Highly constrained cyclic (S,S) -CXaaC- peptides as inhibitors of fibrinogen binding to platelets

Molecular Requirements for the Expression of Antiplatelet Effects by Synthetic Structural Optimized Analogues of the Anticancer Drugs Imatinib and Nilotinib

Background

Platelets play important roles in cancer progression and metastasis, as well as in cancer-associated thrombosis (CAT). Tyrosine kinases are implicated in several intracellular signaling pathways involved in tumor biology, thus tyrosine kinase inhibitors (TKIs) represent an important class of anticancer drugs, based on the concept of targeted therapy.

Purpose

The objective of this study is the design and synthesis of analogues of the TKIs imatinib and nilotinib in order to develop tyrosine kinase inhibitors, by investigating their molecular requirements, which would express antiplatelet properties.

Methods

Based on a recently described by us improved approach in the preparation of imatinib and/or nilotinib analogues, we designed and synthesized in five-step reaction sequences, 8 analogues of imatinib (I-IV), nilotinib (V, VI) and imatinib/nilotinib (VII, VIII). Their inhibitory effects on platelet aggregation and P-selectin membrane expression induced by arachidonic acid (AA), adenosine diphosphate (ADP) and thrombin receptor activating peptide-6 (TRAP-6), in vitro, were studied. Molecular docking studies and calculations were also performed.

Results

The novel analogues V-VIII were well established with the aid of spectroscopic methods. Imatinib and nilotinib inhibited AA-induced platelet aggregation, exhibiting IC₅₀ values of 13.30 μΜ and 3.91 μΜ, respectively. Analogues I and II exhibited an improved inhibitory activity compared with imatinib. Among the nilotinib analogues, V exhibited a 9-fold higher activity than nilotinib. All compounds were less efficient in inhibiting platelet aggregation towards ADP and TRAP-6. Similar results were obtained for the membrane expression of P-selectin. Molecular docking studies showed that the improved antiplatelet activity of nilotinib analogue V is primarily attributed to the number and the strength of hydrogen bonds.

Conclusion

Our results show that there is considerable potential to develop synthetic analogues of imatinib and nilotinib, as TKIs with antiplatelet properties and therefore being suitable to target cancer progression and metastasis, as well as CAT by inhibiting platelet activation.

Clopidogrel Therapy in Patients with Cardiovascular Disease Undergoing Transurethral Resection of the Prostate: A Step Towards Individualization

OBJECTIVES

The objective of this study was to test platelet function pre- and peri-operatively in clopidogrel-treated patients undergoing transurethral resection of the prostate.

METHODS

This was a pilot study involving 20 male patients treated with clopidogrel (75 mg/day) for the secondary prevention of cardiovascular disease and scheduled for elective transurethral resection of the prostate. Platelet function testing with light transmittance aggregometry in platelet-rich plasma of four samples (T0, T1, T2, and T3 drawn on the same day, 3 and 7 days of clopidogrel cessation and 24-h post-operatively, respectively) was performed and evaluated in each patient. P-selectin membrane expression was evaluated using monoclonal antibodies.

RESULTS

The platelet response to adenosine diphosphate 5 µΜ and 20 µΜ at T0 were 42 ± 15 and 60 ± 14%, respectively. After discontinuation of clopidogrel, corresponding maximum aggregation values at T1 were 60 ± 16 and 74 ± 14%, and increased to 69 ± 16 and 79 ± 18% at T2. No significant difference in platelet aggregation values were noted between T1 and T2, while similar aggregation values were recorded at T3.

CONCLUSIONS

Our findings indicate that in patients undergoing transurethral resection of the prostate, platelet activation is similar 3 and 7 days from clopidogrel cessation. These results may be of relevance in subjects at increased thrombotic risk prior to a surgical procedure carrying a high-bleeding risk.

Deconvoluting the Dual Antiplatelet Activity of a Plant Extract

A thorough evaluation of the antiplatelet activity profile of hexane olive leaf extract in human platelets indicated a potent activity accomplished through a two axis inhibition of platelet activation triggered both by ADP and thrombin. To delineate the extract components responsible for this dual activity, an NMR based method was established to determine and quantify the triterpenoid content leading to the characterization of uvaol, erythrodiol, and oleanolic acid. The antiplatelet profile of the total extract and of the 3 determined triterpenoids was evaluated against in vitro platelet aggregation induced by several platelet agonists as also on PAC-1 binding and P-selectin membrane expression both in healthy volunteers and in platelets from patients with an acute coronary syndrome receiving dual antiplatelet therapy with aspirin and ticagrelor. The extract was identified to inhibit ADP-induced platelet activation due to its erythrodiol content and TRAP-induced platelet activation due to the activity of uvaol and oleanolic acid.

A highly constrained cyclic (S,S)-CDC- peptide is a potent inhibitor of carotid artery thrombosis in rabbits

Inhibition of platelet aggregation is indispensable for the treatment of acute arterial thrombotic episodes. We have previously reported the synthesis of a highly constrained cyclic peptide, that incorporates the -CDC- sequence, (S,S) PSRCDCR-NH(2), which potently inhibits aggregation and fibrinogen binding to human platelets in vitro. We have tested the safety and efficacy of the peptide on the electrically induced carotid artery thrombosis experimental rabbit model. The peptide's effects on carotid blood flow, thrombus weight, in vitro and ex vivo platelet aggregation, and bleeding and hemostatic parameters were evaluated. The peptide was administered via the femoral vein. Carotid blood flow was continuously monitored for 90 min after electrical thrombus formation. The peptide, at 12 mg/kg, prevented total artery occlusion and significantly preserved carotid artery's patency compared with placebo and eptifibatide. Furthermore, (S,S) PSRCDCR-NH(2) administration at 12 mg/kg reduced thrombus weight, whereas it inhibited ex vivo ADP, arachidonic acid (AA) and collagen-induced platelet aggregation. Moreover (S,S) PSRCDCR-NH(2) at 12 mg/kg presented significantly higher inhibitory effects on AA and collagen-induced ex vivo platelet aggregation compared to eptifibatide. The peptide at any dose did not affect the coagulation cascade, the bleeding times or the hemostatic response of the animals. Thus highly constrained cyclic peptides like (S,S) PSRCDCR-NH(2) that incorporate the -CDC- motif and fulfil certain conformational criteria represent novel compounds that potently inhibit thrombus formation, ex vivo platelet aggregation and carotid artery occlusion superiorly to other non-RGD peptides, such as YMESRADR, without causing hemorrhagic complications in a rabbit model of arterial thrombosis.