The behaviour of the antimetastatic Ru(III) complex imidazolium [trans-RuCl4(1H-imidazole)(DMSO-S)] (NAMI-A) under physiological conditions and its interactions with human serum albumin (hsA) have been studied using electron paramagnetic resonance spectroscopy (EPR). In physiological buffer at pH 7.4, these experiments demonstrate that the DMSO ligand is replaced rapidly by water, and spectra from the subsequent formation of five other Ru(III) complexes show further aquation processes. Although EPR spectra from mono-nuclear Ru(III) complexes are visible after 24 h in buffer, a significant decrease in the overall signal intensity following the first aquation step is consistent with the formation of oxo-bridged Ru(III) oligomers. Incubation with hsA reveals very rapid binding to the proteinvia hydrophobic interactions. This is followed by coordination through ligand exchange with protein side chains, likely with histidine imidazoles and at least one other specific site. Similar behaviour is observed when the complex is incubated in human serum, indicating that hsA binding dominates speciation in vivo. The addition of ascorbic acid to NAMI-A in buffer leads to quantitative reduction, producing EPR-silent Ru(II) complexes. However, this process is prevented when the complex binds coordinatively to hsA. Together, these results demonstrate the key role that hsA plays in defining the species found in vivo following intravenous treatment with NAMI-A, through prevention of oligomerization and maintenance of the oxidation state, to give protein-bound mono-nuclear Ru(III) species.
利用电子顺磁共振波谱法(EPR)研究了抗转移的Ru(III)
咪唑复合物[trans-RuCl4(
1H-咪唑)(
DMSO-S)](N
AMI-A)在生理条件下的行为及其与人
血清白蛋白(hsA)的相互作用。在pH值为7.4的生理缓冲液中,这些实验表明
DMSO配体迅速被
水取代,随后形成其他五种Ru(III)复合物,显示出进一步的
水合过程。虽然在缓冲液中24小时后可见单核Ru(III)复合物的EPR谱,但第一
水合步骤后总体信号强度的显著下降表明形成了氧桥联的Ru(III)低聚物。与hsA的共孵育显示通过疏
水作用非常迅速地与蛋白质结合。随后通过
配体与蛋白质侧链的交换进行配位,可能与组
氨酸
咪唑和其他至少一个特定位点结合。当该复合物在人血清中共孵育时也观察到类似行为,表明hsA结合在体内主导物种的形成。将
抗坏血酸加入缓冲液中的N
AMI-A中会导致定量还原,产生EPR静默的Ru(II)复合物。然而,当该复合物通过配位与hsA结合时,这一过程被阻止。综上所述,这些结果表明,通过防止低聚化和维持氧化态,hsA在静脉治疗N
AMI-A后体内物种的形成中起着关键作用,形成了与蛋白质结合的单核Ru(III)物种。