Novel thienopyridines as anti-platelet agents

Binsaleh, Naif (2018) Novel thienopyridines as anti-platelet agents. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

Platelets have well-established roles in haemostasis, and this requires a fine balance to maintain platelets in a resting state in the absence of vessel injury and allow rapid activation upon stimulation. Platelet hyperactivity is associated with several serious health conditions such as Acute Coronary Syndrome (ACS), Venous thromboembolism (VTE) Myocardial Infarction and Stroke, and so anti-platelet therapies are a critical tool in the management of such diseases. This thesis evaluated the use of six thienopyridine compounds to modulate platelet activity. Members of the thienopyridine family are currently in clinical use in the UK but the variable response to specific drugs and the associated side effects warrant continued identification and refinement of alternative compounds. The work demonstrated that these six novel thienopyridine derivatives were able to inhibit ADP-induced platelet activation (assessed by CD62P expression, PAC1 binding and platelet-leukocyte aggregate formation) and aggregation (assessed by light-transmission aggregometry) in platelets obtained from healthy participants. Furthermore, the compounds seemed to show enhanced activity when compared with the standard thienopyridine, clopidogrel (active metabolite). The signalling pathways affected by these compounds were studied and found that Ca2+ flux was affected in ADP-stimulated platelets and VASP phosphorylation was maintained. The effects on PLCγ2, cPLA2 and PI3k/Akt were variable and inconsistent. As endothelial cells also have a crucial role in haemostasis and prevention of inappropriate clot formation, and have been shown to be responsive to ADP, this thesis also evaluated the effect of the compounds on endothelial cells adhesion molecule expression. All six compounds were shown to inhibit CD62P, CD62E and VCAM-1 in stimulated HUVEC cells, suggesting a new area for drug development. Finally, the thesis shifted focus on to the role of platelets in immunological responses. Since platelets have been reported to have central roles in cancer development and to sequester proteins from within the microenvironment, the final part of the work looked at whether platelet function can be affected by the tumour cell secretome and attempted to characterise the cytokines responsible for the effects. The results showed that the tumour cell secretome can inhibit platelet activation and aggregation and provides a mechanism by which to explain increased bleeding tendency in cancer patients.