Hypertrophic cardiomyopathy (HCM) is an inherited disease of heart muscle that can be caused by mutations in sarcomere proteins. Clinical diagnosis depends on an abnormal thickening of the heart, but the earliest signs of disease are hyperdynamic contraction and impaired relaxation. Whereas some in vitro studies of power generation by mutant and wild-type sarcomere proteins are consistent with mutant sarcomeres exhibiting enhanced contractile power, others are not. We identified a small molecule, MYK-461, that reduces contractility by decreasing the adenosine triphosphatase activity of the cardiac myosin heavy chain. Here we demonstrate that early, chronic administration of MYK-461 suppresses the development of ventricular hypertrophy, cardiomyocyte disarray, and myocardial fibrosis and attenuates hypertrophic and profibrotic gene expression in mice harboring heterozygous human mutations in the myosin heavy chain. These data indicate that hyperdynamic contraction is essential for HCM pathobiology and that inhibitors of sarcomere contraction may be a valuable therapeutic approach for HCM.

Hypertrophic cardiomyopathy (HCM) is an inherited disease of the heart muscle characterized by otherwise unexplained thickening of the left ventricle. Left ventricular outflow tract (LVOT) obstruction is present in approximately two-thirds of patients and substantially increases the risk of disease complications. Invasive treatment with septal myectomy or alcohol septal ablation can improve symptoms and functional status, but currently available drugs for reducing obstruction have pleiotropic effects and variable therapeutic responses. New medical treatments with more targeted pharmacology are needed, but the lack of preclinical animal models for HCM with LVOT obstruction has limited their development. HCM is a common cause of heart failure in cats, and a subset exhibit systolic anterior motion of the mitral valve leading to LVOT obstruction. MYK-461 is a recently-described, mechanistically novel small molecule that acts at the sarcomere to specifically inhibit contractility that has been proposed as a treatment for HCM. Here, we use MYK-461 to test whether direct reduction in contractility is sufficient to relieve LVOT obstruction in feline HCM. We evaluated mixed-breed cats in a research colony derived from a Maine Coon/mixed-breed founder with naturally-occurring HCM. By echocardiography, we identified five cats that developed systolic anterior motion of the mitral valve and LVOT obstruction both at rest and under anesthesia when provoked with an adrenergic agonist. An IV MYK-461 infusion and echocardiography protocol was developed to serially assess contractility and LVOT gradient at multiple MYK-461 concentrations. Treatment with MYK-461 reduced contractility, eliminated systolic anterior motion of the mitral valve and relieved LVOT pressure gradients in an exposure-dependent manner. Our findings provide proof of principle that acute reduction in contractility with MYK-461 is sufficient to relieve LVOT obstruction. Further, these studies suggest that feline HCM will be a valuable translational model for the study of disease pathology, particularly LVOT obstruction.

LFA-1/ICAM-1 interaction is essential in support of inflammatory and specific T-cell regulated immune responses by mediating cell adhesion, leukocyte extravasation, migration, antigen presentation, formation of immunological synapse, and augmentation of T-cell receptor signaling. The increase of ICAM-1 expression levels in conjunctival epithelial cells and acinar cells was observed in animal models and patients diagnosed with dry eye. Therefore, it has been hypothesized that small molecule LFA-1/ICAM-1 antagonists could be an effective topical treatment for dry eye. In this letter, we describe the discovery of a potent tetrahydroisoquinoline (THIQ)-derived LFA-1/ICAM-1 antagonist (SAR 1118) and its development as an ophthalmic solution for treating dry eye.

Mavacamten is a small molecule modulator of cardiac myosin designed as an orally administered drug for the treatment of patients with hypertrophic cardiomyopathy. The current study objectives were to assess the preclinical pharmacokinetics of mavacamten for the prediction of human dosing and to establish the potential need for clinical pharmacokinetic studies characterizing drug-drug interaction potential. Mavacamten does not inhibit CYP enzymes, but at high concentrations relative to anticipated therapeutic concentrations induces CYP2B6 and CYP3A4 enzymes in vitro. Mavacamten showed high permeability and low efflux transport across Caco-2 cell membranes. In human hepatocytes, mavacamten was not a substrate for drug transporters OATP, OCT and NTCP. Mavacamten was determined to have minimal drug-drug interaction risk. In vitro mavacamten metabolite profiles included phase I- and phase II-mediated metabolism cross-species. Major pathways included aromatic hydroxylation (M1), aliphatic hydroxylation (M2); N-dealkylation (M6), and glucuronidation of the M1-metabolite (M4). Reaction phenotyping revealed CYPs 2C19 and 3A4/3A5 predominating. Mavacamten demonstrated low clearance, high volume of distribution, long terminal elimination half-life and excellent oral bioavailability cross-species. Simple four-species allometric scaling led to predicted plasma clearance, volume of distribution and half-life of 0.51 mL/min/kg, 9.5 L/kg and 9 days, respectively, in human.

ABSTRACT:(؉)-1,4-Dihydro-7-(trans-3-methoxy-4-methylamino-1-pyrrolidinyl)-4-oxo-1-(2-thiazolyl)-1,8-naphthyridine-3-carboxylic acid (voreloxin; formerly SNS-595 or AG-7352) is currently under investigation for the treatment of platinum-resistant ovarian cancer and acute myeloid leukemia. In vitro voreloxin undergoes minimal cytochrome P450 (P450) and UDP glucuronosyltransferase (UGT)-mediated metabolism, and in vivo excretion of unchanged voreloxin as the major species is consistent with the slow rate of metabolism observed in vitro. The objective of the present study was to examine the cross-species metabolic profile of voreloxin and to identify and characterize the metabolites formed in rats. We also investigated baculovirus-expressed human P450s and UGTs to determine which isoforms participated in voreloxin metabolism. Incubations using human, monkey, and rat liver microsomes showed monkey and rat metabolism is similar to human. Voreloxin and metabolites collected from plasma, bile, and urine from rats administered radiolabeled voreloxin were separated by high-performance liquid chromatography, and their structures were elucidated by liquid chromatography/tandem mass spectrometry. Activity of metabolites was determined with authentic reference standards in cellbased cytotoxicity assays. The proposed structures of metabolites suggest that metabolic pathways for voreloxin include glucuronide conjugation, oxidation, N-dealkylation, and O-dealkylation.Voreloxin is a replication-dependent DNA-damaging agent that intercalates DNA and inhibits topoisomerase II, resulting in doublestranded DNA breaks, irreversible G2 arrest, and rapid apoptosis. The topoisomerase II-associated DNA intercalation and DNA damage produced by voreloxin are highly selective and show selectivity for proliferating cells. These targeted DNA-protein interactions may contribute to the broad clinical responses observed with voreloxin to date. The inhibition of topoisomerase II by voreloxin is differentiable from the actions of classic topoisomerase inhibitors, including etoposide, doxorubicin, and topotecan (Stockett et al., 2008). Voreloxin is a naphthyridine-derived small molecule that exists as a zwitterioncontaining carboxylic acid and amine functional groups (Fig. 1). Voreloxin is currently under clinical investigation in acute myeloid leukemia and ovarian cancer (Burris et al., 2007;Lancet et al., 2007).Preclinical pharmacokinetic studies in rats and monkeys showed that voreloxin has dose-proportional exposure, low to moderate clearance, a moderate half-life, and low interindividual variability. In humans, pharmacokinetic estimates show dose linear increase in exposure, low clearance, and a long half-life (Hoch and Silverman, 2007). In vitro studies using rat, monkey, and human liver microsomes indicated that voreloxin undergoes minimal oxidative and conjugative metabolism (Hoch et al., 2005). In addition, in vitro profiling suggests that rat metabolism is a good model of voreloxin human metabolism. In mass balance studies, greater than 90...