Concomitant chemo-radiotherapy in clinical trials: To promote step by step rational development

Unraveling the Complexity of DNA Radiation Damage Using DNA Nanotechnology

Radiation cancer therapies use different ionizing radiation qualities that damage DNA molecules in tumor cells by a yet not completely understood plethora of mechanisms and processes. While the direct action of the radiation is significant, the byproducts of the water radiolysis, mainly secondary low-energy electrons (LEEs, <20 eV) and reactive oxygen species (ROS), can also efficiently cause DNA damage, in terms of DNA strand breakage or DNA interstrand cross-linking. As a result, these types of DNA damage evolve into mutations hindering DNA replication, leading to cancer cell death. Concomitant chemo-radiotherapy explores the addition of radiosensitizing therapeutics commonly targeting DNA, such as platinum derivatives and halogenated nucleosides, to enhance the harmful effects of ionizing radiation on the DNA molecule. Further complicating the landscape of DNA damage are secondary structures such as G-quadruplexes occurring in telomeric DNA. These structures protect DNA from radiation damage, rendering them as promising targets for new and more selective cancer radiation treatments, rather than targeting linear DNA. However, despite extensive research, there is no single paradigm approach to understanding the mysterious way in which ionizing radiation causes DNA damage. This is due to the multidisciplinary nature of the field of research, which deals with multiple levels of biological organization, from the molecular building blocks of life toward cells and organisms, as well as with complex multiscale radiation-induced effects. Also, intrinsic DNA features, such as DNA topology and specific oligonucleotide sequences, strongly influence its response to damage from ionizing radiation. In this Account, we present our studies focused on the absolute quantification of photon- and low-energy electron-induced DNA damage in strategically selected target DNA sequences. Our methodology involves using DNA origami nanostructures, specifically the Rothemund triangle, as a platform to expose DNA sequences to either low-energy electrons or vacuum-ultraviolet (VUV, <15 eV) photons and subsequent atomic force microscopy (AFM) analysis. Through this approach, the effects of the DNA sequence, incorporation of halogenated radiosensitizers, DNA topology, and the radiation quality on radiation-induced DNA strand breakage have been systematically assessed and correlated with fundamental photon- and electron-driven mechanisms underlying DNA radiation damage. At lower energies, these mechanisms include dissociative electron attachment (DEA), where electrons attach to DNA molecules causing strand breaks, and dissociative photoexcitation of DNA. Additionally, further dissociative processes such as photoionization and electron impact contribute to the complex cascade of DNA damage events induced by ionizing radiation. We expect that emerging DNA origami-based approaches will lead to a paradigm shift in research fields associated with DNA damage and suggest future directions, which can foster the development of technological applications in nanomedicine, e.g., optimized cancer treatments or the molecular design of optimized radiosensitizing therapeutics.

Harnessing drug/radiation interaction through daily routine practice: Leverage medical and methodological point of view (MORSE 02-17 study)

BACKGROUND

Safety profile of the interaction between anticancer drugs and radiation is a recurrent question. However, there are little data regarding the non-anticancer treatment (NACT)/radiation combinations. The aim of the present study was to investigate concomitant NACTs in patients undergoing radiotherapy in a French comprehensive cancer center.

METHODS

A prospective cross-sectional study was conducted. All cancer patients undergoing a palliative or curative radiotherapy were consecutively screened for six weeks in 2016. Data on NACTs were collected.

RESULTS

Out of 214 included patients, a NACT was concomitantly prescribed to 155 patients (72%), with a median number of 5 NACTs per patient (range: 1-12). The most prescribed drugs were anti-hypertensive drugs (101 patients, 47.2%), psychotropic drugs (n = 74, 34.6%), analgesics (n = 78, 36.4%), hypolipidemic drugs (n = 57, 26.6%), proton pump inhibitors (n = 46, 21.5%) and antiplatelet drugs (n = 38, 17.8%). Although 833 different molecules were reported, only 20 possible modifiers of cancer biological pathways (prescribed to 74 patients (34.5%)) were identified. Eight out of the 833 molecules (0.9%), belonging to six drug families, have been investigated in 28 ongoing or published clinical trials in combo with radiotherapy. They were prescribed to 63 patients (29.4%).

CONCLUSION

Drug-radiation interaction remains a subject of major interest, not only for conventional anticancer drugs, but also for NACTs. New trial designs are thus required.

Non-DSB clustered DNA lesions induced by ionizing radiation are largely responsible for the loss of plasmid DNA functionality in the presence of cisplatin

The combination of cisplatin and ionizing radiation (IR) increases cell toxicity by both enhancing DNA damage and inhibiting repair mechanisms. Although the formation of cluster DNA lesions, particularly double-strand breaks (DSB) at the site of cisplatin-DNA-adducts has been reported to induce cell death, the contribution of DSB and non-DSB cluster lesions to the cellular toxicity is still unknown. Although both lesions are toxic, it is not always possible to measure their frequency and cell survival in the same model system. To overcome this problem, here, we investigate the effect of cisplatin-adducts on the induction of DSB and non-DSB cluster DNA lesions by IR and determine the impact of such lesions on plasmid functionality. Cluster lesions are two or more lesions on opposite DNA strands with a short distance such that error free repair is difficult or impossible. At a ratio of two cisplatin per plasmid, irradiation of platinated DNA in solution with (137)Cs γ-rays shows enhancements in the formation of DNA DSB and non-DSB cluster lesions by factors of 2.6 and 2.1, respectively, compared to unmodified DNA. However, in absolute terms, the yield for non-DSB cluster lesions is far larger than that for DSB, by a factor of 26. Unmodified and cisplatin-modified DNA were irradiated and subsequently transformed into Escherichia coli to give survival curves representing the functionality of the plasmid DNA as a function of radiation dose. Our results demonstrate that non-DSB cluster lesions are the only toxic lesions present at a sufficient frequency to account for the loss of DNA functionality. Our data also show that Frank-DSB lesions are simply too infrequent to account for the loss of DNA functionality. In conclusion, non-DSB cluster DNA damage is known to be difficult to repair and is probably the lesion responsible for the loss of functionality of DNA modified by cisplatin.