Influence of linker length in shape recognition of B* DNA by dimeric aminoglycosides

Thermodynamics of d(GGGGCCCC) Binding to Neomycin-Class Aminoglycosides

DNA adopts a number of conformations that can affect its binding to other macromolecules. The conformations (A, B, Z) can be sequence- and/or solution-dependent. While AT-rich DNA sequences generally adopt a Canonical B-form structure, GC-rich sequences are more promiscuous. Recognition of GC-rich nucleic acids by small molecules has been much more challenging than the recognition of AT-rich duplexes. Spectrophotometric and calorimetric techniques were used to characterize the binding of neomycin-class aminoglycosides to a GC-rich DNA duplex, G₄C₄, in various ionic and pH conditions. Our results reveal that binding enhances the thermal stability of G₄C₄, with thermal enhancement decreasing with increasing pH and/or Na⁺ concentration. Although G₄C₄ bound to aminoglycosides demonstrated a mixed A- and B-form conformation, circular dichroism studies indicate that binding induces a conformational shift toward A-form DNA. Isothermal titration calorimetry studies reveal that aminoglycoside binding to G₄C₄ is linked to the uptake of protons at pH = 7.0 and that this uptake is pH-dependent. Increased pH and/or Na⁺ concentration results in a decrease in G₄C₄ affinity for the aminoglycosides. The binding affinities of the aminoglycosides follow the expected hierarchy: neomycin > paromomycin > ribostamycin. The salt dependence of DNA binding affinities of aminoglycosides is consistent with at least two drug NH₃⁺ groups participating in electrostatic interactions with G₄C₄. These studies further embellish our understanding of the many factors facilitating recognition of GC-rich DNA structures as guided by their optimum charge and shape complementarity for small-molecule amino sugars.

ANALYSIS OF CARBOHYDRATES AND GLYCOCONJUGATES BY MATRIX-ASSISTED LASER DESORPTION/IONIZATION MASS SPECTROMETRY: AN UPDATE FOR 2015-2016

This review is the ninth update of the original article published in 1999 on the application of matrix-assisted laser desorption/ionization (MALDI) mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2016. Also included are papers that describe methods appropriate to analysis by MALDI, such as sample preparation techniques, even though the ionization method is not MALDI. Topics covered in the first part of the review include general aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, fragmentation and arrays. The second part of the review is devoted to applications to various structural types such as oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides and biopharmaceuticals. Much of this material is presented in tabular form. The third part of the review covers medical and industrial applications of the technique, studies of enzyme reactions and applications to chemical synthesis. The reported work shows increasing use of combined new techniques such as ion mobility and the enormous impact that MALDI imaging is having. MALDI, although invented over 30 years ago is still an ideal technique for carbohydrate analysis and advancements in the technique and range of applications show no sign of deminishing. © 2020 Wiley Periodicals, Inc.

Surface Dependent Dual Recognition of a G-quadruplex DNA With Neomycin-Intercalator Conjugates

G-quadruplexes have been characterized as structures of vital importance in the cellular functioning of several life forms. They have subsequently been established to serve as a therapeutic target of several diseases including cancer, HIV, tuberculosis and malaria. In this paper, we report the binding of aminosugar-intercalator conjugates with a well-studied anti-parallel G-quadruplex derived from Oxytricha Nova G-quadruplex DNA. Of the four neomycin-intercalator conjugates studied with varying surface areas, BQQ-neomycin conjugate displayed the best binding to this DNA G-quadruplex structure with an association constant of K_a = (1.01 ±0.03) × 10⁷ M⁻¹ which is nearly 100-fold higher than the binding of neomycin to this quadruplex. The binding of BQQ-neomycin displays a binding stoichiometry of 1:1 indicating the presence of a single and unique binding site for this G-quadruplex. In contrast, the BQQ-neomycin displays very weak binding to the bacterial A-site rRNA sequence showing that BQQ-does not enhance the neomycin binding to its natural target, the bacterial rRNA A-site. The BQQ-neomycin conjugate is prone to aggregation even at low micromolar concentrations (4 μM) leading to some ambiguities in the analysis of thermal denaturation profiles. Circular dichroism experiments showed that binding of BQQ-neomycin conjugate causes some structural changes in the quadruplex while still maintaining the overall anti-parallel structure. Finally, the molecular docking experiments suggest that molecular surface plays an important role in the recognition of a second site on the G-quadruplex. Overall, these results show that molecules with more than one binding moieties can be made to specifically recognize G-quadruplexes with high affinities. The dual binding molecules comprise of quadruplex groove binding and intercalator units, and the molecular surface of the intercalator plays an important part in enhancing binding interaction to the G-quadruplex structure.

Aminoglycoside Functionalization as a Tool for Targeting Nucleic Acids

Aminoglycoside functionalization as a tool for targeting natural and unnatural nucleic acids holds great promise in their development as diagnostic probes and medicinally relevant compounds. Simple synthetic procedures designed to easily and quickly manipulate amino sugar (neomycin, kanamycin) to more powerful and selective ligands are presented in this chapter. We describe representative procedures for (a) aminoglycoside conjugation and (b) preliminary screening for their nucleic acid binding and selectivity.

An overview of recent advances in duplex DNA recognition by small molecules

As the carrier of genetic information, the DNA double helix interacts with many natural ligands during the cell cycle, and is amenable to such intervention in diseases such as cancer biogenesis. Proteins bind DNA in a site-specific manner, not only distinguishing between the geometry of the major and minor grooves, but also by making close contacts with individual bases within the local helix architecture. Over the last four decades, much research has been reported on the development of small non-natural ligands as therapeutics to either block, or in some cases, mimic a DNA–protein interaction of interest. This review presents the latest findings in the pursuit of novel synthetic DNA binders. This article provides recent coverage of major strategies (such as groove recognition, intercalation and cross-linking) adopted in the duplex DNA recognition by small molecules, with an emphasis on major works of the past few years.

Comprehensive review of chemical strategies for the preparation of new aminoglycosides and their biological activities

A systematic analysis of all synthetic and chemoenzymatic methodologies for the preparation of aminoglycosides for a variety of applications (therapeutic and agricultural) reported in the scientific literature up to 2017 is presented. This comprehensive analysis of derivatization/generation of novel aminoglycosides and their conjugates is divided based on the types of modifications used to make the new derivatives. Both the chemical strategies utilized and the biological results observed are covered. Structure-activity relationships based on different synthetic modifications along with their implications for activity and ability to avoid resistance against different microorganisms are also presented.

Impact of Linker Length and Composition on Fragment Binding and Cell Permeation: Story of a Bisbenzimidazole Dye Fragment

Small molecules that modulate biological functions are targets of modern day drug discovery efforts. In a common platform fragment-based drug discovery, two fragments that bind to adjacent sites on a target are identified and are then linked together using different linkers to identify the linkage for optimum activity. What are not known from these studies are the effects these linkers, which typically contain C, H, and O atoms, have on the properties of the individual fragment. Herein, we investigate such effects in a bisbenzimidazole fragment whose derivatives have a wide range of therapeutic applications in nucleic acid recognition, sensing, and photodynamic therapy and as cellular probes. We report a dramatic effect of linker length and composition of alkynyl (clickable) Hoechst 33258 derivatives in target binding and cell uptake. We show that the binding of Hoechst 33258-modeled bisbenzimidazoles (1-9) that contain linkers of varying lengths (3-21 atoms) display length- and composition-dependent variation in B-DNA stabilization using a variety of spectroscopic methods. For a dodecamer DNA duplex, the thermal stabilization varied from 0.3 to 9.0 °C as the linker length increased from 3 to 21 atoms, respectively. Compounds with linker lengths of ≤11 atoms (such as compounds 1 and 5) are localized in the nucleus, while compounds with long linkers (such as compounds 8 and 9) are distributed in the extranuclear space, as well, with possible interactions with extranuclear targets. These findings provide insights into future drug design by revealing how linkers can influence the biophysical and cellular properties of individual drug fragments.

The Thiophene "Sigma-Hole" as a Concept for Preorganized, Specific Recognition of G⋅C Base Pairs in the DNA Minor Groove

In spite of its importance in cell function, targeting DNA is under-represented in the design of small molecules. A barrier to progress in this area is the lack of a variety of modules that recognize G⋅C base pairs (bp) in DNA sequences. To overcome this barrier, an entirely new design concept for modules that can bind to mixed G⋅C and A⋅T sequences of DNA is reported herein. Because of their successes in biological applications, minor-groove-binding heterocyclic cations were selected as the platform for design. Binding to A⋅T sequences requires hydrogen-bond donors whereas recognition of the G-NH2 requires an acceptor. The concept that we report herein uses pre-organized N-methylbenzimidazole (N-MeBI) thiophene modules for selective binding with mixed bp DNA sequences. The interaction between the thiophene sigma hole (positive electrostatic potential) and the electron-donor nitrogen of N-MeBI preorganizes the conformation for accepting an hydrogen bond from G-NH2 . The compound-DNA interactions were evaluated with a powerful array of biophysical methods and the results show that N-MeBI-thiophene monomer compounds can strongly and selectively recognize single G⋅C bp sequences. Replacing the thiophene with other moieties significantly reduces binding affinity and specificity, as predicted by the design concept. These results show that the use of molecular features, such as sigma-holes, can lead to new approaches for small molecules in biomolecular interactions.

Bacterial lipid membranes as promising targets to fight antimicrobial resistance, molecular foundations and illustration through the renewal of aminoglycoside antibiotics and emergence of amphiphilic aminoglycosides

Membrane anionic lipids as attractive targets in the design of amphiphilic antibacterial drugs active against resistant bacteria: molecular foundations and examples.

Arginine-linked neomycin B dimers: synthesis, rRNA binding, and resistance enzyme activity

The nucleotides comprising the ribosomal decoding center are highly conserved, as they are important for maintaining translational fidelity. The bacterial A-site has a small base variation as compared with the human analogue, allowing aminoglycoside (AG) antibiotics to selectively bind within this region of the ribosome and negatively affect microbial protein synthesis. Here, by using a fluorescence displacement screening assay, we demonstrate that neomycin B (NEO) dimers connected by L-arginine-containing linkers of varying length and composition bind with higher affinity to model A-site RNAs compared to NEO, with IC50 values ranging from ~40-70 nM, and that a certain range of linker lengths demonstrates a clear preference for the bacterial A-site RNA over the human analogue. Furthermore, AG-modifying enzymes (AMEs), such as AG O-phosphotransferases, which are responsible for conferring antibiotic resistance in many types of infectious bacteria, demonstrate markedly reduced activity against several of the L-arginine-linked NEO dimers in vitro. The antimicrobial activity of these dimers against several bacterial strains is weaker than that of the parent NEO.

Structural modifications of the neomycin class of aminoglycosides

This review encompasses comprehensive literature on synthetic modification and biological activities of clinically used neomycin-class aminoglycoside antibiotics to alleviate dose-related toxicity and pathogenic resistance.

A review of patents (2011-2015) towards combating resistance to and toxicity of aminoglycosides

Since the discovery of the first aminoglycoside (AG), streptomycin, in 1943, these broad-spectrum antibiotics have been extensively used for the treatment of Gram-negative and Gram-positive bacterial infections. The inherent toxicity (ototoxicity and nephrotoxicity) associated with their long-term use as well as the emergence of resistant bacterial strains have limited their usage. Structural modifications of AGs by AG-modifying enzymes, reduced target affinity caused by ribosomal modification, and decrease in their cellular concentration by efflux pumps have resulted in resistance towards AGs. However, the last decade has seen a renewed interest among the scientific community for AGs as exemplified by the recent influx of scientific articles and patents on their therapeutic use. In this review, we use a non-conventional approach to put forth this renaissance on AG development/application by summarizing all patents filed on AGs from 2011-2015 and highlighting some related publications on the most recent work done on AGs to overcome resistance and improving their therapeutic use while reducing ototoxicity and nephrotoxicity. We also present work towards developing amphiphilic AGs for use as fungicides as well as that towards repurposing existing AGs for potential newer applications.