Molecular and functional characterisation of a fusion protein suited for tumour specific prodrug activation.

A fusion protein consisting of the humanised Fab fragment of the anti CEA MAb BW 431 and the human beta-glucuronidase was expressed in BHK cells. Functional testing revealed that the specificity and avidity of the humanised V region was similar to the original murine MAb BW 431. Furthermore, the enzymatic activity, pH sensitivity and stability of the human beta-glucuronidase in the fusion protein was comparable to the activity of recombinant human beta-glucuronidase. Using anti-idiotype affinity chromatography, two molecules of a molecular weight of 125 kDa or 250 kDa could be visualized under nonreducing conditions in SDS-PAGE. Reducing conditions revealed a 25 kDa light and 100 kDa heavy chain. Due to its suitable biological characteristics this fusion protein might be an appropriate molecule allowing a site specific antibody directed enzyme prodrug therapy (ADEPT) in vivo.