ABT-378, a highly potent inhibitor of the human immunodeficiency virus protease

Ritonavir-boosted protease inhibitors in HIV therapy

The advent of combination antiretroviral therapy has led to significant improvement in the care of HIV-infected patients. Originally designed as a protease inhibitor (PI), ritonavir is currently exclusively used as a pharmacokinetic enhancer of other protease inhibitors, predominantly due to ritonavir's potent inhibition of the cytochrome P450 3A4 isoenzyme. Ritonavir-boosting of PIs decrease pill burden and frequency of dosing. Boosted PIs are recommended for first-line therapy in treatment and play a key role in the management of treatment-experienced patients. Potential problems associated with PIs include metabolic abnormalities (e.g. dyslipidemia), increased cardiovascular risk, and drug interactions.

Clinical outcomes and management of mechanism-based inhibition of cytochrome P450 3A4

Mechanism-based inhibition of cytochrome P450 (CYP) 3A4 is characterized by NADPH-, time-, and concentration-dependent enzyme inactivation, occurring when some drugs are converted by CYPs to reactive metabolites. Such inhibition of CYP3A4 can be due to the chemical modification of the heme, the protein, or both as a result of covalent binding of modified heme to the protein. The inactivation of CYP3A4 by drugs has important clinical significance as it metabolizes approximately 60% of therapeutic drugs, and its inhibition frequently causes unfavorable drug–drug interactions and toxicity. The clinical outcomes due to CYP3A4 inactivation depend on many factors associated with the enzyme, drugs, and patients. Clinical professionals should adopt proper approaches when using drugs that are mechanism-based CYP3A4 inhibitors. These include early identification of drugs behaving as CYP3A4 inactivators, rational use of such drugs (eg, safe drug combination regimen, dose adjustment, or discontinuation of therapy when toxic drug interactions occur), therapeutic drug monitoring, and predicting the risks for potential drug–drug interactions. A good understanding of CYP3A4 inactivation and proper clinical management are needed by clinical professionals when these drugs are used.

Tetrahydrofuran, tetrahydropyran, triazoles and related heterocyclic derivatives as HIV protease inhibitors

HIV/AIDS remains a formidable disease with millions of individuals inflicted worldwide. Although treatment regimens have improved considerably, drug resistance brought on by viral mutation continues to erode their effectiveness. Intense research efforts are currently underway in search of new and improved therapies. This review is concerned with the design of novel HIV-1 protease inhibitors that incorporate heterocyclic scaffolds and which have been reported within the recent literature (2005-2010). Various examples in this review showcase the essential role heterocycles play as scaffolds and bioisosteres in HIV-1 protease inhibitor drug development. This review will hopefully stimulate the widespread application of these heterocycles in the design of other therapeutic agents.

Looking at the proteases from a simple perspective

Proteases have received enormous interest from the research and medical communities because of their significant roles in several human diseases. Some examples include the involvement of thrombin in thrombosis, HIV-1 protease in Acquired Immune Deficiency Syndrome, cruzain in Trypanosoma cruzi infection, and membrane-type 1 matrix metalloproteinase in tumor invasion and metastasis. Many efforts has been undertaken to design effective inhibitors featuring potent inhibitory activity, specificity, and metabolic stability to those proteases involved in such pathologies. Protease inhibitors usually target the active site, but some of them act by other inhibitory mechanisms. The understanding of the structure-function relationships of proteases and inhibitors has an impact on new inhibitor drugs designing. In this paper, the structures of four proteases (thrombin, HIV-protease, cruzain, and a matrix metalloproteinase) are briefly reviewed, and used as examples of the importance of proteases for the development of new treatment strategies, leading to a longer and healthier life.

The progress made in determining the Mycobacterium tuberculosis structural proteome

Mycobacterium tuberculosis is a highly infectious pathogen that is still responsible for millions of deaths annually. Effectively treating this disease typically requires a course of antibiotics, most of which were developed decades ago. These drugs are, however, not effective against persistent tubercle bacilli and the emergence of drug-resistant stains threatens to make many of them obsolete. The identification of new drug targets, allowing the development of new potential drugs, is therefore imperative. Both proteomics and structural biology have important roles to play in this process, the former as a means of identifying promising drug targets and the latter allowing understanding of protein function and protein–drug interactions at atomic resolution. The determination of M. tuberculosis protein structures has been a goal of the scientific community for the last decade, who have aimed to supply a large amount of structural data that can be used in structure-based approaches for drug discovery and design. Only since the genome sequence of M. tuberculosis has been available has the determination of large numbers of tuberculosis protein structures been possible. Currently, the molecular structures of 8.5% of all the pathogen's protein-encoding ORFs have been determined. In this review, we look at the progress made in determining the M. tuberculosis structural proteome and the impact this has had on the development of potential new drugs, as well as the discovery of the function of crucial mycobaterial proteins.

Antiretroviral therapy outcomes in HIV-infected children after adjusting protease inhibitor dosing during tuberculosis treatment

BACKGROUND

Modification of ritonavir-boosted lopinavir (LPV/r)-based antiretroviral therapy is required for HIV-infected children co-treated for tuberculosis (TB). We aimed to determine virologic and toxicity outcomes among TB/HIV co-treated children with the following modifications to their antiretroviral therapy (ART): (1) super-boosted LPV/r, (2) double-dose LPV/r or (3) ritonavir.

METHODS AND FINDINGS

A medical record review was conducted at two clinical sites in Johannesburg, South Africa. The records of children 6-24 months of age initiating LPV/r-based therapy were reviewed. Children co-treated for TB were categorized based on the modifications made to their ART regimen and were compared to children of the same age at each site not treated for TB. Included are 526 children, 294 (56%) co-treated for TB. All co-treated children had more severe HIV disease, including lower CD4 percents and worse growth indicators, than comparisons. Children in the super-boosted group (n = 156) were as likely to be virally suppressed (<400 copies/ml) at 6 months as comparisons (69.2% vs. 74.8%, p = 0.36). Children in the double-dose (n = 47) and ritonavir groups (n = 91) were significantly less likely to be virally suppressed at 6 months (53.1% and 49.3%) than comparisons (74.8% and 82.1%; p = 0.02 and p<0.0001, respectively). At 12 months only children in the ritonavir group still had lower rates of virological suppression relative to comparisons (63.9% vs 83.3% p<0.05). Grade 1 or greater ALT elevations were more common in the super-boosted (75%) than double-dose (54.6%) or ritonavir (33.9%) groups (p = 0.09 and p<0.0001) but grade 3/4 elevations were observed in 3 (13.6%) of the super-boosted, 7 (15.9%) of the double-dose and 5 (8.9%) of the ritonavir group (p = 0.81 and p = 0.29).

CONCLUSION

Good short-term virologic outcomes were achieved in children co-treated for TB and HIV who received super-boosted LPV/r. Treatment limiting toxicity was rare. Strategies for increased dosing of LPV/r with TB treatment warrant further investigation.

Enhanced delivery of lopinavir to the CNS using Compritol®-based solid lipid nanoparticles

Background: Protease inhibitors such as lopinavir have negligible permeability to the CNS due to blood–brain and blood–cerebrospinal fluid interfaces. An attempt has been made to develop solid lipid nanoparticles to increase the availability of lopinavir in the CNS. Results/Discussion: Solid lipid nanoparticle formulations exhibited a Cmax and Tmax of 632.86 ± 81.61 ng/ml and 25 ± 7.75 min, respectively, with a significant increase in bioavailability in a rat model compared with a free-drug suspension. An appreciable increase in cerebrospinal fluid concentration was detected with solid lipid nanoparticle formulations. Conclusion: Compritol®-based solid lipid nanoparticles with a poloxamer coating can be effectively absorbed through the lymphatic system, prolong the circulation of drug in blood by acting as a reservoir and can effectively target the drug to the CNS due to the combined effect of lipophilicity and surface charge. The high biocompatibility, biodegradability and nontoxicity of compritol make the compritol-based solid lipid nanoparticles an excellent carrier for enhanced CNS delivery of lopinavir.

An integrated pharmacokinetic model for the influence of CYP3A4 expression on the in vivo disposition of lopinavir and its modulation by ritonavir

Lopinavir, a human immunodeficiency virus protease inhibitor, has a very low oral bioavailability, which can be enhanced with a low dose of the CYPA4 inhibitor ritonavir. Our aim was to separately quantify the role of intestinal and hepatic cytochrome P450 3A (CYP3A4) expression on lopinavir disposition in a novel mouse model. Lopinavir and ritonavir were administered to mice selectively expressing human CYP3A4 in the intestine and/or liver. Using nonlinear mixed-effects modeling, we could separately quantify the effects of intestinal CYP3A4 expression, hepatic CYP3A4 expression, and the presence of ritonavir on both the absorption and elimination of lopinavir, which was previously not possible using noncompartmental methods. Intestinal, but not hepatic, CYP3A4-related first-pass metabolism was the major barrier for systemic entry of lopinavir. Relative oral bioavailability of lopinavir in mice expressing both hepatic and intestinal CYP3A4 was only 1.3% when compared with mice that were CYP3A deficient. In presence of ritonavir, relative bioavailability increased to 9.5% due to inhibiton of intestinal, but not due to inhibition of hepatic first-pass metabolism. Hepatic CYP3A4 related systemic clearance was inversely related to ritonavir exposure and not only hepatic but also intestinal CYP3A4 expression contributed to systemic clearance of lopinavir.

Lopinavir/Ritonavir: a review of its use in the management of HIV-1 infection

Lopinavir/ritonavir (Kaletra®) is an orally administered coformulated ritonavir-boosted protease inhibitor (PI) comprising lopinavir and low-dose ritonavir. It is indicated, in combination with other antiretroviral agents, for the treatment of HIV-1 infection in adults, adolescents and children. Lopinavir/ritonavir is available as a tablet, soft-gel capsule and an oral solution for patients with difficulty swallowing. In well designed, randomized clinical trials, lopinavir/ritonavir, in combination with other antiretroviral therapies (ART), provided durable virological suppression and improved immunological outcomes in both ART-naive and -experienced adult patients with virological failure. Furthermore, lopinavir/ritonavir demonstrated a high barrier to the development of resistance in ART-naive patients. More limited data indicate that it is effective in reducing plasma HIV-1 RNA levels in paediatric patients. Lopinavir/ritonavir has served as a well established benchmark comparator for the noninferiority of other ritonavir-boosted PI regimens. Although generally well tolerated, lopinavir/ritonavir is associated with generally manageable adverse gastrointestinal side effects and hypertriglyceridaemia and hypercholesterolaemia, which may require coadministration of lipid-lowering agents to reduce the risk of coronary heart disease. Lopinavir/ritonavir, in combination with other ART agents, is a well established and cost-effective treatment for both ART-naive and -experienced patients with HIV-1 infection and, with successful management of adverse events, continues to have a role as an effective component of ART regimens for the control of HIV-1 infection.

Drug-drug interactions in the treatment of HIV infection: focus on pharmacokinetic enhancement through CYP3A inhibition

The aim of this review is to discuss the effect of pharmacokinetic drug-drug interactions (DDIs) in the antiretroviral treatment of HIV infection. In particular, but not exclusively, DDIs due to the cytochrome P450 3A (CYP3A) inhibitor ritonavir, which is used to increase antiretroviral drug exposure - a technique known as pharmacokinetic enhancement or 'ritonavir boosting'- will be reviewed. The emphasis here will be on the treatment of important co-morbidities common in patients with HIV, including dyslipidaemia, hypertension, tuberculosis and opiate dependence, as well as on the potentially life-threatening interaction between ritonavir and inhalational steroids, and on the effect of acid-reducing agents on some antiretroviral drugs. Finally, further developments with regard to the use of CYP3A-blocking agents to augment the efficacy of antiviral therapy will be discussed.

Computational mutation scanning and drug resistance mechanisms of HIV-1 protease inhibitors

The drug resistance of various clinically available HIV-1 protease inhibitors has been studied using a new computational protocol, that is, computational mutation scanning (CMS), leading to valuable insights into the resistance mechanisms and structure-resistance correction of the HIV-1 protease inhibitors associated with a variety of active site and nonactive site mutations. By using the CMS method, the calculated mutation-caused shifts of the binding free energies linearly correlate very well with those derived from the corresponding experimental data, suggesting that the CMS protocol may be used as a generalized approach to predict drug resistance associated with amino acid mutations. Because it is essentially important for understanding the structure-resistance correlation and for structure-based drug design to develop an effective computational protocol for drug resistance prediction, the reasonable and computationally efficient CMS protocol for drug resistance prediction should be valuable for future structure-based design and discovery of antiresistance drugs in various therapeutic areas.

Molecular Basis for Drug Resistance in HIV-1 Protease

HIV-1 protease is one of the major antiviral targets in the treatment of patients infected with HIV-1. The nine FDA approved HIV-1 protease inhibitors were developed with extensive use of structure-based drug design, thus the atomic details of how the inhibitors bind are well characterized. From this structural understanding the molecular basis for drug resistance in HIV-1 protease can be elucidated. Selected mutations in response to therapy and diversity between clades in HIV-1 protease have altered the shape of the active site, potentially altered the dynamics and even altered the sequence of the cleavage sites in the Gag polyprotein. All of these interdependent changes act in synergy to confer drug resistance while simultaneously maintaining the fitness of the virus. New strategies, such as incorporation of the substrate envelope constraint to design robust inhibitors that incorporate details of HIV-1 protease’s function and decrease the probability of drug resistance, are necessary to continue to effectively target this key protein in HIV-1 life cycle.

Amino acid derivatives, part 4: synthesis and anti-HIV activity of new naphthalene derivatives

A new series of 2-(naphthalen-2-yloxy)-N-[(aryl-5-thioxo-4,5-dihydro-1H-1,2,4-triazol-3-yl)methyl] acetamides 5a-f was synthesized from naphthalene-derived glycine derivative 2 via the hydrazinoacetamide analogs 4a-f. Alternatively, treatment of 4a with H(2)SO(4) afforded 2-(naphthalen-2-yloxy)-N-((5-(phenylamino)-1,3,4-thiadiazol-2-yl)methyl) acetamide 6a. Alkylation or sulphonylation of 5a afforded the S-alkylated derivatives 7 and 8, respectively. Interestingly, treatment of 3 with methoxide ion gave the triazine derivative 9. The synthesized compounds have been screened for their inhibitory activity against HIV-1 and HIV-2 in MT-4 cells. However, 7 was found to be the potent inhibitor in vitro for the replication of HIV-1 (EC(50 )= 0.20 microg/mL), suggesting a new lead in the development of an antiviral agent.

Inhibition of oral midazolam clearance by boosting doses of ritonavir, and by 4,4-dimethyl-benziso-(2H)-selenazine (ALT-2074), an experimental catalytic mimic of glutathione oxidase

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

* The viral protease inhibitor ritonavir is known to inhibit clearance of intravenous midazolam. * ALT-2074, a catalytic mimic of glutathione oxidase, inhibits human cytochrome P450 3A (CYP3A) isoforms in vitro.

WHAT THIS STUDY ADDS

* Short-term administration of low-dose ritonavir increases area under the plasma concentration curve following oral midazolam by a factor of 28. * Therefore ritonavir is an appropriate positive control inhibitor for clinical drug interaction studies involving CYP3A substrates. * Midazolam clearance is weakly inhibited by ALT-2074, consistent with its in vitro profile.

AIMS

We evaluated whether 'boosting' doses of ritonavir can serve as a positive control inhibitor for pharmacokinetic drug-drug interaction studies involving cytochrome P450 3A (CYP3A). The study also determined whether 4,4-dimethyl-benziso-(2H)-selenazine (ALT-2074), an investigational organoselenium compound that acts as a catalytic mimic of glutathione oxidase, inhibits CYP3A metabolism in vivo.

METHODS

Thirteen healthy volunteers received single 3-mg oral doses of midazolam on three occasions: in the control condition, during co-treatment with low-dose ritonavir (three oral doses of 100 mg over 24 h), and during co-treatment with ALT-2074 (three oral doses of 80 mg over 24 h).

RESULTS

Ritonavir increased mean (+/-SE) total area under the curve (AUC) for midazolam by a factor of 28.4 +/- 4.2 (P < 0.001), and reduced oral clearance to 4.2 +/- 0.5% of control (P < 0.001). In contrast, ALT-2074 increased midazolam AUC by 1.25 +/- 0.11 (P < 0.05), and reduced oral clearance to 88 +/- 8% of control.

CONCLUSIONS

Low-dose ritonavir produces extensive CYP3A inhibition exceeding that of ketoconazole (typically 10- to 15-fold midazolam AUC enhancement), and is a suitable positive control index inhibitor for drug-drug interaction studies. ALT-2074 inhibits CYP3A metabolism to a small degree that is of uncertain clinical importance.

In situ formation of nanoparticles upon dispersion of melt extrudate formulations in aqueous medium assessed by asymmetrical flow field-flow fractionation

In recent years melt extrudates (e.g. Meltrex) have proven to be a promising formulation tool for poorly water-soluble and poorly bioavailable drugs. During the hot-melt extrusion process solid dispersions are formed. For several of these formulations improved bioavailabilities have been reported; the mechanism behind, however is still not very well understood. The aim of this study was to investigate whether solid dispersions prepared by melt extrusion upon dispersion in aqueous medium form particles and/or supramolecular assemblies. The formulation investigated here contained the human immunodeficiency virus (HIV) protease inhibitors lopinavir and ritonavir, polyvinylpyrrolidone-vinyl acetate copolymer (Kollidon VA64), sorbitan monolaurate (Span((R)) 20) and hydrophilic fumed silica (Aerosil 200). The aqueous dispersions originating from both, API-containing and placebo formulation were investigated using photon correlation spectroscopy (PCS) and asymmetrical flow field-flow fractionation (AsFlFFF) with subsequent online multi-angle light-scattering (MALS) particle size analysis. The content of both APIs in the AsFlFFF-fractions was quantified using high performance liquid chromatography-mass spectrometry. PCS indicated sub-micron particles. AsFlFFF revealed the co-existence of up to three different types of colloidal to nanoparticulate assemblies in the aqueous dispersions. Even though a complete resolution of the composition of the sub-fractions could not be achieved, the following types could be clearly distinguished: The first fraction eluting from AsFlFFF, appears to be colloidal polymer. Only marginal amounts of the APIs were found associated with the polymer. Secondly, API-rich nanoparticles eluted. Thirdly, nanoparticulate assemblies assigned to sorbitan monolaurate and/or hydrophilic fumed silica were identified. A limited amount of drug was found associated with this fraction. Using AsFlFFF-MALS the size of particles in fractions could be determined. From this experience AsFlFFF is regarded as promising technique for investigation of particles/structures originating during dispersion of melt extrudates in aqueous medium in terms of size and type of nanoparticles and their API-content.

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.

HIV-1 protease inhibitors with a transition-state mimic comprising a tertiary alcohol: improved antiviral activity in cells

By a small modification in the core structure of the previously reported series of HIV-1 protease inhibitors that encompasses a tertiary alcohol as part of the transition-state mimicking scaffold, up to 56 times more potent compounds were obtained exhibiting EC(50) values down to 3 nM. Three of the inhibitors also displayed excellent activity against selected resistant isolates of HIV-1. The synthesis of 25 new and optically pure HIV-1 protease inhibitors is reported, along with methods for elongation of the inhibitor P1' side chain using microwave-accelerated, palladium-catalyzed cross-coupling reactions, the biological evaluation, and X-ray data obtained from one of the most potent analogues cocrystallized with both the wild type and the L63P, V82T, I84 V mutant of the HIV-1 protease.

Identification of a potential pharmacological sanctuary for HIV type 1 in a fraction of CD4(+) primary cells

We have identified a subset of HIV-susceptible CD4(+)CCR5(+) cells in human PBMCs that can efficiently exclude protease inhibitors (PI) due to high P-glycoprotein (P-gp) efflux activity. Phenotypically these cells are heterogeneous, include both T and non-T cells, and some display markers of memory cells. Cells with high P-gp represent 16-56% (median = 37.3) of all CD4(+)CCR5(+) cells in healthy donors, and are selectively depleted in HIV-1-infected individuals (4.1-33%, median = 10.1). A fraction of primary cells productively infected by HIV-1, in vitro, have high P-gp pump activity, demonstrating that infection does not inhibit P-gp function. In agreement with these data, HIV-susceptible cells expressing high levels of P-gp require higher levels of PI for complete inhibition of virus spread. We conclude that the PI concentrations achieved in plasma could be suboptimal for full inhibition of virus spread in high P-gp cells, indicating that they may represent a pharmacological sanctuary for HIV-1.

Current and Novel Inhibitors of HIV Protease

The design, development and clinical success of HIV protease inhibitors represent one of the most remarkable achievements of molecular medicine. This review describes all nine currently available FDA-approved protease inhibitors, discusses their pharmacokinetic properties, off-target activities, side-effects, and resistance profiles. The compounds in the various stages of clinical development are also introduced, as well as alternative approaches, aiming at other functional domains of HIV PR. The potential of these novel compounds to open new way to the rational drug design of human viruses is critically assessed.

How much ritonavir is needed to boost protease inhibitors? Systematic review of 17 dose-ranging pharmacokinetic trials

BACKGROUND

Ritonavir has been evaluated at boosting doses of 50–800 mg daily with seven protease inhibitors: amprenavir, atazanavir, darunavir, indinavir, lopinavir,saquinavir and tipranavir. Minimizing the boosting dose of ritonavir could improve tolerability and lower costs.

METHODS

A MEDLINE search identified 17 phamacokinetic trials using different ritonavir doses with protease inhibitors. The dose of ritonavir used was correlated with plasma levels of each boosted protease inhibitor. For the five pharmacokinetic trials of lopinavir/ritonavir, a meta-analysis was used to estimate the effects of lopinavir dose versus ritonavir dose on lopinavir pharmacokinetics.

RESULTS

Saquinavir, fosamprenavir and darunavir were boosted equally well by lower(50–100 mg) versus higher doses of ritonavir. Indinavir, tipranavir and lopinavir were boosted more by higher ritonavir doses. Data on atazanavir were inconclusive. The ritonavir dose-dependence of boosting effects did not correlate with their bioavailability or their effects on ritonavir plasma levels. Atazanavir and indinavir raised plasma ritonavir levels by 69–72%, whereas saquinavir had no effects on ritonavir. Darunavir,lopinavir, tipranavir and fosamprenavir all lowered ritonavir plasma levels. For the meta-analysis of lopinavir/ritonavir trials, the 200/150 mg twice daily (b.i.d.) dose of lopinavir/ritonavir (one Meltrex 200/50mg tablet and one ritonavir 100mg b.i.d.)showed lopinavir area under the curve and minimum concentration similar to the standard 400/100mg b.i.d. dose.

CONCLUSION

It may be possible to use three protease inhibitors (saquinavir, amprenavir and darunavir) with lower doses of ritonavir. A 200/150 mg b.i.d. dose of lopinavir/ritonavir could lower costs while maintaining very similar lopinavir plasma levels to the standard dose. New pharmaco enhancer drugs may need to be used at different doses to boost different antiretrovirals.

Design and synthesis of novel P2 substituents in diol-based HIV protease inhibitors

The synthesis and SAR of HIV-1 protease inhibitors containing novel P2 structural elements are presented. The inhibitors were designed having hydrogen bond accepting P2 substituents to probe potential favorable interactions to Asp-29/Asp-30 of the HIV-1 protease backbone utilizing inhibitor 3 as a model template. Several inhibitors were synthesized from an L-Val methyl amide P2 motif by appending hydrogen bonding moieties from either the isopropyl side-chain or from the methyl amide portion. The most promising inhibitors 4a and 4e displayed Ki values of 1.0 nM and 0.7 nM respectively and EC50 values in the MT4 cell-based assay of 0.17 microM and 0.33 microM respectively, a slight loss in potency compared to lead inhibitor 3. These inhibitors were also tested against an HIV protease inhibitor resistant strain carrying the M46I, V82F, and I84V mutations. Inhibitors 4a and 4e displayed a 3 and 4 fold change respectively compared with HIV wild type, whereas lead inhibitor 3 showed a higher 9 fold change. This study further demonstrate the chemical tractability of the approach where various P2 substituents can be introduced in just one chemical step from lactone 21 enabling facile modifications of the overall properties in this inhibitor class.

[Lopinavir/ritonavir monotherapy as a simplification strategy in antiretroviral therapy in clinical practice]

Although guidelines for the treatment of HIV-infected patients recommend triple drug antiretroviral therapy, because of the toxicity of these regimens, the complexity of treatment and its costs, other therapeutic options are desirable. Several clinical trials have shown that lopinavir/ritonavir (LPV/r) as a simplification strategy in antiretroviral therapy in HIV-infected patients who maintain suppression of viral replication while receiving conventional treatment regimens is safe and is associated with less toxicity than that due to prolonged exposure to protease inhibitors and nucleoside analogs. The present review summarizes the main results of the various retrospective studies on LPV/r as a simplification strategy of antiretroviral therapy in daily clinical practice.

HIV-1 Gag processing intermediates trans-dominantly interfere with HIV-1 infectivity

Protease inhibitors (PI) act by blocking human immunodeficiency virus (HIV) polyprotein processing, but there is no direct quantitative correlation between the degree of impairment of Gag processing and virion infectivity at low PI concentrations. To analyze the consequences of partial processing, virus particles were produced in the presence of limiting PI concentrations or by co-transfection of wild-type proviral plasmids with constructs carrying mutations in one or more cleavage sites. Low PI concentrations caused subtle changes in polyprotein processing associated with a pronounced reduction of particle infectivity. Dissection of individual stages of viral entry indicated a block in accumulation of reverse transcriptase products, whereas virus entry, enzymatic reverse transcriptase activity, and replication steps following reverse transcription were not affected. Co-expression of low amounts of partially processed forms of Gag together with wild-type HIV generally exerted a trans-dominant effect, which was most prominent for a construct carrying mutations at both cleavage sites flanking the CA domain. Interestingly, co-expression of low amounts of Gag mutated at the CA-SP1 cleavage site also affected processing activity at this site in the wild-type virus. The results indicate that low amounts (<5%) of Gag processing intermediates can display a trans-dominant effect on HIV particle maturation, with the maturation cleavage between CA and SP1 being of particular importance. These effects are likely to be important for the strong activity of PI at concentrations achieved in vivo and also bear relevance for the mechanism of action of the antiviral drug bevirimat.

Nucleoside reverse transcriptase inhibitor-sparing regimen (nonnucleoside reverse transcriptase inhibitor + protease inhibitor) was more likely associated with resistance comparing to nonnucleoside reverse transcriptase inhibitor or protease inhibitor + nucleoside reverse transcriptase inhibitor in the randomized ANRS 121 trial

The use of nonnucleoside reverse transcriptase inhibitor (NNRTI) + protease inhibitor regimen for the treatment of antiretroviral-naive patients was less successful than classical nucleoside reverse transcriptase inhibitor (NRTI) based regimen and associated with more resistance for protease inhibitors and NNRTIs. The selection for NNRTI resistance was particularly observed in patients with high viral load (>100 000 copies/ml) and low efavirenz trough levels (<1100 ng/ml). Contrary to the results observed in trials evaluating mono or dual protease inhibitors strategies, gag gene mutations were not involved in the low efficacy of this strategy. The NNRTI + protease inhibitor strategy should not be recommended as an antiretroviral first-line regimen, particularly in patients with high viral load at baseline.

Insights into drug resistance of mutations D30N and I50V to HIV-1 protease inhibitor TMC-114: free energy calculation and molecular dynamic simulation

The single mutations D30N and I50V are considered as the key residue mutations of the HIV-1 protease drug resistance to inhibitors in clinical use. In this work, molecular dynamics (MD) simulations combined with the molecular mechanics Poisson-Boltzmann surface area (MM-PBSA) method have been performed to investigate the drug-resistant mechanisms of D30N and I50V to an inhibitor TMC-114. The analyses of absolute binding free energies using the separate trajectory approach suggests that the decrease in the van der Waals energy and electrostatic energy in the gas phase results in the drug resistance of D30N to TMC-114, while for I50V, the decrease in the electrostatic energy mainly drive its drug resistance to TMC-114. Detailed binding free energies between TMC-114 and individual protein residues are computed by using a per-residue basis decomposition method, which provides insights into the inhibitor-protein binding mechanism and also explains the drug-resistant mechanisms of mutations D30N and I50V to TMC-114. The study shows that the loss of the hydrogen bond between TMC-114 and the side chain of Asn30' is the main driving force of the resistance of D30N to TMC-114, and in the case of I50V, the increase in the polar solvation energies between TMC-114 and two residues Val50' and Asp30' definitively drives the resistance of I50V to TMC-114. We expect that this work can provide some helpful insights into the nature of mutational effect and aid the future design of better inhibitors.

Simultaneous population pharmacokinetic model for lopinavir and ritonavir in HIV-infected adults

BACKGROUND

Lopinavir is a protease inhibitor indicated for the treatment of HIV infection. It is coformulated with low doses of ritonavir in order to enhance its pharmacokinetic profile. After oral administration, plasma concentrations of lopinavir can vary widely between different HIV-infected patients.

OBJECTIVE

To develop and validate a population pharmacokinetic model for lopinavir and ritonavir administered simultaneously in a population of HIV-infected adults. The model sought was to incorporate patient characteristics influencing variability in the drug concentration and the interaction between the two compounds.

METHODS

HIV-infected adults on stable therapy with oral lopinavir/ritonavir in routine clinical practice for at least 4 weeks were included. A concentration-time profile was obtained for each patient, and blood samples were collected immediately before and 1, 2, 4, 6, 8, 10 and 12 hours after a morning lopinavir/ritonavir dose. Lopinavir and ritonavir concentrations in plasma were determined by high-performance liquid chromatography. First, a population pharmacokinetic model was developed for lopinavir and for ritonavir separately. The pharmacokinetic parameters, interindividual variability and residual error were estimated, and the influence of different patient characteristics on the pharmacokinetics of lopinavir and ritonavir was explored. Then, a simultaneous model estimating the pharmacokinetics of both drugs together and incorporating the influence of ritonavir exposure on oral clearance (CL/F) of lopinavir was developed. Population analysis was performed using nonlinear mixed-effects modelling (NONMEM version V software). The bias and precision of the final model were assessed through Monte Carlo simulations and data-splitting techniques.

RESULTS

A total of 53 and 25 Caucasian patients were included in two datasets for model building and model validation, respectively. Lopinavir and ritonavir pharmacokinetics were described by one-compartment models with first-order absorption and elimination. The presence of advanced liver fibrosis decreased CL/F of ritonavir by nearly half. The volume of distribution after oral administration (Vd/F) and CL/F of lopinavir were reduced as alpha1-acid glycoprotein (AAG) concentrations increased. CL/F of lopinavir was inhibited by ritonavir concentrations following a maximum-effect model (maximum inhibition [Imax] = 1, concentration producing 50% of the I(max) [IC50] = 0.36 mg/L). The final model appropriately predicted plasma concentrations in the model-validation dataset with no systematic bias and adequate precision.

CONCLUSION

A population model to simultaneously describe the pharmacokinetics of lopinavir and ritonavir was developed and validated in HIV-infected patients. Bayesian estimates of the individual parameters of ritonavir and lopinavir could be useful to predict lopinavir exposure based on the presence of advanced liver fibrosis and the AAG concentration in an individual manner, with the aim of maximizing the chances of treatment success.

Viral protease inhibitors

This review provides an overview of the development of viral protease inhibitors as antiviral drugs. We concentrate on HIV-1 protease inhibitors, as these have made the most significant advances in the recent past. Thus, we discuss the biochemistry of HIV-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 limited to viruses that cause chronic disease, viruses that have the potential to cause large-scale epidemics, or viruses that are sufficiently ubiquitous that treating an acute infection would be beneficial even if the infection was ultimately self-limiting. Protease inhibitor development is most advanced for hepatitis C virus (HCV), and we also provide a review of HCV NS3/4A serine protease inhibitor development, including combination therapy and resistance. Finally, we discuss other viral proteases as potential drug targets, including those from Dengue virus, cytomegalovirus, rhinovirus, and coronavirus.

Peptidomimetic therapeutic agents targeting the protease enzyme of the human immunodeficiency virus and hepatitis C virus

During the past two decades, great strides have been made in the design of peptidomimetic drugs for the treatment of viral infections, despite the stigma of poor drug-like properties, low oral absorption, and high clearance associated with such compounds. This Account summarizes the progress made toward overcoming such liabilities and highlights the drug discovery efforts that have focused specifically on human immunodeficiency virus (HIV) and hepatitis C virus (HCV) protease inhibitors. The arsenal against the incurable disease AIDS, which is caused by HIV infection, includes peptidomimetic compounds that target the virally encoded aspartic protease enzyme. This enzyme is essential to the production of mature HIV particles and plays a key role in maintaining infectivity. However, because of the rapid genomic evolution of viruses, an inevitable consequence in the treatment of all viral infections is the emergence of resistance to the drugs. Therefore, the incomplete suppression of HIV in treatment-experienced AIDS patients will continue to drive the search for more effective therapeutic agents that exhibit efficacy against the mutants raised by the earlier generation of protease inhibitors. Currently, a number of substrate-based peptidomimetic agents that target the virally encoded HCV NS3/4A protease are in clinical development. Mechanistically, these inhibitors can be generally divided into activated carbonyls that are transition-state mimics or compounds that tap into the feedback mode of enzyme-product inhibition. In the HCV field, there is justified optimism that a number of these compounds will soon reach commercialization as therapeutic agents for the treatment of HCV infections. Structural research has guided the successful design of both HIV and HCV protease inhibitors. X-ray crystallography, NMR, and computational studies have provided valuable insight in to the free-state preorganization of peptidomimetic ligands and their enzyme-bound conformation. Researchers have designed a variety of novel bioisosteric replacements of amino acids and short peptides that contain all of the required pharmacophore moieties and play a key role in inducing conformational changes to the overall molecule. The knowledge gained from these studies will undoubtedly guide the future design of therapeutic agents and further contribute to the success of this field.

Lopinavir/ritonavir in the treatment of HIV-1 infection: a review

Lopinavir/ritonavir is the first and only coformulated HIV-1 protease inhibitor (PI). Large clinical trials have demonstrated lopinavir/ritonavir's clinical efficacy in both antiretroviral-naïve and -experienced patients. The immunologic and virologic benefits of treatment with this agent have been proven in HIV-infected adults, adolescents, and children. Smaller studies support the use of lopinavir/ritonavir monotherapy as a therapeutic option in certain patients. The drug is characterized by a high genetic barrier to resistance, and appears to be more forgiving of non-adherence than earlier, unboosted PIs. The most frequent side effects observed are diarrhea, nausea, and vomiting. These gastrointestinal adverse effects are generally mild to moderate. Metabolic derangements, including hyperlipidemia and glucose intolerance, have also been observed in lopinavir/ritonavir recipients. As the menu of available antiretroviral agents continues to expand, lopinavir/ritonavir remains a proven and effective drug for the treatment of HIV infection.

Initial therapy with nucleoside reverse transcriptase inhibitor-containing regimens is more effective than with regimens that spare them with no difference in short-term fat distribution: Hippocampe-ANRS 121 Trial

OBJECTIVES

The aim of this study was to evaluate the impact on body fat of nucleoside reverse transcriptase inhibitor (NRTI)-sparing regimens compared with NRTI-containing therapy in HIV-1-infected antiretroviral (ARV)-naive patients.

METHODS

A randomized, multicentre, open-label trial in ARV-naive patients. Subjects were randomized (2:1:1) to receive: (i) an NRTI-sparing regimen consisting of a non-nucleoside reverse transcriptase inhibitor (NNRTI) plus a boosted protease inhibitor (PI/r); or (ii) an NRTI-containing regimen of (a) a PI/r plus two NRTIs or (b) an NNRTI plus two NRTIs. The primary endpoint was the change in subcutaneous limb fat measured by dual-energy X-ray absorptiometry at week (W) 96. Secondary endpoints included the proportion of patients with treatment failure, plasma HIV-RNA (pVL) <50 copies/mL and safety.

RESULTS

One hundred and seventeen patients were enrolled between November 2003 and May 2004: 26% female; 42% from sub-Saharan Africa; median plasma HIV-RNA (pVL) 5.1 log(10) copies/mL; median CD4 count 207 cells/mm(3). A planned interim analysis demonstrated significantly lower treatment and virological responses with the NRTI-sparing strategy, resulting in premature study termination on 19 July 2005. The proportion of patients who remained on their assigned treatment strategy and had pVL <50 copies/mL on the NRTI-sparing regimen was 60.0%, compared with 82.5% on the NRTI-containing regimen at W24 (P = 0.009) and 66.7% and 82.5%, respectively, at W48 (P = 0.059). Treatment failure was associated with the NRTI-sparing strategy in patients with suboptimal adherence and with being from sub-Saharan Africa. No differences in fat distribution were noted.

CONCLUSIONS

An initial NRTI-sparing regimen is less successful and virologically less potent than standard NRTI-containing regimen and should not therefore be used as the first line of treatment.

Enzymatic and structural analysis of the I47A mutation contributing to the reduced susceptibility to HIV protease inhibitor lopinavir

Lopinavir (LPV) is a second-generation HIV protease inhibitor (PI) designed to overcome resistance development in patients undergoing long-term antiviral therapy. The mutation of isoleucine at position 47 of the HIV protease (PR) to alanine is associated with a high level of resistance to LPV. In this study, we show that recombinant PR containing a single I47A substitution has the inhibition constant (K(i) ) value for lopinavir by two orders of magnitude higher than for the wild-type PR. The addition of the I47A substitution to the background of a multiply mutated PR species from an AIDS patient showed a three-order-of-magnitude increase in K(i) in vitro relative to the patient PR without the I47A mutation. The crystal structure of I47A PR in complex with LPV showed the loss of van der Waals interactions in the S2/S2' subsites. This is caused by the loss of three side-chain methyl groups due to the I47A substitution and by structural changes in the A47 main chain that lead to structural changes in the flap antiparallel beta-strand. Furthermore, we analyzed possible interaction of the I47A mutation with secondary mutations V32I and I54V. We show that both mutations in combination with I47A synergistically increase the relative resistance to LPV in vitro. The crystal structure of the I47A/I54V PR double mutant in complex with LPV shows that the I54V mutation leads to a compaction of the flap, and molecular modeling suggests that the introduction of the I54V mutation indirectly affects the strain of the bound inhibitor in the PR binding cleft.

Lopinavir/ritonavir pharmacokinetics in HIV/HCV-coinfected patients with or without cirrhosis

Liver disease may alter the pharmacokinetics of antiretrovirals and produce changes in plasma protein binding. The aim was to evaluate the pharmacokinetics of total and unbound lopinavir (LPV) in HIV-infected patients with and without hepatitis C virus (HCV) coinfection. Fifty-six HIV+ patients receiving lopinavir/ritonavir (LPV/r) (group I = 24 controls; II = 23 HIV/HCV-coinfected; III = 9 cirrhotic HIV/HCV-coinfected) were included. Total (n = 56) and unbound (n = 36) LPV pharmacokinetic parameters were determined at steady-state using validated high-performance liquid chromatography with ultraviolet detection and high-performance liquid chromatography-tandem mass spectrometry methods, respectively. Pharmacokinetic parameters (plasma concentration just before drug administration, peak concentrations in plasma, times to maximum plasma concentration, areas under the plasma concentration-time curve from 0 to 12 hours, and CL/F/kg) of both total and unbound LPV were calculated by standard noncompartmental methods and differences among groups evaluated (Kruskal-Wallis test).LPV apparent oral clearance normalized to body weight (median, interquartile range) was 55 (40-68), 59 (44-69), and 71 (53-78) mL/h/kg for groups I, II, and III, respectively (II vs. I, P = 0.52; III vs. I, P = 0.16). The areas under the plasma concentration-time curve from 0 to 12 hours were 110.4 (80.9-135.2), 103.4 (85.5-131.3), and 92.8 (87.4-116.3) microg h/mL for groups I, II, and III, respectively (II vs. I, P = 0.68; III vs. I, P = 0.71). Chronic liver impairment produced a slight, although not significant, decrease in plasma protein binding. The free-fraction of LPV increased ( approximately 21%) from 0.97% (0.80-1.06) in HIV+/HCV- patients to 1.18% (0.89-1.65) in HIV/HCV+ cirrhotic patients. The apparent oral clearance of unbound LPV (CLu/F/kg) in cirrhotic patients did not change significantly, supporting the concept that the clearance of unbound LPV in liver disease is not affected after being inhibited by low-dose ritonavir co-administration.LPV total and unbound pharmacokinetics were not affected by hepatic impairment, suggesting that no adjustment of LPV/r dose is required for HIV/HCV-coinfected patients with and without cirrhosis and moderate impairment of liver function.

HIV-1 protease inhibitors from inverse design in the substrate envelope exhibit subnanomolar binding to drug-resistant variants

The acquisition of drug-resistant mutations by infectious pathogens remains a pressing health concern, and the development of strategies to combat this threat is a priority. Here we have applied a general strategy, inverse design using the substrate envelope, to develop inhibitors of HIV-1 protease. Structure-based computation was used to design inhibitors predicted to stay within a consensus substrate volume in the binding site. Two rounds of design, synthesis, experimental testing, and structural analysis were carried out, resulting in a total of 51 compounds. Improvements in design methodology led to a roughly 1000-fold affinity enhancement to a wild-type protease for the best binders, from a Ki of 30-50 nM in round one to below 100 pM in round two. Crystal structures of a subset of complexes revealed a binding mode similar to each design that respected the substrate envelope in nearly all cases. All four best binders from round one exhibited broad specificity against a clinically relevant panel of drug-resistant HIV-1 protease variants, losing no more than 6-13-fold affinity relative to wild type. Testing a subset of second-round compounds against the panel of resistant variants revealed three classes of inhibitors: robust binders (maximum affinity loss of 14-16-fold), moderate binders (35-80-fold), and susceptible binders (greater than 100-fold). Although for especially high-affinity inhibitors additional factors may also be important, overall, these results suggest that designing inhibitors using the substrate envelope may be a useful strategy in the development of therapeutics with low susceptibility to resistance.

Seven-year efficacy of a lopinavir/ritonavir-based regimen in antiretroviral-naïve HIV-1-infected patients

OBJECTIVE

Evaluate efficacy and tolerability of lopinavir/ritonavir (LPV/r) plus stavudine and lamivudine long term in antiretroviral-naïve patients.

DESIGN

Open-label follow-up of prospective, randomized, multicenter trial.

METHOD

Antiretroviral-naïve HIV-infected subjects (N = 00) received of 3 doses of LPV/r plus stavudine and lamivudine for 48 weeks then received LPV/r soft-gel capsules 400/00 mg plus stavudine and lamivudine. After 6 years, subjects replaced stavudine with tenofovir.

RESULTS

At 7 years, by intent-to-treat analysis, 61 % had plasma HIV-RNA <400 copies/mL and 59% had < 50 copies/mL. Thirty-nine subjects discontinued treatment due to adverse events (n = 6), personal/other reasons (0), loss to follow-up (9), and noncompliance (4). Among 28 subjects qualifying for drug resistance testing, no protease inhibitor or stavudine resistance was observed and 4 showed lamivudine resistance. Most common drug-related moderate or severe adverse events were diarrhea (28%), nausea (6%), and abdominal pain (11 %). Subjects who received stavudine (median 6.6 years) and switched to tenofovir demonstrated significant improvements in total cholesterol (p = .009), triglycerides (p = .023), apolipoprotein C-III (p < .001 ), adiponectin (p = .008), fasting insulin (p = .04), and leptin (p = .03).

CONCLUSION

LPV/r-based therapy demonstrated sustained efficacy with no protease inhibitor or stavudine resistance through 7 years in antiretroviral-naïve patients. Switching from stavudine to tenofovir resulted in significant improvements in multiple metabolic parameters.

Characterization of a novel human immunodeficiency virus type 1 protease inhibitor, A-790742

A-790742 is a potent human immunodeficiency virus type 1 (HIV-1) protease inhibitor, with 50% effective concentrations ranging from 2 to 7 nM against wild-type HIV-1. The activity of this compound is lowered by approximately sevenfold in the presence of 50% human serum. A-790742 maintained potent antiviral activity against lopinavir-resistant variants generated in vitro as well as against a panel of molecular clones containing proteases derived from HIV-1 patient isolates with multiple protease mutations. During in vitro selection, A-790742 selected two primary mutations (V82L and I84V) along with L23I, L33F, K45I, A71V/A, and V77I in the pNL4-3 background and two other mutations (A71V and V82G) accompanied by M46I and L63P in the HIV-1 RF background. HIV-1 pNL4-3 clones with a single V82L or I84V mutation were phenotypically resistant to A-790742 and ritonavir. Taking these results together, A-790742 displays a favorable anti-HIV-1 profile against both the wild type and a large number of mutants resistant to other protease inhibitors. The selection of the uncommon V82L and V82G mutations in protease by A-790742 suggests the potential for an advantageous resistance profile with this protease inhibitor.

Induction of P-glycoprotein expression and activity by ritonavir in bovine brain microvessel endothelial cells

Extended treatment with human immunodeficiency virus (HIV) protease inhibitors (HPIs) is standard in HIV/AIDS therapy. While these drugs have helped decrease the overall incidence of AIDS defining illnesses, the relative prevalence of HIV/AIDS dementia has increased. HPIs may cause induction of blood-brain barrier (BBB) drug transporters (P-glycoprotein; P-gp) and thereby limit entry of HPIs into brain tissue, increasing the probability that the brain could become an HIV sanctuary site. Using bovine brain microvessel endothelial cells (BMEC) as an in-vitro model of the BBB, the potential for the HIV protease inhibitor ritonavir to cause induction of P-gp activity and expression was examined. BMEC were isolated from fresh cow brain by enzymatic digest and density centrifugation. Primary culture BMEC were co-incubated with ritonavir or vehicle control for 120 h. Quantitative drug accumulation of rhodamine 123 (Rh123) and fluorescence microscopy were used as measures of P-gp activity. P-gp expression was assessed using quantitative Western blotting. Ritonavir decreased Rh123 cell accumulation and increased P-gp immunoreactive protein in a concentration-dependent manner. Fluorescent microscopy mirrored Rh123 quantitative studies. In BMEC pretreated with 30 microM ritonavir, Rh123 accumulation was decreased 40% and immunoreactive P-gp protein increased 2-fold. Collectively, a strong correlation between decreased Rh123 BMEC accumulation and increased P-gp immunoreactive protein was observed (Spearman r2 = 0.77, P < 0.0001). Thus extended exposure of BMEC to ritonavir caused a concentration-dependent increase in P-gp activity and expression. Similar findings may occur at the clinical level with prolonged HIV protease inhibitor use, giving insight into the central nervous system as an HIV sanctuary site and eventual development of HIV dementia.

Design and synthesis of HIV-1 protease inhibitors incorporating oxazolidinones as P2/P2' ligands in pseudosymmetric dipeptide isosteres

A series of novel HIV-1 protease inhibitors based on two pseudosymmetric dipeptide isosteres have been synthesized and evaluated. The inhibitors were designed by incorporating N-phenyloxazolidinone-5-carboxamides into the hydroxyethylene and (hydroxyethyl)hydrazine dipeptide isosteres as P2 and P2' ligands. Compounds with (S)-phenyloxazolidinones attached at a position proximal to the central hydroxyl group showed low nM inhibitory activities against wild-type HIV-1 protease. Selected compounds were further evaluated for their inhibitory activities against a panel of multidrug-resistant protease variants and for their antiviral potencies in MT-4 cells. The crystal structures of lopinavir (LPV) and two new inhibitors containing phenyloxazolidinone-based ligands in complex with wild-type HIV-1 protease have been determined. A comparison of the inhibitor-protease structures with the LPV-protease structure provides valuable insight into the binding mode of the new inhibitors to the protease enzyme. Based on the crystal structures and knowledge of structure-activity relationships, new inhibitors can be designed with enhanced enzyme inhibitory and antiviral potencies.

In vitro selection and characterization of human immunodeficiency virus type 2 with decreased susceptibility to lopinavir

Lopinavir (LPV)-ritonavir has demonstrated durable antiviral activity in human immunodeficiency virus type 1 (HIV-1)-infected antiretroviral-naïve and protease inhibitor (PI)-experienced patients. However, information on LPV activity against HIV-2 and the patterns of mutations in HIV-2 in response to selection by LPV is limited. The activity of LPV against three strains of HIV-2 was assessed and compared to activity against a reference HIV-1 strain. LPV demonstrated activity similar to that observed against HIV-1 in two HIV-2 strains (HIV-2(MS) and HIV-2(CBL-23)) tested. On the other hand, approximately 10-fold-reduced susceptibility was observed with the third HIV-2 strain, HIV-2(CDC310319). Passage of HIV-2(MS) with increasing concentrations of LPV selected mutations V47A and D17N in the HIV-2 protease gene. The introduction of both 17N and 47A either individually or together into HIV-2(ROD) molecular infectious clones showed that the single V47A substitution in HIV-2 resulted in a substantial reduction in susceptibility to LPV. In contrast, this mutant retained wild-type susceptibility to other PIs and appeared to be hypersusceptible to atazanavir and saquinavir.

HIV-infected patients receiving lopinavir/ritonavir-based antiretroviral therapy achieve high rates of virologic suppression despite adherence rates less than 95%

BACKGROUND

The observation that extremely high levels of medication adherence are required to achieve complete virologic suppression is based largely on studies of treatment-experienced patients receiving HIV protease inhibitor (PI)-based therapy without ritonavir boosting. This study aims to define the level of adherence needed to achieve virologic suppression in patients receiving boosted PI-based highly active antiretroviral therapy (HAART) with lopinavir/ritonavir.

METHODS

HIV-infected adults receiving a regimen containing lopinavir/ritonavir were recruited into a prospective, observational study of the relation between adherence to lopinavir/ritonavir and virologic outcomes. Adherence was measured using the Medication Event Monitoring System (MEMS; Aardex, Union City, CA). HIV-1 viral load (VL) was measured at week 24.

RESULTS

The final study population contained 64 subjects. Eighty percent had AIDS, 97% received lopinavir/ritonavir before enrollment, and most had more than 7 years of HAART experience. Mean adherence overall was 73%. Eighty percent and 59% achieved a VL <400 copies/mL and a VL <75 copies/mL, respectively. Mean adherence was 75% in those achieving a VL <75 copies/mL. High rates of virologic suppression were observed in all adherence quartiles, including the lowest quartile (range of adherence: 23.5%-53.3%).

CONCLUSIONS

Moderate levels of adherence can lead to virologic suppression in most patients taking lopinavir/ritonavir-based HAART.

Structural confirmation of regioisomers of Lopinavir impurities using MS and gradient COSY (1H and 13C NMR assignment of Lopinavir impurities)

We report the complete (1)H and (13)C NMR assignment of impurities of six Lopinavir (2S)-N-[(2S, 4S, 5S)-5-{[2-(2,6-dimethylphenoxy)acetyl]amino}-4-hydroxy-1,6-diphenyl hexan-2-yl]-3-methyl-2-(2-oxo-1,3-diazinan-1-yl)butan- amide. Two of the impurities are regioisomers and GCOSY used to differentiate the two structures. The spectral assignments for all six impurities were achieved by concerted application of one and two-dimensional NMR techniques ((1)H NMR, (13)C NMR, DEPT, GCOSY, GHSQC and GHMBC).