Hyperthermia inhibits the motility of gemcitabine-resistant pancreatic cancer PANC-1 cells through the inhibition of epithelial-mesenchymal transition

Pancreatic cancer (PC) is one of the most common types of malignant tumor and the leading cause of cancer-associated mortality worldwide. The chemotherapeutic drug gemcitabine (GEM) is used as a first-line chemotherapeutic agent for advanced PC. However, the acquisition of drug resistance is a major limitation of the clinical effect of GEM and commonly leads to increased metastasis. The occurrence of epithelial-mesenchymal transition (EMT) has been demonstrated to be the underlying mechanism of acquired resistance. It has been reported that heat treatment is able to inhibit EMT in pancreatic adenocarcinoma cells. In the present study the effect of hyperthermia on the sensitivity of GEM-resistant PC cells was investigated. First a GEM-resistant PC cell line PANC-1 (PAN/GEM) was developed and it was demonstrated that drug resistant PAN/GEM cells exhibited significantly increased migratory and invasive abilities compared with control PANC-1 cells using a Transwell assay. EMT was induced in resistant PAN/GEM cells, followed by reduced epithelial marker epithelial (E)-cadherin expression and increased mesenchymal marker Vimentin expression compared with control PANC-1 cells. Next, the Transwell assay demonstrated that the hyperthermia at 42 degrees C for 1 h combined with GEM significantly attenuated migration and invasion in drug resistant PAN/GEM cells, while GEM alone treatment did not significantly affect the migration and invasion. Additionally, EMT in PAN/GEM cells was reversed by hyperthermia, as demonstrated by the restoration of E-cadherin and downregulation of mesenchymal markers Vimentin, matrix metalloproteinase (MMP)2 and MMP9. Furthermore, an MMP2 inhibitor tissue inhibitor of metalloproteinases (TIMP)2 and MMP9 inhibitor TIMP1 were used to treat PAN/GEM cells and it was demonstrated that both inhibitors increased the inhibition of hyperthermia treatment combined with GEM on cell invasion, suggesting an association between cell invasion and MMP2, and MMP9. Additionally, proliferation of PAN/GEM cells following hyperthermia was assessed using an MTT assay. The results demonstrated that proliferation in PAN/GEM cells treated with hyperthermia was significantly inhibited by GEM compared with GEM alone treated cells, indicating that hyperthermia enhanced the inhibition of GEM on cell growth and resensitized the drug-resistant cells to GEM. Overall, the results of the present study suggested that hyperthermia is able to resensitize GEM-resistant PANC-1 cells to GEM by reversing EMT via the regulation of EMT-associated factors, therefore inhibiting cell migration and invasion.