Chemical Repair of Radical Damage to the GC Base Pair by DNA-Bound Bisbenzimidazoles.

The migration of an electron-loss center (hole) in calf thymus DNA to bisbenzimidazole ligands bound in the minor groove is followed by pulse radiolysis combined with time-resolved spectrophotometry. The initially observed absorption spectrum upon oxidation of DNA by the selenite radical is consistent with spin on cytosine (C), as the GC pair neutral radical, followed by the spectra of oxidized ligands. The rate of oxidation of bound ligands increased with an increase in the ratio () ligands per base pair from 0.

Abscopal Gene Expression in Response to Synchrotron Radiation Indicates a Role for Immunological and DNA Damage Response Genes.

Abscopal effects are an important aspect of targeted radiation therapy due to their implication in normal tissue toxicity from chronic inflammatory responses and mutagenesis. Gene expression can be used to determine abscopal effects at the molecular level. Synchrotron microbeam radiation therapy utilizing high-intensity X rays collimated into planar microbeams is a promising cancer treatment due to its reported ability to ablate tumors with less damage to normal tissues compared to conventional broadbeam radiation therapy techniques.

Monitoring DNA Damage and Repair in Peripheral Blood Mononuclear Cells of Lung Cancer Radiotherapy Patients.

Thoracic radiotherapy (RT) is required for the curative management of inoperable lung cancer, however, treatment delivery is limited by normal tissue toxicity. Prior studies suggest that using radiation-induced DNA damage response (DDR) in peripheral blood mononuclear cells (PBMC) has potential to predict RT-associated toxicities. We collected PBMC from 38 patients enrolled on a prospective clinical trial who received definitive fractionated RT for non-small cell lung cancer.

A Functional Immune System Is Required for the Systemic Genotoxic Effects of Localized Irradiation.

Purpose: Nontargeted effects of ionizing radiation, by which unirradiated cells and tissues are also damaged, are a relatively new paradigm in radiobiology. We recently reported radiation-induced abscopal effects (RIAEs) in normal tissues; namely, DNA damage, apoptosis, and activation of the local and systemic immune responses in C57BL6/J mice after irradiation of a small region of the body. High-dose-rate, synchrotron-generated broad beam or multiplanar x-ray microbeam radiation therapy was used with various field sizes and doses.

Radiation Therapy Modulates DNA Repair Efficiency in Peripheral Blood Mononuclear Cells of Patients With Non-Small Cell Lung Cancer.

Purpose: There is growing interest in developing individually tailored cancer radiation therapy (RT), wherein patients with high intrinsic radiosensitivity are identified before commencing treatment, to minimize severe adverse reactions. In a previous retrospective study of severely radiosensitive RT patients, we established a functional assay with a high predictive capability. The assay involves ex vivo irradiation of peripheral blood mononuclear cells and analysis of DNA repair using the γ-H2AX assay.

Localized Synchrotron Irradiation of Mouse Skin Induces Persistent Systemic Genotoxic and Immune Responses.

The importance of nontargeted (systemic) effects of ionizing radiation is attracting increasing attention. Exploiting synchrotron radiation generated by the Imaging and Medical Beamline at the Australian Synchrotron, we studied radiation-induced nontargeted effects in C57BL/6 mice. Mice were locally irradiated with a synchrotron X-ray broad beam and a multiplanar microbeam radiotherapy beam.

Enhanced intrinsic radiosensitivity after treatment with stereotactic radiosurgery for an acoustic neuroma.

Enhanced radiosensitivity is an uncommon phenomenon attributable to deficient DNA repair after radiotherapy which can be assessed with the γ-H2AX assay. Reports of radiosensitivity after stereotactic radiosurgery (SRS) are uncommon. We describe a case where the clinical, radiological and laboratory findings suggest enhanced radiosensitivity after SRS for an acoustic neuroma.

γH2AX foci as a measure of DNA damage: a computational approach to automatic analysis.

The γH2AX focus assay represents a fast and sensitive approach for the detection of one of the critical types of DNA damage - double-strand breaks (DSB) induced by various cytotoxic agents including ionising radiation. Apart from research applications, the assay has a potential in clinical medicine/pathology, such as assessment of individual radiosensitivity, response to cancer therapies, as well as in biodosimetry. Given that generally there is a direct relationship between numbers of microscopically visualised γH2AX foci and DNA DSB in a cell, the number of foci per nucleus represents the most efficient and informative parameter of the assay.

Protection by methylproamine of irradiated human keratinocytes correlates with reduction of DNA damage.

Purpose: The therapeutic ratio for ionising radiation treatment of tumour is a trade-off between normal tissue side-effects and tumour control. Application of a radioprotector to normal tissue can reduce side-effects. Here we study the effects of a new radioprotector on the cellular response to radiation.

Plasmid breakage by (125)I-labelled DNA ligands: effect of DNA-iodine atom distance on breakage efficiency.

Purpose: The aim of the study is to establish the relationship between the efficiency of DNA double-stranded breakage by (125)I-labelled DNA ligands and the distance from the decaying atom to the helical axis.

Materials And Methods: Two new iodinated minor groove binding ligands were synthesized which, on the basis of molecular modelling studies, place the iodine atom at different distances from the DNA helical axis (namely 7.4 and 11.

Clustered DNA lesion sites as a source of mutations during human colorectal tumourigenesis.

The role of gene mutations in tumourigenesis is well understood, however, the mechanism(s) by which they arise are less clear. Indeed, the common assumption that tumourigenic mutations are the result of DNA replication errors is apparently contradicted by the very low division frequency of the cells from which tumours are thought to arise (i.e.

Receptor-mediated DNA-targeted photoimmunotherapy.

We show the efficacy of a therapeutic strategy that combines the potency of a DNA-binding photosensitizer, UV(A)Sens, with the tumor-targeting potential of receptor-mediated endocytosis. The photosensitizer is an iodinated bibenzimidazole, which, when bound in the minor groove of DNA and excited by UV(A) irradiation, induces cytotoxic lesions attributed to a radical species resulting from photodehalogenation. Although reminiscent of photochemotherapy using psoralens and UV(A) irradiation, an established treatment modality in dermatology particularly for the treatment of psoriasis and cutaneous T-cell lymphoma, a critical difference is the extreme photopotency of the iodinated bibenzimidazole, approximately 1,000-fold that of psoralens.

DNA targeted UVA photosensitization: characterization of an extremely photopotent iodinated minor groove binding DNA ligand.

Previous studies have described UVA-induced DNA strand breakage at the binding sites of iodinated DNA minor groove binding bisbenzimidazoles. The DNA breakage, presumably mediated by the carbon-centred ligand radical produced by photodehalogenation, was also shown to be cytotoxic. The earlier studies included a comparison of three ligand isomers, designated ortho-, meta- and para-iodoHoechst, and the efficiency of photo-induction of strand breaks in plasmid DNA proved to be much higher for the ortho-isomer.

DNA breakage by decay of Auger electron emitters: experiments with 123I-iodoHoechst 33258 and plasmid DNA.

The Auger electron-emitting isotope 123I is of interest in the context of potential exploitation of Auger electron emitters in radioimmunotherapy. The efficiency of induction of cytotoxic lesions by decay of DNA-associated 125I, the prototype Auger electron emitter, is well established, but its long half-life (60 days) is a limitation. However, the advantage of the much shorter half-life of 123I (13.

Plasmid DNA breakage by decay of DNA-associated auger emitters: experiments with 123I/125I-iodoHoechst 33258.

Purpose: The Auger emitting isotope 123I has a much shorter half-life (13.2 hours), than 125I, the prototype Auger emitter. Monte Carlo simulations and cell culture studies indicate that decay of 123I covalently incorporated into DNA is about half as effective as 125I in terms of DNA breakage and cytotoxicity.

An improved approach to the analysis of plasmid DNA breakage by decay of DNA-associated auger emitters.

Purpose: To assess DNA breakage by DNA-associated decay of the Auger electron emitter 125I, using an improved analytical approach.

Material And Methods: Breakage of pBR322 plasmid DNA following incubation with DNA-binding ligand Hoechst 33258 labelled with 125I was studied by measuring the conversion of native supercoiled to relaxed and linear forms. The analytical approach that was developed considers two distinct sources of breakage: DNA damage at the site of DNA-associated Auger decay (local effect), and DNA damage from the radiation field created by all decay events in the incubation volume (external breakage).

Plasmid DNA breakage by decay of DNA-associated Auger electron emitters: approaches to analysis of experimental data.

Plasmid DNA is a popular substrate for the assay of DNA strand breakage by a variety of agents. The use of the plasmid assay relies on the assumption that individual damaging events occur at random, which allows the application of Poisson statistics. This assumption is not valid in the case of damage arising from decay of DNA-associated Auger electron emitters, since a single decay event can generate a few breaks in the same DNA strand, which is indistinguishable from a single break in the assay.

In vitro studies with methylproamine: a potent new radioprotector.

New analogues of the minor groove binding ligand Hoechst 33342 have been investigated in an attempt to improve radioprotective activity. The synthesis, DNA binding, and in vitro radioprotective properties of methylproamine, the most potent derivative, are reported. Experiments with V79 cells have shown that methylproamine is approximately 100-fold more potent than the classical aminothiol radioprotector WR1065.