Drug repurposing through Biophysical Insights: Focus on Indoleamine 2,3-Dioxygenase and Tryptophan 2,3-Dioxygenase Dual Inhibitors.

The kynurenine pathway (KP) plays a pivotal role in dampening the immune response in many types of cancer, including TNBC. The intricate involvement of tryptophan degradation via KP serves as a critical regulator in mediating immunosuppression in the tumor microenvironment. The key enzymes that facilitate this mechanism and contribute to tumor progression are indoleamine 2,3-dioxygenase (IDO1) and tryptophan 2,3-dioxygenase (TDO). Despite attempts to use navoximod as a dual-specific inhibitor, its poor bioavailability and lack of clinical efficacy have hampered its utility. To date, no FDA-approved drugs have advanced for dual targeting of these enzymes. Therefore, this study aimed to repurpose the approved drugs from the DrugBank database as novel IDO1/TDO inhibitors. Initially, 2588 FDA-approved compounds were screened by employing molecular docking and pharmacokinetic profiling. Subsequently, methods such as MM-GBSA calculations and machine learning based analysis precisely identified 20 potential lead compounds. The resultant compounds were then assessed for various toxicity endpoints and anticancer activity. The PaccMann server revealed potent anticancer activity, with sensitivities ranging from 0.203 to 24.119 μM against MDA-MB-231 TNBC cell lines. Alongside, the interaction profile with critical residues, strongly reinforced DB06292 (Dapagliflozin) as a compelling hit candidate. Finally, the reliability of the result was corroborated through a rigorous 200 ns molecular dynamics simulation, ensuring the stable binding of the hit against the target proteins. Considering the promising outcomes, we speculate that the proposed hit compound holds strong potential for the management of TNBC.