Preclinical Studies of RUC-4, a Novel Platelet αIIbβ3 Antagonist, in Non-Human Primates and With Human Platelets

Introduction: We are developing the novel αIIbβ3 Antagonist, RUC-4, for subcutaneously (SC)-administered first-point-of-medical-contact treatment for ST Segment Elevated Myocardial Infarction (STEMI).

Methods: We studied the: 1. pharmacokinetics (PK) of RUC-4 at 1.0, 1.93, and 3.86 mg/kg IV, IM, and SC in non-human primates (NHPs); 2. impact of aspirin on RUC-4 IC₅₀ in human platelet-rich plasma (PRP); 3. effect of different anticoagulants on the RUC-4 IC₅₀ in human PRP; and 4. relationship between αIIbβ3 receptor blockade by RUC-4 and inhibition of ADP-induced platelet aggregation.

Results: 1. All doses of RUC-4 were well tolerated, but Animals demonstrated variable temporary bruising. IM and SC RUC-4 reached dose-dependent peak levels within 5-15 min, with T_½ s between 0.28 and 0.56 hrs. Platelet aggregation studies in NHPs receiving IM RUC-4 demonstrated >80% inhibition of the initial slope of ADP-induced aggregation with all 3 doses 30 minutes post-dosing, with subsequent dose-dependent loss of inhibition over 4-5 hours. 2. The RUC-4 IC₅₀ for ADP-induced platelet aggregation was unaffected by aspirin treatment (40±9 nM vs. 37±5 nM; p=0.39). 3. The RUC-4 IC₅₀ was significantly higher in PRP prepared from PPACK-anticoagulated blood compared to citrate-anticoagulated blood using either TRAP (122±17 vs. 66±25 nM; p=0.05; n=4) or ADP (102±22 vs. 54±13; p<0.001; n=5). 4. There was a close correspondence between receptor blockade and inhibition of ADP-induced platelet aggregation, with aggregation inhibition beginning with ~40% receptor blockade and becoming nearly complete at >80% receptor blockade.

Discussion: Based on these results and Others, RUC-4 has now progressed to formal preclinical toxicology studies.