Abstract 3057: ABCG2-positive cells derived from ABCG2-negative pancreatic cancer cells in 3D-culture conditions show high stemness and anti-cancer drug resistance
Authors: Sasaki Norihiko , Hasegawa Fumio , Michishita Masaki , Matsuda Yoko , Arai Tomio , Ishikawa Naoshi , Itakura Yoko , Aida Junko , Takubo Kaiyo , Toyoda Masashi , Ishiwata Toshiyuki 
Published: August 2018

Abstract
ATP-binding cassette subfamily G member 2 (ABCG2), an important multidrug resistance transporter, can mediate the efflux of various chemotherapy drugs and contribute to drug resistance in cancer cells. The correlation between ABCG2 expression and cancer stem cell (CSC) phenotypes has been examined in hepatocellular carcinoma, as well as in glioma, breast, prostate, and colon cancer; however, the results remain controversial. In this study, we compared the characteristics of low- (ABCG2-) and high-expressing (ABCG2+) pancreatic ductal adenocarcinoma (PDAC) cells using a human pancreatic cancerous cell line (PANC-1) because the role of ABCG2 in CSC-related malignant characteristics in PDAC is not well elucidated.
ABCG2- and ABCG2+ PDAC cells were separated using flow cytometric cell sorting. In adherent cell culture conditions, 10% of all PANC-1 cells were ABCG2+. Using transmission electron microscopy, we found that ABCG2+ cells showed more abundant and longer microvilli on the cell surface than ABCG2- cells. Unexpectedly, ABCG2+ cells did not demonstrate significantly greater drug resistance against 5-FU, gemcitabine, and vincristine than ABCG2- cells, as assessed using a WST-8 assay. Furthermore, ABCG2- cells exhibited better sphere formation ability and higher stemness marker expression, including that of Sox2, Oct4, ALDH1, CD44v9, and Nestin, than ABCG2+ cells, as observed using qRT-PCR. Cell growth rates and motilities, examined using the Boyden chamber and scratch assays, were higher in ABCG2- cells than in ABCG2+ cells. However, the epithelial-mesenchymal transition (EMT) ability, assessed by examining the alteration of E-cadherin, N-cadherin, Snail, and Vimentin expression after TGFβ addition, was comparable between ABCG2- and ABCG2+ cells.
In 3D-culture conditions using ultra low-attachment plates, ABCG2- cells formed spheres containing a large number of ABCG2+ cells, and expression of stemness markers in these spheres was higher than that of spheres derived from ABCG2+ cells. Furthermore, spheres derived from ABCG2- cells included large populations of ABCG2+ cells and exhibited high resistance against anti-cancer drugs, presumably depending on ABCG2 expression.
We found that in adherent culture conditions, ABCG2+ PDAC cells do not exhibit stemness and malignant behaviors, but ABCG2+ cells derived from ABCG2- cells after sphere formation have high stemness and anti-cancer drug resistance. This suggests that ABCG2- cells have the capacity to generate ABCG2+ cells, and the malignant potential of ABCG2+ cells in PDAC depends on the environment. The 3D-culture system was expected to mimic in vivo environments. Therefore, ABCG2+ cells in pancreatic cancer tumors may exhibit high stemness and anti-cancer drug resistance. Thus, ABCG2+ cells should be considered as novel therapeutic targets for pancreatic cancer.
Citation Format: Norihiko Sasaki, Fumio Hasegawa, Masaki Michishita, Yoko Matsuda, Tomio Arai, Naoshi Ishikawa, Yoko Itakura, Junko Aida, Kaiyo Takubo, Masashi Toyoda, Toshiyuki Ishiwata. ABCG2-positive cells derived from ABCG2-negative pancreatic cancer cells in 3D-culture conditions show high stemness and anti-cancer drug resistance [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3057.