Dihydromethysticin (DHM) for Lung Cancer Chemoprevention

 描述（由申请人提供）：肺癌在美国每年导致约160，000人死亡，预防对于赢得这场最致命的癌症战争至关重要。由于烟草致癌物对DNA的修饰是肺癌发生的一个主要驱动因素，因此阻断DNA加合物的形成（根本原因）是一种合理的策略。该提案的重点是二氢麻醉椒苦素（DHM）作为一种新型的和高效的化学预防剂，通过阻止烟草致癌物诱导的DNA修饰来抑制肺肿瘤的发生的临床前研究。初步数据表明，DHM（在致癌物暴露期间以50 ppm的剂量在饮食中给予）完全阻断了A/J小鼠中NNK诱导的肺肿瘤形成。一种天然类似物，二氢醉椒素（DHK），是完全无活性的，即使在500 ppm的饮食。这种明显的体内差异表明亚甲二氧基官能团对于DHM的特异性靶向的关键作用。DHM选择性地减少NNAL（NNK的活性代谢物）诱导的肺组织中的DNA加合物。DHM还减少F344大鼠中NNK衍生的DNA加合物，表明其跨物种抗起始潜力。基于DHM在激活芳香烃受体（AHR）中的活性和我们自己的DHM在增加小鼠尿液中葡萄糖醛酸化NNAL的数据，我们提出DHM激活解毒途径是主要的作用机制。在安全性方面，A/J小鼠17周的DHM饮食暴露在500 ppm下未引起不良反应，作为长期使用的肺癌化学预防剂提供了广泛的安全范围。我们的中心假设是，DHM有效地防止烟草致癌物诱导的肺肿瘤发生，至少在主要部分，通过增强致癌物解毒可能通过激活AHR导致在靶肺组织中的致癌DNA加合物的减少。该假设将通过实现以下目标来测试：目标1为了阐明DHM的结构决定因素（即，完整的DHM或其代谢物），因为其对NNK诱导的DNA加合物形成和肺肿瘤起始的异常体内抑制活性。数据还将告知DHM的体内活性形式。目的2探讨DHM抑制NNK诱导的DNA加合物形成和肺肿瘤发生的机制。数据还将告知其防止其他烟草致癌物的潜力，并为未来的转化研究确定替代生物标志物。目的3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。数据将告知其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将在高等哺乳动物基于药物非临床研究质量管理规范（GLP）的毒理学方面处于有利地位，为人类翻译研究的IND申请做准备。机理知识不仅将识别对翻译至关重要的替代生物标志物，而且还将推进我们对NNAL代谢和致癌作用的基本理解。

 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.