Conspectus
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 a...