The antiviral activity and mechanism of action of (S)-[3-hydroxy-2-(phosphonomethoxy)propyl] (HPMP) nucleosides

Recent Advances in Molecular Mechanisms of Nucleoside Antivirals

The search for new drugs has been greatly accelerated by the emergence of new viruses and drug-resistant strains of known pathogens. Nucleoside analogues (NAs) are a prospective class of antivirals due to known safety profiles, which are important for rapid repurposing in the fight against emerging pathogens. Recent improvements in research methods have revealed new unexpected details in the mechanisms of action of NAs that can pave the way for new approaches for the further development of effective drugs. This review accounts advanced techniques in viral polymerase targeting, new viral and host enzyme targeting approaches, and prodrug-based strategies for the development of antiviral NAs.

Potential therapeutic targets for Mpox: the evidence to date

INTRODUCTION

The global Mpox (MPX) disease outbreak caused by the Mpox virus (MPXV) in 2022 alarmed the World Health Organization (WHO) and health regulation agencies of individual countries leading to the declaration of MPX as a Public Health Emergency. Owing to the genetic similarities between smallpox-causing poxvirus and MPXV, vaccine JYNNEOS, and anti-smallpox drugs Brincidofovir and Tecovirimat were granted emergency use authorization by the United States Food and Drug Administration. The WHO also included cidofovir, NIOCH-14, and other vaccines as treatment options.

AREAS COVERED

This article covers the historical development of EUA-granted antivirals, resistance to these antivirals, and the projected impact of signature mutations on the potency of antivirals against currently circulating MPXV. Since a high prevalence of MPXV infections in individuals coinfected with HIV and MPXV, the treatment results among these individuals have been included.

EXPERT OPINION

All EUA-granted drugs have been approved for smallpox treatment. These antivirals show good potency against Mpox. However, conserved resistance mutation positions in MPXV and related poxviruses, and the signature mutations in the 2022 MPXV can potentially compromise the efficacy of the EUA-granted treatments. Therefore, MPXV-specific medications are required not only for the current but also for possible future outbreaks.

Towards the Antiviral Agents and Nanotechnology-Enabled Approaches Against Parvovirus B19

Parvovirus B19 (B19V) as a human pathogenic virus, would cause a wide range of clinical manifestations. Besides the supportive and symptomatic treatments, the only FDA-approved antiviral drug for the treatment of B19V is intravenous immunoglobulins, which however, have limited efficacy and high cost. By far, there are still no virus-specific therapeutics clinically available to treat B19V infection. Therefore, exploiting the potential targets with a deep understanding of the life cycle of B19V, are pivotal to the development of B19V-tailored effective antiviral approaches. This review will introduce antiviral agents via blocking viral invasion, inhibiting the enzymes or regulatory proteins involved in DNA synthesis, and so on. Moreover, nanotechnology-enabled approaches against B19V will also be outlined and discussed through a multidisciplinary perspective involving virology, nanotechnology, medicine, pharmaceutics, chemistry, materials science, and other fields. Lastly, the prospects of the antiviral agents and nanosystems in terms of fabrication, clinical translation and potential breakthroughs will be briefly discussed.

Advances in the Development of Antiviral Strategies against Parvovirus B19

Parvovirus B19 (B19V) is a human pathogenic virus, responsible for an ample range of clinical manifestations. Infections are usually mild, self-limiting, and controlled by the development of a specific immune response, but in many cases clinical situations can be more complex and require therapy. Presently available treatments are only supportive, symptomatic, or unspecific, such as administration of intravenous immunoglobulins, and often of limited efficacy. The development of antiviral strategies against B19V should be considered of highest relevance for increasing the available options for more specific and effective therapeutic treatments. This field of research has been explored in recent years, registering some achievements as well as interesting future perspectives. In addition to immunoglobulins, some compounds have been shown to possess inhibitory activity against B19V. Hydroxyurea is an antiproliferative drug used in the treatment of sickle-cell disease that also possesses inhibitory activity against B19V. The nucleotide analogues Cidofovir and its lipid conjugate Brincidofovir are broad-range antivirals mostly active against dsDNA viruses, which showed an antiviral activity also against B19V. Newly synthesized coumarin derivatives offer possibilities for the development of molecules with antiviral activity. Identification of some flavonoid molecules, with direct inhibitory activity against the viral non-structural (NS) protein, indicates a possible line of development for direct antiviral agents. Continuing research in the field, leading to better knowledge of the viral lifecycle and a precise understanding of virus–cell interactions, will offer novel opportunities for developing more efficient, targeted antiviral agents, which can be translated into available therapeutic options.

Acyclic nucleoside phosphonates containing the amide bond: hydroxy derivatives

Abstract

To study the influence of a linker rigidity and changes in donor-acceptor properties, three series of nucleotide analogs containing a P-X-HN-C(O)- residue (X=CH(OH)CH₂, CH(OH)CH₂CH₂, CH₂CH(OH)CH₂) as a replacement for the P-CH₂-O-CHR- fragment in acyclic nucleoside phosphonates, e.g., adefovir, cidofovir, were synthesized. EDC proved to provide good yields of the analogs from the respective ω-amino-1- or -2-hydroxyalkylphosphonates and nucleobase-derived acetic acids. New phosphorus-nucleobase linkers are characterized by two fragments of the restricted rotation within amide bonds and in four-atom units (P-CH(OH)-CH₂-N, P-CH(OH)-CH₂-C and P-CH₂-CH(OH)-C) in which antiperiplanar disposition of P and N/C atoms was deduced from ¹H and ¹³C NMR spectral data. The synthesized analogs P-X-HNC(O)-CH₂B [X=CH(OH)CH₂, CH(OH)CH₂CH₂, CH₂CH(OH)CH₂] appeared inactive in antiviral assays on a wide variety of DNA and RNA viruses at concentrations up to 100 μM, while two phosphonates showed cytostatic activity towards myeloid leukemia (K-562) and multiple myeloma cells (MM.1S) with IC₅₀ of 28.8 and 40.7 μM, respectively.

Graphical abstract

Acyclic nucleoside phosphonates containing the amide bond

Abstract

To study the influence of a linker rigidity and donor–acceptor properties, the P–CH₂–O–CHR– fragment in acyclic nucleoside phosphonates (e.g., acyclovir, tenofovir) was replaced by the P–CH₂–HN–C(O)– residue. The respective phosphonates were synthesized in good yields by coupling the straight chain of ω-aminophosphonates and nucleobase-derived acetic acids with EDC. Based on the ¹H and ¹³C NMR data, the unrestricted rotation within the methylene and 1,2-ethylidene linkers in phosphonates from series a and b was confirmed. For phosphonates containing 1,3-propylidene (series c) fragments, antiperiplanar disposition of the bulky O,O-diethylphosphonate and substituted amidomethyl groups was established. The synthesized ANPs P–X–HNC(O)–CH₂B (X = CH₂, CH₂CH₂, CH₂CH₂CH₂, CH₂OCH₂CH₂) appeared inactive in antiviral assays against a wide variety of DNA and RNA viruses at concentrations up to 100 μM while marginal antiproliferative activity (L1210 cells, IC₅₀ = 89 ± 16 μM and HeLa cells, IC₅₀ = 194 ± 19 μM) was noticed for the analog derived from (5-fluorouracyl-1-yl)acetic acid and O,O-diethyl (2-aminoethoxy)methylphosphonate.

Graphical abstract