Patient-Reported Outcomes in OlympiA: A Phase III, Randomized, Placebo-Controlled Trial of Adjuvant Olaparib in gBRCA1/2 Mutations and High-Risk Human Epidermal Growth Factor Receptor 2-Negative Early Breast Cancer.

PURPOSE: The OlympiA randomized phase III trial compared 1 year of olaparib (OL) or placebo (PL) as adjuvant therapy in patients with germline BRCA1/2, high-risk human epidermal growth factor receptor 2-negative early breast cancer after completing (neo)adjuvant chemotherapy ([N]ACT), surgery, and radiotherapy. The patient-reported outcome primary hypothesis was that OL-treated patients may experience greater fatigue during treatment. METHODS: Data were collected before random assignment, and at 6, 12, 18, and 24 months. The primary end point was fatigue, measured with the Functional Assessment of Chronic Illness Therapy-Fatigue scale. Secondary end points, assessed with the European Organization for Research and Treatment of Cancer Quality of Life Questionnaire, Core 30 item, included nausea and vomiting (NV), diarrhea, and multiple functional domains. Scores were compared between treatment groups using mixed model for repeated measures. Two-sided P values <.05 were statistically significant for the primary end point. All secondary end points were descriptive. RESULTS: One thousand five hundred and thirty-eight patients (NACT: 746, ACT: 792) contributed to the analysis. Fatigue severity was statistically significantly greater for OL versus PL, but not clinically meaningfully different by prespecified criteria (≥3 points) at 6 months (diff OL v PL: NACT: -1.3 [95% CI, -2.4 to -0.2]; P = .022; ACT: -1.3 [95% CI, -2.3 to -0.2]; P = .017) and 12 months (NACT: -1.6 [95% CI, -2.8 to -0.3]; P = .017; ACT: -1.3 [95% CI, -2.4 to -0.2]; P = .025). There were no significant differences in fatigue severity between treatment groups at 18 and 24 months. NV severity was worse in patients treated with OL compared with PL at 6 months (NACT: 6.0 [95% CI, 4.1 to 8.0]; ACT: 5.3 [95% CI, 3.4 to 7.2]) and 12 months (NACT: 6.4 [95% CI, 4.4 to 8.3]; ACT: 4.5 [95% CI, 2.8 to 6.1]). During treatment, there were some clinically meaningful differences between groups for other symptoms but not for function subscales or global health status. CONCLUSION: Treatment-emergent symptoms from OL were limited, generally resolving after treatment ended. OL- and PL-treated patients had similar functional scores, slowly improving during the 24 months after (N)ACT and there was no clinically meaningful persistence of fatigue severity in OL-treated patients.

Cancer-associated FBXW7 loss is synthetic lethal with pharmacological targeting of CDC7.

The F-box and WD repeat domain containing 7 (FBXW7) tumour suppressor gene encodes a substrate-recognition subunit of Skp, cullin, F-box (SCF)-containing complexes. The tumour-suppressive role of FBXW7 is ascribed to its ability to drive ubiquitination and degradation of oncoproteins. Despite this molecular understanding, therapeutic approaches that target defective FBXW7 have not been identified. Using genome-wide clustered regularly interspaced short palindromic repeats (CRISPR)-Cas9 screens, focussed RNA-interference screens and whole and phospho-proteome mass spectrometry profiling in multiple FBXW7 wild-type and defective isogenic cell lines, we identified a number of FBXW7 synthetic lethal targets, including proteins involved in the response to replication fork stress and proteins involved in replication origin firing, such as cell division cycle 7-related protein kinase (CDC7) and its substrate, DNA replication complex GINS protein SLD5 (GINS4). The CDC7 synthetic lethal effect was confirmed using small-molecule inhibitors. Mechanistically, FBXW7/CDC7 synthetic lethality is dependent upon the replication factor telomere-associated protein RIF1 (RIF1), with RIF1 silencing reversing the FBXW7-selective effects of CDC7 inhibition. The delineation of FBXW7 synthetic lethal effects we describe here could serve as the starting point for subsequent drug discovery and/or development in this area.

Genomic profiling and pre-clinical modelling of breast cancer leptomeningeal metastasis reveals acquisition of a lobular-like phenotype.

Breast cancer leptomeningeal metastasis (BCLM), where tumour cells grow along the lining of the brain and spinal cord, is a devastating development for patients. Investigating this metastatic site is hampered by difficulty in accessing tumour material. Here, we utilise cerebrospinal fluid (CSF) cell-free DNA (cfDNA) and CSF disseminated tumour cells (DTCs) to explore the clonal evolution of BCLM and heterogeneity between leptomeningeal and extracranial metastatic sites. Somatic alterations with potential therapeutic actionability were detected in 81% (17/21) of BCLM cases, with 19% detectable in CSF cfDNA only. BCLM was enriched in genomic aberrations in adherens junction and cytoskeletal genes, revealing a lobular-like breast cancer phenotype. CSF DTCs were cultured in 3D to establish BCLM patient-derived organoids, and used for the successful generation of BCLM in vivo models. These data reveal that BCLM possess a unique genomic aberration profile and highlight potential cellular dependencies in this hard-to-treat form of metastatic disease.

Integrated Multimodal Analyses of DNA Damage Response and Immune Markers as Predictors of Response in Metastatic Triple-Negative Breast Cancer in the TNT Trial (NCT00532727).

PURPOSE: The TNT trial (NCT00532727) showed no evidence of carboplatin superiority over docetaxel in metastatic triple-negative breast cancer (mTNBC), but carboplatin benefit was observed in the germline BRCA1/2 mutation subgroup. Broader response-predictive biomarkers are needed. We explored the predictive ability of DNA damage response (DDR) and immune markers. EXPERIMENTAL DESIGN: Tumor-infiltrating lymphocytes were evaluated for 222 of 376 patients. Primary tumors (PT) from 186 TNT participants (13 matched recurrences) were profiled using total RNA sequencing. Four transcriptional DDR-related and 25 immune-related signatures were evaluated. We assessed their association with objective response rate (ORR) and progression-free survival (PFS). Conditional inference forest clustering was applied to integrate multimodal data. The biology of subgroups was characterized by 693 gene expression modules and other markers. RESULTS: Transcriptional DDR-related biomarkers were not predictive of ORR to either treatment overall. Changes from PT to recurrence were demonstrated; in chemotherapy-naïve patients, transcriptional DDR markers separated carboplatin responders from nonresponders (P values = 0.017; 0.046). High immune infiltration was associated with docetaxel ORR (interaction P values < 0.05). Six subgroups were identified; the immune-enriched cluster had preferential docetaxel response [62.5% (D) vs. 29.4% (C); P = 0.016]. The immune-depleted cluster had preferential carboplatin response [8.0% (D) vs. 40.0% (C); P = 0.011]. DDR-related subgroups were too small to assess ORR. CONCLUSIONS: High immune features predict docetaxel response, and high DDR signature scores predict carboplatin response in treatment-naïve mTNBC. Integrating multimodal DDR and immune-related markers identifies subgroups with differential treatment sensitivity. Treatment options for patients with immune-low and DDR-proficient tumors remains an outstanding need. Caution is needed using PT-derived transcriptional signatures to direct treatment in mTNBC, particularly DDR-related markers following prior chemotherapy.

A HUWE1 defect causes PARP inhibitor resistance by modulating the BRCA1-∆11q splice variant.

Although PARP inhibitors (PARPi) now form part of the standard-of-care for the treatment of homologous recombination defective cancers, de novo and acquired resistance limits their overall effectiveness. Previously, overexpression of the BRCA1-∆11q splice variant has been shown to cause PARPi resistance. How cancer cells achieve increased BRCA1-∆11q expression has remained unclear. Using isogenic cells with different BRCA1 mutations, we show that reduction in HUWE1 leads to increased levels of BRCA1-∆11q and PARPi resistance. This effect is specific to cells able to express BRCA1-∆11q (e.g. BRCA1 exon 11 mutant cells) and is not seen in BRCA1 mutants that cannot express BRCA1-∆11q, nor in BRCA2 mutant cells. As well as increasing levels of BRCA1-∆11q protein in exon 11 mutant cells, HUWE1 silencing also restores RAD51 nuclear foci and platinum salt resistance. HUWE1 catalytic domain mutations were also seen in a case of PARPi resistant, BRCA1 exon 11 mutant, high grade serous ovarian cancer. These results suggest how elevated levels of BRCA1-∆11q and PARPi resistance can be achieved, identify HUWE1 as a candidate biomarker of PARPi resistance for assessment in future clinical trials and illustrate how some PARPi resistance mechanisms may only operate in patients with particular BRCA1 mutations.

Serum-derived extracellular vesicles from breast cancer patients contribute to differential regulation of T-cell-mediated immune-escape mechanisms in breast cancer subtypes.

Background: Intracellular communication within the tumour is complex and extracellular vesicles (EVs) have been identified as major contributing factors for the cell-to-cell communication in the local and distant tumour environments. Here, we examine the differential effects of breast cancer (BC) subtype-specific patient serum and cell-line derived EVs in the regulation of T cell mediated immune responses. Methods: Ultracentrifugation was used to isolate EVs from sera of 63 BC patients, 15 healthy volunteers and 4 human breast cancer cell lines. Longitudinal blood draws for EV isolation for patients on neoadjuvant chemotherapy was also performed. Characterization of EVs was performed by Nanoparticle Tracking Analysis (NTA), transmission electron microscopy (TEM) and immunoblotting. CD63 staining was performed on a tissue microarray of 218 BC patients. In-house bioinformatics algorithms were utilized for the computation of EV associated expression scores within The Cancer Genome Atlas (TCGA) and correlated with tumour infiltrating lymphocyte (TIL) scores. In vitro stimulation of PBMCs with EVs from serum and cell-line derived EVs was performed and changes in the immune phenotypes characterized by flow cytometry. Cytokine profiles were assessed using a 105-plex immunoassay or IL10 ELISA. Results: Patients with triple negative breast cancers (TNBCs) exhibited the lowest number of EVs in the sera; whilst the highest was detected in ER+HER2+ cancers; reflected also in the higher level of CD63+ vesicles found within the ER+HER2+ local tumour microenvironment. Transcriptomic analysis of the TCGA data identified that samples assigned with lower EV scores had significantly higher abundance of CD4+ memory activated T cells, T follicular cells and CD8 T cells, plasma, and memory B cells; whilst samples with high EV scores were more enriched for anti-inflammatory M2 macrophages and mast cells. A negative correlation between EV expression scores and stromal TIL counts was also observed. In vitro experiments confirmed that circulating EVs within breast cancer subtypes have functionally differing immunomodulatory capabilities, with EVs from patients with the most aggressive breast cancer subtype (TNBCs) demonstrating the most immune-suppressive phenotype (decreased CD3+HLA-DR+ but increased CD3+PD-L1 T cells, increased CD4+CD127-CD25hi T regulatory cells with associated increase in IL10 cytokine production). In depth assessment of the cytokine modulation triggered by the serum/cell line derived exosomes confirmed differential inflammatory cytokine profiles across differing breast cancer subtypes. Studies using the MDA-231 TNBC breast cancer cell-line derived EVs provided further support that TNBC EVs induced the most immunosuppressive response within PBMCs. Discussion: Our study supports further investigations into how tumour derived EVs are a mechanism that cancers can exploit to promote immune suppression; and breast cancer subtypes produce EVs with differing immunomodulatory capabilities. Understanding the intracellular/extracellular pathways implicated in alteration from active to suppressed immune state may provide a promising way forward for restoring immune competence in specific breast cancer patient populations.

MND1 and PSMC3IP control PARP inhibitor sensitivity in mitotic cells.

The PSMC3IP-MND1 heterodimer promotes meiotic D loop formation before DNA strand exchange. In genome-scale CRISPR-Cas9 mutagenesis and interference screens in mitotic cells, depletion of PSMC3IP or MND1 causes sensitivity to poly (ADP-Ribose) polymerase inhibitors (PARPi) used in cancer treatment. PSMC3IP or MND1 depletion also causes ionizing radiation sensitivity. These effects are independent of PSMC3IP/MND1's role in mitotic alternative lengthening of telomeres. PSMC3IP- or MND1-depleted cells accumulate toxic RAD51 foci in response to DNA damage, show impaired homology-directed DNA repair, and become PARPi sensitive, even in cells lacking both BRCA1 and TP53BP1. Epistasis between PSMC3IP-MND1 and BRCA1/BRCA2 defects suggest that abrogated D loop formation is the cause of PARPi sensitivity. Wild-type PSMC3IP reverses PARPi sensitivity, whereas a PSMC3IP p.Glu201del mutant associated with D loop defects and ovarian dysgenesis does not. These observations suggest that meiotic proteins such as MND1 and PSMC3IP have a greater role in mitotic DNA repair.

Adjuvant olaparib in the subset of patients from Japan with BRCA1- or BRCA2-mutated high-risk early breast cancer from the phase 3 OlympiA trial.

BACKGROUND: The efficacy and safety of olaparib compared with placebo in the subset of patients from Japan in the phase 3 OlympiA trial (NCT02032823) are reported here and contextualized with reference to the global OlympiA population. METHODS: Patients with germline BRCA1 and/or BRCA2 pathogenic variants and HER2-negative, high-risk early breast cancer who had received neoadjuvant or adjuvant chemotherapy and completed local treatment were eligible. Patients were randomized 1:1 to receive olaparib or placebo for 1 year. PRIMARY ENDPOINT: invasive disease-free survival (IDFS). Secondary endpoints: distant disease-free survival (DDFS), overall survival (OS), and safety. Data are reported from the first pre-specified interim analysis (data cut-off [DCO] March 27, 2020) and the second, event driven, pre-specified interim analysis of OS (DCO July 12, 2021) in patients from Japan. RESULTS: 140 patients were randomized in Japan (olaparib, n = 64; placebo, n = 76). At the first pre-specified interim analysis (median follow-up: 2.9 years), hazard ratios (HRs) for adjuvant olaparib compared with placebo were 0.5 for IDFS (95% confidence interval [CI] 0.18-1.24) and 0.41 for DDFS (95% CI 0.11-1.16). At the second pre-specified interim analysis of OS, three deaths occurred in the olaparib group versus six deaths in the placebo group (HR, 0.62 [95% CI 0.13-2.36]). Findings were consistent with those for the global population. No new safety signals were observed. CONCLUSIONS: While this analysis in a Japanese subset of patients was not powered to detect population-related treatment differences, efficacy and safety analysis results were consistent with the global OlympiA population, suggesting the findings from the global study are generalizable to clinical practice in Japan.

Next-Generation Sequencing and Image-Guided Tissue Sampling: A Primer for Interventional Radiologists.

The discovery of increasing numbers of actionable molecular and gene targets for cancer treatment has driven the demand for tissue sampling for next-generation sequencing (NGS). Requirements for sequencing can be very specific, and inadequate sampling leads to delays in management and decision making. It is important that interventional radiologists are aware of NGS technologies and their common applications and be cognizant of the factors that contribute to successful sample sequencing. This review summarizes the fundamentals of cancer tissue collection and processing for NGS. It elaborates on sequencing technologies and their applications with the aim of providing readers with a working understanding that can enhance their clinical practice. It then describes imaging, tumor, biopsy, and sample collection factors that improve the chances of NGS success. Finally, it discusses future practice, highlighting the problem of undersampling in both clinical and research settings and the opportunities within interventional radiology to address this.

Systemic Therapy for Hereditary Breast Cancers.

Approximately 5% to 10% of all breast cancers are hereditary; many of which are caused by pathogenic variants in genes required for homologous recombination, including BRCA1 and BRCA2. Here we discuss systemic treatment for such breast cancers, including approved chemotherapeutic approaches and also targeted treatment approaches using poly-(ADP ribose) polymerase inhibitors. We also discuss experimental approaches to treating hereditary breast cancer, including new small molecule DNA repair inhibitors and also immunomodulatory agents. Finally, we discuss how drug resistance emerges in patients with hereditary breast cancer, how this might be delayed or prevented, and how biomarker-adapted treatment is molding the future management of hereditary breast cancer.

Practical guidance for running late-phase platform protocols for clinical trials: lessons from experienced UK clinical trials units.

BACKGROUND: Late-phase platform protocols (including basket, umbrella, multi-arm multi-stage (MAMS), and master protocols) are generally agreed to be more efficient than traditional two-arm clinical trial designs but are not extensively used. We have gathered the experience of running a number of successful platform protocols together to present some operational recommendations. METHODS: Representatives of six UK clinical trials units with experience in running late-phase platform protocols attended a 1-day meeting structured to discuss various practical aspects of running these trials. We report and give guidance on operational aspects which are either harder to implement compared to a traditional late-phase trial or are specific to platform protocols. RESULTS: We present a list of practical recommendations for trialists intending to design and conduct late-phase platform protocols. Our recommendations cover the entire life cycle of a platform trial: from protocol development, obtaining funding, and trial set-up, to a wide range of operational and regulatory aspects such as staffing, oversight, data handling, and data management, to the reporting of results, with a particular focus on communication with trial participants and stakeholders as well as public and patient involvement. DISCUSSION: Platform protocols enable many questions to be answered efficiently to the benefit of patients. Our practical lessons from running platform trials will support trial teams in learning how to run these trials more effectively and efficiently.

Dynamic Changes in the NK-, Neutrophil-, and B-cell Immunophenotypes Relevant in High Metastatic Risk Post Neoadjuvant Chemotherapy-Resistant Early Breast Cancers.

PURPOSE: To identify potential immune targets in post-neoadjuvant chemotherapy (NAC)-resistant triple-negative breast cancer (TNBC) and ER+HER2- breast cancer disease. EXPERIMENTAL DESIGN: Following pathology review, 153 patients were identified as having residual cancer burden (RCB) II/III disease (TNBC n = 80; ER+HER2-n = 73). Baseline pre-NAC samples were available for evaluation for 32 of 80 TNBC and 36 of 73 ER+HER2- cases. Bright-field hematoxylin and eosin assessment allowed for tumor-infiltrating lymphocyte (TIL) evaluation in all cases. Multiplexed immunofluorescence was used to identify the abundance and distribution of immune cell subsets. Levels of checkpoints including PD-1/PD-L1 expression were also quantified. Findings were then validated using expression profiling of cancer and immune-related genes. Cytometry by time-of-flight characterized the dynamic changes in circulating immune cells with NAC. RESULTS: RCB II/III TNBC and ER+HER2- breast cancer were immunologically "cold" at baseline and end of NAC. Although the distribution of immune cell subsets across subtypes was similar, the mRNA expression profiles were both subtype- and chemotherapy-specific. TNBC RCB II/III disease was enriched with genes related to neutrophil degranulation, and displayed strong interplay across immune and cancer pathways. We observed similarities in the dynamic changes in B-cell biology following NAC irrespective of subtype. However, NAC induced changes in the local and circulating tumor immune microenvironment (TIME) that varied by subtype and response. Specifically, in TNBC residual disease, we observed downregulation of stimulatory (CD40/OX40L) and inhibitory (PD-L1/PD-1) receptor expression and an increase in NK cell populations (especially non-cytolytic, exhausted CD56dimCD16-) within both the local TIME and peripheral white cell populations. CONCLUSIONS: This study identifies several potential immunologic pathways in residual disease, which may be targeted to benefit high-risk patients.

Opinion: PARP inhibitors in cancer-what do we still need to know?

PARP inhibitors (PARPi) have been demonstrated to exhibit profound anti-tumour activity in individuals whose cancers have a defect in the homologous recombination DNA repair pathway. Here, we describe the current consensus as to how PARPi work and how drug resistance to these agents emerges. We discuss the need to refine the current repertoire of clinical-grade companion biomarkers to be used with PARPi, so that patient stratification can be improved, the early emergence of drug resistance can be detected and dose-limiting toxicity can be predicted. We also highlight current thoughts about how PARPi resistance might be treated.

Functional screening reveals HORMAD1-driven gene dependencies associated with translesion synthesis and replication stress tolerance.

HORMAD1 expression is usually restricted to germline cells, but it becomes mis-expressed in epithelial cells in ~60% of triple-negative breast cancers (TNBCs), where it is associated with elevated genomic instability (1). HORMAD1 expression in TNBC is bimodal with HORMAD1-positive TNBC representing a biologically distinct disease group. Identification of HORMAD1-driven genetic dependencies may uncover novel therapies for this disease group. To study HORMAD1-driven genetic dependencies, we generated a SUM159 cell line model with doxycycline-inducible HORMAD1 that replicated genomic instability phenotypes seen in HORMAD1-positive TNBC (1). Using small interfering RNA screens, we identified candidate genes whose depletion selectively inhibited the cellular growth of HORMAD1-expressing cells. We validated five genes (ATR, BRIP1, POLH, TDP1 and XRCC1), depletion of which led to reduced cellular growth or clonogenic survival in cells expressing HORMAD1. In addition to the translesion synthesis (TLS) polymerase POLH, we identified a HORMAD1-driven dependency upon additional TLS polymerases, namely POLK, REV1, REV3L and REV7. Our data confirms that out-of-context somatic expression of HORMAD1 can lead to genomic instability and reveals that HORMAD1 expression induces dependencies upon replication stress tolerance pathways, such as translesion synthesis. Our data also suggest that HORMAD1 expression could be a patient selection biomarker for agents targeting replication stress.

Phase 1b study of berzosertib and cisplatin in patients with advanced triple-negative breast cancer.

Platinum derivatives are commonly used for the treatment of patients with metastatic triple-negative breast cancer (TNBC). However, resistance often develops, leading to treatment failure. This expansion cohort (part C2) of the previously reported phase 1b trial (NCT02157792) is based on the recommended phase 2 dose of the combination of the ataxia-telangiectasia and Rad3-related (ATR) inhibitor berzosertib and cisplatin observed in patients with advanced solid tumors, including TNBC. Forty-seven patients aged ≥18 years with advanced TNBC received cisplatin (75 mg/m2; day 1) and berzosertib (140 mg/m2; days 2 and 9), in 21-day cycles. Berzosertib was well tolerated, with a similar toxicity profile to that reported previously for this combination. The overall response rate (90% confidence interval) was 23.4% (13.7, 35.8). No relevant associations were observed between response and gene alterations. Further studies combining ATR inhibitors with platinum compounds may be warranted in highly selected patient populations.

Loss of E-cadherin leads to Id2-dependent inhibition of cell cycle progression in metastatic lobular breast cancer.

Invasive lobular breast carcinoma (ILC) is characterized by proliferative indolence and long-term latency relapses. This study aimed to identify how disseminating ILC cells control the balance between quiescence and cell cycle re-entry. In the absence of anchorage, ILC cells undergo a sustained cell cycle arrest in G0/G1 while maintaining viability. From the genes that are upregulated in anchorage independent ILC cells, we selected Inhibitor of DNA binding 2 (Id2), a mediator of cell cycle progression. Using loss-of-function experiments, we demonstrate that Id2 is essential for anchorage independent survival (anoikis resistance) in vitro and lung colonization in mice. Importantly, we find that under anchorage independent conditions, E-cadherin loss promotes expression of Id2 in multiple mouse and (organotypic) human models of ILC, an event that is caused by a direct p120-catenin/Kaiso-dependent transcriptional de-repression of the canonical Kaiso binding sequence TCCTGCNA. Conversely, stable inducible restoration of E-cadherin expression in the ILC cell line SUM44PE inhibits Id2 expression and anoikis resistance. We show evidence that Id2 accumulates in the cytosol, where it induces a sustained and CDK4/6-dependent G0/G1 cell cycle arrest through interaction with hypo-phosphorylated Rb. Finally, we find that Id2 is indeed enriched in ILC when compared to other breast cancers, and confirm cytosolic Id2 protein expression in primary ILC samples. In sum, we have linked mutational inactivation of E-cadherin to direct inhibition of cell cycle progression. Our work indicates that loss of E-cadherin and subsequent expression of Id2 drive indolence and dissemination of ILC. As such, E-cadherin and Id2 are promising candidates to stratify low and intermediate grade invasive breast cancers for the use of clinical cell cycle intervention drugs.

The ubiquitin-dependent ATPase p97 removes cytotoxic trapped PARP1 from chromatin.

Poly (ADP-ribose) polymerase (PARP) inhibitors elicit antitumour activity in homologous recombination-defective cancers by trapping PARP1 in a chromatin-bound state. How cells process trapped PARP1 remains unclear. Using wild-type and a trapping-deficient PARP1 mutant combined with rapid immunoprecipitation mass spectrometry of endogenous proteins and Apex2 proximity labelling, we delineated mass spectrometry-based interactomes of trapped and non-trapped PARP1. These analyses identified an interaction between trapped PARP1 and the ubiquitin-regulated p97 ATPase/segregase. We found that following trapping, PARP1 is SUMOylated by PIAS4 and subsequently ubiquitylated by the SUMO-targeted E3 ubiquitin ligase RNF4, events that promote recruitment of p97 and removal of trapped PARP1 from chromatin. Small-molecule p97-complex inhibitors, including a metabolite of the clinically used drug disulfiram (CuET), prolonged PARP1 trapping and enhanced PARP inhibitor-induced cytotoxicity in homologous recombination-defective tumour cells and patient-derived tumour organoids. Together, these results suggest that p97 ATPase plays a key role in the processing of trapped PARP1 and the response of tumour cells to PARP inhibitors.