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.?Eflornithine ?is an inhibitor of ODC, the first enzyme in eukaryotic polyamine biosynthesis.?Both enantiomers of Eflornithine ?irreversibly inactivate ODC.?Both Eflornithine enantiomers ?suppress ODC activity in a time- and concentration-dependent manner.?The inhibitor dissociation constant (KD) 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 (Kinact) 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.

The typical oral clearances of L-Eflornithine and D-eflornithine are 17.4 and 8.23 liters/h, respectively.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.