Mechanism of gadophrin-2 accumulation in tumor necrosis.

The molecular mechanism by which gadophrin-2 targets necrotic tumor tissue was investigated. Biodistribution studies and magnetic resonance imaging (MRI) and histologic/autoradiographic correlation were performed in xenograft mouse models bearing human tumors (HT 29, WiDr, LX 1). Binding of gadophrin-2 to DNA, lipids, or proteins was determined by fluorescence spectrophotometry. Protein binding was determined by dialysis and gel electrophoresis. Accumulation of gadophrin-2 was low (<0.7% injected dose/g tissue at 24 hours after injection) in viable tumor but higher in necrotic tumor regions and was readily detectable by MRI. Within a given tumor, the agent preferentially localized in the periphery of necrotic areas. Within these regions gadophrin-2 was bound to interstitial albumin and not other proteins, lipids, or DNA. Tumoral accumulation of gadophrin-2 most likely occurs through its binding to plasma albumin and subsequent slow extravasation into the tumor interstitium.