title: In vivo efficacy of platelet-delivered, high specific activity factor VIII variants.
abstract: Ectopically expressed, human B-domainless (hB) factor 8 (F8) in platelets improves hemostasis in hemophilia A mice in several injury models. However, in both a cuticular bleeding model and a cremaster laser arteriole/venule injury model, there were limitations to platelet-derived (p) hBF8 efficacy, including increased clot embolization. We now address whether variants of F8 with enhanced activity, inactivation resistant F8 (IR8) and canine (c) BF8, would improve clotting efficacy. In both transgenic and lentiviral murine model approaches, pIR8 expressed at comparable levels to phBF8, but pcBF8 expressed at only approximately 30%. Both variants were more effective than hBF8 in cuticular bleeding and FeCl(3) carotid artery models. However, in the cremaster injury model, only pcBF8 was more effective, markedly decreasing clot embolization. Because inhibitors of F8 are stored in platelet granules and IR8 is not protected by binding to von Willebrand factor, we also tested whether pIR8 was effective in the face of inhibitors and found that pIR8 is protected from the inhibitors. In summary, pF8 variants with high specific activity are more effective in controlling bleeding, but this improved efficacy was inconsistent between bleeding models, perhaps reflecting the underlying mechanism(s) for the increased specific activity of the studied F8 variants.
authors.affiliation: Department of Pharmacology, University of Pennsylvania School of Medicine, Philadelphia, PA, USA.
authors.forename: Teshell K
authors.initials: TK
authors.lastname: Greene
authors.forename: Cheng
authors.initials: C
authors.lastname: Wang
authors.forename: Jessica D
authors.initials: JD
authors.lastname: Hirsch
authors.forename: Li
authors.initials: L
authors.lastname: Zhai
authors.forename: Jamie
authors.initials: J
authors.lastname: Gewirtz
authors.forename: Michael A
authors.initials: MA
authors.lastname: Thornton
authors.forename: Hongzhi Z
authors.initials: HZ
authors.lastname: Miao
authors.forename: Steven W
authors.initials: SW
authors.lastname: Pipe
authors.forename: Randal J
authors.initials: RJ
authors.lastname: Kaufman
authors.forename: Rodney M
authors.initials: RM
authors.lastname: Camire
authors.forename: Valder R
authors.initials: VR
authors.lastname: Arruda
authors.forename: M Anna
authors.initials: MA
authors.lastname: Kowalska
authors.forename: Mortimer
authors.initials: M
authors.lastname: Poncz
mesh_terms: D000818:Animals; D001792:Blood Platelets / Q000378:metabolism*; D002339:Carotid Arteries / Q000378:metabolism / Q000473:pathology; D004195:Disease Models, Animal; D004285:Dogs; D005169:Factor VIII / Q000008:administration & dosage* / Q000235:genetics* / Q000378:metabolism; D006467:Hemophilia A / Q000517:prevention & control*; D006470:Hemorrhage / Q000517:prevention & control*; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D013927:Thrombosis / Q000517:prevention & control*
chemical_list: D005169:Factor VIII