Fused Heterocyclic Compounds as Potent Indoleamine-2,3-dioxygenase 1 Inhibitors

Abstract

Uncontrolled metabolism of L-tryptophan (L-Trp) in the immune system has been recognized as a critical cellular process in immune tolerance. Indoleamine 2,3-dioxygenase 1 (IDO1) enzyme plays an important role in the metabolism of a local L-Trp through the kynurenine pathway in the immune systems. In this regard, IDO1 has emerged as a therapeutic target for the treatment of diseases that are associated with immune suppression like chronic infections, cancer, and others. In this study, we synthesized a series of pyridopyrimidine, pyrazolopyranopyrimidine, and dipyrazolopyran derivatives. Further lead optimizations directed to the identification of potent compounds, 4j and 4l (IC 50 = 260 and 151 nM, respectively). These compounds also exhibited IDO1 inhibitory activities in the low nanomolar range in MDA-MB-231 cells with very low cytotoxicity. Stronger selectivity for the IDO1 enzyme (>300-fold) over tryptophan 2,3-dioxygenase (TDO) enzyme was also observed for these compounds. Hence, these fused heterocyclic compounds are attractive candidates for the advanced study of IDO1-dependent cellular function and immunotherapeutic applications.

Identification of Substituted 1H‐Indazoles as Potent Inhibitors for Immunosuppressive Enzyme Indoleamine 2,3‐Dioxygenase 1

“…The IDO1 inhibitory activities of the synthesized 1 H ‐indazoles were initially evaluated by spectrophotometric method as described earlier ,, ,. The spectral properties of the compounds (0.1 μM to 100 μM) showed no or little interference with this activity assay.…”

“…The IDO1 enzyme activities in the presence of selected 1 H ‐indazoles were also investigated by HPLC‐analyses for additional validation of their inhibition efficiencies ,. The calculated IC 50 values revealed that the inhibitory efficiencies of the selected compounds are within 0.47–17.9 μM range and follows a similar pattern as that measured by using the spectrophotometric method (Table S2).…”

“…The ligand‐binding propensity to the IDO1 enzyme was examined by UV‐Vis spectral analysis. The optical properties of heme‐group are highly sensitive to the local environment ,,. The IC 50 values of the 1 H ‐indazoles reveal their capability in inhibiting IDO1 enzyme activity, but failed to provide any direct evidence of ligand binding to the active site of the IDO1 enzyme.…”

“…As part of our ongoing heterocyclic drug discovery program, we are focused on finding structurally simple but potent inhibitors of IDO1 enzyme for cancer immunotherapy ,,. Recently, molecular docking analyses and pharmacophore models identified 1 H ‐indazole scaffold as a novel class of IDO1 inhibitor .…”

Effect of Molecular Crowding Agents on the Activity and Stability of Immunosuppressive Enzyme Indoleamine 2,3‐Dioxygenase 1

“…Hence, to investigate the effect of crowding agents on the inhibitory activity of IDO1 enzyme, the activity assay was performed in the presence of few known potent compounds including, N′ ‐hydroxyamidine, 4‐phenyl‐4 H ‐pyran derivatives, 4‐amino‐ N ‐(3‐chloro‐4‐fluorophenyl)‐ N ′‐hydroxy‐1,2,5‐oxadiazole‐3‐carboxymidimade ( 5 l ) and L‐1‐MT (Figure ). Earlier, reported results show that the compounds ( 1‐4 ) have stronger IDO1 inhibitory activity with IC 50 values in the range of 39–437 nM against purified IDO1 enzyme in the presence of idealized diluite buffer solution ,. The other reported compounds 5 l and L‐1‐MT also showed IDO1 inhibitory activity with IC 50 values of 91 nM and 385 μM, respectively under the similar assay conditions (buffer only) ,.…”