Optimizing analgesia by exploiting CB2 agonist functional selectivity

描述(申请人提供)：这是一项研究是否可以利用CB2大麻素受体激动剂的功能选择性来寻找更具体和有效的CB2受体激动剂治疗慢性疼痛的建议。功能选择性(也称为偏向激动论和配基导向转运)是受体信号转导的一种日益受到重视的特性。当一种功能选择性激动剂与能够激活多条信号通路的受体结合时，这些通路中只有一部分被激活，或者激活特定通路的等级顺序效力因激动剂而异。大多数G蛋白偶联受体(GPCRs)参与多种信号通路，为功能选择性提供了许多机会。功能选择性具有实质性的治疗意义。如果应用得当，它可能允许激活有利于治疗特定疾病的特定通路，同时避免激活可能导致不良副作用的通路。因此，功能选择性为GPCR激动剂增加了效力、亚型选择性和内在有效性之外的另一个维度--一个可用于治疗效益的维度。在对CB2受体信号的初步研究中，我们发现几类CB2激动剂具有显著的功能选择性。例如，CB2激动剂的氨基烷基吲哚家族成员激活了几个CB2信号通路，但未能抑制电压依赖性钙通道或内化CB2受体。这种程度的功能选择性无论从机制上还是治疗上都是重要的。从机制上讲，它为我们提供了在特定疼痛状态下识别CB2介导的止痛的信号通路的可能性。在治疗方面，它为我们提供了根据其功能选择性设计可能对疼痛有效的药物的可能性，同时减少了产生不良影响的可能性。该提案将通过两个特定的目标来评估CB2激动剂的功能选择性的治疗潜力。第一个具体目标将完成目前可用的CB2激动剂的信号特征，包括临床失败的CB2激动剂，使用一组生化和基于细胞的功能分析。第二个具体目标是采用体外试验中功能选择性最显著的三种化合物，并使用CB1受体敲除小鼠来检验它们在神经病理性(紫杉醇和脊神经结扎)和炎症性(完全弗氏佐剂)疼痛临床前模型中的有效性。这些功能性选择性CB2激动剂的疗效将与“平衡”的CB2激动剂(CP55,940)进行比较，后者以类似的程度激活所有测试的信号通路(见研究战略中的表1)。这些特定目标的完成将使我们全面了解功能选择性如何有助于CB2配体的治疗效果，并提供丰富的CB2信号的药理学特征，这对于未来评估CB2激动剂的其他治疗适应症至关重要。

DESCRIPTION (provided by applicant): This is a proposal to investigate if CB2 cannabinoid receptor agonist functional selectivity can be exploited to identify more specific and effective CB2 receptor agonists for the treatment of chronic pain. Functional selectivity (also known as biased agonism and ligand-directed trafficking) is an increasingly appreciated property of receptor signaling. When a functionally selective agonist binds to a receptor capable of activating multiple signaling pathways, only a subset of those pathways are activated, or the rank order potency of activating specific pathways varies among agonists. Most G protein-coupled receptors (GPCRs) engage multiple signaling pathways, offering many opportunities for functional selectivity. Functional selectivity has substantial therapeutic implications. Properly applied, it may allow activation of specific pathways that are beneficial for treating a specific condition, while avoiding activation of pathways that may contribute to unwanted side effects. Thus, functional selectivity adds another dimension beyond potency, subtype selectivity and intrinsic efficacy to GPCR agonists-a dimension that may be exploited for therapeutic benefit. In preliminary studies examining CB2 receptor signaling we identified striking functional selectivity in several classes of CB2 agonists. For example, members of the aminoalkylindole family of CB2 agonists activated several CB2 signaling pathways, but failed to inhibit voltage dependent calcium channels or internalize CB2 receptors. This degree of functional selectivity is important for both mechanistic and therapeutic reasons. Mechanistically, it offers us the possibility of identifying the signaling pathways underlying CB2-mediated analgesia in specific pain states. Therapeutically, it offers us the possibility of designing drugs that may be efficacious for pain based upon their functional selectivities, while lessening the possibility of undesired effects. Ths proposal will evaluate the therapeutic potential of functional selectivity of CB2 agonists through two specific aims. The first specific aim will complete the characterization of the signaling of currently available CB2 agonists, including CB2 agonists that have failed clinically, using a battery of biochemical and cell-based functional assays. The second specific aim will take the three compounds with the most striking functional selectivity in the in vitro assays and examine their efficacy in preclinical models of neuropathic (paclitaxel and spinal nerve ligation) and inflammatory (complete Freund's adjuvant) pain using CB1 receptor knockout mice. Efficacy of these functional selective CB2 agonists will be compared to a "balanced"-CB2 agonist (CP55,940) that activates all tested signaling pathways to a similar extent (see Table 1 in Research Strategy). Completion of these specific aims will give us a comprehensive understanding on how functional selectivity contributes to the therapeutic efficacy of CB2 ligands and also provide a rich pharmacological characterization of CB2 signaling that will be crucial for the future evaluation of CB2 agonists for other therapeutic indications.