Prediction of pH-dependent aqueous solubility of Histone Deacetylase (HDAC) inhibitors.

Recently we developed a model for prediction of pH-dependent aqueous solubility of drugs and drug like molecules. In the present work, the model was applied on a series of novel Histone Deacetylases (HDAC) inhibitors discovered at TopoTarget. The applicability of our model was evaluated on the series of HDAC inhibitors by use of Self-Organizing Maps (SOM) and 2D-projection of the HDAC inhibitors on the chemical space of the training data set of the artificial neural network (ANN) module. The model was refined for the particular chemical space of interest, which led to two modifications in the training data set of the ANN. The performance of the original and the two modified versions of the model were evaluated against the commercial software from Simulations-plus and pH-dependent solubility measurements for representative compounds of the series. The results of the evaluation indicate that one can develop models that are more accurate in predicting differences in the solubility of structurally very similar compounds than models that have been trained on structurally unbiased, diverse data sets. Such 'tailor-made' models have the potential to become trustworthy enough to replace time-consuming and expensive medium- and high-throughput solubility experiments by providing results of similar or even better quality.

Synthesis and conformational analysis of fusidic acid side chain derivatives in relation to antibacterial activity.

Novel fusidic acid type antibiotics having flexible side chains are described. Saturation of the double bond between C-17 and C-20 of fusidic acid produces four stereoisomers differing in the configuration at C-17 and C-20. The structure-activity relationship of the stereoisomers was studied using computer-assisted analyses of low-energy conformations and crystallographic data. Only one of the four stereoisomers showed potent antibiotic activity comparable with that of fusidic acid, whereas the other three stereoisomers retained little or no activity. The orientation of the side chain is crucial, and there is only a limited space for bioactive side chain conformations. This investigation demonstrates the essential role of the side chain conformations in relation to antibacterial activity and contradicts earlier assumptions that the Delta17(20) bond is an essential feature in the molecule.

Improved viability and metabolic behavior of hepatocytes after liver storage in the presence of a succinic acid ester.

BACKGROUND: Selected esters of succinic acid were recently proposed as novel nutrients to support ATP generation in cells endangered by an imbalance between the formation and breakdown of this adenine nucleotide. In the present study, a new ester, glycerol-1,2,3-trimethylsuccinate, was examined for its potential beneficial effect in the procedures preceding liver transplantation. METHODS: The viability and metabolic behavior of hepatocytes were examined after perfusion and storage of rat livers for 20 hr at 4 degrees C with a Belzer UW-CSS solution in the absence or presence or 2 mM glycerol-1,2,3-trimethylsuccinate. RESULTS: Although it failed to affect significantly the release of cellular enzymes during storage and the protein or glycogen content of the liver, and was unable to prevent the storage-induced decrease in both biosynthetic activity and D-[U-14C]glucose incorporation into glycogen in isolated hepatocytes, the ester restored to a close-to-normal value the viability of the hepatocytes and opposed the starvation-like effects of liver storage upon both the conversion of D-[U-14C]glucose to 14CO2 and radioactive amino acids and the de novo generation of 14C-labeled D-glucose from [2-14C]pyruvate. CONCLUSIONS: Because succinic acid esters are efficiently metabolized in several cell types, the present results suggest that such esters may have a wide field of application in transplantation procedures.

Stimulation of biosynthetic activity by novel succinate esters in rat pancreatic islets.

Selected esters of succinic acid are currently under investigation as possible insulinotropic agents for the treatment of noninsulin-dependent diabetes mellitus. The aim of the present study was to investigate the effects of ten novel esters of succinic acid upon biosynthetic activity in rat pancreatic islets. In the absence of any other exogenous nutrient, glycerol-3-hydroxy-1,2-dimethyl succinate (0.5 mM), D-arabitol-5-hydroxy-1,2,3,4-tetramethylsuccinate (0.5 mM), and 4-tert-butylsuccinate (2.5 mM) exerted little or no effect upon L-[4-3H]phenylalanine incorporation into trichloroacetic acid-precipitable material. A modest but significant increase in biosynthetic activity to approximately 150% of basal value was found in the presence of L-threitol-1,2,4-trimethylsuccinate (2.0 mM) and ethanediol-1,2-diethylsuccinate (2.5 mM). A two- to five-fold increase in protein biosynthesis was observed in islets exposed to propanediol-1,2-dimethylsuccinate, glycerol-1,2-dimethylsuccinate-3-hydrogenosuccinate, L-threitol-3-succinoyl-1,2,4-trimethylsuccinate, glycerol-1,2-dimethylsuccinate or ethanediol-1,2-dimethylsuccinate (2.5 mM each), these esters being mentioned in order of increasing biological efficiency. There was a significant correlation between these results and the insulinotropic action of the same esters. The present findings thus reinforce the view that such esters act as nutrients in islet cells and, therefore, offer the advantage over pharmacological agents currently used for the treatment of type-2 diabetes in stimulating both the biosynthetic and secretory activity of insulin-producing B-cells.

Early stimulation of acidification rate by novel cytotoxic pyridyl cyanoguanidines in human tumor cells: comparison with m-iodobenzylguanidine.

CHS 828, a newly recognized pyridyl cyanoguanidine, has shown promising antitumor activity both in vitro and in vivo and is presently in early phase I clinical trial in collaboration with EORTC. In this study, the effects of CHS 828 and a series of analogues on extracellular acidification and cytotoxicity were compared with those of m-iodobenzylguanidine (MIBG) in human tumor cells. The extracellular acidification rate was measured using the Cytosensor microphysiometer, and determination of cytotoxicity and proliferation was [(14)C] performed by the fluorometric microculture cytotoxicity assay (FMCA) and measurement of [(14)C]thymidine and leucine uptake. CHS 828 significantly increased the acidification rate during the first 15-24 hr in a concentration-dependent manner. This effect was abolished by removal of glucose from the medium, substituted with 10 mM of pyruvate, indicating stimulated glycolysis as the source of the increased acidification rate. However, CHS 828 induced cytotoxicity at concentrations well below those that affected the rate of acidification; when a series of closely related pyridylguanidine analogues were tested and compared, no apparent relationship between cytotoxicity and acidification could be discerned. Furthermore, comparable increases in the acidification rate were evident in one subline with high-grade resistance to the cytotoxic actions of CHS 828. The results indicate that CHS 828 may share the inhibitory actions of MIBG on mitochondrial respiration with a subsequent increase in glycolysis and acidification rate. However, this mechanism of action appears neither necessary nor sufficient to fully explain the cytotoxic actions of CHS 828 in human tumor cells, actions which remain to be mechanistically clarified.

Metabolism of [1,3-13C]glycerol-1,2,3-tris(methylsuccinate) and glycerol-1,2,3-tris(methyl[2,3-13C]succinate) in rat hepatocytes.

Hepatocytes prepared from overnight-fasted rats were incubated for 120 minutes in the presence of 2.5 mmol/L [1,3-13C]glycerol-1,2,3-tris(methylsuccinate) or glycerol-1,2,3-tris(methyl[2,3-13C]succinate). The identification and quantification of 13C-enriched metabolites by a recently developed method for the deconvolution of nuclear magnetic resonance (NMR) spectra with multiplet structures and constraints documented a virtually complete recovery of [1,3-13C]glycerol-1,2,3-tris(methylsuccinate) in 13C-labeled glycerol, lactic acid, and glucose. In hepatocytes exposed to [1,3-13C]glycerol-1,2,3-tris(methylsuccinate), glucose was symmetrically labeled, with the vast majority of hexose molecules being enriched with 13C on both C1 and C3 and/or C6 and C4. The respective abundance of glucose isotopomers labeled either on both C3 and C4 or on only 1 of these 2 C atoms indicated that the triose phosphates generated from [1,3-13C]glycerol represented 44% +/- 1% of the total amount of triose phosphates incorporated into the hexose. In hepatocytes exposed to glycerol-1,2,3-tris(methyl[2,3-13C]succinate), the recovery of [2,3-13C]succinate, [2,3-13C]fumarate, and either double- or single-labeled malate, lactate, alanine, and glucose accounted for about half the initial 13C content of the ester. The majority of the glucose molecules were now labeled in both C, and C2 or C6 and C5, with a preferential labeling of C6-C5 relative to C1-C2, the paired C6/C1 and C5/C2 ratios averaging 1.33 +/-0.04. These findings show that glycerol-1,2,3-tris(methylsuccinate) is efficiently and extensively metabolized in hepatocytes. They reinforce the concept that the asymmetry of glucose 13C-labeling by triose phosphates generated from Krebs cycle intermediates is modulated by the availability of glycerol-derived triose phosphates. Lastly, the present study indicates that the latter triose esters, under the present experimental conditions which do not aim at duplicating the physiological in vivo situation, are largely directly channelled in the gluconeogenic pathway, with only a limited intrahepatic contribution of the "indirect" pathway involving their back-and-forth interconversion to and from pyruvate.

Examination of structurally selective derivatization of vitamin D(3) analogues by electrospray mass spectrometry.

The structural specificity of vitamin D derivatization by PTAD (4-phenyl-1,2,4-triazoline-3,5-dione) was probed using synthetic analogues and ion trap mass spectrometry. EB 1089, a vitamin D(3) analogue which contains a second site for Diels--Alder cycloaddition on its side-chain, allowed the examination of derivatization modes and comparisons of ion fragment structures. The origins of a PTAD-vitamin D(3) ion fragment, commonly used in metabolite characterization and quantitation of vitamin D(3) analogues (m/z 314), were established; ion trap mass spectrometry revealed that the PTAD comprises a portion of this diagnostic fragment, and is not lost by a retro-Diels--Alder step. Furthermore, the unique structure of the EB 1089 side-chain also permits facile determination of its side-chain metabolism. Use of PTAD derivatization and detection of metabolite-specific ion fragments identify hydroxylation at the end of the EB 1089 sidechain. It is believed that the results from these studies provide a clearer understanding of the mass spectrometry of triazolinedione derivatives, not only in the specific case of EB 1089, but also in their application to other vitamin D compounds.

Potentiation of the insulinotropic and hypoglycemic action of gliquidone by succinic acid esters.

The monoethyl, monopropyl and monoisopropyl esters of succinic acid, administered intravenously at the dose of 2 micromol/g body weight, were found to increase the insulinotropic action of gliquidone (0.2 nmol/g body weight) in anaesthetized rats. The monoisopropyl ester of succinic acid also doubled the hypoglycemic action of gliquidone. These findings indicate that it is possible to design esters of succinic acid that are devoid of the risk of generating methanol by intracellular hydrolysis, and yet susceptible to increase both the insulinotropic and hypoglycemic responses to antidiabetic agents.

Comparison between the insulinotropic potential of ten new esters of succinic acid.

Selected esters of succinic acid are currently under investigation as insulinotropic tools for the treatment of non-insulin-dependent diabetes mellitus. The aim of the present study was to investigate, in isolated rat pancreatic islets, the insulin secretory response to ten novel esters of succinic acid. According to six different methods of comparison, the following hierarchy in insulinotropic potential was established: 4-tert-butyl-succinate < or = glycerol-1,2-dimethylsuccinate-3-hydrogenosuccinate < or = threitol-3-succinoyl-1,2,4-trimethylsuccinate < or = ethanediol-1,2-diethylsuccinate < or = glycerol-1,2-dimethylsuccinate < or = glycerol-3-hydroxy-1,2-dimethylsuccinate < or = arabitol-5-hydroxy-1,2,3,4-tetramethylsuccinate < or = threitol-1,2,4-trimethylsuccinate < or = ethanediol-1,2-dimethylsuccinate < propanediol-1,2-dimethylsuccinate. There was a close correlation (r = 0.823) between the insulinotropic potential and the minimal effective concentration, which ranged between the extreme values of 10 microM and 2.5 mM. In the presence of the esters, the concentration-response relationship for glucose-stimulated insulin release was changed from its typically sigmoidal shape to a hyperbolic pattern, with most agents enhancing insulin output at a low hexose concentration (2.8 mM) but failing to do so at a high glucose level (16.7 mM). Highly potent insulinotropic esters have several advantages over other antidiabetic agents in clinical use.

Polyclonal antibodies to EB1089 (seocalcitol), an analog of 1alpha,25-dihydroxyvitamin D(3)*.

A hapten derivative of EB1089 [1(R),3(S),25-trihydroxy-26,27-dimethyl-9,10-seco-24-homocholesta-5(Z),7(E),10(19),22(E),24(E)-pentaene], a side-chain analog of 1alpha,25-dihydroxyvitamin D(3), was synthesized for raising antibodies with a high specificity for EB1089. The A-ring moiety of EB1089 was replaced in the hapten by a linker for conjugation to a protein. Three polyclonal antibodies were obtained by immunizing rabbits with a BSA-conjugate of the hapten. The antibodies were characterized for titer, avidity and specificity using an enzyme immunoassay with covalently bound EB1089. The three antibodies had similar binding profiles and were highly selective for EB1089 and its metabolites over the naturally occurring vitamin D metabolites. Cross-reactivities with 25-hydroxyvitamin D(3), the most abundant vitamin D metabolite in serum, were in the range 0.01-0.2% relative to EB1089.

Stimulation of insulin release in hereditarily diabetic rats by mixed molecules formed of nateglinide and a succinic acid ester.

Hereditarily diabetic Goto-Kakizaki rats were infused for 5 min with saline, containing as required nateglinide or mixed molecules (HD154 and HD166) with both a nateglinide moiety and a succinic acid ester moiety. The dose of these agents given intravenously amounted to 5.0 nmol/g body weight in all cases. All agents provoked a comparable early increase in plasma insulin concentration. However, HD154 and HD166, but not nateglinide itself, also caused a secondary rise in plasma insulin concentration 30 min after their infusion. It is proposed that mixed molecules formed of both a hypoglycemic sulfonylurea or meglitinide analog and a succinic acid ester may be better able than the antidiabetic agents themselves to evoke a sustained stimulation of insulin release in non-insulin-dependent diabetes.

Metabolism of [1,3-(13)C]glycerol-1,2,3-tris(methylsuccinate) and glycerol-1,2,3-tris(methyl[2,3-(13)C]succinate) in hepatocytes from Goto-Kakizaki rats.

The metabolism of [1,3-(13)C]glycerol-1,2,3-tris(methylsuccinate) and glycerol-1,2,3-tris(methyl[2,3-(13)C] succinate) was examined in hepatocytes prepared from hereditarily diabetic Goto-Kakizaki rats. Over 120 min incubation in the presence of one of the two (13)C-labelled esters (2.5 mM), the output of (13)C-enriched glucose averaged 57.1 +/- 18.5 and 54.1 +/- 22.7 nmol per 10(6) cells, when expressed as [1,3-(13)C]glycerol and [2,3-(13)C] succinate equivalent, respectively. In the case of [1,3-(13)C]glycerol-1,2,3-tris(methyl-succinate), the molecules of glucose were symmetrically labelled. In the case of glycerol-1,2,3-tris(methyl[2,3-(13)C] succinate), however, both the single-labelled and double-labelled isotopomers of glucose contained more (13)C atoms in their C(6)-C(5)-C(4) than C(1)-C(2)-C(3) moiety. These findings indicate that glycerol-1,2,3-tris(methylsuccinate), recently proposed as a novel insulinotropic tool for the treatment of non-insulin-dependent diabetes mellitus, is efficiently metabolized in hepatocytes from diabetic rats, the high rate of gluconeogenesis coinciding with channelling of D-glyceraldehyde-3-phosphate between glyceraldehyde-3-phosphate dehydrogenase and phosphofructoaldolase.

Metabolism of glycerol-1,2,3-trimethylsuccinate in rat pancreatic islets.

The metabolism of 14C-labelled glycerol-1,2,3-trimethylsuccinate (2.0 mM) was examined in rat pancreatic islets. The oxidation of the glycerol moiety of the ester was negligible relative to that of its succinate residues. The oxidation of glycerol-1,2,3-trimethyl[1,4-(14)C]succinate was two times higher than that of glycerol-1,2,3-trimethyl[2,3-(14)C]succinate, this difference being matched by a higher generation of 14C-labelled acidic metabolites and amino acids from the latter than from the former tracer. The total generation of 14CO2 from the ester, uniformly labelled except in its methyl groups, was close to that found for the oxidation of 1.0 mM D-[U-(14)C]glucose. These findings thus reveal that glycerol-1,2,3-trimethylsuccinate is efficiently metabolized in islet cells and support the idea that this ester could be used as a nutrient to bypass defects of D-glucose transport and metabolism in the islet B-cell and, hence, improve proinsulin biosynthesis and insulin release in non-insulin-dependent diabetes mellitus.

Assessment of the nutritional value of glycerol-1,2, 3-tris(methylsuccinate) in fed and starved rats.

The nutritional value of glycerol-1,2,3-tris(methylsuccinate), a novel ester of succinic acid with high insulinotropic efficiency both in vitro and in vivo, was assessed in both fed and starved rats. The infusion of the ester, given in a daily amount (1.2 micromol. g body wt-1) well in excess of what could result from its repeated intravenous administration as an insulinotropic agent in non-insulin-dependent diabetes (0.07 micromol. g body wt-1 for each administration), failed to prevent the fall in body weight, liver and muscle glycogen contents, and plasma d-glucose or insulin concentration, as well as the increase in plasma free fatty acid and beta-hydroxybutyrate concentrations caused by starvation. The sole indications that the ester may serve, to a limited extent, as an alternative nutrient in starved rats consisted in a somewhat higher weight of both liver and paraovarian adipose tissue and somewhat higher activity of liver glucokinase in rats receiving the ester than in animals infused with saline. The low nutritional value of this ester thus answers the objection of its possible role as an extrapancreatic nutrient or gluconeogenic precursor in the perspective of its use as an insulinotropic tool in type 2 diabetes.

Insulinotropic action of novel succinic acid esters.

The insulinotropic action of several new esters of succinic acid was assessed in isolated rat islets incubated in the presence of 7 mM D-glucose. An efficient secretory response was observed with the monobenzyl, monoisopropyl, monoallyl, monopropyl, monoethyl, monobutyl, dibutyl, dipropyl and diallyl esters of succinic acid. This indicates that it is possible to design esters of succinic acid which act as insulin secretagogues, while avoiding the undesirable generation of methanol that otherwise results from the use of either the monomethyl or dimethyl ester of this dicarboxylic acid.

Inhibition of lipases by phosphonates.

Ethyl hexylchlorophosphonate and analogues thereof were investigated as inhibitors of lipases. Both microbial and mammalian lipases were irreversibly inhibited. The inhibition could be monitored by p-nitrophenol release from the corresponding ethyl p-nitrophenyl hexylphosphonate inhibitor. Quantitative analysis of the data indicated that a 1:1 lipase-inhibitor complex was formed during inhibition. Enantioselective inhibition was found for the lipases derived from Candida antarctica and Rhizomucor miehei using pure enantiomers of ethyl p-nitrophenyl hexylphosphonate as inhibitors. Using the same inhibitor, reversed enantioselectivity was found for the protease alpha-chymotrypsin as compared to the two lipases.

Studies on the interaction between the vitamin D receptor and the radiolabelled 20-epi vitamin D analogue GS 1500.

Previous studies have shown that the binding affinity of a vitamin D analogue for the vitamin D receptor (VDR) does not correlate with the biological potency of the compound. In the present investigation the vitamin D analogue GS 1500, which is characterised by an altered stereochemistry at carbon C-20 (20-epi) and an aromatic ring in the side chain, was studied with respect to its interaction with the VDR. Using [3H]-GS 1500 as tracer, the receptor binding properties of GS 1500 were investigated and compared to those of 1,25(OH)2D3. The binding studies did not reveal a different binding site for GS 1500 than the one already established, and the binding affinity was in accordance with previously found values. At the level of VDR interaction with the vitamin D responsive element, GS 1500 did induce a binding complex at a lower concentration than 1,25(OH)2D3, which may help explain the difference in potency.

Structural variants of the vitamin D analogue EB1089 reduce its ligand sensitivity and promoter selectivity.

The nuclear hormone 1alpha,25-dihydroxyvitamin D3 (VD) has important cell-regulatory functions but also a strong calcemic effect. Therefore, various VD analogues have been synthesized and screened for their biological profile. In order to gain more insight into the molecular basis of the high antiproliferative but low calcemic action of the VD analogue EB1089, we characterized this compound in comparison to five structurally related VD analogues. The activities of the six VD analogues in in vitro assays (limited protease digestion assays for determining interaction with monomeric vitamin D receptor (VDR), ligand-dependent gel shift assays for showing the increase of DNA binding of VDR-retinoid X receptor (RXR) heterodimers, and reporter gene assays on different types of VD response elements for demonstrating the efficacy in nuclear VD signalling) were found to represent their biological potency (antiproliferative effect on different malignant cell lines). In this series, EB1089 proved to be the most potent VD analogue; that is, every structural modification (20-epi configuration, cis-configuration at position C24, or changes at the ethyl groups at position C25) appeared to reduce the determined activities mediated through the VDR of these analogues. Moreover, the modifications of EB1089 resulted in a loss of VD response element selectivity, suggesting that this parameter is very critical for the biological profile of this VD analogue.

New esters of succinic acid and mixed molecules formed by such esters and a meglitinide analog: study of their insulinotropic potential.

Eighteen novel esters of succinic acid, including three mixed molecules formed of both succinic acid and nateglinide, were examined for their insulinotropic efficiency in isolated rat pancreatic islets. The secretory response to these esters at increasing concentrations of both d -glucose and the ester itself allowed to identify five esters judged of potential interest for further investigations. They include three molecules with CH(3)-O-CO-CH(2)-CH(2)-CO-NH-CH(R)-CO-O- sequence and two mixed molecules with a nateglinide moiety. The effects of the most potent molecule in the first group and that of two of the esters with a nateglinide moiety upon islet biosynthetic activity in vitro and insulin release in vivo, after either oral or intravenous administration were also investigated. The results suggested that mixed molecules formed of both a succinic acid ester and a meglitinide analog may efficiently stimulate proinsulin biosynthesis and/or insulin release. Further work is required, however, to improve their modality of in vivo administration.

Insulinotropic action of the D-glucosyl and 3-O-methyl-D-glucosyl monomethyl esters of succinic acid.

Succinic acid methyl esters are currently under investigation as potential insulinotropic tools in animal models of non-insulin-dependent diabetes mellitus. The in vivo administration of these esters may result in the undesirable generation of methanol through their intracellular hydrolysis. As a first attempt to circumvert this drawback, we have now investigated whether the esterification of the carboxylic group of succinic acid monomethyl ester by D-glucose or 3-O-methyl-D-glucose affects its insulin-otropic action. Both the 6-O-D-glucosyl and 6-O-(3-O-methyl)-D-glucosyl esters were found to stimulate insulin release in pancreatic islets and the isolated perfused pancreas. The 6-O-D-glucosyl ester also stimulated insulin release after intravenous administration to anaesthetized rats. These findings suggest that the undersirable generation of methanol from the methyl esters of succinic acid could eventually be avoided by using other esters of this dicarboxylic acid, whilst keeping the benefit of their insulinotropic action.