Anti-Gonadotropin Releasing Hormone Vaccines and Their Potential Use in the Treatment of Hormone-Responsive Cancers
The aim of this study was to assess the therapeutic potential of active immunisation with GnRH-glycys-PPD in a hormone-dependent experimental model. Mammary tumours were induced in female rats using dimethylbenzanthracene (DMBA) and the effects of GnRH immunoneutralisation on tumour development were evaluated. High titres of anti-GnRH IgG correlated with a decrease in oestrogen levels and subsequent tumour suppression. A comparison of immunised and non-immunised animals showed that when GnRH-specific IgG levels were at a maximum titre (80-100 micrograms/ml), nearly 10% of the GnRH-glycys-PPD treated animals showed mammary masses, compared with all the non-treated animals at the same stage in the study. When the antibody levels fell, tumour regrowth was observed, but to a level below that observed in the non-treated animals. Following further treatment with the analogue, the tumours regressed again, showing their retention of hormone dependency. This is consistent with other endocrine manipulations in the treatment of breast cancer; the advantages of immunisation with GnRH-glycys lies in its non-toxicity and reduction in side-effects, which were mainly adjuvant-induced.