Fungal Kinases With a Sweet Tooth: Pleiotropic Roles of Their Phosphorylated Inositol Sugar Products in the Pathogenicity of Cryptococcus neoformans Present Novel Drug Targeting Opportunities.

Invasive fungal pathogens cause more than 300 million serious human infections and 1.6 million deaths per year. A clearer understanding of the mechanisms by which these fungi cause disease is needed to identify novel targets for urgently needed therapies. Kinases are key components of the signaling and metabolic circuitry of eukaryotic cells, which include fungi, and kinase inhibition is currently being exploited for the treatment of human diseases. Inhibiting evolutionarily divergent kinases in fungal pathogens is a promising avenue for antifungal drug development. One such group of kinases is the phospholipase C1-dependent inositol polyphosphate kinases (IPKs), which act sequentially to transfer a phosphoryl group to a pre-phosphorylated inositol sugar (IP). This review focuses on the roles of fungal IPKs and their IP products in fungal pathogenicity, as determined predominantly from studies performed in the model fungal pathogen Cryptococcus neoformans, and compares them to what is known in non-pathogenic model fungi and mammalian cells to highlight potential drug targeting opportunities.

Microbial inositol polyphosphate metabolic pathway as drug development target.

Inositol polyphosphates are a diverse and multifaceted class of intracellular messengers omnipresent in eukaryotic cells. These water-soluble molecules regulate many aspects of fundamental cell physiology. Removing this metabolic pathway is deleterious: inositol phosphate kinase null mutations can result in lethality or substantial growth phenotypes. Inositol polyphosphate synthesis occurs through the actions of a set of kinases that phosphorylate phospholipase-generated IP3 to higher phosphorylated forms, such as the fully phosphorylated IP6 and the inositol pyrophosphates IP7 and IP8. Unicellular organisms have a reduced array of the kinases for synthesis of higher phosphorylated inositol polyphosphates, while human cells possess two metabolic routes to IP6. The enzymes responsible for inositol polyphosphate synthesis have been identified in all eukaryote genomes, although their amino acid sequence homology is often barely detectable by common search algorithms. Homology between human and microbial inositol phosphate kinases is restricted to a few catalytically important residues. Recent studies of the inositol phosphate metabolic pathways in pathogenic fungi (Cryptococcus neoformans) and protozoa (Trypanosome brucei) have revealed the importance of the highly phosphorylated inositol polyphosphates to the fitness and thus virulence of these pathogens. Given this, identification of inositol kinase inhibitors specifically targeting the kinases of pathogenic microorganisms is desirable and achievable.

Protein kinase- and lipase inhibitors of inositide metabolism deplete IP7 indirectly in pancreatic ß-cells: Off-target effects on cellular bioenergetics and direct effects on IP6K activity.

Inositol pyrophosphates have emerged as important regulators of many critical cellular processes from vesicle trafficking and cytoskeletal rearrangement to telomere length regulation and apoptosis. We have previously demonstrated that 5-di-phosphoinositol pentakisphosphate, IP7, is at a high level in pancreatic ß-cells and is important for insulin exocytosis. To better understand IP7 regulation in ß-cells, we used an insulin secreting cell line, HIT-T15, to screen a number of different pharmacological inhibitors of inositide metabolism for their impact on cellular IP7. Although the inhibitors have diverse targets, they all perturbed IP7 levels. This made us suspicious that indirect, off-target effects of the inhibitors could be involved. It is known that IP7 levels are decreased by metabolic poisons. The fact that the inositol hexakisphosphate kinases (IP6Ks) have a high Km for ATP makes IP7 synthesis potentially vulnerable to ATP depletion. Furthermore, many kinase inhibitors are targeted to the ATP binding site of kinases, but given the similarity of such sites, high specificity is difficult to achieve. Here, we show that IP7 concentrations in HIT-T15 cells were reduced by inhibitors of PI3K (wortmannin, LY294002), PI4K (Phenylarsine Oxide, PAO), PLC (U73122) and the insulin receptor (HNMPA). Each of these inhibitors also decreased the ATP/ADP ratio. Thus reagents that compromise energy metabolism reduce IP7 indirectly. Additionally, PAO, U73122 and LY294002 also directly inhibited the activity of purified IP6K. These data are of particular concern for those studying signal transduction in pancreatic ß-cells, but also highlight the fact that employment of these inhibitors could have erroneously suggested the involvement of key signal transduction pathways in various cellular processes. Conversely, IP7's role in cellular signal transduction is likely to have been underestimated.

Ethanol Stimulates Endoplasmic Reticulum Inositol Triphosphate and Sigma Receptors to Promote Withdrawal-Associated Loss of Neuron-Specific Nuclear Protein/Fox-3.

BACKGROUND: Prior studies demonstrate that ethanol (EtOH) exposure induces the release of intracellular calcium (CA(2+) ) in modulation of γ-aminobutyric acid-ergic tone and produces concomitant alterations in sigma (σ)-1 protein expression that may contribute to the development EtOH dependence. However, the influence of CA(2+) released from endoplasmic reticulum (ER)-bound inositol triphosphate (IP3) and σ-1 receptors in regulating hippocampal function has yet to be delineated. METHODS: Rat hippocampal explants were subjected to chronic intermittent EtOH (CIE) exposure with or without the addition of IP3 inhibitor xestospongin C (0 to 0.5 µM) or σ-1 receptor antagonist BD-1047 (0 to 80 µM). Hippocampal viability was assessed via immunohistochemical labeling of neuron-specific nuclear protein (NeuN)/Fox-3 in CA1, CA3, and dentate gyrus (DG) subregions. RESULTS: Exposure to CIE produced consistent and significant decreases of NeuN/Fox-3 in each primary cell layer of the hippocampal formation. Co-exposure to xestospongin reversed these effects in the CA1 subregion and significantly attenuated these effects in the CA3 and DG regions. Xestospongin application also significantly increased NeuN/Fox-3 immunofluorescence in EtOH-naïve hippocampi. Co-exposure to 20 µM BD-1047 also reversed the loss of NeuN/Fox-3 during CIE exposure in each hippocampal cell layer, whereas exposure to 80 µM BD-1047 did not alter NeuN/Fox-3 in EtOH-treated hippocampi. By contrast, 80 µM BD-1047 application significantly increased NeuN/Fox-3 immunofluorescence in EtOH-naïve hippocampi in each subregion. CONCLUSIONS: These data suggest that EtOH stimulates ER IP3 and σ-1 receptors to promote hippocampal loss of NeuN/Fox-3 during CIE.

Chemogenetic Characterization of Inositol Phosphate Metabolic Pathway Reveals Druggable Enzymes for Targeting Kinetoplastid Parasites.

Kinetoplastids cause Chagas disease, human African trypanosomiasis, and leishmaniases. Current treatments for these diseases are toxic and inefficient, and our limited knowledge of drug targets and inhibitors has dramatically hindered the development of new drugs. Here we used a chemogenetic approach to identify new kinetoplastid drug targets and inhibitors. We conditionally knocked down Trypanosoma brucei inositol phosphate (IP) pathway genes and showed that almost every pathway step is essential for parasite growth and infection. Using a genetic and chemical screen, we identified inhibitors that target IP pathway enzymes and are selective against T. brucei. Two series of these inhibitors acted on T. brucei inositol polyphosphate multikinase (IPMK) preventing Ins(1,4,5)P3 and Ins(1,3,4,5)P4 phosphorylation. We show that IPMK is functionally conserved among kinetoplastids and that its inhibition is also lethal for Trypanosoma cruzi. Hence, IP enzymes are viable drug targets in kinetoplastids, and IPMK inhibitors may aid the development of new drugs.

Oncostatin M (OSM) protects against cardiac ischaemia/reperfusion injury in diabetic mice by regulating apoptosis, mitochondrial biogenesis and insulin sensitivity.

Oncostatin M (OSM) exhibits many unique biological activities by activating Oß receptor. However, its role in myocardial I/R injury in diabetic mice remains unknown. The involvement of OSM was assessed in diabetic mice which underwent myocardial I/R injury by OSM treatment or genetic deficiency of OSM receptor Oß. Its mechanism on cardiomyocyte apoptosis, mitochondrial biogenesis and insulin sensitivity were further studied. OSM alleviated cardiac I/R injury by inhibiting cardiomyocyte apoptosis through inhibition of inositol pyrophosphate 7 (IP7) production, thus activating PI3K/Akt/BAD pathway, decreasing Bax expression while up-regulating Bcl-2 expression and decreasing the ratio of Bax to Bcl-2 in db/db mice. OSM enhanced mitochondrial biogenesis and mitochondrial function in db/db mice subjected to cardiac I/R injury. On the contrary, OSM receptor Oß knockout exacerbated cardiac I/R injury, increased IP7 production, enhanced cardiomyocyte apoptosis, impaired mitochondrial biogenesis, glucose homoeostasis and insulin sensitivity in cardiac I/R injured diabetic mice. Inhibition of IP7 production by TNP (IP6K inhibitor) exerted similar effects of OSM. The mechanism of OSM on cardiac I/R injury in diabetic mice is partly associated with IP7/Akt and adenine mononucleotide protein kinase/PGC-1α pathway. OSM protects against cardiac I/R Injury by regulating apoptosis, insulin sensitivity and mitochondrial biogenesis in diabetic mice through inhibition of IP7 production.

Potent, selective small molecule inhibitors of type III phosphatidylinositol-4-kinase α- but not ß-inhibit the phosphatidylinositol signaling cascade and cancer cell proliferation.

Two series of inhibitors of type III phosphatidylinositol-4-kinase were identified by high throughput screening and optimised to derive probe compounds that independently and selectively inhibit the α- and the ß-isoforms with no significant activity towards related kinases in the pathway. In a cellular environment, inhibition of the α- but not the ß-subtype led to a reduction in phosphatidylinositol-4-phosphate and phosphatidylinositol-4,5-bisphosphate concentration, causing inhibition of inositol-1-phosphate formation and inhibition of proliferation in a panel of cancer cell lines.

Cigarette smoke (CS) and nicotine delay neutrophil spontaneous death via suppressing production of diphosphoinositol pentakisphosphate.

Diphosphoinositol pentakisphosphate (InsP7), a higher inositol phosphate containing energetic pyrophosphate bonds, is beginning to emerge as a key cellular signaling molecule. However, the various physiological and pathological processes that involve InsP7 are not completely understood. Here we report that cigarette smoke (CS) extract and nicotine reduce InsP7 levels in aging neutrophils. This subsequently leads to suppression of Akt deactivation, a causal mediator of neutrophil spontaneous death, and delayed neutrophil death. The effect of CS extract and nicotine on neutrophil death can be suppressed by either directly inhibiting the PtdIns(3,4,5)P3/Akt pathway, or increasing InsP7 levels via overexpression of InsP6K1, an inositol hexakisphosphate (InsP6) kinase responsible for InsP7 production in neutrophils. Delayed neutrophil death contributes to the pathogenesis of CS-induced chronic obstructive pulmonary disease. Therefore, disruption of InsP6K1 augments CS-induced neutrophil accumulation and lung damage. Taken together, these results suggest that CS and nicotine delay neutrophil spontaneous death by suppressing InsP7 production and consequently blocking Akt deactivation in aging neutrophils. Modifying neutrophil death via this pathway provides a strategy and therapeutic target for the treatment of tobacco-induced chronic obstructive pulmonary disease.

ß-catenin promoter ChIP-chip reveals potential schizophrenia and bipolar disorder gene network.

Therapeutic concentrations of lithium salts inhibit glycogen synthase kinase 3 beta (GSK3ß) and phosphoinositide (PI) signaling suggesting that abnormal activation of these pathways could be a factor in the pathophysiology of bipolar disorder (BD). Involvement of these pathways is also supported by recent genome-wide association studies (GWASs). One way investigators have investigated the molecular basis of BD and the therapeutic action of lithium is by microarray expression studies, since both GSK3ß- and PI-mediated signal transduction pathways are coupled to transcriptional activation and inhibition. However, expression profiling has some limitations and investigators cannot use the approach to analyze fetal brain tissue, arguably the most relevant biological structure related to the development of genetically based psychiatric disorders. To address these shortcomings, the authors have taken a novel approach using chromatin immunoprecipitation-enriched material annealed to microarrays (ChIP-chip) targeting genes in fetal brain tissue bound by ß-catenin, a transcription factor that is directly regulated by GSK3ß. The promoters for 640 genes were found to be bound by ß-catenin, many of which are known schizophrenia (SZ), autism spectrum disorder (ASD), and BD candidates, including CACNA1B, NRNG, SNAP29, FGFR1, PCDH9, and nine others identified in recently published GWASs and genome-wide searches for copy number variants (CNVs). The findings suggest that seemingly disparate candidate genes for SZ and BD can be incorporated into a common molecular network revolving around GSK3ß/ß-catenin signaling. In addition, the finding that a putative lithium-responsive pathway may influence a subgroup of SZ and ASD candidate genes could have therapeutic implications.

Testosterone and dihydrotestosterone inhibit gallbladder motility through multiple signalling pathways.

Testosterone (T) has been shown to cause vasodilation in rabbit coronary arteries through a nongenomic pathway. Part of this T-induced relaxation was shown to be mediated by opening voltage dependent K(+) channels. T infusion also reduces peripheral resistance in human males with heart failure. The effects of T or its active metabolite 5-alpha dihydrotestosterone (DHT) are not well studied. This study investigates the effect of T and DHT on contraction in guinea pig gallbladder strips. T or DHT induced a concentration-dependent relaxation of cholecystokinin octapeptide (CCK)-induced tension. Pretreatment of the strips with PKA inhibitor 14-22 amide myristolated had no significant effect on the relaxation induced by either T or DHT. Pretreatment of strips with 2-APB, an inhibitor of IP(3) induced Ca(2+) release, produced a significant (p<0.001) reduction in the T- or DHT-induced relaxation. Bisindolymaleimide IV and chelerythrine Cl(-) when used in combination had no significant effect on the amount of CCK-induced tension, but significantly (p<0.01) decreased the amount of T- or DHT-induced relaxation. The flavone chrysin, an aromatase inhibitor, and genistein, an isoflavone, each produced a significant (p<0.01) reduction in CCK-induced tension. Chrysin significantly (p<0.05) increased T-induced relaxation; however, genistein had no effect on T-induced relaxation. It is concluded that T and DHT inhibits gallbladder motility rapidly by nongenomic actions of the hormones. Multiple pathways that include inhibition of intracellular Ca(2+) release, inhibition of extracellular Ca(2+) entry, and the actions of PKC may mediate this effect.

Pharmacological characterization of a novel nonpeptide antagonist of the human gonadotropin-releasing hormone receptor, NBI-42902.

Suppression of the hypothalamic-pituitary-gonadal axis by peptides that act at the GnRH receptor has found widespread use in clinical practice for the management of sex-steroid-dependent diseases (such as prostate cancer and endometriosis) and reproductive disorders. Efforts to develop orally available GnRH receptor antagonists have led to the discovery of a novel, potent nonpeptide antagonist, NBI-42902, that suppresses serum LH concentrations in postmenopausal women after oral administration. Here we report the in vitro and in vivo pharmacological characterization of this compound. NBI-42902 is a potent inhibitor of peptide radioligand binding to the human GnRH receptor (K(i) = 0.56 nm). Tritiated NBI-42902 binds with high affinity (K(d) = 0.19 nm) to a single class of binding sites and can be displaced by a range of peptide and nonpeptide GnRH receptor ligands. In vitro experiments demonstrate that NBI-42902 is a potent functional, competitive antagonist of GnRH stimulated IP accumulation, Ca(2+) flux, and ERK1/2 activation. It did not stimulate histamine release from rat peritoneal mast cells. Finally, it is effective in lowering serum LH in castrated male macaques after oral administration. Overall, these data provide a benchmark of pharmacological characteristics required for a nonpeptide GnRH antagonist to effectively suppress gonadotropins in humans and suggest that NBI-42902 may have clinical utility as an oral agent for suppression of the hypothalamic-pituitary-gonadal axis.

N1-Benzoyl-N2-[1-(1-naphthyl)ethyl]-trans-1,2-diaminocyclohexanes: Development of 4-chlorophenylcarboxamide (calhex 231) as a new calcium sensing receptor ligand demonstrating potent calcilytic activity.

A structure-activity relationship (SAR) study was performed principally at the N1 position of N1-arylsulfonyl-N2-[1-(1-naphthyl)ethyl]-trans-1,2-diaminocyclohexanes, a new family of calcilytics acting at the calcium sensing receptor (CaSR). The most active compound in this series was the 4-(trifluoromethoxy)benzenesulfonyl derivative 7e, which displayed an IC50 of 5.4 +/- 0.5 microM with respect to the inhibition of calcium-induced tritiated inositol phosphate ([3H]IP) accumulation in Chinese hamster ovarian (CHO) cells expressing the CaSR. Replacement of the sulfonamide linkage of this compound by a carboxamide led to a 6-fold increase in activity (7m, IC50 = 0.9 +/- 0.2 microM). Among the carboxamides synthesized, one of the most active compounds was the 4-chlorophenylcarboxamide (1S,2S,1'R)-7n (Calhex 231, IC50 = 0.33 +/- 0.02 microM). The absolute configuration of (1S,2S,1'R)-7n was deduced from an X-ray crystallographic study of one of the diastereomers of compound 7d. The stereochemical preference for the (1S,2S,1'R)-isomers can be rationalized on the basis of a three-dimensional model of the calcilytic binding pocket of the CaSR. Removal of the C-1' methyl group or replacement of the 1-naphthyl group by a 2-naphthyl or biphenyl moiety led to appreciable loss of calcilytic activity. Compounds 7e, 7m, and Calhex 231 did not stimulate [3H]IP accumulation in CHO cells expressing or not expressing the CaSR.

Physiological levels of PTEN control the size of the cellular Ins(1,3,4,5,6)P(5) pool.

To understand how a signaling molecule's activities are regulated, we need insight into the processes controlling the dynamic balance between its synthesis and degradation. For the Ins(1,3,4,5,6)P5 signal, this information is woefully inadequate. For example, the only known cytosolic enzyme with the capacity to degrade Ins(1,3,4,5,6)P5 is the tumour-suppressor PTEN [J.J. Caffrey, T. Darden, M.R. Wenk, S.B. Shears, FEBS Lett. 499 (2001) 6 ], but the biological relevance has been questioned by others [E.A. Orchiston, D. Bennett, N.R. Leslie, R.G. Clarke, L. Winward, C.P. Downes, S.T. Safrany, J. Biol. Chem. 279 (2004) 1116 ]. The current study emphasizes the role of physiological levels of PTEN in Ins(1,3,4,5,6)P5 homeostasis. We employed two cell models. First, we used a human U87MG glioblastoma PTEN-null cell line that hosts an ecdysone-inducible PTEN expression system. Second, the human H1299 bronchial cell line, in which PTEN is hypomorphic due to promoter methylation, has been stably transfected with physiologically relevant levels of PTEN. In both models, a novel consequence of PTEN expression was to increase Ins(1,3,4,5,6)P5 pool size by 30-40% (p<0.01); this response was wortmannin-insensitive and, therefore, independent of the PtdIns 3-kinase pathway. In U87MG cells, induction of the G129R catalytically inactive PTEN mutant did not affect Ins(1,3,4,5,6)P(5) levels. PTEN induction did not alter the expression of enzymes participating in Ins(1,3,4,5,6)P5 synthesis. Another effect of PTEN expression in U87MG cells was to decrease InsP6 levels by 13% (p<0.02). The InsP6-phosphatase, MIPP, may be responsible for the latter effect; we show that recombinant human MIPP dephosphorylates InsP6 to D/L-Ins(1,2,4,5,6)P5, levels of which increased 60% (p<0.05) following PTEN expression in U87MG cells. Overall, our data add higher inositol phosphates to the list of important cellular regulators [Y. Huang, R.P. Wernyj, D.D. Norton, P. Precht, M.C. Seminario, R.L. Wange, Oncogene, 24 (2005) 3819 ] the levels of which are modulated by expression of the highly pleiotropic PTEN protein.

Can intervention in inositol phosphate signalling pathways improve therapy for cystic fibrosis?

Airway epithelial cells from cystic fibrosis (CF) individuals cannot secrete adequate Cl- through cystic fibrosis transmembrane regulator, and their Na+ channel (ENaC) activity is increased so that excessive Na+ and water is absorbed from the lumen. These aberrant transport activities can, at least partly, be compensated by pharmacologically increasing the activities of Ca2+-activated Cl- channels (CaCCs). The therapeutic value of this approach is currently being examined in clinical trials of candidate CF drugs such as INS-37217 (Inspire Pharmaceuticals) and Moli1901 (Lantibio, Inc.). This review argues that these drug development programmes will be helped if one can fully understand how the CaCCs are inhibited by inositol 3,4,5,6-tetrakisphosphate (Ins(3,4,5,6)P4), so that there can be pharmacological intervention in this process. Furthermore, genes that encode enzymes controlling Ins(3,4,5,6)P4 metabolism should be viewed as impacting upon CaCC activity; this, in turn, may influence the severity of the CF condition. Expression profiling of genes that regulate inositol phosphate metabolism may also illuminate variability in patient response to treatment regimens that target CaCCs. Compounds have been developed that can activate CaCCs by antagonising their inhibition by Ins(3,4,5,6)P4. One member of this drug family (INO-4995; Inologic) was recently shown to inhibit ENaC, thereby reducing fluid absorbtion by airway epithelial cells.

Minor structural modifications convert the dual TP/CRTH2 antagonist ramatroban into a highly selective and potent CRTH2 antagonist.

Ramatroban, a thromboxane A(2) receptor (TP) antagonist with clinical efficacy in asthma and allergic rhinitis, was recently shown to also antagonize the prostaglandin D(2) receptor CRTH2. Here we report that minor structural changes to ramatroban result in a compound (13) with complete lack of activity on TP but sub-nanomolar potency toward CRTH2. This is the first selective CRTH2 antagonist described to date, and should prove highly valuable in further elucidating the biological significance of CRTH2.

Interleukin-1 beta down-regulates the expression of metabotropic glutamate receptor 5 in cultured human astrocytes.

Expression of metabotropic glutamate receptor 5 (mGluR5) protein is known to be plastic and to depend critically on the astrocytes' microenvironment. In the present study we investigated whether interleukins, which are involved in the immune response following brain injury, could contribute to the regulation of mGluR5 protein in human astrocytes in culture. Using Western blotting and immunocytochemistry, no detectable changes in the expression of the mGluR5 protein were observed with both interleukin 1beta and interleukin 6 in undifferentiated cultures (growing in serum free media). In contrast, in cultures that had been morphologically differentiated by exposure to epidermal growth factor (EGF), addition of interleukin 1beta (but not interleukin 6) reduced mGluR5 protein expression. In addition, stimulation of phosphoinositide hydrolysis by the selective group I agonist (S)-3,5-dihydroxyphenylglycine (DHPG) was reduced after exposure to interleukin 1beta. The suppressive effect on mGluR5 was prevented by the interleukin 1 receptor antagonist. Thus, interleukin 1beta may represent an additional pathway through which mGluR5 expression and function can be modulated in astrocytes under different pathological conditions associated with an inflammatory response.

Nicotinic acid adenine dinucleotide phosphate potentiates neurite outgrowth.

Ca(2+) regulates a spectrum of cellular processes including many aspects of neuronal function. Ca(2+)-sensitive events such as neurite extension and axonal guidance are driven by Ca(2+) signals that are precisely organized in both time and space. These complex cues result from both Ca(2+) influx across the plasma membrane and the mobilization of intracellular Ca(2+) stores. In the present study, using rat cortical neurons, we have examined the effects of the novel intracellular Ca(2+)-mobilizing messenger nicotinic acid adenine dinucleotide phosphate (NAADP) on neurite length and cytosolic Ca(2+) levels. We show that NAADP potentiates neurite extension in response to serum and nerve growth factor and stimulates increases in cytosolic Ca(2+) from bafilomycin-sensitive Ca(2+) stores. Simultaneous blockade of inositol trisphosphate and ryanodine receptors abolished the effects of NAADP on neurite length and reduced the magnitude of NAADP-mediated Ca(2+) signals. This is the first report demonstrating functional NAADP receptors in a mammalian neuron. Interplay between NAADP receptors and more established intracellular Ca(2+) channels may therefore play important signaling roles in the nervous system.

Antagonists of myo-inositol 3,4,5,6-tetrakisphosphate allow repeated epithelial chloride secretion.

Cystic fibrosis (CF) patients suffer from a defect in hydration of mucosal membranes due to mutations in the cystic fibrosis transmembrane regulator (CFTR), an apical chloride channel in mucosal epithelia. Disease expression in CF knockout mice is organ specific, varying with the level of expression of calcium activated Cl(-) channels (CLCA). Therefore, restoring transepithelial Cl(-) secretion by augmenting alternate Cl(-) channels, such as CLCA, could be beneficial. However, CLCA-mediated Cl(-) secretion is transient, due in part to the inhibitory effects of myo-inositol 3,4,5,6-tetrakisphosphate [Ins(3,4,5,6)P(4)]. This suggests that antagonists of Ins(3,4,5,6)P(4) could be useful in treatment of CF. We have, therefore, synthesized a series of membrane-permeant Ins(3,4,5,6)P(4) derivatives, carrying alkyl substituents on the hydroxyl groups and screened them for effects on Cl(-) secretion in a human colonic epithelial cell line, T(84). While membrane-permeant Ins(3,4,5,6)P(4) derivatives had no direct effects on carbachol-stimulated Cl(-) secretion, Ins(3,4,5,6)P(4) derivatives, but not enantiomeric Ins(1,4,5,6)P(4) derivatives, reversed the inhibitory effect of Ins(3,4,5,6)P(4) on subsequent thapsigargin activation of Cl(-) secretion. The extent of the antagonistic effect of the Ins(3,4,5,6)P(4) derivatives varied with the position of the alkyl substituents. Derivatives with a cyclohexylidene ketal or a butyl-chain at the 1-position reversed the Ins(3,4,5,6)P(4)-mediated inhibition of Cl(-) secretion by up to 96 and 85%, respectively, whereas butylation of the 1- and 2-position generated a reversal effect of only 65%. Derivatives carrying the butyl chain only at the 2-position showed no antagonistic effect. These data: (1) Support the hypothesis that Ins(3,4,5,6)P(4) stereospecifically inhibits Ca(2+) activated Cl(-) secretion and that Ins(3,4,5,6)P(4) mediates most, if not all of the cholinergic-mediated inhibition of chloride secretion in T(84) cells; (2) Demonstrate Ins(3,4,5,6)P(4)-mediated inhibition can be completely reversed with rationally designed membrane-permeant Ins(3,4,5,6)P(4) antagonists; (3) Demonstrate that a SAR for membrane-permeant Ins(3,4,5,6) P(4) antagonists can be generated and screened in a physiologically relevant cell-based assay; (4) Indicate that Ins(3,4,5,6)P(4) derivatives could serve as a starting point for the development of therapeutics to treat cystic fibrosis.

2-Chloro N(6)-methyl-(N)-methanocarba-2'-deoxyadenosine-3',5'-bisphosphate is a selective high affinity P2Y(1) receptor antagonist.

1. We reported previously that bisphosphate derivatives of adenosine are antagonists of the P2Y(1) receptor and that modification of the ribose in these analogues is tolerated in the P2Y(1) receptor binding pharmacophore. 2. Here we delineate the pharmacological activity of one such non-nucleotide molecule, 2-chloro N(6)-methyl-(N)-methanocarba-2'-deoxyadenosine-3',5'-bisphosphate (MRS2279), in which the ribose is replaced by a cyclopentane ring constrained in the (N)-conformation by a cyclopropane moiety. 3. MRS2279 antagonized 2MeSADP-stimulated inositol phosphate formation in turkey erythrocyte membranes with competitive kinetics (pK(B)=7.75). High affinity competitive antagonism by MRS2279 was also observed at the human P2Y(1) receptor (pK(B)=8.10) stably expressed in 1321N1 human astrocytoma cells. Antagonism was specific for the P2Y(1) receptor since MRS2279 had no effect on activation of the human P2Y(2), P2Y(4), P2Y(6), or P2Y(11) receptors by their cognate agonists. 4. MRS2279 also did not block the capacity of ADP to act through the Gi/adenylyl cyclase linked P2Y receptor of platelets to inhibit cyclic AMP accumulation. 5. In contrast, the P2Y(1) receptor is known to be obligatory in the process of ADP-induced platelet aggregation, and MRS2279 competitively inhibited ADP-promoted platelet aggregation with an apparent affinity (pK(B)=8.05) similar to that observed at the human P2Y(1) receptor heterologously expressed in 1321N1 cells. 6. Taken together these results illustrate selective high affinity antagonism of the P2Y(1) receptor by a non-nucleotide molecule that should prove useful for pharmacological delineation of this receptor in various tissues.

Cellular signaling by the potent bronchoconstrictor endothelin-1 in airway smooth muscle.

OBJECTIVE: The objective of this study was to determine whether the potent bronchoconstrictor endothelin-1 was coupled to the activation of the inositol phosphate and/or inhibition of the cyclic adenine monophosphate second messenger pathways in porcine airway smooth muscle. DESIGN: Prospective, controlled, in vitro, nonblinded study. SETTING: University biochemical and molecular biological research laboratory. SUBJECTS: Pigs of both genders. INTERVENTIONS: Airway smooth muscle was dissected from the trachea of pigs exsanguinated under anesthesia. Airway smooth muscle from six animals preloaded with 3H-myoinositol was exposed to endothelin-1, carbachol (positive control) or vehicle for 30 mins. Some tissues were pretreated with antagonists selective for the ET(A) (BQ-485) and ET(B) (BQ-788) endothelin receptor subtypes. Newly synthesized 3H-inositol phosphates were recovered by column chromatography. Airway smooth muscle from an additional 7 pigs was homogenized and incubated in the presence of 32P-alpha-adenosine triphosphate, guanosine triphosphate (GTP) and either carbachol or endothelin to measure the inhibitory influence of carbachol (positive control) or endothelin on GTP-stimulated adenylyl cyclase activity. Newly synthesized 32P-cyclic adenosine monophosphate was isolated by sequential column chromatography over Dowex and alumina. MEASUREMENTS AND MAIN RESULTS: Total inositol phosphates increased in porcine airway smooth muscle in response to either carbachol or endothelin. The endothelin receptor antagonist BQ-485 (ET(A) selective) but not BQ-788 (ET(B) selective) dose-dependently inhibited endothelin-1 induced inositol phosphate accumulation. In adenylyl cyclase assays, carbachol (positive control), but not endothelin-1, significantly inhibited GTP-stimulated adenylyl cyclase activity. CONCLUSION: Endothelin-1 couples to the activation of the inositol phosphate pathway via the ET(A) receptor subtype but does not couple to inhibition of the adenylyl cyclase pathway in porcine airway smooth muscle. The potent bronchoconstrictive effects of endothelin likely involve the acute activation of the inositol phosphate pathway in airway smooth muscle.