The recent discovery that the clinically important
antitumor drugs doxorubicin and
daunorubicin alkylate
DNA via catalytic production of
formaldehyde prompted the synthesis of derivatives bearing
formaldehyde. Reaction of the parent drugs with aqueous
formaldehyde at pH 6 produced in 40-50% yield conjugates consisting of two molecules of the parent
drug as
oxazolidine derivatives bound together at their 3'-nitrogens by a methylene group. The structures were established as bis(3'-N-(3'-N,4'-O-methylenedoxorubicinyl)) methane (
Doxoform) and bis(3'-N-(3'-N,4'-O-methylenedaunorubicinyl))methane (
Daunoform) from spectroscopic data. Both derivatives are labile with respect to hydrolysis to the parent drugs. 3'-N,4'-O-Methylenedoxorubicin and 3'-N,4'-O-methylenedaunorubicin are intermediates in the hydrolysis.
Daunoform reacts with the self-complementary deoxyoligonucleotide (GC)4 faster than the combination of
daunorubicin and
formaldehyde at an equivalent concentration to given
drug-
DNA adducts. In spite of hydrolytic instability,
Doxoform is 150-fold more toxic to MCF-7 human
breast cancer cells and 10000-fold more toxic to MCF-7/ADR resistant cells. Toxicity to resistant
cancer cells is interpreted in terms of higher lipophilicity of the derivatives and circumvention of catalytic
formaldehyde production.