Reducing risk in thiopurine therapy

Area of Science:

• Pharmacogenomics
• Immunology
• Oncology

Background:

• Thiopurine drugs (azathioprine, mercaptopurine) are vital for immune regulation disorders and acute lymphoblastic leukemia.
• Despite their age, thiopurines remain essential, often used with anti-TNF biologics as co-immunomodulators.
• Significant advancements in patient management have reduced severe thiopurine toxicity.

Purpose of the Study:

• To highlight the clinical utility of thiopurine methyltransferase (TPMT) and NUDT15 genetic testing.
• To emphasize the importance of personalized thiopurine therapy based on pharmacogenetic profiles.
• To discuss strategies for managing thiopurine toxicity and optimizing treatment response.

Main Methods:

• Review of clinical management strategies for thiopurine therapy.
• Analysis of thiopurine methyltransferase (TPMT) deficiency testing for dose adjustment.
• Monitoring of red cell thioguanine nucleotide (TGN) and methylmercaptopurine (MMP) levels.
• Evaluation of NUDT15 variants' role in myelotoxicity, particularly in Asian populations.
• Assessment of combination therapy with low-dose thiopurines and allopurinol.

Main Results:

• TPMT deficiency testing guides safe initial thiopurine dosing.
• Red cell TGN monitoring aids dose adjustment and identifies non-responders or those at risk.
• High MMP:TGN ratios indicate risk for hepatotoxicity and non-response.
• Combination therapy with low-dose thiopurine and allopurinol resolves hepatotoxicity and improves response.
• NUDT15 variants are a major cause of myelotoxicity in populations with low TPMT deficiency.

Conclusions:

• Pre-treatment genetic testing for TPMT and NUDT15 deficiencies is clinically valuable for all populations.
• Personalized thiopurine therapy, guided by pharmacogenetics, is essential for patient safety and efficacy.
• These genetic screenings represent a critical first step in optimizing thiopurine treatment regimens.