Epithelial to Mesenchymal Transition Contributes to Drug Resistance in Pancreatic Cancer

Abstract

A better understanding of drug resistance mechanisms is required to improve outcomes in patients with pancreatic cancer. Here we characterized patterns of sensitivity and resistance to three conventional chemotherapeutic agents with divergent mechanisms of action (gemcitabine, 5-fluorouracil, and cisplatin) in pancreatic cancer cells. Four (L3.6pl, BxPC-3, CFPAC-1, SU86.86) were sensitive and five (PANC-1, Hs766T, AsPC-1, MIAPaCa-2, Mpanc96) were resistant to all 3 agents based on GI50 (50% growth inhibition). Gene expression profiling and unsupervised hierarchical clustering revealed that the sensitive and resistant cells formed two distinct groups and differed in expression of specific genes including several features of “epithelial-mesenchymal transition” (EMT). Interestingly, an inverse correlation between E-cadherin and its transcriptional suppressor, Zeb-1 was observed in the gene expression data and was confirmed by real time PCR. Independent validation experiment using 5 new pancreatic cancer cell lines confirmed that an inverse correlation between E-cadherin and Zeb-1 correlated closely with resistance to gemcitabine, 5-fluorouracil, and cisplatin. Silencing Zeb-1 in the mesenchymal lines not only increased the expression of E-cadherin but also other epithelial markers such as EVA1 and MAL2 and restored drug sensitivity. Importantly, immunohistochemical analysis of E-cadherin and Zeb-1 in primary tumors confirmed that expression of the two proteins was mutually exclusive (p=0.012). Therefore, our results suggest that Zeb-1 and other regulators of EMT may maintain drug resistance in human pancreatic cancer cells, and therapeutic strategies to inhibit Zeb-1 and reverse EMT should be evaluated.

Mechanism of the Mesenchymal–Epithelial Transition and Its Relationship with Metastatic Tumor Formation

“…ZEB1 and ZEB2 are able to initiate EMT by binding to E-boxes within the E-cadherin promoter and repressing its transcription, and silencing of ZEB1 was shown to increase the expression of E-cadherin (69,70). Downregulation of ZEB2 mRNA via ZEB2 siRNA in 4TO7 cells increased E-cadherin mRNA, and the cells that had stably silenced ZEB2 expression also adopted an epithelial-like morphology (25).…”

E-cadherin contributes to the bystander effect of TK/GCV suicide therapy and enhances its antitumoral activity in pancreatic cancer models

“…29 Although E-cadherin has been prominently studied for its role in tumorigenesis, evidencing that the loss of E-cadherin is a critical initiation step in the epithelial-to-mesenchymal transition associated with the invasiveness of tumors, metastatic dissemination and a poor prognosis for several different types of tumor, 30 there are increasing reports of its contribution to the effectiveness of antitumoral therapies. 17,19,20,31 Moreover, E-cadherin has been proposed as a biomarker for therapies, such as EGFR tyrosine kinase activity inhibitors or other molecules interfering with EGFR signaling. 18,32 Our study data also suggest that E-cadherin expression could be a clinically relevant biomarker for TK/GCV therapy.…”

Epigenetic markers for chemosensitivity and chemoresistance in pancreatic cancer—A review

“…[19][20][21] Physiologic EMT is a fundamental embryological process, characterized by alterations in morphology, cellular architecture, adhesion and migratory potential, allowing epithelially differentiated cells to gain mesenchymal characteristics. In cancer, EMT is implicated in metastasis and chemoresistance.…”

“…Silencing of ZEB1 in mesenchymally differentiated gemcitabine-resistant PC cell lines could partially restore chemosensitivity by increasing the expression of E-cadherin and upregulating epithelial marker genes such as MAL2 and EVA1. 21 …”

“…[83][84][85][86] There is no doubt that NFjB plays a critical role in the processes of EMT and tumor cell invasion and metastasis. 21 A screening by Lu et al for miRNAs that modulate NFjB signaling revealed miRNA-301a as the most potent NFjB activator. MiRNA-301a activates NFjB by downregulating the expression of the NFjB-repressing factor gene.…”