To extend the utility of a renal targeting system using carbohydrate derivatives, we investigated the in vivo tissue distribution in rats of arginine-vasopressin (AVP) derivatives modified at the phenolic hydroxy group of tyrosine by linking it to some sugars, namely D-glucose, D-galactose, D-mannose and L-fucose, via an octamethylene group. The glycosyl and mannosyl derivatives of AVP exhibit renal-selective distribution in vivo. In addition, the glucosyl and mannosyl derivatives exhibited specific binding to the kidney microsomal fraction in vitro. Modification with D-glucose or D-mannose at the tyrosine side chain is a suitable methodology for renal targeting, as well as at N-terminal amine.
To evaluate the effect of introducing a saccharide moiety to poly(amino acids) on tissue distribution, several glycoconjugates of epsilon-(2-methoxyethoxyacetyl)-poly(L-lysine) of three molecular weights were synthesized using an octylene spacer between the sugar and polymer chain. Methoxyethoxyacetylation of the epsilon-amino group of the lysine unit in poly(L-lysine) was useful for avoiding nonspecific distribution to many tissues as the result of cationic charges. The tissue-targeting ability of each saccharide moiety was considered as the actual amount changed in each tissue caused by saccharide modification. Galactose terminated saccharides such as galactose, lactose and N-acetylgalactosamine accumulated exclusively in the liver, probably by the hepatic receptor. These conjugates could therefore be good carriers for a drug delivery system to the liver. On the other hand, the mannosyl and fucosyl conjugates were preferentially delivered to the reticuloendothelial systems such as those in the liver, spleen and bone marrow. In particular, fucosyl conjugates accumulated more in the bone marrow than in the spleen. Xylosyl conjugates accumulated mostly in the liver and lung. Generally, the accumulated amount in the target tissue increased with increasing molecular weight and an increased number of saccharides on one molecule of polymer.
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