Margien L. Seinen

Thiopurine therapy in inflammatory bowel disease patients: Analyses of two 8-year intercept cohorts†

Background: Thiopurines have proven efficacy in long‐term maintenance therapy of inflammatory bowel disease (IBD). Limited data are available with regard to factors predicting effectiveness and failure of long‐term thiopurine use in IBD patients. Methods: The data in this retrospective study are based on an 8‐year intercept cohort of previous or present thiopurine‐using IBD patients. Both cohorts are assessed by descriptive and statistical analysis aimed at determining thiopurine effectiveness and the variables that are predictive for failure of thiopurine therapy. Results: In all, 363 IBD patients were included (60% female), 63% with Crohns disease and 33% with ulcerative colitis. Overall, thiopurines were continued in 145/363 (40%) and discontinued in 208/363 (57%) patients. The proportion of patients still using thiopurines at 3, 6, 12, 24, and 60 months was 73%, 69%, 63%, 51%, and 42%, respectively. Patients discontinued thiopurines due to adverse events (39%), refractoriness (16%), and ongoing remission / patients request (4%). 6‐methylmercaptopurine (6‐MMP) concentration and 6‐MMP/6‐thioguanine nucleotides (6‐TGN) ratio were significant higher in the failure group. Prolonged continuation of thiopurines was associated with a decreased risk of discontinuation. Conclusions: Azathioprine and 6‐mercaptopurine were considered effective in ≈40% of IBD patients after 5 years of treatment. A quarter of the patients discontinued thiopurines within 3 months, mostly due to adverse events. A high 6‐MMP concentration or 6‐MMP/6‐TGN ratio was associated with therapeutic failure. If thiopurine use was successfully initiated in the first months, its use was usually extended over many years, as long‐term use was associated with continuation of therapy. (Inflamm Bowel Dis 2010)

Safety and Effectiveness of Long-term Allopurinol-Thiopurine Maintenance Treatment in Inflammatory Bowel Disease

Background:Thiopurines are the mainstay of conventional maintenance therapy in inflammatory bowel disease (IBD). Unfortunately, up to 50% of patients discontinue immunosuppressive therapy within 2 years due to intolerance or lack of efficacy. Allopurinol with low-dose thiopurine can optimize thiopurine metabolism for IBD patients with preferential shunting toward 6-methyl mercaptopurine (6-MMP) formation. The aim of this study was to assess long-term maintenance effectiveness and tolerability of allopurinol-thiopurine therapy in a larger multicenter cohort of IBD patients. Methods:Enrolled patients who failed monotherapy with thiopurines due to a skewed metabolism were subsequently treated with a combination therapy of allopurinol and low-dose thiopurine. Adverse events were monitored and therapeutic adherence was assessed. Seventy-seven IBD patients were enrolled with a mean follow-up of 19 months. Results:The median 6-thioguanine nucleotide concentration increased from 145 during monotherapy to 271 pmol/8 × 108 red blood cell (RBC) after at least 8 weeks of combination therapy while reducing the thiopurine dosage (P < 0.001). In contrast, median 6-MMP concentrations decreased from 10,110 to 265 pmol/8 × 108 RBC (P < 0.001). Leukopenia occurred in 12 patients (16%), requiring dose adaptation. Liver test abnormalities normalized in 81% of patients after the addition of allopurinol. Sixteen (21%) patients had to discontinue combination therapy. The percentage of patients still using combination therapy at 6, 12, 24, and 60 months was 87%, 85%, 76%, and 65%, respectively. Conclusions:Long-term combination therapy with allopurinol and low-dose thiopurines is an effective and well-tolerated treatment in IBD patients with a skewed thiopurine metabolism.

The effect of allopurinol and low-dose thiopurine combination therapy on the activity of three pivotal thiopurine metabolizing enzymes: Results from a prospective pharmacological study

INTRODUCTION Thiopurine therapy is often discontinued in inflammatory bowel disease (IBD) patients. The xanthine oxidase (XO) inhibitor allopurinol has previously shown to enhance thiopurine efficacy and to prevent adverse reactions, the mechanism of this beneficial interaction is not completely clarified. The aim of this study is to observe possible effects of allopurinol and low-dose thiopurine combination therapy on the activity of three pivotal thiopurine metabolizing enzymes. METHODS A prospective study of IBD patients failing thiopurine therapy due to a skewed thiopurine metabolism was performed. Patients were treated with allopurinol and azathioprine or mercaptopurine. Xanthine oxidase, hypoxanthine-guanine phosphoribosyl transferase (HGPRT) and thiopurine S-methyl transferase (TPMT) activities, and thiopurine metabolites concentrations were measured during thiopurine monotherapy, and after 4 and 12 weeks of combination therapy. RESULTS Of fifteen IBD patients, XO activity decreased from 0.18 (IQR 0.08-0.3) during thiopurine monotherapy to 0.14 (IQR 0.06-0.2) and 0.11 (IQR 0.06-0.2; p=0.008) mU/hour/ml at 4 and 12 weeks, respectively. HGPRT activity increased from 150 (IQR 114-176) to 180 (IQR 135-213) and 204 nmol/(h×mg protein) (IQR 173-213; p=0.013). TPMT activity seemed not to be affected. 6-Thioguanine nucleotide concentrations increased from 138 (IQR 119-188) to 235 (223-304) and to 265 pmol/8×10^8 (IQR 188-344), whereas 6-methyl mercaptopurine ribonucleotides concentrations decreased from 13230 (IQR 7130-17420) to 690 (IQR 378-1325) and 540 (IQR 240-790) pmol/8×10^8 at 4 and 12 weeks of combination therapy (both p<0.001). CONCLUSION Allopurinol and thiopurine combination-therapy seems to increase HGPRT and decrease XO activity in IBD patients, which at least in part may explain the observed changes in thiopurine metabolite concentrations.

Hepatotoxicity associated with 6-methyl mercaptopurine formation during azathioprine and 6-mercaptopurine therapy does not occur on the short-term during 6-thioguanine therapy in IBD treatment

BACKGROUND AND AIMS High concentrations of methylated thiopurine metabolites, such as 6-methyl mercaptopurine, are associated with hepatotoxicity during administration of the conventional thiopurines azathioprine or 6-mercaptopurine in IBD patients. Metabolization of the non-conventional thiopurine 6-thioguanine does not generate 6-methyl mercaptopurine. Hence, the aim of our study was to evaluate hepatotoxicity during 6-thioguanine in IBD patients who previously failed conventional thiopurines due to 6-methyl mercaptopurine associated hepatotoxicity. METHODS A retrospective single center intercept cohort study was performed of IBD patients using 6-thioguanine between January 2006 and July 2010 after failing conventional thiopurine therapy due to 6-methyl mercaptopurine associated hepatotoxicity. The primary outcome was the occurrence of 6-thioguanine induced hepatotoxicity, scaled according to the Common Terminology Criteria for Adverse Events. RESULTS Nineteen patients were included. Median duration of 6-thioguanine therapy (median daily dosage 21 mg (9-24)) was 23 weeks (6-96). Hepatotoxicity did not reoccur in 15 out of 19, whereas grade 1 toxicity persisted in 4 patients (p<0.001). Median aspartate aminotransferase and alanine aminotransferase concentrations decreased from 34 U/l (20-59) and 64 U/l (15-175) to 23 U/l (18-40; p=0.003) and 20 U/l (14-48; p=0.019), respectively. CONCLUSION Hepatotoxicity does not reoccur during 6-thioguanine treatment in most IBD patients who failed conventional thiopurines due to 6-methyl mercaptopurine associated hepatotoxicity. Hence, at least at short-term, 6-thioguanine appears a justifiable alternative thiopurine for these IBD patients.

Allopurinol Enhances the Activity of Hypoxanthine-Guanine Phosphoribosyltransferase in Inflammatory Bowel Disease Patients During Low-Dose Thiopurine Therapy: Preliminary Data of An Ongoing Series

Thiopurines are crucial in the treatment of inflammatory bowel disease. The phenotype of pivotal metabolic enzymes determines whether thioguanine nucleotides (6-TGN) are generated in clinically sufficiently high levels. The first step in activation of thiopurine prodrugs to 6-TGN is catalysis by hypoxanthine-guanine phosphoribosyltransferase (HGPRT). Often, patients exhibit a clinically unfavorable metabolism, leading to discontinuation of conventional thiopurine therapy. The combination of allopurinol and low-dose thiopurine therapy may optimize this variant metabolism, presumably by affecting enzyme activities. We performed a prospective pharmacodynamic study to determine the effect of combination therapy on the activity of HGPRT. The activity of HGPRT and 6-TGN concentrations was measured in red blood cells during thiopurine monotherapy and after 4 weeks of combination therapy. The activity of HGPRT was also measured after 12 weeks of combination therapy. From the results, we conclude that combination therapy increases the activity of HGPRT and subsequently 6-TGN concentrations.

Sustained Clinical Benefit and Tolerability of Methotrexate Monotherapy After Thiopurine Therapy in Patients With Crohn's Disease

BACKGROUND & AIMS Methotrexate is an immunosuppressant that is used to treat patients with Crohns disease (CD). However, there are few data on the long-term effects of methotrexate maintenance therapy for these patients. We assessed the sustained clinical benefits and tolerability of methotrexate monotherapy after thiopurine therapy in patients with CD. METHODS We analyzed data from 3 hospitals on 174 consecutive patients with CD (age, 35 ± 12 y) who received methotrexate monotherapy after thiopurine therapy (23% also did not respond to anti-tumor necrosis factor therapy) from 2000 to 2010. We assessed patient characteristics and the tolerability and sustained clinical benefits of the treatment. Sustained clinical benefit was defined as ongoing use of methotrexate or intentional discontinuation of successful therapy before the end-of-study point. RESULTS The number of patients with sustained clinical benefits from methotrexate monotherapy were 98 (86%), 50 (63%), 27 (47%), and 3 (20%), at 6, 12, 24, and 60 months, respectively. Forty-five patients (26%) discontinued methotrexate because of intolerance, particularly within 6 months after therapy began. Adverse responses generally were mild; only 1 patient required admission to the hospital for infection with cytomegalovirus, and no drug-related deaths were reported. Intolerance of the preceding thiopurine therapy was associated with adverse events during methotrexate therapy. CONCLUSIONS In a large cohort study of patients who received methotrexate monotherapy after thiopurine therapy for CD, 47% continued to receive the therapy or intentionally discontinued successful therapy within 2 years, and 20% did so within 5 years. Long-term use of methotrexate was well tolerated and relatively safe.

Rac Attack: Modulation of the Small GTPase Rac in Inflammatory Bowel Disease and Thiopurine Therapy.

The incidence and prevalence of inflammatory bowel disease (IBD) are increasing. Although the etiology of IBD is unknown, it is thought that genetically susceptible individuals display an inappropriate inflammatory response to commensal microbes, resulting in intestinal tissue damage. Key proteins involved in regulating the immune response, and thus in inflammation, are the small triphosphate-binding protein Rac and its regulatory network. Recent data suggest these proteins to be involved in (dys)regulation of the characteristic inflammatory processes in IBD. Moreover, Rac-gene variants have been identified as susceptibility risk factors for IBD, and Rac1 GTPase signaling has been shown to be strongly suppressed in non-inflamed mucosa compared with inflamed colonic mucosa in IBD. In addition, first-line immunosuppressive treatment for IBD includes thiopurine therapy, and its immunosuppressive effect is primarily ascribed to Rac1 suppression. In this review, we focus on Rac modification and its potential role in the development of IBD, Rac as the molecular therapeutic target in current thiopurine therapy, and the modulation of the Rac signal transduction pathway as a promising novel therapeutic strategy.

Safe use of allopurinol and low-dose mercaptopurine therapy during pregnancy in an ulcerative colitis patient.

To the Editor: Conventional thiopurines (azathioprine [AZA] and mercaptopurine [MP]) are considered the cornerstone in maintenance treatment of inflammatory bowel disease (IBD). Unfortunately, up to 50% of the IBD patients do not tolerate or are refractory to this immunosuppressive therapy. For a few years combination therapy of allopurinol and low-dose thiopurine has been shown to be a successful strategy to optimize thiopurine therapy in IBD patients. Combination therapy modulates the thiopurine metabolism, resulting in higher concentrations of the pharmacologically active 6-thioguanine nucleotides (6-TGN), among others. Conventional thiopurines are considered relatively safe during pregnancy in IBD patients. However, evidence on the safety profile of combination therapy of allopurinol and low-dose thiopurine during pregnancy is lacking. We report a successful outcome of a patient diagnosed with ulcerative colitis who was treated with this combination therapy throughout her entire pregnancy. In addition, intrauterine exposure to thiopurine metabolites was determined. A 25-year-old female with leftsided ulcerative colitis from 2009 was cotreated with MP (75 mg) because of mesalazine refractoriness. After initiation of MP therapy, she developed intolerable gastrointestinal complaints. Measurement of thiopurine metabolites showed a skewed metabolism resulting in a high 6-methylmercaptopurine (6-MMP) concentration of 12,370 pmol/8 · 108 red blood cells (RBC) (normal,5700 pmol/8 · 108) and a low 6-TGN concentration of 181 pmol/8 · 108 RBC (normal range 230–400 pmol/8 · 108RBC). Combination therapy of lowdose MP (25 mg) and 100 mg allopurinol daily was initiated with continuation of mesalazine 4 g/day. The pharmacologically active 6-TGN concentration increased to 346 pmol/8 · 108 RBC and 6-MMP concentration decreased to 940 pmol/8 · 108 RBC. With this combination therapy her disease became clinically quiescent. In 2011 she became pregnant. During the second trimester she developed complaints of diarrhea and blood loss accompanied by increased fecal calprotectin levels. Topical mesalazine therapy was initiated, ameliorating but not completely resolving disease activity. During routine gestational followup (ultrasonography), no fetal abnormalities nor growth restriction was detected. An elective, uncomplicated cesarean section was performed at 39 weeks gestational age. A healthy infant without congenital anomalies was born with an Apgar score of 9/10/10 at 1, 5, and 10 minutes and a birth weight of 3550 g. At delivery, cord blood was collected from the newborn and peripheral blood from mother to assess thiopurine metabolites. 6-TGN concentration in the umbilical cord vein was 88 pmol/8 · 108 and the 6-MMP concentration was undetectable. Maternal levels were 112 pmol/ 8 · 108(6-TGN) and 160 pmol/8 · 108 (6-MMP). Combination therapy modulates thiopurine metabolism, leading to increased 6-TGN and decreased 6-MMP concentrations. Determination of intrauterine thiopurine metabolites showed that only 6-TGN concentrations were detectable in the cord blood of the newborn, in line with observations during monotherapy AZA/MP. Moreover, our research group observed a decrease in 6-TGN and increase of 6-MMP levels during pregnancy. Thiopurine metabolites may be associated with the induction of toxicity. High 6-TGN levels are associated with bone marrow suppression and elevated 6-MMP levels with hepatotoxicity. Combination therapy increases the maternal concentration of 6-TGN, and therefore the risk for maternal and (probably) fetal myelosuppression. Little is known about the safety profile of allopurinol during pregnancy. One case report showed a potential teratogenic effect of allopurinol, while in other studies in pregnant women and neonates no adverse reactions were observed. In conclusion, we report that combination therapy of allopurinol and lowdose thiopurine was not associated with an adverse pregnancy outcome. Moreover, placental transfer and intrauterine exposure to thiopurine metabolites was similar as in patients using monotherapy thiopurine.

Rac1 as a Potential Pharmacodynamic Biomarker for Thiopurine Therapy in Inflammatory Bowel Disease.

Background: Azathioprine and mercaptopurine (MP) are effective in treating patients with inflammatory bowel disease (IBD). Immunosuppressive effects of thiopurines involve T-cell apoptosis after inhibition of GTPase Ras-related C3 botulinum toxin substrate 1 (Rac1). This study aimed to assess whether expression and activity of Rac1 or phosphorylated ezrin-radixin-moesin (pERM) in patients with IBD could provide a useful biomarker for the pharmacodynamic thiopurine effect and might be related to clinical effectiveness. Methods: This was a 2-stage study: stage 1 concerned a cross-sectional cohort of patients with IBD clinically in remission and treated with (n = 10) or without stable weight-based thiopurine therapy (n = 11) and healthy controls (n = 6); stage 2 concerned a prospective study regarding IBD patients with clinically active disease who initiated MP therapy (n = 11) compared with healthy controls (n = 11). Expression and activity of Rac1 and ERM and pERM were determined. Results: The median Rac1 expression was statistically significantly reduced by thiopurine maintenance therapy {0.54 [interquartile range (IQR) 0.47–0.88] versus 0.80 arbitrary units [IQR 0.64–1.46]} compared with patients without immunosuppressive therapy (P = 0.042), but not Rac1 activity and pERM. In responders to MP therapy (n = 6), both median active Rac1 [93 (IQR 81–151) to 76 ng Rac1/mg protein (IQR 62–98)] and Rac1 expression [16.2 (8.8–29.4) to 1.5 arbitrary units (0.9–5.3)] decreased (P = 0.028). In nonresponders (n = 3), Rac1 expression and activity increased. Conclusions: IBD patients treated with thiopurines had a lower expression of Rac1 compared with those not treated with thiopurine. Effective MP therapy led to decreasing concentrations of Rac1-GTP and Rac1 expression. Therefore, Rac1-GTP and expression of Rac1, but not phosphorylation of ERM, form potentially pharmacodynamic markers of therapeutic thiopurine effectiveness in patients with IBD.

Optimizing Thiopurine Therapy in Inflammatory Bowel Disease Among 2 Real-life Intercept Cohorts: Effect of Allopurinol Comedication?

Background: Thiopurines (azathioprine and mercaptopurine) are frequently used immunosuppressive drugs to maintain remission in patients with inflammatory bowel disease. Half of the conventional thiopurine-derivative users have to discontinue treatment within 5 years, mainly because of intolerable adverse events. Over recent years, different strategies to optimize thiopurine treatment were suggested, yet, studies describing the clinical effectiveness of these strategies remain scarce. The aims of this study were to compare tolerability and sustained clinical benefit of conventional thiopurine derivatives therapy among two 5-year real-life intercept cohorts and to assess the clinical value of specifically allopurinol cotherapy. Methods: In this retrospective single-center cohort study, we analyzed data from patients in whom weight-based thiopurine monotherapy was initiated between 2005 and 2009 (cohort 1) or between 2010 and 2014 (cohort 2). The initiation of the second cohort was synchronic to the start of allopurinol-based optimization in our center. Optimization strategies were extracted from patient charts. Results: In total, 105 patients were included (60 in cohort 1, and 45 in cohort 2). Metabolite measurement was performed in 37% versus 84% of the patients (P < 0.001). Subsequent optimization strategies were applied in 33% versus 58% of the patients because of inadequate metabolite concentrations, intolerance, or ineffectiveness (P = 0.01). Allopurinol was coadministered to therapy in 18 patients (40%) in the second cohort. Therapy was switched to thioguanine in 11 versus 6 patients (P > 0.05). Overall, total duration was longer in the second cohort (10.8 versus 34.1 months, P < 0.001). The number of ongoing thiopurine users (20% versus 49%) and sustained clinical benefit (13% versus 38%) were higher in the second cohort (both P < 0.05). This was mainly because of a decrease in hepatotoxicity after optimization (P < 0.01). Conclusions: Optimization of thiopurine therapy by the use of therapeutic drug monitoring with subsequent administration of allopurinol cotherapy successfully enhanced sustained clinical benefit and tolerability in patients with inflammatory bowel disease.