铂、金抗癌药物与靶分子作用过渡态和反应机理的计算研究

Cisplatin(CDDP) is one of the most widely used anticancer drugs in the world. However, the precise mechanism of action of cisplatin at the molecular level, in particular, the reaction dynamics of cisplatin with DNA target, remains elusive, which gives rise to the difficulty for designing and exploiting the new metal-based anticancer drugs those with fewer side effects and more spectrum properties of antitumor activity. It is generally accepted that the primary target of cisplatin is genomic DNA, specifically the N7 position of guanine base. This site of attack first generates monofunctional DNA adducts, and most of them further react to produce interstrand or intrastrand cross-links, which then block replication and/or prevent transcription. They are believed to owe their anticancer activity to their ability to bind covalently to cellular DNA and to alter its structure, thereby affecting subsequent cellular processes that eventually result in the death of the cancer cell.We named it as a molecule ion reaction mechanism. But some experimental work pointed out that the rate of hydrolysis of cisplatin and of platination of DNA is low. Recently, the femtosecond time-resolved laser spectroscopy (fs-TRLS) experiments found that the mechanism may like free radical reaction which caused by the ultrafast electron transfer (UET), namely,free radical reaction mechanism. The project herein intends to use DFT and ONIOM techniques to research the similarities and the differences between these two mechanisms which platinum- and gold-based anticancer binding to DNA and protein residues containing sulfur, nitrogen and selenium from the structures of transition states, free energy barriers, characters of bonding and the essences of the reaction. The project will provide the theoretical information which is practical and valuable for designing and exploiting the novel metal-based anticancer drugs and through the intensive study of the microcosmic process of action of platinum- and gold-based anticancer agent with biological target molecules.

顺铂是目前应用最广的金属抗癌药物，然而它与靶分子作用机理的细节仍然不清楚。这为设计和开发新的毒付作用和抗药性小、更光谱的金属抗癌药物带来了困难。通常认为顺铂首先水解活化，水解产物然后与DNA靶分子作用产生单功能和双功能加合物，阻止了DNA的复制和转录，使DNA结构变形从而杀死癌细胞（分子离子反应机理）。但是实验发现水解和铂化的速度都比较慢。最近飞秒时间分辨超快激光光谱实验发现有可能是超快电子转移产生的游离基反应（游离基反应机理）。本项目拟用DFT和ONIOM方法研究铂和金抗癌药物与DNA和硫、氮、硒蛋白质残基靶分子的游离基反应机理和分子离子反应机理的异同，比较两种反应机理的过渡态结构、活化能垒、作用本质和成键特征。通过深入探讨铂、金抗癌药物与靶分子作用的微观过程，为新型金属抗癌药物分子的设计和开发提供具有实用价值的理论信息。

在本项目研究中，我们用密度泛函DFT-B3LYP和DFT-M06及IEF-PCM溶剂化方法对多核铂配合物BBR3005和BBR3464、亚氨醚类反铂配合物与生物靶分子DNA嘌呤碱基和含硫含氮蛋白质残基的分子离子反应机理进行了研究。结果表明：BBR3464 的抗癌活性强于顺铂。比较B3LYP 和M06 泛函的计算结果，发现在水溶液中，BBR3464 与谷胱甘肽反应的活化能低于与半胱氨酸、蛋氨酸、以及DNA 嘌呤碱基反应的活化能。这说明在动力学上谷胱甘肽是BBR3464 优先进攻的生物靶分子。我们用B3LYP泛函计算得到的顺铂与鸟嘌呤反应的活化能为20.1 kcal/mol更接近实验值18.3 kcal/mol，而用M06 泛函计算的活化能是11.2kcal/mol，显著低于实验数据，表明B3LYP泛函比M06 泛函更适合于Pt-DNA作用体系的计算。对亚氨醚反铂的计算结果表明，无论是单功能还是双功能取代反应，DNA鸟嘌呤的活化能垒均低于腺嘌呤。在双功能取代反应中，含S的半胱氨酸（Cys）、蛋氨酸（Met）及鸟嘌呤能垒相对较低，而含氮的赖氨酸（Lys）及组氨酸残基（His）及腺嘌呤反应能垒相对较高。表明含S蛋白质和DNA鸟嘌呤可能是此类药物的主要靶分子，与实验研究结果吻合。trans-EE与靶分子作用的活化能最低，说明trans-EE的活性高于trans-E及trans-Z，与实验结果一致。.在对吡啶和3-皮考啉反铂配合物与生物靶分子的游离基反应机理的研究中发现，低能电子与药物作用，产生了中性游离基，这些游离基捕捉DNA核糖或者嘌呤碱基和胸腺嘧啶上的氢而增强了DNA链断裂的程度。我们对亚氨醚反铂、经典顺铂和反铂的游离基反应机理的探索表明，这些药物与靶分子的反应活化能趋于零或者是负值，说明这些反应可能是无势垒的。.在对一价和三价金配合物的研究中发现，一价金配合物优先与硒代半胱氨酸的Se位点反应，它们与半胱氨酸、硒代半胱氨酸单功能反应的活性顺序为：Me> Et> i-Pr> n-Pr。 而三价金药物优先与DNA鸟嘌呤和含硫蛋白质残基作用。