Fluorination at the 4 position alters the substrate behavior of L-glutamine and L-glutamate: Implications for positron emission tomography of neoplasias.
J Fluor Chem 2017;
192:58-67. [PMID:
28546645 DOI:
10.1016/j.jfluchem.2016.10.008]
[Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
Two 4-fluoro-L-glutamine diastereoisomers [(2S,4R)-4-FGln, (2S,4S)-4-FGln] were previously developed for positron emission tomography. Label uptake into two tumor cell types was greater with [18F](2S,4R)-4-FGln than with [18F](2S,4S)-4-FGln. In the present work we investigated the enzymology of two diastereoisomers of 4-FGln, two diastereoisomers of 4-fluoroglutamate (4-FGlu) (potential metabolites of the 4-FGln diastereoisomers) and another fluoro-derivative of L-glutamine [(2S,4S)-4-(3-fluoropropyl)glutamine (FP-Gln)]. The two 4-FGlu diastereoisomers were found to be moderate-to-good substrates relative to L-glutamate of glutamate dehydrogenase, aspartate aminotransferase and alanine aminotransferase. Additionally, alanine aminotransferase was shown to catalyze an unusual γ-elimination reaction with both 4-FGlu diastereoisomers. Both 4-FGlu diastereoisomers were shown to be poor substrates, but strong inhibitors of glutamine synthetase. Both 4-FGln diastereoisomers were shown to be poor substrates compared to L-glutamine of glutamine transaminase L and α-aminoadipate aminotransferase. However, (2S,4R)-4-FGln was found to be a poor substrate of glutamine transaminase K, whereas (2S,4S)-4-FGln was shown to be an excellent substrate. By contrast, FP-Gln was found to be a poor substrate of all enzymes examined. Evidently, substitution of H in position 4 by F in L-glutamine/L-glutamate has moderate-to-profound effects on enzyme-catalyzed reactions. The present results: 1) show that 4-FGln and 4-FGlu diastereoisomers may be useful for studying active site topology of glutamate- and glutamine-utilizing enzymes; 2) provide a framework for understanding possible metabolic transformations in tumors of 18F-labeled (2S,4R)-4-FGln, (2S,4S)-4-FGln, (2S,4R)-4-FGlu or (2S,4S)-4-FGlu; and 3) show that [18F]FP-Gln is likely to be much less metabolically active in vivo than are the [18F]4-FGln diastereoisomers.
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