In vitro molecular magnetic resonance imaging detection and measurement of apoptosis using superparamagnetic iron oxide + antibody as ligands for nucleosomes

Recent research in cell biology as well as oncology research has focused on apoptosis or programmed cell death as a means of quantifying the induced effects of treatment. A hallmark of late-stage apoptosis is nuclear fragmentation in which DNA is degraded to release nucleosomes with their associated histones. In this work, a method was developed for detecting and measuring nucleosome concentration in vitro with magnetic resonance imaging (MRI). The indirect procedure used a commercially available secondary antibody-superparamagnetic iron oxide (SPIO) particle complex as a contrast agent that bound to primary antibodies against nucleosomal histones H4, H2A and H2B. Using a multiple-echo spin-echo sequence on a 1.5 T clinical MRI scanner, significant T2 relaxation enhancement as a function of in vitro nucleosomal concentration was measured. In addition, clustering or aggregation of the contrast agent was demonstrated with its associated enhancement in T2 effects. The T2 clustering enhancement showed a complex dependence on relative concentrations of nucleosomes, primary antibody and secondary antibody + SPIO. The technique supports the feasibility of using MRI measurements of nucleosome concentration in blood as a diagnostic, prognostic and predictive tool in the management of cancer.