Immunotoxins, ligand-toxin conjugates and molecular targeting.

Biotechnology provides tools for therapeutic exploitation following advances in the elucidation of protein-to-cell and cell-to-cell interactions. Molecular targeting of bacterial and plant toxins to the desired district of action can be achieved through effector molecules like monoclonal antibodies or protein ligands. Biochemical conjugation of these effectors to SO-6, a single-chain Ribosome Inactivating Protein from Saponaria officinalis, yielded powerful cytotoxic agents that are attractive candidates for therapeutic evaluation. Cloning of the gene for this plant toxin has been achieved. Technologies for expression of protein ligands, such as apolipoproteins or several growth factors, are available in recombinant microorganisms, providing adequate partners for the assembly of targeted chimaeras. Domain engineering of structural and functional regions in effector proteins is now possible and will be carried out with the available technologies to improve existing therapy.