Synergistic inhibition of HIV-1 infection by combinations of soluble polyanions with other potential microbicides

Several polyanionic compounds with potential for use as topically applied microbicides to prevent HIV-1 sexual transmission, such as PRO 2000, are currently in phase III clinical efficacy trials. Microbicidal formulations may well comprise combinations of inhibitors to increase potency, reduce dose and minimize problems of HIV-1 resistance. We have therefore evaluated in vitro, the anti-HIV-1 activity of two leading polyanionic microbicides combined with other antiretroviral agents with microbicidal potential. Dextran sulfate (DS) and PRO 2000 were combined with the neutralizing antibody IgG1b12, the peptide-based fusion inhibitor T20, the CCR5 antagonist TAK779 and the cyanobacterial protein cyanovirin-N. Anti-HIV-1 activity was assessed in a single cycle replication assay using pseudoviruses carrying a luciferase reporter gene and the envelope glycoproteins from HIV-1 isolates JR-FL (R5) and HxB2 (X4), against both immortalized and primary CD4+ cell targets. The data were analyzed for synergy using Calcusyn software. Results indicate that PRO 2000 and DS can act synergistically with most inhibitors tested, although the degree of synergy depends on inhibitor concentration and combination. These data provide a rational basis for testing of microbicide combinations in vivo.     

Clinical development of microbicides for the prevention of HIV infection

The HIV/AIDS pandemic continues its spread at a rate of over 15,000 new infections every day. Sexual transmission of HIV-1 is the dominant mode of this pandemic spread. For the first time since the disease emerged in the early 1980s, about half the 42 million people now living with HIV/AIDS worldwide are women. Worldwide, more than 90 percent of all adolescent and adult HIV infections have resulted from heterosexual intercourse. The "feminization" of the pandemic largely driven by the social, economic, and biological factors warrants urgent attention particularly for the adolescent female population. In the absence of an effective prophylactic anti-HIV therapy or vaccine, current efforts are aimed at developing intravaginal/intrarectal topical formulations of anti-HIV agents or microbicides to curb the mucosal and perinatal HIV transmission. Microbicides would provide protection by directly inactivating HIV or preventing HIV from attaching, entering or replicating in susceptible target cells as well as dissemination from target cells present in semen or the host cells that line the vaginal/rectal wall. Thus, ideally, anti-HIV microbicides should be capable of attacking HIV from different angles. In addition, a contraceptive microbicide could help prevent unintended pregnancies worldwide. To be a microbicide, these agents must be safe, effective following vaginal or rectal administration, and should cause minimal or no genital symptoms following long-term repeated usage. A safe and efficacious anti-HIV microbicide is not yet available despite the fact that more than 60 candidate agents have been identified to have in vitro activity against HIV, 18 of which have advanced to clinical testing. Targeting HIV entry has been a favored approach because it is the first step in the process of infection and several readily available anionic polymeric products seem to variably interfere with these processes are the primary candidates for potential microbicides. Formulations of some anionic polymeric antiviral agents have been tested at various doses and various durations for safety, tolerability, and acceptability in Phase I/II clinical trials (vaginal, rectal, or penile studies) in HIV-uninfected and/or HIV-infected populations. Current multicenter Phase I/II safety and Phase II/III efficacy studies that are being conducted or planned in different geographical locations by various special interest groups are designed for rapid clinical development of candidate products. The currently marketed detergent-type spermicide, nonoxynol-9 (N-9), has failed in Phase III clinical trials, due to the drug-induced formation of localized genital lesions that might in fact actually promote virus transmission. Alternative "first-generation" microbicides that have undergone Phase I/II safety and tolerability studies in HIV-uninfected and/or HIV-infected volunteers include polymeric viral fusion inhibitors (dextrin sulfate/Emmelle, carrageenans [PC-213, PC-503, PC-515/Carraguard], cellulose sulfate/Ushercell, polystyrene sulfonate, naphthalene sulfonate [PIC 024-4/PRO 2000/5], acidifying gel [Carbomer 974P/BufferGel], Lactobacillus (L. crispatus) suppository/CTV-05, detergent-type dual-function barriers [ACIDFORM, GEDA Plus, SURETE, Glyminox/C31G/Savvy, Invisible Condom], herbal extracts [Praneem], and viral replication inhibitors [PMPA/Tenofovir]. For majority of these products, no information is available regarding their long-term mucosal safety, carcinogenicity potential, bioavailability, or efficacy following their extended vaginal or rectal exposure. The irritative genitourinary symptoms reported for a number of these first-generation products in Phase I clinical trials implies that the "soft" preclinical endpoints for mucosal safety established for the use and development of vaginal spermicides may not be rigorous enough for vaginal and rectal microbicides because of the efficient sexual tra virus diversity, and genetic environment. It is now apparent that sexually transmitted R5 HIV-1 viruses have less positive charge on their surface compared with the R4 HIV-1 viruses, which may limit the anionic polymers as topical microbicides despite extensive clinical trials. Nevertheless, their ongoing clinical trials, reviewed here, using optimized formulations, and special populations in various geographic locations are paving the way for future rigorous clinical testing of "mechanism-based" broad-spectrum anti-HIV microbicides that are currently under intense development. It is anticipated that future microbicide trials will focus on combination of products capable of attacking HIV life cycle at multiple steps intended to increase efficacy, limit cross-resistance as well as minimize microbicide-induced host toxicity.     

Small-molecule HIV-1 gp120 inhibitors to prevent HIV-1 entry: an emerging opportunity for drug development

The HIV-1 gp120 envelope protein is an essential component in the multi-tiered viral entry process. Despite the overall genetic heterogeneity of the gp120 glycoprotein, the conserved CD4 binding site provides an attractive antiviral target. Recently, increased efforts aimed at the development of inhibitors of gp120 have been reported. This review focuses primarily on small-molecule gp120 inhibitors and discusses key characteristics of compounds that appear to fall within this class. The preclinical profiles of compounds that prevent gp120 from assuming a conformation favorable for CD4 binding are described in this review. In addition, inhibitors possessing some common structural features, including at least one compound that exhibits sub-nanomolar potency in a cell fusion assay are discussed. A series of compounds that were designed to enhance immune responses to virus via alteration of the gp120 conformation after targeting the CD4 binding pocket are also described. The efficacy of gp120 inhibitors as a microbicide to prevent sexual HIV transmission in the rhesus macaque model is discussed. Results suggest that this class of compounds may have value if included in a microbicide cocktail with inhibitors of alternate mechanisms. Importantly, preliminary results from clinical studies of orally administered BMS-488043 demonstrate that antiviral efficacy can be achieved in humans with a CD4-attachment inhibitor that targets gp120.     

Design, synthesis, and antiviral activity of entry inhibitors that target the CD4-binding site of HIV-1

The CD4 binding site on HIV-1 gp120 has been validated as a drug target to prevent HIV-1 entry to cells. Previously, we identified two small molecule inhibitors consisting of a 2,2,6,6-tetramethylpiperidine ring linked by an oxalamide to a p-halide-substituted phenyl group, which target this site, specifically, a cavity termed "Phe43 cavity". Here we use synthetic chemistry, functional assessment, and structure-based analysis to explore variants of each region of these inhibitors for improved antiviral properties. Alterations of the phenyl group and of the oxalamide linker indicated that these regions were close to optimal in the original lead compounds. Design of a series of compounds, where the tetramethylpiperidine ring was replaced with new scaffolds, led to improved antiviral activity. These new scaffolds provide insight into the surface chemistry at the entrance of the cavity and offer additional opportunities by which to optimize further these potential-next-generation therapeutics and microbicides against HIV-1.     

HIV-1 protease inhibitors in development

Several pharmaceutical companies have developed an increasing number of second generation protease inhibitors (PI) during the last few years. Many of these compounds have been in preclinical trials and some are now in clinical use. All drugs in this category have been designed to be well absorbed and overcome the crucial problem of cross-resistance within this class of compounds. Taking into account the rapid occurrence of PI cross-resistance, clinicians who are treating patients with the HIV-1 infection will need new active PIs in the near future. The clinical and antiviral efficacy of the new molecules versus the older PIs will be investigated through comparative trials that are likely to be completed over the next 12 months. These third-generation PIs currently in development will be the subject of our review.     

HIV-1 protease inhibitors in development

Several pharmaceutical companies have developed an increasing number of second generation protease inhibitors (PI) during the last few years. Many of these compounds have been in preclinical trials and some are now in clinical use. All drugs in this category have been designed to be well absorbed and overcome the crucial problem of cross-resistance within this class of compounds. Taking into account the rapid occurrence of PI cross-resistance, clinicians who are treating patients with the HIV-1 infection will need new active PIs in the near future. The clinical and antiviral efficacy of the new molecules versus the older PIs will be investigated through comparative trials that are likely to be completed over the next 12 months. These third-generation PIs currently in development will be the subject of our review.     

Novel inhibitors of the early steps of the HIV-1 life cycle

Considerable advances have been made on compounds that are active as inhibitors of HIV entry and fusion. The discovery of chemokines a few years ago focused the attention on coreceptor inhibitors in addition to fusion and attachment blockers. During the last 5 years, there has been an intense research activity from both private companies and academic institutions to find effective compounds that are capable of inhibiting the initial steps in the HIV life cycle. Some of the presented compounds demonstrated in vitro synergism, thus there is the rationale of their combined use in HIV-infected individuals. Many entry and fusion inhibitors of HIV are being investigated in controlled clinical trials and there are a number of them that are bioavailable as oral formulations. This is an essential feature for an extended use of these compounds with the purpose of ameliorating patients’ adherence to medications; therefore, preventing the development of drug resistance. Among the many compounds that are being investigated, some are in the preclinical arena and others are more advanced in development stages. Overall, the main aim is to establish the action of these compounds on the immune system (e.g., the balance of the system after shutting off CCR5 or CXCR4 coreceptors) and the possible burden of unexplained side effects. This review focuses on the recent developments in this field with a particular attention on promising compounds in preclinical and clinical trials.     

Novel inhibitors of the early steps of the HIV-1 life cycle

Considerable advances have been made on compounds that are active as inhibitors of HIV entry and fusion. The discovery of chemokines a few years ago focused the attention on coreceptor inhibitors in addition to fusion and attachment blockers. During the last 5 years, there has been an intense research activity from both private companies and academic institutions to find effective compounds that are capable of inhibiting the initial steps in the HIV life cycle. Some of the presented compounds demonstrated in vitro synergism, thus there is the rationale of their combined use in HIV-infected individuals. Many entry and fusion inhibitors of HIV are being investigated in controlled clinical trials and there are a number of them that are bioavailable as oral formulations. This is an essential feature for an extended use of these compounds with the purpose of ameliorating patients' adherence to medications; therefore, preventing the development of drug resistance. Among the many compounds that are being investigated, some are in the preclinical arena and others are more advanced in development stages. Overall, the main aim is to establish the action of these compounds on the immune system (e.g., the balance of the system after shutting off CCR5 or CXCR4 coreceptors) and the possible burden of unexplained side effects. This review focuses on the recent developments in this field with a particular attention on promising compounds in preclinical and clinical trials.     

Entry and fusion inhibitors of HIV

Considerable advances have been made towards finding compounds that are active as inhibitors of the entry and fusion of HIV. The discovery of chemokines a few years ago focused the attention on coreceptor inhibitors, in addition to fusion and attachment blockers. During the past 5 years there has been intense research activity, both from private companies and academic institutions, in order to find effective compounds that are able to inhibit the initial steps in the HIV lifecycle. Some of the presented compounds demonstrated in vitro synergism, thus there is rationale for their combined use in HIV-infected individuals. Many entry and fusion inhibitors of HIV are currently under investigation in controlled clinical trials and a number of them are bioavailable as oral formulations. This is an essential feature for the extended use of these compounds with the purpose of ameliorating patients adherence to medications, thus preventing the development of drug resistance. The focus of this review will be on the most recent developments in this field, with particular attention focused on promising compounds in preclinical and clinical trials.     

An update on multipurpose prevention technologies for the prevention of HIV transmission and pregnancy

ABSTRACT

Introduction: Multipurpose Prevention Technologies (MPTs) are designed to address two or more indications from a single product. The overall goal is to prevent unintended pregnancy and transmission of one or more STIs including HIV-1.

Areas covered: The topics covered herein are advances in over the past three years. Advances include development of novel intravaginal rings capable of releasing microbicides to prevent transmission of HIV-1 and unintended pregnancy. These rings include the potential to prevent transmission of more than one STI and unintended pregnancy. There are also gels that can potentially accomplish the same thing. Finally, combination of a drug and barrier device are also covered.

Expert opinion: There has been considerable advance in this field over the past three years. There is one ring currently in a Phase I clinical trial and others are soon to follow. Some of these drug delivery systems are by necessity rather complicated and hence could be prohibitively expensive in the developing world. Conducting multiple clinical trials to support regulatory approval of two or more indications represents a significant barrier. It remains unclear that women will be more motivated to use MPT products than has been observed in recent microbicide-only clinical trials. Despite these challenges, the need for MPTs remain acute hopefully ensuring they will continue to be developed over the coming years.     

Synthesis of new derivatives of inositolcontaining phospholipid dimer analogs as potential inhibitors of virus adsorption

The majority of known agents against human immunodeficiency virus (HIV) are targeted at the virus enzymes protease and integrase but do not prevent HIV entry into host cells. Therefore, it is critical to seek small polyanionic molecules as potential inhibitors of virus adsorption. Inositol-containing phospholipids, which are naturally occurring biologically active compounds that are involved in cell regulation, may be promising lead compounds for antiviral drug design. In the present study, dimer analogs of inositol-containing phospholipids were synthesized using the H-phosphonate method. Carboxymethyl and sulfate derivatives based on them were obtained and proposed as potential virus adsorption inhibitors.