The HIV-1 protease as a therapeutic target for AIDS

Decomposing the energetic impact of drug-resistant mutations: the example of HIV-1 protease-DRV binding

HIV-1 protease is a major drug target for AIDS therapy. With the appearance of drug-resistant HIV-1 protease variants, understanding the mechanism of drug resistance becomes critical for rational drug design. Computational methods can provide more details about inhibitor-protease binding than crystallography and isothermal titration calorimetry. The latest FDA-approved HIV-1 protease inhibitor is Darunavir (DRV). Herein, each DRV atom is evaluated by free energy component analysis for its contribution to the binding affinity with wild-type protease and ACT, a drug-resistant variant. This information can contribute to the rational design of new HIV-1 protease inhibitors.

Development of a classification scheme for disease-related enzyme information

Background

BRENDA (BRaunschweig ENzyme DAtabase, http://www.brenda-enzymes.org) is a major resource for enzyme related information. First and foremost, it provides data which are manually curated from the primary literature. DRENDA (Disease RElated ENzyme information DAtabase) complements BRENDA with a focus on the automatic search and categorization of enzyme and disease related information from title and abstracts of primary publications. In a two-step procedure DRENDA makes use of text mining and machine learning methods.

Results

Currently enzyme and disease related references are biannually updated as part of the standard BRENDA update. 910,897 relations of EC-numbers and diseases were extracted from titles or abstracts and are included in the second release in 2010. The enzyme and disease entity recognition has been successfully enhanced by a further relation classification via machine learning. The classification step has been evaluated by a 5-fold cross validation and achieves an F1 score between 0.802 ± 0.032 and 0.738 ± 0.033 depending on the categories and pre-processing procedures. In the eventual DRENDA content every category reaches a classification specificity of at least 96.7% and a precision that ranges from 86-98% in the highest confidence level, and 64-83% for the smallest confidence level associated with higher recall.

Conclusions

The DRENDA processing chain analyses PubMed, locates references with disease-related information on enzymes and categorises their focus according to the categories causal interaction, therapeutic application, diagnostic usage and ongoing research. The categorisation gives an impression on the focus of the located references. Thus, the relation categorisation can facilitate orientation within the rapidly growing number of references with impact on diseases and enzymes. The DRENDA information is available as additional information in BRENDA.

Multiple receptor conformation docking and dock pose clustering as tool for CoMFA and CoMSIA analysis - a case study on HIV-1 protease inhibitors

Multiple receptors conformation docking (MRCD) and clustering of dock poses allows seamless incorporation of receptor binding conformation of the molecules on wide range of ligands with varied structural scaffold. The accuracy of the approach was tested on a set of 120 cyclic urea molecules having HIV-1 protease inhibitory activity using 12 high resolution X-ray crystal structures and one NMR resolved conformation of HIV-1 protease extracted from protein data bank. A cross validation was performed on 25 non-cyclic urea HIV-1 protease inhibitor having varied structures. The comparative molecular field analysis (CoMFA) and comparative molecular similarity indices analysis (CoMSIA) models were generated using 60 molecules in the training set by applying leave one out cross validation method, r (loo) (2) values of 0.598 and 0.674 for CoMFA and CoMSIA respectively and non-cross validated regression coefficient r(2) values of 0.983 and 0.985 were obtained for CoMFA and CoMSIA respectively. The predictive ability of these models was determined using a test set of 60 cyclic urea molecules that gave predictive correlation (r (pred) (2) ) of 0.684 and 0.64 respectively for CoMFA and CoMSIA indicating good internal predictive ability. Based on this information 25 non-cyclic urea molecules were taken as a test set to check the external predictive ability of these models. This gave remarkable out come with r (pred) (2) of 0.61 and 0.53 for CoMFA and CoMSIA respectively. The results invariably show that this method is useful for performing 3D QSAR analysis on molecules having different structural motifs.

Oxycodone concentrations are greatly increased by the concomitant use of ritonavir or lopinavir/ritonavir

PURPOSE

this study aimed to investigate the effect of antivirals ritonavir and lopinavir/ritonavir on the pharmacokinetics and pharmacodynamics of oral oxycodone, a widely used opioid receptor agonist used in the treatment of moderate to severe pain.

METHODS

a randomized crossover study design with three phases at intervals of 4 weeks was conducted in 12 healthy volunteers. Ritonavir 300 mg, lopinavir/ritonavir 400/100 mg, or placebo b.i.d. for 4 days was given to the subjects. On day 3, 10 mg oxycodone hydrochloride was administered orally. Plasma concentrations of oxycodone, noroxycodone, oxymorphone, and noroxymorphone were determined for 48 h. Pharmacokinetic parameters were calculated with standard noncompartmental methods. Behavioral effects and experimental cold pain analgesia were assessed for 12 h. ANOVA for repeated measures was used for statistical analysis.

RESULTS

ritonavir and lopinavir/ritonavir increased the area under the plasma concentration-time curve of oral oxycodone by 3.0-fold (range 1.9- to 4.3-fold; P <0.001) and 2.6-fold (range 1.9- to 3.3-fold; P <0.001). The mean (± SD) elimination half-life increased after ritonavir and lopinavir/ritonavir from 3.6 ± 0.6 to 5.6 ± 0.9 h (P <0.001) and 5.7 ± 0.9 h (P <0.001), respectively. Both ritonavir (P <0.001) and lopinavir/ritonavir (P <0.05) increased the self-reported drug effect of oxycodone.

CONCLUSIONS

ritonavir and lopinavir/ritonavir greatly increase the plasma concentrations of oral oxycodone in healthy volunteers and enhance its effect. When oxycodone is used clinically in patients during ritonavir and lopinavir/ritonavir treatment, reductions in oxycodone dose may be needed to avoid opioid-related adverse effects.

Computational study of the resistance shown by the subtype B/HIV-1 protease to currently known inhibitors

Human immunodeficiency virus type 1 protease (HIV-1 PR) is an essential enzyme in the HIV-1 life cycle. As such, this protein represents a major drug target in AIDS therapy, but emerging resistance to antiretroviral inhibitor cocktails, caused by high viral mutation rates, represents a significant challenge in AIDS treatment. Many mutations are not located within the active site or binding pocket, nor they do significantly modify the three-dimensional structural organization of the enzyme; hence, the mechanism(s) by which they alter inhibitor affinity for the protease remains uncertain. In this article, we present an all-atom computational analysis of the dynamic residue-residue coordination between the active site residues and the rest of the protein and of the energetic properties of different HIV-1 PR complexes. We analyze both the wild-type form and mutated forms that induce drug resistance. In particular, the results show differences between the wild type and the mutants in their mechanism of dynamic coordination, in the signal propagation between the active site residues and the rest of the protein, and in the energy networks responsible for the stabilization of the bound inhibitor conformation. Finally, we propose a dynamic and energetic explanation for HIV-1 protease drug resistance, and, through this model, we identify a possible new site that could be helpful in the design of a new family of HIV-1 PR allosteric inhibitors.

Evaluating the substrate-envelope hypothesis: structural analysis of novel HIV-1 protease inhibitors designed to be robust against drug resistance

Drug resistance mutations in HIV-1 protease selectively alter inhibitor binding without significantly affecting substrate recognition and cleavage. This alteration in molecular recognition led us to develop the substrate-envelope hypothesis which predicts that HIV-1 protease inhibitors that fit within the overlapping consensus volume of the substrates are less likely to be susceptible to drug-resistant mutations, as a mutation impacting such inhibitors would simultaneously impact the processing of substrates. To evaluate this hypothesis, over 130 HIV-1 protease inhibitors were designed and synthesized using three different approaches with and without substrate-envelope constraints. A subset of 16 representative inhibitors with binding affinities to wild-type protease ranging from 58 nM to 0.8 pM was chosen for crystallographic analysis. The inhibitor-protease complexes revealed that tightly binding inhibitors (at the picomolar level of affinity) appear to "lock" into the protease active site by forming hydrogen bonds to particular active-site residues. Both this hydrogen bonding pattern and subtle variations in protein-ligand van der Waals interactions distinguish nanomolar from picomolar inhibitors. In general, inhibitors that fit within the substrate envelope, regardless of whether they are picomolar or nanomolar, have flatter profiles with respect to drug-resistant protease variants than inhibitors that protrude beyond the substrate envelope; this provides a strong rationale for incorporating substrate-envelope constraints into structure-based design strategies to develop new HIV-1 protease inhibitors.

Decomposing the energetic impact of drug resistant mutations in HIV-1 protease on binding DRV

Darunavir (DRV) is a high affinity (4.5×10(-12) M, ΔG = -15.2 kcal/mol) HIV-1 protease inhibitor. Two drug-resistant protease variants FLAP+ (L10I, G48V, I54V, V82A) and ACT (V82T, I84V) decrease the binding affinity with DRV by 1.0 kcal/mol and 1.6 kcal/mol respectively. In this study the absolute and relative binding free energies of DRV with wild-type protease, FLAP+ and ACT were calculated with MM-PB/GBSA and thermodynamic integration methods, respectively. Free energy decomposition elucidated that the mutations conferred resistance by distorting the active site of HIV-1 protease so that the residues that lost binding free energy were not limited to the sites of mutation. Specifically the bis-tetrahydrofuranylurethane moiety of DRV maintained interactions with the FLAP+ and ACT variants, whereas the 4 - amino phenyl group lost more binding free energy with the protease in the FLAP+ and ACT complexes than in the wild-type protease which could account for the majority of the loss in binding free energy. This suggested that replacement of the 4 - amino phenyl group might generate new inhibitors less susceptible to the drug resistant mutations.

Target-selective degradation of proteins and oligosaccharides by light-activated hybrid molecules for molecular-targeted photodynamic therapy

Proteins and oligosaccharides are key players in many biological events. The development of novel methods for the selective degradation of targeted proteins and oligosaccharides has attracted much attention in the fields of chemistry, biology and medicine. Target-selective degradations of proteins, such as estrogen receptor-α androgen receptor and HIV-1 protease, by light-activated 2-phenylquinoline-steroid hormone hybrids, porphyrin derivatives and fullerene-sugar hybrids, and target-selective degradation of oligosaccharides, such as a T-antigen disaccharide, by a light-activated anthraquinone-lectin hybrid have been achieved. This novel class of light-activated and molecular-targeted molecules, namely molecular-targeted photosensitizers, promise bright prospects for finding not only molecular-targeted bioprobes for future application in the life sciences but also molecular-targeted drugs for future photodynamic therapy.

Design of potent aspartic protease inhibitors to treat various diseases

In this retrospective, personal review covering our research from the late 1980s until 2007, we outline nearly two-decade worth of our own work on several aspartic protease inhibitors including those affecting renin, HIV-1 protease, plasmepsins, beta-secretase, and HTLV-I protease and we report on aspartic protease inhibitors as potential drugs to treat hypertension, AIDS, malaria, Alzheimer's disease and adult T-cell leukemia, HTLV-I associated myelopathy / tropical spastic paraparesis, and various, respectively, associated diseases. Herein, we describe our methods for rational substrate-based drug design of peptidomimetics that potently inhibit the activity of renin, HIV-1 protease, plasmepsins, beta-secretase, and HTLV-I protease accordingly, using an appropriately selected inhibitory residue that contained a hydroxymethylcarbonyl isostere. Although this non-hydrolyzable isostere mimics the transition state that is formed during protein cleavage of a substrate, the isostere-containing inhibitor is not cleaved. We highlight our optimization studies in which we used various techniques and tools such as truncation studies, natural and non-natural amino acid substitution studies, various moieties to promote chemical and pharmacological stability, X-ray crystallography, computer-assisted docking and dynamic simulations, quantitative structure-activity relationship studies, and various other methods that this review can barely mention.

Computational design and experimental study of tighter binding peptides to an inactivated mutant of HIV-1 protease

Drug resistance in HIV-1 protease, a barrier to effective treatment, is generally caused by mutations in the enzyme that disrupt inhibitor binding but still allow for substrate processing. Structural studies with mutant, inactive enzyme, have provided detailed information regarding how the substrates bind to the protease yet avoid resistance mutations; insights obtained inform the development of next generation therapeutics. Although structures have been obtained of complexes between substrate peptide and inactivated (D25N) protease, thermodynamic studies of peptide binding have been challenging due to low affinity. Peptides that bind tighter to the inactivated protease than the natural substrates would be valuable for thermodynamic studies as well as to explore whether the structural envelope observed for substrate peptides is a function of weak binding. Here, two computational methods-namely, charge optimization and protein design-were applied to identify peptide sequences predicted to have higher binding affinity to the inactivated protease, starting from an RT-RH derived substrate peptide. Of the candidate designed peptides, three were tested for binding with isothermal titration calorimetry, with one, containing a single threonine to valine substitution, measured to have more than a 10-fold improvement over the tightest binding natural substrate. Crystal structures were also obtained for the same three designed peptide complexes; they show good agreement with computational prediction. Thermodynamic studies show that binding is entropically driven, more so for designed affinity enhanced variants than for the starting substrate. Structural studies show strong similarities between natural and tighter-binding designed peptide complexes, which may have implications in understanding the molecular mechanisms of drug resistance in HIV-1 protease.

Pharmacogenetic information derived from analysis of HLA alleles

A large amount of pharmacogenetic information has, in particular, accumulated on the association between human leukocyte antigen (HLA) alleles and hypersensitivity to certain drugs. Prospective HLA typing has dramatically reduced the risk of abacavir hypersensitivity because of its strong association with HLA-B*5701. Significant predisposition to nevirapine hypersensitivity has been reported in Caucasian Australians harboring HLA-DRB1*0101 with high CD4+ T-cell counts, and Sardinians and Japanese harboring HLA-Cw8. A strong association between carbamazepine hypersensitivity and HLA-B*1502 has been reported in Han Chinese. Most Han Chinese individuals with allopurinol-induced severe cutaneous adverse reactions are positive for HLA-B*5801. HLA typing can stratify risk of hypersensitivity to certain drugs and allow personalized treatment, although the patients should be monitored closely even if they are negative for HLA alleles associated with hypersensitivity.

Accurate prediction of protonation state as a prerequisite for reliable MM-PB(GB)SA binding free energy calculations of HIV-1 protease inhibitors

Binding free energies were calculated for the inhibitors lopinavir, ritonavir, saquinavir, indinavir, amprenavir, and nelfinavir bound to HIV-1 protease. An MMPB/SA-type analysis was applied to conformational samples from 3 ns explicit solvent molecular dynamics simulations of the enzyme-inhibitor complexes. Binding affinities and the sampled conformations of the inhibitor and enzyme were compared between different HIV-1 protease protonation states to find the most likely protonation state of the enzyme in the complex with each of the inhibitors. The resulting set of protonation states leads to good agreement between calculated and experimental binding affinities. Results from the MMPB/SA analysis are compared with an explicit/implicit hybrid scheme and with MMGB/SA methods. It is found that the inclusion of explicit water molecules may offer a slight advantage in reproducing absolute binding free energies while the use of the Generalized Born approximation significantly affects the accuracy of the calculated binding affinities.

Darunavir: a nonpeptidic antiretroviral protease inhibitor

BACKGROUND

Protease inhibitors were a major therapeutic breakthrough in the mid-1990s for the treatment of HIV infection, which resulted in improved life expectancy for patients who had failed previous therapies. With time and evolution of the virus, however, there is a new population of patients with treatment-resistant disease and few treatment options. Darunavir is a synthetic nonpeptidic analogue of amprenavir with enhanced activity against resistant virus that became available in 2006.

OBJECTIVES

The purpose of this review was to describe the clinical pharmacology, pharmacokinetic and pharmacodynamic properties, and clinical efficacy of darunavir. Also discussed are the published clinical experience with darunavir, its adverse events, drug interactions, pharmacoeconomics, and dosing and administration.

METHODS

A MEDLINE and EMBASE search (English-language only) was performed from January 1996 through April 2007 using the key words darunavir and TMC114. Abstracts from relevant scientific meetings were searched for the years 2000 through 2007. Additionally, the US Food and Drug Administration Web site was accessed to review the new drug application summary and data presented therein.

RESULTS

Darunavir was found to maintain antiretroviral activity against HIV with protease inhibitor mutations in 6 studies. Clinical efficacy and safety data are limited to 4 controlled and 2 uncontrolled trials. In 2 large Phase IIb clinical studies, viral suppression at 48 weeks to undetectable levels in heavily pretreated patients was achieved in 45% of patients compared with 10% of patients in the control group (P < 0.001). The addition of enfuvirtide enhanced this response rate to 58% compared with 11% of the patients who did not receive enfuvirtide (P < 0.001). Gastrointestinal symptoms, nausea, and headache were the most commonly reported events.

CONCLUSIONS

Darunavir has improved activity against resistant HIV isolates in patients with few treatment choices, particularly when enfuvirtide is added. The safety profile of darunavir is comparable to other protease inhibitors based on early data.

Computational design of novel cyclic urea as HIV-1 protease inhibitor

A series of novel cyclic urea molecules 5,6-dihydroxy-1,3-diazepane-2,4,7-trione as HIV-1 protease inhibitors were designed using computational techniques. The designed molecules were compared with the known cyclic urea molecules by performing docking studies, calculating their ADME (Absorption, Distribution, Metabolism, and Excretion) properties and protein ligand interaction energy. These novel molecules were designed by substituting the P 1/P′ 1 positions (4th and 7th position of 1, 3-diazepan-2-one) with double bonded oxygens. This reduces the molecular weight and increases the bioavailability, indicating better ADME properties. The docking studies showed good binding affinity towards HIV-1 protease. The biological activity of these inhibitors were predicted by a model equation generated by the regression analysis between biological activity (log 1/K i ) of known inhibitors and their protein ligand interaction energy. The synthetic studies are in progress.

Structural analysis of lead fullerene-based inhibitor bound to human immunodeficiency virus type 1 protease in solution from molecular dynamics simulations

Molecular dynamics (MD) simulations of the HIV-1 protease (HIVP) complexed with lead fullerene-based inhibitor (diphenyl C60 alcohol) in the three protonated states, unprotonated (Un-), monoprotonated (Mono-), and diprotonated (Di-) states at Asp25 and Asp25' were performed. As the X-ray structure of the investigated complex is not available, it was built up starting with the X-ray crystallographic structure of the HIVP complexed with non-peptide inhibitor (PDB code: 1AID) and that of the diphenyl C60 alcohol optimized using the integrated ONIOM molecular orbital calculations. The inhibitor was, then, introduced into the enzyme pocket using a molecular docking method. Change of the HIVP binding cavity for all three states were evaluated in terms of distance between the two catalytic residues, Asp25 and Asp25' as well as those between the catalytic residues and the flap regions. The torsional angles formed by the O-C-C-O of the two carboxyl groups of the catalytic dyad show the non-planar configuration with the most frequency at about -45 degrees for the Un-, 35 degrees and -95 degrees for the Mono- and 60 degrees for the Di-systems. At equilibrium, different orientations of the fullerene-based inhibitor in the three protonation states were observed. For the Di-state, the OH group of the inhibitor stably forms hydrogen bonds with the two aspartic residues. It turns to the flap region to form hydrogen bonding to the backbone N of Ile50' for the Un-state. In contrast, the OH group turns to locate between the catalytic and the flap region for the Mono-states. Beside the molecular orientation, the rotation of the OH group of the inhibitor in the Un-state was also detected. In terms of solvation, the carboxylate oxygens of the aspartic residues in the Un- and Mono-states were solvated by one to three water molecules while the OH group in these two states was coordinated by one water molecule. This is in contrast to the Di-state in which no water molecule is available in the radius of 5-6A around the oxygen atoms of the carboxylate groups of enzyme and of the OH group of the inhibitor. The simulated results lead to the conclusion that the active site of the HIVP complexed with the diphenyl C60 alcohol is the diprotonation states on Asp25 and Asp25'.

Crystal structure of lysine sulfonamide inhibitor reveals the displacement of the conserved flap water molecule in human immunodeficiency virus type 1 protease

Human immunodeficiency virus type 1 (HIV-1) protease has been continuously evolving and developing resistance to all of the protease inhibitors. This requires the development of new inhibitors that bind to the protease in a novel fashion. Most of the inhibitors that are on the market are peptidomimetics, where a conserved water molecule mediates hydrogen bonding interactions between the inhibitors and the flaps of the protease. Recently a new class of inhibitors, lysine sulfonamides, was developed to combat the resistant variants of HIV protease. Here we report the crystal structure of a lysine sulfonamide. This inhibitor binds to the active site of HIV-1 protease in a novel manner, displacing the conserved water and making extensive hydrogen bonds with every region of the active site.

Resistant mechanism against nelfinavir of human immunodeficiency virus type 1 proteases

Inhibitors against human immunodeficiency virus type-1 (HIV-1) proteases are finely effective for anti-HIV-1 treatments. However, the therapeutic efficacy is reduced by the rapid emergence of inhibitor-resistant variants of the protease. Among patients who failed in the inhibitor nelfinavir (NFV) treatment, D30N, N88D, and L90M mutations of HIV-1 protease are often observed. Despite the serious clinical problem, it is not clear how these mutations, especially nonactive site mutations N88D and L90M, affect the affinity of NFV or why they cause the resistance to NFV. In this study, we executed molecular dynamics simulations of the NFV-bound proteases in the wild-type and D30N, N88D, D30N/N88D, and L90M mutants. Our simulations clarified the conformational change at the active site of the protease and the change of the affinity with NFV for all of these mutations, even though the 88th and 90th residues are not located in the NFV-bound cavity and not able to directly interact with NFV. D30N mutation causes the disappearance of the hydrogen bond between the m-phenol group of NFV and the 30th residue. N88D mutation alters the active site conformation slightly and induces a favorable hydrophobic contact. L90M mutation dramatically changes the conformation at the flap region and leads to an unfavorable distortion of the binding pocket of the protease, although 90M is largely far apart from the flap region. Furthermore, the changes of binding energies of the mutants from the wild-type protease are shown to be correlated with the mutant resistivity previously reported by the phenotypic experiments.

HLA-B*5701 screening for susceptibility to abacavir hypersensitivity

The introduction of highly active antiretroviral therapy (also known as combination therapy) has transformed the nature of HIV infection from a severe and ultimately fatal disease to that of a manageable chronic condition. HIV drugs are highly efficacious, but their use comes at the cost of a range of drug-related adverse events, including severe drug hypersensitivity reactions (HSRs) that have been most notably associated with abacavir and nevirapine therapy. This article discusses the issues of pharmacogenetic screening, in the light of the strong genetic association of the HLA-B*5701 allele and the susceptibility to developing abacavir HSRs. It also presents the screening's impact on clinical practice and discusses the practical considerations that influence the introduction and cost-effectiveness of such screening.

Substrate envelope and drug resistance: crystal structure of RO1 in complex with wild-type human immunodeficiency virus type 1 protease

In our previous crystallographic studies of human immunodeficiency virus type 1 (HIV-1) protease-substrate complexes, we described a conserved "envelope" that appears to be important for substrate recognition and the selection of drug-resistant mutations. In this study, the complex of HIV-1 protease with the inhibitor RO1 was determined and comparison with the substrate envelope provides a rationale for mutational patterns.

Lopinavir/ritonavir: towards simplifying therapy in HIV infection

Combination antiretroviral therapy has greatly decreased the morbidity and mortality associated with HIV infection, although many agents currently available are limited by difficult dosing requirements, side-effect profiles and the development of resistance. Lopinavir/ritonavir is a coformulation of two protease inhibitors that exploit a favorable drug–drug interaction, yielding sustained increases in plasma levels of lopinavir. This agent has shown excellent therapeutic efficacy in both antiretroviral-naïve and –experienced patients, with a tolerable side-effect profile and without evidence of the development of primary resistance mutations in registrational trials. Once-daily dosing has been approved recently for use in antiretroviral-naïve patients, and US FDA approval was granted recently for a new tablet formulation that decreases the number of pills required for standard dosing.

Lysine sulfonamides as novel HIV-protease inhibitors: Nepsilon-acyl aromatic alpha-amino acids

A series of lysine sulfonamide analogues bearing Nepsilon-acyl aromatic amino acids were synthesized using an efficient synthetic route. Evaluation of these novel protease inhibitors revealed compounds with high potency against wild-type and multiple-protease inhibitor-resistant HIV viruses.

Novel multi-component nanopharmaceuticals derived from poly(ethylene) glycol, retro-inverso-Tat nonapeptide and saquinavir demonstrate combined anti-HIV effects

Background

Current anti-AIDS therapeutic agents and treatment regimens can provide a dramatically improved quality of life for HIV-positive people, many of whom have no detectable viral load for prolonged periods of time. Despite this, curing AIDS remains an elusive goal, partially due to the occurrence of drug resistance. Since the development of resistance is linked to, among other things, fluctuating drug levels, our long-term goal has been to develop nanotechnology-based drug delivery systems that can improve therapy by more precisely controlling drug concentrations in target cells. The theme of the current study is to investigate the value of combining AIDS drugs and modifiers of cellular uptake into macromolecular conjugates having novel pharmacological properties.

Results

Bioconjugates were prepared from different combinations of the approved drug, saquinavir, the antiviral agent, R.I.CK-Tat9, the polymeric carrier, poly(ethylene) glycol and the cell uptake enhancer, biotin. Anti-HIV activities were measured in MT-2 cells, an HTLV-1-transformed human lymphoid cell line, infected with HIV-1 strain Vbu 3, while parallel studies were performed in uninfected cells to determine cellular toxicity. For example, R.I.CK-Tat9 was 60 times more potent than L-Tat9 while the addition of biotin resulted in a prodrug that was 2850 times more potent than L-Tat9. Flow cytometry and confocal microscopy studies suggest that variations in intracellular uptake and intracellular localization, as well as synergistic inhibitory effects of SQV and Tat peptides, contributed to the unexpected and substantial differences in antiviral activity.

Conclusion

Our results demonstrate that highly potent nanoscale multi-drug conjugates with low non-specific toxicity can be produced by combining moieties with anti-HIV agents for different targets onto macromolecules having improved delivery properties.

Modeling of activity of cyclic urea HIV-1 protease inhibitors using regularized-artificial neural networks

Artificial neural networks (ANNs) were used to model both inhibition of HIV-1 protease (K(i)) and inhibition of HIV replication (IC90) for 55 cyclic urea derivatives using constitutional and 2D descriptors. As a preliminary step, linear dependences were established by multiple linear regression (MLR) approaches, selecting the relevant descriptors by genetic algorithm (GA) feature selection. For ANN models non-linear GA feature selection was also applied. Non-linear modeling of K(i) overcame the results of the linear one using four properties, keeping in mind standard Pearson R correlation coefficients (0.931 vs. 0.862) and leave one out (LOO) cross-validation analysis (Q(LOO)2 = 0.703 vs. 0.510). On the other hand, IC90 modeling was insoluble by a linear approach: no predictive model was achieved; however, a non-linear relation was encountered according to statistic results (R = 0.891; Q(LOO)2 = 0.568). The best non-linear models suggested the influence of the presence of nitrogen atoms and the molecular volume distribution in the inhibitor structures on the HIV-1 protease inhibition as well as that the inhibition of HIV replication was dependent on the occurrence of five-member rings. Finally, inhibitors were well distributed regarding its activity levels in a Kohonen self-organizing map built using the input variables of the best non-linear models.

Lopinavir/ritonavir in the treatment of human immunodeficiency virus infection

The importance of combination antiretroviral therapy in HIV-infection has been well established. However, many available agents suffer shortcomings that limit their clinical value, including adverse effects, difficult dosing requirements and rapid development of resistance. Lopinavir/ritonavir (Kaletra) is a member of the protease inhibitor class, specifically designed to address some of these deficits. The drug is a coformulation of lopinavir with low-dose ritonavir, exploiting a favourable drug-drug interaction between the two that yields sustained increases in plasma levels of lopinavir. In large-scale clinical trials, lopinavir/ritonavir has demonstrated superior therapeutic efficacy when compared with other protease inhibitors. It exerts potent antiviral activity in both treatment-naive and experienced patients with an acceptable incidence of adverse effects. De novo development of resistance has not been described in large clinical trials with patients naive to antiretroviral therapy. Lopinavir/ritonavir has recently been approved for once-daily dosing in antiretroviral-naive patients.

Safety and antiviral activity of lopinavir/ritonavir-based therapy in human immunodeficiency virus type 1 (HIV-1) infection

Protease inhibitor-based antiretroviral therapy has been shown to decrease the morbidity and mortality associated with human immunodeficiency virus type 1 (HIV-1) infection. However, many of the available agents in this class suffer shortcomings, including poor tolerability, difficult dosing regimens, and variable drug concentrations which may lead to generation of viral resistance. Lopinavir/ritonavir (Kaletra) has been designed specifically to address some of these shortcomings. Excellent therapeutic efficacy has been documented for lopinavir/ritonavir in multiple clinical trials in both antiretroviral-naive and -experienced patients. Development of resistance is a rare event in persons initiating therapy with lopinavir/ritonavir as their first protease inhibitor. The main side effects associated with lopinavir/ritonavir are gastrointestinal disturbances and elevations of serum lipids. Current antiretroviral therapy guidelines list lopinavir/ritonavir as the consensus first-line protease inhibitor recommended in the initial therapeutic regimen in persons infected with HIV-1.

Antiviral therapies in children: has their time arrived?

The increase in the number and classes of antiviral agents that has occurred since the 1980s is remarkable. The rapid expansion in therapeutic options for previously untreatable illnesses challenges clinicians to gain familiarity and experience with these new drugs, especially with regard to their use in children. This article describes the clinical utilities, pharmacokinetics, and adverse effects of these new drugs to empower practitioners to use them appropriately.

Topological models for the prediction of HIV-protease inhibitory activity of tetrahydropyrimidin-2-ones

Relationship between the topological indices and HIV-protease inhibitory activity of tetrahydropyrimidine-2-ones has been investigated. Three topological indices, Wiener's index--a distance based topological descriptor, Zagreb group parameter--an adjacency based topological descriptor and eccentric connectivity index--an adjacency-cum-distance based topological descriptor were used for the present investigations. A dataset comprising of 80 substituted tetrahydropyrimidine-2-one analogues was selected for the present studies. The values of the Wiener's index, Zagreb group parameter and eccentric connectivity index for each of the 80 compounds comprising the dataset were computed using an in-house computer program. The dataset was divided randomly into training and test sets. Resultant data was analyzed and suitable models were developed after identifying the active ranges in the training set. Subsequently, a biological activity was assigned to each of the compound involved in the test set using these models, which was then compared with the reported HIV-protease inhibitory activity. Accuracy of prediction using these models was found to vary from a minimum of approximately 86% to a maximum of approximately 88%.

Anti-HIV-1 activities in extracts from some medicinal plants as assessed in anin vitro biochemical HIV-1 reverse transcriptase assay

An in vitro HIV-1 reverse transcriptase (RT) assay was used for screening of anti-HIV activity of extracts obtained from some Kenyan medicinal plants. The assay utilises [3H]-methyl thymidine triphosphate (dTTP) as the enzyme substrate and polyadenylic acid.oligodeoxythymidylic acid [poly(rA).p(dT)(12-18)] as the template-primer dimmer. This assay was optimised and standardised with respect to the various experimental parameters in a microtiter plate methodology. The assay was then applied to test for potential antiviral activities of several Kenyan medicinal plant extracts and the concentrations producing 50% inhibition (IC50) of the HIV-1 RT were determined. This assay is described in this report and results obtained with some of the extracts are presented.

Therapy of HIV infection

HIV is a devastating disease caused by the human immunodeficiency virus. Symptoms of illness can manifest in every organ system, including the skin. Although there is no definitive cure, the creation of antiretroviral drugs and aggressive treatment regimens have dramatically altered disease morbidity and mortality. However, the precise drug selection is often difficult and intimidating given the sheer abundance of drug therapies available. In this article, the HIV disease course is reviewed and different classes of antiretroviral medications are presented with emphasis on initial drug regimens, potential adverse effects, particularly those of dermatologic nature, possible drug interactions, patient compliance, and the emergence of drug resistance.

Structural and thermodynamic basis for the binding of TMC114, a next-generation human immunodeficiency virus type 1 protease inhibitor

TMC114, a newly designed human immunodeficiency virus type 1 (HIV-1) protease inhibitor, is extremely potent against both wild-type (wt) and multidrug-resistant (MDR) viruses in vitro as well as in vivo. Although chemically similar to amprenavir (APV), the potency of TMC114 is substantially greater. To examine the basis for this potency, we solved crystal structures of TMC114 complexed with wt HIV-1 protease and TMC114 and APV complexed with an MDR (L63P, V82T, and I84V) protease variant. In addition, we determined the corresponding binding thermodynamics by isothermal titration calorimetry. TMC114 binds approximately 2 orders of magnitude more tightly to the wt enzyme (K(d) = 4.5 x 10(-12) M) than APV (K(d) = 3.9 x 10(-10) M). Our X-ray data (resolution ranging from 2.2 to 1.2 A) reveal strong interactions between the bis-tetrahydrofuranyl urethane moiety of TMC114 and main-chain atoms of D29 and D30. These interactions appear largely responsible for TMC114's very favorable binding enthalpy to the wt protease (-12.1 kcal/mol). However, TMC114 binding to the MDR HIV-1 protease is reduced by a factor of 13.3, whereas the APV binding constant is reduced only by a factor of 5.1. However, even with the reduction in binding affinity to the MDR HIV protease, TMC114 still binds with an affinity that is more than 1.5 orders of magnitude tighter than the first-generation inhibitors. Both APV and TMC114 fit predominantly within the substrate envelope, a property that may be associated with decreased susceptibility to drug-resistant mutations relative to that of first-generation inhibitors. Overall, TMC114's potency against MDR viruses is likely a combination of its extremely high affinity and close fit within the substrate envelope.

Structural basis for coevolution of a human immunodeficiency virus type 1 nucleocapsid-p1 cleavage site with a V82A drug-resistant mutation in viral protease

Maturation of human immunodeficiency virus (HIV) depends on the processing of Gag and Pol polyproteins by the viral protease, making this enzyme a prime target for anti-HIV therapy. Among the protease substrates, the nucleocapsid-p1 (NC-p1) sequence is the least homologous, and its cleavage is the rate-determining step in viral maturation. In the other substrates of HIV-1 protease, P1 is usually either a hydrophobic or an aromatic residue, and P2 is usually a branched residue. NC-p1, however, contains Asn at P1 and Ala at P2. In response to the V82A drug-resistant protease mutation, the P2 alanine of NC-p1 mutates to valine (AP2V). To provide a structural rationale for HIV-1 protease binding to the NC-p1 cleavage site, we solved the crystal structures of inactive (D25N) WT and V82A HIV-1 proteases in complex with their respective WT and AP2V mutant NC-p1 substrates. Overall, the WT NC-p1 peptide binds HIV-1 protease less optimally than the AP2V mutant, as indicated by the presence of fewer hydrogen bonds and fewer van der Waals contacts. AlaP2 does not fill the P2 pocket completely; PheP1' makes van der Waals interactions with Val82 that are lost with the V82A protease mutation. This loss is compensated by the AP2V mutation, which reorients the peptide to a conformation more similar to that observed in other substrate-protease complexes. Thus, the mutant substrate not only binds the mutant protease more optimally but also reveals the interdependency between the P1' and P2 substrate sites. This structural interdependency results from coevolution of the substrate with the viral protease.

Persistence of mutations during replication of an HIV library containing combinations of selected protease mutations

It has been known that, in some cases, accumulation of specific mutations in HIV-1 protease leads to multi-protease inhibitor (PI) resistance. We examined the persistence of mutations detected in HIV-1 clinical isolates cross-resistant to the current PIs using an HIV-1 protease restricted library (HXB2 protease in an HIV-1(NL4-3) background) in the absence of protease inhibitors. The virus library contained combinations of 0-11 amino acid substitutions (4,096 possible combinations) in the protease-encoding region. We examined the frequency of each amino acid substitution in the library using a T cell line, MT-2. The frequency of the amino acid substitutions V82T/I and L90M decreased rapidly with a short half life (t(1/2) < 10 days). However, the mutations M36I, M46I and I84V were relatively persistent: t(1/2) = 34.2, 28.1 and 30.6 days, respectively. Other amino acid substitutions, i.e., L10I, I54V, L63P, A71V and V82A, were well retained (t(1/2) > 36 days). By contrast, the half lives (t(1/2)) of the D30N and N88D mutations associated with nelfinavir (NFV) resistance were only 7.2 and 1.8 days, respectively. These results indicate that this type of the HIV-1 protease restricted library is useful to evaluate the persistence of PI resistance-associated mutations in the absence of drug selective pressure.

Gag non-cleavage site mutations contribute to full recovery of viral fitness in protease inhibitor-resistant human immunodeficiency virus type 1

It is well documented that human immunodeficiency virus type 1 (HIV-1) Gag cleavage site mutations (CSMs) emerge in conjunction with various HIV-1 mutations for protease inhibitor (PI) resistance and improve viral replication capacity, which is reduced by acquisition of the resistance. However, CSMs are not the only mutations that emerge in Gag during treatment; many mutations other than CSMs (non-CSMs) have been found to accumulate in the Gag region. In the present study we demonstrate the important role of Gag non-CSMs with regard to viral fitness recovery. We selected three Gag-protease sequences with different PI resistance-associated mutations and CSMs from patients with antiretroviral treatment failure. To clarify the significance of CSMs and non-CSMs, four types of recombinant viruses with different patterns in each sequence were constructed. These were the GP type (patient-derived Gag and protease), the P type (HXB2 Gag and patient-derived protease), the GP(-c) type (CSMs removed from the GP type), and the P(+c) type (CSMs in the HXB2 Gag frame and patient-derived protease). By comparison of these four types of recombinant viruses in each patient-derived Gag-protease sequence, we found that non-CSMs, which had no systematic pattern, make a significant contribution to viral fitness recovery. Our findings demonstrate a delicate interaction between the in vivo evolution of Gag and protease to evade drug selective pressure and the importance of Gag in evaluating drug-resistant viruses.

Discovery of novel benzothiazolesulfonamides as potent inhibitors of HIV-1 protease

The human immunodeficiency virus (HIV) has been shown to be the causative agent for AIDS. The HIV virus encodes for a unique aspartyl protease that is essential for the production of enzymes and proteins in the final stages of maturation. Protease inhibitors have been useful in combating the disease. The inhibitors incorporate a variety of isosteres including the hydroxyethylurea at the protease cleavage site. We have shown that the replacement of t-butylurea moiety by benzothiazolesulfonamide provided inhibitors with improved potency and antiviral activities. Some of the compounds have shown good oral bioavailability and half-life in rats. The synthesis of benzothiazole derivatives led us to explore other heterocycles. During the course of our studies, we also developed an efficient synthesis of benzothiazole-6-sulfonic acid via a two-step procedure starting from sulfanilamide.

Dimerization Inhibitors of HIV-1 Protease Based on a Bicyclic Guanidinium Subunit

Original inhibitors of HIV-1 protease based on a chiral bicyclic guanidinium scaffold linked to short peptidic mimics of the terminal protease sequences and to a lipophilic group were designed. These inhibitors prevent dimerization of the native protease by an interfacial structure at the highly conserved antiparallel beta-strand involving both the N and C termini that substantially account for dimerization. The preorganized guanidinium spacer introduces additional electrostatic hydrogen-bonding interactions with the C-terminal Phe-99 carboxylate. Lipophilic residues linked to side chains and the guanidinium scaffold are essential for dimerization inhibition as ascertained by Zhang kinetics (4, K(id) = 290 nM; 6 or 6', K(id) = 150 nM; 8, K(id) = 400 nM) combined with a circular dichroism study on the enzyme thermal stability. Remarkably, less hydrophobic compounds result in mixed dimerization (1a and 3) or active site inhibitors (5). Removal of the guanidinium hydrophobic groups leads to less active or inactive ligands.

Lopinavir/ritonavir: a review of its use in the management of HIV infection

Lopinavir is a novel protease inhibitor (PI) developed from ritonavir. Coadministration with low-dose ritonavir significantly improves the pharmacokinetic properties and hence the activity of lopinavir against HIV-1 protease. Coformulated lopinavir/ritonavir was developed for ease of administration and to ensure both drugs are taken together, as part of combination therapy with other antiretroviral agents. Coformulated lopinavir/ritonavir-based regimens provide adequate and durable suppression of viral load and sustained improvements in CD4+ cell counts, as demonstrated in randomised trials in antiretroviral therapy-naive and -experienced adults and children. To date, development of primary resistance to lopinavir/ritonavir has not been observed in 470 antiretroviral therapy-naive patients treated for >48 weeks. The lopinavir/ritonavir-based regimen was more effective than nelfinavir in antiretroviral therapy-naive HIV-1-infected patients in a phase III trial. The coformulation is also effective as 'salvage' therapy, as shown by low cross-resistance rates in patients who failed to respond to treatment with other PIs in phase II trials. Coformulated lopinavir/ritonavir was well tolerated in both antiretroviral therapy-naive and -experienced HIV-1-infected adults and children with low rates of study drug-related treatment discontinuations. The most common adverse event in adults associated with lopinavir/ritonavir was diarrhoea, followed by other gastrointestinal disturbances, asthenia, headache and skin rash. The incidence of moderate-to-severe adverse events in children was low, skin rash being the most common. Changes in body fat composition occurred with equal frequency in lopinavir/ritonavir- and nelfinavir-treated naive patients, through week 60 in a phase III study. Although laboratory abnormalities occurred with similar frequency in both treatment groups, triglycerides grade 3/4 elevations were significantly more frequent with lopinavir/ritonavir. Total cholesterol and triglycerides grade 3/4 elevations appear to occur more frequently in PI-experienced than in PI-naive lopinavir/ritonavir-treated patients. A number of clinically important drug interactions have been reported with lopinavir/ritonavir necessitating dosage adjustments of lopinavir/ritonavir and/or the interacting drugs, and several other drugs are contraindicated in patients receiving the coformulation.

CONCLUSION

Coformulated lopinavir/ritonavir is a novel PI that, in combination with other antiretroviral agents, suppresses plasma viral load and enhances immunological status in therapy-naive and -experienced patients with HIV-1 infection. Lopinavir/ritonavir appears more effective than nelfinavir in 'naive' patients and is also suitable for 'salvage' therapy, because of its high barrier to development of resistance. Given its clinical efficacy, a tolerability profile in keeping with this class of drugs, favourable resistance profile and easy-to-adhere-to administration regimen, coformulated lopinavir/ritonavir should be regarded as a first-line option when including a PI in the management of HIV-1 infection.

OVERVIEW OF PHARMACODYNAMIC PROPERTIES

Lopinavir/ritonavir is a coformulation of two structurally related protease inhibitor (PI) antiretroviral agents. Lopinavir is a highly potent and selective inhibitor of the HIV type 1 (HIV-1) protease, an essential enzyme for production of mature, infective virus. It acts by arresting maturation of HIV-1 thereby blocking its infectivity. Thus, the main antiviral action of lopinavir is to prevent subsequent infections of susceptible cells; it has no effect on cells with already integrated viral DNA. Lopinavir has an approximate, equals 10-fold higher in vitro activity against both wild-type and mutant HIV-1 proteases than ritonavir; however, its in vivo activity is greatly attenuated by a high first-pass hepatic metabolism. The low-dose ritonavir coadministered with lopinavir inhibits metabolic inactivation of lopinavir and acts only as its pharmacokinetic enhancer. Therefore, the antiretroviral activity of roviral activity of coformulated lopinavir/ritonavir 400/100mg twice daily is derived solely from lopinavir plasma concentrations. Combining lopinavir with low-dose ritonavir produces lopinavir concentrations far exceeding those needed to suppress 50% of in vitro and in vivo viral replication in CD4+ cells and monocyte/macrophages (main human reservoirs of HIV-1 infection). Thus far, no resistance to lopinavir has been detected in clinical trials in antiretroviral therapy-naive patients treated for up to 204 weeks and only 12% of HIV-1 strains from patients in whom prior treatment with multiple PIs have failed, have been observed to develop resistance to coformulated lopinavir/ritonavir. A strong negative correlation was found between the number of PI mutations at baseline and the viral response rates achieved with lopinavir/ritonavir-based regimens in PI-experienced patients, indicating that resistance to lopinavir increases with increasing number of PI mutations and that five PI mutations represent the clinically relevant genotypic breakpoint for lopinavir.

OVERVIEW OF PHARMACOKINETIC PROPERTIES

The absolute bioavailability of lopinavir coformulated with ritonavir in humans has not yet been established. Multiple-dosage absorption pharmacokinetics of lopinavir/ritonavir 400/100mg twice daily (the mean peak [C(max)] and trough [C(trough)] plasma concentrations at steady-state and the 12-hour area under the plasma concentration-time curve [AUC(12)] of either drug) were stable in antiretroviral therapy-naive and single PI-experienced adult patients receiving therapy over a 24-week evaluation period. The C(trough) values of lopinavir, achieved with lopinavir/ritonavir 400/100mg twice daily, were median 84-fold higher than the protein binding-adjusted 50% effective concentration (EC(50)) of lopinavir against wild-type HIV-1 in antiretroviral therapy-naive HIV-1-infected patients in a phase II study. Bioavailability of lopinavir administered in either the capsule or the liquid lopinavir/ritonavir formulation can be increased substantially with concurrent ingestion of food with moderate-to-high fat content. At steady state, lopinavir is approximately 98-99% plasma protein bound and the percentage of its unbound (i.e. pharmacologically active) fraction is dependent on total drug plasma concentration. Both lopinavir and ritonavir penetrate poorly into the human genital tracts and the cerebrospinal fluid. Both agents undergo extensive and rapid first-pass metabolism by hepatic cytochrome P450 (CYP) 3A4 isoenzyme. However, ritonavir also potently inhibits this enzyme and acts as a pharmacokinetic enhancer of lopinavir. The elimination half-life and apparent oral clearance of lopinavir average approximately 4-6 hours and approximately 6-7 L/h, respectively, with lopinavir/ritonavir 400/100mg twice daily administration. Less than 3% and 20% of the lopinavir dose is excreted unchanged in the urine and faeces, respectively. Limited data show similar pharmacokinetics of lopinavir in children as in adults.

DRUG INTERACTIONS

Coformulated lopinavir/ritonavir has the potential to interact with wide variety of drugs via several mechanisms, mostly involving the CYP enzymes. Coadministration of lopinavir/ritonavir is contraindicated with certain drugs (i.e. flecainide, propafenone, astemizole, terfenadine, ergot derivatives, cisapride, pimozide, midazolam and triazolam) that are highly dependent on CYP3A or CYP2D6 for clearance and for which elevated plasma concentrations are associated with serious and/or life-threatening events. Coadministration with lopinavir/ritonavir is also not recommended for drugs or herbal products (i.e. rifampicin [rifampin] and St. John's wort [Hypericum perforatum]) that may substantially reduce lopinavir plasma concentrations, or drugs whose plasma concentrations elevated by the coformulation may lead to serious adverse reactions (i.e. simvastatin and lovastatin). However, a recent study in healthy volunteers suggests that adequate lopinavir concentrations may be achieved during rifampicin coadministration by increasing the twice-daily dosage of lopinavir/ritonavir in conjunction with therapeutic drug monitoring. The liquid (but not the capsule) formulation of lopinavir/ritonavir contains 42.4% ethanol (v/v) and should not be coadministered with drugs capable of producing disulfiram-like reactions (e.g. disulfiram, metronidazole). Coadministration with saquinavir or indinavir requires no dosage adjustment, whereas coadministration with amprenavir, nevirapine or efavirenz requires a dosage increase of the coformulation typically by 33%. As the oral bioavailability of both didanosine and lopinavir/ritonavir is significantly affected by concurrent food ingestion, didanosine should be administered 1 hour before or 2 hours after lopinavir/ritonavir has been taken with food. Interactions between lopinavir/ritonavir and other nucleoside reverse transcriptase inhibitors (NRTIs) are not expected. The coformulation is also likely to increase plasma concentrations of non-antiretroviral drugs metabolised through the CYP3A pathway. To reduce the risk of their toxicity when coadministered with lopinavir/ritonavir, the recommended actions include: (i) monitoring of the drug plasma concentration (antiarrhythmics and immunosuppressants) or the international normalised ratio (warfarin); (ii) the use of alternative treatment (atorvastatin) or birth control methods (ethinylestradiol); and (iii) dosage adjustment (clarithromycin [only in patients with renal failure], rifabutin, dihydropyridine calcium-channel blockers, atorvastatin, ketoconazole and itraconazole). (ABSTRACT TRUNCATED)

Indinavir reduces Cryptosporidium parvum infection in both in vitro and in vivo models

The use of highly active antiretroviral therapy in persons with acquired immunodeficiency syndrome has reduced the prevalence of infection with Cryptosporidium parvum and the length and severity of its clinical course. This effect has in most cases been attributed to the recovery of the host immunity; however, some works suggest that human immunodeficiency virus protease inhibitors, indinavir in particular, which is one of the human immunodeficiency virus protease inhibitors used in highly active antiretroviral therapy, may be capable of controlling Microsporidia and Cryptosporidium infections, which are refractory to other treatments. The objective of the present study was to investigate the effect of human immunodeficiency virus protease inhibitors on C. parvum infections. Since preliminary experiments using ritonavir, saquinavir, and indinavir showed a drastic reduction of C. parvum infection both in vivo (neonatal Balb/c mice) and in vitro (human ileocecal adenocarcinoma tumour cell line) models, indinavir alone was tested in successive experiments. In vitro, the treatment of the sporulated oocysts with different concentrations of indinavir reduced the percentage of human ileocecal adenocarcinoma tumour cell line infected cells in a dose-dependent manner. For established infection, the treatment with 50 microM of indinavir decreased the percentage of infected cells in a time-dependent manner. In vivo, mice treated with indinavir at the same time they were infected with the oocysts showed a 93% reduction in the number of oocysts present in the entire intestinal contents and a 91% reduction in the number of intracellular parasites in the ileum. For established infection, indinavir treatment reduced the number of oocysts in the entire intestinal content by about 50% and the number of intracellular parasites in the ileum by about 70%. These data show that indinavir directly interferes with the cycle of C. parvum, resulting in a marked reduction in oocyst shedding and in the number of intracellular parasites. Protease inhibitors could be considered as good candidates for the treatment of cyptosporidiosis in immunosuppressed persons.

Synthesis of a novel cis-proline-derived cyclic type VI beta-turn mimic via ring-closing metathesis

A cis-proline derived cyclic mimic of a type VI beta-turn is synthesized via a ring-closing metathesis reaction. The solution NMR conformational study indicates that the major conformer of the cyclic peptide adopts a type VIa beta-turn in CDCl(3) and a type VIb beta-turn in DMSO-d(6).

Antiretroviral pharmacokinetics in the paediatric population: a review

Characteristics unique to paediatric pharmacotherapy should be considered when treating children infected with human immunodeficiency virus (HIV). Processes of growth and development in the paediatric patient can significantly affect drug absorption and disposition. Immature renal function, altered hepatic enzyme activity and differences in drug absorption lead to variations in systemic exposure of antiretrovirals among children. Paediatric patients are also subject to unique circumstances that may prevent adherence to antiretroviral regimens. The pharmacokinetics of nucleoside reverse transcriptase inhibitors differ significantly among preterm infants, full-term infants and older children. Decreased hepatic glucuronidation activity in neonates results in pharmacokinetic differences in zidovudine disposition when compared with older children. Didanosine, stavudine and lamivudine are renally eliminated, thus resulting in differences among young children with immature renal function. Pharmacokinetic data for non-nucleoside reverse transcriptase inhibitors in children are limited. Decreased elimination of nevirapine among neonates has been observed, primarily due to decreased enzymatic activity. Pharmacokinetic differences across age groups have been noted for efavirenz, but no formal assessments have been conducted in children weighing less than 10kg. Protease inhibitors are metabolised by the cytochrome P450 enzyme system, which is not fully developed in younger children. Decreased metabolism can result in elevated plasma concentrations, thereby increasing the chance of toxicity. Unfortunately, few studies exist evaluating the pharmacokinetics of antiretrovirals in children. As a result, dosage selection of antiretrovirals in children often occurs without adequate data. As the life expectancy of HIV-infected children increases, use of antiretrovirals to prevent disease progression also increases. If prevention of treatment failure continues to be the goal of antiretroviral therapy, the pharmacokinetics of antiretrovirals in children need to be assessed early in the drug development process.

Advance in treatment strategy and immune reconstruction against HIV-1 infection

HIV-1 can be considered an infection of the immune system, resulting in progressive and ultimately profound immune suppression. The availability of highly active antiretroviral therapy (HAART) has resulted in dramatic changes in the disease course in persons fortunate enough to have access to these medications, but long-term therapy is limited by the development of resistance as well as toxicities of the potent medication regimens. Emerging data indicate that individuals who have non-progressive clinical course control HIV-1 immunologically. This has bolstered hope that the immune response might be effectively augmented in persons with HIV infection. Recent data indicating that immediate treatment of acute infection leads to augmentation of antiviral immune responses have provided evidence that the immune system might be enhanced in certain situations. Therefore, investigation in the reconstitution of anti-HIV immune response in patients under HAART should provide encouragement for continuing to explore methods to obtain meaningful and durable immune enhancement as an adjunct to HAART in HIV-1 infection.