Vascular Endothelial Growth Factor C and D Signaling Pathways as Potential Targets for the Treatment of Neovascular Age-Related Macular Degeneration: A Narrative Review.

The development of treatments targeting the vascular endothelial growth factor (VEGF) signaling pathways have traditionally been firstly investigated in oncology and then advanced into retinal disease indications. Members of the VEGF family of endogenous ligands and their respective receptors play a central role in vasculogenesis and angiogenesis during both development and physiological homeostasis. They can also play a pathogenic role in cancer and retinal diseases. Therapeutic approaches have mostly focused on targeting VEGF-A signaling; however, research has shown that VEGF-C and VEGF-D signaling pathways are also important to the disease pathogenesis of tumors and retinal diseases. This review highlights the important therapeutic advances and the remaining unmet need for improved therapies targeting additional mechanisms beyond VEGF-A. Additionally, it provides an overview of alternative VEGF-C and VEGF-D signaling involvement in both health and disease, highlighting their key contributions in the multifactorial pathophysiology of retinal disease including neovascular age-related macular degeneration (nAMD). Strategies for targeting VEGF-C/-D signaling pathways will also be reviewed, with an emphasis on agents currently being developed for the treatment of nAMD.

A Randomized Controlled Trial of OPT-302, a VEGF-C/D Inhibitor for Neovascular Age-Related Macular Degeneration.

PURPOSE: Neovascular (wet) age-related macular degeneration (nAMD) is driven by VEGFs A, C, and D, which promote angiogenesis and vascular permeability. Intravitreal injections of anti-VEGF-A drugs are the standard of care, but these do not inhibit VEGF-C and D, which may explain why many patients fail to respond fully. This trial aimed to test the safety and efficacy of OPT-302, a biologic inhibitor of VEGF-C and D, in combination with the anti-VEGF-A inhibitor ranibizumab. DESIGN: Dose-ranging, phase 2b, randomized, double-masked, sham-controlled trial. PARTICIPANTS: Participants with treatment-naive nAMD were enrolled from 109 sites across Europe, Israel, and the United States. METHODS: Participants were randomized to 6, 4-weekly, intravitreal injections of 0.5 mg OPT-302, 2.0 mg OPT-302, or sham, plus intravitreal 0.5 mg ranibizumab. MAIN OUTCOME MEASURES: The primary outcome was mean change in ETDRS best-corrected visual acuity (BCVA) at 24 weeks. Secondary outcomes (comparing baseline with week 24) were the proportion of participants gaining or losing ≥ 15 ETDRS BCVA letters; area under the ETDRS BCVA over time curve; change in spectral-domain OCT (SD-OCT) central subfield thickness; and change in intraretinal fluid and subretinal fluid on SD-OCT. RESULTS: Of 366 participants recruited from December 1, 2017, to November 30, 2018, 122, 123, and 121 were randomized to 0.5 mg OPT-302, 2.0 mg OPT-302, and sham, respectively. Mean (± standard deviation) visual acuity gain in the 2.0 mg OPT-302 group was significantly superior to sham (+14.2 ± 11.61 vs. +10.8 ± 11.52 letters; P = 0.01). The 0.5 mg OPT-302 group was not significantly different than the sham group (+9.44 ± 11.32 letters; P = 0.83). Compared with sham, the secondary BCVA outcomes favored the 2.0 mg OPT-302 group, with structural outcomes favoring both OPT-302 dosage groups. Adverse events (AEs) were similar across groups, with 16 (13.3%), 7 (5.6%), and 10 (8.3%) participants in the lower-dose, higher-dose, and sham groups, respectively, developing at least 1 serious AE. Two unrelated deaths both occurred in the sham arm. CONCLUSIONS: Significantly superior vision gain was observed with OPT-302 2.0 mg combination therapy, versus standard of care, with favorable safety (ClinicalTrials.gov identifier: NCT03345082). FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found after the references.

Phase 1 Study of OPT-302 Inhibition of Vascular Endothelial Growth Factors C and D for Neovascular Age-Related Macular Degeneration.

PURPOSE: OPT-302 is a novel inhibitor of vascular endothelial growth factor (VEGF)-C and VEGF-D. A phase 1 trial assessed the safety of intravitreal OPT-302 as monotherapy or combined with ranibizumab (Lucentis; Genentech, South San Francisco, CA) in patients with neovascular age-related macular degeneration (nAMD). DESIGN: Open-label, dose escalation followed by a randomized dose expansion. PARTICIPANTS: Fifty-one patients with nAMD who were either treatment naïve (n = 25) or previously were treated with anti-VEGF A therapy (n = 26). METHODS: In the dose escalation, groups of 5 patients in 4 cohorts received ascending doses of OPT-302 (0.3 mg, 1 mg, or 2 mg) in combination with ranibizumab (0.5 mg), or as monotherapy (2 mg). In the dose expansion, 31 patients were randomized (3:1) to OPT-302 (2 mg) in combination with ranibizumab (n = 23) or as monotherapy (n = 8). Participants received three intravitreal treatments of OPT-302 once every 4 weeks either with or without ranibizumab. MAIN OUTCOME MEASURES: Safety and tolerability, OPT-302 pharmacokinetics and immunogenicity, effects on best-corrected visual acuity (BCVA), and anatomic changes. RESULTS: Intravitreal OPT-302 with or without ranibizumab was well tolerated with low systemic exposure, no dose-limiting toxicities and no immunogenicity. In patients receiving OPT-302 monotherapy, 7 of 13 (54%) did not require rescue anti-VEGF-A therapy and the mean change in BCVA from baseline to week 12 was +5.6 letters (range, 0-18 letters). Mean BCVA gains from baseline to week 12 following combination OPT-302 with ranibizumab were +10.8 letters (95% confidence interval [CI], 4-17; n = 18) in treatment-naïve patients and +4.9 letters (95% CI, 3-7; n = 19) in previously treated patients, respectively. Corresponding reductions in mean central subfield thickness at week 12 in both groups were -119 µm (95% CI, -176 to -62 µm) and -54 µm (95% CI, -82 to -26 µm), respectively, whilst 50% of treatment-naïve patients also showed no detectable choroidal neovascularization at week 12 on fluorescein angiography. CONCLUSIONS: Intravitreal OPT-302 inhibition of VEGF-C and -D was well tolerated, and OPT-302 combination therapy may overcome an escape mechanism to VEGF-A suppression in the management of nAMD.

Differential expression of VEGF ligands and receptors in prostate cancer.

BACKGROUND: Prostate cancer disseminates to regional lymph nodes, however the molecular mechanisms responsible for lymph node metastasis are poorly understood. The vascular endothelial growth factor (VEGF) ligand and receptor family have been implicated in the growth and spread of prostate cancer via activation of the blood vasculature and lymphatic systems. The purpose of this study was to comprehensively examine the expression pattern of VEGF ligands and receptors in the glandular epithelium, stroma, lymphatic vasculature and blood vessels in prostate cancer. METHODS: The localization of VEGF-A, VEGF-C, VEGF-D, VEGF receptor (VEGFR)-1, VEGFR-2, and VEGFR-3 was examined in cancerous and adjacent benign prostate tissue from 52 subjects representing various grades of prostate cancer. RESULTS: Except for VEGFR-2, extensive staining was observed for all ligands and receptors in the prostate specimens. In epithelial cells, VEGF-A and VEGFR-1 expression was higher in tumor tissue compared to benign tissue. VEGF-D and VEGFR-3 expression was significantly higher in benign tissue compared to tumor in the stroma and the endothelium of lymphatic and blood vessels. In addition, the frequency of lymphatic vessels, but not blood vessels, was lower in tumor tissue compared with benign tissue. CONCLUSIONS: These results suggest that activation of VEGFR-1 by VEGF-A within the carcinoma, and activation of lymphatic endothelial cell VEGFR-3 by VEGF-D within the adjacent benign stroma may be important signaling mechanisms involved in the progression and subsequent metastatic spread of prostate cancer. Thus inhibition of these pathways may contribute to therapeutic strategies for the management of prostate cancer.

VEGF-D promotes tumor metastasis by regulating prostaglandins produced by the collecting lymphatic endothelium.

Lymphatic metastasis is facilitated by lymphangiogenic growth factors VEGF-C and VEGF-D that are secreted by some primary tumors. We identified regulation of PGDH, the key enzyme in prostaglandin catabolism, in endothelial cells of collecting lymphatics, as a key molecular change during VEGF-D-driven tumor spread. The VEGF-D-dependent regulation of the prostaglandin pathway was supported by the finding that collecting lymphatic vessel dilation and subsequent metastasis were affected by nonsteroidal anti-inflammatory drugs (NSAIDs), known inhibitors of prostaglandin synthesis. Our data suggest a control point for cancer metastasis within the collecting lymphatic endothelium, which links VEGF-D/VEGFR-2/VEGFR-3 and the prostaglandin pathways. Collecting lymphatics therefore play an active and important role in metastasis and may provide a therapeutic target to restrict tumor spread.

Deletion of vascular endothelial growth factor C (VEGF-C) and VEGF-D is not equivalent to VEGF receptor 3 deletion in mouse embryos.

Lymphatic vessels play an important role in the regulation of tissue fluid balance, immune responses, and fat adsorption and are involved in diseases including lymphedema and tumor metastasis. Vascular endothelial growth factor (VEGF) receptor 3 (VEGFR-3) is necessary for development of the blood vasculature during early embryogenesis, but later, VEGFR-3 expression becomes restricted to the lymphatic vasculature. We analyzed mice deficient in both of the known VEGFR-3 ligands, VEGF-C and VEGF-D. Unlike the Vegfr3(-/-) embryos, the Vegfc(-/-); Vegfd(-/-) embryos displayed normal blood vasculature after embryonic day 9.5. Deletion of Vegfr3 in the epiblast, using keratin 19 (K19) Cre, resulted in a phenotype identical to that of the Vegfr3(-/-) embryos, suggesting that this phenotype is due to defects in the embryo proper and not in placental development. Interestingly, the Vegfr3(neo) hypomorphic mutant mice carrying the neomycin cassette between exons 1 and 2 showed defective lymphatic development. Overexpression of human or mouse VEGF-D in the skin, under the K14 promoter, rescued the lymphatic hypoplasia of the Vegfc(+/-) mice in the K14-VEGF-D; Vegfc(+/-) compound mice, suggesting that VEGF-D is functionally redundant with VEGF-C in the stimulation of developmental lymphangiogenesis. Our results suggest VEGF-C- and VEGF-D-independent functions for VEGFR-3 in the early embryo.

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.

Molecular pathways for lymphangiogenesis and their role in human disease.

The lymphatic network functions to return fluid, cells and macromolecules to the circulation. Recent characterization of growth factors that control the growth and development of the lymphatics, and markers which specify lymphatic endothelial cells have enhanced our understanding of this system. Members of the VEGF family of factors are key regulators of these vessels with VEGF-C/VEGF-D and VEGFR-3 being the best validated signalling pathways in lymphangiogenesis. The study of these molecules in various pathologies has shown that they are important in the processes of cancer metastasis and in the formation of lymphoedema. Knowledge of these molecular pathways allows for the generation of modulators of these pathways which could form the basis of novel therapeutic approaches.

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.

Redundant roles of VEGF-B and PlGF during selective VEGF-A blockade in mice.

Vascular endothelial growth factor-A (VEGF-A) and its 2 transmembrane tyrosine-kinase receptors, VEGFR-1 and VEGFR-2, constitute a ligand-receptor signaling system that is crucial for developmental angiogenesis. VEGF-B and placental growth factor (PlGF) activate VEGFR-1 selectively, however, mice lacking either ligand display only minor developmental defects. We hypothesized that the relative contributions of VEGF-B and PlGF to VEGFR-1 signaling may be masked in the presence of VEGF-A, which is abundantly expressed during postnatal development. To test this hypothesis, neonatal or adult mice were treated with a monoclonal antibody (G6-23-IgG) blocking murine VEGF-A or a soluble VEGFR-1 receptor IgG chimeric construct [mFlt(1-3)-IgG], which neutralizes VEGF-A, VEGF-B, and PlGF. Both compounds attenuated growth and survival of neonatal mice to similar extents and the pathophysiologic alterations, including a reduction in organ size and vascularization, changes in gene expression, and hematologic end points, were essentially indistinguishable. In adult mice, we observed only minor changes in response to treatment, which were similar between both anti-VEGF compounds. In conclusion, our findings suggest that PlGF and VEGF-B do not compensate during conditions of VEGF-A blockade, suggesting a minor role for compensatory VEGFR-1 signaling during postnatal development and vascular homeostasis in adults. The absence of compensatory VEGFR-1 signaling by VEGF-B and PlGF may have important implications for the development of anticancer strategies targeting the VEGF ligand/receptor system.

Vascular endothelial growth factor D is dispensable for development of the lymphatic system.

Vascular endothelial growth factor receptor 3 (Vegfr-3) is a tyrosine kinase that is expressed on the lymphatic endothelium and that signals for the growth of the lymphatic vessels (lymphangiogenesis). Vegf-d, a secreted glycoprotein, is one of two known activating ligands for Vegfr-3, the other being Vegf-c. Vegf-d stimulates lymphangiogenesis in tissues and tumors; however, its role in embryonic development was previously unknown. Here we report the generation and analysis of mutant mice deficient for Vegf-d. Vegf-d-deficient mice were healthy and fertile, had normal body mass, and displayed no pathologic changes consistent with a defect in lymphatic function. The lungs, sites of strong Vegf-d gene expression during embryogenesis in wild-type mice, were normal in Vegf-d-deficient mice with respect to tissue mass and morphology, except that the abundance of the lymphatics adjacent to bronchioles was slightly reduced. Dye uptake experiments indicated that large lymphatics under the skin were present in normal locations and were functional. Smaller dermal lymphatics were similar in number, location, and function to those in wild-type controls. The lack of a profound lymphatic phenotype in Vegf-d-deficient mice suggests that Vegf-d does not play a major role in lymphatic development or that Vegf-c or another, as-yet-unknown activating Vegfr-3 ligand can compensate for Vegf-d during development.

Expression of vascular endothelial growth factor receptor-3 by lymphatic endothelial cells is associated with lymph node metastasis in prostate cancer.

PURPOSE: The molecular mechanisms underlying lymph node metastasis are poorly understood, despite the well-established clinical importance of lymph node status in many human cancers. Recently, vascular endothelial growth factor (VEGF)-C and VEGF-D have been implicated in the regulation of tumor lymphangiogenesis and enhancement of lymphatic invasion via activation of VEGF receptor-3. The purpose of this study was to determine the expression pattern of the VEGF-C/VEGF-D/VEGF receptor-3 axis in prostate cancer and its relationship with lymph node metastasis. EXPERIMENTAL DESIGN: The expression pattern of VEGF-C, VEGF-D, and VEGF receptor-3 in localized prostate cancer specimens (n = 37) was determined using immunohistochemistry. RESULTS: Widespread, heterogeneous staining for VEGF-C and VEGF-D was observed in all cancer specimens. Intensity of VEGF-C staining was lower in benign prostate epithelium than in adjacent carcinoma, whereas no difference between benign epithelium and carcinoma was observed for VEGF-D staining. VEGF receptor-3 immunostaining was detected in endothelial cells of lymphatic vessels in 18 of 37 tissue samples. The presence of VEGF receptor-3-positive vessels was associated with lymph node metastasis (P = 0.0002), Gleason grade (P < 0.0001), extracapsular extension (P = 0.0382), and surgical margin status (P = 0.0069). In addition, VEGF receptor-3 staining highlighted lymphatic invasion by VEGF-C-positive/VEGF-D-positive carcinoma cells. CONCLUSIONS: Together, these results suggest that paracrine activation of lymphatic endothelial cell VEGF receptor-3 by VEGF-C and/or VEGF-D may be involved in lymphatic metastasis. Thus the VEGF-C/VEGF-D/VEGF receptor-3 signaling pathway may provide a target for antilymphangiogenic therapy in prostate cancer.

Plasmin activates the lymphangiogenic growth factors VEGF-C and VEGF-D.

Vascular endothelial growth factor (VEGF) C and VEGF-D stimulate lymphangiogenesis and angiogenesis in tissues and tumors by activating the endothelial cell surface receptor tyrosine kinases VEGF receptor (VEGFR) 2 and VEGFR-3. These growth factors are secreted as full-length inactive forms consisting of NH2- and COOH-terminal propeptides and a central VEGF homology domain (VHD) containing receptor binding sites. Proteolytic cleavage removes the propeptides to generate mature forms, consisting of dimers of the VEGF homology domain, that bind receptors with much greater affinity than the full-length forms. Therefore, proteolytic processing activates VEGF-C and VEGF-D, although the proteases involved were unknown. Here, we report that the serine protease plasmin cleaved both propeptides from the VEGF homology domain of human VEGF-D and thereby generated a mature form exhibiting greatly enhanced binding and cross-linking of VEGFR-2 and VEGFR-3 in comparison to full-length material. Plasmin also activated VEGF-C. As lymphangiogenic growth factors promote the metastatic spread of cancer via the lymphatics, the proteolytic activation of these molecules represents a potential target for antimetastatic agents. Identification of an enzyme that activates the lymphangiogenic growth factors will facilitate development of inhibitors of metastasis.

Regenerating lizard tails: a new model for investigating lymphangiogenesis.

Impaired lymphatic drainage in human limbs causes the debilitating swelling termed lymphoedema. In mammals, known growth factors involved in the control of lymphangiogenesis (growth of new lymph vessels) are vascular endothelial growth factors-C and -D (VEGF-C/D). Here we characterize a model of lymphangiogenesis in which the tail of lizards is regenerated without becoming oedematous. Three weeks after the tail is shed (autotomy), there are a small number of large diameter lymphatic vessels in the regenerated tail. Thereafter, the number increases and the diameter decreases. A functional lymphatic network, as determined by lymphoscintigraphy, is established 6 wk after autotomy. The new network differs morphologically and functionally from that in original tails. This lymphatic regeneration is associated with an up-regulation of a reptilian homologue of the VEGF-C/D protein family (rVEGF-C/D), as determined by Western blot analysis using a human reactive VEGF-C polyclonal antibody. Regenerating lizard tails are potentially useful models for studying the molecular basis of lymphangiogenesis with a view to developing possible treatments for human lymphoedema.

Molecular control of lymphangiogenesis.

The lymphatic vasculature plays a critical role in the regulation of body fluid volume and immune function. Extensive research into the molecular mechanisms that control blood vessel growth has led to identification of molecules that also regulate development and growth of the lymphatic vessels. This is generating a great deal of interest in the molecular control of the lymphatics in the context of embryogenesis, lymphatic disorders and tumor metastasis. Studies in animal models carried out over the past three years have shown that the soluble protein growth factors, vascular endothelial growth factor (VEGF)-C and VEGF-D, and their cognate receptor tyrosine kinase, VEGF receptor-3 (VEGFR-3), are critical regulators of lymphangiogenesis. Furthermore, disfunction of VEGFR-3 has recently been shown to cause lymphedema. The capacity to induce lymphangiogenesis by manipulation of the VEGF-C/VEGF-D/VEGFR-3 signaling pathway offers new opportunities to understand the function of the lymphatic system and to develop novel treatments for lymphatic disorders.

The angiogenic and lymphangiogenic factor vascular endothelial growth factor-D exhibits a paracrine mode of action in cancer.

Vascular endothelial growth factor-D (VEGF-D) promotes angiogenesis, lymphangiogenesis and metastatic spread via the lymphatics, however, the mode of VEGF-D action (e.g. paracrine vs. autocrine) was unknown. We analyzed VEGF-D action in human tumors and a mouse model of metastasis. VEGF-D was localized in tumor cells and endothelium in human non-small cell lung carcinoma and breast ductal carcinoma in situ. Tumor vessels positive for VEGF-D were also positive for its receptors, VEGF receptor-2 (VEGFR-2) and/or VEGFR-3 but negative for VEGF-D mRNA, indicating that VEGF-D is secreted by tumor cells and subsequently associates with endothelium via receptor-mediated uptake. The mature form of VEGF-D was detected in tumors demonstrating that VEGF-D is proteolytically processed and bioactive. In a mouse model of metastasis, VEGF-D synthesized in tumor cells became localized on the endothelium and thereby promoted metastatic spread. These data indicate that VEGF-D promotes tumor angiogenesis, lymphangiogenesis and metastatic spread by a paracrine mechanism.

Lymphangiogenesis and cancer metastasis.

Lymphatic vessels are important for the spread of solid tumours, but the mechanisms that underlie lymphatic spread and the role of lymphangiogenesis (the growth of lymphatics) in tumour metastasis has been less clear. This article reviews recent experimental and clinico-pathological data indicating that growth factors that stimulate lymphangiogenesis in tumours are associated with an enhanced metastatic process.

The role of tumor lymphangiogenesis in metastatic spread.

The high mortality rates associated with cancer can be attributed to the metastatic spread of tumor cells from the site of their origin. Tumor cells invade either the blood or lymphatic vessels to access the general circulation and then establish themselves in other tissues. Clinicopathological data suggest that the lymphatics are an initial route for the spread of solid tumors. Detection of sentinel lymph nodes by biopsy provides significant information for staging and designing therapeutic regimens. The role of angiogenesis in facilitating the growth of solid tumors has been well established, but the presence of lymphatic vessels and the relevance of lymphangiogenesis to tumor spread are less clear. Recently, the molecular pathway that signals for lymphangiogenesis and relatively specific markers for lymphatic endothelium have been described allowing analyses of tumor lymphangiogenesis to be performed in animal models. These studies demonstrate that tumor lymphangiogenesis is a major component of the metastatic process and implicate members of the VEGF family of growth factors as key mediators of lymphangiogenesis in both normal biology and tumors.