前药,理想情况下,它们的活性化合物只在作用部位释放,即,在癌细胞中,是提高特异性并因此减少化疗副作用的有希望的方法。一种流行的前药形式是酯类,它们在水解时被激活。由于催化这种水解反应的羧酸酯酶在正常组织中也很丰富,一个推定的前药是否是这种酶的可能底物,因此不仅在目标环境中被激活的危险是非常重要的,即,在癌细胞中。在这项工作中,我们研究了药物分子喜树碱羧酸酯的结合模式,它是拓扑异构酶I的抑制剂,通过分子对接和分子动力学模拟,与人羧酸酯酶2(HCE2)的大小不同。与伊立替康相比,已知是HCE2的底物,表明在这项工作中分析的所有三种前药都可以与HCE2蛋白结合,但不适合随后的水解。我们的数据表明,此外,对于伊立替康基质,一旦从推定的亲核体Ser202到催化三联体的His431的初始质子转移已经发生,即可稳定反应物胜任的姿势。我们的模拟工作还表明,重要的是要超越从分子对接获得的静态模型,并包括酶-配体复合物在溶剂中和在有限温度下的灵活性。在这样的条件下,这项工作中研究的前药不太可能被HCE2酶水解,表明在正常组织中不期望的药物释放的低风险。
Pro-drugs, which ideally release their active compound only at the site of action, i.e., in a cancer cell, are a promising approach towards an increased specificity and hence reduced side effects in chemotherapy. A popular form of pro-drugs is esters, which are activated upon their hydrolysis. Since carboxylesterases that catalyse such a hydrolysis reaction are also abundant in normal tissue, it is of great interest whether a putative pro-drug is a probable substrate of such an enzyme and hence bears the danger of being activated not just in the target environment, i.e., in cancer cells. In this work, we study the binding mode of carboxylesters of the drug molecule camptothecin, which is an inhibitor of topoisomerase I, of varying size to human
carboxylesterase 2 (HCE2) by molecular docking and molecular dynamics simulations. A comparison to irinotecan, known to be a substrate of HCE2, shows that all three pro-drugs analysed in this work can bind to the HCE2 protein, but not in a pose that is well suited for subsequent hydrolysis. Our data suggest, moreover, that for the irinotecan substrate, a reactant-competent pose is stabilised once the initial proton transfer from the putative nucleophile Ser202 to the His431 of the catalytic triad has already occurred. Our simulation work also shows that it is important to go beyond the static models obtained from molecular docking and include the flexibility of enzyme-ligand complexes in solvents and at a finite temperature. Under such conditions, the pro-drugs studied in this work are unlikely to be hydrolysed by the HCE2 enzyme, indicating a low risk of undesired drug release in normal tissue.