Abstract
A monoclonal antibody (MoAb) against α-fetoprotein (AFP), 80G, was obtained by the cell fusion technique. This MoAb was quite difficult to inhibit with free AFP. Complexation of 80G with AFP did not lead to rapid clearance of 80G from circulation, and these immune complexes remained capable of binding to solidphase AFP. Furthermore, pharmacokinetic analysis showed the suitability of MoAb 80G as an active targeting carrier. These results encouraged us to further evaluate the potency of our MoAb 80G as a carrier for targeting AFP-producing hepatoma cells. Four immunotoxins composed of MoAb 80G and a type 1 ribosome-inactivating protein, gelonin, were prepared. They involve two disulfide-linked and two thioether-linked immunotoxins. These immunotoxins (190 kDa) were purified by using a combination of gel filtration and affinity chromatography. The binding activity of immunotoxins against AFP remained as high as that of intact 80G. The in vitro cytotoxic effects of all the immunotoxins were specific against AFP-producing human hepatoma cell line, HuH-7. Of these irnmunotoxins, two containing gelonin modified with 2-iminothiolane were more potent than the others. They showed selective antitumor activity against AFP-producing HuH-7N cells in nude mice(HuH-7 xenograft). However, the disulfide immunotoxin was more toxic to mice than the thioether immunotoxin. These results suggest that our MoAb 80G is a suitable carrier for targeting AFT-producing hepatoma cells, and that our non-cleavable thioether immunotoxin is promising as an AFT-producing hepatomatargeted drug delivery system.
