Micro‐MR angiography of normal and intratumoral vessels in mice using dedicated intravascular MR contrast agents with high generation of polyamidoamine dendrimer core: Reference to pharmacokinetic properties of dendrimer‐based MR contrast agents

Pharmacokinetic characteristics of intravascular macromolecular magnetic resonance imaging (MRI) contrast agents with polyamidoamine dendrimer cores smaller than generation-7 were previously studied in the literature. To evaluate the effects of greater hepatic uptake on the pharmacokinetics of the larger generation dendrimers, the MRI contrast agents GxD-(1B4M-Gd)(2(x+2)) were synthesized with generation-7, -8, and -9 polyamidoamine dendrimers and 2-(p-isothiocyanatobenzyl)-6-methyl-diethylenetriaminepentaacetic acid (1B4M). Their pharmacokinetic characteristics in mice were compared with that of G6D-(1B4M-Gd)(256). In biodistribution and dynamic micro-MRI studies, significantly less renal accumulation of G7D-(1B4M-Gd)(512), G8D-(1B4M-Gd)(1024), and G9D-(1B4M-Gd)(2048) was shown compared to G6D-(1B4M-Gd)(256) (P < 0.01). There was a significantly greater accumulation of G8D-(1B4M-Gd)(1024) and G9D-(1B4M-Gd)(2048) in the liver compared to G6D-(1B4M-Gd)(256) and G7D-(1B4M-Gd)(512) (P < 0.01). The highest blood retention of all dendrimer-based MRI contrast agents was exhibited by G7D-(1B4M-Gd)(512) (P < 0.01). The normal and intratumoral fine vessels of approximately 100 microm diameter were visualized in normal or tumor-bearing mice by high resolution three-dimensional-micro-MR angiographs with G7D-(1B4M-Gd)(512) and G8D-(1B4M-Gd)(1024) with good vessel-to-soft tissue contrast. In summary, increased accumulation in the liver with concomitant decreased uptake in the kidney was caused by increased molecular sizes of the dendrimer-based MRI contrast agents.