Resistance to HIV protease inhibitors

OBJECTIVES: The efficacy and safety of levofloxacin and lomefloxacin in complicated urinary tract infections (UTIs) were compared in a randomized, open-label, multicenter study. METHODS: Outpatients were randomized to receive levofloxacin (250 mg once daily) for 7 to 10 days or lomefloxacin (400 mg once daily) for 14 days. Three hundred thirty-six patients (171 with levofloxacin, 165 with lomefloxacin) were evaluable for microbiologic efficacy, and 461 patients (232 with levofloxacin, 229 with lomefloxacin) for safety. RESULTS: The overall microbiologic eradication rate of pathogens was 95.5% (168 of 176) for levofloxacin and 91.7% (154 of 168) for lomefloxacin. Eradication rates with respect to patients were 95.3% (163 of 171) and 92.1% (152 of 165) for levofloxacin and lomefloxacin, respectively. At the 5 to 9-day post-therapy visit, symptoms were completely resolved in 84.8% of levofloxacin-treated patients and were decreased in 8.2% (93.0% clinical success). Among the lomefloxacin-treated patients, complete resolution was seen in 82.4%, with decreased symptoms in 6.1% (88.5% clinical success). Drug-related adverse events (AEs) were reported by 10 (2.6%) and 18 (5.2%) levofloxacin- and lomefloxacin-treated patients, respectively. Compared with levofloxacin-treated patients, more lomefloxacin-treated patients experienced photosensitivity reactions (3 [1.3%] versus 0) and dizziness (2 [0.9%] versus 0). Nausea (3 [1.3%] versus 1 [0.4%]) was more frequent in the levofloxacin-treated group. Six patients in each treatment group had a gastrointestinal AE (1.7%); rash was reported more frequently with lomefloxacin (4 patients [0.4%]) than with levofloxacin (1 patient [0.4%]). Discontinuation because of AEs was observed in 8 (3.4%) levofloxacin- and 14 (6.1%) lomefloxacin-treated patients. CONCLUSIONS: Once-daily levofloxacin is as effective as and has a superior tolerability profile than lomefloxacin in the treatment of complicated UTIs.     

HIV protease inhibitors: general review

Protease inhibitors are a new class of drugs which has demonstrated activity for the treatment of HIV infection. The function of the HIV protease is to split a polyprotein to create smaller proteins which will be incorporated in the structure of the virus. The eight cleavage sites of the polyprotein constitute a template for the synthesis of potential inhibitors. Today, only inhibitors of the Phe-Pro cleavage have shown an antiproteinase activity specific for HIV. Clinical trials in HIV infection with saquinavir, indinavir, and ritonavir have demonstrated a decrease in viral load measured by plasma HIV-RNA PCR and an increase in CD4 lymphocyte counts. The use of protease inhibitors leads to a more or less rapid selection of mutant resistant viruses. However, these new drugs, either used alone or in combination, constitute a new therapeutic approach for the treatment of HIV disease.     

Protein protease inhibitors in insects and comparison with mammalian inhibitors

1. Studies on insect protein protease inhibitors are summarized. Biochemical, genetic and physiological investigations of the silkworm are performed. 2. In addition, the properties and characteristics of fungal protease inhibitors from the silkworm (Bombyx mori) are described and their importance as defensive functions is emphasized. 3. This review also concerns comparative and evolutionary studies of protease inhibitors from various sources. 4. The biological significance of inhibitors is discussed in view of the extensive experimental results.     

Automated docking and the search for HIV protease inhibitors

This article will discuss the motivations, technologies, and future directions of computational automated docking in the context of the structure-based rational design of HIV-1 protease inhibitors. Docking simulations are widely used for screening of compound libraries to identify new drug leads, employing a simple model for rapid testing of thousands of compounds. Docking simulations are also useful for lead enhancement, using more detailed models to analyze the atomic interactions between inhibitors and target macromolecules. Major advances have been reported in the development of empirical force fields, which now allow assessment of relative binding strength and drug specificity, and extensions of automated docking techniques allow de novo drug design.     

Cyclic HIV protease inhibitors: design and synthesis of orally bioavailable, pyrazole P2/P2' cyclic ureas with improved potency

Highly potent HIV-1 protease (HIVPR) inhibitors have been designed and synthesized by introducing bidentate hydrogen-bonding oxime and pyrazole groups at the meta-position of the phenyl ring on the P2/P2' substituents of cyclic ureas. Nonsymmetrical cyclic ureas incorporating 3(1H)-pyrazolylbenzyl as P2 and hydrophilic functionalities as P2' show potent protease inhibition and antiviral activities against HIV and have good oral bioavailabilities. The X-ray structure of HIVPR.10A complex confirms that the two pyrazole rings of 10A form bidentate hydrogen bonds with the side-chain oxygen (C=O) and backbone nitrogen (N-H) of Asp30/30' of HIVPR.     

Design and synthesis of novel conformationally restricted HIV protease inhibitors

A set of HIV protease inhibitors represented by compound 2 has previously been described. Structural and conformational analysis of this compound suggested that conformational restriction of the P1/P2 portion of the molecule could lead to a novel set of potent protease inhibitors. Thus, probe compounds 3-7 were designed, synthesized, and found to be potent inhibitors of HIV protease.     

Non-peptidic HIV protease inhibitors: C2-symmetry-based design of bis-sulfonamide dihydropyrones

Potent, non-peptidic, dihydropyrone sulfonamide HIV protease inhibitors have been previously described. Crystallographic analysis of dihydropyrone sulfonamide inhibitor/HIV protease complexes suggested incorporation of a second, C2 symmetry-related sulfonamide group. Selected bis-sulfonamide dihydropyrone analogues display high HIV protease inhibitory activity.     

Design, synthesis, and conformational analysis of a novel series of HIV protease inhibitors

A combination of structure-based design and both solution, and solid-phase synthesis were utilized to derive a potent (nM) series of HIV-1 protease inhibitors bearing a structurally novel backbone. Detailed structural analysis of several inhibitors prepared in this series has suggested that rigidification of the P1/P2 region of this class of molecules may result in compounds with improved potency.     

Unsymmetric nonpeptidic HIV protease inhibitors containing anthranilamide as a P2' ligand

A series of novel unsymmetrical anthranilamide-containing HIV protease inhibitors was designed. The structure-activity studies revealed a series of potent P2-P3' inhibitors that incorporate an anthranilamide group at the P2' position. A reduction in molecular weight and lipophilicity is achieved by a judicious choice of P2 ligands (i.e., aromatic, heteroaromatic, carbamate, and peptidic). A systematic investigation led to the 5-thiazolyl carbamate analog 8 m, which exhibited a favorable Cmax/EC50 ratio (> 30), plasma half-life (> 8 h), and potent in vitro antiviral activity (EC50 = 0.2 microM).     

Clinical pharmacology of HIV protease inhibitors: focus on saquinavir, indinavir, and ritonavir

In this review the clinical pharmacology of HIV protease inhibitors, a new class of antiretroviral drugs, is discussed. After considering HIV protease function and structure, the development of inhibitors of HIV protease is presented. Three protease inhibitors are reviewed in more detail: saquinavir, indinavir, and ritonavir. Clinical trial results with these agents are evaluated. Furthermore, adverse effects, resistance, dosage and administration, clinical pharmacokinetics, pharmacokinetic-pharmacodynamic relationships, and drug interactions are discussed.     

HIV protease inhibitors influence the prevalence of oral candidosis in HIV-infected patients: a 2-year study

The introduction of HIV protease inhibitors was accompanied by reduction in HIV-associated opportunistic infections. Therefore, we performed a retrospective study of HIV-infected patients to evaluate the effects of therapy with an HIV protease inhibitor (PI) on oral candidosis. This was of special interest, because an important virulence factor of Candida albicans is the secreted aspartic protease (SAP), which is assigned to the same class of aspartic proteases as HIV protease. Sixty-two patients were examined five times over a period of 2 years. There was a hint at a difference in the frequencies of C. albicans carrier state and manifest oral candidosis in favour of treatment with a PI. In addition, loss of Candida colonization and manifest oral candidosis was observed only in patients with elevation of CD4 cells upon PI. This might explain the effect, which also might go back to a direct inhibition of yeast SAP.     

Design, synthesis, and evaluation of tetrahydropyrimidinones as an example of a general approach to nonpeptide HIV protease inhibitors

Re-examination of the design of the cyclic urea class of HIV protease (HIVPR) inhibitors suggests a general approach to designing novel nonpeptide cyclic HIVPR inhibitors. This process involves the inversion of the stereochemical centers of the core transition-state isostere of the linear HIVPR inhibitors and cyclization of the resulting core using an appropriate cyclizing reagent. As an example, this process is applied to the diamino alcohol class of HIVPR inhibitors to give tetrahydropyrimidinones. Conformational analysis of the tetrahydropyrimidinones and modeling of its interaction with the active site of HIVPR suggested modifications which led to very potent inhibitors of HIVPR (24 with a Ki = 0.018 nM). The X-ray crystallographic structure of the complex of 24 with HIVPR confirms the analysis and modeling predictions. The example reported in this study and other examples that are cited indicate that this process may be generally applicable to other linear inhibitors.     

Molecular basis of resistance to HIV-1 protease inhibition: a plausible hypothesis

The binding thermodynamics of the HIV-1 protease inhibitor acetyl pepstatin and the substrate Val-Ser-Gln-Asn-Tyr-Pro-Ile-Val-Gln, corresponding to one of the cleavage sites in the gag, gag-pol polyproteins, have been measured by direct microcalorimetric analysis. The results indicate that the binding of the peptide substrate or peptide inhibitor is entropically driven; i.e., it is characterized by an unfavorable enthalpy and a favorable entropy change, in agreement with a structure-based thermodynamic analysis based upon an empirical parameterization of the energetics. Dissection of the binding enthalpy indicates that the intrinsic interactions are favorable and that the unfavorable enthalpy originates from the energy cost of rearranging the flap region in the protease molecule. In addition, the binding is coupled to a negative heat capacity change. The dominant binding force is the increase in solvent entropy that accompanies the burial of a significant hydrophobic surface. Comparison of the binding energetics obtained for the substrate with that obtained for synthetic nonpeptide inhibitors indicates that the major difference is in the magnitude of the conformational entropy change. In solution, the peptide substrate has a higher flexibility than the synthetic inhibitors and therefore suffers a higher conformational entropy loss upon binding. This higher entropy loss accounts for the lower binding affinity of the substrate. On the other hand, due to its higher flexibility, the peptide substrate is more amenable to adapt to backbone rearrangements or subtle conformational changes induced by mutations in the protease. The synthetic inhibitors are less flexible, and their capacity to adapt is more restricted. The expected result is a more pronounced effect of mutations on the binding affinity of the synthetic inhibitors. On the basis of the thermodynamic differences in the mode of binding of substrate and synthetic inhibitors, it appears that a key factor to understanding resistance is given by the relative balance of the different forces that contribute to the binding free energy and, in particular, the balance between conformational and solvation entropy.     

Cycloalkylpyranones and cycloalkyldihydropyrones as HIV protease inhibitors: exploring the impact of ring size on structure-activity relationships

Previously, 3-substituted cycloalkylpyranones, such as 2d, have proven to be effective inhibitors of HIV protease. In an initial series of 3-(1-phenylpropyl) derivatives with various cycloalkyl ring sizes, the cyclooctyl analog was the most potent. We became interested in exploring the influence of other structural changes, such as substitution on the phenyl ring and saturation of the 5,6-double bond, on the cycloalkyl ring size structure-activity relationship (SAR). Saturation of the 5,6-double bond in the pyrone ring significantly impacts the SAR, altering the optimal ring size from eight to six. Substitution of a sulfonamide at the meta position of the phenyl ring dramatically increases the potency of these inhibitors, but it does not change the optimal ring size in either the cycloalkylpyranone or the cycloalkyldihydropyrone series. This work has led to the identification of compounds with superb binding affinity for the HIV protease (Ki values in the 10-50 pM range). In addition, the cycloalkyldihydropyrones showed excellent antiviral activity in cell culture, with ED50 values as low as 1 microM.