216 Background: The signaling pathways contributing to DNA-binding protein inhibitor Id1 expression and chemoresistance in pancreatic cancer remain unknown. Id1 plays a role in pancreatic tumor progression with tumor-promoting effects of nicotine regulating protein tyrosine kinase Src activation and Id1 expression, both associated with chemoresistance in other systems. We hypothesize Id1 expression regulates chemoresistance in pancreatic cancer through a nicotine-promoting Src-dependent pathway. Methods: We probed pancreatic cancer cell lines (L3.6pl, PANC-1, Mia-PaCa-2) for innate gemcitabine chemoresistance with cell viability MTT assay and western blot analysis of PARP cleavage programmed cell death. Gemcitabine-sensitive cells were exposed to rising gemcitabine concentrations to establish a resistant subtype, L3.6plGemRes. Protein analysis and mRNA expression were determined by western blot analysis and RT-PCR respectively. Induction of Src phosphorylation or Id1 expression was performed with nicotine (1 μM). Results: Inhibition of c-Src expression was performed with short-interfering RNA (siRNA). Nicotine-induced Src phosphorylation and Id1 expression. Inhibition of Src by siRNA resulted in decreased nicotine-induced Id1 expression. Inhibition of Src and Id1 expression by siRNA in innate or established gemcitabine resistant pancreatic cancer cells resulted in gemcitabine sensitization. To determine if nicotine contributes to gemcitabine chemoresistance, we exposed gemcitabine-sensitive cells to nicotine with subsequent exposure to gemcitabine IC50, 250 ng/ml, and cell viability assays confirmed a 2-fold increase in cell prolilferation and a 4.5-fold reduction in apoptosis. Further, nicotine induced phosphorylation of key signaling enzymes involved in proliferation and apoptosis, Erk1/2 and Akt respectively. Conclusions: In summary, we demonstrate that Id1, through a nicotine-promoting Src-dependent pathway, is necessary for establishment of a chemoresistant phenotype in pancreatic cancer cells. Understanding the signaling pathways involved in pancreatic tumor chemoresistance will lead to therapies resulting in improved tumor responses. No significant financial relationships to disclose.
The Natural Flavonoid Fisetin Inhibits Cellular Proliferation of Hepatic, Colorectal, and Pancreatic Cancer Cells through Modulation of Multiple Signaling Pathways
