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DIDO Report Summary

Project ID: 338954
Funded under: FP7-IDEAS-ERC
Country: Italy

Mid-Term Report Summary - DIDO (Innovative drugs targeting IDO molecular dynamics in autoimmunity and neoplasia)

Indoleamine 2,3-dioxygenase 1 (IDO1) is an enzyme capable of degrading tryptophan, an essential amino acid, and producing kynurenines, i.e., tryptophan catabolites that control excessive immune responses against pathogens (inflammation) and block immune responses against self-structures (autoimmune diseases). Highest expression of IDO1 can be found in dendritic cells (DCs), sentinels of the immune system that instruct T lymphocytes to either mount an effective immune response to destroy the foreign invaders or tolerate (not respond to) the antigens. A deficiency in IDO1 activity, particularly in DCs, has been observed in several experimental models of chronic inflammation and autoimmunity. This appears to be mainly due to the accelerated proteasomal degradation of the enzyme. On the other hand, tumor-bearing animals and also neoplastic patients are often characterized by the overexpression of the IDO1 enzyme, such that effective anti-tumor immunity rarely occurs. In 2011, we discovered that IDO1 is not just an enzyme producing kynurenines but, once phosphorylated by kinases of the Src family, can bind tyrosine phosphatases and triggers a signaling pathway that completely reprograms an immunostimulatory DC into a tolerogenic cell. Among several effects, the activation of the IDO1 signaling pathway leads to a sustained expression of IDO1 itself and production of transforming growth factor beta (TGF-beta), a potent immunosuppressive cytokine. Thus a DC reprogrammed via the IDO1 signaling pathway will be capable to maintain tolerance and thus keep in check auto- and also anti-tumor immunity over the long term. Currently known IDO1 modulators are only IDO1 catalytic inhibitors (still in clinical trials) that can be used in neoplastic patients and, until now, have not shown to be endowed with a significant anti-tumor activity. On the other hand, no drugs potentiating IDO1 activity, to be possibly used in autoimmunity, have been developed so far.
The aim of DIDO is to develop novel drugs capable of acting over the long term by either favouring (thus useful in the therapy of chronic inflammation and autoimmune disease) or inhibiting (useful in neoplasia) the IDO1 signaling. In addition, the aim of DIDO is to possibly identify novel drugs capable of modulating IDO1 proteasomal degradation. To this purpose, the expertise in pharmacology/immunology/biology (PI’s group) has been integrated with the expertise in medicinal chemistry/molecular and computational modeling (team member’s group) to develop such innovative drugs. In the first 30 months of the project, we established a novel, integrated method capable of screening hundreds of compounds with the potential of modulating IDO1 signaling. We screened more than 200 structurally diverse compounds selected from a structure-based virtual screening of ~600.000 small molecules endowed with drug-like or lead-like properties. Of these, 10 compounds were so far proven to be novel, potent IDO1 catalytic inhibitors. We also identified chemical structures capable of modulating the signaling and not catalytic activity of IDO1. Specifically, one of these, VIS-110, did not show significant inhibitory effects on IDO1 catalysis but did promote the IDO1 signaling and, when used in DC cultures, conferred long-term tolerogenic properties capable of blocking the presentation of an autoantigen in vivo in an IDO1-dependent fashion. We also identified two compounds, VIS-308 and VIS-329, capable of protecting IDO1 from proteasomal degradation in both mouse and human DCs. Finally, we unexpectedly discovered an IDO1 catalytic enhancer , i.e., VIS-119, capable of increasing the affinity of IDO1 for its substrate, tryptophan, in both cell and biochemical (using a recombinant IDO1 protein) assays. VIS-119 was also effective in protecting mice from the development of experimental autoimmune encephalomyelitis. The selected molecules will be subjected to studies of structure activity relationships, early ADME profiling, pharmacokinetics, toxicity and efficacy in experimental disease models in the second half period of the project.

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