In vitro cytotoxicities of 1,4-naphthoquinone and hydroxylated 1,4-naphthoquinones to replicating cells.

Using the human hepatoma cell line, HepG2, and the BALB/c mouse fibroblast cell line, 3T3, as the bioindicators in the neutral red cytotoxicity assay, the effect of hydroxyl substitution on the toxicity of 1,4-naphthoquinone was studied. The sequence of potency for the quinones was 5,8-dihydroxy-1,4-naphthoquinone > 5-hydroxy-1,4-naphthoquinone > 1,4-naphthoquinone >> 2-hydroxyl-1,4- naphthoquinone. Pretreatment of the cells with dicoumarol, an inhibitor of DT-diaphorase, enhanced the cytotoxicity of 1,4-naphthoquinone but not of the hydroxylated naphthoquinones. Pretreatment of the BALB/c cells with buthionine sulfoximine, an inhibitor of glutathione synthesis, enhanced the sensitivity of the cells to all the hydroxylated naphthoquinones but not to 1,4-naphthoquinone. A similar pretreatment of the HepG2 cells with buthionine sulfoximine enhanced the toxicity of the 2-hydroxy- and 5,8-dihydroxy-1,4-naphthoquinones but not of 5-hydroxy-1,4-naphthoquinone or of 1,4-naphthoquinone. Some differences were noted in the responses to the hydroxylated 1,4-naphthoquinones between buthionine sulfoximine-treated replicating cells and buthionine sulfoximine-treated isolated rat hepatocytes, a nonreplicating cell in culture. The use of a replicating cell system in studying the mechanisms of the cytotoxicity of quinones may be an important adjunct to studies using the isolated rat hepatocytes, which is the standard model system.