Tryptophan 2,3-dioxygenase (TDO) inhibitors : Identification of new scaffolds using virtual screening

Immunotherapy is a promising novel strategy for cancer therapy. It consists of the therapeutic vaccination of cancer patients to stimulate their (natural) immune system against cancer cells. This approach, however, showed limited efficacy in vivo. Cancer cells are actually able to develop enzymatic mechanisms allowing tumours to resist or escape the immune rejection. Among the enzymes involved, the indoleamine 2,3-dioxygenases IDO and TDO represents potential actors.[1-3] These enzymes catalyse the rapid degradation of tryptophan (Trp) through the kynurenine (KYN) pathway to form quinolinic acid (QA). This results in a local Trp depletion that severely affects the proliferation of T lymphocytes and is thereby profoundly immunosuppressive. This project was funded in part by Télévie (FNRS grant 7.4.543.07) and led in collaboration with the team of Pr Benoit Van Den Eynde (LICR, UCL) and Pr Moreno Galleni (CIP, ULG) aims at developing novel TDO inhibitors using a rational approach. These inhibitors will allow a better understanding of the role of TDO in the phenomenon of immunosuppression, especially in cancerous tumors. In the present poster, we used virtual screening (VS) of the ZINC database of 2.5 million compounds to seek new TDO inhibitory scaffolds. The VS flowchart implemented various filters, including a 3D-database screen, and extensive docking studies in humanized Ralstonia metallidurans TDO (rmTDO), to derive 49 derivatives that were experimentally assayed against the rmTDO. Three compounds showed inhibitory percentage above 50%. These data allow better understanding of how this family of inhibitors interact with TDO. This process is presented on this poster.