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An investigational RNAi therapeutic targeting antithrombin for the treatment of hemophilia A and B

Authors Machin N, Ragni MV

Received 22 May 2018

Accepted for publication 10 July 2018

Published 22 August 2018 Volume 2018:9 Pages 135—140


Checked for plagiarism Yes

Review by Single-blind

Peer reviewer comments 4

Editor who approved publication: Dr Martin H. Bluth

Nicoletta Machin, Margaret V Ragni

Department of Medicine, University of Pittsburgh, Hemophilia Center of Western Pennsylvania, Pittsburgh, PA, USA

Abstract: Fitusiran is an RNA interference therapeutic that targets antithrombin (AT) in the liver and interferes with AT translation by binding and degrading messenger RNA-AT, thereby silencing AT gene expression and preventing AT synthesis. In both preclinical and clinical studies, AT knockdown results in dose-dependent AT lowering when fitusiran is given weekly or monthly subcutaneously. In clinical trials, fitusiran dose escalation has resulted in improved thrombin generation and clinical hemostasis as measured by reduction in annualized bleed rate. Unlike currently licensed drugs, this improvement was not only in patients with hemophilia A but in also those with hemophilia B, with or without inhibitors. In dental and surgical procedures, fitusiran also provided perioperative hemostasis in association with AT lowering. Fitusiran is well tolerated, with minor local injection site reactions, but in one subject with severe hemophilia A, the concomitant use of daily high-dose factor VIII, inconsistent with trial guidance to avoid high, repeat doses of clotting factor, was associated with fatal thrombosis, suggesting the need for caution when using hemostatic agents in conjunction with fitusiran. Preclinical in vitro and in silico studies indicate improvement in thrombin generation in rare bleeding disorder plasmas, including in plasmas from patients with severe factors V, VII, and X deficiency, suggesting potential therapeutic benefit.

Keywords: congenital bleeding disorder, clotting factor, fitusiran, mRNA, novel bypass

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