FR900482, a close cousin of mitomycin C that exploits mitosene-based DNA cross-linking

The class of antitumor antibiotics that includes FR900482 has a very close structural analogy to the mitomycins, one of which, mitomycin C, has been in widespread clinical use for more than 20 years. Like mitomycin C, these antitumor antibiotics are reductively activated in vivo and covalently cross-link DNA as a result of activity of the mitosene moiety generated on reduction. Owing to differences in structure and the attendant mechanistic differences in bioreductive activation between the mitomycins and FR900482, FR900482 does not produce an adventitious superoxide radical anion during reductive activation and thus does not exhibit oxidative strand scission of DNA. It is postulated that the low clinical toxicity of FR900482 relative to mitomycin C is a direct manifestation of the mechanistic differences of bioreductive activation leading to the highly reactive DNA cross-linking mitosenes.

Using Fe(II)-EDTA footprinting, we showed that the two natural products FR900482 (1) and dihydro, FR66979 (3), and the semi-synthetically derived triacetate FK973 (2), display remarkable selectivity for 5' deoxy-CG sequences of DNA, and that this selectivity is abolished upon deletion of the exocyclic N2 amine of either participating guanosine residue. In addition, we investigated the mono alkylation abilities of FR66979 with respect to a number of inosine-substituted oligonucleotides and observed that the FR900482 class of compounds were able to give rise to easily separable orientation isomers of their respective cross-links.

The FR900482 class of antitumor antibiotics cross-link DNA in a fashion analogous to the mitomycins. The cross-linking reaction yields two orientation isomers which are of vastly different electrophoretic mobility and which also exhibit radically different DNA-protein recognition properties upon reaction with AluI restriction endonuclease. In addition, mono-alkylation of DNA by FR66979 shows little, if any, dependence upon pre-covalent interactions deemed necessary for the mitomycins. These insights support the proposal that the FR900482 class of compounds represents a compelling clinical replacement for mitomycin C, given its greatly reduced host toxicity and superior DNA interstrand cross-linking efficacy.