TPMT Testing Before Starting Azathioprine or Mercaptopurine: Surely Just Do It?

Towards personalised medicine in autoimmune hepatitis: Measurement of thiopurine metabolites results in higher biochemical response rates

BACKGROUND & AIMS

Patients with autoimmune hepatitis (AIH) usually receive maintenance therapy with thiopurines, such as azathioprine (AZA) or mercaptopurine. Genetic polymorphisms in AZA metabolism can lead to variations in thioguanine nucleotide (TGN) and 6-methylmercaptopurine, both of which can cause adverse drug reactions (ADRs). In inflammatory bowel disease, a therapeutic TGN range (225-450 pmol/8x10⁸ erythrocytes) has been identified to optimise effectiveness. We evaluated the benefits of a personalised medicine approach to thiopurine dosing, in comparison to standard weight-based dosing.

METHODS

A retrospective matched cohort study of 214 patients with AIH who were seen at King's College between 1999-2019 was performed. Metabolite levels were measured in 109 patients. The control group included 105 patients on weight-based thiopurine dosing with no metabolite monitoring.

RESULTS

Biochemical response (BR) occurred more frequently at 6-month follow-up in patients with metabolite monitoring compared to those on a weight-based regimen (77% vs. 60%, p = 0.008). This remained true with data analysis based on clinicians who measure metabolites and those who do not (BR at 6 months: 84% vs. 64%, p = 0.016). Patients with BR had TGN levels within the therapeutic range of 225-450 pmol/8x10⁸ erythrocytes significantly more often than those who failed to achieve or lost BR (40% vs. 13%, p <0.0001). Moreover, TGN levels within the pre-defined therapeutic range predicted more stable disease within 6 months of testing compared to levels outside the range (p <0.0001). A high proportion of patients with sub-therapeutic TGN levels (75-225 pmol/8x10⁸ erythrocytes) remained in BR (75% vs. 81%, p = 0.589) with fewer ADRs (44% vs. 86%, p = 0.0002) when compared to patients with therapeutic TGN levels.

CONCLUSION

A strategy of personalised medicine using metabolite levels can optimise treatment regimens in AIH, resulting in fewer ADRs whilst maintaining BR.

LAY SUMMARY

This study looked to see if measuring the breakdown products of a medication used in autoimmune hepatitis increases the chances of gaining good control of the disease, when compared to a group of patients who were on a dose of this medication based on their weight. A group of 214 patients with autoimmune hepatitis were split into 2 groups: roughly half had their medication dose adjusted according to measurements of breakdown products in the blood, whilst the other half received their weight-based dose as normal. The results confirmed that using a personalised approach and checking drug breakdown products resulted in fewer side effects and potentially improved control of disease.

Bone marrow inhibition induced by azathioprine in a patient without mutation in the thiopurine S-methyltransferase pathogenic site: A case report

BACKGROUND

Azathioprine (AZA) and its close analog 6-mercaptopurine are thiopurines widely used in the treatment of patients with cancer, organ transplantation, and autoimmune or inflammatory diseases, including systemic lupus erythematosus. Bone marrow inhibition is a common side effect of AZA, and severe bone marrow inhibition is related to decreased thiopurine S-methyltransferase (TPMT) activity.

CASE SUMMARY

We herein report a patient with proliferative lupus nephritis who was using AZA for maintenance therapy, had no common TPMT pathogenic site mutations, and exhibited severe bone marrow inhibition on the 15^th day after oral administration.

CONCLUSION

This report alerts physicians to the fact that even though the TPMT gene has no common pathogenic site mutation, severe myelosuppression may also occur.

Immunomodulation in Autoimmune Interstitial Lung Disease

Interstitial lung diseases (ILDs) associated with autoimmune or systemic disease are increasingly recognized and our pathophysiological understanding rapidly expanding. Treatment modalities, however, are still mainly driven by established disease-modifying antirheumatic drugs (DMARDs) where, despite decades of experience of their use in the underlying diseases such as rheumatoid arthritis, mostly ret-rospective data exist informing their effect on the course of interstitial lung disease (ILD). In recent years, randomized trials investigating the effects of biological DMARDs (bDMARDs) have been completed or are currently running, generating new treatment options for often relentlessly progressive diseases. Herein, we summarize the evidence and current use of both synthetic DMARDs and bDMARDs in the context of ILDs associated with autoimmune/systemic disease.

Thiopurine S-methyltransferase and Pemphigus Vulgaris: A Phenotype-Genotype Study

Background & Objective:

Thiopurine drugs are considered as a treatment modality in various autoimmune disorders including pemphigus vulgaris (PV). These drugs are metabolized by an enzyme “Thiopurine S-methyl transferase” (TPMT). Various variants of this enzyme may have decreased activity leading to serious drug side effects. To investigate the phenotype and genotype of TPMT in PV patients receiving thiopurine drugs.

Methods:

A total of 50 patients (29 women and 21 men) with pemphigus vulgaris treating with standard dose of Thiopurine drugs were selected. Sex, age, result of liver function test and complete blood count were recorded. Genotyping of two common non-functional allele (TPMT*2 and TPMT*3C) by Allele-specific and RFLP-PCR was performed. TPMT enzymatic level was determined by an ELISA based method.

Results:

Of patients, 36 (72%) were found to have normal TPMT level; and 12, (24%) had higher level of enzyme and 2, 4% had low TPMT enzyme, but none of the patients showed mutant TPMT*2 and TPMT*3C alleles. None of the patients showed hepatotoxicity and bone marrow suppression.

Conclusion:

The phenotypic assay based on ELISA method may have false positive and misleading results but genotyping using PCR-RFLP and allele specific PCR is accurate, simple and cost-effective and can be used in patients decided to undergo thiopurine treatment.

Utilizing a user-centered approach to develop and assess pharmacogenomic clinical decision support for thiopurine methyltransferase

Background

A pharmacogenomic clinical decision support tool (PGx-CDS) for thiopurine medications can help physicians incorporate pharmacogenomic results into prescribing decisions by providing up-to-date, real-time decision support. However, the PGx-CDS user interface may introduce errors and promote alert fatigue. The objective of this study was to develop and evaluate a prototype of a PGx-CDS user interface for thiopurine medications with user-centered design methods.

Methods

This study had two phases: In phase I, we conducted qualitative interviews to assess providers’ information needs. Interview transcripts were analyzed through a combination of inductive and deductive qualitative analysis to develop design requirements for a PGx-CDS user interface. Using these requirements, we developed a user interface prototype and evaluated its usability (phase II).

Results

In total, 14 providers participated: 10 were interviewed in phase I, and seven providers completed usability testing in phase II (3 providers participated in both phases). Most (90%) participants were interested in PGx-CDS systems to help improve medication efficacy and patient safety. Interviews yielded 11 themes sorted into two main categories: 1) health care providers’ views on PGx-CDS and 2) important design features for PGx-CDS. We organized these findings into guidance for PGx-CDS content and display. Usability testing of the PGx-CDS prototype showed high provider satisfaction.

Conclusion

This is one of the first studies to utilize a user-centered design approach to develop and assess a PGx-CDS interface prototype for Thiopurine Methyltransferase (TPMT). This study provides guidance for the development of a PGx-CDS, and particularly for biomarkers such as TPMT.

[Myasthenia gravis]

Myasthenia gravis (MG) is an autoimmune disorder caused by antibodies against acetylcholine receptors (AChR) or other structural proteins of the neuromuscular junction. This diminishes cholinergic transmission, thus leading to exercise-induced fatigue and sometimes manifest muscle weakness, including the bulbar and ocular musculature. Whereas ocular MG is as a rule initially symptomatically treated with acetylcholine esterase inhibitors, generalized MG requires long-term immunosuppression. The thymus plays a particular role in the pathophysiology of AChR antibody-positive MG, which can also manifest as a paraneoplastic disorder in the context of a thymoma. This article reviews the basic and advanced treatment options of the different disease subtypes including plasma exchange and immunoglobulins for treatment in a myasthenic crisis. Recently, clinical approval of eculizumab, a complement inhibitor, enriched the pharmacological armamentarium for AChR antibody-positive MG patients not appropriately responding to immunosuppression alone.

Genotype-Guided Thiopurine Dosing Does not Lead to Additional Costs in Patients With Inflammatory Bowel Disease

BACKGROUND AND AIMS

Decreased thiopurine S-methyltransferase [TPMT] enzyme activity increases the risk of haematological adverse drug reactions [ADRs] in patients treated with thiopurines. Clinical studies have shown that in patients with inflammatory bowel disease [IBD], pharmacogenetic TPMT-guided thiopurine treatment reduces this risk of ADRs. The aim of this study was to investigate whether this intervention impacts on healthcare costs and/or quality of life.

METHODS

An a priori defined cost-effectiveness analysis was conducted in the Thiopurine response Optimization by Pharmacogenetic testing in Inflammatory bowel disease Clinics [TOPIC] trial, a randomized controlled trial performed in 30 Dutch hospitals. Patients diagnosed with IBD [age ≥18 years] were randomly assigned to the intervention [i.e. pre-treatment genotyping] or control group. Total costs in terms of volumes of care, and effects in quality-adjusted life years [QALYs], based on EuroQol-5D3L utility scores, were measured for 20 weeks. Mean incremental cost savings and QALYs with confidence intervals were calculated using non-parametric bootstrapping with 1000 replications.

RESULTS

The intervention group consisted of 381 patients and the control group 347 patients. The mean incremental cost savings were €52 per patient [95% percentiles -682, 569]. Mean incremental QALYs were 0.001 [95% percentiles -0.009, 0.010]. Sensitivity analysis showed that the results were robust for potential change in costs of screening, costs of biologicals and costs associated with productivity loss.

CONCLUSIONS

Genotype-guided thiopurine treatment in IBD patients reduced the risk of ADRs among patients carrying a TPMT variant, without increasing overall healthcare costs and resulting in comparable quality of life, as compared to standard treatment.

Pharmacogenetics of treatments for inflammatory bowel disease

INTRODUCTION

Inflammatory bowel disease is a chronic inflammation of the gut whose pathogenesis is still unclear. Although no curative therapy is currently available, a number of drugs are used in induction and maintenance therapy; however, for most of these drugs, a high inter-individual variability in response is observed. Among the factors of this variability, genetics plays an important role. Areas covered: This review summarizes the results of pharmacogenetic studies, considering the most important drugs used and in particular aminosalycilates, glucocorticoids, thiopurines, monoclonal antibodies and thalidomide. Most studies used a candidate gene approach, even if significant breakthroughs have been obtained recently from applying genome-wide studies. When available, also investigations considering epigenetics and pharmacogenetic dosing guidelines have been included. Expert opinion: Only for thiopurines, genetic markers identified as predictors of efficacy or adverse events have allowed the development of dosing guidelines. For the other drugs, encouraging results are available and great expectations rely on the study of epigenetics and integration with pharmacokinetic information, especially useful for biologics. However, to improve therapy of IBD patients with these drugs, for implementation in the clinics of pharmacogenetics, informatic clinical decision support systems and training about pharmacogenetics of health providers are needed.

Pemphigus

Pemphigus is a group of IgG-mediated autoimmune diseases of stratified squamous epithelia, such as the skin and oral mucosa, in which acantholysis (the loss of cell adhesion) causes blisters and erosions. Pemphigus has three major subtypes: pemphigus vulgaris, pemphigus foliaceus and paraneoplastic pemphigus. IgG autoantibodies are characteristically raised against desmoglein 1 and desmoglein 3, which are cell-cell adhesion molecules found in desmosomes. The sites of blister formation can be physiologically explained by the anti-desmoglein autoantibody profile and tissue-specific expression pattern of desmoglein isoforms. The pathophysiological roles of T cells and B cells have been characterized in mouse models of pemphigus and patients, revealing insights into the mechanisms of autoimmunity. Diagnosis is based on clinical manifestations and confirmed with histological and immunochemical testing. The current first-line treatment is systemic corticosteroids and adjuvant therapies, including immunosuppressive agents, intravenous immunoglobulin and plasmapheresis. Rituximab, a monoclonal antibody against CD20⁺ B cells, is a promising therapeutic option that may soon become first-line therapy. Pemphigus is one of the best-characterized human autoimmune diseases and provides an ideal paradigm for both basic and clinical research, especially towards the development of antigen-specific immune suppression treatments for autoimmune diseases.