Department of Genetic Medicine, New York, New York, USA.
Department of Pathology, Weill Cornell Medicine, New York, New York, USA.
Hum Gene Ther. 2023 Jul;34(13-14):605-615. doi: 10.1089/hum.2023.020. Epub 2023 Jul 4.
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 × 10, 5.7 × 10, or 1.8 × 10 gc/kg of AAVrh.10hFXN intravenously (IV) to muscle creatine kinase (mck)-Cre conditional knockout mice, a cardiac and skeletal FXN knockout model. The minimally effective dose was 5.7 × 10 gc/kg, resulting in cardiac hFXN levels of 6.1 ± 4.2 ng/mg and a mild ( < 0.01 compared with phosphate-buffered saline controls) improvement in mortality. A dose of 1.8 × 10 gc/kg resulted in cardiac hFXN levels of 33.7 ± 6.4 ng/mg, a significant improvement in ejection fraction and fractional shortening ( < 0.05, both comparisons) and a 21.5% improvement in mortality ( < 0.001). To determine if the significantly effective dose of 1.8 × 10 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.
弗里德赖希共济失调（FA）是一种威胁生命的常染色体隐性遗传病，其特征是神经和心脏功能障碍。心律失常和心力衰竭是导致过早死亡的主要原因。从 FA 的鼠模型的先前研究中，腺相关病毒（AAV）编码正常人类 frataxin 基因（AAVrh.10hFXN）可有效治疗疾病的心脏表现。然而，由于与毒性相关的高水平人 frataxin（hFXN）基因表达，治疗剂量窗受到限制。作为治疗目标，由于 FA 杂合子没有 FA 的临床症状，我们估计了将纯合子心脏转化为杂合子心脏所需的 frataxin（FXN）水平。在非心脏细胞中，FA 杂合子的正常 FXN 水平为 30-80%（17.7-47.2ng/mg，平均 32.5ng/mg），FA 纯合子为 2-30%正常水平（1.2-17.7ng/mg，平均 9.4ng/mg）。因此，AAV 载体需要将内源性 FA 纯合子中的 FXN 水平提高 >8.3ng/mg。为了确定 AAVrh.10hFXN 的所需剂量，我们通过静脉内（IV）给予肌肉肌酸激酶（mck）-Cre 条件性敲除小鼠 1.8×10、5.7×10 或 1.8×10 gc/kg 的 AAVrh.10hFXN，这是一种心脏和骨骼 FXN 敲除模型。最小有效剂量为 5.7×10 gc/kg，导致心脏 hFXN 水平为 6.1±4.2ng/mg，死亡率有轻度（与磷酸盐缓冲盐水对照相比， <0.01）改善。剂量为 1.8×10 gc/kg 时，心脏 hFXN 水平为 33.7±6.4ng/mg，射血分数和缩短分数明显改善（均 <0.05，两种比较），死亡率提高 21.5%（ <0.001）。为了确定 1.8×10 gc/kg 的显著有效剂量是否可以在大型动物中达到人类 FA 杂合子水平，我们通过 IV 将该剂量给予非人灵长类动物。12 周后，心脏中载体表达的 FXN 为 17.8±4.9ng/mg，与目标人类水平相当。这些数据确定了最小和显著有效的治疗剂量，这对治疗 FA 的心脏表现具有临床意义。
