Microsomal superoxide anion production and NADPH-oxidation in a series of 22 aziridinylbenzoquinones

In vivo activity and hydrophobicity of cytostatic aziridinyl quinones

For a series of 3,6-disubstituted bisaziridinylbenzoquinones the in vivo and in vitro activities against murine tumors, as well as the in vivo toxicity, are analyzed. Properties describing biochemical and physicochemical reactions are also incorporated in the analyses. The important 1-octanol/water partition coefficients were determined, using a fast variation of the shake flask method. New pi'-values were calculated for the substituents in this series. These quinone pi'-values deviate strongly from the standard pi-values, especially for hydrogen-bonding substituents. To discriminate between the toxic and therapeutic activity of the compounds, principal components and partial least squares analyses were applied. Evidence is presented for selective antitumor action of the investigated compounds. The L1210 clonogenic assay only seems to relate to the general cytotoxicity and has no predictive value for in vivo activity for these compounds. The activity is correlated to the hydrophobicity of the quinones. The toxicity correlates with the ease of reduction, contrary to the hypothesis of bioreductive activation as a mechanism for selectivity.

Quantitative structure activity relationship for the acute cytotoxicity of 13 (bis)aziridinyl-benzoquinones: relation to cellular ATP depletion

This study was performed to establish relationships between the structure of 2,5-bis(1-aziridinyl)-1,4-benzoquinones (BABQs) bearing different substituents at the 3- and 6-position and their acute toxic effects in rat hepatocytes. The cell viability, loss of cellular glutathione (GSH+GSSG) and loss of ATP were followed during 4 h of incubation of freshly isolated hepatocytes. The toxicity of these compounds (100 microM) was predicted better by their reactivity with GSH than by their redox cycling in rat liver microsomes. The time of 50% loss of viability (LT50) correlated very well with the time of 50% depletion of ATP (AT50). LT50 could be adequately predicted by using the electronic field parameter (Ftotal) describing the electron withdrawing or donating properties for all the substituents on the quinone-nucleus. 7-(Di)halogen-substituted BABQs that all very rapidly depleted cellular glutathione showed significant differences in AT50 as well as in LT50. This suggests that alterations in ATP levels are important for explaining the differences in cytotoxicity of these compounds.

Diquat-induced oxidative damage in hepatic microsomes: effects of antioxidants

The ability of the redox cycling compound, diquat, to induce lipid peroxidation and oxidative damage was investigated using hepatic microsomes. Antioxidants, with demonstrated efficacy in physical models of oxidative stress, were examined in a diquat model. Diquat (10 microM-3 mM) induced lipid peroxidation (TBARS) in hepatic microsomes prepared from Fischer 344 rats. Diquat (1 mM) also increased protein carbonyl formation, NADPH oxidation and superoxide anion radical production (acetylated cytochrome c reduction). The novel antioxidants U-74,006F, U-78,517G and the known antioxidant, DPPD, decreased diquat-induced lipid peroxidation to levels below that of the control. These antioxidants also decreased protein carbonyl formation caused by diquat. U-74,006F and U-78,517G reduced NADPH oxidation slightly; although this inhibition was statistically significant, the biological significance is questionable. DPPD had no effect on this parameter. U-78,517G inhibited the reduction of acetylated cytochrome c slightly, whereas the other antioxidants had little effect. Thus overall, the increase in NADPH oxidation and the production of superoxide anion by redox cycling of diquat were not substantially affected by antioxidants. Neither did the test compounds show evidence of activity as iron chelators. This leads to the suggestion that antioxidants are preventing diquat-induced oxidative damage by scavenging lipid peroxyl radicals and preventing the propagation of the lipid peroxidation process.