Peptide-conjugated polyamidoamine dendrimer as a nanoscale tumor-targeted T1 magnetic resonance imaging contrast agent.

A tumor-targeting carrier, peptide HAIYPRH (T7)-conjugated polyethylene glycol-modified polyamidoamine dendrimer (PAMAM-PEG-T7) was explored to deliver magnetic resonance imaging (MRI) contrast agents targeting to the tumor cells specifically. Two different types of tumors, liver cancer and early brain glioma model (involved with the blood-brain barrier), were chosen to evaluate the imaging capacity of this contrast agent. PAMAM-PEG-T7 was synthesized, conjugated with diethylene triamine pentaacetic acid (DTPA) and further chelated gadolinium (Gd), yielding GdDTPA-PAMAM-PEG-T7. The result of ICP-AES showed that about 92 Gd ions could be loaded per PAMAM molecule. The calculated longitudinal relaxivity R1 of the GdDTPA-PAMAM-PEG-T7 was 10.7 mm(-1) S(-1) per Gd (984.4 mm(-1) S(-1) per PAMAM), while that of GdDTPA was only 4.8 mm(-1) S(-1). PAMAM-PEG-T7 had better targeting capacity to the liver cancer cells in vitro and in vivo, compared with PAMAM-PEG. The accumulation of PAMAM-PEG-T7 was 162.5% times that of PAMAM-PEG. But for glioma cells, PAMAM-PEG-T7 did not show its specificity. Furthermore, GdDTPA-PAMAM-PEG-T7 could improve the diagnostic efficiency of liver cancer with the enhanced signal (187%), compared to 130% for PAMAM-PEG and 121% for GdDTPA. GdDTPA-PAMAM-PEG-T7 could selectively identify liver cancer but not early glioma. This nanoscaled MRI contrast agent GdDTPA-PAMAM-PEG-T7 might allow for selective and efficient diagnosis of tumors without the natural barrier including liver cancer.