Abstract 2453: P16, a novel monoclonal antibody specifically recognizing human placental growth factor (PLGF), blocks PLGF-VEGFR1 interaction in vitro and inhibits angiogenesis and tumor growth in vivo

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Placental growth factor play (PLGF) is a homolog of vascular endothelial growth factor (VEGF) and binds to VEGF receptor-1. Previous studies have indicated its synergistic role with VEGF in angiogenesis, while a recent study suggested its independent role in promoting growth and metastasis of VEGF-inhibitor-resistant tumors. In order to further investigate the role of PLGF in tumor angiogenesis in relationship to VEGF, we have generated a novel PLGF-specific monoclonal antibody (mAb). Hybridomas secreting PLGF-specific mAbs were obtained by fusing splenocytes from mice immunized with yeast-derived recombinant human PLGF protein with Sp/20 myeloma cells; the mAb clone that showed highest binding affinity, designed as P16, was selected for further study. This P16 mAb recognizes human PLGF, in both native and denatured forms, but not VEGF-A, VEGF-B or VEGF-D. P16 mAb is of IgG1-kappa type. Sequence analysis of cDNA encoding the heavy and light chains of P16 mAb showed novel variable regions. Using P16 mAb in immunohistochemical staining assay, increased levels of PLGF protein were found in a number of human tumors from lung, breast and colon. PLGF proteins were also detected in a wide variety of normal human tissues including lung, stomach, colon and kidney, contrary to previous reports. Importantly, P16 mAb blocked the binding of PLGF to VEGFR-1 in a dose-response manner, and inhibited the PLGF-mediated endothelial cell line growth in vitro. Treatment of human tumor xenografts (A673 rhabdomyosarcoma) in nude mice with P16 mAb resulted in marked inhibition of tumor growth, which is similar in degree to the tumor inhibition by VEGF-specific antibody Bevacizumab. A humanized form of P16 mAb was constructed and showed similar inhibition of tumor growth in xenograft nude mice model. In conclusion, P16 mAb is a novel mAb specifically recognizing human PLGF but not VEGF and blocks the binding of PLGF to its receptor. It inhibits angiogenesis and tumor growth, suggesting an important and independent role of PLGF in tumor growth. Further studies on its mechanisms of action and its clinical applications are under way. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2453.