UBQLN4 Represses Homologous Recombination and Is Overexpressed in Aggressive Tumors.

Genomic instability can be a hallmark of both human genetic disease and cancer. We identify a deleterious UBQLN4 mutation in families with an autosomal recessive syndrome reminiscent of genome instability disorders. UBQLN4 deficiency leads to increased sensitivity to genotoxic stress and delayed DNA double-strand break (DSB) repair. The proteasomal shuttle factor UBQLN4 is phosphorylated by ATM and interacts with ubiquitylated MRE11 to mediate early steps of homologous recombination-mediated DSB repair (HRR). Loss of UBQLN4 leads to chromatin retention of MRE11, promoting non-physiological HRR activity in vitro and in vivo. Conversely, UBQLN4 overexpression represses HRR and favors non-homologous end joining. Moreover, we find UBQLN4 overexpressed in aggressive tumors. In line with an HRR defect in these tumors, UBQLN4 overexpression is associated with PARP1 inhibitor sensitivity. UBQLN4 therefore curtails HRR activity through removal of MRE11 from damaged chromatin and thus offers a therapeutic window for PARP1 inhibitor treatment in UBQLN4-overexpressing tumors.

Ibrutinib combined with immunochemotherapy with or without autologous stem-cell transplantation versus immunochemotherapy and autologous stem-cell transplantation in previously untreated patients with mantle cell lymphoma (TRIANGLE): a three-arm, randomised, open-label, phase 3 superiority trial of the European Mantle Cell Lymphoma Network.

BACKGROUND: Adding ibrutinib to standard immunochemotherapy might improve outcomes and challenge autologous stem-cell transplantation (ASCT) in younger (aged 65 years or younger) mantle cell lymphoma patients. This trial aimed to investigate whether the addition of ibrutinib results in a superior clinical outcome compared with the pre-trial immunochemotherapy standard with ASCT or an ibrutinib-containing treatment without ASCT. We also investigated whether standard treatment with ASCT is superior to a treatment adding ibrutinib but without ASCT. METHODS: The open-label, randomised, three-arm, parallel-group, superiority TRIANGLE trial was performed in 165 secondary or tertiary clinical centres in 13 European countries and Israel. Patients with previously untreated, stage II-IV mantle cell lymphoma, aged 18-65 years and suitable for ASCT were randomly assigned 1:1:1 to control group A or experimental groups A+I or I, stratified by study group and mantle cell lymphoma international prognostic index risk groups. Treatment in group A consisted of six alternating cycles of R-CHOP (intravenous rituximab 375 mg/m2 on day 0 or 1, intravenous cyclophosphamide 750 mg/m2 on day 1, intravenous doxorubicin 50 mg/m2 on day 1, intravenous vincristine 1·4 mg/m2 on day 1, and oral prednisone 100 mg on days 1-5) and R-DHAP (or R-DHAOx, intravenous rituximab 375 mg/m2 on day 0 or 1, intravenous or oral dexamethasone 40 mg on days 1-4, intravenous cytarabine 2 × 2 g/m2 for 3 h every 12 h on day 2, and intravenous cisplatin 100 mg/m2 over 24 h on day 1 or alternatively intravenous oxaliplatin 130 mg/m2 on day 1) followed by ASCT. In group A+I, ibrutinib (560 mg orally each day) was added on days 1-19 of R-CHOP cycles and as fixed-duration maintenance (560 mg orally each day for 2 years) after ASCT. In group I, ibrutinib was given the same way as in group A+I, but ASCT was omitted. Three pairwise one-sided log-rank tests for the primary outcome of failure-free survival were statistically monitored. The primary analysis was done by intention-to-treat. Adverse events were evaluated by treatment period among patients who started the respective treatment. This ongoing trial is registered with ClinicalTrials.gov, NCT02858258. FINDINGS: Between July 29, 2016 and Dec 28, 2020, 870 patients (662 men, 208 women) were randomly assigned to group A (n=288), group A+I (n=292), and group I (n=290). After 31 months median follow-up, group A+I was superior to group A with 3-year failure-free survival of 88% (95% CI 84-92) versus 72% (67-79; hazard ratio 0·52 [one-sided 98·3% CI 0-0·86]; one-sided p=0·0008). Superiority of group A over group I was not shown with 3-year failure-free survival 72% (67-79) versus 86% (82-91; hazard ratio 1·77 [one-sided 98·3% CI 0-3·76]; one-sided p=0·9979). The comparison of group A+I versus group I is ongoing. There were no relevant differences in grade 3-5 adverse events during induction or ASCT between patients treated with R-CHOP/R-DHAP or ibrutinib combined with R-CHOP/R-DHAP. During maintenance or follow-up, substantially more grade 3-5 haematological adverse events and infections were reported after ASCT plus ibrutinib (group A+I; haematological: 114 [50%] of 231 patients; infections: 58 [25%] of 231; fatal infections: two [1%] of 231) compared with ibrutinib only (group I; haematological: 74 [28%] of 269; infections: 52 [19%] of 269; fatal infections: two [1%] of 269) or after ASCT (group A; haematological: 51 [21%] of 238; infections: 32 [13%] of 238; fatal infections: three [1%] of 238). INTERPRETATION: Adding ibrutinib to first-line treatment resulted in superior efficacy in younger mantle cell lymphoma patients with increased toxicity when given after ASCT. Adding ibrutinib during induction and as maintenance should be part of first-line treatment of younger mantle cell lymphoma patients. Whether ASCT adds to an ibrutinib-containing regimen is not yet determined. FUNDING: Janssen and Leukemia & Lymphoma Society.

Optical genome mapping identifies structural variants in potentially new cancer predisposition candidate genes in pediatric cancer patients.

Genetic predisposition is one of the major risk factors for pediatric cancer, with ~10% of children being carriers of a predisposing germline alteration. It is likely that this is the tip of the iceberg and many children are underdiagnosed, as most of the analysis focuses on single or short nucleotide variants, not considering the full spectrum of DNA alterations. Hence, we applied optical genome mapping (OGM) to our cohort of 34 pediatric cancer patients to perform an unbiased germline screening and analyze the frequency of structural variants (SVs) and their impact on cancer predisposition. All children were clinically highly suspicious for germline alterations (concomitant conditions or congenital anomalies, positive family cancer history, particular cancer type, synchronous or metachronous tumors), but whole exome sequencing (WES) had failed to detect pathogenic variants in cancer predisposing genes. OGM detected a median of 49 rare SVs (range 27-149) per patient. By analysis of 18 patient-parent trios, we identified three de novo SVs. Moreover, we discovered a likely pathogenic deletion of exon 3 in the known cancer predisposition gene BRCA2, and identified a duplication in RPA1, which might represent a new cancer predisposition gene. We conclude that optical genome mapping is a suitable tool for detecting potentially predisposing SVs in addition to WES in pediatric cancer patients.

Biallelic variants in CRIPT cause a Rothmund-Thomson-like syndrome with increased cellular senescence.

PURPOSE: Rothmund-Thomson syndrome (RTS) is characterized by poikiloderma, sparse hair, small stature, skeletal defects, cancer, and cataracts, resembling features of premature aging. RECQL4 and ANAPC1 are the 2 known disease genes associated with RTS in >70% of cases. We describe RTS-like features in 5 individuals with biallelic variants in CRIPT (OMIM 615789). METHODS: Two newly identified and 4 published individuals with CRIPT variants were systematically compared with those with RTS using clinical data, computational analysis of photographs, histologic analysis of skin, and cellular studies on fibroblasts. RESULTS: All CRIPT individuals fulfilled the diagnostic criteria for RTS and additionally had neurodevelopmental delay and seizures. Using computational gestalt analysis, CRIPT individuals showed greatest facial similarity with individuals with RTS. Skin biopsies revealed a high expression of senescence markers (p53/p16/p21) and the senescence-associated ß-galactosidase activity was elevated in CRIPT-deficient fibroblasts. RECQL4- and CRIPT-deficient fibroblasts showed an unremarkable mitotic progression and unremarkable number of mitotic errors and no or only mild sensitivity to genotoxic stress by ionizing radiation, mitomycin C, hydroxyurea, etoposide, and potassium bromate. CONCLUSION: CRIPT causes an RTS-like syndrome associated with neurodevelopmental delay and epilepsy. At the cellular level, RECQL4- and CRIPT-deficient cells display increased senescence, suggesting shared molecular mechanisms leading to the clinical phenotypes.

Combined inhibition of EZH2 and ATM is synthetic lethal in BRCA1-deficient breast cancer.

BACKGROUND: The majority of BRCA1-mutant breast cancers are characterized by a triple-negative phenotype and a basal-like molecular subtype, associated with aggressive clinical behavior. Current treatment options are limited, highlighting the need for the development of novel targeted therapies for this tumor subtype. METHODS: Our group previously showed that EZH2 is functionally relevant in BRCA1-deficient breast tumors and blocking EZH2 enzymatic activity could be a potent treatment strategy. To validate the role of EZH2 as a therapeutic target and to identify new synergistic drug combinations, we performed a high-throughput drug combination screen in various cell lines derived from BRCA1-deficient and -proficient mouse mammary tumors. RESULTS: We identified the combined inhibition of EZH2 and the proximal DNA damage response kinase ATM as a novel synthetic lethality-based therapy for the treatment of BRCA1-deficient breast tumors. We show that the combined treatment with the EZH2 inhibitor GSK126 and the ATM inhibitor AZD1390 led to reduced colony formation, increased genotoxic stress, and apoptosis-mediated cell death in BRCA1-deficient mammary tumor cells in vitro. These findings were corroborated by in vivo experiments showing that simultaneous inhibition of EZH2 and ATM significantly increased anti-tumor activity in mice bearing BRCA1-deficient mammary tumors. CONCLUSION: Taken together, we identified a synthetic lethal interaction between EZH2 and ATM and propose this synergistic interaction as a novel molecular combination for the treatment of BRCA1-mutant breast cancer.

Hemophagocytic lymphohistiocytosis after SARS-CoV-2 vaccination.

PURPOSE: The coronavirus disease 2019 (COVID-19) pandemic has led to the approval of novel vaccines with different mechanisms of action. Until now, more than 4.7 billion persons have been vaccinated around the world, and adverse effects not observed in pre-authorization trials are being reported at low frequency. METHODS: We report a case of severe hemophagocytic lymphohistiocytosis (HLH) after SARS-CoV-2 immunization and performed a literature search for all reported cases of COVID-19 vaccine-associated HLH. RESULTS: A 24-year-old female developed HLH after immunization with the mRNA COVID-19 vaccine Comirnaty. Diagnosis was made according to HLH-2004 criteria; the HScore was 259 (> 99% HLH probability) with maximum ferritin of 138.244 µg/L. The patient was initially treated with intravenous immunoglobulins (IVIGs) and dexamethasone without response. The addition of the human interleukin 1 receptor antagonist Anakinra resulted in full recovery within 6 weeks after vaccination. A literature search revealed 15 additional cases of HLH after SARS-CoV-2 vaccination, the majority after immunization with Comirnaty (n = 7) or the viral vector vaccine Vaxzevria (n = 6). Treatment modalities included corticosteroids (n = 13), Anakinra (n = 5), IVIGs (n = 5), and etoposide (n = 2). Eight patients underwent combination treatment. Three of 16 patients died. CONCLUSION: COVID-19 vaccines may occasionally trigger HLH, and Anakinra may be an efficacious treatment option for this condition.

Biallelic variants in YRDC cause a developmental disorder with progeroid features.

The highly conserved YrdC domain-containing protein (YRDC) interacts with the well-described KEOPS complex, regulating specific tRNA modifications to ensure accurate protein synthesis. Previous studies have linked the KEOPS complex to a role in promoting telomere maintenance and controlling genome integrity. Here, we report on a newborn with a severe neonatal progeroid phenotype including generalized loss of subcutaneous fat, microcephaly, growth retardation, wrinkled skin, renal failure, and premature death at the age of 12 days. By trio whole-exome sequencing, we identified a novel homozygous missense mutation, c.662T > C, in YRDC affecting an evolutionary highly conserved amino acid (p.Ile221Thr). Functional characterization of patient-derived dermal fibroblasts revealed that this mutation impairs YRDC function and consequently results in reduced t6A modifications of tRNAs. Furthermore, we established and performed a novel and highly sensitive 3-D Q-FISH analysis based on single-telomere detection to investigate the impact of YRDC on telomere maintenance. This analysis revealed significant telomere shortening in YRDC-mutant cells. Moreover, single-cell RNA sequencing analysis of YRDC-mutant fibroblasts revealed significant transcriptome-wide changes in gene expression, specifically enriched for genes associated with processes involved in DNA repair. We next examined the DNA damage response of patient's dermal fibroblasts and detected an increased susceptibility to genotoxic agents and a global DNA double-strand break repair defect. Thus, our data suggest that YRDC may affect the maintenance of genomic stability. Together, our findings indicate that biallelic variants in YRDC result in a developmental disorder with progeroid features and might be linked to increased genomic instability and telomere shortening.

The bispecific immunoligand ULBP2-aCEA redirects natural killer cells to tumor cells and reveals potent anti-tumor activity against colon carcinoma.

NKG2D, an activating receptor expressed on NK cells and T cells, is critically involved in tumor immunosurveillance. In this study, we explored the potential therapeutic utility of the NKG2D ligand ULBP2 for the treatment of colon carcinoma. To this end we designed a fusion protein consisting of human ULBP2 and an antibody-derived single chain targeting the tumor carcinoembryonic antigen (CEA). The bispecific recombinant fusion protein re-directed NK cells towards malignant cells by binding to both, tumor cells and NK cells, and triggered NK cell-mediated target cell killing in vitro. Moreover, tumor growth was significantly delayed in a syngeneic colon carcinoma mouse model in response to immunoligand treatment. The anti-tumor activity could be attributed to the stimulation of immune cells with an elevated expression of the activation marker CD69 on NK, T and NKT cells and the infiltration of CD45+ immune cells into the solid tumor. In summary, it was demonstrated that immunoligands provide specific tumor targeting by NK cells and exert anti-tumor activity in vitro and in vivo. This technology represents a novel immunotherapeutic strategy for solid tumors with the potential to be further developed for clinical applications.

The challenging aspects of managing adolescents and young adults with Hodgkin's lymphoma.

Cancer in the adolescent and young adult (AYA) is the second leading cause of nonaccidental death with hematological malignancies spiking during this period. Treatment of AYAs with hematological malignancies usually follows either pediatric or adult protocols with sufficient information lacking on subgroup analyses regarding course and outcome. In this review we will outline up-to-date treatment possibilities for AYAs diagnosed with Hodgkin's lymphoma. Early and late toxicities will be addressed and future directions of research suggested.

An inducible Cd79b mutation confers ibrutinib sensitivity in mouse models of Myd88-driven diffuse large B-cell lymphoma.

ABSTRACT: Diffuse large B-cell lymphoma (DLBCL) is the most common aggressive lymphoma and constitutes a highly heterogenous disease. Recent comprehensive genomic profiling revealed the identity of numerous molecularly defined DLBCL subtypes, including a cluster which is characterized by recurrent aberrations in MYD88, CD79B, and BCL2, as well as various lesions promoting a block in plasma cell differentiation, including PRDM1, TBL1XR1, and SPIB. Here, we generated a series of autochthonous mouse models to mimic this DLBCL cluster and specifically focused on the impact of Cd79b mutations in this setting. We show that canonical Cd79b immunoreceptor tyrosine-based activation motif (ITAM) mutations do not accelerate Myd88- and BCL2-driven lymphomagenesis. Cd79b-mutant murine DLBCL were enriched for IgM surface expression, reminiscent of their human counterparts. Moreover, Cd79b-mutant lymphomas displayed a robust formation of cytoplasmic signaling complexes involving MYD88, CD79B, MALT1, and BTK. These complexes were disrupted upon pharmacological BTK inhibition. The BTK inhibitor-mediated disruption of these signaling complexes translated into a selective ibrutinib sensitivity of lymphomas harboring combined Cd79b and Myd88 mutations. Altogether, this in-depth cross-species comparison provides a framework for the development of molecularly targeted therapeutic intervention strategies in DLBCL.

Baseline serum TARC levels predict therapy outcome in patients with Hodgkin lymphoma.

Hodgkin lymphoma (HL) has become one of the best curable cancers. However, better biomarkers are needed for outcome prediction that would allow protecting patients from over- or under-dosing of treatment. Thymus and activation-regulated chemokine/CCL17 (TARC) is highly and specifically elevated in this disease and has been proposed as possible biomarker in HL patients. In this study, we show that pretreatment TARC levels were associated with established clinical risk factors and predictive for response to treatment in a large cohort of HL patients treated in clinical trials by the German Hodgkin Study Group. Moreover, TARC levels also significantly contributed to a novel multivariate model predicting treatment response. These data clearly suggest an important role for this chemokine as biomarker in HL.

Mouse models of diffuse large B cell lymphoma.

Diffuse large B cell lymphoma (DLBCL) is a genetically highly heterogeneous disease. Yet, to date, the vast majority of patients receive standardized frontline chemo-immune-therapy consisting of an anthracycline backbone. Using these regimens, approximately 65% of patients can be cured, whereas the remaining 35% of patients will face relapsed or refractory disease, which, even in the era of CAR-T cells, is difficult to treat. To systematically tackle this high medical need, it is important to design, generate and deploy suitable in vivo model systems that capture disease biology, heterogeneity and drug response. Recently published, large comprehensive genomic characterization studies, which defined molecular sub-groups of DLBCL, provide an ideal framework for the generation of autochthonous mouse models, as well as an ideal benchmark for cell line-derived or patient-derived mouse models of DLBCL. Here we discuss the current state of the art in the field of mouse modelling of human DLBCL, with a particular focus on disease biology and genetically defined molecular vulnerabilities, as well as potential targeting strategies.

Distinct Genetically Determined Origins of Myd88/BCL2-Driven Aggressive Lymphoma Rationalize Targeted Therapeutic Intervention Strategies.

Genomic profiling revealed the identity of at least 5 subtypes of diffuse large B-cell lymphoma (DLBCL), including the MCD/C5 cluster characterized by aberrations in MYD88, BCL2, PRDM1, and/or SPIB. We generated mouse models harboring B cell-specific Prdm1 or Spib aberrations on the background of oncogenic Myd88 and Bcl2 lesions. We deployed whole-exome sequencing, transcriptome, flow-cytometry, and mass cytometry analyses to demonstrate that Prdm1- or Spib-altered lymphomas display molecular features consistent with prememory B cells and light-zone B cells, whereas lymphomas lacking these alterations were enriched for late light-zone and plasmablast-associated gene sets. Consistent with the phenotypic evidence for increased B cell receptor signaling activity in Prdm1-altered lymphomas, we demonstrate that combined BTK/BCL2 inhibition displays therapeutic activity in mice and in five of six relapsed/refractory DLBCL patients. Moreover, Prdm1-altered lymphomas were immunogenic upon transplantation into immuno-competent hosts, displayed an actionable PD-L1 surface expression, and were sensitive to antimurine-CD19-CAR-T cell therapy, in vivo. SIGNIFICANCE: Relapsed/refractory DLBCL remains a major medical challenge, and most of these patients succumb to their disease. Here, we generated mouse models, faithfully recapitulating the biology of MYD88-driven human DLBCL. These models revealed robust preclinical activity of combined BTK/BCL2 inhibition. We confirmed activity of this regimen in pretreated non-GCB-DLBCL patients. See related commentary by Leveille et al., p. 8. This article is highlighted in the In This Issue feature, p. 1.

Genomic Amplification of UBQLN4 Is a Prognostic and Treatment Resistance Factor.

Ubiquilin-4 (UBQLN4) is a proteasomal shuttle factor that directly binds to ubiquitylated proteins and delivers its cargo to the 26S proteasome for degradation. We previously showed that upregulated UBQLN4 determines the DNA damage response (DDR) through the degradation of MRE11A. However, the regulatory mechanism at DNA level, transcriptionally and post-transcriptional levels that control UBQLN4 mRNA levels remains unknown. In this study, we screened 32 solid tumor types and validated our findings by immunohistochemistry analysis. UBQLN4 is upregulated at both mRNA and protein levels and the most significant values were observed in liver, breast, ovarian, lung, and esophageal cancers. Patients with high UBQLN4 mRNA levels had significantly poor prognoses in 20 of 32 cancer types. DNA amplification was identified as the main mechanism promoting UBQLN4 upregulation in multiple cancers, even in the early phases of tumor development. Using CRISPR screen datasets, UBQLN4 was identified as a common essential gene for tumor cell viability in 81.1% (860/1,060) of the solid tumor derived cell lines. Ovarian cancer cell lines with high UBQLN4 mRNA levels were platinum-based chemotherapy resistant, while they were more sensitive to poly (adenosine diphosphate-ribose) polymerase inhibitors (PARPi). Our findings highlight the utilities of UBQLN4 as a significant pan-cancer theranostic factor and a precision oncology biomarker for DDR-related drug resistance.

Regulation of MRE11A by UBQLN4 leads to cisplatin resistance in patients with esophageal squamous cell carcinoma.

Resistance to standard cisplatin-based chemotherapies leads to worse survival outcomes for patients with esophageal squamous cell carcinoma (ESCC). Therefore, there is an urgent need to understand the aberrant mechanisms driving resistance in ESCC tumors. We hypothesized that ubiquilin-4 (UBQLN4), a protein that targets ubiquitinated proteins to the proteasome, regulates the expression of Meiotic Recombination 11 Homolog A (MRE11A), a critical component of the MRN complex and DNA damage repair pathways. Initially, immunohistochemistry analysis was conducted in specimens from patients with ESCC (n = 120). In endoscopic core ESCC biopsies taken from 61 patients who underwent neoadjuvant chemotherapy (NAC) (5-fluorouracil and cisplatin), low MRE11A and high UBQLN4 protein levels were associated with reduced pathological response to NAC (P < 0.001 and P < 0.001, respectively). Multivariable analysis of surgically resected ESCC tissues from 59 patients revealed low MRE11A and high UBLQN4 expression as independent factors that can predict shorter overall survival [P = 0.01, hazard ratio (HR) = 5.11, 95% confidence interval (CI), 1.45-18.03; P = 0.02, HR = 3.74, 95% CI, 1.19-11.76, respectively]. Suppression of MRE11A expression was associated with cisplatin resistance in ESCC cell lines. Additionally, MRE11A was found to be ubiquitinated after cisplatin treatment. We observed an amplification of UBQLN4 gene copy numbers and an increase in UBQLN4 protein levels in ESCC tissues. Binding of UBQLN4 to ubiquitinated-MRE11A increased MRE11A degradation, thereby regulating MRE11A protein levels following DNA damage and promoting cisplatin resistance. In summary, MRE11A and UBQLN4 protein levels can serve as predictors for NAC response and as prognostic markers in ESCC patients.

Targeting DNA Repair, Cell Cycle, and Tumor Microenvironment in B Cell Lymphoma.

The DNA double-strand break (DSB) is the most cytotoxic lesion and compromises genome stability. In an attempt to efficiently repair DSBs, cells activate ATM kinase, which orchestrates the DNA damage response (DDR) by activating cell cycle checkpoints and initiating DSB repair pathways. In physiological B cell development, however, programmed DSBs are generated as intermediates for effective immune responses and the maintenance of genomic integrity. Disturbances of these pathways are at the heart of B cell lymphomagenesis. Here, we review the role of DNA repair and cell cycle control on B cell development and lymphomagenesis. In addition, we highlight the intricate relationship between the DDR and the tumor microenvironment (TME). Lastly, we provide a clinical perspective by highlighting treatment possibilities of defective DDR signaling and the TME in mantle cell lymphoma, which serves as a blueprint for B cell lymphomas.

UBQLN4 promotes non-homologous end joining by repressing DNA end-resection.

Ataxia-telangiectasia-mutated (ATM) promotes homologous recombination (HR)-mediated DNA double-strand break repair. It was recently shown that the proteasomal shuttle factor UBQLN4 facilitates MRE11 degradation to repress HR. Surprisingly, the UBQLN4-MRE11 interaction is ATM-dependent, suggesting that the proximal DNA damage kinase ATM does not only initiate HR, but also limits excessive end resection.

DNA double-strand break repair pathway choice - from basic biology to clinical exploitation.

Mutations in genes encoding components of the DNA damage response (DDR) are among the most frequent aberrations in human tumors. Moreover, a large array of human syndromes is caused by mutations in genes involved in DDR pathways. Among others, homologous recombination repair (HR) of DNA double-strand breaks (DSB) is frequently affected by disabling mutations. While impaired HR is clearly promoting tumorigenesis, it is also associated with an actionable sensitivity against PARP inhibitors. PARP inhibitors have recently received FDA approval for the treatment of breast- and ovarian cancer. However, as with all molecularly targeted agents, acquired resistance limits its use. Both pharmaco-genomic approaches and the study of human genome instability syndromes have led to a profound understanding of PARP inhibitor resistance. These experiments have revealed new insights into the molecular mechanisms that drive mammalian DSB repair. Here, we review recent discoveries in the field and provide a clinical perspective.

MYC paralog-dependent apoptotic priming orchestrates a spectrum of vulnerabilities in small cell lung cancer.

MYC paralogs are frequently activated in small cell lung cancer (SCLC) but represent poor drug targets. Thus, a detailed mapping of MYC-paralog-specific vulnerabilities may help to develop effective therapies for SCLC patients. Using a unique cellular CRISPR activation model, we uncover that, in contrast to MYCN and MYCL, MYC represses BCL2 transcription via interaction with MIZ1 and DNMT3a. The resulting lack of BCL2 expression promotes sensitivity to cell cycle control inhibition and dependency on MCL1. Furthermore, MYC activation leads to heightened apoptotic priming, intrinsic genotoxic stress and susceptibility to DNA damage checkpoint inhibitors. Finally, combined AURK and CHK1 inhibition substantially prolongs the survival of mice bearing MYC-driven SCLC beyond that of combination chemotherapy. These analyses uncover MYC-paralog-specific regulation of the apoptotic machinery with implications for genotype-based selection of targeted therapeutics in SCLC patients.