https://www.gastrojournal.org/article/S0016-5085(00)70140-5/pdf

Pharmacogenomics and metabolite measurement for 6-mercaptopurine therapy in inflammatory bowel disease

Azathioprine and its metabolite 6-mercaptopurine (6-MP) are immunosuppressive drugs that are used in organ transplantation and autoimmune and chronic inflammatory diseases such as Crohn disease. However, their molecular mechanism of action is unknown. In the present study, we have identified a unique and unexpected role for azathioprine and its metabolites in the control of T cell apoptosis by modulation of Rac1 activation upon CD28 costimulation. We found that azathioprine and its metabolites induced apoptosis of T cells from patients with Crohn disease and control patients. Apoptosis induction required costimulation with CD28 and was mediated by specific block- ade of Rac1 activation through binding of azathioprine-generated 6-thioguanine triphosphate (6-Thio-GTP) to Rac1 instead of GTP. The activation of Rac1 target genes such as mitogen-activated protein kinase kinase (MEK), NF-κB, and bcl-xL was suppressed by azathioprine, leading to a mito- chondrial pathway of apoptosis. Azathioprine thus converts a costimulatory signal into an apoptot- ic signal by modulating Rac1 activity. These findings explain the immunosuppressive effects of aza- thioprine and suggest that 6-Thio-GTP derivates may be useful as potent immunosuppressive agents in autoimmune diseases and organ transplantation.

/pdf/cd28-dependent-rac1-activation-is-the-molecular-target-of-3eys2leey8.pdf

CD28-dependent Rac1 activation is the molecular target of azathioprine in primary human CD4+ T lymphocytes.

Objectives To determine the effectiveness of azathioprine and 6-mercaptopurine in inducing remission of active Crohn's disease. Search strategy Studies were selected using the MEDLINE data base (1966 - December 1997), abstracts from major gastrointestinal meetings and references from published articles and reviews. The Cochrane Controlled Trials Register and the Inflammatory Bowel Disease Review Group Trials Register was also searched. Selection criteria Eight randomized placebo controlled trials of azathioprine and 6-mercaptopurine therapy in adult patients were identified: five dealt with active disease and three had multiple therapeutic arms. Data collection and analysis Data were extracted by three independent observers based on the intention to treat principle. Each study was given a quality score based on predetermined criteria. Extracted data were converted to 2X2 tables (response versus no response and antimetabolite versus placebo) and then synthesized into a summary test statistic using the pooled odds ratio and 95% confidence intervals as described by Cochran and Mantel and Haenszel ('Odds Ratio' in MetaView). Main results The odds ratio of a response to azathioprine or 6-mercaptopurine therapy compared with placebo in active Crohn's disease was 2.36 (95% CI 1.57-3.53). This corresponded to a number needed to treat of about 5 to observe an effect of therapy in one patient. When the two trials using 6-mercaptopurine in active disease were excluded from the analysis, the odds ratio of response was 2.04 (CI 1.24 - 3.35). Treatment >/= 17 weeks increased the odds ratio of a response to 2.51 (CI 1.63-3. 88). A steroid sparing effect was seen with an odds ratio of 3.86 (CI 2.14 - 6.96), corresponding to a number needed to treat of about 3 to observe steroid sparing in one patient. Adverse events requiring withdrawal from a trial, principally allergy, leukopenia, pancreatitis, and nausea were increased on therapy with an odds ratio of 3.01 (CI 1.30 - 6.96). The number needed to treat to observe one adverse event in one patient treated with azathioprine or 6-mercaptopurine was 14. Reviewer's conclusions Azathioprine and 6-mercaptopurine are effective therapy for inducing remission in active Crohn's disease. The odds ratio of response increases after >/= 17 weeks of therapy, suggesting that there is a minimum length of time for a trial of azathioprine or 6-mercaptopurine therapy. Adverse events were more common among patients on therapy.

Azathioprine or 6-mercaptopurine for induction of remission in Crohn's disease.

https://www.gastrojournal.org/article/S0016-5085(02)92123-2/pdf

6-MP metabolite profiles provide a biochemical explanation for 6-MP resistance in patients with inflammatory bowel disease.

https://www.gastrojournal.org/article/S0016-5085(06)00015-1/pdf

Association of 6-thioguanine nucleotide levels and inflammatory bowel disease activity: a meta-analysis.

BACKGROUND: 6-Mercaptopurine (6-MP) has confirmed short and longterm efficacy in the treatment of IBD. However, the relation between its metabolism, efficacy, and side effects is not well understood. AIMS: To assay 6-MP metabolites and to correlate levels with drug compliance, disease activity, and adverse effects of treatment. PATIENTS: Heparinised blood was obtained prior to daily administration of 6-MP in 25 adolescent Crohn's disease patients (14 ileocolitis, 11 colitis) receiving 1.2 (range 0.4-1.6) mg/kg/day for a mean of 17 (range 4-65) months. METHODS: Erythrocyte free bases 6-thioguanine (6-TG) and 6-methyl-mercaptopurine (6-MMP) were measured (pmol/8 x 10(8) red blood cells) using reverse phase high performance liquid chromatography. RESULTS: Disease activity (modified Harvey-Bradshaw index) improved significantly with 6-MP (p = 0.001). Clinical remission was achieved in 72% of patients, who stopped taking prednisone, or were successfully weaned to a low alternate day dose (< 0.4 mg/kg/OD). Remission correlated well with erythrocyte 6-TG (p < 0.05), but not 6-MMP levels. Neutropenia was associated with 6-MP use (p < 0.005), but did not correlate with erythrocyte 6-MP metabolite levels. One patient refractory to 6-MP had 6-TG, but no measureable 6-MMP production, suggesting deficient thiopurine methyl-transferase activity or poor compliance. 6-MP induced complications (hepatitis, pancreatitis, and marrow suppression) were generally associated with increased 6-MMP levels. CONCLUSIONS: These results suggest that high performance liquid chromatography measurement of erythrocyte 6-MP metabolites may provide a quantitative assessment of patient responsiveness and compliance to treatment. The data support an immunosuppressive role for 6-TG, and potential cytotoxicity of raised 6-MMP levels.

https://gut.bmj.com/content/gutjnl/39/3/401.full.pdf

6-Mercaptopurine metabolism in Crohn's disease: correlation with efficacy and toxicity.

The effects of 6-mercaptopurine (6MP) in inflammatory bowel disease are believed to be primarily mediated by its metabolite 6-thioguanine (6TG). Our aim was to develop an assay for measuring leukocyte DNA 6TG levels in patients with Crohn's disease, and to correlate them with levels of 6TG in erythrocytes. Heparinized blood was obtained from 15 adolescent Crohn's disease patients receiving 6MP at an average dose of 1.3 mg.kg-1 day-1 (range 0.8-1.6 mg.kg-1 day-1) for a mean of 23.7 months (range 3-71 months). Leukocyte DNA and erythrocyte 6TG levels were measured by an HPLC assay. Leukocyte 6TG levels ranged from 100 to 2305 pmol/mg DNA, while erythrocyte 6TG levels ranged from 64 to 1038 pmol/8 x 10(8) red blood cells, demonstrating significant interpatient variability. Leukocyte DNA 6TG levels correlated directly with erythrocyte 6TG levels, as measured by the Spearman rank correlation coefficient (p < 0.05). The HPLC measurement of erythrocyte and leukocyte DNA 6TG levels can be useful clinically in monitoring compliance, as well as perhaps to tailor drug metabolite levels to achieve the desired clinical effect.

C Cuffari

Papers

6-Mercaptopurine metabolism in Crohn's disease: correlation with efficacy and toxicity.

Quantitation of 6-thioguanine in peripheral blood leukocyte DNA in Crohn's disease patients on maintenance 6-mercaptopurine therapy