Substrate Reduction Therapies for Niemann-Pick C Disease

描述（由申请人提供）：溶酶体贮积症是由与内体-溶酶体系统相关的多种蛋白质缺陷引起的致命遗传性疾病。尼曼-皮克C型（NPC）病是一种胆固醇-鞘糖脂（GSL）储存障碍，最常见的原因是NPC1和NPG2的缺陷。NPC1是一种跨膜蛋白，被认为对溶酶体底物的后吞运输至关重要，NPG2是一种功能未知的可溶性溶酶体蛋白。缺乏任何一种蛋白质都会导致一种基本相同的情况，即受影响的儿童从4-6岁开始出现进行性神经衰退，并在生命的第二个十年发生死亡。在治疗方面的一个重要观察是，受影响的儿童通常在出生时表现正常，只有在细胞内储存和代谢紊乱超过阈值后，才会出现临床症状。这一重要特征表明，出生后存在一个机会之窗，旨在纠正代谢缺陷的治疗可能会将细胞从疾病命运中拯救出来，从而改善或预防脑功能障碍。然而，鼻咽癌疾病的治疗选择非常有限，酶替代和细胞介导的治疗几乎没有带来益处的希望，特别是对于NPC1缺乏症，因为这种蛋白质不是由细胞分泌的。由于缺乏细胞间NPC1蛋白的转移，即使基因治疗也可能只对转导细胞有益。这些明显的限制推动了一种新的治疗选择的发展——可以限制有害底物在大脑和其他器官中积累的药物——被称为底物减少疗法（SRT）。最初的方法是一种GSL合成的小分子抑制剂（N-butyldeoxnorjirimycin, Zavesca），我们率先将其作为鼻咽癌的治疗方法。最近的一项发现表明，一种天然存在的化合物，即胆固醇衍生的神经类固醇异孕烷醇酮（ALLO），在鼻咽癌中具有类似的限制溶酶体储存的能力。虽然ALLO能够实现这种效果的机制尚不清楚，但最近的研究结果表明，它的一个关键特征是它能够作为妊娠X受体（PXR）的配体，从而对许多基因施加转录控制，包括那些控制固醇合成的基因。我们研究的总体目标是通过鼻咽癌小鼠模型优化SRT药物的给药和疗效，测试更多的候选pxr配体化合物，并确定它们对胆固醇和GSL积累的影响，并确定联合使用SRT药物是否会在延缓和/或预防鼻咽癌疾病的临床恶化方面产生更大的疗效。除了测试与NPC影响儿童直接和实际相关的治疗方法外，这些研究还将进一步探索GSLs储存与NPC疾病中胆固醇之间的联系及其与NPC1和NPC2蛋白功能的关系。

DESCRIPTION (provided by applicant): Lysosomal storage disorders are fatal genetic diseases caused by defects in a wide range of proteins associated with the endosomal-lysosomal system. Niemann-Pick type C (NPC) disease is a cholesterol- glycosphingolipid (GSL) storage disorder caused most commonly by defects in NPC1, a transmembrane protein believed critical in retroendocytic trafficking of substrates from lysosomes, and in NPG2, a soluble lysosome protein of unknown function. Absence of either protein causes an essentially identical condition with affected children exhibiting progressive neurological decline beginning at 4-6 years of age and with death occurring in the second decade of life. An important observation in terms of therapy is that affected children most often appear normal at birth and only later, after a threshold of intracellular storage and metabolic disruption has been exceeded, do clinical symptoms develop. This important feature indicates that there is a window of opportunity after birth when therapy aimed at correction of the metabolic defect could potentially rescue cells from their disease fate and thereby ameliorate or prevent brain dysfunction. Therapeutic options for NPC disease, however, are very limited, with enzyme replacement and cell-mediated therapies providing little hope of benefit, particularly for NPC1 deficiency since this protein is not secreted by cells. Even gene therapy will likely only be beneficial to transduced cells again due to the lack of transfer of the NPC1 protein between cells. These clear limitations have driven development of a new therapeutic option - drugs that can limit the build-up of offending substrates in brain and other organs - known as substrate reduction therapy (SRT). An initial approach here was a small molecule inhibitor of GSL synthesis (N-butyldeoxnorjirimycin, Zavesca(r)) which we pioneered as a therapy for NPC disease. A more recent finding suggests that a naturally occurring compound, the cholesterol-derived neurosteroid known as allopregnanolone (ALLO), has a similar ability to limit lysosomal storage in NPC disease. While the mechanism by which ALLO is able to achieve this effect is unknown, recent findings suggest a critical feature is its ability to act as a ligand for the pregnane X receptor (PXR) and thereby to exert transcriptional control over numerous genes, including those controlling sterol synthesis. The overall goals of our study are to optimize the administration and efficacy of SRT agents using the NPC mouse models, to test an expanded number of candidate PXR-ligand compounds and determine their effects, on cholesterol and GSL accumulation, and to determine whether the-use of SRT agents in combination will lead to even greater efficacy in delaying and/or preventing clinical deterioration in NPC disease. In addition to testing therapies of direct and practical relevance to NPC-affected children, these studies will also further explore the linkage between storage of GSLs and cholesterol in NPC disease and their relationship to NPC1 and NPC2 protein function.