Quantitative assessment of lipoprotein metabolism by positron emission tomography with an 18F-containing residualizing label

Residualizing labels for proteins are designed to remain entrapped within cells following uptake and degradation of the carrier protein. In the present work we report the synthesis of a novel residualizing label, N-lactitol-S-([¹⁸F]fluorophenacyl)-cysteamine ([¹⁸F]LCSH, and its use for quantifying the accumulation of low density lipoprotein in tissues in vivo by positron emission tomography (PET). The retention of degradation products in tissues from lipoprotein or from other rapidly catabolized protein pharmaceuticals tagged with [¹⁸F]LCSH reduces leakage of tracer into the plasma compartment. Thus, residualizing labels provide a valuable tool for enhancing signal-to-noise ratios, even during the relatively short interval of PET studies.