Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: UMLS:C0021051 (immunodeficiency)
71,517 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Nucleoside reverse transcriptase inhibitors (NRTIs) are employed in first line therapies for the treatment of human immunodeficiency virus (HIV) infection. They generally lack a 3'-hydroxyl group, and thus when incorporated into the nascent DNA they prevent further elongation. In this report we show that 4'-ethynyl-2-fluoro-2'-deoxyadenosine (EFdA), a nucleoside analog that retains a 3'-hydroxyl moiety, inhibited HIV-1 replication in activated peripheral blood mononuclear cells with an EC(50) of 0.05 nm, a potency several orders of magnitude better than any of the current clinically used NRTIs. This exceptional antiviral activity stems in part from a mechanism of action that is different from approved NRTIs. Reverse transcriptase (RT) can use EFdA-5'-triphosphate (EFdA-TP) as a substrate more efficiently than the natural substrate, dATP. Importantly, despite the presence of a 3'-hydroxyl, the incorporated EFdA monophosphate (EFdA-MP) acted mainly as a de facto terminator of further RT-catalyzed DNA synthesis because of the difficulty of RT translocation on the nucleic acid primer possessing 3'-terminal EFdA-MP. EFdA-TP is thus a translocation-defective RT inhibitor (TDRTI). This diminished translocation kept the primer 3'-terminal EFdA-MP ideally located to undergo phosphorolytic excision. However, net phosphorolysis was not substantially increased, because of the apparently facile reincorporation of the newly excised EFdA-TP. Our molecular modeling studies suggest that the 4'-ethynyl fits into a hydrophobic pocket defined by RT residues Ala-114, Tyr-115, Phe-160, and Met-184 and the aliphatic chain of Asp-185. These interactions, which contribute to both enhanced RT utilization of EFdA-TP and difficulty in the translocation of 3'-terminal EFdA-MP primers, underlie the mechanism of action of this potent antiviral nucleoside.
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PMID:Mechanism of inhibition of HIV-1 reverse transcriptase by 4'-Ethynyl-2-fluoro-2'-deoxyadenosine triphosphate, a translocation-defective reverse transcriptase inhibitor. 1983 73

Preexposure prophylaxis (PrEP) with antiretroviral drugs is a novel human immunodeficiency virus (HIV) prevention strategy. It is generally thought that high systemic and mucosal drug levels are sufficient for protection. We investigated whether GS7340, a next-generation tenofovir (TFV) prodrug that effectively delivers tenofovir diphosphate (TFV-DP) to lymphoid cells and tissues, could protect macaques against repeated weekly rectal simian-human immunodeficiency virus (SHIV) exposures. Macaques received prophylactic GS7340 treatment 3 days prior to each virus exposure. At 3 days postdosing, TFV-DP concentrations in peripheral blood mononuclear cells (PBMCs) were about 50-fold higher than those seen with TFV disoproxil fumarate (TDF), and they remained above 1,000 fmol/10(6) cells for as long as 7 days. TFV-DP accumulated in lymphoid and rectal tissues, with concentrations at 3 days exceeding 500 fmol/10(6) mononuclear cells. Despite high mucosal and systemic TFV levels, GS7340 was not protective. Since TFV-DP blocks reverse transcription by competing with the natural dATP substrate, we measured dATP contents in peripheral lymphocytes, lymphoid tissue, and rectal mononuclear cells. Compared to those in circulating lymphocytes and lymphoid tissue, rectal lymphocytes had 100-fold higher dATP concentrations and dATP/TFV-DP ratios, likely reflecting the activated status of the cells and suggesting that TFV-DP may be less active at the rectal mucosa. Our results identify dATP/TFV-DP ratios as a possible correlate of protection by TFV and suggest that natural substrate concentrations at the mucosa will likely modulate the prophylactic efficacy of nucleotide reverse transcriptase inhibitors.
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PMID:Natural substrate concentrations can modulate the prophylactic efficacy of nucleotide HIV reverse transcriptase inhibitors. 2152 46

Reverse transcriptases (RTs) are typically assayed in vitro with 5-10 mM Mg²⁺, whereas the free Mg²⁺ concentration in cells is much lower. Artificially high Mg²⁺ concentrations used in vitro can misrepresent different properties of human immunodeficiency virus (HIV) RT, including fidelity, catalysis, pausing, and RNase H activity. Here, we analyzed nucleoside (NRTIs) and non-nucleoside RT inhibitors (NNRTIs) in primer extension assays at different concentrations of free Mg²⁺. At low concentrations of Mg²⁺, NRTIs and dideoxynucleotides (AZTTP, ddCTP, ddGTP, and 3TCTP) inhibited HIV-1 and HIV-2 RT synthesis less efficiently than they did with large amounts of Mg²⁺, whereas inhibition by the "translocation-defective RT inhibitor" EFdA (4'-ethynyl-2-fluoro-2'-deoxyadenosine) was unaffected by Mg²⁺ concentrations. Steady-state kinetic analyses revealed that the reduced level of inhibition at low Mg²⁺ concentrations resulted from a 3-9-fold (depending on the particular nucleotide and inhibitor) less efficient incorporation (based on k_cat/K_m) of these NRTIs under this condition compared to incorporation of natural dNTPs. In contrast, EFdATP was incorporated with an efficiency similar to that of its analogue dATP at low Mg²⁺ concentrations. Unlike NRTIs, NNRTIs (nevirapine, efavirenz, and rilviripine), were approximately 4-fold (based on IC₅₀ values) more effective at low than at high Mg²⁺ concentrations. Drug-resistant HIV-1 RT mutants also displayed the Mg²⁺-dependent difference in susceptibility to NRTIs and NNRTIs. In summary, analyzing the efficiency of inhibitors under more physiologically relevant low-Mg²⁺ conditions yielded results dramatically different from those from measurements using commonly employed high-Mg²⁺ in vitro conditions. These results also emphasize differences in Mg²⁺ sensitivity between the translocation inhibitor EFdATP and other NRTIs.
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PMID:Physiological Mg²⁺ Conditions Significantly Alter the Inhibition of HIV-1 and HIV-2 Reverse Transcriptases by Nucleoside and Non-Nucleoside Inhibitors in Vitro. 2793 95


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