Roles of polymorphic COMT, tea polyphenols and proteasome in cancer prevention

多态COMT、茶多酚和蛋白酶体在癌症预防中的作用

• 批准号: 7070198
• 负责人: QING PING DOU
• 金额: $ 25.31万
• 依托单位: WAYNE STATE UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2006
• 资助国家: 美国
• 起止时间: 2006-04-12 至 2011-02-28
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7070198
• 关键词: apoptosis; breast neoplasms; cancer prevention; human; methylation; neoplasm /cancer; neoplastic cell; proteasome; role; tea

DESCRIPTION (provided by applicant): Research has supported proteasome inhibitors as potential novel anticancer drugs and green tea polyphenols (GTPs) as a cancer-preventative agent. We have reported that GTPs, e.g. (-)-epigallocatechin- 3-gallate or EGCG, are potent and specific inhibitors of proteasomal chymotrypsin-like activity (mediated by b5 subunit). Methylation of GTPs, a major biotransformation reaction limiting their cancer-preventative activities in vivo, is mediated by human polymorphic catechol-O-methyltransferase (COMT). The point- mutated COMT, found in -25% of US population, has 3-4-fold decreased enzymatic activity (COMT-LL). It was reported that women tea-drinkers with at least one low activity COMT allele (but not COMT-HH) showed a significantly reduced risk of breast cancer compared with non-tea drinkers, suggesting less protection by methylated polyphenols. To study the responsible mechanism, we hypothesize that O-methylation of GTPs by COMT in breast cancer cells decreases their proteasome-inhibitory and consequently biological activities. This hypothesis is supported by our preliminary results. To further this study, we propose 5 specific Aims. (1) Synthesize O-methylated GTP analogs (by replacing -OH with -OCH3), the deoxy compounds (without the catechol diol), and polyphenol homologs (replacing -OH with -CH2OH) and determine their binding affinity to the proteasomal b5 subunit by employing computational modeling. (2) Evaluate potencies of these synthetic compounds to inhibit the proteasome activity using purified 20S proteasome, breast cancer cell extracts, and intact breast cancer cells. (3) Evaluate the apoptosis-inducing potencies of these synthetic compounds in human breast cancer cells. (4) Determine the effects of over- and under-expression of COMT gene in cultured human breast cancer cells on methylation of GTPs and their proteasome-inhibitory and apoptosis-inducing activities. (5) Determine whether methylation of GTPs is a mechanism to inactivate their biological functions in vivo using nude mice bearing human breast tumor xenografts. These studies should help develop a fundamental understanding about how the polymorphic COMT regulates the biological functions of GTPs in breast cancer cells and the impact of GTP methylation by COMT on the cancer- preventative effects of tea consumption as well as generate important information for designing future cancer prevention clinical trials using GTPs alone or in combination with a COMT inhibitor.

描述（由申请人提供）：研究支持蛋白酶体抑制剂作为潜在的新型抗癌药物，绿色茶多酚（GTP）作为癌症预防剂。我们已经报道了GTP，例如（-）-表没食子儿茶素-3-没食子酸酯或EGCG，是蛋白酶体胰凝乳蛋白酶样活性（由b5亚基介导）的有效和特异性抑制剂。GTP的甲基化是限制其体内癌症预防活性的主要生物转化反应，由人多态性儿茶酚-O-甲基转移酶（COMT）介导。在约25%的美国人群中发现的点突变的COMT具有3-4倍降低的酶活性（COMT-LL）。据报道，与不喝茶的人相比，至少有一个低活性COMT等位基因（但不是COMT-HH）的女性饮茶者患乳腺癌的风险显着降低，这表明甲基化多酚的保护作用较小。为了研究相关机制，我们假设COMT在乳腺癌细胞中对GTP的O-甲基化降低了其蛋白酶体抑制活性，从而降低了其生物活性。这一假设得到了我们的初步结果的支持。为了进一步研究，我们提出了五个具体目标。(1)合成O-甲基化GTP类似物（通过用-OCH 3取代-OH）、脱氧化合物（不含儿茶酚二醇）和多酚同系物（用-CH 2 OH取代-OH），并通过采用计算建模确定它们与蛋白酶体b5亚基的结合亲和力。(2)使用纯化的20 S蛋白酶体、乳腺癌细胞提取物和完整乳腺癌细胞评价这些合成化合物抑制蛋白酶体活性的效力。(3)评价这些合成化合物在人乳腺癌细胞中的促凋亡作用。(4)测定COMT基因在培养的人乳腺癌细胞中的过表达和低表达对GTP甲基化及其蛋白酶体抑制和诱导凋亡活性的影响。(5)使用荷人乳腺肿瘤异种移植物的裸鼠确定GTP甲基化是否是体内破坏其生物学功能的机制。这些研究应该有助于对多态性COMT如何调节乳腺癌细胞中GTP的生物学功能以及COMT对GTP甲基化的影响的基本理解-茶消费的癌症预防效果以及为设计未来的癌症预防临床试验提供重要信息单独使用GTP或与COMT抑制剂组合使用。