The effect of nitrostyrene on cell proliferation and macrophage immune responses

Methamphetamine (MA) use and MA-induced psychosis are associated with increasing aberrations in the compensatory immunoregulatory system, interleukin-1α, and CCL5 levels

There are only a few studies reporting on the immunological profiles of methamphetamine (MA) use, MA dependency, or MA-induced psychosis (MAP). This study measured M1 macrophage, T helper (Th)-1, Th-2, growth factor, and chemokine profiles, as well as the immune inflammatory response system (IRS) and compensatory immunoregulatory system (CIRS) in peripheral blood samples from patients with MA use (n = 51), MA dependence (n = 47), and MAP (n = 43) in comparison with controls (n = 32). We discovered that persistent MA use had a robust immunosuppressive impact on all immunological profiles. The most reliable biomarker profile of MA use is the combination of substantial CIRS suppression and a rise in selected pro-inflammatory cytokines, namely CCL27 (CTACK), CCL11 (eotaxin), and interleukin (IL)-1α. In addition, MA dependency is associated with increased immunosuppression, as demonstrated by lower stem cell factor levels and higher IL-10 levels. MAP is related to a significant decrease in all immunological profiles, particularly CIRS, and an increase in CCL5 (RANTES), IL-1α, and IL-12p70 signaling. In conclusion, long-term MA use and dependency severely undermine immune homeostasis, whereas MAP may be the consequence of increased IL-1α - CCL5 signaling superimposed on strongly depleted CIRS and Th-1 functions. The widespread immunosuppression established in longstanding MA use may increase the likelihood of infectious and immune illness or exacerbate disorders such as hepatitis and AIDS. Furthermore, elevated levels of CCL5, CCL11, CCL27, IL-1α, and/or IL-12p70 may play a role in the peripheral (atherosclerosis, cutaneous inflammation, immune aberrations, hypospermatogenesis) and central (neuroinflammation, neurotoxic, neurodegenerative, depression, anxiety, and psychosis) side effects of MA use.

Synthesis, molecular docking, and binding Gibbs free energy calculation of β-nitrostyrene derivatives: Potential inhibitors of SARS-CoV-2 3CL protease

The outbreak of novel coronavirus disease 2019 (COVID-19), caused by the novel coronavirus (SARS-CoV-2), has had a significant impact on human health and the economic development. SARS-CoV-2 3CL protease (3CLpro) is highly conserved and plays a key role in mediating the transcription of virus replication. It is an ideal target for the design and screening of anti-coronavirus drugs. In this work, seven β-nitrostyrene derivatives were synthesized by Henry reaction and β-dehydration reaction, and their inhibitory effects on SARS-CoV-2 3CL protease were identified by enzyme activity inhibition assay in vitro. Among them, 4-nitro-β-nitrostyrene (compound a) showed the lowest IC₅₀ values of 0.7297 μM. To investigate the key groups that determine the activity of β-nitrostyrene derivatives and their interaction mode with the receptor, the molecular docking using the CDOCKER protocol in Discovery Studio 2016 was performed. The results showed that the hydrogen bonds between β-NO₂ and receptor GLY-143 and the π-π stacking between the aryl ring of the ligand and the imidazole ring of receptor HIS-41 significantly contributed to the ligand activity. Furthermore, the ligand-receptor absolute binding Gibbs free energies were calculated using the Binding Affinity Tool (BAT.py) to verify its correlation with the activity of β-nitrostyrene 3CLpro inhibitors as a scoring function. The higher correlation(r²=0.6) indicates that the absolute binding Gibbs free energy based on molecular dynamics can be used to predict the activity of new β-nitrostyrene 3CLpro inhibitors. These results provide valuable insights for the functional group-based design, structure optimization and the discovery of high accuracy activity prediction means of anti-COVID-19 lead compounds.

gem-Heteroatom-Substituted Fluoroalkenes as Mimics of Amide Derivatives or Phosphates: A Comprehensive Review

gem-Heteroatom-substituted fluoroalkenes have received little attention despite their great potential in medicinal chemistry or in fine chemistry. Indeed, due to the electronic and steric similarity between the fluoroalkene moiety and the amide bond as well as the high strength of the carbon-fluorine bond, these gem-heteroatom-substituted fluoroalkenes could be envisioned as stable mimics of various important organic functions, such as phosphates, carbamates, S-thiocarbamates and ureas. We present herein an overview describing the syntheses over the last decade of heteroatom-substituted fluoroalkenes in geminal position. This review will be divided into several sections covering each the common following heteroatom: oxygen-, nitrogen-, sulfur-, phosphorus-, boron- and silicon-substituted fluoroalkenes.

Design, Synthesis and Biochemical Evaluation of Novel Ethanoanthracenes and Related Compounds to Target Burkitt's Lymphoma

Lymphomas (cancers of the lymphatic system) account for 12% of malignant diseases worldwide. Burkitt’s lymphoma (BL) is a rare form of non-Hodgkin’s lymphoma in which the cancer starts in the immune B-cells. We report the synthesis and preliminary studies on the antiproliferative activity of a library of 9,10-dihydro-9,10-ethanoanthracene based compounds structurally related to the antidepressant drug maprotiline against BL cell lines MUTU-1 and DG-75. Structural modifications were achieved by Diels-Alder reaction of the core 9-(2-nitrovinyl)anthracene with number of dienophiles including maleic anhydride, maleimides, acrylonitrile and benzyne. The antiproliferative activity of these compounds was evaluated in BL cell lines EBV⁻ MUTU-1 and EBV⁺ DG-75 (chemoresistant). The most potent compounds 13j, 15, 16a, 16b, 16c, 16d and 19a displayed IC₅₀ values in the range 0.17–0.38 μM against the BL cell line EBV⁻ MUTU-1 and IC₅₀ values in the range 0.45–0.78 μM against the chemoresistant BL cell line EBV⁺ DG-75. Compounds 15, 16b and 16c demonstrated potent ROS dependent apoptotic effects on the BL cell lines which were superior to the control drug taxol and showed minimal cytotoxicity to peripheral blood mononuclear cells (PBMCs). The results suggest that this class of compounds merits further investigation as antiproliferative agents for BL.

β-Nitrostyrene derivatives attenuate LPS-mediated acute lung injury via the inhibition of neutrophil-platelet interactions and NET release

Acute lung injury (ALI) and the acute respiratory distress syndrome (ARDS) are high-mortality and life-threatening diseases that are associated with neutrophil activation and accumulation within lung tissue. Emerging evidence indicates that neutrophil-platelet aggregates (NPAs) at sites of injury increase acute inflammation and contribute to the development of ALI. Although numerous studies have increased our understanding of the pathophysiology of ALI, there is still a lack of innovative and useful treatments that reduce mortality, emphasizing that there is an urgent need for novel treatment strategies. In this study, a new series of small compounds of β-nitrostyrene derivatives (BNSDs) were synthesized, and their anti-inflammatory bioactivities on neutrophils and platelets were evaluated. The new small compound C7 modulates neutrophil function by inhibiting superoxide generation and elastase release. Compound C7 elicits protective effects on LPS-induced paw edema and acute lung injury via the inhibition of neutrophil accumulation, proinflammatory mediator release, platelet aggregation, myeloperoxidase activity, and neutrophil extracellular trap (NET) release. NET formation was identified as the bridge for the critical interactions between neutrophils and platelets by confocal microscopy and flow cytometry. This research provides new insights for elucidating the complicated regulation of neutrophils and platelets in ALI and sheds further light on future drug development strategies for ALI/ARDS and acute inflammatory diseases.

CYT-Rx20 Inhibits Cervical Cancer Cell Growth and Migration Through Oxidative Stress-Induced DNA Damage, Cell Apoptosis, and Epithelial-to-Mesenchymal Transition Inhibition

OBJECTIVE

The β-nitrostyrene family has been reported to possess anticancer properties. However, the anticancer activity of β-nitrostyrenes on cervical cancer cells and the underlying mechanisms involved remain unexplored. In this study, a β-nitrostyrene derivative CYT-Rx20 (3'-hydroxy-4'-methoxy-β-methyl-β-nitrostyrene) was synthesized, and its anticancer activity on cervical cancer cells and the mechanisms involved were investigated.

METHODS

The effect of CYT-Rx20 on human cervical cancer cell growth was evaluated using cell viability assay. Reactive oxygen species (ROS) generation and annexin V staining were detected by flow cytometry. The protein expression levels of cleaved caspase-3, cleaved caspase-9, cleaved poly (ADPribose) polymerase, γH2AX, β-catenin, Vimentin, and Twist were measured by Western blotting. DNA double-strand breaks were determined by γ-H2AX foci formation and neutral comet assay. Migration assay was used to determine cancer cell migration. Nude mice xenograft was used to investigate the antitumor effects of CYT-Rx20 in vivo.

RESULTS

CYT-Rx20 induced cytotoxicity in cervical cancer cells by promoting cell apoptosis via ROS generation and DNA damage. CYT-Rx20-induced cell apoptosis, ROS generation, and DNA damage were reversed by thiol antioxidants. In addition, CYT-Rx20 inhibited cervical cancer cell migration by regulating the expression of epithelial-to-mesenchymal transition markers. In nude mice, CYT-Rx20 inhibited cervical tumor growth accompanied by increased expression of DNA damage marker γH2AX and decreased expression of mesenchymal markers β-catenin and Twist.

CONCLUSIONS

CYT-Rx20 inhibits cervical cancer cells in vitro and in vivo and has the potential to be further developed into an anti-cervical cancer drug clinically.

CYT-Rx20 inhibits ovarian cancer cells in vitro and in vivo through oxidative stress-induced DNA damage and cell apoptosis

PURPOSE

The β-nitrostyrene family has been previously reported to possess anticancer property. However, the biological effects of β-nitrostyrenes on ovarian cancer and the underlying mechanisms involved remain unclear. In the present study, we synthesized a β-nitrostyrene derivative, CYT-Rx20 3'-hydroxy-4'-methoxy-β-methyl-β-nitrostyrene), and investigated its anticancer effects and the putative pathways of action in ovarian cancer.

METHODS

The effects of CYT-Rx20 were analyzed using cell viability assay, reactive oxygen species (ROS) generation assay, FACS analysis, annexin V staining, immunostaining, comet assay, immunoblotting, soft agar assay, migration assay, nude mice xenograft study and immunohistochemistry.

RESULTS

CYT-Rx20 induced cytotoxicity in ovarian cancer cells by promoting cell apoptosis via ROS generation and DNA damage. CYT-Rx20-induced cell apoptosis, ROS generation and DNA damage were reversed by thiol antioxidants. In addition, CYT-Rx20 inhibited ovarian cancer cell migration by regulating the expression of epithelial to mesenchymal transition (EMT) markers. In nude mice, CYT-Rx20 inhibited ovarian tumor growth accompanied by increased expression of DNA damage marker γH2AX and decreased expression of EMT marker Vimentin.

CONCLUSIONS

CYT-Rx20 inhibits ovarian cancer cells in vitro and in vivo, and has the potential to be further developed into an anti-ovarian cancer drug clinically.

Synthetic β-nitrostyrene derivative CYT-Rx20 as inhibitor of oral cancer cell proliferation and tumor growth through glutathione suppression and reactive oxygen species induction

BACKGROUND

The β-nitrostyrene family possesses anticancer properties. In this study, β-nitrostyrene derivative CYT-Rx20 (3'-hydroxy-4'-methoxy-β-methyl-β-nitrostyrene) was synthesized and investigated its anticancer activity in oral cancer.

METHODS

Anticancer activity of CYT-Rx20 and the underlying mechanisms were analyzed using cell viability assay, reactive oxygen species (ROS) generation assay, fluorescence-activated cell sorter analysis, annexin V staining, comet assay, glutathione (GSH)/glutathione disulfide (GSSG) ratio, immunoblotting, soft agar assay, nude mice xenograft study, and immunohistochemistry.

RESULTS

CYT-Rx20-induced cell apoptosis via ROS generation and mitochondrial membrane potential reduction, associated with release of mitochondrial cytochrome C to cytosol and activation of downstream caspases and poly ADP-ribose polymerase (PARP). Furthermore, CYT-Rx20 induced mitochondrial ROS accumulation and mitochondrial dysfunction, followed by GSH downregulation. CYT-Rx20-induced cell apoptosis, ROS generation, and DNA damage were reversed by thiol antioxidants. In nude mice, CYT-Rx20 inhibited oral tumor growth accompanied by increased expression of γH2AX, GSH reductase, and cleaved-caspase-3.

CONCLUSION

CYT-Rx20 has the potential to be further developed into an antioral cancer drug clinically. © 2017 Wiley Periodicals, Inc. Head Neck 39: 1055-1064, 2017.

The Synthetic β-Nitrostyrene Derivative CYT-Rx20 Inhibits Esophageal Tumor Growth and Metastasis via PI3K/AKT and STAT3 Pathways

The β-nitrostyrene family have been implicated for anti-cancer property. However, the pharmacological role of β-nitrostyrene in esophageal cancer remain unclear. Here, a β-nitrostyrene derivative, CYT-Rx20, was synthesized and assessed for its anti-cancer activities and underlying mechanism in esophageal cancer. CYT-Rx20 induced cytotoxicity in esophageal cancer cells by promoting apoptosis through activation of caspase cascade and poly(ADP-ribose) polymerase (PARP) cleavage. Besides, CYT-Rx20 inhibited esophageal cancer cell migration and invasion by regulating the expression of epithelial to mesenchymal transition (EMT) markers. CYT-Rx20 decreased cell viability and migration through suppression of the PI3K/AKT and STAT3 pathways. Of note, the cytotoxicity and anti-migratory effect of CYT-Rx20 were enhanced by co-treatment with SC79 (AKT activator) or colivelin (STAT3 activator), suggesting the dependency of esophageal cancer cells on AKT and STAT3 for survival and migration, an oncogene addiction phenomenon. In xenograft tumor-bearing mice, CYT-Rx20 significantly reduced tumor growth of the implanted esophageal cancer cells accompanied by decreased Ki-67, phospho-AKT, and phospho-STAT3 expression. In orthotopic esophageal cancer mouse model, decreased tumor growth and lung metastasis with reduced Ki-67 and phospho-STAT3 expression were observed in mice treated with CYT-Rx20. Together, our results suggest that CYT-Rx20 is a potential β-nitrostyrene-based anticancer compound against the tumor growth and metastasis of esophageal cancer.

β-Nitrostyrenes as Potential Anti-leishmanial Agents

Development of new therapeutic approach to treat leishmaniasis has become a priority. In the present study, the antileishmanial effect of β-nitrostyrenes was investigated against in vitro promastigotes and amastigotes. A series of β-nitrostyrenes have been synthesized by using Henry reaction and were evaluated for their antimicrobial activities by broth microdilution assay and in vitro antileishmanial activities against Leishmania donovani promastigotes by following standard guidelines. The most active compounds were futher evaluated for their in vitro antileishmanial activities against intracellular amastigotes. Among the tested β-nitrostyrenes, compounds 7, 8, 9, 12, and 17 exhibited potential activities (MICs range, 0.25–8 μg/mL) against clinically significant human pathogenic fungi. However, the microbactericidal concentrations (MBCs) and the microfungicidal concentrations (MFCs) were found to be either similar or only two-fold greater than the MICs. Anti-leishmanial results demonstrated that compounds 9, 12, 14, and 18 were found to be most active among the tested samples and exhibited 50% inhibitory concentration (IC₅₀) by 23.40 ± 0.71, 37.83 ± 3.74, 40.50 ± 1.47, 55.66 ± 2.84 nM against L. donovani promastigotes and 30.5 ± 3.42, 21.46 ± 0.96, 26.43 ± 2.71, and 61.63 ± 8.02 nM respectively against intracellular L. donovani promastigotes amastigotes respectively which are comparable with standard AmB (19.60 ± 1.71 nM against promastigotes and 27.83 ± 3.26 nM against amastigotes). Compounds 9, 12, 14, and 18 were found to have potent in vitro leishmanicidal activity against L. donovani and found to be non-toxic against mammalian macrophages even at a concentration of 25 μM. Nitric oxide (NO) estimation studies reveals that these compounds are moderately inducing NO levels.

The synthetic β-nitrostyrene derivative CYT-Rx20 induces breast cancer cell death and autophagy via ROS-mediated MEK/ERK pathway

The β-nitrostyrene family has been shown to suppress cancer cell proliferation and induce programmed cell death. However, mechanisms underlying β-nitrostyrenes remain less evaluated. Here, we synthesized a β-nitrostyrene derivative, CYT-Rx20, and characterized its anticancer effect and involving mechanisms in breast cancer. We found that CYT-Rx20 arrested breast cancer cells at G2/M phase and decreased cell viability by activating the caspase cascade, accompanying with increases of poly (ADP-ribose) polymerase (PARP) cleavage and γ-H2AX expression. On the other hand, up-regulation of Beclin-1, ATG5, and LC-3 was observed in CYT-Rx20-induced autophagy, which was evidently shown by transmission electron microscopy. In addition to these, CYT-Rx20-induced breast cancer cell death, intracellular reactive oxygen species (ROS) formation and expression of phospho-ERK1/2, Beclin-1, and LC-3 were significantly reversed in the presence of N-acetyl-l-cysteine (NAC), a thiol antioxidant. Furthermore, the cytotoxicity of CYT-Rx20 was enhanced by co-treatment with the autophagy inhibitor chloroquine or bafilomycin A1, suggesting that an incomplete autophagy process could deteriorate CYT-Rx20-induced cytotoxicity. In nude mice xenograft study, CYT-Rx20 significantly reduced orthotopic tumor growth. Immunohistochemical analysis revealed elevated expression of phospho-ERK1/2 and LC-3 in tumor tissues of the mice treated with CYT-Rx20. Together, we propose that CYT-Rx20 may have potential to be further developed into a β-nitrostyrene-based anticancer compound for the treatment of breast cancer.

Synthesis of γ-nitroaldehydes containing quaternary carbon in the α-position using a 4-oxalocrotonate tautomerase whole-cell biocatalyst

Synthetically valuable quaternary carbon containing γ-nitroaldehydes were obtained from branched chain aldehydes and a range of α,β-unsaturated nitroalkenes by a whole-cell biocatalytic reaction using 4-oxalocrotonate tautomerase as catalyst.

Synthesis and serotonin transporter activity of 1,3-bis(aryl)-2-nitro-1-propenes as a new class of anticancer agents

Structural derivatives of 4-MTA, an illegal amphetamine analogue have been previously shown to have anticancer effects in vitro. In this study we report the synthesis of a series of novel 1,3-bis(aryl)-2-nitro-1-propene derivatives related in structure to 4-MTA. A number of these compounds containing a classic nitrostyrene structure are shown to have antiproliferative activities in vitro in a range of malignant cell lines, particularly against Burkitt's lymphoma derived cell lines, whilst having no effect on 'normal' peripheral blood mononuclear cells. Such effects appear to be independent of the serotonin transporter, a high affinity target for amphetamines and independent of protein tyrosine phosphatases and tubulin dynamics both of which have been previously associated with nitrostyrene-induced cell death. We demonstrate that a number of these compounds induce caspase activation, PARP cleavage, chromatin condensation and membrane blebbing in a Burkitt's lymphoma derived cell line, consistent with these compounds inducing apoptosis in vitro. Although no specific target has yet been identified for the action of these compounds, the cell death elicited is potent, selective and worthy of further investigation.

A neurotransmitter system that regulates macrophage pro-inflammatory functions

Neurotransmitters released through peripheral and autonomic nerves play an important role in the signaling from the cells of the nervous system to lymphocytes, macrophages and other cells of the immune system. Macrophages are related to numerous physiological and pathological inflammatory processes since their cytokines play an important role in the defensive responses against invasive microorganisms, atherosclerosis progress, insulin resistance, behavior deviation, hematopoiesis feedback, degenerative chronic diseases and the stimulation of the hypothalamus-hypophysis-adrenal axis. Production of pro-inflammatory cytokines by macrophages is the main target for the modulatory activity of diverse neurotransmitters. In this brief review, we show how some neurotransmitters released by the central or the autonomic nervous systems down-regulate peripheral macrophages' inflammatory functions to balance immune protective mechanisms, although they can also promote the collateral progress of diverse diseases. The possible therapeutic uses of some neurotransmitters and the agonists or antagonist of their respective receptors are included as well.

Beta-nitrostyrene derivatives as potential antibacterial agents: a structure-property-activity relationship study

A multidisciplinary project was developed, combining the synthesis of a series of beta-nitrostyrene derivatives and the determination of their physicochemical parameters (redox potentials, partition coefficients), to the evaluation of the corresponding antibacterial activity. A complete conformational analysis was also performed, in order to get relevant structural information. Subsequently, a structure-property-activity (SPAR) approach was applied, through linear regression analysis, aiming at obtaining a putative correlation between the physicochemical parameters of the compounds investigated and their antibacterial activity (both against standard strains and clinical isolates). The beta-nitrostyrene compounds displayed a lower activity towards all the tested bacteria relative to the beta-methyl-beta-nitrostyrene analogues. This was observed particularly for the 3-hydroxy-4-methoxy-beta-methyl-beta-nitrostyrene (IVb) against the Gram-positive bacteria (Staphylococcus aureus, Enterococcus faecalis and Enterococcus faecium). The SPAR results revealed the existence of a clear correlation between the redox potentials and the antibacterial activity of the series of beta-nitrostyrene derivatives under study.

Methamphetamine administration produces immunomodulation in mice

The abuse of methamphetamine (MA) is an increasingly growing problem globally and produces serious side effects. In the present study, the immunomodulating effects of MA were examined on the immune system after MA (5 mg/kg body weight) was administered daily orally for 14 d. The immune system was evaluated by the antibody response to sheep red blood cells (SRBC; plaque assay and serum immunoglobulin [Ig] G), natural killer (NK) activity, lymphocyte subpopulations in the spleen and thymus, and concanavalin A (Con A)- and lipopolysaccharide (LPS)-stimulated lymphocyte proliferation using splenocytes. Body weight, spleen weight, and thymus weight generally decreased in MA-treated mice. MA treatment induced an increase in the percentage of CD4(+) cells with simultaneous decrease in the percentages of CD8(+) and double-positive CD4(+)CD8(+) in thymus. MA inhibited the IgM plaque-forming cell number, and lowered the level of IgG, the proliferation of mitogen-stimulated B and T cells, and the growth of granulocyte-macrophage colony-forming units (CFU-GM). Exposure to MA also decreased interleukin-2 production by splenocytes. In contrast, splenic NK activity in exposed mice was significantly enhanced. Taken together, data indicate that the immune system was suppressed by oral MA exposure.

Modulation of murine macrophage function by methamphetamine

The abuse of methamphetamine (MA) is an increasingly growing problem globally and produces serious side effects. In the present study, the immunomodulating effects of MA were examined on murine peritoneal macrophages after MA (5 mg/kg body weight) was administered daily orally for 2 wk. When purified macrophages were stimulated with lipopolysaccharide (LPS), the tumoricidal activity induced by LPS was significantly suppressed by MA. MA also inhibited poly I:C-induced antiviral activity in macrophages and decreased the number of peritoneal macrophages. FACS analysis showed that the expression of CD14 was markedly decreased by MA in LPS-stimulated macrophages. The production of nitric oxide (NO) and tumor necrosis factor (TNF)-alpha: which are known to be major effector molecules in macrophage-mediated cytotoxicity, was decreased by MA. MA produced a significant effect on phagocytosis and interleukin-1 (IL-1) and IL-6 at 14 d. In addition, the level of hydrogen peroxide (H2O2) was not altered by MA. Taken together, these data indicate that MA has a differential immunomodulating effect on macrophage secretory and cellular activities.

Identification of synthetic precursors of amphetamine-like drugs using Raman spectroscopy and ab initio calculations: β-Methyl-β-nitrostyrene derivatives

The present work reports a vibrational spectroscopic study of several beta-methyl-beta-nitrostyrene derivatives, which are important intermediates in the synthesis of illicit amphetamine-like drugs, such as 3,4-methylenedioxymethamphetamine (MDMA), 3,4-methylenedioxyamphetamine (MDA), p-methoxyamphetamine (PMA) and 4-methylthioamphetamine (4-MTA). A complete conformational analysis of 3,4-methylenedioxy-beta-methyl-beta-nitrostyrene (3,4-MD-MeNS), 4-methoxy-beta-methyl-beta-nitrostyrene (4-MeO-MeNS), 4-methylthio-beta-methyl-beta-nitrostyrene (4-MeS-MeNS), was carried out by Raman spectroscopy coupled to ab initio MO calculations--both complete geometry optimisation and harmonic frequency calculation. The Raman spectra show characteristic features of these precursors, which allow their ready differentiation and identification. It was verified that the conformational behaviour of these systems is mainly determined by the stabilising effect of pi-electron delocalisation.

Potent inhibition of human telomerase by nitrostyrene derivatives

Telomerase activity is expressed in most types of cancer cells but not in normal somatic cells, suggesting that telomerase may be an important target for cancer chemotherapy. Inhibition of telomerase results in telomere erosion, leading to the subsequent growth arrest of cancer cells followed by senescence or cell death. In this study, we screened a chemical library for the inhibition of human telomerase, identifying three inhibitors. All compounds contained a common nitrostyrene moiety conjugated to different side chains. One of these compounds, 3-(3,5-dichlorophenoxy)-nitrostyrene (DPNS), showed the most potent inhibitory effect, with 50% inhibition at approximately 0.4 microM and did not inhibit DNA and RNA polymerases, including retroviral reverse transcriptase. A series of enzyme kinetic experiments suggests that DPNS is a mixed-type noncompetitive inhibitor, with an inhibitor-binding site distinct from the binding sites for the telomeric substrate primer and the deoxynucleoside-5'-triphosphates. Extensive propagation of cancer cell line in the presence of DPNS resulted in progressive telomere erosion followed by the induction of senescence phenotype. The results presented here demonstrate that DPNS is a highly selective, small-molecule telomerase inhibitor in vitro and could be useful as a lead molecule for the further development of inhibitors with an improved potential for efficacy in vivo.