Contrasting Cytotoxic Mechanisms Of Similar Antitumour Diaziridinylbenzoquinones

The mechanisms of cytotoxicity of the antitumour diaziridinylbenzoquinones, AZQ and BZQ. have been investigated. HPLC analysis has been used to study the products as well as the rate of decomposition of acid-assisted ring-opening in aqueous medium as a function of pH. Microconcentrators with a molecular weight cutoff of 30 kDa were utilised to study the covalent binding of both compounds to calf thymus DNA. Radical production of both compounds in K562 cell incubations was followed using ESR and their uptake into K562 cells was monitored using radiolabelled compounds. The results show that these two diaziridinylbenzoquinones. although very similar in structure, have diverse mechanisms of cytotoxicity. The implications of these findings are discussed in the light of antitumour action     

Activation And Deactivation Of Quinones Catalyzed By Dt-Diaphorase. Evidence For Bioreductive Activation Of Diaziquone (Azq) In Human Tumor Cells And Detoxification Of Benzene Metabolites In Bone Marrow Stroma

Bioactivation of diaziquone (AZQ) in HT-29 human colon carcinoma cells and detoxification of benzene metabolites in bone marrow stromal cells were used as examples of the potential role of DT-diaphorase in both activation and deactivation processes. HT-29 cell cytosol contained high levels of DT-diaphorase activity and removed AZQ in the presence of either NADH or NADPH. Prior boiling of cytosol. omission of NADH or NADPH or inclusion of dicoumarol. an inhibitor of DT-diaphorase. inhibited removal of AZQ. AZQ-inouced cytotoxicity in HT-29 cells was also inhibited by dicoumarol. Chemical reduction of AZQ in a cell free system enhanced formation of a GSH conjugate of AZQ. Two of the major cell types in bone marrow stroma are macrophages and fibroblastoid stromal cells. A fibroblastoid cell line derived from stromal cells contained approximately fourfold higher levels of DT-diaphorase than macrophages. Inclusion of dicournarol in incubations containing ¹⁴C-hydroquinone and the respective stromal cell type, significantly increased covalent binding of radiolabel to macromolecules in stromal fibroblasts but not in macrophages     

Contrasting Cytotoxic Mechanisms Of Similar Antitumour Diaziridinylbenzoquinones

The mechanisms of cytotoxicity of the antitumour diaziridinylbenzoquinones, AZQ and BZQ. have been investigated. HPLC analysis has been used to study the products as well as the rate of decomposition of acid-assisted ring-opening in aqueous medium as a function of pH. Microconcentrators with a molecular weight cutoff of 30 kDa were utilised to study the covalent binding of both compounds to calf thymus DNA. Radical production of both compounds in K562 cell incubations was followed using ESR and their uptake into K562 cells was monitored using radiolabelled compounds. The results show that these two diaziridinylbenzoquinones. although very similar in structure, have diverse mechanisms of cytotoxicity. The implications of these findings are discussed in the light of antitumour action