title: Balancing antiviral potency and host toxicity: identifying a nucleotide inhibitor with an optimal kinetic phenotype for HIV-1 reverse transcriptase.
abstract: Two novel thymidine analogs, 3'-fluoro-3'-deoxythymidine (FLT) and 2',3'-didehydro-3'-deoxy-4'-ethynylthymidine (Ed4T), have been investigated as nucleoside reverse transcriptase inhibitors (NRTIs) for treatment of HIV infection. Ed4T seems very promising in phase II clinical trials, whereas toxicity halted FLT development during this phase. To understand these different molecular mechanisms of toxicity, pre-steady-state kinetic studies were used to examine the interactions of FLT and Ed4T with wild-type (WT) human mitochondrial DNA polymerase γ (pol γ), which is often associated with NRTI toxicity, as well as the viral target protein, WT HIV-1 reverse transcriptase (RT). We report that Ed4T-triphosphate (TP) is the first analog to be preferred over native nucleotides by RT but to experience negligible incorporation by WT pol γ, with an ideal balance between high antiretroviral efficacy and minimal host toxicity. WT pol γ could discriminate Ed4T-TP from dTTP 12,000-fold better than RT, with only an 8.3-fold difference in discrimination being seen for FLT-TP. A structurally related NRTI, 2',3'-didehydro-2',3'-dideoxythymidine, is the only other analog favored by RT over native nucleotides, but it exhibits only a 13-fold difference (compared with 12,000-fold for Ed4T) in discrimination between the two enzymes. We propose that the 4'-ethynyl group of Ed4T serves as an enzyme selectivity moiety, critical for discernment between RT and WT pol γ. We also show that the pol γ mutation R964C, which predisposes patients to mitochondrial toxicity when receiving 2',3'-didehydro-2',3'-dideoxythymidine to treat HIV, produced some loss of discrimination for FLT-TP and Ed4T-TP. These molecular mechanisms of analog incorporation, which are critical for understanding pol γ-related toxicity, shed light on the unique toxicity profiles observed during clinical trials.
authors.affiliation: Department of Pharmacology, School of Medicine, Yale University, New Haven, Connecticut 06520, USA.
authors.forename: Christal D
authors.initials: CD
authors.lastname: Sohl
authors.forename: Rajesh
authors.initials: R
authors.lastname: Kasiviswanathan
authors.forename: Jiae
authors.initials: J
authors.lastname: Kim
authors.forename: Ugo
authors.initials: U
authors.lastname: Pradere
authors.forename: Raymond F
authors.initials: RF
authors.lastname: Schinazi
authors.forename: William C
authors.initials: WC
authors.lastname: Copeland
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Mitsuya
authors.forename: Masanori
authors.initials: M
authors.lastname: Baba
authors.forename: Karen S
authors.initials: KS
authors.lastname: Anderson
mesh_terms: D019380:Anti-HIV Agents / Q000494:pharmacology*; D000074002:DNA Polymerase gamma; D004272:DNA, Mitochondrial / Q000187:drug effects / Q000378:metabolism; D004259:DNA-Directed DNA Polymerase / Q000378:metabolism; D015224:Dideoxynucleosides / Q000494:pharmacology; D015658:HIV Infections / Q000188:drug therapy / Q000378:metabolism; D054303:HIV Reverse Transcriptase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D015497:HIV-1 / Q000187:drug effects / Q000201:enzymology* / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D009711:Nucleotides / Q000037:antagonists & inhibitors*; D018894:Reverse Transcriptase Inhibitors / Q000494:pharmacology*; D018119:Stavudine / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D019380:Anti-HIV Agents; D004272:DNA, Mitochondrial; D015224:Dideoxynucleosides; D009711:Nucleotides; D018894:Reverse Transcriptase Inhibitors; C486840:2',3'-didehydro-3'-deoxy-4'-ethynylthymidine; D018119:Stavudine; C514824:reverse transcriptase, Human immunodeficiency virus 1; D054303:HIV Reverse Transcriptase; D000074002:DNA Polymerase gamma; D004259:DNA-Directed DNA Polymerase