EFFECT OF STEREOISOMERISM ON THE CELLULAR PHARMACOLOGY OF BETA-ENANTIOMERS OF CYTIDINE ANALOGS IN HEP-G2 CELLS

The beta-L enantiomers of 2',3'-dideoxycytidine (beta-L-ddC) and its 5 -fluoro derivative, 2',3'-dideoxy-5-fluorocytidine (beta-L-FddC), were demonstrated to be active against human immunodeficiency virus (HIV) and hepatitis B virus (HBV) replication in vitro. In the present study , we investigated the cellular pharmacology of beta-L-ddC and beta-L-F ddC and compared it with that of beta-D-2',3'-dideoxy-5-fluorocytidine (beta-D-FddC). beta-L-FddC (10 mu M) was found to be phosphorylated r apidly in Hep-G2 cells to its 5'-mono-, di-, and triphosphate derivati ves with intracellular triphosphate levels achieving 26.6 +/- 10.9 pmo l/10(6) cells after 72 hr. In contrast, the active 5'-phosphorylated d erivative of beta-D-FddC achieved lower levels with triphosphate level s of only 23 +/- 0.5 pmol/10(6) cells under the same conditions. beta- L-ddC was also phosphorylated rapidly. A 5'-diphosphocholine (18.7 +/- 5.8 pmol/10(6) cells) and a 5'-diphosphoethanolamine (13.6 +/- 0.9 pm ol/10(6) cells) derivative were detected in beta-D-FddC-treated cells after 72 hr, whereas in beta-L-FddC- and beta-L-ddC-treated cells, onl y the 5'-diphosphocholine derivative (10.9 +/- 2.8 and 60.4 +/- 5.7 pm ol/10(6) cells, respectively) was detected. beta-L-FddC-5'-triphosphat e (beta-L-FddCTP), beta-D-FddC-5'-triphosphate (beta-D-FddCTP), and be ta-L-ddC-5'-triphosphate (beta-L-ddCTP) followed a single phase elimin ation process with an intracellular half-life (T-1/2) of 10.5, 5.7, an d 12.3 hr, respectively. Furthermore, beta-L-FddCTP, beta-D-FddCTP, an d beta-L-ddCTP levels of 6.7 +/- 2.3, 0.3 +/- 0.1, and 12.0 pmol/10(6) cells, respectively, were still detectable 24 hr following drug remov al. The higher intracellular 5'-triphosphate levels of beta-L-FddC and the extended T-1/2 of its 5'-triphosphate are consistent with the mor e potent in vitro antiviral activity of beta-L-FddC in Hep-G2 cells wh en compared with its beta-D enantiomer, beta-D-FddC. Copyright (C) 199 6 Elsevier Science Inc.