An Antithrombotic Agent, NQ301, Inhibits Thromboxane A2 Receptor and Synthase Activity in Rabbit Platelets

Discovery of napabucasin derivatives for the treatment of tuberculosis

Tuberculosis is the contagious disease responsible for the highest number of deaths worldwide. Here, we screened a commercially available compound library and found napabucasin to possess a moderate anti-tubercular activity against M. tuberculosis H37Ra (MIC 2.5 μg mL-1, 10.4 μM). Three series of napabucasin derivatives were further evaluated for their in vitro anti-tubercular activities against Mtb H37Ra. The activity of most derivatives was either retained or enhanced compared with that of napabucasin. Compound 3s was the most active compound showing a MIC value of 0.3125 μg mL-1 (0.9 μM). Furthermore, several compounds were selected and evaluated against the Mtb H37Rv standard strain and six Mtb clinical isolates. Importantly, these compounds were found to be effective against Mtb clinical isolates with multi-resistance to isoniazid, rifampicin, and ethambutol.

Structure-activity relationship studies for multitarget antithrombotic drugs

Thrombosis is a complex process involving multiple pathways. Currently, therapy relies on the combination of two or more antithrombotic drugs, showing that inhibiting more than one target provides benefits in the prevention and treatment of thrombosis. This review focuses on structure-activity relationship studies of molecules possessing multiple actions against thrombosis, namely, dual inhibitors of coagulation, dual inhibitors of coagulation and platelet aggregation, and also dual inhibitors of platelet aggregation. EP217609 has just entered clinical trials, which raise the expectations on the multitarget strategy to prevent or treat thrombosis.

NP-313, 2-acetylamino-3-chloro-1,4-naphthoquinone, a novel antithrombotic agent with dual inhibition of thromboxane A(2) synthesis and calcium entry

BACKGROUND AND PURPOSE

1,4-Naphthoquinones exhibit antiplatelet activity both in vivo and in vitro. In the present study, we investigated the antiplatelet effect of a novel naphthoquinone derivative NP-313, 2-acetylamino-3-chloro-1,4-naphthoquinone and its mechanism of action.

EXPERIMENTAL APPROACH

We measured platelet aggregation, Ca(2+) mobilization, thromboxane B2 formation and P-selectin expression and examined several enzymatic activities. Furthermore, we used the irradiated mesenteric venules in fluorescein sodium-treated mice to monitor the antithrombotic effect of NP-313 in vivo.

KEY RESULTS

NP-313 concentration-dependently inhibited human platelet aggregation induced by collagen, arachidonic acid, thapsigargin, thrombin and A23187. NP-313 also inhibited P-selectin expression, thromboxane B(2) formation and [Ca(2+) ](i) elevation in platelets stimulated by thrombin and collagen. NP-313 at 10 µM inhibited cyclooxygenase, thromboxane A(2) synthase, and protein kinase Cα, whereas it did not affect phospholipase A(2) or phospholipase C activity. In the presence of indomethacin and an adenosine 5-diphosphate scavenger, NP-313 concentration-dependently inhibited thrombin- and A23187-induced [Ca(2+)](i) increase through its inhibitory effects on Ca(2+) influx, rather than blocking Ca(2+) release from intracellular stores. NP-313 also inhibited thapsigargin-mediated Ca(2+) influx through store-operated calcium channel but had no effect on Ca(2+) influx through store-independent calcium channel evoked by the diacylglycerol analogue 1-oleoyl-2-acetyl-sn-glycerol. Nevertheless, it had little effect on cyclic AMP and cyclic GMP levels. Also, intravenously administered NP-313 dose-dependently inhibited the thrombus occlusion of the irradiated mesenteric vessels of fluorescein-pretreated mice.

CONCLUSIONS AND IMPLICATIONS

Taken together, these results indicate that NP-313 exerts its antithrombotic activity through dual inhibition of thromboxane A(2) synthesis and Ca(2+) influx through SOCC.

Cordycepin (3‘-deoxyadenosine) inhibits human platelet aggregation induced by U46619, a TXA2 analogue

Cordycepin (3′-deoxyadenosine), which comes from Cordyceps militaris, the Chinese medicinal fungal genus Cordyceps, is known to have anti-tumour activity. In this study, we investigated the novel effect of cordycepin on human platelet aggregation that was induced by U46619, a thromboxane A2 (TXA2) analogue. TXA2 is an aggregation-inducing autacoidal molecule that is produced in various agonist-activated platelets. Cordycepin completely inhibited U46619-induced platelet aggregation and simultaneously reduced cytosolic free Ca2+ ([Ca2+]i), which was increased by U46619 (5 μM) up to 66%. Furthermore, the U46619-stimulated phosphorylation of Ca2+-dependent proteins (20 kDa of a myosin light chain and 47 kDa of pleckstrin) was strongly inhibited by cordycepin. These results suggest that cordycepin may have a beneficial effect on autacoidal TXA2-mediated thrombotic diseases by inhibiting TXA2-induced platelet aggregation via suppression of the Ca2+ level.