Are lethal effects of nitracrine on L5178Y cell sublines associated with DNA-protein crosslinks?

Nitracrine (Ledakrin, 1-nitro-9-(3,3-N,N-dimethylaminopropylamino)-acridine) is of interest as a DNA intercalator and alkylator with very high cytotoxic potency, especially against hypoxic cells. DNA-DNA crosslinks [Konopa et al., Chem Biol Interact 43: 175-197, 1983; Pawlak et al., Cancer Res 44: 4289-4296, 1984] or DNA-protein crosslinks (DPCs) [Woynarowski et al., Biochem Pharmacol 38: 4095-4101, 1989; Szmigiero and Studzian, Biochim Biophys Acta 1008: 339-345, 1989] are related to the toxicity of the drug. The cytotoxic effect of and DNA damage induced by nitracrine were measured in two sublines of mouse lymphoma L5178Y, LY-R (resistant to ionizing radiation) and LY-S (sensitive to ionizing radiation). LY-R cells were more sensitive to nitracrine (D10 = 0.11 microM) than LY-S (D10 = 0.35 microM) when treated for 1 hr at 37 degrees. To a DNA-DNA crosslinking agent, mitomycin C, the comparative sensitivity was opposite. LY-R cells were more resistant to this drug than LY-S cells (D10 = 7.1 vs 2.3 microM). DNA damage induced by nitracrine was measured by the alkaline elution method and by nitrocellulose filter binding assay. Nitracrine treatment with biologically relevant concentrations (0.1-3.0 microM, 1 hr, 37 degrees) induced only DPCs. Interstrand crosslinks and DNA breaks were not detected. Nitracrine produced about two times more DPCs in LY-R cells than in LY-S cells. Both sublines removed 50% of initial lesions during 2 hr post-treatment incubation. The greater sensitivity of LY-R cells to nitracrine is thus not related to the efficiency of DNA repair, but may be a consequence of enhanced initial damage in the form of DPCs. This finding is consistent with the latter lesion being responsible for the cytotoxicity of nitracrine.