Measurement of hydroxyl radicals catalyzed in the immediate vicinity of DNA by metal-bleomycin complexes

Protection against chemotherapy- and radiotherapy-induced side effects: A review based on the mechanisms and therapeutic opportunities of phytochemicals

BACKGROUND

Although great achievements have been made in the field of cancer therapy, chemotherapy and radiotherapy remain the mainstay cancer therapeutic modalities. However, they are associated with various side effects, including cardiocytotoxicity, nephrotoxicity, myelosuppression, neurotoxicity, hepatotoxicity, gastrointestinal toxicity, mucositis, and alopecia, which severely affect the quality of life of cancer patients. Plants harbor a great chemical diversity and flexible biological properties that are well-compatible with their use as adjuvant therapy in reducing the side effects of cancer therapy.

PURPOSE

This review aimed to comprehensively summarize the molecular mechanisms by which phytochemicals ameliorate the side effects of cancer therapies and their potential clinical applications.

METHODS

We obtained information from PubMed, Science Direct, Web of Science, and Google scholar, and introduced the molecular mechanisms by which chemotherapeutic drugs and irradiation induce toxic side effects. Accordingly, we summarized the underlying mechanisms of representative phytochemicals in reducing these side effects.

RESULTS

Representative phytochemicals exhibit a great potential in reducing the side effects of chemotherapy and radiotherapy due to their broad range of biological activities, including antioxidation, antimutagenesis, anti-inflammation, myeloprotection, and immunomodulation. However, since a majority of the phytochemicals have only been subjected to preclinical studies, clinical trials are imperative to comprehensively evaluate their therapeutic values.

CONCLUSION

This review highlights that phytochemicals have interesting properties in relieving the side effects of chemotherapy and radiotherapy. Future studies are required to explore the clinical benefits of these phytochemicals for exploitation in chemotherapy and radiotherapy.

The peroxidase activity of bleomycin-Fe3+ is associated with damage to biological components

In this study, bleomycin-Fe(3+) steadily oxidized tetramethylbenzidine (TMB) in the presence of peroxides. However, the ability of bleomycin-Fe(3+) to function as a peroxidase was extremely low compared with that of other peroxidases. A characteristic property of bleomycin-Fe(3+) different from that observed for other peroxidases is its ability to oxidize TMB at the similar rate at both a pH 5 and 8 in the presence of lipid hydroperoxide (LOOH). In the present experiments, hydroxyl radicals (HO•) were generated only when bleomycin-Fe(3+) was incubated with H2O2 at a pH of 5. No generation of HO• was observed during the incubation of bleomycin-Fe(3+) with LOOH. Meanwhile, bleomycin-Fe(3+) induced the formation of LOOH from linoleic acid and alcohol dehydrogenase was inactivated by bleomycin-Fe(3+) with peroxides. Thiobarbituric acid reactive substances were formed from DNA by bleomycin-Fe(3+) with H2O2, and strand breaks were caused by bleomycin-Fe(3+) with LOOH. The oxidative substrates for bleomycin-Fe(3+) blocked the damage to biological components induced by bleomycin-Fe(3+). These results suggest that compound I-like species contribute to the process of damage to biological components induced by bleomycin-Fe(3+).

Extracellular superoxide dismutase in pulmonary fibrosis

Disruption of the oxidant/antioxidant balance in the lung is thought to be a key step in the development of many airway pathologies. Hence, antioxidant enzymes play key roles in controlling or preventing pulmonary diseases related to oxidative stress. The superoxide dismutases (SOD) are a family of enzymes that play a pivotal role protecting tissues from damage by oxidant stress by scavenging superoxide anion, which prevents the formation of other more potent oxidants such as peroxynitrite and hydroxyl radical. Extracellular SOD (EC-SOD) is found predominantly in the extracellular matrix of tissues and is ideally situated to prevent cell and tissue damage initiated by extracellularly produced ROS. EC-SOD has been shown to be protective in several models of interstitial lung disease, including pulmonary fibrosis. In addition, alterations in EC-SOD expression are also present in human idiopathic pulmonary fibrosis (IPF). This review discusses EC-SOD regulation in response to pulmonary fibrosis in animals and humans and reviews possible mechanisms by which EC-SOD may protect against fibrosis.

Synthesis of Coumarin–Polyamine-Based Molecular Probe for the Detection of Hydroxyl Radicals Generated by Gamma Radiation

To develop a molecular probe for detection of hydroxyl radicals in the vicinity of DNA, the coumarin-polyamine complexes, N(1),N(12)-bis[2-oxo-2H-chromene-3-carbonyl]-1,12-diamine-4,9-diazadodecane (5) and tris[2-(2-oxo-2H-chromene-3-carboxamido)ethyl]amine (7), and their hydroxylated derivatives, N(1),N(12)-bis[7-hydroxy-2-oxo-2H-chromene-3-carbonyl]-1,12-diamine-4,9-diazadodecane (6) and tris[2-(7-hydroxy-2-oxo-2H-chromene-3-carboxamido)ethyl]amine (8), have been synthesized. Using computer-generated molecular modeling, the derivatives have been docked onto DNA dodecamer d(CGCGAATTCGCG)(2), the ligand-DNA complexes have been minimized, and the free binding energies (DeltaG(binding)) and inhibition constants (K(i)) have been calculated. Compound 7 is not water-soluble at the concentrations required for the project. When aqueous solutions of 5 are irradiated with gamma rays, the relationship between induced fluorescence and dose is linear in the range of 0 to 10 Gy. The fluorescence emission spectrum of irradiated 5 is similar to that of its dihydroxy derivative 6, indicating conversion of 5 to 6, and induction of fluorescence records formation of hydroxyl radicals in aqueous solution. The dicoumarin-polyamine 5, a novel compound for the detection of hydroxyl radicals close to DNA, is a sensitive and quantitative probe with potential for applications in biological systems.

Fluorescence probes used for detection of reactive oxygen species

Endogenously produced pro-oxidant reactive species are essential to life, being involved in several biological functions. However, when overproduced (e.g. due to exogenous stimulation), or when the levels of antioxidants become severely depleted, these reactive species become highly harmful, causing oxidative stress through the oxidation of biomolecules, leading to cellular damage that may become irreversible and cause cell death. The scientific research in the field of reactive oxygen species (ROS) associated biological functions and/or deleterious effects is continuously requiring new sensitive and specific tools in order to enable a deeper insight on its action mechanisms. However, reactive species present some characteristics that make them difficult to detect, namely their very short lifetime and the variety of antioxidants existing in vivo, capable of capturing these reactive species. It is, therefore, essential to develop methodologies capable of overcoming this type of obstacles. Fluorescent probes are excellent sensors of ROS due to their high sensitivity, simplicity in data collection, and high spatial resolution in microscopic imaging techniques. Hence, the main goal of the present paper is to review the fluorescence methodologies that have been used for detecting ROS in biological and non-biological media.

Structure and function of "metalloantibiotics"

Although most antibiotics do not need metal ions for their biological activities, there are a number of antibiotics that require metal ions to function properly, such as bleomycin (BLM), streptonigrin (SN), and bacitracin. The coordinated metal ions in these antibiotics play an important role in maintaining proper structure and/or function of these antibiotics. Removal of the metal ions from these antibiotics can cause changes in structure and/or function of these antibiotics. Similar to the case of "metalloproteins," these antibiotics are dubbed "metalloantibiotics" which are the title subjects of this review. Metalloantibiotics can interact with several different kinds of biomolecules, including DNA, RNA, proteins, receptors, and lipids, rendering their unique and specific bioactivities. In addition to the microbial-originated metalloantibiotics, many metalloantibiotic derivatives and metal complexes of synthetic ligands also show antibacterial, antiviral, and anti-neoplastic activities which are also briefly discussed to provide a broad sense of the term "metalloantibiotics."

Involvement of DNA polymerase beta in protection against the cytotoxicity of oxidative DNA damage

We had shown previously that DNA polymerase beta (beta-pol) null mouse fibroblasts, deficient in base excision repair (BER), are hypersensitive to monofunctional methylating agents but not to hydrogen peroxide (H2O2). This is surprising because beta-pol is thought to be involved in BER of oxidative as well as methylated DNA damage. We confirm these findings here in early-passage cells. However, with time in culture, beta-pol null cells become hypersensitive to H2O2 and other reactive oxygen species-generating agents. Analysis of in vitro BER reveals a strong deficiency in single-nucleotide BER of 8-oxoguanine (8-oxoG) by both early- and late-passage beta-pol null cell extracts. Therefore, in early-passage wild-type and beta-pol null cells, the capacity for single-nucleotide BER of 8-oxoG does not correlate with cellular sensitivity to H2O2. Expression of beta-pol protein in the late-passage null cells almost completely reverses the H2O2-hypersensitivity phenotype. Methoxyamine (MX) treatment sensitizes late-passage wild-type cells to H2O2 as expected for beta-pol-mediated single-nucleotide BER; however in beta-pol null cells, MX has no effect. The data indicate a role(s) of beta-pol-dependent repair in protection against the cytotoxicity of oxidative DNA damage in wild-type cells.

Synthesis, hydroxyl radical production and cytotoxicity of analogues of bleomycin

Two pyridine analogues of the metal complexing region of the anticancer drug bleomycin and two related but deactivated prodrugs have been linked to a 2,6-diphenylpyridine derivative as a DNA binding unit. The 2,6-diphenylpyridine system is structurally related to known amplifiers of the cytotoxicity of bleomycin. The conjugates were found to bind to DNA more strongly than bleomycin-A2 and were more cytotoxic than the corresponding compounds lacking the DNA binding unit. On exposure of a mixture of cells and prodrugs to hypoxia and then air, the prodrug containing the nitrohistidine unit was not bioreductively activated but the prodrug having an N-oxide group was bioreductively activated. This result represents a novel approach to the improvement of the therapeutic ratio of bleomycin analogues.

On the chemistry of RNA degradation by Fe.bleomycin

The chemistry of RNA degradation by Fe.bleomycin was studied using two RNA substrates that are modified efficiently at a small number of sites by the antitumor antibiotic. Cleavage of tRNAHis precursor transcript by Fe(II).BLM A2 was shown to require O2; cleavage was also observed when the same substrate was treated with Fe(III).BLM A2 + H2O2. Consistent with earlier observations made for DNA, the extent of tRNAHis precursor cleavage was greater for Fe(II).BLM A5 than for Fe(II).BLM A2; the least cleavage was obtained using Fe(II).BLM demethyl A2. By the use of 32P end labeled tRNAHis precursor transcript that was also 3H labeled within the uracil moieties, it was shown that release of uracil was nearly stoichiometric with tRNA strand scission by Fe(II).BLM A2. Nonetheless, treatment of the tRNAHis with hydrazine following BLM-mediated cleavage indicated formation of a new product that must have derived from a BLM-induced lesion. Also employed for characterization of BLM cleavage of RNA were the octanucleotides CGCTAGCG, C3-ribo-CGCTAGCG and C3-ara-CGCTAGCG. Analysis of the products of cleavage indicates that Fe.BLM is capable of mediating cleavage by abstraction of a H atom either from C-4' H or c-1' H of the chimeric oligonucleotides.

Generation of hydroxyl radicals by nucleohistone-bound metal-adriamycin complexes

A recently developed method has been utilized to demonstrate the generation of hydroxyl radicals (HO.) in the immediate proximity of DNA by copper(II)/iron(III)-adriamycin in the presence of ascorbate and hydrogen peroxide. SECCA, a succinylated derivative of coumarin, generates the fluorescent 7-hydroxy-SECCA following reaction with HO.. SECCA was coupled to polylysine or to histone H1 and then complexed to DNA. When HO. was generated in the proximity of DNA by polylysine-coupled iodine-125, which emits short range Auger electrons, 7-hydroxy-SECCA was produced. DMSO was only moderately efficient in reducing the fluorescence induction, demonstrating the "local" generation of HO. in this system. Copper(II)/iron(III)-adriamycin in the presence of ascorbate and hydrogen peroxide generated the fluorescent 7-hydroxy-SECCA both when SECCA was free in solution and when SECCA was DNA-conjugated. With SECCA free in solution, the fluorescence induction was almost eliminated in the presence of HO. scavengers (ethanol, tert-butanol or DMSO) and the relative efficiency of the scavengers in reducing the fluorescence followed their rate constant with HO.. Furthermore, SECCA incubated with a single oxygen-generating compound demonstrated no fluorescence induction. When SECCA was positioned in close proximity to DNA as a SECCA-histone-H1-DNA complex, the relative efficiency of the scavengers in reducing the fluorescence still followed their rate constant with HO.; overall however the scavengers were much less effective in reducing the fluorescence, due presumably to the formation of HO. radical in the immediate vicinity of DNA. These data suggest that copper(II)/iron(III)-adriamycin produces HO. in the presence of ascorbate and hydrogen peroxide whether unbound or bound to DNA and suggest that in the latter case scavengers would not prevent HO. from attacking chromatin. In addition, the ability of DMSO to trap HO. was shown to decrease as the conformation of the H1-DNA complex becomes more compact indicating the strong dependence of the trapping ability on chromatin conformation.