PAR4 (Protease-Activated Receptor 4) Antagonism With BMS-986120 Inhibits Human Ex Vivo Thrombus Formation.

OBJECTIVE: BMS-986120 is a novel first-in-class oral PAR4 (protease-activated receptor 4) antagonist with potent and selective antiplatelet effects. We sought to determine for the first time, the effect of BMS-986120 on human ex vivo thrombus formation. APPROACH AND RESULTS: Forty healthy volunteers completed a phase 1 parallel-group PROBE trial (Prospective Randomized Open-Label Blinded End Point). Ex vivo platelet activation, platelet aggregation, and thrombus formation were measured at 0, 2, and 24 hours after (1) oral BMS-986120 (60 mg) or (2) oral aspirin (600 mg) followed at 18 hours with oral aspirin (600 mg) and oral clopidogrel (600 mg). BMS-986120 demonstrated highly selective and reversible inhibition of PAR4 agonist peptide (100 µM)-stimulated P-selectin expression, platelet-monocyte aggregates, and platelet aggregation (P<0.001 for all). Compared with pretreatment, total thrombus area (µm2/mm) at high shear was reduced by 29.2% (95% confidence interval, 18.3%-38.7%; P<0.001) at 2 hours and by 21.4% (9.3%-32.0%; P=0.002) at 24 hours. Reductions in thrombus formation were driven by a decrease in platelet-rich thrombus deposition: 34.8% (19.3%-47.3%; P<0.001) at 2 hours and 23.3% (5.1%-38.0%; P=0.016) at 24 hours. In contrast to aspirin alone, or in combination with clopidogrel, BMS-986120 had no effect on thrombus formation at low shear (P=nonsignificant). BMS-986120 administration was not associated with an increase in coagulation times or serious adverse events. CONCLUSIONS: BMS-986120 is a highly selective and reversible oral PAR4 antagonist that substantially reduces platelet-rich thrombus formation under conditions of high shear stress. Our results suggest PAR4 antagonism has major potential as a therapeutic antiplatelet strategy. CLINICAL TRIAL REGISTRATION: URL: http://www.clinicaltrials.gov. Unique identifier: NCT02439190.

Long-term electrocardiographic safety monitoring in clinical drug development: A report from the Cardiac Safety Research Consortium.

This white paper, prepared by members of the Cardiac Safety Research Consortium (CSRC), discusses important issues regarding scientific and clinical aspects of long-term electrocardiographic safety monitoring during clinical drug development. To promote multistakeholder discussion of this topic, a Cardiac Safety Research Consortium-sponsored Think Tank was held on 2 December 2015 at the American College of Cardiology's Heart House in Washington, DC. The goal of the Think Tank was to explore how and under what circumstances new and evolving ambulatory monitoring technologies could be used to improve and streamline drug development. This paper provides a detailed summary of discussions at the Think Tank: it does not represent regulatory guidance.

Nf1 has an essential role in endothelial cells.

Neurofibromatosis type 1 (NF1) or von Recklinghausen neurofibromatosis is a genetic disorder that occurs in 1 of 4000 births and is characterized by benign and malignant tumors. Cardiovascular defects also contribute to NF1, though the pathogenesis is still unclear. Deficiency in neurofibromin (encoded by Nf1) in mice results in mid-embryonic lethality owing to cardiac abnormalities previously thought to be secondary to cardiac neural-crest defects. Using tissue-specific gene inactivation, we show that endothelial-specific inactivation of Nf1 recapitulates key aspects of the complete null phenotype, including multiple cardiovascular abnormalities involving the endocardial cushions and myocardium. This phenotype is associated with an elevated level of ras signaling in Nf1(-/-) endothelial cells and greater nuclear localization of the transcription factor Nfatc1. Inactivation of Nf1 in the neural crest does not cause cardiac defects but results in tumors of neural-crest origin resembling those seen in humans with NF1. These results establish a new and essential role for Nf1 in endothelial cells and confirm the requirement for neurofibromin in the neural crest.

Cardiac and vascular functions of the zebrafish orthologues of the type I neurofibromatosis gene NFI.

Von Recklinghausen neurofibromatosis is a common autosomal dominant genetic disorder characterized by benign and malignant tumors of neural crest origin. Significant progress in understanding the pathophysiology of this disease has occurred in recent years, largely aided by the development of relevant animal models. Von Recklinghausen neurofibromatosis is caused by mutations in the NF1 gene, which encodes neurofibromin, a large protein that modulates the activity of Ras. Here, we describe the identification and characterization of zebrafish nf1a and nf1b, orthologues of NF1, and show neural crest and cardiovascular defects resulting from morpholino knockdown, including vascular and cardiac valvular abnormalities. Development of a zebrafish model of von Recklinghausen neurofibromatosis will allow for structure-function analysis and genetic screens in this tractable vertebrate system.

Safety, Tolerability, and Pharmacokinetics of Treprostinil Palmitil Inhalation Powder for Pulmonary Hypertension: A Phase 1, Randomized, Double-Blind, Single- and Multiple-Dose Study.

INTRODUCTION: Treprostinil is a prostacyclin vasodilator widely used for the treatment of pulmonary arterial hypertension (PAH) and, in its inhaled form, for pulmonary hypertension associated with interstitial lung disease (PH-ILD). Treprostinil palmitil inhalation powder (TPIP) is a dry powder formulation of treprostinil palmitil (TP), an ester prodrug of treprostinil. TPIP is designed to provide sustained release of treprostinil in the lung over a prolonged period, potentially enabling a once-daily (QD) dosing regimen and significantly higher tolerated doses compared with currently available treprostinil formulations. This phase 1 study assessed the safety, tolerability, and pharmacokinetics of TP and treprostinil following single and multiple QD administrations of TPIP in healthy volunteers. METHODS: Healthy adults (aged 18-45 years) were randomized to receive single or multiple QD inhalation doses of TPIP. Participants in the single-dose phase received TPIP 112.5, 225, 450, or 675 µg (n = 6/dose) or placebo (n = 2). Participants in the multiple-dose phase received TPIP 225 µg QD for 7 days (n = 6), 112.5 µg QD for 4 days followed by 225 µg QD for 3 days (n = 6), or placebo for 7 days (n = 4). RESULTS: Overall, 41 of 42 participants (97.6%) completed the study. In the single-dose phase, 70.8% (n = 17/24) of TPIP-treated participants experienced a treatment-emergent adverse event (TEAE) vs 0% (n = 0/2) of placebo-treated participants; the most common TEAEs (≥ 20%) were cough (45.8%), dizziness (29.2%), and throat irritation (20.8%). In the multiple-dose phase, 83.3% (n = 10/12) of TPIP-treated participants experienced a TEAE vs 50.0% of placebo-treated participants (n = 2/4); the most common TEAEs were cough (58.3% TPIP vs 50.0% placebo), headache (50.0% vs 0%), nausea (33.3% vs 0%), chest discomfort (33.3% vs 0%), and dizziness (25.0% vs 0%). Most TEAEs were mild; only seven patients experienced a moderate TEAE, and no severe or serious TEAEs occurred. In the multiple-dose phase, participants whose doses were titrated from TPIP 112.5 µg QD to 225 µg QD experienced fewer TEAEs than those who received 225 µg QD at treatment initiation (66.7% vs 100.0%), and all TEAEs with dose titration were mild. After a single dose of TPIP, treprostinil elimination t1/2 was 8.67-11.6 h and exposure was dose proportional, with mean (CV%) Cmax 78.4-717 pg/mL (38.6-72.9%) and AUC0-∞ 1090-5480 pg·h/mL (11.5-30.0%). At steady state (TPIP 225 µg), the mean (CV%) of Cmax, Cmin, and AUCτ were 193-228 pg/mL (32.9-46.4%), 17.6-22.8 ng/mL (43.7-64.4%), and 1680-1820 pg·h/mL (28.7-36.6%), respectively. The elimination t1/2 was 6.84-8.82 h after repeat dosing. No steady-state accumulation was observed. Plasma concentrations of TP were below the limit of quantification (100 pg/mL) at all time points measured. CONCLUSION: TPIP was well tolerated at the doses tested, and dose titration improved tolerability. Treprostinil pharmacokinetics were linear and supportive of a QD treatment regimen. These results support further development of TPIP in patients with PAH and PH-ILD.

Cardiomyocyte-specific loss of neurofibromin promotes cardiac hypertrophy and dysfunction.

RATIONALE: Neurofibromatosis type 1 (NF1) is a common autosomal dominant disorder with a broad array of clinical manifestations, including benign and malignant tumors, and characteristic cutaneous findings. NF1 patients also have an increased incidence of cardiovascular diseases, including obstructive vascular disorders and hypertension. The disease gene, NF1, encodes neurofibromin, a ubiquitously expressed protein that acts, in part, as a Ras-GAP (GTP-ase activating protein), downregulating the activity of activated Ras protooncogenes. In animal models, endothelial and smooth muscle expression of the disease gene is critical for normal heart development and the prevention of vascular disease, respectively. OBJECTIVE: To determine the role of NF1 in the postnatal and adult heart. METHODS AND RESULTS: We generated mice with homozygous loss of the murine homolog Nf1 in myocardium (Nf1mKO) and evaluated their hearts for biochemical, structural, and functional changes. Nf1mKO mice have normal embryonic cardiovascular development but have marked cardiac hypertrophy, progressive cardiomyopathy, and fibrosis in the adult. Hyperactivation of Ras and downstream pathways are seen in the heart with the loss of Nf1, along with activation of a fetal gene program. CONCLUSIONS: This report describes a critical role of Nf1 in the regulation of cardiac growth and function. Activation of pathways known to be involved in cardiac hypertrophy and dysfunction are seen with the loss of myocardial neurofibromin.

Mouse model of Noonan syndrome reveals cell type- and gene dosage-dependent effects of Ptpn11 mutation.

Noonan syndrome is a common human autosomal dominant birth defect, characterized by short stature, facial abnormalities, heart defects and possibly increased risk of leukemia. Mutations of Ptpn11 (also known as Shp2), which encodes the protein-tyrosine phosphatase Shp2, occur in approximately 50% of individuals with Noonan syndrome, but their molecular, cellular and developmental effects, and the relationship between Noonan syndrome and leukemia, are unclear. We generated mice expressing the Noonan syndrome-associated mutant D61G. When homozygous, the D61G mutant is embryonic lethal, whereas heterozygotes have decreased viability. Surviving Ptpn11(D61G/+) embryos ( approximately 50%) have short stature, craniofacial abnormalities similar to those in Noonan syndrome, and myeloproliferative disease. Severely affected Ptpn11(D61G/+) embryos ( approximately 50%) have multiple cardiac defects similar to those in mice lacking the Ras-GAP protein neurofibromin. Their endocardial cushions have increased Erk activation, but Erk hyperactivation is cell and pathway specific. Our results clarify the relationship between Noonan syndrome and leukemia and show that a single Ptpn11 gain-of-function mutation evokes all major features of Noonan syndrome by acting on multiple developmental lineages in a gene dosage-dependent and pathway-selective manner.

The neurofibromin GAP-related domain rescues endothelial but not neural crest development in Nf1 mice.

Neurofibromatosis type I (NF1; also known as von Recklinghausen's disease) is a common autosomal-dominant condition primarily affecting neural crest-derived tissues. The disease gene, NF1, encodes neurofibromin, a protein of over 2,800 amino acids that contains a 216-amino acid domain with Ras-GTPase-activating protein (Ras-GAP) activity. Potential therapies for NF1 currently in development and being tested in clinical trials are designed to modify NF1 Ras-GAP activity or target downstream effectors of Ras signaling. Mice lacking the murine homolog (Nf1) have mid-gestation lethal cardiovascular defects due to a requirement for neurofibromin in embryonic endothelium. We sought to determine whether the GAP activity of neurofibromin is sufficient to rescue complete loss of function or whether other as yet unidentified functions of neurofibromin might also exist. Using cre-inducible ubiquitous and tissue-specific expression, we demonstrate that the isolated GAP-related domain (GRD) rescued cardiovascular development in Nf1(-/-) embryos, but overgrowth of neural crest-derived tissues persisted, leading to perinatal lethality. These results suggest that neurofibromin may possess activities outside of the GRD that modulate neural crest homeostasis and that therapeutic approaches solely aimed at targeting Ras activity may not be sufficient to treat tumors of neural crest origin in NF1.

NF1 regulates a Ras-dependent vascular smooth muscle proliferative injury response.

BACKGROUND: Neurofibromatosis type I (NF1) is a common autosomal dominant disorder with a broad array of clinical manifestations, including benign and malignant tumors, osseous dysplasias, and characteristic cutaneous findings. In addition, NF1 patients have an increased incidence of cardiovascular diseases, including obstructive vascular disorders. In animal models, endothelial expression of the disease gene, NF1, is critical for normal heart development. However, the pathogeneses of the more common vascular disorders are not well characterized. METHODS AND RESULTS: To examine the role of NF1 in vascular smooth muscle, we generated mice with homozygous loss of the murine homolog Nf1 in smooth muscle (Nf1smKO). These mice develop and breed normally. However, in response to vascular injury, they display a marked intimal hyperproliferation and abnormal activation of mitogen-activated protein kinase, a downstream effector of Ras. Vascular smooth muscle cells cultured from these mice also display enhanced proliferation and mitogen-activated protein kinase activity. Smooth muscle expression of the NF1 Ras-regulatory domain (GTPase activating protein-related domain) rescues intimal hyperplasia in Nf1smKO mice and normalizes vascular smooth muscle cell Ras effector activity and proliferation in vitro, similar to blockade of downstream effectors of Ras. CONCLUSIONS: In this in vivo model of NF1 obstructive vascular disease, we have shown that Nf1 regulation of Ras plays a critical role in vascular smooth muscle proliferation after injury. These results suggest opportunities for targeted therapeutics in the prevention and treatment of NF1-related vascular disease and in the treatment of neointimal proliferation in other settings.

Homeobox protein Hop functions in the adult cardiac conduction system.

Hop is an unusual homeobox gene expressed in the embryonic and adult heart. Hop acts downstream of Nkx2-5 during development, and Nkx2-5 mutations are associated with cardiac conduction system (CCS) defects. Inactivation of Hop in the mouse is lethal in half of the expected null embryos. Here, we show that Hop is expressed strongly in the adult CCS. Hop-/- adult mice display conduction defects below the atrioventricular node (AVN) as determined by invasive electrophysiological testing. These defects are associated with decreased expression of connexin40. Our results suggest that Hop functions in the adult CCS and demonstrate conservation of molecular hierarchies between embryonic myocardium and the specialized conduction tissue of the mature heart.

Role of homeodomain-only protein in the cardiac conduction system.

Diseases of the cardiac conduction system (CCS) are a significant health issue in adult patients where few therapeutic options exist outside of expensive, device-based procedures. An evolving paradigm pointing toward several key transcription factors required for CCS development and maintenance may be a group of potential targets for reversing or treating degenerative conduction system disease. Recently, a small homeodomain-only protein (Hop) involved with regulating cardiac development has been identified, which is highly expressed in the adult murine CCS. Targeted disruption of the Hop locus leads to infra-nodal conduction defects with downregulation of connexin40 expression within the confines of the CCS. Loss of Hop does not appear to affect the size or distribution of the mature murine CCS and further studies will be required to determine whether Hop is associated with conduction system disease in humans.

Coronary anatomy in congenitally corrected transposition of the great arteries.

BACKGROUND: The advent of double switch procedures for the treatment of transposition of the great arteries with L-looped ventricles, e.g. typical congenitally corrected transposition of the great arteries, has made delineation of the coronary artery anatomy in these hearts important. Previous studies have suggested a consistently inverted coronary arterial pattern. METHODS: A morphologic study was conducted of the coronary arterial anatomy of all heart specimens in our registry of approximately 2600 hearts with segmental anatomy [S,L,L] (situs solitus of the viscera and atria, ventricular L-loop, and levoposition of the aorta), with anatomical features to permit such repair. RESULTS: Twenty specimens collected between 1965 and 1993 ranged in age from 1 day to 23 years. Transposition of the great arteries or double outlet right ventricle was seen in 12 (60%). One had a single coronary artery that arose from the right anterior sinus and trifurcated. Another had the anterior descending artery arise from the right ventricular coronary artery while the circumflex arose alone, directly above the intercoronary commissure. Eccentric ostia were seen in another four, with one left ventricular coronary artery originating directly above the intercoronary commissure. Right ventricular aorta with pulmonary atresia was in eight of the total (40%). Three had eccentric ostia: one with both arteries from the left posterior sinus, and one with the left ventricular coronary over the intercoronary commissure. None of these specimens had additional coronary anomalies that would further complicate surgery. CONCLUSION: Nearly half of the specimens (45%) had coronary artery abnormalities that could have complicated, but not necessarily precluded, anatomic surgical repair.

Jun is required in Isl1-expressing progenitor cells for cardiovascular development.

Jun is a highly conserved member of the multimeric activator protein 1 transcription factor complex and plays an important role in human cancer where it is known to be critical for proliferation, cell cycle regulation, differentiation, and cell death. All of these biological functions are also crucial for embryonic development. Although all Jun null mouse embryos die at mid-gestation with persistent truncus arteriosus, a severe cardiac outflow tract defect also seen in human congenital heart disease, the developmental mechanisms are poorly understood. Here we show that murine Jun is expressed in a restricted pattern in several cell populations important for cardiovascular development, including the second heart field, pharyngeal endoderm, outflow tract and atrioventricular endocardial cushions and post-migratory neural crest derivatives. Several genes, including Isl1, molecularly mark the second heart field. Isl1 lineages include myocardium, smooth muscle, neural crest, endocardium, and endothelium. We demonstrate that conditional knockout mouse embryos lacking Jun in Isl1-expressing progenitors display ventricular septal defects, double outlet right ventricle, semilunar valve hyperplasia and aortic arch artery patterning defects. In contrast, we show that conditional deletion of Jun in Tie2-expressing endothelial and endocardial precursors does not result in aortic arch artery patterning defects or embryonic death, but does result in ventricular septal defects and a low incidence of semilunar valve defects, atrioventricular valve defects and double outlet right ventricle. Our results demonstrate that Jun is required in Isl1-expressing progenitors and, to a lesser extent, in endothelial cells and endothelial-derived endocardium for cardiovascular development but is dispensable in both cell types for embryonic survival. These data provide a cellular framework for understanding the role of Jun in the pathogenesis of congenital heart disease.

Right aortic arch and coarctation: a rare association.

OBJECTIVES: Understand anatomical and clinical correlatives to coarctation in right aortic arch. BACKGROUND: Coarctation of the aorta is rare in patients with a functional right aortic arch. We reviewed a single institutional experience, examining associated diagnoses, diagnostic methodology, and surgical approaches. METHODS: A retrospective study was performed of our echocardiographic, magnetic resonance imaging, catheterization, and surgical databases from 1988 to 2001. RESULTS: Of 240 patients with right aortic arch, 10 (4.1%) had coarctation, constituting 1.9% of all native coarctations (n = 524). Nine (90%) had long-segment hypoplasia. Six (60%) had an aberrant left subclavian artery or retroesophageal diverticulum, 3 (30%) had mirror image branching, and 1 (10%) had a double arch with an atretic left arch. Other congenital heart defects were seen in 6 (60%) comprising 3 with ventricular septal defects, and one each with double-outlet right ventricle, cor triatriatum, and pulmonary valve abnormality. No patients with long-segment hypoplasia had bicuspid aortic valve. Six (60%) had vascular rings, and 5 (50%) had other associated syndromes. Magnetic resonance imaging and/or echocardiography successfully diagnosed all of these patients. Although long-segment right aortic arch coarctation courses behind the trachea posteriorly, only 2 needed an extra-anatomic (jump) graft; the remainders were repaired with patch angioplasty. CONCLUSION: Coarctation with right aortic arch is rare, constituting 4.1% of all patients with right aortic arch, compared with 5-8% of patients with left aortic arch and congenital heart disease. Nearly all had long-segment hypoplasia without bicuspid aortic valve, and half were part of other syndrome complexes. This association can be diagnosed noninvasively and can often be repaired by patch angioplasty.