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

BACKGROUND: 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. RESULTS: 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. CONCLUSIONS: 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.

Netropsin and spermine conjugates of a water-soluble quinocarcin analog: analysis of sequence-specific DNA interactions.

BACKGROUND: Quinocarcin is the simplest of the bioxalmycin/naphthyridinomycin/tetrazomine/saframycin class of anti-tumor antibiotics, which damage DNA in a process that is inhibited by superoxide dismutase (SOD). The oxazolidine moiety of this class of anti-tumor antibiotics undergoes a redox self-disproportionation reaction of the Cannizzaro type. The reaction is proposed to proceed via an intermediate carbon-centered radical, which then reduces molecular oxygen to give superoxide. We set out to determine whether the DNA-cleavage properties of these anti-tumor antibiotics could be retained in less complex analogs of quinocarcin. RESULTS: A totally synthetic, water-soluble analog of quinocarcin has been prepared. This analog produced superoxide, but had considerably reduced ability to cleave supercoiled circular DNA compared to quinocarcin or tetrazomine. When conjugated to the DNA-binding molecule spermine, however, it cleaved DNA as effectively as quinocarcin at less than 1/10 the concentration. A conjugate with netropsin displayed selective cleavage around the sequence 5'-d(ATTT)-3'. Molecular modeling of the interaction between the conjugate and DNA, together with the pattern of cleavage, indicates that a non-diffusable oxidant is involved in sequence-selective DNA cleavage. The spermine conjugate displayed weak antimicrobial activity. CONCLUSIONS: Knowledge of the stereoelectronic requirements for superoxide production by quinocarcin has allowed us to design a structurally less complex analog which has many of the same physical properties, including water solubility, the ability to produce superoxide and the ability to cleave DNA. Covalently attaching known DNA-binding molecules to this analog gave a compound that produced sequence-specific DNA damage. Our results suggest that a mechanism other than superoxide production can mediate DNA damage by the netropsin conjugate.