In vitro evaluation of 4-[3-(2-nitro-1-imidazolyl)-propylamino]-7-trifluoromethylquinoline hydrochloride (NLTQ-1), a new bioreductive agent as a hypoxia marker by 19F-magnetic resonance spectroscopy (19F-MRS)

19F-labeled bioreductive drugs bound to hypoxic cells in tumors could be detected by nuclear magnetic resonance, provided that they do not lose 19F during their metabolism. NLTQ-1, a 2-nitroimidazole-linked 7-trifluoromethylquinoline, has been synthesized to furnish this aim. NLTQ-1 demonstrated hypoxic selectivities of 7-10 in various cell-lines, in vitro. Uptake studies in V79 cells showed a 5 to 6 fold greater intracellular than extracellular concentration at a range of 100-300 microM input concentrations. A strong sharp peak, which was identified as the parent compound, was observed in the 19F-NMR spectrum of 90% MeCN extracts of V79 cells aerobically exposed to NLTQ-1, indicating that NLTQ-1 was not metabolized under aerobic conditions. Similarly, 19F NMR efflux studies in intact cells showed that the NLTQ-1 was bound to the cells predominantly under hypoxic conditions. 19F-NMR spectra of intact cells, exposed under hypoxic conditions to NLTQ-1, and of their lysates, after precipitation of various cellular components, indicated that possible covalent binding of NLTQ-1 had occurred with macromolecules such as proteins and nucleic acids. Therefore, NLTQ-1 might be suitable as a 19F-MRS/MRI hypoxia probe, although further in vivo work is necessary to verify this matter.

Quantitative 19F NMR study of trifluorothymidine metabolism in rat brain

Metabolism of trifluorothymidine (TFT) and its transport across the blood-brain barrier (BBB) has been measured quantitatively in rats by fluorine-19 nuclear magnetic resonance spectroscopy ((19)F NMR). It is demonstrated that TFT crosses the BBB in micromolar quantities and is metabolized in brain tissue primarily to its free base trifluoromethyluracil (TFMU) by the enzyme thymidine phosphorylase (TP). It is further proposed that the rate of TFMU production can be used as a measure of cerebral TP. The glycols of both TFMU, and to a lesser degree TFT, are generated via an oxidative route. In contrast, the major pathway for hepatic metabolism of this compound is through reduction of the nitrogen base moiety and generation of 5-6-dihydro species followed by ring degradation. Thus, in addition to TFMU as well as the dihydroxy (glycol)-, and the dihydro-species of both TFT and TFMU, alpha-trifluoromethyl-beta-ureidopropionic acid (F(3)MUPA) and alpha-trifluoromethyl-beta-alanine (F(3)MBA) were detected in liver extracts. The total metabolite levels in liver were 2-5 times higher than in the brain. Low levels of fluoride ion were detected in all the extracts from brain and liver, as well as blood and urine. This study characterizes TFT as a potential chemotherapeutic agent for use against brain tumors.

Cerebral metabolism of fluorodeoxyglucose measured with 19F NMR spectroscopy

Brain extracts from rats given various doses of 2-fluoro-2-deoxy-D-glucose ranging from 20 to 300 mg/kg were examined with 19F NMR spectroscopy for fluorinated metabolic products and compared with the in vivo 19F spectra. Based on the analysis of these spectra and comparison with synthetic reference compounds, 2-fluoro-2-deoxy-D-glucose 6-phosphate and 2-fluoro-2-deoxy-D-mannose 6-phosphate were identified as the major metabolites present. 2-Fluoro-2-deoxy-D-6-phosphogluconate was detected only at high doses of 2-fluoro-2-deoxy-D-glucose administered, along with non-phosphorylated 2-fluoro-2-deoxy-D-glucose and 2-fluoro-2-deoxy-D-mannose. Small amounts of two other compounds, which were not identified, were also observed. Presence of the 2-fluoro-2-deoxy-D-mannose 6-phosphate is the result of 2-fluoro-2-deoxy-D-glucose 6-phosphate isomerization at the C2 position catalyzed by phosphoglucose isomerase. Results from the in vitro enzymatic reaction provide support for this hypothesis. Presence of 2-fluoro-2-deoxy-D-mannose may be the result of 2-fluoro-2-deoxy-D-glucose isomerization at the C2 position catalyzed by glucose isomerase or the result of the dephosphorylation of the 2-fluoro-2-deoxy-D-glucose 6-phosphate.