Positive and negative modulation of angiogenesis by VEGFR1 ligands

Vascular endothelial growth factor-A (VEGF-A) is a key target for new antiangiogenic drugs for the treatment of both malignant and nonmalignant human diseases. Vascular effects of VEGF family members are mainly mediated by VEGF receptor 2 (VEGFR2). Conversely, the function and signaling of VEGFR1, which is present on endothelial and nonendothelial cells, are poorly understood. Intriguingly, two of five members in the VEGF family--VEGF-B and placental growth factor (PlGF)--are exclusive ligands for VEGFR1 and do not interact with the other VEGFRs, VEGFR2 and VEGFR3. These VEGFR1-specific ligands may be important therapeutic targets for the treatment of cancer. This Review discusses the distinctive roles of VEGFR1 and its ligands PlGF and VEGF-B in the mediation of angiogenic signaling and considers the therapeutic potential of targeting these particular vascular factors.

Inhibition of vascular endothelial growth factor-a signaling induces hypertension: examining the effect of cediranib (recentin; AZD2171) treatment on blood pressure in rat and the use of concomitant antihypertensive therapy

PURPOSE

Inhibition of vascular endothelial growth factor-A (VEGF) signaling is a key therapeutic approach in oncology given the role of VEGF in angiogenesis and vascular permeability in solid tumors. Clinical trials examining VEGF signaling inhibitors commonly report hypertension. We examined the effect of cediranib, a highly potent VEGF signaling inhibitor, on the blood pressure of rats and the ability of standard antihypertensive agents to modulate the consequences of VEGF signaling inhibition.

EXPERIMENTAL DESIGN

The ability of cediranib to induce hypertensive changes and the effect of giving antihypertensive therapy were investigated in conscious, unrestrained telemetered rats. Two antihypertensive agents were studied: captopril, an angiotensin-converting enzyme inhibitor, and nifedipine, a dihydropyridine calcium channel blocker. The antitumor activity of cediranib, alone and in combination with nifedipine, was also evaluated in a LoVo human colorectal tumor xenograft model in nude rats. All treatments were given orally.

RESULTS

Administration of 0.1 to 1.5 mg/kg/d of cediranib for 4 consecutive days induced a relatively mild hypertensive effect, elevating diastolic blood pressure by 10 to 14 mmHg. Dosing 3 mg/kg/d cediranib for 4 days induced a marked hypertension of 35 to 50 mmHg. Captopril (30 mg/kg, qd) was effective at lowering a 10 mmHg increase in blood pressure but not a 35 to 50 mmHg increase. However, the latter was rapidly reversed by administration of nifedipine (10 mg/kg, bd). Coadministration of nifedipine did not negatively affect the antitumor activity of cediranib (1.5 mg/kg/d).

CONCLUSIONS

Hypertension is a direct consequence of inhibiting VEGF signaling but can be controlled with appropriately selected, standard antihypertensive medication.

VEGF Trap complex formation measures production rates of VEGF, providing a biomarker for predicting efficacious angiogenic blockade

VEGF is the best characterized mediator of tumor angiogenesis. Anti-VEGF agents have recently demonstrated impressive efficacy in human cancer trials, but the optimal dosing of such agents must still be determined empirically, because biomarkers to guide dosing have yet to be established. The widely accepted (but unverified) assumption that VEGF production is quite low in normal adults led to the notion that increased systemic VEGF levels might quantitatively reflect tumor mass and angiogenic activity. We describe an approach to determine host and tumor production of VEGF, using a high-affinity and long-lived VEGF antagonist now in clinical trials, the VEGF Trap. Unlike antibody complexes that are usually rapidly cleared, the VEGF Trap forms inert complexes with tissue- and tumor-derived VEGF that remain stably in the systemic circulation, where they are readily assayable, providing unprecedented capability to accurately measure VEGF production. We report that VEGF production is surprisingly high in non-tumor-bearing rodents and humans, challenging the notion that systemic VEGF levels can serve as a sensitive surrogate for tumor load; tumor VEGF contribution becomes significant only with very large tumor loads. These findings have the important corollary that anti-VEGF therapies must be sufficiently dosed to avoid diversion by host-derived VEGF. We further show that our assay can indicate when VEGF is optimally blocked; such biomarkers to guide dosing do not exist for other anti-VEGF agents. Based on this assay, VEGF Trap doses currently being assessed in clinical trials are in the efficacious range.

Vascular endothelial growth factor trap in non small cell lung cancer

Several drugs currently in development target the vascular endothelial growth factor (VEGF) pathway, a validated target in the treatment of non-small cell lung cancer (NSCLC). Most clinical trial data generated to date have been with either bevacizumab, a monoclonal antibody to VEGF, or small-molecule inhibitors of VEGF receptor (VEGFR) tyrosine kinase activity (sunitinib, sorafenib, and ZD6474). VEGF Trap, an engineered soluble receptor made from extracellular domains of VEGFR1 and VEGFR2, binds to all isoforms of VEGF and to placental growth factor. VEGF Trap binds to VEGF-A and VEGF-B with markedly higher affinity than bevacizumab. The toxicities seen in phase I trials of s.c. and i.v. administration of VEGF Trap, hypertension and proteinuria, are similar to those seen with other molecules that target the VEGF pathway. In the s.c. VEGF Trap phase I trial, significant radiographic improvement was observed in a patient with heavily pretreated NSCLC. Ongoing phase I trials are evaluating combinations of VEGF Trap with platinum-based doublets and single-agent docetaxel. The activity of single-agent VEGF Trap in NSCLC is being assessed in a multicenter phase II trial.

Vascular endothelial growth factor trap blocks tumor growth, metastasis formation, and vascular leakage in an orthotopic murine renal cell cancer model

PURPOSE

Angiogenesis inhibitors have shown clinical benefit in patients with advanced renal cell cancer, but further therapeutic improvement is needed. Vascular endothelial growth factor (VEGF) Trap is a newly developed VEGF-blocking agent with stronger affinity and broader activity than the anti-VEGF antibody bevacizumab. In this study, we tested the activity of VEGF Trap in an orthotopic murine model of renal cancer with spontaneous lung metastases.

EXPERIMENTAL DESIGN

Murine syngeneic renal cell carcinoma cells (RENCA) transfected with a luciferase-expressing vector were injected into the renal capsule of BALB/c mice. I.p. treatment with VEGF Trap or control protein (10 or 25 mg/kg twice weekly) was started shortly after tumor injection to prevent tumor development (prevention model) or after established tumors were formed to inhibit tumor growth and metastasis formation (intervention model).

RESULTS

In the prevention model, VEGF Trap inhibited tumor growth by 87 +/- 14% compared with control (P=0.007) and significantly prolonged survival. In the intervention model, VEGF Trap inhibited tumor growth by 74 +/- 9% (P<0.001) and the formation of lung metastases was inhibited by 98% (P<0.004). Microvascular density was reduced by 66% due to VEGF Trap treatment (P<0.001). In addition, VEGF Trap prevented fibrinogen leakage into the tumor microenvironment representative for reduced vascular leaking as shown by immunohistochemical staining.

CONCLUSIONS

VEGF Trap is a potent inhibitor of RENCA tumor growth and metastasis formation and blocks the biological function of VEGF in vivo. These results support further clinical development of VEGF Trap for renal cell cancer and other cancer types.

Novel Approaches in Advancing the Treatment of Epithelial Ovarian Cancer: The Role of Angiogenesis Inhibition

Despite an aggressive approach of surgical cytoreduction and adjuvant combination chemotherapy, ovarian cancer mortality remains a significant problem. We are entering a new era of cancer therapeutics in which targeted therapies offer the potential for improvement in long-term disease control with fewer toxicities. The greatest success of targeted therapy to date in the setting of epithelial ovarian carcinoma has come from angiogenesis inhibition. This review will focus on the role of angiogenesis in normal ovarian function as well as in ovarian carcinoma development and disease progression. Current knowledge about the molecular pathways involved in angiogenesis and various approaches to angiogenesis inhibition in the treatment of ovarian cancer are discussed. Current data regarding the role of bevacizumab and other novel agents in the treatment of ovarian carcinoma are summarized.

Biological Aspects and Binding Strategies of Vascular Endothelial Growth Factor in Renal Cell Carcinoma

Vascular endothelial growth factor (VEGF) is a key mediator in the pathogenesis of renal cell carcinoma (RCC). VEGF is up-regulated in clear cell RCC as a result of loss of the von Hippel-Lindau tumor suppressor gene and subsequent activation of the hypoxia response pathway. VEGF expression drives the migration and proliferation of endothelial cells to support the extensive angiogenesis in RCC. Strategies have been developed to bind and neutralize VEGF and have been investigated in RCC with promising results. Bevacizumab, a VEGF ligand-binding antibody, has shown prolonged time-to-progression versus placebo in treatment-refractory RCC patients and is being investigated currently in multiple RCC settings. VEGF-Trap is also a VEGF binding molecule with ongoing investigation in RCC.

Targeting growth factors and angiogenesis; using small molecules in malignancy

Targeted biologic therapy for cancer has evolved from the laboratory to active clinical protocols and applied clinical practice in selected patients. Major targets include epidermal growth factor, and vascular endothelial growth factor receptors which are commonly expressed in gastro-intestinal cancers head & neck and lung cancers, and to some degree breast and gynecologic malignancy. Down stream signal transduction pathway inhibition of B-raf and N-ras mutations are examined in melanoma. New approaches involving re-packaging of chemotherapeutic agents are being exemplified in the nanoparticle formulation of paclitaxel which provides increased access to endothelial and tumor cells with potential enhanced therapeutic efficacy compared to the conventional version solubilized in a cremophor.

Biology and clinical development of vascular endothelial growth factor-targeted therapy in renal cell carcinoma

PURPOSE

To review the biology of renal cell carcinoma (RCC) leading to vascular endothelial growth factor (VEGF) overexpression and the clinical results of VEGF blockade in metastatic RCC.

METHODS

A review of relevant published literature regarding VEGF, von Hippel-Lindau (VHL) gene inactivation and VEGF overexpression in RCC was performed. Further, a review of the mechanism, toxicity, and clinical development of VEGF-targeted therapy in metastatic RCC was undertaken.

RESULTS

VEGF is the major proangiogenic protein that exerts a biologic effect through interaction with cellular receptors. The majority of sporadic clear-cell RCC tumors are characterized by VHL tumor suppressor gene inactivation. The resulting VHL gene silencing leads to VEGF overexpression. An antibody to VEGF (bevacizumab) has demonstrated a significant prolongation of time to disease progression compared with placebo in patients with metastatic RCC. Small molecules with inhibitory effects against the VEGF receptor have undergone initial clinical testing in metastatic RCC with substantial objective response rates.

CONCLUSION

Therapeutic targeting of VEGF in RCC has strong biologic rationale and preliminary clinical efficacy. Further investigation will determine the optimal timing, sequence, and utility of these agents in RCC.