Study Of The Egfr, Src And Stat3 Pathway In Pancreatic Cancer

Cancer is associated with many molecular aberrations that support the malignant phenotype. In that regard, aberrant activation of epidermal growth factor receptor (EGFR), Src, and signal transducer and activator of transcription 3 (Stat3) occur concurrently in pancreatic cancer and are implicated in the disease phenotype. Notwithstanding, increasing evidence indicates that therapies that target only EGFR or Src are rather ineffective in modulating the cancer phenotype. The poor therapeutic outcome of the monotherapies targeting EGFR or Src may in part be due to the increased incidence of signaling cross-talks among aberrant signaling pathways in cancer. Molecular details of the signaling integration between EGFR, Src and Stat3, however, are lacking. Understanding how the aberrant EGFR, Src and Stat3 pathways are integrated in pancreatic cancer would facilitate the design of effective multipletargeted, clinically feasible therapeutic modalities. Our study shows that in pancreatic cancer cell lines, aberrant Src activity promotes abnormal EGFR activation through the phosphorylation of the EGFR motifs, Tyr845, Tyr1068 and Tyr1086. Furthermore, aberrantly-active EGFR and Src together induce constitutive activation of Stat3 in pancreatic cancer cells. Evidence further shows that EGFR, Src and Stat3 physically associated into a heteromeric complex. Significantly, the EGFR, Src and Stat3 heteromeric complex is detectable in the nucleus and functions as a transcriptionallyactive complex to induce the c-Myc gene. Of therapeutic significance, the concurrent inhibition of Stat3 and EGFR or Src promoted greater viability loss and apoptosis of pancreatic cancer cells in vitro, and induced stronger tumor growth inhibition in xenografts of human pancreatic cancer. Altogether, our studies suggest that the iii heteromeric EGFR, Src, and Stat3 complex may serve as an additional novel mechanism of support of the pancreatic cancer phenotype. Furthermore, our studies provide evidence that the concurrent targeting of Stat3 and EGFR or Stat3 and Src could be a more effective therapeutic approach for human pancreatic cancer

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

Enhanced Sensitivity of Pancreatic Cancer Cells to Concurrent Inhibition of Aberrant Signal Transducer and Activator of Transcription 3 and Epidermal Growth Factor Receptor or SrcS⃞

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

A Cell-permeable Stat3 SH2 Domain Mimetic Inhibits Stat3 Activation and Induces Antitumor Cell Effects in Vitro*

Given the role of constitutively active Signal Transducer and Activator of Transcription (Stat) 3 in human tumors, Stat3 inhibitors would be useful as novel therapeutics and as tools for probing Stat3-mediated tumor processes. We herein report that a 28-mer peptide, SPI, derived from the Stat3 SH2 domain, replicates Stat3 biochemical properties. Studies show SPI and Stat3 (or Stat3 SH2 domain) bind with similar affinities to known Stat3-binding phosphotyrosine (pY) peptide motifs, including those of the epidermal growth factor receptor (EGFR) and the high-affinity, IL-6R/gp130-derived pY-peptide, GpYLPQTV-NH2. Consequently, SPI functions as a potent and selective inhibitor of Stat3 SH2 domain:pTyr interactions and disrupts the binding of Stat3 to the IL-6R/gp130 peptide, GpYLPQTV-NH2. Fluorescence imaging and immunofluorescence staining/laser-scanning confocal microscopy show SPI is cell membrane-permeable, associates with the cytoplasmic tail of EGFR in NIH3T3/hEGFR, and is present in the cytoplasm, but strongly localized at the plasma membrane and in the nucleus in malignant cells harboring persistently active Stat3. Moreover, SPI specifically blocks constitutive Stat3 phosphorylation, DNA binding activity, and transcriptional function in malignant cells, with little or no effect on the induction of Stat1, Stat5, and Erk1/2MAPK pathways, or on general pTyr profile at the concentrations that inhibit Stat3 activity. Significantly, treatment with SPI of human breast, pancreatic, prostate, and non-small cell lung cancer cells harboring constitutively active Stat3 induced extensive morphology changes, associated with viability loss and apoptosis. Our study identifies SPI as a novel molecular probe for interrogating Stat3 signaling and that functions as a selective inhibitor of Stat3 activation with antitumor cell effects