naphthoquinones and 3-aminobenzamide

The human colon carcinoma cell line Caco-2 was exposed to the oxidative stress-inducing agents menadione (MEN), 2,3-dimethoxy-1,4-naphthoquinone, and hydrogen peroxide. All three agents caused DNA damage which was assessed by alkaline unwinding. Further, all three agents induced intensive NAD+ depletion, followed by a decrease in intracellular ATP and viability. Inhibition of poly(ADP-ribose) polymerase (PARP, EC 2.4.2.30) by 3-aminobenzamide prevented the depletion of NAD+. These cells had a higher viability and ATP content. The most pronounced effect was observed with 25 microM of MEN, while at higher levels a partial preservation of NAD+ was observed with no effect on ATP or viability. The chelation of intracellular calcium by bis-(o-aminophenoxy)-ethane-N,N,N1,N1-tetraacidic acid/tetraacetoxymethyl) ester also prevented the dramatic loss of NAD+, demonstrating that Ca2+ is an activating factor in PARP-mediated cell killing.

Topics: Adenosine Triphosphate; Benzamides; Caco-2 Cells; Calcium; Cell Death; Chelating Agents; DNA Damage; DNA, Neoplasm; Egtazic Acid; Glutathione; Humans; Hydrogen Peroxide; Kinetics; NAD; Naphthoquinones; Oxidants; Oxidative Stress; Poly(ADP-ribose) Polymerase Inhibitors; Vitamin K

This study assessed the ability of 11 established and potential radiosensitizing agents to retard the repair of radiation-induced DNA damage with a view to enhancing the immunosuppressive effects of in vivo lymphoid irradiation. The capability of irradiated rat thymocytes to repair DNA damage was assessed by an adaptation of the fluorimetric unwinding method. Three compounds, 3-aminobenzamide (3-AB), novobiocin and flavone-8-acetic acid (FAA), inhibited repair significantly. We also report the effect of low-dose irradiation combined with repair inhibitors on the relationship between DNA strand breaks, fragmentation, cell viability and use of nicotinamide adenine dinucleotide (NAD). DNA fragmentation was increased by 1 mM/1 FAA, 1 mM/l novobiocin and 50 microM/l RS-61443 within 3 h of incubation. The latter two compounds also proved cytotoxic. All three drugs augmented the effect of ionizing radiation on the use of NAD. Of the agents investigated, FAA showed the most promise for augmenting the immunosuppressive action of irradiation at nontoxic, pharmacokinetically achievable concentrations.

Topics: Animals; Antineoplastic Agents; Aphidicolin; Benzamides; Cytarabine; DNA Damage; DNA Repair; Doxorubicin; Flavonoids; Gamma Rays; Kinetics; Naphthoquinones; Novobiocin; Radiation-Sensitizing Agents; Rats; Rats, Sprague-Dawley; T-Lymphocytes; Time Factors; Vidarabine

Two agents, 3-aminobenzamide (3-AB) and beta lapachone, that inhibit repair of mammalian cell DNA damaged by methyl methane sulfonate (MMS), also coordinately blocked both DNA replication (incorporation of 3H-thymidine) and thymidylate synthase (TS) activity. Aphidicolin also inhibited both 3H-TDR incorporation and TS in damaged cells, the former more strongly than the latter, in a manner not coordinated with lethality. It is proposed that the DNA lesions created by MMS and modified by repair inhibit semiconservative DNA synthesis by allosterically interacting with the DNA replication replitase complex, so as to block its overall function and also the activity of TS, one of its enzymes.

Topics: Antibiotics, Antineoplastic; Aphidicolin; Benzamides; Cell Line; Diterpenes; DNA Repair; DNA Replication; Fibroblasts; Humans; Kinetics; Male; Methyl Methanesulfonate; Methyltransferases; Naphthoquinones; Skin; Thymidylate Synthase