Current status of thiopurine analogues in the treatment in Crohn's disease

Pharmacotherapy of inflammatory bowel diseases: efficacy performance and safety management

Treatment of inflammatory bowel diseases IBD (Crohns disease, ulcerative colitis) is aimed at achieving clinical, endoscopic and histological remission, minimizing surgical complications, and ensuring a normal quality of life. However, the use of medical treatment is potentially associated with various adverse events, among which infectious complications, malignant neoplasms, as well as myelotoxicity, hepatotoxicity, skin lesions and others. The risk of side effects depends on the type of drug therapy (5-aminosalicylates, thiopurines, biologicals, etc.), the duration of treatment, the presence of extra-intestinal manifestations, etc. The article provides an overview of data on both the effectiveness and frequency of various side effects of the main classes of drugs in IBD, presents methods of investigation which can predict the effectiveness and development of side effects, the implementation of which can be considered as a variant of personalized therapy in IBD.

Clinical predictors of thiopurine-related adverse events in Crohn's disease

AIM: To determine the incidence and predictors of thiopurine-related adverse events.

METHODS: Subjects with Crohn’s disease who were followed in the Alberta Inflammatory Bowel Disease Consortium patient database registry were identified. Retrospective chart review was conducted between August 5^th, 2010 and June 1^st, 2012. We collected data on: age at diagnosis; sex; disease location and behaviour at time of prescribing thiopurine; perianal fistulising disease at or prior to thiopurine prescription; smoking status at time of thiopurine prescription, use of corticosteroid within 6 mo of diagnosis; dosage, age at onset, and cessation of 5-aminosalicyclic acid (5-ASA); anti-tumour necrosis factor medication exposure and intestinal resection before thiopurine prescription. The primary outcome of interest was the first adverse event that led to discontinuation of the first thiopurine medication used. Logistic regression models were used to associate clinical characteristics with outcomes after adjusting for potential confounders. Risk estimates were presented as odds ratios (OR) with 95% CI. Effect modification by age and sex were explored.

RESULTS: Our cohort had a median follow-up duration of 5.8 years [interquartile range (IQR 25^th-75^th) 2.7-9.1]. Thiopurine therapy was discontinued in 31.3% of patients because of: hypersensitivity reactions (7.1%), acute pancreatitis (6.2%), gastrointestinal intolerance (5.4%), leucopenia (3.7%), hepatotoxicity (3.4%), infection (1.1%) and other reasons (4.3%). A higher incidence of thiopurine withdrawal was observed in patients over the age of 40 (39.4%, P = 0.007). A sex-by-age interaction (P = 0.04) was observed. Females older than 40 years of age had an increased risk of thiopurine discontinuation due to an adverse event (age above 40 vs age below 40, adjusted OR = 2.8; 95%CI: 1.4-5.6). In contrast, age did not influence thiopurine withdrawal in males (age above 40 vs below 40, adjusted OR = 0.9; 95%CI: 0.4-2.1). Other clinical variables (disease location and phenotype, perianal disease, smoking history, history of intestinal resection and prior 5-ASA or corticosteroid use) were not associated with an increased risk an adverse event leading to therapy cessation.

CONCLUSION: Thiopurine withdrawal due to adverse events is commoner in women over the age of 40 at prescription. These findings need to be replicated in other cohorts.

Glutathione transferases in the bioactivation of azathioprine

The prodrug azathioprine is primarily used for maintaining remission in inflammatory bowel disease, but approximately 30% of the patients suffer adverse side effects. The prodrug is activated by glutathione conjugation and release of 6-mercaptopurine, a reaction most efficiently catalyzed by glutathione transferase (GST) A2-2. Among five genotypes of GST A2-2, the variant A2*E has threefold-fourfold higher catalytic efficiency with azathioprine, suggesting that the expression of A2*E could boost 6-mercaptopurine release and adverse side effects in treated patients. Structure-activity studies of the GST A2-2 variants and homologous alpha class GSTs were made to delineate the determinants of high catalytic efficiency compared to other alpha class GSTs. Engineered chimeras identified GST peptide segments of importance, and replacing the corresponding regions in low-activity GSTs by these short segments produced chimeras with higher azathioprine activity. By contrast, H-site mutagenesis led to decreased azathioprine activity when active-site positions 208 and 213 in these favored segments were mutagenized. Alternative substitutions indicated that hydrophobic residues were favored. A pertinent question is whether variant A2*E represents the highest azathioprine activity achievable within the GST structural framework. This issue was addressed by mutagenesis of H-site residues assumed to interact with the substrate based on molecular modeling. The mutants with notably enhanced activities had small or polar residues in the mutated positions. The most active mutant L107G/L108D/F222H displayed a 70-fold enhanced catalytic efficiency with azathioprine. The determination of its structure by X-ray crystallography showed an expanded H-site, suggesting improved accommodation of the transition state for catalysis.

Prophylactic systemic P2X7 receptor blockade prevents experimental colitis

BACKGROUND

The P2X7 receptor (P2X7-R) is a non-selective adenosine triphosphate-gated cation channel present in epithelial and immune cells, and involved in inflammatory response. Extracellular nucleotides released in conditions of cell stress or inflammation may function as a danger signal alerting the immune system from inflammation. We investigated the therapeutic action of P2X7-R blockade in a model of inflammatory bowel disease.

METHODS

Rats with trinitrobenzene sulfonic (TNBS) acid-induced colitis were treated with the P2X7-R antagonists A740003 or brilliant blue G (BBG) through intra-peritoneal (IP) or intra-colonic (IC) injection prior to colitis induction. Clinical and endoscopic follow-up, histological scores, myeloperoxidase activity, densities of collagen fibers and goblet cells were evaluated. P2X7-R expression, NF-kappa B and Erk activities, and densities of T-cells and macrophages were analyzed by immunoperoxidase. The inflammatory response was determined by measuring inflammatory cytokines in cultures of colon explants, by enzyme-linked immunosorbent assay. Colonic apoptosis was determined by the TUNEL assay.

RESULTS

IP-BBG significantly attenuated the severity of colitis, myeloperoxidase activity, collagen deposition, densities of lamina propria T-cells and macrophages, while maintaining goblet cell densities. IP-BBG inhibited the increase in P2X7-R expression in parallel with apoptotic rates. TNF-α and interleukin-1β stabilized in low levels, while TGF-β and interleukin-10 did not change following IP-BBG-therapy. Colonic NF-kappa-B and Erk activation were significantly lower in IP-BBG-treated animals. Prophylactic IP-A740003 also protected rats against the development of TNBS-colitis.

CONCLUSIONS

Prophylactic systemic P2X7-R blockade is effective in the prevention of experimental colitis, probably due to a systemic anti-inflammatory action, interfering with a stress-inflammation amplification loop mediated by P2X7-R.

Clinical effects of adalimumab treatment with concomitant azathioprine in Japanese Crohn’s disease patients

AIM: To assess adalimumab’s efficacy with concomitant azathioprine (AZA) for induction and maintenance of clinical remission in Japanese Crohn’s disease (CD) patients.

METHODS: This retrospective, observational, single-center study enrolled 28 consecutive CD patients treated with adalimumab (ADA). Mean age and mean disease duration were 38.1 ± 11.8 years and 11.8 ± 10.1 years, respectively. The baseline mean Crohn’s disease activity index (CDAI) and C-reactive protein were 177.8 ± 82.0 and 0.70 ± 0.83 mg/dL, respectively. Twelve of these patients also received a concomitant stable dose of AZA. ADA was subcutaneously administered: 160 mg at week 0, 80 mg at week 2, followed by 40 mg every other week. Clinical response and remission rates were assessed via CDAI and C-reactive protein for 24 wk.

RESULTS: The mean CDAI at weeks 2, 4, 8, and 24 was 124.4, 120.2, 123.6, and 135.1, respectively. The CDAI was significantly decreased at weeks 2 and 4 with ADA and was significantly suppressed at 24 wk with ADA/AZA. Overall clinical remission rates at weeks 4 and 24 were 66.7% and 63.2%, respectively. Although no statistically significant difference in C-reactive protein was demonstrated, ADA with AZA resulted in a greater statistically significant improvement in CDAI at 24 wk, compared to ADA alone.

CONCLUSION: Scheduled ADA with concomitant AZA may be more effective for clinical remission achievement at 24 wk in Japanese Crohn’s disease patients.