The receptor binding fragment of alpha-fetoprotein is a promising new vector for the selective delivery of antineoplastic agents.

The alpha-fetoprotein (AFP) binding protein, a putative AFP receptor, is a tumour marker that is present on the surfaces of malignant cells. AFP enters cells through receptor-mediated endocytosis. The recombinant C-terminal fragment of AFP (AFP-3BC, which consists of amino acid residues 473-596) was obtained by the expression in Escherichia coli. AFP-3BC was shown to be bound specifically to the AFP putative receptor on tumour cells and accumulated by endocytosis in these cells in a similar manner to that of full-length human AFP. In lymphocytes, the binding and endocytosis of AFP-3BC were absent. Thus, the AFP receptor binding site was shown experimentally to be located within the AFP-3BC sequence. A conjugate of synthesised AFP-3BC with the antitumour antibiotic doxorubicin (DOX-AFP-3BC) demonstrated high antitumour activity in vitro. Thus, AFP-3BC can be used successfully as a vector for the targeted selective delivery of drugs into tumour cells.