Cryo-EM Structures Delineate a pH-Dependent Switch that Mediates Endosomal Positioning of SARS-CoV-2 Spike Receptor-Binding Domains

The SARS-CoV-2 spike employs mobile receptor-binding domains (RBDs) to engage the ACE2 receptor and to facilitate virus entry. Antibodies can engage RBD but some, such as CR3022, fail to inhibit entry despite nanomolar spike affinity. Here we show the SARS-CoV-2 spike to have low unfolding enthalpy at serological pH and up to 10-times more unfolding enthalpy at endosomal pH, where we observe significantly reduced CR3022 affinity. Cryo-EM structures -at serological and endosomal pH- delineated spike recognition of up to three ACE2 molecules, revealing RBD to freely adopt the 'up' conformation. In the absence of ACE2, single-RBD-up conformations dominated at pH 5.5, resolving into a locked all-down conformation at lower pH. Notably, a pH-dependent refolding region (residues 824-858) at the spike-interdomain interface displayed dramatic structural rearrangements and mediated RBD positioning and spike shedding of antibodies like CR3022. An endosomal mechanism involving spike-conformational change can thus facilitate immune evasion from RBD-'up'-recognizing antibody.

Garcinoic Acid Is a Natural and Selective Agonist of Pregnane X Receptor

Pregnane X receptor (PXR) is a master xenobiotic-sensing transcription factor and a validated target for immune and inflammatory diseases. The identification of chemical probes to investigate the therapeutic relevance of the receptor is still highly desired. In fact, currently available PXR ligands are not highly selective and can exhibit toxicity and/or potential off-target effects. In this study, we have identified garcinoic acid as a selective and efficient PXR agonist. The properties of this natural molecule as a specific PXR agonist were demonstrated by the screening on a panel of nuclear receptors, the assessment of the physical and thermodynamic binding affinity, and the determination of the PXR-garcinoic acid complex crystal structure. Cytotoxicity, transcriptional, and functional properties were investigated in human liver cells, and compound activity and target engagement were confirmed in vivo in mouse liver and gut tissue. In conclusion, garcinoic acid is a selective natural agonist of PXR and a promising lead compound toward the development of new PXR-regulating modulators.

Abstract P2-14-23: Successful intraoperative margin assessment in DCIS and invasive breast cancer with diffuison-weighted MRI using the Clearsight™ system

Aim

Aim of our study is to evaluate the performance of the ClearSight™ system (ClearCut Medical, Ltd.) in assessing surgical margins for DCIS and IBC in breast conserving surgery

Material and Methods

The ClearSight™ system utilizes a diffusion-weighted-imaging (DWI) protocol to create 2D surface maps showing T2*, a MR parameter related to the tissue's apparent diffusion coefficient (ADC), with a depth penetration of 1.5mm. ADC is a highly accurate differentiator for irregular versus normal tissue.

From November 2017 a prospective, blinded post marketing study (N=63), evaluating the performance of the ClearSight™ system has been conducted in the Breast Centre at the Agaplesion Markus Krankenhaus, Frankfurt, Germany. After standard evaluation with ultrasound and/or X-ray, the specimens were scanned with the ClearSight™ system, and results were compared with the final histopathology results on a margin per margin bases, applying a simple T2* threshold to flag irregular tissue.

Results

Breast specimens' margins from 60 patients were analyzed. Pursuant to the breast conserving surgery (BCS), 348 margins were scanned by the ClearSight™ system. A rigid T2* threshold comparison with the pathology findings resulted in a sensitivity of 80% and specificity of 84%. Accuracy for invasive and in-situ cancers was found to be similar for tissues scanned within one hour after excision. After that sensitivity for DCIS started to drop and was found to be 56% after 2 hours. Further accuracy improvements can be achieved if the reading physician is free to apply an intuitive diffusion map interpretation rather than adhere to a fixed threshold.

Conclusion

The data suggest that ClearSightTM can reduce excision rates by a robust 80% if the excised breast tissue is scanned within one hour. Tissue drying impacts sensitivity for DCIS negatively. Free map interpretation leads to better results than a fixed threshold.

Citation Format: Thill M, Kelling K, van Haasteren V, Traub L, Nölke J, Szwarcfiter I, Shapiro M, Schon A, Aulmann S. Successful intraoperative margin assessment in DCIS and invasive breast cancer with diffuison-weighted MRI using the Clearsight™ system [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P2-14-23.

Epidural analgesia in children: planning, organization and development of a new program

BACKGROUND

The goal of the present work is to describe the development and results of the pediatric epidural analgesia program at the ''Hospital Nacional de Pediatria Prof. Dr. J. P. Garrahan'' in Argentina.

METHODS

Patients with thoracotomy, abdominal surgery, osteotomy, amputations or severe trauma were included in the program. The program provided training to the entire staff, control and record of pain treatment and its consequences, 24 h a day availability of anesthesia staff and standard polices and procedures.

RESULTS

One hundred fifty children under 16 years of age (median age 11 years, median weight 35 kg) were included in the program during the first 18 months. The median of maximum pain reported during activity was 1 (interquartile range 1 to 4 points) using the Visual Analogue Scale (VAS) or Objective Pain Scale (OPS). Eighty seven children (CI 95% 50% to 67%) presented with postoperative nausea and vomiting, urinary retention, itching, motor blockade or sedation. No patient presented with respiratory depression, hypotension, local anaesthetic toxicity, epidural catheter related infection or death during the program evaluation. The postoperative care program enabled a 98-day reduction in treatment in the intensive care unit.

CONCLUSION

The safe use of pediatric epidural analgesia in general wards may require the careful selection of patients, systematic assessment by trained personnel, training of medical and nursing personnel, clear distribution of responsibilities, use of printed indications, systematic record of pain, sedation and complications, information and education of patients and parents, supply of systems for airway resuscitation and management and continuous quality control and revision of the methods.

Partial purification and characterization of nuclear ribonuclease P from wheat

Ribonuclease P (RNase P) from wheat nuclei has been purified over 1000-fold, using wheat germ extract as starting material and a combination of poly(ethylenglycol) precipitation and column chromatography. The enzyme was shown to be of nuclear origin by its characteristic ionic requirements; for optimum activity it requires 0.5-1.5 mM Mg2+, which can be partly replaced by Mn2+. With about 100 kDa, wheat nuclear RNase P has the lowest molecular mass reported so far for a eukaryotic RNase P. The enzyme has an isoelectric point of 5.0 and a buoyant density of 1.34 g/ml in CsCl, suggesting the presence of a nucleic acid component; it is, however, insensitive against treatment with micrococcal nuclease. Wheat germ RNase P requires an intact tertiary structure of the pre-tRNA substrate; its cleavage efficiency is also influenced by the presence of an intron, and by the nature of the 3' terminus of the substrate. The apparent Km and Vmax for an intronless plant pre-tRNA(Tyr) are 10.3 nM and 1.12 fmol/min, respectively.