A novel hepatic-targeting system for therapeutic cytokines that delivers to the hepatic asialoglycoprotein receptor, but avoids receptor-mediated endocytosis.
OBJECTIVE
To demonstrate the utilities of a synthetic low-affinity ligand ((Gal)3) for the asialoglycoprotein receptor (ASGP-R) as a hepatic targeting device for therapeutic cytokines.


METHODS
The site-specific incorporation of (Gal)3 or a typical high-affinity ligand (GaINAc)3 into IL-2 was catalyzed by microbial transglutaminase. The anti-tumor activities, pharmacokinetic profiles and receptor-mediated endocytosis in hepatocytes of the ligand-IL-2 conjugates were examined in mouse.


RESULTS
The (Gal)3 has approximately 50 times lower affinity to ASGP-R than (GalNAc)3. Nevertheless, the antitumor effects were in the order of (Gal)3-IL-2 > unmodified IL-2 > (GalNAc)3-IL-2. The systemic elimination and the hepatic uptake of (GalNAc)374L-2 were more rapid than (Gal)3-IL-2. The ratio of the rate constant representing dissociation from the cell-surface receptor (k(off) to that representing endocytosis of the ligand (k(int) was greater for (Gal)3-IL-2 than (GalNAc)s-IL-2, suggesting that (Gal)3-IL-2 preferably avoids internalization due to its lower affinity to the receptor. The simulation studies demonstrated that (Gal)3-L-2 was present in the hepatic extracellular space for a longer period than (GaINAc)3 IL-2.


CONCLUSIONS
The (Gal)3 ligand increases the therapeutic efficacy of IL-2 by enhancing its exposure to the cell-surface. The k(off)/k(int) affects the targeting efficacy of the conjugates to ASGP-R.
Sato
Haruya
H
Pharmaceutical Research Laboratories, Ajinomoto Co., Inc. Suzuki-cho, Kawasaki-ku, 210-8681, Japan.
Kato
Yukio
Y
Hayasi
Eiko
E
Tabata
Tomoyuki
T
Suzuki
Manabu
M
Takahara
Yoshiyuki
Y
Sugiyama
Yuichi
Y
D000818:Animals; D037263:Asialoglycoprotein Receptor / Q000378:metabolism*; D002478:Cells, Cultured; D016207:Cytokines / Q000008:administration & dosage* / Q000493:pharmacokinetics; D016503:Drug Delivery Systems / Q000379:methods*; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology*; D005260:Female; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D023041:Xenograft Model Antitumor Assays / Q000379:methods
D037263:Asialoglycoprotein Receptor; D016207:Cytokines