In Vivo Therapy of Local Tumor Progression by Targeting Vascular Endothelium with EMAP-II Roderich E. Schwarz 1 and Margaret A. Schwarz Department of Surgery, Divisions of Surgical Oncology and Surgical Sciences, University of Medicine and Dentistry of New Jersey, Robert Wood Johnson Medical School, and The Cancer Institute of New Jersey, New Brunswick, New Jersey Submitted for publication August 29, 2003 Background. Continued growth of solid tumors be- yond a critical diameter is thought to require active angiogenic mechanisms, the inhibition of which car- ries therapeutic potential. We tested this strategy in an in vivo model of local tumor progression utilizing an agent with previously identified direct antiendo- thelial properties. Materials and methods. Nonmetastatic C 6 glioma cells (10 6 per animal) were injected subcutaneously into the flank of nude mice with 6 to 8 animals per treatment group. Nodules at the injection site were measured at day 3 and every fourth day thereafter until day 15. Endothelial-monocyte-activating polypep- tide II (EMAP-II), a substance known to induce endo- thelial cell apoptosis, was injected intraperitoneally daily from day 3 to day 15 at doses of 8 g/kg (low dose) and 80 g/kg (high dose). Tumor growth kinetics, his- tologic parameters, and tissue expression of VEGF were studied. Results. Tumor growth was significantly decreased in the EMAP-II-treated animals. Median tumor volume (in mm 3 ) at day 15 was 2311 (Control), 727 (low dose), and 454 (high dose, P  0.003). Median tumor weight (g) measured 1.8 (Control, 0.95 low dose), and 0.9 (high dose, P  0.06). Median 12-day specific tumor growth rate (in mm 3 /day) per group was 191, 60, and 36 (P  0.003). Decreased tumor growth after EMAP-II treat- ment correlated with significantly reduced microves- sel counts, higher vascular thrombosis rate, and re- duced tumor cell proliferation indices within the neoplastic tissue. Tumor levels, but not serum levels, of VEGF were significantly reduced after EMAP-II treatment. At the doses administered, there was no obvious systemic toxicity. EMAP-II had no direct cyto- toxic or antiproliferative effects on tumor cells in vitro. Conclusions. Daily administration of the antiendo- thelial agent EMAP-II led to a significant retardation of tumor growth, but no complete cancer abrogation. The findings support the hypothesis of an in vivo ther- apeutic benefit to antiangiogenic therapy with an agent that displays specific toxicity in vitro against endothelial cells. The mechanism of action remains unclear, but likely involves vascular thrombosis and leads to decreased VEGF expression. © 2004 Elsevier Inc. All rights reserved. Key Words: endothelial-monocyte activating polypep- tide II; angiogenesis; tumor cell proliferation; endo- thelial cell toxicity. INTRODUCTION Progressive growth of solid tumors beyond a diame- ter of 2 to 3 mm 3 is thought to require active angiogenic mechanisms [1]. The formation of new tumor microves- sels from preexisting vasculature requires a complex interaction between tumor cells, endothelial cells, stro- mal elements, and matrix components, which remain only partly understood to date. There is evidence, how- ever, that endothelial cell division is required for suc- cessful tumor neovascularization [2, 3]. Inhibition of endothelial cell function may therefore represent an effective pathway toward the downregulation of tumor growth. We have previously shown that endothelial- monocyte-activating polypeptide II (EMAP-II) pos- sesses direct antiendothelial effects in vitro and in vivo [4]. EMAP-II, which is found within stromal compo- nents of various organs during fetal development [5], is processed by unknown mechanisms to a mature 21- kDa form (mEMAP-II) that functions as a potent anti- 1 To whom correspondence and reprint requests should be ad- dressed at Department of Surgery, University of Medicine and Den- tistry of New Jersey, Robert Wood Johnson Medical School, The Cancer Institute of New Jersey, 195 Little Albany Street, New Brunswick, NJ 08903-2681. Fax: (732) 235-8098. E-mail: r.schwarz@umdnj.edu. Journal of Surgical Research 120, 64 –72 (2004) doi:10.1016/j.jss.2003.10.005 64 0022-4804/04 $30.00 © 2004 Elsevier Inc. All rights reserved.