Figure 9: Dormant human TRCs by IFN-γ are also abrogated by blocking IDO1-AhR pathway.

(a) A375 or primary human melanoma cells were cultured in soft 3D fibrin gels for 2 days and then treated with IFN-γ (150 ng ml⁻¹ or 200 ng ml⁻¹) for the indicated days. (b–d) A375 or primary human melanoma TRCs treated with IFN-γ for 3 days were subjected to cell cycle analysis (b), glucose consumption assay (c) or SA-β gal staining (d). (e) A375 cells grown in rigid plate or soft 3D gels were treated with IFN-γ (150 ng ml⁻¹) for 3 days and then subjected to western blot against phospho-STAT1, STAT1, IDO1, p27 and β-actin, respectively. (f) A375 TRCs treated with IFN-γ (150 ng ml⁻¹) were immunostained with anti-AhR antibody (green) and DAPI (blue), and observed under confocal microscope. (g) A375 TRCs were treated with Kyn (150 μM) or Kyn+DMF (20 μM) for 48 h. The colony size was calculated. (h,i) A375 cells were treated with IFN-γ (150 ng ml⁻¹) in the presence or absence of 1-MT (0.2 mM) or DMF (20 μM) for 3 days. The colony size was quantified (h) and colony number was counted (i). (j) NOD-SCID mice (n=8 per group) with human MCF-7 breast cancer (7 × 7 mm) were treated with IFN-γ/1-MT for 1 week. The tumour growth was measured. (k) IFN-γ activates p-STAT1 pathway to trigger apoptosis in differentiated cells, while IFN-γ switches from the p-STAT1 pathway to the IDO-Kyn-AhR-p27 cascade to induce TRC dormancy. The relative colony size in this figure was calculated by comparing the colony size in other groups with the colony size in the PBS (d2) group, which was set to 1. Data shown are representative of three independent experiments and error bars represent mean±s.e.m., NS, no significant difference (Student’s t-test).