Role of vascular endothelial growth factor in ovarian cancer: inhibition of ascites formation by immunoneutralization

Abstract

Ovarian cancer is characterized by the rapid growth of solid intraperitoneal tumors and large volumes of ascitic fluid. Vascular endothelial growth factor (VEGF) augments tumor growth by inducing neovascularization and may stimulate ascites formation by increasing vascular permeability. We examined the role of VEGF in ovarian carcinoma using in vivo models in which intraperitoneal or subcutaneous tumors were induced in immunodeficient mice using the human ovarian carcinoma cell line SKOV-3. After tumor engraftment (7 to 10 days), some mice were treated with a function-blocking VEGF antibody (A4.6.1) specific for human VEGF. A4.6.1 significantly (P < 0.05) inhibited subcutaneous SKOV-3 tumor growth compared with controls. However, tumor growth resumed when A4.6.1 treatment was discontinued. In mice bearing intraperitoneal tumors (IP mice), ascites production and intraperitoneal carcinomatosis were detected 3 to 7 weeks after SKOV-3 inoculation. Importantly, A4.6.1 completely inhibited ascites production in IP mice, although it only partially inhibited intraperitoneal tumor growth. Tumor burden was variable in A4.6.1-treated IP mice; some had minimal tumor, whereas in others tumor burden was similar to that of controls. When A4.6.1 treatment was stopped, IP mice rapidly (within 2 weeks) developed ascites and became cachectic. These data suggest that in ovarian cancer, tumor-derived VEGF is obligatory for ascites formation but not for intraperitoneal tumor growth. Neutralization of VEGF activity may have clinical application in inhibiting malignant ascites formation in ovarian cancer.

Figure 1.

Histological appearance of intraperitoneal SKOV-3 tumors (T) derived from PBS-treated and antibody-treated (A4.6.1) mice approximately 5 weeks after intraperitoneal cell inoculation. H&E staining of 10-μm paraffin sections. Bar = 500 μm.

Figure 2.

Effect of neutralization of tumor-derived VEGF activity on the growth of subcutaneous SKOV-3 tumors. Mice were treated with either PBS or antibody (A4.6.1, 100 μg) intraperitionally twice weekly for approximately 4 weeks. In A, all mice were killed at 30 days. In B, treatments were reversed at day 29. Numbers in parentheses represent the number of tumors analyzed in each group.

Figure 3.

Effect of neutralization of tumor-derived VEGF on intraperitoneal SKOV-3 tumor development and ascites production in mice inoculated intraperitoneally with SKOV-3 cells. Shown are outcomes for individual animals in three separate experiments. Tumor burden was assessed qualitatively as follows: ++++, High, many clusters of large (5 to 10 mm in diameter) solid tumors easily visible in the peritoneal cavity; +++, Moderate, clusters of tumors (3 to 5 mm in diameter) readily visible but spread not as extensive as High; ++, Low, large tumors not apparent but small foci visible on peritoneum, omentum, uterine fat pads, and diaphragm; +, Scare, only small foci seen on peritoneum, omentum, and diaphragm. Extent of ascites production also was determined qualitatively as follows: +++, High, marked abdominal swelling with 5 to 10 ml of bloody ascites; ++, Moderate, distinct abdominal swelling with 3 to 5 ml of clear ascites; +, Low, no abdominal swelling, small volume of clear ascitic fluid detected at postmortem examination; −, No ascites detected.