BER Pathway Research Articles

Analyzing the Temperature Dependence of Titania Photocatalysis: Kinetic Competition between Water Oxidation Catalysis and Back Electron-Hole Recombination.

This study examines the kinetic origins of the temperature dependence of photoelectrochemical water oxidation on nanostructured titania photoanodes. We observe that the photocurrent is enhanced at 50 °C relative to 20 °C, with this enhancement being most pronounced (by up to 70%) at low anodic potentials (<+0.6 V vs RHE). Over this low potential range, the photocurrent magnitude is largely determined by kinetic competition between water oxidation catalysis (WOC) and recombination between surface holes and bulk electrons (back electron-hole recombination, BER). We quantify the BER process by transient photocurrent analyses under pulsed irradiation. Remarkably, we find that the kinetics of BER (∼90 ms half-time) are independent of temperature. In contrast, the kinetics of WOC, determined from the analysis of the photoinduced absorption of accumulated surface holes, are found to accelerate up to 2-fold at 50 °C relative to 20 °C. We conclude that the enhanced photocurrent densities observed in the low-applied potential region result primarily from the accelerated WOC, reducing losses due to the competing BER pathway. At higher applied potentials (>+0.6 V vs RHE), a smaller (∼10%) enhancement in photocurrent density is observed at 50 °C relative to 20 °C. Photoinduced absorption studies, correlated with studies using triethanolamine as a hole scavenger, indicate that this more modest enhancement at anodic potentials primarily results from an enhanced charge separation efficiency. We conclude by discussing the implications of these results for the practical application of photoanodic WOC under solar irradiation, influenced by these temperature-independent and -dependent underlying kinetic processes.

Effect of kynurenic acid on enzymatic activity of the DNA base excision repair pathway in specific areas of the sheep brain

Relatively low levels of antioxidant enzymes coupled with high oxygen metabolism result in the formation of numerous oxidative DNA damages in the tissues of the central nervous system. Recently, kynurenic acid (KYNA), knowns for its neuroprotective properties, has gained increasing attention in this context. Therefore, our hypothesis assumed that increased KYNA levels in the brain would positively influence mRNA expression of selected enzymes of the base excision repair pathway as well as enhance their efficiency in excising damaged nucleobases in specific areas of the sheep brain. The study was conducted on adult anestrous sheep (n = 18), in which two different doses of KYNA (20 and 100 μg/day) were infused into the third brain ventricle for three days. Molecular and biochemical analysis included the hypothalamus (preoptic and mediol-basal areas), hippocampus (CA3 field) and amygdala (central amygdaloid nucleus), dissected from the brain of sheep euthanized immediately after the last infusion. The results revealed a significant increase P < 0.001) in the relative mRNA abundance of N-methylpurine DNA glycosylase (MPG) following administration of both dose of KYNA across all examined tissues. The transcription of thymine-DNA glycosylase (TDG) increased significantly (P < 0.001) in all tissues in response to the lower KYNA dose compared to the control group. Moreover, 8-oxoguanine (8-oxoG) DNA glycosylase (OGG1) mRNA levels were also higher in both animal groups (P < 0.001). In addition, in the hypothalamus, hippocampus and amygdala, AP endonuclease 1 (APE1) mRNA expression increased under both doses of KYNA. Moreover, the both dose of KYNA significantly stimulated the efficiency of 8-oxoG excision in hypothalamus and amygdala (P < 0.05–0.001). The lower and higher doses of KYNA significantly influenced the effectiveness of εA and εC in all structures (P < 0.01–0.001). In conclusion, the favorable effect of KYNA in the brain may include the protection of genetic material in nerve and glial cells by stimulating the expression and efficiency of BER pathway enzymes.

AGEs induce MMP-9 promoter demethylation through the GADD45α-mediated BER pathway to promote breast cancer metastasis in patients with diabetes.

Scientific evidence has linked diabetes to a higher incidence and increased aggressiveness of breast cancer; however, mechanistic studies of the numerous regulators involved in this process are insufficiently thorough. Advanced glycation end products (AGEs) play an important role in the chronic complications of diabetes, but the mechanisms of AGEs in breast cancer are largely unexplored. In this study, we first demonstrate that high AGE levels in breast cancer tissues are associated with the diabetic state and poor patient outcomes. Furthermore, AGEs interact with the receptor for AGEs (RAGE) to promote breast cancer cell migration and invasion. Mechanistically, based on RNA sequencing (RNA-seq) analysis, we reveal that growth arrest and DNA damage gene 45α (GADD45α) is a vital protein upregulated by AGEs through a P53-dependent pathway. Next, GADD45α recruits thymine DNA glycosylase for base excision repair to form the demethylation complex at the promoter region of MMP-9 and enhance MMP-9 transactivation through DNA demethylation. Overall, our results indicate a critical regulatory role of AGEs in patients with breast cancer and diabetes and reveal a novel mechanism of epigenetic modification in promoting breast cancer metastasis.

Talazoparib enhances the quinacrine-mediated apoptosis in patient-derived oral mucosa CSCs by inhibiting BER pathway through the modulation of GCN5 and P300.

The presence of cancer stem cells (CSCs) in the tumor microenvironment (TME) is majorly responsible for the development and recurrence of cancer. Earlier reports suggested that upon DNA damage, poly-(ADP-ribose) polymerase-1 (PARP-1) helps in chromatin modulation and DNA repair process, thereby promoting CSC survival. But whether a combination of DNA damaging agents along with PARP inhibitors can modulate chromatin assembly, inhibit DNA repair processes, and subsequently target CSCs is not known. Hence, we have investigated the effect of nontoxic bioactive compound quinacrine (QC) and a potent PARP inhibitor Talazoparib in patient-derived oral mucosa CSCs (OM-CSCs) and in vivo xenograft mice preclinical model systems. Data showed that QC + Talazoparib inhibited the PARP-1-mediated chromatin remodelers' recruitment and deregulated HAT activity of GCN5 (general control nonderepressible-5) and P300 at DNA damage site, thereby preventing the access of repair proteins to the damaged DNA. Additionally, this combination treatment inhibited topoisomerase activity, induced topological stress, and induced apoptosis in OM-CSCs. Similar results were observed in an in vivo xenograft mice model system. Collectively, the data suggested that QC + Talazoparib treatment inhibited BER pathway, induced genomic instability and triggered apoptosis in OM-CSCs through the deregulation of PARP-1-mediated chromatin remodelers (GCN5 and P300) activity. Schematic representation of QC + Talazoparib-induced apoptosis in oral mucosa CSCs. (1) Induction of DNA damage takes place after QC treatment (2) PARP1-mediated PARylation at the site of DNA damage, which recruits multiple chromatin remodelers (3) Acetylation at the histone tails relax the structure of chromatin and recruits the BER pathway proteins at the site of DNA damage. (4) BER pathway activated at the site of DNA damage. (5) CSCs survive after successful repair of DNA damage. (6) Treatment of QC-treated CSCs with PARP inhibitor Talazoparib (7) Inhibition of PARylation results in failure of chromatin remodelers to interact with PARP1. (8) Inhibition of acetylation status leads to chromatin compaction. (9) BER pathway proteins are not recruited at the site of DNA damage, resulting in inhibition of BER pathway and accumulation of unrepaired DNA damage, leading to apoptosis and cell death.

DNA damage response and repair gene mutations are associated with tumor mutational burden and outcomes to platinum-based chemotherapy/immunotherapy in advanced NSCLC patients

BackgroundDNA damage response and repair (DDR) genes are crucial for maintaining the integrity of the genome. This study aims to explore the correlation of DDR gene mutations with TMB, clinical characteristics, and outcomes to platinum-based chemotherapy and platinum-based chemotherapy/immunotherapy in non-small cell lung cancer (NSCLC) without EGFR and ALK alterations.MethodsTumor tissue from 49 patients with stage III or IV NSCLC who were without EGFR and ALK alterations were analyzed using targeted next-generation sequencing (NGS). Among them, 13 patients received first-line platinum-based chemotherapy, 32 patients received first-line platinum-based chemotherapy/immunotherapy.ResultsIn these NSCLC patients without EGFR and ALK alterations, the frequently mutated genes included TP53, KMT2D and KRAS, the most frequently mutated DDR gene was FANCG, DDR gene mutations were detected in 20 patients. The mutation frequency of homologous recombination (HR) pathway was significantly higher in lung squamous cell carcinoma (LUSC) than that in lung adenocarcinoma (LUAD) (30.8% vs. 5.7%). Among DDR positive patients, a lower percentage exhibited metastasis. Patients with DDR gene mutations, cell-cycle checkpoint pathway mutations, and BER pathway mutations had significantly higher TMB compared to those without corresponding mutations. In the patients receiving platinum-based chemotherapy/immunotherapy, the disease control rate was significantly lower in the DDR-positive group compared with that in the DDR-negative group (55.6% vs. 100.0%). Among LUAD patients receiving platinum-based chemotherapy/immunotherapy, we observed a worse overall survival (OS) in DDR-positive group, as well as poorer progression-free survival(PFS)and OS in BER-positive and FANCG mutated group.ConclusionsDDR gene mutations are associated with tumor metastasis, TMB, and outcomes to platinum-based chemotherapy/immunotherapy in advanced NSCLC patients.

Parp Inhibitors and Radiotherapy: A New Combination for Prostate Cancer (Systematic Review).

PARPi, in combination with ionizing radiation, has demonstrated the ability to enhance cellular radiosensitivity in different tumors. The rationale is that the exposure to radiation leads to both physical and biochemical damage to DNA, prompting cells to initiate three primary mechanisms for DNA repair. Two double-stranded DNA breaks (DSB) repair pathways: (1) non-homologous end-joining (NHEJ) and (2) homologous recombination (HR); and (3) a single-stranded DNA break (SSB) repair pathway (base excision repair, BER). In this scenario, PARPi can serve as radiosensitizers by leveraging the BER pathway. This mechanism heightens the likelihood of replication forks collapsing, consequently leading to the formation of persistent DSBs. Together, the combination of PARPi and radiotherapy is a potent oncological strategy. This combination has proven its efficacy in different tumors. However, in prostate cancer, there are only preclinical studies to support it and, recently, an ongoing clinical trial. The objective of this paper is to perform a review of the current evidence regarding the use of PARPi and radiotherapy (RT) in PCa and to give future insight on this topic.

Synthetic PARP-1 Inhibitors Reported During the Last Decade

Background: Cancer is the world's second largest cause of death and is responsible for an estimated 9.6 million mortalities in 2018. Poly-ADP-ribose polymerases (PARPs) are enzymes and family of proteins, involved in many cellular processes, including DNA repair, gene regulation, chromatin remodeling, and apoptosis. The first characterized and best known member of the PARP family is poly(ADP-ribose) polymerase 1 (PARP-1). PARP-1 is a major protein for DNA single-strand breaks in the BER pathway (base excision repair) (SSBs). Objective: The objective of this article was to compile synthetic PARP-1 inhibitors reported in the last decade Methods: In the present manuscript, bibliographic investigation was carried out by scrutinizing peerreviewed articles from online/offline databases. The inclusion criteria consisted of the most relevant studies indicating the relationship between PARP-1 and cancer in textbooks/edited books and peer-reviewed papers from scientific databases, like SCOPUS, PUBMED, NISCAIR, and Google Scholar since 2010 to 2020. Only the studies published in English language were searched/considered. The exclusion criteria consisted of the studies on other PARP isoforms than PARP-1. The studies thus obtained were classified according to the heterocyclic moieties, year of publication, etc. The data compiled in this article is a systematic review of the reported studies. Results: The literature reports indicated that a number of PARP-1 inhibitors reported have IC50 value in nanomolar concentration. Conclusion: PARP-1 is an essential target for anti-cancer drug discovery. Further, research for more effective and safe PARP-1 inhibitors is carried out and we may discover some novel PARP-1 inhibitors in the near future.

OGG1 inhibition suppresses African swine fever virus replication

African swine fever virus (ASFV) is an important pathogen that causes a highly contagious and lethal disease in swine, for which neither a vaccine nor treatment is available. The DNA repair enzyme 8-oxoguanine DNA glycosylase 1 (OGG1), which excises the oxidative base lesion 8-oxo-7,8-dihydroguanine (8-oxoG), has been linked to the pathogenesis of different diseases associated with viral infections. However, the role of OGG1-base excision repair (BER) in ASFV infection has been poorly investigated. Our study aimed to characterize the alteration of host reactive oxygen species (ROS) and OGG1 and to analyse the role of OGG1 in ASFV infection. We found that ASFV infection induced high levels and dynamic changes in ROS and 8-oxoG and consistently increased the expression of OGG1. Viral yield, transcription level, and protein synthesis were reduced in ASFV-infected primary alveolar macrophages (PAMs) treated by TH5487 or SU0268 inhibiting OGG1. The expression of BER pathway associated proteins of ASFV was also suppressed in OGG1-inhibited PAMs. Furthermore, OGG1 was found to negatively regulate interferon β (IFN-β) production during ASFV infection and IFN-β could be activated by OGG1 inhibition with TH5487 and SU0268, which blocked OGG1 binding to 8-oxoG. Additionally, the interaction of OGG1 with viral MGF360-14-L protein could disturb IFN-β production to further affect ASFV replication. These results suggest that OGG1 plays the crucial role in successful viral infection and OGG1 inhibitors SU0268 or TH5487 could be used as antiviral agents for ASFV infection.

Acetylation of p62 regulates base excision repair through interaction with APE1.

p62, a well-known adaptor of autophagy, plays multiple functions in response to various stresses. Here, we report a function for p62 in base excision repair that is distinct from its known functions. Loss of p62 impairs base excision repair capacity and increases the sensitivity of cancer cells to alkylating and oxidizing agents. In response to alkylative and oxidative damage, p62 is accumulated in the nucleus,acetylated by hMOF,and deacetylated by SIRT7, and acetylated p62 is recruited to chromatin. The chromatin-enriched p62 directly interacts with APE1, a key enzyme of the BER pathway, and promotes its endonuclease activity, which facilitates BER and cell survival. Collectively, our findings demonstrate that p62 is a regulator of BER and provide further rationale for targeting p62 as a cancer therapeutic strategy.

Impact of Polymorphism in Base Excision Repair and Nucleotide Excision Repair Genes and Risk of Cervical Cancer: A Case-Control Study.

Background:Last few years, several studies all over the world revealed the association of DNA repair genes with risk of developing different type of cancers, but were ambiguous to support the evidences in case of cervical cancer risk. These differences in earlier studies directed us to study the association of polymorphisms of BER genes (XRCC1, hOGG1, XPC) and NER genes (XPC, XPD) with cervical cancer susceptibility in the women of rural population of Maharashtra. Materials and Methods:The genetic polymorphism in BER and NER pathway genes was studied by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method using DNA isolated from intravenous blood samples of patients and normal controls. The study included 400 clinically confirmed cervical cancer patients and 400 healthy women from a tertiary care hospital (Krishna Hospital and Medical Research Centre) of south-western Maharashtra. The association of polymorphisms was confirmed by Odds ratio (OR) with 95% confidence interval. Results:The single nucleotide polymorphism (SNP) of BER genes including XRCC1, hOGG1 and APE1 were analyzed and the results were noted that 27466AA (OR=4.88; 95% CI: 3.61- 6.60; p<0.0001) and 28152AA (OR=2.89; 95% CI: 1.57- 5.31; p=0.0005) genotypes of XRCC1 (rs25489, rs25487) were significantly associated with cervical cancer risk. The 1245GG genotype of hOGG1 (rs1052133) (OR=45.30; 95% CI: 3.76- 7.46; p=0.001) also showed significant correlation, whereas 2197GG genotype of APE1 (rs1130409) gene showed negative association with cervical carcinogenesis (OR=0.59; 95% CI: 0.35- 0.97; p=0.005). Similarly when we studied SNPs of NER genes including XPC and XPD genes, 21151TT genotype of XPC (rs 2228000) was positively associated with cervical cancer development and 23591AA genotype of XPD (rs1799793) showed negative association (OR=0.34; 95% CI: 0.17- 0.64; p=0.001). Conclusion:The findings from this study supported that rs25489, rs25487SNPs of XRCC1, rs1052133 of hOGG1 and rs2228000 of XPC may increase cervical cancer risk, whereas rs1130409 SNP of APE1 and rs1799793 SNP of XPD gene lower the risk of cervical cancer in the studied population.

Interlocking activities of DNA polymerase β in the base excision repair pathway

SignificanceBase excision repair (BER) is one of the major DNA repair pathways used to fix a myriad of cellular DNA lesions. The enzymes involved in BER, including DNA polymerase β (Polβ), have been identified and characterized, but how they act together to efficiently perform BER has not been fully understood. Through gel electrophoresis, mass spectrometry, and kinetic analysis, we discovered that the two enzymatic activities of Polβ can be interlocked, rather than functioning independently from each other, when processing DNA intermediates formed in BER. The finding prompted us to hypothesize a modified BER pathway. Through conventional and time-resolved X-ray crystallography, we solved 11 high-resolution crystal structures of cross-linked Polβ complexes and proposed a detailed chemical mechanism for Polβ's 5'-deoxyribose-5-phosphate lyase activity.

Dose response to methylating agents in the γH2AX, SCE and colony formation assays: Effect of MGMT and MPG overexpression

Cells have developed diverse protective mechanisms that enable them to tolerate low doses of genotoxic compounds. DNA repair processes attenuate the mutagenic and carcinogenic effects of alkylating agents, and multiple studies indicate a key role of specific DNA repair factors and pathways in establishing non-linear dose response relationships. Using an overexpression approach, we investigated the impact of O6-methylguanine-DNA-methyltransferase (MGMT), which repairs O6-methylguanine (O6MeG) in a damage reversal reaction, and N-methylpurine-DNA glycosylase (MPG), which acts as an apical enzyme in the BER pathway, on the DNA damage response to the alkylating agents MNNG and MMS. Our data indicate a clear protective effect of MGMT against MNNG-induced nuclear γH2AX foci formation, sister chromatid exchanges (SCE) and cytotoxicity, as determined in the colony formation assay. MGMT protected with similar efficiency against MMS-induced cytotoxicity and γH2AX foci formation, but suppressed SCE induction only weakly, which indicates that recombination events induced by MMS result from other lesions than O6MeG. In contrast, overexpression of MPG had only a very mild protective effect on the cellular defense against MMS and MNNG. Collectively, our data indicate that overexpression of MGMT results in non-linear DNA damage responses to O6MeG inducers. In contrast, MPG overexpression has only minor impact on the DNA damage response to alkylating drugs, indicating that other downstream enzymes in the BER pathway are limiting.

Proposed hypothesis of GSK-3 β inhibition for stimulating Wnt/β-catenin signaling pathway which triggers liver regeneration process.

Almost every human organ has a poor ability to regenerate, notable exceptions are liver, skin, gut, etc. Molecular and cellular underpinnings of liver regeneration might pave the way for novel treatments concerned with chronic liver disorder. Such treatments would eliminate the disadvantages of liver transplantation, such as a scarcity of donor organs, a lengthy waitlist, significant medical expenses, surgical complications, and the necessity for lifelong immunosuppressive medications. Advancement in the development of regenerative therapy is giving hope to those suffering from end-stage liver disorder. The regeneration process is unique, intricate, and well coordinated, which involve the interaction of numerous signaling pathways, cytokines, and growth factor. Various signaling pathways for liver regeneration are HO-1/BER pathway, Tweak/Fn14 signaling pathway, Hippo pathway, Wnt/beta-catenin pathway, Hedgehog signaling pathway, bile acids repairing pathway, serotonin (5HT) pathway, estrogen pathway, thyrotropin-releasing hormone (TRH) pathway, insulin repairing pathway, etc. The in vitro scientific literature revealed that numerous GSK-3 β inhibitors (LY 2090314, AR-A014418, Tideglusib, Solasodine, CHIR99021, 9-ING-41, SB-216763) play an important role in stimulating the liver regeneration process. Similarly, from the above discussion, the direction is highlighted to emphasize the proposed molecular Wnt/β-catenin signaling pathway which is associated with GSK-3 β inhibition for the induction of the repairing and regeneration process.

Integrative genomic and transcriptomic analysis reveals prognostic markers and immune subtype in Chinese ovarian clear cell carcinoma.

e17529 Background: Ovarian clear cell carcinoma (OCCC) is a subtype of ovarian cancer characterized by chemo-resistance and poor survival. Herein, we performed comprehensive genomic and transcriptomic profiling of OCCC tissues to identify prognostic markers and immune subtype in Chinese patients. Methods: A total of 61 patients were included, comprising 41 early-stage and 19 late-stage tumors. Tissue samples were collected before chemotherapy and subjected to capture-based targeted sequencing using a panel consisting of 520 cancer related genes and whole transcriptomic sequencing. Genetic alterations, tumor mutation burden (TMB), microsatellite instability (MSI), and gene expression were evaluated. Association analysis was performed to evaluate clinical and genetic factors with platinum-sensitivity and treatment effects. A nomogram was constructed to predict survival outcomes. Single sample Gene Set Enrichment analysis (ssGSEA) was performed with gene expression profile and immune gene sets. Results: Genetic alterations were mainly identified in ARID1A (49%), PIK3CA (48%), TP53 (18%), ATM (15%), SMARCA4 (13%) and PRKDC (13%). Co-occurrence of mutations in ARID1A with PIK3CA and PRKDC were observed (p &lt; 0.05). Meanwhile, no alterations were identified in BRCA1/2. Patients harboring ATM mutations tended to be platinum sensitive compared to those wildtype counterparts (p &lt; 0.05). In patients with stage IV OCCC, mutations of ARID1A, PIK3CA, SMARCA4 and the HRR pathway were also related to higher percentage of platinum-sensitivity, though significance was not achieved. Mutations of FGFR2, NOTCH1 and the BER pathway were more frequently identified in patients with stage II to IV than stage I (p &lt; 0.05). Patients harboring alterations at chromosome 8q covering genes such as PRKDC showed better overall survival (OS) (p &lt; 0.05). Both clinical factors and frequently mutated genes were used to construct a nomogram for progression-free survival (PFS) prediction. The clinical factors (stage, platinum response and residual disease) in combination with genetic mutations ( ATM and SMARCA4) showed better performance in predicting PFS than clinical factors alone (concordance index 0.85 vs. 0.74, p &lt; 0.01). Transcriptomic analysis with ssGSEA of immune pathway revealed an immune subtype with enrichment of PD-1 signaling. OCCC patients with this immune subtype showed poor PFS and OS. Integration of genomic and transcriptomic analysis showed that the immune subtype patients had higher mutation rate of PIK3CA. Conclusions: The mutational profiles of OCCC were varied in patients with different platinum response and tumor stages. An immune subtype of OCCC with poor survival and enrichment of PD-1 signaling was identified. Our study identified several potential prognostic markers of OCCC at genetic level and revealed an immune subtype for potential immunotherapy.

Plasmodium Ape1 is a multifunctional enzyme in mitochondrial base excision repair and is required for efficient transition from liver to blood stage infection

The malaria parasite has a single mitochondrion which carries multiple tandem repeats of its 6 kb genome encoding three proteins of the electron transport chain. There is little information about DNA repair mechanisms for mitochondrial genome maintenance in Plasmodium spp. Of the two AP-endonucleases of the BER pathway encoded in the parasite nuclear genome, the EndoIV homolog PfApn1 has been identified as a mitochondrial protein with restricted functions. We explored the targeting and biochemical properties of the ExoIII homolog PfApe1. PfApe1 localized in the mitochondrion and exhibited AP-site cleavage, 3′-5′ exonuclease, 3′-phosphatase, nucleotide incision repair (NIR) and RNA cleavage activities indicating a wider functional role than PfApn1. The parasite enzyme differed from human APE1 in possessing a large, disordered N-terminal extension. Molecular modelling revealed conservation of structural domains but variations in DNA-interacting residues and an insertion in the α-8 loop suggested differences with APE1. Unlike APE1, where AP-site cleavage and NIR activities could be mutually exclusive based on pH and Mg2+ ion concentration, PfApe1 was optimally active under similar conditions suggesting that it can function both as an AP-endonuclease in BER and directly cleave damaged bases in NIR under similar physiological conditions. To investigate the role of Ape1 in malaria life cycle, we disrupted the gene by double-cross-over homologous recombination. Ape1 knockout (KO) P. berghei parasites showed normal development of blood and mosquito stages. However, inoculation of mice with Ape1 KO salivary gland sporozoites revealed a reduced capacity to initiate blood stage infection. Ape1 KO parasites underwent normal liver stage development until merozoites egressed from hepatocytes. Our results indicated that the delay in pre-patent period was due to the inability of Ape1 KO merosomes to infect erythrocytes efficiently.

Impairment of Base Excision Repair in Dermal Fibroblasts Isolated From Nevoid Basal Cell Carcinoma Patients.

The nevoid basal cell carcinoma syndrome (NBCCS), also called Gorlin syndrome is an autosomal dominant disorder whose incidence is estimated at about 1 per 55,600–256,000 individuals. It is characterized by several developmental abnormalities and an increased predisposition to the development of basal cell carcinomas (BCCs). Cutaneous fibroblasts from Gorlin patients have been shown to exhibit an increased sensitivity to ionizing radiations. Mutations in the tumor suppressor gene PTCH1, which is part of the Sonic Hedgehog (SHH) signaling pathway, are responsible for these clinical manifestations. As several genetic mutations in the DNA repair genes are responsible of photo or radiosensitivity and high predisposition to cancers, we hypothesized that these effects in Gorlin syndrome might be due to a defect in the DNA damage response (DDR) and/or the DNA repair capacities. Therefore, the objective of this work was to investigate the sensitivity of skin fibroblasts from NBCCS patients to different DNA damaging agents and to determine the ability of these agents to modulate the DNA repair capacities. Gorlin fibroblasts showed high radiosensitivity and also less resistance to oxidative stress-inducing agents when compared to control fibroblasts obtained from healthy individuals. Gorlin fibroblasts harboring PTCH1 mutations were more sensitive to the exposure to ionizing radiation and to UVA. However, no difference in cell viability was shown after exposure to UVB or bleomycin. As BER is responsible for the repair of oxidative DNA damage, we decided to assess the BER pathway efficacy in Gorlin fibroblasts. Interestingly, a concomitant decrease of both BER gene expression and BER protein activity was observed in Gorlin fibroblasts when compared to control. Our results suggest that low levels of DNA repair within Gorlin cells may lead to an accumulation of oxidative DNA damage that could participate and partly explain the radiosensitivity and the BCC-prone phenotype in Gorlin syndrome.

Base excision repair and its implications to cancer therapy.

Base excision repair (BER) has evolved to preserve the integrity of DNA following cellular oxidative stress and in response to exogenous insults. The pathway is a coordinated, sequential process involving 30 proteins or more in which single strand breaks are generated as intermediates during the repair process. While deficiencies in BER activity can lead to high mutation rates and tumorigenesis, cancer cells often rely on increased BER activity to tolerate oxidative stress. Targeting BER has been an attractive strategy to overwhelm cancer cells with DNA damage, improve the efficacy of radiotherapy and/or chemotherapy, or form part of a lethal combination with a cancer specific mutation/loss of function. We provide an update on the progress of inhibitors to enzymes involved in BER, and some of the challenges faced with targeting the BER pathway.

Phase I study of TRC102 in combination with cisplatin and pemetrexed in patients with advanced solid tumors/Phase II study of TRC102 with pemetrexed in patients with mesothelioma refractory to pemetrexed and cisplatin or carboplatin.

9055 Background: Treatment options remain limited in malignant pleural mesothelioma refractory to pemetrexed +/- platinum. TRC102 (methoxyamine hydrochloride) is a novel biochemical inhibitor of the BER pathway. Available data support the hypothesis that TRC102 bound DNA is a substrate for topoisomerase II, which cleaves TRC102-bound DNA sites to produce strand breaks in cancer cells that cause cellular apoptosis and enhance the cytotoxic effects of chemotherapy. Methods: This was a parallel cohort trial of a Phase I of TRC102 in combination with cisplatin (CDDP) and pemetrexed in patients with advanced solid tumors (Arm A) and a Phase II of TRC102 with pemetrexed in patients with mesothelioma refractory to platinum and pemetrexed (Arm B). Results: In Arm A dose escalation, 16 pts (11M/5F) were treated; 9 evaluable through 3 TRC102 dose levels (50, 75, and 100 mg/day, PO), with CDDP 60 mg/m2 and pemetrexed 500 mg/m2 (levels 1- 3); and 5 evaluable at TRC102 100 mg/day PO, CDDP 75 mg/m2, pemetrexed 500 mg/m2 (level 4). Cycles were every 21 days. There were no DLT’s, establishing level 4 as the RP2D. The only grade 4 treatment-related AE was thrombocytopenia on cycle 22 (level 2). Cycle 1 grade 3 AEs were 1 hypophosphatemia (level 1) and 1 leukopenia (level 2). There were 3 PRs (all parotid salivary gland tumors). Median PFS (95%CI) = 7.1% (1.4 – 15.5) mos. Arm B was designed as the first stage of a two stage Gehan design trial of patients with mesothelioma who had progressed on or recurred within 6 months of pemetrexed + platinum frontline treatment. 14 pts were treated with TRC102 50 mg/day D1-4 and pemetrexed 500 mg/m2 every 21 days. There were 2 PRs (both in epithelioid cancer of which 1 was confirmed), meeting the pre-specified criteria for continued interest ( &gt; 0/14). mPFS (95% CI) was 4.3 (1.4 - 6.8) mos. 8 pts had stable disease for at least 1 cycle (4 stable at cycles 6, 9, 10 and 12). There were 1 grade 4 neutropenia and 5 grade 3 AE’s (1 each – anemia, neutropenia, leukopenia, fatigue, hyponatremia). Conclusions: TRC102 in combination with CDDP and pemetrexed exhibited antitumor activity, particularly in salivary gland tumors, and a tolerable safety profile at the doses tested. The combination of TRC102 and pemetrexed demonstrated activity in malignant mesothelioma that progressed on prior pemetrexed. Additional studies are warranted to confirm preliminary signals of activity. Clinical trial information: NCT02535312.

MP82-04 THE COPY NUMBER VARIATION SIGNATURES IN UPPER TRACT UROTHELIAL CARCINOMA DEFINE DISTINCT SUBTYPES WITH PROGNOSTIC RELEVANCE

You have accessJournal of UrologyBladder Cancer: Upper Tract Transitional Cell Carcinoma II (MP82)1 Apr 2020MP82-04 THE COPY NUMBER VARIATION SIGNATURES IN UPPER TRACT UROTHELIAL CARCINOMA DEFINE DISTINCT SUBTYPES WITH PROGNOSTIC RELEVANCE Bao Guan, Huan Lu, Yuan Liang, Yanqing Gong, Shiming He, Qun He, Xuesong Li, Liqun Zhou*, and Weimin Ci Bao GuanBao Guan More articles by this author , Huan LuHuan Lu More articles by this author , Yuan LiangYuan Liang More articles by this author , Yanqing GongYanqing Gong More articles by this author , Shiming HeShiming He More articles by this author , Qun HeQun He More articles by this author , Xuesong LiXuesong Li More articles by this author , Liqun Zhou*Liqun Zhou* More articles by this author , and Weimin CiWeimin Ci More articles by this author View All Author Informationhttps://doi.org/10.1097/JU.0000000000000974.04AboutPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail Abstract INTRODUCTION AND OBJECTIVE: To conduct an integrated analysis of copy-number signatures and identify its prognostic value in Upper tract urothelial carcinoma (UTUC). METHODS: We performed WGS in 90 UTUC primary tumor samples, and the preoperative urine cell-free DNA from 94 patients with urothelial carcinoma (26 UTUCs; 68 bladder cancers) were analyzed by shallow whole genome sequencing(WGS). Non-negative matrix factorization (NMF) was applied to resolve CNV signatures. Next we halved this cohort in terms of the median signature contribution, and outcomes of this classification were analyzed. An independent cohort from The Cancer Genome Atlas (TCGA) bladder cancer was also bisected around the median correlation between tumor CNV component and a CNV signature component, then the outcomes analysis were conducted. Association with survival was evaluated using Kaplan-Meier and multivariable Cox regression methods. All statistical tests were two-sided. RESULTS: This 90 UTUC cohort defined Six copy number signatures (Signature1-6). Cohort patients was classified to six groups (Sig1-6) according to copy number signature’s maximum contribution. Signature6 was correlated with SNV signature 3 and 11. Besides, mutational frequency of Sig6 in BER, NER and HR pathway is much higher than the other groups. Kaplan-Meier curves showed that Sig6 has a favorable outcome. Based on the ratio of CNV in genome and contribution of signature 6 in 90 UTUC patients, this cohort can be classified into three subgroups: 1) wGIIlow, which did not exhibit a dominant copy number variation whose wGII were less than 0.1, showed significantly higher number of age-related mutational signature 1 and was associated with positive lymph node, lower percentage of CD3+ lymphocyte and stromal TIMC; 2) sig6low, which possessed lower proportion of signature 6, is significantly relavant with Sessile tumor architecture; and 3) sig6high subgroup, which exhibited higher proportion of signature 6, showed higher ratio of microsatellite instability sites. Kaplan-Meier plots revealed that the sig6high subgroup exhibited favourable outcomes compared with the sig6low and wGII-low subgroup. In muscle-invasive UTUC patients, the sig6high subgroup also exhibited best outcomes, the wGIIlow subgroup shown the worst outcomes. In multivariate Cox regression proportional analyses adjusted for the effects of clinicopathologic variables, the contribution of sig6 were still an independent prognostic factor for CSS and MFS. we verified the predictive value of signature 6 in the TCGA bladder cohort, the sig6high group in the TCGA UCB cohort also show better overall survival and metastasis-free survival. CONCLUSIONS: A novel CNV signature maybe be a promising predictive biomarker for UTUC patients in future prospective clinical trials. Source of Funding: We thank Gengyan Xiong and Lei Zhang for scientific inputs about the manuscript as well as Han Hao, Qin Tang and Xiaoteng Yu for assistance with clinicopathological characterizations. This work was supported by CAS Strategic Priority Research Program (XDA16010102 to W.C.), the National Key R&D Program of China (2018YFC2000100 to W.C.), CAS (QYZDB-SSW-SMC039 to W.C.), the National Natural Science Foundation of China (7152146 to X.L., 81672541 to W.C. and 81672546 to L.Z.), K.C. Wong Education Foundation to W.C., the Clinical Features Research of Capital (Z151100004015173 to L.Z.), the Capital Health Research and Development of Special (2016-1-4077 to L.Z.). © 2020 by American Urological Association Education and Research, Inc.FiguresReferencesRelatedDetails Volume 203Issue Supplement 4April 2020Page: e1246-e1247 Advertisement Copyright & Permissions© 2020 by American Urological Association Education and Research, Inc.MetricsAuthor Information Bao Guan More articles by this author Huan Lu More articles by this author Yuan Liang More articles by this author Yanqing Gong More articles by this author Shiming He More articles by this author Qun He More articles by this author Xuesong Li More articles by this author Liqun Zhou* More articles by this author Weimin Ci More articles by this author Expand All Advertisement PDF downloadLoading ...

Expression deregulation of DNA repair pathway genes in gastric cancer

This study was designed to check correlation of mRNA and protein expression of BER pathway genes(XRCC1, OGG1) and a proliferation marker (Ki-67) in 100 gastric tissue samples and controls (adjacent uninvolved area). The expression was estimated usingreal time PCR and immunohistochemistry. Genomic instability was also calculated in the same study cohort using 8-OHdG assay, DNA fragmentation assay and comet assay. A significant downregulation of XRCC1 (p < 0.0001) and OGG1 (p < 0.0001) expression was observed in gastric cancer tumors vs controls. When analyzed with spearman correlation, significant positive correlation was observed between OGG1 vs XRCC1 (r = 0.319*, p < 0.02) and significant negative correlation was observed between OGG1 vs Ki-67 (r = −0.462**, p < 0.001) and XRCC1 vs Ki-67 (r = −0.589**, p < 0.001) in gastric cancer tumors. Significantly higher level of 8-OHdG, when compared to controls, was observed in gastric cancer tumors (p < 0.0001). DNA fragmentation assay and comet assay showed the formation of increased ladder patterns and comets in gastric cancer tumors when compared with controls These findings suggest that dysregulation of XRCC1, OGG1 combined with overexpression of Ki-67 may contribute to progression of gastric cancer and may help to sub-classify patients within diverse risk groups for therapeutic advantages.