Reduction in thrombus formation by PG-1 F(ab')2, an anti-guinea pig platelet glycoprotein Ib monoclonal antibody.

Abstract

We have recently demonstrated that intraperitoneal injection into guinea pigs of F(ab') 2 fragments of PG-1, a murine monoclonal antibody recognizing the guinea pig homologue of human platelet glycoprotein Ib, produces virtually complete functional block of the platelet von Willebrand factor receptor without inducing a hemorrhagic state. To assess the ability of this antibody to protect against thrombosis resulting from laser-induced injury to mesenteric small arteries, we injected guinea pigs with either PG-1 F(ab') 2 (2.3 mg/kg) or with buffer alone 24 hours before study. For each animal, four mesenteric vessels were studied consecutively for 15 minutes each. The number of thrombi, time to first thrombus, and time to embolization of first thrombi were recorded. In the control animals most individual vessels had three to four thrombi, whereas in the antibody-treated animals, vessels most frequently had only a single thrombus or even none at all. The mean number of thrombi per vessel in the antibody-treated animals (1.125) was significantly lower than the mean in the control animals (3.40), with p< 0.001. However, there was no significant difference between groups with respect to time to first thrombus after laser injury. Detachment of thrombi in the control animals occurred in an easily recordable, discrete fashion, with 75% of first thrombi embolizing in less than 5 minutes. In the antibody-treated animals, gradual dissolution rather than discrete detachment was typically observed. In 31% of the vessels studied in these animals, no embolus occurred; for the remaining vessels only 9% of thrombi were observed to embolize within 5 minutes of their formation. PG-1 F(ab') 2 treatment accordingly served to break the repetitive cycle of thrombus production, embolization, and rethrombosis in this model system. MoAbs recognizing membrane glycoproteins (GPs) of guinea pig platelets that show very close structural homology to human platelet GPIb/IX and GPIIb/IIIa have been developed. MoAb PG-1 in particular recognizes the guinea pig homologue of human GPIb in surface-labeled platelets and in metabolically labeled megakaryocytes. PG-1 F(ab') 2 , as well as intact PG-1, incubated in vitro with washed guinea pig platelets inhibits the von

Recombinant von Willebrand Factor Fragment AR545C Inhibits Platelet Aggregation and Enhances Thrombolysis With rtPA in a Rabbit Thrombosis Model

“…40 Monoclonal antibodies to GPIb and to GPIb binding sites of vWF have been shown to inhibit thrombus formation in an experimental thrombosis procedure using a dye-pulsed laser in mesenteric arteries of guinea pigs. 41 Synthetic peptides of vWF corresponding to GPIb binding domain (spanning from amino acids 474 to 488 and 692 to 708) inhibited thrombus formation in the same model. 42 The recombinant T116 fragment (amino acids 449 to 728) has also been shown to be effective in the carotid artery stenosis model in pigs and monkeys.…”

Inhibition of the von Willebrand (VWF)–collagen interaction by an antihuman VWF monoclonal antibody results in abolition of in vivo arterial platelet thrombus formation in baboons

“…8 One line of search for antiplatelet drugs in the prevention of thrombosis is focusing on the inhibition of the VWF-GPIb axis. Compounds that interact with GPIb␣, such as the GPIb-binding snake venom proteins echicetin and crotalin, 9,10 an antiguinea pig GPIb antibody, 11 a recombinant A1 domain fragment (VCL), 12 and recently an antihuman GPIb antibody 13 or compounds that bind to VWF, such as anti-A1-VWF-monoclonal antibodies (mAbs) 14,15 or aurin tricarboxylic acid (ATA), 16 indeed, inhibit thrombus formation in vivo.…”

Antithrombotic Effect of Platelet Glycoprotein Ib–Blocking Monoclonal Antibody Fab Fragments in Nonhuman Primates

“…21 In another guinea pig model, the fragments could effectively reduce thrombus formation on a laser-induced injury. 20 However this PG-1 antibody is specific for guinea pig platelets and does not cross-react with human platelets. Part of this rather surprising lack of in vivo studies is due to the low cross-reactivity of the anti-human GPIb MoAbs with platelets from commonly used laboratory animals.…”

“…19 We are aware of only 2 successful in vivo studies on guinea pigs, in which F(abЈ) 2 fragments of PG-1, a monoclonal anti-guinea pig GPIb antibody, were used. 20,21 These fragments were shown to significantly prolong the time to arterial microvascular graft thrombosis without prolonging the bleeding time. 21 In another guinea pig model, the fragments could effectively reduce thrombus formation on a laser-induced injury.…”