Antibody- and gene-directed enzyme prodrug therapy are two-step targeting s
trategies designed to improve the selectivity of antitumour agents. The app
roaches are based on the activation of specially designed prodrugs by antib
ody-enzyme conjugates targeted to tumour-associated antigens (ADEPT) or by
enzymes expressed by exogenous genes in tumour cells (GDEPT). Herein the de
sign, synthesis, physico-chemical and biological properties, kinetics and c
linical trials of the prodrugs and the enzymes carboxypeptidase G2 and nitr
oreductase are reviewed for ADEPT and GDEPT.