Chain-fluorinated polyamines as tumor markers--IV. Comparison of 2-fluoroputrescine and 2,2-difluoroputrescine as substrates of spermidine synthase in vitro and in vivo.
1. 2-Fluoroputrescine has a high affinity for spermidine synthase (Km 12 microM) and obeys normal Michaelis-Menten kinetics. 2. The only product of the spermidine synthase-catalysed aminopropylation of 2-fluoroputrescine is 6-fluorospermidine. Formation of the isomeric 7-fluorospermidine could not be detected. 3. 2,2-Difluoroputrescine has even a higher affinity for spermidine synthase than putrescine and 2-fluoroputrescine; however, at concentrations greater than 25 microM one observes inhibition of the aminopropylation reaction. 4. Competition experiments between putrescine and 2,2-difluoroputrescine revealed mixed type inhibition. 5. HTC cells in suspension culture incorporated only small amounts of 2-fluoroputrescine, and even less in the case of 2,2-difluoroputrescine, if they were exposed to 10 microM concentrations of these diamines for up to 24 hr. However, in the presence of 0.5 mM DFMO, a concentration not sufficient to decrease cell growth significantly, but sufficient to decrease cellular putrescine and spermidine concentrations, the uptake of the chain-fluorinated diamines and their transformation into the fluorinated polyamine analogues was dramatically enhanced. In comparison with the difluoro analogues the accumulation rate of monofluoropolyamines was greater by a factor of about two. 6. 6-Fluorospermidine and 6-fluorospermine could be detected in significant quantities in nearly all tissues of mice 48 hr after a single dose (500 mg/kg) of 2-fluoroputrescine. In an analogous experiment with 2,2-difluoroputrescine, the formation of chain-fluorinated polyamines was considerably smaller. 7. Pretreatment of Lewis lung carcinoma bearing C57BL mice with alpha-difluoromethylornithine enhanced the incorporation of 2-fluoroputrescine into all organs, except the brain. Tumor and small intestines showed by far the highest accumulation of 6-fluoropolyamines. 8. Under identical experimental conditions the accumulation of chain-fluorinated polyamines in tumor tissue was more than twice as high with 2-fluoroputrescine as precursor than with the same dose of 2,2-difluoroputrescine. In normal tissues the difference between the uptake of 2-fluoroputrescine and 2,2-difluoroputrescine was usually even greater. 9. From the fact that the accumulation of 6-fluoropolyamines is less selective in tumors than that of 6,6-difluoropolyamines, and from the lower detection sensitivity due to its lower fluorine content, we conclude that 2,2-difluoroputrescine is more advantageous as a tumor marker than 2-fluoroputrescine for detection with 19F-NMR spectroscopy.(ABSTRACT TRUNCATED AT 400 WORDS)
Dezeure
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Merrell Dow Research Institute, Strasbourg, France.
Sarhan
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Seiler
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D000818:Animals; D001665:Binding Sites; D014408:Biomarkers, Tumor / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D008114:Liver Neoplasms, Experimental / Q000201:enzymology* / Q000378:metabolism; D008175:Lung Neoplasms / Q000201:enzymology* / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D011073:Polyamines / Q000378:metabolism*; D011700:Putrescine / Q000031:analogs & derivatives* / Q000378:metabolism; D051381:Rats; D013095:Spermidine / Q000378:metabolism; D013096:Spermine / Q000378:metabolism
D014408:Biomarkers, Tumor; D011073:Polyamines; C050613:2-fluoroputrescine; C054484:2,2-difluoroputrescine; D013096:Spermine; D013095:Spermidine; D011700:Putrescine