title: Rac1 as a Potential Pharmacodynamic Biomarker for Thiopurine Therapy in Inflammatory Bowel Disease.
abstract: 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.
  
  
  
  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.
  
  
  
  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.
  
  
  
  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.
authors.affiliation: Departments of *Gastroenterology and Hepatology and †Physiology, VU University Medical Center, Amsterdam; and ‡Department of Gastroenterology, Geriatrics, Internal and Intensive Care Medicine (Co-MIK), Zuyderland Medical Center, Heerlen-Sittard-Geleen, the Netherlands.
authors.forename: Margien L
authors.initials: ML
authors.lastname: Seinen
authors.forename: Geerten P
authors.initials: GP
authors.lastname: van Nieuw Amerongen
authors.forename: Nanne K H
authors.initials: NK
authors.lastname: de Boer
authors.forename: Chris J J
authors.initials: CJ
authors.lastname: Mulder
authors.forename: Jan
authors.initials: J
authors.lastname: van Bezu
authors.forename: Adriaan A
authors.initials: AA
authors.lastname: van Bodegraven
mesh_terms: D000328:Adult; D001379:Azathioprine / Q000493:pharmacokinetics / Q000627:therapeutic use*; D054316:Biomarkers, Pharmacological / Q000097:blood* / Q000378:metabolism; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007166:Immunosuppressive Agents / Q000493:pharmacokinetics / Q000627:therapeutic use; D015212:Inflammatory Bowel Diseases / Q000097:blood* / Q000188:drug therapy*; D008297:Male; D015122:Mercaptopurine / Q000493:pharmacokinetics / Q000627:therapeutic use*; D008875:Middle Aged; D010750:Phosphoproteins / Q000096:biosynthesis / Q000097:blood; D010766:Phosphorylation / Q000187:drug effects; D011446:Prospective Studies; D017923:Sodium-Hydrogen Exchangers / Q000096:biosynthesis / Q000097:blood; D055815:Young Adult; D020830:rac1 GTP-Binding Protein / Q000096:biosynthesis / Q000097:blood*
chemical_list: D054316:Biomarkers, Pharmacological; D007166:Immunosuppressive Agents; D010750:Phosphoproteins; C107953:RAC1 protein, human; D017923:Sodium-Hydrogen Exchangers; C093376:sodium-hydrogen exchanger regulatory factor; D015122:Mercaptopurine; D020830:rac1 GTP-Binding Protein; D001379:Azathioprine