Decreased cardiac contractility is a central feature of systolic heart failure. Existing drugs increase cardiac contractility indirectly through signaling cascades but are limited by their mechanism-related adverse effects. To avoid these limitations, we previously developed omecamtiv mecarbil, a small-molecule, direct activator of cardiac myosin. Here, we show it binds to the myosin catalytic domain and operates by an allosteric mechanism to increase the transition rate of myosin into the strongly actin-bound force-generating state. Paradoxically, it inhibits adenosine 5′-triphosphate (ATP) turnover in the absence of actin, which suggests that it stabilizes an actin-bound conformation of myosin. In animal models, omecamtiv mecarbil increases cardiac function by increasing the duration of ejection without changing the rates of contraction. Cardiac myosin activation may provide a new therapeutic approach for systolic heart failure.

The rat anterior pituitary gland (AP) receives all of its blood supply via the hypophyseal portal circulation. We now report, in rats with estradiol (E2)-induced prolactin-secreting tumors, that newly formed arteries directly supply the AP and that this arteriogenesis is closely correlated with the sensitivity of two strains of rats to the tumorigenic action of E2. Fischer 344 rats, a strain extremely sensitive to E2, and Sprague-Dawley rats, a less sensitive strain, were ovariectomized and implanted with E2-filled or empty Silastic capsules. Ten to 63 days later, microspheres (15 Itm) were injected into the heart. Normally microspheres do not reach the AP because they are trapped in the primary portal capillary plexus. Some animals were also perfused with vascular cast material. In Fischer rats, after 63 days of E2, the pituitary weight, serum prolactin, and number of microspheres in the AP were 5-, 42-, and 18-fold greater than control values, respectively. The same parameters in E2-treated Sprague-Dawley rats were 2-, 27-, and 7-fold greater than control values. Vascular casts from E2-treated Fischer rats revealed numerous arteries entering the AP. No arteries to the AP were observed in Sprague-Dawley controls. These results show that E2-induced tumorigenesis of the AP is associated with the development of a direct arterial blood supply. We hypothesize that the regions supplied by these new arteries would receive systemic blood containing subphysiological concentrations of dopamine. The loss of dopaminergic inhibition in concert with E2 stimulation may lead to tumor formation.Prolactin-secreting pituitary tumors can be induced in rats by prolonged treatment with estrogen (1-3). The size of the anterior pituitary gland (AP) of estrogen-treated animals is markedly increased, which is associated with increased mitotic activity (4). The primary cells affected are prolactin (PRL)-producing cells, lactotrophs. Estrogen stimulates both PRL synthesis and proliferation of lactotrophs (4-7). Different strains of rats have different susceptibilities to the tumorigenic action of estrogen, with the Fischer 344 strain being particularly sensitive (8,9).The mechanisms by which estrogen mediates tumor induction most likely include direct effects on lactotrophs, as well as indirect effects via alterations in the hypothalamic regulation of lactotrophs. PRL secretion (10) and synthesis (11) have been shown to be tonically inhibited by dopamine produced in the tuberoinfundibular neurons. Dopamine also appears to be involved in the control of the cell division of lactotrophs. Destruction of the tuberoinfundibular neurons results in an increased density of lactotrophs (12) and the blockade of dopamine receptors with antagonists increases DNA synthesis and the mitotic index of the AP (13). These findings have led us and others (14) to hypothesize that tumor development could involve escape of the AP from hypothalamic dopamine regulation. Dopamine is released from hypothalamic neurons into the hypophyseal portal vascular ple...

We report the design, synthesis, and optimization of the first, selective activators of cardiac myosin. Starting with a poorly soluble, nitro-aromatic hit compound (1), potent, selective, and soluble myosin activators were designed culminating in the discovery of omecamtiv mecarbil (24). Compound 24 is currently in clinical trials for the treatment of systolic heart failure.

No abstract

Another class of growth hormone (GH) secretagogues has been discovered by altering the backbone structure ofa flexible linear GH-releasing peptide (GHRP). In vitro and in vivo characterization confirms these GH secretagogues as the most potent and smallest (Mr < 500) reported. Anabolic efficacy is demonstrated in rodents with intermittent delivery. A convergent model of the bioactive conformation of GHRPs is developed and is supported by the NMR structure of a highly potent cyclic analog of GHRP-2. The model and functional data provide a logical framework for the further design of low-molecular weight secretagogues and illustrate the utility of an interdisciplinary approach to elucidating potential bound-state conformations of flexible peptide ligands.Growth hormone (GH) regulates optimal statural growth in children and body composition in adults. The pulsatile release of GH from the pituitary somatotrophs is controlled by a complex endocrine interaction involving hypothalamic neuronal hormones that induce (via GH-releasing hormone, GHRH) or suppress (via somatostatin) GH secretion. Discovered before GHRH, the GH-releasing peptides (GHRPs) were derived by systematically optimizing the GH-releasing activities of Met-enkephalin (1, 2). The GHRPs and GHRH directly stimulate GH secretion by the pituitary (3, 4) via different mechanisms (5, 6), and a synergistic response is observed when the two are co-administered (7,8). More potent GH secretagogues have subsequently been developed by further modification of the GHRPs (9), and recently a nonpeptidyl lead series was identified by screening (10). Despite considerable interest in these molecules as a potential alternative to injectable recombinant human GH therapy, their clinical use is currently limited by low oral bioavailability and a poor understanding of the pharmacodynamic profile required for optimal efficacy. Neither an endogenous counterpart nor its receptors have been reported.The intrinsic (in vitro) secretagogue activity of the prototype peptide GHRP-6 (His-DTrp-Ala-Trp-DPhe-Lys-NH2) results primarily from the charged side chain of the N-terminal histidine and the central aromatic residues; the C-terminal lysine residue, although not absolutely required for in vitro activity, appears to contribute significantly to in vivo potency (11). Activity is enhanced when DTrp2 is replaced by D-2-(2-naphthyl)alanine (D2Nal), and the N-terminal charge is delivered by the stereochemically analogous backbone nitrogen of D-alanine (GHRP-2, DAla-D2Nal-Ala-Trp-DPhe-Lys-NH2) (9,12). No potent cyclic analogs of GHRP have been reported, and little progress has been made in determining the topographical requirements for GHRP bioactivity, thus frustrating efforts to design secretagogues with improved pharmacological properties.We describe here a strategy that has produced a highly active cyclic analog of GHRP-2 that is structured in water. We have also determined a minimal set of functional interactions that are actually required for GHRP activity, leading to the develop...