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

描述（由申请人提供）：可卡因成瘾是一个令人烦恼的公共卫生问题，迄今尚未开发出有效的药物疗法。天然衍生的生物活性化合物已成为现代药物开发的丰富来源。我们的CERC项目“酒精和药物滥用的替代疗法”（P01-AT- 002038）由NCCAM资助，从杨胡连块茎中分离出8种异喹啉生物碱，包括l -四氢棕榈碱（L-THP），这是中国用于治疗鸦片吸烟的草药（NPI-025）的五种成分之一，已有150多年的历史。有趣的是，在中国临床上，L-THP作为一种具有镇静/催眠特性的镇痛药已经使用了30多年，最近用于治疗海洛因成瘾。在动物模型中，L-THP降低了可卡因的强化特性和戒断后可卡因寻求的恢复。重要的是，L-THP本身没有奖励效应，表明不存在滥用责任。最近，马里兰大学的王家北博士获得了美国国立卫生研究院的资助，在美国进行了一项关于L-THP治疗可卡因成瘾的临床试验。尽管L-THP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DA受体的五种亚型（D1- D5）具有低亲和力或无亲和力（见C.1.2）。此外，它不结合约60神经递质受体，离子通道和转运体参与疼痛调节和药物成瘾，我们筛选（见C.1.2）。在小鼠或大鼠中给予L- thp后，我们在血清中发现单去甲基化类似物L-紫堇胺（L- cp）和L-紫堇胺（L- cd）是主要代谢物，L-异紫堇胺（L- icp）是次要代谢物（见C.1.3）。我们还发现，L-ICP对DA受体具有中高亲和力（见C.1.4），并减少了可卡因诱导的过度运动、行为致敏和条件性位置偏好（见C.1.5-1.8）。因此，我们假设L-THP是一种前药，其作用是由于去甲基化代谢物作用于多个DA受体来调节可卡因诱导的行为。因此，我们建议进一步对L-THP及其去甲基化代谢物进行药理学表征，以更好地了解其作用机制。我们的具体目标是：(1)制备L-THP并化学合成其代谢物，以获得足够数量的药理学研究；(2)确定L-THP的代谢和药动学特征；(3)鉴定主要代谢物对DA受体和其他靶点的药理活性；(4)检查L-THP及其代谢物对可卡因自我给药和戒断后重新寻求药物的影响。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发现开辟新的途径。由于L-THP的主要副作用之一是镇静，我们提出的研究可能会产生具有较少镇静作用的候选药物，正如我们对L-ICP所证明的那样。

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.