Dihydromethysticin (DHM) for Lung Cancer Chemoprevention

 描述（由申请人提供）：在美国，肺癌每年导致约 160,000 人死亡，预防对于赢得对抗这种最致命癌症的战争至关重要。由于烟草致癌物质对 DNA 的修饰是肺癌发生的主要驱动因素之一，因此阻止 DNA 加合物形成（根本原因）是一种可行的策略。该提案重点关注二氢甲基霉素 (DHM) 作为一种新型高效化学预防剂的临床前研究，该化学预防剂通过防止烟草致癌物诱导的 DNA 修饰来抑制肺部肿瘤的发生。初步数据表明，DHM（在致癌物暴露期间以饮食中 50 ppm 的剂量给予）完全阻止了 NNK 诱导的 A/J 小鼠肺部肿瘤形成。天然类似物二氢卡瓦因 (DHK) 即使在饮食中添加 500 ppm 也完全没有活性。如此显着的体内差异表明亚甲二氧基官能团对于 DHM 的特异性靶向具有至关重要的作用。 DHM 选择性减少肺组织中 NNAL（NNK 的活性代谢物）诱导的 DNA 加合物。 DHM 还减少了 F344 大鼠中 NNK 衍生的 DNA 加合物，表明其具有跨物种抗启动潜力。根据报道的 DHM 激活芳烃受体 (AHR) 的活性以及我们自己的 DHM 增加小鼠尿液中葡萄糖醛酸化 NNAL 的数据，我们提出 DHM 激活解毒途径作为主要作用机制。就安全性而言，A/J 小鼠饮食接触 500 ppm 的 DHM 17 周未造成任何不良影响，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 至少在很大程度上是通过激活 AHR 来增强致癌物的解毒作用，从而减少目标肺组织中致癌 DNA 加合物，从而有效地预防烟草致癌物诱导的肺部肿瘤发生。该假设将通过实现以下目标进行检验： 目标 1 阐明 DHM（即完整的 DHM 或其代谢物）的结构决定因素，因为它对 NNK 诱导的 DNA 加合物形成和肺肿瘤起始具有特殊的体内抑制活性。数据还将告知 DHM 的体内活性形式。目标 2 研究增强解毒作用作为 DHM 抑制 NNK 诱导的 DNA 加合物形成和肺肿瘤发生的关键机制。数据还将揭示其预防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。目标 3 评估 DHM 对 NNK 诱导的 F344 大鼠肺肿瘤发生和 BaP 诱导的 A/J 小鼠肺肿瘤发生的功效。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 将在高等哺乳动物中基于良好实验室规范 (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。机制知识不仅可以识别对翻译至关重要的替代生物标志物，还可以增进我们对 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.