Protease Drug Research Articles

Evaluation of novel Saquinavir analogs for resistance mutation compatibility and potential as an HIV-Protease inhibitor drug.

A fundamental issue related to therapy of HIV-1 infection is the emergence of viral mutations which severely limits the long term efficiency of the HIV-protease (HIV-PR) inhibitors. Development of new drugs is therefore continuously needed. Chemoinformatics enables to design and discover novel molecules analogous to established drugs using computational tools and databases. Saquinavir, an anti-HIV Protease drug is administered for HIV therapy. In this work chemoinformatics tools were used to design structural analogs of Saquinavir as ligand and molecular dockings at AutoDock were performed to identify potential HIV-PR inhibitors. The analogs S1 and S2 when docked with HIV-PR had binding energies of -4.08 and -3.07 kcal/mol respectively which were similar to that for Saquinavir. The molecular docking studies revealed that the changes at N2 of Saquinavir to obtain newly designed analogs S1 (having N2 benzoyl group at N1) and S2 (having 3-oxo-3phenyl propanyl group at N2) were able to dock with HIV-PR with similar affinity as that of Saquinavir. Docking studies and computationally derived pharmacodynamic and pharmacokinetic properties׳ comparisons at ACD/I-lab establish that analog S2 has more potential to evade the problem of drug resistance mutation against HIV-1 PR subtype-A. S2 can be further developed and tested clinically as a real alternative drug for HIV-1 PR across the clades in future.

HIV-1 Protease-Substrate Coevolution in Nelfinavir Resistance

Resistance to various human immunodeficiency virus type 1 (HIV-1) protease inhibitors (PIs) challenges the effectiveness of therapies in treating HIV-1-infected individuals and AIDS patients. The virus accumulates mutations within the protease (PR) that render the PIs less potent. Occasionally, Gag sequences also coevolve with mutations at PR cleavage sites contributing to drug resistance. In this study, we investigated the structural basis of coevolution of the p1-p6 cleavage site with the nelfinavir (NFV) resistance D30N/N88D protease mutations by determining crystal structures of wild-type and NFV-resistant HIV-1 protease in complex with p1-p6 substrate peptide variants with L449F and/or S451N. Alterations of residue 30's interaction with the substrate are compensated by the coevolving L449F and S451N cleavage site mutations. This interdependency in the PR-p1-p6 interactions enhances intermolecular contacts and reinforces the overall fit of the substrate within the substrate envelope, likely enabling coevolution to sustain substrate recognition and cleavage in the presence of PR resistance mutations. Resistance to human immunodeficiency virus type 1 (HIV-1) protease inhibitors challenges the effectiveness of therapies in treating HIV-1-infected individuals and AIDS patients. Mutations in HIV-1 protease selected under the pressure of protease inhibitors render the inhibitors less potent. Occasionally, Gag sequences also mutate and coevolve with protease, contributing to maintenance of viral fitness and to drug resistance. In this study, we investigated the structural basis of coevolution at the Gag p1-p6 cleavage site with the nelfinavir (NFV) resistance D30N/N88D protease mutations. Our structural analysis reveals the interdependency of protease-substrate interactions and how coevolution may restore substrate recognition and cleavage in the presence of protease drug resistance mutations.

Computing Clinically Relevant Binding Free Energies of HIV-1 Protease Inhibitors.

The use of molecular simulation to estimate the strength of macromolecular binding free energies is becoming increasingly widespread, with goals ranging from lead optimization and enrichment in drug discovery to personalizing or stratifying treatment regimes. In order to realize the potential of such approaches to predict new results, not merely to explain previous experimental findings, it is necessary that the methods used are reliable and accurate, and that their limitations are thoroughly understood. However, the computational cost of atomistic simulation techniques such as molecular dynamics (MD) has meant that until recently little work has focused on validating and verifying the available free energy methodologies, with the consequence that many of the results published in the literature are not reproducible. Here, we present a detailed analysis of two of the most popular approximate methods for calculating binding free energies from molecular simulations, molecular mechanics Poisson–Boltzmann surface area (MMPBSA) and molecular mechanics generalized Born surface area (MMGBSA), applied to the nine FDA-approved HIV-1 protease inhibitors. Our results show that the values obtained from replica simulations of the same protease–drug complex, differing only in initially assigned atom velocities, can vary by as much as 10 kcal mol–1, which is greater than the difference between the best and worst binding inhibitors under investigation. Despite this, analysis of ensembles of simulations producing 50 trajectories of 4 ns duration leads to well converged free energy estimates. For seven inhibitors, we find that with correctly converged normal mode estimates of the configurational entropy, we can correctly distinguish inhibitors in agreement with experimental data for both the MMPBSA and MMGBSA methods and thus have the ability to rank the efficacy of binding of this selection of drugs to the protease (no account is made for free energy penalties associated with protein distortion leading to the over estimation of the binding strength of the two largest inhibitors ritonavir and atazanavir). We obtain improved rankings and estimates of the relative binding strengths of the drugs by using a novel combination of MMPBSA/MMGBSA with normal mode entropy estimates and the free energy of association calculated directly from simulation trajectories. Our work provides a thorough assessment of what is required to produce converged and hence reliable free energies for protein–ligand binding.

Molecular Docking Investigation of the Binding Interactions of Macrocyclic Inhibitors with HCV NS3 Protease and its Mutants (R155K, D168A and A156V)

Hepatitis C Virus (HCV) non-structural protein 3 (NS3) protease drug resistance poses serious challenges on the design of an effective treatment. Substrate Envelope Hypothesis, "the substrates of HCV NS3/4A protease have a consensus volume inside the active site called substrate envelope" is used to design potent and specific drugs to overcome this problem. Using molecular docking, we studied the binding interaction of the different inhibitors and protein and evaluated the effect of three different mutations (R155K, D168A and A156V) on the binding of inhibitors. P2-P4 macrocycles of 5A/5B and modified 5A/5B hexapeptide sequences have the best scores against the wild-type protein -204.506 and -206.823kcal/mole, respectively. Also, charged P2-P4 macrocycles of 3/4A and 4A/4B hexapeptide sequences have low scores with the wild-type protein -200.467 and -203.186kcal/mole, respectively. R155K mutation greatly affects the conformation of the compounds inside the active site. It inverts its orientations, and this is because the large and free side chain of K155 which restricts the conformation of the large P2-P4 macrocycle. The conformation of charged P2-P4 macrocycle of 3/4A hexapeptide sequence in wild-type, A156V and D168A proteins is nearly equal; while that of charged P2-P4 macrocycle of 4A/4B hexapeptide sequence is different. Nevertheless, these compounds have a slight increase of Van der Waals volume compared to that of substrates, they are potent against mutations and have good scores. Therefore, the suggested drugs can be used as an effective treatment solving HCV NS3/4A protease drug resistance problem.

Differential Sensitivity of 5′UTR-NS5A Recombinants of Hepatitis C Virus Genotypes 1−6 to Protease and NS5A Inhibitors

Hepatitis C virus (HCV) therapy will benefit from the preclinical evaluation of direct-acting antiviral (DAA) agents in infectious culture systems that test the effects on different virus genotypes. We developed HCV recombinants comprising the 5' untranslated region-NS5A (5-5A) from genotypes 1-6 and 2a(JFH1) NS5B-3' untranslated region, and tested the effects of NS3 protease and NS5A inhibitors on these recombinants. The HCV 5-5A recombinants with previously identified mutations in the NS3-helicase (F1464L), NS4A (A1672S), and NS5B (D2979G) were adapted and improved, by incorporating additional recovered mutations that increased their propagation in Huh7.5 cells. Concentration-response profiles were determined for each DAA agent in replicate infected Huh7.5 cells. Developed efficient 1a(H77), 1a(TN), 3a(S52), 4a(ED43), 5a(SA13), and 6a(HK6a) 5-5A recombinants did not require mutations after viral passage in the NS3 protease or NS5A domain-I regions targeted by the drugs. They were inhibited in a concentration-dependent manner by the NS3 protease inhibitors telaprevir, boceprevir, asunaprevir, simeprevir, vaniprevir, faldaprevir, and MK-5172 and by the NS5A inhibitor daclatasvir. The 1a(TN) 5-5A and JFH1-independent full-length viruses had similar levels of sensitivity to the DAA agents, validating the 5-5A recombinants as surrogates for full-length viruses in DAA testing. Compared with the 1a(TN) full-length virus, the 3a(S52) 5-5A recombinant was highly resistant to all protease inhibitors, and the 4a(ED43) recombinant was highly resistant to telaprevir and boceprevir, but most sensitive to other protease inhibitors. Compared with other protease inhibitors, MK-5172 had exceptional potency against all HCV genotypes. The NS5A inhibitor daclatasvir had the highest potency observed, but with genotype-dependent activity. The mutations F1464L, A1672S, and D2979G permitted the development of efficient HCV recombinants comprising genotype-specific 5' untranslated region-NS5A (5-5A), which include the natural NS3 protease and NS5A domain-I drug targets. The robust replication of adapted 5-5A recombinants allowed for direct comparison of NS3 protease and NS5A inhibitors against HCV strains of genotypes 1-6.

Ligand Bioactive Conformation Plays a Critical Role in the Design of Drugs That Target the Hepatitis C Virus NS3 Protease

A ligand-focused strategy employed NMR, X-ray, modeling, and medicinal chemistry to expose the critical role that bioactive conformation played in the design of a variety of drugs that target the HCV protease. The bioactive conformation (bound states) were determined for key inhibitors identified along our drug discovery pathway from the hit to clinical compounds. All adopt similar bioactive conformations for the common core derived from the hit peptide DDIVPC. A carefully designed SAR analysis, based on the advanced inhibitor 1 in which the P1 to P3 side chains and the N-terminal Boc were sequentially truncated, revealed a correlation between affinity and the relative predominance of the bioactive conformation in the free state. Interestingly, synergistic conformation effects on potency were also noted. Comparisons with clinical and recently marketed drugs from the pharmaceutical industry showed that all have the same core and similar bioactive conformations. This suggested that the variety of appendages discovered for these compounds also properly satisfy the bioactive conformation requirements and allowed for a large variety of HCV protease drug candidates to be designed.

Disruption of Oligomerization and Dehydroalanine Formation as Mechanisms for ClpP Protease Inhibition

Over 100 protease inhibitors are currently used in the clinics, and most of them use blockage of the active site for their mode of inhibition. Among the protease drug targets are several enzymes for which the correct multimeric assembly is crucial to their activity, such as the proteasome and the HIV protease. Here, we present a novel mechanism of protease inhibition that relies on active-site-directed small molecules that disassemble the protease complex. We show the applicability of this mechanism within the ClpP protease family, whose members are tetradecameric serine proteases and serve as regulators of several cellular processes, including homeostasis and virulence. Compound binding to ClpP in a substoichiometric fashion triggers the formation of completely inactive heptamers. Moreover, we report the selective β-sultam-induced dehydroalanine formation of the active site serine. This reaction proceeds through sulfonylation and subsequent elimination, thereby obliterating the catalytic charge relay system. The identity of the dehydroalanine was confirmed by mass spectrometry and crystallography. Activity-based protein profiling experiments suggest the formation of a dehydroalanine moiety in living S. aureus cells upon β-sultam treatment. Collectively, these findings extend our view on multicomponent protease inhibition that until now has mainly relied on blockage of the active site or occupation of a regulatory allosteric site.

Sequence and structure based models of HIV-1 protease and reverse transcriptase drug resistance.

BackgroundSuccessful management of chronic human immunodeficiency virus type 1 (HIV-1) infection with a cocktail of antiretroviral medications can be negatively affected by the presence of drug resistant mutations in the viral targets. These targets include the HIV-1 protease (PR) and reverse transcriptase (RT) proteins, for which a number of inhibitors are available on the market and routinely prescribed. Protein mutational patterns are associated with varying degrees of resistance to their respective inhibitors, with extremes that can range from continued susceptibility to cross-resistance across all drugs.ResultsHere we implement statistical learning algorithms to develop structure- and sequence-based models for systematically predicting the effects of mutations in the PR and RT proteins on resistance to each of eight and eleven inhibitors, respectively. Employing a four-body statistical potential, mutant proteins are represented as feature vectors whose components quantify relative environmental perturbations at amino acid residue positions in the respective target structures upon mutation. Two approaches are implemented in developing sequence-based models, based on use of either relative frequencies or counts of n-grams, to generate vectors for representing mutant proteins. To the best of our knowledge, this is the first reported study on structure- and sequence-based predictive models of HIV-1 PR and RT drug resistance developed by implementing a four-body statistical potential and n-grams, respectively, to generate mutant attribute vectors. Performance of the learning methods is evaluated on the basis of tenfold cross-validation, using previously assayed and publicly available in vitro data relating mutational patterns in the targets to quantified inhibitor susceptibility changes.ConclusionOverall performance results are competitive with those of a previously published study utilizing a sequence-based strategy, while our structure- and sequence-based models provide orthogonal and complementary prediction methodologies, respectively. In a novel application, we describe a technique for identifying every possible pair of RT inhibitors as either potentially effective together as part of a cocktail, or a combination that is to be avoided.

Replication of the subgenomic hepatitis C virus replicon in the presence of the NS3 protease inhibitors: a stochastic model

The hepatitis C virus (HCV) belongs to Flaviviridae family and causes hazardous liver diseases leading frequently to cirrhosis and hepatocellular carcinoma. HCV is able to rapidly acquire drug resistance and for this reason there is currently no effective anti-HCV therapy in spite of appearance of new potential drugs. Mathematical models are relevant to predict the efficacy of potential drugs against virus or host targets. One of the promising targets for development of new drugs is the viral NS3 protease. Here we developed a stochastic model of the subgenomic HCV replicon replication in Huh-7 cells and in the presence of the NS3 protease inhibitors. Along with consideration of the stochastic nature of the subgenomic HCV replicon replication the model takes into account the existence and generation of main NS3 protease drug resistant mutants, namely BILN-2061 (A156T, D168V, R155Q), VX-950 (A156S, A156T, T54A) and SCH-503034 (A156T, A156S, T54A). The model reproduces well the viral RNA kinetics in the cell from the moment of the subgenomic HCV replicon transfection to steady state, as well as the viral RNA suppression kinetics in the presence of NS3 protease inhibitors BILN-2061, VX-950 and SCH-503034. We showed that the resistant mutants should be taken into account for the correct description of biphasic kinetics of the viral RNA suppression. The mutants selected in the presence of different inhibitor concentrations have maximal replication capacity in the given inhibitor concentration range. Our model can be used to interpret the results of the new anti-HCV drug testing in replicon systems, as well as to predict the efficacy of new potential drugs and optimize the regimen of their use.

Crystallographic study of multi-drug resistant HIV-1 protease lopinavir complex: Mechanism of drug recognition and resistance

Lopinavir (LPV) is a second generation HIV-1 protease inhibitor. Drug resistance has rapidly emerged against LPV since its US FDA approval on September 15, 2000. Mutations at residues 32I, L33F, 46I, 47A, I54V, V82A, I84V, and L90M render the protease drug resistant against LPV. We report the crystal structure of a clinical isolate multi-drug resistant (MDR) 769 HIV-1 protease (resistant mutations at residues 10, 36, 46, 54, 62, 63, 71, 82, 84, and 90) complexed with LPV and the in vitro enzymatic IC50 of LPV against MDR 769. The structural and functional studies demonstrate significant drug resistance of MDR 769 against LPV, arising from reduced interactions between LPV and the protease target.

Insights into the mechanism of drug resistance: X-ray structure analysis of multi-drug resistant HIV-1 protease ritonavir complex

Ritonavir (RTV) is a first generation HIV-1 protease inhibitor with rapidly emerging drug resistance. Mutations at residues 46, 54, 82 and 84 render the HIV-1 protease drug resistant against RTV. We report the crystal structure of multi-drug resistant (MDR) 769 HIV-1 protease (carrying resistant mutations at residues 10, 36, 46, 54, 62, 63, 71, 82, 84 and 90) complexed with RTV and the in vitro enzymatic IC50 of RTV against MDR HIV-1 protease. The structural and functional studies demonstrate significant drug resistance of MDR HIV-1 protease against RTV, arising from reduced hydrogen bonds and Van der Waals interactions between RTV and MDR HIV-1 protease.

Pretreatment Resistance to Hepatitis C Virus Protease Inhibitors Boceprevir/Telaprevir in Hepatitis C Subgenotype 1A-Infected Patients from Manitoba

Traditional therapy with pegylated interferon and ribavirin combined with the new protease inhibitors boceprevir or telaprevir has demonstrated improved outcomes in hepatitis C virus (HCV)-infected patients. Prevalence data regarding pre-existing drug-resistant variants to these two new virus inhibitors in the Canadian population are not available. To detect pre-existing mutations conferring resistance to boceprevir and⁄or telaprevir in Canadian patients infected with HCV genotype 1a. Resistance-associated mutations (RAMs) were evaluated in 85 patients infected with HCV genotype 1a who had not yet received antiviral therapy. The NS3 protease gene was sequenced and common RAMs were identified based on a recently published list. The overall prevalence of pre-existing RAMs to boceprevir and telaprevir was higher compared with other similar studies. All of the observed RAMs were associated with a low level of resistance. A surprisingly high proportion of patients had the V55A RAM (10.6%). None of the mutations associated with a high level of resistance were observed. The simultaneous presence of two low-level resistance mutations (V36L and V55A) was observed in only one patient. Three other patients had both T54S RAM and V55I mutations, which may require a higher concentration of the protease drugs. The prevalence of various mutations in Aboriginal Canadian patients was higher (37.5%) compared with Caucasians (16.39%) (P=0.038). The present study was the first to investigate pre-existing drug resistance to boceprevir⁄telaprevir in Canadian HCV-infected patients. A relatively high proportion of untreated HCV genotype 1a patients in Manitoba harbour low-level RAMs, especially patients of Aboriginal descent, which may contribute to an increased risk of treatment failure.

Predictors of CD4+ T-Cell Counts of HIV Type 1–Infected Persons After Virologic Failure of All 3 Original Antiretroviral Drug Classes

Low CD4(+) T-cell counts are the main factor leading to clinical progression in human immunodeficiency virus type 1 (HIV-1) infection. We aimed to investigate factors affecting CD4(+) T-cell counts after triple-class virological failure. We included individuals from the COHERE database who started antiretroviral therapy from 1998 onward and who experienced triple-class virological failure. CD4(+) T-cell counts obtained after triple-class virologic failure were analyzed using generalized estimating equations. The analyses included 2424 individuals with a total of 23 922 CD4(+) T-cell count measurements. In adjusted models (excluding current viral load and year), CD4(+) T-cell counts were higher with regimens that included boosted protease inhibitors (increase, 22 cells/µL [95% confidence interval {CI}, 3.9-41]; P = .017) or drugs from the new classes (increase, 39 cells/µL [95% CI, 15-62]; P = .001), compared with nonnucleoside reverse-transcriptase inhibitor-based regimens. These associations disappeared when current viral load and/or calendar year were included. Compared with viral levels of <2.5 log(10) copies/mL, levels of 2.5-3.5, 3.5-4.5, 4.5-5.5, and >5.5 log(10) copies/mL were associated with CD4(+) T-cell count decreases of 51, 84, 137, and 186 cells/µL, respectively (P < .001). The approximately linear inverse relationship between log(10) viral load and CD4(+) T-cell count indicates that there are likely immunologic benefits from lowering viral load even by modest amounts that do not lead to undetectable viral loads. This is important for patients with low CD4(+) T-cell counts and few drug options.

Prolonged and Substantial Discordance in Prevalence of Raltegravir-Resistant HIV-1 in Plasma versus PBMC Samples Revealed by 454 “Deep” Sequencing

The evolution of drug resistance mutations in plasma samples is relatively well-characterized. However, the viral population and diversity in other body compartments such as peripheral blood mononuclear cells (PBMC) remains poorly understood. Previous studies have mostly focused on protease and reverse transcriptase drug resistance mutations (DRMs). In this study, we used 454 “deep” sequencing technology to observe and quantify longitudinally the prevalence of resistance mutations associated with the integrase inhibitor, raltegravir, in plasma versus PBMC samples from a San Francisco-based cohort. Four heavily treatment-experienced subjects were monitored in this study over a median of 1.2 years since the initiation of raltegravir-containing regimens. We observed a consistent discordance in the prevalence of DRMs, but not resistance pathway(s), in the plasma versus PBMC viral populations. In the final paired samples that were tested while the subjects were on a raltegravir-containing regimen, DRM prevalence reached 100% in plasma but remained 1% in PBMC on day 177 post-therapy in Subject 3180 (Q148H/G140S), 100% in plasma and 36% in PBMC on day 224 in Subject 3242 (N155H), 78% in plasma and 11–12% in PBMC on day 338 in Subject 3501 (Q148H/G140S), and 100% in plasma and 0% in PBMC on day 197 in Subject 3508 (Y143R). Furthermore, absolute sequence homology comparison between the two compartments revealed that 21% - 99% of PBMC sequences had no match in plasma, whereas 14% - 100% of plasma sequences had no match in PBMC. Overall, our observations suggested that plasma and PBMC hosted drastically different HIV-1 populations even after a prolonged exposure to raltegravir selection pressure.

Activity‐Based Probes for the Study of Proteases: Recent Advances and Developments

Proteases are important targets for the treatment of human disease. Several protease inhibitors have failed in clinical trials due to a lack of in vivo specificity, indicating the need for studies of protease function and inhibition in complex, disease-related models. The tight post-translational regulation of protease activity complicates protease analysis by traditional proteomics methods. Activity-based protein profiling is a powerful technique that can resolve this issue. It uses small-molecule tools-activity-based probes-to label and analyze active enzymes in lysates, cells, and whole animals. Over the last twelve years, a wide variety of protease activity-based probes have been developed. These synthetic efforts have enabled techniques ranging from real-time in vivo imaging of protease activity to high-throughput screening of uncharacterized proteases. This Review introduces the general principles of activity-based protein profiling and describes the recent advancements in probe design and analysis techniques, which have increased the knowledge of protease biology and will aid future protease drug discovery.

Development and evaluation of an assay for HIV-1 protease and reverse transcriptase drug resistance genotyping of all major group-M subtypes

BackgroundHigh cost and varying sensitivity for non-B HIV-1 subtypes limits application of current commercial kits for HIV-1 drug resistance genotyping of all major HIV-1 group-M subtypes. ObjectivesOur research aimed to develop and validate an assay specific for all major HIV-1 group-M subtypes for use as an alternative to commercial assays for HIV-1 protease (PR) and reverse transcriptase (RT) drug resistance genotyping. Study designA nested RT-PCR encompassing the entire PR and RT up to amino acid 321 of HIV-1 was designed to detect HIV-1 group-M subtypes. Primers compatible with group-M subtypes were defined and analytical sensitivity of the assay evaluated using a panel of reference viruses for subtypes A–H and CRF01_AE. The assay was subsequently evaluated on 246 plasma samples from HIV-1 infected individuals harboring various group-M subtypes and viral loads (VLs). ResultsAll major group-M HIV-1 subtypes were detected with an overall analytical sensitivity of 1.00E+03 RNA copies/ml. Application of the genotyping assay on 246 primarily African clinical samples comprising subtypes A (n=52; 21.7%), B (n=12; 5.0%), C (n=127; 52.9%), D (n=25; 10.4%), CRF01_AE (n=10; 4.2%), and CRF02_AG (n=10; 4.2%), and unassigned variants (n=10; 4.2%), VL range 4.32E+02–8.63E+06 (median 2.66E+04) RNA copies/ml, was ∼98% successful. ConclusionsA group-M subtype-independent genotyping assay for detection of HIV-1 drug resistance was developed. The described assay can serve as an alternative to commercial assays for HIV-1 drug resistance genotyping in routine diagnostics, and for surveillance and monitoring of drug resistance in resource-limited settings (RLS).

An in‐house HIV genotyping assay for the detection of drug resistance mutations in Southeast Asian patients infected with HIV‐1

Genotyping for HIV drug resistance is costly and beyond the means for many Southeast Asian patients, who are self-funded. This prompted the development of a more cost-effective, in-house assay for an ethnically diverse, Southeast Asian population at the National University Hospital in Singapore, using Sanger-based sequencing. Plasma samples from 20 treatment-failure patients with a broad spectrum of HIV drug resistance mutations were used to validate this assay clinically. Blinded testing gave concordant results for 7/7 (100%) protease drug resistance-related mutations, including one major and six minor mutations, and 111/116 (95.7%) reverse-transcriptase (RT) drug resistance-related mutations, including 65 nucleoside RT inhibitors (NRTI) and 46 non-nucleoside RT inhibitors (NNRTI) mutations. There were five discordant results, involving three NRTI- and two NNRTI-resistance-associated mutations. Highly conserved primers designed to have a wide coverage of the HIV pol gene (covering the entire protease and 395 codons of the RT region) enabled efficient multi-ethnic population-based genotyping. Reagents for this in-house test cost around 60% less than those for commercially available assays (SGD150 vs. SGD350 per sample). In addition, this assay also identified mutations located within the C-terminal domain (codons 312-560) of RT that are beyond the reach of most published and commercial GRTs. Currently, most research on C-terminal drug-resistance-related mutations has been conducted on HIV subtype B infections. Therefore this assay enables further study of these C-terminal mutations in Southeast Asian populations, where there is a high prevalence of CRF01_AE and other non-subtype B HIV infections.

Evaluating the Potency of Small Molecules to Combat Resistance Based on Docking Structures: An Application to the HIV Protease

HIV-1 protease is an important drug target for the therapy of AIDS. Up to date nine protease drugs have been approved by the U.S. Food and Drug Administration. However, the efficacy of these drugs is limited by the drug-resistant mutants of the protease which can become dominant in the viral population in several months. As it often takes years of effort and millions of dollars to develop a drug, evaluating the potency of a compound to combat resistance at the early stage of drug development would is no doubt invaluable. In this study, we present a new procedure to predict HIV protease mutants that can be resistant to a specific compounds based on docking structure. We exploited molecular interaction energy components (MIECs) between the ligand and the protease residues to characterize the docking poses. A classification method called Support Vector Machine (SVM) is then employed to distinguish resistant from non-resistant mutants. Most interestingly, leave-one-drug-out test showed that our strategy can be generalized to evaluate potency of new drug lead, which suggests the possibility of evaluating the potency to combat resistance for small molecules found from virtual screening.

Protease Activity: Meeting Its Theranostic Potential

This themed issue provides up-to-date review and research articles covering the theranostic applications in the combined fields of protease research, diagnostics and drug development.

Detection of distinct human immunodeficiency virus Type 1 circulating recombinant forms in Northeast Brazil

The extraordinary genetic diversity and immune evasion of human immunodeficiency virus (HIV) pose significant challenges for vaccine development and antiretroviral therapy efficacy. The objective of this study was to characterize the molecular profile of HIV-1 epidemic in Salvador, Bahia, Brazil, determining the genetic subtypes and the presence of antiretroviral resistance mutations. HIV-1 pol DNA sequences from 57 individuals infected with HIV were obtained by PCR, followed by sequencing. The subtypes were determined by phylogenetic analyses and the intersubtype recombination was investigated by bootscanning. The pol subtypes were compared with gag and env subtypes. Antiretroviral susceptibility was evaluated through the Stanford HIV resistance Database. The subtypes frequencies were: 77.2% of subtype B, 1.8% of subtype F1, and 21.0% of BF recombinant forms. Two intergenic and three intragenic BF recombinant patterns were observed. Six (10.5%) viruses were related to CRF28/CRF29, two were related to CRF12 (3.5%), and one (1.8%) was CRF39. Fourteen (24.6%) strains carried one or more mutations associated with at least intermediate resistance: 24.6% had resistance to nucleoside reverse transcriptase inhibitors, 21.0% to non-nucleoside reverse transcriptase inhibitors, and 7% to protease inhibitors. The substitutions I54V (7.0%), M184V (14.0%), and K103N (10.5%) were the most frequent within each class of drugs. The results show a high diversity of BF genotypes and a lower prevalence of major reverse transcriptase and protease drug resistance mutations in Salvador, compared with other regions of Brazil. These findings may contribute to improve treatment strategies of patients infected with HIV-1 from this Brazilian region.