Prevention of DNA Replication Stress by CHK1 Leads to Chemoresistance Despite a DNA Repair Defect in Homologous Recombination in Breast Cancer

Chromosomal instability not only has a negative effect on survival in triple-negative breast cancer, but also on the well treatable subgroup of luminal A tumors. This suggests a general mechanism independent of subtypes. Increased chromosomal instability (CIN) in triple-negative breast cancer (TNBC) is attributed to a defect in the DNA repair pathway homologous recombination. Homologous recombination (HR) prevents genomic instability by repair and protection of replication. It is unclear whether genetic alterations actually lead to a repair defect or whether superior signaling pathways are of greater importance. Previous studies focused exclusively on the repair function of HR. Here, we show that the regulation of HR by the intra-S-phase damage response at the replication is of overriding importance. A damage response activated by Ataxia telangiectasia and Rad3 related-checkpoint kinase 1 (ATR-CHK1) can prevent replication stress and leads to resistance formation. CHK1 thus has a preferred role over HR in preventing replication stress in TNBC. The signaling cascade ATR-CHK1 can compensate for a double-strand break repair error and lead to resistance of HR-deficient tumors. Established methods for the identification of HR-deficient tumors for Poly(ADP-Ribose)-Polymerase 1 (PARP1) inhibitor therapies should be extended to include analysis of candidates for intra-S phase damage response

Burnout among surgeons before and during the SARS-CoV-2 pandemic: an international survey

Background: SARS-CoV-2 pandemic has had many significant impacts within the surgical realm, and surgeons have been obligated to reconsider almost every aspect of daily clinical practice. Methods: This is a cross-sectional study reported in compliance with the CHERRIES guidelines and conducted through an online platform from June 14th to July 15th, 2020. The primary outcome was the burden of burnout during the pandemic indicated by the validated Shirom-Melamed Burnout Measure. Results: Nine hundred fifty-four surgeons completed the survey. The median length of practice was 10 years; 78.2% included were male with a median age of 37 years old, 39.5% were consultants, 68.9% were general surgeons, and 55.7% were affiliated with an academic institution. Overall, there was a significant increase in the mean burnout score during the pandemic; longer years of practice and older age were significantly associated with less burnout. There were significant reductions in the median number of outpatient visits, operated cases, on-call hours, emergency visits, and research work, so, 48.2% of respondents felt that the training resources were insufficient. The majority (81.3%) of respondents reported that their hospitals were included in the management of COVID-19, 66.5% felt their roles had been minimized; 41% were asked to assist in non-surgical medical practices, and 37.6% of respondents were included in COVID-19 management. Conclusions: There was a significant burnout among trainees. Almost all aspects of clinical and research activities were affected with a significant reduction in the volume of research, outpatient clinic visits, surgical procedures, on-call hours, and emergency cases hindering the training. Trial registration: The study was registered on clicaltrials.gov "NCT04433286" on 16/06/2020

The histone methyltransferase DOT1L is required for proper DNA damage response, DNA repair, and modulates chemotherapy responsiveness

Abstract Background Disruptor of telomeric silencing 1-like (DOT1L) is a non-SET domain containing methyltransferase known to catalyze mono-, di-, and tri-methylation of histone 3 on lysine 79 (H3K79me). DOT1L-mediated H3K79me has been implicated in chromatin-associated functions including gene transcription, heterochromatin formation, and DNA repair. Recent studies have uncovered a role for DOT1L in the initiation and progression of leukemia and other solid tumors. The development and availability of small molecule inhibitors of DOT1L may provide new and unique therapeutic options for certain types or subgroups of cancer. Methods In this study, we examined the role of DOT1L in DNA double-strand break (DSB) response and repair by depleting DOT1L using siRNA or inhibiting its methyltransferase activity using small molecule inhibitors in colorectal cancer cells. Cells were treated with different agents to induce DNA damage in DOT1L-depleted or -inhibited cells and analyzed for DNA repair efficiency and survival. Further, rectal cancer patient samples were analyzed for H3K79me3 levels in order to determine whether it may serve as a potential marker for personalized therapy. Results Our results indicate that DOT1L is required for a proper DNA damage response following DNA double-strand breaks by regulating the phosphorylation of the variant histone H2AX (γH2AX) and repair via homologous recombination (HR). Importantly, we show that small molecule inhibitors of DOT1L combined with chemotherapeutic agents that are used to treat colorectal cancers show additive effects. Furthermore, examination of H3K79me3 levels in rectal cancer patients demonstrates that lower levels correlate with a poorer prognosis. Conclusions In this study, we conclude that DOT1L plays an important role in an early DNA damage response and repair of DNA double-strand breaks via the HR pathway. Moreover, DOT1L inhibition leads to increased sensitivity to chemotherapeutic agents and PARP inhibition, which further highlights its potential clinical utility. Our results further suggest that H3K79me3 can be useful as a predictive and or prognostic marker for rectal cancer patients

High levels of RAD51 perturb DNA replication elongation and cause unscheduled origin firing due to impaired CHK1 activation

<p>In response to replication stress ATR signaling through CHK1 controls the intra-S checkpoint and is required for the maintenance of genomic integrity. Homologous recombination (HR) comprises a series of interrelated pathways that function in the repair of DNA double strand breaks and interstrand crosslinks. In addition, HR, with its key player RAD51, provides critical support for the recovery of stalled forks during replication. High levels of RAD51 are regularly found in various cancers, yet little is known about the effect of the increased RAD51 expression on intra-S checkpoint signaling. Here, we describe a role for RAD51 in driving genomic instability caused by impaired replication and intra-S mediated CHK1 signaling by studying an inducible RAD51 overexpression model as well as 10 breast cancer cell lines. We demonstrate that an excess of RAD51 decreases I-Sce-I mediated HR despite formation of more RAD51 foci. Cells with high RAD51 levels display reduced elongation rates and excessive dormant origin firing during undisturbed growth and after damage, likely caused by impaired CHK1 activation. In consequence, the inability of cells with a surplus of RAD51 to properly repair complex DNA damage and to resolve replication stress leads to higher genomic instability and thus drives tumorigenesis.</p

Outcome and recanalization rate of tandem basilar artery occlusion treated by mechanical thrombectomy

International audienceArrière-plan: Les occlusions de l’artère basilaire en tandem (tBAO) sont définies comme des occlusions concomitantes de l’artère basilaire basilaire et de l’artère vertébrale dominante extracrânienne. Le pronostic d’une telle tBAO traitée par thrombectomie mécanique (MT) a été peu rapporté. Le but de notre étude était de comparer l’innocuité et l’efficacité de la MT chez les patients atteints de tBAO par rapport à ceux présentant des occlusions d’artères basilaires non tandem (ntBAO).Patients et méthodes: Analyse rétrospective d’une base de données de patients ayant subi une MT dans deux centres universitaires. Tous les patients traités pour BAO ont été récupérés. Les patients atteints de tBAO, défini comme une BAO concomitante et une occlusion extracrânienne de l’artère vertébrale (VA) ou une sténose sévère ≥70% (segment V1 ou proximal V2) ont été comparés aux patients atteints de ntBAO.Résultats: Au total, 15 patients atteints de tBAO et 74 patients atteints de ntBAO ont été recrutés. Une reperfusion réussie (thrombolyse modifiée dans le score d’infarctus cérébral ≥2b) a été obtenue dans 73,3 % contre 90,5 % (RC = 0,29, IC à 95 % : 0,07-1,15), un bon résultat clinique (échelle de Rankin modifiée à 3 mois ≤2) a été atteint par 26,7 % contre 32,4 % (RC = 0,76 ; IC à 95 % : 0,24-2,63) et la mortalité à 3 mois était de 46,7 % contre 31 % (RC = 1,94 ; IC à 95 % : 0,63-6) des patients atteints de tBAO par rapport à ntBAO, respectivement. Deux patients (13,3 %) atteints de tBAO et trois (4 %) de ntBAO présentaient une hémorragie intracrânienne symptomatique (RC = 3,64 ; IC à 95 % : 0,55-24).Conclusion: La thrombectomie mécanique chez les patients présentant une occlusion de l’artère basilaire en tandem a tendance à être associée à des taux plus faibles de reperfusion réussie et à de bons résultats cliniques, ainsi qu’à un taux de mortalité plus élevé. Des études multicentriques plus vastes sont justifiées pour mieux préciser la sélection et la prise en charge appropriées de ces patients