Antitumor activity of sugar-modified cytosine nucleosides

The Persistence of Hydrogen Bonds in Pyrimidinones: From Solution to Crystal

Pyrimidinone scaffolds are present in a wide array of molecules with synthetic and pharmacological utility. The inherent properties of these compounds may be attributed to intermolecular interactions analogous to the interactions that molecules tend to establish with active sites. Pyrimidinones and their fused derivatives have garnered significant interest due to their structural features, which resemble nitrogenous bases, the foundational building blocks of DNA and RNA. Similarly, pyrimidinones are predisposed to forming N-H···O hydrogen bonds akin to nitrogenous bases. Given this context, this study explored the supramolecular features and the predisposition to form hydrogen bonds in a series of 18 substituted 4-(trihalomethyl)-2(1H)-pyrimidinones. The formation of hydrogen bonds was observed in solution via nuclear magnetic resonance (NMR) spectroscopy experiments, and subsequently confirmed in the crystalline solid state. Hence, the 18 compounds were crystallized through crystallization assays by slow solvent evaporation, followed by single-crystal X-ray diffraction (SC-XRD). The supramolecular cluster demarcation was employed to evaluate all intermolecular interactions, and all crystalline structures exhibited robust hydrogen bonds, with an average energy of approximately -21.64 kcal mol-1 (∼19% of the total stabilization energy of the supramolecular clusters), irrespective of the substituents at positions 4, 5, or 6 of the pyrimidinone core. To elucidate the nature of these hydrogen bonds, an analysis based on the quantum theory of atoms in molecules (QTAIM) revealed that the predominant intermolecular interactions are N-H···O (average of -16.55 kcal mol-1) and C-H···O (average of -6.48 kcal mol-1). Through proposing crystallization mechanisms based on molecular stabilization energy data and contact areas between molecules and employing the supramolecular cluster and retrocrystallization concepts, it was determined that altering the halogen (F/Cl) at position 4 of the pyrimidinone nucleus modifies the crystallization mechanism pathway. Notably, the hydrogen bonds present in the initial proposed steps were confirmed by 1H NMR experiments using concentration-dependent techniques.

Apoptosis, necroptosis, and pyroptosis as alternative cell death pathways induced by chemotherapeutic agents?

For decades, common chemotherapeutic drugs have been established to trigger apoptosis, the preferred immunologically "silent" form of cell death. The primary objective of this review was to show that various FDA-approved chemotherapeutic drugs, including cisplatin, cyclosporine, doxorubicin, etoposide, 5-fluorouracil, gemcitabine, paclitaxel, or vinblastine can trigger necroptosis and pyroptosis. We aimed to provide the advantages and disadvantages of the induction of the given type of cell death by chemotherapeutical agents. Moreover, we give a short overview of the molecular mechanism of each type of cell death and indicate the existing crosstalks between cell death types. Finally, we provide a comparison of cell death types to facilitate the exploration of cell death types induced by other chemotherapeutical agents. Understanding the cell death pathway induced by a drug can lessen side effects and assist the discovery of new combinations with synergistic effects and low systemic toxicity.

Water-Soluble Pd-Imidate Complexes as Versatile Catalysts for the Modification of Unprotected Halonucleosides

Modification of unprotected nucleosides has been attracting continuous interest, since these building blocks themselves and their phosphate-upgraded corresponding nucleotides have shown a plethora of uses in fields like biochemistry or pharmacy. Pd-catalyzed cross-coupling reactions, conducted in water or its mixtures with polar organic solvents, have frequently been the researchers' choice for the functionalization of the purine/pyrimidine base of the unprotected nucleosides. In this scenario, the availability of hydrophilic ligands and its water-soluble palladium complexes has markedly set the pace of the advances. The approach of our group to the synthesis of such complexes, Pd-imidates specifically, has faced critical stages, namely the jump to synthesize water soluble complexes from our experience working in conventional solvents, the preparation of phosphine free complexes and the overall goal of getting catalytic systems able to work close to room temperature. The continuous feedback with Kapdi's group, experienced in the chemistry of nucleosides, has produced over the last decade the interesting results in both fields presented here.

Carbohydrate-based drugs launched during 2000-2021

Carbohydrates are fundamental molecules involved in nearly all aspects of lives, such as being involved in formating the genetic and energy materials, supporting the structure of organisms, constituting invasion and host defense systems, and forming antibiotics secondary metabolites. The naturally occurring carbohydrates and their derivatives have been extensively studied as therapeutic agents for the treatment of various diseases. During 2000 to 2021, totally 54 carbohydrate-based drugs which contain carbohydrate moities as the major structural units have been approved as drugs or diagnostic agents. Here we provide a comprehensive review on the chemical structures, activities, and clinical trial results of these carbohydrate-based drugs, which are categorized by their indications into antiviral drugs, antibacterial/antiparasitic drugs, anticancer drugs, antidiabetics drugs, cardiovascular drugs, nervous system drugs, and other agents.

Ribonucleotide reductase: Implications of thiol S-nitrosylation and tyrosine nitration for different subunits

Ribonucleotide reductase (RNR) is a multi-subunit enzyme responsible for catalyzing the rate-limiting step in the production of deoxyribonucleotides essential for DNA synthesis and repair. The active RNR complex is composed of multimeric R1 and R2 subunits. The RNR catalysis involves the formation of tyrosyl radicals in R2 subunits and thiyl radicals in R1 subunits. Despite the quaternary structure and cofactor diversity, all the three classes of RNR have a conserved cysteine residue at the active site which is converted into a thiyl radical that initiates the substrate turnover, suggesting that the catalytic mechanism is somewhat similar for all three classes of the RNR enzyme. Increased RNR activity has been associated with malignant transformation, cancer cell growth, and tumorigenesis. Efforts concerning the understanding of RNR inhibition in designing potent RNR inhibitors/drugs as well as developing novel approaches for antibacterial, antiviral treatments, and cancer therapeutics with improved radiosensitization have been made in clinical research. This review highlights the precise and potent roles of NO in RNR inhibition by targeting both the subunits. Under nitrosative stress, the thiols of the R1 subunits have been found to be modified by S-nitrosylation and the tyrosyl radicals of the R2 subunits have been modified by nitration. In view of the recent advances and progresses in the field of nitrosative modifications and its fundamental role in signaling with implications in health and diseases, the present article focuses on the regulations of RNR activity by S-nitrosylation of thiols (R1 subunits) and nitration of tyrosyl residues (R2 subunits) which will further help in designing new drugs and therapies.

New Derivatives of 5-Substituted Uracils: Potential Agents with a Wide Spectrum of Biological Activity

Pyrimidine nucleoside analogues are widely used to treat infections caused by the human immunodeficiency virus (HIV) and DNA viruses from the herpes family. It has been shown that 5-substituted uracil derivatives can inhibit HIV-1, herpes family viruses, mycobacteria and other pathogens through various mechanisms. Among the 5-substituted pyrimidine nucleosides, there are not only the classical nucleoside inhibitors of the herpes family viruses, 2'-deoxy-5-iodocytidine and 5-bromovinyl-2'-deoxyuridine, but also derivatives of 1-(benzyl)-5-(phenylamino)uracil, which proved to be non-nucleoside inhibitors of HIV-1 and EBV. It made this modification of nucleoside analogues very promising in connection with the emergence of new viruses and the crisis of drug resistance when the task of creating effective antiviral agents of new types that act on other targets or exhibit activity by other mechanisms is very urgent. In this paper, we present the design, synthesis and primary screening of the biological activity of new nucleoside analogues, namely, 5'-norcarbocyclic derivatives of substituted 5-arylamino- and 5-aryloxyuracils, against RNA viruses.

Green synthesis of triazolo-nucleoside conjugates via azide–alkyne C–N bond formation

Modified nucleosides are the core precursors for the synthesis of artificial nucleic acids, and are important in the field of synthetic and medicinal chemistry. In order to synthesize various triazolo-compounds, copper and ruthenium catalysed azide–alkyne 1,3-dipolar cycloaddition reactions also known as click reaction have emerged as a facile and efficient tool due to its simplicity and convenient conditions. Introduction of a triazole ring in nucleosides enhances their therapeutic value and various photophysical properties. This review primarily focuses on the plethora of synthetic methodologies being employed to synthesize sugar modified triazolyl nucleosides, their therapeutic importance and various other applications.

Biocatalyst-mediated selective acylation and deacylation chemistry on the secondary hydroxyl/amine groups of nucleosides

Nucleosides play a pivotal role in biological systems and therefore have attracted a lot of interest as chemotherapeutic agents in drug discovery. Over the years biocatalysts have emerged as a sustainable alternative to conventional synthetic catalysts. As a nature's catalyst, they exhibit excellent selectivity, remarkable tolerance, and help in carrying out eco-friendly benign processes. The use of a biocatalyst as a regio- and enantioselective catalyst is particularly relevant in the transformations of nucleosides and their analogs because of the presence of multiple chiral centres. Herein, we discuss the recent advances in the Pseudomonas Cepacia Lipase mediated selective acylation and deacylation reactions of the secondary hydroxyl and amino groups of nucleosides and their analogs.

A convenient synthesis of branched-chain nucleoside isothiocyanates via aza-Claisen rearrangement

Stereocontrolled introduction of a nitrogen atom at either C-2' or C-3' positions of nucleosides derived from uridine, 4-N-benzoylcytidine and adenosine was investigated. An efficient and rapid procedure was employed for creating new chiral centers at C-2' and C-3' positions using [3,3]-sigmatropic aza-Claisen rearrangement of allyl thiocyanates under conventional and microwave conditions. Structure of isothiocyanate products was confirmed by 1-D and 2-D NMR spectral analyses including selective ¹H 1-D-NOE experiments.

Stimuli-responsive nanoparticles based on poly acrylic derivatives for tumor therapy

Serve side effects caused by discriminate damage of chemotherapeutic drugs to normal cell and cancer cells remain a main obstacle in clinic. Hence, continuous efforts have been made to find ways to effectively enhance drug delivery and reduce side effects. Recent decades have witnessed impressive progresses in fighting against cancer, with improved understanding of tumor microenvironment and rapid development in nanoscale drug delivery system (DDS). Nanocarriers based on biocompatible materials provide possibilities to improve antitumor efficiency and minimize off-target effects. Among all kinds of biocompatible materials applied in DDS, polymeric acrylic derivatives such as poly(acrylamide), poly(acrylic acid), poly(N-isopropylacrylamide) present inherent biocompatibility and stimuli-responsivity, and relatively easy to be functionalized. Furthermore, nanocarrier based on polymeric acrylic derivatives have demonstrated high drug encapsulation, improved uptake efficiency, prolonged circulation time and satisfactory therapeutic outcome in tumor. In this review, we aim to discuss recent progress in design and development of stimulus-responsive poly acrylic polymer based nanocarriers for tumor targeting drug delivery.

Gemcitabine-Loaded Magnetically Responsive Poly(ε-caprolactone) Nanoparticles against Breast Cancer

A reproducible and efficient interfacial polymer disposition method has been used to formulate magnetite/poly(ε-caprolactone) (core/shell) nanoparticles (average size ≈ 125 nm, production performance ≈ 90%). To demonstrate that the iron oxide nuclei were satisfactorily embedded within the polymeric solid matrix, a complete analysis of these nanocomposites by, e.g., electron microscopy visualizations, energy dispersive X-ray spectroscopy, Fourier-transform infrared spectroscopy, electrophoresis, and contact angle goniometry was conducted. The magnetic responsive behaviour of these nanoparticles was quantitatively characterized by the hysteresis cycle and qualitatively investigated by visualization of the colloid under exposure to a 0.4 T magnet. Gemcitabine entrapment into the polymeric shell reported adequate drug loading values (≈11%), and a biphasic and pH-responsive drug release profile (≈ four-fold faster Gemcitabine release at pH 5.0 compared to pH 7.4). Cytotoxicity studies in MCF-7 human breast cancer cells proved that the half maximal inhibitory concentration of Gem-loaded nanocomposites was ≈ two-fold less than that of the free drug. Therefore, these core/shell nanoparticles could have great possibilities as a magnetically targeted Gemcitabine delivery system for breast cancer treatment.

Antitumor Effect of Sugar-Modified Cytosine Nucleosides on Growth of Adult T-Cell Leukemia Cells in Mice

Adult T-cell leukemia (ATL) is a CD4⁺ T-cell neoplasm caused by human T-cell leukemia virus type I. As the prognosis for patients with ATL remains extremely poor due to resistance to conventional chemotherapy regimens, introduction of novel therapeutic agents is needed. Previous studies have reported that nucleosides 2′-deoxy-2′-methylidenecytidine (DMDC) and its derivative 2′-deoxy-2′-methylidene-5-fluorocytidine (FDMDC) exhibit antitumor activities in T-cell acute lymphoblastic leukemia (T-ALL) and solid tumor cell lines. Another nucleoside, 1-(2-azido-2-deoxy-β-D-arabinofuranosyl)cytosine (cytarazid), is considered a therapeutic drug with antitumor activity in human solid tumors. In this study, we investigated the effects of these nucleosides on cell growth in vitro and in vivo using relevant leukemia cell lines and NOD/Shi-scid, IL-2Rg^null (NOG) mice, respectively. The nucleosides demonstrated significant cytotoxic effects in ATL and T-ALL cell lines. Intraperitoneal administration of FDMDC and DMDC into tumor-bearing NOG mice resulted in significant suppression of tumor growth without lethal side effects. Our findings support a therapeutic application of these nucleosides against tumor progression by targeting DNA polymerase-dependent DNA synthesis in patients with ATL.

Design, synthesis and cytotoxic evaluation of truncated 3'-deoxy- 3', 3' difluororibofuranosyl pyrimidine nucleosides

Truncated 3'-deoxy- 3', 3' difluororibofuranosyl pyrimidine nucleoside derivatives were synthesized from d-ribose via β-apioribo pyrimidine nucleoside intermediates 11a-c. The synthetic approach signifies that truncation at C3' position of apioribose ring of 13a-c by oxidative cleavage of diols with Pb(OAc)₄ and followed by fluorination with DAST as key steps. Cytotoxic evaluation of synthesized truncated nucleoside derivatives 16a-c and 19a-c were tested against MCF7 and MDA-MB-231 breast cancer cell lines. However, only 19a was shown minimal growth suppression activity on MDA-MB-231 cancer cell lines.

Discovery, Synthesis, and Scale-up of Efficient Palladium Catalysts Useful for the Modification of Nucleosides and Heteroarenes

Nucleic acid derivatives are imperative biomolecules and are involved in life governing processes. The chemical modification of nucleic acid is a fascinating area for researchers due to the potential activity exhibited as antiviral and antitumor agents. In addition, these molecules are also of interest toward conducting useful biochemical, pharmaceutical, and mutagenic study. For accessing such synthetically useful structures and features, transition-metal catalyzed processes have been proven over the years to be an excellent tool for carrying out the various transformations with ease and under mild reaction conditions. Amidst various transition-metal catalyzed processes available for nucleoside modification, Pd-catalyzed cross-coupling reactions have proven to be perhaps the most efficient, successful, and broadly applicable reactions in both academia and industry. Pd-catalyzed C-C and C-heteroatom bond forming reactions have been widely used for the modification of the heterocyclic moiety in the nucleosides, although a single catalyst system that could address all the different requirements for nucleoside modifications isvery rare or non-existent. With this in mind, we present herein a review showcasing the recent developments and improvements from our research groups toward the development of Pd-catalyzed strategies including drug synthesis using a single efficient catalyst system for the modification of nucleosides and other heterocycles. The review also highlights the improvement in conditions or the yield of various bio-active nucleosides or commercial drugs possessing the nucleoside structural core. Scale ups wherever performed (up to 100 g) of molecules of commercial importance have also been disclosed.

Synthesis, molecular modeling and anti-cancer evaluation of a series of quinazoline derivatives

Quinazolines were surveyed as biologically relevant moieties against different cancer cell lines, so in the present study, we analyzed novel derivatives as target-oriented chemotherapeutic anti-cancer drugs. A series of 3-substituted 2-thioxo-2,3-dihydro-1H-quinazolin-4-ones 4a-e were synthesized via the reaction of 2-aminobenzoic acid (1) with isothiocyanate derivatives 2a-e. S-alkylation and S-glycosylation were carried via the reaction of 4a-e with alkyl halides and α-glycopyranosyl bromides 7a,b under anhydrous alkaline and glycoside conditions, respectively. The S-alkylated and S-glycosylated structures, and not that of the N-alkylated and N-glycosylated isomers, have been selected for the products. Conformational analysis has been studied by homo- and heteronuclear two-dimensional NMR methods (DQF-COSY, HMQC, and HMBC). The S site of alkylation and glycosylation were determined from the ¹H, ¹³C heteronuclear multiple-quantum coherence (HMQC) experiments. All derivatives were subjected to molecular docking calculations, which selected some derivatives (5n, 8c, 8g, 9c, and 9a) as promising ones based on their excellent binding affinities towards the EGFR tyrosine kinase molecular target. The in vitro cytotoxic activity against MCF-7 and HepG2 cell lines showed effective anti-proliferative activity of the analyzed derivatives with lower IC₅₀ values especially 9a with IC₅₀ = 2.09 and 2.08 μM against MCF-7 and HepG2, respectively, and their treatments were safe against the normal cell line Gingival mesenchymal stem cells (GMSC). Moreover, RT-PCR reaction investigated the apoptotic pathway for the compound 9a, which activated the P53 genes and its related genes. So, further work is recommended for developing it as a chemotherapeutic drug.

Nucleoside analogs as a radiosensitizer modulating DNA repair, cell cycle checkpoints, and apoptosis

The combination of low dose of radiation and an anticancer drug is a potent strategy for cancer therapy. Nucleoside analogs are known to have a radiosensitizing effects via the inhibition of DNA damage repair after irradiation. Certain types of nucleoside analogs have the inhibitory effects on RNA synthesis, but not DNA synthesis, with multiple functions in cell cycle modulation and apoptosis. In this review, the most up-to-date findings regarding radiosensitizing nucleoside analogs will be discussed, focusing especially on the mechanisms of action.

Synthesis and Cytostatic Effect of 3'-deoxy-3'-C-Sulfanylmethyl Nucleoside Derivatives with d-xylo Configuration

A small library of 3’-deoxy-C3’-substituted xylofuranosyl-pyrimidine nucleoside analogues were prepared by photoinduced thiol-ene addition of various thiols, including normal and branched alkyl-, 2-hydroxyethyl, benzyl-, and sugar thiols, to 3’-exomethylene derivatives of 2’,5’-di-O-tert-butyldimethylsilyl-protected ribothymidine and uridine. The bioactivity of these derivatives was studied on tumorous SCC (mouse squamous carcinoma cell) and immortalized control HaCaT (human keratinocyte) cell lines. Several alkyl-substituted analogues elicited promising cytostatic activity in low micromolar concentrations with a slight selectivity toward tumor cells. Near-infrared live-cell imaging revealed SCC tumor cell-specific mitotic blockade via genotoxicity of analogue 10, bearing an n-butyl side chain. This analogue essentially affects the chromatin structure of SCC tumor cells, inducing a condensed nuclear material and micronuclei as also supported by fluorescent microscopy. The results highlight that thiol-ene chemistry represents an efficient strategy to discover novel nucleoside analogues with non-natural sugar structures as anticancer agents.

Phase II study of DFP-10917, a deoxycytidine analog, given by 14-day continuous intravenous infusion for chemotherapy-refractory advanced colorectal cancer

Background DFP-10917 is a cytotoxic deoxycytidine analogue that causes DNA fragmentation, G₂/M-phase arrest, and apoptosis. This agent has been shown to have antitumor activity against colorectal cancer (CRC) in preclinical studies and to be tolerable in patients. The purpose of our phase II trial was to evaluate the safety, efficacy and pharmacogenomics of DFP-10917 as well as DNA damage studies in patients with advanced CRC refractory to cytotoxic chemotherapy. Methods In this single-arm, Simon two-stage, phase II trial, patients with chemotherapy-refractory advanced CRC received 2.0 mg/m²/day DFP-10917 via 14-day continuous infusion. Enrollment criteria included age ≥ 18 years, Eastern Cooperative Oncology Group status of 0 or 1, and adequate organ function. The primary endpoint was 3-month progression-free survival, defined as the proportion of patients who did not have progressive disease or death within 3 months of starting therapy. All patients who received any amount of DFP-10917 were included in the safety analysis. DNA damage study was assessed by comet assay. Results Of 28 patients initially enrolled, 26 received DFP-10917. Three patients (12%) were progression free at 3 months. The median progression-free survival was 1.3 months (95% confidence interval, 1.3-1.6 months). There were no complete or partial responses. Most patients (n = 20, 77%) had progressive disease, and only six (23%) had stable disease at any time. The trial was terminated according to the pre-planned stopping rule. The most frequent (≥5%) medication-related grade 3 or higher adverse events were neutropenia (n = 10, 38%), fatigue (n = 4, 15%), anemia (n = 3, 12%), and leukopenia (n = 3, 12%). DNA strand-breaks were detected after infusion (medians of % tail intensity were 2.89 and 12.64 on day 1 and day 15, respectively, p < 0.001, sign test). Conclusion Overall, single-agent DFP-10917 did not show meaningful antitumor activity in chemotherapy-refractory advanced CRC. The safety profile of DFP-10917 was tolerable and similar to that observed in earlier clinical studies.

Two phase I, pharmacokinetic, and pharmacodynamic studies of DFP-10917, a novel nucleoside analog with 14-day and 7-day continuous infusion schedules

Purpose DFP-10917 is a novel deoxycytidine analog with a unique mechanism of action. Brief exposure to high concentrations of DFP-10917 inhibits DNA polymerase resulting in S-phase arrest, while prolonged exposure to DFP-10917 at low concentration causes DNA fragmentation, G2/M-phase arrest, and apoptosis. DFP-10917 demonstrated activity in tumor xenografts resistant to other deoxycytidine analogs. Experimental design Two phase I studies assessed the safety, pharmacokinetic, pharmacodynamic and preliminary efficacy of DFP-10917. Patients with refractory solid tumors received DFP-10917 continuous infusion 14-day on/7-day off and 7-day on/7-day off. Enrollment required age > 18 years, ECOG Performance Status 0-2 and adequate organ function. Results 29 patients were dosed in both studies. In 14-day infusion, dose-limiting toxicities (DLT) consisting of febrile neutropenia and thrombocytopenia occurred at 4.0 mg/m²/day. At 3.0 mg/m²/day, 3 patients experienced neutropenia in cycle 2. The dose of 2.0 mg/m²/day was well tolerated in 6 patients. In 7-day infusion, grade 4 neutropenia was DLT at 4.0 mg/m²/day. The maximum tolerated dose was 3 mg/m²/day. Other toxicities included nausea, vomiting, diarrhea, neutropenia, and alopecia. Eight patients had stable disease for >12 weeks. Paired comet assays performed for 7 patients showed an increase in DNA strand breaks at day 8. Pharmacokinetic data showed dose-proportionality for steady-state concentration and AUC of DFP-10917 and its primary metabolite. Conclusion Continuous infusion of DFP-10917 is feasible and well tolerated with myelosuppression as main DLT. The recommended doses are 2.0 mg/m²/day and 3.0 mg/m²/day on the 14-day and 7-day continuous infusion schedules, respectively. Preliminary activity was suggested. Pharmacodynamic data demonstrate biological activity at the tested doses.

C5-Morpholinomethylation of N1-sulfonylcytosines by a one-pot microwave assisted Mannich reaction

A fast and efficient route for the introduction of a morpholinomethyl moiety in the C5 position of the sulfonylated cytosine nucleobase has been developed.

Preparation of intravenous injection nanoformulation via co-assemble between cholesterylated gemcitabine and cholesterylated mPEG: enhanced cellular uptake and intracellular drug controlled release

The objective of this study was to prepare the CHS-mPEG/CHS-dFdC nanoformulation could be administrated through intravenous injection in nude mice. Particularly, CHS-mPEG was selected to co-assemble with CHS-dFdC to improve the prodrug concentration and enhance the stability of nanoformulation. The nanoformulation could be prepared by codissolution-coprecipitation. All of the nanoformulations kept stable in PBS at 4 °C or simulative human plasma at 37 °C. As molar ratios of CHS-mPEG₁₉₀₀/CHS-dFdC increased from 0.1/1 to 2/1, the weight concentration of CHS-dFdC increased from 2.5 to 15 mg/mL. It was found the optimal CHS-mPEG₁₉₀₀/CHS-dFdC nanoformulation displayed controlled drug release in simulative lysosome condition. The amount of released dFdC reached up to 90% within 10 h. It also exhibited enhanced cellular uptake ability, 7-folds higher than that of dFdC during 2.5 h incubation. And it showed superior cytotoxicity resulted from the enhanced cellular uptake ability on BxPC-3 cells.

Substrates and Inhibitors of SAMHD1

SAMHD1 hydrolyzes 2'-deoxynucleoside-5'-triphosphates (dNTPs) into 2'-deoxynucleosides and inorganic triphosphate products. In this paper, we evaluated the impact of 2' sugar moiety substitution for different nucleotides on being substrates for SAMHD1 and mechanisms of actions for the results. We found that dNTPs ((2'R)-2'-H) are only permissive in the catalytic site of SAMHD1 due to L150 exclusion of (2'R)-2'-F and (2'R)-2'-OH nucleotides. However, arabinose ((2'S)-2'-OH) nucleoside-5'-triphosphates analogs are permissive to bind in the catalytic site and be hydrolyzed by SAMHD1. Moreover, when the (2'S)-2' sugar moiety is increased to a (2'S)-2'-methyl as with the SMDU-TP analog, we detect inhibition of SAMHD1’s dNTPase activity. Our computational modeling suggests that (2'S)-2'-methyl sugar moiety clashing with the Y374 of SAMHD1. We speculate that SMDU-TP mechanism of action requires that the analog first docks in the catalytic pocket of SAMHD1 but prevents the A351-V378 helix conformational change from being completed, which is needed before hydrolysis can occur. Collectively we have identified stereoselective 2' substitutions that reveal nucleotide substrate specificity for SAMHD1, and a novel inhibitory mechanism for the dNTPase activity of SAMHD1. Importantly, our data is beneficial for understanding if FDA-approved antiviral and anticancer nucleosides are hydrolyzed by SAMHD1 in vivo.

Metabolism, Biochemical Actions, and Chemical Synthesis of Anticancer Nucleosides, Nucleotides, and Base Analogs

Nucleoside, nucleotide, and base analogs have been in the clinic for decades to treat both viral pathogens and neoplasms. More than 20% of patients on anticancer chemotherapy have been treated with one or more of these analogs. This review focuses on the chemical synthesis and biology of anticancer nucleoside, nucleotide, and base analogs that are FDA-approved and in clinical development since 2000. We highlight the cellular biology and clinical biology of analogs, drug resistance mechanisms, and compound specificity towards different cancer types. Furthermore, we explore analog syntheses as well as improved and scale-up syntheses. We conclude with a discussion on what might lie ahead for medicinal chemists, biologists, and physicians as they try to improve analog efficacy through prodrug strategies and drug combinations.

A Nucleoside Anticancer Drug, 1-(3-C-Ethynyl-β-D-Ribo-Pentofuranosyl)Cytosine, Induces Depth-Dependent Enhancement of Tumor Cell Death in Spread-Out Bragg Peak (SOBP) of Proton Beam

The effect of 1-(3-C-ethynyl-β-D-ribo-pentofuranosyl)cytosine (ECyd) on proton-induced cell death was evaluated in human lung carcinoma cell line A549 and Chinese hamster fibroblast cell line V79 to enhance relative biological effectiveness (RBE) within the spread-out Bragg peak (SOBP) of proton beams. Treatment with ECyd significantly enhanced the proton-induced loss of clonogenicity and increased senescence at the center, but not at the distal edge of SOBP. The p53-binding protein 1 foci formation assay showed that ECyd decelerated the rate of DNA double-strand break (DSB) repair at the center, but not the distal region of SOBP, suggesting that the ECyd-induced enhancement of proton-induced cell death is partially associated with the inhibition of DSB repair. This study demonstrated that ECyd enhances proton-induced cell killing at all positions of SOBP, except for the distal region and minimizes the site-dependent differences in RBE within SOBP. Thus, ECyd is a unique radiosensitizer for proton therapy that may be useful because it levels the biological dose within SOBP, which improves tumor control and reduces the risk of adverse effects at the distal edge of SOBP.

Gemcitabine-based polymer-drug conjugate for enhanced anticancer effect in colon cancer

In this study, we have demonstrated gemcitabine (GEM)-conjugated amphiphilic biodegradable polymeric drug carriers. Our aim was to increase the chemotherapeutic potential of GEM in colon cancer by forming a unique polymer-drug conjugates. The polymer-drug conjugate micelles were nanosized with a typical spherical shape. The GEM-conjugated methoxy poly(ethylene glycol)-poly(lactic acid) (GEM-PL) exhibited a controlled release of drug in both the pH conditions. The developed GEM-PL efficiently killed the HT29 cancers cells in a typical time dependent manner. The clonogenic assay further confirmed the superior anticancer effect of GEM-PL which showed least number of colonies. GEM-PL formulation exhibited a significantly higher apoptosis of cancer cells (∼25%) when stained using Annexin-V/PI kit. Conjugation of GEM to the mPEG-PLA significantly enhanced the blood circulation potential in animal model compared to that of free GEM. GEM-PL could prevent quick elimination of the drug and can provide sufficient time for the greater accumulation of GEM at the tumor sites. GEM-PL showed a remarkable tumor regression effect as evident from the lowest tumor volume in HT-29 containing tumor model. Overall, mPEG-PLA/GEM conjugates showed the potential of polymer-based drug targeting and might hold significant clinical potential in the treatment of colon cancers.

Delivery of Gemcitabine Prodrugs Employing Mesoporous Silica Nanoparticles

In this paper, mesoporous silica nanoparticles (MSNs) were studied as vehicles for the delivery of the antitumoral drug gemcitabine (GEM) and of its 4-(N)-acyl derivatives, (4-(N)-valeroyl-(C5GEM), 4-(N)-lauroyl-(C12GEM) and 4-(N)-stearoyl-gemcitabine (C18GEM)). The loading of the GEM lipophilic prodrugs on MSNs was explored with the aim to obtain both a physical and a chemical protection of GEM from rapid plasmatic metabolization. For this purpose, MSNs as such or with grafted aminopropyl and carboxyethyl groups were prepared and characterized. Then, their different drug loading capacity in relation to the nature of the functional group was evaluated. In our experimental conditions, GEM was not loaded in any MSNs, while C12GEM was the most efficiently encapsulated and employed for further evaluation. The results showed that loading capacity increased with the presence of functional groups on the nanoparticles; similarly, the presence of functional groups on MSNs' surface influenced the drug release profile. Finally, the cytotoxicity of the different preparations was evaluated and data showed that C12GEM loaded MSNs are less cytotoxic than the free drug with an activity that increased with the incubating time, indicating that all these systems are able to release the drug in a controlled manner. Altogether, the results demonstrate that these MSNs could be an interesting system for the delivery of anticancer drugs.

Silicon(IV) phthalocyanines substituted axially with different nucleoside moieties. Effects of nucleoside type on the photosensitizing efficiencies and in vitro photodynamic activities

A series of new silicon(IV) phthalocyanines (SiPcs) di-substituted axially with different nucleoside moieties have been synthesized and evaluated for their singlet oxygen quantum yields (ΦΔ) and in vitro photodynamic activities. The adenosine-substituted SiPc shows a lower photosensitizing efficiency (ΦΔ=0.35) than the uridine- and cytidine-substituted analogs (ΦΔ=0.42-0.44), while the guanosine-substituted SiPc exhibits a weakest singlet oxygen generation efficiency with a ΦΔ value down to 0.03. On the other hand, replacing axial adenosines with chloro-modified adenosines and purines can result in the increase of photogenerating singlet oxygen efficiencies of SiPcs. The formed SiPcs 1 and 2, which contain monochloro-modified adenosines and dichloro-modified purines respectively, appear as efficient photosensitizers with ΦΔ of 0.42-0.44. Both compounds 1 and 2 present high photocytotoxicities against HepG2 and BGC823 cancer cells with IC50 values ranging from 9nM to 33nM. The photocytotoxicities of these two compounds are remarkably higher than the well-known anticancer photosensitizer, chlorin e6 (IC50=752nM against HepG2 cells) in the same condition. As revealed by confocal microscopy, for both cell lines, compound 1 can essentially bind to mitochondria, while compound 2 is just partially localized in mitochondria. In addition, the two compounds induce cell death of HepG2 cells likely through apoptosis.

Stereo- and regio-selective synthesis of 3′-C-substituted-(N)-methanocarba adenosines as potential anticancer agents

Synthesis of 3′-C-substituted-(N)-methanocarba adenosines using stereoselective cyclopropanation, stereoselective nucleophilic addition, regioselective isopropylidene cleavage and regioselective cyclic sulfate condensation.

The halo-substituent effect on Pseudomonas cepacia lipase-mediated regioselective acylation of nucleosides: A comparative investigation

In this work, comparative experiments were explored to investigate the substrate specificity of Pseudomonas cepacia lipase in regioselective acylation of nucleosides carrying various substituents (such as the H, F, Cl, Br, I) at 2'- and 5-positions. Experimental data indicated that the catalytic performance of the enzyme depended very much on the halo-substituents in nucleosides. The increased bulk of 2'-substituents in ribose moiety of the nucleoside might contribute to the improved 3'-regioselectivity (90-98%, nucleosides a-d) in enzymatic decanoylation, while the enhancement of regioselectivity (93-99%) in 3'-O-acylated nucleosides e-h could be attributable to the increasing hydrophobicity of the halogen atoms at 5-positions. With regard to the chain-length selectivity, P. cepacia lipase displayed the highest 3'-regioselectivity toward the longer chain (C14) as compared to shorter (C6 and C10) ones. The position, orientation and property of the substituent, specific structure of the lipase's active site, and acyl structure could account for the diverse results.

A general method for N-glycosylation of nucleobases promoted by (p-Tol)2SO/Tf2O with thioglycoside as donor

35 nucleosides were synthesized by coupling thioglycosides with pyrimidines and purines under the preactivation of (p-Tol)₂SO/Tf₂O in high yields and with β-stereoselectivities.

Synthesis and hybridization property of a boat-shaped pyranosyl nucleic acid containing an exocyclic methylene group in the sugar moiety

A boat-shaped pyranosyl nucleic acid (BsNA) having an exocyclic methylene group in the sugar moiety was synthesized to investigate the possibility that the axial H3' of original BsNA is the cause of its duplex destabilization. The synthesized BsNA analog was chemically stable against various nucleophiles. From the thermal stability of duplex oligonucleotides including the BsNA analog, it was found that the duplex-forming ability can be sensitive to the size of functional groups at the 3'-position.

Influence of organic solvents on catalytic behaviors and cell morphology of whole-cell biocatalysts for synthesis of 5'-arabinocytosine laurate

A whole-cell based method was developed for the regioselective synthesis of arabinocytosine laurate. Among the seven kinds of bacteria strains tested in the acylation reaction, Pseudomonas fluorescens gave the highest productivity and a higher 5′-regioselectivity than 99%. Compared with pure organic solvents, the use of organic solvent mixtures greatly promoted the yield of the whole-cell catalyzed reaction, but showed little influence on the 5′-regioselectivity. Of all the tested solvent mixtures, the best reaction result was found in isopropyl ether/pyridine followed by isopentanol/pyridine. However, the whole-cells showed much lower thermostability in isopropyl ether/pyridine than in THF-pyridine. To better understand the toxic effects of the organic solvents on P. fluorescens whole-cells and growing cells were further examined. Significant influences of organic solvents on the biomass of the cells were found, which differed depending on the type of solvents used. SEM analysis visually revealed the changes in the surface morphology of whole-cells and growing cells cultured in media containing various organic solvents, in terms of surface smoothness, bulges and changed cell sizes. Results demonstrated that organic toxicity to cell structure played an important role in whole-cell mediated catalysis.

3'-ethynylcytidine, an RNA polymerase inhibitor, combined with cisplatin exhibits a potent synergistic growth-inhibitory effect via Vaults dysfunction

BACKGROUND

We previously reported that 3'-ethynylcytidine (ECyd, TAS-106), an RNA polymerases inhibitor, enhances the anti-tumor efficacy of platinum in several tumor types in both in vitro and in vivo tumor models. However, the molecular mechanisms underlying the ECyd-induced enhancement remain elusive.

METHODS

Cisplatin (CDDP)-resistant head and neck cancer KB cells were established by stepwise dose escalation with CDDP. The combination effect of ECyd and CDDP were assessed using isobologram analysis. The transcriptional and post-translational statuses of several molecules were detected using real-time PCR, immunoblot analysis and immunocytochemistry. Xenograft assays were used to confirm the mechanisms underlying the ECyd induced enhancement of CDDP anti-tumor efficacy in vivo.

RESULTS

ECyd sensitized KB to CDDP by inhibiting the drug transporter Vault complex (Vaults). First, we showed that Vaults were overexpressed in CDDP-resistant KB cells. The suppression of major vault protein (MVP) by RNA interference restored the sensitivity to CDDP. Next, we showed that ECyd significantly sensitized the resistant cells to CDDP, compared with the parental paired cell line. A molecular analysis revealed that ECyd inhibited the synthesis of vRNAs as well as the induction of MVP, both of which are critical components of Vaults as a drug transporter. Furthermore, we found that the synergistic effect of ECyd and CDDP was correlated with the MVP expression level when the effect was analyzed in additional cancer cell lines. Finally, we demonstrated that ECyd decreased the vRNAs expression level in xenograft tumor.

CONCLUSIONS

Our data indicated the ability of ECyd to cancel the resistance of cancer cells to CDDP by inhibiting the Vaults function and the decrease of Vaults expression itself, and the ability of the combination therapy with CDDP and ECyd to offer a new strategy for overcoming platinum resistance. Moreover, the study results suggest that Vaults could be a biomarker for stratifying patients who may benefit from the combination therapy with ECyd and platinum.