Cytotoxic Sesquiterpenoid Quinones and Quinols, and an 11-Membered Heterocycle, Kauamide, from the Hawaiian Marine Sponge Dactylospongia elegans.

Several known sesquiterpenoid quinones and quinols (1-9), and kauamide (10), a new polyketide-peptide containing an 11-membered heterocycle, were isolated from the extracts of the Hawaiian marine sponge Dactylospongia elegans. The planar structure of 10 was determined from spectroscopic analyses, and its relative and absolute configurations were established from density functional theory (DFT) calculations of the GIAO NMR shielding tensors, and advanced Marfey's analysis of the N-MeLeu residue, respectively. Compounds 1 and 3 showed moderate inhibition of ß-secretase 1 (BACE1), whereas 1-9 exhibited moderate to potent inhibition of growth of human glioma (U251) cells. Compounds 1-2 and 4-7 were also active against human pancreatic carcinoma (Panc-1) cells.

Bromotyrosine-derived metabolites from an Indonesian marine sponge in the family Aplysinellidae (Order Verongiida).

Seven new bromotyrosine-derived metabolites, purpuramine M-N (1-2), araplysillin VII-XI (3-7) and six known compounds (8-13) were isolated from an Indonesian sponge belonging to the family Aplysinellidae (Order Verongiida). The structures of the new compounds were determined by extensive NMR experiments and mass spectrometric measurements. These compounds were screened against BACE1 and five cancer cell lines.

Iridoid glycosides from Barleria lupulina.

Phytochemical investigation of an extract of the aerial part of Barleria lupulina resulted in the identification of four new iridoid glycosides (1-4), together with 14 known analogues (5-18). The structures of 1-4 were determined through 1D and 2D NMR spectroscopic data analysis, HRMS, and acid hydrolysis. This is the first report of iridoid glycosides with a formate group. The free-radical scavenging activity of compounds 9, 12, and 15-17 was assessed using the DPPH assay. Compounds 16 and 17 scavenged DPPH radicals weakly with IC50 values of 97.5 and 78.6 µg/mL, respectively.

Identification of Oct4-activating compounds that enhance reprogramming efficiency.

One of the hurdles for practical application of induced pluripotent stem cells (iPSC) is the low efficiency and slow process of reprogramming. Octamer-binding transcription factor 4 (Oct4) has been shown to be an essential regulator of embryonic stem cell (ESC) pluripotency and key to the reprogramming process. To identify small molecules that enhance reprogramming efficiency, we performed a cell-based high-throughput screening of chemical libraries. One of the compounds, termed Oct4-activating compound 1 (OAC1), was found to activate both Oct4 and Nanog promoter-driven luciferase reporter genes. Furthermore, when added to the reprogramming mixture along with the quartet reprogramming factors (Oct4, Sox2, c-Myc, and Klf4), OAC1 enhanced the iPSC reprogramming efficiency and accelerated the reprogramming process. Two structural analogs of OAC1 also activated Oct4 and Nanog promoters and enhanced iPSC formation. The iPSC colonies derived using the Oct4-activating compounds along with the quartet factors exhibited typical ESC morphology, gene-expression pattern, and developmental potential. OAC1 seems to enhance reprogramming efficiency in a unique manner, independent of either inhibition of the p53-p21 pathway or activation of the Wnt-ß-catenin signaling. OAC1 increases transcription of the Oct4-Nanog-Sox2 triad and Tet1, a gene known to be involved in DNA demethylation.

Identification of a disruptor of the MDM2-p53 protein-protein interaction facilitated by high-throughput in silico docking.

NSC 333003 has been identified from the NCI Diversity Set as an inhibitor of the MDM2-p53 protein-protein interaction by in silico docking (virtual screening). Its potency and chemical characteristics render it well suited for lead optimization studies that can result in more potent analogs with improved drug-like properties. Its synthesis was achieved using an acid catalyzed condensation reaction from commercially available benzothiazole hydrazine and pyridyl phenyl ketone in refluxing methanol. Stereochemical implications for this compound are described.

Glucocorticoid Signaling Enhances Expression of Glucose-Sensing Molecules in Immature Pancreatic Beta-Like Cells Derived from Murine Embryonic Stem Cells In Vitro.

Pluripotent stem cells may serve as an alternative source of beta-like cells for replacement therapy of type 1 diabetes; however, the beta-like cells generated in many differentiation protocols are immature. The maturation of endogenous beta cells involves an increase in insulin expression starting in late gestation and a gradual acquisition of the abilities to sense glucose and secrete insulin by week 2 after birth in mice; however, what molecules regulate these maturation processes are incompletely known. In this study, we aim to identify small molecules that affect immature beta cells. A cell-based assay, using pancreatic beta-like cells derived from murine embryonic stem (ES) cells harboring a transgene containing an insulin 1-promoter driven enhanced green fluorescent protein reporter, was used to screen a compound library (NIH Clinical Collection-003). Cortisone, a glucocorticoid, was among five positive hit compounds. Quantitative reverse transcription-polymerase chain reaction analysis revealed that glucocorticoids enhance the gene expression of not only insulin 1 but also glucose transporter-2 (Glut2; Slc2a2) and glucokinase (Gck), two molecules important for glucose sensing. Mifepristone, a pharmacological inhibitor of glucocorticoid receptor (GR) signaling, reduced the effects of glucocorticoids on Glut2 and Gck expression. The effects of glucocorticoids on ES-derived cells were further validated in immature primary islets. Isolated islets from 1-week-old mice had an increased Glut2 and Gck expression in response to a 4-day treatment of exogenous hydrocortisone in vitro. Gene deletion of GR in beta cells using rat insulin 2 promoter-driven Cre crossed with GRflox/flox mice resulted in a reduced gene expression of Glut2, but not Gck, and an abrogation of insulin secretion when islets were incubated in 0.5 mM d-glucose and stimulated by 17 mM d-glucose in vitro. These results demonstrate that glucocorticoids positively regulate glucose sensors in immature murine beta-like cells.

CCR9-mediated signaling through ß-catenin and identification of a novel CCR9 antagonist.

Elevated levels of chemokine receptor CCR9 expression in solid tumors may contribute to poor patient prognosis. In this study, we characterized a novel CCR9-mediated pathway that promotes pancreatic cancer cell invasion and drug resistance, indicating that CCR9 may play a critical role in cancer progression through activation of ß-catenin. We noted that the CCL25/CCR9 axis in pancreatic cancer cells induced the activation of ß-catenin, which enhanced cell proliferation, invasion, and drug resistance. CCR9-mediated activation of ß-catenin and the resulting downstream effects were effectively inhibited by blockade of the PI3K/AKT pathway, but not by antagonism of Wnt. Importantly, we discovered that CCR9/CCL25 increased the lethal dose of gemcitabine, suggesting decreased efficacy of anti-cancer drugs with CCR9 signaling. Through in silico computational modeling, we identified candidate CCR9 antagonists and tested their effects on CCR9/ß-catenin regulation of cell signaling and drug sensitivity. When combined with gemcitabine, it resulted in synergistic cytotoxicity. Our results show that CCR9/ß-catenin signaling enhances pancreatic cancer invasiveness and chemoresistance, and may be a highly novel therapeutic target.

Baicalein upregulates DDIT4 expression which mediates mTOR inhibition and growth inhibition in cancer cells.

Baicalein is a natural flavone that exhibits anticancer properties. Using microarrays we found that DDIT4 was the highest transcript induced by baicalein in cancer cells. We confirmed in multiple cancer cell lines large, dose-related expression of DDIT4 by quantitative RT-PCR and immunoblot, which correlates with growth inhibition. Time course experiments demonstrate that DDIT4 is rapidly inducible, with high expression maintained for several days in vitro. Induction of DDIT4 expression is p53 independent based on evaluation of p53 knockout cells. Since DDIT4 is known to inhibit mTORC1 activity we confirmed that baicalein suppresses phosphorylation of mTORC1 targets. Using RNA interference we demonstrate that mTORC1 activity and growth inhibition by baicalein is attenuated by knockdown of DDIT4. We furthermore demonstrate suppression of established tumors by baicalein in a mouse model of breast cancer with increased DDIT4 expression in the tumors. Finally, we demonstrate that baicalein upregulates DDIT4 and causes mTORC1 and growth inhibition in platinum resistant cancer cells in marked contrast to platinum chemotherapy treatment. These studies demonstrate that baicalein inhibits mTORC1 through DDIT4 expression, and may be useful in cancer chemotherapy and chemoprevention.

A small-molecule blocking ribonucleotide reductase holoenzyme formation inhibits cancer cell growth and overcomes drug resistance.

Ribonucleotide reductase (RNR) is an attractive target for anticancer agents given its central function in DNA synthesis, growth, metastasis, and drug resistance of cancer cells. The current clinically established RNR inhibitors have the shortcomings of short half-life, drug resistance, and iron chelation. Here, we report the development of a novel class of effective RNR inhibitors addressing these issues. A novel ligand-binding pocket on the RNR small subunit (RRM2) near the C-terminal tail was proposed by computer modeling and verified by site-directed mutagenesis and nuclear magnetic resonance (NMR) techniques. A compound targeting this pocket was identified by virtual screening of the National Cancer Institute (NCI) diverse small-molecule database. By lead optimization, we developed the novel RNR inhibitor COH29 that acted as a potent inhibitor of both recombinant and cellular human RNR enzymes. COH29 overcame hydroxyurea and gemcitabine resistance in cancer cells. It effectively inhibited proliferation of most cell lines in the NCI 60 human cancer panel, most notably ovarian cancer and leukemia, but exerted little effect on normal fibroblasts or endothelial cells. In mouse xenograft models of human cancer, COH29 treatment reduced tumor growth compared with vehicle. Site-directed mutagenesis, NMR, and surface plasmon resonance biosensor studies confirmed COH29 binding to the proposed ligand-binding pocket and offered evidence for assembly blockade of the RRM1-RRM2 quaternary structure. Our findings offer preclinical validation of COH29 as a promising new class of RNR inhibitors with a new mechanism of inhibition, with broad potential for improved treatment of human cancer.

Identification of anti-malarial compounds as novel antagonists to chemokine receptor CXCR4 in pancreatic cancer cells.

Despite recent advances in targeted therapies, patients with pancreatic adenocarcinoma continue to have poor survival highlighting the urgency to identify novel therapeutic targets. Our previous investigations have implicated chemokine receptor CXCR4 and its selective ligand CXCL12 in the pathogenesis and progression of pancreatic intraepithelial neoplasia and invasive pancreatic cancer; hence, CXCR4 is a promising target for suppression of pancreatic cancer growth. Here, we combined in silico structural modeling of CXCR4 to screen for candidate anti-CXCR4 compounds with in vitro cell line assays and identified NSC56612 from the National Cancer Institute's (NCI) Open Chemical Repository Collection as an inhibitor of activated CXCR4. Next, we identified that NSC56612 is structurally similar to the established anti-malarial drugs chloroquine and hydroxychloroquine. We evaluated these compounds in pancreatic cancer cells in vitro and observed specific antagonism of CXCR4-mediated signaling and cell proliferation. Recent in vivo therapeutic applications of chloroquine in pancreatic cancer mouse models have demonstrated decreased tumor growth and improved survival. Our results thus provide a molecular target and basis for further evaluation of chloroquine and hydroxychloroquine in pancreatic cancer. Historically safe in humans, chloroquine and hydroxychloroquine appear to be promising agents to safely and effectively target CXCR4 in patients with pancreatic cancer.

Bortezomib induces apoptosis and growth suppression in human medulloblastoma cells, associated with inhibition of AKT and NF-ĸB signaling, and synergizes with an ERK inhibitor.

Medulloblastoma is the most common brain tumor in children. Here, we report that bortezomib, a proteasome inhibitor, induced apoptosis and inhibited cell proliferation in two established cell lines and a primary culture of human medulloblastomas. Bortezomib increased the release of cytochrome c to cytosol and activated caspase-9 and caspase-3, resulting in cleavage of PARP. Caspase inhibitor (Z-VAD-FMK) could rescue medulloblastoma cells from the cytotoxicity of bortezomib. Phosphorylation of AKT and its upstream regulator mTOR were reduced by bortezomib treatment in medulloblastoma cells. Bortezomib increased the expression of Bad and Bak, pro-apoptotic proteins, and p21Cip1 and p27Kip1, negative regulators of cell cycle progression, which are associated with the growth suppression and induction of apoptosis in these tumor cells. Bortezomib also increased the accumulation of phosphorylated IĸBα, and decreased nuclear translocation of NF-ĸB. Thus, NF-ĸB signaling and activation of its downstream targets are suppressed. Moreover, ERK inhibitors or downregulating ERK with ERK siRNA synergized with bortezomib on anticancer effects in medulloblastoma cells. Bortezomib also inhibited the growth of human medulloblastoma cells in a mouse xenograft model. These findings suggest that proteasome inhibitors are potentially promising drugs for treatment of pediatric medulloblastomas.

Colitis locus on chromosome 2 impacting the severity of early-onset disease in mice deficient in GPX1 and GPX2.

BACKGROUND: Genetic background has a profound effect on inflammatory bowel disease. The Gpx1 and Gpx2 double knockout (GPX1/2-DKO) mice on a mixed C57BL/6 (B6) and 129S1/SvimJ (129) background exhibit spontaneous ileocolitis. The DKO mice on a B6 background have mild ileocolitis. We characterized the 129 DKO mice to identify a genetic locus affecting disease severity. METHODS: We backcrossed B6;129 DKO mice to 129 and analyzed for ileocolitis penetrance and severity at N5, N7, and N10. By correlating disease severity with single-nucleotide polymorphism (SNP) markers, we identified a colitis locus. RESULTS: As early as 9 days of age, 129 DKO N5 and N10 mice showed disease signs and morbidity. The N10 DKO mice had the severest colitis with nearly complete penetrance and high morbidity compared with other generations or backgrounds. 129 DKO mice had elevated colonic KC and SAA3 expression, shorter colon length, and cecal E. coli overgrowth compared to B6 DKO mice. Analysis of the B6 loci in 129 N5, N7, and N10 cohorts pointed to a region of chromosome 2: 119 Mbp contributing to mild symptoms. CONCLUSIONS: GPX1/2-DKO mice on 129 genetic background have the most aggressive colitis compared to B6;129 and B6 colonies. A B6 locus significantly contributing the resistance resides on chromosome 2: 119 Mbp. This region coincides with cytokine-deficiency-induced colitis susceptibility, Cdcs3, identified in the resistant B6 and sensitive C3H/HeJBir (C3Bir) with IL-10 deficiency. A three-way SNP analysis between 129, B6, and C3Bir locus points the major candidate genes to B2m, Dnajc17, Duox2, Pla2g4b, Pla2g4e, Pla2g4f and Slc30a4.

Identification of a natural compound by cell-based screening that enhances interferon regulatory factor-1 activity and causes tumor suppression.

The transcription factor interferon regulatory factor-1 (IRF-1) is induced by many tumor-suppressive stimuli and can mediate antiproliferative and proapoptotic effects in cancer cells. Thus, identifying agents that enhance IRF-1 activity may be an effective approach to cancer therapy. A cell-based screening assay was developed to identify extracts and compounds that could enhance IRF-1 activity, using an IRF-1-dependent luciferase reporter cell line. Through this approach, we identified a natural product extract and a known active component of this extract, baicalein, which causes a marked increase in IRF-1-dependent reporter gene expression and IRF-1 protein, with modulation of known IRF-1 targets PUMA and cyclin D1. Baicalein causes suppression of growth in vitro in multiple cancer cell lines in the low micromolar range. IRF-1 plays a role in this growth suppression as shown by significant resistance to growth suppression in a breast cancer cell line stably transfected with short hairpin RNA against IRF-1. Finally, intraperitoneal administration of baicalein by repeated injection causes inhibition of growth in both xenogeneic and syngeneic mouse models of cancer without toxicity to the animals. These findings indicate that identifying enhancers of IRF-1 activity may have utility in anticancer therapies and that cell-based screening for activation of transcription factors can be a useful approach for drug discovery.

Inhibitors of Src homology-2 domain containing protein tyrosine phosphatase-2 (Shp2) based on oxindole scaffolds.

Screening of the NCI diversity set of compounds has led to the identification of 5 (NSC-117199), which inhibits the protein tyrosine phosphatase (PTP) Shp2 with an IC50 of 47 microM. A focused library incorporating an isatin scaffold was designed and evaluated for inhibition of Shp2 and Shp1 PTP activities. Several compounds were identified that selectively inhibit Shp2 over Shp1 and PTP1B with low to submicromolar activity. A model for the binding of the active compounds is proposed.

Selective chemical probe inhibitor of Stat3, identified through structure-based virtual screening, induces antitumor activity.

S3I-201 (NSC 74859) is a chemical probe inhibitor of Stat3 activity, which was identified from the National Cancer Institute chemical libraries by using structure-based virtual screening with a computer model of the Stat3 SH2 domain bound to its Stat3 phosphotyrosine peptide derived from the x-ray crystal structure of the Stat3beta homodimer. S3I-201 inhibits Stat3.Stat3 complex formation and Stat3 DNA-binding and transcriptional activities. Furthermore, S3I-201 inhibits growth and induces apoptosis preferentially in tumor cells that contain persistently activated Stat3. Constitutively dimerized and active Stat3C and Stat3 SH2 domain rescue tumor cells from S3I-201-induced apoptosis. Finally, S3I-201 inhibits the expression of the Stat3-regulated genes encoding cyclin D1, Bcl-xL, and survivin and inhibits the growth of human breast tumors in vivo. These findings strongly suggest that the antitumor activity of S3I-201 is mediated in part through inhibition of aberrant Stat3 activation and provide the proof-of-concept for the potential clinical use of Stat3 inhibitors such as S3I-201 in tumors harboring aberrant Stat3.

Discovery of a novel shp2 protein tyrosine phosphatase inhibitor.

Shp2 is a nonreceptor protein tyrosine phosphatase (PTP) encoded by the PTPN11 gene. It is involved in growth factorinduced activation of mitogen-activated protein (MAP) kinases Erk1 and Erk2 (Erk1/2) and has been implicated in the pathogenicity of the oncogenic bacterium Helicobacter pylori. Moreover, gain-of-function Shp2 mutations have been found in childhood leukemias and Noonan syndrome. Thus, small molecule Shp2 PTP inhibitors are much needed reagents for evaluation of Shp2 as a therapeutic target and for chemical biology studies of Shp2 function. By screening the National Cancer Institute (NCI) Diversity Set chemical library, we identified 8-hydroxy-7-(6-sulfonaphthalen-2-yl)diazenyl-quinoline-5-sulfonic acid (NSC-87877) as a potent Shp2 PTP inhibitor. Molecular modeling and site-directed mutagenesis studies suggested that NSC-87877 binds to the catalytic cleft of Shp2 PTP. NSC-87877 cross-inhibited Shp1 in vitro, but it was selective for Shp2 over other PTPs (PTP1B, HePTP, DEP1, CD45, and LAR). It is noteworthy that NSC-87877 inhibited epidermal growth factor (EGF)-induced activation of Shp2 PTP, Ras, and Erk1/2 in cell cultures but did not block EGF-induced Gab1 tyrosine phosphorylation or Gab1-Shp2 association. Furthermore, NSC-87877 inhibited Erk1/2 activation by a Gab1-Shp2 chimera but did not affect the Shp2-independent Erk1/2 activation by phorbol 12-myristate 13-acetate. These results identified NSC-87877 as the first PTP inhibitor capable of inhibiting Shp2 PTP in cell cultures without a detectable off-target effect. Our study also provides the first pharmacological evidence that Shp2 mediates EGF-induced Erk1/2 MAP kinase activation.