Indoleamine 2,3-dioxygenase (IDO) is emerging as an important new therapeutic drug target for the treatment of cancer characterized by pathological immune suppression. IDO catalyzes the rate-limiting step of tryptophan degradation along the kynurenine pathway. Reduction in local tryptophan concentration and the production of immunomodulatory tryptophan metabolites contribute to the immunosuppressive effects of IDO. Presence of IDO on dentritic cells in tumor-draining lymph nodes leading to the activation of T cells toward forming immunosuppressive microenvironment for the survival of tumor cells has confirmed the importance of IDO as a promising novel anticancer immunotherapy drug target. On the other hand, Withaferin A (WA) - active constituent of Withania Somnifera ayurvedic herb has shown to be having a wide range of targeted anticancer properties. In the present study conducted here is an attempt to explore the potential of WA in attenuating IDO for immunotherapeutic tumor arresting activity and to elucidate the underlying mode of action in a computational approach. Our docking and molecular dynamic simulation results predict high binding affinity of the ligand to the receptor with up to -11.51 kcal/mol of energy and 3.63 nM of IC50 value. Further, de novo molecular dynamic simulations predicted stable ligand interactions with critically important residues SER167; ARG231; LYS377, and heme moiety involved in IDO's activity. Conclusively, our results strongly suggest WA as a valuable small ligand molecule with strong binding affinity toward IDO.
For the treatment of cancer, Indoleamine 2,3-dioxygenase (IDO) is emerging as an important new therapeutic drug target characterized by pathological immune suppression. On the other hand, Withaferin A (WA)-active constituent of Withania somnifera ayurvedic herb has shown to be having a wide range of targeted anti cancer properties. Previously, we have elucidated the potential of WA in attenuating the Indoleamine 2,3-dioxygenase for immunotherapeutic tumor arresting activity using computational approaches. In this present study, a Ligand based virtual screening with a threshold of >50% similarity was performed, based on the structure of Withaferin A using ZINC database, to perform a structure based virtual screening on IDO, targeting key residues involved in its functionality. 33 compounds were identified as promising IDO inhibitors which are similar to the structure of WA based on free binding energy and ADME constraints, compared to Withaferin A.
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