User:Hopur32009/Development and Discovery of HIV Protease Inhibitors
Many major physiological processes depend on regulation of
History
Human immunodeficiency virus (HIV) is a lentivirus that has two major species, HIV-1 which causes the majority of the epidemic, and HIV-2, a close relative whose distribution is concentrated in western Africa.[6] HIV infection was first described in 1981 in San Fransisco and New York City.[7] In 1985, HIV was identified as the causative agent of acquired immune deficiency syndrome (AIDS) and its complete genome was immediately available. This knowledge paved the way for the development of selective inhibitors.[6] HIV-2 carries a slightly lower risk of transmission than HIV-1 and infection tends to progress more slowly to AIDS.[7] In common usage HIV usually implies HIV-1.[8] HIV-1 protease is one of the best known
Life cycle of HIV
![](http://upload.wikimedia.org/wikipedia/commons/thumb/3/35/HIV_gross_cycle_only.png/200px-HIV_gross_cycle_only.png)
HIV belongs to the class of viruses called
The HIV replication cycle is shown in Figure 1.
Mechanism of action
There are several steps in the HIV life cycle that may be interfered with, thus stopping the replication of the virus. A very critical step is the proteolytic cleavage of the polypeptide precursors into mature enzymes and structural proteins catalyzed by HIV protease.[12] HIV protease inhibitors are peptide-like chemicals that competitively inhibit the action of the virus aspartyl protease. These drugs prevent proteolytic cleavage of HIV Gag and Pol polyproteins that include essential structural and enzymatic components of the virus. This prevents the conversion of HIV virus particles into their mature infectious form.[6] Protease inhibitors can alter
Design
Protease inhibitors were designed to mimic the transition state of the protease's actual substrates. A peptide linkage consisting of –NH-CO- is replaced by an hydroxyethylen group (-CH2-CH(OH)-) which the protease is unable to cleave. HIV protease inhibitors fit the active site of the HIV aspartic protease and were rationally designed utilizing knowledge of the aspartyl protease's mode of action. The most promising transition state mimic was hydroxyethylamine which lead to the discovery of the first protease inhibitor, saquinavir. Following that discovery, other HIV protease inhibitors were designed using the same principle.[15]
Binding site
![](http://upload.wikimedia.org/wikipedia/commons/thumb/9/9a/HIV_protease_1KJF.png/300px-HIV_protease_1KJF.png)
The HIV protease is a C2-symmetric homodimeric enzyme consisting of two 99
HIV proteases catalyze the hydrolysis of peptide bonds with high sequence selectivity and catalytic proficiency. The mechanism of the HIV protease shares many features with the rest of the aspartic protease family although the full detailed mechanism of this enzyme is not fully understood.[12] The water molecule seems to play a role in the opening and closing of the flaps as well as increasing the affinity between enzyme and substrate. The aspartyl residues are involved in the hydrolysis of the peptide bonds.[17] The preferred cleavage site for this enzyme is the N-terminal side of proline residues, especially between phenylalanine and proline or tyrosine and proline.[6][16]
Development
The first HIV protease inhibitor, saquinavir, is a peptidomimetic hydroxyethylamine[6] and was marketed in 1995.[18] It is a transition state analogue of a native substrate of the protease.[6] The observation that HIV-1 protease cleaves the sequences containing the dipeptides Tyr-Pro or Phe-Pro was the basic design criterion.[19] Addition of the decahydroisoquinoline (DIQ) group was one of the most significant modifications that led to the discovery of saquinavir. This substituent improves aqueous solubility and potency by limiting the conformational freedom of the inhibitor.[20] Saquinavir is effective against both HIV-1 and HIV-2[5] and is usually well tolerated but high serum concentration is not achieved.[11]
Ritonavir, a peptidomimetic HIV protease inhibitor, was marketed in 1996.[18] It was designed to fit the C2-symmetry in the binding site of the protease.[6] The developers of ritonavir, Abbott Laboratories, started with compounds that were active against the virus but had poor bioavailability. Some improvements were made, for example the terminal phenyl residues were removed and pyridyl groups put instead to add water solubility. The final product of these improvements was ritonavir.[19] Significant gastrointestinal side effects and a large pill burden are ritonavir's main drawbacks and is therefore not used as a single treatment.[11] However, it is a strong inhibitor of the cytochrome P450 enzyme mediated metabolism[19] and it is only used in a combination therapy with other protease inhibitors for pharmacokinetic boosting.[11]
Indinavir, which is a peptidomimetic hydroxyethylene HIV protease inhibitor, reached the market in 1996.[6][18] The design of indinavir was guided by molecular modeling and the X-ray crystal structure of the inhibited enzyme complex. The terminal phenyl constituents contribute hydrophobic binding to increase potency.[19] It is an analogue of the phenylalanine-proline cleavage site of the HIV Gag-polyprotein.[6]
Nelfinavir was the first protease inhibitor that was not peptidomimetic. In the design process of nelfinavir, an orally bioavailable and nonpeptidic inhibitor, iterative protein cocrystal structure analysis of peptidic inhibitors was used and parts of the inhibitors were replaced by nonpeptidic substituents.[19] Nelfinavir contains a novel 2-methyl-3-hydroxybenzamide group, whereas
its carboxyl terminal contains the same DIQ group as saquinavir.[19]
Nelfinavir was marketed in 1997
Amprenavir reached the market in 1999.
Lopinavir was marketed in 2000[18] and was originally designed to diminish the interactions of the inhibitor with Val82 of the HIV-1 protease, a residue that is often mutated in the drug resistant strains of the virus.[19] It is a peptidomimetic HIV protease inhbitor[6] and its core is identical to that of ritonavir. Instead of the 5-thiazolyl end group in ritonavir, lopinavir has a phenoxyacetyl group and the 2-isopropylthiazolyl group in ritonavir was replaced by a modified valine in which the amino terminal had a six-membered cyclic urea attached.[19]
Fosamprenavir was marketed in 2003[18] and is a phosphoester prodrug that is rapidly and extensively metabolized to amprenavir.[21] The solubility and bioavailability is better than of amprenavir[6] which results in reduced daily pill burden.[22]
Atazanavir was marketed in 2003[18] and is an azapeptide protease inhibitor[18] designed to fit the C2-symmetry of the enzyme binding site.[11] Atazanavir showed better resistant profiles than previous HIV protease inhibitors.[4] It is unique among the other protease inhibitors as it can only be
Tipranavir is a nonpeptidic HIV-1 protease inhibitor[11] and reached the market in 2005.[18] Unlike other HIV protease inhibitors on the market, tipranavir was developed from a nonpeptidic coumarin template and its antiprotease activity was discovered by high-throughput screening.[23] This sulfonamide containing 5,6-dihydro-4-hydroxy-2-pyrone had emerged from screenings of 3-substituted coumarins and dihydropyrones.[24] It possesses broad antiviral activity against multiple protease inhibitor resistant HIV-1.[25]
Darunavir reached the market in 2006[18] and is a nonpeptidic analogue of amprenavir, with a critical change at the terminal tetrahydrofuran (THF) group. Instead of a single THF group, darunavir contains two THF groups fused in the compound, to form a bis-THF moiety which makes it more effective than amprenavir. With this structural change, the stereochemistry around the bis-THF moiety confers orientational changes, that allows for continued binding with the protease which has developed a resistance for amprenavir.[26]
All the FDA approved protease inhibitors are listed in Table 1.
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File:Ritonavir-structure.jpg | ![]() |
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Saquinavir | Ritonavir | Indinavir | Nelfinavir |
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Amprenavir | Lopinavir | Fosamprenavir | Atazanavir |
File:Tipranavir - structure.jpg | ![]() |
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Tipranavir | Darunavir |
Structure-activity relationship
![](http://upload.wikimedia.org/wikipedia/commons/thumb/d/df/Sarmynd2.jpg/300px-Sarmynd2.jpg)
All the HIV protease inhibitors on the market contain a central core motif consisting of a hydroxyethylen scaffold, with the only exception being the central core of tipranavir, which is based on a coumarin scaffold.
In Figure 3 is a simplified image of a protease inhibitor binding to the active site of the HIV-1 protease.
Resistance
Mutations that code for alterations of the conformational shape facilitate resistance of HIV to protease inhibitors.[26] The locations of these mutations are primarily in the active site of the HIV protease enzyme as well as outside of the active site. Active site mutations have been shown to directly change the interactions of the inhibitors with the protease whilst non-active site mutations are considered to affect by other mechanisms, like influencing dimer stability and conformational flexibility.[30] Over 100 single gene
There is no general strategy to tackle the problem of drug resistance. Researches directed towards development of new therapies to cure AIDS are focused on avoiding cross-resistance to drugs that are already on the market.[12]
Current status
In november 2009 Darunavir was still the most recent HIV protease inhibitor to reach the market.[33] In 2006,
See also
Integrase inhibitor
Entry inhibitor
External links
Hoffmann-La Roche: http://www.roche.com/index.htm (Saquinavir)
Japan Tobacco: http://www.jt.com/ (Nelfinavir)
Merck & Co.: http://www.merck.com/about/ (Indinavir)
Bristol-Myers Squibb: http://www.bms.com/pages/default.aspx (Atazanavir)
GlaxoSmithKline: http://www.gsk.com/ (Amprenavir, Fosamprenavir)
Abbott Laboratories: http://www.abbott.com/global/url/home/en_US (Ritonavir, Lopinavir)
Boehringer Ingelheim: http://www.boehringer-ingelheim.com/corporate/home/home.asp (Tipranavir)
Tibotec: http://www.tibotec.com/ (Darunavir)
References
- ^ Cuccioloni, M. et al. (2009) Natural Occurring Polyphenols as Template for Drug Design. Focus on Serine Proteases. Chemical biology and drug design. 74;1-15.
- ^ Chen, X. et al. (2003) Synthesis and SAR Studies of Potent HIV Protease Inhibitors Containing Novel Dimethylphenoxyl Acetates as P2 Ligands. Bioorganic & Medicinal Chemistry Letters. 13;3657-3660.
- ^ Adachi, M. et al. (2009) Structure of HIV-1 protease in complex with potent inhibitor KNI-272 determined by high-resolution X-ray and neutron crystallography. Proceedings of the national academy of scienses of the United States of America. 12; 4641-4646
- ^ a b Yanchunas, J. et al. (2005) Molecular Basis for Increased Susceptibility of Isolates with Atazanavir Resistance-Conferring Substitution I50L to Other Protease Inhibitors. Antimicrobial Agent and Chemotherapy. 40;3825-3832.
- ^ a b Brower, E.T., et al. Inhibition of HIV-2 protease by HIV-1 protease inhibitors in clinical use. Chemical Biology & Drug Design. 71;298-305.
- ^ a b c d e f g h i j k l m n o p Brunton, L.L., Lazo, J.S. and Parker, K.L. (2006) Goodman and Gilmans´s The Pharmacological Basis of Therapeutics (11th edition). United States of America: McGraw-Hill.
- ^ a b http://emedicine.medscape.com/article/211316-overview, retrieved: October 27th 2009
- ^ Kurup, A., Mekapati, S.B., Garg, R. and Hansch, C. (2003) HIV-1 Protease Inhibitors: A Comparative QSAR Analysis. Current Medicinal Chemistry. 10;1679-1688
- ^ Shi, H., Liu, K., Leong, W.W.Y. and Yao, S.Q. (2009) Expedient solid-phase synthesis of both symmetric and asymmetric diol libraries targeting aspartic proteases. Bioorganic & Medicinal Chemistry Letters. 19;3945-3948.
- ^ Turk, B. (2006) Targeting proteases: successes, failures and future prospects. Nature Reviews Drug Discovery. 5;785-799
- ^ a b c d e f g [1] Graziani, A.L., et al(2009), HIV Protease Inhibitors. Retrieved: October 30th 2009
- ^ a b c d e f Brik, A. and Wong, C.H. (2003) HIV-1 protease: mechanism and drug discovery. Organic & Biomolecular Chemistry. 1(1); 5-14.
- ^ Warnke, D., Barreto, J. and Temesgen, Z. (2007) Antiretroviral drugs. Journal of Clinical Pharmacology. 47(12); 1570-1579.
- ^ Kim, R.J., Wilson, C.G., Wabitsch, M., Lazar, M.A. and Steppan, C.M. (2006) HIV protease inhibitor-specific alterations in human adipocyte differentiation and metabolism. Obesity. 14; 994-1002.
- ^ a b De Clercq, E. (2009) The history of antiretrovirals: key discoveries over the past 25 years. Reviews in Medical Virology. 19; 287-299.
- ^ a b c Mimoto, T., Hattori, N., Takaku, H. et al. (2000) Structure-activity relationship of orally potent tripeptide-based HIV protease inhibitors containing hydroxymethylcarbonyl isostere. Chemical & Pharmaceutical Bulletin. 48(9); 1310-1326.
- ^ a b c Perez, M.A.S., Fernandes, P.A. and Ramos, M.J. (2007) Drug design: New inhibitors for HIV-1 protease based on Nelfinavir as lead. Journal of Molecular Graphics and Modelling. 26; 634-642.
- ^ a b c d e f g h i j k Flexner, C. (2007) HIV drug development: the next 25 years. Nature Reviews Drug Discovery. 6; 959-966.
- ^ a b c d e f g h i j k Wlodawer, A. (2002) Rational approach to AIDS drug design through structural biology. Annual Review of Medicine. 53; 595-614.
- ^ Smith, H.J. and Simons, C. (2005) Enzymes and Their Inhibition: Drug Development (6th edition). United State of America: CRC press
- ^ Chapman, T.M., Plosker, G.L. and Perry, C.M. (2004) Fosamprenavir – A Review of its Use in the Management of Antiretroviral Therapy-naive Patients with HIV Infection. Drugs. 64; 2101-2124.
- ^ a b c d e McCoy, C. (2007) Darunavir: A nonpeptidic antiretroviral protease inhibitor. Clinical Therapeutics. 29(8); 1559-1576.
- ^ Liu, F., Kovalevsky, A.Y., Tie, Y., Ghosh, A.K., Harrison, R.W. and Weber, I.T. (2008) Effect of Flap Mutations on Structure of HIV-protease and Inhibition by Saquinavir and Darunavir. Journal of Molecular Biology. 381(1); 102-115
- ^ Lebon, F. and Ledecq, M. (2000) Approaches to the Design of Effective HIV-1 Protease Inhibitors. Current Medicinal Chemistry. 7; 455-477.
- ^ Blum, A. et al. (2008) Achiral oligoamines as versatile tool for the development of aspartic protease inhibitors. Bioorganic & Medicinal Chemistry. 16; 8574-8586.
- ^ Bihani, S. C., Das, A., Prashar, V., Ferrer, J.-L. and Hosur; M.V. (2009) Resistance mechanism revealed by crystal structures of unliganded nelfinavir-resistant HIV-1 protease non-active site mutants N88D and N88S. Biochemical and Biophysical Research Communications. 389; 295-300.
- ^ Lemke,T.L., Williams, D.A., Roche, V.F. and Zito, S.W. (2008) Foye´s Principles of Medicinal Chemistry ( 6th edition). United States of America: Lippincott williams & Wilkins, a Wolters Kluwer business.
- ^ a b Maarseveen, N.V. and Boucher, C. (2008) Antiretroviral Resistance in Clinical Practice. London: Mediscript Ltd.
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- ^ [2]GSK and Concert Pharmaceuticals form alliance to develop novel deuterium-modified drugs. Retrieved november 4th. 2009.
- ^ [3] GlaxoSmithKline discontinues clinical development of investigational protease inhibitor brecanavir (640385). Retrieved november 4th. 2009.