Immunohistochemical Detection of Antitumor, Antimetastasis, and Antiangiogenesis Effects of a Vascular Endothelial Growth Factor Receptor 2 Kinase Inhibitor in an Orthotopic Breast Cancer Metastasis Model

Abstract

Antiangiogenic agents such as vascular endothelial growth factor receptor 2 (VEGFR2) inhibitors may prove most efficacious in the setting of early disease and in the prevention of dissemination and growth of micrometastases. This hypothesis was tested in a metastatic orthotopic rat model of breast cancer with the use of a novel orally bioavailable VEGFR2 kinase inhibitor, MK-0888. Mat B III rat mammary cancer cells were implanted into the mammary fat pads of syngeneic female F344 rats. Primary tumor growth was very aggressive, with micrometastases detected 8 days after cell implantation in ipsilateral axillary and inguinal lymph nodes. Lung metastases were detected 15 days after cell implantation by histological analysis. MK-0888 suppressed primary and metastatic tumor growth and reduced the incidence of metastasis in a dose- and schedule-dependent manner. Inhibitions of primary and metastatic tumor growth, as well as intratumoral antiangiogenesis effects, were detected in situ by immunohistochemical analysis of tumor cells, endothelial cell proliferation, microvascular density, and blood vessel maturity. In the Mat B III rat mammary cancer metastasis model, our results provide further evidence supporting the ongoing clinical development of VEGFR2 kinase inhibitors, as well as clinically applicable in situ detection and verification of the inhibitor effect in tumor and metastasis biopsies. (The J Histotechnol 33(1):15–24, 2010)Submitted November 20, 2009; accepted February 8, 2010.