via simulation.

RESULTS

Data from 105 patients were analyzed, with 34 ceasing due to toxicity. The baseline dropout hazard and baseline random censoring hazard were best described by step functions changing over discrete time intervals. No statistically significant associations with teriflunomide exposure metrics were identified. Of the screened covariates, carriers of the C allele of CYP1A2 rs762551 had a 2.29 fold increase in cessation hazard compared with non-carriers (95% CI 2.24, 2.34, P = 0.016).

CONCLUSIONS

A time-to-event model described the time between leflunomide initiation and cessation due to side effects. The C allele of CYP1A2 rs762551 was linked to increased leflunomide toxicity, while no association with teriflunomide exposure was identified. Future research should continue to investigate exposure-toxicity relationships, as well as potentially toxic metabolites.

Semiphysiologically Based Pharmacokinetic Model of Leflunomide Disposition in Rheumatoid Arthritis Patients

A semiphysiologically based pharmacokinetic (semi-PBPK) population model was used to evaluate the influence of enterohepatic recycling and protein binding, as well as the effect of genetic variability in CYP1A2, CYP2C19, and ABCG2, on the large interindividual variability of teriflunomide (active metabolite) concentrations following leflunomide administration in rheumatoid arthritis (RA) patients. The model was developed with total and free teriflunomide concentrations determined in RA patients taking leflunomide, as well as mean teriflunomide concentrations following the administration of leflunomide or teriflunomide extracted from the literature. Once developed, the 15-compartment model was able to predict total and free teriflunomide concentrations and was used to screen demographic and genotypic covariates, of which only fat-free mass and liver function (ALT) improved prediction. This approach effectively evaluated the effects of multiple covariates on both total and free teriflunomide concentrations, which have only been explored previously through simplistic one-compartment models for total teriflunomide.

Inhibition of p70 S6 kinase (S6K1) activity by A77 1726 and its effect on cell proliferation and cell cycle progress

Leflunomide is a novel immunomodulatory drug prescribed for treating rheumatoid arthritis. It inhibits the activity of protein tyrosine kinases and dihydroorotate dehydrogenase, a rate-limiting enzyme in the pyrimidine nucleotide synthesis pathway. Here, we report that A77 1726, the active metabolite of leflunomide, inhibited the phosphorylation of ribosomal protein S6 and two other substrates of S6K1, insulin receptor substrate-1 and carbamoyl phosphate synthetase 2, in an A375 melanoma cell line. A77 1726 increased the phosphorylation of AKT, p70 S6 (S6K1), ERK1/2, and MEK through the feedback activation of the IGF-1 receptor–mediated signaling pathway. Invitro kinase assay revealed that leflunomide and A77 1726 inhibited S6K1 activity with IC₅₀ values of approximately 55 and 80 μM, respectively. Exogenous uridine partially blocked A77 1726–induced inhibition of A375 cell proliferation. S6K1 knockdown led to the inhibition of A375 cell proliferation but did not potentiate the antiproliferative effect of A77 1726. A77 1726 stimulated bromodeoxyuridine incorporation in A375 cells but arrested the cell cycle in the S phase, which was reversed by addition of exogenous uridine or by MAP kinase pathway inhibitors but not by rapamycin and LY294002 (a phosphoinositide 3-kinase inhibitor). These observations suggest that A77 1726 accelerates cell cycle entry into the S phase through MAP kinase activation and that pyrimidine nucleotide depletion halts the completion of the cell cycle. Our study identified a novel molecular target of A77 1726 and showed that the inhibition of S6K1 activity was in part responsible for its antiproliferative activity. Our study also provides a novel mechanistic insight into A77 1726–induced cell cycle arrest in the S phase.

Individualization of leflunomide dosing in rheumatoid arthritis patients

Leflunomide is largely considered to be a second-line treatment option for rheumatoid arthritis (RA). Those who fail to respond, tend to progress to treatment with expensive biological agents, which can also be associated with serious toxicities. Optimizing leflunomide treatment to meet the needs of individuals would hence be beneficial in terms of patient outcomes and health care expenditure. In this respect, therapeutic drug monitoring (TDM) may be useful, as plasma concentrations of leflunomide's active metabolite, teriflunomide, correlate with response to treatment, but are highly variable between patients. A number of pharmacogenetic markers have also been identified that influence response and toxicity. Incorporation of these findings into clinical practice could facilitate more efficient use of leflunomide.

Using a simple HPLC approach to identify the enzymatic products of UTL-5g, a small molecule TNF-α inhibitor, from porcine esterase and from rabbit esterase

UTL-5g is a novel small-molecule chemoprotector that lowers hepatotoxicity, nephrotoxicity, and myelotoxicity induced by cisplatin through TNF-α inhibition among other factors. As a prelude to investigating the metabolites of UTL-5g, we set out to identify the enzymatic products of UTL-5g under the treatment of both porcine liver esterase (PLE) and rabbit liver esterase (RLE). First, a number of mixtures made by UTL-5g and PLE were incubated at 25°C. At predetermined time points, individual samples were quenched by acetonitrile, vortexed, and centrifuged. The supernatants were then analyzed by reversed-phase HPLC (using a C18 column). The retention times and UV/vis spectra of individual peaks were compared to those of UTL-5g and its two postulated enzymatic products; thus the enzymatic products of UTL-5g were tentatively identified. Secondly, a different HPLC method (providing different retentions times) was used to cross-check and to confirm the identities of the two enzymatic products. Based on the observations, it was concluded that under the treatment of PLE, the major enzymatic products of UTL-5g were 5-methyliosxazole-3-carboxylic acid (ISOX) and 2,4-dichloroaniline (DCA). Treatment of UTL-5g by RLE also provided the same enzymatic products of UTL-5g from esterase. These results indicate that the peptide bond in UTL-5g was cleaved by PLE/RLE. Michaelis-Menten kinetics showed that the Km values of UTL-5g were 2.07mM with PLE and 0.37mM with RLE indicating that UTL-5g had a higher affinity with RLE. In summary, by a simple HPLC approach, we have concluded that the peptide bond in UTL-5g was cleaved by esterase from either porcine liver or rabbit liver in vitro and afforded DCA (at a mole ratio of 1:1) and ISOX. However, further studies are needed in order to determine whether UTL-5g is metabolized by microsomal enzymes to produce ISOX and DCA.

Polymorphisms in cytochrome P450 2C19 enzyme and cessation of leflunomide in patients with rheumatoid arthritis

Introduction

Rational selection of disease modifying anti-rheumatic drugs in the treatment of rheumatoid arthritis (RA) has many potential advantages, including rapid disease control, reduced long-term disability and reduced overall cost to the healthcare system. Inter-individual genetic differences are particularly attractive as markers to predict efficacy and toxicity, as they can be determined rapidly prior to drug selection. The aims of this study, therefore, were to investigate the association between differences in genes associated with the metabolism, clearance and efficacy of leflunomide with its cessation in a group of rheumatoid arthritis patients who were treated with an intensive contemporary, treat-to-target approach.

Methods

This retrospective cohort study identified all individuals who received leflunomide and were enrolled in the Early Arthritis inception cohort at the Royal Adelaide Hospital between 2001 and July 2011. Inclusion criteria were age (>18) and a diagnosis of rheumatoid arthritis. Patients were excluded if a DNA sample was not available, if they withdrew from the cohort or if clinical data were insufficient. Subjects were followed for 12 months or until either another disease modifying antirheumatic drug was added or leflunomide was ceased. The following single nucleotide polymorphisms (SNPs) were determined: CYP2C19*2 (rs4244285), CYP2C19*17 (rs12248560), ABCG2 421C>A (rs2231142), CYP1A2*1F (rs762551) and DHODH 19C>A (rs3213422). The effects of variables on cessation were assessed with Cox Proportional Hazard models.

Results

Thirty-three of 78 (42.3%) patients ceased leflunomide due to side effects. A linear trend between cytochrome P450 2C19 (CYP2C19) phenotype and leflunomide cessation was observed, with poor and intermediate metabolizers ceasing more frequently (adjusted Hazard Ratio = 0.432 for each incremental change in phenotype, 95% CI 0.237 to 0.790, P = 0.006). Previously observed associations between cytochrome P450 1A2 (CYP1A2) and dihydro-orotate dehydrogenase (DHODH) genotype and toxicity were not apparent, but there was a trend for ATP-binding cassette sub-family G member 2 (ABCG2) genotype to be associated with cessation due to diarrhea.

Conclusions

CYP2C19 phenotype was associated with cessation due to toxicity, and since CYP2C19 intermediate and poor metabolizers have lower teriflunomide concentrations, it is likely that they have a particularly poor risk:benefit ratio when using this drug.

Leflunomide: a drug with a potential beyond rheumatology

Leflunomide, an inhibitor of the dihydroorotase dehydrogenase and thereby pyrimidine synthesis, was introduced and licensed for the treatment of rheumatoid arthritis in 1998. In the following years, its antiviral properties were discovered and the drug was used in solid organ transplantation for polyomavirus type BK or cytomegalovirus infection. Owing to its long half-life and weak interaction with the cytochrome system, special considerations apply in the use of this drug. This article summarizes the clinical experience with leflunomide in rheumatology and in the evolving field of transplantation.

Effect of ABCG2 genotypes on the pharmacokinetics of A771726, an active metabolite of prodrug leflunomide, and association of A771726 exposure with serum uric acid level

OBJECTIVE

It has been reported that leflunomide and its active metabolite, A771726, are substrates of the ABCG2 (BCRP) transporter in vitro. Recent genome-wide association studies have shown that ABCG2 transporter modulates serum uric acid (UA) levels. We explored the role of ABCG2 genotypes in the pharmacokinetics of A771726 and the relationship between serum UA levels and pharmacokinetics of A771726 in healthy participants.

METHODS

Twenty-four healthy individuals were recruited and genotyped for ABCG2. After administration of a single dose of 20 mg leflunomide, plasma concentrations of A771726 were measured. Serum UA levels were measured just before medication, and ABCG2 c.421C>A and c.34G> A polymorphism were genotyped.

RESULTS

ABCG2 c.421C>A but not c.34G>A substantially influenced the pharmacokinetics of A771726. A771726 C(max) was 30% higher, area under the concentration-time curve (AUC) 83% larger, and oral clearance (CL/F) 41% lower in c.421C>A carriers than in noncarriers. Serum UA levels were also higher in carriers than in noncarriers and exhibited a strong and positive correlation with A771726 AUC (Spearman r = 0.6746, P = 0.0003), but a negative correlation was observed with A771726 CL/F (Spearman r = -0.6616, P = 0.0004).

CONCLUSION

ABCG2 c.421C>A but not c.34G>A polymorphism appears to be a major determinant of interindividual variability in A771726 disposition. Additionally, serum UA levels exhibited a strong correlation with exposure to A771726.

Effect of ABCG2 genotypes on the pharmacokinetics of A771726, an active metabolite of prodrug leflunomide, and association of A771726 exposure with serum uric acid level

OBJECTIVE

It has been reported that leflunomide and its active metabolite, A771726, are substrates of the ABCG2 (BCRP) transporter in vitro. Recent genome-wide association studies have shown that ABCG2 transporter modulates serum uric acid (UA) levels. We explored the role of ABCG2 genotypes in the pharmacokinetics of A771726 and the relationship between serum UA levels and pharmacokinetics of A771726 in healthy participants.

METHODS

Twenty-four healthy individuals were recruited and genotyped for ABCG2. After administration of a single dose of 20 mg leflunomide, plasma concentrations of A771726 were measured. Serum UA levels were measured just before medication, and ABCG2 c.421C>A and c.34G> A polymorphism were genotyped.

RESULTS

ABCG2 c.421C>A but not c.34G>A substantially influenced the pharmacokinetics of A771726. A771726 C(max) was 30% higher, area under the concentration-time curve (AUC) 83% larger, and oral clearance (CL/F) 41% lower in c.421C>A carriers than in noncarriers. Serum UA levels were also higher in carriers than in noncarriers and exhibited a strong and positive correlation with A771726 AUC (Spearman r = 0.6746, P = 0.0003), but a negative correlation was observed with A771726 CL/F (Spearman r = -0.6616, P = 0.0004).

CONCLUSION

ABCG2 c.421C>A but not c.34G>A polymorphism appears to be a major determinant of interindividual variability in A771726 disposition. Additionally, serum UA levels exhibited a strong correlation with exposure to A771726.

The effect of leflunomide on cycling and activation of T-cells in HIV-1-infected participants

Background

The pathogenesis of immunodeficiency due to human immunodeficiency virus (HIV)-1 is incompletely understood, but immune activation is believed to play a central role. Immunomodulatory agents that decrease immune activation may be useful in the treatment of HIV-1 infection.

Methodology

A randomized, double blind, placebo-controlled pilot study of leflunomide for 28 days was performed in participants with HIV-1 infection who were not receiving antiretroviral therapy. Participants randomized to leflunomide were subsequently treated with cholestyramine until leflunomide levels were below detection limit.

Findings

Treatment with leflunomide was well tolerated with mostly low-grade adverse events. Leflunomide administration reduced cycling of CD4 T cells (by ex vivo bromodeoxyuridine uptake and Ki67 expression) and decreased expression of activation markers (HLA-DR/CD38 co-expression) on CD8 T cells in peripheral blood. In addition, decreased expression of HIV-1 co-receptors was observed in both CD4 and CD8 T cells in the leflunomide group. There were no significant changes in naïve and memory T cell subsets, apoptosis of T cells or markers of microbial translocation.

Conclusions

Leflunomide was effective in reducing immune activation in the setting of chronic HIV-1 infection suggesting that targeting immune activation with immunomodulatory agents may be a feasible strategy.

Trial Registration

ClinicalTrials.gov NCT00101374

Structure, function, regulation and polymorphism and the clinical significance of human cytochrome P450 1A2

Human CYP1A2 is one of the major CYPs in human liver and metabolizes a number of clinical drugs (e.g., clozapine, tacrine, tizanidine, and theophylline; n > 110), a number of procarcinogens (e.g., benzo[a]pyrene and aromatic amines), and several important endogenous compounds (e.g., steroids). CYP1A2 is subject to reversible and/or irreversible inhibition by a number of drugs, natural substances, and other compounds. The CYP1A gene cluster has been mapped on to chromosome 15q24.1, with close link between CYP1A1 and 1A2 sharing a common 5'-flanking region. The human CYP1A2 gene spans almost 7.8 kb comprising seven exons and six introns and codes a 515-residue protein with a molecular mass of 58,294 Da. The recently resolved CYP1A2 structure has a relatively compact, planar active site cavity that is highly adapted for the size and shape of its substrates. The architecture of the active site of 1A2 is characterized by multiple residues on helices F and I that constitutes two parallel substrate binding platforms on either side of the cavity. A large interindividual variability in the expression and activity of CYP1A2 has been observed, which is largely caused by genetic, epigenetic and environmental factors (e.g., smoking). CYP1A2 is primarily regulated by the aromatic hydrocarbon receptor (AhR) and CYP1A2 is induced through AhR-mediated transactivation following ligand binding and nuclear translocation. Induction or inhibition of CYP1A2 may provide partial explanation for some clinical drug interactions. To date, more than 15 variant alleles and a series of subvariants of the CYP1A2 gene have been identified and some of them have been associated with altered drug clearance and response and disease susceptibility. Further studies are warranted to explore the clinical and toxicological significance of altered CYP1A2 expression and activity caused by genetic, epigenetic, and environmental factors.

Induction of EMT-like phenotypes by an active metabolite of leflunomide and its contribution to pulmonary fibrosis

Drug-induced interstitial lung disease (ILD), particularly pulmonary fibrosis, is a serious clinical concern and myofibroblasts have been suggested to have a major role, with it recently being revealed that some of these myofibroblasts are derived from lung epithelial cells through epithelial-mesenchymal transition (EMT). In this study, we examined the EMT-inducing abilities of drugs known to induce ILD clinically. EMT-like phenotypes were induced by A771726, an active metabolite of leflunomide having an inhibitory effect on dihydroorotate dehydrogenase (DHODH). Smad-interacting protein 1 (a transcription factor regulating EMT) and the Notch-signaling pathway but not transforming growth factor-β was shown to be involved in A771726-induced EMT-like phenotypes. When the cultures were supplemented with exogenous uridine, the A771726-induced EMT-like phenotypes and activation of the Notch-signaling pathway disappeared. Similarly, an A771726 analog without inhibitory activity on DHODH produced no induction, suggesting that this process is mediated through the inhibition of DHODH. In vivo, administration of leflunomide stimulated bleomycin-induced EMT-like phenomenon in pulmonary tissue, and exacerbated bleomycin-induced pulmonary fibrosis, both of which were suppressed by coadministration of uridine. Taken together, these findings suggest that leflunomide-dependent exacerbation of bleomycin-induced pulmonary fibrosis is mediated by stimulation of EMT of lung epithelial cells, providing the first evidence that drug-induced pulmonary fibrosis involves EMT of these cells.

Benefit-risk assessment of leflunomide: an appraisal of leflunomide in rheumatoid arthritis 10 years after licensing

Evidence is accumulating for the early sustained usage of disease-modifying anti-rheumatic drugs (DMARDs) in rheumatoid arthritis. Leflunomide was licensed for the treatment of rheumatoid arthritis in 1998. Postmarketing surveillance, case reports and observational studies have highlighted less common or unexpected adverse events. Therefore, it is appropriate that we review the benefit-risk profile of leflunomide after 10 years of widespread usage. A wide-based search of relevant literature was performed to formulate this assessment. The improvements in rheumatoid arthritis shown by double-blind, randomized controlled trials (RCTs) of leflunomide have now been shown to be maintained beyond 4 years in open-label extension studies. Leflunomide is comparable to methotrexate, but better than sulfasalazine at 24 months in only one study. However, tolerance in clinical practice research shows higher than expected withdrawal rates due to both toxicity and lack of efficacy when compared with methotrexate and placebo. Adverse events reported include gastrointestinal upset, hypertension, headache, hepatotoxicity and hair loss, as well as predisposition to infection and peripheral neuropathy. The incidence of gastrointestinal adverse effects for leflunomide is similar to sulfasalazine but higher than those seen with methotrexate. Serious drug-induced hepatotoxicity leading to hospitalization is rare (0.02%), but isolated fatalities from liver failure have been documented. It is considered likely, but not yet proven, that there may be an increased incidence of weight loss and interstitial lung disease with leflunomide. Leflunomide in combination with methotrexate or sulfasalazine is an effective regimen in RCTs utilizing placebo controls, but more research is needed to confirm its effectiveness in combination with other DMARDs, particularly biologicals. The active metabolite of leflunomide is teratogenic in animal studies and is also found in breast milk. Therefore, contraception is advised in both males and females of child-bearing potential. There are genetic, pharmacokinetic and biochemical reasons to explain variation in both patient response and adverse event profile. Hence, blood and blood pressure monitoring are recommended and therapeutic drug monitoring should be considered in clinical nonresponders. Leflunomide is an effective DMARD that sustains a clinical and radiological response comparable to sulfasalazine and methotrexate. However, adverse effects necessitate frequent monitoring. It should be used with caution in those of child-bearing potential and with pre-existing lung and liver disease.

Investigation of the influence of CYP1A2 and CYP2C19 genetic polymorphism on 2-Cyano-3-hydroxy-N-[4-(trifluoromethyl)phenyl]-2-butenamide (A77 1726) pharmacokinetics in leflunomide-treated patients with rheumatoid arthritis

Leflunomide is a disease-modifying antirheumatic drug used for the treatment of rheumatoid arthritis (RA). Cytochromes P450, mainly CYP1A2 and CYP2C19, may be involved in the transformation of leflunomide to leflunomide metabolite (A77 1726, 2-cyano-3-hydroxy-N-[4-(trifluoromethyl)phenyl]-2-butenamide). The aim of this study was to investigate whether genetic polymorphisms in CYP1A2 and CYP2C19 influence leflunomide pharmacokinetics, treatment response, and the occurrence of adverse drug reactions (ADRs). The study included 67 patients with RA and 4 patients with polyarthritis resembling RA and psoriasis treated with leflunomide. A77 1726 steady-state plasma concentrations were determined by validated high-performance liquid chromatography with UV detection. A population pharmacokinetic model was developed to estimate the oral clearance (CL/F) and volume of distribution (V/F). A genotyping approach was used to determine C-163A, C-729T, and T-739G in the CYP1A2 gene as well as single nucleotide polymorphisms that characterize CYP2C19*2, *3, *4, and *17 alleles. A large interindividual variability in trough A77 1726 steady-state plasma concentrations was observed (from 1.9 to 156.9 mg/l). A77 1726 CL/F was 71% higher in carriers of the CYP2C19*2 allele compared with noncarriers. The A77 1726 average steady-state plasma concentration was associated with the treatment response. Patients with a greater decrease in C-reactive protein (CRP) had higher average steady-state plasma A77 1726 concentrations: 49.7 +/- 39.0 mg/l in patients with DeltaCRP of more than 8.5 mg/l compared with 24.8 +/- 13.7 mg/l in patients with DeltaCRP of <or=8.5 mg/l (p = 0.015). No association of A77 1726 steady-state plasma concentrations with the occurrence of ADRs was observed. Our results suggest that genetic variability in leflunomide-metabolizing enzymes influences leflunomide metabolite concentrations that are associated with the treatment response but not with leflunomide-induced toxicity.

Computational discovery of novel low micromolar human pregnane X receptor antagonists

Very few antagonists have been identified for the human pregnane X receptor (PXR). These molecules may be of use for modulating the effects of therapeutic drugs, which are potent agonists for this receptor (e.g., some anticancer compounds and macrolide antibiotics), with subsequent effects on transcriptional regulation of xenobiotic metabolism and transporter genes. A recent novel pharmacophore for PXR antagonists was developed using three azoles and consisted of two hydrogen bond acceptor regions and two hydrophobic features. This pharmacophore also suggested an overall small binding site that was identified on the outer surface of the receptor at the AF-2 site and validated by docking studies. Using computational approaches to search libraries of known drugs or commercially available molecules is preferred over random screening. We have now described several new smaller antagonists of PXR discovered with the antagonist pharmacophore with in vitro activity in the low micromolar range [S-p-tolyl 3',5-dimethyl-3,5'-biisoxazole-4'-carbothioate (SPB03255) (IC(50), 6.3 microM) and 4-(3-chlorophenyl)-5-(2,4-dichlorobenzylthio)-4H-1,2,4-triazol-3-ol (SPB00574) (IC(50), 24.8 microM)]. We have also used our computational pharmacophore and docking tools to suggest that most of the known PXR antagonists, such as coumestrol and sulforaphane, could also interact on the outer surface of PXR at the AF-2 domain. The involvement of this domain was also suggested by further site-directed mutagenesis work. We have additionally described an FDA approved prodrug, leflunomide (IC(50), 6.8 microM), that seems to be a PXR antagonist in vitro. These observations are important for predicting whether further molecules may interact with PXR as antagonists in vivo with potential therapeutic applications.

Genetic polymorphism of CYP1A2 and the toxicity of leflunomide treatment in rheumatoid arthritis patients

OBJECTIVE

Leflunomide is a disease-modifying antirheumatic drug used for treating rheumatoid arthritis (RA). In vitro studies demonstrated that cytochromes P450 (CYPs), mainly CYP1A2 and CYP2C19, might be involved in leflunomide activation. The aim of our study was to investigate whether genetic polymorphisms of CYP1A2, CYP2C19, and CYP2C9 influence leflunomide toxicity.

METHODS

A genotyping approach was used to determine CYP1A2*1F, CYP2C19*2, CYP2C19*17, CYP2C9*2, and CYP2C9*3 alleles in 105 RA patients.

RESULTS

Leflunomide treatment was well tolerated by 62 patients, whereas 43 patients discontinued the treatment within the first year due to toxicity. Patients with CYP1A2*1F CC genotype had a 9.7-fold higher risk for overall leflunomide-induced toxicity than did the carriers of CYP1A2*1F A allele [P = 0.002, odds ratio = 9.708, 95% confidence interval = 2.276-41.403]. No significant association between the CYP2C19 and CYP2C9 genotypes and the leflunomide toxicity was observed.

CONCLUSION

Our results suggest that the CYP1A2*1F allele may be associated with leflunomide toxicity in RA patients.