Abstract

A specific sugar-modified peptide has previously been shown to have renal targeting potential in vivo and to have a specific binding site which has been identified in the kidney membrane fraction. In this report, we studied the inhibitory effects of glycosylated derivatives on the binding of [³H]Glc-O-C8-AVP [a glucosylated derivative of Arg⁸-vasopressin (AVP),K_d = 55 nM] to clarify the structural requirements necessary for renal recognition. Glc-S-C7-Me (octyl β-d-thioglucoside) markedly inhibited the binding, to a much greater extent than Glc-O-C7-Me (octyl β-d-glucoside) and Gal-S-C7-Me (octyl β-d-thiogalactoside). Also, [³H]Glc-S-C7-Me was shown to have a specific binding site on the kidney membrane (K_d = 17 nM, B_max = 24 pmol/mg protein) rather than the liver membrane and, in addition, Glc-S-C7-Me exhibited effective and selective renal uptake in vivo. To examine the possibility that Glc-S-C7-Me might be of practical use as a renal targeting vector, AVP, tryptamine and 4-nitrobenz-2-oxa-1,3-diazole were modified with Glc-S-C8- and the tissue uptake of the resulting derivatives was evaluated. All of these derivatives showed clear renal targeting potential because the apparent uptake clearance by the kidney was greater than 3 ml/min/g kidney in each case. As far as the AVP derivatives were concerned, derivatives having different numbers of methylene groups were compared with Glc-S-C8-AVP. Glc-S-C11-AVP exhibited increased kidney targeting potential, whereas that of Glc-S-C5-AVP was reduced. These differences suggest that the “alkylglycoside” moiety is important for renal uptake. In addition, these renally targeted derivatives inhibited the binding of [³H]Glc-S-C7-Me to the kidney membrane fraction. Our findings allow us to conclude that the alkylglycoside is a suitable candidate vector for renal targeting.