Differential Mechanisms of Tenofovir and Tenofovir Disoproxil Fumarate Cellular Transport and Implications for Topical Preexposure Prophylaxis

Abstract

Intravaginal rings releasing tenofovir (TFV) or its prodrug, tenofovir disoproxil fumarate (TDF), are being evaluated for HIV and herpes simplex virus (HSV) prevention. The current studies were designed to determine the mechanisms of drug accumulation in human vaginal and immune cells. The exposure of vaginal epithelial or T cells to equimolar concentrations of radiolabeled TDF resulted in over 10-fold higher intracellular drug levels than exposure to TFV. Permeability studies demonstrated that TDF, but not TFV, entered cells by passive diffusion. TDF uptake was energy independent but its accumulation followed nonlinear kinetics, and excess unlabeled TDF inhibited radiolabeled TDF uptake in competition studies. The carboxylesterase inhibitor bis-nitrophenyl phosphate reduced TDF uptake, suggesting saturability of intracellular carboxylesterases. In contrast, although TFV uptake was energy dependent, no competition between unlabeled and radiolabeled TFV was observed, and the previously identified transporters, organic anion transporters ( T opical preexposure prophylaxis (PrEP) with tenofovir (TFV)-based drugs could provide a female-initiated method for the prevention of HIV and genital herpes simplex virus (HSV) infections in women (1). Pericoital dosing with 1% vaginal TFV gel reduced HIV acquisition by 39% overall and by 54% in highly adherent women (2, 3) and reduced HSV-2 acquisition by 51% in the CAPRISA 004 trial (4). However, the same gel did not provide protection against HIV in the Vaginal and Oral Interventions to Control the Epidemic (VOICE) and Follow-On Consortium for Tenofovir Studies (FACTS) 001 phase 3 trials, presumably reflecting low adherence (5, 6). Women with detectable TFV in their plasma at the first quarterly visit were less likely to acquire HIV than women with no drug detected (adjusted hazard ratio, 0.34; 95% confidence interval [CI], 0.13 to 0.87; P ϭ 0.02) in a secondary analysis of VOICE data, but the interpretation of this is complex, as women at highest risk for HIV acquisition were less likely to be adherent (5). These findings underscore the need for drugs and delivery systems that mitigate the difficulties associated with adherence.Intravaginal rings (IVRs) designed to deliver TFV and tenofovir disoproxil fumarate (TDF) are currently in early clinical development (7,8). A TDF ring completely protected macaques against 16 weekly intravaginal challenges with simian HIV (8) and also was highly protective in more susceptible, medroxyprogesteronetreated animals (9). Nonhuman primate challenge studies with the TFV IVR have not been published. Consistent with in vitro antiviral studies, 0.3% TDF gel provided significantly greater protection than 1% TFV gel in mice challenged intravaginally with HSV-2 (10). Moreover, the 0.3% TDF gel demonstrated significantly greater protection than 1% TFV gel in mice transgenic for human CD4, CCR5, and cyclin T1 against HIV and HSV-2 (11). These findings may reflect differences in drug pharmacokinetics (PK).The mechanisms of TFV and TDF cellular tran...

Long-acting combination anti-HIV drug suspension enhances and sustains higher drug levels in lymph node cells than in blood cells and plasma

“…At steady state, the intracellular TFV-DP ratio was ∼61% in both human and macaque PBMCs [10–13]. Even with TFV, which exhibits 10- to 100-fold lower cell uptake in vitro [18], our data suggest that TLC-ART101 enhanced intracellular TFV and TFV-DP drug concentrations in NHP PBMCs and LNMCs, and substantially enhanced exposure. Even after weight-based adjustments, TLC-ART101 still provided a several thousand-fold increase in intracellular drug exposure versus TDF or TAF.…”

Vaginal microbiome modulates topical antiretroviral drug pharmacokinetics

“…The efficacy of topical PrEP is impacted by tissue permeability, transport into and out of cells, metabolism, and stability in the complex and dynamic mucosal environment. We previously showed that TFV enters human female genital tract (FGT) epithelial and immune cells by endocytosis, reflecting little or no organic anion transporter (OAT) expression (8)(9)(10). In contrast, the prodrugs TFV disoproxil fumarate (TDF) and TFV alafenamide (TAF) passively diffuse into cells, where they are metabolized by intracellular enzymes to TFV (10,11).…”

“…We previously showed that TFV enters human female genital tract (FGT) epithelial and immune cells by endocytosis, reflecting little or no organic anion transporter (OAT) expression (8)(9)(10). In contrast, the prodrugs TFV disoproxil fumarate (TDF) and TFV alafenamide (TAF) passively diffuse into cells, where they are metabolized by intracellular enzymes to TFV (10,11). The differences in transport mechanisms are reflected by their relative potency; TDF and TAF inhibit HIV-1 and HSV-2 in human cell or explant tissue and murine models at 100-fold lower concentrations than TFV (10)(11)(12)(13)(14)(15).…”

Assessment of Drug Interaction Potential Between the Hepatitis C Virus Direct‐Acting Antiviral Agents Elbasvir/Grazoprevir and the Nucleotide Analog Reverse‐Transcriptase Inhibitor Tenofovir Disoproxil Fumarate

“…Common side effects that are associated with TDF are new‐onset or worsening renal impairment, lactic acidosis from severe hepatomegaly, and decreases in bone mineral density . Following administration, TDF is hydrolyzed by carboxylesterases to tenofovir . Tenofovir is renally eliminated by a combination of glomerular filtration and active tubular secretion .…”

“…9 Following administration, TDF is hydrolyzed by carboxylesterases to tenofovir. 10,11 Tenofovir is renally eliminated by a combination of glomerular filtration and active tubular secretion. 11,12 Tenofovir is a substrate of human organic anion transporter 1 (OAT1) and OAT3 but not of human organic cation transporter 2.…”