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Background and Purpose: Myeloid-derived suppressor cells (MDSCs) represent a major obstacle to cancer treatment, as they negatively regulate anti-tumour immunity through the suppression of tumour-specific T lymphocytes. Thus, the efficacy of immunotherapies may be improved by targeting MDSCs. In this study, we assessed the ability of hydrogen sulfide (H 2 S), a gasotransmitter whose anti-cancer effects are well known, to inhibit the accumulation and immunosuppressive functions of MDSCs in melanoma., Experimental Approach: Effects of H 2 S on the host immune response to cancer were evaluated using an in vivo syngeneic model of murine melanoma. B16F10-melanoma-bearing mice were treated with the H 2 S donor, diallyl trisulfide (DATS) and analysed for content of MDSCs, dendritic cells (DCs) and T cells. Effects of H 2 S on expression of immunosuppressive genes in MDSCs and on T cell proliferation were evaluated., Key Results: In melanoma-bearing mice, DATS inhibited tumour growth, and this effect was associated with a reduction in the frequency of MDSCs in the spleen, in the blood as well as in the tumour micro-environment. In addition, we found that CD8 + T cells and DCs were increased. Furthermore, DATS reduced the immuno-suppressive activity of MDSCs, restoring T cell proliferation., Conclusions and Implications: The H 2 S donor compound, DATS, inhibited the expansion and the suppressive functions of MDSCs, suggesting a novel role for H 2 S as a modulator of MDSCs in cancer. Therefore, H 2 S donors may provide a novel approach for enhancing the efficacy of melanoma immunotherapy., Linked Articles: This article is part of a themed section on Hydrogen Sulfide in Biology & Medicine. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v177.4/issuetoc., (© 2019 The British Pharmacological Society.)

Chronic inflammation contributes to tumor initiation in colitis-associated colorectal cancer (CRC). Indeed, inflammatory bowel disease (IBD) patients show an increased risk of developing CRC. Cancer immune evasion is a major issue in CRC and preclinical and clinical evidence has defined a critical role for myeloid-derived suppressor cells (MDSCs) that contribute to tumor growth and progression by suppressing T-cells and modulating innate immune responses. MDSCs comprise a heterogeneous population of immature myeloid cells that can be distinct in two subtypes: CD11b + Ly6G + Ly6C low with granulocytic phenotype (G-MDSCs) and CD11b + Ly6G - Ly6C high with monocytic phenotype (M-MDSCs). Hydrogen sulfide (H 2 S) is an endogenous gaseous signaling molecule that regulates various physiological and pathophysiological functions. In particular, several studies support its anti-inflammatory activity in experimental colitis and ulcer. However, the role of the H 2 S pathway in innate immune-mediated IBD has not yet been elucidated. To better define a possible link between MDSCs and H 2 S pathway in colitis-associated CRC development, we used an innate immune-mediated IBD model induced by infection with the bacterium Helicobacter hepaticus ( Hh ), closely resembling human IBD. Here, we demonstrated an involvement of MDSCs in colitis development. A significant time-dependent increase of both G-MDSCs and M-MDSCs was observed in the colon and in the spleen of Hh -infected mice. Following, we observed that chronic oral administration of the H 2 S donor DATS reduced colon inflammation by limiting the recruitment of G-MDSCs in the colon of Hh -infected mice. Thus, we identify the metabolic pathway l-cysteine/H 2 S as a possible new player in the immunosuppressive mechanism responsible for the MDSCs-promoted colitis-associated cancer development.

In humans, two main metabolic enzymes synthesize hydrogen sulfide (H2 S): cystathionine γ lyase (CSE) and cystathionine β synthase (CBS). A third enzyme, 3-mercaptopyruvate sulfurtransferase (3-MST), synthesizes H2 S in the presence of the substrate 3-mercaptopyruvate (3-MP). The immunohistochemistry analysis performed on human melanoma samples demonstrated that CSE expression was highest in primary tumors, decreased in the metastatic lesions and was almost silent in non-lymph node metastases. The primary role played by CSE was confirmed by the finding that the overexpression of CSE induced spontaneous apoptosis of human melanoma cells. The same effect was achieved using different H2 S donors, the most active of which was diallyl trisulfide (DATS). The main pro-apoptotic mechanisms involved were suppression of nuclear factor-κB activity and inhibition of AKT and extracellular signal-regulated kinase pathways. A proof of concept was obtained in vivo using a murine melanoma model. In fact, either l-cysteine, the CSE substrate, or DATS inhibited tumor growth in mice. In conclusion, we have determined that the l-cysteine/CSE/H2 S pathway is involved in melanoma progression., (© 2014 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.)

Inflammation plays a key role in tumor promotion and development. Indeed, cyclooxygenase-2 (COX-2) expression is strongly associated with different types of cancer. An emerging class of compounds with significant anti-inflammatory properties is the hydrogen sulfide-releasing non-steroidal anti-inflammatory drugs (H 2 S-NSAIDs). They consist of a traditional NSAID to which an H 2 S-releasing moiety is covalently attached. We have recently demonstrated that H 2 S donors inhibit melanoma cell proliferation. In the current study, we evaluated the potential beneficial effects of a new H 2 S-releasing derivative of naproxen, ATB-346 [2-(6-methoxynapthalen-2-yl)-propionic acid 4-thiocarbamoyl phenyl ester] which inhibits COX activity but also releases H 2 S. We used cell culture and a mouse melanoma model to evaluate the effect of ATB-346 on: i) in vitro growth of human melanoma cells; ii) in vivo melanoma development in mice. Cell culture studies demonstrated that ATB-346 reduced the in vitro proliferation of human melanoma cells and this effect was associated to induction of apoptosis and inhibition of NF-κB activation. Moreover, ATB-346 had novel Akt signaling inhibitory properties. Daily oral dosing of ATB-346 (43 μmol/kg) significantly reduced melanoma development in vivo. This study shows that ATB-346, a novel H 2 S-NSAID, inhibits human melanoma cell proliferation by inhibiting pro-survival pathways associated with NF-κB and Akt activation. Furthermore, oral treatment with ATB-346 inhibits melanoma growth in mice. In conclusion, the combination of inhibition of cyclooxygenase and delivery of H 2 S by ATB-346 may offer a promising alternative to existing therapies for melanoma. [ABSTRACT FROM AUTHOR]

Background: The need for new drugs in melanoma treatment is of great relevance. Indeed, current therapies for the treatment of metastatic melanoma offer a limited clinical benefit and only in recent years there has been an advancement due to the identification of new molecular targets . Hydrogen sulphide (H2S) is endogenously produced by the action of three enzymes CBS, CSE and the newly discovered 3-MST . While H2S is cytoprotective at physiological concentrations, it seems to have pro-apoptotic actions in cancer cells . However, to date there are not definitive reports on the role played by H2S in cancer development. Aim of this study was to determine the possible involvement of H2S in human melanoma. Methods: The study has been performed by using some relevant human melanoma cell lines such as A375, WM115 and SK-Mel-28. HaCat, a normal human fibroblast cell line, has been used as control. Cellular proliferation was evaluated by the MTT assay. Apoptosis was assayed by flow cytometry analysis by double staining with Annexin V and propidium iodide (PI). NF-kB/DNA-binding activity was evaluated by electrophoretic mobility shift assay. Expression of CBS, CSE, 3-MST was assayed by quantitative real time RT-PCR, expression of Bcl-2, XIAP, c-FLIP, caspase 3, PARP, IKBa and Akt/p-Akt was determined by western blotting. Levels of H2S in the supernatant and in total cellular extracts were assayed by colorimetric assay. Results: Diallyl trisulfide (DATS) is a garlic-derived polysulfide able to release H2S . Our results demonstrate that DATS greatly suppressed, in a time and concentration-dependent manner, proliferation of the three human melanoma cell lines used. The most striking effect was obtained on the A375 cell line whose proliferation was inhibited, following incubation with DATS (10–30–100μM, 72h) by 30%, 70%, and 78% respectively (p <0.001). This effect well correlated with the significant increase in H2S levels found in both supernatants and cellular lysates. Conversely, DATS up to 300 μM did not affect proliferation of HaCat. DATS-induced inhibition of A375 proliferation (10–100μM, 72h) was almost completely reversed by haemoglobin (10μM; p <0.001) a scavenger of H2S. Moreover, DATS-induced inhibition of A375 proliferation was due to the induction of apoptosis as demonstrated by FACS analysis with Annexin V/PI staining and further confirmed by the inhibition of Bcl-2, XIAP, FLIP, as well as by the cleavage and consequent activation of caspase-3 and inactivation of poly (ADP ribose) polymerase (PARP-1). Constitutive NF-kB and activated Akt expression have been described in melanoma. We also demonstrated that H2S released by DATS suppressed both constitutive NF-kB/DNA-binding activity and Akt phosphorylation suggesting that the apoptotic effect observed following exposure to H2S was consistent with the signal transduction pathways activated. Conclusion: In conclusion, we demonstrate that H2S triggers, in relevant human melanoma cell lines, an apoptotic effect. This effect, in turn, activates downstream a signal pattern that candidates H2S as a possible novel therapeutic/target or diagnostic tool. [Copyright &y& Elsevier]