Preformulation studies of EFdA, a novel nucleoside reverse transcriptase inhibitor for HIV prevention

Co-delivery of an HIV prophylactic and contraceptive using PGSU as a long-acting multipurpose prevention technology

OBJECTIVES

Poly(glycerol sebacate) urethane (PGSU) elastomers formulated with 4'-ethynyl-2-fluoro-2'-deoxyadenosine (EFdA), levonorgestrel (LNG), or a combination thereof can function as multipurpose prevention technology implants for prophylaxis against HIV and unintended pregnancies. For these public health challenges, long-acting drug delivery technologies may improve patient experience and adherence. Traditional polymers encounter challenges delivering multiple drugs with dissimilar physiochemical properties. PGSU offers an alternative option that successfully delivers hydrophilic EFdA alongside hydrophobic LNG.

METHODS

This article presents the formulation, design, and characterization of PGSU implants, highlighting the impact of API loading, dimensions, and individual- versus combination-loading on release rates.

RESULTS

Co-delivery of hydrophilic EFdA alongside hydrophobic LNG acted as a porogen to accelerate LNG release. Increasing the surface area of LNG-only implants increased LNG release. All EFdA-LNG, EFdA-only, and LNG-only formulated implants demonstrated low burst release and linear release kinetics over 245 or 122 days studied to date.

CONCLUSION

PGSU co-delivers two APIs for HIV prevention and contraception at therapeutically relevant concentrations in vitro from a single bioresorbable, elastomeric implant. A new long-acting polymer technology, PGSU demonstrates linear-release kinetics, dual delivery of APIs with disparate physiochemical properties, and biocompatibility through long-term subcutaneous implantation. PGSU can potentially meet the demands of complex MPT or fixed-dose combination products, where better solutions can serve and empower patients.

Reservoir-Style Polymeric Drug Delivery Systems: Empirical and Predictive Models for Implant Design

Controlled drug delivery systems can provide sustained release profiles, favorable pharmacokinetics, and improved patient adherence. Here, a reservoir-style implant comprising a biodegradable polymer, poly(ε-caprolactone) (PCL), was developed to deliver drugs subcutaneously. This work addresses a key challenge when designing these implantable drug delivery systems, namely the accurate prediction of drug release profiles when using different formulations or form factors of the implant. The ability to model and predict the release behavior of drugs from an implant based on their physicochemical properties enables rational design and optimization without extensive and laborious in vitro testing. By leveraging experimental observations, we propose a mathematical model that predicts the empirical parameters describing the drug diffusion and partitioning processes based on the physicochemical properties of the drug. We demonstrate that the model enables an adequate fit predicting empirical parameters close to experimental values for various drugs. The model was further used to predict the release performance of new drug formulations from the implant, which aligned with experimental results for implants exhibiting zero-order release kinetics. Thus, the proposed empirical models provide useful tools to inform the implant design to achieve a target release profile.

Transport and Permeation Properties of Dapivirine: Understanding Potential Drug-Drug Interactions

The dapivirine (DPV) vaginal ring was developed by the nonprofit International Partnership for Microbicides (IPM) for reducing the risk of HIV infection. A clinical study (IPM 028) showed that concomitant use of the DPV ring and miconazole (MIC) altered DPV pharmacokinetic profile. In this work, we investigated whether or not DPV transport and permeation contributed to the observed DPV-MIC interaction. Our study evaluated the interaction between DPV and several transporters that are highly expressed in the human female reproductive tract, including MRP1, MRP4, P-gp, BCRP, and ENT1, using vesicular and cellular systems. We also evaluated the impact of DPV/MIC on cellular tight junctions by monitoring transepithelial electrical resistance with the Ussing chamber. Lastly, we evaluated the effect of MIC on DPV permeability across human cervical tissue. Our findings showed that DPV was not a substrate of MRP1, MRP4, P-gp, BCRP, or ENT1 transporters. Additionally, DPV did not inhibit the activity of these transporters. DPV, MIC, and their combination also did not disrupt cellular tight junctions. MIC did not affect DPV tissue permeability but significantly reduced DPV tissue levels. Therefore, our results suggest that the DPV-MIC interaction is not due to these five transporters, altered tight junction integrity, or altered tissue permeability.

Synthesis of nucleotide analogues, EFdA, EdA and EdAP, and the effect of EdAP on hepatitis B virus replication

4'-Ethynyl-2-fluoro-2'-deoxyadenosine (EFdA) and 4'-ethynyl-2'-deoxyadenosine (EdA) are nucleoside analogues which inhibit human immunodeficiency virus type 1 (HIV-1) reverse transcriptase. EdAP, a cyclosaligenyl (cycloSal) phosphate derivative of EdA, inhibits the replication of the influenza A virus. The common structural feature of these compounds is the ethynyl group at the 4'-position. In this study, these nucleoside analogues were prepared by a common synthetic strategy starting from the known 1,2-di-O-acetyl-D-ribofuranose. Biological evaluation of EdAP revealed that this compound reduced hepatitis B virus (HBV) replication dose-dependently without cytotoxicity against host cells tested in this study.

A Multiple Dose Phase 1 Assessment of Rilpivirine Long Acting in a Model of Preexposure Prophylaxis Against HIV

The MWRI-01 study characterized the safety, acceptability, pharmacokinetic (PK), and pharmacodynamic (PD) profile of rilpivirine (RPV) long acting (LA) in a model of preexposure prophylaxis (PrEP). Prospective, open-label Phase 1 study. The safety and acceptability of three repeated doses of RPV LA were monitored. Blood, tissue (rectal, cervical, and vaginal), and biological fluids (vaginal and endocervical) were collected at baseline and at 1- to 2-month intervals throughout the study for PK and PD assessment. Eight women and four men received three intramuscular doses of 1,200 mg of RPV LA given 8 weeks apart. There were a total of 195 adverse events (AEs) reported, of which 138 (70.8%) were Grade 1 and 55 (28.2%) were Grade 2. The most common AE was injection site pain. Geometric mean (90% confidence interval) plasma RPV concentrations at 56 days after the first and third doses were 39 (33-45) ng/mL (female)/29 (17-40) ng/mL (male) and 59 (45-62) ng/mL (female)/40 (30-51) ng/mL (male), respectively. Exposure to RPV LA was associated with significant inhibition of HIV-1_BaL viral replication in the ex vivo rectal explant model (p < .0001) that persisted for up to 4 months after the third dose of RPV LA. In contrast, no viral suppression was seen in cervicovaginal tissue. Multiple dose administration of RPV LA was safe and well tolerated, and was associated with prolonged suppression of viral replication in rectal explant tissue.

Design, Synthesis, and Biological Evaluation of EdAP, a 4'-Ethynyl-2'-Deoxyadenosine 5'-Monophosphate Analog, as a Potent Influenza a Inhibitor

Influenza A viruses leading to infectious respiratory diseases cause seasonal epidemics and sometimes periodic global pandemics. Viral polymerase is an attractive target in inhibiting viral replication, and 4′-ethynyladenosine, which has been reported as a highly potent anti-human immunodeficiency virus (HIV) nucleoside derivative, can work as an anti-influenza agent. Herein, we designed and synthesized a 4′-ethynyl-2′-deoxyadenosine 5′-monophosphate analog called EdAP (5). EdAP exhibited potent inhibition against influenza virus multiplication in Madin–Darby canine kidney (MDCK) cells transfected with human α2-6-sialyltransferase (SIAT1) cDNA and did not show any toxicity toward the cells. Surprisingly, this DNA-type nucleic acid analog (5) inhibited the multiplication of influenza A virus, although influenza virus is an RNA virus that does not generate DNA.

Long-Acting Anti-HIV Drugs Targeting HIV-1 Reverse Transcriptase and Integrase

One of the major factors contributing to HIV-1 drug resistance is suboptimal adherence to combination antiretroviral therapy (cART). Currently, recommended cART for HIV-1 treatment is a three-drug combination, whereas the pre-exposure prophylaxis (PrEP) regimens consist of one or two antivirals. Treatment regimens require adherence to a once or twice (in a subset of patients) daily dose. Long-acting formulations such as injections administered monthly could improve adherence and convenience, and thereby have potential to enhance the chances of expected outcomes, although long-lasting drug concentrations can also contribute to clinical issues like adverse events and development of drug resistance. Globally, two long-acting antivirals have been approved, and fifteen are in clinical trials. More than half of investigational long-acting antivirals target HIV-1 reverse transcriptase (HIV-1 RT) and/or integrase (HIV-1 IN). Here, we discuss the status and potential of long-acting inhibitors, including rilpivirine (RPV), dapivirine (DPV), and 4-ethynyl-2-fluoro-2-deoxyadenosine (EFdA; also known as MK-8591), which target RT, and cabotegravir (CAB), which targets IN. The outcomes of various clinical trials appear quite satisfactory, and the future of long-acting HIV-1 regimens appears bright.

Gastric retention pellets of edaravone with enhanced oral bioavailability: Absorption mechanism, development, and in vitro/in vivo evaluation

Absorption mechanism of edaravone (EDR) was studied to inform the preparation of gastric retention pellets with the aim to enhance its oral bioavailability. Three different models, namely, Caco-2 cells model, in situ single-pass intestinal perfusion model, and everted gut sac model in rats, were employed to characterize the gastrointestinal absorption kinetics of EDR. And it was found that passive transfer plays a vital role for the transport of EDR, and acidic condition is preferable for EDR absorption. Further, it is likely that EDR acts as a substrate for P-glycoprotein and multidrug-resistance protein. And hence, an orally available gastric retention pellets were developed accordingly. Pharmacokinetic experiments performed with rats and beagles showed that the absolute bioavailability of EDR solution and enteric-coated pellets following oral administration were 33.85% ± 2.45% and 7.64% ± 1.03%, indicating that stomach absorption is better than intestinal adsorption for EDR. However, the gastric retention pellets resulted in 68.96% absolute bioavailability and about 200% relative bioavailability in comparison to EDR solution, which was 9 times that of enteric-coated pellets. The present work demonstrates that gastric retention pellets has excellent potential as oral administration route for EDR.

Vaginal Microbicide Film Combinations of Two Reverse Transcriptase Inhibitors, EFdA and CSIC, for the Prevention of HIV-1 Sexual Transmission

PURPOSE

EFdA is a potent nucleoside reverse transcriptase inhibitor (NRTI) with activity against a wide spectrum of wild-type and drug resistant HIV-1 variants. CSIC is a tight-binding non-nucleoside reverse transcriptase inhibitor (NNRTI) with demonstrated anti-HIV properties important for use in topical prevention of HIV transmission. The objective of this study was to develop and characterize film-formulated EFdA and CSIC for use as a female-controlled vaginal microbicide to prevent sexual transmission of HIV.

METHODS

Assessments of EFdA- and CSIC-loaded films included physicochemical characteristics, in vitro cytotoxicity, epithelia integrity studies, compatibility with the normal vaginal Lactobacillus flora and anti-HIV bioactivity evaluations.

RESULTS

No significant change in physicochemical properties or biological activity of the combination films were noted during 3 months storage. In vitro cytotoxicity and bioactivity testing showed that 50% cytotoxic concentration (CC50) of either EFdA or CSIC was several orders of magnitude higher than the 50% effective concentration (EC50) values. Film-formulated EFdA and CSIC combination showed additive inhibitory activity against wild type and drug-resistant variants of HIV. Epithelial integrity studies demonstrated that the combination vaginal film had a much lower toxicity to HEC-1A monolayers compared to that of VCF®, a commercial vaginal film product containing nonoxynol-9. Polarized ectocervical explants showed films with drug alone or in combination were effective at preventing HIV infection.

CONCLUSIONS

Our data suggest that vaginal microbicide films containing a combination of the NRTI EFdA and the NNRTI CSIC have potential to prevent HIV-1 sexual transmission.

In vitro transport characteristics of EFdA, a novel nucleoside reverse transcriptase inhibitor using Caco-2 and MDCKII cell monolayers

4'-Ethynyl-2-fluoro-2'-deoxyadenosine (EFdA) is a novel nucleoside reverse transcriptase inhibitor with a unique mechanism of action and highly potent activity against both wild-type and clinically relevant drug resistant HIV-1 variants. Furthermore, in vivo efficacy and safety evaluations have shown EFdA to be a promising therapeutic candidate for use in the treatment of HIV infection. However, little is known about the pharmacokinetic and biopharmaceutical properties of EFdA. In this study, we evaluated cellular EFdA transport using Caco-2 and Madin-Darby Canine Kidney II (MDCKII) in vitro cell models. Studies using Caco-2 cell monolayers showed that EFdA efflux ratios were >2.0, suggesting that active drug transport mechanisms may play a role in EFdA flux. ABCB1 transporter (PGP1) inhibition was assessed using the acetomethoxy derivate of calcein (calcein-AM) as a fluorescent probe in both wild-type MDCKII and PGP1 overexpressing MDCKII cells. Nonetheless, our data showed that EFdA is not a substrate of PGP1. Additionally, comparative bidirectional flux of EFdA and Lucifer yellow (LY, a well-known paracellular marker) was studied over a range of EFdA concentrations. In MDCKII monolayers, EFdA had an apparent permeability coefficient (Papp) (a-b) of <1×10(-6)cm/s. The Papp values significantly increased in the presence of the paracellular permeability enhancer, indicating that EFdA primarily permeates via the paracellular route.

Probing the molecular mechanism of action of the HIV-1 reverse transcriptase inhibitor 4'-ethynyl-2-fluoro-2'-deoxyadenosine (EFdA) using pre-steady-state kinetics

The novel antiretroviral 4'-ethynyl-2-fluoro-2'-deoxyadenosine (EFdA) is a potent nucleoside HIV-1 reverse transcriptase (RT) inhibitor (NRTI). Unlike other FDA-approved NRTIs, EFdA contains a 3'-hydroxyl. Pre-steady-state kinetics showed RT preferred incorporating EFdA-TP over native dATP. Moreover, RT slowly inserted nucleotides past an EFdA-terminated primer, resulting in delayed chain termination with unaffected fidelity. This is distinct from KP1212, another 3'-hydroxyl-containing RT inhibitor considered to promote viral lethal mutagenesis. New mechanistic features of RT inhibition by EFdA are revealed.

Development of a vaginal delivery film containing EFdA, a novel anti-HIV nucleoside reverse transcriptase inhibitor

The aim of this work was to develop a fast-dissolving film formulation containing EFdA for potential use as a topical vaginal microbicide for prevention of HIV sexual transmission. Solid state compatibility approaches were used to screen commonly used polymers for formulation development. Factorial design and desirability function were used to investigate the effect of two variables, the ratio of the polymers and the concentration of selected plasticizer on four mechanical responses including tensile strength, elongation at break, toughness and elastic modulus for optimization of the film formulation. Assessments of EFdA-loaded films included physicochemical characteristics, in vitro cytotoxicity, epithelia integrity, ex vivo permeability and bioactivity test. The optimal placebo film was composed of PVA, HPMC E5 and propylene glycol (7:3:3, w/w), and its mechanical characteristics were comparable to those of VCF(®) film (a commercial vaginal film product). Permeability studies using human ectocervical explants showed that there was no significant difference in cumulative permeated amount of EFdA between EFdA film and free EFdA. The results of in vitro cytotoxicity and bioactivity testing showed that 50% cytotoxic concentration (CC50) was several orders of magnitude higher than 50% effective concentration (EC50) of EFdA. Furthermore, epithelial integrity study showed that EFdA-loaded film had a much lower toxicity to HEC-1A cell monolayers as compared to VCF(®). Therefore, EFdA-loaded vaginal film may be considered as a promising vaginal microbicide for HIV prevention.