Cellular uptake and release of two contrasting iron chelators

Desferrioxamine and CP94 (1,2diethyl-3 -hydroxypyridin-4-one) are metal chelators used or proposed for use in the clinical treatment of iron overload. Recent data on their capacity to deplete intracellular iron led to the conjecture that the differences observed arose from the different membrane-penetration properties of the two compounds. The time-course of accumulation and subsequent release of [C-14]CP94 by the rat visceral yolk sac in-vitro was compared with that of [C-14]desferrioxamine and for I-125- labelled poly(vinylpyrrolidone), a marker for fluid-phase endocytosis. The results indicate that [C-14]CP94 crosses the plasma and lysosome membranes rapidly whereas [C-14]desferrioxamine and I-125-labelled poly(vinylpyrrolidone) are effectively incapable of crossing these membranes, entering cells only by endocytosis. It is concluded that although CP94 readily enters and leaves cells, desferrioxamine has the potential to accumulate to high concentration in the lysosomes and complex with intralysosomal iron. The results support and extend the proposed correlation between pharmacological activity and capacity for membrane penetration.