H 2 S suppresses indoleamine 2, 3-dioxygenase 1 and exhibits immunotherapeutic efficacy in murine hepatocellular carcinoma

Abstract

Background

Over-expression and over-activation of immunosuppressive enzyme indoleamine 2, 3 -dioxygenase 1 (IDO1) is a key mechanism of cancer immune escape. However, the regulation of IDO1 has not been fully studied. The relation between hydrogen sulfide (H₂S) and IDO1 is unclear.

Methods

The influences of endogenous and exogenous H₂S on the expression of IDO1, iNOS and NF-κB and STAT3 signaling proteins were investigated using qPCR or western blot, and the production of nitric oxide (NO) was analyzed by nitrate/nitrite assay in Cse^−/− mice and MCF-7 and SGC-7901 cells. The effect of H₂S on IDO1 activity was investigated by HPLC and in-vitro enzymatic assay. The effect of H₂S on tryptophan metabolism was tested by luciferase reporter assay in MCF-7 and SGC-7901 cells. The correlation between H₂S-generating enzyme CSE and IDO1 was investigated by immunostaining and heatmaps analysis in clinical specimens and tissue arrays of hepatocellular carcinoma (HCC) patients. The immunotherapeutic effects of H₂S on H22 HCC-bearing mice were investigated.

Results

Using Cse^−/− mice, we found that H₂S deficiency increased IDO1 expression and activity, stimulated NF-κB and STAT3 pathways and decreased the expression of NO-generating enzyme Inos. Using IDO1-expressing MCF-7 and SGC-7901 cells, we found that exogenous H₂S inhibited IDO1 expression by blocking STAT3 and NF-κB pathways, and decreased IDO1 activity via H₂S/NO crosstalk, and combinedly decreased the tryptophan metabolism. The negative correlation between H₂S-generating enzyme CSE and IDO1 was further validated in clinical specimens and tissue arrays of HCC patients. Additionally, H₂S donors effectively restricted the tumor development in H22 HCC-bearing mice via downregulating IDO1 expression, inducing T-effector cells and inhibiting MDSCs.

Conclusions

Thus, H₂S, as a novel negative regulator of IDO1, shows encouraging antitumor immunotherapeutic effects and represents a novel therapeutic target in cancer therapy.

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