Dihydromethysticin (DHM) for Lung Cancer Chemoprevention

 描述(由申请人提供)：肺癌每年在美国造成约16万人死亡，预防将是赢得这场最致命癌症战争的关键。由于烟草致癌物的DNA修饰是肺癌发生的主要驱动因素之一，因此阻止DNA加合物的形成(根本原因)是一个合理的策略。二氢甲硫菌素(DHM)是一种新型、高效的化学预防药物，通过阻止烟草致癌物诱导的DNA修饰来抑制肺癌的发生，是一项临床前研究。初步数据显示，DHM(在致癌物暴露期间给予50ppm的饮食)完全阻止NNK诱导的A/J小鼠肺部肿瘤的形成。一种天然类似物二氢卡瓦因(DHK)在饮食中即使在500ppm时也完全没有活性。体内这种明显的差异表明亚甲二氧基官能团在DHM的特异性靶向中起着至关重要的作用。DHM选择性降低NNAL(NNK的活性代谢物)诱导的肺组织DNA加合物。DHM还减少了F344大鼠NNK衍生的DNA加合物，表明其具有跨物种抗起始潜能。根据已报道的DHM激活芳香烃受体(AHR)的活性和我们自己的DHM增加小鼠尿中葡萄糖醛酸化NNAL的数据，我们认为DHM激活解毒途径是其主要作用机制。在安全性方面，DHM对A/J小鼠17周的膳食暴露在500ppm时没有不良影响，作为长期使用的肺癌化学预防药物提供了广泛的安全边际。我们的中心假设是，DHM有效地预防了烟草致癌物诱导的肺肿瘤的发生，至少在很大程度上是通过激活AHR，减少靶肺组织中的致癌DNA加合物来增强致癌物的解毒作用。目的1阐明DHM(即完整的DHM或其代谢物)的结构决定簇(S)对NNK诱导的DNA加合物形成和肺肿瘤形成具有特殊的体内抑制活性。数据还将为体内活性形式的DHM提供信息。目的探讨增强解毒作用是DHM抑制NNK诱导的DNA加合物形成和肺肿瘤形成的关键机制。数据还将告知其预防其他烟草致癌物质的潜力，并为未来的翻译研究确定替代生物标记物。目的评价DHM对NNK诱导的F344大鼠肺肿瘤和BaP诱导的A/J小鼠肺肿瘤的抑制作用。数据将告知它的跨物种适用性和致癌物特异性。如果结果支持我们的假设，DHM将为高等哺乳动物基于良好实验室规范(GLP)的毒理学做好准备，为IND应用于人类翻译研究做准备。这些机制知识不仅将识别对翻译至关重要的替代生物标记物，而且还将促进我们对NNAL代谢和癌症发生的基本理解。

 DESCRIPTION (provided by applicant): Lung cancer causes ~160,000 deaths annually in the U.S. and prevention will be crucial to win the war on this deadliest cancer. Since DNA modification by tobacco carcinogens is one major driver for lung cancer initiation, blocking DNA adduct formation (the root cause) is a plausible strategy. This proposal focuses on the preclinical studies of dihydromethysticin (DHM) as a novel and highly efficacious chemopreventive agent that inhibits lung tumor initiation via preventing tobacco carcinogen-induced DNA modification. Preliminary data demonstrate that DHM (given during carcinogen exposure period at a dose of 50 ppm in diet) completely blocked NNK-induced lung tumor formation in A/J mice. A natural analog, dihydrokavain (DHK), was completely inactive even at 500 ppm in diet. Such a sharp in vivo difference suggests a crucial role of methylenedioxy functional group for specific targeting by DHM. DHM selectively reduced NNAL (the active metabolite of NNK)-induced DNA adducts in the lung tissues. DHM also reduced NNK-derived DNA adducts in F344 rats, indicating its cross-species anti-initiation potential. Based on the reported activity of DHM in activating aryl hydrocarbon receptor (AHR) and our own data of DHM in increasing glucuronidated NNAL in mouse urine, we propose that DHM activates detoxification pathways as the primary mechanism of action. With respect to safety, 17-week dietary exposure of DHM to A/J mice caused no adverse effects at 500 ppm, affording a wide safety margin as a lung cancer chemopreventive agent for long-term use. Our central hypothesis is that DHM effectively prevents tobacco carcinogen-induced lung tumorigenesis, at least in major part, by enhancing carcinogen detoxification potentially via activating AHR leading to a reduction in oncogenic DNA adducts in the target lung tissues. This hypothesis will be tested by accomplishing the following aims: Aim 1 To elucidate the structural determinant(s) of DHM (i.e., intact DHM or its metabolite) for its exceptional in vivo inhibitory activities against NNK-induced DNA adduct formation and lung tumor initiation. Data will also inform the in vivo active form of DHM. Aim 2 To investigate enhanced detoxification as a key mechanism of DHM to inhibit NNK-induced DNA adduct formation and lung tumor initiation. Data will also inform its potential to protect against other tobacco carcinogens and identify surrogate biomarkers for future translational studies. Aim 3 To evaluate the efficacy of DHM against NNK-induced lung tumorigenesis in F344 rats and BaP-induced lung tumorigenesis in A/J mice. Data will inform its cross-species applicability and carcinogen specificity. If the results support our hypothesis, DHM will be well positioned for Good Laboratory Practice (GLP)-based toxicology in higher mammals in preparation for an IND application for human translation studies. The mechanistic knowledge will not only identify surrogate biomarkers critical for translation, but also advance our basic understanding about NNAL metabolism and carcinogenesis.