Viral infection protease inhibitors

These drugs are peptidyl analogs that reversibly inhibit the proteinase that is essential for the final step of viral proliferation. Protease inhibitors have revolutionized HIV therapy, reducing infections by opportunistic organisms, and prolonging and improving the lives of most patients. 

Protease inhibitors HfV protease is essential for virus infectivity because protease is needed for viral replication. Protease inhibitors bind reversibly to the active site of HfV protease preventing protease from cleaving the viral precursor polypeptide and blocking viral maturation. Immature viral particles are noninfectious. Amprenavir (APV) Agenerase 50 mg capsule 15 mg/ml solutions Itraconazole, fluconazole, ketoconazole, voriconazole,... 

For using flow cytometry to measure viral titer, approximately 1-5 X 10 cells can be infected with 100 pi of virus, and following infection for 2 h, cells were washed once and resuspended into 1 ml fresh medium. To prevent secondary infection, protease inhibitors can be added and infected cells are culmred for 2-3 days and analyzed by flow cytometry to measure the percentage of infected cells. 

The most recent advance in treating HIV infections has been to simultaneously attack the virus on a second front using a protease inhibitor. Recall from Section 27.10 that proteases are enzymes that catalyze the hydrolysis of proteins at specific points. When HIV uses a cell s DNA to synthesize its own proteins, the initial product is a long polypeptide that contains several different proteins joined together. To be useful, the individual proteins must be separated from the aggregate by protease-catalyzed hydrolysis of peptide bonds. Protease inhibitors prevent this hydrolysis and, in combination with reverse transcriptase inhibitors, slow the reproduction of HIV. Dramatic reductions in the viral load in HIV-infected patients have been achieved with this approach. 

A final but important consideration is viral mutation. Certain mutant HIV strains are resistant to one or more of the protease inhibitors, and even for patients who respond initially to protease inhibitors it is possible that mutant viral forms may eventually thrive in the infected individual. The search for new and more effective protease inhibitors is ongoing. 

Abstract This review provides an overview of the development of viral protease inhibitors as antiviral drugs. We concentrate on HlV-1 protease inhibitors, as these have made the most significant advances in the recent past. Thus, we discuss the biochemistry of HlV-1 protease, inhibitor development, clinical use of inhibitors, and evolution of resistance. Since many different viruses encode essential proteases, it is possible to envision the development of a potent protease inhibitor for other viruses if the processing site sequence and the catalytic mechanism are known. At this time, interest in developing inhibitors is Umited to viruses that cause chronic disease, viruses that have the potential to cause large-scale epidemics, or viruses that are sufQciently ubiquitous that treating an acute infection would be... 

The requirements of protease inhibitors as drugs in terms of potency, pharmacokinetics, and toxicity will vary depending on the nature of the infection and the goals of therapy. At one extreme is treatment of HlV-1, a chroific infection that requires life-long therapy and full suppression of viral replication. At the other extreme is the treatment of human rhinovirus (i.e., the cold virus), where short-term treatment to blunt viremia will likely be sufficient to reduce the unwanted symptoms of a cold. In all cases, viral proteases represent very attractive targets with familiar mechanisms of catalysis that frequently allow for the design of transition state analogs and with distinct specificities from host proteases. 

The reported risk factors for HIV-associated sensory neuropathy are varied and may have changed since the availability of HAART. In the pre-HAART era, age, nutritional deficiencies, alcohol exposure, higher HIV viral load, and low CD4 counts (Moyle and Sadler 1998 Childs et al. 1999), as well as mood, other neurologic disorders and functional abnormalities (Schifitto et al. 2002) were neuropathy risk factors. In the HAART era, the use of NRTI (Cherry et al. 2006 Pettersen et al. 2006) and exposure to protease inhibitor (PI) medication (Pettersen et al. 2006 Smyth et al. 2007) are considered additional risk factors. Although hepatitis C mono-infection has been associated with peripheral nerve disease, and there is... 

Inhibiting viral replication with combination of potent antiretroviral therapy has been the most clinically successful strategy in the treatment of HIV infection. There have been three primary groups of drugs used nucleoside and nonnucleoside reverse transcriptase inhibitors and protease inhibitors (Pis) (Table 40-5). 

Other potent peptide mimetic NS3 protease inhibitors have been reported that incorporate a serine trap on the C-terminal end of the peptide. Thus, the inhibitory activity of telaprevir (VX-950, 59), (7nM vs. NS3, 300 nM vs. the la replicon) is based on truncation of the polypeptide substrate, maximizing binding by alteration of amino acids at the scissile site, and capping both N- and C-terminal ends, the latter with a known dicarbonyl serine trap. This compound has exhibited impressive antiviral activity in animals, and showed a 4.4 log drop in viral load in genotype 1-infected patients in a Phase lb clinical trial [110]. Telaprevir is expected to enter Phase 3 clinical trials in 2007. Additional bicyclo-proline-based P2 tetrapeptides, represented by analog 60 (Kj = 22 nM), have been explored. Although the compounds are selective inhibitors of NS3, little or no cell-based replicon activity was reported, presumably due to poor cellular permeability [111-114], A diastereomer of telaprevir, has been reported to inhibit the replicon with an EC50 of 0.55 pM [115]. 

Peptidases encoded by many viruses play essential roles at various stages of viral replication, including the coordinated assembly and maturation of virons [7a]. Viral peptidases have become important drug targets in the treatment of viral infections. Of note are inhibitors of proteases of the human immunodeficiency virus (HIV), particularly HIV-1 protease (HIV-1 retropepsin, EC 3.4.23.16) and HIV-2 protease [47-50], Drugs in this class, which include indinavir, ritonavir, and saquinavir, are useful in the treatment of AIDS, especially when administered as a cocktail together with one of the drugs that act on the viral retrotranscriptase (e.g., didanosine, stavudine, and zidovudine (AZT)). 

HIV infection Tipranavir, coadministered with ritonavir 200 mg, is indicated for combination antiretroviral treatment of HIV-1-infected adult patients with evidence of viral replication, who are highly treatment-experienced or have HIV-1 strains resistant to multiple protease inhibitors (Pis). 

Pharmacology Atazanavir is an azapeptide HIV-1 protease inhibitor. The compound selectively inhibits the virus-specific processing of viral Gag and Gag-Pol polyproteins in HIV-1-infected cells, thus preventing formation of mature virions. Pharmacokinetics ... 

Antibodies against the virus but also amantadine and derivatives, interfere with host cell penetration. There are nucleoside analogues such as aciclovir and ganciclovir, which interfere with DNA synthesis, especially of herpes viruses. Others like zidovudine and didanosine, inhibit reverse transcriptase of retroviruses. Recently a number of non-nucleoside reverse transcriptase inhibitors was developed for the treatment of HIV infections. Foscarnet, a pyrophosphate analogue, inhibits both reverse transcriptase and DNA synthesis. Protease inhibitors, also developed for the treatment of HIV infections, are active during the fifth step of virus replication. They prevent viral replication by inhibiting the activity of HIV-1 protease, an enzyme used by the viruses to cleave nascent proteins for final assembly of new vi-rons. 

Single agents are seldom used to treat HIV infection. Instead, multidrug therapy is used to counteract the rapid mutation rate of HIV and to minimize drug toxicity. Highly active antiretroviral therapy (HAART) uses combinations of reverse transcriptase inhibitors and protease inhibitors (Table 51.1). In this system, drugs working by different mechanisms produce a sequential blockade of steps required for viral reproduction. It is... 

Mechanism of Action An antiviral that acts as an HIV-1 protease inhibitor, selectively preventing the processing of viral precursors found in cells infected with HIV-1. Therapeutic Effect Prevents the formation of mature HIV cells. 

Mecfianism of Action A protease inhibitor that suppresses HIV protease, an enzyme necessary for splitting viral polyprotein precursors into mature and infectious viral particles. Therapeutic Effect Interrupts HIV replication, slowing the progression of HIV infection. 

Although any of these seven steps could be a druggable target, most of the antiviral agents clinically employed for non-AIDS infections act on the synthesis or assembly of either purines or pyrimidines (steps 3 and 4). For AIDS, reverse transcriptase inhibitors block transcription of the HIV RNA genome into DNA, thereby preventing synthesis of viral mRNA and protein protease inhibitors act on the synthesis of late proteins (steps 5 and 6). 

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