Ella Ioffe

VEGF-Trap: A VEGF blocker with potent antitumor effects

Vascular endothelial growth factor (VEGF) plays a critical role during normal embryonic angiogenesis and also in the pathological angiogenesis that occurs in a number of diseases, including cancer. Initial attempts to block VEGF by using a humanized monoclonal antibody are beginning to show promise in human cancer patients, underscoring the importance of optimizing VEGF blockade. Previous studies have found that one of the most effective ways to block the VEGF-signaling pathway is to prevent VEGF from binding to its normal receptors by administering decoy-soluble receptors. The highest-affinity VEGF blocker described to date is a soluble decoy receptor created by fusing the first three Ig domains of VEGF receptor 1 to an Ig constant region; however, this fusion protein has very poor in vivo pharmacokinetic properties. By determining the requirements to maintain high affinity while extending in vivo half life, we were able to engineer a very potent high-affinity VEGF blocker that has markedly enhanced pharmacokinetic properties. This VEGF-Trap effectively suppresses tumor growth and vascularization in vivo, resulting in stunted and almost completely avascular tumors. VEGF-Trap-mediated blockade may be superior to that achieved by other agents, such as monoclonal antibodies targeted against the VEGF receptor.

Angiopoietin-1 protects the adult vasculature against plasma leakage.

Pathological increases in vascular leakage lead to edema and swelling, causing serious problems in brain tumors, in diabetic retinopathy, after strokes, during sepsis and also in inflammatory conditions such as rheumatoid arthritis and asthma. Although many agents and disease processes increase vascular leakage, no known agent specifically makes vessels resistant to leaking. Vascular endothelial growth factor (VEGF) and the angiopoietins function together during vascular development, with VEGF acting early during vessel formation, and angiopoietin-1 acting later during vessel remodeling, maturation and stabilization. Although VEGF was initially called vascular permeability factor, there has been less focus on its permeability actions and more effort devoted to its involvement in vessel growth and applications in ischemia and cancer. Recent transgenic approaches have confirmed the profound permeability effects of VEGF (refs. 12–14), and have shown that transgenic angiopoietin-1 acts reciprocally as an anti-permeability factor when provided chronically during vessel formation, although it also profoundly affects vascular morphology when thus delivered. To be useful clinically, angiopoietin-1 would have to inhibit leakage when acutely administered to adult vessels, and this action would have to be uncoupled from its profound angiogenic capabilities. Here we show that acute administration of angiopoietin-1 does indeed protect adult vasculature from leaking, countering the potentially lethal actions of VEGF and inflammatory agents.

Angiopoietin-2 functions as an autocrine protective factor in stressed endothelial cells

Angiopoietin (Ang)-2, a context-dependent agonist/antagonist for the vascular-specific Tie2 receptor, is highly expressed by endothelial cells at sites of normal and pathologic angiogenesis. One prevailing model suggests that in these settings, Ang-2 acts as an autocrine Tie2 blocker, inhibiting the stabilizing influence of the Tie2 activator Ang-1, thereby promoting vascular remodeling. However, the effects of endogenous Ang-2 on cells that are actively producing it have not been studied in detail. Here, we demonstrate that Ang-2 expression is rapidly induced in endothelial cells by the transcription factor FOXO1 after inhibition of the phosphatidylinositol 3-kinase/Akt pathway. We employ RNAi and blocking antibodies to show that in this setting, Ang-2 unexpectedly functions as a Tie2 agonist, bolstering Akt activity so as to provide negative feedback on FOXO1-regulated transcription and apoptosis. In addition, we show that Ang-2, like Ang-1, activates Tie2/Akt signaling in vivo, thereby inhibiting the expression of FOXO1 target genes. Consistent with a role for Ang-2 as a Tie2 activator, we demonstrate that Ang-2 inhibits vascular leak. Our data suggests a model in which Ang-2 expression is induced in stressed endothelial cells, where it acts as an autocrine Tie2 agonist and protective factor.

Angiopoietins have distinct modular domains essential for receptor binding, dimerization and superclustering.

Angiopoietins are a recently discovered family of angiogenic factors that interact with the endothelial receptor tyrosine kinase Tie2, either as agonists (angiopoietin-1) or as context-dependent agonists/antagonists (angiopoietin-2). Here we show that angiopoietin-1 has a modular structure unlike any previously characterized growth factor. This modular structure consists of a receptor-binding domain, a dimerization motif and a superclustering motif that forms variable-sized multimers. Genetic engineering of precise multimers of the receptor-binding domain of angiopoietin-1, using surrogate multimerization motifs, reveals that tetramers are the minimal size required for activating endothelial Tie2 receptors. In contrast, engineered dimers can antagonize endothelial Tie2 receptors. Surprisingly, angiopoietin-2 has a modular structure and multimerization state similar to that of angiopoietin-1, and its antagonist activity seems to be a subtle property encoded in its receptor-binding domain.

Suppression of diabetic retinopathy with angiopoietin-1.

Diabetic retinopathy remains a leading cause of irreversible blindness. A critical early pathology in the disease is the adhesion of leukocytes to the retinal vasculature, a process that occurs, in part, via intercellular adhesion molecule-1. Once leukocyte adhesion occurs, endothelial cell injury ensues, as does blood-retinal barrier breakdown. Here we show that angiopoietin-1 can prevent and reverse these diabetic retinal vascular changes in both new and established diabetes. Angiopoietin-1, when given intravitreally to newly diabetic rats, normalized retinal vascular endothelial growth factor (VEGF) and intercellular adhesion molecule-1 mRNA and protein levels, leading to reductions in leukocyte adhesion, endothelial cell injury, and blood-retinal barrier breakdown. When an adenovirus coding for angiopoietin-1 was given systemically to mice with established diabetes, it similarly inhibited leukocyte adhesion and endothelial cell injury and blood-retinal barrier breakdown. These changes coincided with reductions in retinal eNOS, nitric oxide, Akt (protein kinase B), and MAP kinase activity, known mediators of VEGF bioactivity and leukocyte adhesion. When endogenous VEGF bioactivity was inhibited with a soluble Flt-1/Fc chimera, retinal Akt kinase activity was significantly reduced in vivo. Taken together, these data document new vascular and anti-inflammatory bioactivities for angiopoietin-1 and identify it as the first naturally occurring protein that directly protects the retinal vasculature in diabetes.

Angiopoietin-1 therapy enhances fibrosis and inflammation following folic acid-induced acute renal injury

The loss of interstitial capillaries is a feature of several experimental models of renal disease and this contributes to secondary kidney injury. Angiopoietin-1 is a secreted growth factor which binds to Tie-2 present on endothelia to enhance cell survival thereby stabilizing capillary architecture in-vitro. Previous studies showed that angiopoietin-1 prevented renal capillary and interstitial lesions following experimental ureteric obstruction. We tested here the effect of angiopoietin-1 treatment on capillary loss and associated tubulointerstitial damage known to follow recovery from folic acid-induced tubular necrosis and acute renal injury. We found that delivery of angiopoietin-1 by adenoviral vectors stabilized peritubular capillaries in folic acid nephropathy but this was accompanied by profibrotic and inflammatory effects. These results suggest that the use of endothelial growth factor therapy for kidney disease may have varying outcomes that depend on the disease model tested.

Resistance to Anti-VEGF Therapy Mediated by Autocrine IL6/STAT3 Signaling and Overcome by IL6 Blockade

Anti-VEGF therapies benefit several cancer types, but drug resistance that limits therapeutic response can emerge. We generated cell lines from anti-VEGF-resistant tumor xenografts to investigate the mechanisms by which resistance develops. Of all tumor cells tested, only A431 (A431-V) epidermoid carcinoma cells developed partial resistance to the VEGF inhibitor aflibercept. Compared with the parental tumors, A431-V tumors secreted greater amounts of IL6 and exhibited higher levels of phospho-STAT3. Notably, combined blockade of IL6 receptor (IL6R) and VEGF resulted in enhanced activity against A431-V tumors. Similarly, inhibition of IL6R enhanced the antitumor effects of aflibercept in DU145 prostate tumor cells that displays high endogenous IL6R activity. In addition, post hoc stratification of data obtained from a clinical trial investigating aflibercept efficacy in ovarian cancer showed poorer survival in patients with high levels of circulating IL6. These results suggest that the activation of the IL6/STAT3 pathway in tumor cells may provide a survival advantage during anti-VEGF treatment, suggesting its utility as a source of response biomarkers and as a therapeutic target to heighten efficacious results. Cancer Res; 76(8); 2327-39. ©2016 AACR.

Characterization of the anti-PD-1 antibody REGN2810 and its antitumor activity in human PD-1 knock-in mice

The Programmed Death-1 (PD-1) receptor delivers inhibitory checkpoint signals to activated T cells upon binding to its ligands PD-L1 and PD-L2 expressed on antigen-presenting cells and cancer cells, resulting in suppression of T-cell effector function and tumor immune evasion. Clinical antibodies blocking the interaction between PD-1 and PD-L1 restore the cytotoxic function of tumor antigen-specific T cells, yielding durable objective responses in multiple cancers. This report describes the preclinical characterization of REGN2810, a fully human hinge-stabilized IgG4(S228P) high-affinity anti–PD-1 antibody that potently blocks PD-1 interactions with PD-L1 and PD-L2. REGN2810 was characterized in a series of binding, blocking, and functional cell-based assays, and preclinical in vivo studies in mice and monkeys. In cell-based assays, REGN2810 reverses PD-1–dependent attenuation of T-cell receptor signaling in engineered T cells and enhances responses of human primary T cells. To test the in vivo activity of REGN2810, which does not cross-react with murine PD-1, knock-in mice were generated to express a hybrid protein containing the extracellular domain of human PD-1, and transmembrane and intracellular domains of mouse PD-1. In these mice, REGN2810 binds the humanized PD-1 receptor and inhibits growth of MC38 murine tumors. As REGN2810 binds to cynomolgus monkey PD-1 with high affinity, pharmacokinetic and toxicologic assessment of REGN2810 was performed in cynomolgus monkeys. High doses of REGN2810 were well tolerated, without adverse immune-related effects. These preclinical studies validate REGN2810 as a potent and promising candidate for cancer immunotherapy. Mol Cancer Ther; 16(5); 861–70. ©2017 AACR.

Abstract 266: Antitumor activity of REGN2810, a fully human anti-PD-1 monoclonal antibody, against MC38.Ova tumors grown in immune-competent humanized PD-1 mice

Programmed Cell Death Protein 1 (PD-1), is an inhibitory checkpoint receptor, expressed in an activation-induced manner on T cells. PD-1 signals upon binding to its ligands PD-L1 and PD-L2, expressed on APCs and some types of cancer cells, and delivers inhibitory signals to T cells, promoting T-cells functional exhaustion in a tumor microenvironment. Clinically, antibodies (Abs) that block the interaction between PD-1 and PD-L1 can release the cytotoxic function of tumor-specific T cells, yielding durable objective responses in multiple cancer types. REGN2810 is a fully human hinge-stabilized IgG4P monoclonal Ab that binds to the extracellular domain of human PD-1 with high affinity and specificity. REGN2810 was selected using a combination of binding studies (Surface Plasmon Resonance [SPR]-Biacore), enzyme-linked immunosorbent assays (ELISA), novel engineered cell-based bioassays, and preclinical studies in mouse models. REGN2810 was investigated in PD-1 humanized mice, an approach that allows direct testing of clinical PD-1 Ab that does not cross-react with mouse PD-1. Humanized PD-1 mice were created by Velocigene technology to express a humanized hybrid PD-1 protein comprising the extracellular portion of human PD-1 and the transmembrane and intracellular portion of mouse PD-1. Humanized PD-1 mice were validated for inducible cell surface expression of hybrid PD-1 protein on activated T-cells, intact PD-1/PD-L1 signaling and immune responses. A weakly immunogenic murine colorectal cancer cell line MC38 was engineered to express ovalbumin (MC38.Ova) in order to increase tumor immunogenicity and allow monitoring of T-cell immune responses to well-defined antigenic ovalbumin peptides. Prophylactic treatment with REGN2810 PD-1 Ab significantly suppressed growth of subcutaneous syngeneic MC38.Ova tumors in humanized PD-1 mice in a dose dependent manner, and improved mouse survival. Therapeutic treatment with REGN2810 also promoted dose dependent regression of established MC38.Ova tumors in humanized PD-1 mice. Treatment with REGN2810 induced CD8 T cells proliferation and cytokine production in spleens of tumor bearing huPD-1 mice. The mechanism of action and robust anti-tumor efficacy of REGN2810 support its clinical development for the treatment of human cancers. Citation Format: Elena Burova, Omaira Allbritton, William Poueymirou, Venus Lai, Janelle White, Dimitris Skokos, Nicholas Papadopoulos, Drew Murphy, Israel Lowy, Ella Ioffe, Gavin Thurston. Antitumor activity of REGN2810, a fully human anti-PD-1 monoclonal antibody, against MC38.Ova tumors grown in immune-competent humanized PD-1 mice. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 266. doi:10.1158/1538-7445.AM2015-266

Abstract B113: In vivo characterization of anti-PD-1 antibody REGN2810 in human PD-1 knock-in mice

The Programmed Death-1 (PD-1) receptor is an immunologic inhibitory checkpoint, expressed by activated T cells. PD-1 signals upon binding to its ligands PD-L1 and PD-L2 expressed on antigen presenting cells and some types of cancer cells, and delivers inhibitory signals to T cells, resulting in suppression of T-cell effector function. In cancer patients, PD-1 is expressed on tumor-infiltrating lymphocytes and inhibits antitumor immune responses through ligand binding. Clinically, it has been shown that antibodies (Abs) that block the interaction between PD-1 and PD-L1 can release the cytotoxic function of tumor-specific T cells, yielding durable objective responses in multiple cancer types. This study describes preclinical characterization of REGN2810, a fully human hinge-stabilized IgG4 monoclonal Ab that binds to the extracellular domain of human PD-1 with high affinity and specificity and inhibits interaction of PD-1 with its ligands. Taking advantage of the ability of human PD-1 to interact with murine PD-L1, we generated a mouse with human PD-1 gene knock-in allowing direct testing of our anti-human PD-1 Ab. Human PD-1 knock-in mice express a hybrid protein containing the extracellular portion of human PD-1, and transmembrane and intracellular domains of mouse PD-1. We demonstrated functional PD-1/PD-L1 signaling and immune responses in this model, and confirmed REGN2810 binding to hybrid PD-1 receptor on mouse T cells in vivo following REGN2810 injections. Prophylactic and therapeutic treatments of subcutaneous syngeneic tumors with REGN2810 in human PD-1 knock-in mice resulted in a dose-dependent suppression of tumor growth. Currently REGN2810 anti-PD-1 Ab is in phase 1 clinical trials for oncology indications. Citation Format: Elena Burova, Omaira Allbritton, William Poueymirou, Venus Lai, Janelle Waite, Dimitris Skokos, Nicholas Papadopoulos, Drew Murphy, Israel Lowy, Ella Ioffe, Gavin Thurston. In vivo characterization of anti-PD-1 antibody REGN2810 in human PD-1 knock-in mice. [abstract]. In: Proceedings of the CRI-CIMT-EATI-AACR Inaugural International Cancer Immunotherapy Conference: Translating Science into Survival; September 16-19, 2015; New York, NY. Philadelphia (PA): AACR; Cancer Immunol Res 2016;4(1 Suppl):Abstract nr B113.