Effect of 2-(1-piperazinyl)-4H-pyrido[1,2-a]pyrimidin-4-one (AP155) on human platelets in vitro

Screening of Synthetic Heterocyclic Compounds as Antiplatelet Drugs

BACKGROUND

Antiplatelet drugs represent the keystone in the treatment and prevention of diseases of ischemic origin, including coronary artery disease. The current palette of drugs represents efficient modalities in most cases, but their effect can be limited in certain situations or associated with specific side effects. In this study, representatives of compounds selected from series having scaffolds with known or potential antiplatelet activity were tested. These compounds were previously synthetized by us, but their biological effects have not yet been reported.

OBJECTIVE

The aim of this study was to examine the antiplatelet and anticoagulation properties of selected compounds and determine their mechanism of action.

METHODS

Antiplatelet activity of compounds and their mechanisms of action were evaluated using human blood by impedance aggregometry and various aggregation inducers and inhibitors and compared to appropriate standards. Cytotoxicity was tested using breast adenocarcinoma cell cultures and potential anticoagulation activity was also determined.

RESULTS

In total, four of 34 compounds tested were equally or more active than the standard antiplatelet drug acetylsalicylic acid (ASA). In contrast to ASA, all 4 active compounds decreased platelet aggregation triggered not only by collagen, but also partly by ADP. The major mechanism of action is based on antagonism at thromboxane receptors. In higher concentrations, inhibition of thromboxane synthase was also noted. In contrast to ASA, the tested compounds did not block cyclooxygenase-1.

CONCLUSION

The most active compound, 2-amino-4-(1H-indol-3-yl)-6-nitro-4H-chromene-3-carbonitrile (2-N), which is 4-5x times more potent than ASA, is a promising compound for the development of novel antiplatelet drugs.

Pyrido[1,2-a]pyrimidinium ions--a novel bridgehead nitrogen heterocycles: synthesis, characterisation, and elucidation of DNA binding and cell imaging properties

A novel class of bridgehead nitrogen heterocycles, pyrido[1,2-a]pyrimidinium ions, has been readily synthesized by a two-step one-pot reaction in high yields (up to 93%). These ionic compounds are bench stable and moisture tolerant and have highly fluorescent properties (quantum yield up to 0.65). A characteristic bright bluish fluorescence was observed in polar solvents such as acetonitrile and fluorescent intensity gradually diminishes with decreasing the polarity of the medium, which becomes almost negligible in toluene. These compounds also show interesting bioactivity. DNA interaction, imaging, and viability experiments with human leukemic Jurkat and KG-1A cells revealed that they are potential candidates for cancer diagnosis.

Reaction of Aryl Isothiocyanate with Pyridines and Dialkyl Acetylenedicarboxylates to Afford Novel Heterocycles

The reactive intermediate produced in the reaction between pyridines and dialkyl acetylenedicarboxylates was trapped by aryl isothiocyanates to afford 2-thioxo-1,9a-dihydro-2 H-pyrido [1,2, a]pyrimidine derivatives in good yields.

Synthesis, in vitro antiplatelet activity and molecular modelling studies of 10-substituted 2-(1-piperazinyl)pyrimido[1,2-a]benzimidazol-4(10H)-ones

The multistep preparation of the new 10-substituted 2-(1-piperazinyl)pyrimido[1,2-a]benzimidazol-4(10H)-ones 6a-o, and of the two isomers 10-ethyl-2-(diethylamino)pyrimido[1,2-a]benzimidazol-4(10H)-one 6p and 10-ethyl-4-(diethylamino)pyrimido[1,2-a]benzimidazol-2(10H)-one 13, as well as the in vitro evaluation of their inhibitory activity on human platelet aggregation induced in platelet-rich plasma by ADP, collagen or the Ca(2+) ionophore A23187 were here described. Nine out of fifteen 2-(1-piperazinyl)derivatives (6g-o) showed good inhibitory properties towards all the platelet aggregation agonists used. Moreover, a molecular modelling study has been performed on two of the best compounds of this series (6i and 6o) to confirm in silico their interactions with the catalytic site of human platelet PDE3, using the X-ray data of the PDE3B isoform in complex with an inhibitor.

Application of high-throughput screening to identify a novel alphaIIb-specific small- molecule inhibitor of alphaIIbbeta3-mediated platelet interaction with fibrinogen

Small-molecule alphaIIbbeta3 antagonists competitively block ligand binding by spanning between the D224 in alphaIIb and the MIDAS metal ion in beta3. They variably induce conformational changes in the receptor, which may have undesirable consequences. To identify alphaIIbbeta3 antagonists with novel structures, we tested 33 264 small molecules for their ability to inhibit the adhesion of washed platelets to immobilized fibrinogen at 16 muM. A total of 102 compounds demonstrated 50% or more inhibition, and one of these (compound 1, 265 g/mol) inhibited ADP-induced platelet aggregation (IC(50): 13+/- 5 muM), the binding of soluble fibrinogen to platelets induced by mAb AP5, and the binding of soluble fibrinogen and a cyclic RGD peptide to purified alphaIIbbeta3. Compound 1 did not affect the function of GPIb, alpha2beta1, or the other beta3 family receptor alphaVbeta3. Molecular docking simulations suggest that compound 1 interacts with alphaIIb but not beta3. Compound 1 induced partial exposure of an alphaIIb ligand-induced binding site (LIBS), but did not induce exposure of 2 beta3 LIBS. Transient exposure of purified alphaIIbbeta3 to eptifibatide, but not compound 1, enhanced fibrinogen binding ("priming"). Compound 1 provides a prototype for small molecule selective inhibition of alphaIIbbeta3, without receptor priming, via targeting alphaIIb.

Synthesis and in vitro antiplatelet activity of new 4-(1-piperazinyl)coumarin derivatives. Human platelet phosphodiesterase 3 inhibitory properties of the two most effective compounds described and molecular modeling study on their interactions with phosphodiesterase 3A catalytic site

The synthesis and in vitro antiplatelet activity significant data of coumarin derivatives 5i-x and quinolin-2(1H)-one derivatives 22a,b, as well as the corresponding structure-activity relationships are described. The recently reported 8-methyl-4-(1-piperazinyl)-7-(3-pyridylmethoxy)coumarin 5f and its potent 7-(2-morpholinoethoxy)-substituted new analogue 5u were notably more effective inhibitors of pure human platelet PDE3 than milrinone and cilostazol: these data were related, through a molecular modeling study, with the molecular interactions of the four compounds with the human PDE3A catalytic site.

Synthesis of a new series of heterocyclic scaffolds for medicinal purposes

A new series of substituted 8-fluro-4H-pyrimido[2,1-b] [1,3]benzothiazole-4-ones () substituted 7-methyl-4H-isoxazolo[2,3-a]pyrimidin-4-ones, and substituted 2-methyl-5,6,7,8-tetrahydro-9H-isoxazolo[2,3-a]pyridopyrimidin-9-ones, compounds I-VII, have been prepared via condensation of beta-keto esters with 2-aminopyridine derivatives, in the presence of polyphosphoric acid. The same technique has also been used to prepare diazepine compounds, VIII-X, by condensation of a gamma-keto ester with 2-aminopyridine derivatives. Details of synthetic procedures are shown. The new compounds have been characterized by elemental analysis, GC-MS, FT-IR and NMR spectrometry. Antibacterial, antifungal and anticancer (cytotoxic) activities, for three of these compounds, have been investigated and are presented.

Synthesis and in vitro inhibitory activity on human platelet aggregation of novel properly substituted 4-(1-piperazinyl)coumarins

Pursuing our chemical and biological studies in this field, we described the multistep preparation of the new 5-, 6-, or 7-alkoxy and 7-alkoxy-8-methyl substituted 4-(1-piperazinyl)coumarins 5d-v, as well as the in vitro evaluation of their inhibitory activity on human platelet aggregation induced in platelet-rich plasma by ADP, collagen or the Ca(2+) ionophore A23187. Compounds 5h-j,p,r-u showed notably high activity towards all the platelet aggregation inducers used, and the most active one, 8-methyl-4-(1-piperazinyl)-7-(3-pyridylmethoxy)coumarin (5t), proved to be a potent in vitro antiplatelet agent.

Mechanisms involved in the antiplatelet activity of 8-methyl-4-(1-piperazinyl)-7-(3-pyridinylmethoxy)-2H-1-benzopyran-2-one (RC414)

The effect on human platelets of 8-methyl-4-(1-piperazinyl)-7-(3-pyridinylmethoxy)-2H-1-benzopyran-2-one (RC414) was tested in vitro by measuring aggregation induced by several agonists, cAMP and cGMP levels, cAMP phosphodiesterase and PKC activities and [Ca2+]i. The RC414 effect on nitric oxide production was also evaluated. RC414 in a dose-dependent manner inhibited aggregation both in platelet rich plasma and in washed platelets. It was particularly effective in platelets challenged by collagen, ADP and thrombin: IC50 values are 0.51 +/- 0.12 microM, 0.98 +/- 0.36 microM and 1.00 +/- 0.15 microM, respectively. RC414 increased cAMP levels, through the specific inhibition of the cAMP high affinity phosphodiesterase (IC50 = 1.73 +/- 0.35 microM). RC414 reduced [Ca2+]i transients and PKC activation induced by thrombin. In addition RC414 was able to increase nitric oxide formation involving the stimulation of constitutive nitric oxide synthase enzyme. In conclusion, RC414 exerts its powerful anti-platelet activity by increasing cAMP intracellular levels and nitric oxide formation.

Transport of L-arginine and nitric oxide formation in human platelets

The results of the present study show that human platelets take up l-arginine by two transport systems which are compatible with the systems y+ and y+L. These Na+independent transporters have been distinguished by treating platelets with N-ethylmaleimide that blocks selectively system y+. System y+, that accounts for 30-40% of the total transport, is characterized by low affinity for l-arginine, is unaffected by l-leucine, is sensitive to changes of membrane potential and to trans-stimulation. The other component of l-arginine transport identified with the system y+L (approximately 60-70% of the total flux) shows high affinity for l-arginine, is insensitive to N-ethylmaleimide treatment, unaffected by changes in membrane potential, sensitive to trans-stimulation and inhibited by l-leucine in the presence of Na+. Moreover a strict correlation between l-arginine transport and nitric oxide (NO) production in whole cells was found. N-ethylmaleimide and l-leucine decreased NO production as well as cGMP elevation, and the effect on NO and cGMP were closely related. It is likely that the l-arginine transport systems y+ and y+L are both involved in supplying substrate for NO production and regulation in human platelets.

Coumarin, chromone, and 4(3H)-pyrimidinone novel bicyclic and tricyclic derivatives as antiplatelet agents: synthesis, biological evaluation, and comparative molecular field analysis

As a further part of our chemical and biological studies in this field, we describe the multistep preparations of the properly substituted 2-(1-piperazinyl)chromone 1b, 4-(1-piperazinyl)coumarins 5c-h, their linear benzo-fused analogues 4a,b and 8a,b, bicyclic (15e-g) and tricyclic (15h,i) fused derivatives of 6-(1-piperazinyl)pyrimidin-4(3H)-one, and of the 4H-pyrido[1,2-a]pyrimidine derivatives 9b,c. The in vitro evaluation of their inhibitory properties towards human platelet aggregation induced in platelet-rich plasma by ADP, collagen, or the Ca (2+)ionophore A23187 showed the high activity of compounds 5d-g and 15f,g,i, among which the coumarins 5g and 5d proved to be, in that order, the most effective in vitro antiplatelet agents until now synthesized by us. Thus, in order to consider also the 4-aminocoumarin structural class, we developed a new statistically significant 3-D QSAR model, more general than the one previously obtained, through a further CoMFA study based on the antiplatelet activity data and molecular steric and electrostatic potentials of both the previously studied and herein described compounds.

Modulation of L-arginine transport and nitric oxide production by gabexate mesylate

Gabexate mesylate, a non-antigenic synthetic inhibitor of trypsin-like serine proteinases, is a drug used efficiently in the treatment of pancreatitis and disseminated intravascular coagulation and as a regional anticoagulant for haemodialysis. Considering the structural similarity between L-arginine and gabexate mesylate, the effect of this drug on L-arginine transport, nitric oxide (NO) formation and constitutive NO synthase activity in human platelets was investigated. Data have shown that gabexate mesylate inhibited competitively L-arginine uptake by increasing the K(m) value from 22+/-2 to 86+/-6 microM. The K(i) value was 158 microM at pH 7.4 and 37 degrees. Furthermore, gabexate mesylate decreased dose and time-dependent nitrite and nitrate formation (NO(x) release) and cGMP accumulation in whole cells. In addition, gabexate mesylate inhibited constitutive nitric oxide synthase in a cell-free extract. We concluded that gabexate mesylate could be considered an effective modulator of cellular NO synthesis.

Synthesis, antiplatelet activity and comparative molecular field analysis of substituted 2-amino-4H-pyrido[1,2-a]pyrimidin-4-ones, their congeners and isosteric analogues

2-(1-Piperazinyl)-4H-pyrido[1,2-a]pyrimidin-4-one (5a) is a recently described in vitro inhibitor of human platelet aggregation which specifically inhibits the activity of high affinity cAMP phosphodiesterase. A number of substitution derivatives, isosteres, and analogues of 5a were now synthesized and tested in vitro for their inhibitory activity on human platelet aggregation induced in platelet-rich plasma by ADP, collagen, or the Ca2+ ionophore A23187. Among the most effective compounds, the 6-methyl, 8-methyl and 6,8-dimethyl derivatives of 5a resulted nearly as active as the lead when platelet aggregation was induced by ADP or A23187, but less active when collagen was the inducer. On the basis of present results and those previously obtained by us in this and 2-aminochromone structural fields, we have developed a statistically significant 3-D QSAR model, using comparative molecular field analysis (CoMFA), describing the variation of the antiplatelet activity in terms of molecular steric and electrostatic potential changes.

N-ethylmaleimide inhibition of thrombin-induced platelet aggregation

The data presented in this report show that N-ethylmaleimide (NEM) is a powerful inhibitor of thrombin-induced platelet aggregation. NEM increased guanosine 3', 5'-cyclic monophosphate (cGMP) and adenosine 3', 5'-cyclic monophosphate (cAMP) levels in intact cells. The inhibition of cAMP high-affinity phosphodiesterase and cGMP phosphodiesterase was implicated in the elevation of the cyclic nucleotides. NEM dose dependently blocked the thrombin-stimulated, but not the phorbol myristate acetate-dependent phosphorylation of the protein kinase C substrate pleckstrin. Myosin light chain phosphorylation was also inhibited by NEM. In addition, the sulphydryl reagent inhibited Ca2+ mobilisation induced by thrombin. The data indicate that phospholipase C activation by thrombin is interrupted by NEM at the level of receptor-mediated signal transduction.

Mechanism of action of two new pyrimidoquinoline and isoquinoline derivatives in human platelets

In the present study the "in vitro" influence of 3-(1-piperazinyl)-1H-pyrimido[1,2-a]quinolin-1-one (AQ11) and 2-(piperazinyl)-4H-pyrimido[2,1-a]isoquinolin-4-one (IQ3b) on human platelet aggregation, cAMP elevation, cytosolic calcium and fibrinogen binding has been investigated. Both drugs inhibited platelet aggregation in a concentration-dependent manner. In PRP AQ11 was slightly more active than IQ3b when aggregation was induced by ADP, collagen, A23187 or PMA, whereas in washed platelets challenged by thrombin, IQ3b was more effective than AQ11. Both compounds produced increase in cAMP intracellular level being the effect potentiated by the adenylate cyclase activator iloprost and IQ3b was more powerful than AQ11. Moreover IQ3b was more effective in inhibiting cAMP in high affinity phosphodiesterase (IC50 values: IQ3b 11 +/- 5 microM; AQ11 43 +/- 8 microM) and calcium elevation (IC50 values: IQ3b 9 +/- 4 microM; AQ11 32 +/- 6 microM). These compounds also inhibited fibrinogen binding in platelets challenged by ADP or thrombin. The results suggest that these new potent agents inhibit platelet phosphodiesterase activity causing an elevation in cAMP levels sufficient to inhibit calcium rise and fibrinogen binding. This mechanism can be responsible for the ability of the compounds to prevent platelet aggregation.