Release of Prostaglandin E1 from N-(2-Hydroxypropyl)methacrylamide Copolymer Conjugates by Bone Cells

摘要

Bone-targeting N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-PGE1 conjugates, containing cathepsin K sensitive spacers, were incubated with induced osteoclasts and osteoblasts, their precursors, and control non-skeletal cells. The release of PGE1 was monitored by an HPLC assay. In both murine and human cell lines, osteoclasts appeared to be the most active cells in the cleavage (PGE1 release). Incubation with osteoblasts also resulted in fast PGE1 release, whereas precursor and control cells released PGE1 with a substantially slower rate than bone cells (apparently through ester bond cleavage). Experiments in the presence of inhibitors revealed that other enzymes, in addition to cathepsin K, were participating in the cleavage of the conjugate. Confocal fluorescence studies exposed internalization of the conjugate by endocytosis with ultimate localization in the lysosomal/endosomal compartment.