Magnetic resonance imaging using gadolinium labeled monoclonal antibody

Gadolinium was attached to antibodies and tested in vitro and in vivo for its effect on proton relaxation enhancement. Using the cyclic anhydride method, dicthylenetriaminepentaacctic acid (DTPA) was attached to albumin, IgG and anti-CEA monoclonal antibody. Gadolinium (Gd) was then chelated to the protein complexes forming protein-DTPA-Gd complex. With this technique approximately 9 atoms of Gd could be attached to each albumin molecule, 4 to each IgG molecule and 1.5 to each monoclonal antibody molecule. The minimal in vitro concentration of Gd in the form of IgG-DTPA-Gd necessary to produce proton relaxation enhancement at 0.35 tesla was 10⁻ mM. An in vivo experiment using anticarcinoembryonic antigen (CEA) monoclonal anti-body-DTPA-Gd in hamsters implanted with human colon carcinoma resulted in a tumor concentration of Gd of less than 10^-4 mM. No enhancement of the tumors was detected at that concentration. For monoclonal antibodies to function as selective MR contrast agents, substantial advances in technology must occur.