Abstract 4960: Serial in vivo orthotopic passage of human pancreatic cancer cells selects for increased stem cell-like behavior

Abstract

Abstract The aim of this study was to determine if stem-like properties of cancer cells increase after serial orthotopic passages in nude mice. Orthotopic mouse models of human pancreatic cancer cell lines were established by injecting 1x106 BxPC-3 RFP or Panc-1 GFP cells into the pancreas of nude mice. Cell lines were generated from primary pancreatic tumors after each passage. Cells (1x106) of the passaged cell lines were orthotopically injected into another set of mice and this process was repeated until a decreased host-mouse survival plateau was reached. To evaluate stem-like characteristics, 1x106 cells of the parental (P0) and multiply-passaged BxCP-3 RFP (P6) and Panc-1 GFP (P7) cell lines were orthotopically implanted into mice. The mice were followed until they were premorbid. In a second group of mice, the P0 and P6/7 lines were injected subcutaneously at different cell concentrations (102, 5 x 102, 103, 104, 105 cells) to determine the minimum cell number for tumor initiation. Additional orthotopic models were generated to evaluate differences in tumor progression and sensitivities to the chemotherapeutic agent, gemcitabine. In vitro proliferation and migration assays were performed on all four cell lines as well. The P6 and P7 lines demonstrated more aggressive behavior with regard to tumorigenicity, proliferation, tumor growth, migration, metastasis, progression, and chemotherapy resistance. A significantly fewer number of P6-passaged BxPC-3 cells (100 cells, p=0.02) and P7 Panc-1 cells (500 cells, p=0.005) were required for tumor initiation in mice by 6 weeks compared to their respective P0 lines. The P6/7 lines produced larger tumors at 6 weeks post implantation (p<0.001). Passaged lines also demonstrated greater proliferation and migration capabilities in vitro. This translated into the development of a significantly greater degree of cachexia, ascites, and greater metastatic tumor burden (p≤0.019) at 6 weeks in mice harboring the passaged tumors. There was a significantly greater extent of metastatic disease in liver and lung samples from mice with tumors generated from P6/7 lines. The P6/7 lines' average time to metastasis and overall survival were reduced by more than one-half (p<0.001). Both P6/7 lines were less sensitive to gemcitabine (p≤0.009). Thus, serial passaging allows for in vivo selection of more aggressive variants of the human pancreatic cancer cell lines BxPC-3 and Panc-1, which are also resistant to gemcitabine, suggesting that stem-like cells are being selected. Citation Format: Cristina Metildi, Sharmeela Kaushal, Robert M. Hoffman, Michael Bouvet. Serial in vivo orthotopic passage of human pancreatic cancer cells selects for increased stem cell-like behavior. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4960. doi:10.1158/1538-7445.AM2014-4960