A major obstacle compromising the successful application of many of the new targeted anticancer drugs, including angiogenesis inhibitors, is the empiricism associated with determining an effective biological/therapeutic dose because many of these drugs express optimum therapeutic activity below the maximum tolerated dose, if such a dose can be defined. Hence, surrogate markers are needed to help determine optimal dosing. Here we describe such a molecular marker, increased plasma levels of vascular endothelial growth factor (VEGF), in normal or tumor-bearing mice that received injections of an anti-VEGF receptor (VEGFR)-2 monoclonal antibody, such as DC101. Rapid increases of mouse VEGF (e.g., within 24 hours) up to 1 order of magnitude were observed after single injections of DC101 in non-tumorbearing severe combined immunodeficient or nude mice; similar increases in human plasma VEGF were detected in human tumor-bearing mice. RAFL-1, another anti-VEGFR-2 antibody, also caused a significant increase in plasma VEGF. In contrast, increases in mouse VEGF levels were not seen when small molecule VEGFR-2 inhibitors were tested in normal mice. Most importantly, the increases in plasma VEGF were induced in a dose-dependent manner, with the maximum values peaking when doses previously determined to be optimally therapeutic were used. Plasma VEGF should be considered as a possible surrogate pharmacodynamic marker for determining the optimal biological dose of antibody drugs that block VEGFR-2 (KDR) activity in a clinical setting.

The growth of any solid tumor depends on angiogenesis. Among the known angiogenic factors, basic fibroblast growth factor (bFGF) and vascular endothelial growth factor (VEGF), are potent and representative factors involved in tumor development. It has been reported that bFGF and VEGF showed a synergistic effect in both in vitro and in vivo angiogenesis. However, the interaction of these factors on tumor development and angiogenesis, including hepatocellular carcinoma (HCC), has not yet been elucidated. In this study, we examined the combined effect of bFGF and VEGF overexpression by means of a combination of a retroviral tetracycline (tet)-regulated (Retro-Tet) gene expression system, which can manipulate the gene expression in vivo by providing tet in the drinking water, and a conventional plasmid gene expression system. In an allograft study, bFGF and VEGF overexpression synergistically increased tumor growth and angiogenesis in the murine HCC cells. This synergistic effect also was found in established tumors. VEGF messenger RNA (mRNA) expression in the tumor was increased 3.1-fold by bFGF-overexpression, and the bFGF-induced tumor development was significantly attenuated by treatment with KDR/ Flk-1 neutralizing monoclonal antibody. In conclusion, these results suggest that bFGF synergistically augments VEGF-mediated HCC development and angiogenesis at least partly by induction of VEGF through KDR/Flk-1. (HEPATOLOGY 2002;35:834-842.)

Purpose: Vascular endothelial growth factor receptor-1 (VEGFR-1) plays important roles in promotion of tumor growth by mediating cellular functions in tumor vascular endothelium and cancer cells. Blockade of VEGFR-1activation has been shown to inhibit pathologic angiogenesis and tumor growth, implicating VEGFR-1 as a potential therapeutic target for the treatment of cancer. We have thus developed a VEGFR-1 antagonist human monoclonal antibody designated as IMC-18F1 and evaluated its antitumor activity in preclinical experimental models to show the therapeutic potential of the antibody for cancer treatment in clinic. Experimental Design: Human IgG transgenic mice were used for generation of anti-VEGFR-1 antibodies. Anti-VEGFR-1-specific blocking antibodies were identified using solid-phase binding and blocking assays. Inhibitory antitumor cell activity of IMC-18F1 was assessed in cell-based kinase and growth assays. Pharmacokinetic/pharmacodynamic studies were done to determine the association of antibody blood level with antitumor efficacy of the antibody in vivo. Antitumor efficacy of the anti-VEGFR-1antibodies as monotherapy and in combination with cytotoxic agents was evaluated in human breast cancer xenograft models.

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The vascular endothelial growth factor-A (VEGF-A