Quantification of single-strand DNA lesions caused by the topoisomerase II poison etoposide using single DNA molecule imaging

Biological Amyloids Chemically Damage DNA

Amyloid fibrils are protein polymers noncovalently assembled through β-strands arranged in a cross-β structure. Biological amyloids were considered chemically inert until we and others recently demonstrated their ability to catalyze chemical reactions in vitro. To further explore the functional repertoire of amyloids, we here probe if fibrils of α-synuclein (αS) display chemical reactivity toward DNA. We demonstrate that αS amyloids bind DNA at micromolar concentrations in vitro. Using the activity of DNA repair enzymes as proxy for damage, we unravel that DNA-amyloid interactions promote chemical modifications, such as single-strand nicks, to the DNA. Double-strand breaks are also evident based on nanochannel analysis of individual long DNA molecules. The amyloid fold is essential for the activity as no DNA chemical modification is detected with αS monomers. In a yeast cell model, there is increased DNA damage when αS is overexpressed. Chemical perturbation of DNA adds another chemical reaction to the set of activities emerging for biological amyloids. Since αS amyloids are also found in the nuclei of neuronal cells of Parkinson's disease (PD) patients, and increased DNA damage is a hallmark of PD, we propose that αS amyloids contribute to PD by direct chemical perturbation of DNA.

Single-molecule toxicogenomics: Optical genome mapping of DNA-damage in nanochannel arrays

Quantitative genomic mapping of DNA damage may provide insights into the underlying mechanisms of damage and repair. Sequencing based approaches are bound to the limitations of PCR amplification bias and read length which hamper both the accurate quantitation of damage events and the ability to map them to structurally complex genomic regions. Optical Genome mapping in arrays of parallel nanochannels allows physical extension and genetic profiling of millions of long genomic DNA fragments, and has matured to clinical utility for characterization of complex structural aberrations in cancer genomes. Here we present a new mapping modality, Repair-Assisted Damage Detection - Optical Genome Mapping (RADD-OGM), a method for single-molecule level mapping of DNA damage on a genome-wide scale. Leveraging ultra-long reads to assemble the complex structure of a sarcoma cell-line genome, we mapped the genomic distribution of oxidative DNA damage, identifying regions more susceptible to DNA oxidation. We also investigated DNA repair by allowing cells to repair chemically induced DNA damage, pinpointing locations of concentrated repair activity, and highlighting variations in repair efficiency. Our results showcase the potential of the method for toxicogenomic studies, mapping the effect of DNA damaging agents such as drugs and radiation, as well as following specific DNA repair pathways by selective induction of DNA damage. The facile integration with optical genome mapping enables performing such analyses even in highly rearranged genomes such as those common in many cancers, a challenging task for sequencing-based approaches.

Design and in vitro anticancer assessment of a click chemistry-derived dinuclear copper artificial metallo-nuclease

Copper compounds with artificial metallo-nuclease (AMN) activity are mechanistically unique compared to established metallodrugs. Here, we describe the development of a new dinuclear copper AMN, Cu2-BPL-C6 (BPL-C6 = bis-1,10-phenanthroline-carbon-6), prepared using click chemistry that demonstrates site-specific DNA recognition with low micromolar cleavage activity. The BPL-C6 ligand was designed to force two redox-active copper centres-central for enhancing AMN activity-to bind DNA, via two phenanthroline ligands separated by an aliphatic linker. DNA-binding experiments, involving circular dichroism spectroscopy, agarose gel electrophoresis and fluorescence quenching, revealed a preference for binding with adenine-thymine-rich DNA. The oxidative cleavage mechanism of Cu2-BPL-C6 was then elucidated using in vitro molecular and biophysical assays, including in-liquid atomic force microscopy analysis, revealing potent DNA cleavage mediated via superoxide and hydrogen peroxide oxidative pathways. Single-molecule analysis with peripheral blood mononuclear cells identified upregulated single-strand DNA lesions in Cu2-BPL-C6-treated cells. Using specific base excision repair (BER) enzymes, we showed that Endo IV selectively repairs these lesions indicating that the complex generates apurinic and apyrimidinic adducts. Broad spectrum anticancer evaluation of BPL-C6 was performed by the National Cancer Institute's 60 human cell line screen (NCI-60) and revealed selectivity for certain melanoma, breast, colon and non-small cell lung cancer cell lines.

Bimodal effects on lipid droplets induced in cancer and non-cancer cells by chemotherapy drugs as revealed with a green-emitting BODIPY fluorescent probe

Lipid droplets (LDs) are cytoplasmic lipid-rich organelles with important roles in lipid storage and metabolism, cell signaling and membrane biosynthesis. Additionally, multiple diseases, such as obesity, fatty liver, cardiovascular diseases and cancer, are related to the metabolic disorders of LDs. In various cancer cells, LD accumulation is associated with resistance to cell death, reduced effectiveness of chemotherapeutic drugs, and increased proliferation and aggressiveness. In this work, we present a new viscosity-sensitive, green-emitting BODIPY probe capable of distinguishing between ordered and disordered lipid phases and selectively internalising into LDs of live cells. Through the use of fluorescence lifetime imaging microscopy (FLIM), we demonstrate that LDs in live cancer (A549) and non-cancer (HEK 293T) cells have vastly different microviscosities. Additionally, we quantify the microviscosity changes in LDs under the influence of DNA-damaging chemotherapy drugs doxorubicin and etoposide. Finally, we show that doxorubicin and etoposide have different effects on the microviscosities of LDs in chemotherapy-resistant A549 cancer cells.

Super-resolution GSDIM microscopy unveils distinct nanoscale characteristics of DNA repair foci under diverse genotoxic stress

DNA double-strand breaks initiate the DNA damage response (DDR), leading to the accumulation of repair proteins at break sites and the formation of the-so-called foci. Various microscopy methods, such as wide-field, confocal, electron, and super-resolution microscopy, have been used to study these structures. However, the impact of different DNA-damaging agents on their (nano)structure remains unclear. Utilising GSDIM super-resolution microscopy, here we investigated the distribution of fluorescently tagged DDR proteins (53BP1, RNF168, MDC1) and γH2AX in U2OS cells treated with γ-irradiation, etoposide, cisplatin, or hydroxyurea. Our results revealed that both foci structure and their nanoscale ultrastructure, including foci size, nanocluster characteristics, fluorophore density and localisation, can be significantly altered by different inducing agents, even ones with similar mechanisms. Furthermore, distinct behaviours of DDR proteins were observed under the same treatment. These findings have implications for cancer treatment strategies involving these agents and provide insights into the nanoscale organisation of the DDR.

Single-molecule approaches for DNA damage detection and repair: A focus on Repair Assisted Damage Detection (RADD)

The human genome is continually exposed to various stressors, which can result in DNA damage, mutations, and diseases. Among the different types of DNA damage, single-strand lesions are commonly induced by external stressors and metabolic processes. Accurate detection and quantification of DNA damage are crucial for understanding repair mechanisms, assessing environmental impacts, and evaluating response to therapy. However, traditional techniques have limitations in sensitivity and the ability to detect multiple types of damage. In recent years, single-molecule fluorescence approaches have emerged as powerful tools for precisely localizing and quantifying DNA damage. Repair Assisted Damage Detection (RADD) is a single-molecule technique that employs specific repair enzymes to excise damaged bases and incorporates fluorescently labeled nucleotides to visualize the damage. This technique provides valuable insights into repair efficiency and sequence-specific damage. In this review, we discuss the principles and applications of RADD assays, highlighting their potential for enhancing our understanding of DNA damage and repair processes.