New Class Of Antiretroviral Agents Research Articles

The discovery and design of novel HIV-1 capsid modulators and future perspectives

ABSTRACT Introduction Although combination antiretroviral therapy (cART) has achieved significant success in treating HIV, the emergence of multidrug-resistant viruses and cumulative medication toxicity make it necessary to find new classes of antiretroviral agents with novel mechanisms of action. With high sequence conservation, the HIV-1 capsid (CA) protein has attracted attention as a prospective therapeutic target due to its crucial structural and regulatory functions in the HIV-1 replication cycle. Area covered Herein, the authors provide a cutting-edge overview of current advances in the design and discovery of CA modulators, PF74, GS-6207 and their derivativeswhich targets a therapeutically attractive NTD-CTD interprotomer pocket within the hexameric configuration of HIV-1 CA. The discovery and development of these compounds, and derivatives thereof, have provided valuable information for the design of second-generation CA-targeting antivirals. Expert opinion Despite some successes in designing and discovering HIV-1 CA modulators, more studies are required to decipher which chemical groups confer specific desirable properties. The future of CA-modulating compounds may lie in covalent inhibition and the creation of proteolysis-targeting chimeras (PROTACs). Moreover, biological interrogation of the process of CA uncoating, virus–host interactions, and studies on the lattice-binding restriction factors may improve our knowledge of HIV-1 CA and support the design of new antiviral agents.

HIV-1 integrase tetramers are the antiviral target of pyridine-based allosteric integrase inhibitors.

Allosteric HIV-1 integrase (IN) inhibitors (ALLINIs) are a promising new class of antiretroviral agents that disrupt proper viral maturation by inducing hyper-multimerization of IN. Here we show that lead pyridine-based ALLINI KF116 exhibits striking selectivity for IN tetramers versus lower order protein oligomers. IN structural features that are essential for its functional tetramerization and HIV-1 replication are also critically important for KF116 mediated higher-order IN multimerization. Live cell imaging of single viral particles revealed that KF116 treatment during virion production compromises the tight association of IN with capsid cores during subsequent infection of target cells. We have synthesized the highly active (-)-KF116 enantiomer, which displayed EC50 of ~7 nM against wild type HIV-1 and ~10 fold higher, sub-nM activity against a clinically relevant dolutegravir resistant mutant virus suggesting potential clinical benefits for complementing dolutegravir therapy with pyridine-based ALLINIs.

Identification of novel 2-benzoxazolinone derivatives with specific inhibitory activity against the HIV-1 nucleocapsid protein

In this report, we present a new benzoxazole derivative endowed with inhibitory activity against the HIV-1 nucleocapsid protein (NC). NC is a 55-residue basic protein with nucleic acid chaperone properties, which has emerged as a novel and potential pharmacological target against HIV-1. In the pursuit of novel NC-inhibitor chemotypes, we performed virtual screening and in vitro biological evaluation of a large library of chemical entities. We found that compounds sharing a benzoxazolinone moiety displayed putative inhibitory properties, which we further investigated by considering a series of chemical analogues. This approach provided valuable information on the structure-activity relationships of these compounds and, in the process, demonstrated that their anti-NC activity could be finely tuned by the addition of specific substituents to the initial benzoxazolinone scaffold. This study represents the starting point for the possible development of a new class of antiretroviral agents targeting the HIV-1 NC protein.

Identification of potent maturation inhibitors against HIV-1 clade C.

Antiretroviral therapy has led to a profound improvement in the clinical care of HIV-infected patients. However, drug tolerability and the evolution of drug resistance have limited treatment options for many patients. Maturation inhibitors are a new class of antiretroviral agents for treatment of HIV-1. They act by interfering with the maturation of the virus by blocking the last step in Gag processing: the cleavage of the capsid-spacer peptide 1 (CA-SP1) intermediate to mature CA by the viral protease (PR). The first-in-class maturation inhibitor bevirimat (BVM) failed against a subset of HIV-1 isolates in clinical trials due to polymorphisms present in the CA-SP1 region of the Gag protein. Sequence analysis indicated that these polymorphisms are more common in non-clade B strains of HIV-1 such as HIV-1 clade C. Indeed, BVM was found to be ineffective against HIV-1 clade C molecular clones tested in this study. A number of BVM analogs were synthesized by chemical modifications at the C-28 position to improve its activity. The new BVM analogs displayed potent activity against HIV-1 clade B and C and also reduced infectivity of the virus. This study identifies novel and broadly active BVM analogs that may ultimately demonstrate efficacy in the clinic.

6,7-Dihydroxyisoindolin-1-one and 7,8-Dihydroxy-3,4-Dihydroisoquinolin- 1(2H)-one Based HIV-1 Integrase Inhibitors.

Integrase (IN) is an essential viral enzyme required for HIV-1 replication, which has been targeted by anti-AIDS therapeutics. Integrase strand transfer inhibitors (INSTIs) represent a new class of antiretroviral agents developed for the treatment of HIV-1 infections. Important structural features that are shared by many INSTIs include a coplanar arrangement of three heteroatoms that chelate two catalytic Mg(2+) ions in the IN active site and a linked halophenyl ring that binds in the hydrophobic pocket formed by the complex of IN with viral DNA. We recently reported bicyclic 6,7-dihydroxyoxoisoindolin-1-one-based IN inhibitors. In the current study, we modified these inhibitors in three ways. First, we increased the spacer length between the metalchelating triad and the halophenyl group. Second, we replaced the indoline [5,6] bicycle with a fused dihydroxyisoquinolinones [6,6] ring system. Finally, we prepared bis-6,7-dihydroxyisoindolin-1-one-4-sulfonamides as dimeric HIV-1 IN inhibitors. These new analogues showed low micromolar inhibitory potency in in vitro HIV-1 integrase assays.

Recent Advances in the Development of Small-Molecular Inhibitors Target HIV Integrase-LEDGF/p75 Interaction.

Lens epithelium-derived growth factor (LEDGF/p75) plays an essential role in the HIV-1 replication. It acts by tethering integrase (IN) into the host cellular chromatin. Due to its significance of the IN-LEDGF/p75 interaction affords a novel therapeutic approach for the design of new classes of antiretroviral agents. To date, many small molecules have been found to be the inhibitors of INLEDGF/ p75 interaction. This review summarizes recent advances in the development of potential structure-based IN-LEDGF/p75 interaction inhibitors. The work will be helpful to shed light on the antiretroviral drug development pipeline in the next future.

Structure-activity relationships of a novel capsid targeted inhibitor of HIV-1 replication.

Despite the considerable successes of highly active antiretroviral therapy (HAART) for the treatment of HIV/AIDS, cumulative drug toxicities and the development of multidrug-resistant virus necessitate the search for new classes of antiretroviral agents with novel modes of action. The HIV-1 capsid (CA) protein has been structurally and functionally characterized as a druggable target. We have recently designed a novel small molecule inhibitor I-XW-053 using the hybrid structure based method to block the interface between CA N-terminal domains (NTD–NTD interface) with micromolar affinity. In an effort to optimize and improve the efficacy of I-XW-053, we have developed the structure activity relationship of I-XW-053 compound series using ligand efficiency methods. Fifty-six analogues of I-XW-053 were designed that could be subclassified into four different core domains based on their ligand efficiency values computed as the ratio of binding efficiency (BEI) and surface efficiency (SEI) indices. Compound 34 belonging to subcore-3 showed an 11-fold improvement over I-XW-053 in blocking HIV-1 replication in primary human peripheral blood mononuclear cells (PBMCs). Surface plasmon resonance experiments confirmed the binding of compound 34 to purified HIV-1 CA protein. Molecular docking studies on compound 34 and I-XW-053 to HIV-1 CA protein suggested that they both bind to NTD–NTD interface region but with different binding modes, which was further validated using site-directed mutagenesis studies.

Three Main Mutational Pathways in HIV-2 Lead to High-Level Raltegravir and Elvitegravir Resistance: Implications for Emerging HIV-2 Treatment Regimens

Human immunodeficiency virus type 2 (HIV-2) is intrinsically resistant to non-nucleoside reverse transcriptase inhibitors and exhibits reduced susceptibility to several of the protease inhibitors used for antiretroviral therapy of HIV-1. Thus, there is a pressing need to identify new classes of antiretroviral agents that are active against HIV-2. Although recent data suggest that the integrase strand transfer inhibitors raltegravir and elvitegravir may be beneficial, mutations that are known to confer resistance to these drugs in HIV-1 have been reported in HIV-2 sequences from patients receiving raltegravir-containing regimens. To examine the phenotypic effects of mutations that emerge during raltegravir treatment, we constructed a panel of HIV-2 integrase variants using site-directed mutagenesis and measured the susceptibilities of the mutant strains to raltegravir and elvitegravir in culture. The effects of single and multiple amino acid changes on HIV-2 replication capacity were also evaluated. Our results demonstrate that secondary replacements in the integrase protein play key roles in the development of integrase inhibitor resistance in HIV-2. Collectively, our data define three major mutational pathways to high-level raltegravir and elvitegravir resistance: i) E92Q+Y143C or T97A+Y143C, ii) G140S+Q148R, and iii) E92Q+N155H. These findings preclude the sequential use of raltegravir and elvitegravir (or vice versa) for HIV-2 treatment and provide important information for clinical monitoring of integrase inhibitor resistance in HIV-2–infected individuals.

Compensatory mutations rescue the virus replicative capacity of VIRIP-resistant HIV-1

VIRIP has been identified as a highly specific natural inhibitor of HIV-1 that blocks HIV-1 gp41-dependent fusion by interacting with the gp41 fusion peptide. Two analogues of VIRIP (VIR-353 and VIR-576) with a few amino acid changes increase its antiretroviral potency by two orders of magnitude in cell culture. VIR-576 has been shown effective in a phase I/II clinical trial. Resistance to VIRIP and its analogue VIR-353 were generated after long-term passage in cell culture suggesting a high genetic barrier to resistance. Mutations conferring resistance to VIRIP and VIR-353 significantly reduced virus fitness. However, accumulation of additional mutations rescued the replication capacity of the virus while retaining resistance to VIR-353 and full sensitivity to T20. Combinations of VIR-353 and T20 had an additive effect on the inhibition of wild type HIV-1 replication, but only a single agent was active when combinations were tested against T20-resistant HIV-1, suggesting that both gp41 peptides do not interfere with each other in their binding to gp41. Our results provide additional support to the development of a new class of antiretroviral agents targeting gp41-dependent fusion.

Development of Cell-type specific anti-HIV gp120 aptamers for siRNA delivery

The global epidemic of infection by HIV has created an urgent need for new classes of antiretroviral agents. The potent ability of small interfering (si)RNAs to inhibit the expression of complementary RNA transcripts is being exploited as a new class of therapeutics for a variety of diseases including HIV. Many previous reports have shown that novel RNAi-based anti-HIV/AIDS therapeutic strategies have considerable promise; however, a key obstacle to the successful therapeutic application and clinical translation of siRNAs is efficient delivery. Particularly, considering the safety and efficacy of RNAi-based therapeutics, it is highly desirable to develop a targeted intracellular siRNA delivery approach to specific cell populations or tissues. The HIV-1 gp120 protein, a glycoprotein envelope on the surface of HIV-1, plays an important role in viral entry into CD4 cells. The interaction of gp120 and CD4 that triggers HIV-1 entry and initiates cell fusion has been validated as a clinically relevant anti-viral strategy for drug discovery. Herein, we firstly discuss the selection and identification of 2'-F modified anti-HIV gp120 RNA aptamers. Using a conventional nitrocellulose filter SELEX method, several new aptamers with nanomolar affinity were isolated from a 50 random nt RNA library. In order to successfully obtain bound species with higher affinity, the selection stringency is carefully controlled by adjusting the conditions. The selected aptamers can specifically bind and be rapidly internalized into cells expressing the HIV-1 envelope protein. Additionally, the aptamers alone can neutralize HIV-1 infectivity. Based upon the best aptamer A-1, we also create a novel dual inhibitory function anti-gp120 aptamer-siRNA chimera in which both the aptamer and the siRNA portions have potent anti-HIV activities. Further, we utilize the gp120 aptamer-siRNA chimeras for cell-type specific delivery of the siRNA into HIV-1 infected cells. This dual function chimera shows considerable potential for combining various nucleic acid therapeutic agents (aptamer and siRNA) in suppressing HIV-1 infection, making the aptamer-siRNA chimeras attractive therapeutic candidates for patients failing highly active antiretroviral therapy (HAART).

Development of Cell-type specific anti-HIV gp120 aptamers for siRNA delivery

The global epidemic of infection by HIV has created an urgent need for new classes of antiretroviral agents. The potent ability of small interfering (si)RNAs to inhibit the expression of complementary RNA transcripts is being exploited as a new class of therapeutics for a variety of diseases including HIV. Many previous reports have shown that novel RNAi-based anti-HIV/AIDS therapeutic strategies have considerable promise; however, a key obstacle to the successful therapeutic application and clinical translation of siRNAs is efficient delivery. Particularly, considering the safety and efficacy of RNAi-based therapeutics, it is highly desirable to develop a targeted intracellular siRNA delivery approach to specific cell populations or tissues. The HIV-1 gp120 protein, a glycoprotein envelope on the surface of HIV-1, plays an important role in viral entry into CD4 cells. The interaction of gp120 and CD4 that triggers HIV-1 entry and initiates cell fusion has been validated as a clinically relevant anti-viral strategy for drug discovery. Herein, we firstly discuss the selection and identification of 2'-F modified anti-HIV gp120 RNA aptamers. Using a conventional nitrocellulose filter SELEX method, several new aptamers with nanomolar affinity were isolated from a 50 random nt RNA library. In order to successfully obtain bound species with higher affinity, the selection stringency is carefully controlled by adjusting the conditions. The selected aptamers can specifically bind and be rapidly internalized into cells expressing the HIV-1 envelope protein. Additionally, the aptamers alone can neutralize HIV-1 infectivity. Based upon the best aptamer A-1, we also create a novel dual inhibitory function anti-gp120 aptamer-siRNA chimera in which both the aptamer and the siRNA portions have potent anti-HIV activities. Further, we utilize the gp120 aptamer-siRNA chimeras for cell-type specific delivery of the siRNA into HIV-1 infected cells. This dual function chimera shows considerable potential for combining various nucleic acid therapeutic agents (aptamer and siRNA) in suppressing HIV-1 infection, making the aptamer-siRNA chimeras attractive therapeutic candidates for patients failing highly active antiretroviral therapy (HAART).

Enfuvirtide injection site reactions: A clinical and histopathological appraisal

Enfuvirtide was the first of a new class of antiretroviral agents termed 'fusion inhibitors' used for the treatment of HIV-1 infection. Enfuvirtide is administered subcutaneously and injection site reactions (ISR) are commonplace (98%). The aim of this study was to analyse in detail the histopathological changes associated with striking ISR seen in four patients. Biopsies were obtained at various times post-injection and were reviewed histologically. The changes in epidermal, dermal and subcutaneous connective tissue and the presence and nature of the inflammatory cellular infiltrate were noted. An immunohistochemical assessment was undertaken. All biopsy specimens demonstrated striking changes in the dermal connective tissue. Alteration in collagen was the most prominent feature and resembled a morphoea/scleroderma-like process. These changes persisted well beyond cessation of enfuvirtide (>1 year). The relative populations of dermal dendritic cells (DDC) (types 1 (Factor XIIIa) and 2 (CD34+)) were analysed and a reciprocal relationship between DDC subpopulations was observed akin to that observed in other sclerosing and fibrosing conditions. This study details histopathological changes associated with enfuvirtide ISR. We postulate that changes in DDC populations may contribute to the pathogenesis of the sclerotic process observed with enfuvirtide ISR.

HIV-1 Entry, Inhibitors, and Resistance

Entry inhibitors represent a new class of antiretroviral agents for the treatment of infection with HIV-1. While resistance to other HIV drug classes has been well described, resistance to this new class is still ill defined despite considerable clinical use. Several potential mechanisms have been proposed: tropism switching (utilization of CXCR4 instead of CCR5 for entry), increased affinity for the coreceptor, increased rate of virus entry into host cells, and utilization of inhibitor-bound receptor for entry. In this review we will address the development of attachment, fusion, and coreceptor entry inhibitors and explore recent studies describing potential mechanisms of resistance.

Maraviroc for Previously Treated Patients With R5 HIV-1 Infection

Gulick RM, Lalezari J, Goodrich J, et al. N Engl J Med . 2008;359(14):1429–1441 PURPOSE OF THE STUDY. Although there are now >20 anti-HIV medications, new agents are still needed. HIV drug resistance is highly prevalent and 15% of newly infected patients in the United States have drug-resistant virus. In addition, enhanced safety and tolerability and improved convenience would enhance adherence to antiretroviral regimens. HIV uses 1 of 2 chemokine receptors, in addition to CD4, to gain entry into a cell, chemokine receptor 5 (CCR5) and α-chemokine receptor 4 (CXCR4). HIV that uses CCR5 is the primary type of virus that is transmitted through sexual or perinatal exposure. CCR5 antagonists are a new class of antiretroviral agents. The purpose of this study was to evaluate a CCR5 antagonist, maraviroc, …

Integrase inhibitors in salvage therapy regimens for HIV-1 infection

To review current knowledge and the role of integrase inhibitors in the setting of HIV salvage therapy. We will discuss results from recent studies and literature and comment on the potential for integrase inhibitors in defined clinical settings. Raltegravir has been studied most intensively in treatment-experienced patients and is the first integrase inhibitor that has been licensed for use in this patient group. Most studies have shown good tolerability data and very potent virus suppression. In patients with limited treatment options, switching from enfuvirtide appears to be well tolerated, whereas switching from a protease inhibitor-based regimen may increase the rates of viral failure. Elvitegravir also showed good results in early phase clinical trials and is currently undergoing phase III clinical trials. Given that integrase inhibitors belong to a new class of antiretroviral agents with a diverse drug resistance profile, and are active against both chemokine (C-C motif) receptor 5 and chemokine (C-X-C motif) receptor 4 strains, they are exciting additions to salvage therapy regimen. Raltegravir and elvitegravir are metabolized via different pathways, which will affect their respective use. The major limitation for the use of integrase inhibitors is a potentially low threshold for viral drug resistance, so functional monotherapy must be avoided.

Susceptibility of Human Immunodeficiency Virus Type 1 to the Maturation Inhibitor Bevirimat Is Modulated by Baseline Polymorphisms in Gag Spacer Peptide 1

In this study, we evaluated baseline susceptibility to bevirimat (BVM), the first in a new class of antiretroviral agents, maturation inhibitors. We evaluated susceptibility to BVM by complete gag genotypic and phenotypic testing of 20 patient-derived human immunodeficiency virus type 1 isolates and 20 site-directed mutants. We found that reduced BVM susceptibility was associated with naturally occurring polymorphisms at positions 6, 7, and 8 in Gag spacer peptide 1.

Maraviroc: a new CCR5 antagonist

Maraviroc is a small molecule and a member of a new class of antiretroviral compounds known as CCR5 antagonists, which block R5-tropic HIV entry into CD4 cells. HIV entry into the cell requires binding to a CD4 molecule and, in the majority of cases, to a coreceptor, either chemokine coreceptor 4 (CXCR4) or 5 (CCR5). In August 2007, the US FDA approved maraviroc for use in combination with other antiretroviral agents for treatment-experienced adults infected with CCR5-tropic HIV-1 only and who have evidence of viral replication. Maraviroc prevents the virus from entering uninfected cells by blocking the CCR5 coreceptor. Maraviroc has two dose formulations (150- and 300-mg tablets) and can be taken with or without food. The dosing recommendations are based on concomitant medications due to drug interactions. It is excreted primarily in the feces, with approximately 25% via urine. The safety and efficacy of maraviroc have not been established in pregnant women or pediatric patients. Maraviroc has been shown to achieve an undetectable HIV-1 RNA level in clinically advanced, class 3 antiretroviral treatment-experienced adults with evidence of CCR5-tropic HIV-1 replication despite ongoing antiretroviral therapy. It is generally well tolerated and its development is responding to a desperate need for new classes of antiretroviral agents that can target novel steps of the HIV lifecycle and do not share crossresistance with currently available therapy.

Maraviroc for Previously Treated Patients with R5 HIV-1 Infection

CC chemokine receptor 5 antagonists are a new class of antiretroviral agents. We conducted two double-blind, placebo-controlled, phase 3 studies--Maraviroc versus Optimized Therapy in Viremic Antiretroviral Treatment-Experienced Patients (MOTIVATE) 1 and MOTIVATE 2--with patients who had R5 human immunodeficiency virus type 1 (HIV-1) only. They had been treated with or had resistance to three antiretroviral-drug classes and had HIV-1 RNA levels of more than 5000 copies per milliliter. The patients were randomly assigned to one of three antiretroviral regimens consisting of maraviroc once daily, maraviroc twice daily, or placebo, each of which included optimized background therapy (OBT) based on treatment history and drug-resistance testing. Safety and efficacy were assessed after 48 weeks. A total of 1049 patients received the randomly assigned study drug; the mean baseline HIV-1 RNA level was 72,400 copies per milliliter, and the median CD4 cell count was 169 per cubic millimeter. At 48 weeks, in both studies, the mean change in HIV-1 RNA from baseline was greater with maraviroc than with placebo: -1.66 and -1.82 log(10) copies per milliliter with the once-daily and twice-daily regimens, respectively, versus -0.80 with placebo in MOTIVATE 1, and -1.72 and -1.87 log(10) copies per milliliter, respectively, versus -0.76 with placebo in MOTIVATE 2. More patients receiving maraviroc once or twice daily had HIV-1 RNA levels of less than 50 copies per milliliter (42% and 47%, respectively, vs. 16% in the placebo group in MOTIVATE 1; 45% in both maraviroc groups vs. 18% in MOTIVATE 2; P<0.001 for both comparisons in each study). The change from baseline in CD4 counts was also greater with maraviroc once or twice daily than with placebo (increases of 113 and 122 per cubic millimeter, respectively, vs. 54 in MOTIVATE 1; increases of 122 and 128 per cubic millimeter, respectively, vs. 69 in MOTIVATE 2; P<0.001 for both comparisons in each study). Frequencies of adverse events were similar among the groups. Maraviroc, as compared with placebo, resulted in significantly greater suppression of HIV-1 and greater increases in CD4 cell counts at 48 weeks in previously treated patients with R5 HIV-1 who were receiving OBT. (ClinicalTrials.gov numbers, NCT00098306 and NCT00098722.)

Reviews Of Anti‐infective Agents: Maraviroc: The First of a New Class of Antiretroviral Agents

Maraviroc is the first US Food and Drug Administration-approved drug from a new class of antiretroviral agents that targets a host protein, the chemokine receptor CCR5, rather than a viral target. Binding of maraviroc to this cell-surface protein results in blocking human immunodeficiency virus type 1 (HIV-1) attachment to the coreceptor and prevents the virus from entering CD4+ cells. In this review, we include the details of the discoveries that led to the development of this drug. The drug's pharmacology, including pharmacokinetics and drug interactions, is discussed, as are the clinical efficacy studies that led to licensure. HIV-1 mechanisms of resistance to maraviroc, assays to determine viral coreceptor use (tropism), drug safety, and clinical use of maraviroc are discussed at length.

Integrase polymorphism and HIV-1 group O diversity

Integrase polymorphism and HIV-1 group O diversity