Bioconjugates containing the
GnRH-III hormone decapeptide as a targeting moiety are able to deliver chemotherapeutic agents specifically to
cancer cells expressing
GnRH receptors, thereby increasing their local efficacy while limiting the peripheral toxicity. However, the number of
GnRH receptors on
cancer cells is limited and they desensitize under continuous
hormone treatment. A possible approach to increase the receptor mediated
tumor targeting and consequently the
cytostatic effect of the bioconjugates would be the attachment of more than one chemotherapeutic agent to one
GnRH-III molecule. Here we report on the design, synthesis and biochemical characterization of multifunctional bioconjugates containing
GnRH-III as a targeting moiety and
daunorubicin as a chemotherapeutic agent. Two different
drug design approaches were pursued. The first one was based on the bifunctional [(4)Lys]-
GnRH-III (Glp-His-Trp-Lys-His-Asp-Trp-Lys-Pro-Gly-NH(2)) containing two
lysine residues in positions 4 and 8, whose ε-amino groups were used for the coupling of
daunorubicin. In the second
drug design, the native
GnRH-III (Glp-His-Trp-Ser-His-Asp-Trp-Lys-Pro-Gly-NH(2)) was used as a scaffold; an additional
lysine residue was coupled to the ϵ-amino group of (8) Lys in order to generate two free amino groups available for conjugation of
daunorubicin. The in vitro stability/degradation of all synthesized compounds was investigated in human serum, as well as in the presence of rat liver lysosomal homogenate. Their cellular uptake was determined on human
breast cancer cells and the
cytostatic effect was evaluated on human breast, colon and
prostate cancer cell lines. Compared with a monofunctional compound, both
drug design approaches resulted in multifunctional bioconjugates with increased
cytostatic effect.