Gadolinium-conjugated folate-poly(ethylene glycol)-polyamidoamine dendrimer-carboxyl nanoparticles as potential tumor-targeted, circulation-prolonged macromolecular magnetic resonance imaging contrast agents. II

A new macromolecular gadolinium-based magnetic resonance imaging (MRI) contrast agent, folic acid (FA)-poly(ethylene glycol) (PEG)-polyamidoamine dendrimer (PAMAM)-Gd, was synthesized with a core of PAMAM, which was modified with conjugates of FA and PEG and then chelated by gadolinium ions. The final products, with FA as the targeting moiety, were evaluated for their tumor-targeting MRI contrast-agent potential. The concentration detection limits in vitro; contrast-enhanced MRI in the heart, kidney, and liver of mice; and metabolism of FA-PEG-PAMAM-Gd were measured by a Siemens Tim Trio human MRI scanner at 3 T. Transmission electron microscopy was used to determine the targeting of FA-PEG-PAMAM-Gd to human epidermoid carcinomas cell lines (KB) or murine aneuploid fibrosarcoma cell lines (L929). The toxicity was also assayed to evaluate the biocompatibility of this contrast agent. The minimum detectable concentration of FA-PEG_4K-PAMAM-Gd (where the subscript 4K indicates a molecular weight of 4000 Da) was 15-fold lower than that of the commercially available contrast agent gadopentetate dimeglumine. The MRI images displayed a gradual persistent signal enhancement on tumors, and millimeter-sized (∼ 3 mm) tumors were well visualized with FA-PEG_4K-PAMAM-Gd. In conclusion, the dendritic complexes were well suited for use as an FA-mediated targeting contrast agent for early diagnosis of tumors in mice. The dendritic contrast agents displayed lower concentration detection limits, which suggests their future use in molecular imaging.