Small DNA circles as bacterial topoisomerase I inhibitors

Preparation of topoisomers of short circular dsDNA with defined linking number by accurate topological control

Short DNA catenanes [circular double-stranded DNA (dsDNA)] have attracted considerable interest for constructing nanostructures and nanomachines, as well as understanding DNA topology. The study of topoisomers of a circular dsDNA with a definite linking number (Lk) is essential but very difficult for simplifying the complex problems about DNA topology. The topoisomers are difficult to prepare, especially in the case that two strands are completely complementary. In this study, using a model system, we prepared all eight topoisomers (Lk0-Lk7) of a 79-bp-long circular dsDNA (8-14 nm in size) by utilizing aid-DNA to prevent undesired hybridization. By rapid ligation before strand displacement, high selectivity (>75%) for most topoisomers (31% for Lk1) was achieved under the strict topological control. All eight topoisomers with high purity were obtained after purification. Using a gel shift assay with Z-DNA-specific binding proteins, as well as by circular dichroism chromatography and enzymatic digestion, it was found that Z-DNA forms for topoisomers Lk0-Lk6, and Lk0-Lk5 can be converted to Lk6 by topoisomerase I. The approach developed in this study can significantly contribute to DNA or RNA topology, particularly the effect of topological constraints on DNA structures and functions.

Type IA Topoisomerases as Targets for Infectious Disease Treatments

Infectious diseases are one of the main causes of death all over the world, with antimicrobial resistance presenting a great challenge. New antibiotics need to be developed to provide therapeutic treatment options, requiring novel drug targets to be identified and pursued. DNA topoisomerases control the topology of DNA via DNA cleavage-rejoining coupled to DNA strand passage. The change in DNA topological features must be controlled in vital processes including DNA replication, transcription, and DNA repair. Type IIA topoisomerases are well established targets for antibiotics. In this review, type IA topoisomerases in bacteria are discussed as potential targets for new antibiotics. In certain bacterial pathogens, topoisomerase I is the only type IA topoisomerase present, which makes it a valuable antibiotic target. This review will summarize recent attempts that have been made to identify inhibitors of bacterial topoisomerase I as potential leads for antibiotics and use of these inhibitors as molecular probes in cellular studies. Crystal structures of inhibitor-enzyme complexes and more in-depth knowledge of their mechanisms of actions will help to establish the structure-activity relationship of potential drug leads and develop potent and selective therapeutics that can aid in combating the drug resistant bacterial infections that threaten public health.

Nanoformulations to Enhance the Bioavailability and Physiological Functions of Polyphenols

Polyphenols are micronutrients that are widely present in human daily diets. Numerous studies have demonstrated their potential as antioxidants and anti-inflammatory agents, and for cancer prevention, heart protection and the treatment of neurodegenerative diseases. However, due to their vulnerability to environmental conditions and low bioavailability, their application in the food and medical fields is greatly limited. Nanoformulations, as excellent drug delivery systems, can overcome these limitations and maximize the pharmacological effects of polyphenols. In this review, we summarize the biological activities of polyphenols, together with systems for their delivery, including phospholipid complexes, lipid-based nanoparticles, protein-based nanoparticles, niosomes, polymers, micelles, emulsions and metal nanoparticles. The application of polyphenol nanoparticles in food and medicine is also discussed. Although loading into nanoparticles solves the main limitation to application of polyphenolic compounds, there are some concerns about their toxicological safety after entry into the human body. It is therefore necessary to conduct toxicity studies and residue analysis on the carrier.

Antibacterial Therapeutic Agents Composed of Functional Biological Molecules

Antibacterial agents are a group of materials that selectively destroy bacteria by interfering with bacterial growth or survival. With the emergence of resistance phenomenon of bacterial pathogens to current antibiotics, new drugs are frequently entering into the market along with the existing drugs, and the alternative compounds with antibacterial functions are being explored. Due to the advantages of their inherent biochemical and biophysical properties including precise targeting ability, biocompatibility, biodegradability, long blood circulation time, and low cytotoxicity, biomolecules such as peptides, carbohydrates, and nucleic acids have huge potential for the antimicrobial application and have been extensively studied in recent years. In this review, antimicrobial therapeutic agents composed of three kinds of functional biological molecules were summarized. In addition, the research progress of antibacterial mechanism, chemical modification, and nanoparticle coupling of those biomolecules were also discussed.