Population pharmacokinetics of azathioprine active metabolite in patients with inflammatory bowel disease and dosage regimens optimisation

A Rapid and Reliable Absorbance Assay to Identify Drug-Drug Interactions with Thiopurine Drugs

BACKGROUND

Thiopurine methyltransferase (TPMT) plays a crucial role in the detoxification of thiopurine drugs, including the antimetabolites azathioprine and 6-mercaptopurine (6-MP) used to treat autoimmune diseases and various cancers. These drugs interfere with DNA synthesis by inhibiting the production of purine-containing nucleotides, leading to the death of rapidly dividing cells. TPMT inactivates thiopurine drugs by methylating at the thiol group. The activity of TPMT can vary significantly between individuals, and its activity is impacted by co-administered drugs, altering the effectiveness and toxicity of thiopurine drugs. TPMT is inhibited by many drugs that are co-administered to treat symptoms associated with diseases treated with thiopurines. For example, aspirin and other anti-inflammatory drugs, including olsalazine, sulfasalazine, and balsalazide, inhibit TPMT. The impact of TPMT genotypes on its methylating activity is well defined, and genotyping patients to identify TPMT metabolizer status is common clinical practice. Unfortunately, there has been no concerted effort to comprehensively identify drugs on the market that impact TPMT activity. The inhibition of TPMT by co-administered drugs could in part be responsible for idiosyncratic toxicities associated with thiopurine drug therapy.

METHODS

Here, we report a facile approach to produce large quantities of recombinant TPMT and a high-throughput assay that utilizes the shift in absorbance due to the methylation of thiopurines to report on TPMT activity.

RESULTS AND CONCLUSIONS

With purified TPMT on hand and the absorbance activity assay, we confirmed several compounds that inhibit TPMT, and the results were comparable to a mass spectral assay that measured 6-MP methylation. Understanding the impact of co-administered drugs on TPMT activity will improve the safety and efficacy of thiopurine-based treatment regimens.

Analysis of Azathioprine Metabolites in Autoimmune Hepatitis Patient Blood-Method Development and Validation

Autoimmune hepatitis (AIH) is a chronic inflammatory liver disease treated by steroids and immunomodulator thiopurine drugs such as azathioprine (AZA). AZA is metabolized in the human body into bioactive forms such as 6-thioguanine (6-TG) and 6-methyl-mercaptopurine (6-MMP). Monitoring the levels of bioactive AZA metabolites is very important for proper treatment of patients. In this study, our aim was to develop and validate a fast and sensitive ultra-high performance liquid chromatography-mass spectrometry (UHPLC-MS) method for the analysis of 6-TG and 6-MMP from blood samples of patients with AIH to monitor the level of these bioactive metabolites. The detection and quantification of the analytes was carried out by Selected Reaction Monitoring (SRM)-based targeted mass spectrometry. The method was validated according to the EMA guidelines. Blood samples from patients with AIH treated with AZA were analysed with the developed method. The method was successfully validated with appropriate accuracy and precision for the target biomolecules and their concentration in the samples from patients with AIH was determined. The developed and validated UHPLC-MS method enables the fast and precise analysis of AZA metabolites.

Drug rediscovery in gastroenterology: from off-label to on-label use of thioguanine in inflammatory bowel disease

Drug rediscovery refers to the principle of using 'old' drugs outside the indications mentioned in the summary of product characteristics. In the past decades, several drugs were rediscovered in a wide variety of medical fields. One of the most recent examples is the unconditional registration of thioguanine (TG), a thiopurine derivative, in patients with inflammatory bowel disease in the Netherlands. In this paper, we aim to visualise potential hurdles that hamper drug rediscovery in general, emphasise the global need for optimal use and development of potentially useful drugs, and provide an overview of the registration process for TG in the Netherlands. With this summary, we aim to guide drug rediscovery trajectories in the near future.

Immunosuppressive Drugs

Immunosuppressant is a class of medicines that inhibit or decrease the intensity of the immune response in the body. Most of these medications are used to allow the body less likely to resist a transplanted organ. In solid organ transplantation, immunosuppressive agents are needed for the activation of early-stage immunosuppression, the management of late-stage immunosuppression or for the maintenance of organ rejection. The emergence of novel agents and improvements in immunosuppression regimens after transplantation are significant factors leading to this progress. However, these drugs also increase the risk of infection, cancers and specific adverse side effects specific to each agent in patients particularly in pregnant women and fertility issues. Corona virus disease being hot topic of debate is has given positive outcome to immunosuppressive drugs however need more attention in future. Transplant centers across the world utilize multiple immunosuppression protocols; nevertheless, each patient can require an individually formulated immunosuppression regimen to manage the advantages and possible damage of treatment thus eliminating the likelihood of their primary disease recurrence.