In Vitro Virology Profile of Tenofovir Alafenamide, a Novel Oral Prodrug of Tenofovir with Improved Antiviral Activity Compared to That of Tenofovir Disoproxil Fumarate

Unachieved antiviral strategies with acyclic nucleoside phosphonates: Dedicated to the memory of dr. Salvatore "Sam" Joseph Enna

Many acyclic nucleoside phosphonates such as cidofovir, adefovir dipivoxil, tenofovir disoproxil fumarate, and tenofovir alafenamide have been marketed for the treatment or prophylaxis of infectious diseases. Here, this review highlights potent acyclic nucleoside phosphonates for their potential in the treatment of retrovirus (e.g., human immunodeficiency virus) and DNA virus (e.g., adeno-, papilloma-, herpes- and poxvirus) infections. If properly assessed and/or optimized, some potent acyclic nucleoside phosphonates can be possibly applied in the control of current and emerging infectious diseases.

Cell Culture Evaluation Hints Widely Available HIV Drugs Are Primed for Success if Repurposed for HTLV-1 Prevention

With an estimated 10 million people infected, the deltaretrovirus human T-cell lymphotropic virus type 1 (HTLV-1) is the second most prevalent pathogenic retrovirus in humans after HIV-1. Like HIV-1, HTLV-1 overwhelmingly persists in a host via a reservoir of latently infected CD4+ T cells. Although most patients are asymptomatic, HTLV-1-associated pathologies are often debilitating and include adult T-cell leukaemia/lymphoma (ATLL), which presents in mature adulthood and is associated with poor prognosis with short overall survival despite treatment. Curiously, the strongest indicator for the development of ATLL is the acquisition of HTLV-1 through breastfeeding. There are no therapeutic or preventative regimens for HTLV-1. However, antiretrovirals (ARVs), which target the essential retrovirus enzymes, have been developed for and transformed HIV therapy. As the architectures of retroviral enzyme active sites are highly conserved, some HIV-specific compounds are active against HTLV-1. Here, we expand on our work, which showed that integrase strand transfer inhibitors (INSTIs) and some nucleoside reverse transcriptase inhibitors (NRTIs) block HTLV-1 transmission in cell culture. Specifically, we find that dolutegravir, the INSTI currently recommended as the basis of all new combination antiretroviral therapy prescriptions, and the latest prodrug formula of the NRTI tenofovir, tenofovir alafenamide, also potently inhibit HTLV-1 infection. Our results, if replicated in a clinical setting, could see transmission rates of HTLV-1 and future caseloads of HTLV-1-associated pathologies like ATLL dramatically cut via the simple repurposing of already widely available HIV pills in HTLV-1 endemic areas. Considering our findings with the old medical saying "it is better to prevent than cure", we highly recommend the inclusion of INSTIs and tenofovir prodrugs in upcoming HTLV-1 clinical trials as potential prophylactics.

Small Molecule Drugs Targeting Viral Polymerases

Small molecules that specifically target viral polymerases-crucial enzymes governing viral genome transcription and replication-play a pivotal role in combating viral infections. Presently, approved polymerase inhibitors cover nine human viruses, spanning both DNA and RNA viruses. This review provides a comprehensive analysis of these licensed drugs, encompassing nucleoside/nucleotide inhibitors (NIs), non-nucleoside inhibitors (NNIs), and mutagenic agents. For each compound, we describe the specific targeted virus and related polymerase enzyme, the mechanism of action, and the relevant bioactivity data. This wealth of information serves as a valuable resource for researchers actively engaged in antiviral drug discovery efforts, offering a complete overview of established strategies as well as insights for shaping the development of next-generation antiviral therapeutics.

Erratum to: Progress Note 2024: Curing HIV; Not in My Lifetime or Just Around the Corner?

[This corrects the article DOI: 10.20411/pai.v8i2.665.].

Progress Note 2024: Curing HIV; Not in My Lifetime or Just Around the Corner?

Once a death sentence, HIV is now considered a manageable chronic disease due to the development of antiretroviral therapy (ART) regimens with minimal toxicity and a high barrier for genetic resistance. While highly effective in arresting AIDS progression and rendering the virus untransmissible in people living with HIV (PLWH) with undetectable viremia (U=U) [1, 2]), ART alone is incapable of eradicating the "reservoir" of resting, latently infected CD4+ T cells from which virus recrudesces upon treatment cessation. As of 2022 estimates, there are 39 million PLWH, of whom 86% are aware of their status and 76% are receiving ART [3]. As of 2017, ART-treated PLWH exhibit near normalized life expectancies without adjustment for socioeconomic differences [4]. Furthermore, there is a global deceleration in the rate of new infections [3] driven by expanded access to pre-exposure prophylaxis (PrEP), HIV testing in vulnerable populations, and by ART treatment [5]. Therefore, despite outstanding issues pertaining to cost and access in developing countries, there is strong enthusiasm that aggressive testing, treatment, and effective viral suppression may be able to halt the ongoing HIV epidemic (ie, UNAIDS' 95-95-95 targets) [6-8]; especially as evidenced by recent encouraging observations in Sydney [9]. Despite these promising efforts to limit further viral transmission, for PLWH, a "cure" remains elusive; whether it be to completely eradicate the viral reservoir (ie, cure) or to induce long-term viral remission in the absence of ART (ie, control; Figure 1). In a previous salon hosted by Pathogens and Immunity in 2016 [10], some researchers were optimistic that a cure was a feasible, scalable goal, albeit with no clear consensus on the best route. So, how are these cure strategies panning out? In this commentary, 8 years later, we will provide a brief overview on recent advances and failures towards identifying determinants of viral persistence and developing a scalable cure for HIV. Based on these observations, and as in the earlier salon, we have asked several prominent HIV cure researchers for their perspectives.

Prodrugs as empowering tools in drug discovery and development: recent strategic applications of drug delivery solutions to mitigate challenges associated with lead compounds and drug candidates

The delivery of a drug to a specific organ or tissue at an efficacious concentration is the pharmacokinetic (PK) hallmark of promoting effective pharmacological action at a target site with an acceptable safety profile. Sub-optimal pharmaceutical or ADME profiles of drug candidates, which can often be a function of inherently poor physicochemical properties, pose significant challenges to drug discovery and development teams and may contribute to high compound attrition rates. Medicinal chemists have exploited prodrugs as an informed strategy to productively enhance the profiles of new chemical entities by optimizing the physicochemical, biopharmaceutical, and pharmacokinetic properties as well as selectively delivering a molecule to the site of action as a means of addressing a range of limitations. While discovery scientists have traditionally employed prodrugs to improve solubility and membrane permeability, the growing sophistication of prodrug technologies has enabled a significant expansion of their scope and applications as an empowering tool to mitigate a broad range of drug delivery challenges. Prodrugs have emerged as successful solutions to resolve non-linear exposure, inadequate exposure to support toxicological studies, pH-dependent absorption, high pill burden, formulation challenges, lack of feasibility of developing solid and liquid dosage forms, first-pass metabolism, high dosing frequency translating to reduced patient compliance and poor site-specific drug delivery. During the period 2012-2022, the US Food and Drug Administration (FDA) approved 50 prodrugs, which amounts to 13% of approved small molecule drugs, reflecting both the importance and success of implementing prodrug approaches in the pursuit of developing safe and effective drugs to address unmet medical needs.

Switching Tenofovir Disoproxil Fumarate (TDF) to Tenofovir Alafenamide Fumarate (TAF) in Hepatitis B/HIV Co-Infection: A Feasibility Study

PURPOSE

Tenofovir alafenamide (TAF) delivers the active metabolite more efficiently to target cells compared with tenofovir disoproxil fumarate (TDF). Recent studies suggest that TAF is efficacious in treatment naïve individuals who are co-infected with HBV/HIV and may have superior effects on HBV e antigen (HBeAg) seroconversion in this setting. The primary objective of this study was to explore the feasibility of switching from TDF to TAF in HBV/HIV co-infection.

METHODS

In this single-arm, multicenter, open-label study, we recruited patients (n = 20) who were on stable TDF-based antiviral therapy for at least 12 months. All participants had undetectable HIV RNA and HBV DNA levels at the time of screening and were converted to a TAF-based treatment regimen (TAF + emtricitabine + third agent) for 48 weeks.

FINDINGS

Twenty-seven individuals were invited to take part in the screening process; 3 met the exclusion criteria and a further 4 withdrew consent prior to enrolment. The remaining participants were predominantly male (70%), non-cirrhotic (95%) and of Afro-Caribbean ethnicity (60%). All were co-infected with HIV-1 and established on long-term antiretroviral treatment prior to enrolment (median 6.5 years). No adverse events related to the study drug were observed, and most patients (89.5%) maintained undetectable HIV RNA and HBV DNA throughout the follow-up period.

IMPLICATIONS

Switching from TDF to TAF in HBV/HIV co-infection was safe, well tolerated and maintained virological suppression in most patients. Additional studies are needed to confirm these findings in larger cohorts and explore other endpoints.

Development of tenofovir monobenzyl ester phosphonoamidate prodrugs with improved anti-hepatitis B virus activity and intrahepatic tenofovir enrichment

Various tenofovir (TFV) prodrugs have been developed by introducing masking groups to the hydroxyls of the monophosphonate group to enhance intestinal absorption efficiency and therapeutic effects. However, the reported TFV prodrugs have drawbacks such as low bioavailability, systemic toxicity caused by their breakdown in non-targeted tissues, and potential low intracellular conversion efficiency. In the present study, we developed a class of TFV monobenzyl ester phosphonoamidate prodrugs without substitutions on the benzene ring. Compared with previous TFV prodrugs, compounds 3a and 3b developed in the present study showed higher anti-hepatitis B virus activity, stronger stability and higher levels of intrahepatic enrichment of the metabolic product (TFV), indicating the potential of these compounds as novel prodrugs with high efficiency and low systemic toxicity for the treatment of hepatitis B.

Nucleos(t)ide analogs for hepatitis B virus infection differentially regulate the growth factor signaling in hepatocytes

BACKGROUND

Recent clinical studies have suggested that the risk of developing HCC might be lower in patients with chronic hepatitis B receiving tenofovir disoproxil fumarate than in patients receiving entecavir, although there is no difference in biochemical and virological remission between the 2 drugs.

METHODS

The effects of nucleoside analogs (NsAs; lamivudine and entecavir) or nucleotide analogs (NtAs; adefovir disoproxil, tenofovir disoproxil fumarate, and tenofovir alafenamide) on cell growth and the expression of growth signaling molecules in hepatoma cell lines and PXB cells were investigated in vitro. The tumor inhibitory effects of NsAs or NtAs were evaluated using a mouse xenograft model, and protein phosphorylation profiles were investigated. The binding of NsAs or NtAs to the insulin receptor (INSR) was investigated by thermal shift assays.

RESULTS

NtAs, but not NsAs, showed direct growth inhibitory effects on hepatoma cell lines in vitro and a mouse model in vivo. A phosphoprotein array revealed that INSR signaling was impaired and the levels of phosphorylated (p)-INSRβ and downstream molecules phosphorylated (p)-IRS1, p-AKT, p-Gab1, and p-SHP2 were substantially reduced by NtAs. In addition, p-epidermal growth factor receptor and p-AKT levels were substantially reduced by NtAs. Similar findings were also found in PXB cells and nontumor lesions of liver tissues from patients with chronic hepatitis B. Prodrug NtAs, but not their metabolites (adefovir, adefovir monophosphate, adefovir diphosphate, tenofovir, tenofovir monophosphate, and tenofovir diphosphate), had such effects. A thermal shift assay showed the binding of NtAs to INSRβ.

CONCLUSIONS

NtAs (adefovir disoproxil, tenofovir disoproxil fumarate, and tenofovir alafenamide), which are adenine derivative acyclic nucleotide analogs, potentially bind to the ATP-binding site of growth factor receptors and inhibit their autophosphorylation, which might reduce the risk of HCC in patients with chronic hepatitis B.

The Application of Prodrugs as a Tool to Enhance the Properties of Nucleoside Reverse Transcriptase Inhibitors

Antiretroviral Therapy (ART) is an effective treatment for human immunodeficiency virus (HIV) which has transformed the highly lethal disease, acquired immunodeficiency syndrome (AIDS), into a chronic and manageable condition. However, better methods need to be developed for enhancing patient access and adherence to therapy and for improving treatment in the long term to reduce adverse effects. From the perspective of drug discovery, one promising strategy is the development of anti-HIV prodrugs. This approach aims to enhance the efficacy and safety of treatment, promoting the development of more appropriate and convenient systems for patients. In this review, we discussed the use of the prodrug approach for HIV antiviral agents and emphasized nucleoside reverse transcriptase inhibitors. We comprehensively described various strategies that are used to enhance factors such as water solubility, bioavailability, pharmacokinetic parameters, permeability across biological membranes, chemical stability, drug delivery to specific sites/organs, and tolerability. These strategies might help researchers conduct better studies in this field. We also reported successful examples from the primary therapeutic classes while discussing the advantages and limitations. In this review, we highlighted the key trends in the application of the prodrug approach for treating HIV/AIDS.

Effect of P-glycoprotein and Cotreatment with Sofosbuvir on the Intestinal Permeation of Tenofovir Disoproxil Fumarate and Tenofovir Alafenamide Fumarate

PURPOSE

We aimed to compare the effects of P-glycoprotein (ABCB1) on the intestinal uptake of tenofovir disoproxil fumarate (TDF), tenofovir alafenamide fumarate (TAF), and metabolites, tenofovir isoproxil monoester (TEM) and tenofovir (TFV), and to study the molecular mechanism of drug-drug interaction (DDI) between sofosbuvir (SOF) and TDF/TAF.

METHODS

Bidirectional transport experiments in Caco-2 cells and accumulation studies in precision-cut intestinal slices prepared from the ileal segment of rodent (rPCIS) and human (hPCIS) intestines were performed.

RESULTS

TDF and TAF were extensively metabolised but TAF exhibited greater stability. ABCB1 significantly reduced the intestinal transepithelial transfer and uptake of the TFV(TDF) and TFV(TAF)-equivalents. However, TDF and TAF were absorbed more efficiently than TFV and TEM. SOF did not inhibit intestinal efflux of TDF and TAF or affect intestinal accumulation of TFV(TDF) and TFV(TAF)-equivalents but did significantly increase the proportion of absorbed TDF.

CONCLUSIONS

TDF and TAF likely produce comparable concentrations of TFV-equivalents in the portal vein and the extent of permeation is reduced by the activity of ABCB1. DDI on ABCB1 can thus potentially affect TDF and TAF absorption. SOF does not inhibit ABCB1-mediated transport of TDF and TAF but does stabilise TDF, albeit without affecting the quantity of TFV(TDF)-equivalents crossing the intestinal barrier. Our data thus suggest that reported increases in the TFV plasma concentrations in patients treated with SOF and TDF result either from a DDI between SOF and TDF that does not involve ABCB1 or from a DDI involving another drug used in combination therapy.

Broadening access to tenofovir alafenamide for the treatment and prevention of HIV-1 infection

INTRODUCTION

Tenofovir alafenamide (TAF), a prodrug of tenofovir, achieves higher intracellular concentrations of tenofovir-diphosphate and 90% lower plasma concentrations of tenofovir compared to tenofovir disoproxil fumarate (TDF). TAF is associated with improved renal and bone safety outcomes.

AREAS COVERED

We review the efficacy and safety of TAF-containing regimens in adults and pediatrics. We highlight safety data during pregnancy, drug interactions during co-administration with tuberculosis treatment, and critical knowledge gaps to be addressed for the successful implementation of TAF in low- and middle-income countries. We performed a search on MEDLINE PubMed and conference websites for relevant articles published from January 2010 to March 2023.

EXPERT OPINION

Current evidence demonstrates that TAF has similar efficacy and tolerability, superior bone and renal safety, and higher rates of dyslipidemia and weight gain, compared with TDF. However, there are several knowledge gaps, in specific sub-populations, that require action. Emerging data suggests that TAF is safe during pregnancy, although fuller safety data to support TAF use in pregnancy is needed. Similarly, there is a lack of evidence that TAF can be used in combination with rifamycin-based tuberculosis treatment in PWH and TB. Further studies are needed to fill knowledge gaps and support the wider rollout of TAF.

Design, Synthesis, Biological Evaluation, and Crystallographic Study of Novel Purine Nucleoside Phosphorylase Inhibitors

Purine nucleoside phosphorylase (PNP) is a well-known molecular target with potential therapeutic applications in the treatment of T-cell malignancies and/or bacterial/parasitic infections. Here, we report the design, development of synthetic methodology, and biological evaluation of a series of 30 novel PNP inhibitors based on acyclic nucleoside phosphonates bearing a 9-deazahypoxanthine nucleobase. The strongest inhibitors exhibited IC₅₀ values as low as 19 nM (human PNP) and 4 nM (Mycobacterium tuberculosis (Mt) PNP) and highly selective cytotoxicity toward various T-lymphoblastic cell lines with CC₅₀ values as low as 9 nM. No cytotoxic effect was observed on other cancer cell lines (HeLa S3, HL60, HepG2) or primary PBMCs for up to 10 μM. We report the first example of the PNP inhibitor exhibiting over 60-fold selectivity for the pathogenic enzyme (MtPNP) over hPNP. The results are supported by a crystallographic study of eight enzyme-inhibitor complexes and by ADMET profiling in vitro and in vivo.

Antiretroviral Treatment of HIV-2 Infection: Available Drugs, Resistance Pathways, and Promising New Compounds

Currently, it is estimated that 1-2 million people worldwide are infected with HIV-2, accounting for 3-5% of the global burden of HIV. The course of HIV-2 infection is longer compared to HIV-1 infection, but without effective antiretroviral therapy (ART), a substantial proportion of infected patients will progress to AIDS and die. Antiretroviral drugs in clinical use were designed for HIV-1 and, unfortunately, some do not work as well, or do not work at all, for HIV-2. This is the case for non-nucleoside reverse transcriptase inhibitors (NNRTIs), the fusion inhibitor enfuvirtide (T-20), most protease inhibitors (PIs), the attachment inhibitor fostemsavir and most broadly neutralizing antibodies. Integrase inhibitors work well against HIV-2 and are included in first-line therapeutic regimens for HIV-2-infected patients. However, rapid emergence of drug resistance and cross-resistance within each drug class dramatically reduces second-line treatment options. New drugs are needed to treat infection with drug-resistant isolates. Here, we review the therapeutic armamentarium available to treat HIV-2-infected patients, as well as promising drugs in development. We also review HIV-2 drug resistance mutations and resistance pathways that develop in HIV-2-infected patients under treatment.

Overview of the development of HBV small molecule inhibitors

Like tuberculosis and Acquired Immune Deficiency Syndrome (AIDS), hepatitis B is a globally recognized major public health threat. Although there are many small-molecule drugs for the treatment of hepatitis B, the approved drugs cannot eradicate the pathogenic culprit covalently closed circular DNA in patients, so the patients need long-term medication to control HBV amplification. Driven by a high unmet medical need, many pharmaceutical companies and research institutions have been engaged in the development of anti-HBV drugs to achieve a functional cure for chronic hepatitis B as soon as possible. This review summarizes the pathogenesis of hepatitis B virus and the research progress in the development of anti-HBV small molecule drugs, and introduces the cccDNA formation and transcription inhibitors and core inhibitors in detail, especially emphasizes the role of chinese herbal medicine in the treatment of chronic hepatitis B. Furthermore, this review proposes three potential strategies for cccDNA eradication in the future. We believe this review will provide meaningful guidance to achieve a functional cure for viral hepatitis B in the future.

A phase I study to assess safety, pharmacokinetics, and pharmacodynamics of a vaginal insert containing tenofovir alafenamide and elvitegravir

Background

New multi-purpose prevention technology (MPT) products are needed to prevent human immunodeficiency virus (HIV) and herpes simplex virus type 2 (HSV2). In this study, we evaluated a fast-dissolve insert that may be used vaginally or rectally for prevention of infection.

Objective

To describe the safety, acceptability, multi-compartment pharmacokinetics (PK), and in vitro modeled pharmacodynamics (PD) after a single vaginal dose of an insert containing tenofovir alafenamide (TAF) and elvitegravir (EVG) in healthy women.

Methods

This was a Phase I, open-label, study. Women (n=16) applied one TAF (20mg)/EVG (16mg) vaginal insert and were randomized (1:1) to sample collection time groups for up to 7 days post dosing. Safety was assessed by treatment-emergent adverse events (TEAEs). EVG, TAF and tenofovir (TFV) concentrations were measured in plasma, vaginal fluid and tissue, and TFV-diphosphate (TFV-DP) concentration in vaginal tissue. PD was modeled in vitro by quantifying the change in inhibitory activity of vaginal fluid and vaginal tissue against HIV and HSV2 from baseline to after treatment. Acceptability data was collected by a quantitative survey at baseline and post treatment.

Results

The TAF/EVG insert was safe, with all TEAEs graded as mild, and acceptable to participants. Systemic plasma exposure was low, consistent with topical delivery, while high mucosal levels were detected, with median TFV vaginal fluid concentrations exceeding 200,000 ng/mL and 1,000 ng/mL for up to 24 hours and 7 days post dosing, respectively. All participants had vaginal tissue EVG concentrations of > 1 ng/mg at 4 and 24 hours post dosing. The majority had tissue TFV-DP concentrations exceeding 1000 fmol/mg by 24 - 72 hours post dosing. Vaginal fluid inhibition of HIV-1 and HSV-2 in vitro significantly increased from baseline and was similarly high at 4 and 24 hours post dosing. Consistent with high tissue TFV-DP concentrations, p24 HIV antigen production from ectocervical tissues infected ex vivo with HIV-1 significantly decreased from baseline at 4 hours post dosing. HSV-2 production from tissue also decreased post treatment.

Conclusions

A single dose of TAF/EVG inserts met PK benchmarks, with PK data supporting an extended window of high mucosal protection. PD modeling supports mucosal protection against both HIV-1 and HSV-2. The inserts were safe and highly acceptable.

Clinical trial registration

ClinicalTrials.gov, identifier NCT03762772.

In Vitro Susceptibility of HIV Isolates with High Growth Capability to Antiretroviral Drugs

It has been considered that reduced susceptibility to antiretroviral drugs is influenced by drug adherence, drug tolerance and drug-resistance-related mutations in the HIV genome. In the present study, we assessed the intrinsic high viral growth capability as a potential viral factor that may influence their susceptibility to antiretroviral drugs using an in vitro model. Phytohemagglutinin-activated peripheral blood mononuclear cells (1.5 × 10⁶ cells) were infected with HIV isolates (10⁶ copies/mL). The culture was carried out at different concentrations (0.001-20 μM) of 13 synthetic antiretroviral compounds (six nucleoside/nucleotide reverse transcriptase inhibitors, one non-nucleoside reverse transcriptase inhibitor, four integrase inhibitors, and two protease inhibitors), and HIV production was assessed using HIV-RNA copies in culture. The 90% inhibitory concentration (IC₉₀) and pharmacokinetics of an antiretroviral agent were used as parameters to determine the reduced antiretroviral drug susceptibility of HIV isolates with high growth capability to synthetic antiretroviral compounds. The high growth capability of HIV isolates without any known drug resistance-related mutation affected their susceptibility to tenofovir (IC₉₀ = 2.05 ± 0.40 μM), lamivudine (IC₉₀ = 6.83 ± 3.96 μM), emtricitabine (IC₉₀ = 0.68 ± 0.37 μM), and efavirenz (IC₉₀ = 3.65 ± 0.77 μM). These antiretroviral drugs showed IC₉₀ values close to or above the maximum plasma concentration against HIV isolates with high growth capability without any known drug resistance-related mutation. Our results may contribute to the development of effective strategies to tailor and individualize antiretroviral therapy in patients harboring HIV isolates with high growth capability.

Single dose topical inserts containing tenofovir alafenamide fumarate and elvitegravir provide pre- and post-exposure protection against vaginal SHIV infection in macaques

BACKGROUND

Vaginal products for HIV prevention that can be used on-demand before or after sex may be a preferable option for women with low frequency or unplanned sexual activity or who prefer not to use daily or long-acting pre-exposure prophylaxis (PrEP). We performed dose ranging pharmacokinetics (PK) and efficacy studies of a vaginally applied insert containing tenofovir alafenamide fumarate (TAF) and elvitegravir (EVG) in macaques under PrEP or post-exposure prophylaxis (PEP) modalities.

METHODS

PK studies were performed in 3 groups of pigtailed macaques receiving inserts with different fixed-dose combinations of TAF and EVG (10/8, 20/16 and 40/24 mg). PrEP and PEP efficacy of a selected insert was investigated in a repeat exposure vaginal SHIV transmission model. Inserts were administered 4 h before (n = 6) or after (n = 6) repeated weekly SHIV exposures. Infection outcome was compared with macaques receiving placebo inserts (n = 12).

FINDINGS

Dose ranging studies showed rapid and sustained high drug concentrations in vaginal fluids and tissues across insert formulations with minimal dose proportionality. TAF/EVG (20/16 mg) inserts were selected for efficacy evaluation. Five of the 6 animals receiving these inserts 4 h before and 6/6 animals receiving inserts 4 h after SHIV exposure were protected after 13 challenges (p = 0.0088 and 0.0077 compared to placebo, respectively). The calculated PrEP and PEP efficacy was 91.0% (95% CI = 32.2%-98.8%) and 100% (95% CI = undefined), respectively.

INTERPRETATION

Inserts containing TAF/EVG provided high protection against vaginal SHIV infection when administered within a 4 h window before or after SHIV exposure. Our results support the clinical development of TAF/EVG inserts for on-demand PrEP and PEP in women.

FUNDING

Funded by CDC intramural funds, an interagency agreement between CDC and USAID (USAID/CDC IAA AID-GH-T-15-00002), and by the U.S. President's Emergency Plan for AIDS Relief (PEPFAR) through the U.S. Agency for International Development (USAID) under a Cooperative Agreement (AID-OAA-A-14-00010) with CONRAD/Eastern Virginia Medical School.

HIV nucleoside reverse transcriptase inhibitors

More than 40 years into the pandemic, HIV remains a global burden and as of now, there is no cure in sight. Fortunately, highly active antiretroviral therapy (HAART) has been developed to manage and suppress HIV infection. Combinations of two to three drugs targeting key viral proteins, including compounds inhibiting HIV reverse transcriptase (RT), have become the cornerstone of HIV treatment. This review discusses nucleoside reverse transcriptase inhibitors (NRTIs), including chain terminators, delayed chain terminators, nucleoside reverse transcriptase translocation inhibitors (NRTTIs), and nucleotide competing RT inhibitors (NcRTIs); focusing on their history, mechanism of action, resistance, and current clinical application, including long-acting regimens.

Improved pharmacokinetics of tenofovir ester prodrugs strengthened the inhibition of HBV replication and the rebalance of hepatocellular metabolism in preclinical models

Tenofovir (TFV) ester prodrugs, a class of nucleotide analogs (NAs), are the first-line clinical anti-hepatitis B virus (HBV) drugs with potent antiviral efficacy, low resistance rate and high safety. In this work, three marketed TFV ester drugs, tenofovir disoproxil fumarate (TDF), tenofovir alafenamide fumarate (TAF) and tenofovir amibufenamide fumarate (TMF), were used as probes to investigate the relationships among prodrug structures, pharmacokinetic characteristics, metabolic activations, pharmacological responses and to reveal the key factors of TFV ester prodrug design. The results indicated that TMF and TAF exhibited significantly stronger inhibition of HBV DNA replication than did TDF in HBV-positive HepG2.2.15 cells. The anti-HBV activity of TMF was slightly stronger than TAF after 9 days of treatment (EC₅₀ 7.29 ± 0.71 nM vs. 12.17 ± 0.56 nM). Similar results were observed in the HBV decline period post drug administration to the HBV transgenic mouse model, although these three TFV prodrugs finally achieved the same anti-HBV effect after 42 days treatments. Furthermore, TFV ester prodrugs showed a correcting effect on disordered host hepatic biochemical metabolism, including TCA cycle, glycolysis, pentose phosphate pathway, purine/pyrimidine metabolism, amino acid metabolism, ketone body metabolism and phospholipid metabolism. The callback effects of the three TFV ester prodrugs were ranked as TMF > TAF > TDF. These advantages of TMF were believed to be attributed to its greater bioavailability in preclinical animals (SD rats, C57BL/6 mice and beagle dogs) and better target loading, especially in terms of the higher hepatic level of the pharmacologically active metabolite TFV-DP, which was tightly related to anti-HBV efficacy. Further analysis indicated that stability in intestinal fluid determined the actual amount of TFV prodrug at the absorption site, and hepatic/intestinal stability determined the maintenance amount of prodrug in circulation, both of which influenced the oral bioavailability of TFV prodrugs. In conclusion, our research revealed that improved pharmacokinetics of TFV ester prodrugs (especially intestinal stability) strengthened the inhibition of HBV replication and the rebalance of hepatocellular metabolism, which provides new insights and a basis for the design, modification and evaluation of new TFV prodrugs in the future.

Pre-Clinical Evaluation of Tenofovir and Tenofovir Alafenamide for HIV-1 Pre-Exposure Prophylaxis in Foreskin Tissue

Background: HIV-1 pre-exposure prophylaxis (PrEP) has focused predominantly on protective efficacy in receptive sex, with limited research on the dosing requirements for insertive sex. We pre-clinically assessed the ex vivo pharmacokinetic–pharmacodynamic (PK–PD) profile of tenofovir (TFV) and tenofovir alafenamide (TAF) in foreskin tissue. Methods: Inner and outer foreskin explants were exposed to serial dilutions of TFV or TAF prior to addition of HIV-1_BaL at a high (HVT) or a low viral titer (LVT). Infection was assessed by measurement of p24 in foreskin culture supernatants. TFV, TAF and TFV–diphosphate (TFV–DP) concentrations were measured in tissues, culture supernatants and dosing and washing solutions. Results: Dose–response curves were obtained for both drugs, with greater potency observed against LVT. Inhibitory equivalency mimicking oral dosing was defined between 1 mg/mL of TFV and 15 µg/mL of TAF against HVT challenge. Concentrations of TFV–DP in foreskin explants were approximately six-fold higher after ex vivo dosing with TAF than with TFV. Statistically significant negative linear correlations were observed between explant levels of TFV or TFV–DP and p24 concentrations following HVT. Conclusions: Pre-clinical evaluation of TAF in foreskin explants revealed greater potency than TFV against penile HIV transmission. Clinical evaluation is underway to support this finding.

Approved HIV reverse transcriptase inhibitors in the past decade

HIV reverse transcriptase (RT) inhibitors are the important components of highly active antiretroviral therapies (HAARTs) for anti-HIV treatment and pre-exposure prophylaxis in clinical practice. Many RT inhibitors and their combination regimens have been approved in the past ten years, but a review on their drug discovery, pharmacology, and clinical efficacy is lacking. Here, we provide a comprehensive review of RT inhibitors (tenofovir alafenamide, rilpivirine, doravirine, dapivirine, azvudine and elsulfavirine) approved in the past decade, regarding their drug discovery, pharmacology, and clinical efficacy in randomized controlled trials. Novel RT inhibitors such as islatravir, MK-8504, MK-8507, MK8583, IQP-0528, and MIV-150 will be also highlighted. Future development may focus on the new generation of novel antiretroviral inhibitors with higher bioavailability, longer elimination half-life, more favorable side-effect profiles, fewer drug-drug interactions, and higher activities against circulating drug-resistant strains.

Candidate antiviral drugs for COVID-19 and their environmental implications: a comprehensive analysis

Emerging from Wuhan, China, SARS-CoV-2 is the new global threat that killed millions of people, and many are still suffering. This pandemic has not only affected people but also caused economic crisis throughout the world. Researchers have shown good progress in revealing the molecular insights of SARS-CoV-2 pathogenesis and developing vaccines, but effective treatment against SARS-CoV-2-infected patients are yet to be found. Several vaccines are available and used in many countries, while many others are still in clinical or preclinical studies. However, this involves a long-term process, considering the safety procedures and requirements and their long-term protection capacity and in different age groups are still questionable. Therefore, at present, the drug repurposing of the existing therapeutics previously designed against other viral diseases seems to be the only practical approach to mitigate the current situation. The safety of most of these therapeutic agents has already been tested. Recent clinical reports revealed promising therapeutic efficiency of several drugs such as remdesivir, tenofovir disoproxil fumarate, azithromycin, lopinavir/ritonavir, chloroquine, baricitinib, and cepharanthine. Besides, plasma therapies were used to treat patients and prevent fatal outcomes. Thus, in this article, we have summarized the epidemiological and clinical data from several clinical trials conducted since the beginning of the pandemic, emphasizing the efficiency of the known agents against SARS-CoV-2 and their harmful side effects on the human body as well as their environmental implications. This review shows a clear overview of the current pharmaceutical perspective on COVID-19 treatment.

Asociación Mexicana de Hepatología A.C. Clinical guideline on hepatitis B

Hepatitis B virus (HBV) infection continues to be a worldwide public health problem. In Mexico, at least three million adults are estimated to have acquired hepatitis B (total hepatitis B core antibody [anti-HBc]-positive), and of those, 300,000 active carriers (hepatitis B surface antigen [HBsAg]-positive) could require treatment. Because HBV is preventable through vaccination, its universal application should be emphasized. HBV infection is a major risk factor for developing hepatocellular carcinoma. Semi-annual liver ultrasound and serum alpha-fetoprotein testing favor early detection of that cancer and should be carried out in all patients with chronic HBV infection, regardless of the presence of advanced fibrosis or cirrhosis. Currently, nucleoside/nucleotide analogues that have a high barrier to resistance are the first-line therapies.

Asociación Mexicana de Hepatología A.C. Clinical guideline on hepatitis B

Hepatitis B virus (HBV) infection continues to be a worldwide public health problem. In Mexico, at least three million adults are estimated to have acquired hepatitis B (total hepatitis B core antibody [anti-HBc]-positive), and of those, 300,000 active carriers (hepatitis B surface antigen [HBsAg]-positive) could require treatment. Because HBV is preventable through vaccination, its universal application should be emphasized. HBV infection is a major risk factor for developing hepatocellular carcinoma. Semi-annual liver ultrasound and serum alpha-fetoprotein testing favor early detection of that cancer and should be carried out in all patients with chronic HBV infection, regardless of the presence of advanced fibrosis or cirrhosis. Currently, nucleoside/nucleotide analogues that have a high barrier to resistance are the first-line therapies.

Pharmacokinetic modelling to estimate intracellular favipiravir ribofuranosyl-5'-triphosphate exposure to support posology for SARS-CoV-2

Objectives

Favipiravir has discrepant activity against SARS-CoV-2 in vitro, concerns about teratogenicity and pill burden, and an unknown optimal dose. This analysis used available data to simulate the intracellular pharmacokinetics of the favipiravir active metabolite [favipiravir ribofuranosyl-5′-triphosphate (FAVI-RTP)].

Methods

Published in vitro data for intracellular production and elimination of FAVI-RTP in Madin–Darby canine kidney cells were fitted with a mathematical model describing the time course of intracellular FAVI-RTP as a function of favipiravir concentration. Parameter estimates were then combined with a published population pharmacokinetic model in Chinese patients to predict human intracellular FAVI-RTP. In vitro FAVI-RTP data were adequately described as a function of concentrations with an empirical model, noting simplification and consolidation of various processes and several assumptions.

Results

Parameter estimates from fittings to in vitro data predict a flatter dynamic range of peak to trough for intracellular FAVI-RTP (peak to trough ratio of ∼1 to 1) when driven by a predicted free plasma concentration profile, compared with the plasma profile of parent favipiravir (ratio of ∼2 to 1). This approach has important assumptions, but indicates that, despite rapid clearance of the parent from plasma, sufficient intracellular FAVI-RTP may be maintained across the dosing interval because of its long intracellular half-life.

Conclusions

Population mean intracellular FAVI-RTP concentrations are estimated to be maintained above the Km for the SARS-CoV-2 polymerase for 9 days with a 1200 mg twice-daily regimen (following a 1600 mg twice-daily loading dose on day 1). Further evaluation of favipiravir as part of antiviral combinations for SARS-CoV-2 is warranted.

A Review and Clinical Understanding of Tenofovir: Tenofovir Disoproxil Fumarate versus Tenofovir Alafenamide

HIV is a serious chronic medical condition. Significant improvements in antiretroviral therapy have led to a transformation in its management. No curative treatment is available for HIV, and lifelong therapy is required with a combination of agents to control viral replication and prevent complications. Some of the older agents are notorious for many side effects, making patient compliance difficult, which is critical to preventing HIV resistance. Tenofovir is one of the newer, more tolerable, nucleotide reverse transcriptase inhibitors on the market; is a mainstay of many antiretroviral therapy combinations; and is now available in 2 different formulations, tenofovir disoproxil fumarate (TDF) and, the more recent, tenofovir alafenamide (TAF). These 2 formulations have very different pharmacokinetics, which seem to affect their efficacy and safety. This manuscript provides insight into the history of TDF and TAF development, their unique pharmacokinetics and pharmacology, clinically important adverse effects, monitoring, interactions, resistance, review of clinical studies, and guideline recommendations and clinical applications for tenofovir’s various indications.

Selected Thoughts on Hydrophobicity in Drug Design

The fundamental aim of drug design in research and development is to invent molecules with selective affinity towards desired disease-associated targets. At the atomic loci of binding surfaces, systematic structural variations can define affinities between drug candidates and biomolecules, and thereby guide the optimization of safety, efficacy and pharmacologic properties. Hydrophobic interaction between biomolecules and drugs is integral to binding affinity and specificity. Examples of antiviral drug discovery are discussed.

Pharmacokinetic modelling to estimate intracellular favipiravir ribofuranosyl-5'-triphosphate exposure to support posology for SARS-CoV-2

Background

The role of favipiravir as a treatment for COVID-19 is unclear, with discrepant activity against SARS-CoV-2 in vitro , concerns about teratogenicity and pill burden, and an unknown optimal dose. In Vero-E6 cells, high concentrations are needed to inhibit SARS-CoV-2 replication. The purpose of this analysis was to use available data to simulate intracellular pharmacokinetics of favipiravir ribofuranosyl-5⍰-triphosphate (FAVI-RTP) to better understand the putative applicability as a COVID-19 intervention.

Methods

Previously published in vitro data for the intracellular production and elimination of FAVI- RTP in MDCK cells incubated with parent favipiravir was fitted with a mathematical model to describe the time course of intracellular FAVI-RTP concentrations as a function of incubation concentration of parent favipiravir. Parameter estimates from this model fitting were then combined with a previously published population PK model for the plasma exposure of parent favipiravir in Chinese patients with severe influenza (the modelled free plasma concentration of favipiravir substituting for in vitro incubation concentration) to predict the human intracellular FAVI-RTP pharmacokinetics.

Results

In vitro FAVI-RTP data was adequately described as a function of in vitro incubation media concentrations of parent favipiravir with an empirical model, noting that the model simplifies and consolidates various processes and is used under various assumptions and within certain limits. Parameter estimates from the fittings to in vitro data predict a flatter dynamic range of peak to trough for intracellular FAVI-RTP when driven by a predicted free plasma concentration profile.

Conclusion

This modelling approach has several important limitations that are discussed in the main text of the manuscript. However, the simulations indicate that despite rapid clearance of the parent drug from plasma, sufficient intracellular FAVI-RTP may be maintained across the dosing interval because of its long intracellular half-life. Population average intracellular FAVI-RTP concentrations are estimated to maintain the Km for the SARS-CoV-2 polymerase for 3 days following 800 mg BID dosing and 9 days following 1200 mg BID dosing after a 1600 mg BID loading dose on day 1. Further evaluation of favipiravir as part of antiviral combinations for SARS-CoV-2 is warranted.

Biocatalytic routes to anti-viral agents and their synthetic intermediates

An assessment of biocatalytic strategies for the synthesis of anti-viral agents, offering guidelines for the development of sustainable production methods for a future COVID-19 remedy.

A New Approach to Developing Long-Acting Injectable Formulations of Anti-HIV Drugs: Poly(Ethylene Phosphoric Acid) Block Copolymers Increase the Efficiency of Tenofovir against HIV-1 in MT-4 Cells

Despite the world’s combined efforts, human immunodeficiency virus (HIV), the causative agent of AIDS, remains one of the world’s most serious public health challenges. High genetic variability of HIV complicates the development of anti-HIV vaccine, and there is an actual clinical need for increasing the efficiency of anti-HIV drugs in terms of targeted delivery and controlled release. Tenofovir (TFV), a nucleotide-analog reverse transcriptase inhibitor, has gained wide acceptance as a drug for pre-exposure prophylaxis or treatment of HIV infection. In our study, we explored the potential of tenofovir disoproxil (TFD) adducts with block copolymers of poly(ethylene glycol) monomethyl ether and poly(ethylene phosphoric acid) (mPEG-b-PEPA) as candidates for developing a long-acting/controlled-release formulation of TFV. Two types of mPEG-b-PEPA with numbers of ethylene phosphoric acid (EPA) fragments of 13 and 49 were synthesized by catalytic ring-opening polymerization, and used for preparing four types of adducts with TFD. Antiviral activity of [mPEG-b-PEPA]TFD or tenofovir disoproxil fumarate (TDF) was evaluated using the model of experimental HIV infection in vitro (MT-4/HIV-1_IIIB). Judging by the values of the selectivity index (SI), TFD exhibited an up to 14-fold higher anti-HIV activity in the form of mPEG-b-PEPA adducts, thus demonstrating significant promise for further development of long-acting/controlled-release injectable TFV formulations.

In Vitro Exposure of Leukocytes to HIV Preexposure Prophylaxis Decreases Mitochondrial Function and Alters Gene Expression Profiles

The use of antiretroviral therapy (ART) as preexposure prophylaxis (PrEP) is an effective strategy for preventing HIV acquisition. The cellular consequences of PrEP exposure, however, have not been sufficiently explored to determine potential effects on health in individuals without HIV. In this study, peripheral blood mononuclear cells (PBMCs) from people without HIV were exposed to tenofovir disoproxil fumarate (TDF) or emtricitabine (FTC) overnight. Mitochondrial mass and function were measured by flow cytometry and an Agilent XFp analyzer.

The use of antiretroviral therapy (ART) as preexposure prophylaxis (PrEP) is an effective strategy for preventing HIV acquisition. The cellular consequences of PrEP exposure, however, have not been sufficiently explored to determine potential effects on health in individuals without HIV. In this study, peripheral blood mononuclear cells (PBMCs) from people without HIV were exposed to tenofovir disoproxil fumarate (TDF) or emtricitabine (FTC) overnight. Mitochondrial mass and function were measured by flow cytometry and an Agilent XFp analyzer. Monocyte-derived macrophages (MDMs) were differentiated in 20% autologous serum for 5 days in the presence or absence of TDF or FTC, and surface markers, lipid uptake, and efferocytosis were measured by flow cytometry. MDM gene expression was measured using transcriptome sequencing (RNA-seq). Plasma lipids were measured using mass spectrometry. PBMCs exposed to TDF or FTC had decreased maximal oxygen consumption rate (OCR) and reduced mitochondrial mass. Exposure to PrEP also increased reactive oxygen species (ROS) production from monocyte subsets. Compared to MDMs cultured in medium alone, cells differentiated in the presence of TDF (829 genes) or FTC (888 genes) had significant changes in gene expression. Further, PrEP-exposed MDMs had decreased mitochondrial mass and displayed increased lipid uptake and reduced efferocytosis. Plasma biomarkers and lipid levels were also altered in vivo in individuals receiving a PrEP regimen. In conclusion, exposure of leukocytes to TDF or FTC resulted in decreased mitochondrial function and altered functional and transcriptional profiles. These findings may have important implications for the metabolic and immunologic consequences of PrEP in populations at risk for HIV acquisition.

On the Single-Crystal Structure of Tenofovir Alafenamide Mono-Fumarate: A Metastable Phase Featuring a Mixture of Co-Crystal and Salt

Tenofovir alafenamide (TAF) is a prodrug of tenofovir as a potent nucleotide reverse transcriptase inhibitor. It serves as the key component of Genvoya^® for the first-line treatment of human immunodeficiency virus infection (HIV) and is the active component of Vemlidy^® for the treatment of chronic hepatitis B. Vemlidy^® is also a monotherapeutic regimen formulated as TAF hemifumarate (1; TAF:fumarate = 2:1). In this work, we report for the first time the single-crystal structure of TAF fumarate hemihydrate (2, TAF:fumarate:H₂O = 2:2:1). Compound 2 is initially documented as a salt in which one proton of the fumaric acid migrates to the amine group of the adenine moiety in TAF. It was recently proposed that ca. 20–30% proton is transferred to the N atom on the aromatic adenine backbone. We herein provide definitive single-crystal X-ray diffraction results to confirm that 2, though phase pure, is formed as a mixture of co-crystal (75%) and salt (25%). It features two pairs of TAF fumarates, wherein one of the four H atoms on the fumaric acid is transferred to the N atom of the adjacent adenine moiety while the other three carboxylates remain in their intrinsic acid form. Compound 2 is a metastable phase during the preparation of 1 and can be isolated by halting the reaction during the refluxing of TAF and fumaric acid in acetonitrile (MeCN). Our report complements the previous characterizations of TAF monofumarate, and its elusive structural patterns are finally deciphered.

Tenofovir Alafenamide Fumarate Therapy for HIV Treatment: Cardiometabolic and Renal Safety

Antiretroviral treatment based on tenofovir alafenamide fumarate (TAF) is increasingly recommended, as it maintains the viral suppression and improves renal function and bone density in comparison with tenofovir disoproxil fumarate (TDF). We carried out a retrospective cohort study including experienced patients who switched treatment from TDF to TAF. Serum lipids and glucose, renal function, body mass index (BMI), and cardiovascular risk were evaluated before and 3 and 6 months after the initiation of TAF-based treatment. We identified 85 patients on TAF-based treatment. The majority were men (82.9%), smokers (70%), and older than 40 years. Significant increases in lipids and BMI were noted, but cardiovascular risk remained <7.5%. Renal function remained normal with a notable improvement among patients with renal impairment. These results suggest that TAF has no significant effect on glucose and does not meaningfully increase cardiovascular risk, despite an elevation in serum lipids. It also exhibits renal safety. However, the increase of BMI was significant. Further studies are needed to confirm these findings in larger patient series and over longer follow-up periods.

Elvitegravir/Cobicistat/Emtricitabine/Tenofovir Alafenamide in the Treatment of HIV-Infected Patients: Experience with the First 100 Patients from Qatar

Background

To describe our experience with the use of Elvitegravir/Cobicistat/Emtricitabine/Tenofovir Alafenamide (EVG/COBI/FTC/TAF) in the treatment of HIV-infected patients in Qatar including both naïve and treatment experienced. We also report the reasons for switching to EVG/COBI/FTC/TAF in treatment-experienced patients, response to treatment, and tolerability.

Method

Review of the medical records of the first 100 HIV-infected patients treated with EVG/COBI/FTC/TAF.

Results

Among the 100 HIV-infected patients who were treated with EVG/COBI/FTC/TAF, 64 were Qatari and the rest were from other nationalities. 80 patients were males and 20 were females. 29 were treatment naïve, and 71 were treatment experienced. Among treatment-experienced patients, the most common reasons for switch to EVG/COBI/FTC/TAF were safety concerns, followed by regimen simplification and adverse drug reaction of the previous regimen (40%, 14%, and 13%, respectively). Treatment response to EVG/COBI/FTC/TAF leading to undetectable viral load in naïve patients was 69%, and in treatment-experienced patients, it was 83% with an overall response among all patients of 79%. Excluding those who left the country and whose data were not available, the response rate will be 86%. Tolerability was excellent with mild side effects and no discontinuation due to side effects.

Conclusion

Experience with the use of EVG/COBI/FTC/TAF in 100 patients with HIV infection in Qatar was favourable both in treatment naïve patients and in those who were treatment experienced with an excellent tolerability.

Intracellular Tenofovir-Diphosphate and Emtricitabine-Triphosphate in Dried Blood Spots Following Tenofovir Alafenamide: The TAF-DBS Study

BACKGROUND

Tenofovir alafenamide (TAF), in combination with FTC, was recently approved for PrEP in the United States. The objective of this study was to assess the relationship between tenofovir-diphosphate (TFV-DP) and emtricitabine-triphosphate (FTC-TP) in dried blood spots (DBS) with adherence to TAF/FTC.

METHODS

TAF-DBS was a randomized, crossover clinical study of TFV-DP in DBS, following directly observed dosing of 33%, 67%, or 100% of daily TAF (25 mg)/FTC (200 mg). Healthy volunteers were randomized to 2 different, 12-week dosing regimens, separated by a 12-week washout. DBS were collected weekly. TFV-DP and FTC-TP were extracted from two 7-mm punches and assayed with LC-MS/MS.

RESULTS

Thirty-seven participants (17 female, 7 African American, and 6 Hispanic) were included. TFV-DP exhibited a mean half-life of 20.8 days (95% confidence interval: 19.3 to 21.3). The slope for TFV-DP versus dosing arm was 1.14 (90% confidence interval: 1.07 to 1.21). The mean (SD) TFV-DP after 12 weeks was 657 (186), 1451 (501), and 2381 (601) fmol/2 7-mm punches for the 33%, 67%, and 100% arms. The following adherence interpretations are proposed: <450 fmol/punches, <2 doses/wk; 450-949 fmol/punches, 2-3 doses/wk; 950-1799 fmol/punches, 4-6 doses/wk; and ≥1800 fmol/punches, 7 doses/wk. FTC-TP was quantifiable for 1 week after drug cessation in 50%, 92%, and 100% of participants in the 33%, 67%, and 100% arms, respectively.

CONCLUSION

TFV-DP in DBS after TAF/FTC exhibited a long half-life and was linearly associated with dosing, similar to its predecessor tenofovir disoproxil fumarate. FTC-TP was quantifiable for up to 1 week after drug cessation. Together, these moieties provide complementary measures of cumulative adherence and recent dosing for TAF/FTC.

The crosstalk between antiretrovirals pharmacology and HIV drug resistance

INTRODUCTION

The clinical development of antiretroviral drugs has been followed by a rapid and concomitant development of HIV drug resistance. The development and spread of HIV drug resistance is due on the one hand to the within-host intrinsic HIV evolutionary rate and on the other to the wide use of low genetic barrier antiretrovirals.

AREAS COVERED

We searched PubMed and Embase on 31 January 2020, for studies reporting antiretroviral resistance and pharmacology. In this review, we assessed the molecular target and mechanism of drug resistance development of the different antiretroviral classes focusing on the currently approved antiretroviral drugs. Then, we assessed the main pharmacokinetic/pharmacodynamic of the antiretrovirals. Finally, we retraced the history of antiretroviral treatment and its interconnection with antiretroviral worldwide resistance development both in , and middle-income countries in the perspective of 90-90-90 World Health Organization target.

EXPERT OPINION

Drug resistance development is an invariably evolutionary driven phenomenon, which challenge the 90-90-90 target. In high-income countries, the antiretroviral drug resistance seems to be stable since the last decade. On the contrary, multi-intervention strategies comprehensive of broad availability of high genetic barrier regimens should be implemented in resource-limited setting to curb the rise of drug resistance.

Tenofovir prodrugs potently inhibit Epstein-Barr virus lytic DNA replication by targeting the viral DNA polymerase

Epstein-Barr virus (EBV) is a ubiquitous human γ-herpesvirus that establishes life-long infection and increases the risk for the development of several cancers and autoimmune diseases. The mechanisms by which chronic EBV infection leads to subsequent disease remain incompletely understood. Lytic reactivation plays a central role in the development of EBV-driven cancers and may contribute to other EBV-associated diseases. Thus, the clinical use of antivirals as suppressive therapy for EBV lytic reactivation may aid efforts aimed at disease prevention. Current antivirals for EBV have shown limited clinical utility due to low potency or high toxicity, leaving open the need for potent antivirals suitable for long-term prophylaxis. In the present study, we show that tenofovir disoproxil fumarate (TDF) and tenofovir alafenamide (TAF), drugs with excellent safety profiles used clinically for HIV prevention, inhibit EBV lytic DNA replication, with respective IC50 values of 0.30 μM and 84 nM. In a cell-based assay, TAF was 35- and 24-fold and TDF was 10- and 7-fold more potent than acyclovir and penciclovir, respectively, and TAF was also twice as potent as ganciclovir. The active metabolite of tenofovir prodrugs, tenofovir-diphosphate, inhibited the incorporation of dATP into a primed DNA template by the EBV DNA polymerase in vitro. In contrast to acyclovir, treatment of cells during latency for 24 h with TAF still inhibited EBV lytic DNA replication at 72 h after drug was removed. Our results suggest that tenofovir prodrugs may be particularly effective as inhibitors of EBV lytic reactivation, and that clinical studies to address critical questions about disease prevention are warranted.

Planning HIV therapy to prevent future comorbidities: patient years for tenofovir alafenamide

Since the introduction of suppressive antiretroviral therapy (ART), HIV has become a chronic disease, with infected people in high-income countries approaching similar life expectancy to the general population. As this population ages, an increasing number of people with HIV are living with age-, treatment-, and disease-related comorbidities. Lifestyle factors such as smoking, alcohol abuse, and substance misuse have a role in age-related comorbidity. Some degree of immune dysfunction is suggested by the presence of markers of immune activation/inflammation despite effective suppression of HIV replication. Cumulative exposure to some antiretroviral drugs contributes to HIV-associated comorbidities, with risk increasing with age. Specifically, tenofovir disoproxil fumarate (TDF), ritonavir-boosted atazanavir, and ritonavir-boosted lopinavir are associated with renal impairment, and TDF is known to cause loss of bone mineral density. Tenofovir alafenamide (TAF) was developed to improve on the safety profile of TDF, while maintaining its efficacy. TAF has better stability in plasma, and higher intracellular accumulation of tenofovir diphosphate in target cells, which has resulted in improved antiviral activity at lower doses with improved renal and bone safety. TAF has been studied extensively in randomized clinical trials and real-world studies. TAF-based regimens are recommended over TDF-containing regimens for the improved safety profile.

Pharmacokinetics of a weekly transdermal delivery system of tenofovir alafenamide in hairless rats

Tenofovir alafenamide (TAF) is a potent prodrug of tenofovir (TFV) for HIV prophylaxis, and HIV and HBV treatment. Compared to oral daily doses, transdermal administration of TAF may be more advantageous for long-term adherence by offering sustained drug delivery and reduced dosing frequency. Here, we described the plasma pharmacokinetics (PK) of an optimized once-weekly suspension transdermal delivery system (TDS) for TAF (96 mg/25 cm² of TDS) in female hairless rats. Over the study period, the TAF TDS delivered an overall low level of TAF (median: 1.43 [0.02-3.28] ng/mL) and a sustained level of the stable metabolite and parent drug, TFV. Relative to the projected exposure corresponding to six-day oral daily doses, a comparable TAF exposure but a substantially lower TFV exposure was resulted from the TAF TDS, suggesting a lower risk of TFV-associated adverse effects. TAF, TFV, and phosphorylated TFVs (TFV-monophosphate and diphosphate) were found distributed in vaginal tissue, the portal of entry for HIV during male-to-female sexual transmission. Skin adhesion and tolerance were acceptable given the animal model used. PK evaluation of the TAF TDS in hairless rats demonstrates the proof of concept that transdermal delivery can be an alternative route for a sustained, once-weekly systemic delivery of TAF.

Co-crystals, Salts or Mixtures of Both? The Case of Tenofovir Alafenamide Fumarates

Tenofovir alafenamide fumarate (TAF) is the newest prodrug of tenofovir that constitutes several drug products used for the treatment of HIV/AIDS. Although the solid-state properties of its predecessor tenofovir disoproxil fumarate have been investigated and described in the literature, there are no data in the scientific literature on the solid state properties of TAF. In our report, we describe the preparation of two novel polymorphs II and III of tenofovir alafenamide monofumarate (TA MF2 and TA MF3). The solid-state structure of these compounds was investigated in parallel to the previously known tenofovir alafenamide monofumarate form I (TA MF1) and tenofovir alafenamide hemifumarate (TA HF). Interestingly, the single-crystal X-ray diffraction of TA HF revealed that this derivative exists as a co-crystal form. In addition, we prepared a crystalline tenofovir alafenamide free base (TA) and its hydrochloride salt (TA HCl), which enabled us to determine the structure of TA MF derivatives using ¹⁵N-ssNMR (¹⁵N-solid state nuclear magnetic resonance). Surprisingly, we observed that TA MF1 exists as a mixed ionization state complex or pure salt, while TA MF2 and TA MF3 can be obtained as pure co-crystal forms.

Tenofovir alafenamide use in pregnant and lactating women living with HIV

Introduction: Tenofovir alafenamide (TAF)-containing fixed-dose drug combinations (FDCs) are increasingly being used in managing pregnant women living with HIV. However, TAF is not currently recommended during pregnancy due to limited pharmacokinetic and safety data. TAF, a newer nucleotide phosphonamidate prodrug of tenofovir (TFV), achieves high levels of tenofovir-diphosphate in lymphoid cells and hepatocytes, and 90% lower systemic concentrations of TFV compared to tenofovir disoproxil fumarate (TDF), thereby maximizing TAF's antiviral efficacy, potency and clinical safety.Areas covered: This review discusses the currently available information on the pharmacology of TAF in pregnant women living with HIV. Pharmacokinetic studies with TAF during pregnancy have yielded varying results compared to postpartum, but TAF exposures during pregnancy have been within the range of those typically observed in non-pregnant adults. The efficacy and safety of TAF in treatment-naïve pregnant women living with HIV is currently being evaluated in the VESTED study, a phase-III NIH randomized clinical trial.Expert opinion: Initial pregnancy data suggest that TAF-based FDCs have high efficacy and low risk of adverse effects during pregnancy. TAF is likely to become part of first-line regimens for use in pregnant women living with HIV once additional pregnancy data from phase III trials are available.

Antiretroviral potency of 4'-ethnyl-2'-fluoro-2'-deoxyadenosine, tenofovir alafenamide and second-generation NNRTIs across diverse HIV-1 subtypes

Objectives

4'-Ethnyl-2'-fluoro-2'-deoxyadenosine (EFdA) is a novel translocation-defective reverse transcriptase inhibitor. We investigated the virological and biochemical inhibitory potentials of EFdA against a broad spectrum of subtype-specific chimeric viruses and compared it with tenofovir alafenamide, nevirapine, efavirenz, rilpivirine and etravirine.

Methods

pNL4.3 chimeric viruses encoding gag-pol from treatment-naive patients (n = 24) and therapy-failure patients (n = 3) and a panel of reverse transcriptase inhibitor-resistant strains (n = 7) were used to compare the potency of reverse transcriptase inhibitor drugs. The phenotypic drug susceptibility assay was performed using TZM-bl cells. In vitro inhibition assays were done using patient-derived reverse transcriptase. IC50 values of NNRTIs were calculated using a PicoGreen-based spectrophotometric assay. Steady-state kinetics were used to determine the apparent binding affinity (Km.dNTP) of triphosphate form of EFdA (EFdA-TP) and dATP.

Results

Among the chimeric treatment-naive viruses, EFdA had an ex vivo antiretroviral activity [median (IQR) EC50 = 1.4 nM (0.6-2.1 nM)] comparable to that of tenofovir alafenamide [1.6 nM (0.5-3.6 nM)]. Subtype-specific differences were found for etravirine (P = 0.004) and rilpivirine (P = 0.017), where HIV-1C had the highest EC50 values. EFdA had a greater comparative efficiency [calculated by dividing the efficiency of monophosphate form of EFdA (EFdA-MP) incorporation (kcat.EFdA-TP/Km.EFdA-TP) over the efficiency of dATP incorporation (kcat.dATP/Km.dATP)] compared with the natural substrate dATP, with a fold change of between 1.6 and 3.2. Ex vivo analysis on reverse transcriptase inhibitor-resistant strains showed EFdA to have a higher potency. Despite the presence of rilpivirine DRMs, some non-B strains showed hypersusceptibility to rilpivirine.

Conclusions

Our combined virological and biochemical data suggest that EFdA inhibits both WT and reverse transcriptase inhibitor-resistant viruses efficiently in a subtype-independent manner. In contrast, HIV-1C is least susceptible to etravirine and rilpivirine.

Synthesis and Antimicrobial Evaluation of γ-Borono Phosphonate Compounds in Escherichia coli and Mycobacterium smegmatis

Drug resistance in bacteria is a serious threat, and drugs with novel modes of action are constantly needed. Fosmidomycin is a naturally occurring antibiotic that inhibits the nonmevalonate pathway via inhibition of the enzyme 1-deoxylulose-5-phosphate reductoisomerase (DXR). This work is the first report in which a boronic acid is evaluated as an isostere of the retrohydroxamate moiety of fosmidomycin. We report the novel synthesis of a γ-borono phosphonate analog of fosmidomycin and its corresponding prodrugs. We evaluate the inhibition of DXR and the antimicrobial activity of γ-borono phosphonate compounds against Escherichia coli wild type, E. coli Δglycerol-3-phosphate transporter, and Mycobacterium smegmatis. Despite its structural similarities, the γ-borono phosphonate compound shows antimicrobial activity against E. coli with a mechanism of action that is different from fosmidomycin. This was proven with an underutilized method for studying in vitro inhibition of the MEP pathway in E. coli via isopentenyl pyrophosphate chemical rescue. These results indicate that these compounds may serve as a promising scaffold for developing a new class of antimicrobial agents.

A long acting nanoformulated lamivudine ProTide

A long acting (LA) hydrophobic and lipophilic lamivudine (3TC) was created as a phosphoramidate pronucleotide (designated M23TC). M23TC improved intracellular delivery of active triphosphate metabolites and enhanced antiretroviral and pharmacokinetic (PK) profiles over the native drug. A single treatment of human monocyte derived macrophages (MDM) with nanoformulated M23TC (NM23TC) improved drug uptake, retention, intracellular 3TC triphosphates and antiretroviral activities in MDM and CD4⁺ T cells. PK tests of NM23TC administered to Sprague Dawley rats demonstrated sustained prodrug and drug triphosphate levels in blood and tissues for 30 days. The development of NM23TC remains a substantive step forward in producing LA slow effective release antiretrovirals for future clinical translation.

Comparison of the Antiviral Activity of Bictegravir against HIV-1 and HIV-2 Isolates and Integrase Inhibitor-Resistant HIV-2 Mutants

We compared the activity of the integrase inhibitor bictegravir against HIV-1 and HIV-2 using a culture-based, single-cycle assay. Values of 50% effective concentrations ranged from 1.2 to 2.5 nM for 9 HIV-1 isolates and 1.4 to 5.6 nM for 15 HIV-2 isolates. HIV-2 integrase mutants G140S/Q148R and G140S/Q148H were 34- and 110-fold resistant to bictegravir, respectively; other resistance-associated mutations conferred ≤5-fold changes in bictegravir susceptibility. Our findings indicate that bictegravir-based antiretroviral therapy should be evaluated in HIV-2-infected individuals.

Twenty-Five Years of Lamivudine: Current and Future Use for the Treatment of HIV-1 Infection

Supplemental Digital Content is Available in the Text.

Innovation in medicine is a dynamic, complex, and continuous process that cannot be isolated to a single moment in time. Anniversaries offer opportunities to commemorate crucial discoveries of modern medicine, such as penicillin (1928), polio vaccination (inactivated, 1955; oral, 1961), the surface antigen of the hepatitis B virus (1967), monoclonal antibodies (1975), and the first HIV antiretroviral drugs (zidovudine, 1987). The advent of antiretroviral drugs has had a profound effect on the progress of the epidemiology of HIV infection, transforming a terminal, irreversible disease that caused a global health crisis into a treatable but chronic disease. This result has been driven by the success of antiretroviral drug combinations that include nucleoside reverse transcriptase inhibitors such as lamivudine. Lamivudine, an L-enantiomeric analog of cytosine, potently affects HIV replication by inhibiting viral reverse transcriptase enzymes at concentrations without toxicity against human polymerases. Although lamivudine was approved more than 2 decades ago, it remains a key component of first-line therapy for HIV because of its virological efficacy and ability to be partnered with other antiretroviral agents in traditional and novel combination therapies. The prominence of lamivudine in HIV therapy is highlighted by its incorporation in recent innovative treatment strategies, such as single-tablet regimens that address challenges associated with regimen complexity and treatment adherence and 2-drug regimens being developed to mitigate cumulative drug exposure and toxicities. This review summarizes how the pharmacologic and virologic properties of lamivudine have solidified its role in contemporary HIV therapy and continue to support its use in emerging therapies.

Alpha-carboxynucleoside phosphonates: direct-acting inhibitors of viral DNA polymerases

Acyclic nucleoside phosphonates represent a well-defined class of clinically used nucleoside analogs. All acyclic nucleoside phosphonates need intracellular phosphorylation before they can bind viral DNA polymerases. Recently, a novel class of alpha-carboxynucleoside phosphonates have been designed to mimic the natural 2'-deoxynucleotide 5'-triphosphate substrates of DNA polymerases. They contain a carboxyl group in the phosphonate moiety linked to the nucleobase through a cyclic or acyclic bridge. Alpha-carboxynucleoside phosphonates act as viral DNA polymerase inhibitors without any prior requirement of metabolic conversion. Selective inhibitory activity against retroviral reverse transcriptase and herpesvirus DNA polymerases have been demonstrated. These compounds have a unique mechanism of inhibition of viral DNA polymerases, and provide possibilities for further modifications to optimize and fine tune their antiviral DNA polymerase spectrum.