Phase I Study on VEGF Vaccination in Metastatic Solid Tumors

Angiogenesis (the formation of new blood vessels from pre-existing blood vessels) plays an important role in the growth and spread of tumors. Angiogenesis is regulated by a balance of activators and inhibitors. One of the angiogenic activators is the vascular endothelial growth factor (VEGF, also referred to as VEGF-A). Over the past decade, several angiogenesis inhibitors have been discovered and implemented in the therapy of cancer patients. Bevacizumab (a humanized monoclonal antibody that inhibits VEGF-A) has been shown to improve survival in different tumor types in first and second line therapy when given in various chemotherapy combinations. Furthermore, research has shown a survival benefit of continued VEGF suppression with bevacizumab beyond first progression in metastatic colorectal cancer. So although repeated use of bevacizumab as a chronic therapy is much desired, currently this is not feasible because of substantial disadvantages of bevacizumab therapy. First, since bevacizumab only offers temporary VEGF neutralization, it needs frequent repeated administration. Secondly, bevacizumab is an intravenous therapy, which requires hospitalization on each administration. Third, bevacizumab has very high production costs. These specific drawbacks of longer term monoclonal antibody therapy could be circumvented by the use of a therapeutic cancer vaccine targeting VEGF. A vaccine is able to induce sustained VEGF suppression and can be administered via an intramuscular (IM) injection. In addition, a vaccine will likely inhibit VEGF more effectively as compared to bevacizumab, because a vaccine induces a polyclonal antibody response, resulting in higher avidity binding. Furthermore, it is believed that endogenous antibodies have a better tumor penetrating capacity, as compared to exogenously administered antibodies. The vaccine hVEGF26-104 is a truncated synthetic peptide mimic of the VEGF protein and consists of 79 amino acids (residue 26-104). The vaccine contains an antigen that directs the body's own polyclonal antibody response towards the active site of the endogenous VEGF molecule. After binding of the antibodies to endogenous VEGF this hormone will no longer be able to bind to its receptors (VEGFR1 and VEGFR2) and consequently will no longer exert its pro-angiogenic effect. To enhance the immune response, RFASE, which belongs to the adjuvant group of sulpholipopolysaccharides, will be used as an adjuvant.

Primary objectives - To investigate the safety and tolerability profile of hVEGF26-104/RFASE. - To determine the effective dose of hVEGF26-104/RFASE required to neutralize VEGF in serum, defined as a VEGF level below 9,0 pg/mL.

Secondary objectives - To determine the anti-VEGF antibody titer, induced by hVEGF26-104/RFASE administration. - To determine the effective dose of hVEGF26-104/RFASE required to neutralize VEGF in plasma and in a platelet sample. - To assess the effect of VEGF neutralization in a functional Ba/F3-R2 cell proliferation assay.

Exploratory objectives - To assess the cellular anti-tumor immune response induced by hVEGF26-104/RFASE administration. - To assess immunomodulatory effects upon hVEGF26-104/RFASE administration. - To make a preliminary assessment of hVEGF26-104/RFASE to suppress angiogenesis within the tumor. - To assess the immune infiltration and the regulation of endothelial cell adhesion molecules within the tumor.

This is an open label single center phase I study. A "3 + 3 " dose escalation design will be used. The study will investigate sequential cohorts consisting of 3 patients to be enrolled and treated at the applicable dose level. The study medication consists of 1.0 mL hVEGF26-104 (in escalating doses of 62.5, 125, 250 and 500 µg/mL) combined with 1.0 mL RFASE (fixed dose of 20 mg/mL). Eligible subjects will receive three IM injections with hVEGF26-104/RFASE on days 0 (primer), 14 and 28 (boosters). To assess potential toxicity of the adjuvant RFASE, the 3 patients enrolled in the first cohort of the study (62.5 μg/mL) will receive a single injection with 1.0 mL RFASE (fixed dose of 20 mg/mL) as a single agent 14 days prior to the first immunization with hVEGF26-104/RFASE. If none out of 3 patients experiences dose limiting toxicity (DLT) at a certain dose level, one can proceed to the next dose level. If one patient experiences a DLT at a certain dose level, another 3 patients will be assigned at the same dose level. In the highest dose escalation cohort, at least 6 patients will be enrolled. If VEGF is no longer neutralized, but there is no sign of progression either; the patient will receive another booster of hVEGF26-104/RFASE in order to achieve VEGF neutralization again. This booster can be repeated until progressive disease, death or other reasons for withdrawal from the study.

Eligible subjects will receive three intramuscular injections with hVEGF26-104/RFASE in dose-escalation on days 0 (primer), 14 and 28 (boosters), followed by an observation period of 6 weeks. Blood will be drawn at given timepoints to assess safety, immunogenicity and angiogenesis parameters. At screening, a tumor biopsy will be performed for a baseline assessment of angiogenesis and immune infiltration. In the case that VEGF is neutralized 8 weeks after first hVEGF26-104 administration, the patient will be asked to undergo another biopsy at week 10 to assess any possible change in angiogenesis and immune infiltration in the tumor. If VEGF is no longer neutralized, but there is no sign of progression either; the patient will receive another booster of hVEGF26-104/RFASE in order to achieve VEGF neutralization again.