2016 Scientific Sessions Sol Sherry Distinguished Lecturer in Thrombosis

Abstract

Activated protein C (APC), derived from the plasma protease zymogen, protein C, is antithrombotic and anti-inflammatory. In preclinical injury models, recombinant APC provides neuroprotection for multiple injuries, including ischemic stroke. APC acts directly on brain endothelial cells and neurons by initiating cell signaling that requires multiple receptors. Two or more major APC receptors mediate APC’s neuroprotective cell signaling. When bound to endothelial cell protein C receptor, APC can cleave protease activated receptor 1 causing biased cytoprotective signaling that reduces ischemia-induced injury. Pharmacologic APC alleviates bleeding induced by tissue plasminogen activator (tPA) in murine ischemic stroke studies. Remarkably, APC’s signaling promotes neurogenesis. The signaling-selective recombinant variant of APC, “3K3A-APC”, was engineered to lack most of APC’s anticoagulant activity but retain APC’s cell signaling actions. Recombinant 3K3A-APC is in ongoing NIH-funded clinical trials for ischemic stroke.

Thrombotic Regulation From the Endothelial Cell Perspectives

“…Activated protein C regulates anticoagulation, inflammation, cell death, and maintains vascular permeability. 39,40 These functions are primarily mediated by proteolytically inactivating factor Va and factor VIIIa. Patients with deficiencies in protein C experience increased risk of thrombosis.…”

Targeting PAR1: Now What?

“…These signaling-selective APC variants were constructed to have limited anticoagulant activity by mutating N-linked glycan sites and/or residues in APC important for interaction with FVa or Protein S: 3K3A-APC (KKK191-193AAA), RR229/230AA, 5A-APC (KKK191-193AAA+ RR229/230AA), RD222/237CC, K193E, D36A/L38D/A39, L38D and L38D/N329Q [22,69–71]. The non-anticoagulant forms of APC stimulated PAR1-mediated cytoprotective signaling in vitro and exerted beneficial effects in murine models of sepsis and ischemic stroke [22,69–71] As cytoprotective-selective variants circumvent bleeding problems associated with APC’s anti-coagulant function, these variants are promising agents for clinical applications. 3K3A-APC is currently the only variant that has advanced to clinical trials.…”

“…In a mouse model, APC protected against brain hemorrhage in a PAR1-dependent manner [96]. An APC mutant (3K3A-APC) that lacks anticoagulant activity and acts solely by stimulation of PAR1-mediated cytoprotective has been tested in preclinical models of ischemic stroke [69]. More recently, 3K3A-APC was shown to stimulate restoration neuronal repair by neuronal stem cells transplanted into brains following ischemia [97].…”

Final Results of the RHAPSODY Trial: A Multi‐Center, Phase 2 Trial Using a Continual Reassessment Method to Determine the Safety and Tolerability of 3K3A‐APC, A Recombinant Variant of Human Activated Protein C, in Combination with Tissue Plasminogen Activator, Mechanical Thrombectomy or both in Moderate to Severe Acute Ischemic Stroke

“…This decrease in the anticoagulant activity of 3K3A-APC relative to wt-APC should reduce the risk of bleeding in patients, which was a serious side effect of wt-APC or DrotAA 30 . In animal models of stroke 12, 13, 31 , traumatic brain injury 9 and ALS 10 , 3K3A-APC exerted beneficial effects that were equivalent to, and sometimes greater than those of wt-APC 2, 6, 7, 32 .…”