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The tissue distribution and biodynamics of 18F-labelled 5-fluorouracil (FU) are described and studied for correlation with its in vivo antitumor activity. The in vivo model consisted of Balb/c mice bearing a FU sensitive (Colon 26-10 carcinoma) tumor in the left and a less responsive (Colon 26 carcinoma) tumor in the right abdominal side of the animal. Distribution and efflux of 18F-label from tumor, blood, and other tissues were determined by obduction at 0.5, 1, 2, 4, and 6 h postintravenous injection. For a comparison, the 18F-labeled 5-fluoro-6-hydroxy and cis-5-fluoro-6-ethoxy uracil adducts were studied in the same in vivo model. For 18F-FU it was found that the 18F-label tumor kinetics rapidly fell into a biphasic mode: a relatively short 18F beta phase (18F t1/2 beta 21 +/- 3 min), linked with the total body metabolic capacity and clearance of the animal, and a longer 18F gamma phase, linked with the intrinsic intratumoral FU metabolism (Colon 26-10: 18F t1/2 gamma 10.3 h; Colon 26: 18F t1/2 gamma 5.6 h). It is proposed that the observed faster 18F efflux of the less responsive Colon 26 corresponds to an enhanced breakdown of 5-fluoronucleotides to 5-fluoronucleosides and subsequent elimination from the tumor cells. It is concluded that on PET scanning, measurement of the dynamic 18F t1/2 gamma and 18F t1/2 beta parameter is of prime importance for an insight in the in vivo tumor biology of a patient.

The formation of RNA and DNA adducts by the environmental pollutant 2-nitrofluorene (2-NF) has been investigated in rat liver in vivo. The adduct pattern was studied after trifluoroacetic acid hydrolysis of DNA or RNA, followed by analysis of the adducts by HPLC. This was also done by enzymatic hydrolysis of DNA, followed by 32P-postlabeling. Both after oral and i.v. administration of [3H]2-NF, one major adduct was found. This adduct did not co-migrate with one of the known adducts of 2-(acetyl)-aminofluorene, N-deoxyguanosin-8-yl-2-aminofluorene (dG-C8-AF), which could have been formed after nitroreduction of 2-NF. 32P-Postlabeling revealed that two minor adducts were also formed, one of which was dG-C8-AF. The observation that the major adduct was also formed after i.v. administration of 2-NF to bile duct-catheterized rats makes a role for the intestinal microflora in the formation of this adduct very unlikely. In vitro experiments with inhibitors of the enzyme epoxide hydrolase indicated that epoxidation of 2-NF may play a role in the microsomal bioactivation of this compound.

The activation of 2-nitrofluorene (2-NF) to reactive intermediates that bind covalently to DNA, RNA and protein has been investigated both in vitro and in the rat in vivo. In vitro, such binding was catalyzed by the hepatic microsomal fraction, was NADPH dependent and could be inhibited by SKF 525A, an inhibitor of cytochrome P450. The generation of reactive intermediates therefore is most likely catalyzed by cytochrome P450. Covalent binding of 2-NF could not be prevented by glutathione, N-acetylcysteine and other thiol-containing compounds. It could be partially prevented by guanosine, presumably because it traps the reactive intermediate(s). Under normal oxygenation conditions 2-NF was also covalently bound in freshly isolated hepatocytes; pretreatment of rats with an inducer of cytochrome P450, Aroclor 1254, gave rise to a higher rate of covalent binding in hepatocytes. Covalent binding of 2-NF to cellular macromolecules also occurred in vivo, both after oral and i.v. administration. Pentachlorophenol, a selective sulfation inhibitor, did not influence the covalent binding of 2-NF; therefore, the reactive intermediate is not formed by sulfation of N-hydroxy-2-acetylaminofluorene, which could be a metabolite of 2-NF. It is concluded that the reactive intermediates most likely can be formed from 2-NF by the cytochrome P450 enzyme system.

The fluorination of 1,4-benzo- and naphthoquinones using [18F]acetylhypofluorite is described. For compounds with electron-donating substituents fair to good radiochemical yields have been reached.