The histone methyltransferase G9a as a therapeutic target to override gemcitabine resistance in pancreatic cancer

• Published in: Oncotarget Vol. 7; no. 38; pp. 61136 - 61151
• Main Authors: Pan, Mei-Ren, Hsu, Ming-Chuan, Luo, Chi-Wen, Chen, Li-Tzong, Shan, Yan-Shen, Hung, Wen-Chun
• Format: Journal Article
• Language: English
• Published: United States Impact Journals LLC 20.09.2016
• Subjects: Aged; Animals; Antimetabolites, Antineoplastic - pharmacology; Cell Line, Tumor; Cell Movement; Deoxycytidine - analogs & derivatives; Deoxycytidine - pharmacology; Drug Resistance, Neoplasm; Extracellular Matrix - metabolism; Female; Gene Expression Profiling; Gene Expression Regulation, Neoplastic; HEK293 Cells; Histocompatibility Antigens - metabolism; Histone Demethylases - metabolism; Histone-Lysine N-Methyltransferase - metabolism; Humans; Interleukin-8 - metabolism; Male; Mice; Middle Aged; Neoplasm Invasiveness; Neoplasm Metastasis; Neoplastic Stem Cells - metabolism; Pancreatic Neoplasms - drug therapy; Pancreatic Neoplasms - genetics; Pancreatic Neoplasms - metabolism; Pancreatic Stellate Cells - metabolism; Receptors, Interleukin-8A - metabolism; Research Paper; RNA, Small Interfering - metabolism; lysine demethylase; drug resistance; interleukin-8; pancreatic stellate cell
• ISSN: 1949-2553; 1949-2553
• DOI: 10.18632/oncotarget.11256

Gemcitabine (GEM) resistance is a critical issue for pancreatic cancer treatment. The involvement of epigenetic modification in GEM resistance is still unclear. We established a GEM-resistant subline PANC-1-R from the parental PANC-1 pancreatic cancer cells and found the elevation of various chromatin-modifying enzymes including G9a in GEM-resistant cells. Ectopic expression of G9a in PANC-1 cells increased GEM resistance while inactivation of G9a in PANC-1-R cells reduced it. Challenge of PANC-1 cells with GEM increased the expression of stemness markers including CD133, nestin and Lgr5 and promoted sphere forming activity suggesting chemotherapy enriched cancer cells with stem-like properties. Inhibition of G9a in PANC-1-R cells reduced stemness and invasiveness and sensitized the cells to GEM. We revealed interleukin-8 (IL-8) is a downstream effector of G9a to increase GEM resistance. G9a-overexpressing PANC-1-R cells exhibited autocrine IL-8/CXCR1/2 stimulation to increase GEM resistance which could be decreased by anti-IL-8 antibody and G9a inhibitor. IL-8 released by cancer cells also activated pancreatic stellate cell (PSC) to increase GEM resistance. In orthotopic animal model, GEM could not suppress tumor growth of PANC-1-R cells and eventually promoted tumor metastasis. Combination with G9a inhibitor and GEM reduced tumor growth, metastasis, IL-8 expression and PSC activation in animals. Finally, we showed that overexpression of G9a correlated with poor survival and early recurrence in pancreatic cancer patients. Collectively, our results suggest G9a is a therapeutic target to override GEM resistance in the treatment of pancreatic cancer.