ABSTRACT
BACKGROUND: Mim8 is a novel, next-generation factor VIIIa mimetic in development for subcutaneous prophylactic treatment of patients with hemophilia A with and without inhibitors. In vitro and in vivo models indicate that Mim8 has a distinct hemostatic potential. OBJECTIVES: To test the nonclinical safety and pharmacodynamics of Mim8. METHODS: The Mim8 nonclinical safety program in cynomolgus monkeys consisted of three studies of 4-26 weeks in duration with Mim8 doses ranging from 0.3-60 mg/kg/week intravenously or subcutaneously. After sacrifice, macroscopic and microscopic pathological examinations were performed. RESULTS: Mim8 was well tolerated with no noteworthy clinical observations. No signs of excessive coagulation or pathological macroscopic or microscopic findings were observed at doses 0.3-3 mg/kg/week subcutaneous. Thrombosis-related findings were detected during histopathological examination in a small proportion of animals (16%) receiving doses ranging 6-20 mg/kg/week. Dose-dependent increases in factor X (FX) and factor IX (FIX) concentrations were observed. Shortening of activated partial thromboplastin time (APTT) and increased thrombin generation under ex vivo hemophilia A-like conditions were observed at all Mim8 dose levels. CONCLUSIONS: Thrombosis-related findings observed at doses above 6 mg/kg/week Mim8 may have been exaggerated pharmacological reactions to a procoagulant compound in normocoagulant animals. Increases in FX and FIX concentrations could be because of a half-life prolongation due to binding to Mim8, but were limited at clinically relevant exposure levels. Subcutaneous administration of up to 3 mg/kg/week (several fold greater than expected clinical exposure) for 26 weeks resulted in relevant pharmacodynamic effects, observed in thrombin generation and APTT, with no signs of thrombi or excessive coagulation activation.
Subject(s)
Hemophilia A , Thrombosis , Animals , Factor IX/metabolism , Factor X , Humans , Macaca fascicularis/metabolism , Thrombin/metabolism , Thrombosis/prevention & controlABSTRACT
OBJECTIVES: PAPP-A has become the principal biochemical serum marker in first trimester screening for Down syndrome, the original data being based on results of a radioimmunoassay (RIA). Recent observations using sandwich ELISA technology have proposed PAPP-A as a potential marker in patients with acute coronary syndrome (ACS). The aims of the present study were to demonstrate (i) the importance of antibody specificity, (ii) the potential pitfalls in changing assay technology, (iii) the importance of strict definition of technology, and (iv) the application of a well-defined assay technology on sera from patients with ACS. DESIGN AND METHODS: Candidate monoclonal antibodies (Mab) were identified by immunohistochemistry, Western blot and the absence of positive signals (ELISA) with normal, non-pregnant serum as antigen source. The ELISA technology was standardized against the original PAPP-A RIA and the WHO reference preparation (WHO 78/610). Results different from those obtained by the original RIA led to ELISA modifications with respect to dilution buffer and enzymatic digestion of the Mab. RESULTS: The first generation ELISA revealed serum measurements from a pool of non-pregnant (n=103) individuals which, compared to the RIA, seemed to be false positive. The false positive reaction was abolished by addition of bovine serum (BS) to the dilution buffer. Subsequent analysis of individual sera (n=103) indicated that 7/103 were still false positive. This reaction was eliminated by introduction of F(ab')(2)-fragment of the indicator antibody. This modified ELISA revealed that serum PAPP-A levels in ACS were statistically significantly higher than in controls (p<0.001). Moreover, serum PAPP-A in ACS patients with ST-segment elevation (STEMI) were higher (p<0.001) compared to patients without ST-segment elevation (NSTEMI). Immunohistochemical analysis failed to identify PAPP-A in the atherosclerotic plaques.
