Immunization with a recombinant GnRH vaccine conjugated to heat shock protein 65 inhibits tumor growth in orthotopic prostate cancer mouse model.

We have previously shown that anti-GnRH antibodies responses can be induced by synthetic GnRH3-hinge-MVP peptide. In this study, GnRH3-hinge-MVP of conjugation to heat shock protein 65 was used as an adjuvant-free vaccine to assess the therapeutic effects of GnRH immunoneutralisation on tumor development in the mice model. Compared with mice treated with Hsp65 and PBS, mice of the o.t. model receiving in situ treatment GnRH3-hinge-MVP-Hsp65 had significant prolongation of survival and suppression of local tumor growth. Serum levels of both testosterone and luteinizing hormone were reduced by treatment with GnRH3-hinge-MVP-Hsp65 (p<0.05). Further analyses of cell mediated immune responses showed that GnRH3-hinge-MVP-Hsp65 induced stronger lymphocyte proliferative responses and higher levels of IFN-gamma (p<0.001). The conjugation of the recombinant GnRH peptide to Hsp65 could be considered a promising approach for the development of an efficacious vaccine against the prostate cancer.