Synthesis and evalution of a monoreactive DOTA derivative for indium-111-based
residualizing label to estimate protein pharmacokinetics.
ABSTRACT
The purpose of this study was to develop an indium-111 (111In)-based residualizing label for estimating the pharmacokinetics of proteins.
1,4,7,10-Tetraazacyclododecane-N,N',N",N'"-tetraacetic acid (DOTA), which produced a highly stable and hydrophilic
111In chelate, was selected as the chelating site, and the monoreactive DOTA
derivative with a tetrafluorophenyl group as the protein binding site (mDOTA)
was designed to avoid cross-linkings of proteins. mDOTA was synthesized
with an overall yield of 11%. The stability in murine plasma, the radioactivity
retention in the catabolic sites of proteins and the radiochemical yields
of 111In-labelled proteins via mDOTA were investigated using human serum albumin
(HSA), galactosyl-neoglycoalbumin (NGA) and cytochrome c (cyt c) as model
proteins. 111In-labelled HSAvia mDOTA was highly stable for 5 days after incubation
in murine plasma. Long retention of radioactivity in the catabolic sites
was observed after injection of 111In-DOTA-NGA in mice, due to the slow elimination of the radiometabolite
from the lysosome. At a chelator concentration of 42.2 ƒÊm, 111In-DOTA-cyt c was produced with over 91 % radiochemical yield. On the other
hand, 111In-DOTA-lysineand 111In-DOTA were obtained with high radiochemical yields at lower chelator
concentrations. These findings indicated that mDOTA would be an appropriate
111In-Iabelling agent for estimating protein pharmacokinetics.These findings
also suggested that the introduction of a protein binding site at a position
distal from the unmodified DOTA structure would be preferable to preparing
111In-DOTA-labelled proteins with higher specific activity.