Mechanism of Action of L THP as an Alternative Therapy for Cocaine Addiction

描述(申请人提供)：可卡因成瘾是一个令人烦恼的公共卫生问题，目前还没有有效的药物治疗方法。天然衍生的生物活性化合物是现代药物开发的丰富来源。在中华儿科研究中心资助的项目“酒精和药物滥用的替代疗法”(P01-AT-002038)的资助下，从延胡索的块茎中分离并鉴定了包括L-延胡索乙素在内的8种异喹啉生物碱。延胡索是中国治疗鸦片吸烟150多年的中草药之一。有趣的是，L四氢叶酸在中国的临床上已经使用了30多年，作为一种具有镇静/催眠作用的止痛药，最近被用于治疗海洛因成瘾。在动物模型中，L-THP降低了可卡因的增强作用和戒断后寻求可卡因的恢复。重要的是，L-THP本身没有奖励效应，表明没有滥用责任。最近，马里兰大学的王家贝博士获得了美国国立卫生研究院的资助，将在美国进行L-THP治疗可卡因成瘾的临床试验。尽管L-雷公藤多苷的临床应用历史悠久，但其作用机制尚不清楚。虽然一些体内效应似乎是由多巴胺受体介导的，但我们发现L-THP对五种亚型(D1-D5)的DA受体的亲和力很低或没有亲和力(见C.1.2)。此外，它没有结合我们筛选的大约60个神经递质受体、离子通道和涉及痛觉调制和药物成瘾的转运体(见C.1.2)。在小鼠和大鼠灌胃给药后，我们发现血清中的主要代谢物为去甲基化类似物L-延胡索碱(L-CP)和L-延胡索乙胺(L-CD)，而L-异可比林(L-ICP)为次要代谢物(见C.1.3)。我们还发现，L-ICP对DA受体具有中到高的亲和力(见C.1.4)，并能降低可卡因诱导的多动、行为敏感化和条件性位置偏爱(见C.1.5-1.8)。因此，我们推测L-THP是一种前药，其作用机制是通过作用于多个DA受体的去甲基化代谢物来调节可卡因诱导的行为。因此，我们建议对L-THP及其去甲基化代谢物进行进一步的药理学研究，以更好地了解其作用机制。我们的具体目标是(1)制备并化学合成足够数量的L-THP及其代谢物，用于药理研究；(2)测定L-THP的代谢和药代动力学；(3)鉴定主要代谢物对DA受体和其他靶点的药理活性；(4)检测L-THP及其代谢物对可卡因自身给药和戒断后恢复用药的影响。本研究将加深对L-THP作用机制的认识，为基于机制的可卡因成瘾药物开发开辟新的途径。由于L-THP的主要副作用之一是镇静，我们拟议的研究可能会产生镇静较少的候选药物，就像我们在L-ICP中所展示的那样。

DESCRIPTION (provided by applicant): Cocaine addiction is a vexing public health problem for which no effective pharmacotherapies have been developed. Naturally derived bioactive compounds have been a rich source for modern drug development. Under our CERC program project "Alternative Therapies for Alcohol and Drug Abuse" (P01-AT- 002038) funded by NCCAM, eight isoquinoline alkaloids, including L-tetrahydropalmatine (L-THP), were isolated and characterized from tubers of Corydalis yanhuso, which is one of the five components of an herbal remedy (NPI-025) used in China to treat opium smoking for over 150 years. Interestingly, L-THP has been used clinically in China for more than 30 years as an analgesic with sedative/hypnotic properties and recently to treat heroin addiction. In animal models, L-THP reduced reinforcing property of cocaine and reinstatement of cocaine seeking following withdrawal. Importantly, L-THP itself had no rewarding effect, suggesting absence of abuse liability. Recently, Dr. Jia-Bei Wang of the University of Maryland received an NIH grant to conduct a clinical trial on L-THP for treatment of cocaine addiction in the US. Despite its long history of clinical use, the mechanisms of action of L-THP are not clear. Although some in vivo effects appear to be mediated by dopamine receptors, we found that L-THP had low or no affinity for the five subtypes (D1- D5) of DA receptors (see C.1.2). In addition, it did not bind t about 60 neurotransmitter receptors, ion channels, and transporters involved in pain modulation and drug addiction that we screened (see C.1.2). Following L-THP administration in mice or rats, we identified in serum the mono-demethylated analogs L- corypalmine (L-CP) and L-corydalmine (L-CD) to be the major metabolites and L-isocorypalmine (L-ICP) to be a minor metabolite (see C.1.3). We also found that L-ICP had moderate to high affinity for DA receptors (see C.1.4) and reduced cocaine-induced hyperlocomotion, behavioral sensitization and conditioned place preference (See C.1.5-1.8). Thus, we hypothesize that L-THP is a prodrug and its effects are due to demethylated metabolites acting on multiple DA receptors to modulate cocaine-induced behaviors. Consequently, we propose to further pharmacologically characterize L-THP and its demethylated metabolites to gain a better understanding of the mechanisms of action. Our specific aims are to (1) prepare L-THP and chemically synthesize its metabolites in sufficient quantity for pharmacological studies; (2) determine the metabolism and pharmacokinetic profiles of L-THP; (3) identify pharmacological activity of major metabolites at DA receptors and other targets; and (4) examine the effects of L-THP and its metabolites on cocaine self administration and reinstatement of drug seeking following withdrawal. The proposed research will enhance the understanding of mechanisms of action of L-THP, which may open a new avenue for mechanism-based drug discovery for cocaine addiction. As one of the major side effects of L-THP is sedation, our proposed study may yield candidate drugs with less sedation, as we have demonstrated for L-ICP.