A novel indole-3-propanamide exerts its immunosuppressive activity by inhibiting JAK3 in T cells.

We previously identified an indole-3-propanamide derivative, 3-[1-(4-chlorobenzyl)indol-3-yl]-N-(pyridin-4-yl)propanamide (AD412), as a potential immunosuppressive agent. Here, we document that AD412 inhibited the proliferative response of CD3/CD28-stimulated human T cells without inhibiting their interleukin 2 (IL-2) production and also inhibited the proliferation of CTL-L2 cells in response to IL-2. These results prompted us to analyze the effect of our compound on the three main signaling pathways coupled to the IL-2 receptor. We provide evidence that AD412 inhibited the JAK1/3-dependent phosphorylations of Akt, STAT5a/b, and ERK1/2 in IL-2-stimulated CTL-L2 cells. In contrast, AD412 had little effect on the JAK1/2-dependent INF-gamma-induced phosphorylation of STAT1 in U266 cells. This suggested a preferential inhibition of JAK3 over JAK1 or JAK 2 activities by AD412 that was confirmed by in vitro kinase assays with purified JAK2 and JAK3 kinases. In addition, we provide evidence that the inhibition of IL-2 response by AD412 was not due to inhibition of IL-2Ralpha up-regulation because neither AD412 nor JAK3 inhibitors described previously [4-[(3-bromo-4-hydroxyphenyl)amino]-6,7-dimethoxyquinazoline (WHI-P154) and alpha-cyano-(3,4-dihydroxy)-N-benzylcinnamid (AG-490)] significantly inhibited IL-2-induced IL-2Ralpha overexpression. Finally, we further document the immunosuppressive activity of AD412 in vivo by showing that its administration per os significantly prolonged heart allograft graft survival. This molecule may thus represent an interesting lead compound to develop new immunosuppressive agents in the field of transplantation and autoimmune diseases.