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KD:1.3±0.3 μM (Ornithine decarboxylase, ODC)
Eflornithine (D/L-DFMO) is an inhibitor of ODC, the first enzyme in eukaryotic polyamine biosynthesis. Both enantiomers of Eflornithine (DFMO) irreversibly inactivate ODC. Both Eflornithine enantiomers (L-Eflornithine and D-Eflornithine) suppress ODC activity in a time- and concentration-dependent manner. The inhibitor dissociation constant (K
D
) values for the formation of enzyme-inhibitor complexes are 28.3±3.4, 1.3±0.3 and 2.2±0.4 μM respectively for D-Eflornithine, L-Eflornithine and Eflornithine. The inhibitor inactivation constants (K
inact
) for the irreversible step were 0.25±0.03, 0.15±0.03 and 0.15±0.03 min
-1
respectively for D-Eflornithine, L-Eflornithine and Eflornithine. Treatment of human colon tumour-derived HCT116 cells with either L-Eflornithine or D- Eflornithine decreases the cellular polyamine contents in a concentration-dependent manner. The enantiomers display different potencies in vitro, with the L-enantiomer having up to a 20-fold higher affinity for the target enzyme ornithine decarboxylase.
The L-Eflornithine also appears to be more potent in cultured
T.brucei gambiense
parasites.
The more potent L-Eflornithine is present at much lower concentrations in both plasma and cerebrospinal fluid (CSF) than those of the D-Eflornithine. The plasma concentrations of L-Eflornithine are on average 52% of the D-enantiomer concentrations. The typical oral clearances of L-Eflornithine and D-eflornithine are 17.4 and 8.23 liters/h, respectively.