A Pilot Study to Evaluate the Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of escalating multiple oral doses of AG-348 in subjects with stable sickle cell disease

镰状细胞病（SCD）是一种多系统疾病，与急性临床事件和进行性器官损害有关。由镰状红细胞引起的微血管闭塞引发的发作性疼痛是最常见的急性并发症，也是住院治疗的主要原因。SCD的管理策略发展非常缓慢，急性疼痛的治疗仍然限于阿片类药物的支持治疗。直到2017年，唯一批准的SCD疗法是羟基脲（HU），用于降低急性疼痛危象的频率，但并非普遍有效。除HU外，正常红细胞输注被广泛用于治疗严重镰状危象，但该策略具有局限性（无法统一获得，伴有同种免疫、溶血性输血反应和输血铁过载的风险）。唯一的治愈性治疗是骨髓移植，但这种选择具有很大的风险，并受到组织相容性供体的限制。 由于SCD的根本原因是脱氧-HbS的聚合，因此有很强的理由探索可以抑制/减少聚合过程本身的试剂。HbS仅在脱氧时聚合，其氧合受几个因素影响，一个关键因素是红细胞中的2，3-二磷酸甘油酸（2，3-DPG）浓度。 增加的细胞内2，3-DPG降低氧结合并稳定血红蛋白的脱氧形式（T形式）。此外，增加的2，3-DPG浓度降低细胞内红细胞pH，进一步促进HbS聚合。2，3-DPG是糖酵解途径中的中间底物，是红细胞中ATP产生的唯一来源。丙酮酸激酶（PK）是糖酵解最后一步的关键酶; PK将磷酸烯醇丙酮酸转化为丙酮酸，产生50%的总红细胞ATP，这是维持红细胞膜完整性所必需的。降低的PK活性导致上游酶底物的积累，包括2，3-DPG，其有利于脱氧-HbS的聚合。在患有SCD的人中，甚至在通常无症状的镰状携带者中，降低的氧亲和力将有利于HbS的脱氧及其聚合，从而镰状化。事实上，PK缺陷和镰状细胞性状的组合导致急性镰状综合征先前已在两个病例中报道。 目前减少HbS聚合的方法包括通过多种策略诱导胎儿血红蛋白和通过增加血红蛋白对氧的亲和力靶向HbS聚合的药物（例如，Voxelotor /GBT 440）。增加红细胞PK（PK-R）活性，导致细胞内2，3-DPG浓度降低，为阻碍HbS聚合和急性镰状疼痛提供了潜在的有吸引力的治疗靶点。AG-348是一种新型的口服生物可利用的PK-R小分子变构激活剂，最近被FDA批准用于治疗丙酮酸激酶缺乏症。临床前AG-348数据和其他数据的概述支持血液糖酵解中间体的剂量依赖性变化，这与在所有多次递增剂量下检测的糖酵解途径激活一致，支持AG-348在治疗镰状细胞病中的潜在作用。本研究的总体目的是确定AG-348在SCD受试者中的临床安全性和耐受性。

Sickle cell disease (SCD) is a multisystem disorder associated with episodes of acute clinical events and progressive organ damage. Episodic pain, triggered by micro-vasoocclusion induced by sickled red blood cells, is the most common acute complication and the leading cause of hospitalization. Management strategies for SCD have evolved very slowly, and treatment of acute pain is still limited to supportive therapy with opioid medication. Until recently in 2017, the only approved therapy for SCD was hydroxyurea (HU), indicated to reduce frequency of acute painful crises but not universally effective. In addition to HU, transfusions with normal red blood cells are widely used to treat severe sickle crises, but this strategy has limitations (not uniformly accessible, accompanied by risks of alloimmunization, hemolytic transfusion reactions and transfusional iron overload). The only curative treatment is bone marrow transplantation, but this option carries significant risks and is limited by the availability of histocompatible donors. As the root cause of SCD is polymerization of deoxy-HbS, there is a strong rationale for exploring agents that could inhibit/reduce the polymerization process itself. HbS polymerizes only when deoxygenated, its oxygenation is influenced by a few factors, one key factor being the 2,3- diphosphoglycerate (2,3-DPG) concentration in the red blood cell. Increased intracellular 2,3-DPG decreases oxygen binding and stabilizes the deoxygenated form (T form) of hemoglobin. In addition, increased 2,3-DPG concentration decreases intracellular red cell pH further promoting HbS polymerization. 2,3-DPG is an intermediate substrate in the glycolytic pathway, the only source of ATP production in red blood cells. Pyruvate kinase (PK) is a key enzyme in the final step of glycolysis; PK converts phosphoenolpyruvate to pyruvate, creating 50% of the total red cell ATP that is essential for maintaining integrity of the red cell membrane. Reduced PK activity leads to accumulation of the upstream enzyme substrates, including 2,3-DPG, that favours polymerization of deoxy-HbS. In humans with SCD, and even in sickle carriers who are generally asymptomatic, reduced oxygen affinity will favour deoxygenation of HbS and its polymerisation, and thus sickling. Indeed, the combination of PK deficiency and sickle cell trait causing an acute sickling syndrome has been previously reported in two cases. Current approaches to reduce HbS polymerization include fetal haemoglobin induction via multiple strategies and drugs that targets HbS polymerization through increasing affinity of hemoglobin for oxygen (eg. Voxelotor / GBT440). Increasing red cell PK (PK-R) activity, leading to a decrease in intracellular 2,3-DPG concentration, presents a potentially attractive therapeutic target for thwarting HbS polymerization and acute sickle pain. AG-348 is a novel, orally bioavailable, small molecule allosteric activator of PK-R, that was recently FDA approved for the treatment of pyruvate kinase deficiency. Overview of the preclinical AG-348 data and other data support dose-dependent changes in blood glycolytic intermediates consistent with glycolytic pathway activation at all multiple ascending doses tested, supporting the potential role of AG-348 in the treatment of sickle cell disease. The overall objective of the present study is to determine the clinical safety and tolerability of AG-348 in subjects with SCD.