Selective targeting of sodium channel blockers to pain-sensing neurons

描述（由申请人提供）：疼痛是通过在称为伤害感受器的特定初级感觉神经元群中产生动作电位来发出信号的。在不丧失意识的情况下，最有效的止痛方式是局部麻醉剂，它通过抑制电压依赖性钠通道，从而抑制电兴奋性来起作用。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，它们可以通过细胞膜进入神经元。这些麻醉药进入并抑制所有神经元的兴奋性，而不仅仅是伤害感受器，因此除了阻断疼痛外，还会产生许多不良影响（包括瘫痪和自主神经信号的阻断）。这项研究是基于最近的一项发现，通过将永久带电的利多卡因衍生物（QX- 314）与辣椒素（TRPV1通道的激动剂）共同应用，钠通道阻断药物可以选择性地靶向伤害感受器。提案中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感受器。本研究的总体目标是确定TRPV1激活剂和带电钠通道阻滞剂的组合，以优化对伤害感觉神经元兴奋性的阻断。需要解决的具体问题包括：带电钠通道阻滞剂有效进入的尺寸限制是多少？阻滞剂进入的时间如何取决于TRPV1激动剂的性质和浓度？阻断剂的进入和积累是否可以通过激活蛋白激酶C来增强？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阻断不同类型的钠通道的相对效力是什么？这些钠通道已知对伤害感受器的兴奋性很重要。这些问题将通过膜片钳实验对大鼠背根神经节神经元的天然TRPV1通道和钠通道进行研究，并利用克隆TRPV1通道的异源表达进行实验。表征这些机制将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疼痛缓解的新临床治疗方法。这种治疗方法对于分娩、外科手术和牙科手术中的选择性疼痛缓解非常有利，也可能适用于某些形式的慢性神经性疼痛。公共卫生相关性：该研究的目标是开发一种基于钠通道阻断药物选择性靶向痛觉神经元的疼痛新治疗方法。通过将永久带电的利多卡因衍生物与辣椒素（TRPV1通道的激动剂）共同应用，可以阻断痛觉神经元的电兴奋性，但不能阻断其他类型的神经元，从而避免传统局部麻醉时发生的运动麻痹和自主神经纤维阻滞。除了允许特定疼痛的局部麻醉（例如牙科手术和小手术），这可能会改善分娩和胸外科手术的硬膜外麻醉，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.