Studies on bleomycin-DNA and bleomycin-iron interactions

Schiff bases in medicinal chemistry: a patent review (2010-2015)

INTRODUCTION

Schiff bases are synthetically accessible and structurally diverse compounds, typically obtained by facile condensation between an aldehyde, or a ketone with primary amines. Schiff bases contain an azomethine (-C = N-) linkage that stitches together two or more biologically active aromatic/heterocyclic scaffolds to form various molecular hybrids with interesting biological properties. Schiff bases are versatile metal complexing agents and have been known to coordinate all metals to form stable metal complexes with vast therapeutic applications. Areas covered: This review aims to provide a comprehensive overview of the various patented therapeutic applications of Schiff bases and their metal complexes from 2010 to 2015. Expert opinion: Schiff bases are a popular class of compounds with interesting biological properties. Schiff bases are also versatile metal complexing ligands and have been used to coordinate almost all d-block metals as well as lanthanides. Therapeutically, Schiff bases and their metal complexes have been reported to exhibit a wide range of biological activities such as antibacterial including antimycobacterial, antifungal, antiviral, antimalarial, antiinflammatory, antioxidant, pesticidal, cytotoxic, enzyme inhibitory, and anticancer including DNA damage.

Phase-directed therapy: TSG-6 targeted to early inflammation improves bleomycin-injured lungs

Previous reports demonstrated that bleomycin-induced injury of lungs in mice can be improved by the administration of murine multipotent adult stem/progenitor cells (MSCs) from the bone marrow. Recently some of the beneficial effects of MSCs have been explained by the cells being activated by signals from injured tissues to express the inflammation modulating protein TNF-α-stimulated gene/protein 6 (TSG-6). In this study, we elected to test the hypothesis that targeting the early phase of bleomycin-induced lung injury with systemic TSG-6 administration may produce therapeutic effects such as preventing the deterioration of lung function and increasing survival by modulation of the inflammatory cascade. Lung injury in C57Bl/6J mice was induced by intratracheal administration of bleomycin. Mice then received intravenous injections of TSG-6 or sham controls. Pulse oximetry was used to monitor changes in lung function. Cell infiltration was evaluated by flow cytometry, cytokine expression was measured by ELISA assays, and lungs were assessed for histological attributes. The results demonstrated that intravenous infusion of TSG-6 during the early inflammatory phase decreased cellular infiltration into alveolar spaces. Most importantly, it improved both the subsequent decrease in arterial oxygen saturation levels and the survival of the mice. These findings demonstrated that the beneficial effects of TSG-6 in a model of bleomycin-induced lung injury are largely explained by the protein modulating the early inflammatory phase. Similar phase-directed strategy with TSG-6 or other therapeutic factors that MSCs produce may be useful for other lung diseases and diseases of other organs.

The presence of two modes of binding to calf thymus DNA by metal-free bleomycin: a low frequency Raman study

Double-stranded DNA is targeted by bleomycin in cancer cells and ambiguity exists as to its mode of DNA binding. A conventional Raman study was performed on drug/DNA complexes in which the low frequency spectral region (560-930 cm(-1)) was examined at two temperatures (19 and 30 degrees C). At 30 degrees C, a global Raman hypochromism was observed consistent with partial intercalation of the bithiazole moiety. At 19 degrees C, Raman hypochromism (increased base pair stacking) was detected for bands associated with GC base pairs while Raman hyperchromism (base pair destacking) was evident for bands associated with AT base pairs. These results suggest that intercalation of the bithiazole moiety occurs with greater disruption of the more efficiently stacked AT base pairs at the lower temperature. Evidence for minor groove binding was indicated by an increase in the population of bands corresponding to C3' endo sugar conformations resulting from drug induced local desolvation of the DNA polymer.

A systematic approach toward the analysis of drug-DNA interactions using Raman spectroscopy: the binding of metal-free bleomycins A(2) and B(2) to calf thymus DNA

Bleomycins A(2) and B(2) are the two active components in the antineoplastic drug Blenoxane. DNA is targeted by this drug in cancer cells and the mode of action of this drug involves DNA binding. Ambiguity exists as to the way in which bleomycin binds to DNA. Raman spectroscopy was used to examine both calf thymus DNA and a bleomycin/DNA complex at two temperatures. A curvefitting technique was applied to these spectra for a spectral region obscured by many overlapping bands associated with the nucleotide bases in order to derive information about frequencies, bandwidths, and intensities of the vibrational modes in this region. This allowed identification and analysis of bands associated with specific assigned nucleotide base residues. Upon binding of bleomycin, several significant changes in bandwidth, intensities, and frequencies relative to uncomplexed DNA were observed consistently at both higher (30 degrees C) and lower (19 degrees C) temperature. The data presented here support at least a partial intercalation mode of binding for bleomycin that is temperature dependent and more pronounced at the more physiologically relevant temperature of 30 degrees C.

NMR studies of the interaction of bleomycin with (dC-dG)3

The interaction of bleomycin A2 and Zn(II)-bleomycin A2 with the oligonucleotide (dC-dG)3 has been monitored by nuclear magnetic resonance spectroscopy. Binding of the drug to the oligonucleotide is indicated by an upfield shift of the bithiazole proton resonances consistent with partial intercalation of this group between base pairs. The effect of temperature and ionic strength on the binding of both free bleomycin and the Zn(II) complex has been studied. Consistent with earlier studies on polynucleotides, the rate of exchange between the free drug and the drug-oligonucleotide complex is rapid on the 1H NMR chemical shift time scale. Binding of the oligonucleotide induced changes in resonances assigned to protons in the metal-binding region of Zn(II)-bleomycin. Intermolecular nuclear Overhauser effect enhancements between bleomycin and the oligonucleotide have not been detected.

The role of redox-active metals in the mechanism of action of bleomycin

Belomycin is a glycopeptide antibiotic routinely used to treat human cancer. It is commonly thought to exert its biological effects as a metallodrug, which oxidatively damages DNA. This review systematically examines the properties of bleomycin which contribute to its reaction with DNA in vitro and may be important in the breakage of DNA in cells. Because strand cleavage results from the reductive activation of dioxygen by metallobleomycins, the mechanism of this process is given primary attention. Current understanding of the structures of the coordination sites of various metallobleomycins, their thermodynamic stabilities, their propensity to form adduct species, and their properties in ligand substitution reactions provide a foundation for consideration of the chemistry of dioxygen activation as well as a basis for thinking about the metal-speciation of bleomycin in biological systems. Oxidation-reduction pathways of iron-bleomycin, copper-bleomycin, and other metal-bleomycin species with O2 are then examined, including information on photochemical activation. With this background, structural and thermodynamic features of the binding interactions of DNA with bleomycin, its metal complexes, and adducts of metallobleomycins are reviewed. Then, the DNA cleavage reaction involving iron-bleomycin is scrutinized on the basis of the preceding discussion. Particular emphasis is placed on the constraints which the presence of DNA places on the mechanism of dioxygen activation. Similarly, the reactions of other metalloforms of bleomycin with DNA are reviewed. The last topic is an analysis of current understanding of the relationship of bleomycin-induced cellular DNA damage to the model developed above, which has evolved on the basis of chemical experimentation. Consideration is given to the question of the importance of DNA strand breakage caused by bleomycin for the mechanism of cytotoxic activity of the drug.

Molecular basis for potentiation of bleomycin-mediated degradation of DNA by polyamines. Experimental and molecular mechanical studies

The bleomycin-mediated degradation of DNA is stimulated (amplified) by certain DNA binding compounds, such as polyamines, that distort the double helix. Computer modelling studies suggest that putrescine (1), spermidine (2), and spermine (3) bind preferentially on the floor of the major groove of (dGdC)5.(dGdC)5. This interaction results in a bend of the oligomer helix toward the major groove and enlargement of the minor groove, both effects being in the order 1 less than 2 less than 3. These polyamine-induced distortions, as obtained from theoretical studies, parallel the experimental values of the amplification activities of 1-3 in the bleomycin-mediated degradation of poly(dGdC).poly(dGdC). The amplification mechanism of non-competitive binding of amplifier molecules in the major groove, and bleomycin in the minor groove, is proposed. It is suggested that the amplifier-induced conformational changes of the DNA helix increase affinity of the activated bleomycin complex toward the DNA minor groove and, consequently, result in an increased efficiency of the bleomycin-mediated degradation of the helix.

Mössbauer, EPR and NMR studies of the acid-induced reduction and changes in spin state of ferric bleomycin

Iron-57 Mössbauer, electron paramagnetic resonance (EPR) and H-1 nuclear magnetic resonance (NMR) studies of iron-bleomycin complexes in the pH range from 1.0 to 6.0 are reported. Sequential protonation of the ligands produces a variety of high-spin and low-spin complexes of the metal. Of particular interest is the reversible equilibrium between Fe(III)- and oxygen-stable Fe(II)-bleomycin. Below pH 3.5 Fe(II) complexes form, with maximal reduction occurring at approximately pH 2. At still lower pH, Fe(III) complexes unassociated with bleomycin become dominant. The observed reduction in the absence of exogenous reducing agents suggests the possible involvement of intramolecular autoreduction in bleomycin-mediated DNA degradation.

Peptide antibiotics, beta-lactams, and related compounds

In the field of natural peptides, beta-lactams, and related compounds, recent exciting developments are discussed. The increasing interest in this class of bioactive amino-acid derived structures has been attributed to the use of new directed screens (enzyme inhibition assays, beta-lactam detection, immunomodulator studies), new and improved applications (antibiotic, transplantation, and cancer chemotherapy), and advances in functional studies (DNA binding peptides, nucleotide complexones, cell wall and protein processing inhibitors). Peptides offer unique access to modifications and analog production by in vivo (directed biosynthesis) and in vitro procedures (enzymatic synthesis) due to their general linear precursors permitting point replacements. Of special interest are recent developments in the genetics of these compounds (cyclic peptides and beta-lactams), which will find applications in production methods in the near future.