naphthoquinones and 2-3-bis(2-hydroxyethylsulfanyl)-(1-4)naphthoquinone

The CDC25 phosphatases are key regulators of normal cell division and the cell's response to DNA damage. Earlier studies suggested non-overlapping roles for each isoform during a specific cell cycle phase. However, recent data suggest that multiple CDC25 isoforms cooperate to regulate each cell cycle transition. For instance, although CDC25A was initially thought to exclusively regulate the G(1)-S transition, recent data demonstrate a significant role for CDC25A in the G(2)-M transition. Further evidence demonstrates that in addition to the ATM/ATR-CHK pathway, a p38-MAPKAP pathway is also involved in controlling CDC25 activity during G(2)/M checkpoint activation. Together with the fact that CDC25 overexpression is reported in many cancers, these data highlight the significance of developing specific CDC25 inhibitors for cancer therapy.

Topics: Animals; Benzoquinones; cdc25 Phosphatases; Cell Cycle; Cell Cycle Proteins; Humans; Isoenzymes; Models, Biological; Naphthoquinones; Neoplasms; Quinolones; Quinones; Thiazoles

SARS-CoV-2 is responsible for COVID-19, a human disease that has caused over 2 million deaths, stretched health systems to near-breaking point and endangered economies of countries and families around the world. Antiviral treatments to combat COVID-19 are currently lacking. Remdesivir, the only antiviral drug approved for the treatment of COVID-19, can affect disease severity, but better treatments are needed. SARS-CoV-2 encodes 16 non-structural proteins (nsp) that possess different enzymatic activities with important roles in viral genome replication, transcription and host immune evasion. One key aspect of host immune evasion is performed by the uridine-directed endoribonuclease activity of nsp15. Here we describe the expression and purification of nsp15 recombinant protein. We have developed biochemical assays to follow its activity, and we have found evidence for allosteric behaviour. We screened a custom chemical library of over 5000 compounds to identify nsp15 endoribonuclease inhibitors, and we identified and validated NSC95397 as an inhibitor of nsp15 endoribonuclease in vitro. Although NSC95397 did not inhibit SARS-CoV-2 growth in VERO E6 cells, further studies will be required to determine the effect of nsp15 inhibition on host immune evasion.

Topics: Allosteric Regulation; Animals; Antiviral Agents; Chlorocebus aethiops; Drug Evaluation, Preclinical; Endoribonucleases; Enzyme Assays; Fluorescence; High-Throughput Screening Assays; In Vitro Techniques; Kinetics; Naphthoquinones; Reproducibility of Results; SARS-CoV-2; Small Molecule Libraries; Solutions; Vero Cells; Viral Nonstructural Proteins

Topics: Antineoplastic Agents; cdc25 Phosphatases; Cell Line, Tumor; Cell Survival; Enzyme Inhibitors; Humans; MAP Kinase Kinase 7; Models, Molecular; Molecular Docking Simulation; Naphthoquinones

NSC 95397, a quinone-based small molecule compound, has been identified as an inhibitor for dual-specificity phosphatases, including mitogen-activated protein kinase phosphatase-1 (MKP-1). MKP-1 is known to inactivate mitogen-activated protein kinases by dephosphorylating both of their threonine and tyrosine residues. Moreover, owing to their participation in tumorigenesis and drug resistance in colon cancer cells, MKP-1 is an attractive therapeutic target for colon cancer treatment. We therefore investigated the inhibitory activity of NSC 95397 against three colon cancer cell lines including SW480, SW620, and DLD-1, and their underlying mechanisms. The results demonstrated that NSC 95397 reduced cell viability and anchorage-independent growth of all the three colon cancer cell lines through inhibited proliferation and induced apoptosis via regulating cell-cycle-related proteins, including p21, cyclin-dependent kinases, and caspases. Besides, by using mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase (ERK) inhibitor U0126, we provided mechanistic evidence that the antineoplastic effects of NSC 95397 were achieved via inhibiting MKP-1 activity followed by ERK1/2 phosphorylation. Conclusively, our results indicated that NSC 95397 might serve as an effective therapeutic intervention for colon cancer through regulating MKP-1 and ERK1/2 pathway.

Topics: Apoptosis; Biomarkers; Caspase 3; Cell Cycle Proteins; Cell Line, Tumor; Cell Proliferation; Cell Survival; Colonic Neoplasms; Dual-Specificity Phosphatases; Humans; MAP Kinase Signaling System; Naphthoquinones; Tumor Stem Cell Assay

Cell division cycle 25 (CDC25) protein phosphatases regulate cell cycle progression through the activation of cyclin-dependent kinases (CDKs), but they are also involved in chromatin modulation and transcriptional regulation. CDC25 inhibition is regarded as a possible therapeutic strategy for the treatment of human malignancies, including acute myeloid leukemia (AML). We investigated the in vitro effects of CDC25 inhibitors on primary human AML cells derived from 79 unselected patients in suspension cultures. Both the previously well-characterized CDC25 inhibitor NSC95397, as well as five other inhibitors (BN82002 and the novel small molecular compounds ALX1, ALX2, ALX3, and ALX4), only exhibited antiproliferative effects for a subset of patients when tested alone. These antiproliferative effects showed associations with differences in genetic abnormalities and/or AML cell differentiation. However, the responders to CDC25 inhibition could be identified by analysis of global gene expression profiles. The differentially expressed genes were associated with the cytoskeleton, microtubules, and cell signaling. The constitutive release of 28 soluble mediators showed a wide variation among patients and this variation was maintained in the presence of CDC25 inhibition. Finally, NSC95397 had no or only minimal effects on AML cell viability. In conclusion, CDC25 inhibition has antiproliferative effects on primary human AML cells for a subset of patients, and these patients can be identified by gene expression profiling.

Topics: Antineoplastic Agents; Biomarkers, Pharmacological; cdc25 Phosphatases; Cell Survival; Computational Biology; Cytoskeletal Proteins; Enzyme Inhibitors; Ethylamines; Gene Expression Profiling; Gene Expression Regulation, Leukemic; Genetic Heterogeneity; Humans; Leukemia, Myeloid, Acute; Microtubule Proteins; Myeloid Cells; Naphthoquinones; Nitro Compounds; Pharmacogenetics; Primary Cell Culture; Signal Transduction; Small Molecule Libraries

The CDC25B inhibitor NSC-95397 triggers apoptosis of tumor cells and is thus considered for the treatment of malignancy. The substance is effective in part by modification of gene expression. Similar to apoptosis of nucleated cells erythrocytes may undergo eryptosis, the suicidal erythrocyte death characterized by cell shrinkage and cell membrane scrambling with phosphatidylserine translocation to the erythrocyte surface. Eryptosis may be triggered by increase of cytosolic Ca2+ activity ([Ca2+]i), oxidative stress, ceramide, as well as activation of protein kinases. The present study explored, whether NSC-95397 induces eryptosis and, if so, to shed some light on the mechanisms involved.. Phosphatidylserine exposure at the cell surface was estimated from annexin-V-binding, cell volume from forward scatter, [Ca2+]i from Fluo3-fluorescence, ROS formation from DCFDA dependent fluorescence, and ceramide abundance utilizing specific antibodies.. A 48 hours exposure of human erythrocytes to NSC-95397 significantly increased the percentage of annexin-V-binding cells (≥ 1 µM), significantly decreased forward scatter (≥ 2.5 µM), and significantly increased Fluo3-fluorescence (≥ 1 µM), DCFDA fluorescence (5 µM) and ceramide abundance (≥ 5 µM). The effect of NSC-95397 (5 µM) on annexin-V-binding was slightly, but significantly blunted by removal of extracellular Ca2+ and by addition of the protein kinase C inhibitor staurosporine (1 µM).. NSC-95397 triggers cell shrinkage and phospholipid scrambling of the erythrocyte cell membrane, an effect in part requiring entry of Ca2+ and activation of staurosporine sensitive kinase(s).

Topics: Calcium; cdc25 Phosphatases; Ceramides; Cytosol; Egtazic Acid; Enzyme Inhibitors; Eryptosis; Humans; Naphthoquinones; Oxidative Stress; Phosphatidylserines; Protein Kinase C; Protein Kinase Inhibitors; Reactive Oxygen Species; Scattering, Radiation

Carboxyl-terminal binding protein (CtBP) is a transcriptional corepressor that suppresses multiple proapoptotic and epithelial genes. CtBP is overexpressed in many human cancers, and its overexpression increases stem cell-like features, epithelial-mesenchymal transition, and cancer cell survival. Knockdown of CtBP also increases apoptosis independent of p53 in cell culture. Therefore, targeting CtBP with small molecules that disrupt its interaction with transcription factor partners may be an effective cancer therapy. To elicit its corepressing effect, CtBP binds to a conserved peptide motif in each transcription factor partner. We developed an AlphaScreen high-throughput screening assay to monitor the interaction between CtBP and E1A (which mimics the interaction between CtBP and its transcriptional partners). We screened the LOPAC library of 1280 bioactive compounds and identified NSC95397, which inhibits the CtBP-E1A interaction (IC50 = 2.9 µM). The inhibitory activity of NSC95397 was confirmed using two secondary assays and a counterscreen. NSC95397 also behaved as a weak substrate of CtBP dehydrogenase activity and did not inhibit another dehydrogenase, lactase dehydrogenase. Finally, NSC95397 was able to disrupt CtBP-mediated transcriptional repression of a target gene. These studies present a new possibility for the development of a therapeutic agent targeting tumors through disrupting the CtBP transcriptional complex.

Topics: Alcohol Oxidoreductases; Carrier Proteins; DNA-Binding Proteins; Dose-Response Relationship, Drug; Drug Discovery; Gene Expression Regulation; High-Throughput Screening Assays; Humans; Naphthoquinones; Protein Binding; Reproducibility of Results; Small Molecule Libraries; Substrate Specificity; Transcription, Genetic

NSC95397 (2,3-bis-[(2-hydroxyethyl)thio]-1,4-naphthoquinone) is a CDC25 inhibitor with anti-cancer properties. Since the anti-inflammatory activity of this compound has not yet been explored, the aim of this study was to examine whether this compound is able to modulate the inflammatory process. Toll like receptor (TLR)-mediated inflammatory responses were induced by lipopolysaccharide (LPS), a TLR4 ligand, and pam3CSK, a TLR2 ligand, in peritoneal macrophages and RAW264.7. The molecular mechanism of NSC95397's anti-inflammatory activity was studied using immunoblotting analysis, nuclear fractionation, immunoprecipitation, overexpression strategies, luciferase reporter gene assays, and kinase assays. NSC95397 dose-dependently suppressed the production of nitric oxide (NO), tumor necrosis factor (TNF)-α, and prostaglandin (PG)E2, and diminished the mRNA expression of inflammatory genes such as inducible NO synthase (iNOS), cyclooxygenase (COX)-2, interferon (IFN)-β, and TNF-α in peritoneal macrophages and RAW264.7 cells that were stimulated by LPS and pam3CSK. This compound also clearly blocked the activation of NF-κB (p65), AP-1 (c-Fos/c-Jun), and IRF-3 in LPS-treated RAW264.7 cells and TRIF- and MyD88-overexpressing HEK293 cells. In addition, biochemical and molecular approaches revealed that this compound targeted AKT, IKKα/β, MKK7, and TBK1. Therefore, these results suggest that the anti-inflammatory function of NSC95397 can be attributed to its inhibition of multiple targets such as AKT, IKKα/β, MKK7, and TBK1.

Topics: Animals; Anti-Inflammatory Agents, Non-Steroidal; cdc25 Phosphatases; Cell Line; Cell Survival; Male; Mice; Mice, Inbred C57BL; Naphthoquinones; Protein Serine-Threonine Kinases

To investigate the effect of JAKs-STATs signal pathway on expression of S100A4 in pulmonary arterial smooth muscle cells (PASMCs), the action of S100A4 and hypoxia induced factor 1 (HIF-1) on the proliferation of hypoxic PASMCs. The results showed that S100A4 immunostaining was localized in the cytoplasm and nuclei of PASMCs exposure to hypoxia and it was predominantly expressed in rhomboid cells (R-SMCs). The mRNA and protein levels of S100A4 expression increased in PASMCs after hypoxic stimulus for 4, 8, 16 h. The immunofluorescence intensity and protein levels of S100A4 were suppressed, and the number of R-SMCs was reduced, when pretreatment with HIF-1α siRNA, STAT3 siRNA, S100A4 siRNA, and S100A4 inhibitor NSC 95397. Pretreatment with HIF-1α siRNA and anti-IL-6 antibodies, the levels of phospho-JAK2, -STAT3, and S100A4 were decreased, while HIF-1α kept stable in hypoxic cells. Importantly, pretreatment with HIF-1α siRNA, anti-IL-6 antibodies, STAT3 siRNA, and S100A4 siRNA, significantly attenuated the proliferation of PASMCs exposure to hypoxia. These data demonstrate that S100A4 is predominantly expressed in hypoxic R-SMCs, and regulated by the activation of JAK2-STAT3 signal pathway, which is dependent on hypoxia-induced HIF-1α expression. These results suggest that JAK2-STAT3 and HIF-1α could serve as targets for the regulation of phenotype modulation of PASMCs during the process of pulmonary vessel lesions.

Topics: Animals; Blotting, Western; Cell Hypoxia; Cell Proliferation; Cell Shape; Cells, Cultured; Gene Expression Regulation; Hypoxia-Inducible Factor 1, alpha Subunit; Immunohistochemistry; Janus Kinase 2; Muscle, Smooth, Vascular; Myocytes, Smooth Muscle; Naphthoquinones; Pulmonary Artery; Rats; Rats, Sprague-Dawley; Reverse Transcriptase Polymerase Chain Reaction; RNA Interference; S100 Calcium-Binding Protein A4; S100 Proteins; STAT3 Transcription Factor

We investigated a physiological role for ERK, a member of the MAPK family, in the hypotonic stimulation of epithelial Na(+) channel (ENaC)-mediated Na(+) reabsorption in renal epithelial A6 cells. We show that hypotonic stress causes a major dephosphorylation of ERK following a rapid transient phosphorylation. PD98059 (a MEK inhibitor) increases dephosphorylated ERK and enhances the hypotonic-stress-stimulated Na(+) reabsorption. ERK dephosphorylation is mediated by MAPK phosphatase (MKP). Hypotonic stress activates p38, which in turn induces MKP-1 and to a lesser extent MKP-3 mRNA expression. Inhibition of p38 suppresses MKP-1 induction, preventing hypotonic stress from dephosphorylating ERK. Inhibition of MKP-1 and -3 by the inhibitor NSC95397 also suppresses the hypotonicity-induced dephosphorylation of ERK. NSC95397 reduces both β- and γ-ENaC mRNA expression and ENaC-mediated Na(+) reabsorption stimulated by hypotonic stress. In contrast, pretreatment with PD98059 significantly enhances mRNA and protein expression of β- and γ-ENaC even under isotonic conditions. However, PD98059 only stimulates Na(+) reabsorption in response to hypotonic stress, suggesting that ERK inactivation by itself (i.e., under isotonic conditions) is not sufficient to stimulate Na(+) reabsorption, even though ERK inactivation enhances β- and γ-ENaC expression. Based on these results, we conclude that hypotonic stress stimulates Na(+) reabsorption through at least two signaling pathways: 1) induction of MKP-1 that suppresses ERK activity and induces β- and γ-ENaC expression, and 2) promotion of translocation of the newly synthesized ENaC to the apical membrane.

Topics: Animals; Cells, Cultured; Dual Specificity Phosphatase 1; Dual Specificity Phosphatase 6; Enzyme Inhibitors; Epithelial Cells; Epithelial Sodium Channels; Extracellular Signal-Regulated MAP Kinases; Flavonoids; Hypotonic Solutions; Kidney; MAP Kinase Kinase 4; Models, Animal; Naphthoquinones; p38 Mitogen-Activated Protein Kinases; Signal Transduction; Up-Regulation; Xenopus laevis

Overexpression of S100A4, a member of the S100 family of Ca(2+)-binding proteins, is associated with a number of human pathologies, including fibrosis, inflammatory disorders, and metastatic disease. The identification of small molecules that disrupt S100A4/target interactions provides a mechanism for inhibiting S100A4-mediated cellular activities and their associated pathologies. Using an anisotropy assay that monitors the Ca(2+)-dependent binding of myosin-IIA to S100A4, NSC 95397 was identified as an inhibitor that disrupts the S100A4/myosin-IIA interaction and inhibits S100A4-mediated depolymerization of myosin-IIA filaments. Mass spectrometry demonstrated that NSC 95397 forms covalent adducts with Cys81 and Cys86, which are located in the canonical target binding cleft. Mutagenesis studies showed that covalent modification of just Cys81 is sufficient to inhibit S100A4 function with respect to myosin-IIA binding and depolymerization. Remarkably, substitution of Cys81 with serine or alanine significantly impaired the ability of S100A4 to promote myosin-IIA filament disassembly. As reversible covalent cysteine modifications have been observed for several S100 proteins, we propose that modification of Cys81 may provide an additional regulatory mechanism for mediating the binding of S100A4 to myosin-IIA.

Topics: cdc25 Phosphatases; Chromatography, Liquid; Cysteine; Cytoskeleton; Humans; Naphthoquinones; Nonmuscle Myosin Type IIA; Peptide Fragments; Protein Binding; Recombinant Proteins; S100 Calcium-Binding Protein A4; S100 Proteins; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization

The aim of this study was to investigate the apoptosis resulting from NSC 95397, brefeldin A, bortezomib and sanguinarine in neuroendocrine tumor cell lines.. A multiparametric high-content screening assay for measurement of apoptosis was used. The human pancreatic carcinoid cell line, BON-1, human typical bronchial carcinoid cell line NCI-H727 and the human atypical bronchial carcinoid cell line NCI-H720 were tested. After incubation with cytotoxic drugs, the DNA-binding dye Hoechst 33342, fluorescein-tagged probes that covalently bind active caspase-3 and chloromethyl-X-rosamine to detect mitochondrial membrane potential were added. Image acquisition and quantitative measurement of fluorescence was performed using automated image capture and analysis instrument ArrayScan. In addition, nuclear morphology was examined on microscopic slides stained with May-Grunewald-Giemsa.. A time- and dose-dependent activation of caspase-3 and increase in nuclear fragmentation and condensation were observed for the drugs using a multiparametric apoptosis assay. These results were confirmed with nuclear morphological examination on microscopic slides.. NSC 95397, brefeldin A, bortezomib and sanguinarine induced caspase-3 activation with modest changes in nuclear morphology.

Topics: Apoptosis; Benzophenanthridines; Boronic Acids; Bortezomib; Brefeldin A; Carcinoid Tumor; Carcinoma, Bronchogenic; Cell Line, Tumor; Drug Screening Assays, Antitumor; Humans; Isoquinolines; Lung Neoplasms; Naphthoquinones; Neuroendocrine Tumors; Pancreatic Neoplasms; Pyrazines

There is a large need for better pharmacological treatment of neuroendocrine tumors. The aim of this study was to investigate and quantify the cytotoxic potentiating effects resulting from a combination of five substances, NSC 95397, emetine, CGP-74514A hydrochloride, Brefeldin A and sanguinarine chloride, chosen from a previous screening of 1,280 pharmacologically active agents on neuroendocrine tumor cells, with standard cytotoxic agents currently used in the treatment of neuroendocrine tumors.. The human pancreatic carcinoid cell line BON-1, human typical bronchial carcinoid cell line NCI-H727 and the human atypical bronchial carcinoid cell line NCI-H720 were used. Combinations between doxorubicin, etoposide, oxaliplatin, docetaxel, and each one of the five agents were studied and simultaneous exposures were explored using the median-effect method.. Most of the combinations of NSC-95397 and emetine with doxorubicin, etoposide, docetaxel, and oxaliplatin showed synergism, and their remaining combinations were additive. Almost all of the CGP-74514A hydrochloride interactions were additive, while brefeldin A and sanguinarine displayed less synergy but more additive and antagonistic interactions in combination with the standard drugs.. The synergistic and additive interactions make NSC-95397, emetine, and CGP-74514A hydrochloride potential candidates for incorporation into combination chemotherapy regimens and these drugs might be the suitable candidates for further clinical studies in patients with bronchial carcinoids and pancreatic endocrine tumors.

Topics: 2-Aminopurine; Antineoplastic Combined Chemotherapy Protocols; Bronchial Neoplasms; Carcinoid Tumor; Cell Line, Tumor; Drug Screening Assays, Antitumor; Drug Synergism; Emetine; Humans; Naphthoquinones; Neuroendocrine Tumors; Pancreatic Neoplasms

Mitogen-activated protein kinase phosphatase (MKP)-1 is a dual-specificity phosphatase that negatively regulates the activity of mitogen-activated kinases and that is overexpressed in human tumors. Contemporary studies suggest that induction of MKP-1 during chemotherapy may limit the efficacy of clinically used antineoplastic agents. Thus, MKP-1 is a rational target to enhance anticancer drug activity, but suitable small-molecule inhibitors of MKP-1 are currently unavailable. Here, we have used a high-content, multiparameter fluorescence-based chemical complementation assay for MKP activity in intact mammalian cells to evaluate the cellular MKP-1 and MKP-3 inhibitory activities of four previously described, quinone-based, dual-specificity phosphatase inhibitors, that is, NSC 672121, NSC 95397, DA-3003-1 (NSC 663284), and JUN-1111. All compounds induced formation of reactive oxygen species in mammalian cells, but only one (NSC 95397) inhibited cellular MKP-1 and MKP-3 with an IC(50) of 13 mumol/L. Chemical induction of MKP-1 by dexamethasone protected cells from paclitaxel-induced apoptosis but had no effect on NSC 95397. NSC 95397 phenocopied the effects of MKP-1 small inhibitory RNA by reversing the cytoprotective effects of dexamethasone in paclitaxel-treated cells. Isobologram analysis revealed synergism between paclitaxel and NSC 95397 only in the presence of dexamethasone. The data show the power of a well-defined cellular assay for identifying cell-active inhibitors of MKPs and support the hypothesis that small-molecule inhibitors of MKP-1 may be useful as antineoplastic agents under conditions of high MKP-1 expression.

Topics: Antineoplastic Combined Chemotherapy Protocols; Breast Neoplasms; Cell Survival; Cytoprotection; Dexamethasone; Drug Evaluation, Preclinical; Drug Resistance, Neoplasm; Drug Synergism; Dual Specificity Phosphatase 1; Dual Specificity Phosphatase 6; HeLa Cells; Humans; Mitogen-Activated Protein Kinase Phosphatases; Models, Biological; Naphthoquinones; Paclitaxel; Quinones; Reactive Oxygen Species; Tumor Cells, Cultured

Cdc25 phosphatases have been considered as attractive drug targets for anticancer therapies due to the correlation of their overexpression with a wide variety of cancers. To gain insight into designing new potent inhibitors, we investigate the dynamic properties of Cdc25B and its complex with a 1,4-naphtoquinone inhibitor NSC 95397 by means of molecular dynamics simulations in aqueous solution. It is shown from the calculated dynamic properties that the malleability of the residues 530-532 residing at the start of C-terminal region around the active site should be responsible for the catalytic action of Cdc25B. However, binding of the inhibitor in the active site leads to a substantial decrease in the motional amplitude of the flexible residues, due to the hydrophobic interactions with the side chain of Met531. The simulation results also indicate that at least four hydrogen bonds are involved in the enzyme-inhibitor complex. Among them, the hydrogen bond between the side chain carboxylate group of Glu478 and one of the hydroxyl groups of the inhibitor is found to be the most significant binding force stabilizing the inhibitor in the active site. This result supports the previous experimental implication that the possession of a single hydroxyl group is sufficient for the inhibitory activity of 1,4-naphthoquinone inhibitors.

Topics: Catalytic Domain; cdc25 Phosphatases; Computer Simulation; Drug Design; Humans; Hydrogen Bonding; Hydrophobic and Hydrophilic Interactions; Ligands; Models, Molecular; Naphthoquinones; Protein Structure, Secondary; Time Factors

We report on the fluorinated form of NSC 95397 as a Cdc25B inhibitor, which is predicted to be only an arylator of cysteine-containing proteins, without generating reactive oxygen species.

Topics: Antineoplastic Agents; Binding Sites; cdc25 Phosphatases; Cell Cycle Proteins; Chromogenic Compounds; Fluorine; Kinetics; Models, Molecular; Naphthoquinones; Protein Binding; Thermodynamics

Gap junctional intercellular communication (GJC) varies during progression of the cell cycle. We propose here that Cdc25A, a dual specificity phosphatase crucial for cell cycle progression, is linked to connexin (Cx) phosphorylation and the modulation of GJC. Inhibition of Cdc25 phosphatases in rat liver epithelial cells employing a 1,4-naphthoquinone-based inhibitor, NSC95397, induced cell cycle arrest, tyrosine phosphorylation of the epidermal growth factor receptor (EGFR), and activation of extracellular signal-regulated kinases ERK-1 and -2. ERK activation was blocked by specific inhibitors of MAPK/ERK kinases 1/2 or of the EGFR tyrosine kinase. An EGFR-dephosphorylation assay suggested that Cdc25A interacts with the EGFR, with inhibition by NSC95397 resulting in activation of the receptor. As a consequence of ERK activation, Cx43 was phosphorylated, resulting in a downregulation of GJC. Loss of GJC was prevented by inhibition of ERK activation. In summary, cell cycle and GJC are connected via Cdc25A and the EGFR-ERK pathway.

Topics: Animals; cdc25 Phosphatases; Cells, Cultured; Connexin 43; Enzyme Activation; Enzyme Inhibitors; Epithelial Cells; ErbB Receptors; G1 Phase; Gap Junctions; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Molecular Structure; Naphthoquinones; Phosphorylation; Rats; Resting Phase, Cell Cycle; Signal Transduction

Cdc25 phosphatases are important in cell cycle control and activate cyclin-dependent kinases (Cdk). Efforts are currently under way to synthesize specific small-molecule Cdc25 inhibitors that might have anticancer properties. NSC 95397, a protein tyrosine phosphatase antagonist from the National Cancer Institute library, was reported to be a potent Cdc25 inhibitor. We have synthesized two hydroxyl derivatives of NSC 95397, monohydroxyl-NSC 95397 and dihydroxyl-NSC 95397, which both have enhanced activity for inhibiting Cdc25s. The new analogues, especially dihydroxyl-NSC 95397, potently inhibited the growth of human hepatoma and breast cancer cells in vitro. They influenced two signaling pathways. The dual phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) was induced, likely due to inhibition of the ERK phosphatase activity in Hep 3B cell lysate but not the dual specificity ERK phosphatase MKP-1. They also inhibited Cdc25 enzymatic activities and induced tyrosine phosphorylation of the Cdc25 target Cdks. Addition of hydroxyl groups to the naphthoquinone ring thus enhanced the potency of NSC 95397. These two new compounds may be useful probes for the biological functions of Cdc25s and have the potential for disrupting the cell cycle of growing tumor cells.

Topics: Antineoplastic Agents; Biotinylation; Blotting, Western; Breast Neoplasms; Carcinoma, Hepatocellular; cdc25 Phosphatases; Cell Cycle Proteins; Cell Line, Tumor; Cell Proliferation; Cell-Free System; DNA; Dual Specificity Phosphatase 1; Flavonoids; Flow Cytometry; Humans; Immediate-Early Proteins; Immunoprecipitation; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Naphthoquinones; Phosphoprotein Phosphatases; Phosphorylation; Protein Phosphatase 1; Protein Tyrosine Phosphatases; Signal Transduction; Time Factors; Transfection; Tyrosine

The serine/threonine kinase Raf-1 is a major regulator of the mitogen activated protein kinase (MAPK) pathway, which has been associated with the progression of prostate cancer to the more advanced and androgen-independent disease. Cdc25A phosphatase has been implicated in the regulation of Raf-1 and the MAPK pathway.. We used a novel and potent Cdc25A inhibitor, 2,3-bis-[2-hydroxyethylsulfonyl]-[1,4] naphthoquinone (NSC 95397), and its congener (2-mercaptoethanol)-3-methyl-1, 4-naphthoquinone (NSC 672121) to study the role of Cdc25A on the MAPK pathway in human prostate cancer cells.. We found Raf-1 physically interacted with Cdc25A in PC-3 and LNCap cells and inhibitors of Cdc25A induced both extracellular signal-regulated kinase (Erk) activation and Raf-1 tyrosine phosphorylation. NSC 95397 attenuated Cdc25A and Raf-1 interactions due to accelerated degradation of Cdc25A, which was mediated by proteasome degradation. The MAPK kinase (MEK) inhibitor U0126 completely inhibited Erk activation by NSC 95397 and NSC 672121.. These results indicate Cdc25A phosphatase regulates Raf-1/MEK/Erk kinase activation in human prostate cancer cells.

Topics: Blotting, Western; Butadienes; cdc25 Phosphatases; Cell Line, Tumor; Enzyme Inhibitors; Humans; Leupeptins; Male; MAP Kinase Signaling System; Mitogen-Activated Protein Kinases; Naphthoquinones; Nitriles; Phosphorylation; Prostatic Neoplasms; Proto-Oncogene Proteins c-raf

Cdc25 dual-specificity phosphatases coordinate cell cycle progression and cellular signaling. Consequently, Cdc25 inhibitors represent potential anticancer agents. We evaluated >10,000 compounds for inhibition of human Cdc25 phosphatases and identified many potent and selective inhibitors, which all contained a quinone. Bioreductive enzymes frequently detoxify or activate quinones. Therefore, we evaluated the effect of NAD(P)H:quinone oxidoreductase-1 (NQO1) and reductase-rich microsomes on the activity of three quinone-containing Cdc25 inhibitors: 2-(2-hydroxyethylsulfanyl)-3-methyl-1,4-naphthoquinone (Cpd 5, compound 5; NSC 672121), 2,3-bis-(2-hydroxyethylsulfanyl)-1,4-naphthoquinone (NSC 95397), and 6-chloro-7-(2-morpholin-4-yl-ethylamino)quinoline-5,8-dione (NSC 663284). Each inhibitor was reduced by human NQO1 (K(m) of 0.3-0.5 microM) but none by microsomes. Compounds were evaluated with six cancer cell lines containing different amounts of NQO1: HT-29 (1056 nmol/mg/min), HCT116 (660 nmol/mg/min), sublines HCT116-R30A (28 nmol/mg/min) and HCT-116R30A/NQ5 (934 nmol/mg/min), MDA-MB-231/Q2 (null NQO1), and subline MDA-MB-231/Q6 (124 nmol/mg/min) but containing similar amounts of microsomal cytochrome P450 reductase and cytochrome b(5) reductase. Growth inhibition and G2/M arrest by Cpd 5 was proportional to NQO1 levels, requiring 4- to 5-fold more Cpd 5 to inhibit HCT-116 or HCT-116R30A/NQ5 compared with HCT-116R30A. In contrast, in all tested cell lines irrespective of NQO1 level, growth inhibition and G2/M arrest by NSC 95375 and NSC 663284 were similar (average IC(50) of 1.3 +/- 0.3 and 2.6 +/- 0.4 microM, respectively). NSC 95375 and NSC 663284 also caused similar Cdk1 hyperphosphorylation, indicating similar Cdc25 inhibition. However, lower Cpd 5 concentrations were needed to produce Cdk1 hyperphosphorylation in sublines with minimal NQO1. Thus, NQO1 detoxified Cpd 5, probably by reducing it to a less active hydroquinone, whereas NSC 95397- and NSC 663284-generated cytotoxicity was unaffected by NQO1.

Topics: CDC2 Protein Kinase; cdc25 Phosphatases; Cell Division; Cell Fractionation; Cell Line; Dicumarol; G2 Phase; HT29 Cells; Humans; Microsomes; Mitosis; NAD(P)H Dehydrogenase (Quinone); Naphthoquinones; Phosphorylation; Quinolones; Quinones; Recombinant Proteins; Tumor Cells, Cultured

Topics: Animals; cdc25 Phosphatases; Cell Cycle; Drug Design; Enzyme Inhibitors; Humans; Models, Molecular; Naphthoquinones; Protein Conformation; Substrate Specificity

Small molecules provide powerful tools to interrogate biological pathways but many important pathway participants remain refractory to inhibitors. For example, Cdc25 dual-specificity phosphatases regulate mammalian cell cycle progression and are implicated in oncogenesis, but potent and selective inhibitors are lacking for this enzyme class. Thus, we evaluated 10,070 compounds in a publicly available chemical repository of the National Cancer Institute for in vitro inhibitory activity against oncogenic, full-length, recombinant human Cdc25B. Twenty-one compounds had mean inhibitory concentrations of <1 microM; >75% were quinones and >40% were of the para-naphthoquinone structural type. Most notable was NSC 95397 (2,3-bis-[2-hydroxyethylsulfanyl]-[1,4]naphthoquinone), which displayed mixed inhibition kinetics with in vitro K(i) values for Cdc25A, -B, and -C of 32, 96, and 40 nM, respectively. NSC 95397 was more potent than any inhibitor of dual specificity phosphatases described previously and 125- to 180-fold more selective for Cdc25A than VH1-related dual-specificity phosphatase or protein tyrosine phosphatase 1b, respectively. Modification of the bis-thioethanol moiety markedly decreased enzyme inhibitory activity, indicating its importance for bioactivity. NSC 95397 showed significant growth inhibition against human and murine carcinoma cells and blocked G(2)/M phase transition. A potential Cdc25 site of interaction was postulated based on molecular modeling with these quinones. We propose that inhibitors based on this chemical structure could serve as useful tools to probe the biological function of Cdc25.

Topics: Amino Acid Motifs; Binding Sites; cdc25 Phosphatases; Cell Cycle; Cell Cycle Proteins; Cell Division; Drug Evaluation, Preclinical; Enzyme Inhibitors; Humans; Kinetics; Models, Molecular; Naphthoquinones; Tumor Cells, Cultured