Characteristics of a new MRI contrast agent prepared from polypropyleneimine dendrimers, generation 2.

RATIONALE AND

OBJECTIVES

Dendrimer-based magnetic resonance imaging (MRI) contrast agents offer many advantages including high levels of amplification. The objective of this research was to test the adequacy and viability of a new family of dendrimers for use as MRI contrast agents in vitro and in vivo.

METHODS

Dendrimers based on 1,4-diaminobutane core polypropyleneimine (PPI) generation 2 and ammonia core polyamidoamine dendrimers had the free surface amines conjugated to a diethylenetriaminepentaacetic acid derivative followed by complex formation with gadolinium. Relaxivity measurements were made on an IBM Field Cycling Relaxometer. Biodistribution and pharmacokinetic studies were examined with the radiotracer 153Gd in rats and a counting window of 95 to 105 keV. MRI images were conducted at 4.7 T.

RESULTS

The relaxivity of the PPI agent exceeded that of the corresponding generation polyamidoamine (PAMAM) agent. Uptake occurred in the liver, spleen, and kidney. Pharmacokinetic studies showed a biexponential decay with excretion half-lives of 3 hours and 33.6 days respectively. The agent increased the contrast enhancement, 1 hour after injection, of T1-weighted images by 52%.

CONCLUSIONS

This PPI agent resulted in significant contrast signal enhancement. This family of agent may also provide a valuable contrast agent backbone.