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

研究支持蛋白酶体抑制剂作为潜在的新型抗癌药物和绿色茶 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）。GTP的甲基化，限制其癌症预防的主要生物转化反应 在体内的活性，是由人类多态性儿茶酚-O-甲基转移酶（COMT）介导的。关键是- 在约25%的美国人口中发现的突变的COMT具有3-4倍降低的酶活性（COMT-LL）。它 据报道，至少有一个低活性COMT等位基因（但不是COMT-HH）的女性饮茶者显示， 与不喝茶的人相比，患乳腺癌的风险显着降低，这表明茶的保护作用较小。 甲基化多酚为了研究其作用机制，我们假设GTP的O-甲基化 通过COMT在乳腺癌细胞中降低其蛋白酶体抑制活性，从而降低其生物活性。 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。（一） 合成O-甲基化GTP类似物（通过用-OCH 3代替-OH），脱氧化合物（没有 儿茶酚二醇）和多酚同系物（用-CH 2 OH代替-OH），并测定它们的结合亲和力 蛋白酶体B5亚基。(2)评价这些药物的效力 使用纯化的20 S蛋白酶体抑制蛋白酶体活性的合成化合物，乳腺癌细胞 提取物和完整的乳腺癌细胞。(3)评价这些合成药物的诱导骨质疏松效力 人类乳腺癌细胞中的化合物。(4)确定COMT过度表达和表达不足的影响 基因在培养的人乳腺癌细胞中对GTP甲基化及其蛋白酶体抑制和 诱发骨质疏松症的活动。(5)确定GTP的甲基化是否是一种机制， 使用携带人乳腺肿瘤异种移植物的裸鼠进行体内生物学功能。这些研究应 有助于发展关于多态COMT如何调节生物学特性的基本理解。 GTP在乳腺癌细胞中的功能以及COMT对GTP甲基化的影响 茶消费的预防作用以及为设计未来癌症提供重要信息 使用GTP单独或与COMT抑制剂组合的预防临床试验。

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.