Safety and Therapeutic Profile of a GnRH-Based Vaccine Candidate Directed to Prostate Cancer. A 10-Year Follow-Up of Patients Vaccinated With Heberprovac.

Heberprovac is a GnRH based vaccine candidate containing 2.4 mg of the GnRHm1-TT peptide as the main active principle; 245 µg of the very small size proteoliposomes adjuvant (VSSP); and 350 µL of Montanide ISA 51 VG oil adjuvant. The aim of this study was to assess the safety and tolerance of the Heberprovac in advanced prostate cancer patients as well as its capacity to induce anti-GnRH antibodies, the subsequent effects on serum levels of testosterone and PSA and the patient overall survival. The study included eight patients with histologically-proven advanced prostate cancer with indication for hormonal therapy, who received seven intramuscular immunizations with Heberprovac within 18 weeks. Anti-GnRH antibody titers, testosterone and PSA levels, as well as clinical parameters were recorded and evaluated. The vaccine was well tolerated. Significant reductions in serum levels of testosterone and PSA were seen after four immunizations. Castrate levels of testosterone were observed in all patients at the end of the immunization schedule, which remained at the lowest level for at least 20 months. In a 10-year follow-up three out of six patients who completed the entire trial survived. In contrast only one out eight patients survived in the same period in a matched randomly selected group receiving standard anti-hormonal treatment. Heberprovac vaccination showed a good security profile, as well as immunological, biochemical and, most importantly, clinical benefit. The vaccinated group displayed survival advantage compared with the reference group that received standard treatment. These results warrant further clinical trials with Heberprovac involving a larger cohort.

Gradual reduction of testosterone using a gonadotropin-releasing hormone vaccination delays castration resistance in a prostate cancer model.

In a previous study aimed to design a novel prostate cancer vaccine, the authors of the present study demonstrated the advantage of combining the adjuvants Montanide ISA 51 with very small size proteoliposomes (VSSP) to promote a significant humoral immune response to gonadotropin-releasing hormone (GnRH) in healthy animals. The present study compared the efficacy of this vaccine formulation versus the standard treatment currently available in terms of preventing the development of tumors in DD/S mice injected with Shionogi carcinoma (SC) 115 cells. The results demonstrated that 5 non-vaccinated control mice exhibited a fast tumor growth, and succumbed to the disease within 19-31 days. Mice immunized with the GnRH/Montanide ISA 51/VSSP vaccine exhibited a moderate decline in testosterone levels that was associated with a decrease in anti-GnRH antibody titers, which lead to a sustained tumor growth inhibition. In total, 2 mice in the immunized group exhibited complete remission of the tumor for the duration of the present study. In addition, castrated mice, which were used as a control for standard hormonal therapy, exhibited an accelerated decrease in tumor size. However, tumor relapse was observed between days 50 and 54, and between days 65 and 85, following the injection of SC 155 cells. Therefore, these mice were sacrificed at day 90. The present study concludes that the slow and moderate reduction of testosterone levels observed using the GnRH-based vaccine may delay the appearance of castration resistance in a Shionogi prostate cancer model. These findings suggest that this vaccine may be used to delay castration resistance in patients with prostate cancer.

Gonadotrophin releasing hormone-based vaccine, an effective candidate for prostate cancer and other hormone-sensitive neoplasms.

Prostate growth, development, functions, and neoplastic transformation is androgen dependent. Estrogens have similar effects in the ovary and breast. Previous studies using gonadotrophin releasing hormone (GnRH/LHRH) vaccines have shown the usefulness of immunization against this hormone in prostate (PC) and breast cancer (BC). We have synthesized a peptide mutated at position 6 and attached to the 830-844 tetanic toxoid (TT) helper T cell sequence in the same synthesis process. After repeated pig immunizations, we have demonstrated a vaccine that significantly decreased testes size (p < 0.001), prostate (p < 0.01), seminal vesicles (p < 0.01), and testosterone (T) castration [0.05 nM ml(-1) (p < 0. 01)]. Similar results were obtained in adult male and female healthy dogs and Macaca fascicularis models. These data indicate that this GnRHm1-TT vaccine is safe and able to induce significant tumor growth inhibition in the Dunning R3327-H rat androgen responsive prostate tumor model. In these rats, the immunization induced high anti-GnRH titers concomitant with T castration reduction (p < 0.01) in 90% of the animals tested. In addition, 70% of the responders exhibited tumor growth inhibition (p = 0.02) and a survival rate approximately three times longer that those of untreated rats. These data indicate that GnRHm1-TT vaccine may be a potential candidate in the treatment of PC, BC, and other hormone-dependent cancers.

Immunotherapy of prostate cancer in a murine model using a novel GnRH based vaccine candidate.

Previous studies with gonadotrophin releasing hormone (GnRH/LHRH) vaccines have shown the usefulness of immunization against this hormone in prostate cancer. To this end, we have generated a completely synthetic peptide modified at position 6 and attached to the 830-844 tetanic toxoid (TT) helper T cell sequence. Through this work we have demonstrated that the GnRHm1-TT molecule was highly immunogenic when it is formulated as an oil-based emulsion adjuvated with Montanide ISA 51. That results correlated directly with testosterone reduction and tumor growth inhibition of the Dunning R3327-H androgen responsive prostate tumor model in rats. GnRHm1-TT, proved to be safe and useful for future clinical trials.