The synthesis of a novel enediyne 2, and its cytotoxicity and activation by the nitroreductase enzyme NR2 from Esherichia coli B, are described. In contrast to closely related analogues, 2 exhibits a 90-fold increase in cytotoxicity against UV4 cells in the presence of the enzyme and NADH, suggesting its potential as a prodrug for Antibody-Directed Enzyme Prodrug Therapy in conjunction with E. coil nitroreductase.
Antibody-directed enzyme prodrug, therapy (ADEPT) is a technique of increasing interest in cancer chemotherapy. In this approach, a tumour specific antibody-enzyme conjugate is administered, and accumulates selectively on the surface of the antigen-expressing tumor cells. After a suitable time interval, when the conjugate has cleared ~om normal tissue, a prodrug is administered and is preferentially activated by the antibody-enzyme conjugate. A number of ADEPT systems are in various stages of development and have been reviewed. I One approach uses as the enzyme an aerobic nitroreductase from E. coli B 2 which, in conjunction with NADH or NADPH, reduces certain aromatic nitro groups to the corresponding hydroxylamines. 3 A number of 4-nila'obenzyloxycarbonyl derivatives, including those of 4aminoaniline mustard, actinomycin D, mitomycin C, and doxorubicin, have been shown to be substrates for the enzyme, although the degree of activation differs widely. 4 Reduction of the 4nitrobenzyloxycarbonyl moiety in these prodmgs affords the corresponding 4-hydroxylaminobenzyloxyearbonyl derivatives which, through increased electron release to the system stabilizing the developing positive charge on the benzylic carbon, readily fragment to release an active drug (effeetor) (Scheme 1). Because the amount of drug delivered in this way is limited, it is an advantage if very potent effeetor can be released.