Topical Microbicides and HIV Prevention in the Female Genital Tract

Worldwide, HIV disproportionately affects women who are often unable to negotiate traditional HIV preventive strategies such as condoms. In the absence of an effective vaccine or cure, chemoprophylaxis may be a valuable self-initiated alternative. Topical microbicides have been investigated as one such option. The first generation topical microbicides were non-specific, broad-spectrum antimicrobial agents, including surfactants, polyanions, and acid buffering gels, that generally exhibited contraceptive properties. After extensive clinical study, none prevented HIV infection, and their development was abandoned. Second generation topical microbicides include agents with selective mechanisms of antiviral activity. Most are currently being used for, or have previously been explored as, drugs for treatment of HIV. The most advanced of these is tenofovir 1% gel: the first topical agent shown to significantly reduce HIV infection by 39% compared to placebo. This review summarizes the evolution of topical microbicides for HIV chemoprophylaxis, highlights important concepts learned, and offers current and future considerations for this area of research

Pharmacokinetics of Antiretrovirals in Genital Secretions and Anatomic Sites of HIV Transmission: Implications for HIV Prevention

The incidence of HIV remains alarmingly high in many parts of the world. Prophylactic use of antiretrovirals, capable of concentrating in the anatomical sites of transmission, may reduce the risk of infection after an unprotected sexual exposure. To date, orally and topically administered antiretrovirals have exhibited variable success in preventing HIV transmission in large-scale clinical trials. Antiretroviral mucosal pharmacokinetics may help explain the outcomes of these investigations. Penetration and accumulation of antiretrovirals into sites of transmission can influence dosing strategies and pre-exposure prophylaxis clinical trial design. Antiretroviral tissue distribution varies widely within and between drug classes, attributed in part to their physicochemical properties and tissue-specific drug transporter expression. Nucleoside (-tide) reverse transcriptase inhibitors, the CCR5 antagonist maraviroc, and the integrase inhibitor raltegravir demonstrate the highest penetration into the male and female reproductive tracts and colorectal tissue relative to blood. This review will describe antiretroviral exposure in anatomic sites of transmission, and place these findings in context with the prevention of HIV and the efficacy of pre-exposure prophylactic strategies

Formulation, pharmacokinetics and pharmacodynamics of topical microbicides

The development of safe topical microbicides that effectively prevent human immunodeficiency virus (HIV) infection is a major goal in curbing the human immunodeficiency virus pandemic. A number of past failures resulting from mucosal toxicity or lack of efficacy have informed the field. Products that caused toxicity to the female genital tract mucosa, and thereby increased the likelihood of HIV acquisition, included nonoxynol 9, cellulose sulfate, and C31 G vaginal gel Savvy®. Topical products that were ineffective in preventing HIV infection include BufferGel®, Carraguard®, and PRO 2000®. Antiretroviral drugs such as tenofovir and dapivirine formulated into microbicide products have shown promise, but there is much to learn about ideal product formulation and acceptability, and drug distribution and disposition (pharmacokinetics). Current formulations for water-soluble molecules include vaginally or rectally applied gels, vaginal rings, films and tablets. Dosing strategies (e.g. coitally dependent or independent) will be based on the pharmacokinetics of the active ingredient and the tolerance for less than perfect adherence

Clinical Pharmacokinetic, Pharmacodynamic and Drug-Interaction Profile of the Integrase Inhibitor Dolutegravir

Dolutegravir is a second generation integrase strand transfer inhibitor (INSTI) currently under review by the US FDA for marketing approval. Dolutegravir’s in vitro, protein adjusted 90% inhibitory concentration (IC90) for wild-type virus is 0.064 μg/ml, and it retains in vitro anti-HIV 1 activity across a broad range of viral phenotypes known to confer resistance to the currently marketed INSTIs, raltegravir and elvitegravir. Dolutegravir has a half-life (t½) of 13 to 14 hours and maintains concentrations over the in vitro, protein adjusted IC90 for more than 30 hours following a single dose. Additionally, dolutegravir has comparatively low intersubject variability compared to raltegravir and elvitegravir. A plasma exposure-response relationship has been well described, with antiviral activity strongly correlating to trough concentration (Ctrough) values. Phase III trials have assessed the antiviral activity of dolutegravir compared with efavirenz and raltegravir in antiretroviral (ARV)-naïve patients and found dolutegravir to achieve more rapid and sustained virologic suppression in both instances. Additionally, studies of dolutegravir activity in patients with known INSTI-resistant mutations have been favorable, indicating that dolutegravir retains activity in a variety of INSTI resistant phenotypes. Much like currently marketed INSTIs, dolutegravir is very well tolerated. Because dolutegravir inhibits the renal transporter, organic cation transporter (OCT) 2, reduced tubular secretion of creatinine leads to non-progressive increases in serum creatinine. These serum creatinine increases have not been associated with decreased glomerular filtration rate or progressive renal impairment. Dolutegravir’s major and minor metabolic pathways are UDP glucuronosyltransferase (UGT)1A1 and cytochrome (CYP)3A4, respectively, and it neither induces nor inhibits CYP isozymes. Thus dolutegravir has a modest drug interaction profile. However, antacids significantly decrease dolutegravir plasma exposure and should be separated by 2 hours before, or 6 hours after, a dolutegravir dose. In summary, dolutegravir is the first of the second generation INSTIs, which exhibits a predictable pharmacokinetic profile and a well-defined exposure-response relationship. Dolutegravir retains activity despite the presence of some class resistant mutations and achieves rapid and sustained virologic suppression in ARV-naïve and -experienced patients. Clinically dolutegravir is poised to become a commonly used component of antiretroviral regimens

An accurate and precise high-performance liquid chromatography method for the rapid quantification of the novel HIV integrase inhibitor raltegravir in human blood plasma after solid phase extraction

The quantification of the HIV integrase inhibitor raltegravir in blood plasma is described using solid phase extraction (SPE) coupled with an accurate high-performance liquid chromatography assay with ultraviolet (UV) detection. The method was validated over the range of 20–10,000ng/mL using simple sample preparation and chromatography. The SPE method was optimized to be selective and highly efficient. The buffer’s ionic strength and pH were optimized for retaining RAL and the internal standard on the column, the percentage of methanol was optimized in the cleaning step to remove unwanted plasma contaminants, and the type and amount of acid was optimized for complete elution of the compounds. This method has no interference with other potentially co-administered antiretrovirals or common drugs. Average recoveries for the extraction method were consistently high: 90% for raltegravir and 90% for the internal standard diazepam. This method was found to be accurate and precise. Within day (n=6) and between day (n=18) accuracies ranged from 97.5% to 104.4%. Within-day (n=6) and between-day (n=18) precision ranged from 1.4% to 3.8%, and from 2.4% to 7.9%, respectively. This is the first published method to use simple UV technology and reliable SPE extraction methodology for the quantification of raltegravir in human plasma. This method can be easily implemented in most bioanalytical laboratories

Drug Interactions with New and Investigational Antiretrovirals

More than 20 individual and fixed-dose combinations of antiretrovirals are approved for the treatment of human immunodeficiency virus (HIV) infection. However, owing to the ongoing limitations of drug resistance and adverse effects, new treatment options are still required. A number of promising new agents in existing or new drug classes are in development or have recently been approved by the US FDA. Since these agents will be used in combination with other new and existing antiretrovirals, understanding the potential for drug interactions between these compounds is critical to their appropriate use. This article summarizes the drug interaction potential of new and investigational protease inhibitors (darunavir), non-nucleoside reverse transcriptase inhibitors (etravirine and rilpivirine), chemokine receptor antagonists (maraviroc, vicriviroc and INCB 9471), integrase inhibitors (raltegravir and elvitegravir) and maturation inhibitors (bevirimat)

Pharmacology of HIV integrase inhibitors

The purpose of this paper is to review recent and relevant pharmacology data for three HIV integrase inhibitors: raltegravir (marketed), dolutegravir and elvitegravir (both in Phase III drug development)

Quantifying the HIV-1 integrase inhibitor raltegravir in female genital tract secretions using high-performance liquid chromatography with ultraviolet detection

Understanding the pharmacokinetics of drugs in peripheral body compartments, such as the genital tract, is particularly important in the infectious diseases arena. However, extracting drugs from small volumes of viscous, proteinacious substances like cervicovaginal fluid is particularly challenging. The goal of this study was to develop a method to quantify raltegravir, an HIV-1 integrase inhibitor, in the female genital tract. The method included sample preparation with perchloric acid followed by solid-phase extraction, separation with reverse-phase high-performance liquid chromatography, and detection with an ultraviolet wavelength of 218 nm. The method was linear from 0.05 to 10.0 mg/L, with minimal endogenous interference. The method was accurate (1.2–11.0% deviation) and precise (1.1–12.6% CV) for both within and between-day analyses. The ability to detect raltegravir in the female genital tract is essential for future investigations of raltegravir as an agent for prevention of HIV acquisition, and this method will be used for clinical studies further evaluating pharmacokinetic–pharmacodynamic relationships in this body compartment

Antiretroviral Pharmacology in Mucosal Tissues

Strategies to prevent HIV infection using pre-exposure prophylaxis (PrEP) are required to curtail the HIV pandemic. The mucosal tissues of the genital and rectal tracts play a critical role in HIV acquisition, but antiretroviral (ARV) disposition and correlates of efficacy within these tissues are not well understood. Pre-clinical and clinical strategies to describe ARV pharmacokinetic-pharmacodynamic relationships (PK/PD) within mucosal tissues are currently being investigated. In this review, we summarize the physiochemical and biologic factors influencing ARV tissue exposure. Further, we discuss the necessary steps to generate relevant PK/PD data and the challenges associated with this process. Finally, we suggest how pre-clinical and clinical data might be practically translated into optimal PrEP dosing strategies for clinical trials testing using mathematical modeling and simulation

Sex Hormones Regulate Tenofovir-Diphosphate in Female Reproductive Tract Cells in Culture

The conflicting results of recent pre-exposure prophylaxis (PrEP) trials utilizing tenofovir (TFV) to prevent HIV infection in women led us to evaluate the accumulation of intracellular TFV-diphosphate (TFV-DP) in cells from the female reproductive tract (FRT) and whether sex hormones influence the presence of TFV-DP in these cells. Following incubation with TFV, isolated epithelial cells, fibroblasts, CD4+ T cells and CD14+ cells from the FRT as well as blood CD4+ T cells and monocyte-derived macrophages convert TFV to TFV-DP. Unexpectedly, we found that TFV-DP concentrations (fmol/million cells) vary significantly with the cell type analyzed and the site within the FRT. Epithelial cells had 5-fold higher TFV-DP concentrations than fibroblasts; endometrial epithelial cells had higher TFV-DP concentrations than cells from the ectocervix. Epithelial cells had 125-fold higher TFV-DP concentrations than FRT CD4+ T cells, which were comparable to that measured in peripheral blood CD4+ T cells. These findings suggest the existence of a TFV-DP gradient in the FRT where epithelial cells \u3e fibroblasts \u3e CD4+ T cells and macrophages. In other studies, estradiol increased TFV-DP concentrations in endometrial and endocervical/ectocervical epithelial cells, but had no effect on fibroblasts or CD4+ T cells from FRT tissues. In contrast, progesterone alone and in combination with estradiol decreased TFV-DP concentrations in FRT CD4+ T cells. Our results suggest that epithelial cells and fibroblasts are a repository of TFV-DP that is under hormonal control. These cells might act either as a sink to decrease TFV availability to CD4+ T cells and macrophages in the FRT, or upon conversion of TFV-DP to TFV increase TFV availability to HIV-target cells. In summary, these results indicate that intracellular TFV-DP varies with cell type and location in the FRT and demonstrate that estradiol and/or progesterone regulate the intracellular concentrations of TFV-DP in FRT epithelial cells and CD4+ T cells