Zalunfiban

Understanding the pharmacodynamic effects of platelet inhibitors is standard for developing more effective antithrombotic therapies. An example is the antithrombotic treatment of acute coronary syndrome (ACS), in particular ST-elevated myocardial infarction (STEMI) patients who are in need for rapid acting strong antithrombotic therapy despite the use of aspirin and oral P2Y12-inhibitors. In this study, we evaluated two injectable platelet inhibitors under clinical development (the P2Y12 antagonist selatogrel and the GPIIb-IIIa antagonist zalunfiban) that may be amenable to pre-hospital treatment of STEMI patients. Platelet reactivity was assessed at inhibitor concentrations that represent clinically relevant levels of platelet inhibition (IC20-50%, 1/2Cmax, and Cmax). Light transmission aggregometry (LTA), was used to evaluate the initial rate of aggregation (primary slope, PS) and maximal aggregation (MA). Both adenosine diphosphate (ADP) and thrombin receptor agonist peptide (TRAP) were used as agonists. Zalunfiban demonstrated similar inhibition of platelet aggregation when blood was collected in PPACK or TSC, whereas selatogrel demonstrated greater inhibition in PPACK. In this study, using PPACK anticoagulant, selatogrel and zalunfiban affected PS in response to ADP equivalently at all drug concentrations tested. In contrast, zalunfiban had significantly greater potency at its Cmax concentration compared to selatogrel using TRAP as agonist. Upon evaluation of MA responses at lower doses, selatogrel had greater inhibition of MA in response to ADP than zalunfiban; however, at concentrations that represent Cmax, the drugs were equivalent. Zalunfiban also had greater inhibition of MA in response to TRAP at the Cmax dose. These data suggest that zalunfiban may provide greater protection in reducing thrombus formation than selatogrel, especially since thrombin is an early, key primary agonist in the pathophysiology of thrombotic events.

Zalunfiban (RUC-4) is a novel, subcutaneously administered glycoprotein IIb/IIIa inhibitor (GPI) designed for prehospital treatment to initiate reperfusion in the infarct-related artery (IRA) before primary percutaneous coronary intervention in patients with ST-elevation myocardial infarction (STEMI). Since GPIs have been reported to rapidly reperfuse IRAs, we assessed whether there was a dose-dependent relationship between zalunfiban treatment and angiographic reperfusion indices and thrombus grade of the IRA at initial angiogram in patients with STEMI.

This was a post hoc analysis from the open-label Phase IIa study that investigated the pharmacodynamics, pharmacokinetics, and tolerability of three doses of zalunfiban - 0.075, 0.090 and 0.110 mg/kg - in STEMI patients. This analysis explored dose-dependent associations between zalunfiban and three angiographic indices of the IRA, namely coronary and myocardial blood flow and thrombus burden. Zalunfiban was administered in the cardiac catheterization laboratory prior to vascular access, ∼10 to 15 minutes before the initial angiogram. All angiographic data were analyzed by a blinded, independent, core laboratory.

Twentyfour out of 27 STEMI patients were evaluable for angiographic analysis (0.075 mg/kg [n=7], 0.090 mg/kg [n=9], and 0.110 mg/kg [n=8]). TIMI flow grade 2 or 3 was seen in 1/7 patients receiving zalunfiban at 0.075 mg/kg, in 6/9 patients receiving 0.090 mg/kg, and in 7/8 patients receiving 0.110 mg/kg (p_trend = 0.004). A similar trend was observed based on TIMI flow grade 3. Myocardial perfusion was also related to zalunfiban dose (p_trend = 0.005) as reflected by more frequent TIMI myocardial perfusion grade 3. Consistent with the dose-dependent trends in greater coronary and myocardial perfusion, TIMI thrombus ≥4 grade was inversely related to zalunfiban dose (p_trend = 0.02).

This post hoc analysis found that higher doses of zalunfiban administered in the cardiac catheterization lab prior to vascular access were associated with greater coronary and myocardial perfusion, and lower thrombus burden at initial angiogram in patients with STEMI undergoing primary percutaneous coronary intervention.