We highlight methodological caveats potentially arising from these pitfalls and conclude that current derivatization strategies often fail to adequately capture physiological speciation of sulfur species.

Background and Purpose ATB‐346 is a hydrogen sulfide (H2S)‐releasing anti‐inflammatory and analgesic drug. Animal studies demonstrated negligible gastrointestinal (GI) damage despite marked inhibition of COX activity and significant analgesic and anti‐inflammatory effects. In humans, ATB‐346 (250 mg once daily) was found to inhibit COX to the same extent as naproxen (550 mg twice daily). Experimental Approach Two hundred forty‐four healthy volunteers completed a 2‐week, double‐blind study, taking either ATB‐346 (250 mg once daily) or naproxen (550 mg twice daily), with upper GI ulceration being examined endoscopically. Key Results Forty‐two per cent of the subjects taking naproxen developed at least one ulcer (≥3‐mm diameter), while only 3% of the subjects taking ATB‐346 developed at least one ulcer. The two drugs produced comparable and substantial (>94%) suppression of COX activity. Subjects in the naproxen group developed more ulcers per subject than ATB‐346‐treated subjects and a greater incidence of larger ulcers (≥5‐mm diameter). The incidence of dyspepsia, abdominal pain, gastro‐oesophageal reflux, and nausea was lower with ATB‐346 than with naproxen. Subjects treated with ATB‐346 had significantly higher plasma levels of H2S than those treated with naproxen. Conclusions and Implications This Phase 2B study provides unequivocal evidence for a marked reduction of GI toxicity of the H2S‐releasing analgesic/anti‐inflammatory drug, ATB‐346, as compared to the conventional dose of naproxen that produced equivalent suppression of COX. 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

Basal-like breast cancer (BLBC) is the most aggressive subtype of breast tumors with poor prognosis and limited molecular-targeted therapy options. We show that BLBC cells have a high Cys demand and reprogrammed Cys metabolism. Patient-derived BLBC tumors from four different cohorts exhibited elevated expression of the transsulfuration enzyme cystathione β-synthetase (CBS). CBS silencing (shCBS) made BLBC cells less invasive, proliferate slower, more vulnerable to oxidative stress and cystine (CySSCy) deprivation, prone to ferroptosis, and less responsive to HIF1-α activation under hypoxia. shCBS xenograft tumors grew slower than controls and exhibited impaired angiogenesis and larger necrotic areas. Sulfur metabolite profiling suggested that realigned sulfide/persulfide-inducing functions of CBS are important in BLBC tumor progression. Supporting this, the exclusion of serine, a substrate of CBS for producing Cys but not for producing sulfide/persulfide, did not exacerbate CySSCy deprivation–induced ferroptosis in shCBS BLBC cells. Impaired Tyr phosphorylation was detected in shCBS cells and xenografts, likely due to persulfidation-inhibited phosphatase functions. Overexpression of cystathione γ-lyase (CSE), which can also contribute to cellular sulfide/persulfide production, compensated for the loss of CBS activities, and treatment of shCBS xenografts with a CSE inhibitor further blocked tumor growth. Glutathione and protein-Cys levels were not diminished in shCBS cells or xenografts, but levels of Cys persulfidation and the persulfide-catabolizing enzyme ETHE1 were suppressed. Finally, expression of enzymes of the oxidizing Cys catabolism pathway was diminished, but expression of the persulfide-producing CARS2 was elevated in human BLBC tumors. Hence, the persulfide-producing pathways are major targetable determinants of BLBC pathology that could be therapeutically exploited.

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