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Targeting neuropilin-1 to inhibit VEGF signaling in cancer: Comparison of therapeutic approaches.

Mac Gabhann F, Popel AS - PLoS Comput. Biol. (2006)

Bottom Line: Using the first molecularly detailed computational model of VEGF and its receptors, we have shown previously that the VEGFR-Neuropilin interactions explain the observed differential effects of VEGF isoforms on VEGF signaling in vitro, and demonstrated potent VEGF inhibition by an antibody to Neuropilin-1 that does not block ligand binding but blocks subsequent receptor coupling.The model predicts that blockade of Neuropilin-VEGFR coupling is significantly more effective than other approaches in decreasing VEGF-VEGFR2 signaling.In addition, tumor types with different receptor expression levels respond differently to each of these treatments.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America. feilim@jhu.edu

ABSTRACT
Angiogenesis (neovascularization) plays a crucial role in a variety of physiological and pathological conditions including cancer, cardiovascular disease, and wound healing. Vascular endothelial growth factor (VEGF) is a critical regulator of angiogenesis. Multiple VEGF receptors are expressed on endothelial cells, including signaling receptor tyrosine kinases (VEGFR1 and VEGFR2) and the nonsignaling co-receptor Neuropilin-1. Neuropilin-1 binds only the isoform of VEGF responsible for pathological angiogenesis (VEGF165), and is thus a potential target for inhibiting VEGF signaling. Using the first molecularly detailed computational model of VEGF and its receptors, we have shown previously that the VEGFR-Neuropilin interactions explain the observed differential effects of VEGF isoforms on VEGF signaling in vitro, and demonstrated potent VEGF inhibition by an antibody to Neuropilin-1 that does not block ligand binding but blocks subsequent receptor coupling. In the present study, we extend that computational model to simulation of in vivo VEGF transport and binding, and predict the in vivo efficacy of several Neuropilin-targeted therapies in inhibiting VEGF signaling: (a) blocking Neuropilin-1 expression; (b) blocking VEGF binding to Neuropilin-1; (c) blocking Neuropilin-VEGFR coupling. The model predicts that blockade of Neuropilin-VEGFR coupling is significantly more effective than other approaches in decreasing VEGF-VEGFR2 signaling. In addition, tumor types with different receptor expression levels respond differently to each of these treatments. In designing human therapeutics, the mechanism of attacking the target plays a significant role in the outcome: of the strategies tested here, drugs with similar properties to the Neuropilin-1 antibody are predicted to be most effective. The tumor type and the microenvironment of the target tissue are also significant in determining therapeutic efficacy of each of the treatments studied.

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Schematics of VEGF Transport in Tumors, VEGF Receptor Binding, and Therapeutic Strategies(A) Schematic of the in vivo model. Parenchymal cells secrete VEGF; VEGF121 is freely diffusible, but VEGF165 can be sequestered by proteoglycans in the ECM (light gray) and the basement membranes (dark gray). The isoforms bind to VEGF receptors on the endothelial cells.(B) VEGF isoforms bind to VEGFR2 that transduces the angiogenic signal intracellularly. VEGF121 does not bind Neuropilin-1; VEGF165 may bind both VEGFR2 and Neuropilin-1 simultaneously. Thus there are two pathways for the binding of VEGF165 to the signaling VEGFR2 receptor: first by binding directly, and second by binding Neuropilin-1 and then diffusing laterally on the cell surface to couple to VEGFR2. VEGFR1, which modulates the signaling of VEGFR2, binds both isoforms of VEGF. VEGFR1 also binds directly to Neuropilin-1. This complex is permissive for VEGF121–VEGFR1 binding but not VEGF165–VEGFR1; thus, high levels of Neuropilin-1 displace VEGF165 from VEGFR1, making it available for VEGFR2 binding. Only VEGF165 binds directly to the ECM binding site (represented by GAG chains).(C) By targeting Neuropilin-1, we can target specifically VEGF165-induced signaling. Three methods for targeting Neuropilin-1 are analyzed here: blockade of Neuropilin-1 expression (e.g., using siRNA); blockade of VEGF–Neuropilin binding (e.g., using a fragment of placental growth factor to occupy the binding site); and blockade of VEGFR–Neuropilin coupling (e.g., using an antibody for Neuropilin-1 that does not interfere with VEGF–Neuropilin binding).
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pcbi-0020180-g001: Schematics of VEGF Transport in Tumors, VEGF Receptor Binding, and Therapeutic Strategies(A) Schematic of the in vivo model. Parenchymal cells secrete VEGF; VEGF121 is freely diffusible, but VEGF165 can be sequestered by proteoglycans in the ECM (light gray) and the basement membranes (dark gray). The isoforms bind to VEGF receptors on the endothelial cells.(B) VEGF isoforms bind to VEGFR2 that transduces the angiogenic signal intracellularly. VEGF121 does not bind Neuropilin-1; VEGF165 may bind both VEGFR2 and Neuropilin-1 simultaneously. Thus there are two pathways for the binding of VEGF165 to the signaling VEGFR2 receptor: first by binding directly, and second by binding Neuropilin-1 and then diffusing laterally on the cell surface to couple to VEGFR2. VEGFR1, which modulates the signaling of VEGFR2, binds both isoforms of VEGF. VEGFR1 also binds directly to Neuropilin-1. This complex is permissive for VEGF121–VEGFR1 binding but not VEGF165–VEGFR1; thus, high levels of Neuropilin-1 displace VEGF165 from VEGFR1, making it available for VEGFR2 binding. Only VEGF165 binds directly to the ECM binding site (represented by GAG chains).(C) By targeting Neuropilin-1, we can target specifically VEGF165-induced signaling. Three methods for targeting Neuropilin-1 are analyzed here: blockade of Neuropilin-1 expression (e.g., using siRNA); blockade of VEGF–Neuropilin binding (e.g., using a fragment of placental growth factor to occupy the binding site); and blockade of VEGFR–Neuropilin coupling (e.g., using an antibody for Neuropilin-1 that does not interfere with VEGF–Neuropilin binding).

Mentions: Vascular endothelial growth factor (VEGF) is a family of secreted glycoproteins and critical regulators of angiogenesis [7,8]. In vitro, VEGF increases endothelial cell survival, proliferation, and migration. In vivo, it increases vascular permeability, activates endothelial cells, and acts as a chemoattractant for nascent vessel sprouts. Multiple splice isoforms of VEGF exist; the two most abundant in the human are VEGF121 and VEGF165. Both isoforms bind to the VEGF receptor tyrosine kinases (VEGFRs) to induce signals. VEGF165 also interacts with nonsignaling Neuropilin co-receptors and with proteoglycans of the extracellular matrix (ECM) [9,10] (Figure 1). The binding sites on VEGF165 for VEGFR2 and Neuropilin-1 are nonoverlapping, so VEGF165 may bind both simultaneously [9]. There are thus two parallel pathways for VEGF165 to bind its signaling receptor: binding directly to VEGFR2; and binding to Neuropilin-1, which presents VEGF to VEGFR2 (coupling the two receptors together). VEGF121 can only form VEGFR2 complexes directly [10]. The VEGF165–Neuropilin interaction is thus of particular value as a therapeutic target because VEGF165 is the isoform of VEGF that has been identified as inducing pathological angiogenesis [11,12]: aberrant angiogenic signaling may be targeted while allowing the normal levels of physiological VEGF signaling to continue.


Targeting neuropilin-1 to inhibit VEGF signaling in cancer: Comparison of therapeutic approaches.

Mac Gabhann F, Popel AS - PLoS Comput. Biol. (2006)

Schematics of VEGF Transport in Tumors, VEGF Receptor Binding, and Therapeutic Strategies(A) Schematic of the in vivo model. Parenchymal cells secrete VEGF; VEGF121 is freely diffusible, but VEGF165 can be sequestered by proteoglycans in the ECM (light gray) and the basement membranes (dark gray). The isoforms bind to VEGF receptors on the endothelial cells.(B) VEGF isoforms bind to VEGFR2 that transduces the angiogenic signal intracellularly. VEGF121 does not bind Neuropilin-1; VEGF165 may bind both VEGFR2 and Neuropilin-1 simultaneously. Thus there are two pathways for the binding of VEGF165 to the signaling VEGFR2 receptor: first by binding directly, and second by binding Neuropilin-1 and then diffusing laterally on the cell surface to couple to VEGFR2. VEGFR1, which modulates the signaling of VEGFR2, binds both isoforms of VEGF. VEGFR1 also binds directly to Neuropilin-1. This complex is permissive for VEGF121–VEGFR1 binding but not VEGF165–VEGFR1; thus, high levels of Neuropilin-1 displace VEGF165 from VEGFR1, making it available for VEGFR2 binding. Only VEGF165 binds directly to the ECM binding site (represented by GAG chains).(C) By targeting Neuropilin-1, we can target specifically VEGF165-induced signaling. Three methods for targeting Neuropilin-1 are analyzed here: blockade of Neuropilin-1 expression (e.g., using siRNA); blockade of VEGF–Neuropilin binding (e.g., using a fragment of placental growth factor to occupy the binding site); and blockade of VEGFR–Neuropilin coupling (e.g., using an antibody for Neuropilin-1 that does not interfere with VEGF–Neuropilin binding).
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC1761657&req=5

pcbi-0020180-g001: Schematics of VEGF Transport in Tumors, VEGF Receptor Binding, and Therapeutic Strategies(A) Schematic of the in vivo model. Parenchymal cells secrete VEGF; VEGF121 is freely diffusible, but VEGF165 can be sequestered by proteoglycans in the ECM (light gray) and the basement membranes (dark gray). The isoforms bind to VEGF receptors on the endothelial cells.(B) VEGF isoforms bind to VEGFR2 that transduces the angiogenic signal intracellularly. VEGF121 does not bind Neuropilin-1; VEGF165 may bind both VEGFR2 and Neuropilin-1 simultaneously. Thus there are two pathways for the binding of VEGF165 to the signaling VEGFR2 receptor: first by binding directly, and second by binding Neuropilin-1 and then diffusing laterally on the cell surface to couple to VEGFR2. VEGFR1, which modulates the signaling of VEGFR2, binds both isoforms of VEGF. VEGFR1 also binds directly to Neuropilin-1. This complex is permissive for VEGF121–VEGFR1 binding but not VEGF165–VEGFR1; thus, high levels of Neuropilin-1 displace VEGF165 from VEGFR1, making it available for VEGFR2 binding. Only VEGF165 binds directly to the ECM binding site (represented by GAG chains).(C) By targeting Neuropilin-1, we can target specifically VEGF165-induced signaling. Three methods for targeting Neuropilin-1 are analyzed here: blockade of Neuropilin-1 expression (e.g., using siRNA); blockade of VEGF–Neuropilin binding (e.g., using a fragment of placental growth factor to occupy the binding site); and blockade of VEGFR–Neuropilin coupling (e.g., using an antibody for Neuropilin-1 that does not interfere with VEGF–Neuropilin binding).
Mentions: Vascular endothelial growth factor (VEGF) is a family of secreted glycoproteins and critical regulators of angiogenesis [7,8]. In vitro, VEGF increases endothelial cell survival, proliferation, and migration. In vivo, it increases vascular permeability, activates endothelial cells, and acts as a chemoattractant for nascent vessel sprouts. Multiple splice isoforms of VEGF exist; the two most abundant in the human are VEGF121 and VEGF165. Both isoforms bind to the VEGF receptor tyrosine kinases (VEGFRs) to induce signals. VEGF165 also interacts with nonsignaling Neuropilin co-receptors and with proteoglycans of the extracellular matrix (ECM) [9,10] (Figure 1). The binding sites on VEGF165 for VEGFR2 and Neuropilin-1 are nonoverlapping, so VEGF165 may bind both simultaneously [9]. There are thus two parallel pathways for VEGF165 to bind its signaling receptor: binding directly to VEGFR2; and binding to Neuropilin-1, which presents VEGF to VEGFR2 (coupling the two receptors together). VEGF121 can only form VEGFR2 complexes directly [10]. The VEGF165–Neuropilin interaction is thus of particular value as a therapeutic target because VEGF165 is the isoform of VEGF that has been identified as inducing pathological angiogenesis [11,12]: aberrant angiogenic signaling may be targeted while allowing the normal levels of physiological VEGF signaling to continue.

Bottom Line: Using the first molecularly detailed computational model of VEGF and its receptors, we have shown previously that the VEGFR-Neuropilin interactions explain the observed differential effects of VEGF isoforms on VEGF signaling in vitro, and demonstrated potent VEGF inhibition by an antibody to Neuropilin-1 that does not block ligand binding but blocks subsequent receptor coupling.The model predicts that blockade of Neuropilin-VEGFR coupling is significantly more effective than other approaches in decreasing VEGF-VEGFR2 signaling.In addition, tumor types with different receptor expression levels respond differently to each of these treatments.

View Article: PubMed Central - PubMed

Affiliation: Department of Biomedical Engineering, Johns Hopkins University School of Medicine, Baltimore, Maryland, United States of America. feilim@jhu.edu

ABSTRACT
Angiogenesis (neovascularization) plays a crucial role in a variety of physiological and pathological conditions including cancer, cardiovascular disease, and wound healing. Vascular endothelial growth factor (VEGF) is a critical regulator of angiogenesis. Multiple VEGF receptors are expressed on endothelial cells, including signaling receptor tyrosine kinases (VEGFR1 and VEGFR2) and the nonsignaling co-receptor Neuropilin-1. Neuropilin-1 binds only the isoform of VEGF responsible for pathological angiogenesis (VEGF165), and is thus a potential target for inhibiting VEGF signaling. Using the first molecularly detailed computational model of VEGF and its receptors, we have shown previously that the VEGFR-Neuropilin interactions explain the observed differential effects of VEGF isoforms on VEGF signaling in vitro, and demonstrated potent VEGF inhibition by an antibody to Neuropilin-1 that does not block ligand binding but blocks subsequent receptor coupling. In the present study, we extend that computational model to simulation of in vivo VEGF transport and binding, and predict the in vivo efficacy of several Neuropilin-targeted therapies in inhibiting VEGF signaling: (a) blocking Neuropilin-1 expression; (b) blocking VEGF binding to Neuropilin-1; (c) blocking Neuropilin-VEGFR coupling. The model predicts that blockade of Neuropilin-VEGFR coupling is significantly more effective than other approaches in decreasing VEGF-VEGFR2 signaling. In addition, tumor types with different receptor expression levels respond differently to each of these treatments. In designing human therapeutics, the mechanism of attacking the target plays a significant role in the outcome: of the strategies tested here, drugs with similar properties to the Neuropilin-1 antibody are predicted to be most effective. The tumor type and the microenvironment of the target tissue are also significant in determining therapeutic efficacy of each of the treatments studied.

Show MeSH
Related in: MedlinePlus