A PEGylated alternating copolymeric prodrug of sulfur dioxide with glutathione responsiveness for Irinotecan delivery.

In this study, an enhanced anticancer strategy combining the chemotherapy from antineoplastics with the oxidative damage from a sulfur dioxide (SO2) prodrug is presented. Based on the characteristics of a high glutathione (GSH) level in the tumor microenvironment, a novel GSH-responsive SO2 polymeric prodrug mPEG-b-P(PA-alt-GDNs) was designed and synthesized via a ring-opening alternating copolymerization and "click" reaction. The GSH-sensitive mechanism of the polymer was investigated in detail. Furthermore, Irinotecan was loaded into the polymeric prodrug nanoparticles by a self-assembly method with a drug loading content of 12.3 wt% and a loading efficiency of 42.2%. The drug-loaded nanoparticles showed a sensitive response to high concentrations of GSH in the tumor cells and rapidly released both Irinotecan and SO2. The depletion of GSH and the release of SO2 were supposed to increase the level of reactive oxygen species in the tumor cell, which, in combination with the released Irinotecan, exerted an enhanced anti-proliferative effect against HepG2 cells. Finally, Irinotecan-loaded nanoparticles exhibited a stronger antitumor effect than free antineoplastics in HepG2 cells. Thus, these results indicated that our polymeric prodrug SO2 is a promising candidate for chemotherapeutic drug delivery and would be a new weapon in anticancer treatment.

Near-Infrared Light-Triggered Sulfur Dioxide Gas Therapy of Cancer.

The exploitation of gas therapy platforms holds great promise as a "green" approach for selective cancer therapy, however, it is often associated with some challenges, such as uncontrolled or insufficient gas generation and unclear therapeutic mechanisms. In this work, a gas therapy approach based on near-infrared (NIR) light-triggered sulfur dioxide (SO2) generation was developed, and the therapeutic mechanism as well as in vivo antitumor therapeutic efficacy was demonstrated. A SO2 prodrug-loaded rattle-structured upconversion@silica nanoparticles (RUCSNs) was constructed to enable high loading capacity without obvious leakage and to convert NIR light into ultraviolet light so as to activate the prodrug for SO2 generation. In addition, SO2 prodrug-loaded RUCSNs showed high cell uptake, good biocompatibility, intracellular tracking ability, and high NIR light-triggered cytotoxicity. Furthermore, the cytotoxic SO2 was found to induce cell apoptosis accompanied by the increase of intracellular reactive oxygen species levels and the damage of nuclear DNA. Moreover, efficient inhibition of tumor growth was achieved, associated with significantly prolonged survival of mice. Such NIR light-triggered SO2 therapy may provide an effective strategy to stimulate further development of synergistic cancer therapy platforms.

A diarylethene as the SO2 gas generator upon UV irradiation.

A closed-ring isomer of a diarylethene having a sulfone group works as the reagent for SO2 gas generation with thermal stability even at 70 °C, and it rapidly reverts to the open-ring isomer and generates the SO2 gas to induce cell death upon UV irradiation.

Benzosultines as sulfur dioxide (SO2) donors.

In order to understand precise biological roles of sulfur dioxide (SO(2)), reliable SO(2) donors, compounds that produce SO(2) under physiological conditions, are necessary. The design and development of 1-phenyl-benzosultine as an efficient SO(2) donor is reported. This compound undergoes cycloreversion to generate SO(2) upon dissolution in aqueous buffer at 37 °C with a yield of 89% and a half-life of 39 min and shows SO(2)-like biological activity in a DNA cleavage assay.

Hydroxylamine as an oxygen nucleophile: substitution of sulfonamide by a hydroxyl group in benzothiazole-2-sulfonamides.

Benzothiazole-2-sulfonamides react with an excess of hydroxylamine in aqueous solutions to form 2-hydroxybenzothiazole, sulfur dioxide, and the corresponding amine. Mechanistic studies that employ a combination of structure-reactivity relationships, oxygen labeling experiments, and (in)direct detection of intermediates and products reveal that the reaction proceeds via oxygen attack, and that oxygen incorporated in the 2-hydroxybenzothiazole product derives from hydroxylamine. The reaction, which is performed under mild conditions, can be used as a deprotection method for cleavage of benzothiazole-2-sulfonyl-protected amino acids.

[Construction of high sulphite-producing industrial strain of Saccharomyces cerevisiae].

In the process of beer storage and transportation, off-flavor can be produced for oxidation of beer. Sulphite is important for stabilizing the beer flavor because of its antioxidant activity. However, the low level of sulphite synthesized by the brewing yeast is not enough to stabilize beer flavor. Three enzymes involve sulphite biosynthesis in yeast. One of them, APS kinase (encoded by MET14) plays important role in the process of sulphite formation. In order to construct high sulphite-producing brewing yeast strain for beer production, MET14 gene was cloned and overexpressed in industrial strain of Saccharomyces cerevisiae. Primer 1 (5'-TGTGAATTCCTGTACACCAATGGCTACT-3', EcoR I) and primer 2 (5'-TATAAGCTTGATGA GGTGGATGAAGACG-3', HindIII) were designed according to the MET14 sequence in GenBank. A 1.1kb DNA fragment containing the open reading frame and terminator of MET14 gene was amplified from Saccharomyces cerevisiae YSF-5 by PCR, and inserted into YEp352 to generate recombinant plasmid pMET14. To express MET14 gene properly in S. cerevisiae, the recombinant expression plasmids pPM with URA3 gene as the selection marker and pCPM with URA3 gene and copper resistance gene as the selection marker for yeast transformation were constructed. In plasmid pPM, the PGK1 promoter from plasmid pVC727 was fused with the MET14 gene from pMET14, and the expression cassette was inserted into the plasmid YEp352. The dominant selection marker, copper-resistance gene expression cassette CUP1-MTI was inserted in plasmid pPM to result in pCPM. Restriction enzyme analysis showed that plasmids pPM and pCPM were constructed correctly. The laboratory strain of S. cerevisiae YS58 with ura3, trp1, leu2, his4 auxotroph was transformed with plasmid pPM. Yeast transformants were screened on synthetic minimal medium (SD) containing leucine, histidine and tryptophan. The sulphite production of the transformants carrying pPM was 2 fold of that in the control strain YS58, which showed that the MET14 gene on plasmid pPM was expressed functionally in YS58. The industrial brewing yeast strain YSF-38 was transformed with the plasmid pCPM and yeast transformants were selected on YEPD medium containing 4mmol/L copper sulphate. The recombinant strain carrying pCPM showed a 3.2-fold increase in sulphite production when compared to the host strain YSF-38 under laboratory culture conditions. Flask fermentation under brewing-like conditions was performed in Tsingtao Beer Brewery. The sulphite production of the recombinant strain began to be higher than that of the host strain YSF-38 at the fourth day and reached the maximum at the eighth day. At the end of fermentation, the sulphite produced by recombinant strain is 1.4 fold of that in the host strain. The overexpression of MET14 gene in both laboratory and industrial strains of S. cerevisiae increases the sulphite formation. It is the first time to construct high sulphite-producing industrial strain by functional expression of MET14 in S. cerevisiae. Such study provides the foundation for construction of an excellent brewing yeast strain that can produce proper sulphite and can be used in commercial beer production.

Study of bisulfite and metabisulfite aerosol generation systems.

Sulfur (IV) aerosols may be generated only as the fully neutralized sulfite by nebulization techniques. Attempts to generate bisulfite and metabisulfite aerosols result in the production of sulfite aerosols and large amounts of SO2. Previous toxicologic studies on metabisulfite and bisulfite aerosols apparently documented the effects of high concentrations of gaseous SO2.