Enhanced inhibition of protein disulfide isomerase and anti-thrombotic activity of a rutin derivative: rutin:Zn complex.

Rutin is a flavonoid that exists in plants and in commonly consumed foods. In recent years, rutin has been demonstrated to have anti-thrombotic efficacy through its inhibition of protein disulfide isomerase. However, the low aqueous solubility and high dose limit the therapeutic applications of rutin. In this study, we found that the chelation of zinc ions increased rutin aqueous solubility by 4-fold. More importantly, the thus-formed rutin:Zn complex inhibited PDI activity more potently than rutin itself. In a murine model with electric current-induced arterial thrombosis, the rutin:Zn complex slowed mouse arterial occlusion compared to rutin without increasing bleeding risk. Thus, the zinc chelation not only improved rutin aqueous solubility but achieved stronger inhibition of PDI. Furthermore, zinc chelation of a selected list of flavonoids containing the adjacent keto and phenoxy groups also increased their inhibition of PDI. Hence, our study provides a strategy to promote flavonoids' anti-thrombotic properties.

Novel pH-Triggered Doxorubicin-Releasing Nanoparticles Self-Assembled by Functionalized ß-Cyclodextrin and Amphiphilic Phthalocyanine for Anticancer Therapy.

Cyclodextrins (CDs), as pharmaceutical excipients with excellent biocompatibility, non-immunogenicity, and low toxicity in vivo, are widely used to carry drugs by forming inclusion complexes for improving the solubility and stability of drugs. However, the limited space of CDs' lipophilic central cavity affects the loading of many drugs, especially with larger molecules. In this study, ß-CDs were modified by acetonization to improve the affinity for the chemotherapy drug doxorubicin (DOX), and doxorubicin-adsorbing acetalated ß-CDs (Ac-CD:DOX) self-assembled to nanoparticles, followed by coating with the amphiphilic zinc phthalocyanine photosensitizer ZnPc-(PEG)5 for antitumor therapy. The final product ZnPc-(PEG)5:Ac-CD:DOX was demonstrated to have excellent stability and pH-sensitive drug release characteristics. The cell viability and apoptosis assay showed synergistic cytotoxic effects of chemotherapy and phototherapy. The mechanism of cytotoxicity was analyzed in terms of intracellular reactive oxygen species, mitochondrial membrane potential, and subcellular localization. More importantly, in vivo experiments indicated that ZnPc-(PEG)5:Ac-CD:DOX possessed significant tumor targeting, prominent antitumor activity, and less side effects. Our strategy expands the application of CDs as drug carriers and provides new insights into the development of CD chemistry.

Inhibition of the Citrus Canker Pathogen Using a Photosensitizer Assisted by Sunlight Irradiation.

Citrus canker, induced by bacterial infection, seriously affects the growth and productivity of citrus around the world and has attracted strong research interest. The current treatment for this disease uses copper salts to inactivate the pathogenic bacteria: Xanthomonas citri subsp. citri (Xcc) strain. However, copper salts may have a negative impact on the environment or plant. In this work, we identify a chemical compound, 2,6-diiodo-1,3,5,7-tetramethyl-8-(P-benzoic acid)-4,4'-difluoroboradiazaindacene (DIBDP), to inactivate the pathogenic Xcc strain (29-1). DIBDP is activated by sunlight and generates reactive oxygen species to kill the bacteria. In order to overcome the degradation of DIBDP under sunlight, an adjuvant agent was identified to limit the photodegradation of DIBDP by forming a photosensitizer complex (PSC). This complex demonstrated significant antimicrobial activity to Xcc 29-1, which was 64-fold more potent than the copper biocides. The antimicrobial efficacy of PSC on citrus leaves infected by Xcc 29-1 also was much stronger than copper agent and, at the same time, the PSC was safe to the host exposed to sunlight. Thus, this PSC is a promising antibacterial agent to control citrus canker disease.

A substrate-driven allosteric switch that enhances PDI catalytic activity.

Protein disulfide isomerase (PDI) is an oxidoreductase essential for folding proteins in the endoplasmic reticulum. The domain structure of PDI is a-b-b'-x-a', wherein the thioredoxin-like a and a' domains mediate disulfide bond shuffling and b and b' domains are substrate binding. The b' and a' domains are connected via the x-linker, a 19-amino-acid flexible peptide. Here we identify a class of compounds, termed bepristats, that target the substrate-binding pocket of b'. Bepristats reversibly block substrate binding and inhibit platelet aggregation and thrombus formation in vivo. Ligation of the substrate-binding pocket by bepristats paradoxically enhances catalytic activity of a and a' by displacing the x-linker, which acts as an allosteric switch to augment reductase activity in the catalytic domains. This substrate-driven allosteric switch is also activated by peptides and proteins and is present in other thiol isomerases. Our results demonstrate a mechanism whereby binding of a substrate to thiol isomerases enhances catalytic activity of remote domains.