Designer Thiopurine-analogues for Optimised Immunosuppression in Inflammatory Bowel Diseases

Background and Aims: The clinical use of azathioprineand 6- mercaptopurineis limited by their delayed onsetof actionand potential side effects such as myelosuppression and hepatotoxicity. As these drugs specifically target the Vav1/ Rac1signalling pathway in T lamina proprialymphocytes via their metabolite 6- thio- GTP, we studied expression and optimised suppression of this pathway in inflammatory bowel diseases [IBD]. Methods: Rac1and Vav1expressions were analysed in mucosal immune cells in IBD patients. Targeted molecular modelling of the 6- thio- GTPmolecule was performed to optimise Rac1blockade; 44 modified designer thiopurine-analogues were tested for apoptosis induction, potential toxicity, and immunosuppression. Activation of the Vav1/ Rac1pathway in lymphocytes was studied in IBD patients and in lamina propriaimmune cells in the presence or absence of thiopurine-analogues. Results: Several thiopurine-analogues induced significantly higher T cell apoptosis than 6- mercaptopurine. We identified a compound, denoted B-0N, based on its capacity to mediate earlier and stronger induction of T cell apoptosis than 6- mercaptopurine. B-0N-treatment resulted in accelerated inhibition of Rac1activity in primary peripheral blood T cells as well as in intestinal lamina propriaimmune cells. Compared with 6- thio- GTPand 6- mercaptopurine, B-0N-treatment was associated with decreased myelo- and hepatotoxicity. Conclusions: The Vav1/ Rac1pathway is activated in mucosal immune cells in IBD. The designer thiopurine-analogue B-0N induces immunosuppression more potently than 6- mercaptopurine.