背景:X连锁出血性疾病血友病B,由凝血因子IX(FIX)基因突变引起,导致其功能部分或全部丧失,需要终身FIX替代疗法。尽管新的重组FIX(rIX)疗法如白蛋白融合蛋白(rIX-FP)可以延长血浆半衰期,从而减少给药频率,静脉(IV)注射的复杂性仍然存在。
目的:该研究旨在表征具有预期增强的比活性的rIX-FP变体,这将利用rIX-FP的优异药代动力学(PK)概况,具有皮下(SC)给药的有益特征。
方法:两种rIX-FP变体,R338L(“帕多瓦变体”)和R338L/E410K,在体外进行了表征。在IV和SC施用这些变体(基于抗原水平给药)后,在FIX缺陷型小鼠中评价FIX抗原和活性水平的PK谱。在尾夹出血模型中在IV和SC施用(基于活性的给药)后测试最有希望的变体的功效。市售的野生型(WT)rIX-FP产物用作比较物。
结果:与rIX(WT)-FP相比,两种rIX-FP变体均显示体外比活性增加4至5倍,而FXIa介导的激活是rIX(WT)-FP和rIX(R338L)-FP最快的。与rIX(WT)-FP和rIX(R338L/E410K)-FP相比,rIX(R338L)-FP在IV和SC给药后表现出更高的FIX活性暴露,并证明了对rIX(WT)-FP在减少FIX缺陷小鼠的出血时间和失血方面的可比功效,这些小鼠需要〜4倍的低蛋白量。
结论:rIX(R338L)-FP被证明是SC给药的有希望的候选药物,表现出增加的比活性与更高的基于活性的暴露相结合,并表明在较低蛋白质剂量下的功效。
BACKGROUND: The X-linked bleeding disorder Hemophilia B, caused by mutation(s) in the coagulation factor IX (FIX) gene, leads to partial or total loss of its function requiring lifelong FIX replacement therapy. Although new recombinant FIX (rIX) therapeutics like albumin-fusion proteins (rIX-FP) enable longer plasma half-life and thus less frequent administration, the complexity of intravenous (IV) injection remains.
OBJECTIVE: The study aims to characterize rIX-FP variants with anticipated enhanced specific activity, which would leverage rIX-FP\'s superior pharmacokinetic (PK) profile with beneficial characteristics for subcutaneous (SC) administration.
METHODS: Two rIX-FP variants, R338L (\"Padua-variant\") and R338L/E410K, were characterized in vitro. PK profiles of FIX antigen and activity levels were evaluated in FIX-deficient mice after IV and SC administration of these variants (dosing based on antigen levels). The efficacy of the most promising variant was tested after IV and SC administration (dosing based on activity) in a tail-clip bleeding model. A marketed wildtype (WT) rIX-FP product served as the comparator.
RESULTS: Both rIX-FP variants showed a 4- to 5-fold increase in specific activity in vitro compared to rIX(WT)-FP, whilst FXIa-mediated activation was the fastest for rIX(WT)-FP and rIX(R338L)-FP. Compared to rIX(WT)-FP and rIX(R338L/E410K)-FP, rIX(R338L)-FP exhibited higher FIX activity exposure after IV and SC administration, and demonstrated comparable efficacy towards rIX(WT)-FP in reducing bleeding time and blood loss in FIX-deficient mice requiring ∼4 times lower protein amount.
CONCLUSIONS: rIX(R338L)-FP was shown to be a promising candidate for SC administration, exhibiting increased specific activity combined with higher activity-based exposure, and indicating efficacy at lower protein dose.