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)