Evidence That Anemia Accelerates AS Progression Via Shear-Induced TGF-ß1 Activation: Heyde's Syndrome Comes Full Circle.

The severity of aortic stenosis (AS) is associated with acquired von Willebrand syndrome (AVWS) and gastrointestinal bleeding, leading to anemia (Heyde's syndrome). We investigated how anemia is linked with AS and AVWS using the LA100 mouse model and patients with AS. Induction of anemia in LA100 mice increased transforming growth factor (TGF)-ß1 activation, AVWS, and AS progression. Patients age >75 years with severe AS had higher plasma TGF-ß1 levels and more severe anemia than AS patients age <75 years, and there was a correlation between TGF-ß1 and anemia. These data are compatible with the hypothesis that the blood loss anemia of Heyde's syndrome contributes to AS progression via WSS-induced activation of platelet TGF-ß1 and additional gastrointestinal bleeding via WSS-induced AVWS.

Critical Analysis of Thrombocytopenia Associated With Glycoprotein IIb/IIIa Inhibitors and Potential Role of Zalunfiban, a Novel Small Molecule Glycoprotein Inhibitor, in Understanding the Mechanism(s).

Thrombocytopenia is a rare but serious complication of the intravenous glycoprotein IIb/IIIa (GPIIb/IIIa; integrin αIIbß3) receptor inhibitors (GPIs), abciximab, eptifibatide, and tirofiban. The thrombocytopenia ranges from mild (50 000-100 000 platelets/µL), to severe (20 000 to <50 000/µL), to profound (<20 000/µL). Profound thrombocytopenia appears to occur in <1% of patients receiving their first course of therapy. Thrombocytopenia can be either acute (<24 hours) or delayed (up to ~14 days). Both hemorrhagic and thrombotic complications have been reported in association with thrombocytopenia. Diagnosis requires exclusion of pseudothrombocytopenia and heparin-induced thrombocytopenia. Therapy based on the severity of thrombocytopenia and symptoms may include drug withdrawals and treatment with steroids, intravenous IgG, and platelet transfusions. Abciximab-associated thrombocytopenia is most common and due to either preformed antibodies or antibodies induced in response to abciximab (delayed). Readministration of abciximab is associated with increased risk of thrombocytopenia. Evidence also supports an immune basis for thrombocytopenia associated with the 2 small molecule GPIs. The latter bind αIIbß3 like the natural ligands and thus induce the receptor to undergo major conformational changes that potentially create neoepitopes. Thrombocytopenia associated with these drugs is also immune-mediated, with antibodies recognizing the αIIbß3 receptor only in the presence of the drug. It is unclear whether the antibody binding depends on the conformational change and whether the drug contributes directly to the epitope. Zalunfiban, a second-generation subcutaneous small molecule GPI, does not induce the conformational changes; therefore, data from studies of zalunfiban will provide information on the contribution of the conformational changes to the development of GPI-associated thrombocytopenia.

Building an infrastructure to support the development, conduct, and reporting of informative clinical studies: The Rockefeller University experience.

Introduction: Clinical trials are a vital component of translational science, providing crucial information on the efficacy and safety of new interventions and forming the basis for regulatory approval and/or clinical adoption. At the same time, they are complex to design, conduct, monitor, and report successfully. Concerns over the last two decades about the quality of the design and the lack of completion and reporting of clinical trials, characterized as a lack of "informativeness," highlighted by the experience during the COVID-19 pandemic, have led to several initiatives to address the serious shortcomings of the United States clinical research enterprise. Methods and Results: Against this background, we detail the policies, procedures, and programs that we have developed in The Rockefeller University Center for Clinical and Translational Science (CCTS), supported by a Clinical and Translational Science Award (CTSA) program grant since 2006, to support the development, conduct, and reporting of informative clinical studies. Conclusions: We have focused on building a data-driven infrastructure to both assist individual investigators and bring translational science to each element of the clinical investigation process, with the goal of both generating new knowledge and accelerating the uptake of that knowledge into practice.

Prepercutaneous coronary intervention Zalunfiban dose-response relationship to target vessel blood flow at initial angiogram in st-elevation myocardial infarction - A post hoc analysis of the cel-02 phase IIa study.

BACKGROUND: Zalunfiban (RUC-4) is a novel, subcutaneously administered glycoprotein IIb/IIIa inhibitor (GPI) designed for prehospital treatment to initiate reperfusion in the infarct-related artery (IRA) before primary percutaneous coronary intervention in patients with ST-elevation myocardial infarction (STEMI). Since GPIs have been reported to rapidly reperfuse IRAs, we assessed whether there was a dose-dependent relationship between zalunfiban treatment and angiographic reperfusion indices and thrombus grade of the IRA at initial angiogram in patients with STEMI. METHODS: This was a post hoc analysis from the open-label Phase IIa study that investigated the pharmacodynamics, pharmacokinetics, and tolerability of three doses of zalunfiban - 0.075, 0.090 and 0.110 mg/kg - in STEMI patients. This analysis explored dose-dependent associations between zalunfiban and three angiographic indices of the IRA, namely coronary and myocardial blood flow and thrombus burden. Zalunfiban was administered in the cardiac catheterization laboratory prior to vascular access, ∼10 to 15 minutes before the initial angiogram. All angiographic data were analyzed by a blinded, independent, core laboratory. RESULTS: Twentyfour out of 27 STEMI patients were evaluable for angiographic analysis (0.075 mg/kg [n=7], 0.090 mg/kg [n=9], and 0.110 mg/kg [n=8]). TIMI flow grade 2 or 3 was seen in 1/7 patients receiving zalunfiban at 0.075 mg/kg, in 6/9 patients receiving 0.090 mg/kg, and in 7/8 patients receiving 0.110 mg/kg (ptrend = 0.004). A similar trend was observed based on TIMI flow grade 3. Myocardial perfusion was also related to zalunfiban dose (ptrend = 0.005) as reflected by more frequent TIMI myocardial perfusion grade 3. Consistent with the dose-dependent trends in greater coronary and myocardial perfusion, TIMI thrombus ≥4 grade was inversely related to zalunfiban dose (ptrend = 0.02). CONCLUSION: This post hoc analysis found that higher doses of zalunfiban administered in the cardiac catheterization lab prior to vascular access were associated with greater coronary and myocardial perfusion, and lower thrombus burden at initial angiogram in patients with STEMI undergoing primary percutaneous coronary intervention.

Prehospital treatment with zalunfiban (RUC-4) in patients with ST- elevation myocardial infarction undergoing primary percutaneous coronary intervention: Rationale and design of the CELEBRATE trial.

BACKGROUND: Early and complete restoration of target vessel patency in ST-elevation myocardial infarction (STEMI) is associated with improved outcomes. Oral P2Y12 inhibitors have failed to demonstrate either improved patency or reduced mortality when administered in the prehospital setting. Thus, there is a need for antiplatelet agents that achieve prompt and potent platelet inhibition, and that restore patency in the prehospital setting. Zalunfiban, a novel subcutaneously administered glycoprotein IIb/IIIa inhibitor designed for prehospital administration, has shown to achieve rapid, high-grade platelet inhibition that exceeds that of P2Y12 inhibitors. Whether prehospital administration of zalunfiban can improve clinical outcome is unknown. HYPOTHESIS: The present study is designed to assess the hypothesis that a single, prehospital injection of zalunfiban given in the ambulance, in addition to standard-of-care in patients with STEMI with intent to undergo primary percutaneous coronary intervention (PCI) will improve clinical outcome compared to standard-of-care with placebo. STUDY DESIGN: The ongoing CELEBRATE trial (NCT04825743) is a phase 3, randomized, double-blinded, placebo-controlled, international trial. Patients with STEMI intended to undergo primary PCI will receive treatment with a single subcutaneous injection containing either zalunfiban dose 1 (0.110 mg/kg), zalunfiban dose 2 (0.130 mg/kg) or placebo, and the study drug will be administered in the ambulance before transportation to the hospital. A target of 2499 patients will be randomly assigned to one of the treatment groups in a 1:1:1 ratio, ie, to have approximately 833 evaluable patients per group. The primary efficacy outcome is a ranked 7-point scale on clinical outcomes. The primary safety outcome is severe or life-threatening bleeding according to the Global Use of Strategies to Open Occluded Coronary Arteries (GUSTO) criteria. SUMMARY: The CELEBRATE trial will assess whether a single prehospital subcutaneous injection of zalunfiban in addition to standard-of-care in patients with STEMI with intent to undergo primary PCI will result in improved clinical outcome.

Variability in International Society on Thrombosis and Haemostasis-Scientific and Standardization Committee endorsed Bleeding Assessment Tool (ISTH-BAT) score with normal aging in healthy females: contributory factors and clinical significance.

BACKGROUND: Bleeding assessment tools are key screening tests used in the evaluation of patients with suspected inherited bleeding disorders. The International Society on Thrombosis and Haemostasis-Scientific and Standardization Committee endorsed Bleeding Assessment Tool (ISTH-BAT) has differing reference ranges for adult males (0-3), adult females (0-5), and children (0-2), reflecting differing bleeding symptoms and exposure to hemostatic challenges in these healthy population subgroups. Age is known to markedly impact bleeding score in individuals with von Willebrand disease. However, the influence of age on bleeding score in healthy adult controls is poorly understood. OBJECTIVES: We aimed to assess variability in ISTH-BAT score with age among healthy control females. METHODS: We used the legacy "Merging Project" dataset of normal healthy controls upon which current ISTH-BAT normal ranges are based. We included women, totaling 646 individuals. The normal range (middle 95th percentile) of total ISTH-BAT and grouped subdomain scores between age quartiles was assessed. RESULTS: The normal range of ISTH-BAT scores increased with age, ranging from 0 to 4 in the youngest quartile (age range, 18-30) to 0 to 6 in the oldest (age range, 52-88). This increased variability with aging was related both to high menorrhagia domain scores in older women and an increase in postprocedural bleeding with accumulated exposure to hemostatic challenges. CONCLUSIONS: Cumulatively, our data highlight that normal aging leads to increased variability in bleeding scores in healthy adult females. Further refinement of the ISTH-BAT with age-adjusted reference ranges may improve the sensitivity and specificity of the tool among females.

Structure-Based Discovery of a Novel Class of Small-Molecule Pure Antagonists of Integrin αVß3.

Inhibitors of integrin αVß3 have therapeutic promise for a variety of diseases. Most αVß3-targeting small molecules patterned after the RGD motif are partial agonists because they induce a high-affinity, ligand-binding conformation and prime the receptor to bind the ligand without an activating stimulus, in part via a charge-charge interaction between their aspartic acid carboxyl group and the metal ion in the metal-ion-dependent adhesion site (MIDAS). Building upon our previous studies on the related integrin αIIbß3, we searched for pure αVß3 antagonists that lack this typical aspartic acid carboxyl group and instead engage through direct binding to one of the coordinating residues of the MIDAS metal ion, specifically ß3 E220. By in silico screening of two large chemical libraries for compounds interacting with ß3 E220, we indeed discovered a novel molecule that does not contain an acidic carboxyl group and does not induce the high-affinity, ligand-binding state of the receptor. Functional and structural characterization of a chemically optimized version of this compound led to the discovery of a novel small-molecule pure αVß3 antagonist that (i) does not prime the receptor to bind the ligand and does not induce hybrid domain swing-out or receptor extension as judged by antibody binding and negative-stain electron microscopy, (ii) binds at the RGD-binding site as predicted by metadynamics rescoring of induced-fit docking poses and confirmed by a cryo-electron microscopy structure of the compound-bound integrin, and (iii) coordinates the MIDAS metal ion via a quinoline moiety instead of an acidic carboxyl group.

It's the water! The open and shut case of drug-induced integrin activation.

Integrin receptors are established drug targets, but many of the drugs that have been developed act as partial agonists, inducing the receptor into a high-affinity, ligand-binding state. Lin et al. discovered a general mechanism to circumvent this problem-stabilizing a key water molecule that prevents receptor activation. Their findings are likely to impact future therapeutic development.

KL2 scholars' perceptions of factors contributing to sustained translational science career success.

Introduction: Identifying the most effective ways to support career development of early stage investigators in clinical and translational science should yield benefits for the biomedical research community. Institutions with Clinical and Translational Science Awards (CTSA) offer KL2 programs to facilitate career development; however, the sustained impact has not been widely assessed. Methods: A survey comprised of quantitative and qualitative questions was sent to 2144 individuals that had previously received support through CTSA KL2 mechanisms. The 547 responses were analyzed with identifying information redacted. Results: Respondents held MD (47%), PhD (36%), and MD/PhD (13%) degrees. After KL2 support was completed, physicians' time was divided 50% to research and 30% to patient care, whereas PhD respondents devoted 70% time to research. Funded research effort averaged 60% for the cohort. Respondents were satisfied with their career progression. More than 95% thought their current job was meaningful. Two-thirds felt confident or very confident in their ability to sustain a career in clinical and translational research. Factors cited as contributing to career success included protected time, mentoring, and collaborations. Conclusion: This first large systematic survey of KL2 alumni provides valuable insight into the group's perceptions of the program and outcome information. Former scholars are largely satisfied with their career choice and direction, national recognition of their expertise, and impact of their work. Importantly, they identified training activities that contributed to success. Our results and future analysis of the survey data should inform the framework for developing platforms to launch sustaining careers of translational scientists.

Stakeholder Engagement In a Comparative Effectiveness/Implementation Study to Prevent Staphylococcus Aureus Infection Recurrence: CA-MRSA Project (CAMP2).

BACKGROUND: Methicillin-resistant or methicillin-sensitive Staphylococcus aureus skin and soft tissue infections pose serious clinical and public health challenges. Few protocols exist for outpatient education, decolonization and decontamination. OBJECTIVES: This trial implemented infection prevention protocols in homes via community health workers/Promotoras. METHODS: We engaged clinicians, patient stakeholders, clinical and laboratory researchers, New York-based federally qualified health centers and community hospital emergency departments. The Clinician and Patient Stakeholder Advisory Committee (CPSAC) convened in person and remotely for shared decision-making and trial oversight. RESULTS: The intervention trial consented participants with skin and soft tissue infections from Methicillin-resistant Staphylococcus aureus or methicillin-sensitive Staphylococcus aureus, completed home visits, obtained surveillance cultures from index patients and household members and sampled household environmental surfaces at baseline and three months. LESSONS LEARNED: The retention of the CPSAC during the trial demonstrated high levels of engagement. CONCLUSIONS: CPSAC was highly effective throughout design and execution by troubleshooting recruitment and home visit challenges.

The Rockefeller Team Science Leadership training program: Curriculum, standardized assessment of competencies, and impact of returning assessments.

The ability to effectively lead an interdisciplinary translational team is a crucial component of team science success. Most KL2 Clinical Scholars have been members of scientific teams, but few have been team science leaders. There is a dearth of literature and outcome measures of effective Team Science Leadership in clinical and translational research. We focused our curriculum to emphasize Team Science Leadership, developed a list of Team Science Leadership competencies for translational investigators using a modified Delphi method, and incorporated the competencies into a quantitative evaluation survey. The survey is completed on entry and annually thereafter by the Scholar; the Scholar's primary mentor and senior staff who educate and interact with the Scholar rate the Scholar at the end of each year. The program leaders and mentor review the results with each Scholar. The survey scales had high internal consistency and good factor structure. Overall ratings by mentors and senior staff were generally high, but ratings by Scholars tended to be lower, offering opportunities for discussion and career planning. Scholars rated the process favorably. A Team Science Leadership curriculum and periodic survey of attained competencies can inform individual career development and guide team science curriculum development.

Application of Auxiliary VerifyNow Point-of-Care Assays to Assess the Pharmacodynamics of RUC-4, a Novel αIIbß3 Receptor Antagonist.

Introduction Prehospital therapy of ST-elevation myocardial infarction (STEMI) with αIIbß3 antagonists improves clinical outcomes, but they are difficult to use in prehospital settings. RUC-4 is a novel αIIbß3 antagonist being developed for prehospital therapy of STEMI that rapidly achieves high-grade platelet inhibition after subcutaneous administration. Standard light transmission aggregometry (LTA) is difficult to perform during STEMI, so we applied VerifyNow (VN) assays to assess the pharmacodynamics of RUC-4 relative to aspirin and ticagrelor. Methods Blood from healthy volunteers was anticoagulated with phenylalanyl-prolyl-arginyl chloromethyl ketone (PPACK) or sodium citrate, treated in vitro with RUC-4, aspirin, and/or ticagrelor, and tested with the VN ADP + PGE 1 , iso-TRAP, and base channel (high concentration iso-TRAP + PAR-4 agonist) assays. The results were correlated with both ADP (20 µM)-induced LTA and flow cytometry measurement of receptor occupancy and data from individuals treated in vivo with RUC-4. Results RUC-4 inhibited all three VN assays, aspirin did not affect the assays, and ticagrelor markedly inhibited the ADP + PGE 1 assay, slightly inhibited the iso-TRAP assay, and did not inhibit the base channel assay. RUC-4's antiplatelet effects were potentiated in citrate compared with PPACK. Cut-off values were determined to correlate the results of the VN iso-TRAP and base channel assays with 80% inhibition of LTA. Conclusion The VN assays can differentiate the early potent anti-αIIbß3 effects of RUC-4 from delayed effects of P2Y12 antagonists in the presence of aspirin. These pharmacodynamic assays can help guide the clinical development of RUC-4 and potentially be used to monitor RUC-4's effects in clinical practice.

Comparative Effectiveness Study of Home-Based Interventions to Prevent CA-MRSA Infection Recurrence.

Recurrent skin and soft tissue infections (SSTI) caused by Community-Associated Methicillin-Resistant Staphylococcus aureus (CA-MRSA) or Methicillin-Sensitive Staphylococcus aureus (CA-MSSA) present treatment challenges. This community-based trial examined the effectiveness of an evidence-based intervention (CDC Guidelines, topical decolonization, surface decontamination) to reduce SSTI recurrence, mitigate household contamination/transmission, and improve patient-reported outcomes. Participants (n = 186) were individuals with confirmed MRSA(+)/MSSA(+) SSTIs and their household members. During home visits; Community Health Workers/Promotoras provided hygiene instructions; a five-day supply of nasal mupirocin; chlorhexidine for body cleansing; and household disinfecting wipes (Experimental; EXP) or Usual Care Control (UC CON) pamphlets. Primary outcome was six-month SSTI recurrence from electronic health records (EHR). Home visits (months 0; 3) and telephone assessments (months 0; 1; 6) collected self-report data. Index patients and participating household members provided surveillance culture swabs. Secondary outcomes included household surface contamination; household member colonization and transmission; quality of life; and satisfaction with care. There were no significant differences in SSTI recurrence between EXP and UC in the intent-to-treat cohort (n = 186) or the enrolled cohort (n = 119). EXP participants showed reduced but non-significant colonization rates. EXP and UC did not differ in household member transmission, contaminated surfaces, or patient-reported outcomes. This intervention did not reduce clinician-reported MRSA/MSSA SSTI recurrence. Taken together with other recent studies that employed more intensive decolonization protocols, it is possible that a promotora-delivered intervention instructing treatment for a longer or repetitive duration may be effective and should be examined by future studies.

Re-engineering The Clinical Research Enterprise in Response to COVID-19: The Clinical Translational Science Award (CTSA) experience and proposed playbook for future pandemics.

The 2020 COVID-19 pandemic has had a profound impact on the clinical research enterprises at the 60 Clinical and Translational Science Award (CTSA) Hubs throughout the nation. There was simultaneously a need to expand research to obtain crucial data about disease prognosis and therapy and enormous limitations on conducting research as localities and institutions limited travel and person-to-person contact. These imperatives resulted in major changes in the way research was conducted, including expediting Institutional Review Board review, shifting to remote interactions with participants, centralizing decision-making in prioritizing research protocols, establishing biobanks, adopting novel informatics platforms, and distributing study drugs in unconventional ways. National CTSA Steering Committee meetings provided an opportunity to share best practices and develop the idea of capturing the CTSA program experiences in a series of papers. Here we bring together the recommendations from those papers in a list of specific actions that research sites can take to strengthen operations and prepare for similar future public health emergencies. Most importantly, creative innovations developed in response to the COVID-19 pandemic deserve serious consideration for adoption as new standards, thus converting the painful trauma of the pandemic into "post-traumatic growth" that makes the clinical research enterprise stronger, more resilient, and more effective.

CTSA pharmacies: Contribution to research and public health during the COVID-19 pandemic.

INTRODUCTION: In March 2020, academic medical center (AMC) pharmacies were compelled to implement practice changes in response to the COVID-19 pandemic. These changes were described by survey data collected by the Clinical and Translational Science Awards (CTSA) program which were interpreted by a multi-institutional team of AMC pharmacists and physician investigators. METHODS: The CTSA program surveyed 60 AMC pharmacy departments. The survey included event timing, impact on pharmacy services, and corrective actions taken. RESULTS: Almost all departments (98.4%) reported at least one disruption. Shortages of personal protective equipment (PPE) were common (91.5%) as were drug shortages (66.0%). To manage drug shortages, drug prioritization protocols were utilized, new drug supply vendors were identified (79.3%), and onsite compounding was initiated. PPE shortages were managed by incorporating the risk mitigation strategies recommended by FDA and others. Research pharmacists supported new clinical research initiatives at most institutions (84.0%), introduced use of virtual site visits, and shipped investigational drugs directly to patients. Some pharmacies formulated novel investigational products for clinical trial use. Those AMC pharmacies within networked health systems assisted partner rural and inner-city hospitals by sourcing commercial and investigational drugs to alleviate local disease outbreaks and shortages in underserved populations. Pharmacy-based vaccination practice was expanded to include a wider range of pediatric and adult vaccines. CONCLUSION: The COVID-19 pandemic radically altered hospital pharmacy practice. By adopting innovative methods and adapting to regulatory imperatives, pharmacies at CTSA sites played an extremely important role supporting continuity of care and collaborating on critical clinical research initiatives.

Pharmacokinetics, pharmacodynamics, and tolerability of subcutaneous administration of a novel glycoprotein IIb/IIIa inhibitor, RUC-4, in patients with ST-segment elevation myocardial infarction.

BACKGROUND: Pre-hospital platelet inhibition in patients with ST-segment elevation myocardial infarction (STEMI) may improve outcomes. RUC-4 is a novel, second-generation glycoprotein IIb/IIIa inhibitor designed for first-point-of-medical-contact treatment for STEMI by subcutaneous injection. AIMS: The open-label, phase 2A, CEL-02 trial aimed to assess the pharmacodynamics (PD), pharmacokinetics (PK), and tolerability of RUC-4 in STEMI patients undergoing primary PCI (pPCI). METHODS: A total of 27 STEMI patients received a weight-adjusted subcutaneous injection of RUC-4 before pPCI in escalating doses (0.075 mg/kg [n=8], 0.090 mg/kg [n=9], or 0.110 mg/kg [n=10]). RESULTS: The primary PD endpoint of high-grade (≥77%) inhibition of the VerifyNow iso-TRAP assay at 15 minutes was met in 3/8, 7/8, and 7/8 patients in the three cohorts with a dose-response relationship (mean inhibition [min - max] of 77.5% [65.7%-90.6%], 87.5% [73.8%-93.1%], and 91.7% [76.4%-99.3%], respectively; ptrend=0.002). Fifty percent (50%) inhibition remained after 89.1 (38.0-129.7), 104.2 (17.6-190.8), and 112.4 (19.7-205.0) minutes. Injection site reactions or bruising were observed in 1 (4%) and 11 (41%) patients, respectively. Mild access-site haematomas occurred in 6 (22%), and severe access-site haematomas occurred in 2 patients (7%). No thrombocytopaenia was observed within 72 hours post dose. CONCLUSIONS: In patients with STEMI, a single subcutaneous dose of RUC-4 at 0.075, 0.090, and 0.110 mg/kg showed dose-response high-grade inhibition of platelet function within 15 minutes.

Pre-Hospital Antiplatelet Therapy for STEMI Patients Undergoing Primary Percutaneous Coronary Intervention: What We Know and What Lies Ahead.

Early recanalization of the infarct-related artery to achieve myocardial reperfusion is the primary therapeutic goal in patients with ST-elevation myocardial infarction (STEMI). To decrease the duration of ischaemia, continuous efforts have been made to improve pre-hospital treatment and to target the early period after symptom onset. In this period the platelet content of the fresh coronary thrombus is maximal and the thrombi are dynamic, and thus more susceptible to powerful antiplatelet agents. There have been substantial advances in antiplatelet therapy in the last three decades with several classes of oral and intravenous antiplatelet agents with different therapeutic targets, pharmacokinetics, and pharmacodynamic properties. New parenteral drugs achieve immediate inhibition of platelet aggregation, and fast and easy methods of administration may create the opportunity to bridge the initial gap in platelet inhibition observed with oral P2Y12 inhibitors. Moreover, potential future management of STEMI could directly involve patients in the process of care with self-administered antiplatelet agents designed to achieve rapid reperfusion. However, the potential anti-ischaemic benefits of potent antiplatelet agents will need to be balanced against their risk of increased bleeding. This study presents a comprehensive and updated review of pre-hospital antiplatelet therapy among STEMI patients undergoing primary percutaneous intervention and explores new therapies under development.

Electron microscopy shows that binding of monoclonal antibody PT25-2 primes integrin αIIbß3 for ligand binding.

The murine monoclonal antibody (mAb) PT25-2 induces αIIbß3 to bind ligand and initiate platelet aggregation. The underlying mechanism is unclear, because previous mutagenesis studies suggested that PT25-2 binds to the αIIb ß propeller, a site distant from the Arg-Gly-Asp-binding pocket. To elucidate the mechanism, we studied the αIIbß3-PT25-2 Fab complex by negative-stain and cryo-electron microscopy (EM). We found that PT25-2 binding results in αIIbß3 partially exposing multiple ligand-induced binding site epitopes and adopting extended conformations without swing-out of the ß3 hybrid domain. The cryo-EM structure showed PT25-2 binding to the αIIb residues identified by mutagenesis but also to 2 additional regions. Overlay of the cryo-EM structure with the bent αIIbß3 crystal structure showed that binding of PT25-2 creates clashes with the αIIb calf-1/calf-2 domains, suggesting that PT25-2 selectively binds to partially or fully extended receptor conformations and prevents a return to its bent conformation. Kinetic studies of the binding of PT25-2 compared with mAbs 10E5 and 7E3 support this hypothesis. We conclude that PT25-2 induces αIIbß3 ligand binding by binding to extended conformations and by preventing the interactions between the αIIb and ß3 leg domains and subsequently the ßI and ß3 leg domains required for the bent-closed conformation.