Rapamycin-induced endothelial cell death and tumor vessel thrombosis potentiate cytotoxic therapy against pancreatic cancer.
OBJECTIVE
Despite current chemotherapies, pancreatic cancer remains an uncontrollable, rapidly progressive disease. Here, we tested an approach combining a recently described antiangiogenic drug, rapamycin, with standard gemcitabine cytotoxic therapy on human pancreatic tumor growth.


METHODS
Tumor growth was assessed in rapamycin and gemcitabine-treated nude mice orthotopically injected with metastatic L3.6pl human pancreatic cancer cells. H&E staining was performed on tumors, along with Ki67 staining for cell proliferation and immunohistochemical terminal deoxynucleotidyl transferase-mediated nick end labeling and CD31 analysis. Rapamycin-treated tumor vessels were also directly examined in dorsal skin-fold chambers for blood flow after thrombosis induction. Cell death in human umbilical vein endothelial cells was assessed by flow cytometry after annexin-V staining.


RESULTS
Rapamycin therapy alone inhibited tumor growth and metastasis more than gemcitabine, with remarkable long-term tumor control when the drugs were combined. Mechanistically, H&E analysis revealed tumor vessel endothelium damage and thrombosis with rapamycin treatment. Indeed, dorsal skin-fold chamber analysis of rapamycin-treated tumors showed an increased susceptibility of tumor-specific vessels to thrombosis. Furthermore, terminal deoxynucleotidyl transferase-mediated nick end labeling/CD31 double staining of orthotopic tumors demonstrated apoptotic endothelial cells with rapamycin treatment, which also occurred with human umbilical vein endothelial cells in vitro. In contrast, gemcitabine was not antiangiogenic and, despite its known cytotoxicity, did not reduce proliferation in orthotopic tumors; nevertheless, rapamycin did reduce tumor proliferation.


CONCLUSIONS
Our data suggest a novel mechanism whereby rapamycin targets pancreatic tumor endothelium for destruction and thrombosis. We propose that rapamycin-based vascular targeting not only reduces tumor vascularization, it decreases the number of proliferating tumor cells to be destroyed by gemcitabine, thus introducing a new, clinically feasible strategy against pancreatic cancer.
Bruns
Christiane J
CJ
Department of Surgery, University of Regensburg, Regensburg, Germany.
Koehl
Gudrun E
GE
Guba
Markus
M
Yezhelyev
Maksim
M
Steinbauer
Markus
M
Seeliger
Hendrik
H
Schwend
Astrid
A
Hoehn
Anna
A
Jauch
Karl-Walter
KW
Geissler
Edward K
EK
D020533:Angiogenesis Inhibitors / Q000627:therapeutic use*; D000818:Animals; D001783:Blood Flow Velocity / Q000187:drug effects; D016923:Cell Death; D002455:Cell Division / Q000187:drug effects; D003841:Deoxycytidine / Q000031:analogs & derivatives* / Q000627:therapeutic use; D004730:Endothelium, Vascular / Q000187:drug effects / Q000473:pathology*; D006801:Humans; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009389:Neovascularization, Pathologic / Q000188:drug therapy*; D010190:Pancreatic Neoplasms / Q000098:blood supply* / Q000473:pathology*; D020123:Sirolimus / Q000627:therapeutic use*; D014183:Transplantation, Heterologous; D000093542:Gemcitabine
D020533:Angiogenesis Inhibitors; D003841:Deoxycytidine; D020123:Sirolimus; D000093542:Gemcitabine