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

Islatravir: evaluation of clinical development for HIV and HBV

INTRODUCTION

Islatravir (ISL) is a nucleoside reverse transcriptase translocation inhibitor (NRTTI) that inhibits HIV RT through multiple mechanisms. Contrary to all approved NtRTIs, islatravir retains a 3'OH group. In vitro and clinical data show that ISL is an ultrapotent investigational drug with high tolerability.

AREAS COVERED

The historical development of islatravir and its mechanisms of HIV and HBV inhibition and resistance are covered. Additionally, the outcomes of Phase I and Phase II clinical trials are discussed.

EXPERT OPINION

Current first-line antiretroviral therapy, preexposure, and postexposure prophylactic interventions are highly effective in maintaining low or undetectable viral load. Despite these measures, an unusually high rate of new infections every year warrants developing novel antivirals that can suppress drug-resistant HIV and improve compliance. ISL, an NRTTI once deemed a long-acting drug, was placed on a clinical hold. The outcome of ongoing clinical trials with a reduced ISL dose will decide its future clinical application. Additionally, MK-8527, which inhibits HIV via same mechanism as that of ISL may supersede ISL. Data on ISL inhibition of HBV are scarce, and preclinical data show dramatically lower ISL efficacy against HBV than currently preferred nucleos(t)ide drugs, indicating that ISL may not be a potent anti-HBV drug.

Evaluating Islatravir Administered Via Microneedle Array Patch for Long-Acting HIV Pre-exposure Prophylaxis Using Physiologically Based Pharmacokinetic Modelling

BACKGROUND AND OBJECTIVES

Technologies for long-acting administration of antiretrovirals (ARVs) for the prevention and treatment of HIV are at the forefront of research initiatives aiming to tackle issues surrounding drug adherence with the current standard of once-daily oral administration. Islatravir (ISL) is an emerging ARV that shows promising characteristics for long-acting prevention and treatment both orally as well as through alternative routes of administration. Microneedle array patches (MAPs) are a pain-free and discreet transdermal delivery technology that offer extended-release administration of nanoparticulate drugs. This study aimed to utilise physiologically based pharmacokinetic (PBPK) modelling to predict the pharmacokinetics resulting from ISL administered via MAP and to identify key MAP characteristics required to sustain effective concentrations over extended dosing intervals.

METHODS

A PBPK model describing the conversion of ISL to ISL-triphosphate (ISL-TP) and its whole-body disposition was developed and verified against observed clinical data for orally administered ISL in healthy adults. An intradermal PBPK model was integrated with the ISL PBPK model to predict the dose and nanoparticle release rate required for MAP administration strategies capable of achieving a minimum ISL-TP target concentration of 0.05 pmol/10⁶ PBMCs over extended dosing intervals. MAP design was limited to a maximum therapeutic area of 20 cm² with a dose loading of 4.09 mg/cm² and a minimum duration of 3 months. Due to the lack of available clinical data, a range of nanoparticle release rates and MAP bioavailability scenarios were simulated to provide an overview of potential clinical outcomes.

RESULTS

The ISL PBPK model was successfully verified, with predicted vs observed ratios falling within 0.5-2-fold. ISL MAP doses ranging from 15 to 80 mg were predicted to sustain ISL-TP concentrations above the minimum target concentration at 3, 6 and 12 months after administration. Nanoparticle release rate and MAP bioavailability were found to have a major impact on whether dosing strategies achieved the criteria. Minimum doses of 15 mg and 60 mg with a nanoparticle release rate of 0.0005 h^-1 and bioavailability ranging from 25 to 100% were predicted to achieve effective ISL-TP concentrations up to 3 and 6 months, respectively. Doses of 15 mg and 30 mg with a nanoparticle release rate of 0.0005 h^-1 were also able to attain the target concentration up to 6 months after MAP administration, albeit with a minimum bioavailability of 75% and 50%, respectively. Furthermore, when simulating a bioavailability of 100%, an 80 mg ISL MAP was predicted to sustain ISL-TP concentrations above the minimum target concentration up to 12 months after administration.

CONCLUSIONS

The ISL PBPK model successfully predicted ISL and ISL-TP pharmacokinetics across a range of orally administered regimens. The integrated intradermal PBPK model outlined optimal MAP dose and nanoparticle release rates for effective ISL-TP concentrations up to 12 months, providing justification for further investigation of ISL as a candidate for MAP administration.

Two Dipeptide-Bound Pyrralines with Ile or Ala: A Study on Their Synthesis, Transport across Caco-2 Cell Monolayers, and Interaction with Aminopeptidase N

In this study, pyrralylisoleucine (Pyrr-Ile) and pyrralylalanine (Pyrr-Ala), two dipeptide-bound pyrralines with different C-termini were synthesized as the representatives of dietary advanced glycation end products (dAGEs). The structures of Pyrr-Ile and Pyrr-Ala were characterized by high-resolution mass spectrometry, nuclear magnetic resonance, and Fourier transform infrared spectroscopy. Then, the transport of Pyrr-Ile and Pyrr-Ala across intestinal epithelial cells was investigated using Caco-2 cell monolayers, and their interaction with aminopeptidase N (APN) was analyzed. The results showed that the apparent permeability coefficient (P_app) of Pyrr-Ala was (14.1 ± 2.26) × 10^-7 cm·s^-1 calculated by free pyrraline, while the P_app values of Pyrr-Ile were (32.4 ± 5.35) × 10^-7 and (19.1 ± 1.46) × 10^-7 cm·s^-1 when they were, respectively, calculated according to their dipeptide-bound or free form. Both Pyrr-Ala and Pyrr-Ile were potential substrates of APN, and their hydrolysis by APN may make the intact transmembrane transport of Pyrr-Ala and Pyrr-Ile more difficult, especially for Pyrr-Ala. Besides, the occurrence of product inhibition in hydrolysis of Pyrr-Ile was possible. Pyrr-Ile and Pyrr-Ala were different in P_app values and transport forms, which suggested that the C-terminus may play an important role in their transport across the Caco-2 cell monolayers. In addition, the results highlight the intact transmembrane transport of dipeptide-bound pyrraline.

Avoiding Drug Resistance in HIV Reverse Transcriptase

HIV reverse transcriptase (RT) is an enzyme that plays a major role in the replication cycle of HIV and has been a key target of anti-HIV drug development efforts. Because of the high genetic diversity of the virus, mutations in RT can impart resistance to various RT inhibitors. As the prevalence of drug resistance mutations is on the rise, it is necessary to design strategies that will lead to drugs less susceptible to resistance. Here we provide an in-depth review of HIV reverse transcriptase, current RT inhibitors, novel RT inhibitors, and mechanisms of drug resistance. We also present novel strategies that can be useful to overcome RT's ability to escape therapies through drug resistance. While resistance may not be completely avoidable, designing drugs based on the strategies and principles discussed in this review could decrease the prevalence of drug resistance.

Nanoparticles Mediating the Sustained Puerarin Release Facilitate Improved Brain Delivery to Treat Parkinson's Disease

Recent work has highlighted the potential of puerarin (PU) as a valuable compound to treat Parkinson's disease (PD), but its undesirable water solubility and bioavailability have constrained its utility. In this study, we sought to develop nanoparticles (NPs) that could be used to encapsulate PU, thereby extending its in vivo half-life and improving its bioavailability and accumulation in the brain to treat the symptoms of PD. We prepared spherical NPs (88.36 ± 1.67 nm) from six-armed star-shaped poly(lactide-co-glycolide) (6-s-PLGA) NPs that were used to encapsulate PU (PU-NPs) with 89.52 ± 1.74% encapsulation efficiency, 42.97 ± 1.58% drug loading, and a 48 h sustained drug release. NP formation and drug loading were largely mediated by hydrophobic interactions, while changes in the external environment led these NPs to become increasingly hydrophilic, thereby leading to drug release. Relative to PU alone, PU-NPs exhibited significantly improved cellular internalization, permeation, and neuroprotective effects. Upon the basis of Förster resonance energy transfer (FRET) of NPs-administered zebrafish, we were able to determine that these NPs were rapidly absorbed into circulation whereupon they were able to access the brain. We further conducted oral PU-NPs administration to rats, revealing significant improvements in PU accumulation within the plasma and brain relative to rats administered free PU. In MPTP-mediated neurotoxicity in mice, we found that PU-NPs treatment improved disease-associated behavioral deficits and depletion of dopamine and its metabolites. These findings indicated that PU-NPs represent a potentially viable approach to enhancing PU oral absorption, thus improving its delivery to the brain wherein it can aid in the treatment of PD.

4'-Ethynyl-2-fluoro-2'-deoxyadenosine, MK-8591: a novel HIV-1 reverse transcriptase translocation inhibitor

PURPOSE OF REVIEW

4'-Ethynyl-2-fluoro-2'-deoxyadenosine (EFdA) is a nucleoside reverse transcriptase inhibitor (NRTI) with a novel mechanism of action, unique structure, and amongst NRTIs, unparalleled anti-HIV-1 activity. We will summarize its structure and function, antiviral activity, resistance profile, and potential as an antiretroviral for use in the treatment and preexposure prophylaxis of HIV-1 infection.

RECENT FINDINGS

EFdA is active against wild-type (EC50 as low as 50 pmol/l) and most highly NRTI-resistant viruses. The active metabolite, EFdA-triphosphate, has been shown to have a prolonged intracellular half-life in human and rhesus (Rh) blood cells. As a result, single drug doses tested in simian immunodeficiency virus mac251-infected Rh macaques and HIV-1-infected individuals exhibited robust antiviral activity of 7-10 days duration. Preclinical studies of EFdA as preexposure prophylaxis in the Rh macaque/simian/human immunodeficiency virus low-dose intrarectal challenge model have shown complete protection when given in clinically relevant doses.

SUMMARY

EFdA is a novel antiretroviral with activity against both wild-type and NRTI-resistant viruses. As a result of the prolonged intracellular half-life of its active moiety, it is amenable to flexibility in dosing of at least daily to weekly and perhaps longer.

Pharmacokinetics of Jaspine B and Enhancement of Intestinal Absorption of Jaspine B in the Presence of Bile Acid in Rats

We aimed to investigate the pharmacokinetics and the underlying mechanisms of the intestinal absorption, distribution, metabolism, and excretion of Jaspine B in rats. The oral bioavailability of Jaspine B was 6.2%, but it decreased to 1.6% in bile-depleted rats and increased to 41.2% (normal) and 23.5% (bile-depleted) with taurocholate supplementation (60 mg/kg). Consistent with the increased absorption in the presence of bile salts, rat intestinal permeability of Jaspine B also increased in the presence of 10 mM taurocholate or 20% bile. Further studies demonstrated that the enhanced intestinal permeability with bile salts was due to increased lipophilicity and decreased membrane integrity. Jaspine B was designated as a highly tissue-distributed compound, because it showed large tissue to plasma ratios in the brain, kidney, heart, and spleen. Moreover, the recovery of Jaspine B from the feces and urine after an intravenous administration was about 6.3%, suggesting a substantial metabolism of Jaspine B. Consistent with this observation, 80% of the administered Jaspine B was degraded after 1 h incubation with rat liver microsomes. In conclusion, the facilitated intestinal permeability in the presence of bile salts could significantly increase the bioavailability of Jaspine B and could lead to the development of oral formulations of Jaspine B with bile salts. Moreover, the highly distributed features of Jaspine B in the brain, kidney, heart, and spleen should be carefully considered in the therapeutic effect and toxicity of this compound.

Exposure Characteristics of the Analogous β-Carboline Alkaloids Harmaline and Harmine Based on the Efflux Transporter of Multidrug Resistance Protein 2

Harmaline and harmine occur naturally in plants and are distributed endogenously in human and animal tissues. The two β-carboline alkaloids possess potential for treating Alzheimer's disease, Parkinson's disease, depression and other central nervous system diseases. However, studies have showed that the two compounds have similar structures but with quite different bioavailability. The aim of this study was to elucidate the exposure difference and characterize the in vitro transport, metabolism, and pharmacokinetic properties of harmaline and harmine. The results showed that the harmaline and harmine transport across the Caco-2 and MDCK cell monolayers was varied as the time, concentration, pH and temperature changed. The absorption of harmaline and harmine was significantly decreased when ES (OATPs inhibitor), TEA (OCTs/OCTNs substrate), NaN₃ (adenosine triphosphate inhibitor), or sodium vanadate (ATPase Na⁺/K⁺-dependent inhibitor) was added. However, when given MK571 and probenecid (the typical MRP2 inhibitor), the P_appAB of harmine was increased (1.62- and 1.27-folds), and the efflux ratio was decreased from 1.59 to 0.98 and from 1.59 to 1.19, respectively. In addition, the uptake ratio of harmine at 1 μM was >2.65 in the membrane vesicles expressing human MRP2. Furthermore, harmine could slightly up-regulate the expression of MRP2, which implying harmine might be the substrate of MRP2. Particularly, the CL_int-value for harmine was ~1.49-folds greater than that of harmaline in human liver microsomes. It was worth noting that the F-value of harmine was increased 1.96-folds after harmine co-administration with probenecid. To summarize, comprehensive analysis indicated that harmaline and harmine were absorbed by transcellular passive diffusion and a pH- and Na⁺-dependent mechanism might be mediated by OATPs and OCTs/OCTNs. MRP2 but MDR1 or BCRP might be involved in the transport of harmine. Furthermore, harmine was more unstable and easily metabolized than harmaline. All these findings suggested that harmine not only appears be an MRP2 substrate, but also possesses weak metabolic stability, and eventually leads to a low oral bioavailability. Taken together, the elucidated absorption, transport, metabolism as well as pharmacokinetic characteristics of harmaline and harmine provide useful information for designing delivery systems, pharmacological applications and avoiding drug-drug interactions.

Intestinal permeation enhancers for oral peptide delivery

Intestinal permeation enhancers (PEs) are one of the most widely tested strategies to improve oral delivery of therapeutic peptides. This article assesses the intestinal permeation enhancement action of over 250 PEs that have been tested in intestinal delivery models. In depth analysis of pre-clinical data is presented for PEs as components of proprietary delivery systems that have progressed to clinical trials. Given the importance of co-presentation of sufficiently high concentrations of PE and peptide at the small intestinal epithelium, there is an emphasis on studies where PEs have been formulated with poorly permeable molecules in solid dosage forms and lipoidal dispersions.