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Chapter 4 : Nucleoside Analogue Inhibitors of Human Immunodeficiency Virus Reverse Transcriptase
Authors:
Jérôme Deval1,
Matthias Götte2
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Affiliations:
1: Roche Palo Alto, 3431 Hillview Avenue, Palo Alto, CA 94304;
2: Department of Microbiology & Immunology, McGill University, Montreal, Quebec, Canada
Content Type: Monograph
Publication Year:
2009
Category: Viruses and Viral Pathogenesis; Clinical Microbiology
Book DOI:
10.1128/9781555815493
Chapter DOI:
10.1128/9781555815493.ch4
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Abstract:
More than 20 different antiretroviral agents have been approved for human immunodeficiency virus (HIV) treatment. These compounds target distinct stages in the life cycle of this retrovirus that include (i) its entry into the cytoplasm, which marks the beginning of the infection; (ii) the process of reverse transcription, i.e., the conversion of the single-stranded RNA genome into double-stranded DNA; (iii) the integration of proviral, double-stranded DNA into the host chromosome; and (iv) the processing of viral precursor proteins at later stages. These steps are vital for viral replication, and with the exception of the entry process, each of the aforementioned reactions involves viral enzymes, i.e., the reverse transcriptase (RT), the integrase, and the protease, respectively, that can be targeted by antiretroviral drugs. This chapter focuses on nucleoside analogue RT inhibitors (NRTIs) in the context of mechanisms of action and resistance and on the implications for the development of future strategies designed to counteract resistance. All approved NRTIs show a broad spectrum of antiviral activity against HIV-1, HIV- 2, and sometimes even hepatitis B virus (HBV), which points to structurally highly related active sites. A given mutation or mutational cluster can affect susceptibility to different NRTIs to various degrees, which makes it difficult to group the mutations. It will be interesting to investigate how established and novel NRTIs can be most effectively combined with new classes of compounds with the ultimate goal of further reducing the risk of resistance development, while maintaining high standards regarding problems associated with toxicities and dosing.
Citation:
Deval J, Götte M.
2009.
Nucleoside Analogue Inhibitors of Human Immunodeficiency Virus Reverse Transcriptase,
p 51-70.
In
LaFemina, Ph. D. R (ed),
Antiviral Research.
ASM Press, Washington, DC.
doi: 10.1128/9781555815493.ch4
Key Concept Ranking
- DNA Synthesis
- 0.4726755
- Hepatitis B virus
- 0.45390382
- Tenofovir Disoproxil Fumarate
- 0.44800895
0.4726755
Figures
Nucleoside Analogue Inhibitors of Human Immunodeficiency Virus Reverse Transcriptase
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Citation:
Deval J, Götte M.
2009.
Nucleoside Analogue Inhibitors of Human Immunodeficiency Virus Reverse Transcriptase,
p 51-70.
In
LaFemina, Ph. D. R (ed),
Antiviral Research.
ASM Press, Washington, DC.
doi: 10.1128/9781555815493.ch4
/content/10.1128/9781555815493.ch04.ch04fig01
Figure 1.
Crystal structure of HIV-1 RT. (A) Ribbon representation of the apoenzyme. Subdomains of p66 are labeled. (B) Molecular surface of HIV-1 RT, with the same orientation as in panel A. (C) Binary complex of the enzyme with its polynucleotide substrate. The distance between the active site of the polymerase domain and the RNase H domain is shown by arrows.
10.1128/9781555815493/f0052-01_thmb.gif
10.1128/9781555815493/f0052-01.gif
Figure 1.
Crystal structure of HIV-1 RT. (A) Ribbon representation of the apoenzyme. Subdomains of p66 are labeled. (B) Molecular surface of HIV-1 RT, with the same orientation as in panel A. (C) Binary complex of the enzyme with its polynucleotide substrate. The distance between the active site of the polymerase domain and the RNase H domain is shown by arrows.
Citation:
Deval J, Götte M.
2009.
Nucleoside Analogue Inhibitors of Human Immunodeficiency Virus Reverse Transcriptase,
p 51-70.
In
LaFemina, Ph. D. R (ed),
Antiviral Research.
ASM Press, Washington, DC.
doi: 10.1128/9781555815493.ch4
/content/10.1128/9781555815493.ch04.ch04fig02
Figure 2.
Spatial constraints for drug design. (A) Simplified scheme of the catalytic reaction of phosphoryl transfer. The hydroxyl at the 3’ end of the primer attacks the α-phosphate of the incoming nucleotide. Two metal ions (designated A and B) stabilize the positioning of the triphosphate group, in coordination with the aspartic acids (bottom) and two positively charged residues (top). (B) Targeted sites for modifications on nucleosides.
10.1128/9781555815493/f0054-01_thmb.gif
10.1128/9781555815493/f0054-01.gif
Figure 2.
Spatial constraints for drug design. (A) Simplified scheme of the catalytic reaction of phosphoryl transfer. The hydroxyl at the 3’ end of the primer attacks the α-phosphate of the incoming nucleotide. Two metal ions (designated A and B) stabilize the positioning of the triphosphate group, in coordination with the aspartic acids (bottom) and two positively charged residues (top). (B) Targeted sites for modifications on nucleosides.
Citation:
Deval J, Götte M.
2009.
Nucleoside Analogue Inhibitors of Human Immunodeficiency Virus Reverse Transcriptase,
p 51-70.
In
LaFemina, Ph. D. R (ed),
Antiviral Research.
ASM Press, Washington, DC.
doi: 10.1128/9781555815493.ch4
/content/10.1128/9781555815493.ch04.ch04fig03
Figure 3.
Chemical structures of currently approved NRTIs.
10.1128/9781555815493/f0055-01_thmb.gif
10.1128/9781555815493/f0055-01.gif
Figure 3.
Chemical structures of currently approved NRTIs.
Citation:
Deval J, Götte M.
2009.
Nucleoside Analogue Inhibitors of Human Immunodeficiency Virus Reverse Transcriptase,
p 51-70.
In
LaFemina, Ph. D. R (ed),
Antiviral Research.
ASM Press, Washington, DC.
doi: 10.1128/9781555815493.ch4
/content/10.1128/9781555815493.ch04.ch04fig04
Figure 4.
Route of metabolic activation of NRTIs by kinases. Examples of activation of AZT and tenofovir show the number of steps required to generate the corresponding active nucleotides prior to chain termination.
10.1128/9781555815493/f0056-01_thmb.gif
10.1128/9781555815493/f0056-01.gif
Figure 4.
Route of metabolic activation of NRTIs by kinases. Examples of activation of AZT and tenofovir show the number of steps required to generate the corresponding active nucleotides prior to chain termination.
Citation:
Deval J, Götte M.
2009.
Nucleoside Analogue Inhibitors of Human Immunodeficiency Virus Reverse Transcriptase,
p 51-70.
In
LaFemina, Ph. D. R (ed),
Antiviral Research.
ASM Press, Washington, DC.
doi: 10.1128/9781555815493.ch4
/content/10.1128/9781555815493.ch04.ch04fig05
Figure 5.
NRTI resistance (adapted from reference
42a
).
10.1128/9781555815493/f0058-01_thmb.gif
10.1128/9781555815493/f0058-01.gif
Figure 5.
NRTI resistance (adapted from reference 42a ).
Citation:
Deval J, Götte M.
2009.
Nucleoside Analogue Inhibitors of Human Immunodeficiency Virus Reverse Transcriptase,
p 51-70.
In
LaFemina, Ph. D. R (ed),
Antiviral Research.
ASM Press, Washington, DC.
doi: 10.1128/9781555815493.ch4
/content/10.1128/9781555815493.ch04.ch04fig06
Figure 6.
Reaction scheme for NRTI incorporation and drug resistance. After formation of the nucleoprotein complex (E*DNAn), chain termination by NRTIs at position DNAn+1 requires an initial binding step [measured by Kd
(NRTI)], followed by a catalytic step (kpol
) with PPi as a side product (
43
). Mutations such as M184V (Kd
effect) or K65R (kpol
effect) confer resistance of HIV-1 RT by discriminating against NRTIs. On the other hand, TAMs increase the pyrophosphorolytic properties of HIV-1 RT, mainly observed on the incorporation of AZT-MP.
10.1128/9781555815493/f0059-01_thmb.gif
10.1128/9781555815493/f0059-01.gif
Figure 6.
Reaction scheme for NRTI incorporation and drug resistance. After formation of the nucleoprotein complex (E*DNAn), chain termination by NRTIs at position DNAn+1 requires an initial binding step [measured by Kd (NRTI)], followed by a catalytic step (kpol ) with PPi as a side product ( 43 ). Mutations such as M184V (Kd effect) or K65R (kpol effect) confer resistance of HIV-1 RT by discriminating against NRTIs. On the other hand, TAMs increase the pyrophosphorolytic properties of HIV-1 RT, mainly observed on the incorporation of AZT-MP.
Citation:
Deval J, Götte M.
2009.
Nucleoside Analogue Inhibitors of Human Immunodeficiency Virus Reverse Transcriptase,
p 51-70.
In
LaFemina, Ph. D. R (ed),
Antiviral Research.
ASM Press, Washington, DC.
doi: 10.1128/9781555815493.ch4
/content/10.1128/9781555815493.ch04.ch04fig07
Figure 7.
Scheme of enzyme positioning on its nucleic acid substrate. The nucleotide binding site is occupied by the end of the primer directly after phosphoryl transfer. RT translocates by one base at a time to free the N site prior to each catalytic step.
10.1128/9781555815493/f0061-01_thmb.gif
10.1128/9781555815493/f0061-01.gif
Figure 7.
Scheme of enzyme positioning on its nucleic acid substrate. The nucleotide binding site is occupied by the end of the primer directly after phosphoryl transfer. RT translocates by one base at a time to free the N site prior to each catalytic step.
Citation:
Deval J, Götte M.
2009.
Nucleoside Analogue Inhibitors of Human Immunodeficiency Virus Reverse Transcriptase,
p 51-70.
In
LaFemina, Ph. D. R (ed),
Antiviral Research.
ASM Press, Washington, DC.
doi: 10.1128/9781555815493.ch4
/content/10.1128/9781555815493.ch04.ch04fig08
Figure 8.
Role of the RNase H domain in AZT resistance. Mutations identified in the connection and RNase H domains have been shown to decrease the RNAse H activity. By slowing down the rate of template switching, these mutations increase the residence time of RT, which allows excision of the chain terminator.
10.1128/9781555815493/f0062-01_thmb.gif
10.1128/9781555815493/f0062-01.gif
Figure 8.
Role of the RNase H domain in AZT resistance. Mutations identified in the connection and RNase H domains have been shown to decrease the RNAse H activity. By slowing down the rate of template switching, these mutations increase the residence time of RT, which allows excision of the chain terminator.
Citation:
Deval J, Götte M.
2009.
Nucleoside Analogue Inhibitors of Human Immunodeficiency Virus Reverse Transcriptase,
p 51-70.
In
LaFemina, Ph. D. R (ed),
Antiviral Research.
ASM Press, Washington, DC.
doi: 10.1128/9781555815493.ch4
/content/10.1128/9781555815493.ch04.ch04fig09
Figure 9.
Names and chemical structures of NNRTIs in development.
10.1128/9781555815493/f0065-01_thmb.gif
10.1128/9781555815493/f0065-01.gif
Figure 9.
Names and chemical structures of NNRTIs in development.
Citation:
Deval J, Götte M.
2009.
Nucleoside Analogue Inhibitors of Human Immunodeficiency Virus Reverse Transcriptase,
p 51-70.
In
LaFemina, Ph. D. R (ed),
Antiviral Research.
ASM Press, Washington, DC.
doi: 10.1128/9781555815493.ch4
References
/content/book/10.1128/9781555815493.ch04
1.
Ahluwalia, G. S.,, W. Y. Gao,, H. Mitsuya, and, D. G. Johns. 1996. 2’,3’-Didehydro-3’-deoxythymidine: regulation of its metabolic activation by modulators of thymidine-5’-triphosphate biosynthesis. Mol. Pharmacol. 50: 160– 165.
2.
Arion, D.,, N. Kaushik,, S. McCormick,, G. Borkow, and, M. A. Parniak. 1998. Phenotypic mechanism of HIV-1 resistance to 3’-azido-3’-deoxythymidine (AZT): increased polymerization processivity and enhanced sensitivity to pyrophosphate of the mutant viral reverse transcriptase. Biochemistry 37: 15908– 15917.
3.
Arts, E. J., and, S. F. Le Grice. 1998. Interaction of retroviral reverse transcriptase with template-primer duplexes during replication. Prog. Nucleic Acid Res. Mol. Biol. 58: 339– 393.
4.
Balzarini, J.,, P. Herdewijn, and, E. De Clercq. 1989. Differential patterns of intracellular metabolism of 2’,3’-didehydro-2’,3’-dideoxythymidine and 3’-azido-2’,3’-dideoxythymidine, two potent anti-human immunodeficiency virus compounds. J. Biol. Chem. 264: 6127– 6133.
5.
Basavapathruni, A.,, C. M. Bailey, and, K. S. Anderson. 2004. Defining a molecular mechanism of synergy between nucleoside and nonnucleoside AIDS drugs. J. Biol. Chem. 279: 6221– 6224.
6.
Bazmi, H. Z.,, J. L. Hammond,, S. C. Cavalcanti,, C. K. Chu,, R. F. Schinazi, and, J. W. Mellors. 2000. In vitro selection of mutations in the human immunodeficiency virus type 1 reverse transcriptase that decrease susceptibility to (-)-beta- D-dioxolane-guanosine and suppress resistance to 3’-azido-3’-deoxythymidine. Antimicrob. Agents Chemother. 44: 1783– 1788.
7.
Belleau, B.,, D. Dixit,, N. Nguyen-Ba, and, J. L. Kraus. 1989. Proceedings of the 5th International Conference on AIDS, Montreal, abstr. TC01:515.
8.
Boucher, C. A.,, N. Cammack,, P. Schipper,, R. Schuurman,, P. Rouse,, M. A. Wainberg, and, J. M. Cameron. 1993. High-level resistance to (-) enantiomeric 2’-deoxy-3’-thiacytidine in vitro is due to one amino acid substitution in the catalytic site of human immunodeficiency virus type 1 reverse transcriptase. Antimicrob. Agents Chemother. 37: 2231– 2234.
9.
Boyer, P. L.,, S. G. Sarafianos,, E. Arnold, and, S. H. Hughes. 2001. Selective excision of AZTMP by drug-resistant human immunodeficiency virus reverse transcriptase. J. Virol. 75: 4832– 4842.
10.
Boyer, P. L.,, S. G. Sarafianos,, P. K. Clark,, E. Arnold, and, S. H. Hughes. 2006. Why do HIV-1 and HIV-2 use different pathways to develop AZT resistance? PLoS Pathog. 2: e10.
11.
Brehm, J. H.,, D. Koontz,, J. D. Meteer,, V. Pathak,, N. SluisCremer, and, J. W. Mellors. 2007. Selection of mutations in the connection and RNase H domains of human immunodeficiency virus type 1 reverse transcriptase that increase resistance to 3’-azido-3’-dideoxythymidine. J. Virol. 81: 7852– 7859.
12.
Budihas, S. R.,, I. Gorshkova,, S. Gaidamakov,, A. Wamiru,, M. K. Bona,, M. A. Parniak,, R. J. Crouch,, J. B. McMahon,, J. A. Beutler, and, S. F. Le Grice. 2005. Selective inhibition of HIV-1 reverse transcriptase-associated ribonuclease H activity by hydroxylated tropolones. Nucleic Acids Res. 33: 1249– 1256.
13.
Carroll, S. S.,, J. Geib,, D. B. Olsen,, M. Stahlhut,, J. A. Shafer, and, L. C. Kuo. 1994. Sensitivity of HIV-1 reverse transcriptase and its mutants to inhibition by azidothymidine triphosphate. Biochemistry 33: 2113– 2120.
14.
Chong, Y.,, K. Borroto-Esoda,, P. A. Furman,, R. F. Schinazi, and, C. K. Chu. 2002. Molecular mechanism of DApd/DXG against zidovudine- and lamivudine- drug resistant mutants: a molecular modelling approach. Antivir. Chem. Chemother. 13: 115– 128.
15.
Cihlar, T.,, A. S. Ray,, C. G. Boojamra,, L. Zhang,, H. Hui,, G. Laflamme,, J. E. Vela,, D. Grant,, J. Chen,, F. Myrick,, K. L. White,, Y. Gao,, K. Y. Lin,, J. L. Douglas,, N. T. Parkin,, A. Carey,, R. Pakdaman, and, R. L. Mackman. 2008. Design and profiling of GS-9148, a novel nucleotide analog active against nucleoside-resistant variants of human immunodeficiency virus type 1, and its orally bio-available phosphonoamidate prodrug, GS-9131. Antimicrob. Agents Chemother. 52: 655– 665.
16.
Das, K.,, X. Xiong,, H. Yang,, C. E. Westland,, C. S. Gibbs,, S. G. Sarafianos, and, E. Arnold. 2001. Molecular modeling and biochemical characterization reveal the mechanism of hepatitis B virus polymerase resistance to lamivudine (3TC) and emtricitabine (FTC). J. Virol. 75: 4771– 4779.
17.
de Muys, J. M.,, H. Gourdeau,, N. Nguyen-Ba,, D. L. Taylor,, P. S. Ahmed,, T. Mansour,, C. Locas,, N. Richard,, M. A. Wainberg, and, R. F. Rando. 1999. Anti-human immunodeficiency virus type 1 activity, intracellular metabolism, and pharmacokinetic evaluation of 2’-deoxy-3’-oxa-4’-thiocytidine. Antimicrob. Agents Che-mother. 43: 1835– 1844.
18.
Descamps, D.,, F. Damond,, S. Matheron,, G. Collin,, P. Campa,, S. Delarue,, S. Pueyo,, G. Chene, and, F. Brun-Vezinet. 2004. High frequency of selection of K65R and Q151M mutations in HIV-2 infected patients receiving nucleoside reverse transcriptase inhibitors containing regimen. J. Med. Virol. 74: 197– 201.
19.
Deval, J.,, B. Selmi,, J. Boretto,, M. P. Egloff,, C. Guerreiro,, S. Sarfati, and, B. Canard. 2002. The molecular mechanism of multidrug resistance by the Q151M human immunodeficiency virus type 1 reverse transcriptase and its suppression using alpha-boranophosphate nucleotide analogues. J. Biol. Chem. 277: 42097– 42104.
20.
Domaoal, R. A.,, M. McMahon,, C. L. Thio,, C. M. Bailey,, J. Tirado-Rives,, A. Obikhod,, M. Detorio,, K. L. Rapp,, R. F. Siliciano,, R. F. Schinazi, and, K. S. Anderson. 2008. Pre-steady-state kinetic studies establish entecavir 5’-triphosphate as a substrate for HIV-1 reverse transcriptase. J. Biol. Chem. 283: 5452– 5459.
21.
Doublie, S.,, M. R. Sawaya, and, T. Ellenberger. 1999. An open and closed case for all polymerases. Struct. Fold Des. 7: R31– R35.
22.
Ehteshami, M.,, G. L. Beilhartz,, B. J. Scarth,, E. P. Tchesnokov,, S. McCormick,, B. Wynhoven,, P. R. Harrigan, and, M. Götte. 2008. Connection domain mutations N3481 and A360V in HIV-1 reverse transcriptase enhance resistance to 3’-azido-3’-deoxythymidine through both RNase H-dependent and -independent mechanisms. J. Biol. Chem. 32: 22222– 22232.
23.
Ehteshami, M., and, M. Götte. 2008. Effects of mutations in the connection and RNase H domains of HIV-1 reverse transcriptase on drug susceptibility. AIDS Rev. 10: 224– 235.
24.
Ehteshami, M.,, B. J. Scarth,, E. P. Tchesnokov,, C. Dash,, S. F. Le Grice,, S. Hallenberger,, D. Jochmans, and, M. Götte. 2008. Mutations M184V and Y115F in HIV-1 reverse transcriptase discriminate against “nucleotide-competing reverse transcriptase inhibitors.” J. Biol. Chem. 283: 29904– 29911.
25.
El Safadi, Y.,, V. Vivet-Boudou, and, R. Marquet. 2007. HIV-1 reverse transcriptase inhibitors. Appl. Microbiol. Biotechnol. 75: 723– 737.
26.
Feng, J. Y., and, K. S. Anderson. 1999. Mechanistic studies examining the efficiency and fidelity of DNA synthesis by the 3TC-resistant mutant (184V) of HIV-1 reverse transcriptase. Biochemistry 38: 9440– 9448.
27.
Feng, J. Y.,, A. A. Johnson,, K. A. Johnson, and, K. S. Anderson. 2001. Insights into the molecular mechanism of mitochondrial toxicity by AIDS drugs. J. Biol. Chem. 276: 23832– 23837.
28.
Feng, J. Y.,, J. Shi,, R. F. Schinazi, and, K. S. Anderson. 1999. Mechanistic studies show that (-)-FTC-TP is a better inhibitor of HIV-1 reverse transcriptase than 3TC-TP. FASEB J. 13: 1511– 1517.
29.
Frankel, F. A.,, B. Marchand,, D. Turner,, M. Götte, and, M. A. Wainberg. 2005. Impaired rescue of chain-terminated DNA synthesis associated with the L74V mutation in human immunodeficiency virus type 1 reverse transcriptase. Antimicrob. Agents Che-mother. 49: 2657– 2664.
30.
Fung, H. B.,, E. A. Stone, and, F. J. Piacenti. 2002. Tenofovir disoproxil fumarate: a nucleotide reverse transcriptase inhibitor for the treatment of HIV infection. Clin. Ther. 24: 1515– 1548.
31.
Gao, Q.,, Z. Gu,, M. A. Parniak,, J. Cameron,, N. Cammack,, C. Boucher, and, M. A. Wainberg. 1993. The same mutation that encodes low-level human immunodeficiency virus type 1 resistance to 2’,3’-dideoxyinosine and 2’,3’-dideoxycytidine confers high-level resistance to the (-) enantiomer of 2’,3’-dideoxy-3’-thiacyti-dine. Antimicrob. Agents Chemother. 37: 1390– 1392.
32.
Garcia-Lerma, J. G.,, P. J. Gerrish,, A. C. Wright,, S. H. Qari, and, W. Heneine. 2000. Evidence of a role for the Q151L mutation and the viral background in development of multiple dideoxynucleo-side-resistant human immunodeficiency virus type 1. J. Virol. 74: 9339– 9346.
33.
Götte, M. 2006. Effects of nucleotides and nucleotide analogue inhibitors of HIV-1 reverse transcriptase in a ratchet model of polymerase translocation. Curr. Pharm. Des. 12: 1867– 1877.
34.
Götte, M. 2007. Should we include connection domain mutations of HIV-1 reverse transcriptase in HIV resistance testing. PLoS Med. 4: e346.
35.
Götte, M.,, X. Li, and, M. A. Wainberg. 1999. HIV-1 reverse transcription: a brief overview focused on structure-function relationships among molecules involved in initiation of the reaction. Arch. Biochem. Biophys. 365: 199– 210.
36.
Gu, Z.,, Q. Gao,, H. Fang,, H. Salomon,, M. A. Parniak,, E. Goldberg,, J. Cameron, and, M. A. Wainberg. 1994. Identification of a mutation at codon 65 in the IKKK motif of reverse transcriptase that encodes human immunodeficiency virus resistance to 2’,3’-dideoxycytidine and 2’,3’-dideoxy-3’-thiacytidine. Antimicrob. Agents Chemother. 38: 275– 281.
37.
Gu, Z.,, M. A. Wainberg,, N. Nguyen-Ba,, L. L’Heureux,, J. M. de Muys,, T. L. Bowlin, and, R. F. Rando. 1999. Mechanism of action and in vitro activity of 1’,3’-dioxolanylpurine nucleoside analogues against sensitive and drug-resistant human immunodeficiency virus type 1 variants. Antimicrob. Agents Chemother. 43: 2376– 2382.
38.
Hanna, G. J.,, V. A. Johnson,, D. R. Kuritzkes,, D. D. Richman,, A. J. Brown,, A. V. Savara,, J. D. Hazelwood, and, R. T. D’Aquila. 2000. Patterns of resistance mutations selected by treatment of human immunodeficiency virus type 1 infection with zidovudine, didanosine, and nevirapine. J. Infect. Dis. 181: 904– 911.
39.
Hetherington, S.,, A. R. Hughes,, M. Mosteller,, D. Shortino,, K. L. Baker,, W. Spreen,, E. Lai,, K. Davies,, A. Handley,, D. J. Dow,, M. E. Fling,, M. Stocum,, C. Bowman,, L. M. Thurmond, and, A. D. Roses. 2002. Genetic variations in HLA-B region and hypersensitivity reactions to abacavir. Lancet 359: 1121– 1122.
40.
Himmel, D. M.,, S. G. Sarafianos,, S. Dharmasena,, M. M. Hossain,, K. McCoy-Simandle,, T. Ilina,, A. D. Clark, Jr.,, J. L. Knight,, J. G. Julias,, P. K. Clark,, K. Krogh-Jespersen,, R. M. Levy,, S. H. Hughes,, M. A. Parniak, and, E. Arnold. 2006. HIV-1 reverse transcriptase structure with RNase H inhibitor dihydroxy benzoyl naphthyl hydrazone bound at a novel site. ACS Chem. Biol. 1: 702– 712.
41.
Huang, M.,, A. Maynard,, J. A. Turpin,, L. Graham,, G. M. Janini,, D. G. Covell, and, W. G. Rice. 1998. Anti-HIV agents that selectively target retroviral nucleocapsid protein zinc fingers without affecting cellular zinc finger proteins. J. Med. Chem. 41: 1371– 1381.
42.
Hussain, M., and, A. S. Lok. 1999. Mutations in the hepatitis B virus polymerase gene associated with antiviral treatment for hepatitis B. J. Viral Hepat. 6: 183– 194.
43.
Iversen, A. K.,, R. W. Shafer,, K. Wehrly,, M. A. Winters,, J. I. Mull-ins,, B. Chesebro, and, T. C. Merigan. 1996. Multidrug-resistant human immunodeficiency virus type 1 strains resulting from combination antiretroviral therapy. J. Virol. 70: 1086– 1090.
44.
Jacobo-Molina, A.,, J. Ding,, R. G. Nanni,, A. D. Clark, Jr.,, X. Lu,, C. Tantillo,, R. L. Williams,, G. Kamer,, A. L. Ferris,, P. Clark, et al. 1993. Crystal structure of human immunodeficiency virus type 1 reverse transcriptase complexed with double-stranded DNA at 3.0 A resolution shows bent DNA. Proc. Natl. Acad. Sci. USA 90: 6320– 6324.
45.
Jochmans, D.,, J. Deval,, B. Kesteleyn,, H. Van Marck,, E. Bettens,, I. De Baere,, P. Dehertogh,, T. Ivens,, M. Van Ginderen,, B. Van Schoubroeck,, M. Ehteshami,, P. Wigerinck,, M. Götte, and, K. Hertogs. 2006. Indolopyridones inhibit human immunodeficiency virus reverse transcriptase with a novel mechanism of action. J. Virol. 80: 12283– 12292.
46.
Johnson, A. A.,, A. S. Ray,, J. Hanes,, Z. Suo,, J. M. Colacino,, K. S. Anderson, and, K. A. Johnson. 2001. Toxicity of antiviral nucleo-side analogs and the human mitochondrial DNA polymerase. J. Biol. Chem. 276: 40847– 40857.
47.
Johnson, V. A.,, F. Brun-Vézinet,, B. Clotet,, H. F. Günthard,, D. R. Kuritzkes,, D. Pillay,, J. M. Schapiro, and, D. D. Richman. 2007. Update of the drug resistance mutations in HIV-1: 2007. Top HIV Med. 15: 119– 125.
48.
Kati, W. M.,, K. A. Johnson,, L. F. Jerva, and, K. S. Anderson. 1992. Mechanism and fidelity of HIV reverse transcriptase. J. Biol. Chem. 267: 25988– 25997.
49.
Keulen, W.,, N. K. Back,, A. van Wijk,, C. A. Boucher, and, B. Berkhout. 1997. Initial appearance of the 184Ile variant in lamivu-dine-treated patients is caused by the mutational bias of human immunodeficiency virus type 1 reverse transcriptase. J. Virol. 71: 3346– 3350.
50.
Klumpp, K., and, T. Mirzadegan. 2006. Recent progress in the design of small molecule inhibitors of HIV RNase H. Curr. Pharm. Des. 12: 1909– 1922.
51.
Kodama, E. I.,, S. Kohgo,, K. Kitano,, H. Machida,, H. Gatanaga,, S. Shigeta,, M. Matsuoka,, H. Ohrui, and, H. Mitsuya. 2001. 4’-Ethynyl nucleoside analogs: potent inhibitors of multidrug-resistant human immunodeficiency virus variants in vitro. Antimicrob. Agents Chemother. 45: 1539– 1546.
52.
Kohlstaedt, L. A.,, J. Wang,, J. M. Friedman,, P. A. Rice, and, T. A. Steitz. 1992. Crystal structure at 3.5 A resolution of HIV-1 reverse transcriptase complexed with an inhibitor. Science 256: 1783– 1790.
53.
Kool, E. T. 2002. Active site tightness and substrate fit in DNA replication. Annu. Rev. Biochem. 71: 191– 219.
54.
Krebs, R.,, U. Immendorfer,, S. H. Thrall,, B. M. Wohrl, and, R. S. Goody. 1997. Single-step kinetics of HIV-1 reverse transcriptase mutants responsible for virus resistance to nucleoside inhibitors zidovudine and 3-TC. Biochemistry 36: 10292– 10300.
55.
Lacey, S. F.,, J. E. Reardon,, E. S. Furfine,, T. A. Kunkel,, K. Bebenek,, K. A. Eckert,, S. D. Kemp, and, B. A. Larder. 1992. Biochemical studies on the reverse transcriptase and RNase H activities from human immunodeficiency virus strains resistant to 3’-azido-3’-deoxythymidine. J. Biol. Chem. 267: 15789– 15794.
56.
Langley, D. R.,, A. W. Walsh,, C. J. Baldick,, B. J. Eggers,, R. E. Rose,, S. M. Levine,, A. J. Kapur,, R. J. Colonno, and, D. J. Tenney. 2007. Inhibition of hepatitis B virus polymerase by entecavir. J. Virol. 81: 3992– 4001.
57.
Larder, B. A., and, S. D. Kemp. 1989. Multiple mutations in HIV-1 reverse transcriptase confer high-level resistance to zidovudine (AZT). Science 246: 1155– 1158.
58.
Larder, B. A.,, S. D. Kemp, and, P. R. Harrigan. 1995. Potential mechanism for sustained antiretroviral efficacy of AZT-3TC combination therapy. Science 269: 696– 699.
59.
Lin, T. S.,, R. F. Schinazi, and, W. H. Prusoff. 1987. Potent and selective in vitro activity of 3’-deoxythymidin-2’-ene (3’-deoxy-2’,3’-didehydrothymidine) against human immunodeficiency virus. Biochem. Pharmacol. 36: 2713– 2718.
60.
Maeda, Y.,, D. J. Venzon, and, H. Mitsuya. 1998. Altered drug sensitivity, fitness, and evolution of human immunodeficiency virus type 1 with pol gene mutations conferring multi-dideoxynucleoside resistance. J. Infect. Dis. 177: 1207– 1213.
61.
Mallal, S.,, D. Nolan,, C. Witt,, G. Masel,, A. M. Martin,, C. Moore,, D. Sayer,, A. Castley,, C. Mamotte,, D. Maxwell,, I. James, and, F. T. Christiansen. 2002. Association between presence of HLA-B*5701, HLA-DR7, and HLA-DQ3 and hypersensitivity to HIV-1 reverse-transcriptase inhibitor abacavir. Lancet 359: 727– 732.
62.
Marchand, B.,, E. P. Tchesnokov, and, M. Götte. 2007. The pyro-phosphate analogue foscarnet traps the pre-translocational state of HIV-1 reverse transcriptase in a Brownian ratchet model of polymerase translocation. J. Biol. Chem. 282: 3337– 3346.
63.
Marchand, B.,, K. L. White,, J. K. Ly,, N. A. Margot,, R. Wang,, M. McDermott,, M. D. Miller, and, M. Götte. 2007. Effects of the translocation status of human immunodeficiency virus type 1 reverse transcriptase on the efficiency of excision of tenofovir. Antimicrob. Agents Chemother. 51: 2911– 2919.
64.
Mas, A.,, B. M. Vazquez-Alvarez,, E. Domingo, and, L. MenendezArias. 2002. Multidrug-resistant HIV-1 reverse transcriptase: involvement of ribonucleotide-dependent phosphorolysis in cross-resistance to nucleoside analogue inhibitors. J. Mol. Biol. 323: 181– 197.
65.
McMahon, M. A.,, B. L. Jilek,, T. P. Brennan,, L. Shen,, Y. Zhou,, M. Wind-Rotolo,, S. Xing,, S. Bhat,, B. Hale,, R. Hegarty,, C. R. Chong,, J. O. Liu,, R. F. Siliciano, and, C. L. Thio. 2007. The HBV drug entecavir—effects on HIV-1 replication and resistance. N. Engl. J. Med. 356: 2614– 2621.
66.
Menendez-Arias, L. 2008. Mechanisms of resistance to nucleoside analogue inhibitors of HIV-1 reverse transcriptase. Virus Res. 134: 124– 146.
67.
Merta, A.,, I. Votruba,, J. Jindrich,, A. Holy,, T. Cihlar,, I. Rosenberg,, M. Otmar, and, T. Y. Herve. 1992. Phosphorylation of 9-(2-phosphonomethoxyethyl)adenine and 9-(S)-(3-hydroxy-2-phosphonomethoxypropyl)adenine by AMP(dAMP) kinase from L1210 cells. Biochem. Pharmacol. 44: 2067– 2077.
68.
Meyer, P. R.,, S. E. Matsuura,, A. M. Mian,, A. G. So, and, W. A. Scott. 1999. A mechanism of AZT resistance: an increase in nucleotide-dependent primer unblocking by mutant HIV-1 reverse transcriptase. Mol. Cell 4: 35– 43.
69.
Meyer, P. R.,, S. E. Matsuura,, D. Zonarich,, R. R. Chopra,, E. Pendarvis,, H. Z. Bazmi,, J. W. Mellors, and, W. A. Scott. 2003. Relationship between 3’-azido-3’-deoxythymidine resistance and primer unblocking activity in foscarnet-resistant mutants of human immunodeficiency virus type 1 reverse transcriptase. J. Virol. 77: 6127– 6137.
70.
Meyer, P. R.,, A. J. Smith,, S. E. Matsuura, and, W. A. Scott. 2006. Chain-terminating dinucleoside tetraphosphates are substrates for DNA polymerization by human immunodeficiency virus type 1 reverse transcriptase with increased activity against thymidine analogue-resistant mutants. Antimicrob. Agents Chemother. 50: 3607– 3614.
71.
Mitsuya, H.,, K. J. Weinhold,, P. A. Furman,, M. H. St Clair,, S. N. Lehrman,, R. C. Gallo,, D. Bolognesi,, D. W. Barry, and, S. Broder. 1985. 3’-Azido-3’-deoxythymidine (BW A509U): an antiviral agent that inhibits the infectivity and cytopathic effect of human T-lymphotropic virus type III/lymphadenopathy-associated virus in vitro. Proc. Natl. Acad. Sci. USA 82: 7096– 7100.
72.
Naeger, L. K.,, N. A. Margot, and, M. D. Miller. 2002. ATP-dependent removal of nucleoside reverse transcriptase inhibitors by human immunodeficiency virus type 1 reverse transcriptase. Anti-microb. Agents Chemother. 46: 2179– 2184.
73.
Nakashima, H.,, T. Matsui,, S. Harada,, N. Kobayashi,, A. Matsuda,, T. Ueda, and, N. Yamamoto. 1986. Inhibition of replication and cytopathic effect of human T cell lymphotropic virus type III/ lymphadenopathy-associated virus by 3’-azido-3’-deoxythymi-dine in vitro. Antimicrob. Agents Chemother. 30: 933– 937.
74.
Nikolenko, G. N.,, K. A. Delviks-Frankenberry,, S. Palmer,, F. Maldarelli,, M. J. Fivash, Jr.,, J. M. Coffin, and, V. K. Pathak. 2007. Mutations in the connection domain of HIV-1 reverse transcriptase increase 3’-azido-3’-deoxythymidine resistance. Proc. Natl. Acad. Sci. USA 104: 317– 322.
75.
Nikolenko, G. N.,, S. Palmer,, F. Maldarelli,, J. W. Mellors,, J. M. Coffin, and, V. K. Pathak. 2005. Mechanism for nucleoside analog-mediated abrogation of HIV-1 replication: balance between RNase H activity and nucleotide excision. Proc. Natl. Acad. Sci USA 102: 2093– 2098.
76.
Ohrui, H. 2006. 2’-deoxy-4’-C-ethynyl-2-fluoroadenosine, a nucleoside reverse transcriptase inhibitor, is highly potent against all human immunodeficiency viruses type 1 and has low toxicity. Chem. Rec. 6: 133– 143.
77.
Parikh, U. M.,, D. C. Barnas,, H. Faruki, and, J. W. Mellors. 2006. Antagonism between the HIV-1 reverse-transcriptase mutation K65R and thymidine-analogue mutations at the genomic level. J. Infect. Dis. 194: 651– 660.
78.
Radzio, J., and, N. Sluis-Cremer. 2008. Efavirenz accelerates HIV-1 reverse transcriptase ribonuclease H cleavage, leading to diminished zidovudine excision. Mol. Pharmacol. 73: 601– 606.
79.
Ray, A. S.,, E. Murakami,, A. Basavapathruni,, J. A. Vaccaro,, D. Ulrich,, C. K. Chu,, R. F. Schinazi, and, K. S. Anderson. 2003. Probing the molecular mechanisms of AZT drug resistance mediated by HIV-1 reverse transcriptase using a transient kinetic analysis. Biochemistry 42: 8831– 8841.
80.
Reardon, J. E. 1993. Human immunodeficiency virus reverse transcriptase. A kinetic analysis of RNA-dependent and DNA-dependent DNA polymerization. J. Biol. Chem. 268: 8743– 8751.
81.
Richard, N.,, H. Salomon,, M. Oliveira,, R. Rando,, T. Mansour,, Z. Gu, and, M. A. Wainberg. 2000. Selection of resistance-conferring mutations in HIV-1 by the nucleoside reverse transcriptase inhibitors (+/-)dOTC and (+/-)dOTFC. Antivir. Chem. Chemother. 11: 359– 365.
82.
Sarafianos, S. G.,, K. Das,, A. D. Clark, Jr.,, J. Ding,, P. L. Boyer,, S. H. Hughes, and, E. Arnold. 1999. Lamivudine (3TC) resistance in HIV-1 reverse transcriptase involves steric hindrance with beta-branched amino acids. Proc. Natl. Acad. Sci. USA 96: 10027– 10032.
83.
Sarafianos, S. G.,, K. Das,, J. Ding,, P. L. Boyer,, S. H. Hughes, and, E. Arnold. 1999. Touching the heart of HIV-1 drug resistance: the fingers close down on the dNTP at the polymerase active site. Chem. Biol. 6: R137– R146.
84.
Schinazi, R. F.,, R. M. Lloyd, Jr.,, M. H. Nguyen,, D. L. Cannon,, A. McMillan,, N. Ilksoy,, C. K. Chu,, D. C. Liotta,, H. Z. Bazmi, and, J. W. Mellors. 1993. Characterization of human immunodeficiency viruses resistant to oxathiolane-cytosine nucleosides. Antimicrob. Agents Chemother. 37: 875– 881.
85.
Schinazi, R. F.,, A. McMillan,, D. Cannon,, R. Mathis,, R. M. Lloyd,, A. Peck,, J. P. Sommadossi,, M. St Clair,, J. Wilson,, P. A. Furman, et al. 1992. Selective inhibition of human immunodeficiency viruses by racemates and enantiomers of cis-5-fluoro-1-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl]cytosine. Antimicrob. Agents Chemother. 36: 2423– 2431.
86.
Selmi, B.,, J. Boretto,, S. R. Sarfati,, C. Guerreiro, and, B. Canard. 2001. Mechanism-based suppression of dideoxynucleotide resistance by K65R human immunodeficiency virus reverse transcriptase using an alpha-boranophosphate nucleoside analogue. J. Biol. Chem. 276: 48466– 48472.
87.
Selmi, B.,, J. Deval,, K. Alvarez,, J. Boretto,, S. Sarfati,, C. Guerreiro, and, B. Canard. 2003. The Y181C substitution in 3’-azido-3’-deoxythymidine-resistant human immunodeficiency virus, type 1, reverse transcriptase suppresses the ATP-mediated repair of the 3’-azido-3’-deoxythymidine 5’-monophosphate-terminated primer. J. Biol. Chem. 278: 40464– 40472.
88.
Shafer, R. W.,, A. K. Iversen,, M. A. Winters,, E. Aguiniga,, D. A. Katzenstein,, T. C. Merigan, et al. 1995. Drug resistance and heterogeneous long-term virologic responses of human immunodeficiency virus type 1-infected subjects to zidovudine and didanosine combination therapy. J. Infect. Dis. 172: 70– 78.
89.
Shafer, R. W.,, M. J. Kozal,, M. A. Winters,, A. K. Iversen,, D. A. Katzenstein,, M. V. Ragni,, W. A. Meyer III,, P. Gupta,, S. Rasheed,, R. Coombs, et al. 1994. Combination therapy with zidovudine and didanosine selects for drug-resistant human immunodeficiency virus type 1 strains with unique patterns of pol gene mutations. J. Infect. Dis. 169: 722– 729.
90.
Shirasaka, T.,, R. Yarchoan,, M. C. O’Brien,, R. N. Husson,, B. D. Anderson,, E. Kojima,, T. Shimada,, S. Broder, and, H. Mitsuya. 1993. Changes in drug sensitivity of human immunodeficiency virus type 1 during therapy with azidothymidine, dideoxycyti-dine, and dideoxyinosine: an in vitro comparative study. Proc. Natl. Acad. Sci. USA 90: 562– 566.
91.
Sluis-Cremer, N.,, D. Arion,, U. Parikh,, D. Koontz,, R. F. Schinazi,, J. W. Mellors, and, M. A. Parniak. 2005. The 3’-azido group is not the primary determinant of 3’-azido-3’-deoxythymidine (AZT) responsible for the excision phenotype of AZT-resistant HIV-1. J. Biol. Chem. 280: 29047– 29052.
92.
Smith, A. J.,, P. R. Meyer,, D. Asthana,, M. R. Ashman, and, W. A. Scott. 2005. Intracellular substrates for the primer-unblocking reaction by human immunodeficiency virus type 1 reverse transcriptase: detection and quantitation in extracts from quiescent- and activated-lymphocyte subpopulations. Antimicrob. Agents Che-mother. 49: 1761– 1769.
93.
Smith, A. J., and, W. A. Scott. 2006. The influence of natural substrates and inhibitors on the nucleotide-dependent excision activity of HIV-1 reverse transcriptase in the infected cell. Curr. Pharm. Des. 12: 1827– 1841.
94.
Sommadossi, J. P.,, R. F. Schinazi,, C. K. Chu, and, M. Y. Xie. 1992. Comparison of cytotoxicity of the (-)- and (-)-enantiomer of 2’,3’-dideoxy-3’-thiacytidine in normal human bone marrow progenitor cells. Biochem. Pharmacol. 44: 1921– 1925.
95.
Taylor, D. L.,, P. S. Ahmed,, A. S. Tyms,, L. J. Wood,, L. A. Kelly,, P. Chambers,, J. Clarke,, J. Bedard,, T. L. Bowlin, and, R. F. Rando. 2000. Drug resistance and drug combination features of the human immunodeficiency virus inhibitor, BCH-10652 [(+/-)-2’-deoxy-3’-oxa-4’-thiocytidine, dOTC]. Antivir. Chem. Che-mother. 11: 291– 301.
96.
Tchesnokov, E. P.,, A. Obikhod,, R. F. Schinazi, and, M. Götte. 2008. Delayed chain termination protects the anti-hepatitis B virus drug entecavir from excision by HIV-1 reverse transcriptase. J. Biol. Chem. 283: 34218– 34228.
97.
Tenney, D. J.,, R. E. Rose,, C. J. Baldick,, S. M. Levine,, K. A. Pokornowski,, A. W. Walsh,, J. Fang,, C. F. Yu,, S. Zhang,, C. E. Mazzucco,, B. Eggers,, M. Hsu,, M. J. Plym,, P. Poundstone,, J. Yang, and, R. J. Colonno. 2007. Two-year assessment of entecavir resistance in lamivudine-refractory hepatitis B virus patients reveals different clinical outcomes depending on the resistance substitutions present. Antimicrob. Agents Chemother. 51: 902– 911.
98.
Tong, W.,, C. D. Lu,, S. K. Sharma,, S. Matsuura,, A. G. So, and, W. A. Scott. 1997. Nucleotide-induced stable complex formation by HIV-1 reverse transcriptase. Biochemistry 36: 5749– 5757.
99.
Tuske, S.,, S. G. Sarafianos,, A. D. Clark, Jr.,, J. Ding,, L. K. Naeger,, K. L. White,, M. D. Miller,, C. S. Gibbs,, P. L. Boyer,, P. Clark,, G. Wang,, B. L. Gaffney,, R. A. Jones,, D. M. Jerina,, S. H. Hughes, and, E. Arnold. 2004. Structures of HIV-1 RT-DNA complexes before and after incorporation of the anti-AIDS drug tenofovir. Nat. Struct. Mol. Biol. 11: 469– 474.
100.
Vivet-Boudou, V.,, J. Didierjean,, C. Isel, and, R. Marquet. 2006. Nucleoside and nucleotide inhibitors of HIV-1 replication. Cell. Mol. Life Sci. 63: 163– 186.
101.
White, K. L.,, J. M. Chen,, J. Y. Feng,, N. A. Margot,, J. K. Ly,, A. S. Ray,, H. L. Macarthur,, M. J. McDermott,, S. Swaminathan, and, M. D. Miller. 2006. The K65R reverse transcriptase mutation in HIV-1 reverses the excision phenotype of zidovudine resistance mutations. Antivir. Ther. 11: 155– 163.
102.
Yahi, N.,, C. Tamalet,, C. Tourres,, N. Tivoli,, F. Ariasi,, F. Volot,, J. A. Gastaut,, H. Gallais,, J. Moreau, and, J. Fantini. 1999. Mutation patterns of the reverse transcriptase and protease genes in human immunodeficiency virus type 1-infected patients undergoing combination therapy: survey of 787 sequences. J. Clin. Microbiol. 37: 4099– 4106.
103.
Yap, S. H.,, C. W. Sheen,, J. Fahey,, M. Zanin,, D. Tyssen,, V. D. Lima,, B. Wynhoven,, M. Kuiper,, N. Sluis-Cremer,, P. R. Harrigan, and, G. Tachedjian. 2007. N348I in the connection domain of HIV-1 reverse transcriptase confers zidovudine and nevira-pine resistance. PLoS Med. 4: e335.
104.
Yarchoan, R.,, R. W. Klecker,, K. J. Weinhold,, P. D. Markham,, H. K. Lyerly,, D. T. Durack,, E. Gelmann,, S. N. Lehrman,, R. M. Blum,, D. W. Barry, et al. 1986. Administration of 3’-azido-3’-deoxythymidine, an inhibitor of HTLV-III/LAV replication, to patients with AIDS or AIDS-related complex. Lancet 1: 575– 580.
105.
Zhang, D.,, A. M. Caliendo,, J. J. Eron,, K. M. DeVore,, J. C. Kaplan,, M. S. Hirsch, and, R. T. D’Aquila. 1994. Resistance to 2’,3’-dideoxycytidine conferred by a mutation in codon 65 of the human immunodeficiency virus type 1 reverse transcriptase. Antimicrob. Agents Chemother. 38: 282– 287.