Abstract: Background and purpose: Gemcitabine (GEM) is a first-line chemotherapy drug for pancreatic cancer. With the emergence of clinical drug resistance, the efficacy of chemotherapy has been greatly reduced, while the expression of secretory clusterin (sCLU) was closely related to chemotherapy resistance in multiple tumors. This study aimed to explore the effects of secretory clusterin on oxidative damage in MIA PaCa-2 cells treated by GEM and preliminary mechanism of resistance to GEM. Methods: MIA PaCa-2 was exposed to GEM and sCLU intervened groups with different concentrations (0, 0.63, 1.25, 2.50, 5.00 and 10.0 μg/mL) for 24 hours. The intervened concentration of GEM was 5.4 μmol/L. The inhibition rates of cell proliferation were determined by CCK- 8. Cell reactive oxygen species (ROS) was measured by dichloro-dihydro-fluorescein diacetate (DCFH-DA) method. Superoxide dismutase (SOD) activity and catalase (CAT) activity were measured by their corresponding assay kits respectively. Results: Compared with the negative control group (0 μg/mL), the inhibition rates of the GEM groups and sCLU intervened groups were significantly increased (P<0.05) in a distinct dose-effect manner. At a low concentration of 0.63 μg/mL, the inhibition rates of the GEM groups were higher than those of the sCLU intervened groups, while the trend was reversed in high concentration range. Compared with the negative control group (0 μg/mL), the intracellular ROS levels, SOD and CAT activity of the GEM and sCLU intervened groups significantly increased (P<0.05). ROS levels presented a distinct dose-effect relationship while the SOD and CAT activities increased first and then decreased along with the increase of GEM concentrations. The ROS levels of the GEM group were lower than those of the sCLU intervened group at the same dose (P<0.05). The SOD activities of the GEM group were higher than those of the sCLU intervened group, while the CAT activities were opposite at the concentrations of 5.00 and 10.00 μg/mL (P<0.05). Conclusion: GEM exposure can inhibit the growth of MIA PaCa-2 cells. After GEM exposure, the ROS levels, SOD and CAT activity of MIA PaCa-2 cells can be changed by sCLU intervention. GEM resistance could be regulated by sCLU through oxidative damage effect.

Key words: Secretory clusterin, Gemcitabine, MIA PaCa-2 cells, Oxidative damage, Chemotherapy resistance