Chebulagic acid is a potent alpha-glucosidase inhibitor

Chebulagic acid, isolated form Terminalia chebula Retz, proved to be a reversible and non-competitive inhibitor of maltase with a K(i) value of 6.6 muM. The inhibitory influence of chebulagic acid on the maltase-glucoamylase complex was more potent than on the sucrase-isomaltase complex. The magnitude of alpha-glucosidase inhibition by chebulagic acid was greatly affected by its origin. These results show a use for chebulagic acid in managing type-2 diabetes.     

2-fluorourocanic acid, a potent reversible inhibitor of urocanase.

The K_i for the interaction of 2-fluorourocanic acid with urocanase (from $\text{Pseudomonas fluorescens}$) is 1000 times as great as K_m for the natural substrate, urocanic acid, whereas enzymatic hydration of the fluoro analog occurs $\text{ca}$. 100 times more slowly. Inhibition is competive and is eventually overcome by utilization of the analog. By contrast, 4-fluoro- and 2-amino-urocanic acid are neither significant inhibitors nor substrates for the enzyme. 2-Fluorourocanic acid may prove a useful tool for blocking the utilization of histidine as a one-carbon source in metabolism.     

Novel binding mode of a potent and selective tankyrase inhibitor

Tankyrases (TNKS1 and TNKS2) are key regulators of cellular processes such as telomere pathway and Wnt signaling. IWRs (inhibitors of Wnt response) have recently been identified as potent and selective inhibitors of tankyrases. However, it is not clear how these IWRs interact with tankyrases. Here we report the crystal structure of the catalytic domain of human TNKS1 in complex with IWR2, which reveals a novel binding site for tankyrase inhibitors. The TNKS1/IWR2 complex provides a molecular basis for their strong and specific interactions and suggests clues for further development of tankyrase inhibitors.     

Esterastin: a potent inhibitor of lysosomal acid lipase

The effect of a fungal metabolite, esterastin, on lysosomal acid lipase purified from rabbit liver was studied. Esterastin inhibited the enzyme activity very strongly (IC50, about 80 nM). The inhibition of acid lipase by esterastin was competitive with respect to the substrate and the inhibition constant for esterastin was 90 nM. Esterastin was less inhibitory to other lipolytic enzymes, such as pancreatic lipase and carboxylesterase. Thus esterastin is a potent new inhibitor of lysosomal acid lipase.     

A novel metal-chelating inhibitor of protein farnesyltransferase

A novel metal chelator comprising a 4-(naphthalen-1-yl)pyridine and 2-aminoethanethiol was synthesized. This showed inhibitory activity against human protein farnesyltransferase with IC(50) 1.9 microM, induced morphological change in K-ras-NRK cells at 0.5 microg/mL and showed growth inhibition of K-ras-NRK cells with IC(50) 0.32 microg/mL.     

3-Mercaptopropionic acid, a potent inhibitor of fatty acid oxidation in rat heart mitochondria

The effects of several short-chain mercapto acids on the rate of respiration supported by either palmitoylcarnitine, octanoate, or pyruvate was studied with coupled rat heart mitochondria. 3-Mercaptopropionic acid was found to be a potent inhibitor of respiration sustained by palmitoylcarnitine or octanoate, whereas under identical conditions respiration with pyruvate as a substrate was unaffected. 2-Mercaptoacetic acid also inhibits palmitoylcarnitine-supported respiration, but only at much higher concentrations of the inhibitor. 2-Mercaptopropionic acid has virtually no effect. Incubation of mitochondria with 3-mercaptopropionic acid did not cause the irreversible inactivation of any beta-oxidation enzyme. Since 3-mercaptopropionic acid did not inhibit beta-oxidation in uncoupled mitochondria, it appears that this compound must first be metabolized in an energy-dependent reaction before it becomes inhibitory. 3-Mercaptopropionyl-CoA and three of its S-acyl derivatives, all of which are likely mitochondrial metabolites of 3-mercaptopropionic acid, were tested for their capacity to inhibit the individual enzymes of beta-oxidation. 3-Mercaptopropionyl-CoA inhibits only acyl-CoA dehydrogenase, whereas S-myristoyl-3-mercaptopropionyl-CoA inhibits reversibly several beta-oxidation enzymes. All observations together lead us to suggest that the inhibition of beta-oxidation by 3-mercaptopropionic acid in coupled rat heart mitochondria is most likely a consequence of the reversible inhibition of acyl-CoA dehydrogenase by long-chain S-acyl-3-mercaptopropionyl-CoA thioesters and possibly by 3-mercaptopropionyl-CoA.     

Tannic acid, a potent inhibitor of epidermal growth factor receptor tyrosine kinase

Increasing evidence supports the hypothesis that tannic acid, a plant polyphenol, exerts anticarcinogenic activity in chemically induced cancers. In the present study, tannic acid was found to strongly inhibit tyrosine kinase activity of epidermal growth factor receptor (EGFr) in vitro (IC50 = 323 nM). In contrast, the inhibition by tannic acid of p60(c-src) tyrosine kinase (IC50 = 14 microM) and insulin receptor tyrosine kinase (IC50 = 5 microM) was much weaker. The inhibition of EGFr tyrosine kinase by tannic acid was competitive with respect to ATP and non-competitive with respect to peptide substrate. In cultured cells, growth factor-induced tyrosine phosphorylation of growth factor receptors, including EGFr, platelet-derived growth factor receptor, and basic fibroblast growth factor receptor, was inhibited by tannic acid. No inhibition of insulin-induced tyrosine phosphorylation of insulin receptor and insulin-receptor substrate-1 was observed. EGF-stimulated growth of HepG2 cells was inhibited in the presence of tannic acid. The inhibition of serine/threonine-specific protein kinases, including cAMP-dependent protein kinase, protein kinase C and mitogen-activated protein kinase, by tannic acid was only detected at relatively high concentration, IC50 being 3, 325 and 142 microM respectively. The molecular modeling study suggested that tannic acid could be docked into the ATP binding pockets of either EGFr or insulin receptor. These results demonstrate that tannic acid is an in vitro potent inhibitor of EGFr tyrosine kinase.     

Aurin tricarboxylic acid, the anti-AIDS compound, prevents the binding of interferon-alpha to its receptor

Binding of HIV to its receptor, the CD4 molecule of lymphocytes, can be prevented by chemical agents. These agents could be considered as potential anti-AIDS drugs. We have shown that aurin tricarboxylic acid (ATA, 3 microM) specifically blocks the binding of gp120, the HIV coat protein, to the CD4 molecule. We have also found that ATA prevents the binding of interferon-alpha to its receptor in a dose-dependent manner (12-50 microM range). Membrane potential shift, associated with binding of interferon-alpha to its receptor, was also blocked by ATA in a dose-dependent fashion. Our results indicate that potential anti-AIDS drugs should be screened for such undesired side effects.     

The phytotoxic lichen metabolite, usnic acid, is a potent inhibitor of plant p-hydroxyphenylpyruvate dioxygenase

The lichen secondary metabolite usnic acid exists as a (−) and a (+) enantiomer, indicating a or β projection of the methyl group at position 9b, respectively. (−)-Usnic caused a dose-dependent bleaching of the cotyledonary tissues associated with a decrease of both chlorophylls and carotenoids in treated plants whereas no bleaching was observed with the (+) enantiomer. (−)-Usnic acid inhibited protophorphyrinogen oxidase activity (I₅₀=3 μM), but did not lead to protoporphyrin IX accumulation. Bleaching appears to be caused by irreversible inhibition of the enzyme 4-hydroxyphenylpyruvate dioxygenase by (−)-usnic acid (apparent IC₅₀=50 nM).     

Sifuvirtide, a potent HIV fusion inhibitor peptide

Enfuvirtide (ENF) is currently the only FDA approved HIV fusion inhibitor in clinical use. Searching for more drugs in this category with higher efficacy and lower toxicity seems to be a logical next step. In line with this objective, a synthetic peptide with 36 amino acid residues, called Sifuvirtide (SFT), was designed based on the crystal structure of gp41. In this study, we show that SFT is a potent anti-HIV agent with relatively low cytotoxicity. SFT was found to inhibit replication of all tested HIV strains. The effective concentrations that inhibited 50% viral replication (EC₅₀), as determined in all tested strains, were either comparable or lower than benchmark values derived from well-known anti-HIV drugs like ENF or AZT, while the cytotoxic concentrations causing 50% cell death (CC₅₀) were relatively high, rendering it an ideal anti-HIV agent.A GST-pull down assay was performed to confirm that SFT is a fusion inhibitor. Furthermore, the activity of SFT on other targets in the HIV life cycle was also investigated, and all assays showed negative results. To further understand the mechanism of action of HIV peptide inhibitors, resistant variants of HIV-1_IIIB were derived by serial virus passage in the presence of increasing doses of SFT or ENF. The results showed that there was cross-resistance between SFT and ENF.In conclusion, SFT is an ideal anti-HIV agent with high potency and low cytotoxicity, but may exhibit a certain extent of cross-resistance with ENF.     

Phosphatidylinositol-3,5-Bisphosphate is a potent and selective inhibitor of acid sphingomyelinase

Acid sphingomyelinase (A-SMase, EC 3.1.4.12) catalyzes the lysosomal degradation of sphingomyelin to phosphorylcholine and ceramide. Inherited deficiencies of acid sphingomyelinase activity result in various clinical forms of Niemann-Pick disease, which are characterised by massive lysosomal accumulation of sphingomyelin. Sphingomyelin hydrolysis by both, acid sphingomyelinase and membrane-associated neutral sphingomyelinase, plays also an important role in cellular signaling systems regulating proliferation, apoptosis and differentiation. Here, we present a potent and selective novel inhibitor of A-SMase, L-alpha-phosphatidyl-D-myo-inositol-3,5-bisphosphate (PtdIns3,5P2), a naturally occurring substance detected in mammalian, plant and yeast cells. The inhibition constant Ki for the new A-SMase inhibitor PtdIns3,5P2 is 0.53 microM as determined in a micellar assay system with radiolabeled sphingomyelin as substrate and recombinant human A-SMase purified from insect cells. Even at concentrations of up to 50 microM, PtdIns3,5P2 neither decreased plasma membrane-associated, magnesium-dependent neutral sphingomyelinase activity, nor was it an inhibitor of the lysosomal hydrolases beta-hexosaminidase A and acid ceramidase. Other phosphoinositides tested had no or a much weaker effect on acid sphingomyelinase. Different inositol-bisphosphates were studied to elucidate structure-activity relationships for A-SMase inhibition. Our investigations provide an insight into the structural features required for selective, efficient inhibition of acid sphingomyelinase and may also be used as starting point for the development of new potent A-SMase inhibitors optimised for diverse applications.     

Aurinetricarboxylic acid: a potent inhibitor of glucose-6-phosphate dehydrogenase.

Inhibition by aurinetricarboxylic acid (ATA) of glucose-6-phosphate (G6P) dehydrogenase was "competitive" with respect to G6P and "mixed type" with respect to NADP+. Inhibited enzyme bound two molecules of ATA. Kinetic constants, Km, Ki at varying pH suggested possible binding of the inhibitor by the sulfhydryl of the enzyme; of the several enzymes tested only milk xanthine oxidase and G6P dehydrogenase from bovine adrenal was inhibited by ATA.     

Stachybotrydial, a potent inhibitor of fucosyltransferase and sialyltransferase

Elevated expression of fucosylated glycoconjugates and fucosyltransferases (Fuc-Ts) is found in various tumor cells and has been correlated with aspects of tumor progression such as cell adhesion and metastasis. Thus, fucosyltransferase inhibitors are potentially useful as anti-tumor agents. In the present study, three known spirocyclic drimanes (1, 2, and 3) were isolated from the culture broth of the fungus Stachybotrys cylindrospora. Compound 1 (stachybotrydial) exhibits potent inhibitory activity against alpha1,3-fucosyltransferase (Fuc-TV) during screening, while compounds 2 and 3 show no such inhibitory activity. Kinetic analysis indicates that compound 1 is an uncompetitive inhibitor with respect to GDP-fucose and a noncompetitive inhibitor with respect to N-acetyllactosamine with Ki values of 10.7 and 9.7 microM, respectively. In addition, all three compounds also possess inhibitory activity against sialyltransferase (ST) but not against beta1,4-galactosyltransferase. These observations provide novel chemical structure information that will help in the design of novel Fuc-T and ST inhibitors.     

N-Benzyloxycarbonyl-valyl-prolinal, a potent inhibitor of post-proline cleaving enzyme

A peptide aldehyde inhibitor possessing prolinal at the carboxyl terminus was designed as an inhibitor of post-proline cleaving enzyme by analogy with peptide aldehyde inhibitors of serine and thiol proteases. N-Benzyloxycarbonyl-valyl-prolinal was found to be a potent inhibitor of post-proline cleaving enzyme from ascidian sperm with a K1 value of 2.4 nM. The presence of the aldehyde portion of the inhibitor, as well as its prolonged incubation with the enzyme, is indispensable for the potent inhibitory activity of the inhibitor. These results indicate that N-benzyloxycarbonyl-valyl-prolinal functions as a transition-state aldehyde inhibitor of post-proline cleaving enzyme.     

Purification and characterization of a unique, potent inhibitor of apamin binding from Leiurus quinquestriatus hebraeus venom

An inhibitor of apamin binding has been purified to homogeneity in three chromatographic steps from the venom of the scorpion, Leiurus quinquestriatus hebraeus. The inhibitor, which we have named leiurotoxin I, represents less than 0.02% of the venom protein. It is a 3.4-kDa peptide with little structural homology to apamin although it has some homology to other scorpion toxins such as charybdotoxin, noxiustoxin, and neurotoxin P2. Leiurotoxin I completely inhibits 125I-apamin binding to rat brain synaptosomal membranes (Ki = 75 pM). Thus, it is 10-20-fold less potent than apamin. Leiurotoxin I is not a strictly competitive inhibitor of this binding reaction. Like apamin, leiurotoxin I blocks the epinephrine-induced relaxation of guinea pig teniae coli (ED50 = 6.5 nM), while having no effect on the rate or force of contraction in guinea pig atria or rabbit portal vein preparations. Thus, leiurotoxin I of scorpion venom and apamin of honeybee venom demonstrate similar activities in a variety of tissues, yet are structurally unrelated peptides. These two peptides should be useful in elucidating the role of the small conductance, Ca2+-activated K+ channels in different tissues.     

Phenyl-n-butylborinic acid is a potent transition state analog inhibitor of lipolytic enzymes

The cholesterol esterase and lipoprotein lipase catalyzed hydrolyses of the water-soluble substrate p-nitrophenyl butyrate are competitively inhibited by butaneboronic acid and phenylboronic acid. Phenyl-n-butylborinic acid has been synthesized and characterized as an ultrapotent transition state analog inhibitor: Ki = 2.9 +/- 0.6 nM and 1.7 +/- 0.3 microM for the cholesterol esterase and lipoprotein lipase reactions, respectively. These results are interpreted in terms of transition state structure and stabilization.     

Soyasaponin I, a potent and specific sialyltransferase inhibitor

A growing number of reports demonstrate that hypersialylation, which is observed in certain pathological processes, such as oncogenic transformation, tumor metastasis, and invasion, is associated with enhanced sialyltransferase (ST) activity. There is therefore a need for the development of ST inhibitors to modulate ST activity and thus alleviate the disease processes caused by STs. In the present study, soyasaponin I had been discovered to be a potent and specific ST inhibitor by screening strategy from 7500 samples including micribial extracts and natural products. Kinetic analysis shows that it is a CMP-Neu5Ac competitive inhibitor with for ST3Gal I with an inhibition constant (K(i)) of 2.1 microM. In addition, it is only active against ST, but not against the other tested glycosyltransferases and glycosidases. Our study is the first report to discover ST inhibitor by screening method and also to provide the new chemical structure information that should be useful in the development of other novel ST inhibitors.     

Anthraflavic acid is a potent and specific inhibitor of cytochrome P-448 activity

Consideration of the computer-optimised dimensions of anthraflavic acid indicates that it is essentially a planar molecule with a large area/depth ratio, that would preferentially interact with the polycyclic aromatic hydrocarbon-induced family of cytochrome P-450 proteins (cytochromes P-448). Anthraflavic acid was a potent inhibitor of the O-deethylations of ethoxycoumarin and ethoxyresorufin, both catalysed primarily by cytochromes P-448, in Arochlor-1254-induced hepatic microsomes. Similarly anthraflavic acid markedly inhibited the mutagenicity of 2-amino-6-methyldipyrido[1,2-a:3',2'-d]imidazole (Glu-P-I) in the Ames test. In contrast, it has no effect on the dealkylation of pentoxyresorufin, a reaction catalysed primarily by the phenobarbital-induced cytochromes P-450, and NADPH-dependent reduction of cytochrome c. It is concluded that anthraflavic acid is a potent and specific inhibitor of cytochrome P-448 activity.     

Hypochlorous acid is a potent inhibitor of GST P1-1.

Glutathione S-transferase is a phase II detoxification enzyme that can be inactivated by H(2)O(2). During oxidative stress various other reactive oxygen species are generated that are more reactive than the relatively stable H(2)O(2). Hypochlorous acid (HOCl) is a powerful oxidant which is highly reactive towards a range of biological substrates. We studied the influence of HOCl on the activity of GST P1-1. HOCl inhibits purified glutathione S-transferase P1-1 in a concentration dependent manner with an IC(50)-value of 0.6 microM, which is more than 1000 times as low as IC(50) reported for H(2)O(2). HOCl lowered the V(max) value, but did not affect the K(m) for CDNB. Our results show that HOCl is a potent, non-competitive inhibitor of GST P1-1. The relevance of this effect is discussed.