Homologous Recombination Repair Pathway Research Articles

Mutation characteristics of cancer susceptibility genes in Chinese ovarian cancer patients

IntroductionThe association between mutations in susceptibility genes and the occurrence of ovarian cancer has been extensively studied. Previous research has primarily concentrated on genes involved in the homologous recombination repair pathway, particularly BRCA1 and BRCA2. However, a wider range of genes related to the DNA damage response pathways has not been fully explored.MethodsTo investigate the mutation characteristics of cancer susceptibility genes in the Chinese ovarian cancer population and the associations between gene mutations and clinical data, this study initially gathered a total of 1171 Chinese ovarian cancer samples and compiled a dataset of germline mutations in 171 genes.ResultsIn this study, it was determined that MC1R and PRKDC were high-frequency ovarian cancer susceptibility genes in the Chinese population, exhibiting notable distinctions from those in European and American populations; moreover high-frequency mutation genes, such as MC1R: c.359T>C and PRKDC: c.10681T>A, typically had high-frequency mutation sites. Furthermore, we identified c.8187G>T as a characteristic mutation of BRCA2 in the Chinese population, and the CHEK2 mutation was significantly associated with the early onset of ovarian cancer, while the CDH1 and FAM175A mutations were more prevalent in Northeast China. Additionally, Fanconi anemia pathway-related genes were significantly associated with ovarian carcinogenesis.ConclusionIn summary, this research provided fundamental data support for the optimization of ovarian cancer gene screening policies and the determination of treatment, and contributed to the precise intervention and management of patients.

Retraction Note: RAD54L promotes progression of hepatocellular carcinoma via the homologous recombination repair pathway.

Retraction Note: RAD54L promotes progression of hepatocellular carcinoma via the homologous recombination repair pathway.

Comprehensive Genomic Characterization in Ovarian Low-Grade and chemosensitive and chemoresistant High-Grade Serous Carcinomas.

Genomic characterization of serous ovarian carcinoma (SOC), which includes low-grade serous carcinoma (LGSC) and high-grade serous carcinoma (HGSC), remains necessary to improve efficacy of platinum-based chemotherapy. The aim was to investigate the genomic variations in these SOC groups, also in relation to chemoresponse. 45 samples SOC were retrospectively analyzed by Next Generation Sequencing (NGS) on DNA/RNA extracts from formalin-fixed, paraffin-embedded (FFPE) tumor samples obtained at diagnosis. HGSCs were classified as platinum-resistant and platinum-sensitive. In the LGSC group, 44% of the carcinomas had mutually exclusive variants in the RAS/RAF pathway, while additional likely oncogenic variants in the CDKN2A, SMARCA4 and YAP1 genes were observed in the remaining LGSCs. Tumor mutation burden (TMB) was significantly lower in the intrinsically chemoresistant LGSC group than in the HGSC group. In the HGSC cohort, TP53 variants were found in 90% and homologous recombination repair (HRR) pathway variants in 41% of the neoplasms. HGSCs of the chemoresistant group without classic mutations in the HRR pathway were characterized by additional variants in FGFR2 and with a FGFR3::TACC3 fusion. In addition, HGSCs showed MYC, CCNE1 and AKT2 gains that were almost exclusively observed in the chemosensitive HGSC group. These results suggest that very low TMB and MYC, CCNE1 and AKT2 gains in SOC patients may be biomarkers related to platinum treatment efficacy. Thorough genomic characterization of SOCs prior to treatment might lead to more specific platinum-based chemotherapy therapy strategies.

Expression of DNA Repair Genes in Ewing Sarcoma.

Ewing sarcoma is an aggressive mesenchymal malignancy commonly affecting children and young adolescents. The molecular basis of this neoplasia is well reported with the formation of the EWSR1/FLI1 fusion gene being the most common genetic finding. However, this fusion gene has not been targeted therapeutically nor is being used as a prognostic marker. Its relevance regarding the molecular steps leading to Ewing sarcoma genesis are yet to be defined. The generation of the oncogenic EWSR1/FLI1 fusion gene, can be attributed to the simultaneous introduction of two DNA double-strand breaks (DSBs). The scope of this study is to detect any association between DNA repair deficiency and the clinicopathological aspects of Ewing's sarcoma disease. We have conducted an expression analysis of 35 patients diagnosed with Ewing sarcoma concerning the genes involved in non-homologous end joining (NHEJ) and homologous recombination (HR) repair pathways. We have analyzed the expression levels of 6 genes involved in NHEJ (XRCC4, XRCC5, XRCC6, POLλ, POLμ) and 9 genes involved in HR (RAD51, RAD52, RAD54, BRCA1, BRCA2, FANCC, FANCD, DNTM1, BRIT1) using real time PCR. Age, sex, location of primary tumor, tumor size, KI67, mitotic count, invasion of adjacent tissues and treatment were the clinicopathological parameters included in the statistical analysis. Our results show that both these DNA repair pathways are deregulated in Ewing sarcoma. In addition, low expression of the xrcc4 gene has been associated with better overall survival probability (p=0.032). Our results, even though retrospective and in a small number of patients, highlight the importance of DSBs repair and propose a potential therapeutic target for this type of sarcoma.

Abstract PO3-08-09: Unique molecular signatures of germline mutations in low expression of human epidermal growth factor receptor 2 (HER2) breast cancer

Abstract Background: Overexpression of human epidermal growth factor receptor 2 (HER2) in breast cancer (BC) is associated with lower survival and higher risk of disease recurrence. A new subtype of HER2-low BC which has been proposed from several studies demonstrates that HER2-low patients have distinct somatically genetic alterations and clinical outcomes. We have previously reported that HER2-low BC had distinct clinical and somatic mutational feature compared with HER2-zero and HER2-high tumors. We have therefore extended studies by comparing germline mutation expression among these HER2 subgroups. Methods: 530 Chinese women with BC were enrolled in a prospective protocol between May 2021 to March 2023 at Guangdong Provincial People's Hospital. Genomics data was generated from a gene panel that surveys 102 tumor mutations. Germline variants were classified into pathogenic (P), likely pathogenic (LP), variant of uncertain significance (VUS), likely benign (LB) and benign (B) groups according to the ACMG/AMP Standards and Guidelines. The cohort was divided into three groups based on HER2 status as HER2-zero (n = 107), HER2-low (n = 259), and HER2-high (n = 127) according to immunohistochemistry and/or fluorescence in situ hybridization results. Results: The most common mutated genes were ATM, FANCD2, ATR, BRACA2, RECQL4 and APC. A total of 71 pathogenic or likely pathogenic (P/LP) mutations were identified in 25 cancer susceptibility genes from 64 patients (12.16%). The most frequent mutated P/LP genes are BRCA2, BRCA1, PALB2, PMS2, MUTYH and PTEN in the HER2-low group; BRCA2, BRCA1 and PALB2 in the HER2-zero cohort; Interestingly, among the nine HER2-high patients, we detected unique P/LP genes in each sample including MRE11, FANCM, ATM, FLCN, NTRK1, TP53, BRCA1, CHEKE2 and FANCA. In addition to P/LP mutations, 751 variants of uncertain significance (VUS) in 95 cancer susceptibility genes were also detected in 361 patients (68.11%). The most frequent mutated VUS mutations occurred genes are FANCD2, ATM, RECQL4, RAD54B and ATR in HER2-low group; ATM, FANCA, POLE, MSH2 and FANCD2 in HER2-zero cohort; and ATM, BRCA2, RECQL4, POLE, FANCI and FANCM for HER2-high patients. Most of mutated genes were homologous recombination repair (HRR) or DNA damage repair (DDR) pathway related genes. Several genes were differentially altered across HER2 subgroups, including the mutation frequency of the BMPR1A (p=0.0344), MSH2 (p=0.0103), and RAD51C (p=0.0336) genes that were significantly higher in HER2-zero group. It’s worth noting that RAD51C was only mutated in HER2-zero subgroup. BMPR1A and MSH2 were also mutated in HER2-low patients. Differentially mutated genes in specific HER2 subgroups may contribute to better research and choice of future therapeutic approaches. In 115 patients who received neoadjuvant therapy and 84 of them were evaluable for pathological response data, HER2-low patients had lower pathological complete response (pCR) rates than HER2-zero and HER2-high subgroups (p=0.0008). In particular, DDR pathway gene ERCC1 have significantly higher mutation frequency in pCR patients (p=0.0115). Conclusion: HER2-low BC patients have distinct germline mutational signatures and differential clinical outcomes under neoadjuvant systemic therapy. These results have provided additional evidence that HER2-low patients comprise a fourth subtype of BC that needs to be accounted for separately in terms of clinical treatment and outcome reporting. Keywords: breast cancer, germline mutations, human epidermal growth factor receptor 2 (HER2), HER2-low, targeted therapy, next-generation sequencing Table 1. List of most frequent mutated genes in HER2-zero, HER2-low and HER2-high groups Citation Format: Ning Liao, Weiqi Zhang, Liangqiu Liu, Wendy Wu, Siqi Wang, Li Cao, Jianguo Lai, Xueying Zhang, Airong Yang, Yulei Wang, Cheukfai Li, Guochun Zhang, Chongyang Ren, Lingzhu Wen. Unique molecular signatures of germline mutations in low expression of human epidermal growth factor receptor 2 (HER2) 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 PO3-08-09.

Abstract LB271: Synergistic anti-tumor efficacy in olaparib-sensitive and -resistant models via simultaneously inhibition of USP1 and PARP

Abstract SIM0501 is a potent, orally bioavailable, specific inhibitor for USP1. We have explored its combination with olaparib, an approved PARP inhibitor, in both in vitro cancer cell lines and in vivo tumor models. Specifically, SIM0501 showed synergistic effect with olaparib on cell lines across different cancer types, including breast, ovarian, and prostate cancers. Most of these cell lines contain mutations in the homologous recombinational repair (HRR) pathway, which is likely the reason for their susceptibility to the combined inhibition on USP1 and PARP. In the in vivo efficacy studies, SIM0501 dose-dependently inhibited tumor growth when combined with olaparib, including BRCA1-mutated MDA-MB-436, BRCA-wildtype olaparib-resistant OVCAR3, and olaparib-resistant ovarian PDX models. Further, in the MDA-MB-436 model, delayed addition of olaparib to SIM0501 showed comparable efficacy with simultaneous combination treatment, suggesting the flexibility in add-on dosing strategy. Regarding the biomarker research, dose-dependent increase of Ub-PCNA was demonstrated by western blot (WB) following in vivo efficacy studies. Moreover, we have developed robust IHC detection method for Ub-PCNA, which correlated well with WB results. Since Ub-PCNA is a direct target of USP1, these results will facilitate the clinical assessment of target engagement by SIM0501. In summary, SIM0501 demonstrates strong synergistic anti-tumor growth effect in combination with PARP inhibitors in both in vitro and in vivo pharmacology studies, which supports the clinical testing of SIM0501, in combination with PARP inhibitors in patients harboring HRR mutations. Citation Format: Shuqun Yang, Zhengtao Li, Lei Zhou, Feng Zhou, Xiaokang Qin, Liting Xue, Piaopiao Xu, Jianxing Tang, Wendy Wang, Renhong Tang. Synergistic anti-tumor efficacy in olaparib-sensitive and -resistant models via simultaneously inhibition of USP1 and PARP [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(7_Suppl):Abstract nr LB271.

Abstract 5606: The role of KMT2C in the homologous recombination repair in epithelial ovarian cancer

Abstract Background: Epithelial ovarian cancer (EOC) with homologous recombination (HR) deficiency is susceptible to PARP inhibitor therapy due to synthetic lethality. Identification of the patient population for PARP inhibitor therapy is imperative to reduce recurrence of EOC and improve the survival outcomes of patients. Current biomarkers for PARP inhibitor therapy consist of an array of genes involved in the HR repair pathway in EOC, including BRCA1, BRCA2 and PALB2. Through TCGA analysis, we found that the lysine (K)-specific methyltransferase 2C (KMT2C) gene is mutated in 10.3% of all EOC patients and considerably enriched in BRCA1 mutated EOC patients. However, the role of KMT2C in HR repair and PARP inhibitor sensitivity of EOC remains largely undefined. Methods: BRCA2-mutated PEO1 and BRCA2-wild type PEO1-NR cells were transfected with KMT2C siRNA and assayed for KMT2C protein expression by western blotting. DR-GFP (HR) and EJ5-GFP (NHEJ)-SKOV3 cell lines were co-transfected with the ISceI-expressing plasmid pCBA-ISceI and KMT2C siRNA. GFP-positive cells were analyzed by flow cytometry. SKOV3 cells were transfected with KMT2C siRNA and the expression of BRCA2 and Rad51 mRNA was determined using quantitative RT-PCR analysis. Results: siRNA-mediated knockdown of KMT2C resulted in marked down-regulation of KMT2C protein in PEO1 and PEO1-NR cells. KMT2C knockdown caused a significant decrease in ISceI-induced HR activity in DR-GFP-SKOV3 cells (p < 0.05). In contrast, KMT2C knockdown had no effects on ISceI-induced NHEJ activity in EJ5-GFP-SKOV3 cells. As a control, Rad51 knockdown caused complete suppression of HR activity and had no effects on NHEJ activity. Furthermore, quantitative RT-PCR analysis of key HR genes showed that KMT2C knockdown resulted in a moderate but significant down-regulation of BRCA2 (p < 0.05) and Rad51 (p < 0.01) expression in SKOV3 cells. Conclusion: Our results suggest that KMT2C partakes in the HR repair pathway in EOC. However, the contribution of KMT2C to HR activity is not rate-limiting. Based on the known function of KMT2C in histone modification, we speculate that KMT2C serves to positively regulate the transcription of HR genes and therefore promote HR activity. Future investigation into the exact roles of KMT2C in HR repair, etiology of EOC, and diagnostic biomarkers for the PARP inhibitor sensitivity of EOC is warranted. Citation Format: Mirielle C. Ma, Z. Ping Lin, Elena S. Ratner. The role of KMT2C in the homologous recombination repair in epithelial ovarian cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5606.

Abstract 567: Fisetin sensitizes triple negative breast cancer cells to radiation

Abstract Triple negative breast cancer (TNBC) represents a highly aggressive subtype, constituting approximately 20% of all breast cancer cases. Y-box binding protein-1 (YB-1) is often overexpressed in various tumor types and has been implicated in conferring resistance to cell death induced by radiotherapy. Fisetin, a flavonoid compound with demonstrated anti-cancer properties, operates in part through inhibiting phosphorylation of YB-1 by p90 ribosomal S6 kinase (RSK). In this study, we investigated the potential synergistic effects of combining fisetin with radiotherapy in TNBC. The activation status of the RSK signaling pathway was assessed in both total cell lysate and subcellular fractions using Western blotting. A standard clonogenic assay was employed to evaluate post-irradiation cell survival. To investigate the frequency of double-strand breaks (DSBs) and chromosomal aberrations, γH2AX foci assay and 3-color fluorescence in situ hybridization analyses were conducted, respectively. The DSB repair pathways targeted by fisetin were examined in cells expressing genomically integrated reporter constructs by quantifying green fluorescence protein expression through flow cytometry. Apoptosis and autophagy were measured using flow cytometric quantification of sub-G1 cells and the assessment of LC3-II protein expression, respectively. Kinase array and phosphoproteomics analyses were carried out to study the potential impact of fisetin on the signaling involved in the DNA damage response (DDR) after irradiation. We demonstrated that fisetin mimics the effects of RSK pharmacological inhibitors in terms of effect on YB-1 phosphorylation. Treatment with fisetin increased frequency of DSB in non-irradiated cells and impaired repair of DSB after irradiation. Fisetin attenuated DSB repair by suppressing the classical non-homologous end-joining and homologous recombination repair pathways. The frequency of chromosomal aberration was enhanced by fisetin treatment. The effect of fisetin on inhibiting DSB repair was partially YB-1 dependent. Phosphoproteomic analysis revealed that fisetin inhibits DDR signaling, which leads to radiosensitization in TNBC cells, as shown in combination with single dose or fractionated doses irradiation. Fisetin neither inhibited DSB repair nor radiosensitized normal human fibroblast HSF7 cells. The radiosensitizing effect of fisetin was not attributed to enhancing apoptosis or modulating autophagy. In summary, combining fisetin with radiotherapy may enhance TNBC radiotherapy outcomes. -This research was supported by a grant from the German Research Council (DFG,TO 685/2-3). Citation Format: Shayan Khozooei, Soundaram Veerappan, Mahmoud Toulany. Fisetin sensitizes triple negative breast cancer cells to radiation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 567.

Characteristics of germline DNA damage response gene mutations in ovarian cancer in Southwest China

DNA damage response (DDR) pathways are responsible for repairing endogenous or exogenous DNA damage to maintain the stability of the cellular genome, including homologous recombination repair (HRR) pathway, mismatch repair (MMR) pathway, etc. In ovarian cancer, current studies are focused on HRR genes, especially BRCA1/2, and the results show regional and population differences. To characterize germline mutations in DDR genes in ovarian cancer in Southwest China, 432 unselected ovarian cancer patients underwent multi-gene panel testing from October 2016 to October 2020. Overall, deleterious germline mutations in DDR genes were detected in 346 patients (80.1%), and in BRCA1/2 were detected in 126 patients (29.2%). The prevalence of deleterious germline mutations in BRCA2 is higher than in other studies (patients are mainly from Eastern China), and so is the mismatch repair genes. We identified three novel BRCA1/2 mutations, two of which probably deleterious (BRCA1 p.K1622* and BRCA2 p.L2987P). Furthermore, we pointed out that deleterious mutations of FNACD2 and RECQL4 are potential ovarian cancer susceptibility genes and may predispose carriers to ovarian cancer. In conclusion, our study highlights the necessity of comprehensive germline mutation detection of DNA damage response genes in ovarian cancer patients, which is conducive to patient management and genetic counseling.

Characterization of Incidental Pathogenic Germline Findings Detected via ctDNA among Patients with Non-Small Cell Lung Cancer in a Predominantly Hispanic/Latinx Population.

Pathogenic germline variants (PGVs) may be under-detected as causative etiologies in patients with non-small cell lung cancer (NSCLC). The prevalence of PGVs has been reported between 1 and 15% of patients, depending on the patient population. The rate within Hispanic/Latinx populations remains unknown. We retrospectively analyzed the genomic results (Guardant360, Redwood City, CA, USA) of 878 patients with advanced or metastatic NSCLC at five centers in South Florida, USA, from 2019 to 2022 to analyze the rate of incidental PGVs (iPGVs) identified via circulating cell-free tumor DNA (ctDNA). We then stratified the results by tumor histology, age, gender, race, ethnicity, genetic pathway, and co-mutations. Twenty-one iPGVs were identified (21/878 = 2.4%). Among the 21 iPGVs identified, 14 patients were female (66.7%) and 7 were male (33.3%), with a median age of 67 years and tobacco history of 2.5 pack-years. In total, 52.4% of patients identified as Hispanic/Latinx (n = 11) of any race; 19.0% as Ashkenazi Jewish (n = 4), 9.5% as non-Hispanic/Latinx black (n = 2), and 19.0% as non-Hispanic/Latinx white (n = 4). iPGVs in the homologous recombination repair pathway were solely expressed in this cohort (10 ATM, 8 BRCA2, and 3 BRCA1). In total, 76% (16/21) of patients with iPGVs co-expressed somatic alterations, with 56% (9/16) demonstrating alterations in targetable genes. Overall, our real-world findings offer a point prevalence of iPGVs in patients with NSCLC of diverse populations, such as patients who report Hispanic/Latinx ethnicity.

The effect of mesenchymal stem cells administration on DNA repair gene expressions in critically ill COVID-19 patients: prospective controlled study

When the studies are evaluated, immunomodulatory effect of MSCs, administration in critically ill patients, obstacle situations in use and side effects, pulmonary fibrosis prevention, which stem cells and their products, regeneration effect, administration route, and dosage are listed under the main heading like. The effect of MSC administration on DNA repair genes in COVID-19 infection is unknown. Our aim is to determine the effect of mesenchymal stem cells (MSCs) therapy applied in critically ill patients with coronavirus infection on DNA repair pathways and genes associated with those pathways. Patients (n = 30) divided into two equal groups. Group-1: Patients in a critically ill condition, Group-2: Patients in critically ill condition and transplanted MSCs. The mechanism was investigated in eleven genes of five different pathways; Base excision repair: PARP1, Nucleotide excision repair (NER): RAD23B and ERCC1, Homologous recombinational repair (HR): ATM, RAD51, RAD52 and WRN, Mismatch repair (MMR): MLH1, MSH2, and MSH6, Direct reversal repair pathway: MGMT. It was found that MSCs application had a significant effect on 6 genes located in 3 different DNA damage response pathways. These are NER pathway genes; RAD23 and ERCC1, HR pathway genes; ATM and RAD51, MMR pathway genes; MSH2 and MSH6 (p < 0.05). Two main points were shown. First, as a result of cellular damage in critical patients with COVID-19, DNA damage occurs and then DNA repair pathways and genes are activated in reaction to this situation. Second, administration of MSC to patients with COVID-19 infection plays a positive role by increasing the expression of DNA repair genes located in DNA damage pathways.

A Somatic BRCA2-Mutated Pancreatic Adenocarcinoma With Sustained Exceptional Response to Modified FOLFIRINOX.

Homologous recombination repair (HRR) pathway deficiency opens multiple therapeutic avenues within pancreatic cancer. Patients with HRR deficiency-associated gene mutations such as BRCA1, BRCA2, and PALB2 are more susceptible to platinum-based chemotherapies and in those with somatic BRCA mutations, PARP inhibitor therapy prolongs progression-free survival. The case discussed herein illustrates the therapeutic opportunities offered through the identification of HRR deficiency in pancreatic cancer, as well as the challenges associated with treatment and prevention of central nervous system metastases in long-term survivors of pancreatic cancer.

Germline Mutations of Holliday Junction Resolvase Genes in Multiple Primary Malignancies Involving Lung Cancer Lead to PARP Inhibitor Sensitization.

The incidence of multiple primary malignancies (MPM) involving lung cancer has increased in recent decades. There is an urgent need to clarify the genetic profile of such patients and explore more efficacious therapy for them. Peripheral blood samples from MPM involving patients with lung cancer were assessed by whole-exome sequencing (WES), and the identified variants were referenced for pathogenicity using the public available database. Pathway enrichment analysis of mutated genes was performed to identify the most relevant pathway. Next, the effects of mutations in relevant pathway on function and response to targeted drugs were verified by in vitro and in vivo experiments. Germline exomes of 71 patients diagnosed with MPM involving lung cancer were sequenced. Pathway enrichment analysis shows that the homologous recombination repair (HRR) pathway has the strongest correlation. Moreover, HRR genes, especially key Holliday junction resolvases (HJR) genes (GEN1, BLM, SXL4, and RMI1), were most frequently mutated, unlike the status in the samples from patients with lung cancer only. Next, we identified a total of seven mutations in HJR genes led to homologous recombination DNA repair deficiency and rendered lung cancer cells sensitive to PARP inhibitor treatment, both in vitro and in vivo. This is the first study to map the profile of germline mutations in patients with MPM involving lung cancer. This study may shed light on early prevention and novel targeted therapies for MPM involving patients with lung cancer with HJR mutations.

NUDT16 regulates CtIP PARylation to dictate homologous recombination repair.

CtIP initiates DNA end resection and mediates homologous recombination (HR) repair. However, the underlying mechanisms of CtIP regulation and how the control of its regulation affects DNA repair remain incompletely characterized. In this study, NUDT16 loss decreases CtIP protein levels and impairs CtIP recruitment to double-strand breaks (DSBs). Furthermore, overexpression of a catalytically inactive NUDT16 mutant is unable to rescue decreased CtIP protein and impaired CtIP recruitment to DSBs. In addition, we identified a novel posttranslational modification of CtIP by ADP-ribosylation that is targeted by a PAR-binding E3 ubiquitin ligase, RNF146, leading to CtIP ubiquitination and degradation. These data suggest that the hydrolase activity of NUDT16 plays a major role in controlling CtIP protein levels. Notably, ADP-ribosylation of CtIP is required for its interaction with NUDT16, its localization at DSBs, and for HR repair. Interestingly, NUDT16 can also be ADP-ribosylated. The ADP-ribosylated NUDT16 is critical for CtIP protein stability, CtIP recruitment to DSBs, and HR repair in response to DNA damage. In summary, we demonstrate that NUDT16 and its PARylation regulate CtIP stability and CtIP recruitment to DSBs, providing new insights into our understanding of the regulation of CtIP-mediated DNA end resection in the HR repair pathway.

Genomic Features of Homologous Recombination Deficiency in Breast Cancer: Impact on Testing and Immunotherapy.

Genomic instability is one of the well-established hallmarks of cancer. The homologous recombination repair (HRR) pathway plays a critical role in correcting the double-stranded breaks (DSB) due to DNA damage in human cells. Traditionally, the BRCA1/2 genes in the HRR pathway have been tested for their association with breast cancer. However, defects in the HRR pathway (HRD, also termed 'BRCAness'), which has up to 50 genes, have been shown to be involved in tumorigenesis and treatment susceptibility to poly-ADP ribose polymerase inhibitors (PARPis), platinum-based chemotherapy, and immune checkpoint inhibitors (ICIs). A reliable consensus on HRD scores is yet to be established. Emerging evidence suggests that only a subset of breast cancer patients benefit from ICI-based immunotherapy. Currently, albeit with limitations, the expression of programmed death-ligand 1 (PDL1) and tumor mutational burden (TMB) are utilized as biomarkers to predict the favorable outcomes of ICI therapy in breast cancer patients. Preclinical studies demonstrate an interplay between the HRR pathway and PDL1 expression. In this review, we outline the current understanding of the role of HRD in genomic instability leading to breast tumorigenesis and delineate outcomes from various clinical trials. Furthermore, we discuss potential strategies for combining HRD-targeted therapy with immunotherapy to achieve the best healthcare outcomes in breast cancer patients.

Histologic patterns in prostatic adenocarcinoma are not predictive of mutations in the homologous recombination repair pathway

Somatic or germline homologous recombination repair (HRR) pathway gene mutations are commonly detected in prostate cancer, especially in advanced disease, and are associated with response to poly (ADP-ribose) polymerase (PARP) inhibitors. In this study, we evaluated whether histological patterns are predictive of HRR pathway gene mutations. The study population comprised 130 patients with advanced prostate carcinoma who underwent comprehensive genomic profiling (CGP) of tumor tissue at a CLIA-certified laboratory. HRR genes in the study included BRCA1, BRCA2, ATM, BARD1, BRIP, CHEK2, MRE11A, NBN, PALB2, RAD51C, RAD51D, EMSY, ATR, CHEK1, and FAM175A. Overall, 38 patients had mutations in BRCA1/2, 36 in other HRR genes, and 56 were negative for HRR mutations. All cases were re-reviewed and quantified by two genitourinary pathologists blinded to mutational status for the following histological patterns of prostate carcinoma: cribriform, ductal, intraductal carcinoma (IDC), small cell carcinoma, signet ring-like pattern, and lobular carcinoma-like pattern. Discordances were resolved by consensus review. Histologic patterns were analyzed for any correlation with mutations in HRR pathway genes (grouped as BRCA1/2 mutated or non-BRCA1/2 mutated) compared to tumors without mutations in HRR genes by Chi-square testing. Patterns with >20 % and >30 % of tumor volume were additionally evaluated for correlation with mutational status. We found no significant association between HRR pathway mutations and cribriform pattern, IDC, ductal carcinoma, small cell carcinoma, signet ring-like pattern, or lobular carcinoma-like patterns. Tumors with >20 % or >30 % histologic patterns by volume also demonstrated no significant association with mutational status. This study suggests that histopathologic examination alone is insufficient to distinguish prostate cancer with germline or somatic mutations in HRR pathway genes, highlighting the continuing importance of ancillary molecular diagnostics in guiding therapy selection for prostate cancer patients who may benefit from PARP inhibitors.

PARP Inhibitors in Prostate Cancer – Understanding the Current Landscape

Poly (ADP [adenosine diphosphate]-ribose) polymerase inhibitors (PARPi) are a current standard of care treatment option for patients with metastatic castration resistant prostate cancer (mCRPC), defined as prostate cancers that continue to progress despite treatment with the usual first-line androgen-deprivation therapies. PARPi’s function by targeting faulty homologous recombination repair pathways that result in cytotoxic double strand DNA break (DSB) accumulation in prostate cancer cells. While the efficacy of PARPi’s as a monotherapy option in mCRCP has been demonstrated clinically, the added utility of PARPi’s in combination with other anti-cancer agents is still being explored. This article will review the scientific rationale behind PARP-inhibitors, discuss the germline and somatic mutation testing critical to identifying predictive biomarkers for PARPi efficacy, and present the currently approved PARPi combination therapies and their indications. This review will also examine the incidence and management of PARPi toxicity, summarize ongoing trials, and propose areas of future study.

TRIP13 Enhances Radioresistance of Lung Adenocarcinoma Cells through the Homologous Recombination Pathway

Radiation therapy is one of the most common treatments for non-small cell lung cancer (NSCLC). However, the insensitivity of some tumor cells to radiation is one of the major reasons for the poor efficacy of radiotherapy and the poor prognosis of patients, and exploring the underlying mechanisms behind radioresistance is the key to solving this clinical challenge. This study aimed to identify the molecules associated with radioresistance in lung adenocarcinoma (LUAD), identified thyroid hormone receptor interactor 13 (TRIP13) as the main target initially, and explored whether TRIP13 is related to radioresistance in LUAD and the specific mechanism, with the aim of providing theoretical basis and potential targets for the combination therapy of LUAD patients receiving radiotherapy in the clinic. Three datasets, GSE18842, GSE19188 and GSE33532, were selected from the Gene Expression Omnibus (GEO) database and screened for differentially expressed genes (|log FC|>1.5, P<0.05) in each of the three datasets using the R 4.1.3 software, and then Venn diagram was used to find out the differentially expressed genes common to the three datasets. The screened differential genes were then subjected to protein-protein interaction (PPI) analysis and module analysis with the help of STRING online tool and Cytoscape software, and survival prognosis analysis was performed for each gene with the help of Kaplan-Meier Plotter database, and the TRIP13 gene was identified as the main molecule for subsequent studies. Subsequently, the human LUAD cell line H292 was irradiated with multiple X-rays using a sub-lethal dose irradiation method to construct a radioresistant cell line, H292DR. The radioresistance of H292DR cells was verified using cell counting kit-8 (CCK-8) assay and clone formation assay. The expression levels of TRIP13 in H292 and H292DR cells were measured by Western blot. Small interfering RNA (siRNA) was used to silence the expression of TRIP13 in H292DR cells and Western blot assay was performed. The clone formation ability and migration ability of H292DR cells were observed after TRIP13 silencing, followed by the detection of changes in the expression levels of proteins closely related to homologous recombination, such as ataxia telangiectasia mutated (ATM) protein. Screening of multiple GEO datasets, validation of external datasets and survival analysis revealed that TRIP13 was highly expressed in LUAD and was associated with poor prognosis in LUAD patients who had received radiation therapy. And the results of gene set enrichment analysis (GSEA) of TRIP13 suggested that TRIP13 might be closely associated with LUAD radioresistance by promoting homologous recombination repair after radiation therapy. Experimentally, TRIP13 expression was found to be upregulated in H292DR, and silencing of TRIP13 was able to increase the sensitivity of H292DR cells to radiation. TRIP13 is associated with poor prognosis in LUAD patients treated with radiation, possibly by promoting a homologous recombination repair pathway to mediate resistance of LUAD cells to radiation.

Exploring DNA repair deficient CHO cell response to low dose rate radiation

IntroductionDNA double-strand breaks (DSBs) induced by ionizing radiation pose a significant threat to genome integrity, necessitating robust repair mechanisms. This study explores the responses of repair-deficient cells to low dose rate (LDR) radiation. Non-homologous end joining (NHEJ) and homologous recombination (HR) repair pathways play pivotal roles in maintaining genomic stability. The hypothesis posits distinct cellular outcomes under LDR exposure compared to acute radiation, impacting DNA repair mechanisms and cell survival. Materials and methodsChinese hamster ovary (CHO) cells, featuring deficiencies in NHEJ, HR, Fanconi Anemia, and PARP pathways, were systematically studied. Clonogenic assays for acute and LDR gamma-ray exposures, cell growth inhibition analyses, and γ-H2AX foci assays were conducted, encompassing varied dose rates to comprehensively assess cellular responses. ResultsNHEJ mutants exhibited an unexpected inverse dose rate effect, challenging conventional expectations. HR mutants displayed unique radiosensitivity patterns, aligning with responses to major DNA-damaging agents. LDR exposure induced cell cycle alterations, growth delays, and giant cell formation, revealing context-dependent sensitivities. γ-H2AX foci assays indicated DSB accumulation during LDR exposure. DiscussionThese findings challenge established paradigms, emphasizing the intricate interplay between repair pathways and dose rates. The study offers comprehensive insights into repair-deficient cell responses, urging a reevaluation of conventional dose-response models and providing potential avenues for targeted therapeutic strategies in diverse radiation scenarios.

Epigenetic reshaping through damage: promoting cell fate transition by BrdU and IdU incorporation

BackgroundThymidine analogs have long been recognized for their ability to randomly incorporate into DNA. However, the precise mechanisms through which thymidine analogs facilitate cell fate transition remains unclear.ResultsHere, we discovered a strong correlation between the dosage dependence of thymidine analogs and their ability to overcome reprogramming barrier. The extraembryonic endoderm (XEN) state seems to be a cell's selective response to DNA damage repair (DDR), offering a shortcut to overcome reprogramming barriers. Meanwhile, we found that homologous recombination repair (HRR) pathway causes an overall epigenetic reshaping of cells and enabling them to overcome greater barriers. This response leads to the creation of a hypomethylated environment, which facilitates the transition of cell fate in various reprogramming systems. We term this mechanism as Epigenetic Reshaping through Damage (ERD).ConclusionOverall, our study finds that BrdU/IdU can activate the DNA damage repair pathway (HRR), leading to increased histone acetylation and genome-wide DNA demethylation, regulating somatic cell reprogramming. This offers valuable insights into mechanisms underlying cell fate transition.Graphical