Friedreich's ataxia (FA) is a life-threatening autosomal recessive disorder characterized by neurological and cardiac dysfunction. Arrhythmias and heart failure are the main cause of premature death. From prior studies in murine models of FA, adeno-associated virus encoding the normal human frataxin gene (AAVrh.10hFXN) effectively treated the cardiac manifestations of the disease. However, the therapeutic dose window is limited by high level of human frataxin (hFXN) gene expression associated with toxicity. As a therapeutic goal, since FA heterozygotes have no clinical manifestations of FA, we estimated the level of frataxin (FXN) necessary to convert the heart of a homozygote to that of a heterozygote. In noncardiac cells, FA heterozygotes have 30-80% of normal FXN levels (17.7-47.2 ng/mg, average 32.5 ng/mg) and FA homozygotes 2-30% normal levels (1.2-17.7 ng/mg, average 9.4 ng/mg). Therefore, an AAV vector would need to augment endogenous in an FA homozygote by >8.3 ng/mg. To determine the required dose of AAVrh.10hFXN, we administered 1.8 × 1011, 5.7 × 1011, or 1.8 × 1012 gc/kg of AAVrh.10hFXN intravenously (IV) to muscle creatine kinase (mck)-Cre conditional knockout Fxn mice, a cardiac and skeletal FXN knockout model. The minimally effective dose was 5.7 × 1011 gc/kg, resulting in cardiac hFXN levels of 6.1 ± 4.2 ng/mg and a mild (p < 0.01 compared with phosphate-buffered saline controls) improvement in mortality. A dose of 1.8 × 1012 gc/kg resulted in cardiac hFXN levels of 33.7 ± 6.4 ng/mg, a significant improvement in ejection fraction and fractional shortening (p < 0.05, both comparisons) and a 21.5% improvement in mortality (p < 0.001). To determine if the significantly effective dose of 1.8 × 1012 gc/kg could achieve human FA heterozygote levels in a large animal, this dose was administered IV to nonhuman primates. After 12 weeks, the vector-expressed FXN in the heart was 17.8 ± 4.9 ng/mg, comparable to the target human levels. These data identify both minimally and significantly effective therapeutic doses that are clinically relevant for the treatment of the cardiac manifestations of FA.

中文翻译：

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确定 AAVrh.10hFXN 治疗弗里德赖希共济失调心脏表现的安全有效静脉剂量。

弗里德赖希共济失调 (FA) 是一种危及生命的常染色体隐性遗传疾病，其特征是神经和心脏功能障碍。心律失常和心力衰竭是过早死亡的主要原因。根据先前对 FA 小鼠模型的研究，编码正常人 frataxin 基因 (AAVrh.10hFXN) 的腺相关病毒可有效治疗该疾病的心脏表现。然而，治疗剂量窗口受到与毒性相关的高水平人frataxin (hFXN)基因表达的限制。作为治疗目标，由于 FA 杂合子没有 FA 的临床表现，我们估计了将纯合子心脏转变为杂合子心脏所需的 frataxin (FXN) 水平。在非心肌细胞中，FA 杂合子的 FXN 水平为正常水平的 30-80%（17.7-47.2 ng/mg，平均 32.5 ng/mg），FA 纯合子的 FXN 水平为正常水平的 2-30%（1.2-17.7 ng/mg，平均 9.4 ng/mg）。毫克）。因此，AAV 载体需要将 FA 纯合子中的内源性增强 >8.3 ng/mg。为了确定所需的 AAVrh.10hFXN 剂量，我们向肌肉肌酸激酶 (mck)-Cre 条件敲除 Fxn 小鼠静脉内 (IV) 施用 1.8 × 1011、5.7 × 1011 或 1.8 × 1012 gc/kg 的 AAVrh.10hFXN，心脏和骨骼 FXN 敲除模型。最低有效剂量为 5.7 × 1011 gc/kg，导致心脏 hFXN 水平为 6.1 ± 4.2 ng/mg，死亡率略有改善（与磷酸盐缓冲盐水对照相比，p < 0.01）。1.8 × 1012 gc/kg 的剂量导致心脏 hFXN 水平为 33.7 ± 6.4 ng/mg，射血分数和缩短分数显着改善（p < 0.05，两个比较），死亡率降低 21.5%（p < 0.001） ）。为了确定 1.8 × 1012 gc/kg 的显着有效剂量是否可以在大型动物中达到人 FA 杂合子水平，对该剂量进行静脉注射给非人灵长类动物。12 周后，心脏中载体表达的 FXN 为 17.8 ± 4.9 ng/mg，与人类目标水平相当。这些数据确定了与治疗 FA 心脏表现临床相关的最低有效治疗剂量和显着有效治疗剂量。