COMPARISON OF THE BIOLOGICAL PROPERTIES OF 2 ANTI-MUCIN-1 ANTIBODIES PREPARED FOR IMAGING AND THERAPY

A comparison was made between the murine anti-MUC1 antibody BC2 (which reacts with the peptide epitope APDTR) and the ''humanised'' antibody hCTMO1 from CellTech, which reacts with the MUC1 epitope RPAP. Prelim inary studies demonstrated that hCTMO1 was a ''good'' antibody whereas BC2 was not. Various parameters were determined and conclusions reach ed. (a) Affinity: the affinity of hCTMO1 was 2.60x10(7)M(-1) and that of BC2 was 1.36x10(7)M(-1): we did not consider these numbers to be su bstantially different, although hCTMO1 was clearly of higher affinity than BC2. (b) On/off rate at 4 degrees C: both antibodies bound effect ively to the MUG-1 transfectant MOR5-CF2; the association rate for hCT MO1 was 3.8 times that of BC2 and the dissociation rate for BC2 was tw ice as fast as that of hCTMO1. (c) On/off rates at 37 degrees C: at 37 degrees C the association rate for hCTMO1 was greater than that of BC 2. (d) Internalization: hCTMO1 was also more efficient at internalisin g bound antibody; 70% of bound hCTMO1 was internalised, whilst 6% of b ound BC2 was internalised. From these studies it was clear that, while hCTMO1 was of similar affinity to BC2, the faster uptake and internal isation and lower off rate indicated that it was likely to be a superi or antibody; this was proven in vivo. (e) Localisation: hCTMO1 bound m uch better in vivo than BC2 (68% compared to 28%). (f) Therapeutic exp eriments: BC2-idarubicin conjugates were essentially ineffective in er adicating tumours in mice whereas hCTMO1-idarubicin had a dramatic eff ect on breast cancer tumour cells growing in mice. We conclude that th e simple measurements on/off rates and internalisation at 37 degrees C are the most important parameters to use to determine antibody effect iveness, prior to embarking on clinical studies.