Standardization of CDI-mediated DTPA-coupling to IgG and IgG2a antibodies for 113mIn labeling.

A systematic analysis of various factors involved in the CDI-mediated coupling of DTPA to IgG have been carried out, in order to optimize the labeling yield of a monoclonal antibody labeled to high specific activity. Various CDI-to-DTPA ratios were tested, followed by a range of DTPA (activated) to IgG ratios. Specific activities as high as 600 Ci/mmol could be obtained following labeling with 113mIn, when an IgG : DTPA : CDI ratio of 0.01 : 1:20 was used. Other aspects, such as the volume of each of the reactants, the pH and the reaction times, were also standardized to yield a labeled IgG2a (KS1/4) that could be consistently tested for biodistribution and tumor-binding.