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Immunomodulatory imide drugs (IMiDs) are central components of therapy for multiple myeloma (MM). IMiDs bind cereblon (CRBN), an adaptor for the CUL4-DDB1-RBX1 E3 ligase to change its substrate specificity and induce degradation of 'neosubstrate' transcription factors that are essential to MM cells. Mechanistic studies to date have largely focussed on mediators of therapeutic activity and insight into clinical IMiD toxicities is less developed. We adopted BioID2-dependent proximity labelling (BioID2-CRBN) to characterise the CRBN interactome in the presence and absence of various IMiDs and the proteasome inhibitor, bortezomib. We aimed to leverage this technology to further map CRBN interactions beyond what has been achieved by conventional proteomic techniques. In support of this approach, analysis of cells expressing BioID2-CRBN following IMiD treatment displayed biotinylation of known CRBN interactors and neosubstrates. We observed that bortezomib alone significantly modifies the CRBN interactome. Proximity labelling also suggested that IMiDs augment the interaction between CRBN and proteins that are not degraded, thus designating 'neointeractors' distinct from previously disclosed 'neosubstrates'. Here we identify Non-Muscle Myosin Heavy Chain IIA (MYH9) as a putative CRBN neointeractor that may contribute to the haematological toxicity of IMiDs. These studies provide proof of concept for proximity labelling technologies in the mechanistic profiling of IMiDs and related E3-ligase-modulating drugs.

BACKGROUND: Hypotension following orthopaedic surgery has been associated with increased morbidity and mortality. Rapid response teams (RRT) review patients on hospital wards with hypotension. AIM: To evaluate the epidemiology of hypotensive RRT activations in adult orthopaedic patients to identify contributing factors and areas for future quality improvement. METHODS: Timing of RRT activations, presumed causes of hypotension and associated treatments were assessed. RESULTS: Among 963 RRT activations in 605 patients over 3 years, the first calls of 226 of 605 patients were due to hypotension, and 213 (94.2%) of 226 had sufficient data for analysis. The median age was 79 (interquartile range 66-87) years; 58 (27.2%) were male, and comorbidities were common. Most (68%) surgery was emergent, and 75.1% received intraoperative vasopressors for hypotension. Most activations occurred within 24 h of surgery, and hypovolaemia, infection and arrhythmias were common presumed causes. Fluid boluses occurred in 173 (81.2%), and the time between surgery and RRT activation was 10 (4.0-26.5) h. in cases where fluid boluses were given, compared with 33 (15.5-61.5) h. where they were not (P < 0.001). Blood transfusion (30, 14.1%) and withholding of medications were also common. Hospital mortality was 8.5% (18), and 13.6% (29) were admitted to critical care at some stage. In-hospital death was associated with older age, functional dependence, arrhythmia and presumed infection. CONCLUSIONS: Hypotension-related RRT calls in orthopaedic patients are common. Future interventional studies might focus on perioperative fluid therapy and vaso-active medications, as well as withholding of anti-hypertensive medications preoperatively.