Recombinational Repair Of DNA Damage Research Articles

Tumour-intrinsic PDL1 signals regulate the Chk2 DNA damage response in cancer cells and mediate resistance to Chk1 inhibitors

BackgroundAside from the canonical role of PDL1 as a tumour surface-expressed immune checkpoint molecule, tumour-intrinsic PDL1 signals regulate non-canonical immunopathological pathways mediating treatment resistance whose significance, mechanisms, and therapeutic targeting remain incompletely understood. Recent reports implicate tumour-intrinsic PDL1 signals in the DNA damage response (DDR), including promoting homologous recombination DNA damage repair and mRNA stability of DDR proteins, but many mechanistic details remain undefined.MethodsWe genetically depleted PDL1 from transplantable mouse and human cancer cell lines to understand consequences of tumour-intrinsic PDL1 signals in the DNA damage response. We complemented this work with studies of primary human tumours and inducible mouse tumours. We developed novel approaches to show tumour-intrinsic PDL1 signals in specific subcellular locations. We pharmacologically depleted tumour PDL1 in vivo in mouse models with repurposed FDA-approved drugs for proof-of-concept clinical translation studies.ResultsWe show that tumour-intrinsic PDL1 promotes the checkpoint kinase-2 (Chk2)-mediated DNA damage response. Intracellular but not surface-expressed PDL1 controlled Chk2 protein content post-translationally and independently of PD1 by antagonising PIRH2 E3 ligase-mediated Chk2 polyubiquitination and protein degradation. Genetic tumour PDL1 depletion specifically reduced tumour Chk2 content but not ATM, ATR, or Chk1 DDR proteins, enhanced Chk1 inhibitor (Chk1i) synthetic lethality in vitro in diverse human and murine tumour models, and improved Chk1i efficacy in vivo. Pharmacologic tumour PDL1 depletion with cefepime or ceftazidime replicated genetic tumour PDL1 depletion by reducing tumour Chk2, inducing Chk1i synthetic lethality in a tumour PDL1-dependent manner, and reducing in vivo tumour growth when combined with Chk1i.ConclusionsOur data challenge the prevailing surface PDL1 paradigm, elucidate important and previously unappreciated roles for tumour-intrinsic PDL1 in regulating the ATM/Chk2 DNA damage response axis and E3 ligase-mediated protein degradation, suggest tumour PDL1 as a biomarker for Chk1i efficacy, and support the rapid clinical potential of pharmacologic tumour PDL1 depletion to treat selected cancers.

Management and Clinical Outcomes of Breast Cancer in Women Diagnosed with Hereditary Cancer Syndromes in a Clinic-Based Sample from Colombia.

This study aimed to investigate prognosis and survival differences in 82 breast cancer patients with germline pathogenic/likely pathogenic variants (PVs) treated and followed at the Breast Unit of the Instituto Nacional de Cancerología, Colombia (INC-C) between 2018 and 2021. Median age at diagnosis was 46 years, with 62.2% presenting locally advanced tumors, 47.6% histological grade 3, and 35.4% with triple-negative breast cancer (TNBC) subtype. Most carriers, 74.4% (61/82), had PVs in known breast cancer susceptibility genes (i.e., "associated gene carriers" group, considered inherited breast cancer cases): BRCA2 (30), BRCA1 (14), BARD1 (4), RAD51D (3), TP53 (2), PALB2 (2), ATM (2), CHEK2 (1), RAD51C (1), NF1 (1), and PTEN (1). BRCA1-2 represented 53.7%, and homologous recombination DNA damage repair (HR-DDR) genes associated with breast cancer risk accounted for 15.9%. Patients with PVs in non-breast-cancer risk genes were combined in a different category (21/82; 25.6%) (i.e., "non-associated gene carriers" group, considered other breast cancer cases). Median follow-up was 38.1 months, and 24% experienced recurrence, with 90% being distant. The 5-year Disease-Free Survival (DFS) for inherited breast cancer cases was 66.5%, and for other breast cancer cases it was 88.2%. In particular, for carriers of PVs in the BRCA2 gene, it was 37.6%. The 5-year Overall Survival (OS) rates ranged from 68.8% for those with PVs in BRCA2 to 100% for those with PVs in other HR-DDR genes. Further studies are crucial for understanding tumor behavior and therapy response differences among Colombian breast cancer patients with germline PVs.

Next generation sequencing reveals a high prevalence of pathogenic mutations in homologous recombination DNA damage repair genes among patients with uterine sarcoma

ObjectiveInvestigate the incidence of homologous recombination DNA damage response (HR-DDR) genomic alterations among patients with uterine sarcoma. MethodsThe American Association for Cancer Research GENIE v13.0 database was accessed and patients with uterine leiomyosarcoma, adenosarcoma, undifferentiated uterine sarcoma, high-grade endometrial stromal sarcoma, low-grade endometrial stromal sarcoma, and endometrial stromal sarcoma not otherwise specified were identified. We determined the incidence of pathogenic alterations in the following genes involved in HR-DDR: ATM, ARID1A, ATRX, BAP1, BARD1, BLM, BRCA2, BRCA1, BRIP1, CHEK2, CHEK1, FANCA, FANCC, FANCD2, FANCE, FANCF, FANCG, FANCL, MRE11, NBN, PALB2, RAD50, RAD51, RAD51B, RAD51C, RAD51D, WRN. Data from the OncoKB database, as provided by cBioPortal, was utilized to determine the presence of pathogenic genomic alterations. ResultsA total of 509 patients contributing with 525 samples were identified. Median patient age at sample collection was 56 years while the majority were White (80.7%). The most common histologic subtype was leiomyosarcoma (63.8%) followed by adenosarcoma (12.3%). The overall incidence of HR-DDR genomic alterations was 28.2%. The most commonly altered genes were ATRX (18.2%), BRCA2 (4%), and RAD51B (2.6%). The highest incidence of HR-DDR genomic alterations was observed among patients with leiomyosarcoma (35.4%), adenosarcoma (27%) and undifferentiated uterine sarcoma (30%), while those with low-grade endometrial stromal sarcoma had the lowest (2.9%) incidence. ConclusionsApproximately 1 in 3 patients with uterine sarcoma harbor a pathogenic alteration in HR-DDR genes. Incidence is high among patients with uterine leiomyosarcoma and adenosarcoma.

Stability of Rad51 recombinase and persistence of Rad51 DNA repair foci depends on post-translational modifiers, ubiquitin and SUMO

The DNA double-strand breaks are particularly deleterious, especially when an error-free repair pathway is unavailable, enforcing the error-prone recombination pathways to repair the lesion. Cells can resume the cell cycle but at the expense of decreased viability due to genome rearrangements. One of the major players involved in recombinational repair of DNA damage is Rad51 recombinase, a protein responsible for presynaptic complex formation. We previously showed that an increased level of this protein promotes the usage of illegitimate recombination. Here we show that the level of Rad51 is regulated via the ubiquitin-dependent proteolytic pathway. The ubiquitination of Rad51 depends on multiple E3 enzymes, including SUMO-targeted ubiquitin ligases. We also demonstrate that Rad51 can be modified by both ubiquitin and SUMO. Moreover, its modification with ubiquitin may lead to opposite effects: degradation dependent on Rad6, Rad18, Slx8, Dia2, and the anaphase-promoting complex, or stabilization dependent on Rsp5. We also show that post-translational modifications with SUMO and ubiquitin affect Rad51's ability to form and disassemble DNA repair foci, respectively, influencing cell cycle progression and cell viability in genotoxic stress conditions. Our data suggest the existence of a complex E3 ligases network that regulates Rad51 recombinase's turnover, its molecular activity, and access to DNA, limiting it to the proportions optimal for the actual cell cycle stage and growth conditions, e.g., stress. Dysregulation of this network would result in a drop in cell viability due to uncontrolled genome rearrangement in the yeast cells. In mammals would promote the development of genetic diseases and cancer.

Radiosensitivity and early onset cancer

The article is concerned with the radioprotection of a substantial radiosensitive population who present with cancer in early adulthood and will probably be treated with radiotherapy. A theory of radiation-induced health effects based on the induction of DNA double strand breaks is used to associate the radio-sensitivity of carriers of the BRCA1 and BRCA2 genes and the PALB2 gene with the defects in the homologous recombination repair of DNA damage found in the carriers. It is concluded that the defects in homologous recombination repair in these carriers will lead to an increased level of somatic mutations in all their cells and that this increased level of somatic mutations throughout their lifetime is, essentially, the reason that the carriers develop early onset cancer. This is a direct consequence of the more rapid accumulation of the cancer-inducing somatic mutations than the normal, slower accumulation in non-carriers. The radiotherapeutic treatment of these carriers needs to proceed with some care, taking account of their increased radio-sensitivity, and this suggests a need for international recognition and guidance of their radioprotection within the medical profession.

The spectrum of homologous recombination deficiency in cervical cancer: Is it also a cervical issue?

5543 Background: Tumors deficient in homologous recombination DNA damage repair (HR-DDR) demonstrate sensitivity to therapeutic agents targeting the HR-DDR pathway, such as poly-ADP ribose phosphate (PARP) inhibitors. The landscape of homologous recombination deficiency (HRD) is not well-characterized for cervical cancer; thus, we sought to analyze the prevalence of somatic pathogenic gene variants (PGVs) in HRD genes in cervical cancers. Methods: The American Association for Cancer Research’s (AACR) Project Genomics Evidence Neoplasia Information Exchange (GENIE) database version 13.0 was queried for all cervical cancer tumors via cBioPortal (http://genie.cbioportal.org). This is a publicly available, multi-institutional database of next-generation sequencing (NGS) genomic profiles of multiple tumors. PGV frequencies of 27 genes involved in HR-DDR were descriptively reported for cervical cancer tumors, with histologic stratification: ATM, ARID1A, ATRX, BRCA1, BRCA2, BARD1, BRIP1, BLM, BAP1, CHEK1, CHEK2, FANCA, FANCC, FANCD2, FANCE, FANCF, FANCG, FANCL, MRE11, NBN, PALB2, RAD50, RAD51, RAD51B, RAD51C, RAD51D, WRN. Results: A total of 857 cervical tumors from 817 patients were included for analysis. At least one somatic PGV in an HRD gene was found in 16.5% of all tumors (141/857). When stratified by histological subtypes with at least 25 tumors sequenced, highest frequencies of ≥1 PGV in HRD genes were observed in mucinous cervical cancer (13/66, 19.7%), cervical adenocarcinoma (48/262, 18.3%), squamous cell cervical cancer (53/349, 15.2%), adenosquamous cervical cancer (6/43, 14.0%) and neuroendocrine cervical cancers (5/42, 11.9%). Substantial rates of PGVs in HRD genes were also observed in histological subtypes with fewer than 25 sequenced tumors. Across all tumors, HRD genes with the highest frequencies of PGVs were ARID1A (9%), BAP1 (3%), ATM (1.6%) and BRCA1 (1.6%). Conclusions: NGS data demonstrate a substantial rate of somatic PGVs in HRD genes in cervical cancers, including among HPV related subtypes. These data suggest the need to expand routine functional HRD status assessment to cervical cancers in order to further characterize the landscape of HRD in these tumors. Furthermore, genetically driven clinical trials are warranted to evaluate the efficacy of HRD-targeted therapies such as PARP inhibitors, ataxia telangiectasia, and Rad-3 related kinase (ATR) inhibitors. [Table: see text]

Phase II clinical trial of olaparib plus pembrolizumab in the treatment of patients with advanced biliary tract cancer.

4087 Background: Over 20% of biliary tract cancers (BTCs) carry mutations in homologous recombination DNA damage repair (HR-DDR) pathways. The PARP inhibitor olaparib (O) blocks tumor DNA repair and may induce response in BTCs with such mutations. Furthermore, HR-DDR mutations may engender neoantigens that improve response to immune checkpoint inhibitors. We propose that treatment with O and the anti-PD-1 monoclonal antibody pembrolizumab (P) will produce a durable anti-tumor response to BTC, especially in patients with HR-DDR mutations. Methods: Consent for participation was obtained. Eligibility criteria included age > 18 years with an ECOG score of ≤1 and a histologic diagnosis of advanced or metastatic BTC with progression of disease (PD) on prior first-line therapy. Treatment featured oral O (300 mg twice daily) plus intravenous P (200 mg every 3 weeks). Response was measured radiographically using RECIST 1.1 guidelines. The primary endpoint was overall response rate (ORR), with the alternative hypothesis that O + P would improve ORR compared to historical controls (versus the null hypothesis of no improvement). Type I and II error rates were set at 5% and 15%, respectively. Simon’s optimal two-stage design was used. Planned sample size was 13 patients in the first stage. Continuation to the second stage would only occur if ≥3 patients demonstrated response. The second stage was planned to include 20 additional patients (N = 33 total), which was based on the number needed to demonstrate an improvement in ORR from 17.5% in historical controls to at least 35.0%. Results: Of 21 eligible patients, 14 were accrued between June 2020 and March 2022, and 13 were evaluable for efficacy. Patients had a median age of 63 years, were primarily female (71%), Caucasian (50%), and with metastatic disease (93%). Patients received a mean of 6.5 cycles of therapy. Best treatment response included partial response (N = 2), stable disease (N = 5), and PD (N = 6). The ORR was 15.3% (95% CI = 0.02-0.45). Of the partial responders, 1 patient achieved a duration of response of 8 months (mos), and 1 has ongoing response at 24 mos. Median (med) time to progression was 7.7 mos (95% CI = 1.2-9.3), med progression free survival was 5.5 mos (95% CI = 1.2-7.7), and med overall survival was 11.9 mos (95% CI = 5.5-15.4). Most patients (64%) developed at least one treatment-related adverse event (trAE). Grade 3 trAEs were experienced in 5 patients (36%) and included anemia (N = 3), diarrhea (N = 1), and transaminitis (N = 1). Conclusions: While O + P has acceptable safety and toxicity, the study did not achieve significant improvement in the primary endpoint. However, the two patients who demonstrated durable treatment response were found to have HR-DDR tumor mutations (including RAD51, ATM, and BRCA2), necessitating further research into the efficacy of O + P for patients with similar tumor genomes. Clinical trial information: NCT04306367 .

Implementation of multigene panel testing for breast and ovarian cancer in South Africa: A step towards excellence in oncology for the public sector.

Translation of genomic knowledge into public health benefits requires the implementation of evidence-based recommendations in clinical practice. In this study, we moved beyond BRCA1/2 susceptibility testing in breast and ovarian cancer patients to explore the application of pharmacogenetics across multiple genes participating in homologous recombination DNA damage repair. This involved the utilisation of next-generation sequencing (NGS) at the intersection of research and service delivery for development of a comprehensive genetic testing platform in South Africa. Lack of international consensus regarding risk categorization of established cancer susceptibility genes and the level of evidence required for prediction of drug response supported the development of a central database to facilitate clinical interpretation. Here we demonstrate the value of this approach using NGS to 1) determine the variant spectrum applicable to targeted therapy and implementation of prevention strategies using the 15-gene Oncomine™ BRCA Expanded Panel, and 2) searched for novel and known pathogenic variants in uninformative cases using whole exome sequencing (WES). Targeted NGS performed as a routine clinical service in 414 South African breast and/or ovarian cancer patients resulted in the detection of 48 actionable variants among 319 (15%) cases. BRCA1/2-associated cancers were identified in 70.8% of patients (34/48, including two double-heterozygotes), with the majority (35.3%, 12/34) representing known South African founder variants. Detection of actionable variants in established non-BRCA1/2 risk genes contributed 29% to the total percentage (14/48), distributed amongst ATM, CHEK2, BARD1, BRIP1, PALB2 and TP53. Experimental WES using a virtually constructed multi-cancer NGS panel in 16 genetically unresolved cases (and four controls) revealed novel protein truncating variants in the basal cell carcinoma gene PTCH1 (c.4187delG) and the signal transmission and transduction gene KIT (c.930delA) involved in crucial cellular processes. Based on these findings, the most cost-effective approach would be to perform BRCA1/2 founder variant testing at referral, followed by targeted multigene panel testing if clinically indicated and addition of WES in unresolved cases. This inventive step provides a constant flow of new knowledge into the diagnostic platform via a uniquely South African pathology-supported genetic approach implemented for the first time in this context to integrate research with service delivery.

Targeting RAD51-Mediated Homologous Recombination as a Treatment for Advanced Solid and Hematologic Malignancies: Opportunities and Challenges Ahead.

RAD51 is integral in homologous recombination DNA damage repair and has garnered much interest as both a biomarker and potential therapeutic target in oncology. Multiple in vitro and in vivo studies have demonstrated its role as a predictive marker, particularly in the context of platinum-based therapies and poly ADP-ribose polymerase (PARP) inhibitors. In this review, we highlight the development of RAD51 inhibitors, with a focus on novel molecules and ongoing clinical trials. Despite many efforts to develop effective and tolerable direct RAD51 inhibitors, identification of these agents remains challenging. Clinically, however, there may be a role of pharmacological indirect RAD51 inhibition.

Multidimensional Molecular Profiling of Metastatic Triple-Negative Breast Cancer and Immune Checkpoint Inhibitor Benefit.

In metastatic triple-negative breast cancer (mTNBC), consistent biomarkers of immune checkpoint inhibitor (ICI) therapy benefit remain elusive. We evaluated the immune, genomic, and transcriptomic landscape of mTNBC in patients treated with ICIs. We identified 29 patients with mTNBC treated with pembrolizumab or atezolizumab, either alone (n = 9) or in combination with chemotherapy (n = 14) or targeted therapy (n = 6), who had tumor tissue and/or blood available before ICI therapy for whole-exome sequencing. RNA sequencing and CIBERSORTx-inferred immune population analyses were performed (n = 20). Immune cell populations and programmed death-ligand 1 expression were assessed using multiplexed immunofluorescence (n = 18). Clonal trajectories were evaluated via serial tumor/circulating tumor DNA whole-exome sequencing (n = 4). Association of biomarkers with progression-free survival and overall survival (OS) was assessed. Progression-free survival and OS were longer in patients with high programmed death-ligand 1 expression and tumor mutational burden. Patients with longer survival also had a higher relative inferred fraction of CD8+ T cells, activated CD4+ memory T cells, M1 macrophages, and follicular helper T cells and enrichment of inflammatory gene expression pathways. A mutational signature of defective repair of DNA damage by homologous recombination was enriched in patients with both shorter OS and primary resistance. Exploratory analysis of clonal evolution among four patients treated with programmed cell death protein 1 blockade and a tyrosine kinase inhibitor suggested that clonal stability post-treatment was associated with short time to progression. This study identified potential biomarkers of response to ICIs among patients with mTNBC: high tumor mutational burden; presence of CD8+, CD4 memory T cells, follicular helper T cells, and M1 macrophages; and inflammatory gene expression pathways. Pretreatment deficiencies in the homologous recombination DNA damage repair pathway and the absence of or minimal clonal evolution post-treatment may be associated with worse outcomes.

Fibroblast growth factor signalling influences homologous recombination-mediated DNA damage repair to promote drug resistance in ovarian cancer

BackgroundOvarian cancer patients frequently develop chemotherapy resistance, limiting treatment options. We have previously shown that individuality in fibroblast growth factor 1 (FGF1) expression influences survival and chemotherapy response.MethodsWe used MTT assays to assess chemosensitivity to cisplatin and carboplatin following shRNA-mediated knockdown or heterologous over-expression of FGF1 (quantified by qRT-PCR and immunoblot analysis), and in combination with the FGFR inhibitors AZD4547 and SU5402, the ATM inhibitor KU55933 and DNA-PK inhibitor NU7026. Immunofluorescence microscopy was used to quantify the FGF1-dependent timecourse of replication protein A (RPA) and γH2AX foci formation.ResultsPharmacological inhibition of FGF signalling reversed drug resistance in immortalised cell lines and in primary cell lines from drug-resistant ovarian cancer patients, while FGF1 over-expression induced resistance. Ataxia telangiectasia mutated (ATM) phosphorylation, but not DNA adduct formation was FGF1 dependent, following cisplatin or carboplatin challenge. Combining platinum drugs with the ATM inhibitor KU55933, but not with the DNA-PK inhibitor NU7026 re-sensitised resistant cells. FGF1 expression influenced the timecourse of damage-induced RPA and γH2AX nuclear foci formation.ConclusionDrug resistance arises from FGF1-mediated differential activation of high-fidelity homologous recombination DNA damage repair. FGFR and ATM inhibitors reverse platinum drug resistance, highlighting novel combination chemotherapy approaches for future clinical trial evaluation.

Colon Tumors in Enterotoxigenic Bacteroides fragilis (ETBF)-Colonized Mice Do Not Display a Unique Mutational Signature but Instead Possess Host-Dependent Alterations in the APC Gene.

ABSTRACTEnterotoxigenic Bacteroides fragilis (ETBF) is consistently found at higher frequency in individuals with sporadic and hereditary colorectal cancer (CRC) and induces tumorigenesis in several mouse models of CRC. However, whether specific mutations induced by ETBF lead to colon tumor formation has not been investigated. To determine if ETBF-induced mutations impact the Apc gene, and other tumor suppressors or proto-oncogenes, we performed whole-exome sequencing and whole-genome sequencing on tumors isolated after ETBF and sham colonization of Apcmin/+ and Apcmin/+Msh2fl/flVC mice, as well as whole-genome sequencing of organoids cocultured with ETBF. Our results indicate that ETBF-induced tumor formation results from loss of heterozygosity (LOH) of Apc, unless the mismatch repair system is disrupted, in which case, tumor formation results from new acquisition of protein-truncating mutations in Apc. In contrast to polyketide synthase-positive Escherichia coli (pks+ E. coli), ETBF does not produce a unique mutational signature; instead, ETBF-induced tumors arise from errors in DNA mismatch repair and homologous recombination DNA damage repair, established pathways of tumor formation in the colon, and the same genetic mechanism accounting for sham tumors in these mouse models. Our analysis informs how this procarcinogenic bacterium may promote tumor formation in individuals with inherited predispositions to CRC, such as Lynch syndrome or familial adenomatous polyposis (FAP).IMPORTANCE Many studies have shown that microbiome composition in both the mucosa and the stool differs in individuals with sporadic and hereditary colorectal cancer (CRC). Both human and mouse models have established a strong association between particular microbes and colon tumor induction. However, the genetic mechanisms underlying putative microbe-induced colon tumor formation are not well established. In this paper, we applied whole-exome sequencing and whole-genome sequencing to investigate the impact of ETBF-induced genetic changes on tumor formation. Additionally, we performed whole-genome sequencing of human colon organoids exposed to ETBF to validate the mutational patterns seen in our mouse models and begin to understand their relevance in human colon epithelial cells. The results of this study highlight the importance of ETBF colonization in the development of sporadic CRC and in individuals with hereditary tumor conditions, such as Lynch syndrome and familial adenomatous polyposis (FAP).

The Additional Diagnostic Benefit of Pancreatic Cancer Molecular Profiling After Germline Testing.

Germline genetic testing is universally recommended for patients with pancreatic cancer to guide therapeutic selection, but tumor molecular profiling (TMP) is not. We aimed to determine the real-world additional diagnostic benefit of TMP after germline testing for detecting therapeutically actionable alterations. Medical records and genetic test reports were reviewed for all patients who underwent germline testing and TMP at the University of California San Francisco during January 2016-January 2020. The detection rate of actionable alterations with germline testing alone was compared to that with both germline testing and TMP. Among 738 eligible patients, 144 (20%) met study criteria. Germline testing detected 10 actionable alterations in 10 patients. Tumor molecular profiling identified 3 new therapeutic targets among these 10 patients and 45 targets in 41 additional patients, increasing the number of patients with actionable findings from 10 (7%) to 51 (35%). Most actionable alterations (35/58, 60%) involved genes associated with the Homologous Recombination DNA Damage Repair pathway. Tumor molecular profiling after germline testing increased the detection of actionable alterations by 5-fold. Tumor molecular profiling is a necessary complement to germline genetic testing to fully inform therapeutic decision making for all patients with pancreatic cancer.

Prevalence of Germline Sequence Variations Among Patients With Pancreatic Cancer in China

A higher incidence of pancreatic cancer has been reported in the Chinese population compared with the White population, but genetic differences are unknown to date. Large-sample germline testing for both familial and sporadic pancreatic cancers has been conducted predominantly in White populations, whereas similar studies in Chinese populations are limited. To assess the prevalence of germline sequence variations in patients with pancreatic diseases in China. This genetic association study was a case series that included genetic data from patients with pancreatic ductal adenocarcinoma (PDAC) or non-PDAC pancreatic diseases seen at The First Affiliated Hospital of Nanjing Medical University in Nanjing, China, between January 2006 and December 2017 (Nanjing cohort). Comparator group data were obtained for a US cohort from Johns Hopkins Hospital (JHH), a population from East Asia from the Exome Aggregation Consortium (ExAC) database, and the larger population from China from the ChinaMAP database. Data were updated and analyzed in July 2021. Next-generation sequencing technology was used to examine the prevalence of deleterious variations in 59 genes of the included Chinese patients with DNA extracted from peripheral blood samples. The Fisher exact test was used to assess differences among the frequencies of germline variations in the study patients vs the comparator groups. A total of 1009 patients with PDAC (627 [62.1%] male; mean [SD] age, 62.8 [10.2] years) and 885 with non-PDAC diseases (477 [53.9%] male; mean [SD] age, 52.0 [15.9] years) from the Nanjing cohort were included for genetic analysis; all were Han Chinese individuals. Pathogenic variations were detected in 63 patients with PDAC (6.2%; 95% CI, 4.7%-7.7%). Variations in BRCA2 (odds ratio [OR], 3.2; 95% CI, 1.4-7.7; P = .008) and PALB2 (OR, 5.2; 95% CI, 1.6-17.0; P = .007) were significantly associated with pancreatic risk in the Nanjing cohort. Pathogenic variants of genes associated with homologous recombination DNA damage repair, including ATM, BRCA1/2, PALB2, BRIP1, FANCA, FANCC, RAD51D, and XRCC2, were found in 34 patients with PDAC (3.4%). No Ashkenazi Jewish-specific BRCA2 variation (p.Ser1982fs) was detected. The odds ratio of a SPINK1 variation in patients with PDAC was 3.2 (95% CI, 1.8-5.7; P < .001) in the Nanjing cohort compared with the ExAC cohort. Variations in the pancreatic secretory enzyme genes CPA1 and CPB1 were not detected in the Nanjing cohort. In this genetic association study, sporadic pancreatic cancer was associated with pathogenic germline variations in a cohort from China. These findings provide insights into the genetic background of pancreatic cancer in the Han Chinese population with PDAC.

IKZF1 selectively enhances homologous recombination repair by interacting with CtIP and USP7 in multiple myeloma.

Rationale: In multiple myeloma (MM), the activities of non-homologous end joining (NHEJ) and homologous recombination repair (HR) are increased compared with healthy controls. Whether and how IKZF1 as an enhancer of MM participates in the DNA repair pathway of tumor cells remains elusive.Methods: We used an endonuclease AsiSI-based system and quantitative chromatin immunoprecipitation assay (qChIP) analysis to test whether IKZF1 is involved in DNA repair. Immunopurification and mass spectrometric (MS) analysis were performed in MM1.S cells to elucidate the molecular mechanism that IKZF1 promotes DNA damage repair. The combination effect of lenalidomide or USP7 inhibitor with PARP inhibitor on cell proliferation was evaluated using MM cells in vitro and in vivo.Results: We demonstrate that IKZF1 specifically promotes homologous recombination DNA damage repair in MM cells, which is regulated by its interaction with CtIP and USP7. In this process, USP7 could regulate the stability of IKZF1 through its deubiquitinating activity. The N-terminal zinc finger domains of IKZF1 and the ubiquitin-like domain of USP7 are necessary for their interaction. Furthermore, targeted inhibition IKZF1 or USP7 could sensitize MM cells to PARP inhibitor treatment in vitro and in vivo.Conclusions: Our findings identify USP7 as a deubiquitinating enzyme for IKZF1 and uncover a new function of IKZF1 in DNA damage repair. In translational perspective, the combination inhibition of IKZF1 or USP7 with PARP inhibitor deserves further evaluation in clinical trials for the treatment of MM.

Randomized Phase II Study of PARP Inhibitor ABT-888 (Veliparib) with Modified FOLFIRI versus FOLFIRI as Second-line Treatment of Metastatic Pancreatic Cancer: SWOG S1513.

PARP inhibitors synergize with topoisomerase inhibitors, and veliparib plus modified (m) FOLFIRI (no 5-FU bolus) had preliminary activity in metastatic pancreatic cancers. This study evaluated the safety and efficacy of second-line treatment with veliparib and mFOLFIRI versus FOLFIRI (control) for metastatic pancreatic cancer. This randomized phase II clinical trial led by the SWOG Cancer Research Network enrolled patients between September 1, 2016 and December 13, 2017. The median follow-up was 9 months (IQR 1-27). BRCA1/2 and homologous recombination DNA damage repair (HR-DDR) genetic defects were tested in blood and tumor biopsies. Patients received veliparib 200 mg twice daily, days 1-7 with mFOLFIRI days 3-5, or FOLFIRI in 14-day cycles. After 123 of planned 143 patients were accrued, an interim futility analysis indicated that the veliparib arm was unlikely to be superior to control, and the study was halted. Median overall survival (OS) was 5.4 versus 6.5 months (HR, 1.23; P = 0.28), and median progression-free survival (PFS) was 2.1 versus 2.9 months (HR, 1.39; P = 0.09) with veliparib versus control. Grade 3/4 toxicities were more common with veliparib (69% vs. 58%, P = 0.23). For cancers with HR-DDR defects versus wild-type, median PFS and OS were 7.3 versus 2.5 months (P = 0.05) and 10.1 versus 5.9 months (P = 0.17), respectively, with FOLFIRI, and 2.0 versus 2.1 months (P = 0.62) and 7.4 versus 5.1 months (P = 0.10), respectively, with veliparib plus mFOLFIRI. Veliparib plus mFOLFIRI did not improve survival for metastatic pancreatic cancer. FOLFIRI should be further studied in pancreatic cancers with HR-DDR defects.

Investigating tumor molecular profiling as a possible contributor to racial/ethnic disparities in pancreatic cancer.

6522 Background: A variety of biologic, socioeconomic, and treatment-related factors may contribute to the racial/ethnic disparities observed in pancreatic ductal adenocarcinoma (PDAC) outcomes. As tumor molecular profiling (TMP) is now recommended for patients (pts) with advanced PDAC to inform treatment selection, we hypothesized that rates of TMP, detection of actionable alterations (AA), and use of molecularly-targeted treatments differ across different racial/ethnic groups and may contribute to disparate outcomes. Methods: This retrospective analysis included all Non-Hispanic White (NWH), Asian, Hispanic/Latinx (H/L), and Black/African American (B/AfrAm) pts with PDAC who underwent TMP at UCSF over a 4-yr period. Medical records were reviewed for demographic and disease-specific data. Alterations classified as ‘pathogenic’ or ‘likely pathogenic’ in TMP clinical reports were included, and were categorized as ‘actionable’ if there was clinical or preclinical evidence of benefit from targeted therapy in any cancer. Associations between NHW and other groups were tested with Fishers exact test. Results: Between 1/2016-1/2020, 159/727 (22%) pts underwent PDAC TMP. 60 AA were detected in 54 pts. Rates of TMP or AA detection were not associated with racial/ethnic group (Table). Most AA (33/60, 55%) were associated with the Homologous Recombination DNA Damage Repair (HR-DDR) pathway ( ARID1A n = 15 , ATM n = 7 , and BRCA1 n = 5). Other common AA included PIK3CA alterations (n = 6), CDK4/6 amplifications (n = 5), AKT2 amplifications (n = 4) and KRAS G12C mutation (n = 4). Molecular targets differed between groups (HR-DDR genes comprised 55% AA in NHW vs 100% in H/L, p = 0.03). Regarding treatment, rates of platinum chemotherapy for HR-DDR gene-altered PDAC differed significantly between groups. Three NHW pts with HR-DDR alterations received a PARP-inhibitor +/- ATR inhibitor. Conclusions: To our knowledge, this is the first study to report PDAC TMP rates and therapeutic implications across racial/ethnic groups. Acknowledging the limitations of sample size and what defines AA, we observed no significant differences in rates of testing nor AA detection. Further study is needed to evaluate whether rates of molecularly-informed treatment selection contribute to racial/ethnic disparities in clinical outcomes. As therapeutic advances increase the likelihood of identifying AA, equitable access to both TMP and targeted treatments must be ensured for all pts with PDAC.[Table: see text]

The marginal diagnostic benefit of pancreatic cancer molecular profiling after germline testing.

10513 Background: Germline genetic testing is now universally recommended for patients (pts) with pancreatic ductal adenocarcinoma (PDAC) for purposes of both familial screening and therapeutic guidance. Treatment selection can be further informed by tumor molecular profiling (TMP) to identify targetable somatic alterations in pts with advanced disease, but this is inconsistently applied. Determination of the rate of actionable findings identified with TMP after germline testing, which we term marginal diagnostic benefit, may inform practice patterns and workflow in this patient population. Methods: This retrospective analysis included all pts with PDAC who underwent germline testing and TMP at UCSF over a 4-yr period. Medical records were reviewed for demographics, disease-specific data, and germline testing/TMP clinical reports. Alterations classified as ‘pathogenic’ or ‘likely pathogenic’ were included, and were deemed ‘actionable’ if there was clinical or preclinical evidence of benefit from targeted therapy in any cancer, as previously described. Results: From 1/2016-1/2020, 144/738 (20%) UCSF pts with PDAC completed both germline testing and TMP. Germline testing identified actionable pathogenic alterations in 10 (7%). TMP confirmed 8/10 of these alterations and identified 3 additional therapeutic targets. Among the 134 pts without actionable germline findings, TMP identified 45 new therapeutic targets in 41 (31%) pts, increasing the overall rate of actionable findings from 7% to 35%. Most (35/58, 60%) actionable alterations involved genes associated with the Homologous Recombination DNA Damage Repair (HR-DDR) pathway (Table). 80% of pts with HR-DDR pathway alterations (9/10 germline, 19/25 somatic) received platinum-based chemotherapy. Four pts were treated with targeted therapy based on test results: PARP-inhibitor (n = 2, germline BRCA1 and PALB2 mutations), PARP-inhibitor + ATR inhibitor (n = 1, somatic ARID1A mutation) and mTOR inhibitor (n = 1, somatic STK11 deletion). Conclusions: In this analysis, PDAC TMP after germline testing increased the detection of actionable alterations (the marginal diagnostic benefit) by five-fold. As more somatic tumor alterations become actionable with the development of targeted therapeutics, TMP is a necessary complement to germline testing to fully inform personalized treatment decisions for all pts with PDAC.[Table: see text]

RECQL5 mutations as a potential efficacious predictor of immunotherapy in melanoma patients.

e21547 Background: Gene mutations in DNA damage repair (DDR) pathway were reported to affect the clinical response to immune checkpoint inhibitors (ICIs) by driving mutagenicity. Previous studies showed that RECQL5 is involved in RAD51-mediated strand invasion for homologous recombination DNA damage repair (HR-DDR). RECQL5 encoding RecQ protein-like 5 (RECQL5) is a member of RecQ helicase family and was discovered to play a tumor-suppressive or oncogenic role in various cancers. However, the association between RECQL5 mutation and ICI efficacy has not been revealed. Methods: Data of nine publicly independent cohorts of NSCLC, melanoma, and pan-cancer were retrieved (Rizvi, MSKCC, OAK/POPLAR, Van Allen, Hugo, Synder, Miao and Samstein cohorts) to investigate the correlation between RECQL5 mutations and clinical events including overall survival (OS), progression-free survival (PFS), objective response rate (ORR), and clinical benefit rate (CBR). Wilcoxon test was used for comparing tumor mutational burden (TMB) between RECQL5-mutated patients and their wild-type counterparts. In addition, the correlation between infiltration of immune cells and RECQL5 mutation status was also analyzed by QUANTISEO using data of SKCM cohort (n=466) from TCGA database. Statistical significance was set at P = 0.05. Results: RECQL5 mutations were most commonly seen in melanoma patients and the detection rate was 4%-8% in melanoma patients from cohort Van Allen, Hugo, Synder, and Miao. RECQL5 mutation was not detected in other cancers except for one lung cancer case. In the three melanoma cohorts (Van Allen, Synder, Miao) with OS data available, the OS of the RECQL5-mutated patients was 2 to 3 times longer than that of the RECQL5-wt patients. In Synder cohort, the difference in OS between these two subsets was statistically significant (53.9 months vs 25.0 months, P = 0.045). In addition, the occurrence of RECQL5 mutations was correlated with higher CBR both in Miao ( P = 0.017) and Synder cohorts ( P = 0.011). No difference was observed in the PFS or ORR between these two subsets. Notably, RECQL5 mutations were associated with higher TMB levels both in Miao (32.6 mut/Mb vs 7.9 mut/Mb, P = 0.016) and Synder cohorts (1124 mut/Mb vs 358 mut/Mb, P = 0.033). Moreover, RECQL5 mutations were found to be correlated with increased infiltration of CD4+ T cells (no-regulatory) ( P = 0.037), B cells ( P = 0.13) and decreased infiltration of regulatory CD4+ T cells ( P = 0.02) in RECQL5-mutated tumors over RECQL5-wt tumors. Conclusions: RECQL5 mutations can serve as a potential predictor for a durable response to ICIs in melanoma. Moreover, the occurrence of RECQL5 mutations was correlated with higher TMB level as well as infiltration of immune cells, indicating the underlying mechanism of its predictive effect.

Prevalence of Homologous Recombination Pathway Gene Mutations in Melanoma: Rationale for a New Targeted Therapeutic Approach

Homologous recombination DNA damage repair (HR-DDR) deficient patients with various solid tumors have been treated with PARP inhibitors. However, the clinical characteristics of patients with melanoma who have HR-DDR gene mutations and the consequences of PARP inhibition are poorly understood. We compared the commercially available next-generation sequencing data from 84 patients with melanomas from our institution with a dataset of 1,986 patients as well as 1,088 patients profiled in cBioportal. In total, 21.4% of patients had ≥1 functional HR-DDR mutation, most commonly involving BRCA1, ARID1A, ATM, ATR, and FANCA. Concurrent NF1, BRAF, and NRAS mutations were found in 39%, 39%, and 22% of cases, respectively. HR-DDR gene mutation was associated with high tumor mutational burden and clinical response to checkpoint blockade. A higher prevalence of HR-DDR mutations was observed in the datasets from Foundation Medicine (Cambridge, CA) and those from the Cancer Genome Atlas. Treatment of HR-DDR‒mutated patient-derived xenograft models of melanoma with PARP inhibitor produced significant antitumor activity invivo and was associated with increased apoptotic activity. RNA sequencing analysis of PARP inhibitor-treated tumors indicated alterations in the pathways involving extracellular matrix remodeling, cell adhesion, and cell-cycle progression. Melanomas with HR-DDR mutations represent a unique subset, which is more likely to benefit from checkpoint blockade and may be targeted with PARP inhibitor.