Development of a water-soluble prodrug of doxorubicin-formaldehyde conjugate, a labile, active metabolite of doxorubicin, is described. The lead compound is the doxorubicin-salicylamide N-Mannich base, N-(2-hydroxybenzamidomethyl)-doxorubicin (doxsaliform), prepared in 72% yield from reaction of salicylamide with doxorubicin in the presence of formaldehyde. Doxsaliform releases doxorubicin-formaldehyde conjugate under physiological conditions with a half-life of 57 min. The stability of the prodrug is augmented both by salt formation in acidic media and by covalent modification of the 2-hydroxyl of the salicylamide moiety. Doxsaliform is 4 fold more active than doxorubicin against MCF-7 breast and PC-3 prostate cancer cell lines and 10 fold more active against the doxorubicin resistant MCF-7 / ADR cell line.