Homologous Recombination Repair Research Articles

Homologous Recombination Repair Gene Mutations in Prostate Cancer: Prevalence and Clinical Value.

Despite advances in our understanding of the molecular landscape of prostate cancer and the development of novel biomarker-driven therapies, the prognosis of patients with metastatic prostate cancer that is resistant to conventional hormonal therapy remains poor. Data suggest that a significant proportion of patients with metastatic castration-resistant prostate cancer (mCRPC) have mutations in homologous recombination repair (HRR) genes and may benefit from poly(ADP-ribose) polymerase (PARP) inhibitors. However, the adoption of HRR gene mutation testing in prostate cancer remains low, meaning there is a missed opportunity to identify patients who may benefit from targeted therapy with PARP inhibition, with or without novel hormonal agents. Here, we review the current knowledge regarding the clinical significance of HRR gene mutations in prostate cancer and discuss the efficacy of PARP inhibition in patients with mCRPC. This comprehensive overview aims to increase the clinical implementation of HRR gene mutation testing and inform future efforts in personalized treatment of prostate cancer.

CK2-HTATSF1-TOPBP1 signaling axis modulates tumor chemotherapy response.

Homologous recombination (HR) plays a key role in maintaining genomic stability, and the efficiency of the HR system is closely associated with tumor response to chemotherapy. Our previous work reported that CK2 kinase phosphorylates HTATSF1 Ser748 (pS748) to facilitate HTATSF1 interaction with TOPBP1, which in turn, promotes RAD51 recruitment and HR repair. However, the clinical implication of the CK2-HTATSF1-TOPBP1 pathway in tumorigenesis and chemotherapeutic response remains to be elucidated. Here, we report that the CK2-HTATSF1-TOPBP1 axis is generally hyperactivated in multiple malignancies and renders breast tumors less responsive to chemotherapy. In contrast, deletion mutations of each gene in this axis, which also occur in breast and lung tumor samples, predict higher HR deficiency (HRD) scores, and tumor cells bearing a loss-of-function mutation of HTATSF1 are vulnerable to PARP inhibitors (PARPis) or platinum drugs. Taken together, our study suggests that the integrity of the CK2-HTATSF1-TOPBP1 axis is closely linked to tumorigenesis, and serves as an indicator of tumor HR status and modulates chemotherapy response.

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.

Genome editing outcomes reveal mycobacterial NucS participates in a short-patch repair of DNA mismatches.

In the canonical DNA mismatch repair (MMR) mechanism in bacteria, if a nucleotide is incorrectly mis-paired with the template strand during replication, the resulting repair of this mis-pair can result in the degradation and re-synthesis of hundreds or thousands of nucleotides on the newly-replicated strand (long-patch repair). While mycobacteria, which include important pathogens such as Mycobacterium tuberculosis, lack the otherwise highly-conserved enzymes required for the canonical MMR reaction, it was found that disruption of a mycobacterial mismatch-sensitive endonuclease NucS results in a hyper-mutative phenotype, leading to the idea that NucS might be involved in a cryptic, independently-evolved DNA MMR mechanism, perhaps mediated by homologous recombination (HR) with a sister chromatid. Using oligonucleotide recombination, which allows us to introduce mismatches specifically into the genomes of a model for M. tuberculosis, Mycobacterium smegmatis, we find that NucS participates in a direct repair of DNA mismatches where the patch of excised nucleotides is largely confined to within ∼5-6 bp of the mis-paired nucleotides, which is inconsistent with mechanistic models of canonical mycobacterial HR or other double-strand break (DSB) repair reactions. The results presented provide evidence of a novel NucS-associated mycobacterial MMR mechanism occurring in vivo to regulate genetic mutations in mycobacteria.

Comparative effectiveness of first-line systemic treatments for metastatic castration-resistant prostate cancer: a systematic review and network meta-analysis.

No head-to-head trials had been performed to estimate the relative effectiveness of poly ADP-ribose polymerase inhibitor (PARPi) and androgen receptor signaling inhibitor (ARSi) in the first-line treatment for metastatic castration-resistant prostate cancer (mCRPC). We aimed to perform a systematic review and network meta-analysis to evaluate the comparative effectiveness of various systemic treatment agents for patients with mCRPC. A comprehensive literature search was conducted for abstracts and full-text articles from the database's inception through April 27, 2023. The study concentrated on assessing radiographic progression-free survival (rPFS) for both overall and homologous recombination repair mutation (HRRm) population, with overall survival (OS) as the secondary measure. Under the Bayesian framework, the overall effect was pooled using the fixed-effects model in base case analysis. Scenario analysis using restricted mean survival time (RMST) methods was performed to test the robustness of the results. Nine studies with 6,830 patients and 8 unique treatment options were included. Network meta-analysis demonstrated that talazoparib in combination with enzalutamide (TALA + ENZA; overall population, hazard ratio [HR], 0.20; 95% credible interval [CrI]: 0.16-0.26; RMST, 3.51; 95% confidence interval [CI] 2.46-4.60; HRRm population, HR, 0.15; 95% CrI: 0.09-0.23; RMST, 4.14; 95% CI 2.84-5.39) was superior to other treatments in the first-line setting in terms of rPFS. The results of Bayesian framework and RMST models showed consistent efficacy ranks. When extrapolated to overall survival benefit, within the Bayesian framework, olaparib plus abiraterone acetate and prednisone (OLAP + AAP) achieved the highest OS benefit for the overall population, which was not statistically significant when compared to TALA + ENZA. However, TALA + ENZA achieved the highest OS benefit at 3years by applying RMST. We suggest that talazoparib in combination with enzalutamide is probably a preferred treatment agent for the overall population and HRRm patients with mCRPC. Given the limitations of network framework and the modeling assumptions undertaken to finalize the analyses, results should be cautiously interpreted.

PARP inhibitor synthetic lethality in ATM biallelic mutant cancer cell lines is associated with BRCA1/2 and RAD51 downregulation

PARP inhibitor synthetic lethality in ATM biallelic mutant cancer cell lines is associated with BRCA1/2 and RAD51 downregulation

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.

Iron promotes ovarian cancer malignancy and advances platinum resistance by enhancing DNA repair via FTH1/FTL/POLQ/RAD51 axis

Iron is crucial for cell DNA synthesis and repair, but an excess of free iron can lead to oxidative stress and subsequent cell death. Although several studies suggest that cancer cells display characteristics of ‘Iron addiction’, an ongoing debate surrounds the question of whether iron can influence the malignant properties of ovarian cancer. In the current study, we initially found iron levels increase during spheroid formation. Furthermore, iron supplementation can promote cancer cell survival, cancer spheroid growth, and migration; vice versa, iron chelators inhibit this process. Notably, iron reduces the sensitivity of ovarian cancer cells to platinum as well. Mechanistically, iron downregulates DNA homologous recombination (HR) inhibitor polymerase theta (POLQ) and relieves its antagonism against the HR repair enzyme RAD51, thereby promoting DNA damage repair to resist chemotherapy-induced damage. Additionally, iron tightly regulated by ferritin (FTH1/FTL) which is indispensable for iron-triggered DNA repair. Finally, we discovered that iron chelators combined with platinum exhibit a synergistic inhibitory effect on ovarian cancer in vitro and in vivo. Our findings affirm the pro-cancer role of iron in ovarian cancer and reveal that iron advances platinum resistance by promoting DNA damage repair through FTH1/FTL/POLQ/RAD51 pathway. Our findings highlight the significance of iron depletion therapy, revealing a promising avenue for advancing ovarian cancer treatment.

Familial and hereditary pancreatic cancer in Japan.

As in Western countries, familial pancreatic cancer accounts for 5-7% of pancreatic cancer (PC) in Japan. Opportunities for diagnosing hereditary pancreatic cancer (HPC) are increasing owing to the coverage of companion diagnostics and cancer genomic profiling by national health insurance in patients with unresectable or recurrent PC refractory to standard chemotherapies. HPC is recognized in 7% of PCs and 15% of familial pancreatic cancer, including germline variants of BRCA1/2, ATM, PALB2, APC, and mismatch repair genes. Individuals with 5-fold or greater inherited risks of PC are recommended to undergo pancreatic surveillance according to Japanese guidelines. The imaging modalities for this surveillance include endoscopic ultrasound, magnetic resonance cholangiopancreatography, abdominal ultrasound, and enhanced computed tomography. Currently, a nationwide prospective surveillance study is ongoing in Japan. Platinum-based chemotherapy is an effective pancreatic cancer treatment in patients with variants of homologous recombination repair genes (BRCA1/2 and PALB2); however, the use of platinum regimens solely based on familial/personal cancer history remains controversial. The efficacy of olaparib maintenance therapy, as confirmed by the POLO study, has significantly impacted the clinical treatment of advanced PC patients in Japan. Since the initiation of precision cancer medicine in 2019, genetic medicine for PC patients has expanded in Japan.

Cutibacterium acnes invades prostate epithelial cells to induce BRCAness as a possible pathogen of prostate cancer

AbstractBackgroundAbundant evidence suggests that chronic inflammation is linked to prostate cancer and that infection is a possible cause of prostate cancer.MethodsTo identify microbiota or pathogens associated with prostate cancer, we investigated the transcriptomes of 20 human prostate cancer tissues. We performed de novo assembly of nonhuman sequences from RNA‐seq data.ResultsWe identified four bacteria as candidate microbiota in the prostate, including Moraxella osloensis, Uncultured chroococcidiopsis, Cutibacterium acnes, and Micrococcus luteus. Among these, C. acnes was detected in 19 of 20 prostate cancer tissue samples by immunohistochemistry. We then analyzed the gene expression profiles of prostate epithelial cells infected in vitro with C. acnes and found significant changes in homologous recombination (HR) and the Fanconi anemia pathway. Notably, electron microscopy demonstrated that C. acnes invaded prostate epithelial cells and localized in perinuclear vesicles, whereas analysis of γH2AX foci and HR assays demonstrated impaired HR repair. In particular, BRCA2 was significantly downregulated in C. acnes–infected cells.ConclusionsThese findings suggest that C. acnes infection in the prostate could lead to HR deficiency (BRCAness) which promotes DNA double‐strand breaks, thereby increasing the risk of cancer development.

RAD18 O-GlcNAcylation promotes translesion DNA synthesis and homologous recombination repair

RAD18, an important ubiquitin E3 ligase, plays a dual role in translesion DNA synthesis (TLS) and homologous recombination (HR) repair. However, whether and how the regulatory mechanism of O-linked N-acetylglucosamine (O-GlcNAc) modification governing RAD18 and its function during these processes remains unknown. Here, we report that human RAD18, can undergo O-GlcNAcylation at Ser130/Ser164/Thr468, which is important for optimal RAD18 accumulation at DNA damage sites. Mechanistically, abrogation of RAD18 O-GlcNAcylation limits CDC7-dependent RAD18 Ser434 phosphorylation, which in turn significantly reduces damage-induced PCNA monoubiquitination, impairs Polη focus formation and enhances UV sensitivity. Moreover, the ubiquitin and RAD51C binding ability of RAD18 at DNA double-strand breaks (DSBs) is O-GlcNAcylation-dependent. O-GlcNAcylated RAD18 promotes the binding of RAD51 to damaged DNA during HR and decreases CPT hypersensitivity. Our findings demonstrate a novel role of RAD18 O-GlcNAcylation in TLS and HR regulation, establishing a new rationale to improve chemotherapeutic treatment.

Modification Effects of Homologous Recombination Repair Gene Polymorphisms on the Associations Between Urinary Metals and Breast Cancer Risk.

Metals are recognized as important factors related to breast cancer (BC) risk. Homologous recombination repair (HRR) genes might modify the toxicity of metals by influencing the distribution and metabolism of metal compounds. This study aims to investigate the modification effects of single nucleotide polymorphisms (SNPs) in HRR genes on the associations between urinary metals and BC risk. A total of 685 BC cases and 741 controls were recruited from October 2009 to December 2012. Twenty-one metals were analyzed in urine samples using inductively coupled plasma mass spectrometry (ICP-MS), and three SNPs (LIG3 rs1052536, RFC1 rs6829064, and RAD54L rs17102086) were genotyped. We identified significant interactions between four metals and two SNPs on the risk of BC. For LIG3 rs1052536 C/T variant, participants with CT/TT genotypes exposed to higher cobalt (Co) levels had higher BC risk compared to those with CC genotype (Pinteraction = 0.048). For RAD54L rs17102086 T/C variant, participants with TT genotype who were exposed to higher levels of zinc (Zn), Co, arsenic (As), and strontium (Sr) had more pronounced BC risk than the CC/TC genotypes (all Pinteraction < 0.05). This study showed compelling evidence for the interaction between genetic variants within the HRR system and urinary metals on BC risk. Our findings highlight the need to consider genetic makeup when evaluating the carcinogenic or protective potential of metals.

The GATAD2B-NuRD complex drives DNA:RNA hybrid-dependent chromatin boundary formation upon DNA damage.

Double-strand breaks (DSBs) are the most lethal form of DNA damage. Transcriptional activity at DSBs, as well as transcriptional repression around DSBs, are both required for efficient DNA repair. The chromatin landscape defines and coordinates these two opposing events. However, how the open and condensed chromatin architecture is regulated remains unclear. Here, we show that the GATAD2B-NuRD complex associates with DSBs in a transcription- and DNA:RNA hybrid-dependent manner, to promote histone deacetylation and chromatin condensation. This activity establishes a spatio-temporal boundary between open and closed chromatin, which is necessary for the correct termination of DNA end resection. The lack of the GATAD2B-NuRD complex leads to chromatin hyperrelaxation and extended DNA end resection, resulting in homologous recombination (HR) repair failure. Our results suggest that the GATAD2B-NuRD complex is a key coordinator of the dynamic interplay between transcription and the chromatin landscape, underscoring its biological significance in the RNA-dependent DNA damage response.

HMGN1 loss sensitizes lung cancer cells to chemotherapy

The high mobility group nucleosome binding (HMGN) family, constitutes a large family of non-histone protein family known to bind the acidic patch of the nucleosomes with various key cellular functions. Several studies have highlighted the pivotal roles of HMGNs in the pathogenic process of various cancer types. However, the roles of HMGN family in lung adenocarcinoma (LUAD) have not been fully elucidated. Herein, integrative analyses of multiple-omics data revealed that HMGNs frequently exhibit dysregulation in LUAD. Subsequent analysis of the clinical relevance of HMGN1 demonstrated its association with poor prognosis in LUAD and its potential as a diagnostic marker to differentiate LUAD from healthy controls. Additionally, functional enrichment analysis suggested that HMGN1 was mainly involved in DNA repair. To corroborate these findings, cellular experiments were conducted, confirming HMGN1’s crucial involvement in homologous recombination repair and its potential to enhance the sensitivity of LUAD cells to standard chemotherapeutic drugs. This study proposes HMGN1 as a novel prognostic biomarker and a promising target for chemotherapy in lung adenocarcinoma.

Tenascin C as a novel zinc finger protein 750 target regulating the immunogenicity via DNA damage in lung squamous cell carcinoma

Modulation of DNA damage repair in lung squamous cell carcinoma (LUSC) can result in the generation of neoantigens and heightened immunogenicity. Therefore, understanding DNA damage repair mechanisms holds significant clinical relevance for identifying targets for immunotherapy and devising therapeutic strategies. Our research has unveiled that the tumor suppressor zinc finger protein 750 (ZNF750) in LUSC binds to the promoter region of tenascin C (TNC), leading to reduced TNC expression. This modulation may impact the malignant behavior of tumor cells and is associated with patient prognosis. Additionally, single-cell RNA sequencing (scRNA-seq) of LUSC tissues has demonstrated an inverse correlation between ZNF750/TNC expression levels and immunogenicity. Manipulation of the ZNF750-TNC axis in vitro within LUSC cells has shown differential sensitivity to CD8+ cells, underscoring its pivotal role in regulating cellular immunogenicity. Further transcriptome sequencing analysis, DNA damage repair assay, and single-strand break analyses have revealed the involvement of the ZNF750-TNC axis in determining the preference for homologous recombination (HR) repair or non-homologous end joining (NHEJ) repair of DNA damage. with involvement of the Hippo/ERK signaling pathway. In summary, this study sheds light on the ZNF750-TNC axis's role in DNA damage repair regulation in LUSC, laying a groundwork for future translational research in immune cell therapy for LUSC.

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 PO2-08-11: The MAGIC study: Universal whole genome tumour and germline sequencing of newly diagnosed breast cancer identifies a high proportion of ER+ BRCA-like tumours

Abstract Background: Identification of germline mutations in hereditary breast cancer (HBC) genes can have profound benefits in the treatment of breast cancer (BC) and manging risk for patient and the family. In addition, sequencing of the tumours can reveal clinically relevant somatic features, such as homologous recombination deficiency (HRD) and mutational signatures, that can guide treatment which are not discernible by germline sequencing alone. We hypothesised that current standard of care where women diagnosed with BC are not routinely offered tumour sequencing is suboptimal as fails to exploit all therapeutic vulnerabilities which can be exploited in the treatment of BC. The MAGIC study is the first prospective trial in Australia of unselected invasive BCs in general oncology practice combining both germline and tumour sequencing. Methods: The MAGIC study included a total of 651 consecutive consented patients presenting with non-metastatic BC between June 2020 to March 2023. It included invasive BC, high-grade DCIS and pleomorphic LCIS. The sequencing was conducted in two phases; for phase one, 157 cases underwent whole genome sequencing (WGS) on both germline and matched BC DNA while for phase two, 494 cases underwent only germline whole exome sequencing. Germline variants were interrogated for pathogenic variants in BRCA1, BRCA2, PALB2, ATM, CHEK2, BARD1, BRIP1, RAD51B, RAD51C, RAD51D, MLH1, MSH2, MSH6, PMS2, CDH1, PTEN, STK11, TP53 and NTHL1. Tumour homologous recombination (HR) repair deficiency was calculated using HRDetect (Nat Med 2017;23:517). For BCs showing a high HRDetect score ( &amp;gt;0.75) all HBC gene promoter CpG islands were assessed for hypermethylation using the Twist NGS Methylation system. Mutational signatures were calculated from somatic mutations identified from whole genome sequenced BCs using the DeconstructSig package in R (Genome Biol. 2016;17:31) and referenced against the COSMIC v2 signature catalogue. Results: Actionable germline variants in any HBC gene were identified in 7.7% of cases (7.8% of invasive and 6.1% of in situ BC) with 5.2% having an actionable mutation in an HR pathway gene (BRCA1, BRCA2, PALB2 and RAD51C). Most cases with pathogenic variants showed bi-allelic inactivation in the tumour. All BRCA1, BRCA2 and PALB2 tumours showed high HRDetect and/or HRD scores consistent with loss of HR repair function, indicating them to be the underlying hereditary driver of the BC. One BC with a pathogenic PMS2 variant showed retention of the wild-type allele with no evidence of a mismatch repair mutational signature suggesting PMS2 was not the driver of this BC. Of the 157 BC in phase one that underwent WGS and did not have a germline pathogenic HBC gene variant, 16% (18/117 invasive and 3/13 DCIS) had an HRDetect score of &amp;gt;0.7 indicative of a homologous recombination repair defect and therefore biologically a “BRCA-like” tumour. Of these 21 BRCA-like cases, only 3 invasive BCs had clear somatic bi-allelic inactivation of an HBC gene that could explain the high HRDetect score (2 BRCA1 and 1 BRCA2). One of the 21 BRCA-like cases had a germline variant of unknown significance (VUS) in an HBC gene (a BRCA2 missense variant in an ER+ tumour. The tumour showed loss of the wild-type allele). Of the BRCA-like cases, 71% were ER positive which included 3 invasive lobular cancers. Conclusion: Tumour sequencing identified three times as many cases that might be eligible for HR repair defect targeted therapy than germline testing alone (16% versus 5.2%). Unlike a previous study (Ann Oncol., 2019 30:1071-1079), the majority of the BRCA-like BCs were ER+ with no evidence of a VUS in a known HBC gene suggesting these are driven by novel germline or somatic mutations in genes involved in DNA HR repair. Citation Format: Ian Campbell, Lisa Devereux, Kirsten Hogg, Luxi Lal, Michelle Sinclair, Lesley Stafford, Magnus Zethoven, Anita Skandarajah, Paul James, Geoffrey Lindeman, Bruce Mann, Dilanka De Silva. The MAGIC study: Universal whole genome tumour and germline sequencing of newly diagnosed breast cancer identifies a high proportion of ER+ BRCA-like tumours [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PO2-08-11.

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 PO1-16-03: GDP-mannose enhances the efficacy of PARP inhibitors and immunotherapy in triple-negative breast cancer

Abstract Background: Triple-negative breast cancer (TNBC) patients with high HRD scores benefit from poly (ADP-ribose) polymerase (PARP) inhibitors, while those with low HRD scores still lack therapeutic options. Homologous recombination deficiency (HRD) induction is an effective strategy to broaden the indications of PARP inhibitors. Metabolic reprogramming is a critical feature of TNBC. In this study, we aimed to explore novel metabolic biomarkers for HRD and new strategy for sensitizing PARP inhibitors. Methods: We utilized TNBC metabolomics to systematically evaluate metabolites that were correlated with HRD. A crucial metabolite, GDP-mannose (GDP-M), that impedes homologous recombination repair (HR) and sensitizes PARP inhibitors was identified and functionally validated. We further explored the detailed mechanism and proposed a potential treatment strategy utilizing GDP-M for TNBC in preclinical models. Results: Systematic metabolomic analysis revealed that GDP-mannose (GDP-M) was significantly enriched in basal-like tumors with HRD. GDP-M promoted cisplatin-induced DNA double-strand breaks by inducing HRD. Mechanistically, the low expression of the upstream enzyme GMPPA led to the endogenous upregulation of GDP-M, which further promoted the ubiquitin-mediated degradation of BRCA2 to inhibit HR. GMPPA expression and GDP-M could serve as predictive biomarkers for HRD and the response to PARP inhibitors. Therapeutically, we validated that the combination of GDP-M and PARP inhibitors synergistically inhibit tumor growth in multiple preclinical models. Moreover, GDP-M supplementation plus PARP inhibition activated STING-dependent antitumor immunity and further augmented the efficacy of anti-PD-1 antibodies. Conclusions: GDP-M promotes the degradation of BRCA2 and thus enhances the sensitivity of PARP inhibitors in TNBC. The combination of GDP-M, PARP inhibitors and anti-PD-1 immunotherapy may be a potential treatment strategy for HRD-low TNBC. Citation Format: Yi Xiao, Jiahan Ding, Yi-Zhou Jiang, Zhi-Ming Shao, Genhong Di, Fan Yang, Xiaoqing Song. GDP-mannose enhances the efficacy of PARP inhibitors and immunotherapy in triple-negative 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 PO1-16-03.