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

总结 胸苷激酶2（TK2）是一种线粒体酶，其执行顺序磷酸化中的第一个 生产脱氧胸苷三磷酸和脱氧胞苷三磷酸的步骤， 线粒体DNA合成。TK2的遗传缺陷导致线粒体DNA的消耗和线粒体DNA的丢失。 功能性线粒体这些事件导致TK2缺乏，这是一种表现为进行性的疾病 肌病，主要是骨骼肌和横膈膜，以及偶尔的神经系统疾病， 癫痫发作这种疾病最具侵略性的形式是在婴儿期发病，大多数幼儿在婴儿期死亡。 一年的诊断。 TK2缺乏症发病机制的阐明导致了两种潜在的治疗选择， 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使用脱氧胞苷和脱氧胸苷 (dC+dT）和分子旁路疗法由施用单磷酸dC和dT的组合组成。 单磷酸（dCMP+dTMP）。任一组合对均显示逆转疾病进展， 延长TK2缺乏症患者的生命。dC+dT的组合目前正在临床开发中 并且以非常高的剂量（每天约8至>50克）施用于患有以下病症的患者： 吞咽困难，其中一部分人需要进食管。此外，dC+dT提供以下益处： 底物增强疗法，但不是分子旁路疗法。 MitoRainbow正在进行MTR1的临床前开发，MTR1是一种单药二核苷酸， 所有四种治疗性化合物（dC、dT、dCMP和dTMP）在体内，从而提供了两种底物增强 和分子旁路疗法。MTR1通过肠胃外给药以口服给药的剂量的<1%给药。 dT+dC。预计该方法可提供上级生物利用度和易用性，以达到阈值 有效治疗TK2缺乏症。 在本直接至II期SBIR中，我们将（1）生产MTR1原料药（目标1），（2）进行临床前， 小型猪的非GLP PK和急性耐受性研究（目的2），和（3）进行IND使能生物分析、PK， 安全性研究（Aim 3）完成这些目标将为MitoRainbow提交IND提供足够的数据 与FDA合作，并在TK2缺乏症患者中启动MTR1制剂的临床研究。

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.