IDO1 expression is sufficient to produce kynurenine in MDA-MB-231 cells.A, representative Western blot of IDO1 protein expression in TNF/IFN-ɣ-stimulated MDA-MB-231 cells, pretreated with increasing concentrations of ouabain or 0.05% DMSO, and transfected with an IDO1 targeting siRNA pool or nontargeting control (NTC) siRNA pool. B, kynurenine assay of TNF/IFN-ɣ-stimulated MDA-MB-231 cells, pretreated with increasing concentrations of ouabain or 0.05% DMSO, and transfected with an IDO1 targeting siRNA pool or nontargeting control (NTC) siRNA pool. Three independent experiments. C, representative Western blot of IDO1 protein expression in MDA-MB-231 cells transfected with pIDO1-FLAG or empty vector and pretreated with 0.05% DMSO (ctrl), 100 nM ouabain (OUA), no stimulation (no stim), or TNF/IFN-ɣ. D, kynurenine assay of MDA-MB-231 cells transfected with pIDO1-FLAG or empty vector and pretreated with 0.05% DMSO or 100 nM ouabain or no stimulation or TNF/IFN-ɣ. Three independent experiments. ∗p < 0.05, one-way ANOVA Tukey’s post-hoc. IDO1, indoleamine-pyrrole 2′,3′-dioxygenase 1.