Bz423 promotes procoagulant platelet formation independently of OSCP.

Platelet activation is a key driver of in arterial thrombosis and myocardial infarction. Despite current anti-platelet therapies, mortality and morbidity from myocardial infarction remain high. Alternative anti-platelet therapies are needed that can reduce the risk of myocardial infarction without further increasing bleeding risk. Activated platelets rapidly diverge into distinct subpopulations. 'Procoagulant' platelets form through a mitochondria-dependent pathway. These procoagulant platelets expose phosphatidylserine (PS), which localises and amplifies the coagulation cascade leading to a large increase in thrombin generation and stable thrombosis. Procoagulant platelet formation may be a new target for anti-platelet therapies. A key regulatory step controlling progression to procoagulant platelets is opening of the mitochondrial permeability transition pore (mPTP). OSCP acts as a regulatory node for mPTP activity. Since mPTP opening regulates procoagulant platelet formation, we hypothesised that OSCP might also be a key regulatory node in platelets. OSCP is a target of the immunomodulatory benzodiazepine, Bz-423. In this study, we show that Bz-423 increased procoagulant platelet formation. This was associated with mitochondrial hyperpolarisation prior to platelet activation, and increased mPTP opening after activation. Cellular thermal shift assays (CETSA) showed that both Bz-423 and a structurally similar benzodiazepine, 4-chloro-dizaepam, bind OSCP in platelets. Despite this, only Bz-423 increased procoagulant platelet formation. Our findings indicate that Bz-423 promotes procoagulant platelet progression through a target distinct from OSCP.