Low Levels Of DNA Damage Research Articles

A comparative study of different antiviral treatment protocols in HCV related cryoglobulinemic vasculitis

The treatment of HCV and its sequelae are used to be predominantly based on Interferon (IFN). However, this was associated with significant adverse events as a result of its immunostimulant capabilities. Since their introduction, the directly acting antiviral drugs (DAAs), have become the standard of care to treat of HCV and its complications including mixed cryoglobulinemic vasculitis (MCV). In spite of achieving sustained viral response (SVR), there appeared many reports describing unwelcome complications such as hepatocellular and hematological malignancies as well as relapses. Prolonged inflammation induced by a multitude of factors, can lead to DNA damage and affects BAFF and APRIL, which serve as markers of B-cell proliferation. We compared, head-to-head, three antiviral protocols for HCV–MCV treatment As regards the treatment response and relapse, levels of BAFF and APRIL among pegylated interferon α-based and free regimens (Sofosbuvir + Ribavirin; SOF–RIBA, Sofosbuvir + Daclatasvir; SOF–DACLA). Regarding clinical response HCV–MCV and SVR; no significant differences could be identified among the 3 different treatment protocols, and this was also independent form using IFN. We found no significant differences between IFN-based and free regimens DNA damage, markers of DNA repair, or levels of BAFF and APRIL. However, individualized drug-to-drug comparisons showed many differences. Those who were treated with IFN-based protocol showed decreased levels of DNA damage, while the other two IFN-free groups showed increased DNA damage, being the worst in SOF–DACLA group. There were increased levels of BAFF through follow-up periods in the 3 protocols being the best in SOF–DACLA group (decreased at 24 weeks). In SOF–RIBA, CGs relapsed significantly during the follow-up period. None of our patients who were treated with IFN-based protocol had significant clinico-laboratory relapse. Those who received IFN-free DAAs showed a statistically significant relapse of constitutional manifestations. Our findings suggest that IFN-based protocols are effective in treating HCV–MCV similar to IFN-free protocols. They showed lower levels of DNA damage and repair. We believe that our findings may offer an explanation for the process of lymphoproliferation, occurrence of malignancies, and relapses by shedding light on such possible mechanisms.

#2372 Investigating the effects of low-level and transient DNA damage on kidney health in a novel mouse model of aging

Abstract Background and Aims Increasing life expectancy worldwide underscores the importance of addressing the effects of aging on organ and cell function. Aging is characterized by a gradual decline in organ function that varies among individuals and is influenced by lifestyle choices and various external factors that induce DNA stress. This mismatch between kidney aging and an individual's lifespan contributes to the increase in end-stage renal disease. Among the kidney's constituent cells, the proximal tubules are frequently damaged by external factors such as ischemia and drugs. Our research has focused on DNA damage and its repair mechanisms (DDR) caused by these injuries, and we have previously shown that extensive DNA damage beyond the capacity of DDR or abnormalities in DDR cause cellular senescence in proximal tubules, resulting in incomplete renal repair after injury (Kishi et al. Sci Transl Med 2019, J Clin Invest 2019). In this study, we extend these studies and test whether acquired and mild DNA stress induces renal senescence using a novel mouse model of aging, the Inducible Changes to the Epigenome (ICE) mouse (Hayano et al. Cell. 2023). Method ICE mice were generated by mating I-PpoI STOP/+ mice with CreERT2/+ mice. I-PpoI, an endonuclease, cleaves DNA only upon administration of tamoxifen and the resulting DNA damage is subsequently repaired by the DDR. To induce transient DNA damage, 4- to 6-month-old mice were fed a tamoxifen-containing diet for 3 weeks and then housed until they reached 14 months of age. A comprehensive renal analysis was then performed, which included renal tissue evaluation, single-nucleus RNA sequencing, q-PCR, and Western blot analysis for phenotypic analysis of mouse kidneys. Results No significant histological changes were observed in the kidney tissues between the ICE mice and the control group, and the levels of interstitial fibrosis were comparable. To ensure unbiased evaluation, we performed single-nucleus RNA-seq. In ICE mice, there was an increased presence of proximal tubules with incomplete repair expressing KIM-1 and VCAM-1. In addition, ICE mice showed increased gene expression of DNA repair-related enzymes (Mgmt) in proximal tubules and evidence of cellular senescence. No differences in mitochondrial number or biosynthetic capacity were observed. Conclusion The consequences of short-term and transient DNA damage were found to have lasting effects on the kidney. In particular, significant changes were observed in the proximal tubules, where DNA instability and accelerated cellular senescence were evident, suggesting an impaired repair phenotype within the proximal tubules. This may be related to increased susceptibility to various external stimuli. For further detailed analysis, studies using proximal tubule-specific ICE mice are currently performed.

Abstract PO2-04-14: Dual Inhibition of WEE1 and PKMYT1 Synergistically Overcomes CDK4/6 Inhibitor Resistance in Breast Cancer

Abstract Cyclin-dependent kinase 4/6 inhibitors (CDK4/6i) are approved for the treatment of advanced estrogen receptor-positive, HER2-negative (ER+ve) breast cancer when combined with endocrine therapy. However, the emergence of resistance to CDK4/6 inhibitors poses a significant clinical challenge. This study investigates the mechanisms underlying CDK4/6 inhibitor resistance and identifies a common occurrence of high replication stress in triple-negative breast cancer (TNBC) and CDK4/6 inhibitor-resistant ER+ve breast cancers. While ER+ve breast cancer patients have benefited from targeted therapy, TNBC patients, particularly those without germline BRCA1/2 or PALB2 mutations, lack effective treatment options. TNBC and CDK4/6 inhibitor-resistant ER+ve breast cancer cells exhibit an increased dependence on cell cycle arrest to repair replication stress-induced DNA damage. Failure to exit the cell cycle results in excessive DNA damage, thereby limiting their proliferative potential. Based on these findings, we hypothesize that dual inhibition of WEE1 and PKMYT1, two kinases involved in G2/M cell cycle transition and crucial for cell cycle arrest and DNA damage repair, could synergistically inhibit tumor growth. Although WEE1 and PKMYT1 share a common function in promoting G2/M cell cycle transition through CDK1 phosphorylation, their functions are not entirely redundant, suggesting that targeting both kinases may elicit a synergistic response. Recent clinical trials have shown resistance to WEE1-targeted monotherapies, emphasizing the need for combining WEE1 inhibitors with other agents, such as PKMYT1 inhibitors. We demonstrate the synergistic effects of WEE1 inhibitor (MK1775/AZD1775) and PKMYT1 inhibitor (RP6306) in a panel of TNBC and ER+ve breast cancer cells with acquired palbociclib resistance (PalboR). Combination treatment with both inhibitors leads to excessive unrepaired DNA damage, as indicated by increased γH2AX foci following 48 hours of combination treatment, whereas single-agent treatments induce significantly lower levels of DNA damage. Furthermore, we observed the AZD1775/RP6306 combination decreases the expression of the DNA repair protein Rad51 in PalboR cells. To evaluate the clinical potential of dual WEE1 and PKMYT1 inhibition, we generated organoids from metastatic breast cancer lesions of patients who had progressed on CDK4/6 inhibitors for ex vivo studies. Our results demonstrate that dual inhibition of WEE1 and PKMYT1 is more effective than single-agent treatments in eliminating CDK4/6 inhibitor-resistant organoids. Additionally, using patient-derived xenograft mouse models from patients who had progressed on palbociclib and endocrine treatment, we show that the AZD1775/RP6306 combination exhibits superior tumor suppression effects compared to single agents. Overall, this study highlights the potential therapeutic benefits of dual inhibition of WEE1 and PKMYT1 in overcoming CDK4/6 inhibitor resistance in TNBC and ER+ve breast cancer patients. These findings provide a rationale for future clinical trials aimed at exploring the clinical utility of this combination therapy. Citation Format: Mei-Kuang Chen, Grace DeAlessandro, Tuyen Bui, Khandan Keyomarsi. Dual Inhibition of WEE1 and PKMYT1 Synergistically Overcomes CDK4/6 Inhibitor Resistance in Breast Cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-04-14.

Comparison of DNA damage in granulosa cells of women undergoing controlled ovarian stimulation in in vitro fertilization protocols with the recombinant human follicle-stimulating hormones Corneumon®, Gonal-F®, Pergoveris® and Puregon®: a randomized trial.

To compare the DNA damage in granulosa cells (GCs) of women undergoing ovarian-stimulated cycles with four widely used recombinant human follicle-stimulating hormones (rhFSH) in in vitro fertilization (IVF) protocols (Corneumon®, Gonal-F®, Pergoveris® and Puregon®). A randomized trial was carried out at a Mexican hospital. GCs were isolated from 18 women with infertility undergoing assisted reproductive techniques (ART). Four controlled ovarian stimulation (COS) protocols including Corneumon®, Gonal-F®, Pergoveris® or Puregon® were used. GCs DNA damage was assessed by the Comet assay. Two parameters were measured: comet tail length (CTL), and Olive tail moment (OTM, the percentage of DNA in the tail multiplied by the distance between the center of the tail and head). Use of the different hrFSH in COS caused variable and statistically significant levels of DNA damage in GCs of infertile women. CTL was similar in the Corneumon® and Pergoveris® groups (mean values of 48.73 and 55.18, respectively) and Corneumon® CTL was significantly lower compared to the Gonal-F® and Puregon® groups (mean values of 61.98 and 91.17, respectively). Mean OTM values were significantly lower in Corneumon® and Pergoveris® groups, compared to Gonal-F® and Puregon® groups (25.59, 27.35, 34.76, and 47.27, respectively). Use of Corneumon® and Pergoveris® in COS caused statistically significantly lower levels of DNA damage in GCs of infertile women undergoing ART, which could potentially correlate with better reproductive outcomes.

Cold-induced skin darkening does not protect amphibian larvae from UV-associated DNA damage.

Amphibian declines are sometimes correlated with increasing levels of ultraviolet radiation (UVR).While disease is often implicated in declines, environmental factors such as temperature and UVR play an important role in disease epidemiology. The mutagenic effects of UVR exposure on amphibians are worse at low temperatures. Amphibians from cold environments may be more susceptible to increasing UVR. However, larvae of some species demonstrate cold acclimation, reducing UV-induced DNA damage at low temperatures. Understanding of the mechanisms underpinning this response is lacking. We reared Limnodynastes peronii larvae in cool (15°C) or warm (25°C) waters before acutely exposing them to 1.5 h of high intensity (80 µW cm-2 ) UVBR. We measured the color of larvae and mRNA levels of a DNA repair enzyme. We reared larvae at 25°C in black or white containers to elicit a skin color response, and then measured DNA damage levels in the skin and remaining carcass following UVBR exposure. Cold-acclimated larvae were darker and displayed lower levels of DNA damage than warm-acclimated larvae. There was no difference in CPD-photolyase mRNA levels between cold- and warm-acclimated larvae. Skin darkening in larvae did not reduce their accumulation of DNA damage following UVR exposure. Our results showed that skin darkening does not explain cold-induced reductions in UV-associated DNA damage in L. peronii larvae. Beneficial cold-acclimation is more likely underpinned by increased CPD-photolyase abundance and/or increased photolyase activity at low temperatures.

Acute and subchronic effects of petroleum on the freshwater fish Hoplias aff. malabaricus.

Petroleum water soluble fraction (WSF) impairs organisms, but damages may vary among cell and tissue levels. The aim of the present study was to evaluate the acute (24 h, 48 h, 72 h) and subchronic effects (36 days) of WSF (0%, 25% and 100%) in juveniles of the Neotropical top predator fish Hoplias aff. malabaricus. The effects of WSF were evaluated at a molecular level using the comet assay and micronucleus test for genome damage; and at a morphological level through histological identification of liver pathologic lesions. In both acute and subchronic exposure we found low levels of DNA damage (< 10% of comet tail) and non-significant frequency of micronucleus in WSF exposed fish. The most significant liver lesions in WSF exposed fish were fatty vacuolization, hypertrophy and focal necrosis. Since these tissue injuries were progressive and persistent, their irreversibility may negatively affect fish recruitment, even in a such resistant top predator.

Osnovni principi otkrivanja oštećenja DNK pomoću alkalnog komet testa

The Comet assay is a highly sensitive and rapid method for detecting DNA damage at the level of individual cells. It measures single-stranded and double-stranded DNA breaks, alkali-labile, incomplete excision repair and cross-linking sites. A major advantage of the Comet assay is its applicability to both proliferating and non-proliferating cells, and it can be performed on all types of eukaryotic cells. The basic principle of the alkaline Comet assay is to lyse the biological membranes to release proteins bound to the DNA, followed by a short-term electrophoresis at a pH above 13. Through this process, the DNA fragments migrate and form a comet-like shape, which is visualized by staining with a DNA-binding fluorescent dye. The extent of electrophoretic migration is proportional to the amount of DNA damage. Key advantages of the Comet assay include sensitivity-the assay can detect low levels of DNA damage, versatility-it can be used with a small amount of test substance, speed-results are usually available within 24 to 48 hours, and broad applicability-the method is suitable for numerous purposes, including molecular epidemiology, occupational exposure studies, environmental biomonitoring, antigenotoxicity assessments and clinical research. Overall, the Comet assay provides valuable data for a range of scientific and clinical fields, making it a versatile and powerful tool for assessing DNA damage.

Sirtuin 6 activation rescues the age-related decline in DNA damage repair in primary human chondrocytes.

While advanced age is widely recognized as the greatest risk factor for osteoarthritis (OA), the biological mechanisms behind this connection remain unclear. Previous work has demonstrated that chondrocytes from older cadaveric donors have elevated levels of DNA damage as compared to chondrocytes from younger donors. The purpose of this study was to determine whether a decline in DNA repair efficiency is one explanation for the accumulation of DNA damage with age, and to quantify the improvement in repair with activation of Sirtuin 6 (SIRT6). After acute damage with irradiation, DNA repair was shown to be more efficient in chondrocytes from young (≤45 years old) as compared to middle-aged (50-65 years old) or older (>70 years old) cadaveric donors. Activation of SIRT6 with MDL-800 improved the repair efficiency, while inhibition with EX-527 reduced the rate of repair and increased the percentage of cells that retain high levels of damage. In addition to affecting repair after acute damage, treating chondrocytes from older donors with MDL-800 for 48 hours significantly reduced the amount of baseline DNA damage. Chondrocytes isolated from the knees of mice between 4 months and 22 months of age revealed both an increase in DNA damage with aging, and a decrease in DNA damage following MDL-800 treatment. Lastly, treating murine cartilage explants with MDL-800 lowered the percentage of chondrocytes with high p16 promoter activity, which supports the concept that using SIRT6 activation to maintain low levels of DNA damage may prevent the initiation of senescence.

Drug like HSP27 cross linkers with chromenone structure ameliorates pulmonary fibrosis.

Background: Pulmonary fibrosis (PF) is a progressive lung disease characterized by fibroblast accumulation and collagen deposition, resulting in lung scarring and impaired gas exchange. Current treatments for idiopathic pulmonary fibrosis (IPF) have limited efficacy and significant side effects. Heat shock protein 27 (HSP27) has emerged as a potential therapeutic target for PF due to its involvement in fibrotic processes. However, effective HSP27 inhibitors for PF treatment are still lacking. Methods: To assess the anti-fibrotic effects of NA49, we utilized murine PF models induced by radiation (IR) or bleomycin (BLM). We administered NA49 to the PF mice and evaluated its impact on lung fibrosis progression. We also investigated the molecular mechanisms underlying NA49's effects, focusing on its inhibition of EMT-related signaling pathways. Results: In our study, we evaluated the potential of a novel HSP27 inhibitor, NA49, in preclinical models of PF. NA49 effectively suppressed PF development in radiation and bleomycin-induced PF models. It reduced fibrosis, inhibited NFkB signaling, and downregulated EMT-related molecules. Importantly, we evaluated the safety profile of NA49 by assessing its impact on DNA strand breakage. Compared to previous HSP27 inhibitors, NA49 showed lower levels of DNA damage in human lung epithelial cells, and suggests that NA49 may have reduced toxicity compared to other HSP27 inhibitors. Overall, our results demonstrate that NA49 effectively inhibits PF development in preclinical models. It reduces lung fibrosis, inhibits EMT-related signaling pathways, and exhibits improved safety profiles. These findings highlight the potential of NA49 as a promising candidate for the treatment of PF. Conclusion: NA49 exhibited significant anti-fibrotic effects, inhibiting fibrosis development and EMT-related signaling pathways. Moreover, NA49 showed improved safety profiles compared to previous HSP27 inhibitors.

The Role of Chromatin Assembly Factors in Induced Mutagenesis at Low Levels of DNA Damage.

The problem of low-dose irradiation has been discussed in the scientific literature for several decades, but it is impossible to come to a generally accepted conclusion about the presence of any specific features of low-dose irradiation in contrast to acute irradiation. We were interested in the effect of low doses of UV radiation on the physiological processes, including repair processes in cells of the yeast Saccharomyces cerevisiae, in contrast to high doses of radiation. Cells utilize excision repair and DNA damage tolerance pathways without significant delay of the cell cycle to address low levels of DNA damage (such as spontaneous base lesions). For genotoxic agents, there is a dose threshold below which checkpoint activation is minimal despite the measurable activity of the DNA repair pathways. Here we report that at ultra-low levels of DNA damage, the role of the error-free branch of post-replicative repair in protection against induced mutagenesis is key. However, with an increase in the levels of DNA damage, the role of the error-free repair branch is rapidly decreasing. We demonstrate that with an increase in the amount of DNA damage from ultra-small to high, asf1Δ-specific mutagenesis decreases catastrophically. A similar dependence is observed for mutants of gene-encoding subunits of the NuB4 complex. Elevated levels of dNTPs caused by the inactivation of the SML1 gene are responsible for high spontaneous reparative mutagenesis. The Rad53 kinase plays a key role in reparative UV mutagenesis at high doses, as well as in spontaneous repair mutagenesis at ultra-low DNA damage levels.

Deoxycytidine kinase (dCK) inhibition is synthetic lethal with BRCA2 deficiency.

BRCA2 is a well-established cancer driver in several human malignancies. While the remarkable success of PARP inhibitors proved the clinical potential of targeting BRCA deficiencies, the emergence of resistance mechanisms underscores the importance of seeking novel Synthetic Lethal (SL) targets for future drug development efforts. In this work, we performed a BRCA2-centric SL screen with a collection of plant-derived compounds from South America. We identified the steroidal alkaloid Solanocapsine as a selective SL inducer, and we were able to substantially increase its potency by deriving multiple analogs. The use of two complementary chemoproteomic approaches led to the identification of the nucleotide salvage pathway enzyme deoxycytidine kinase (dCK) as Solanocapsine's target responsible for its BRCA2-linked SL induction. Additional confirmatory evidence was obtained by using the highly specific dCK inhibitor (DI-87), which induces SL in multiple BRCA2-deficient and KO contexts. Interestingly, dCK-induced SL is mechanistically different from the one induced by PARP inhibitors. dCK inhibition generates substantially lower levels of DNA damage, and cytotoxic phenotypes are associated exclusively with mitosis, thus suggesting that the fine-tuning of nucleotide supply in mitosis is critical for the survival of BRCA2-deficient cells. Moreover, by using a xenograft model of contralateral tumors, we show that dCK impairment suffices to trigger SL in-vivo. Taken together, our findings unveil dCK as a promising new target for BRCA2-deficient cancers, thus setting the ground for future therapeutic alternatives to PARP inhibitors.

Abstract P4-08-09: Deoxycytidine kinase (dCK) inhibition is synthetic lethal with BRCA2-deficiency

Abstract BRCA2 is a well-established cancer driver in several human malignancies. While the remarkable success of PARP inhibitors proved the clinical potential of targeting BRCA deficiencies, the emergence of resistance mechanisms underscores the importance of seeking novel Synthetic Lethal (SL) targets for future drug development efforts. In this work, we performed a BRCA2-centric SL screen with a collection of plant-derived compounds from South America. We identified the steroidal alkaloid Solanocapsine as a selective SL inducer, and we were able to substantially increase its potency by deriving multiple analogs. The use of two complementary chemoproteomic approaches led to the identification of the nucleotide salvage pathway enzyme deoxycytidine kinase (dCK) as Solanocapsine’s target responsible for its BRCA2-liked SL induction. Additional confirmatory evidence was obtained by using a highly specific dCK inhibitor (DI-87), which induces SL in multiple BRCA2-deficient and KO contexts. Interestingly, dCK-induced SL is mechanistically different from the one induced by PARP inhibitors. dCK inhibition generates substantially lower levels of DNA damage, and cytotoxic phenotypes are associated exclusively with mitosis, thus suggesting that the fine-tuning of nucleotide supply in mitosis is critical for the survival of BRCA2-deficient cells. Moreover, by using a xenograft model of contralateral tumors, we show that dCK impairment suffices to trigger SL in-vivo. Taken together, our findings unveil dCK as a promising new target for BRCA2-deficient cancers, which provides future therapeutic alternatives to PARP inhibitors. Citation Format: María L. Guantay, Cintia A. Garro, Sebastian Siri, María Pansa, Sonja Ghidelli-Disse, Natalia Paviolo, Ana Racca, Viviana Nicotra, Caius Radu, José L. Bocco, Rosana Felice, Israel Gloger, Marcel Muelbaier, Gerard Drewes, Kevin Madauss, Manuela García, Vanesa Gottifredi, Gastón Soria. Deoxycytidine kinase (dCK) inhibition is synthetic lethal with BRCA2-deficiency [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr P4-08-09.

Surgically retrieved spermatozoa for ICSI cycles in non-azoospermic males with high sperm DNA fragmentation in semen.

Intracytoplasmic sperm injection (ICSI)using surgically retrieved spermatozoa outside the classic context of azoospermia has been increasingly used to overcome infertility. The primary indications include high levelsofsperm DNA damage in ejaculated spermatozoa and severe oligozoospermia or cryptozoospermia, particularly in couples with ICSI failurefor no apparent reason. Current evidence suggests that surgically retrieved spermatozoa for ICSI in the above context improves outcomes, mainly concerning pregnancy and miscarriage rates. The reasons are not fully understood but may be related to the lower levels of DNA damage in spermatozoa retrieved from the testis compared with ejaculated counterparts. These findings are consistent with the notion that excessive sperm DNA damage can be a limiting factor responsible for the failure to conceive. Using testicular in preference of low-quality ejaculated spermatozoa bypasses post-testicular sperm DNA damage caused primarily by oxidative stress, thusincreasing the likelihood of oocyte fertilization by genomically intact spermatozoa. Despite the overall favorable results, data remain limited, andmainly concern males with confirmed sperm DNA damage in the ejaculate. Additionally, information regarding the health of ICSI offspring resulting from theuseofsurgicallyretrievedspermatoaofnon-azoospermicmales is still lacking. Efforts should be made to improve the male partner's reproductive health for safer ICSI utilization. A comprehensive andrological evaluation aiming to identify and treat the underlying male infertility factor contributing to sperm DNA damage is essential for achieving this goal.

A comparison between the Felix™ electrophoretic system of sperm isolation and conventional density gradient centrifugation: a multicentre analysis

PurposeDeveloping optimized techniques for the isolation of human spermatozoa possessing low levels of DNA damage is an important objective for the ART industry. The purpose of this study was to compare a novel electrophoretic system (Felix™) of sperm isolation with a conventional method involving density gradient centrifugation (DGC).MethodsFive international ART Centres in Australia, India, Sweden, the USA, and China have collaborated in order to compare the quality of the sperm populations isolated by Felix™ and DGC in terms of processing time, sperm concentration, motility, vitality, and DNA integrity as assessed by 3 methods: SCSA, Halo, and TUNEL.ResultsAcross all centers, 112 comparisons were performed. Although significant differences were noted between centers in terms of the quality of the semen samples subjected for analysis, overall, both methods were equally capable of isolating populations of spermatozoa exhibiting high levels of vitality and progressive motility. The absolute numbers of spermatozoa recovered were significantly (p < 0.001) lower with the Felix™ device although sperm quality was higher with 4/5 centers reporting a significant improvement in DNA integrity relative to DGC (p < 0.01–p < 0.001). In practical terms, the Felix™ device featured a standardized 6 min preparation time whereas clinical DGC protocols varied from center to center but generally took around 40 min to complete.ConclusionsThe Felix™ device is a positive technical development capable of isolating suspensions of highly motile spermatozoa exhibiting low levels of DNA damage in a fraction of the time taken by conventional procedures such as DGC.

Deficiency for SAMHD1 activates MDA5 in a cGAS/STING-dependent manner.

Defects in nucleic acid metabolizing enzymes can lead to spontaneous but selective activation of either cGAS/STING or RIG-like receptor (RLR) signaling, causing type I interferon-driven inflammatory diseases. In these pathophysiological conditions, activation of the DNA sensor cGAS and IFN production are linked to spontaneous DNA damage. Physiological, or tonic, IFN signaling on the other hand is essential to functionally prime nucleic acid sensing pathways. Here, we show that low-level chronic DNA damage in mice lacking the Aicardi-Goutières syndrome gene SAMHD1 reduced tumor-free survival when crossed to a p53-deficient, but not to a DNA mismatch repair-deficient background. Increased DNA damage did not result in higher levels of type I interferon. Instead, we found that the chronic interferon response in SAMHD1-deficient mice was driven by the MDA5/MAVS pathway but required functional priming through the cGAS/STING pathway. Our work positions cGAS/STING upstream of tonic IFN signaling in Samhd1-deficient mice and highlights an important role of the pathway in physiological and pathophysiological innate immune priming.

FLASH irradiation induces lower levels of DNA damage ex vivo, an effect modulated by oxygen tension, dose, and dose rate.

FLASH irradiation reportedly produces less normal tissue toxicity, while maintaining tumour response. To investigate oxygen's role in the 'FLASH effect', we assessed DNA damage levels following irradiation at different oxygen tensions, doses and dose rates. Samples of whole blood were irradiated (20 Gy) at various oxygen tensions (0.25-21%) with 6 MeV electrons at dose rates of either 2 kGy/s (FLASH) or 0.1 Gy/s (CONV), and subsequently with various doses (0-40 Gy) and intermediate dose rates (0.3-1000 Gy/s). DNA damage of peripheral blood lymphocytes (PBL) were assessed by the alkaline comet assay. Following 20 Gy irradiation, lower levels of DNA damage were induced for FLASH, the difference being significant at 0.25% (p < 0.05) and 0.5% O2 (p < 0.01). The differential in DNA damage at 0.5% O2 was found to increase with total dose and dose rate, becoming significant for doses ≥20 Gy and dose rates ≥30 Gy/s. This study shows, using the alkaline comet assay, that lower levels of DNA damage are induced following FLASH irradiation, an effect that is modulated by the oxygen tension, and increases with the total dose and dose rate of irradiation, indicating that an oxygen related mechanism, e.g. transient radiation-induced oxygen depletion, may contribute to the tissue sparing effect of FLASH irradiation. This paper is first to directly show that FLASH-induced DNA damage is modulated by oxygen tension, total dose and dose rate, with FLASH inducing significantly lower levels of DNA damage for doses ≥20 Gy and dose rates ≥30 Gy/s, at 0.5% O2.

A pooled analysis of molecular epidemiological studies on modulation of DNA repair by host factors

Levels of DNA damage represent the dynamics between damage formation and removal. Therefore, to better interpret human biomonitoring studies with DNA damage endpoints, an individual’s ability to recognize and properly remove DNA damage should be characterized. Relatively few studies have included DNA repair as a biomarker and therefore, assembling and analyzing a pooled database of studies with data on base excision repair (BER) was one of the goals of hCOMET (EU-COST CA15132). A group of approximately 1911 individuals, was gathered from 8 laboratories which run population studies with the comet-based in vitro DNA repair assay. BER incision activity data were normalized and subsequently correlated with various host factors. BER was found to be significantly higher in women. Although it is generally accepted that age is inversely related to DNA repair, no overall effect of age was found, but sex differences were most pronounced in the oldest quartile (>61 years). No effect of smoking or occupational exposures was found. A body mass index (BMI) above 25 kg/m2 was related to higher levels of BER. However, when BMI exceeded 35 kg/m2, repair incision activity was significantly lower. Finally, higher BER incision activity was related to lower levels of DNA damage detected by the comet assay in combination with formamidopyrimidine DNA glycosylase (Fpg), which is in line with the fact that oxidatively damaged DNA is repaired by BER. These data indicate that BER plays a role in modulating the steady-state level of DNA damage that is detected in molecular epidemiological studies and should therefore be considered as a parallel endpoint in future studies.

Effect of UV Radiation and Other Abiotic Stress Factors on DNA of Different Wild Plant Species Grown in Three Successive Seasons in Alpine and Subalpine Regions

Plants in natural ecosystems are exposed to a combination of UV radiation, ionizing radiation (IR) and other abiotic factors. These factors change with the altitude. We investigated DNA alterations of some wild plants of different plant families in natural ecosystems at three altitudes in Rila Mountain, Bulgaria (1500, 1782, and 2925 m above sea level (a.s.l.) exposed to UV radiation, IR and other abiotic stresses, to assess the tolerance of plant species to the changing environmental conditions in three successive growth seasons. For this purpose, physicochemical, cytogenetic, and molecular methods were applied. DNA damage was assessed by micronucleus test and molecular method comet assay adapted and applied by us to wild plant species from Onagraceae, Rosaceae, Boraginaceae, Saxifragaceae, Orobanchaceae, Asteraceae and Poaceae families, growing at three different altitudes. Variability in the DNA sensitivity and the level of tolerance was observed among the plant species in response to combined abiotic factors assessed by induced DNA damage and gross beta activity. The studied representatives of Poaceae were less susceptible than the other studied species at all three altitudes and showed close level of DNA injuries to that of unaffected control plant grown in laboratory conditions. The lower levels of DNA damage of these wild plant species corresponded to their lower ability to accumulate radionuclides. There was a particularly pronounced low level of DNA injuries in the plant species at the highest altitude. The level of DNA damage showed correlation with the values of some abiotic environmental factors. The results would contribute to the elucidation of the extent of adaptation of plant species to the continuously changing environment and would be useful in selecting sensitive herbaceous monitor species for environmental impact assessment at mountain and alpine sites.

Measurement of oxidatively damaged DNA in mammalian cells using the comet assay: Reflections on validity, reliability and variability

The comet assay is a simple technique for measurements of low levels of DNA damage and repair in single cells. However, there is variation in background levels of DNA damage in peripheral blood mononuclear cells (PBMCs). This variation has been documented by inter-laboratory ring-trials where identical samples have been analysed in different laboratories using the formamidopyrimidine DNA glycosylase (Fpg)-modified comet assay. The coefficient of variation of background levels of Fpg-sensitive sites was 128 % in the first inter-laboratory validation trial called European Standards Committee on Oxidative DNA Damage. The variation was reduced to 44 % by the end of the project. Subsequent ring-trials by the European Comet Assay Validation Group showed similar inter-laboratory variation in Fpg-sensitive sites in PBMCs (45 %). The lowest inter-laboratory variation in Fpg-sensitive sites in PBMCs was 12 % when using calibration to standardize comet assay descriptors. Introduction of standard comet assay procedures was surprisingly unsuccessful as certain laboratories experienced technical problems using unaccustomed assay conditions. This problem was alleviated by using flexible assay standard conditions rather than a standard protocol in a ring-trial by the hCOMET group. The approach reduced technical problems, but the inter-laboratory variation in Fpg-sensitive sites was not reduced. The ring-trials have not pinpointed specific assay steps as major determinants of the variation in DNA damage levels. It is likely that small differences in several steps cause inter-laboratory variation. Although this variation in reported DNA damage levels causes concern, ring-trials have also shown that the comet assay is a reliable tool in biomonitoring studies.

Inhibition of PARP1 Reduces Cell Viability and Increases Markers of DNA Damage in Fanconi Anemia-Mutated Acute Myeloid Leukemia

Introduction:Fanconi Anemia (FA) is a hereditary disorder characterized by deficiencies in DNA damage repair and genome instability with a high propensity for bone marrow failure (BMF) and malignancies such as acute myeloid leukemia (AML). Clinically, FA patients experience greater toxicity than non-FA patients when treated with cytotoxic chemotherapy used for AML treatment, so there is a need for alternative treatments to be developed for FA-mutated AML.Poly (ADP-ribose) polymerase 1 (PARP1) is an important enzyme involved in the recognition and repair of DNA breaks. There has been recent clinical success in treating cancers with defective DNA damage repair with PARP inhibitors, an example of synthetic lethality. Therefore we hypothesize that PARP inhibition (PARPi) is an effective strategy for treating FA-mutated AML. Recent studies have shown that PARP1 is overexpressed in many cancers, including AML, and that higher PARP1 expression is associated with worse patient outcomes. Here, we investigate the anti-tumor effects of a PARP inhibitor, olaparib, on FA-mutated and wild-type (WT) AML cells and investigate the activity of downstream DNA repair pathways in response to PARPi.Methods/Results:To determine the effects of PARPi on AML and FA-mutated AML cells in vitro, we treated four cell lines, one FA-wild type AML line and three patient-derived FA-mutated AML lines, with olaparib for 1, 4, 8, 24, and 48 hours. Preliminary data suggest that olaparib treatment decreases protein expression of both PARP1 and PAR (from activation of PARP) compared to vehicle controls.To evaluate the effect of PARPi on DNA damage in AML we measured γH2AX expression by western blotting and immunofluorescence, and found that, although γH2AX expression was not significantly increased in FA-wild type AML cells, there was a significant increase in γH2AX expression in SB1685 FA-mutated AML cells treated with olaparib compared to controls after 4 hours of treatment (p-value < 0.05).To further evaluate the ability of olaparib to inhibit DNA damage repair, we treated our cells with olaparib and performed single-cell alkaline electrophoresis COMET assay. We found that, while the WT cell line was able to repair its DNA over time (indicated by lower levels of DNA damage after 48 hours of olaparib exposure compared to earlier time points), our FA-mutated AML cell lines had more DNA damage after 48 hours of treatment compared to controls. These data suggest that, while cells proficient in DNA repair are capable of repairing DNA damage even when exposed to PARPi, cells that have mutations in their ability to repair DNA damage are not only less able to repair DNA damage over time but also show increased DNA damage over time when exposed to PARPi.To better understand the effects of this increase in DNA damage, we treated our cells with olaparib and assayed for cell viability over 96 hours. We found that, while WT AML cells did not have significantly decreased cell viability after 96 hours, FA-mutated cell lines trended towards significant decrease in cell viability at 96 hours. These cell lines were also stained with Annexin V to investigate apoptotic activity. Our results indicate that olaparib is able to induce apoptosis in our FA-mutated cells after 24 hours of treatment and that, as treatment continues, the percent of Annexin V-positive cells increases compared to controls.To investigate downstream DNA damage response to PARPi, we treated our cells with olaparib and analyzed the expression of DNA Ligase III, Mre11, XRCC1, and Rad51-enzymes involved in various DNA repair pathways. We found that expression levels of XRCC1 increased over 48 hours in our WT AML cells, suggesting a response to the DNA damaging effects of PARPi. In our FA-mutated SB1685 cells, we found a decrease in XRCC1, DNA Ligase III, and Rad51. The expression levels of these enzymes in the other FA-mutated cell lines were more variable, suggesting that the impact of PARPi on downstream DNA repair pathways may be different across different cell lines.Conclusions:Our data suggest that PARP inhibition may be a potential therapy for the treatment of acute myeloid leukemia. In particular, leukemia with mutations in DNA repair mechanisms may be more responsive to PARP inhibition due to resulting DNA damage and synthetic lethality. Thus, PARP inhibitors have the potential to be an effective therapeutic strategy for the treatment of FA-mutated AML. DisclosuresNo relevant conflicts of interest to declare.