Targeting immunotherapy using the avidin-biotin system for a human colon adenocarcinoma in vitro.

A new method of targeting immunotherapy using the avidin-biotin system in vitro was investigated. Both an anti-carcinoembryonic antigen monoclonal antibody (anti-CEA MAb) and an anti-cancer drug, neocarzinostatin (NCS), were biotinylated. A human colon adenocarcinoma cell line (LoVo) was immunized with biotinylated anti-CEA MAb; avidin was added, and the cell line was incubated with various concentrations of biotinylated NCS for either 72 h or 7 min. In the incubation for 72 h, the IC50 was similar (approximately 0.45 microgram/ml) for biotinylated NCS for LoVo cells immunized with biotinylated anti-CEA MAb and those without immunization. In the incubation for 7 min, the IC50 (concentration producing 50% cytotoxicity) of biotinylated NCS for LoVo cells immunized with biotinylated anti-CEA MAb (0.35 microgram/ml) was five times less than that of non-immunized LoVo cells (1.8 micrograms/ml). Thus the present system has the potential to reduce the dosage of anti-cancer drugs needed, and this strategy seems likely to be a valuable clinical tool in targeting immunotherapy.