Objectives: To determine the immunogenicity, antiangiogenicity and antitumor efficacy of an active immunization strategy using VEGF peptides. Methods: Candidate VEGF epitopes were identified using a computer-aided analysis employing specific correlates for antigenicity. These epitopes were synthesized, purified, and combined the measles virus fusion (MVF) protein, a T-cell epitope. Anti-VEGF peptide antibodies were elicited in rabbits following primary and booster vaccination. Immunogenicity was determined with ELISA, Western blot and immunoprecipitation. Inhibition of VEGF binding to VEGF receptor (R) was assessed using the Fluorokine assay. Antiangiogenicity was determined with assays of proliferation, migration, invasion, tube formation, and the aortic ring assay. Antitumor efficacy was determined using a transgenic mouse model that develops spontaneous pancreatic islet tumors under the influence of VEGF (RIP1-Tag2 mouse). Specifically, mice were vaccinated and boosted with the multivalent VEGF peptide vaccine and tumor growth was assessed at 12 weeks. Comparisons of antiangiogenicity and antitumor efficacy were made using the Student’s t-test or chi-square tests were appropriate. Results: VEGF peptides from the predicted antigenic region elicited high-titer antibodies in rabbits; these antibodies recognized rhVEGF by ELISA. Antibodies immunoprecipitated rmVEGF and tumors from RIP1-Tag2 mice confirming their specificity. Peptide antibodies prevented VEGF from binding to the VEGFR. In vitro, the rabbit anti-VEGF peptide antibodies led to a significant decrease in VEGF-mediated invasion into Matrigel, cellular proliferation, migration through a membrane, formation of tubes, and growth of vessels from rat aortic rings (antipeptide antibodies versus control P<0.05 for all comparisons). Active immunotherapy with the multivalent VEGF peptide vaccine led a significant decrease in pancreatic islet tumor growth in the RIP1-Tag2 mice (median tumor volume 330 mm3 vs. 75 mm3, P=0.01). Conclusion: Rabbit anti-VEGF peptide antibodies are immunogenic, specific, and anti-angiogenic. In a transgenic mouse model, active immunotherapy with the multivalent VEGF peptide vaccine leads to significant reduction in tumor volume. Given the importance of VEGF in ovarian carcinogenesis, active immunization with a VEGF peptide vaccine may be a biologically relevant strategy for the treatment of ovarian cancer.
[Proc Amer Assoc Cancer Res, Volume 47, 2006]