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Abstract

Carmustine and lomustine are nitrosourea antitumor chemotherapeutic agents which were used to determine whether or not they could affect arylamine N-acetyltransferase (NAT) activity and DNA-2-aminofluorene adducts in rat glial tumor cell line (C6 glioma). The NAT activity was measured by high preformance liquid chromatography (HPLC) assaying for the amounts of N-acetyl-2-aminofluorene (AAF) and N-acetyl-p-aminobenzoic acid (N-Ac-PABA) and remaining 2-aminofluorene (AF) and p-aminobenzoic acid (PABA). The results indicate that NAT activity in glial tumor cell cytosols and intact tumor cells were decreased by carmustine and lomustine in a dose-dependent manner. The apparent values of Km and Vmax of NAT from rat glial tumor cell also decreased after co-treatment of carmustine and lomustine in both examined cytosols and intact cells. Following exposure of glial tumor cells to the various concentrations of AF with or without co-treatment with carmustine and lomustine, DNA-AF adducts were determined by using gamma-[32p]-dATP and HPLC. The DNA-AF adducts in rat glial tumor cells were decreased by co-treatment with carmustine and lomustine. This report is the first demonstration to show carmustine and lomustine did inhibit rat glial tumor cells NAT activity and DNA-AF adduct formation.

Electrochemical Genotoxicity Screening for Arylamines Bioactivated by N-Acetyltransferase

“…In addition, nitrenium ions (5) can isomerize to proximal carbonium ions (6) that target the N 2 position of guanines producing AF-N 2 -guanine (8) and AAF-N 2 -guanine. 23 Previous arylamine genotoxicity studies addressing 2-AF metabolism have employed animal models, 45,47,56 in vitro cell lines, [42][43][44] or microsomal 57 or bacterial assays (i.e., Ames test) 58 that contain a range of phase I and phase II enzymes. Researchers employed selective inhibitors to demonstrate the importance of NAT in the bioactivation of 2-AF.…”

“…This helped establish the proposed metabolic pathway in Scheme 4. [42][43][44] However, to our knowledge, there have been no studies that have solely monitored the role of NAT in the formation of reactive metabolites in a purified system.…”

“…In the second pathway, 2-AF is converted to 2-AAF ( 2 ) by cytosolic NAT. Many papers have indicated that N-acetylation of 2-AF plays a role in metabolic activation to carcinogens. − , Species 2 undergoes hydroxylation by cyt P450 1A2 forming N−OH−2-AAF ( 3 ), which undergoes either intramolecular acetyl transfer or sulfonation to give reactive metabolites. The sulfonation of 3 is the only known branch point in this mechanism that produces N-acetylated DNA adducts, 2-AAF−guanine, due to the enhanced leaving ability of the sulfoxy moiety.…”

“…2-AF−DNA adduct formation in mice was used as an indicator of arylamine-induced DNA damage . NAT inhibitor studies in rat glial tumor cells, mouse leukemia cells, and human bladder carcinoma cells showed good correlation with 2-AF−DNA adduct formation. NAT-generated electrophiles leading to 2-AF−nucleobase adducts is thought to be a predominant pathway for mutagenic and carcinogenic effects associated with exposure to arylamines .…”

Exploring the Pivotal Neurophysiologic and Therapeutic Potentials of Vitamin C in Glioma

“…Hung established that rat glial tumor cells possess N-acetyltransferase (NAT) properties [ 123 ]. Furthermore, the rat's brain tissue was able to modulate NAT activity as well as the stimulation of N-acetylation of 2-aminofluorene (AF) ( Figure 2 ) [ 124 ].…”