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When DNA repair is inadequate it increases the chances of the genome becoming unstable and it undergoes a malignant mutation. The deficiency of DNA repair PARP proteins may be leveraged for cancer therapy by increasing genomic instability and causing massive DNA damage in cancer cells. DNA repair components are under increased demand in cancer cells because of the continuous replication of DNA. The oncogenic loss of BRCA and an inefficient DNA repair led to cancer cells being dependent on particular DNA repair pathways, like the Poly (ADP-ribose) polymerase pathway. Breast cancer gene 1 and 2 plays a crucial role in DNA repair and genome integrity explaining how BRCA1 and BRCA2 mutations raise the menace of cancer. PARP inhibitors inhibit the base exclusion repair pathway, resulting in the buildup of unrepaired single strand breaks, which cause inflated replication forks in the S phase and subsequently the development of damaging double stranded breaks. Cells having BRCA mutations are unable to repair DNA breaks, leading to apoptosis and eventually death of cancer cells. Numerous indicators, such as a lack of homologous recombination and a high degree of replication pressure, indicate that this therapy will be very effective. Combining PARP inhibitors with chemotherapy, an immune checkpoint inhibitor, and a targeted drug is an effective strategy for combating PARP inhibitors resistance. Several PARP-based combination approaches are in preclinical and clinical development. Various clinical trials are successfully completed and some are undergoing to evaluate the efficacy of these molecules. This review will describe the current views and clinical updates on PARP inhibitors.

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DNA single-strand breaks (SSBs) have attracted much interest since they are highly related to carcinogenesis and ageing. Herein, we report a new liquid crystal (LC)-based sensor for the detection of DNA SSBs generated by reactive oxygen species (ROS) created from the Fenton reaction. The adsorption of single-stranded DNA (ssDNA) onto the cationic surfactant-laden aqueous/LC interface interferes with the surfactant layer, inducing a planar orientation of the LCs. However, the DNA SSBs generated by the Fenton reaction-produced ROS result in a decrease of the electrostatic interactions between the ssDNA and cationic surfactant molecules, causing rearrangement of the surfactant layer and reorientation of the LCs back to a homeotropic alignment. The changes in orientation of the LCs caused by the DNA SSBs are simply converted and observed as a shift from a bright optical image of the LCs to a dark one under a polarized light microscope. With this simple LC-based approach, the DNA SSBs could be detected more effectively and rapidly without any complex instrumentation or intricate processes. Therefore, our research provides a novel strategy for the detection of DNA damage as well as better insight into the DNA-damaging process.

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Here, we present two approaches to map DNA double-strand breaks (DSBs) and single-strand breaks (SSBs) in the genome of human cells. We named these methods respectively DSB-Seq and SSB-Seq. We tested the DSB and SSB-Seq in HCT1116, human colon cancer cells, and validated the results using the topoisomerase 2 (Top2)-poisoning agent etoposide (ETO). These methods are powerful tools for the direct detection of the physiological and pathological "breakome" of the DNA in human cells.

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BACKGROUND AND PURPOSE: High linear energy transfer (LET) radiotherapy offers superior dose conformity and biological effectiveness compared with low-LET radiotherapy, representing a promising alternative for radioresistant tumours. A prevailing hypothesis is that energy deposition along the high-LET particle trajectories induces DNA lesions that are more complex and clustered and therefore more challenging to repair. The precise molecular mechanisms underlying the differences in radiobiological effects between high-LET and low-LET radiotherapies remain unclear. MATERIAL AND METHODS: Human fibroblasts were irradiated with high-LET carbon ions or low-LET photons. At 0.5h and 5h post exposure, the DNA-damage pattern in the chromatin ultrastructure was visualised using gold-labelled DNA-repair factors. The induction and repair of single-strand breaks, double-strand breaks (DSBs), and clustered lesions were analysed in combination with terminal dUTP nick-end labelling of DNA breaks. RESULTS: High-LET irradiation induced clustered lesions with multiple DSBs along ion trajectories predominantly in heterochromatic regions. The cluster size increased over time, suggesting inefficient DSB repair. Low-LET irradiation induced many isolated DSBs throughout the nucleus, most of which were efficiently rejoined. CONCLUSIONS: The clustering of DSBs in heterochromatin following high-LET irradiation perturbs efficient DNA repair, leading to greater biological effectiveness of high-LET irradiation versus that of low-LET irradiation.

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Low- and high-linear energy transfer (LET) ionising radiation are effective cancer therapies, but produce structurally different forms of DNA damage. Isolated DNA damage is repaired efficiently; however, clustered lesions may be more difficult to repair, and are considered as significant biological endpoints. We investigated the formation and repair of DNA double-strand breaks (DSBs) and clustered lesions in human fibroblasts after exposure to sparsely (low-LET; delivered by photons) and densely (high-LET; delivered by carbon ions) ionising radiation. DNA repair factors (pKu70, 53BP1, γH2AX, and pXRCC1) were detected using immunogold-labelling and electron microscopy, and spatiotemporal DNA damage patterns were analysed within the nuclear ultrastructure at the nanoscale level. By labelling activated Ku-heterodimers (pKu70) the number of DSBs was determined in electron-lucent euchromatin and electron-dense heterochromatin. Directly after low-LET exposure (5 min post-irradiation), single pKu70 dimers, which reflect isolated DSBs, were randomly distributed throughout the entire nucleus with a linear dose correlation up to 30 Gy. Most euchromatic DSBs were sensed and repaired within 40 min, whereas heterochromatic DSBs were processed with slower kinetics. Essentially all DNA lesions induced by low-LET irradiation were efficiently rejoined within 24h post-irradiation. High-LET irradiation caused localised energy deposition within the particle tracks, and generated highly clustered DNA lesions with multiple DSBs in close proximity. The dimensions of these clustered lesions along the particle trajectories depended on the chromatin packing density, with huge DSB clusters predominantly localised in condensed heterochromatin. High-LET irradiation-induced clearly higher DSB yields than low-LET irradiation, with up to ∼ 500 DSBs per µm(3) track volume, and large fractions of these heterochromatic DSBs remained unrepaired. Hence, the spacing and quantity of DSBs in clustered lesions influence DNA repair efficiency, and may determine the radiobiological outcome.

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Studies in human and animals have demonstrated that nutritionally induced low birth-weight followed by rapid postnatal growth increases the risk of metabolic syndrome and cardiovascular disease. Although the mechanisms underlying such nutritional programming are not clearly defined, increased oxidative-stress leading to accelerated cellular aging has been proposed to play an important role. Using an established rodent model of low birth-weight and catch-up growth, we show here that post-weaning dietary supplementation with coenzyme Q10, a key component of the electron transport chain and a potent antioxidant rescued many of the detrimental effects of nutritional programming on cardiac aging. This included a reduction in nitrosative and oxidative-stress, telomere shortening, DNA damage, cellular senescence and apoptosis. These findings demonstrate the potential for postnatal antioxidant intervention to reverse deleterious phenotypes of developmental programming and therefore provide insight into a potential translatable therapy to prevent cardiovascular disease in at risk humans.