Preparation and in vitro evaluation of 99mTc‐labelled bovine lactadherin as a novel radioligand for apoptosis detection

Abstract

AbstractLactadherin is an opsonin, which binds with high affinity to phosphatidylserine exposed on the surface of apoptotic cells via its C1C2 domains. Phagocytosis of the apoptotic cells is then facilitated by an Arg‐Gly‐Asp (RGD)‐ mediated binding to macrophages surface integrins. The present report describes the synthesis of 99mTc‐HYNIC–lactadherin with a radiochemical yield of 88±5% (n= 3) and a specific activity of 41±5 µCi/µg (n=3) when purified. Purified 99mTc‐HYNIC–lactadherin was shown to be stable for at least 5 h when supplemented with 1.5 mg/ml fatty‐acid‐free BSA. The radiolabelled protein retained its phospholipid binding ability that was verified by its ability to bind to apoptotic HL60 leukaemia cells. The apoptotic cells demonstrated a RGD independent 3‐ to 4‐fold excess binding of the radioactive component relative to control cells. Surplus of unlabelled lactadherin almost completely inhibited the binding of 99mTc‐HYNIC–lactadherin. Collectively our data indicate that 99mTc‐HYNIC–lactadherin is potentially useful as a new molecular binding tool for the identification of apoptotic cells. Copyright © 2007 John Wiley & Sons, Ltd.