Megan E. Baldwin

Tumor refractoriness to anti-VEGF treatment is mediated by CD11b+Gr1+ myeloid cells

Vascular endothelial growth factor (VEGF) is an essential regulator of normal and abnormal blood vessel growth. A monoclonal antibody (mAb) that targets VEGF suppresses tumor growth in murine cancer models and human patients. We investigated cellular and molecular events that mediate refractoriness of tumors to anti-angiogenic therapy. Inherent anti-VEGF refractoriness is associated with infiltration of the tumor tissue by CD11b+Gr1+ myeloid cells. Recruitment of these myeloid cells is also sufficient to confer refractoriness. Combining anti-VEGF treatment with a mAb that targets myeloid cells inhibits growth of refractory tumors more effectively than anti-VEGF alone. Gene expression analysis in CD11b+Gr1+ cells isolated from the bone marrow of mice bearing refractory tumors reveals higher expression of a distinct set of genes known to be implicated in active mobilization and recruitment of myeloid cells. These findings indicate that, in our models, refractoriness to anti-VEGF treatment is determined by the ability of tumors to prime and recruit CD11b+Gr1+ cells.

Corneal avascularity is due to soluble VEGF receptor-1.

Corneal avascularity—the absence of blood vessels in the cornea—is required for optical clarity and optimal vision, and has led to the cornea being widely used for validating pro- and anti-angiogenic therapeutic strategies for many disorders. But the molecular underpinnings of the avascular phenotype have until now remained obscure and are all the more remarkable given the presence in the cornea of vascular endothelial growth factor (VEGF)-A, a potent stimulator of angiogenesis, and the proximity of the cornea to vascularized tissues. Here we show that the cornea expresses soluble VEGF receptor-1 (sVEGFR-1; also known as sflt-1) and that suppression of this endogenous VEGF-A trap by neutralizing antibodies, RNA interference or Cre-lox-mediated gene disruption abolishes corneal avascularity in mice. The spontaneously vascularized corneas of corn1 and Pax6+/- mice and Pax6+/- patients with aniridia are deficient in sflt-1, and recombinant sflt-1 administration restores corneal avascularity in corn1 and Pax6+/- mice. Manatees, the only known creatures uniformly to have vascularized corneas, do not express sflt-1, whereas the avascular corneas of dugongs, also members of the order Sirenia, elephants, the closest extant terrestrial phylogenetic relatives of manatees, and other marine mammals (dolphins and whales) contain sflt-1, indicating that it has a crucial, evolutionarily conserved role. The recognition that sflt-1 is essential for preserving the avascular ambit of the cornea can rationally guide its use as a platform for angiogenic modulators, supports its use in treating neovascular diseases, and might provide insight into the immunological privilege of the cornea.

Abstract LB-284: The novel therapeutic monoclonal antibody VGX-100 neutralises VEGF-C and inhibits tumor growth and metastasis in subcutaneous and orthotopic models of human cancer.

Proceedings: AACR 102nd Annual Meeting 2011‐‐ Apr 2‐6, 2011; Orlando, FL Angiogenesis and lymphangiogenesis are important processes facilitating tumor growth and metastasis. Growth factors that stimulate blood and lymphatic proliferation within tumors are therefore potential targets for anti-cancer therapies. Proof of concept of the clinical utility of anti-angiogenic drugs was first established by the FDA/EMEA-approved drug bevacizumab (Avastin®) which blocks VEGF binding to its receptors VEGFR-1 and VEGFR-2, the latter being the key receptor signaling for angiogenesis. However, patients treated with bevacizumab may be refractory or develop resistance to bevacizumab, suggesting upregulation of alternative pro-angiogenic proteins that allow tumors to bypass the inhibition of VEGF signalling. VEGF-C is a logical candidate for inducing resistance to bevacizumab via this mechanism since it is also a ligand for the angiogenic receptor VEGFR-2 and for VEGFR-3 which is upregulated on tumor-associated vascular endothelium. VGX-100 is a highly specific, fully human monoclonal antibody for VEGF-C that blocks VEGF-C binding to both VEGFR-2 and VEGFR-3. Here we demonstrate that VGX-100 has an additive effect in combination with docetaxel and/or anti-VEGF (bevacizumab) in several tumor models, suggesting that VEGF-C may be an important mediator of the resistance to existing anti-VEGF therapies. Further, we demonstrate that in an orthotopic model of prostate cancer, that inhibition of VEGF-C alone by VGX-100 monotherapy is sufficient to inhibit tumor growth and significantly reduce the incidence of tumor metastasis to local lymph nodes. These data indicate that VGX-100 has exciting potential as a cancer therapeutic by targeting a key factor involved in angiogenesis, lymphangiogenesis and tumor metastasis and is expected to complement chemotherapy and/or other anti-angiogenic compounds in the clinic. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr LB-284. doi:10.1158/1538-7445.AM2011-LB-284

Abstract 2442: VGX-100, a novel therapeutic monoclonal antibody targeting VEGF-C that inhibits tumor growth

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Angiogenesis and lymphangiogenesis are important contributors to the growth and metastasis of a wide variety of tumor types. Therapeutic targeting of the angiogenic vascular endothelial growth factor (VEGF) is now an FDA-approved treatment for several cancers. Vascular endothelial growth factor-C (VEGF-C) has also been demonstrated to stimulate angiogenesis and lymphangiogenesis in a number of experimental systems, and is essential for development of the lymphatic system during embryogenesis. In addition, expression of VEGF-C drives tumor progression and metastasis in mouse models of cancer, and is associated with poor prognosis in many human cancers. Targeting VEGF-C is therefore a highly promising strategy for novel therapeutics, with the potential to disrupt both angiogenesis and lymphangiogenesis. VGX-100 is a highly specific, fully human monoclonal antibody for VEGF-C that does not bind to other members of the VEGF family. In vitro testing demonstrates that VGX-100 blocks binding of VEGF-C to both VEGF receptor-2 and VEGF receptor-3, and inhibits the proliferation of blood vascular (HUVEC) and lymphatic endothelial cells in response to VEGF-C stimulation. Here we demonstrate anti-tumor efficacy through the use of xenograft models of human cancer, with VGX-100 treatment significantly inhibiting tumor growth in several models. These findings demonstrate that VGX-100 has great potential for development as a new cancer therapeutic, with potential clinical utility in combination with existing therapies or in patients refractory to existing anti-angiogenic agents. 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 2442.

Vascular Endothelial Growth Factor Antibodies for Anti-Angiogenic Therapy

The first antibody described to block human VEGF-A is the mouse monoclonal antibody A4.6.1, originally identified based on its ability to block endothelial cell proliferation stimulated by recombinant human VEGF-A. HuMAb VEGF (bevacizumab), a humanized derivative of A4.6.1, was approved in the USA and Europe for the treatment of colorectal cancer in combination with standard chemotherapy and is currently being developed as an anti-cancer therapeutic in a large variety of human cancer types as single-agent therapy or in combination with other anti-cancer modalities, including cytotoxic compounds and radiation. Given the clinical success of the first-generation anti-VEGF antibody, second-generation anti-VEGF antibodies are likely to enter clinical development in the near future. In order to select for antibodies with improved therapeutic activities, the role of epitope binding, binding kinetics and potential effector functions will need to be investigated carefully using relevant preclinical models. One major limitation in the interpretation of data generated in preclinical animal models is the difficulty in defining the extent to which pharmacologic and physiologic responses mimic those in humans. This is particularly true when the therapeutic compounds of interest interact differentially with the human and host VEGF protein, such as in the case of first-and second-generation anti-VEGF antibodies. In this chapter, we review the efficacy, pharmacokinetic, safety and biodistribution data of first-and second-generation anti-VEGF antibodies and provide an update on the status of the pre-clinical model development to study the efficacy and safety of various compounds blocking human VEGF-A in non-primate models.