Pharmacokinetics and tissue retention of (Gd-DTPA)-cystamine copolymers, a biodegradable macromolecular magnetic resonance imaging contrast agent

Purpose. To investigate the pharmacokinetics, long-term tissue retention of Gd(III) ions, and magnetic resonance imaging (MRI) contrast enhancement of extracellular biodegradable macromolecular Gd( III) complexes, (Gd-DTPA)-cystamine copolymers (GDCC), of different molecular weights. Methods. The pharmacokinetics of blood clearance and long-term Gd( III) retention of GDCC were investigated in Sprague-Dawley rats. Pharmacokinetic parameters were calculated by using a two-compartment model. The blood pool contrast enhancement of GDCC was evaluated in Sprague-Dawley rats on a Siemens Trio 3T MR scanner. Gd-(DTPA-BMA) was used as a control. Results. The alpha phase half-life of Gd-(DTPA-BMA) and GDCC with molecular weights of 18,000 (GDCC-18) and 60,000 Da (GDCC-60) was 0.48 +/- 0.16 min, 1.08 +/- 0.24 min, and 1.74 +/- 0.57 min, and the beta phase half-life was 21.2 +/- 5.5 min, 26.5 +/- 5.9 min, and 53.7 +/- 15.9 min, respectively. GDCC had minimal long-term Gd tissue retention comparable to that of Gd-( DTPA-BMA). GDCC resulted in more significant contrast enhancement in the blood pool than Gd-( DTPA-BMA). Conclusions. GDCC provides a prolonged blood pool retention time for effective MRI contrast enhancement and then clears rapidly with minimal accumulation of Gd ( III) ions. It is promising for further development as a blood pool MRI contrast agent.