A Persulfide Donor Responsive to Reactive Oxygen Species: Insights into Reactivity and Therapeutic Potential

A Stimuli-Responsive Small-Molecule Metal-Carrying Prochelator: A Novel Prodrug Design Strategy for Metal Complexes

Selective activation of prodrugs is an important approach to reduce the side effects of disease treatment. We report a prodrug design concept for metal complexes, termed "metal-carrying prochelator", which can co-carry a metal ion and chelator within a single small-molecule compound and remain inert until it undergoes a specifically triggered intramolecular chelation to synthesize a bioactive metal complex in situ for targeted therapy. As a proof-of-concept, we designed a H₂ O₂ -responsive small-molecule prochelator, DPBD, based on the strong chelator diethyldithiocarbamate (DTC) and copper. DPBD can carry Cu²⁺ (DPBD-Cu) and respond to elevated H₂ O₂ levels in tumor cells by releasing DTC, which rapidly chelates Cu²⁺ from DPBD-Cu affording a DTC-copper complex with high cytotoxicity, realizing potent antitumor efficacy with low systemic toxicity. Thus, with its unique intramolecularly triggered activation mechanism, this concept based on a small-molecule metal-carrying prochelator can help in the prodrug design of metal complexes.

Prodrugs of Persulfide and Sulfide: Is There a Pharmacological Difference between the Two in the Context of Rapid Exchanges among Various Sulfur Species In Vivo?

Sulfide and persulfide are chemically different and one might expect persulfide to be more effective in mediating sulfur signaling because persulfide can directly modify protein cysteine residue. However, rapid scrambling, and interconversions occur among sulfur species. Then there is the question of whether the chemical reactivity differences between sulfide and persulfide would translate into pharmacological differences. Utilizing a delivery system to generate pure hydrogen sulfide (H₂ S), hydrogen persulfide (H₂ S₂ ), and N-acetyl-l-cysteine persulfide (N-CysSSH), we examined the activities of sulfide and persulfide in vitro and in vivo. Persulfide prodrugs exhibited increased activities compared to the H₂ S prodrug. In particular, the H₂ S₂ prodrug offers much-elevated analgesic effects compared to the H₂ S prodrug in vivo. Persulfide prodrugs also possess a reduced level of toxicity compared to the H₂ S prodrug in vivo, indicating persulfide might represent a better therapeutic paradigm than H₂ S.

Orchestrating Nitric Oxide and Carbon Monoxide Signaling Molecules for Synergistic Treatment of MRSA Infections

The local delivery of gaseous signaling molecules (GSMs) has shown promising therapeutic potential. However, although GSMs have a subtle interplay in physiological and pathological conditions, the co-delivery of different GSMs for therapeutic purposes remains unexplored. Herein, we covalently graft a nitric oxide (NO)-releasing N-nitrosamine moiety onto the carbon monoxide (CO)-releasing 3-hydroxyflavone (3-HF) antenna, resulting in the first NO/CO-releasing donor. Under visible light irradiation, photo-mediated co-release of NO and CO reveals a superior antimicrobial effect toward Gram-positive bacteria with a combination index of 0.053. The synergy of NO and CO hyperpolarizes and permeabilizes bacterial membranes, which, however, shows negligible hemolysis and no evident toxicity toward normal mammalian cells. Moreover, the co-release of NO and CO can efficiently treat MRSA infection in a murine skin wound model, showing a better therapeutic capacity than vancomycin.

Targeted Delivery of Persulfides to the Gut: Effects on the Microbiome

Persulfides (R-SSH) have been hypothesized as potent redox modulators and signaling compounds. Reported herein is the synthesis, characterization, and in vivo evaluation of a persulfide donor that releases N-acetyl cysteine persulfide (NAC-SSH) in response to the prokaryote-specific enzyme nitroreductase. The donor, termed NDP-NAC, decomposed in response to E. coli nitroreductase, resulting in release of NAC-SSH. NDP-NAC elicited gastroprotective effects in mice that were not observed in animals treated with control compounds incapable of persulfide release or in animals treated with Na2 S. NDP-NAC induced these effects by the upregulation of beneficial small- and medium-chain fatty acids and through increasing growth of Turicibacter sanguinis, a beneficial gut bacterium. It also decreased the populations of Synergistales bacteria, opportunistic pathogens implicated in gastrointestinal infections. This study reveals the possibility of maintaining gut health or treating microbiome-related diseases by the targeted delivery of reactive sulfur species.

A Dinuclear Persulfide-Bridged Ruthenium Compound is a Hypoxia-Selective Hydrogen Sulfide (H2 S) Donor

Hydrogen sulfide (H2 S) is a gaseous molecule that has received attention for its role in biological processes and therapeutic potential in diseases, such as ischemic reperfusion injury. Despite its clinical relevance, delivery of H2 S to biological systems is hampered by its toxicity at high concentrations. Herein, we report the first metal-based H2 S donor that delivers this gas selectively to hypoxic cells. We further show that H2 S release from this compound protects H9c2 rat cardiomyoblasts from an in vitro model of ischemic reperfusion injury. These results validate the utility of redox-activated metal complexes as hypoxia-selective H2 S-releasing agents for use as tools to study the role of this gaseous molecule in complex biological systems.

Alleviating Cellular Oxidative Stress through Treatment with Superoxide-Triggered Persulfide Prodrugs

Overproduction of superoxide anion (O2.- ), the primary cellular reactive oxygen species (ROS), is implicated in various human diseases. To reduce cellular oxidative stress caused by overproduction of superoxide, we developed a compound that reacts with O2.- to release a persulfide (RSSH), a type of reactive sulfur species related to the gasotransmitter hydrogen sulfide (H2 S). Termed SOPD-NAC, this persulfide donor reacts specifically with O2.- , decomposing to generate N-acetyl cysteine (NAC) persulfide. To enhance persulfide delivery to cells, we conjugated the SOPD motif to a short, self-assembling peptide (Bz-CFFE-NH2 ) to make a superoxide-responsive, persulfide-donating peptide (SOPD-Pep). Both SOPD-NAC and SOPD-Pep delivered persulfides/H2 S to H9C2 cardiomyocytes and lowered ROS levels as confirmed by quantitative in vitro fluorescence imaging studies. Additional in vitro studies on RAW 264.7 macrophages showed that SOPD-Pep mitigated toxicity induced by phorbol 12-myristate 13-acetate (PMA) more effectively than SOPD-NAC and several control compounds, including common H2 S donors.

Activity-Based Sensing: A Synthetic Methods Approach for Selective Molecular Imaging and Beyond

Emerging from the origins of supramolecular chemistry and the development of selective chemical receptors that rely on lock-and-key binding, activity-based sensing (ABS)-which utilizes molecular reactivity rather than molecular recognition for analyte detection-has rapidly grown into a distinct field to investigate the production and regulation of chemical species that mediate biological signaling and stress pathways, particularly metal ions and small molecules. Chemical reactions exploit the diverse chemical reactivity of biological species to enable the development of selective and sensitive synthetic methods to decipher their contributions within complex living environments. The broad utility of this reaction-driven approach facilitates application to imaging platforms ranging from fluorescence, luminescence, photoacoustic, magnetic resonance, and positron emission tomography modalities. ABS methods are also being expanded to other fields, such as drug and materials discovery.