Comparison of the inhibition of the cytosolic phospholipase A2-mediated arachidonic acid release by several indole-2-carboxylic acids and 3-(pyrrol-2-yl)propionic acids in bovine and in human platelets

Evaluation of inhibitors of the arachidonic acid cascade with intact platelets using an on-line dilution and on-line solid phase extraction HPLC-MS method

An automatic on-line dilution/on-line solid phase extraction (SPE) system has been developed for the detection of metabolites of the arachidonic acid cascade in platelets. The method allows the direct injection of larger quantities of centrifugates from cell suspensions previously treated with an equal volume of an acetonitrile/methanol mixture for protein precipitation. The method was used to study the effect of inhibitors of platelet arachidonic acid cascade enzymes (cytosolic phospholipase A₂α, cyclooxygenase-1, thromboxane synthase, 12-lipoxygenase) and related targets (cyclooxygenase-2, microsomal prostaglandin E synthase-1, 5-lipoxygenase) in intact platelets after stimulation with calcium ionophore A23187. In addition to enzyme inhibition, the cell-damaging properties of the test compounds was determined by measuring the release of serotonin from the platelets into the incubation buffer.

Design, synthesis, and biological evaluation of 3-(1-Aryl-1H-indol-5-yl)propanoic acids as new indole-based cytosolic phospholipase A2α inhibitors

This article describes the design, synthesis, and biological evaluation of new indole-based cytosolic phospholipase A2α (cPLA2α, a group IVA phospholipase A2) inhibitors. A screening-hit compound from our library, (E)-3-{4-[(4-chlorophenyl)thio]-3-nitrophenyl}acrylic acid (5), was used to design a class of 3-(1-aryl-1H-indol-5-yl)propanoic acids as new small molecule inhibitors. The resultant structure-activity relationships studied using the isolated enzyme and by cell-based assays revealed that the 1-(p-O-substituted)phenyl, 3-phenylethyl, and 5-propanoic acid groups on the indole core are essential for good inhibitory activity against cPLA2α. Optimization of the p-substituents on the N1 phenyl group led to the discovery of 56n (ASB14780), which was shown to be a potent inhibitor of cPLA2α via enzyme assay, cell-based assay, and guinea pig and human whole-blood assays. It displayed oral efficacy toward mice tetradecanoyl phorbol acetate-induced ear edema and guinea pig ovalbumin-induced asthma models.

Structure–activity relationship studies of 3-dodecanoylindole-2-carboxylic acid inhibitors of cytosolic phospholipase A2α-mediated arachidonic acid release in intact platelets: variation of the keto moiety

Recently we found that 1-methyldodecanoylindole-2-carboxylic acid (1) and 1-[2-(4-carboxyphenoxy)ethyl]-3-dodecanoylindole-2-carboxylic acid (4) were inhibitors of the cytosolic phospholipase A2alpha (cPLA2alpha)-mediated arachidonic acid release in calcium ionophore A23187-stimulated human platelets with IC50-values of 4.8 microM (1) and 0.86 microM (4). We have now replaced the 3-acyl residue of these compounds by alkylated sulfinyl-, sulfony-, sulfinamoyl-, sulfamoyl-, carbonylamino-, or carbonylaminomethyl-substituents. Structure-activity relationship studies revealed that the pronounced cellular activity of 4 strongly depends on the presence of the 3-acyl moiety. Surprisingly, when testing 4 and its derivatives in an assay with the isolated cPLA2, none of these compounds showed an inhibitory potency at 10 microM indicating that they do not inhibit cPLA2alpha in the cells by a direct interaction with the active site of the enzyme.

Design and Synthesis of 1-Indol-1-yl-propan-2-ones as Inhibitors of Human Cytosolic Phospholipase A2α

The synthesis and structure-activity relationship study of a series of 1-indol-1-yl-3-phenoxypropan-2-one inhibitors of cytosolic phospholipase A(2)alpha (cPLA(2)alpha) are described. The compounds were evaluated in a vesicle assay with isolated cPLA(2)alpha and in cellular assays with intact human platelets. Systematic variation led to 3-methylhydrogen 1-[3-(4-decyloxyphenoxy)-2-oxopropyl]indole-3,5-dicarboxylate (57), which revealed the highest activity against the isolated enzyme. With an IC(50) value of 4.3 nM in this assay, it is one of the most potent in vitro cPLA(2)alpha inhibitors known today.

HPLC assay with UV spectrometric detection for the evaluation of inhibitors of cytosolic phospholipase A2

A non-radioactive spectrometric assay for the evaluation of inhibitors of cytosolic phospholipase A(2) (cPLA(2)) is described. The enzyme was isolated from human platelets applying anion exchange chromatography. Sonicated covesicles consisting of 0.2mM 1-stearoyl-2-arachidonoyl-sn-glycero-3-phosphocholine and 0.1mM 1,2-dioleoyl-sn-glycerol were used as enzyme substrate. The cPLA(2) activity was determined by measuring the arachidonic acid released by the enzyme with reversed-phase HPLC and UV detection at 200 nm after cleaning up the samples by solid phase extraction. Two known cPLA(2) inhibitors were used to validate the test assay.

High-performance liquid chromatographic assay with ultraviolet spectrometric detection for the evaluation of inhibitors of secretory phospholipase A(2)

A non-radioactive spectrometric assay for the evaluation of inhibitors of pancreatic group IB and non-pancreatic group IIA secretory phospholipase A(2) (sPLA(2)) is described. Mixed-micelles consisting of 1 mM of a 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphoglycerol and 6 mM of sodium deoxycholate were used as substrate. The enzyme activity was determined directly without any sample clean-up by measuring the sPLA(2)-mediated oleic acid release with reversed-phase HPLC and UV-detection at 200 nm. The known sPLA(2) inhibitors MJ33 and AR-C 67047MI were analyzed in this assay for their inhibitory potency. While MJ33 revealed only a very weak inhibition of group IB and IIA sPLA(2) at the highest test concentration (33 microM), AR-C 67047MI proved to be a potent inhibitor of both enzymes with IC(50)-values of 0.36 and 0.14 microM, respectively.

Determination of the cell lytic properties of amphiphilic inhibitors of the cytosolic phospholipase A2 against human platelets by measuring the liberation of serotonin with high-performance liquid chromatography and fluorescence detection

A procedure for the determination of the influence of detergents on the cell integrity of human platelets by measuring the release of serotonin with high-performance liquid chromatography and fluorescence detection is presented. After exposure of the platelets to the test compounds the cells and cell fragments, respectively, are centrifuged off. In the supernatants the liberated serotonin is determined directly without a further sample clean up. The amphiphilic inhibitors of cytosolic phospholipase A2 (cPLA2), arachidonyltrifluoromethyl ketone (AACOCF3), palmityltrifluoromethyl ketone (PACOCF3) and methyl arachidonylfluorophosphonate (MAFP), and the polyoxyethylene detergent Brij 58 were investigated for their cell lytic properties with this method. All compounds lysed the platelets liberating serotonin at a concentration of 33 microM. AACOCF, and Brij 58 even caused cell lysis at lower concentrations.

Novel 3-dodecanoylindole-2-carboxylic acid inhibitors of cytosolic phospholipase A(2)

Derivatives of 1-[2-(4-carboxyphenoxy)ethyl]-3-dodecanoylindole-2-carboxylic acid (4) with modified substituents at the indole-1-position were synthesized and evaluated for their ability to inhibit the arachidonic acid release in human platelets mediated by the cytosolic phospholipase A(2). One of the most active compounds obtained was 26 with an IC(50) of 0.44 microM.