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

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.

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.

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.