Many of the major physiological processes depend on the regulation of proteolytic enzyme activity and there are dramatic consequences when the balance between the enzyme and its substrate is disrupted. In this prospective, the discovery of small molecule ligands, such as protease inhibitors, which can modulate catalytic activity have a tremendous therapeutic effect. Therefore, HIV protease inhibition is one of the most important approaches to therapeutic interventions in HIV infection and its development is considered to be a major success of structural-based drug design. They are very effective against HIV and since the 1990s have been a key component of anti-retroviral therapy for HIV/AIDS.
Video Discovery and development of HIV-protease inhibitors
Histori
Human immunodeficiency virus (HIV) is a lentivirus that has two main species, HIV-1 which causes the majority of epidemics, and HIV-2, close relatives whose distribution is concentrated in western Africa. HIV infection was first described in 1981 in San Francisco and New York City. In 1985, HIV was identified as the causative agent of the acquired immune deficiency syndrome (AIDS) and the complete genome was immediately available. This knowledge paves the way for the development of selective inhibitors.
HIV-2 carries a slightly lower risk of transmission than HIV-1 and infection tends to develop more slowly into AIDS. In general use HIV usually implies HIV-1.
The HIV-1 protease is one of the best known aspartic proteases, and an attractive target for the treatment of AIDS.
After the discovery of HIV protease it only takes 10 years for its first inhibitor to reach the market. The first report of a highly selective antagonist against HIV proteases was lowered in 1987. The first stage Saquinavir trial was started in 1989 and it was the first HIV protease inhibitor approved for prescription use in 1995. Four months later, two other protease inhibitors, ritonavir and indinavir, approved. In 2009, ten protease inhibitors had reached the market for the treatment of HIV but one protease inhibitor, amprenavir, was withdrawn from the market in 2004.
Maps Discovery and development of HIV-protease inhibitors
HIV life cycle
HIV is a class of viruses called retroviruses, which carry genetic information in the form of RNA. HIV infects T cells that carry CD4 antigens on its surface. When HIV infects its target cells, it requires the incorporation of viral and cell membranes. The first step is the interaction between envelope virus virus (gp120, gp41) and specific cell surface receptor (eg CD4 receptor) in target cells. Then the virus binds to the chemokine chemokine CXCR4 or CCR5, resulting in a conformational change in the envelope protein. This fusion creates the pores through which the viral capsid enters the cell. After entering the cell, viral RNA is transcribed back to DNA by the first enzyme encoded by the virus, ie reverse transcriptase. DNA virus enters the nucleus where it is integrated into the genetic material of the cell by integrase, the second enzyme encoded by the virus. Activation of host cells leads to transcription of viral DNA to mRNA. The MRNA is then translated into viral proteins and virally encoded viral enzymes, the HIV proteases, are needed to separate the viral polyprotein precursors into individual mature proteins. Viral RNA and viral proteins converge on the cell surface into new virions. Shoots virions from cells and is released to infect other cells. All infected cells are finally killed by this extensive cell damage, from destruction of the host's genetic system to the shoots and virion release.
Action mechanism
There are several steps in the life cycle of HIV that may be disrupted, thus stopping virus replication. A very important step is the proteolytic cleavage of polypeptide precursors into mature enzymes and structural proteins catalyzed by HIV proteases. HIV protease inhibitors are chemicals such as peptides that competitively inhibit the action of aspartil viral proteases. These medicines prevent proteolytic cleavage of HIV Gag and Pol polyproteins that include important structural and enzymatic components of the virus. This prevents the conversion of HIV particles into their adult infections.
Protease inhibitors can alter the metabolism of adipocytes that cause lipodystrophy, a common side effect associated with the use of most HIV protease inhibitors. Many mechanisms have been proposed, such as inhibition of adipocyte differentiation, triglyceride accumulation and increased lipolysis. Theories that consider the effects of protease inhibitors on insulin-stimulated glucose uptake are also associated with lipodystrophy syndrome. It is possible that protease inhibitors may cause a decrease in insulin-induced tyrosine phosphorylation from IRS-1, representing inhibition of the initial steps in insulin signaling. Decreased adiponectin secretion and induced interleukin-6 expression associated with HIV protease inhibitors may also contribute to inhibition of insulin-induced glucose uptake.
Design
Protease inhibitors are designed to mimic the true transition state of the protease substrates. A peptide relationship consisting of -NH-CO- is replaced by a hydroxyethylene group (-CH 2 -CH (OH) -) that can not be cleaved by proteases. HIV protease inhibitors correspond to the HIV aspartate active protease sites and are rationally designed using the knowledge of how aspartil proteases work. The most promising transition status is hydroxyethylamine which results in the discovery of the first protease inhibitor, saquinavir. Following the discovery, other HIV protease inhibitors were designed using the same principles.
Binding site
The HIV protease is a C2-symmetric homodimeric enzyme consisting of two 99 amino acid monomers. Each monomer contributes an important aspartic acid residue to catalysis, Asp-25 and Asp-25 '. The HIV protease has the Asp-Thr-Gly sequence, which is preserved among other protease protease enzyme mammals. The expanded beta-sheet region of the monomer, known as the flap, is part of a substrate binding site with two aspartile residues located at the bottom of the hydrophobic cavity. Each flexible flap contains three characteristic regions: an outwardly elongated side chain (Met46, Phe53), longitudinal hydrophobic chains (Ile47, Ile54), and glycine-rich areas (Gly48, 49, 51, 52). Ile50 stays at the end of the turn and when the enzyme is unchained, the water molecule makes the hydrogen bond into Ile50's backbone on each monomer.
The HIV protease catalyzes the hydrolysis of peptide bonds with high sequence selectivity and catalytic proficiency. The HIV protease mechanism has many features with residual aspartic protease families although the complete complete mechanism of this enzyme is not yet fully understood. Water molecules seem to play a role in the opening and closing of flaps as well as increasing the affinity between enzymes and substrates. Aspartil residue is involved in hydrolysis of peptide bonds. The preferred cleavage location for this enzyme is the N-terminal side of the proline residue, especially between phenylalanine and proline or tyrosine and proline.
Development
The first HIV protease inhibitor, saquinavir, was hydroxyethylamine peptidomimetics and was marketed in 1995. It is an analog transition state from the original substrates of proteases. The observation that HIV-1 protease bypasses sequences containing Tyr-Pro or Phe-Pro dipeptides is the basic design criterion. The addition of the decahydroisoquinoline (DIQ) group is one of the most significant modifications that lead to the discovery of saquinavir. This substituent increases the solubility and potency of water by limiting the freedom of inhibitor conformation. Saquinavir is effective against HIV-1 and HIV-2 and is usually well tolerated but high serum concentrations are not achieved.
Ritonavir, a peptidomimetic HIV protease inhibitor, was marketed in 1996. It was designed to fit the C2-symmetry on protease binding sites. The ritonavir developers, Abbott Laboratories, started off with an active compound against the virus but had poor bioavailability. Some improvements are made, eg terminal phenyl residue is released and the pyridyl group is introduced as a substitute for the addition of water solubility. The end product of this improvement is ritonavir. Significant gastrointestinal side effects and large pill burden are the main disadvantages of ritonavir and therefore are not used as a single treatment. However, it is a strong inhibitor of the metabolism mediated by the cytochrome P450 enzyme and is only used in combination therapy with other protease inhibitors to improve pharmacokinetics.
Indinavir, which is a protease inhibitor of peptidomimetic hydroxyethylene HIV, reached the market in 1996. Indinavir design is guided by molecular modeling and X-ray crystalline structures of inhibited enzyme complexes. Terminal phenyl constituents contribute to hydrophobic binding to increase potential. This is an analogue of the phenylalanine-proline cleavage site of HIV Gag-polyprotein.
Nelfinavir is the first nonpeptidomimetic protease inhibitor. In the nelfinavir design process, inhibitors are available orally and nonpeptidically, analysis of recurrent kokerik protein structures of peptidic inhibitors is used and parts of inhibitors are replaced by nonpeptide substituents. Nelfinavir contains a new 2-methyl-3-hydroxybenzamide group, while its carboxyl terminal contains the same DIQ group as saquinavir. Nelfinavir was marketed in 1997 and is the first protease inhibitor indicated for pediatric AIDS.
Amprenavir reached the market in 1999. This is a N -ubstituted amino-sulfonamide nonpeptide HIV protease inhibitor and shares some common features with previous protease inhibitors. It has a core similar to saquinavir but with different functional groups at both ends. At one end it has a tetrahydrofuran carbamate group and at the other end is isobutylphenyl sulfonamide with additional amides. This structure produces fewer chiral centers, which makes it easier to synthesize and gives it enhanced aqueous solubility. Which in turn provides better oral bioavailability. However, amprenavir was withdrawn from the market in 2004 because fosamprenavir, its prodrug, proved superior in many aspects.
Lopinavir was marketed in 2000 and was originally designed to reduce the interaction of inhibitors with Val82 from the HIV-1 protease, a residue that is often mutated in drug-resistant strains of the virus. This is a peptidomimetic protease inhbitor and essentially the same as ritonavir. Instead of the 5-thiazolyl group in ritonavir, lopinavir has a phenoxyacetyl group and the 2-isopropylthiazolyl group in ritonavir is replaced by a modified valine in which the amino terminal has an inherent six-membered cyclic urea.
Fosamprenavir was marketed in 2003 and is a phosphoester prodrug that is rapidly and extensively metabolized into amprenavir. Solubility and bioavailability are better than amprenavir which results in reduced daily pill burden.
Atazanavir was marketed in 2003 and is an azapeptide protease inhibitor designed to adjust C2-symmetry from enzyme binding sites. Atazanavir showed a better resistance profile than previous HIV protease inhibitors. It is unique among other protease inhibitors because it can only be absorbed in an acidic environment.
Tipranavir was a nonprivate HIV protease inhibitor and reached the market in 2005. Unlike other HIV protease inhibitors on the market, tipranavir was developed from nonpeptidic coumarin templates and antiprotease activity was found with high throughput screening. This sulphonamide containing 5,6-dihydro-4-hydroxy-2-pyramid has emerged from the coumarin and dihydropyran 3-substitution play. It has extensive antiviral activity against some HIV-1 resistant protease inhibitors.
Darunavir reached the market in 2006 and is a nonpeptide amprenavir analogue, with an important change in the tetrahydrofuran terminal group (THF). Instead of one group of THF, darunavir contains two groups of THF that converge in the compound, forming a bis-THF group that makes it more effective than amprenavir. With these structural changes, the stereochemistry around the bis-THF port confers a change in orientation, allowing it to continue binding with proteases that have developed resistance to amprenavir.
All FDA approved protease inhibitors are listed below.
Activity-structure relations
All of the HIV protease inhibitors on the market contain a central core motive consisting of a hydroxyethylene scaffold, with the only exception being the central core of tipranavir, based on the coumarin scaffold. A very important group of HIV protease inhibitors are the hydroxyl groups on the core motifs that form hydrogen bonds with carboxylic acids on Asp-25 and Asp-25 residues at the binding sites. Hydrogen bonds between water molecules, associated with Ile50 and Ile50 ', and carbonyl groups of peptidomimetic inhibitors seem to connect them with flap regions. On the other hand, in nonpeptide inhibitors, there is a proton acceptor that replaces the coordinated water molecules and interacts directly with two Ile50 residues in the enzyme flap. Special bags in HIV protease binding sites, often referred to as S1, S1 ', S2 and S2', recognize hydrophobic amino acids on natural substrates. Potential inhibitors containing hydrophobic groups that complement this area are therefore increased. Some residues on the enzyme binding sites are capable of forming hydrogen bonds with hydrophilic groups in the inhibitor, eg with THF groups in amprenavir and darunavir. Because darunavir has a bis-THF portion, not a part of THF as in amprenavir, darunavir can form more hydrogen bonds and increase binding energy.
Resistance
Mutations that code for conformational changes facilitate HIV resistance to protease inhibitors. The location of these mutations is primarily in the active sites of HIV protease enzymes as well as outside the active site, including at the location of the protease splitting in Gag-Pol polyprotein precursors. Site cleavage has a very diverse order, so proteases recognize its substrate not based on sequence but 3D form conserved substrate sharing when bound to active site. This conserved form has been named substrate envelope . Active site mutations have been shown to directly alter inhibitor interactions, and most occur in positions where the protease residue inhibitor contacts outside the substrate envelope. Non-active site mutations are considered to be affected by other mechanisms, such as affecting dimer stability and conformational flexibility.
More than 100 single point gene mutations have been described, which are at least 26 specific for protease inhibitors. Of these, there are about 15 major or major mutations that are significant enough to alter drug activity. Many mutated residues are found in HIV-1 proteases that cause drug resistance, eg Leu33 changes to Ile, Val, or Phe; Val82 to Ala, Phe, Leu, or Thr; Ile84 to Val; and Leu90 to Meet. Different mutations affect various protease inhibitors. For example, mutations in Leu90 proved to affect saquinavir and nelfinavir while indinavir activity was affected by mutations in Met46, Val82, and Ile84, and fosamprenavir was affected when Ile50 changed to Val and on Ile84. Combination mutations can make high-grade drug resistance but a single mutation is usually not the same as drug resistance to protease inhibitors. Mutations can be divided into primary and secondary mutations. Primary mutations often have little effect on resistance. The chemical structure of most protease inhibitors is very similar, so it is not surprising that some primary mutations simultaneously cause resistance to some protease inhibitors. Cross-resistance is one of the major problems of PI treatment. Additional mutations that appear in proteases during persistent PI therapy are often referred to as secondary mutations. This can lead to high-level protease inhibitor resistance.
The Stanford HIV RT and the Protease Sequence Database (also called "HIV Drug Resistance Database") were established in 1998 with HIV reverse transcriptase and protease sequences from people with a typical history of antiretroviral treatment, and are publicly available to question resistance mutations and genotype - treatment, genotype-phenotype, and genotype-yield correlation: http://hivdb.stanford.edu
Although substrate envelopes provide a general strategy for designing inhibitors that mimic the substrate and remain inside the envelope to avoid the resistance provided by most active site mutations, there is no general strategy to address drug resistance issues, especially since they are far from active sites. Research directed at developing new therapies to cure AIDS is focused on avoiding cross-resistance to existing drugs on the market.
Current status
By January 2018 darunavir is still the latest HIV protease inhibitor to reach the market.
In 2006, GlaxoSmithKline halted the phase II clinical development of brecanavir, a protease inhibitor studied for HIV treatment, due to an insurmountable problem regarding formulations.
In the summer of 2009, GlaxoSmithKline and Concert Pharmaceuticals announced their collaboration to develop and commercialize deuterium-containing drugs. One of them is CTP-518, a protease inhibitor for the treatment of HIV, which is expected to enter phase I clinical trials in the second half of 2009. CTP-518 is a new HIV protease inhibitor developed by replacing certain key hydrogen atoms from atazanavir with deuterium. Pre-clinical studies have shown that this modification fully retains antiviral potency but can clearly slow the liver metabolism and thus increase the half-life and plasma trough rate. Therefore, CTP-518 has the potential to be the first HIV protease inhibitor to eliminate the need for doses together with a boosting agent, such as ritonavir.
See also
- Antiretroviral drugs
- Inverted transcriptase inhibitor
- Integrase inhibitor
- Inhibitor entry
- Invention and development of non-nucleoside reverse transcriptase inhibitor
References
Source of the article : Wikipedia
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