E2F3 induces DNA damage repair, stem-like properties and therapy resistance in breast cancer

Therapy resistance is a major hurdle to the treatment of human malignant tumors. Both DNA damage repair and stem-like properties contribute to chemoresistance and radioresistance. E2F transcription factor 3 (E2F3) is overexpressed in breast cancer tissues, and promotes proliferation of breast cancer cells. Higher E2F3 level is associated with shorter survival of breast cancer patients. Functional studies further showed that E2F3 promotes S-phage entry, DNA replication, DNA damage repair and stem-like properties. Accordingly, E2F3 knockdown sensitizes breast cancer cells to DNA-damaging agents Adriamycin, Cisplatin, Olaparib and X-ray. Forkhead box M1 (FOXM1) is a downstream molecule of E2F3 signaling, mediating the effects of E2F3 on breast cancer cells. In an m6A methyltransferase METTL14-dependent manner, YTH RNA binding protein F2 (YTHDF2) increase E2F3 mRNA stability and expression, promotes DNA damage repair and induces therapy resistance. These data demonstrate that YTHDF2-E2F3 pathway is a novel target to overcome chemoresistance and radioresistance in breast cancer.

SiR-DNA/SiR-Hoechst-induced chromosome entanglement generates severe anaphase bridges and DNA damage

SiR-DNA/SiR-Hoechst is a far-red fluorescent DNA probe that is routinely used for live-cell imaging of cell nuclei in interphase and chromosomes during mitosis. Despite being reported to induce DNA damage, SiR-DNA has been used in more than 300 research articles, covering topics like mitosis, chromatin biology, cancer research, cytoskeletal research, and DNA damage response. Here, we used live-cell imaging to perform a comprehensive analysis of the effects of SiR-DNA on mitosis of four human cell lines (RPE-1, DLD-1, HeLa, and U2OS). We report a dose-, time-, and light-dependent effect of SiR-DNA on chromosome segregation. We found that, upon the exposure to light during imaging, nanomolar concentrations of SiR-DNA induce non-centromeric chromosome entanglement that severely impairs sister chromatid segregation and spindle elongation during anaphase. This causes DNA damage that is passed forward to the following cell cycle, thereby having a detrimental effect on genome integrity. Our findings highlight the drawbacks in using SiR-DNA for investigation of late mitotic events and DNA damage-related topics and urge the use of alternative labeling strategies to study these processes.

Beyond the surface: Consequences of methyl tert-butyl ether (MTBE) exposure on oxidative stress, haematology, genotoxicity, and histopathology in rainbow trout

Concerns have been raised about the possible environmental effects of methyl tert-butyl ether (MTBE), which is widely used as a gasoline additive. This research aimed to look at the consequences of MTBE contamination on rainbow trout (Oncorhynchus mykiss), emphasizing oxidative stress, genotoxicity, and histopathological damage. After determining the LC50-96 h value, the effects of sub-lethal doses of MTBE (0 (control), 90, 180, and 450 ppm) on rainbow trout were investigated. In fish tissues, the levels of oxidative stress indicators such as malondialdehyde (MDA) and superoxide dismutase (SOD) were measured. The comet assay, which measures DNA damage in erythrocytes, was used to determine genotoxicity. Histopathological examinations were done on liver and gill tissues to examine potential structural anomalies. The results of this study show that MTBE exposure caused considerable alterations in rainbow trout. Increased oxidative stress was demonstrated by elevated MDA levels and decreased SOD activity, while the comet assay revealed dose-dependent DNA damage, implying genotoxic effects. Histopathological study revealed liver and gill tissue abnormalities, including cell degeneration, necrosis, and inflammation. Overall, this research highlights the possible sub-lethal effects of MTBE contamination on rainbow trout, stressing the need of resolving this issue. Future research should look at the impacts of chronic MTBE exposure and the possibility of bioaccumulation in fish populations.

UHRF1 promotes spindle assembly and chromosome congression by catalyzing EG5 polyubiquitination

UHRF1 is an epigenetic coordinator bridging DNA methylation and histone modifications. Additionally, UHRF1 regulates DNA replication and cell cycle, and its deletion induces G1/S or G2/M cell cycle arrest. The roles of UHRF1 in the regulation of G2/M transition remain poorly understood. UHRF1 depletion caused chromosome misalignment, thereby inducing cell cycle arrest at mitotic metaphase, and these cells exhibited the defects of spindle geometry, prominently manifested as shorter spindles. Mechanistically, UHRF1 protein directly interacts with EG5, a kinesin motor protein, during mitosis. Furthermore, UHRF1 induced EG5 polyubiquitination at the site of K1034 and further promoted the interaction of EG5 with spindle assembly factor TPX2, thereby ensuring accurate EG5 distribution to the spindles during metaphase. Our study clarifies a novel UHRF1 function as a nuclear protein catalyzing EG5 polyubiquitination for proper spindle architecture and faithful genomic transmission, which is independent of its roles in epigenetic regulation and DNA damage repair inside the nucleus. These findings revealed a previously unknown mechanism of UHRF1 in controlling mitotic spindle architecture and chromosome behavior and provided mechanistic evidence for UHRF1 deletion-mediated G2/M arrest.

In vitro screening of genotoxicity and mutagenicity of pyriproxyfen in human lymphocytes and Salmonella typhimurium TA98 and TA100 strains

Pyriproxyfen (PPX) is a pesticide/larvicide used to increase productivity in agriculture against insects by inhibiting development of insects' larvae. In this study, cytotoxic, genotoxic, and mutagenic effects of PPX were investigated in human peripheral lymphocytes and Salmonella typhimurium strains by performing chromosomal aberration, micronucleus (MN) tests, and Ames test, respectively. For the chromosome aberration (CA) and MN methods, blood from four healthy donors (two men and two women, nonsmokers) were used. Two hundred microliters of blood was inoculated into PbMax medium and prepared according to International Guidelines. For the Ames test, S. typhimurium TA98 and TA100 strains were used to detect frameshift and base pair substitution mutagens, respectively. PPX induced both the CA percentage and MN frequency in human peripheral lymphocytes and exhibited cytotoxic effects. In addition, it showed a mutagenic effect at all doses in TA98 and TA100 strains in the presence of S9mix; however, no such effect was observed in the absence of S9mix. According to the obtained results, it can be said that PPX has genotoxic and mutagenic potentials.

Development of 4,4'-dibromobinaphthalene analogues with potent photo-inducible DNA cross-linking capability and cytotoxicity towards breast MDA-MB 468 cancer cells

Photoinduced DNA cross-linking process showed advantages of high spatio-temporal resolution and control. We have designed, synthesized, and characterized several 4,4'-dibromo binaphthalene analogues (1a-f) that can be activated by 350 nm irradiation to induce various DNA damage, including DNA interstrand cross-links (ICL) formation, strand cleavages, and alkaline labile DNA lesions. The degree and types of DNA damage induced by these compounds depend on the leaving groups of the substrates, pH value of the buffer solution, and DNA sequences. The DNA ICL products were produced from the carbocations formed via the oxidation of free radicals photo-generated from 1a-f. Most of these compounds alone exhibited minimum cytotoxicity towards cancer cells while 350 nm irradiation greatly improved their anticancer effects (up to 40-fold enhancement) because of photo-induced cellular DNA damage. This work provides guidance for further design of photo-inducible DNA cross-linking agents as potent photo-activated anticancer prodrugs with good control over toxicity and selectivity.

Acute and subchronic effects of ibuprofen on the ten spotted live-bearer fish Cnesterodon decemmaculatus (Jenyns, 1842)

Ibuprofen (IBP) is an anti-inflammatory drug found in aquatic environments, potentially toxic for the biota. We exposed the test fish C. decemmaculatus to two environmentally relevant concentrations (50 and 100 μg IBP/L) for 4 and 12 d and evaluated the effect on some biomarkers. Micronucleus test, nuclear abnormality test and comet assay indicated cyto-genotoxicity at both concentrations and exposure periods. Oxidative stress and biochemical biomarkers were not affected, excepting muscle AChE activity for 4 d. Muscle metabolic biomarkers showed significant decrease in ETS, lipid and protein content, while carbohydrate content was not affected. The CEA index increased at the lower IBP concentration for 4 and 12 d, possibly due to changes in body energy reserves. A full-factorial GLM performed to assess the effects of IBP and exposure times showed that the metabolic and genotoxicity biomarkers were the most sensitive to IBP toxicity, mainly at 50 μg IBP/L for 4 d.

Insights into mechanism of DNA damage and repair-apoptosis in digestive gland of female scallop Chlamys farreri under benzo[a]pyrene exposure during reproductive stage

As one of the most carcinogenic persistent organic pollutants (POPs), benzo[a]pyrene (B [a]P) brings high toxicity to marine bivalves. Digestive gland is the most important metabolism-related organ of aquatic animals. This study conducted the digestive gland transcriptome of Chlamys farreri under B[a]P treatment at reproductive stages. And the reproductive-stage dependence metabolism-DNA repair-apoptosis process of scallops under 0, 0.04, 0.4 and 4 μg/L B[a]P was studied by qRT-PCR. The results demonstrated that the detoxification metabolism was disturbed after ovulation except for CYP3A4. In antioxidant system, antioxidant enzyme CAT and GPX, and GGT1 (one of the non-enzymatic antioxidants synthesis gene) continuously served the function of antioxidant defense. Three types of DNA repair were activated under B[a]P stress, however, DNA strand breaks were still serious. B[a]P exposure weakened death receptor pathway as well as enhanced mitochondrial pathway, surprisingly suppressing apoptosis in scallops. In addition, ten indicators were screened by Spearman correlation analysis. This study will provide sound theoretical basis for bivalve toxicology and contribute to the biomonitoring of marine POPs pollution.

Is a non-cytotoxic and non-genotoxic novel bioinspired dipeptide structure synthesis possible for theragnostic applications?

The diagnosis and treatment of the diseases in a certain coordination is a subject that has been emphasized in recent years. Theragnostics approaches allow simultaneous diagnosis and treatment of chronic diseases such as cancer. An ideal theragnostic should be biocompatible and can be used safely in humans. Although several types of theragnostics have been developed, none of yet satisfied these criteria. Bioinspired materials with noble metal centers encapsulating therapeutic and imaging agents were shown to possess theragnostic activities. In this study, it was aimed to synthesize, characterize, and evaluate the cytotoxic and genotoxic effects of self-assembly of diphenylalanine (Phe-Phe) dipeptides presence of mercury (Hg2+) ions to be used for theragnostic. Cytotoxicity and genotoxicity studies were done in mouse fibroblast (NIH/3T3) cells by 3-(4,5-Dimethylthiazol-2-yl)- 2,5-diphenyltetrazolium bromide (MTT) and single cell gel electrophoresis (Comet) assays, respectively. It was found that cell viability decreased in a dose-dependent manner in 24-, 48-, and 72-h treatment. Also, Phe-Phe dipeptides did not cause any significant changes in DNA damage at the concentrations of 1, 2, and 5 mg/mL in 4- and 24-h exposures. In the 48-h exposure, Phe-Phe peptide exposure at concentrations of 2 and 5 mg/mL caused a significant increase in DNA damage and in the 72-h of exposure, a significant increase in DNA damage was observed at all studied concentrations. According to the results of the study, it can be said that Phe-Phe dipeptides presence of Hg2+ ions are biocompatible and can be used safely for theragnostic purposes.

Genotoxic and genoprotective effects of phytoestrogens: a systematic review

Phytoestrogens are xenoestrogens found in plants with a myriad of health benefits. However, various studies reported the genotoxic effects of these substances. Thus, we reviewed in vitro and in vivo studies published in PubMed, Scopus, and Web of Science to evaluate the genotoxic and the genoprotective potential of phytoestrogens. Only studies written in English and intended to study commercially available phytoestrogens were included. The screening was performed manually. Moreover, the underlying mechanism of action of phytoestrogens was described. Around half of those studies (43%) reported genoprotective results. However, several studies revealed positive results for genotoxicity with specific model organisms and with dose/concentration dependence. The assessment of the selected articles showed substantial differences in the used concentrations and a biphasic response was recorded in some phytoestrogens. As far as we know, this is the first study to assess the genotoxic and genoprotective effects of phytoestrogens systematically.

Sulfoxaflor insecticide exhibits cytotoxic or genotoxic and apoptotic potential via oxidative stress-associated DNA damage in human blood lymphocytes cell cultures

The need for foodstuff that emerged with the rapidly increasing world population made fertilizers and pesticides inevitable to obtain maximum efficiency from existing agricultural areas. Sulfoxaflor is currently the only member of the new sulfoximine insecticide subclass of nicotinic acetylcholine receptor agonists. In the study, it was aimed to determine the in vitro genetic, oxidative damage potential, genotoxic and apoptotic effects of three different concentrations (10 µg/mL, 20 µg/mL and 40 µg/mL) of sulfoxaflor insecticide in the cultures of blood lymphocytes. In this study, the single-cell gel electrophoresis (comet), Cytokinesis Block Micronuclues Test (MN test), flow cytometry and measurement of Catalase (CAT) enzyme activity were used to determine genotoxic, apoptotic effects and oxidative damage potential, respectively. It found that there is a decrease in CPBI values and Live cell numbers. It was observed an increase in late apoptotic and necrotic cell numbers, Micronucleus frequency, and Comet analysis parameters (GDI and DCP). There is a significant difference between negative control and all concentration of insecticide for Cytokinesis Block Proliferation Index (CBPI) values and late apoptotic, necrotic and viable cell counts. An increase in CAT enzyme levels was observed at 10 and 20 µg/mL concentrations compared to control., It is found that CAT enzyme activity was inhibited at concentrations of 40 µg/mL. This study is crucial as it is the first study to investigate the impact of Sulfoxaflor insecticide on peripheral blood lymphocyte cells. The genotoxic, oxidative damage, and apoptotic effects of Sulfoxafluor insecticide on the results obtained and its adverse effects on other organisms raise concerns about health and safety.

Mutagenicity and genotoxicity assessment of the emerging mycotoxin Versicolorin A, an Aflatoxin B1 precursor

Aflatoxin B1 (AFB1) is the most potent natural carcinogen among mycotoxins. Versicolorin A (VerA) is a precursor of AFB1 biosynthesis and is structurally related to the latter. Although VerA has already been identified as a genotoxin, data on the toxicity of VerA are still scarce, especially at low concentrations. The SOS/umu and miniaturised version of the Ames test in Salmonella Typhimurium strains used in the present study shows that VerA induces point mutations. This effect, like AFB1, depends primarily on metabolic activation of VerA. VerA also induced chromosomal damage in metabolically competent intestinal cells (IPEC-1) detected by the micronucleus assay. Furthermore, results from the standard and enzyme-modified comet assay confirmed the VerA-mediated DNA damage, and we observed that DNA repair pathways were activated upon exposure to VerA, as indicated by the phosphorylation and/or relocation of relevant DNA-repair biomarkers (γH2AX and 53BP1/FANCD2, respectively). In conclusion, VerA induces DNA damage without affecting cell viability at concentrations as low as 0.03 μM, highlighting the danger associated with VerA exposure and calling for more research on the carcinogenicity of this emerging food contaminant.

Assessment of urinary aromatic amines in Brazilian pregnant women and association with DNA damage: Influence of genetic diversity, lifestyle, and environmental and socioeconomic factors

Aromatic amines (AAs) are polar organic chemicals with a wide environmental distribution originating from various sources, such as tobacco smoke, diesel exhaust, and dermal absorption from textile products with azo dyes. The toxicity profile of AAs is directly related to the amino group's metabolic activation and the generation of the reactive intermediate, forming DNA adducts and potential carcinogenicity. Urinary levels of 8-hydroxy-2'-deoxyguanosine (8OHdG) are an important biomarker of DNA damage. Since AAs have been shown to cross the placental barrier, being a risk factor for adverse birth outcomes, prenatal exposure is a great public health concern. The present study aimed to measure the urinary levels of 58 AAs in Brazilian pregnant women (n = 300) and investigated the impact of this exposure on DNA damage by quantifying 8OHdG levels. The influence of tobacco smoke exposure and dermal absorption of AAs by clothes on urinary levels was also assessed. The results showed a 100% detection rate for eight AAs, two of them regulated by the European Union (2,6-dimethylaniline and 2,4-diaminotolune). Hundreds of AAs may be derived from aniline, which here showed a median of 1.38 ng/mL. Aniline also correlated positively with 2,6-dimethylaniline, p-aminophenol, and other AAs, suggesting exposure to multiple sources. The present findings suggest that both tobacco smoke and dermal contact with clothes containing azo dyes are potential sources that might strongly influence urinary levels of AAs in Brazilian pregnant women. A multiple regression linear model (R2 = 0.772) suggested that some regulated AAs (i.e., 2-naphthylamine and 4-aminobiphenyl), nicotine, smoke habit, age, and Brazilian region could induce DNA damage occurrence, increasing the levels of 8OHdG. Given the limited available data on human exposure to carcinogenic AAs, as well as the lack of toxicological information on those non-regulated, further studies focused on measuring their levels in human fluids and the potential exposure sources are clearly essential.

Effects of green tea polyphenols against metal-induced genotoxic damage: underlying mechanistic pathways

This review is based upon evidence from the published effects of green tea polyphenols (GTP) on genotoxic damage induced by metals with carcinogenic potential. First, the relationship between GTP and antioxidant defense system is provided. Subsequently, the processes involved in the oxidative stress generated by metals and their relationship to oxidative DNA damage is examined. The review demonstrated that GTP generally decrease oxidative DNA damage induced by exposure to metals such as arsenic (As), cadmium (Cd), cobalt (Co), copper (Cu), chromium (Cr), iron (Fe), and lead (Pb). The pathways involved in these effects are related to: (1) direct scavenging of free radicals (FR); (2) activation of mechanisms to repair oxidative DNA damage; (3) regulation of the endogenous antioxidant system; and (4) elimination of cells with genetic damage via apoptosis. The results obtained in the studies reviewed demonstrate potential for possible use of GTP to prevent and treat oxidative damage in populations exposed to metals. Further, GTP may be considered as adjuvants to treatments for metal-associated diseases related to oxidative stress and DNA damage.

DNA damage resulting from human endocrine disrupting chemical exposure: Genotoxicity, detection and dietary phytochemical intervention

In recent years, exposure to endocrine disrupting chemicals (EDCs) has posed an increasing threat to human health. EDCs are major risk factors in the occurrence and development of many diseases. Continuous DNA damage triggers severe pathogenic consequences, such as cancer. Beyond their effects on the endocrine system, EDCs genotoxicity is also worthy of attention, owing to the high accessibility and bioavailability of EDCs. This review investigates and summarizes nearly a decade of DNA damage studies on EDC exposure, including DNA damage mechanisms, detection methods, population marker analysis, and the application of dietary phytochemicals. The aims of this review are (1) to systematically summarize the genotoxic effects of environmental EDCs (2) to comprehensively summarize cutting-edge measurement methods, thus providing analytical solutions for studies on EDC exposure; and (3) to highlight critical data on the detoxification and repair effects of dietary phytochemicals. Dietary phytochemicals decrease genotoxicity by playing a major role in the detoxification system, and show potential therapeutic effects on human diseases caused by EDC exposure. This review may support research on environmental toxicology and alternative chemo-prevention for human EDC exposure.

Do hairdressers comprise a high risk group for genotoxicity? A systematic review

BACKGROUND AND OBJECTIVES

Nowadays, hair dye products are widely used for aesthetic purposes, in which it generates chemical exposure to customers and, mainly, hairdressers. The aim of this systematic review was designed to elucidate the following question: are hair dye products able to induce DNA damage in hairdressers?

METHODS

Studies were included in our analyses if they met the following criteria: (1) studies measuring genetic damage in vivo; (2) studies published in English; (3) studies that provided data clearly presented in scientific standards.

RESULTS

Full manuscripts from 13 studies were carefully selected in this setting. Our results demonstrate that hair dye products may contain chemical agents able to induce DNA strand breaks or chromosome damage since the majority of studies demonstrated positive findings for genotoxicity. A total of 7 studies (out of 13) had strong or moderate rates in the quality assessment. The type of genotoxicity assay and sample selection criteria time influenced the outcome.

CONCLUSION

In summary, our results reveal that hairdressers are occupationally exposed to genotoxic agents. Such findings are very important for protecting these professionals who are continuously exposed to chemicals for long periods.

Evaluation of in vitro cytotoxic and genotoxic effects of the 3-(3,4-dihydroxyphenyl)-8-hydroxycoumarin

A wide variety of natural and synthetic coumarins present therapeutic potential. Therefore, the assessment of their safety for humans is essential. 3-(3,4-Dihydroxyphenyl)-8-hydroxycoumarin is a coumarin derivative with antioxidant properties, among other biological activities. The aim of this study is to evaluate the cytotoxic and genotoxic potential of this molecule on peripheral blood mononuclear cells (PBMC) and human hepatocellular carcinoma cells (HepG2/C3A). The results obtained for the cytotoxicity assays, evaluated by the trypan blue staining assay, using concentrations between 0.1 and 20 μg/mL, showed that there is no decrease in cell viability for both cell lines. The MTT assay showed a significant decrease in the viability of HepG2/C3A cells at the highest concentrations tested, after 48 h, for all the tested concentrations, after 72 h of exposure. Regarding the genotoxic assays, the data obtained by the comet assay and the micronucleus test, up to the tested concentration of 10 μg/mL, do not show significant DNA damage and/or chromosomal mutations, for both cell lines. However, at the highest tested concentration of 20 μg/mL, a small but significant genotoxic effect was observed in PBMC. In view of the observed results, it can be concluded that the 3-(3,4-dihydroxyphenyl)-8-hydroxycoumarin, up to a concentration of 10 μg/mL, does not present genotoxic effects in human cells with and without liver enzymes metabolism. Additional studies with higher concentrations of this molecule need to be performed to address its complete biosafety.

Radiation in Combination with Immune Checkpoint Blockade and DNA Damage Response Inhibitors in Mice: Dosage Optimization in MC38 Syngeneic Tumors via Modelling and Simulation

Clinical trials assessing the impact of radiotherapy (RT) in combination with DNA damage response pathway inhibitors (DDRis) and/or immune checkpoint blockade are currently ongoing. However, current methods for optimizing dosage and schedule are limited. A mathematical model was developed to capture the impacts of RT in combination with DDRi and/or anti-PD-L1 [immune checkpoint inhibitor (ICI)] on tumor immune interactions in the MC38 syngeneic tumor model. The model was fitted to datasets that assessed the impact of RT in combination with the DNA protein kinase inhibitor (DNAPKi) AZD7648. The model was further fitted to datasets from studies that were used to assess both RT/ICI combinations as well as RT/ICI combinations followed by concurrent administration of the poly ADP ribose polymerase inhibitor (PARPi) olaparib. Nonlinear mixed-effects modeling was performed followed by internal validation with visual predictive checks (VPC). Simulations of alternative dosage regimens and scheduling were performed to identify optimal candidate dosage regimens of RT/DNAPKi and RT/PARPi/ICI. Model fits and VPCs confirmed a successful internal validation for both datasets and demonstrated very small differences in the median, lower, and upper percentile values of tumor diameters between RT/ICI and RT/PARPi/ICI, which indicated that the triple combination of RT/PARPi/ICI at the given dosage and schedule does not provide additional benefit compared with ICI in combination with RT. Simulation of alternative dosage regimens indicated that lowering the dosage of ICI to between 2 and 4 mg/kg could induce similar benefits to the full dosage regimen, which could be of translational benefit. SIGNIFICANCE STATEMENT: This work provides a mixed-effects model framework to quantify the effects of combination radiotherapy/DNA damage response pathway inhibitors/immune checkpoint inhibitors in preclinical tumor models and identify optimal dosage regimens, which could be of translational benefit.

A Mathematical Model to Investigate the Effects of Ceralasertib and Olaparib in Targeting the Cellular DNA Damage Response Pathway

The ataxia-telangiectasia and Rad3-related (ATR) inhibitor ceralasertib and the poly (ADP-ribose) polymerase (PARP) inhibitor olaparib have shown synergistic activity, in vitro, in the FaDu ATM-knockout cell line. It was found that combining these drugs with lower doses and for shorter treatment periods induced greater or equal toxicity in cancer cells than using either as a single agent. Here, we developed a biologically motivated mathematical model governed by a set of ordinary differential equations, considering the cell cycle-specific interactions of olaparib and ceralasertib. By exploring a range of different possible drug mechanisms, we have studied the effects of their combination as well as which drug interactions are the most prominent. After careful model selection, the model was calibrated and compared with relevant experimental data. We have used this developed model further to investigate other doses of olaparib and ceralasertib in combination, which can be potentially helpful in exploring optimized dosage and delivery. SIGNIFICANCE STATEMENT: Drugs that target cellular DNA damage repair pathways are now being used as a new way to maximize the effect of multimodality treatments such as radiotherapy. Here, we develop a mathematical model to investigate the effects of ceralasertib and olaparib, two drugs that target DNA damage response pathways.