Synthesis, conformation, biodistribution, and hormone-related in vitro antitumor activity of a gonadotropin-releasing hormone antagonist-branched polypeptide conjugate.
Since permanently high levels of GnRH analogues are necessary to exert direct and/or indirect antitumor effect on mammary tumors, much emphasis was put on the development of retarded-release devices (e.g. microcapsules) for GnRH derivatives. Alternatively, these compounds can be covalently coupled to high-molecular mass carrier molecules for the design of bioconjugates acting as (a) prodrugs producing prolonged release or (b) macromolecular therapeutics. In order to evaluate the feasibility of this approach, a prototype construct has been prepared with a potent GnRH antagonist Ac(D-Trp1,3, D-Cpa2, D-Lys6, D-Ala10)-GnRH (MI-1544). As a carrier, a representative of a new generation of synthetic, biodegradable branched poly[Lys(Xi-DL-Alam)] (XAK) type polypeptides with poly(L-lysine) backbone has been used in which X is an acetylated derivative of glutamic acid (AcEAK). This polyanionic polypeptide with free gamma-carboxyl groups was conjugated to MI-1544, which has only a single amino group at position 6. In this paper, we describe (i) the synthesis and structure (primary structure, conformation) properties of the MI-1544-AcEAK conjugate with a 33% degree of substitution, (ii) the effect of the covalent attachment of MI-1544 to AcEAK on its blood clearance and tissue distribution, and (iii) the hormone-related indirect (ovulation inhibitory) or direct (antiproliferative) antitumor activity of the conjugate studied by in vitro assays. Data obtained with 111In- and 125I-labeled conjugates have demonstrated that in fact the body/blood survival of MI-1544 was prolonged by 1.5-3 times. The direct in vitro antitumor effect of MI-1544 was maintained or even enhanced in the MI-1544-AcEAK conjugate. Furthermore, we have shown that this conjugate was able to antagonize the effect of GnRH in vitro or to act as free MI-1544 both in short- and long-term inhibition of ovulation even after single subcutaneous injection. These data suggest that it is feasible to use a biodegradable polymeric polypeptide for development of a macromolecular therapeutic with GnRH antagonists.
Mezö
G
G
Research Group of Peptide Chemistry, Hungarian Academy of Sciences, Budapest, Hungary.
Mezö
I
I
Pimm
M V
MV
Kajtár
J
J
Seprödi
J
J
Teplán
I
I
Kovács
M
M
Vincze
B
B
Pályi
I
I
Idei
M
M
Szekerke
M
M
Hudecz
F
F
D000818:Animals; D002851:Chromatography, High Pressure Liquid; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000493:pharmacokinetics; D006727:Hormone Antagonists / Q000138:chemical synthesis* / Q000737:chemistry / Q000493:pharmacokinetics; D007986:Luteinizing Hormone / Q000378:metabolism; D051379:Mice; D008807:Mice, Inbred BALB C; D010060:Ovulation / Q000187:drug effects; D051381:Rats; D017208:Rats, Wistar; D014018:Tissue Distribution
D006727:Hormone Antagonists; D007987:Gonadotropin-Releasing Hormone; C040278:MI 1544; D007986:Luteinizing Hormone