Effects of beta-L-3 '-azido-3 '-deoxythymidine 5 '-triphosphate on host and viral DNA polymerases

We have previously reported that several beta-L-thymidine analogues includi ng beta-L-3'-azido-3'-deoxythymidine (beta-L-AZT), beta-L-3'-fluoro-2',3'-d ideoxythymidine (beta-L-FLT) and beta-L-2',3'-didehydro-2',3'-dideoxythymid ine (beta-L-D4T) did not inhibit HIV replication in human peripheral blood mononuclear (PBM) cells whereas their corresponding P-D-counterparts are kn own as potent and selective anti-HIV agents [Faraj et al., 1997. Nucleoside s and Nucleotides 16, 1287-1290]. In order to gain insight on the lack of a ntiviral activities of these beta-L-derivatives, in vitro enzymatic steady state studies were conducted in the present study with beta-L-AZT. beta-L-A ZT 5'-triphosphate (L-AZTTP) was chemically synthesized and found to modera tely inhibit wild-type HIV reverse transcriptase (HIV-1 RT) with a K-i valu e of 2 mu M; while lacking any inhibitory effect towards human DNA polymera se alpha, beta or gamma. However, the inhibitory effect of L-AZTTP towards HIV-1 RT was very modest (266-fold less potent) when compared to its isomer beta-D-AZT 5'-triphosphate (D-AZTTP) which exhibits a K-i value of 0.0075 mu M and this finding was further confirmed by DNA chain termination assay. These data suggest that the absence of antiviral activity of the parent be ta-L-AZT may in part be explained by the poor inhibition of the targeted vi ral enzyme by L-AZTTP, the active metabolite. Finally, L-AZTTP was found to lack affinity for the mutant RT at position 184 (M184V) demonstrating that this mutation confers resistance not only to beta-L-2',3'-dideoxycytidine analogs as previously reported by our group [Faraj et al., 1994. Antimicrob . Agents Chemother. 38, 2300-2305] but as well as to beta-L-2',3'-dideoxyth ymidine analogs. (C) 2000 Elsevier Science B.V. All rights reserved.