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Salvage radiotherapy (SRT) is the first-line treatment for prostate cancer patients with biochemical recurrence following radical prostatectomy, and new specific radiosensitizers are in urgent need to enhance SRT effect. MLN4924 (also known as Pevonedistat), a specific inhibitor of NEDD8-activating enzyme, has recently entered phase I/II clinical trials in several malignancies. By inhibiting cullin neddylation, MLN4924 inactivates Cullin-RING ligases (CRL), which have been validated as an attractive radiosensitizing target. In our study, we demonstrate that MLN4924 can be used as a potent radiosensitizer in hormone-resistant prostate cancer cells. We found that MLN4924 inhibited cullin neddylation and sensitized prostate cancer cells to irradiation (IR). Mechanistically, MLN4924 enhanced IR-induced G2 cell-cycle arrest, by inducing accumulation of WEE1/p21/p27, three well-known CRL substrates. Importantly, siRNA knockdown of WEE1/p21/p27 partially abrogated MLN4924-induced G2 cell-cycle arrest, indicating a causal role of WEE1/p21/p27 in MLN4924-induced radiosensitization. Further mechanistic studies revealed that induction of DNA damage and apoptosis also contributed to MLN4924 radiosensitization in hormone-resistant prostate cancer cells. Our findings lay the foundation for future application of MLN4924 as a potential radiosensitizer in hormone refractory prostate cancer (HRPC)., Competing Interests: The authors declare that there is no conflicts of interests regarding the publication of this paper.

On the basis of the potent antiviral activity of acyclovir and ganciclovir, selenoacyclovir (2a) and selenoganciclovir (2b) were designed based on bioisoteric rationale and synthesized via the diselenide 7 as the key intermediate. Compound 2a exhibited potent anti-HSV-1 and -2 activities while 2b exerted moderate anti-HCMV activity, indicating that these nucleosides can serve as a novel template for the development of new antiviral agents.

A series of 2'-β-substituted-6'-fluoro-cyclopentenyl-pyrimidines and -purines 8 and 9 were successfully synthesized from d-ribose in a regio- and stereoselective manner. The functionalization at the C2-position of 6'-fluoro-cyclopentenyl nucleosides was achieved via regioselective protection of a hydroxyl group at the C3-position and stereoselective formation of C2-triflate followed by direct SN2 reaction with a fluoro or azido nucleophile. All the synthesized compounds were evaluated for their anticancer activities in several tumor cell lines, but were found to be neither active nor toxic.

Stereoselective synthesis of D-5-homo-4-selenoribose, serving as a versatile intermediate for the synthesis of 4'-selenonucleosides 12a-c, was accomplished using Sharpless asymmetric epoxidation, regioselective cleavage of the α,β-epoxide, and stereoselective reduction of the ketone as the key steps.

The 2'-substituted-4'-selenoribofuranosyl pyrimidines 3a-3j were synthesized from D-ribose and assayed for anticancer activity. The 2'-azido and 2'-fluoro groups with a ribo configuration were introduced by the regioselective opening of the O2,2'-anhydronucleosides with sodium azide and (HF)x-pyridine, respectively. Among the compounds tested, only 2'-fluoro derivative 3j was found to exhibit significant anticancer activity, but was much less potent than the corresponding 2'-arabino analogue 2c. This study will provide medicinal chemists with the insight into the identification of structural requirements for the anticancer activity for the developments of biologically active nucleosides.

Endocannabinoids can affect multiple cellular targets, such as cannabinoid (CB) receptors, transient receptor potential cation channel, subfamily V, member 1 (TRPV1) and peroxisome proliferator-activated receptor γ (PPARγ). The stimuli to induce adipocyte differentiation in hBM-MSCs increase the gene transcription of the CB1 receptor, TRPV1 and PPARγ. In this study, the effects of three endocannabinoids, N-arachidonoyl ethanolamine (AEA), N-arachidonoyl dopamine (NADA) and 2-arachidonoyl glycerol (2-AG), on adipogenesis in hBM-MSCs were evaluated. The adipocyte differentiation was promoted by AEA whereas inhibited by NADA. No change was observed by the treatment of non-cytotoxic concentrations of 2-AG. The difference between AEA and NADA in the regulation of adipogenesis is associated with their effects on PPARγ transactivation. AEA can directly activate PPARγ. The effect of AEA on PPARγ in hBM-MSCs may prevail over that on the CB1 receptor mediated signal transduction, giving rise to the AEA-induced promotion of adipogenesis. In contrast, NADA had no effect on the PPARγ activity in the PPARγ transactivation assay. The inhibitory effect of NADA on adipogenesis in hBM-MSCs was reversed not by capsazepine, a TRPV1 antagonist, but by rimonabant, a CB1 antagonist/inverse agonist. Rimonabant by itself promoted adipogenesis in hBM-MSCs, which may be interpreted as the result of the inverse agonism of the CB1 receptor. This result suggests that the constantly active CB1 receptor may contribute to suppress the adipocyte differentiation of hBM-MSCs. Therefore, the selective CB1 agonists that are unable to affect cellular PPARγ activity inhibit adipogenesis in hBM-MSCs.

Liver cancer is the second-most frequent cause of cancer death in the world and is highly treatment resistant. We reported previously that inhibition of neddylation pathway with specific NAE inhibitor MLN4924, suppressed the malignant phenotypes of liver cancer. However, during the process, MLN4924 induces pro-survival autophagy as a mechanism of drug resistance. Here, we report that blockage of autophagy with clinically-available autophagy inhibitors (e.g. chloroquine) significantly enhanced the efficacy of MLN4924 on liver cancer cells by triggering apoptosis. Mechanistically, chloroquine enhanced MLN4924-induced up-regulation of pro-apoptotic proteins (e.g. NOXA) and down-regulation of anti-apoptotic proteins. Importantly, the down-regulation of NOXA expression via siRNA silencing substantially attenuated apoptosis of liver cancer cells. Further mechanistic studies revealed that blockage of autophagy augmented MLN4924-induced DNA damage and reactive oxygen species (ROS) generation. The elimination of DNA damage or blockage of ROS production significantly reduced the expression of NOXA, and thereby attenuated apoptosis and reduced growth inhibition of liver cancer cells. Moreover, blockage of autophagy enhanced the efficacy of MLN4924 in an orthotopic model of human liver cancer, with induction of NOXA and apoptosis in tumor tissues. These findings provide important preclinical evidence for clinical investigation of synergistic inhibition of neddylation and autophagy in liver cancer.

Background: 4'-seleno-homonucleosides were synthesized as next-generation nucleosides, and their cellular phosphorylation was studied to confirm the hypothesis that bulky selenium atom can sterically hinder the approach of cellular nucleoside kinase to the 5'-OH for phosphorylation., Results: 4'-seleno-homonucleosides (n = 2), with one-carbon homologation, were synthesized through a tandem seleno-Michael addition-SN2 ring cyclization. LC-MS analysis demonstrated that they were phosphorylated by cellular nucleoside kinases, resulting in anticancer activity., Conclusion: The bulky selenium atom played a key role in deciding the phosphorylation by cellular nucleoside kinases. [Formula: see text].

Therapeutic intervention in neddylation pathway is an emerging area for cancer treatment. Herein, we evaluated the clinical relevance and therapeutic potential of targeting this pathway in intrahepatic cholangiocarcinoma (ICC). Immunohistochemistry of neddylation pathway components in a cohort of 322 cases showed that E1 (NAE1 and UBA3) and E2 (UBC12) enzymes, as well as global NEDD8 conjugation, were upregulated in over 2/3 of human ICC. Notably, NAE1 was identified as an independent prognosticator for postoperative recurrence (P=0.009) and a combination of NEDD8 and NAE1 provided a better power for predicting patient clinical outcomes. In vitro treatment with MLN4924, a small-molecule NEDD8-activating enzyme inhibitor, led to a dose-dependent decrease of viability in both established and primary cholangiocarcinoma cell lines. Additionally, MLN4924 exhibited at least additive effect when combined with cisplatin. By blocking cullins neddylation, MLN4924 inactivated Cullin-Ring ligase (CRL) and caused the accumulation of CRL substrates that triggered cell cycle arrest, senescence or apoptosis. Meanwhile, MLN4924 was well-tolerated and significantly inhibited tumor growth in xenograft model of cholangiocarcinoma. Taken together, our findings indicated that upregulated neddylation pathway was involved in ICC progression and interference in this pathway could be a promising target for ICC therapy.

Based on the potent anticancer activity of the D-arabino-configured cytosine nucleoside ara-C, novel 2'-substituted-4'-selenoarabinofuranosyl pyrimidines 3a-3u, comprising azido, fluoro, and hydroxyl substituents at C-2' were designed, synthesized, and evaluated for anticancer activity. The 2'-azido group was stereoselectively introduced by the Mitsunobu reaction using diphenylphosphoryl azide (DPPA), and the 2'-fluoro group was stereoselectively introduced through the double inversions of stereochemistry via the episelenium intermediate, which was formed by the participation of the selenium atom. Among the compounds tested, the 2'-fluoro derivative 3t (X = NH2, Y = H, R = F) was found to be the most potent anticancer agent and showed more potent anticancer activity than the control, ara-C in all tested human cancer cell lines (HCT116, A549, SNU638, T47D, and PC-3) except the leukemia cell lines (K562). The anticancer activity of the 2'-substituted-4'-selenonucleosides is in the following order: 2'-F > 2'-OH > 2'-N3., (Copyright © 2014 Elsevier Masson SAS. All rights reserved.)

Background: A number of oncoproteins and tumor suppressors are known to be neddylated, but whether the neddylation pathway is entirely activated in human cancer remains unexplored., Methods: NEDD8-activating enzyme (NAE) (E1) and NEDD8-conjugating enzyme (E2) expression and global-protein neddylation were examined by immunohistochemistry, immunoblotting, and real-time polymerase chain reaction analysis. Cell proliferation, clonogenic survival, migration, and motility in vitro, as well as tumor formation and metastasis in vivo, were determined upon neddylation inhibition by MLN4924, an investigational NEDD8-activating enzyme inhibitor. Survival was analyzed with Kaplan-Meier methods and compared by the log-rank test. All statistical tests were two-sided., Results: The entire neddylation pathway, including NEDD8-activating enzyme E1, NEDD8-conjugating enzyme E2, and global-protein neddylation, is overactivated in both lung adenocarcinoma and squamous-cell carcinoma. Compared with lung adenocarcinoma patients with low expression, those with high expression had worse overall survival (NEDD8-activating enzyme E1 subunit 1 [NAE1]: hazard ratio [HR] = 2.07, 95% confidence interval [CI] = 0.95 to 4.52, P = .07; ubiquitin-conjugating enzyme E2M (UBC12): HR = 13.26, 95% CI = 1.77 to 99.35, P = .01; global protein neddylation: HR = 3.74, 95% CI = 1.65 to 8.47, P = .002). Moreover, inhibition of neddylation by the NAE inhibitor MLN4924 statistically significantly suppressed proliferation, survival, migration, and motility of lung cancer cells in vitro and tumor formation and metastasis in vivo. At the molecular level, MLN4924 inactivated Cullin-RING E3 ligases, led to accumulation of tumor-suppressive Cullin-RING E3 ligase substrates and induced phorbol-12-myristate-13-acetate-induced protein 1 (NOXA)-dependent apoptosis or cellular senescence., Conclusions: Our study highlights the overactivated neddylation pathway in lung cancer development and as a promising therapeutic target., (© The Author 2014. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.)

A novel cytidine analog fluorocyclopentenylcytosine (RX-3117; TV-1360) was characterized for its cytotoxicity in a 59-cell line panel and further characterized for cytotoxicity, metabolism and mechanism of action in 15 additional cancer cell lines, including gemcitabine-resistant variants. In both panels sensitivity varied 75-fold (IC50: 0.4- > 30 μM RX-3117). RX-3117 showed a different sensitivity profile compared to cyclopentenyl-cytosine (CPEC) and azacytidine, substrates for uridine-cytidine-kinase (UCK). Dipyridamole, an inhibitor of the equilibrative-nucleoside-transporter protected against RX-3117. Uridine and cytidine protected against RX-3117, but deoxycytidine (substrate for deoxycytidine-kinase [dCK]) not, although it protected against gemcitabine, demonstrating that RX-3117 is a substrate for UCK and not for dCK. UCK activity was abundant in all cell lines, including the gemcitabine-resistant variants. RX-3117 was a very poor substrate for cytidine deaminase (66,000-fold less than gemcitabine). RX-3117 was rapidly metabolised to its nucleotides predominantly the triphosphate, which was highest in the most sensitive cells (U937, A2780) and lowest in the least sensitive (CCRF-CEM). RX-3117 did not significantly affect cytidine and uridine nucleotide pools. Incorporation of RX-3117 into RNA and DNA was higher in sensitive A2780 and low in insensitive SW1573 cells. In sensitive U937 cells 1 μM RX-3117 resulted in 90% inhibition of RNA synthesis but 100 μM RX-3117 was required in A2780 and CCRF-CEM cells. RX-3117 at IC50 values did not affect the integrity of RNA. DNA synthesis was completely inhibited in sensitive U937 cells at 1 μM, but in other cells even higher concentrations only resulted in a partial inhibition. At IC50 values RX-3117 downregulated the expression of DNA methyltransferase. In conclusion, RX-3117 showed a completely different sensitivity profile compared to gemcitabine and CPEC, its uptake is transporter dependent and is activated by UCK. RX-3117 is incorporated into RNA and DNA, did not affect RNA integrity, depleted DNA methyltransferase and inhibited RNA and DNA synthesis. Nucleotide formation is related with sensitivity.

Although A₃AR agonists exhibit a variety of biological activities including anticancer effects, their possible anti-angiogenic effects have not yet been investigated. In the present study, we assayed the anti-angiogenic activity of thio-Cl-IB-MECA, a novel A₃AR agonist, in cultured HUVECs and mES/EB-derived endothelial cells. Thio-Cl-IB-MECA inhibited migration and tube formation by endothelial cells and dramatically decreased ex vivo microvessel sprouting in cultured mouse aortic rings. The anti-angiogenic activity of thio-Cl-IB-MECA was associated with suppression of the expression of the endothelial biomarker PECAM via regulation of PI3K/AKT/mTOR and ERK signaling in mES/EB-derived endothelial cells., (Copyright © 2013 Elsevier Inc. All rights reserved.)

The multiunit Cullin (CUL)-RING E3 ligase (CRL) controls diverse biological processes by targeting a mass of substrates for ubiquitination and degradation, whereas its dysfunction causes carcinogenesis. Post-translational neddylation of CUL, a process triggered by the NEDD8-activating enzyme E1 subunit 1 (NAE1), is required for CRL activation. Recently, MLN4924 was discovered via a high-throughput screen as a specific NAE1 inhibitor and first-in-class anticancer drug. By blocking CUL neddylation, MLN4924 inactivates CRL and causes the accumulation of CRL substrates that trigger cell cycle arrest, senescence and/or apoptosis to suppress the growth of cancer cells in vitro and in vivo. Recently, we found that MLN4924 also triggers protective autophagy in response to CRL inactivation. MLN4924-induced autophagy is attributed partially to the inhibition of mechanistic target of rapamycin (also known as mammalian target of rapamycin, MTOR) activity by the accumulation of the MTOR inhibitory protein DEPTOR, as well as reactive oxygen species (ROS)-induced stress. Moreover, the blockage of autophagy response enhances apoptosis in MLN4924-treated cells. Together, our findings not only reveal autophagy as a novel cellular response to CRL inactivation by MLN4924, but also provide a piece of proof-of-concept evidence for the combination of MLN4924 with autophagy inhibitors to enhance therapeutic efficacy.

Posttranslational neddylation of cullins in the Cullin-Ring E3 ligase (CRL) complexes is needed for proteolytic degradation of CRL substrates, whose accumulation induces cell-cycle arrest, apoptosis, and senescence. The Nedd8-activating enzyme (NAE) is critical for neddylation of CRL complexes and their growth-promoting function. Recently, the anticancer small molecule MLN4924 currently in phase I trials was determined to be an inhibitor of NAE that blocks cullin neddylation and inactivates CRL, triggering an accumulation of CRL substrates that trigger cell-cycle arrest, apoptosis, and senescence in cancer cells. Here, we report that MLN4924 also triggers autophagy in response to CRL inactivation and that this effect is important for the ability of MLN4924 to suppress the outgrowth of liver cancer cells in vitro and in vivo. MLN4924-induced autophagy was attributed partially to inhibition of mTOR activity, due to accumulation of the mTOR inhibitory protein Deptor, as well as to induction of reactive oxygen species stress. Inhibiting autophagy enhanced MLN4924-induced apoptosis, suggesting that autophagy is a survival signal triggered in response to CRL inactivation. In a xenograft model of human liver cancer, MLN4924 was well-tolerated and displayed a significant antitumor effect characterized by CRL inactivation and induction of autophagy and apoptosis in liver cancer cells. Together, our findings support the clinical investigation of MLN4924 for liver cancer treatment and provide a preclinical proof-of-concept for combination therapy with an autophagy inhibitor to enhance therapeutic efficacy., (©2012 AACR.)

On the basis of the potent biological activity of cyclopentenyl-pyrimidines, fluorocyclopentenyl-pyrimidines were designed and synthesized from D-ribose. Among these, the cytosine derivative 5a showed highly potent antigrowth effects in a broad range of tumor cell lines and very potent antitumor activity in a nude mouse tumor xenograft model implanted with A549 human lung cancer cells. However, its 2'-deoxycytidine derivative 5b did not show any antigrowth effects, indicating that 2'-hydroxyl group is essential for the biological activity.

Fluoro-homoneplanocin A (4) was synthesized from d-ribose, via the enyne ring-closing metathesis of 9, the stereoselective opening of epoxide 23a with fluoride, and a simultaneous oxidation-elimination reaction. The key intermediate 8 is expected to serve as a versatile intermediate for the synthesis of carbanucleosides., (© 2012 American Chemical Society)

An improved synthesis of DNA-dependent protein kinase inhibitor, IC86621 is described. This developed method provides an easy access to this simple molecule by using amination, acetylation and Fries rearrangement reactions.

Truncated N(6)-substituted-4'-oxo- and 4'-thioadenosine derivatives with C2 or C8 substitution were studied as dual acting A(2A) and A(3) adenosine receptor (AR) ligands. The lithiation-mediated stannyl transfer and palladium-catalyzed cross-coupling reactions were utilized for functionalization of the C2 position of 6-chloropurine nucleosides. An unsubstituted 6-amino group and a hydrophobic C2 substituent were required for high affinity at the hA(2A)AR, but hydrophobic C8 substitution abolished binding at the hA(2A)AR. However, most of synthesized compounds displayed medium to high binding affinity at the hA(3)AR, regardless of C2 or C8 substitution, and low efficacy in a functional cAMP assay. Several compounds tended to be full hA(2A)AR agonists. C2 substitution probed geometrically through hA(2A)AR docking was important for binding in order of hexynyl > hexenyl > hexanyl. Compound 4g was the most potent ligand acting dually as hA(2A)AR agonist and hA(3)AR antagonist, which might be useful for treatment of asthma or other inflammatory diseases.

The stereoselective amination of various chiral benzylic ethers using chlorosulfonyl isocyanate is developed, and the application of this method to the total synthesis of a potent antidepressant, (+)-sertraline, from readily available 1-naphthol is also described.

S-adenosylhomocysteine hydrolase (SAHH), a cellular enzyme that plays a key role in methylation reactions including those required for maturation of viral mRNA, is an important drug target in the discovery of antiviral agents. While targeting the active site is a straightforward strategy of enzyme inhibition, evidence of allosteric modulation of active site in many enzymes underscores the molecular origin of signal transduction. Information of co-evolving sequences in SAHH family and the key residues for functional dynamics that can be identified using native topology of the enzyme provide glimpses into how the allosteric signaling network, dispersed over the molecular structure, coordinates intra- and intersubunit conformational dynamics. To study the link between the allosteric communication and functional dynamics of SAHHs, we performed Brownian dynamics simulations by building a coarse-grained model based on the holo and ligand-bound structures. The simulations of ligand-induced transition revealed that the signal of intrasubunit closure dynamics is transmitted to form intersubunit contacts, which in turn invoke a precise alignment of active site, followed by the dimer-dimer rotation that compacts the whole tetrameric structure. Further analyses of SAHH dynamics associated with ligand binding provided evidence of both induced fit and population shift mechanisms and also showed that the transition-state ensemble is akin to the ligand-bound state. Besides the formation of enzyme-ligand contacts at the active site, the allosteric couplings from the residues distal to the active site are vital to the enzymatic function., (© 2011 American Chemical Society)

The stereoselective synthesis of truncated 3'-aminocarbanucleosides 4a-d via a stereo- and regioselective conversion of a diol 9 to bromoacetate 11a and their binding affinity towards the human A(3) adenosine receptor are described.

Adenosine, a purine nucleoside, is released from metabolically active cells into extracellular space and plays an important role in various pathophysiological processes. Adenosine regulates many biological responses including inflammation by the interaction with their receptors such as A₁, A(2A), A(2B), and A₃. Especially, A₃ adenosine receptor (A₃AR) is considered to be expressed in macrophage cells. To the end, A₃AR agonists have been reported to have an anti-inflammatory activity. In our continuous efforts to develop new anti-inflammatory agents, we found a novel adenosine analog, 2-chloro-N⁶-(3-iodobenzyl)-4'-thioadenosine-5'-N-methyluronamide (thio-Cl-IB-MECA), was a potent human A₃AR agonist. The study was designed to investigate whether thio-Cl-IB-MECA has an anti-inflammatory potential in mouse macrophage RAW 264.7 cells and mouse sepsis model in vivo. Thio-Cl-IB-MECA exhibited an effective anti-inflammatory activity. The expression of pro-inflammatory biomarkers including inducible nitric oxide synthase (iNOS), interleukin-1β (IL-1β), and tumor necrosis factor (TNF-α) was suppressed by the treatment of thio-Cl-IB-MECA in the protein and mRNA levels in lipopolysaccharide (LPS)-stimulated mouse macrophage RAW 264.7 cells. Further examination revealed that thio-Cl-IB-MECA inhibited LPS-induced phosphatidylinositol 3-kinase (PI3 kinase)/Akt activation, NF-kB binding activity, and β-catenin expression. In addition, in in vivo LPS-induced mouse endotoxemia model, thio-Cl-IB-MECA exerted the increase of survival rate compared to vehicle-treated mouse. The analysis of the protein levels of iNOS, IL-1β, and TNF-α was also suppressed by the compound-treated groups in lung tissues. These results suggest that thio-Cl-IB-MECA might have an anti-inflammatory activity through the inhibition of pro-inflammatory cytokine expression by modulating PI3K/Akt and NF-κB signaling pathways., (Copyright © 2011 Elsevier GmbH. All rights reserved.)

MLN4924 (1), which is in clinical trials as an anticancer agent, was stereoselectively synthesized from d-ribose via a route involving stereoselective reduction, regioselective cleavage of an isopropylidene moiety, and selective displacement of a cyclic sulfate moiety as key steps., (© 2011 American Chemical Society)

The X-ray crystal structure of human S-adenosylhomocysteine (AdoHcy) hydrolase was first determined as a tetrameric form bound with the novel mechanism-based inhibitor fluoroneplanocin A (4b). The crystallized enzyme complex showed the closed conformation and turned out to be the intermediate of mechanism-based inhibition. It confirmed that the cofactor depletion by 3'-oxidation of fluoroneplanocin A contributes to the enzyme inhibition along with the irreversible covalent modification of AdoHcy hydrolase. In addition, a series of haloneplanocin A analogues (4b-e and 5b-e) were designed and synthesized to characterize the binding role and reactivity of the halogen substituents and the 4'-CH(2)OH group. The biological evaluation and molecular modeling studies identified the key pharmacophores and structural requirements for the inhibitor binding of AdoHcy hydrolase. The inhibitory activity was decreased as the size of the halogen atom increased and/or if the 4'-CH(2)OH group was absent. These results could be utilized to design new therapeutic agents operating via AdoHcy hydrolase inhibition.

Homologated analogues 3a and 3b of potent and selective A 3 adenosine receptor ligands, IB-MECA and dimethyl-IB-MECA were synthesized from commercially available 1- O -acetyl-2,3,5-tri- O -benzoyl-β-d-ribofuranose ( 4 ) via Co 2 (CO) 8 -catalyzed siloxymethylation as a key step. Unfortunately, homologated analogues 3a and 3b did not show significant binding affinities at three subtypes of adenosine receptors, indicating that free rotation, resulting from homologation, induced unfavorable interactions in the binding site of the receptor maybe due to the presence of many conformations.

We synthesized homologated truncated 4'-thioadenosine analogues 3 in which a methylene (CH(2)) group was inserted in place of the glycosidic bond of a potent and selective A(3) adenosine receptor antagonist 2. The analogues were designed to induce maximum binding interaction in the binding site of the A(3) adenosine receptor. However, all homologated nucleosides were devoid of binding affinity at all subtypes of adenosine receptors, indicating that free rotation through the single bond allowed the compound to adopt an indefinite number of conformations, disrupting the favorable binding interaction essential for receptor recognition., (Copyright © 2010 Elsevier Ltd. All rights reserved.)

The truncated C2- and C8-substituted-4'-thioadenosine derivatives 4a-d were synthesized from D-mannose, using palladium-catalyzed cross coupling reactions as key steps. In this study, an A(3) adenosine receptor (AR) antagonist, truncated 4'-thioadenosine derivative 3 was successfully converted into a potent A(2A)AR agonist 4a (K(i) = 7.19 ± 0.6 nM) by appending a 2-hexynyl group at the C2-position of a derivative of 3 that was N(6)-substituted. However, C8-substitution greatly reduced binding affinity at the human A(2A)AR. All synthesized compounds 4a-d maintained their affinity at the human A(3)AR, but 4a was found to be a competitive A(3)AR antagonist/A(2A)AR agonist in cyclic AMP assays. This study indicates that the truncated C2-substituted-4'-thioadenosine derivatives 4a and 4b can serve as a novel template for the development of new A(2A)AR ligands.

Background: Human A(3) adenosine receptor (A(3)AR) plays an essential role in several physiopathological processes. Thus far, A(3)AR-selective ligands have been evaluated as anti-inflammation and anticancer therapeutic agents. Among these ligands, truncated thio-Cl-IB-MECA is a newly reported antagonist, and its function has not been studied., Materials and Methods: Cell viability was measured by MTS assay. Cell cycle progression was analysed by propidium iodide (PI) flow cytometric assay. The apoptotic effects were investigated by Hoechst staining and annexin V-FITC/PI staining. The signal-transduction mechanism was explored by Western blot., Results: Truncated thio-Cl-IB-MECA induced the growth arrest of T24 cells at sub-G(1) phase and provoked apoptosis but not necrosis. Apoptotic death was mediated by the activation of extracellular signal-regulated kinase (ERK) and c-Jun N-terminal kinase (JNK)., Conclusion: Since truncated thio-Cl-IB-MECA induces anti-proliferation and apoptotic effects via ERK and JNK activation, it may function as an anticancer agent in human bladder cancer cells.

The first synthesis of 4'-selenothymidine (1), a novel DNA building block, and 4'-seleno-AZT (2) was accomplished from 2-deoxy-d-ribose via stereoselective formation of 2-deoxy-4-seleno-d-furanose 17 and a Pummerer-type base condensation as key steps. 4'-Selenothymidine (1) was discovered to adopt the same 2'-endo/3'-exo conformation as thymidine, which is unusual in that 4'-selenouridine has the opposite conformation to that of uridine.

The purpose of the study was to determine whether novel, selective antagonists of human A3 adenosine receptors (ARs) derived from the A3-selective agonist Cl-IB-MECA lower intraocular pressure (IOP) and act across species. IOP was measured invasively with a micropipette by the Servo-Null Micropipette System (SNMS) and by non-invasive pneumotonometry during topical drug application. Antagonist efficacy was also assayed by measuring inhibition of adenosine-triggered shrinkage of native bovine nonpigmented ciliary epithelial (NPE) cells. Five agonist-based A3AR antagonists lowered mouse IOP measured with SNMS tonometry by 3-5 mm Hg within minutes of topical application. Of the five agonist derivatives, LJ 1251 was the only antagonist to lower IOP measured by pneumotonometry. No effect was detected pneumotonometrically over 30 min following application of the other four compounds, consonant with slower, smaller responses previously measured non-invasively following topical application of A3AR agonists and the dihydropyridine A3AR antagonist MRS 1191. Latanoprost similarly lowered SNMS-measured IOP, but not IOP measured non-invasively over 30 min. Like MRS 1191, agonist-based A3AR antagonists applied to native bovine NPE cells inhibited adenosine-triggered shrinkage. In summary, the results indicate that antagonists of human A3ARs derived from the potent, selective A3 agonist Cl-IB-MECA display efficacy in mouse and bovine cells, as well. When intraocular delivery was enhanced by measuring mouse IOP invasively, five derivatives of the A3AR agonist Cl-IB-MECA lowered IOP but only one rapidly reduced IOP measured non-invasively after topical application. We conclude that derivatives of the highly-selective A3AR agonist Cl-IB-MECA can reduce IOP upon reaching their intraocular target, and that nucleoside-based derivatives are promising A3 antagonists for study in multiple animal models.

On the basis of a bioisosteric rationale, 4'-thionucleoside analogues of IB-MECA (N(6)-(3-Iodo-benzyl)-9-(5'-methylaminocarbonyl-beta-d-ribofuranosyl)adenine), which is a potent and selective A(3) adenosine receptor (AR) agonist, were synthesized from d-gulonic acid gamma-lactone. The 4'-thio analogue (5h) of IB-MECA showed extremely high binding affinity (K(i)=0.25 nM) at the human A(3)AR and was more potent than IB-MECA (K(i)=1.4 nM). Bulky substituents at the 5'-uronamide position, such as cyclohexyl and 2-methylbenzyl, in this series of 2-H nucleoside derivatives were tolerated in A(3)AR binding, although small alkyl analogues were more potent.

The first synthesis of 2'-deoxy-2'-fluoro-4'-selenoarabinofuranosyl pyrimidines as potent anticancer agents was accomplished using the DAST fluorination as a key step. It was first revealed that selenium atom participated in the DAST fluorination of 4'-selenonucleosides and that conformational bias induced by bulky selenium acted as a decisive factor in the DAST fluorination. Among compounds tested, 2'-F-4'-seleno-ara-C (4a) exhibited highly potent anticancer activity in all cancer cell lines tested and was more potent than ara-C (1).

On the basis of potent and selective binding affinity of truncated 4'-thioadenosine derivatives at the human A(3) adenosine receptor (AR), their bioisosteric 4'-oxo derivatives were designed and synthesized from commercially available 2,3-O-isopropylidene-D-erythrono lactone. The derivatives tested in AR binding assays were substituted at the C2 and N(6) positions. All synthesized nucleosides exhibited potent and selective binding affinity at the human A(3) AR. They were less potent than the corresponding 4'-thio analogues, but showed still selective to other subtypes. The 2-Cl series generally were better than the 2-H series in view of binding affinity and selectivity. Among compounds tested, compound 5d (X=Cl, R=3-bromobenzyl) showed the highest binding affinity (K(i)=13.0+/-6.9 nM) at the hA(3) AR with high selectivity (at least 88-fold) in comparison to other AR subtypes. Like the corresponding truncated 4'-thio series, compound 5d antagonized the action of an agonist to inhibit forskolin-stimulated adenylate cyclase in hA(3) AR-expressing CHO cells. Although the 4'-oxo series were less potent than the 4'-thio series, this class of human A(3) AR antagonists is also regarded as another good template for the design of A(3) AR antagonists and for further drug development.

On the basis of inhibitory activity of truncated cyclopentenyl cytosine against S-adenosylhomocysteine hydrolase (SAH), its fluorocyclopentenyl pyrimidine derivatives were efficiently synthesized from D-ribose via electrophilic fluorination as a key step. The final nucleosides were evaluated for SAH inhibitory activity, among which the uracil derivative 9 showed significant inhibitory activity (IC(50) = 8.53 microM). They were also evaluated for cytotoxic effects in several human cancer cell lines such as fibro sarcoma, stomach cancer, leukemia, and colon cancer, but they did not show any cytotoxic effects up to 100 microM, indicating that 4'-hydroxymethyl groups are essential for the anticancer activity.

Novel D- and l-4'-thioadenosine derivatives lacking the 4'-hydroxymethyl moiety were synthesized, starting from d-mannose and d-gulonic gamma-lactone, respectively, as potent and selective species-independent A 3 adenosine receptor (AR) antagonists. Among the novel 4'-truncated 2-H nucleosides tested, a N(6)-(3-chlorobenzyl) derivative 7c was the most potent at the human A 3 AR (K i = 1.5 nM), but a N(6)-(3-bromobenzyl) derivative 7d showed the optimal species-independent binding affinity.

We have prepared 50-modified derivatives of adenosine and a corresponding (N)-methanocarba nucleoside series containing a bicyclo[3.1.0]hexane ring system in place of the ribose moiety. The compounds were examined in binding assays at three subtypes of adenosine receptors (ARs) and in functional assays at the A3 AR. The H-bonding ability of a group of 9-riboside derivatives containing a 50-uronamide moiety was reduced by modification of the NH; however these derivatives did not display the desired activity as selective A3 AR antagonists, as occurs with 50-N,N-dimethyluronamides. However, truncated (N)-methanocarba analogues lacking a 40-hydroxymethyl group were highly potent and selective antagonists of the human A3 AR. The compounds were synthesized from D-ribose using a reductive free radical decarboxylation of a 50-carboxy intermediate. A less efficient synthetic approach began with L-ribose, which was similar to the published synthesis of (N)-methanocarba A3AR agonists. Compounds 33b-39b (N6-3-halobenzyl and related arylalkyl derivatives) were potent A3AR antagonists with binding Ki values of 0.7-1.4 nM. In a functional assay of [35S]GTPcS binding, 33b (3-iodobenzyl) completely inhibited stimulation by NECA with a KB of 8.9 nM. Thus, a highly potent and selective series of A3AR antagonists has been described.

Fluoroneplanocin A, designed as a potent mechanism-based irreversible inhibitor of S-adenosylhomocysteine hydrolase (SAH), is synthesized from D-ribose via a key D-cyclopentenone intermediate. This intermediate is synthesized using a stereoselective Grignard reaction, a ring-closing metathesis (RCM) reaction, and oxidative rearrangement as key steps.

On the basis of high binding affinity of 2-hexynyl-N(6)-methyladenosine and N(6)-substituted-4'-thioadenosine derivatives at the A3 adenosine receptor (AR), novel 2-alkynyl-substituted-N(6)-methyl-4'-thioadenosine derivatives, combining the characteristics of two classes of nucleosides were designed and synthesized from D-gulonic gamma-lactone via palladium-catalyzed cross coupling reaction as a key step. Among compounds tested, only compound 3b showed moderate binding affinity at the human A3 adenosine receptor without binding affinities at other subtypes.

On the basis of potent anti-hepatitis C virus (HCV) activity of 2'-C-hydroxymethyladenosine, 3'-C-hydroxymethyl-substituted pyrimidine and purine nucleosides as potential anti-HCV agents were designed and synthesized from D-xylose via stereoselective Grignard reaction and conversion of the vinyl into hydroxymethyl group as key steps.

Human A3 adenosine receptor (A3AR) agonists showed the anti-tumor activity in various in vitro and in vivo studies. The present study investigates the anti-proliferative effect of a novel adenosine analog 2-chloro-N6-(3-iodobenzyl)-4'-thioadenosine-5'-N-methyluronamide (thio-Cl-IB-MECA) in A549 human lung cancer cells. Thio-Cl-IB-MECA induced arrest of cell cycle progression in G0/G1 phase at lower concentrations (up to 20 microM) and apoptotic cell death at a higher concentration (80 microM), which were manifested by down-regulation of cyclin D1, c-myc, and CDK4, activation of caspase-3 and -9, and cleavage of poly(ADP-ribose) polymerase (PARP). The activation of Akt-mediated signaling was also inhibited by treatment with thio-Cl-IB-MECA. These data might suggest the potential therapeutic value of an adenosine analog in the treatment of human lung cancer.

Stereoselective synthesis of novel 2',3'-didehydro-2',3'-dideoxy-4'-selenonucleosides (4'-seleno-d4Ns) 4a- c was accomplished via 4'-selenoribofuranosyl pyrimidines 11a- c, as key intermediates. 4'-Selenoribofuranosyl pyrimidines 11a- c were efficiently synthesized from d-ribose or d-gulonic gamma-lactone using a Pummerer-type condensation as a key step. Introduction of 2',3'-double bond was achieved by treating cyclic 2',3'-thiocarbonate with 1,3-dimethyl-2-phenyl-1,3,2-diazaphospholidine.

On the basis of high binding affinity of 3'-aminoadenosine derivatives 2b at the human A3 adenosine receptor (AR), 3'-acetamidoadenosine derivatives 3a-e were synthesized from 1,2:5,6-di-O-isopropylidene-D-glucose via stereoselective hydroboration as a key step. Although all synthesized compounds were totally devoid of binding affinity at the human A3AR, our results revealed that 3'-position of adenosine can only be tolerated with small size of a hydrogen bonding donor like hydroxyl or amino group in the binding site of human A3AR.

On the basis of potent and selective A(3) adenosine receptor (AR) antagonist, 2-chloro-N(6)-(3-iodobenzyl)-4'-thioadenosine-5'-N,N-dimethyluronamide, structure-activity relationships were studied for a series of 5'-N,N-dialkyluronamide derivatives, synthesized from D-gulonic gamma-lactone. From this study, it was revealed that removal of the hydrogen bond-donating ability of the 5'-uronamide was essential for the pure A(3)AR antagonism. 5'-N,N-Dimethyluronamide derivatives exhibited higher binding affinity than larger 5'-N,N-dialkyl or 5'-N,N-cycloalkylamide derivatives, indicating that steric factors are crucial in binding to the human A(3)AR. A N(6)-(3-bromobenzyl) derivative 6c (K(i)=9.32 nM) exhibited the highest binding affinity at the human A(3)AR with very low binding affinities to other AR subtypes.

The first synthesis of 4'-selenonucleosides was achieved using a Pummerer-type condensation as a key step. All stereoelectronic effects shown in 4'-oxonucleosides were overwhelmed by the size of selenium and steric interactions, driving the conformation to the C2'-endo/ C3'-exo twist (Southern) conformation.

Analogues of the P2X(7) receptor antagonist KN-62, modified at the piperazine and arylsulfonyl groups, were synthesized and assayed at the human P2X(7) receptor for inhibition of BzATP-induced effects, that is, uptake of a fluorescent dye (ethidium bromide) in stably transfected HEK293 cells and IL-1beta release in differentiated THP-1 cells. Substitution of the arylsulfonyl moiety with a nitro group increased antagonistic potency relative to methyl substitution, such that compound 21 was slightly more potent than KN-62. Substitution with D-tyrosine in 36 and sterically bulky tyrosyl 2,6-dimethyl groups [corrected] in 9 enhanced antagonistic potency.

The structure of 2',3'-didehydro-2',3'-dideoxynucleosides (d4Ns) was applied to design the novel bioisosteric 4'-seleno-d4Ns as potential inhibitors of human immunodeficiency virus reverse transcriptase (HIV RT). Conversion of 2',3'-dihydroxyl groups of 4'-selenoribofuranosyl pyrimidines into the olefin was accomplished by treatment of cyclic 2',3'-thiocarbonate with 1,3-dimethyl-2-phenyl-1,3,2-diazaphospholidine.

4'-Thioadenosines have been discovered as novel templates for A(3) adenosine ligands. Among these, 4'-thioadenosine-5'-monoalkyluronamides were discovered as novel potent and selective A(3) adenosine receptor agonists, while 4'-thioadenosine-5'-dialkyluronamides and truncated 4'-thioadenosine derivatives exhibited potent and selective antagonism at the A(3) adenosine receptor.

Improved syntheses of potent and selective A3 adenosine receptor agonists, Cl-IB-MECA and thio-Cl-IB-MECA were accomplished from cheap stating material, D-ribose. New synthetic methods were found to be superior to old methods from the viewpoint of use of cheap starting material, number of steps, and overall yields.

The role of adenosine A3 receptors in synaptic transmission under severe (7 min) and shorter (2-5 min) ischemic conditions, obtained by oxygen and glucose deprivation (OGD), was investigated in rat hippocampal slices. The effects of selective A3 agonists or antagonists were examined on field excitatory postsynaptic potentials (fEPSPs) extracellularly recorded at the dendritic level of the CA1 pyramidal region. The novel, selective A3 antagonist LJ1251 ((2R,3R,4S)-2-(2-chloro-6-(3-iodobenzylamino)-9H-purin-9-yl)tetrahydrothiophene-3,4-diol, 0.1-10 nM) protected hippocampal slices from irreversible fEPSP depression induced by severe OGD and prevented or delayed the appearance of anoxic depolarization. Similar results were obtained when severe OGD was carried out with a long, receptor-desensitizing exposure to various selective A3 agonists: 5'-N-methylcarboxamidoadenosine derivatives Cl-IB-MECA (N6-(3-iodobenzyl)-2-chloro), VT72 (N6-methoxy-2-phenylethynyl), VT158 (N6-methoxy-2-phenylethynyl), VT160 (N6-methoxy-2-(2-pyridinyl)-ethynyl), and VT163 (N6-methoxy-2-p-acetylphenylethynyl) and AR132 (N6-methyl-2-phenylethynyladenosine). The selective A3 antagonist MRS1523 (3-propyl-6-ethyl-5-[(ethylthio)carbonyl]-2-phenyl-4-propyl-3-pyridine carboxylate, 100 nM) reduced fEPSP depression evoked by 2-min OGD and induced a faster recovery of fEPSP amplitude after 5-min OGD. Similar results were obtained for 2- or 5-min OGD applied in the presence of each of the A3 agonists tested. Shorter exposure to A3 agonists significantly delayed the recovery of fEPSP amplitude after 5-min OGD. This indicates that A3 receptors, stimulated by selective A3 agonists, undergo desensitization during OGD. It is inferred that CA1 hippocampal A3 receptors stimulated by adenosine released during brief ischemia (2 and 5 min) might exert A1-like protective effects on neurotransmission. Severe ischemia would transform the A3 receptor-mediated effects from protective to injurious.