Repligen Corporation, Waltham, Massachusetts, United States of America.
PLoS One. 2013 May 17;8(5):e63958. doi: 10.1371/journal.pone.0063958. Print 2013.
Friedreich ataxia is a progressive neurodegenerative disorder caused by GAA triplet repeat expansions or point mutations in the FXN gene and, ultimately, a deficiency in the levels of functional frataxin protein. Heterozygous carriers of the expansion express approximately 50% of normal frataxin levels yet manifest no clinical symptoms, suggesting that therapeutic approaches that increase frataxin may be effective even if frataxin is raised only to carrier levels. Small molecule HDAC inhibitor compounds increase frataxin mRNA and protein levels, and have beneficial effects in animal models of FRDA.
METHODOLOGY/PRINCIPAL FINDINGS: To gather data supporting the use of frataxin as a therapeutic biomarker of drug response we characterized the intra-individual stability of frataxin over time, determined the contribution of frataxin from different components of blood, compared frataxin measures in different cell compartments, and demonstrated that frataxin increases are achieved in peripheral blood mononuclear cells. Frataxin mRNA and protein levels were stable with repeated sampling over four and 15 weeks. In the 15-week study, the average CV was 15.6% for protein and 18% for mRNA. Highest levels of frataxin in blood were in erythrocytes. As erythrocytes are not useful for frataxin assessment in many clinical trial situations, we confirmed that PBMCs and buccal swabs have frataxin levels equivalent to those of whole blood. In addition, a dose-dependent increase in frataxin was observed when PBMCs isolated from patient blood were treated with HDACi. Finally, higher frataxin levels predicted less severe neurological dysfunction and were associated with slower rates of neurological change.
CONCLUSIONS/SIGNIFICANCE: Our data support the use of frataxin as a biomarker of drug effect. Frataxin levels are stable over time and as such a 1.5 to 2-fold change would be detectable over normal biological fluctuations. Additionally, our data support buccal cells or PBMCs as sources for measuring frataxin protein in therapeutic trials.
弗里德赖希共济失调是一种进行性神经退行性疾病，由 FXN 基因中的 GAA 三核苷酸重复扩展或点突变引起，最终导致功能性 frataxin 蛋白水平降低。扩展的杂合子携带者表达约正常 frataxin 水平的 50%，但没有表现出临床症状，这表明即使 frataxin 仅升高至携带者水平，增加 frataxin 的治疗方法也可能有效。小分子 HDAC 抑制剂化合物可增加 frataxin mRNA 和蛋白水平，并在 FRDA 的动物模型中具有有益作用。
方法/主要发现：为了收集支持使用 frataxin 作为药物反应治疗生物标志物的数据，我们研究了 frataxin 随时间的个体内稳定性，确定了血液不同成分中 frataxin 的贡献，比较了不同细胞区室中的 frataxin 测量值，并证明了外周血单核细胞中可实现 frataxin 的增加。frataxin mRNA 和蛋白水平在 4 周和 15 周的重复采样中稳定。在 15 周的研究中，蛋白的平均 CV 为 15.6%，mRNA 的平均 CV 为 18%。血液中 frataxin 水平最高的是红细胞。由于在许多临床试验情况下红细胞对 frataxin 的评估没有用，因此我们证实 PBMC 和口腔拭子具有与全血相当的 frataxin 水平。此外，当用 HDACi 处理从患者血液中分离的 PBMC 时，观察到 frataxin 的剂量依赖性增加。最后，frataxin 水平越高，预测神经功能障碍越不严重，与神经变化的速度越慢相关。
结论/意义：我们的数据支持使用 frataxin 作为药物作用的生物标志物。frataxin 水平随时间稳定，因此在正常生物学波动范围内可检测到 1.5 到 2 倍的变化。此外，我们的数据支持口腔细胞或 PBMC 作为治疗试验中测量 frataxin 蛋白的来源。
