MTR1: A Dinucleotide Substrate Enhancement and Molecular ByPass Therapy for Thymidine Kinase 2 Deficiency

摘要 胸苷激酶2(TK2)是一种线粒体酶，它执行第一个顺序的磷酸化 产生脱氧胸苷三磷酸和脱氧胞苷三磷酸的步骤，这是 线粒体DNA合成。TK2的遗传缺陷导致线粒体DNA枯竭和基因缺失 功能线粒体。这些事件导致TK2缺乏，这是一种进行性疾病 肌病，主要是骨骼肌和横隔肌，以及偶尔的神经疾病，如 癫痫发作。这种疾病最具侵袭性的形式是在婴儿时期发病，这些蹒跚学步的孩子大多在 一年的诊断。 对TK2缺乏症发病机制的阐明导致了两种潜在的治疗方案被评估 根据同情使用计划：(1)底物增强治疗和(2)分子旁路治疗。 底物增强疗法包括联合应用脱氧胞苷和脱氧胸苷 (DC+DT)和分子旁路治疗包括联合应用DC单磷酸盐和DT 单磷酸盐(dCMP+DTMP)。任何一对组合都被证明可以逆转疾病的进展，并 延长TK2缺乏症患者的生命。DC+DT的联合治疗目前正处于临床研究阶段 在患有以下疾病的患者中以非常高的剂量(每天约8克至50克不等)服用 吞咽困难，其中一部分需要喂食管才能进食。此外，DC+DT还具有以下优势 底物增强疗法，但不是分子旁路疗法。 MitoRain博正在进行MTR1的临床前开发，MTR1是一种单剂二核苷酸，其代谢产物 所有四种治疗化合物(DC，dT，dCMP和DTMP)都在体内，因此提供了两种底物增强 和分子搭桥疗法。MTR1按口服剂量的1%通过肠外给药给药 DT+DC。这种方法有望提供卓越的生物利用度和易用性，以达到阈值 治疗TK2缺乏症的有效性。 在这项直接到第二阶段的SBIR中，我们将(1)制造MTR1药物物质(目标1)，(2)进行临床前， 非GLP PK和小型猪急性耐受性研究(目标2)，以及(3)进行启用IND的生物分析，PK， 和安全研究(目标3)。这些目标的完成将为MitoRain博提交IND提供足够的数据 与FDA合作，并启动对TK2缺乏症患者MTR1药物产品的临床研究。

SUMMARY Thymidine Kinase 2 (TK2) is a mitochondrial enzyme that performs the first of the sequential phosphorylation steps that produce deoxythymidine triphosphates and deoxycytidine triphosphates, which are required for mitochondrial DNA synthesis. Genetic deficiency of TK2 results in depletion of mitochondrial DNA and loss of functional mitochondria. These events result in TK2 deficiency, a disease that manifests as progressive myopathy, primarily of skeletal muscle and the diaphragm, and occasional neurological disorders such as seizures. The most aggressive form of the disease has its onset in infancy, and most of these toddlers die within a year of diagnosis. Elucidation of the pathogenesis of TK2 deficiency has led to two potential treatment options that were evaluated under a compassionate use program: (1) substrate enhancement therapy and (2) molecular bypass therapy. Substrate enhancement therapy consists of administering combinations of deoxycytidine and deoxythymidine (dC+dT) and molecular bypass therapy consists of administering combinations of dC monophosphate and dT monophosphate (dCMP+dTMP). Either combination pair was shown to reverse disease progression and lengthen the lives of patients with TK2 deficiency. The combination of dC+dT is currently in clinical development and is administered at very high doses (ranging from approximately 8 to >50 grams daily) in patients who have difficulty swallowing, a subset of whom require feeding tubes to eat. Furthermore, dC+dT offers the benefit of substrate enhancement therapy, but not molecular bypass therapy. MitoRainbow is pursuing preclinical development of a MTR1, a single-agent dinucleotide that is metabolized to all four therapeutic compounds (dC, dT, dCMP and dTMP) in vivo, thus providing both substrate enhancement and molecular bypass therapies. MTR1 is administered by parenteral administration at <1% the dose of oral dT+dC. This approach is anticipated to provide superior bioavailability and ease of use to reach the threshold of effectiveness to treat TK2 deficiency. In this Direct-to-Phase II SBIR we will (1) manufacture MTR1 drug substance (Aim 1), (2) perform a preclinical, non-GLP PK, and acute tolerability study in minipigs (Aim 2), and (3) conduct IND-enabling bioanalytical, PK, and safety studies (Aim 3). Completion of these Aims will provide sufficient data for MitoRainbow to file an IND with the FDA, and to initiate clinical investigations of MTR1 drug product in patients with TK2 deficiency.