Post-transcriptional regulation and subcellular localization of G-protein γ7 subunit: implications for striatal function and behavioral responses to cocaine.

The striatal D1 dopamine receptor (D1R) and A2a adenosine receptor (A2aR) signaling pathways play important roles in drug-related behaviors. These receptors activate the Golf protein comprised of a specific combination of αolfß2γ7 subunits. During assembly, the γ7 subunit sets the cellular level of the Golf protein. In turn, the amount of Golf protein determines the collective output from both D1R and A2aR signaling pathways. This study shows the Gng7 gene encodes multiple γ7 transcripts differing only in their non-coding regions. In striatum, Transcript 1 is the predominant isoform. Preferentially expressed in the neuropil, Transcript 1 is localized in dendrites where it undergoes post-transcriptional regulation mediated by regulatory elements in its 3' untranslated region that contribute to translational suppression of the γ7 protein. Earlier studies on gene-targeted mice demonstrated loss of γ7 protein disrupts assembly of the Golf protein. In the current study, morphological analysis reveals the loss of the Golf protein is associated with altered dendritic morphology of medium spiny neurons. Finally, behavioral analysis of conditional knockout mice with cell-specific deletion of the γ7 protein in distinct populations of medium spiny neurons reveals differential roles of the Golf protein in mediating behavioral responses to cocaine. Altogether, these findings provide a better understanding of the regulation of γ7 protein expression, its impact on Golf function, and point to a new potential target and mechanisms for treating addiction and related disorders.

Development of small molecule inhibitors targeting RNA helicase DHX33 as anti-cancer agents.

RNA helicase DHX33 has been identified to be a critical factor in promoting cancer development. Genetic deletion of DHX33 significantly blocks tumorigenesis. Importantly, its helicase activity was found to be pivotal for exerting cellular functions. Herein we used a helicase-based high throughput screening (HTS) to discover DHX33 inhibitors from Chembridge chemical library containing 15,000 small molecules. We identified a hit compound containing benzimidazole ring that demonstrated activity against DHX33 with certain selectivity. Further structural optimization led to the design and synthesis of a series of analog inhibitors. Considering the potential role of DHX33 in cancer development, the compounds were evaluated based on the cytotoxicity activity in U251-MG cancer cells in vitro. Among them, compound IVa (KY386) was identified to be a selective inhibitor for DHX33 helicase with potent anti-cancer activity and moderate metabolic stability. These results support the promising role of DHX33 inhibitors for development of novel anti-cancer drugs.

A universal dual mechanism immunotherapy for the treatment of influenza virus infections.

Seasonal influenza epidemics lead to 3-5 million severe infections and 290,000-650,000 annual global deaths. With deaths from the 1918 influenza pandemic estimated at >50,000,000 and future pandemics anticipated, the need for a potent influenza treatment is critical. In this study, we design and synthesize a bifunctional small molecule by conjugating the neuraminidase inhibitor, zanamivir, with the highly immunogenic hapten, dinitrophenyl (DNP), which specifically targets the surface of free virus and viral-infected cells. We show that this leads to simultaneous inhibition of virus release, and immune-mediated elimination of both free virus and virus-infected cells. Intranasal or intraperitoneal administration of a single dose of drug to mice infected with 100x MLD50 virus is shown to eradicate advanced infections from representative strains of both influenza A and B viruses. Since treatments of severe infections remain effective up to three days post lethal inoculation, our approach may successfully treat infections refractory to current therapies.

Differing roles for short chain fatty acids and GPR43 agonism in the regulation of intestinal barrier function and immune responses.

Inflammatory bowel disease (IBD) is associated with a loss of intestinal barrier function and dysregulated immune responses. It has been shown that short chain fatty acids (SCFAs) are protective in IBD and that GPR43 mediates the protective effects of SCFAs. In this study, we investigated the effects of SCFAs in comparison to highly specific GPR43 agonists on human intestinal epithelial and immune cells. Our results confirm that SCFAs are enhancers of barrier function in intestinal epithelial cells. Additionally, SCFAs also displayed potent immunoregulatory properties based upon the ability to inhibit LPS-induced cytokine production in PBMC, and human T cell proliferation and cytokine production. Unexpectedly, and in contrast to the current belief, specific GPR43 agonists failed to exhibit similar barrier enhancing and anti-inflammatory properties. These findings demonstrate that SCFA possess broad protective functions in IBD and agonizing GPR43 alone is unlikely to be beneficial in patients.

The R21C Mutation in Cardiac Troponin I Imposes Differences in Contractile Force Generation between the Left and Right Ventricles of Knock-In Mice.

We investigated the effect of the hypertrophic cardiomyopathy-linked R21C (arginine to cysteine) mutation in human cardiac troponin I (cTnI) on the contractile properties and myofilament protein phosphorylation in papillary muscle preparations from left (LV) and right (RV) ventricles of homozygous R21C(+/+) knock-in mice. The maximal steady-state force was significantly reduced in skinned papillary muscle strips from the LV compared to RV, with the latter displaying the level of force observed in LV or RV from wild-type (WT) mice. There were no differences in the Ca(2+) sensitivity between the RV and LV of R21C(+/+) mice; however, the Ca(2+) sensitivity of force was higher in RV-R21C(+/+) compared with RV-WT and lower in LV- R21C(+/+) compared with LV-WT. We also observed partial loss of Ca(2+) regulation at low [Ca(2+)]. In addition, R21C(+/+)-KI hearts showed no Ser23/24-cTnI phosphorylation compared to LV or RV of WT mice. However, phosphorylation of the myosin regulatory light chain (RLC) was significantly higher in the RV versus LV of R21C(+/+) mice and versus LV and RV of WT mice. The difference in RLC phosphorylation between the ventricles of R21C(+/+) mice likely contributes to observed differences in contractile force and the lower tension monitored in the LV of HCM mice.

Discovery of Potent and Simplified Piperidinone-Based Inhibitors of the MDM2-p53 Interaction.

Continued optimization of the N-substituent in the piperidinone series provided potent piperidinone-pyridine inhibitors 6, 7, 14, and 15 with improved pharmacokinetic properties in rats. Reducing structure complexity of the N-alkyl substituent led to the discovery of 23, a potent and simplified inhibitor of MDM2. Compound 23 exhibits excellent pharmacokinetic properties and substantial in vivo antitumor activity in the SJSA-1 osteosarcoma xenograft mouse model.

Optimization beyond AMG 232: discovery and SAR of sulfonamides on a piperidinone scaffold as potent inhibitors of the MDM2-p53 protein-protein interaction.

We recently reported on the discovery of AMG 232, a potent and selective piperidinone inhibitor of the MDM2-p53 interaction. AMG 232 is being evaluated in human clinical trials for cancer. Continued exploration of the N-alkyl substituent of this series, in an effort to optimize interactions with the MDM2 glycine-58 shelf region, led to the discovery of sulfonamides such as compounds 31 and 38 that have similar potency, hepatocyte stability and rat pharmacokinetic properties to AMG 232.

Discovery of AMG 232, a potent, selective, and orally bioavailable MDM2-p53 inhibitor in clinical development.

We recently reported the discovery of AM-8553 (1), a potent and selective piperidinone inhibitor of the MDM2-p53 interaction. Continued research investigation of the N-alkyl substituent of this series, focused in particular on a previously underutilized interaction in a shallow cleft on the MDM2 surface, led to the discovery of a one-carbon tethered sulfone which gave rise to substantial improvements in biochemical and cellular potency. Further investigation produced AMG 232 (2), which is currently being evaluated in human clinical trials for the treatment of cancer. Compound 2 is an extremely potent MDM2 inhibitor (SPR KD = 0.045 nM, SJSA-1 EdU IC50 = 9.1 nM), with remarkable pharmacokinetic properties and in vivo antitumor activity in the SJSA-1 osteosarcoma xenograft model (ED50 = 9.1 mg/kg).

Evaluating insulin secretagogues in a humanized mouse model with functional human islets.

OBJECTIVE: To develop a rapid, easy and clinically relevant in vivo model to evaluate novel insulin secretagogues on human islets, we investigated the effect of insulin secretagogues on functional human islets in a humanized mouse model. MATERIALS/METHODS: Human islets were transplanted under the kidney capsule of streptozotocin (STZ)-induced diabetic mice with immunodeficiency. Human islet graft function was monitored by measuring non-fasting blood glucose levels. After diabetes was reversed, human islet transplanted mice were characterized physiologically by oral glucose tolerance and pharmacologically with clinically proven insulin secretagogues, glucagon-like peptide-1 (GLP-1), exenatide, glyburide, nateglinide and sitagliptin. Additionally, G protein-coupled receptor 40 (GPR40) agonists were evaluated in this model. RESULTS: Long-term human islet graft survival could be achieved in immunodeficient mice. Oral glucose challenge in human islet transplanted mice resulted in an immediate incremental increase of plasma human C-peptide, while the plasma mouse C-peptide was undetectable. Treatments with GLP-1, exenatide, glyburide, nateglinide and sitagliptin effectively increased plasma human C-peptide levels and improved postprandial glucose concentrations. GPR40 agonists also stimulated human C-peptide secretion and significantly improved postprandial glucose in the human islet transplanted mice. CONCLUSIONS: Our studies indicate that a humanized mouse model with human islet grafts could mimic the in vivo characteristics of human islets and could be a powerful tool for the evaluation of novel insulin secretagogues or other therapeutic agents that directly and/or indirectly target human ß cells.

Generation and functional characterization of knock-in mice harboring the cardiac troponin I-R21C mutation associated with hypertrophic cardiomyopathy.

The R21C substitution in cardiac troponin I (cTnI) is the only identified mutation within its unique N-terminal extension that is associated with hypertrophic cardiomyopathy (HCM) in man. Particularly, this mutation is located in the consensus sequence for ß-adrenergic-activated protein kinase A (PKA)-mediated phosphorylation. The mechanisms by which this mutation leads to heart disease are still unclear. Therefore, we generated cTnI knock-in mouse models carrying an R21C mutation to evaluate the resultant functional consequences. Measuring the in vivo levels of incorporated mutant and WT cTnI, and their basal phosphorylation levels by top-down mass spectrometry demonstrated: 1) a dominant-negative effect such that, the R21C+/- hearts incorporated 24.9% of the mutant cTnI within the myofilament; and 2) the R21C mutation abolished the in vivo phosphorylation of Ser(23)/Ser(24) in the mutant cTnI. Adult heterozygous (R21C+/-) and homozygous (R21C+/+) mutant mice activated the fetal gene program and developed a remarkable degree of cardiac hypertrophy and fibrosis. Investigation of cardiac skinned fibers isolated from WT and heterozygous mice revealed that the WT cTnI was completely phosphorylated at Ser(23)/Ser(24) unless the mice were pre-treated with propranolol. After propranolol treatment (-PKA), the pCa-tension relationships of all three mice (i.e. WT, R21C+/-, and R21C+/+) were essentially the same. However, after treatment with propranolol and PKA, the R21C cTnI mutation reduced (R21C+/-) or abolished (R21C+/+) the well known decrease in the Ca(2+) sensitivity of tension that accompanies Ser(23)/Ser(24) cTnI phosphorylation. Altogether, the combined effects of the R21C mutation appear to contribute toward the development of HCM and suggest that another physiological role for the phosphorylation of Ser(23)/Ser(24) in cTnI is to prevent cardiac hypertrophy.

The first synthetic agonists of FFA2: Discovery and SAR of phenylacetamides as allosteric modulators.

Free fatty acid receptor 2 (FFA2) is a G-protein coupled receptor for which only short-chain fatty acids (SCFAs) have been reported as endogenous ligands. We describe the discovery and optimization of phenylacetamides as allosteric agonists of FFA2. These novel ligands can suppress adipocyte lipolysis in vitro and reduce plasma FFA levels in vivo, suggesting that these allosteric modulators can serve as pharmacological tools for exploring the potential function of FFA2 in various disease conditions.

Functional effects of a restrictive-cardiomyopathy-linked cardiac troponin I mutation (R145W) in transgenic mice.

The human cardiac troponin I (hcTnI) mutation R145W has been associated with restrictive cardiomyopathy. In this study, simultaneous measurements of ATPase activity and force in skinned papillary fibers from hcTnI R145W transgenic mice (Tg-R145W) were explored. Tg-R145W fibers showed an approximately 13-16% increase in maximal Ca(2+)-activated force and ATPase activity compared to hcTnI wild-type transgenic mice. The force-generating cross-bridge turnover rate (g) and the energy cost (ATPase/force) were the same in all groups of fibers. Also, the Tg-R145W fibers showed a large increase in the Ca(2+) sensitivity of both force development and ATPase. In intact fibers, the mutation caused prolonged force and intracellular [Ca(2+)] transients and increased time to peak force. Analysis of force and Ca(2+) transients showed that there was a 40% increase in peak force in Tg-R145W muscles, which was likely due to the increased Ca(2+) transient duration. The above cited results suggest that: (1) there would be an increase in resistance to ventricular filling during diastole resulting from the prolonged force and Ca(2+) transients that would result in a decrease in ventricular filling (diastolic dysfunction); and (2) there would be a large (approximately 53%) increase in force during systole, which may help to partly compensate for diastolic dysfunction. These functional results help to explain the mechanisms by which these mutations give rise to a restrictive phenotype.

Malignant familial hypertrophic cardiomyopathy D166V mutation in the ventricular myosin regulatory light chain causes profound effects in skinned and intact papillary muscle fibers from transgenic mice.

Transgenic (Tg) mice expressing approximately 95% of the D166V (aspartic acid to valine) mutation in the ventricular myosin regulatory light chain (RLC) shown to cause a malignant familial hypertrophic cardiomyopathy (FHC) phenotype were generated, and the skinned and intact papillary muscle fibers from the Tg-D166V mice were examined using a Guth muscle research system. A large increase in the Ca(2+) sensitivity of force and ATPase (Delta pCa(50)>0.25) and a significant decrease in maximal force and ATPase were observed in skinned muscle fibers from Tg-D166V mice compared with control mice. The cross-bridge dissociation rate g was dramatically decreased, whereas the energy cost (ATPase/force) was slightly increased in Tg-D166V fibers compared with controls. The calculated average force per D166V cross-bridge was also reduced. Intact papillary muscle data demonstrated prolonged force transients with no change in calcium transients in Tg-D166V fibers compared with control fibers. Histopathological examination revealed fibrotic lesions in the hearts of the older D166V mice. Our results suggest that a charge effect of the D166V mutation and/or a mutation-dependent decrease in RLC phosphorylation could initiate the slower kinetics of the D166V cross-bridges and ultimately affect the regulation of cardiac muscle contraction. Profound cellular changes observed in Tg-D166V myocardium when placed in vivo could trigger a series of pathological responses and result in poor prognosis for D166V-positive patients.

Functional consequences of the human cardiac troponin I hypertrophic cardiomyopathy mutation R145G in transgenic mice.

In this study, we addressed the functional consequences of the human cardiac troponin I (hcTnI) hypertrophic cardiomyopathy R145G mutation in transgenic mice. Simultaneous measurements of ATPase activity and force in skinned papillary fibers from hcTnI R145G transgenic mice (Tg-R145G) versus hcTnI wild type transgenic mice (Tg-WT) showed a significant decrease in the maximal Ca(2+)-activated force without changes in the maximal ATPase activity and an increase in the Ca(2+) sensitivity of both ATPase and force development. No difference in the cross-bridge turnover rate was observed at the same level of cross-bridge attachment (activation state), showing that changes in Ca(2+) sensitivity were not due to changes in cross-bridge kinetics. Energy cost calculations demonstrated higher energy consumption in Tg-R145G fibers compared with Tg-WT fibers. The addition of 3 mm 2,3-butanedione monoxime at pCa 9.0 showed that there was approximately 2-4% of force generating cross-bridges attached in Tg-R145G fibers compared with less than 1.0% in Tg-WT fibers, suggesting that the mutation impairs the ability of the cardiac troponin complex to fully inhibit cross-bridge attachment under relaxing conditions. Prolonged force and intracellular [Ca(2+)] transients in electrically stimulated intact papillary muscles were observed in Tg-R145G compared with Tg-WT. These results suggest that the phenotype of hypertrophic cardiomyopathy is most likely caused by the compensatory mechanisms in the cardiovascular system that are activated by 1) higher energy cost in the heart resulting from a significant decrease in average force per cross-bridge, 2) slowed relaxation (diastolic dysfunction) caused by prolonged [Ca(2+)] and force transients, and 3) an inability of the cardiac TnI to completely inhibit activation in the absence of Ca(2+) in Tg-R145G mice.

Prolonged Ca2+ and force transients in myosin RLC transgenic mouse fibers expressing malignant and benign FHC mutations.

Clinical studies have revealed that mutations in the ventricular myosin regulatory light chain (RLC) lead to the development of familial hypertrophic cardiomyopathy (FHC), an autosomal dominant disease characterized by left ventricular hypertrophy, myofibrillar disarray and sudden cardiac death. While mutations in other contractile proteins have been studied widely by others, there is no report elucidating the mechanism(s) associated with FHC-linked RLC mutations. In this study, we have assessed the functional consequences of two RLC mutations, R58Q and N47K, in transgenic mice. Clinical phenotypes associated with these mutations included inter-ventricular hypertrophy, abnormal ECG findings and the R58Q mutation caused multiple cases of premature sudden cardiac death. Simultaneous measurements of the ATPase and force in transgenic skinned papillary muscle fibers from mutated versus control mice showed an increase in the Ca(2+) sensitivity of ATPase and steady-state force only in R58Q fibers. The calculated energy cost or rate of dissociation of force generating myosin cross-bridges (ATPase/force ratio) plotted as a function of activation state was the same in all groups of fibers. Both mutations caused prolonged [Ca(2+)] transients in electrically stimulated intact papillary muscles; however, the R58Q mutation also resulted in a significantly prolonged force transient. Our results suggest that the phenotypes of FHC observed in patients harboring these RLC mutations correlate with the extent of physiological changes monitored in transgenic fibers. Cardiac hypertrophy observed in patients is most likely caused by the activation of compensatory mechanisms ensuing from higher workloads due to incomplete relaxation as evidenced by prolonged [Ca(2+)] transients for both N47K and R58Q fibers. Furthermore, the poor prognosis of the R58Q patients may be associated with more severe diastolic dysfunction due to the slower off-rate of Ca(2+) from troponin C leading to longer force and [Ca(2+)] transients and increased Ca(2+) sensitivity of ATPase and force.

Endograft technology: a delivery vehicle for intravascular gene therapy.

PURPOSE: The purpose of this study was to determine whether vascular smooth muscle cells (SMCs) suffused into a bilayered stent graft retain and express a retrovirally transduced gene for 7 months in vivo. METHODS: SMCs harvested from dog jugular vein were retrovirally transduced to introduce genes for tissue plasminogen activator (t-PA) and beta-galactosidase. These cells were then suffused into a novel dual-layered Dacron graft and cultured for 36 to 48 hours. The grafts were mounted on a Palmaz stent and balloon- expanded in the infrarenal aorta of the SMC donor dogs (n = 6). Grafts were recovered at 1, 2, 3, 4, 5, and 7 months. A control endograft suffused with SMCs transduced with only the beta-galactosidase gene was placed in the dogs with grafts recovered at 2, 3, and 4 months. t-PA antigen concentration and expression were analyzed with an enzyme-linked immunosorbent assay. RESULTS: Retained engineered SMCs (blue nuclei) were identified in the explanted grafts, neointima, and underlying aorta with X-gal staining. The t-PA antigen concentration and t-PA activity from the SMCs recovered from the grafts remained elevated for the duration of the experiment (7 months) at levels significantly higher (3.7 +/- 0.2 ng/mL per 10(5) cells per 24 hours and 1.4 +/- 0.1 IU/mL per 10(5) cells per 24 hours) than in control endografts (0.5 +/- 0.03 ng/mL per 10(5) cells per 24 hours and 0.07 +/- 0.00 IU/mL per 10(5) cells per 24 hours; P <.001). No graft stenosis was observed. CONCLUSION: Retrovirally engineered vascular SMCs survived the implantation trauma, repopulated each graft, migrated into the underlying aorta, and expressed the transduced genes for the 7-month duration of the experiment. This bilayered Dacron endograft model provides a platform to study direct intravascular gene therapy.