Pharmacological Suppression of Rod Opsin as Therapy for Retinitis Pigmentosa

描述（由申请人提供）：视网膜色素变性（RP）是一种影响10万美国人的视网膜遗传性疾病，是25-60岁成人失明的主要原因。目前还没有批准的治疗方法，基因治疗虽然有希望，但由于潜在基因突变的多样性而受到限制。视杆细胞视蛋白是感光细胞外节的主要蛋白成分，其异常定位长期以来被认为是RP动物模型中感光细胞死亡前的主要事件。最近，在两个小鼠模型的睫状体病，减少视杆细胞视蛋白表达的遗传方法被证明显着延迟，否则是一个快速损失的光感受器在视网膜的外核层。Orphagen发现了一种以前未发现的孤儿受体的特异性小分子配体，该受体在感光层中表达，对早期视网膜发育至关重要。在原代新生大鼠视网膜培养物中，该受体的拮抗剂（IC 50 < 250 nM）以受体特异性方式部分抑制视杆视蛋白表达。在大鼠中玻璃体内注射后，本发明的探针化合物也显著抑制视杆视蛋白mRNA。研究结果表明，相同受体的临床拮抗剂将降低估计40%的RP患者的感光细胞变性率，其中视杆视蛋白的错误定位是视杆细胞死亡的一个因素。为了响应PAR-09-260，神经系统小分子探针的优化，我们建议确定一种体内原理验证所需的更有效的拮抗剂 问题研究连续两次每天5 mg玻璃体内注射本发明探针化合物导致视杆视蛋白mRNA的适度25%抑制。然而，目前的探针化合物的效力对于开发可以在四周内递送有效眼内剂量的实验性缓释制剂来说太低，这是在许多啮齿动物RP模型中可测量地抑制光感受器变性所需的持续时间。在目标1中，我们基于在Orphagen开发的专有拮抗剂的3-D计算模型，从商业化合物库中鉴定新的受体拮抗剂支架，以便扩展后续药物化学的起点;在目标2中，我们进行集中的药物化学以增加效力，目标是在原代视网膜培养物中实现对于视杆视蛋白抑制的IC 50 < 40 nM;在目标3中，我们选择了具有改善的效力和功效的先导化合物（在〜 lmg/玻璃体内注射时视杆视蛋白mRNA抑制>30%）并评估视网膜功能（通过ERG测定）以排除视网膜毒性。如果1期SBIR目标成功完成，我们计划在2期制定用于玻璃体内缓释的主要受体拮抗剂，并在RP的啮齿动物模型中进行有效性和安全性研究，这将证明启动开发这种新型药物用于临床。

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.