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Molecular glues and bifunctional small molecules, such as targeted protein degraders, induce protein proximity to mediate gain-of-function pharmacology. Emerging technologies that synthetically manipulate protein surfaces to create neoproteins, and the development of covalent chemical probes for intra- and inter-protein surface labeling are described. Ligand-directed protein surface modification strategies have the potential to enhance the induced-proximity pharmacology toolkit and expand the druggable proteome, and this Opinion considers the opportunities and challenges that lie ahead.
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BACKGROUND: Abbreviated breast MRI (FAST MRI) is being introduced into clinical practice to screen women with mammographically dense breasts or with a personal history of breast cancer. This study aimed to optimise diagnostic accuracy through the adaptation of interpretation-training. METHODS: A FAST MRI interpretation-training programme (short presentations and guided hands-on workstation teaching) was adapted to provide additional training during the assessment task (interpretation of an enriched dataset of 125 FAST MRI scans) by giving readers feedback about the true outcome of each scan immediately after each scan was interpreted (formative assessment). Reader interaction with the FAST MRI scans used developed software (RiViewer) that recorded reader opinions and reading times for each scan. The training programme was additionally adapted for remote e-learning delivery. STUDY DESIGN: Prospective, blinded interpretation of an enriched dataset by multiple readers. RESULTS: 43 mammogram readers completed the training, 22 who interpreted breast MRI in their clinical role (Group 1) and 21 who did not (Group 2). Overall sensitivity was 83% (95%CI 81-84%; 1994/2408), specificity 94% (95%CI 93-94%; 7806/8338), readers' agreement with the true outcome kappa = 0.75 (95%CI 0.74-0.77) and diagnostic odds ratio = 70.67 (95%CI 61.59-81.09). Group 1 readers showed similar sensitivity (84%) to Group 2 (82% p = 0.14), but slightly higher specificity (94% v. 93%, p = 0.001). Concordance with the ground truth increased significantly with the number of FAST MRI scans read through the formative assessment task (p = 0.002) but by differing amounts depending on whether or not a reader had previously attended FAST MRI training (interaction p = 0.02). Concordance with the ground truth was significantly associated with reading batch size (p = 0.02), tending to worsen when more than 50 scans were read per batch. Group 1 took a median of 56 seconds (range 8-47,466) to interpret each FAST MRI scan compared with 78 (14-22,830, p < 0.0001) for Group 2. CONCLUSIONS: Provision of immediate feedback to mammogram readers during the assessment test set reading task increased specificity for FAST MRI interpretation and achieved high diagnostic accuracy. Optimal reading-batch size for FAST MRI was 50 reads per batch. Trial registration (25/09/2019): ISRCTN16624917.
Subject(s)
Breast Neoplasms , Learning Curve , Magnetic Resonance Imaging , Mammography , Humans , Female , Breast Neoplasms/diagnostic imaging , Breast Neoplasms/diagnosis , Magnetic Resonance Imaging/methods , Mammography/methods , Middle Aged , Early Detection of Cancer/methods , Prospective Studies , Aged , Sensitivity and Specificity , Image Interpretation, Computer-Assisted/methods , Breast/diagnostic imaging , Breast/pathologyABSTRACT
Background: Acute inpatient mental health services report high levels of safety incidents. The application of patient safety theory has been sparse, particularly concerning interventions that proactively seek patient perspectives. Objective(s): Develop and evaluate a theoretically based, digital monitoring tool to collect real-time information from patients on acute adult mental health wards about their perceptions of ward safety. Design: Theory-informed mixed-methods study. A prototype digital monitoring tool was developed from a co-design approach, implemented in hospital settings, and subjected to qualitative and quantitative evaluation. Setting and methods: Phase 1: scoping review of the literature on patient involvement in safety interventions in acute mental health care; evidence scan of digital technology in mental health contexts; qualitative interviews with mental health patients and staff about perspectives on ward safety. This, alongside stakeholder engagement with advisory groups, service users and health professionals, informed the development processes. Most data collection was virtual. Phase 1 resulted in the technical development of a theoretically based digital monitoring tool that collected patient feedback for proactive safety monitoring. Phase 2: implementation of the tool in six adult acute mental health wards across two UK NHS trusts; evaluation via focused ethnography and qualitative interviews. Statistical analysis of WardSonar data and routine ward data involving construction of an hour-by-hour data set per ward, permitting detailed analysis of the use of the WardSonar tool. Participants: A total of 8 patients and 13 mental health professionals participated in Phase 1 interviews; 33 staff and 34 patients participated in Phase 2 interviews. Interventions: Patients could use a web application (the WardSonar tool) to record real-time perceptions of ward safety. Staff could access aggregated, anonymous data to inform timely interventions. Results: Coronavirus disease 2019 restrictions greatly impacted the study. Stakeholder engagement permeated the project. Phase 1 delivered a theory-based, collaboratively designed digital tool for proactive patient safety monitoring. Phase 2 showed that the tool was user friendly and broadly acceptable to patients and staff. The aggregated safety data were infrequently used by staff. Feasibility depended on engaged staff and embedding use of the tool in ward routines. There is strong evidence that an incident leads to increased probability of further incidents within the next 4 hours. This puts a measure on the extent to which social/behavioural contagion persists. There is weak evidence to suggest that an incident leads to a greater use of the WardSonar tool in the following hour, but none to suggest that ward atmosphere predicts future incidents. Therefore, how often patients use the tool seems to send a stronger signal about potential incidents than patients' real-time reports about ward atmosphere. Limitations: Implementation was limited to two NHS trusts. Coronavirus disease 2019 impacted design processes including stakeholder engagement; implementation; and evaluation of the monitoring tool in routine clinical practice. Higher uptake could enhance validity of the results. Conclusions: WardSonar has the potential to provide a valuable route for patients to communicate safety concerns. The WardSonar monitoring tool has a strong patient perspective and uses proactive real-time safety monitoring rather than traditional retrospective data review. Future work: The WardSonar tool can be refined and tested further in a post Coronavirus disease 2019 context. Study registration: This study is registered as ISRCTN14470430. Funding: This award was funded by the National Institute for Health and Care Research (NIHR) Health and Social Care Delivery Research programme (NIHR award ref: NIHR128070) and is published in full in Health and Social Care Delivery Research; Vol. 12, No. 14. See the NIHR Funding and Awards website for further award information.
Mental health wards can feel unsafe. We know that patients and staff have different ideas about what makes a hospital ward safe or unsafe. Patients are often the first to know when the atmosphere on a ward becomes tense but, often, no one asks them for input or feedback at the time. We worked with service users and staff to develop new technology to make it easy for patients to tell staff about changes in the ward atmosphere. We put everyone's ideas together and some technical developers then built a digital safety tool to use on a tablet computer. Patients put in anonymous information about the ward atmosphere and staff can read it straight away. We tested it on six adult acute mental health wards for 10 weeks. We asked patients and staff what they thought about the tool and we looked at how it was being used. Patients and staff liked the look of the tool on the tablet computer. Some staff said they did not need it because they could tell how patients were feeling, but patients told us that staff did not talk with them much and did not always know when patients were feeling tense. Coronavirus disease 2019 made life difficult on the wards. Most ward managers said the tool could be helpful, but they had not had time to get used to it on the wards. Occasionally, the tablet computers were out of action. Many staff tried hard to use the tool. Most patient information was gathered when it was calm, perhaps because staff were not too busy to help them. We found that this tool could help staff know about tensions on the ward, but they need to get used to it and bring it into ward routines.
Subject(s)
COVID-19 , Patient Safety , Humans , Adult , Male , Female , COVID-19/epidemiology , Psychiatric Department, Hospital/organization & administration , United Kingdom , Qualitative Research , Middle Aged , Digital Technology , Mental Health Services/organization & administration , State Medicine/organization & administration , Patient Participation/methodsABSTRACT
Sulfonyl fluoride EM12-SF was developed previously to covalently engage a histidine residue in the sensor loop of cereblon (CRBN) in the E3 ubiquitin ligase complex CRL4CRBN. Here, we further develop the structure-activity relationships of additional sulfonyl fluoride containing ligands that possess a range of cereblon binding potencies in cells. Isoindoline EM364-SF, which lacks a key hydrogen bond acceptor present in CRBN molecular glues, was identified as a potent binder of CRBN. This led to the development of the reversible molecular glue CPD-2743, that retained cell-based binding affinity for CRBN and degraded the neosubstrate IKZF1 to the same extent as EM12, but unlike isoindolinones, lacked SALL4 degradation activity (a target linked to teratogenicity). CPD-2743 had high permeability and lacked efflux in Caco-2 cells, in contrast to the isoindolinone iberdomide. Our methodology expands the repertoire of sulfonyl exchange chemical biology via the advancement of medicinal chemistry design strategies.
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WHAT IS KNOWN ON THE SUBJECT: Mental health wards can feel unsafe. We know that patients and staff have different ideas about what makes a hospital ward safe or unsafe. Patients are often the first to know when the atmosphere on a ward becomes tense, but often, no one asks them for their views. Patients and staff are experts and should be included in discussions about how to make wards safer. WHAT THIS PAPER ADDS TO EXISTING KNOWLEDGE: We got together with some service users and staff, and made an app that helps patients to tell staff when they are not feeling safe on a mental health ward. We tried it out on six wards and we asked patients and staff what they thought. The app was easy to use and most people liked the look of it. Patients said staff did not talk with them enough and so they liked using the app. However, some staff said they could tell how patients were feeling without an app and so they did not need it. Ward managers told us that staff were often very busy and did not always have time to use the app. WHAT ARE THE IMPLICATIONS FOR PRACTICE: This app could help staff know straightaway when patients do not feel safe on the ward, so that they can act quickly to calm things down. To make the most of the app, staff need to get used to it and bring it into ward routines. ABSTRACT: INTRODUCTION: Safety improvement on mental health wards is of international concern. It should incorporate patient perspectives. AIM: Implementation and evaluation of 'WardSonar', a digital safety-monitoring tool for adult acute mental health wards, developed with stakeholders to communicate patients' real-time safety perceptions to staff. METHOD: Six acute adult mental health wards in England implemented the tool in 2022. Evaluation over 10 weeks involved qualitative interviews (34 patients, 33 staff), 39 focused ethnographic observations, and analysis of pen portraits. RESULTS: Implementation and evaluation of the WardSonar tool was feasible despite challenging conditions. Most patients valued the opportunity to communicate their immediate safety concerns, stating that staff had a poor understanding of them. Some staff said the WardSonar tool could help enhanced ward safety but recognised a need to incorporate its use into daily routines. Others said they did not need the tool to understand patients' safety concerns. DISCUSSION: Foreseeable challenges, including staff ambivalence and practical issues, appeared intensified by the post-COVID-19 context. IMPLICATIONS FOR PRACTICE: The WardSonar tool could improve ward safety, especially from patients' perspectives. Future implementation could support staff to use the real-time data to inform proactive safety interventions.
Subject(s)
Mobile Applications , Patient Safety , Psychiatric Department, Hospital , Humans , Patient Safety/standards , Adult , Male , Middle AgedABSTRACT
In small molecule organic chemistry, the heuristic insight into ring-forming processes that was enabled by Baldwin's rules some 50 years ago proved a step-change in the role of mechanistically guided synthesis. It created a lens upon and marker of fundamental stereoelectronic and conformation-guided chemical processes. However, despite the widespread role of stereoelectronics and conformational control in Biology, no equivalent coherent exploitation of trapped, ring-forming processes yet exists in biomolecules. In the development of a minimal ring-closing process in intact proteins that might prove suitable in a coherent rule-set, we have tested endo-trig ring-closing conjugate thioether lanthionine (Lan) -CH2-S-CH2- formation as a limiting cyclization. Spontaneous Lan formation in proteins is rare if not non-existent and when found in natural product cyclic peptides it requires the mediation of corresponding biosynthetic enzymes as well as productive reactive conformations to guide it. Here, we show that within a conformationally flexible and functionally important protein loop - the MAPK kinase phosphorylation-targeted activation loop - Lan ring-closing is possible. Ring-closing proves to be critically dependent on the location of a trig electrophilic site in just one of two regioisomeric potential precursors to allow phosphosite-to-phosphosite 'stapling'. This first example of spontaneous protein thioether ring-closing/'stapling' and its accessibility from just one precursor (despite the potential for both to form an identical 'staple') now reveals the potential for Lan formation not only as an accessible form of minimal stapling in proteins but also as an exquisitely sensitive probe of associated protein geometries. We suggest that the use of this (as well as the development of other such, intramolecular protein traps that are dependent on inherent protein-controlled reactivity rather than forced crosslinking) may allow the broader trapping and mapping of relevant, even minor, protein states. In this way, protein ring formation may enable a form of extended 'bio-Baldwin's rules' that help to delineate relevant protein conformational space.
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Many cereblon (CRBN) ligands have been used to develop proteolysis targeting chimeras (PROTACs), but all are reversible binders of the E3 ubiquitin ligase. We recently described the use of sulfonyl exchange chemistry to design binders that covalently engage histidine 353 in CRBN for the first time. Here we show that covalent CRBN ligands can be used to develop efficient PROTAC degraders. We demonstrate that the fluorosulfate PROTAC FS-ARV-825 covalently labels CRBN in vitro, and in cells the BRD4 degrader is insensitive to wash-out and competition by potent reversible CRBN ligands, reflecting enhanced pharmacodynamics. We anticipate that covalent CRBN-based PROTACs will enhance degradation efficiencies, thus expanding the scope of addressable targets using the heterobifunctional degrader modality.
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Site-specific modification of amino acid residues in protein binding pockets using sulfonyl exchange chemistry expands the druggable proteome by enabling the development of covalent modulators that target residues beyond cysteine. Sulfonyl fluoride and triazole electrophiles were incorporated previously into the cereblon (CRBN) molecular glue degrader EM12, to covalently engage His353 within the CRBN sensor loop, but these probes had poor human plasma stability. Attenuation of intrinsic reactivity through the development of sulfonyl pyrazoles, imidazoles, and nucleobases enhanced plasma stability, and several compounds retained efficient labeling of His353. For example, sulfonyl imidazole EM12-SO2Im covalently blocked the CRBN binding site and possessed excellent metabolic stability in human plasma, liver microsomes, and hepatocytes. These results highlight the potential suitability of sulfonyl imidazole and related sulfur(VI)-diazole exchange (SuDEx) warheads for covalent drug development and further exemplify the therapeutic promise of site-specific histidine targeting.
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Targeted protein degradation has become a popular strategy to expand the druggable proteome, but therapeutic options for membrane proteins are limited. Sun et al. have now developed R-spondin chimeras (ROTACs) that effectively mediate lysosomal degradation of PD-L1, thus providing a modular platform that may be applicable to other membrane proteins.
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Targeted protein degradation (TPD) has emerged as a potentially transformational therapeutic modality with considerable promise. Molecular glue degraders remodel the surface of E3 ligases inducing interactions with neosubstrates resulting in their polyubiquitination and proteasomal degradation. Molecular glues are clinically precedented and have demonstrated the ability to degrade proteins-of-interest (POIs) previously deemed undruggable due to the absence of a traditional small molecule binding pocket. Heterobifunctional proteolysis targeting chimeras (PROTACs) possess ligands for an E3 complex and the POIs, which are chemically linked together, and similarly hijack the ubiquitin machinery to deplete the target. There has been a recent surge in the number of degraders entering clinical trials, particularly directed toward cancer. Nearly all utilize CRL4CRBN as the E3 ligase, and a relatively limited diversity of POIs are currently targeted. In this review, we provide an overview of the degraders in clinical trials and provide a perspective on the lessons learned from their development and emerging human data that will be broadly useful to those working in the TPD field.
Subject(s)
Neoplasms , Proteins , Humans , Proteins/metabolism , Ubiquitin-Protein Ligases/metabolism , Proteolysis , Neoplasms/drug therapyABSTRACT
INTRODUCTION: Covalent drug discovery has traditionally focused on targeting cysteine, but the amino acid is often absent in protein binding sites. This review makes the case to move beyond cysteine labeling using sulfur (VI) fluoride exchange (SuFEx) chemistry to expand the druggable proteome. AREAS COVERED: Recent advances in SuFEx medicinal chemistry and chemical biology are described, which have enabled the development of covalent chemical probes that site-selectively engage amino acid residues (including tyrosine, lysine, histidine, serine, and threonine) in binding pockets. Areas covered include chemoproteomic mapping of the targetable proteome, structure-based design of covalent inhibitors and molecular glues, metabolic stability profiling, and synthetic methodologies that have expedited the delivery of SuFEx modulators. EXPERT OPINION: Despite recent innovations in SuFEx medicinal chemistry, focused preclinical research is required to ensure the field moves from early chemical probe discovery to the delivery of transformational covalent drug candidates. The authors believe that covalent drug candidates designed to engage residues beyond cysteine using sulfonyl exchange warheads will likely enter clinical trials in the coming years.
Subject(s)
Fluorides , Proteome , Humans , Fluorides/chemistry , Cysteine , Sulfur/chemistry , Drug DiscoveryABSTRACT
Heterobifunctional degraders, known as proteolysis targeting chimeras (PROTACs), theoretically possess a catalytic mode-of-action, yet few studies have either confirmed or exploited this potential advantage of event-driven pharmacology. Degraders of oncogenic EML4-ALK fusions were developed by conjugating ALK inhibitors to cereblon ligands. Simultaneous optimization of pharmacology and compound properties using ternary complex modeling and physicochemical considerations yielded multiple catalytic degraders that were more resilient to clinically relevant ATP-binding site mutations than kinase inhibitor drugs. Our strategy culminated in the design of the orally bioavailable derivative CPD-1224 that avoided hemolysis (a feature of detergent-like PROTACs), degraded the otherwise recalcitrant mutant L1196M/G1202R in vivo, and commensurately slowed tumor growth, while the third generation ALK inhibitor drug lorlatinib had no effect. These results validate our original therapeutic hypothesis by exemplifying opportunities for catalytic degraders to proactively address binding site resistant mutations in cancer.
Subject(s)
Antineoplastic Agents , Lung Neoplasms , Humans , Anaplastic Lymphoma Kinase , Antineoplastic Agents/pharmacology , Receptor Protein-Tyrosine Kinases , Lung Neoplasms/drug therapy , Protein Kinase Inhibitors/pharmacology , Mutation , Drug Resistance, Neoplasm , Oncogene Proteins, Fusion/geneticsABSTRACT
The ability to rapidly and selectively modulate cellular protein levels using small molecules is essential for studying complex biological systems. Degradation tags, such as dTAG, allow for selective protein removal with a specific degrader molecule, but their utility is limited by the large tag size (>12 kDa) and the low efficiency of fusion product gene knock-in. Here, we describe the development of a short 24 amino acid peptide tag that enables cell-based quantification and covalent functionalization of proteins to which it is fused. The minimalistic peptide, termed HiBiT-SpyTag, incorporates the HiBiT peptide for protein level quantification and SpyTag, which forms a spontaneous isopeptide bond in the presence of the SpyCatcher protein. Transient expression of dTAG-SpyCatcher efficiently labels HiBiT-SpyTag-modified BRD4 or IRE1α in cells, and subsequent treatment with the dTAG13 degrader results in efficient protein removal without the need for full dTAG knock-in. We also demonstrate the utility of HiBiT-SpyTag for validating the degradation of the endoplasmic reticulum (ER) stress sensor IRE1α, which led to the development of the first PROTAC degrader of the protein. Our modular HiBiT-SpyTag system represents a valuable tool for the efficient development of degraders and for studying other proximity-induced pharmacology.
Subject(s)
Chromatography, Affinity , Molecular Probes , Peptides , Proteolysis , Endoribonucleases , Nuclear Proteins , Peptides/chemistry , Protein Serine-Threonine Kinases , Transcription Factors , Molecular Probes/chemistry , Molecular Probes/metabolism , Proteolysis Targeting Chimera/chemistry , Proteolysis Targeting Chimera/metabolism , Chromatography, Affinity/methodsABSTRACT
Thalidomide and its derivatives are molecular glues that bind cereblon (CRBN), a component of an E3 ubiquitin ligase complex, and mediate protein interactions with neosubstrates resulting in their polyubiquitination and proteasomal degradation. The structural features of neosubstrate binding have been elucidated that highlight key interactions with a ß-hairpin degron containing a glycine, which is present in a wide-range of proteins, including zinc-finger transcription factors such as IKZF1, and the translation termination factor GSPT1. Here, we profile 14 closely-related thalidomide derivatives in CRBN occupancy, and IKZF1 and GSPT1 degradation cell-based assays, and use crystal structures, computational docking and molecular dynamics to delineate subtle structure-activity relationships. Our findings will enable the rational design of CRBN modulators in the future, and help avoid the degradation of GSPT1 which is broadly cytotoxic.
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Small molecule ligands of cereblon (CRBN), a component of an E3 ubiquitin ligase complex, such as immunomodulatory drugs (IMiDs) or proteolysis targeting chimeras (PROTACs), induce new interactions between the E3 and a target protein that is subsequently polyubiquitinated and proteasomally degraded. The development of new degraders requires validation of CRBN-dependence and existing methods include the use of engineered CRBN knockout cell lines, or PROTACs directed to CRBN itself. Technical limitations of these approaches necessitate a simple and rapid pharmacological method of CRBN inhibition. We developed a sulfonyl fluoride covalent CRBN ligand based on the IMiD EM12 called EM12-SO2F that was designed to engage His353 on the surface of the IMiD binding site. EM12-SO2F does not act as a molecular glue degrader like other IMiDs, and instead serves as an inhibitor of such function by blocking the degrader binding site. We demonstrate utility of EM12-SO2F by inhibiting the degradation of the zinc-finger transcription factor and CRBN neosubstrate IKZF1 by the molecular glue degrader lenalidomide. Increasingly, libraries of degrader molecules are being screened phenotypically to identify starting points for hit elaboration, that simultaneously reveals new therapeutic targets amenable to degradation. Indeed, targeted protein degradation has become an exciting new therapeutic modality and EM12-SO2F augments the chemical biology toolbox that will advance this area of drug discovery research.
Subject(s)
Immunomodulating Agents , Ubiquitin-Protein Ligases , Ubiquitin-Protein Ligases/metabolism , Proteolysis , Lenalidomide , Cell LineABSTRACT
Measurement of target engagement in cells is critical to understand the molecular pharmacology of drugs and chemical probes. Many targeted protein degraders engage the E3 ligase CRL4CRBN and induce proximity with target neosubstrates resulting in their polyubiquitination and subsequent proteasomal degradation. Here we describe the development of a sensitive and robust cellular NanoBRET-based assay that measures occupancy of the CRBN ligand binding site. The assay is based on a bioluminescence resonance energy transfer (BRET) between NanoLuc luciferase tagged CRBN and a BODIPY-lenalidomide tracer which can be competed out by CRBN ligands, including PROTACs and molecular glues. The assay is compatible with a 384-well plate setup, does not require transfections and can be performed in a single day with only 3-4h of laboratory time. The protocols can be used to design other NanoLuc fusion engagement assays based on BODIPY tracers.
Subject(s)
Ubiquitin-Protein Ligases , Ubiquitin-Protein Ligases/metabolism , Ubiquitination , Lenalidomide/pharmacology , Ligands , ProteolysisABSTRACT
Background: The high documentation demands and limited time in direct patient care in the first year of internal medicine residency represent concerns for burnout and low job satisfaction in this important year of training. Objective: To assess the effect of scribes on the time PGY-1 residents spent on various work tasks. Methods: Participants were 24 PGY-1 internal medicine residents on two inpatient medicine teams at one site for 6 months (September 2019-February 2020). Residents were assigned a scribe during the first or second 2 weeks of a 4-week rotation and had no scribe for the other 2 weeks. Time study observers documented resident work activities. Residents ranked the meaningfulness of work activities via survey at the end of each 2-week period. Results: Of 24 residents, 18 (75%) completed the survey at both time points. Residents ranked patient care as the most meaningful and EHR work as the least meaningful work activity. EHR work claimed the largest percentage of time, with or without a scribe (mean, 33.2% and 39%, respectively). With a scribe, residents spent significantly less time (-5.8%, P < 0.0001) in EHR work and significantly more time (1.3%, P = 0.0267) in direct patient care and coordinating patient care (3.0%, P < 0.0001). Conclusions: The presence of a scribe with PGY-1 internal medicine residents on inpatient teams resulted in a significantly greater percentage of total work time spent in work they considered most meaningful and a significantly lower percentage of total work time in work they considered least meaningful.
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OBJECTIVE: To investigate any association between expressions of parents' continuing bond with their stillborn baby and bereavement adaptation. BACKGROUND: Continuing bonds theory suggests that bereaved parents adapt to the loss of their child by sharing and transforming mental representations of the child, allowing them to be integrated into parents' everyday lives. Little is known about the mental health benefits of expressing continuing bonds following stillbirth. This study examined any association between aspects of parents' relationship with their stillborn baby, social support for the relationship, and bereavement adaptation. METHODS: Cross-sectional questionnaire study. Parents of stillborn babies (N=170) completed an online questionnaire examining engagement in continuing bonds expressions; characteristics of parents' relationship with their stillborn baby and their experience of sharing it; social support, and meaning-making. Measures of mental health were included to quantify bereavement adaptation. RESULTS: Regression analyses showed that time since death, meaning-making, engaging with nature, and legacy building are positively linked to bereavement adaptation. Risk factors included inadequate social support for the relationship, a greater desire to share it more freely, an increased sense of integration with baby, and societal pressure to move on. CONCLUSION: Key aspects of parents' ongoing relationship with their stillborn baby and the social context are related to bereavement adaptation.