Gd-DTPA l-Cystine Bisamide Copolymers as Novel Biodegradable Macromolecular Contrast Agents for MR Blood Pool Imaging
作者:Todd L. Kaneshiro、Tianyi Ke、Eun-Kee Jeong、Dennis L. Parker、Zheng-Rong Lu
DOI:10.1007/s11095-006-0024-0
日期:2006.6
The purpose of this study was to synthesize biodegradable Gd-DTPA l-cystine bisamide copolymers (GCAC) as safe and effective, macromolecular contrast agents for magnetic resonance imaging (MRI) and to evaluate their biodegradability and efficacy in MR blood pool imaging in an animal model. Three new biodegradable GCAC with different substituents at the cystine bisamide [R = H (GCAC), CH2CH2CH3 (Gd-DTPA l-cystine bispropyl amide copolymers, GCPC), and CH(CH3)2 (Gd-DTPA cystine bisisopropyl copolymers, GCIC)] were prepared by the condensation copolymerization of diethylenetriamine pentaacetic acid (DTPA) dianhydride with cystine bisamide or bisalkyl amides, followed by complexation with gadolinium triacetate. The degradability of the agents was studied in vitro by incubation in 15 μM cysteine and in vivo with Sprague-Dawley rats. The kinetics of in vivo contrast enhancement was investigated in Sprague-Dawley rats on a Siemens Trio 3 T scanner. The apparent molecular weight of the polydisulfide Gd(III) chelates ranged from 22 to 25 kDa. The longitudinal (T 1) relaxivities of GCAC, GCPC, and GCIC were 4.37, 5.28, and 5.56 mM−1 s−1 at 3 T, respectively. The polymeric ligands and polymeric Gd(III) chelates readily degraded into smaller molecules in incubation with 15 μM cysteine via disulfide–thiol exchange reactions. The in vitro degradation rates of both the polymeric ligands and macromolecular Gd(III) chelates decreased as the steric effect around the disulfide bonds increased. The agents readily degraded in vivo, and the catabolic degradation products were detected in rat urine samples collected after intravenous injection. The agents showed strong contrast enhancement in the blood pool, major organs, and tissues at a dose of 0.1 mmol Gd/kg. The difference of their in vitro degradability did not significantly alter the kinetics of in vivo contrast enhancement of the agents. These novel GCAC are promising contrast agents for cardiovascular and tumor MRI, which are later cleaved into low molecular weight Gd(III) chelates and rapidly cleared from the body.
本研究的目的是合成可生物降解的 Gd-DTPA l-胱氨酸双酰胺共聚物(GCAC),作为安全有效的磁共振成像(MRI)大分子造影剂,并在动物模型中评估其生物降解性和在磁共振血池成像中的功效。三种新型可生物降解 GCAC 的胱氨酸双酰胺取代基各不相同[R = H(GCAC)、CH2CH2CH3(Gd-DTPA l-胱氨酸双丙基酰胺共聚物,GCPC)和 CH(CH3)2(Gd-DTPA 胱氨酸双丙基共聚物,GCIC)]、通过二乙烯三胺五醋酸(DTPA)二酸酐与胱氨酸双酰胺或双烷基酰胺缩合共聚,然后与三乙酸钆络合制备而成。通过在 15 μM 半胱氨酸中进行体外培养,以及在 Sprague-Dawley 大鼠体内培养,对这些制剂的降解性进行了研究。在西门子 Trio 3 T 扫描仪上对 Sprague-Dawley 大鼠体内对比度增强的动力学进行了研究。聚二硫化钆(III)螯合物的表观分子量在 22 到 25 kDa 之间。GCAC、GCPC和GCIC在3 T时的纵向(T 1)弛豫度分别为4.37、5.28和5.56 mM-1 s-1。聚合配体和聚合钆(III)螯合物在与 15 μM 半胱氨酸培养时很容易通过二硫-硫醇交换反应降解成更小的分子。聚合物配体和大分子钆(III)螯合物的体外降解率都随着二硫键周围立体效应的增加而降低。这些制剂在体内很容易降解,在静脉注射后收集的大鼠尿液样本中可以检测到分解代谢的降解产物。在剂量为 0.1 mmol Gd/kg 时,这些制剂在血液池、主要器官和组织中显示出强烈的对比度增强。它们体外降解性的差异并没有明显改变体内造影剂对比度增强的动力学。这些新型 GCAC 是用于心血管和肿瘤磁共振成像的有前途的造影剂,它们随后会被分解成低分子量的 Gd(III)螯合物,并迅速从体内清除。