4'-Ethynyl-2-fluoro-2'-deoxyadenosine (EFdA) inhibits HIV-1 reverse transcriptase with multiple mechanisms

J Biol Chem. 2014 Aug 29;289(35):24533-48. doi: 10.1074/jbc.M114.562694. Epub 2014 Jun 26.


4'-Ethynyl-2-fluoro-2'-deoxyadenosine (EFdA) is a nucleoside analog that, unlike approved anti-human immunodeficiency virus type 1 (HIV-1) nucleoside reverse transcriptase inhibitors, has a 3'-OH and exhibits remarkable potency against wild-type and drug-resistant HIVs. EFdA triphosphate (EFdA-TP) is unique among nucleoside reverse transcriptase inhibitors because it inhibits HIV-1 reverse transcriptase (RT) with multiple mechanisms. (a) EFdA-TP can block RT as a translocation-defective RT inhibitor that dramatically slows DNA synthesis, acting as a de facto immediate chain terminator. Although non-translocated EFdA-MP-terminated primers can be unblocked, they can be efficiently converted back to the EFdA-MP-terminated form. (b) EFdA-TP can function as a delayed chain terminator, allowing incorporation of an additional dNTP before blocking DNA synthesis. In such cases, EFdA-MP-terminated primers are protected from excision. (c) EFdA-MP can be efficiently misincorporated by RT, leading to mismatched primers that are extremely hard to extend and are also protected from excision. The context of template sequence defines the relative contribution of each mechanism and affects the affinity of EFdA-MP for potential incorporation sites, explaining in part the lack of antagonism between EFdA and tenofovir. Changes in the type of nucleotide before EFdA-MP incorporation can alter its mechanism of inhibition from delayed chain terminator to immediate chain terminator. The versatility of EFdA in inhibiting HIV replication by multiple mechanisms may explain why resistance to EFdA is more difficult to emerge.

Keywords: AIDS; Antivirals; EFdA; Enzyme Inhibitor; Human Immunodeficiency Virus (HIV); NRTIs; Nucleoside/Nucleotide Analogue; Reverse Transcriptase; Reverse Transcription.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Base Sequence
  • Catalytic Domain
  • Cell Line
  • DNA Primers
  • Deoxyadenosines / pharmacology*
  • HIV Reverse Transcriptase / antagonists & inhibitors*
  • HIV Reverse Transcriptase / metabolism
  • Kinetics
  • Reverse Transcriptase Inhibitors / pharmacology*
  • Surface Plasmon Resonance


  • DNA Primers
  • Deoxyadenosines
  • Reverse Transcriptase Inhibitors
  • reverse transcriptase, Human immunodeficiency virus 1
  • HIV Reverse Transcriptase
  • 4'-ethynyl-2-fluoro-2'-deoxyadenosine