ARE LETHAL EFFECTS OF NITRACRINE ON L5178Y CELL SUBLINES ASSOCIATED WITH DNA-PROTEIN CROSS-LINKS

Nitracrine (Ledakrin, tro-9-(3,3-N,N-dimethylaminopropylamino)-acridin e) is of interest as a DNA intercalator and alkylator with very high c ytotoxic 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) [Woyn arowski et al., Biochem Pharmacol 38: 4095-4101, 1989, Szmigiero and S tudzian, Biochim Biophys Acta 1008: 339-345, 19891 are related to the toxicity of the drug. The cytotoxic effect of and DNA damage induced b y nitracrine were measured in two sublines of mouse lymphoma L5178Y, L Y-R (resistant to ionizing radiation) and LY-S (sensitive to ionizing radiation). LY-R cells were more sensitive to nitracrine (D10 = 0. 11 muM) than LY-S (D10 = 0.35 muM) when treated for 1 hr at 37-degrees. T o a DNA-DNA crosslinking agent, mitomycin C, the comparative sensitivi ty was opposite. LY-R cells were more resistant to this drug than LY-S cells (D10 = 7.1 vs 2.3 muM). DNA damage induced by nitracrine was me asured by the alkaline elution method and by nitrocellulose filter bin ding assay. Nitracrine treatment with biologically relevant concentrat ions (0. 1-3.0 muM, 1 hr, 37-degrees) induced only DPCs. Interstrand c rosslinks and DNA breaks were not detected. Nitracrine produced about two times more DPCs in LY-R cells than in LY-S cells. Both sublines re moved 50% of initial lesions during 2 hr post-treatment incubation. Th e 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 th e latter lesion being responsible for the cytotoxicity of nitracrine.