Addition of Allopurinol for Altering Thiopurine Metabolism to Optimize Therapy in Patients with Inflammatory Bowel Disease

Detailed resume of S-methyltransferases: Categories, structures, biological functions and research advancements in related pathophysiology and pharmacotherapy

Methylation is a vital chemical reaction in the metabolism of many drugs, neurotransmitters, hormones, and exogenous compounds. Among them, S-methylation plays a significant role in the biotransformation of sulfur-containing compounds, particularly chemicals with sulfhydryl groups. Currently, only three S-methyltransferases have been reported: thiopurine methyltransferase (TPMT), thiol methyltransferase (TMT), and thioether methyltransferase (TEMT). These enzymes are involved in various biological processes such as gene regulation, signal transduction, protein repair, tumor progression, and biosynthesis and degradation reactions in animals, plants, and microorganisms. Furthermore, they play pivotal roles in the metabolic pathways of essential drugs and contribute to the advancement of diseases such as tumors. This paper reviews the research progress on relevant structural features, metabolic mechanisms, inhibitor development, and influencing factors (gene polymorphism, S-adenosylmethionine level, race, sex, age, and disease) of S-methyltransferases. We hope that a better comprehension of S-methyltransferases will help to provide a reference for the development of novel strategies for related disorders and improve long-term efficacy.

Optimizing Thiopurine Therapy with a Xanthine Oxidase Inhibitor in Patients with Systemic Autoimmune Diseases: A Single-Centre Experience

Background

Thiopurines are a mainstay of therapy for autoimmune diseases. However, up to 20% to 30% of patients experience overproduction of the methylated metabolites, known as 6-MMP, to the detriment of the active metabolite, 6-thioguanine nucleotide (6-TGN). These patients, commonly referred to as "shunters", are predisposed to thiopurine resistance and hepatotoxicity. In patients with inflammatory bowel diseases, the combination of thiopurine with a xanthine oxidase inhibitor (XOI) is used to reverse this skewed metabolism and to prevent treatment failure or hepatotoxicity. Data on the use of this strategy for patients with other diseases are limited.

Objectives

To investigate and describe the use of thiopurine-XOI combination therapy in shunters with systemic autoimmune diseases.

Methods

Shunters treated in the study hospital between January 1, 2005, and December 31, 2015, were identified using the hospital's laboratory database, and clinical data were collected retrospectively. For each patient with optimization of thiopurine therapy, clinical and laboratory data were assessed over a 6-month period.

Results

Thirty-four patients were identified as shunters; for 14 of these patients, thiopurine therapy was optimized with an XOI. In these 14 patients, the median dose of azathioprine was reduced from 1.95 to 0.78 mg/kg with combination therapy. In addition, median 6-TGN level increased from 135 to 385 pmol/8 × 10⁸ erythrocytes (p = 0.001); furthermore, 6-TGN levels rose to above 235 pmol/8 ×10⁸ erythrocytes for 11 of the 14 patients. Conversely, the median 6-MMP level decreased from 6267 to 271 pmol/8 × 10⁸ erythrocytes (p = 0.001). Except for a 12% increase in mean corpuscular volume, no clinically significant changes in blood count were recorded. Notable infections were reported in 3 patients, and 1 patient had to discontinue treatment because of cytopenia. After 6 months, median prednisone daily dose was reduced by 74%, from 16.7 mg to 4.4 mg (p = 0.005), and 4 patients had been weaned off corticosteroids. Of the 14 patients, 11 (79%) were in full remission, and 2 (14%) were in partial remission.

Conclusion

Optimizing thiopurine therapy with an XOI may be a safe and effective strategy for patients with systemic autoimmune diseases.

Association between Thiopurines Use and Pregnancy Outcomes in Female Patients with Inflammatory Bowel Disease: A Meta-Analysis

BACKGROUND

Conflicting data exist regarding the influence of thiopurines exposure on adverse pregnancy outcomes in female patients with inflammatory bowel disease (IBD).

OBJECTIVE

The aim of this study was to provide an up-to-date and comprehensive assessment of the safety of thiopurines in pregnant IBD women.

METHODS

All relevant articles reporting pregnancy outcomes in women with IBD received thiopurines during pregnancy were identified from the databases (PubMed, Embase, Cochrane Library, and ClinicalTrials.gov) with the publication data up to April 2020. Data of included studies were extracted to calculate the relative risk (RR) of multiple pregnancy outcomes: congenital malformations, low birth weight (LBW), preterm birth, small for gestational age (SGA), and spontaneous abortion. The meta-analysis was performed using the random-effects model.

RESULTS

Eight studies matched with the inclusion criteria and a total of 1201 pregnant IBD women who used thiopurines and 4189 controls comprised of women with IBD received drugs other than thiopurines during pregnancy were included. Statistical analysis results demonstrated that the risk of preterm birth was significantly increased in the thiopurine-exposed group when compared to IBD controls (RR, 1.34; 95% CI, 1.00-1.79; p=0.049; I² =41%), while no statistically significant difference was observed in the incidence of other adverse pregnancy outcomes.

CONCLUSION

Thiopurines used in women with IBD during pregnancy is not associated with congenital malformations, LBW, SGA, or spontaneous abortion, but appears to have an association with an increased risk of preterm birth.

Thiopurines in Inflammatory Bowel Disease. How to Optimize Thiopurines in the Biologic Era?

Thiopurines have been a cornerstone in the treatment of inflammatory bowel disease (IBD). Although they have been used for more than 50 years, there are still some unsolved issues about their efficacy and, also, some safety concerns, mainly the risk of myelosuppression and life-threatening lymphoproliferative disorders. Furthermore, the development of biological therapy raises the question whether there is still a role for thiopurines in the IBD treatment algorithm. On the other hand, limited cost and wide availability make thiopurines a reasonable option in settings of limited resources and increasing prevalence of IBD. In fact, there is a growing interest in optimizing thiopurine therapy, since pharmacogenomic findings suggest that a personalized approach based on the genotyping of some molecules involved in its metabolism could be useful to prevent side effects. Polymorphisms of thiopurine methyltransferase enzyme (TPMT) that result in low enzymatic activity have been associated with an increased risk of myelotoxicity, especially in Caucasians; however, in Asians it is assumed that the variants of nudix hydrolase 15 (NUDT15) are more relevant in the development of toxicity. Age is also important, since in elderly patients the risk of complications seems to be increased. Moreover, the primo-infection of Epstein Barr virus and cytomegalovirus under thiopurine treatment has been associated with severe lymphoproliferative disorders. In addition to assessing individual characteristics that may influence thiopurines treatment outcomes, this review also discusses other strategies to optimize the therapy. Low-dose thiopurines combined with allopurinol can be used in hypermethylators and in thiopurine-related hepatotoxicity. The measurement of metabolites could be useful to assess compliance, identify patients at risk of adverse events and also facilitating the management of refractory patients. Thioguanine is also a rescue therapy in patients with toxicity related to conventional thiopurine therapy. Finally, the current indications for thiopurines in monotherapy or in combination with biologics, as well as the optimal duration of treatment, are also reviewed.

Allopurinol to Prevent Mercaptopurine Adverse Effects in Children and Young Adults With Acute Lymphoblastic Leukemia

Mercaptopurine (6MP) is used to treat acute lymphoblastic leukemia (ALL) and is metabolized by hypoxanthine guanine phosphoribosal transferase to form 6-thioguanine nucleotide (6TGN). It is also metabolized by thiopurine methyl-transferase to produce 6-methylmercaptopurine (6MMP). Elevated levels of 6MMP have been associated with toxic effects that may interfere with therapy. Allopurinol is known to inhibit thiopurine methyl-transferase which reduces red cell 6MMP and increases 6TGN. Allopurinol has been utilized successfully in adult and pediatric patients with inflammatory bowel disease who have experienced 6MMP related gastrointestinal toxicity. Between August 2015 and August 2018 we started 25 patients with ALL in maintenance on allopurinol in combination with a reduced dose of 6MP. They all had unacceptable side-effects from elevated 6MMP, including abdominal pain, nausea, vomiting, decreased appetite, hypoglycemia, fatigue, and liver toxicity. In addition many had a facial rash. All patients showed resolution of symptoms within a few weeks after starting allopurinol. The red cell levels of 6MMP rapidly declined in the first month. The red cell levels of 6TGN transiently increased in spite of the lower 6MP dose. There was no decrease in absolute neutrophil count or hemoglobin. Platelets decreased slightly not requiring therapy modification. Elevated bilirubin normalized, and alanine aminotransferase decreased significantly with most normalizing. All patients continued on allopurinol with reduced dose 6MP until completing therapy. Allopurinol, in conjunction with a reduced dose of 6MP, effectively resolves 6MMP related side-effects in ALL patients on maintenance chemotherapy. This approach may lead to increased adherence to oral 6MP during ALL maintenance in patients with 6MMP induced side-effects.

Nonbiologic Immune Suppression in Ulcerative Colitis

This article reviews nonbiologic immunosuppressive agents in the induction and maintenance of remission of ulcerative colitis. Based on meta-analyses and North American guidelines, azathioprine, mercaptopurine, and methotrexate monotherapy are not recommended for induction therapy. Thiopurines are recommended in combination with infliximab. Tofacitinib has been shown to be an effective induction agent. Cyclosporine or tacrolimus are calcineurin inhibitors that can be used as induction therapy. Thiopurine monotherapy is suggested or recommended as maintenance therapy for patients who have achieved steroid-induced remission. Methotrexate monotherapy is not recommended. Tofacitinib has been shown to be an effective maintenance agent in moderate to severe disease.

Drug Interaction Between Febuxostat and Thiopurine Antimetabolites: A Review of the FDA Adverse Event Reporting System and Medical Literature

BACKGROUND

There is a known drug interaction (DI) between xanthine oxidase (XO) inhibitors and the thiopurine immunosuppressants, azathioprine (AZA) and mercaptopurine (6-MP). Xanthine oxidase inhibition increases concentrations of AZA and 6-MP active metabolites, possibly resulting in myelosuppression. When allopurinol is used with AZA or 6-MP, dose reduction of AZA or 6-MP is recommended. Febuxostat is a newer XO inhibitor approved for the treatment of gout.

OBJECTIVE

To determine the clinical impact of the febuxostat-thiopurine DI.

DESIGN AND SETTING

Case series derived from the U.S. Food and Drug Administration Adverse Event Reporting System (FAERS) and published medical literature.

PATIENTS

Nineteen patients who received concomitant febuxostat and either AZA or 6-MP.

MEASUREMENTS

Laboratory and clinical data.

RESULTS

Nineteen cases reporting myelosuppressive events were identified in patients receiving febuxostat with AZA or 6-MP. Eighteen cases were treated with the combination of AZA and febuxostat. A median of 1.6 months elapsed from initiation of the drug combination until discovery of the event. Sixteen cases required hospitalization; 15 reported administration of blood products. Thirteen cases reported resolution of the event with discontinuation of both drugs, two reported discontinuation of the thiopurine only, and one reported discontinuation of febuxostat only.

LIMITATIONS

Thiopurine monotherapy may cause myelosuppression. Complications of immunosuppression that may contribute to the real-world morbidity and mortality associated with the febuxostat-thiopurine DI were not examined. Finally, FAERS data are limited by the voluntary nature of reporting.

CONCLUSION

Current febuxostat labeling contraindicates concomitant administration of febuxostat with either AZA or 6-MP. This case series demonstrates that the DI can result in clinically significant adverse events and is supportive of current febuxostat labeling.

Evolving Considerations for Thiopurine Therapy for Inflammatory Bowel Diseases-A Clinical Practice Update: Commentary

Thiopurines (azathioprine, mercaptopurine, thioguanine) and methotrexate are widely used in a variety of clinical management scenarios for ulcerative colitis and Crohn's disease. With the introduction of biologic therapies over the last 2 decades, controversies have emerged as to how these immunomodulators should be used in clinical practice, either alone as monotherapies or in combination with biologic therapies. Here, we provide a summary of evidence and our interpretations regarding how physicians can or should incorporate these agents into clinical practice. We have organized the review into sections regarding their utility as monotherapy or as combination therapy with biologics and safety considerations. Clinical pharmacologic considerations are important regarding both efficacy and safety.

The teratogenicity of allopurinol: A comprehensive review of animal and human studies

Allopurinol is widely used in the management of multiple disorders including gout, kidney stones and inflammatory bowel disease. Despite of long-term experience, its safety in pregnancy has been debated due to reports on possible teratogenicity. We aimed to review the literature on the safety of allopurinol in pregnancy and offspring. In animals, allopurinol induced species-specific reproductive toxicity. In humans, a total of 53 allopurinol exposed infants were reported in the literature. Major congenital malformations were reported in two cases with a comparable pattern of multiple abnormalities. Five other infants had minor birth defects. In conclusion, the association between allopurinol and teratogenicity appears to be weak and limited to two reports with uncertain causality. However, the available data are insufficient to make a certain judgement, and as allopurinol treatment evolves, report and prospective follow-up of all exposed infants (i.e. deviant and normal cases) should be encouraged.