Structure–Activity Relationships for CYP4B1 Bioactivation of 4-Ipomeanol Congeners: Direct Correlation between Cytotoxicity and Trapped Reactive Intermediates
作者:John P. Kowalski、Matthew G. McDonald、Dale Whittington、Miklos Guttman、Michele Scian、Marco Girhard、Helmut Hanenberg、Constanze Wiek、Allan E. Rettie
DOI:10.1021/acs.chemrestox.9b00330
日期:2019.12.16
Cytochrome P450 4B1 (CYP4B1) has been explored as a candidate enzyme in suicide gene systems for its ability to bioactivate the natural product 4-ipomeanol (IPO) to a reactive species that causes cytotoxicity. However, metabolic limitations of IPO necessitate discovery of new “pro-toxicant” substrates for CYP4B1. In the present study, we examined a series of synthetically facile N-alkyl-3-furancarboxamides for cytotoxicity in HepG2 cells expressing CYP4B1. This compound series maintains the furan warhead of IPO while replacing its alcohol group with alkyl chains of varying length (C1–C8). Compounds with C3–C6 carbon chain lengths showed similar potency to IPO (LD50 ≈ 5 μM). Short chain analogs (<3 carbons) and long chain analogs (>6 carbons) exhibited reduced toxicity, resulting in a parabolic relationship between alkyl chain length and cytotoxicity. A similar parabolic relationship was observed between alkyl chain length and reactive intermediate formation upon trapping of the putative enedial as a stable pyrrole adduct in incubations with purified recombinant rabbit CYP4B1 and common physiological nucleophiles. These parabolic relationships reflect the lower affinity of shorter chain compounds for CYP4B1 and increased ω-hydroxylation of the longer chain compounds by the enzyme. Furthermore, modest time-dependent inhibition of CYP4B1 by N-pentyl-3-furancarboxamide was completely abolished when trapping agents were added, demonstrating escape of reactive intermediates from the enzyme after bioactivation. An insulated CYP4B1 active site may explain the rarely observed direct correlation between adduct formation and cell toxicity reported here.
细胞色素 P450 4B1(CYP4B1)能将天然产物 4-异戊醇(IPO)生物活化为一种会导致细胞毒性的活性物质,因此一直被视为自杀基因系统中的候选酶。然而,由于 IPO 的代谢限制,有必要为 CYP4B1 寻找新的 "促毒性 "底物。 在本研究中,我们考察了一系列合成简便的 N-烷基-3-呋喃羧酰胺在表达 CYP4B1 的 HepG2 细胞中的细胞毒性。 该化合物系列保留了 IPO 的呋喃弹头,同时用不同长度(C1-C8)的烷基链取代其醇基。碳链长度为 C3-C6 的化合物显示出与 IPO 相似的效力(LD50 ≈ 5 μM)。短链类似物(<3 个碳原子)和长链类似物(>6 个碳原子)的毒性降低,烷基链长度与细胞毒性之间呈抛物线关系。在与纯化的重组兔 CYP4B1 和常见的生理亲核物进行孵育时,将推定的烯酮捕获为稳定的吡咯加合物时,也观察到烷基链长度与反应性中间体形成之间存在类似的抛物线关系。这些抛物线关系反映了短链化合物对 CYP4B1 的亲和力较低,以及该酶对长链化合物的ω-羟基化作用增强。此外,加入诱捕剂后,N-戊基-3-呋喃甲酰胺对 CYP4B1 的适度时间依赖性抑制完全消失,这表明生物活化后反应性中间产物从酶中逸出。一个绝缘的 CYP4B1 活性位点可能解释了这里报告的很少观察到的加合物形成与细胞毒性之间的直接相关性。