Methylproamine protects against ionizing radiation by preventing DNA double-strand breaks

What's Changed in 75 Years of RadRes? - An Australian Perspective on Selected Topics

Several scientific themes are reviewed in the context of the 75-year period relevant to this special platinum issue of Radiation Research. Two criteria have been considered in selecting the scientific themes. One is the exposure of the associated research activity in the annual meetings of the Radiation Research Society (RRS) and in the publications of the Society's Journal, thus reflecting the interest of members of RRS. The second criteria is a focus on contributions from Australian members of RRS. The first theme is the contribution of radiobiology to radiation oncology, featuring two prominent Australian radiation oncologists, the late Rod Withers and his younger colleague, Lester Peters. Two other themes are also linked to radiation oncology; preclinical research aimed at developing experimental radiotherapy modalities, namely microbeam radiotherapy (MRT) and Auger endoradiotherapy. The latter has a long history, in contrast to MRT, especially in Australia, given that the associated medical beamline at the Australian Synchrotron in Melbourne only opened in 2011. Another theme is DNA repair, which has a trajectory parallel to the 75-year period of interest, given the birth of molecular biology in the 1950s. The low-dose radiobiology theme has a similar timeline, predominantly prompted by the nuclear era, which is also connected to the radioprotector theme, although radioprotectors also have a long-established potential utility in cancer radiotherapy. Finally, two themes are associated with biodosimetry. One is the micronucleus assay, highlighting the pioneering contribution from Michael Fenech in Adelaide, South Australia, and the other is the γ-H2AX assay and its widespread clinical applications.

In silico investigation of DNA minor groove binding bibenzimidazoles in the context of UVA phototherapy

The versatility of DNA minor groove binding bibenzimidazoles extends to applications in cancer therapy, beyond their typical use as DNA stains. In the context of UV_A phototherapy, a series of halogenated analogues designated ortho-, meta-, and para-iodoHoechst have been investigated. Phototoxicity involves dehalogenation of the ligands following exposure to UV_A light, resulting in the formation of a carbon-centred radical. While the cytotoxic mechanisms have been well established, the nature and severity of DNA damage induced by the ortho-, meta-, and para-iodoHoechst isomers requires clarification. Our aims were to measure and compare the binding constants of iodoHoechst analogues, and to determine the proximity of the carbon-centred radicals formed following photodehalogenation to the C1', C4', and C5' DNA carbons. We performed molecular docking studies, as well as classical molecular dynamics simulations to investigate the interactions of Hoechst ligands with DNA including a well-defined B-DNA dodecamer containing the high affinity AATT minor groove binding site. Docking highlighted the binding of Hoechst analogues to AATT regions in oligonucleotides, nucleosomes, and origami DNA helical bundles. Further, MD simulations demonstrated the stability of Hoechst ligands in the AATT-containing minor groove over microsecond trajectories. Our findings reiterate that the efficiency of dehalogenation per se, rather than the proximity of the carbon-centred radicals to the DNA backbone, is responsible for the extreme phototoxicity of the ortho- isomer compared to the meta- and para-iodoHoechst isomers. More generally, our analyses are in line with the potential utility of ortho-iodoHoechst in DNA-targeted phototherapy, particularly if combined with a cell-specific delivery system.

Application of Multifunctional Nanomaterials in Radioprotection of Healthy Tissues

Radiotherapy has been extensively used in clinic for malignant tumors treatment. However, a severe challenge of it is that the ionizing radiation needed to kill tumors inevitably causes damage to surrounding normal tissues. Although some of the molecular radioprotective drugs, such as amifostine, have been used as clinical adjuvants to radio-protect healthy tissues, their shortcomings such as short systemic circulation time and fast biological clearing from the body largely hinder the sustained bioactivity. Recently, with the rapid development of nanotechnology in the biological field, the multifunctional nanomaterials not only establish powerful drug delivery systems to improve the molecular radioprotective drugs' biological availability, but also open a new route to develop neozoic radioprotective agents because some nanoparticles possess intrinsic radioprotective abilities. Therefore, considering these overwhelming superiorities, this review systematically summarizes the advances in healthy tissue radioprotection applications of multifunctional nanomaterials. Furthermore, this review also points out a perspective of nanomaterial designs for radioprotection applications and discusses the challenges and future outlooks of the nanomaterial-mediated radioprotection.

A review of the logistic role of L-carnitine in the management of radiation toxicity and radiotherapy side effects

Radiation therapy is a key modality in the treatment of different cancer types. Fatigue is the most common side effect of radiotherapy, while others include nausea, hair loss, skin irritation, anemia, infertility, cardiovascular disease, cognitive impairment and even the development of second cancers. Studies in experimental animals have shown protective effects of carnitine against exposure of various organs to ionizing radiation, whereas carnitine deficiency is known to enhance radiation-induced toxicity. This report summarizes the recent literature on the adverse effects of radiotherapy and the impact of radiation on carnitine homeostasis. Although some studies have demonstrated the prophylactic benefits of carnitine against the toxic effects of chemotherapy, the role of carnitine in the prognosis and management of cancer patients receiving radiotherapy is not clear and needs to be explored.

Evaluation of the efficacy of radiation-modifying compounds using γH2AX as a molecular marker of DNA double-strand breaks

Radiation therapy is a widely used therapeutic approach for cancer. To improve the efficacy of radiotherapy there is an intense interest in combining this modality with two broad classes of compounds, radiosensitizers and radioprotectors. These either enhance tumour-killing efficacy or mitigate damage to surrounding non-malignant tissue, respectively. Radiation exposure often results in the formation of DNA double-strand breaks, which are marked by the induction of H2AX phosphorylation to generate γH2AX. In addition to its essential role in DDR signalling and coordination of double-strand break repair, the ability to visualize and quantitate γH2AX foci using immunofluorescence microscopy techniques enables it to be exploited as an indicator of therapeutic efficacy in a range of cell types and tissues. This review will explore the emerging applicability of γH2AX as a marker for monitoring the effectiveness of radiation-modifying compounds.

Potential use of HMG-CoA reductase inhibitors (statins) as radioprotective agents

HMG-CoA reductase inhibitors (statins) are widely used in the therapy of hypercholesterolemia. Apart from their lipid-lowering activity, they have pleiotropic effects that are attributed to the inhibition of regulatory proteins, including Ras-homologous (Rho) GTPases. Here, we discuss the potential usefulness of statins to prevent normal tissue damage provoked by radiotherapy. Statins reduce the mRNA expression of pro-inflammatory and pro-fibrotic cytokines stimulated by ionizing radiation in vitro and alleviate IR-induced inflammation and fibrosis in vivo. The currently available data indicate that statins accelerate the rapid repair of DNA double-strand breaks and, moreover, mitigate the DNA damage response induced by IR. Furthermore, statins increase the mRNA expression of DNA repair factors in vivo. Thus, although the molecular mechanisms involved are still ambiguous, preclinical data concordantly show a promising radioprotective capacity of statins.