Effect of Rapamycin Alone and in Combination with Antiangiogenesis Therapy in an Orthotopic Model of Human Pancreatic Cancer

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Abstract
Purpose: The overall 5-year survival of patients with pancreatic cancer remains in vivo. Experimental Design: Human pancreatic cancer AsPC-1 cells were orthotopically injected into severe combined immunodeficient/beige mice to evaluate primary tumor growth and liver metastasis after treatment with rapamycin alone or in combination with anti-vascular endothelial growth factor antibody 2C3. Tumor cell proliferation was determined by bromodeoxyuridine incorporation. To detect tumor cell apoptosis, the terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling assay was used. Tumor angiogenesis was investigated by using a monoclonal anti-CD31 antibody. All statistical tests were two-sided. Results: Rapamycin, alone and in combination with 2C3, strongly inhibited primary and metastatic tumor growth in an orthotopic pancreatic cancer animal model. Furthermore, the combination therapy significantly improved the effect on liver metastasis compared with single treatment with either rapamycin (P = 0.0128) or 2C3 (P = 0.0099). Rapamycin alone inhibited pancreatic tumor cell proliferation, induced apoptosis, and decreased tumor angiogenesis. Nevertheless, the combination therapy showed a significant, stronger inhibition of tumor cell proliferation (P = 0.0002 versus rapamycin alone and P < 0.0001 versus 2C3 alone). The induction of apoptosis was significantly higher than in the rapamycin-treated group (P = 0.0039). Additionally, the combination therapy further improved suppression of tumor cell angiogenesis compared with rapamycin treatment (P = 0.029) Conclusions: Our studies propose new therapeutic strategies to inhibit both primary and metastatic tumor growth in pancreatic cancer. Considering the fact that liver metastasis is a crucial problem in advanced stages of pancreatic cancer, the combination therapy of rapamycin plus anti-vascular endothelial growth factor antibody 2C3 is a significant advantage compared with single treatment with rapamycin.