A Functional Nuclear Epidermal Growth Factor Receptor, Src and Stat3 Heteromeric Complex in Pancreatic Cancer Cells

Evidence is presented for the nuclear presence of a functional heteromeric complex of epidermal growth factor (EGFR), Src and the Signal Transducer and Activator of Transcription (Stat)3 proteins in pancreatic cancer cells. Stat3 remains nuclear and associated with Src or EGFR, respectively, upon the siRNA knockdown of EGFR or Src, demonstrating the resistance of the complex to the modulation of EGFR or Src alone. Significantly, chromatin immunoprecipitation (ChIP) analyses reveal the nuclear EGFR, Src and Stat3 complex is bound to the c-Myc promoter. The siRNA knockdown of EGFR or Src, or the pharmacological inhibition of Stat3 activity only marginally suppressed c-Myc expression. By contrast, the concurrent modulation of Stat3 and EGFR, or Stat3 and Src, or EGFR and Src strongly suppressed c-Myc expression, demonstrating that the novel nuclear heteromeric complex intricately regulates the c-Myc gene. The prevalence of the transcriptionally functional EGFR, Src, and Stat3 nuclear complex provides an additional and novel mechanism for supporting the pancreatic cancer phenotype and explains in part the insensitivity of pancreatic cancer cells to the inhibition of EGFR, Src or Stat3 alone

Enhanced Sensitivity Of Pancreatic Cancer Cells To Concurrent Inhibition Of Aberrant Signal Transducer And Activator Of Transcription 3 And Epidermal Growth Factor Receptor Or Src [S]

Many molecular aberrations occur in pancreatic cancer. Although aberrant epidermal growth factor receptor (EGFR), Src, and signal transducer and activator of transcription 3 (Stat3) are implicated in pancreatic cancer, therapies that target only one of these entities are undermined by signaling cross-talk. In the human pancreatic cancer lines, Panc-1 and Colo-357, pY845EGFR, pY1068EGFR, pY1086EGFR, and pY1173EGFR levels and pY416c-Src are concurrently elevated with aberrantly active Stat3 in a complex signaling cross-talk. Thus, understanding the signaling integration would facilitate the design of effective multiple-targeted therapeutic modalities. In Panc-1 and Colo-357 lines, pY845EGFR, pY1068EGFR, and pY1086EGFR levels are responsive to c-Src inhibition in contrast to pY1173EGFR, which is EGFR kinase-dependent. Constitutively active Stat3 is sensitive to both EGFR and Src inhibition, but the early suppression of aberrantly active Stat3 in response to the inhibition of EGFR and Src is countered by a Janus kinase (Jaks)-dependent reactivation, suggesting that Jaks activity is a compensatory mechanism for Stat3 induction. The inhibition of EGFR, Src, or Stat3 alone induced weak biological responses. By contrast, the concurrent inhibition of Stat3 and EGFR or Src induced greater viability loss and apoptosis and decreased the migration/invasion of pancreatic cancer cells in vitro. Significantly, the concurrent inhibition, compared with monotargeting modality, induced stronger human pancreatic tumor growth inhibition in xenografts. We infer that the tumor growth inhibition in vivo is caused by the simultaneous suppression of the abnormal functions of Stat3 and EGFR or Src. These studies strongly suggest that the concurrent targeting of Stat3 and EGFR or Src could be a beneficial therapeutic approach for pancreatic cancer. Copyright © 2010 by The American Society for Pharmacology and Experimental Therapeutics

Analysis of the impact of an increase in goods and services tax (GST) in Singapore

To compare and contrast the impact of the 2003 increase in GST from 3% to 4% to that of 1994 introduction of GST at 3% on the consumers' viewpoint

Artificially Induced Protein-Membrane Anchorage With Cholesterol-Based Recognition Agents As A New Therapeutic Concept

Keeping harm at bay: In an in vitro strategy to prevent the cellular motility of oncogenic STAT3 protein, protein-membrane anchorage was induced by the use of a rationally designed cholesterol-based protein-membrane anchor in breast-tumor cells. (The fluorescence image shows the localization of the protein to the liposome boundary of a multilamellar vesicle.) Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Coordination Complex Sh2 Domain Proteomimetics: An Alternative Approach To Disrupting Oncogenic Protein-Protein Interactions

We report the first application of coordination complexes as functional proteomimetics of the Src homology 2 (SH2) phosphopeptide-binding domain. As a proof-of-concept, functionalized bis-dipicolylamine (BDPA) copper(ii) complexes are shown to disrupt oncogenic Stat3-Stat3 protein complexes and elicit promising anti-tumour activity. © The Royal Society of Chemistry 2010

Disruption Of Transcriptionally Active Stat3 Dimers With Non-Phosphorylated, Salicylic Acid-Based Small Molecules: Potent In Vitro And Tumor Cell Activities

In summary, we have developed a library of analogues of the previously reported Stat3 inhibitor S3I-201, the most potent member of which displays more than twice the original potency for Stat3 dimer disruption. Furthermore, the most active analogues SF-1-066 and SF-1-121 have shown impressive in vitro and whole-cell activities; this is possibly a result of the successful occupation of a third, hydrophobic subpocket of the Stat3 SH2 domain. In general, our studies demonstrate that appropriate scaffold extension into this subpocket, which is believed to be occupied by the R1 substituent, resulted in significant increases in potency, thereby validating our approach to enhancing the Stat3 inhibitory activity of S3I-201. Future synthetic studies are currently focused upon developing extended agents with optimized occupation of the R1 subpocket, as well as optimizing the sulfonamide portion of our inhibitors to enhance interactions in the tosylamide-binding subpocket. © 2009 Wiley-VCH Verlag GmbH & Co. KGaA

Identification Of A Non-Phosphorylated, Cell Permeable, Small Molecule Ligand For The Stat3 Sh2 Domain

Signal transducer and activator of transcription 3 (Stat3) protein is a cytosolic transcription factor that is aberrantly activated in numerous human cancers. Inhibitors of activated Stat3-Stat3 protein complexes have been shown to hold therapeutic promise for the treatment of human cancers harboring activated Stat3. Herein, we report the design and synthesis of a focused library of salicylic acid containing Stat3 SH2 domain binders. The most potent inhibitor, 17o, effectively disrupted Stat3-phosphopeptide complexes (K i = 13 μM), inhibited Stat3-Stat3 protein interactions (IC 50 = 19 μM) and silenced intracellular Stat3 phosphorylation and Stat3-target gene expression profiles. Inhibition of Stat3 function in both breast and multiple myeloma (MM) tumor cells correlated with induced cell death (EC 50 = 10 and 16 μM, respectively). © 2011 Elsevier Ltd. All rights reserved

Design, Synthesis And In Vitro Characterization Of Novel Hybrid Peptidomimetic Inhibitors Of Stat3 Protein

Aberrant activation of oncogenic signal transducer and activator of transcription 3 (STAT3) protein signaling pathways has been extensively implicated in human cancers. Given STAT3\u27s prominent dysregulatory role in malignant transformation and tumorigenesis, there has been a significant effort to discover STAT3-specific inhibitors as chemical probes for defining the aberrant STAT3-mediated molecular events that support the malignant phenotype. To identify novel, STAT3-selective inhibitors suitable for interrogating STAT3 signaling in tumor cells, we explored the design of hybrid molecules by conjugating a known STAT3 inhibitory peptidomimetic, ISS610 to the high-affinity STAT3-binding peptide motif derived from the ILR/gp-130. Several hybrid molecules were examined in in vitro biophysical and biochemical studies for inhibitory potency against STAT3. Lead inhibitor 14aa was shown to strongly bind to STAT3 (K D = 900 nM), disrupt STAT3:phosphopeptide complexes (K i = 5 μM) and suppress STAT3 activity in in vitro DNA binding activity/electrophoretic mobility shift assay (EMSA). Moreover, lead STAT3 inhibitor 14aa induced a time-dependent inhibition of constitutive STAT3 activation in v-Src transformed mouse fibroblasts (NIH3T3/v-Src), with 80% suppression of constitutively-active STAT3 at 6 h following treatment of NIH3T3/v-Src. However, STAT3 activity recovered at 24 h after treatment of cells, suggesting potential degradation of the compound. Results further showed a suppression of aberrant STAT3 activity in NIH3T3/v-Src by the treatment with compound 14aa-OH, which is the non-pTyr version of compound 14aa. The effect of compounds 14aa and 14aa-OH are accompanied by a moderate loss of cell viability. © 2011 Elsevier Ltd. All rights reserved

Antagonism Of The Stat3-Stat3 Protein Dimer With Salicylic Acid Based Small Molecules

More than 50 new inhibitors of the oncogenic Stat3 protein were identified through a structure-activity relationship (SAR) study based on the previously identified inhibitor S3I-201 (IC 50=86μM, K i\u3e300μM). A key structural feature of these inhibitors is a salicylic acid moiety, which, by acting as a phosphotyrosine mimetic, is believed to facilitate binding to the Stat3 SH2 domain. Several of the analogues exhibit higher potency than the lead compound in inhibiting Stat3 DNA binding activity, with an invitro IC 50 range of 18.7-51.9μM, and disruption of Stat3-pTyr peptide interactions with K i values in the 15.5-41μM range. One agent in particular exhibited potent inhibition of Stat3 phosphorylation in both breast and multiple myeloma tumor cells, suppressed the expression of Stat3 target genes, and induced antitumor effects in tumor cells harboring activated Stat3 protein. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim