Roles of nitric oxide synthase inhibition and vascular endothelial growth factor receptor-2 inhibition on vascular morphology and function in an in vivo model of pancreatic cancer.
OBJECTIVE
Both nitric oxide (NO) and vascular endothelial growth factor (VEGF) mediate tumor vascular function. Because these molecules regulate one another's expression, we hypothesized that NO synthase (NOS) inhibition produces effects comparable to those of anti-VEGF therapy on human pancreatic cancer xenografts.


METHODS
L3.6pl human pancreatic cancer cells were s.c. implanted in nude mice. On day 6, mice were randomized to receive (a) PBS (control), (b) DC101 [VEGF receptor 2 (VEGFR-2) antibody] by i.p. injection, (c) N-nitro-l-arginine (NNLA; NOS inhibitor) in the drinking water, or (d) both DC101 and NNLA. Mice were killed on day 20.


RESULTS
DC101 and NNLA as single agents inhibited tumor growth by approximately 50% to 60% (P < 0.008 for both). Furthermore, combined therapy inhibited mean tumor growth by 89% (P < 0.008). Combined inhibition of VEGFR-2 and NOS also decreased mean vessel counts by 65% (P < 0.03) and vessel area by 80% versus controls (P < 0.001). In contrast to DC101 where vessel diameter was similar to control, NNLA decreased mean vessel diameter by 42% (P < 0.001). NNLA also led to a 54% (P < 0.03) decrease in tumor uptake of the perfusion marker Hoechst 33342 versus controls whereas DC101 decreased Hoechst 33342 staining by 43% (P < 0.03). The combination of inhibitors decreased perfusion by 73% (P < 0.03).


CONCLUSIONS
Although VEGFR-2 can mediate NOS activity, the combination of VEGFR-2 and NOS inhibition significantly increased the antivascular effect over single agent therapy. The addition of NOS inhibition led to an even further alteration of tumor vessel morphology and vascular perfusion compared with VEGFR-2 blockade, suggesting that NO and VEGFR-2 have distinct but complementary effects on the tumor vasculature.
Camp
E Ramsay
ER
Department of Surgical Oncology, The University of Texas M.D. Anderson Cancer Center, Houston, Texas, USA.
Yang
Anthony
A
Liu
Wenbiao
W
Fan
Fan
F
Somcio
Ray
R
Hicklin
Daniel J
DJ
Ellis
Lee M
LM
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000494:pharmacology* / Q000627:therapeutic use; D017209:Apoptosis / Q000187:drug effects; D001808:Blood Vessels / Q000737:chemistry / Q000187:drug effects / Q000473:pathology; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology / Q000627:therapeutic use; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D051379:Mice; D008819:Mice, Nude; D009389:Neovascularization, Pathologic / Q000378:metabolism / Q000473:pathology / Q000517:prevention & control; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D019335:Nitroarginine / Q000494:pharmacology* / Q000627:therapeutic use; D010190:Pancreatic Neoplasms / Q000098:blood supply / Q000473:pathology / Q000517:prevention & control*; D019408:Platelet Endothelial Cell Adhesion Molecule-1 / Q000032:analysis; D011897:Random Allocation; D040301:Vascular Endothelial Growth Factor Receptor-2 / Q000276:immunology*; D023041:Xenograft Model Antitumor Assays
D000911:Antibodies, Monoclonal; D004791:Enzyme Inhibitors; D019408:Platelet Endothelial Cell Adhesion Molecule-1; D019335:Nitroarginine; D019001:Nitric Oxide Synthase; D040301:Vascular Endothelial Growth Factor Receptor-2