Selective targeting of sodium channel blockers to pain-sensing neurons

描述(由申请人提供)：疼痛是通过在被称为伤害性感受器的特定群体的初级感觉神经元中产生动作电位来发出信号的。在不丧失意识的情况下，最有效的止痛形式是通过给药局部麻醉剂，这种麻醉剂通过抑制电压依赖的钠通道从而抑制电兴奋性而起作用。临床上使用的局部麻醉剂是至少部分以疏水、不带电的形式存在的分子，可以通过细胞膜进入神经元。这些麻醉剂进入并抑制所有神经元的兴奋性，而不仅仅是伤害性感受器，因此除了阻断疼痛外，还可能产生许多不良影响(包括瘫痪和自主神经信号传导受阻)。这项拟议的研究是基于最近的一项发现，即通过将利多卡因(QX-314)的永久带电衍生物(QX-314)与TRPV1通道激动剂辣椒素共同应用，可以选择性地将钠通道阻断药物靶向伤害性感受器。该提案中的初步数据支持的基本假设是，QX-314可以通过TRPV1通道形成的孔进入伤害性感受器。这项拟议研究的总体目标是确定TRPV1激动剂和带电钠通道阻滞剂的组合，以优化伤害性感觉神经元的兴奋性阻断。要解决的具体问题包括：带电的钠通道阻滞剂有效进入的大小限制是多少？阻滞剂进入的时间进程如何取决于TRPV1激动剂的性质和浓度？蛋白激酶C的激活能增强阻滞剂的进入和蓄积吗？是否有TRPV1激动剂允许QX-314进入而不首先刺激动作电位的激发？细胞内QX-314阻断已知对伤害性感受器兴奋性很重要的不同类型的钠通道的相对效力是什么？这些问题将通过对大鼠背根神经节神经元中天然TRPV1通道和钠通道的膜片钳实验来解决，并使用克隆的TRPV1通道的异源表达进行额外的实验。这些机制的特征应该有助于开发基于带电钠通道阻滞剂靶向进入痛觉神经元的新的止痛临床治疗方法。这样的治疗对于分娩、手术和牙科手术中更具选择性的疼痛缓解应该是非常有利的，可能对某些形式的慢性神经源性疼痛也是如此。公共卫生相关性：这项研究的目标是开发一种新的疼痛治疗方法，其基础是选择性地将钠通道阻断药物靶向疼痛感觉神经元。通过将永久带电的利多卡因衍生物与TRPV1通道激动剂辣椒素共同应用，可以阻断痛觉神经元的电兴奋，但不能阻断其他类型神经元的电兴奋，从而避免传统局部麻醉所发生的运动性瘫痪和自主神经纤维堵塞。除了允许特定疼痛的局部麻醉(例如，用于牙科手术和小手术)外，这可能会改善分娩和胸部手术的硬膜外麻醉，并可能改善某些形式的慢性神经性疼痛的治疗。

DESCRIPTION (provided by applicant): Pain is signaled by generation of action potentials in a specific population of primary sensory neurons known as nociceptors. The most effective form of pain relief without loss of consciousness is provided by administration of local anesthetics, which act by inhibiting voltage-dependent sodium channels and thereby depressing electrical excitability. Clinically-used local anesthetics are molecules that exist at least partially in a hydrophobic, uncharged form that can enter neurons through the cell membrane. These anesthetics enter and inhibit excitability in all neurons, not just nociceptors, and thus can have many undesirable effects (including paralysis and block of autonomic signaling) in addition to blocking pain. The proposed research is based on a recent finding that sodium channel blocking drugs can be targeted selectively to nociceptors by co-applying a permanently charged derivative of lidocaine (QX- 314) with capsaicin, an agonist for TRPV1 channels. The underlying hypothesis, supported by the preliminary data in the proposal, is that QX-314 can enter nociceptors by passing through the pore formed by TRPV1 channels. The overall goal of the proposed research is to identify combinations of TRPV1 activators and charged sodium channel blockers that optimize the block of excitability of nociceptive sensory neurons. Specific questions to be addressed include: What is the size limit for effective entry of charged sodium channel blockers? How does the time course of blocker entry depend on the nature and concentration of the TRPV1 agonist? Can blocker entry and accumulation be enhanced by activation of protein kinase C? Are there TRPV1 agonists that allow QX-314 entry without first stimulating firing of action potentials? What is the relative potency of intracellular QX-314 for blocking the different types of sodium channels known to be important for excitability of nociceptors? These questions will be addressed using patch clamp experiments on native TRPV1 channels and sodium channels in rat dorsal root ganglion neurons, with additional experiments using heterologous expression of cloned TRPV1 channels. Characterizing these mechanisms should facilitate the development of new clinical treatments for pain relief based on the targeted entry of charged sodium channel blockers into pain-sensing neurons. Such treatments should be highly advantageous for more selective pain relief in childbirth, surgery, and dental procedures and possibly for some forms of chronic neurogenic pain. PUBLIC HEALTH RELEVANCE: The goal of the research is to develop a new treatment for pain based on selective targeting of sodium channel blocking drugs to pain-sensing neurons. By co-applying a permanently charged lidocaine derivative with capsaicin, an agonist for TRPV1 channels, it is possible to block electrical excitability in pain-sensing neurons but not in other types of neurons, thus avoiding the motor paralysis and block of autonomic fibers that occurs with conventional local anesthesia. Besides allowing pain-specific local anesthesia (e.g. for dental procedures and minor surgery), this may lead to improved epidural anesthesia in childbirth and thoracic surgery and possibly improved treatments for some forms of chronic neuropathic pain.