Discovery of a small molecule RXFP3/4 agonist that increases food intake in rats upon acute central administration.

The relaxin family peptide receptors have been implicated in numerous physiological processes including energy homeostasis, cardiac function, wound healing, and reproductive function. Two family members, RXFP3 and RXFP4, are class A GPCRs with endogenous peptide ligands (relaxin-3 and insulin-like peptide 5 (INSL5), respectively). Polymorphisms in relaxin-3 and RXFP3 have been associated with obesity, diabetes, and hypercholesterolemia. Moreover, central administration of relaxin-3 in rats has been shown to increase food intake, leading to body weight gain. Reported RXFP3 and RXFP4 ligands have been restricted to peptides (both endogenous and synthetic) as well as a low molecular weight positive allosteric modulator requiring a non-endogenous orthosteric ligand. Described here is the discovery of the first potent low molecular weight dual agonists of RXFP3/4. The scaffold identified is competitive with a chimeric relaxin-3/INSL5 peptide for RXFP3 binding, elicits similar downstream signaling as relaxin-3, and increases food intake in rats following acute central administration. This is the first report of small molecule RXFP3/4 agonism.

3,5-diarylazoles as novel and selective inhibitors of protein kinase D.

The synthesis and preliminary studies of the SAR of novel 3,5-diarylazole inhibitors of Protein Kinase D (PKD) are reported. Notably, optimized compounds in this class have been found to be active in cellular assays of phosphorylation-dependant HDAC5 nuclear export, orally bioavailable, and highly selective versus a panel of additional putative histone deacetylase (HDAC) kinases. Therefore these compounds could provide attractive tools for the further study of PKD/HDAC5 signaling.

Identification of orally available naphthyridine protein kinase D inhibitors.

A novel 2,6-naphthyridine was identified by high throughput screen (HTS) as a dual protein kinase C/D (PKC/PKD) inhibitor. PKD inhibition in the heart was proposed as a potential antihypertrophic mechanism with application as a heart failure therapy. As PKC was previously identified as the immediate upstream activator of PKD, PKD vs PKC selectivity was essential to understand the effect of PKD inhibition in models of cardiac hypertrophy and heart failure. The present study describes the modification of the HTS hit to a series of prototype pan-PKD inhibitors with routine 1000-fold PKD vs PKC selectivity. Example compounds inhibited PKD activity in vitro, in cells, and in vivo following oral administration. Their effects on heart morphology and function are discussed herein.

Identification of potent and selective amidobipyridyl inhibitors of protein kinase D.

The synthesis and biological evaluation of potent and selective PKD inhibitors are described herein. The compounds described in the present study selectively inhibit PKD among other putative HDAC kinases. The PKD inhibitors of the present study blunt phosphorylation and subsequent nuclear export of HDAC4/5 in response to diverse agonists. These compounds further establish the central role of PKD as an HDAC4/5 kinase and enhance the current understanding of cardiac myocyte signal transduction. The in vivo efficacy of a representative example compound on heart morphology is reported herein.

Dilated cardiomyopathy resulting from high-level myocardial expression of Cre-recombinase.

BACKGROUND: Conditional gene inactivation in mice using the bacteriophage P1 Cre-loxP recombination system requires transgenic expression of Cre-recombinase driven by a tissue-specific or inducible promoter. METHODS AND RESULTS: Using the cardiac alpha-myosin-heavy-chain promoter, the most commonly used myocardial-specific transgenic promoter, we created transgenic mice expressing Cre-recombinase in the heart. Seven transgenic lines developed dilated cardiomyopathy and premature death from congestive heart failure. One founder line that survived long enough to propagate had extremely high-level Cre recombinase expression. Transgenic lines that expressed low levels remained healthy. The high-expressing strain developed heart failure over a very predictable and reproducible time course. Detailed examination of the high-expressing strain revealed important molecular, cellular, and pharmacologic hallmarks of cardiomyopathy. First, "fetal genes" such as atrial natriuretic factor and brain natriuretic protein were expressed, a marker of pathologic cardiac hypertrophy and heart failure. Second, an increased incidence of cardiac myocyte apoptosis was present. Third, treatment of mice with captopril or metoprolol, drugs that delay the progression of heart failure, improved survival. CONCLUSION: Cre-recombinase when expressed at high levels may cause organ dysfunction, which could be mistaken for an effect of conditional gene inactivation. In addition, the stereotypic cardiomyopathy and disease progression in the characterized, high-expressing transgenic strain suggests its utility as a model to study the effects of pharmacologic or genetic manipulations in heart failure.

Haploinsufficiency of the cardiac transcription factor Nkx2-5 variably affects the expression of putative target genes.

Heterozygous mutations of the cardiac transcription factor Nkx2-5 cause congenital heart disease. To elucidate the molecular pathways of transcription factor mutant phenotypes or diseases, direct targets are commonly sought in studies of homozygous null mutant animals and by heterologous promoter-reporter gene transactivation assays. The expression of putative target genes in a physiologic range of transcription factor concentration, however, is often not examined. Heterozygous Nkx2-5 knockout (Nkx2-5+/-) mice have no more than half-normal levels of Nkx2-5 protein. We therefore measured the mRNA expression of four putative targets of the cardiac transcription factor Nkx2-5 in wild-type and Nkx2-5+/- animals in a variety of developmental and pathologic states. Wild-type and Nkx2-5+/- embryonic hearts expressed similar levels of atrial natriuretic factor (ANF), brain natriuretic peptide (BNP), the RNA helicase Csm, and homeodomain only protein HOP. In the failing adult ventricle, ANF and BNP were up-regulated to the same extent in wild-type and Nkx2-5+/- myocardium. Csm and HOP were down-regulated in heart failure, and Nkx2-5+/- hearts expressed about half-normal levels in healthy and failing states. No consistent relationship existed between the expression of putative transcriptional targets and Nkx2-5 gene dosage in the physiologically relevant range. Any dependence of gene expression on Nkx2-5 gene dosage is affected by factors specific to the individual gene and the physiologic context.

Function follows form: cardiac conduction system defects in Nkx2-5 mutation.

Mutations of Nkx2-5 cause congenital heart disease and atrioventricular block in man. The altered expression of an electrophysiologic protein regulated by Nkx2-5 was originally presumed to cause the conduction defect, but when no such protein was found, an alternative hypothesis was considered. In pediatric patients, the association of certain cardiac malformations with congenital atrioventricular block suggests that errors in specific developmental pathways could cause both an anatomic and a physiologic defect. We therefore hypothesized that Nkx2-5 insufficiency perturbs the conduction system during development, which in turn manifests as a postnatal conduction defect. Experimental results from Nkx2-5 knockout mouse models support the developmental hypothesis. Hypoplasia of the atrioventricular node, His bundle, and Purkinje system can explain in whole or in part specific conduction and electrophysiologic defects present in Nkx2-5 haploinsufficiency.