Labelling of proteins with 11C in high specific radioactivity: [11C]albumin and [11C]transferrin

A method for the 11C-labelling of proteins for use in positron emission tomography is presented. Human iron-free transferrin and human serum albumin were treated with [11C]cyanogen bromide of high specific radioactivity under physiological conditions to give the labelled proteins in high radiochemical yields using a simple and rapid procedure. In a typical experiment, 2.0 GBq of [11C]albumin was obtained in 28-32 min synthesis time counted from the end of bombardment. The radiochemical purity was in all cases > 98% and the specific radioactivity varied with the amount of protein between 10.7-141 GBq mumol-1 (0.3-3.8 Ci mumol-1). The radiochemical yield of labelled product as a function of pH and protein concentration was studied. The labelled products were characterized using both high performance liquid chromatography and high performance capillary electrophoresis with u.v.-and radiodetection in series.