Pharmacological Suppression of Rod Opsin as Therapy for Retinitis Pigmentosa

描述(申请人提供)：视网膜色素变性(RP)是一种遗传性视网膜疾病，影响10万美国人，是25-60岁成年人失明的主要原因。目前还没有被批准的治疗这种疾病的方法，基因治疗虽然很有希望，但因为潜在的基因突变的多样性而受到限制。视杆蛋白是光感受器外节高表达的主要蛋白质成分，其异常定位长期以来被认为是RP动物模型中光感受器细胞死亡之前的一个重要事件。最近，在两种睫毛病变的小鼠模型中，通过遗传方法减少视杆蛋白的表达被证明显著延缓了视网膜外核层感光细胞的快速丧失。Orphagen已经发现了一种以前未被探索的孤儿受体的特定小分子配体，该受体在光感受器层表达，对早期视网膜发育至关重要。在原代新生大鼠视网膜培养中，该受体的拮抗剂(IC50&lt；250 NM)以受体特异性的方式部分抑制视蛋白的表达。在大鼠玻璃体内注射后，我们目前的探针化合物也显著抑制视杆蛋白mRNA。研究结果表明，对同一受体的临床拮抗剂将降低约40%的RP患者的光感受器退行性变的发生率，其中视杆视蛋白的错误定位是导致视杆感光细胞死亡的一个因素。作为对PAR-09-260《神经系统小分子探针的优化》的响应，我们建议确定一种更有效的拮抗剂，这是体内原理验证所必需的 学习。每天连续两次玻璃体内注射5毫克的当前探针化合物，可导致视杆蛋白mRNA适度抑制25%。然而，目前的探针化合物的效力太低，无法开发一种实验性的缓释制剂，可以在四周内提供有效的眼内剂量，这一持续时间在许多啮齿动物RP模型中可测量地抑制光感受器退化。在目标1中，我们基于Orphagen开发的专利拮抗剂的三维计算模型，从商业化合物库中鉴定新的受体拮抗剂支架，以扩大后续药物化学的起点；在目标2中，我们进行重点药物化学以提高效力，目标是在原代视网膜培养中实现IC50和40 nM的视蛋白抑制；在目标3中，我们选择具有更高效力和效率的先导化合物(视杆蛋白mRNA抑制和玻璃体内注射30%)，并评估视网膜功能(通过ERG确定)以排除视网膜毒性。如果第一阶段SBIR的目标成功完成，我们计划在第二阶段研制出用于玻璃体内持续释放的先导受体拮抗剂，并在RP的啮齿动物模型上进行有效性和安全性研究，以证明开始开发这一临床使用的新药类别是合理的。

DESCRIPTION (provided by applicant): Retinitis pigmentosa (RP), a hereditary disease of the retina affecting 100,000 Americans, is the major cause of blindness in adults aged 25-60. There is no approved therapy for the disease and gene therapy, while promising, is limited because of the diversity of underlying genetic mutations. The abnormal localization of rod opsin, the highly-expressed major protein constituent of the photoreceptor outer segment, has long been recognized as a major event preceding photoreceptor cell death in animal models of RP. Recently, in two mouse models of ciliopathy, a reduction in rod opsin expression by genetic methods was shown to markedly delay what is otherwise a rapid loss of photoreceptors in the outer nuclear layer of the retina. Orphagen has discovered specific small molecule ligands to a previously unexplored orphan receptor that is expressed in the photoreceptor layer and is essential for early retinal development. In primary neonatal rat retinal cultures, antagonists (IC50 < 250 nM) to this receptor partially suppress rod opsin expression in a receptor-specific manner. After intravitreal injection in rats, our current probe compound also significantly suppresses rod opsin mRNA. The findings suggest that a clinical antagonist to the same receptor will reduce the rate of photoreceptor degeneration for the estimated 40% of RP patients where mislocalization of rod opsin is a factor in rod photoreceptor cell death. In response to PAR-09-260, Optimization of Small Molecule Probes for the Nervous System, we propose to identify a substantially more potent antagonist necessary for in vivo proof-of-principle studies. Two consecutive daily 5 mg intravitreal injections of the current probe compound cause a modest 25% suppression of rod opsin mRNA. However, the potency of the current probe compound is too low for development of an experimental slow release formulation that could deliver an effective intraocular dose over four weeks, a duration required to measurably inhibit photoreceptor degeneration in many rodent RP models. In Aim 1, we identify new receptor antagonist scaffolds, from commercial compound libraries, based on a 3-D computational model of the proprietary antagonists developed at Orphagen, in order to expand starting points for subsequent medicinal chemistry; in Aim 2, we carry out focused medicinal chemistry to increase potency with the goal of achieving an IC50 < 40 nM for rod opsin suppression in primary retinal cultures; and in Aim 3, we select a lead compound with improved potency and efficacy (rod opsin mRNA inhibition >30% at ¿ 1 mg/ intravitreal injection) and evaluate retinal function (determined by ERG) to exclude retinal toxicity. If Phase 1 SBIR aims are successfully completed, we plan in Phase 2 to formulate the lead receptor antagonist for sustained intravitreal release and to carry out efficacy and safety studies in rodent models of RP that would justify initiating development of this novel drug class for clinical use.