An Overview of Marketed Nucleoside and Nucleotide Analogs

FNC (4'-azido-2'-deoxy-2'-fluoro(arbino)cytidine) as an Effective Therapeutic Agent for NHL: ROS Generation, Cell Cycle Arrest, and Mitochondrial-Mediated Apoptosis

Cytotoxic nucleoside analogs (NAs) hold great promise in cancer therapeutics by mimicking endogenous nucleosides and interfering with crucial cellular processes. Here, we investigate the potential of the novel cytidine analog, 4'-azido-2'-deoxy-2'-fluoro(arbino)cytidine (FNC), as a therapeutic agent for Non-Hodgkin lymphoma (NHL) using Dalton's lymphoma (DL) as a T-cell lymphoma model. FNC demonstrated dose- and time-dependent inhibition of DL cell growth and proliferation. IC-50 values of FNC were measured at 1 µM, 0.5 µM, and 0.1 µM after 24, 48, and 72 h, respectively. Further elucidation of FNC's mechanism of action uncovers its role in inducing apoptosis in DL cells. Notable DNA fragmentation and nuclear condensation point to activated apoptotic pathways. FNC-induced apoptosis was concomitant with changes in cellular membranes, characterized by membrane rupture and altered morphology. The robust anticancer effects of FNC are linked to its capacity to induce reactive oxygen species (ROS) production, prompting oxidative stress-mediated apoptosis. Additionally, FNC disrupted mitochondrial membrane potential (MMP), leading to mitochondrial dysfunction, further promoting apoptosis. Dysregulation of apoptotic genes, with upregulation of Bax and downregulation of Bcl-2 and Bcl-xl, implicates the mitochondrial-mediated apoptosis pathway. Furthermore, FNC-induced G2/M phase cell cycle arrest was mediated through modulation of the cell cycle inhibitor p21. Overall, this study highlights the potential of FNC as a promising therapeutic agent for NHL.

Synthesis of 2'-O-Methyl/2'-O-MOE-L-Nucleoside Derivatives and Their Applications: Preparation of G-Quadruplexes, Their Characterization, and Stability Studies

Nucleosides and their analogues constitute an important family of molecules with potential antiviral and antiproliferative activity. The enantiomers of natural nucleosides, l-nucleoside derivatives, which have comparable biological activity but more favorable toxicological properties and greater metabolic stability than d-nucleosides, have emerged as a new class of therapeutic agents. Furthermore, l-nucleosides can be used as a building block to prepare l-oligonucleotides, which have identical physical properties in terms of solubility, hybridization kinetics, and duplex thermal stability as d-oligonucleotides but completely orthogonal in nature. Consequently, they are resistant to nuclease degradation, nontoxic, and immunologically passive, which are desirable properties for biomedical applications. Herein, we describe the synthesis of several 2'-O-methyl/2'-O-MOE-l-nucleoside pyrimidine derivatives and their incorporation into G-rich oligonucleotides. Finally, we evaluated the stability and resistance against nucleases of these new G-quadruplexes, demonstrating the potential of the l-nucleosides described in this work in providing enhanced nuclease resistance with a minimal impact in the nucleic acid structural properties.

Antiviral Effect of 5'-Arylchalcogeno-3-aminothymidine Derivatives in SARS-CoV-2 Infection

The understanding that zidovudine (ZDV or azidothymidine, AZT) inhibits the RNA-dependent RNA polymerase (RdRp) of SARS-CoV-2 and that chalcogen atoms can increase the bioactivity and reduce the toxicity of AZT has directed our search for the discovery of novel potential anti-coronavirus compounds. Here, the antiviral activity of selenium and tellurium containing AZT derivatives in human type II pneumocytes cell model (Calu-3) and monkey kidney cells (Vero E6) infected with SARS-CoV-2, and their toxic effects on these cells, was evaluated. Cell viability analysis revealed that organoselenium (R3a-R3e) showed lower cytotoxicity than organotellurium (R3f, R3n-R3q), with CC50 ≥ 100 µM. The R3b and R3e were particularly noteworthy for inhibiting viral replication in both cell models and showed better selectivity index. In Vero E6, the EC50 values for R3b and R3e were 2.97 ± 0.62 µM and 1.99 ± 0.42 µM, respectively, while in Calu-3, concentrations of 3.82 ± 1.42 µM and 1.92 ± 0.43 µM (24 h treatment) and 1.33 ± 0.35 µM and 2.31 ± 0.54 µM (48 h) were observed, respectively. The molecular docking calculations were carried out to main protease (Mpro), papain-like protease (PLpro), and RdRp following non-competitive, competitive, and allosteric inhibitory approaches. The in silico results suggested that the organoselenium is a potential non-competitive inhibitor of RdRp, interacting in the allosteric cavity located in the palm region. Overall, the cell-based results indicated that the chalcogen-zidovudine derivatives were more potent than AZT in inhibiting SARS-CoV-2 replication and that the compounds R3b and R3e play an important inhibitory role, expanding the knowledge about the promising therapeutic capacity of organoselenium against COVID-19.

Industrial potential of the enzymatic synthesis of nucleoside analogs: existing challenges and perspectives

Nucleoside phosphorylases have progressed from an enzymatic curiosity to a viable synthetic tool. However, despite the recent advances in nucleoside phosphorylase-catalyzed nucleoside synthesis, the widespread application of these enzymes in industrial processes is still lacking. We attribute this gap to three key challenges, which are outlined in this short review. To address these persistent obstacles, we believe that biocatalytic nucleoside synthesis needs to embrace interdisciplinary partnerships with the fields of organic chemistry, process engineering, and flow chemistry.

An expeditious synthesis of novel DNA nucleobase mimics of (+)-anisomycin

A glycal based expeditious synthesis of novel nucleoside analogues of (+)-anisomycin is reported. Readily available tri-O-benzyl-D-glucal was converted to a partially protected trihydroxypyrrolidine that is used as a common scaffold for the introduction of various nucleobases at the primary hydroxyl centre. Nucleoside analogues possessing all four DNA bases have been synthesized. Selective acetylation at C3 position was carried out with two of these unnatural nucleosides in order to mimic the structure of (+)-anisomycin. Cytotoxicity studies of some of these nucleosides showed that they display weaker activity on HeLa cells than Ara-C.

SARS-CoV-2 nsp14 Exoribonuclease Removes the Natural Antiviral 3′-Deoxy-3′,4′-didehydro-cytidine Nucleotide from RNA

The on-going global pandemic of COVID-19 is caused by SARS-CoV-2, which features a proofreading mechanism to facilitate the replication of its large RNA genome. The 3′-to-5′ exoribonuclease (ExoN) activity of SARS-CoV-2 non-structural protein 14 (nsp14) removes nucleotides misincorporated during RNA synthesis by the low-fidelity viral RNA-dependent RNA polymerase (RdRp) and thereby compromises the efficacy of antiviral nucleoside/nucleotide analogues. Here we show biochemically that SARS-CoV-2 nsp14 can excise the natural antiviral chain-terminating nucleotide, 3′-deoxy-3′,4′-didehydro-cytidine 5′-monophosphate (ddhCMP), incorporated by RdRp at the 3′ end of an RNA strand. Nsp14 ExoN processes an RNA strand terminated with ddhCMP more efficiently than that with a non-physiological chain terminator 3′-deoxy-cytidine monophosphate (3′-dCMP), whereas RdRp is more susceptible to chain termination by 3′-dCTP than ddhCTP. These results suggest that nsp14 ExoN could play a role in protecting SARS-CoV-2 from ddhCTP, which is produced as part of the innate immune response against viral infections, and that the SARS-CoV-2 enzymes may have adapted to minimize the antiviral effect of ddhCTP.