Discovery of Novel GPVI Receptor Antagonists by Structure-Based Repurposing

Abstract

Inappropriate platelet aggregation creates a cardiovascular risk that is largely managed with thienopyridines and aspirin. Although effective, these drugs carry risks of increased bleeding and drug ‘resistance’, underpinning a drive for new antiplatelet agents. To discover such drugs, one strategy is to identify a suitable druggable target and then find small molecules that modulate it. A good and unexploited target is the platelet collagen receptor, GPVI, which promotes thrombus formation. To identify inhibitors of GPVI that are safe and bioavailable, we docked a FDA-approved drug library into the GPVI collagen-binding site in silico. We now report that losartan and cinanserin inhibit GPVI-mediated platelet activation in a selective, competitive and dose-dependent manner. This mechanism of action likely underpins the cardioprotective effects of losartan that could not be ascribed to its antihypertensive effects. We have, therefore, identified small molecule inhibitors of GPVI-mediated platelet activation, and also demonstrated the utility of structure-based repurposing.

Inhibition of Glycoprotein VI Clustering by Collagen as a Mechanism of Inhibiting Collagen-Induced Platelet Responses: The Example of Losartan

“…In agreement with others [ 18 ] we have observed that losartan (22 μM) delayed collagen-triggered protein tyrosine phosphorylation and reduced its extent (data not shown). The phosphorylation of the GPVI signaling subunit FcRγ examined by immunoprecipitation, was reduced in the samples of losartan-treated platelets compared to control samples confirming that that losartan impacts the initial phase of the GPVI signaling pathway.…”

“…Losartan dose-dependently inhibited the aggregation of human washed platelets induced by 1 μg.mL -1 collagen with an IC50 of 6.5 μM ( Fig 1A ) in agreement with recently reported data [ 18 ]. Furthermore, losartan inhibited the exposure of P-selectin induced by 10 μg.mL -1 collagen with an IC50 of 6.3 μM.…”

“…However, functional studies were performed using losartan concentrations capable of blocking the TXA2-dependent platelet responses to collagen, and there was no direct experimental evidence that losartan inhibited the binding of GPVI to collagen. Interestingly, Taylor et al recently reported that losartan is more potent on GPVI than on TP, the TXA2 receptor [ 18 ]. Yet, several questions remain pending with respect to the mechanism by which losartan inhibits GPVI activation by collagen: inhibition of collagen binding to GPVI or of GPVI dimerization/clustering?…”

Platelet Hyperreactivity in Diabetes: Focus on GPVI Signaling—Are Useful Drugs Already Available?

“…Originally used in pain relief, aspirin is now additionally used alone or in combination with other antiplatelet treatments as a standard therapy for the primary and secondary prevention of heart attack and stroke. Losartan (an angiotensin II receptor 1 inhibitor) used in the treatment of hypertension was discovered using structure-based repurposing to have anti-GPVI effects (41). In a recent study investigating the effects of a therapeutic dose of losartan on collagen-induced platelet activation, however, no statistically significant differences were observed between treated and nontreated patients with respect to a biological antiplatelet effect (42).…”

Comparison of the GPVI inhibitors losartan and honokiol

“…Losartan, an angiotensin II receptor antagonist, has been proposed to inhibit clustering but not binding of GPVI to collagen [15,16], leading to inhibition of platelet activation in vitro and reduced platelet accumulation after carotid injury in mice [17][18][19][20]. Honokiol is a natural bioactive molecule isolated from Magnolia species, which is used in traditional Chinese medicine.…”