Cytotoxic and migration inhibitory effects of bisphosphonates on macrophages

Two in vitro model systems were developed to facilitate investigation of the mechanisms by which bisphosphonates block bone resorption. These systems assess the cytotoxic and the migration inhibitory activities of bisphosphonates using mouse peritoneal macrophages as osteoclast surrogates. Several bisphosphonates, 3-amino-1-hydroxypropylidene-1,1-bisphosphonate (AHPrBP), dichloromethylene bisphosphonate (Cl2MBP), 1-hydroxyethylidene-1,1-bisphosphonate (HEBP), 1-hydroxybutylidene-1,1-bisphosphonate (HBBP), 1-hydroxyhexylidene-1,1-bisphosphonate (HHBP), and 1-hydroxyoctylidene-1,1-bisphosphonate (HOBP), possess the same relative activities in these systems as they do in bone resorption systems. Calcium ion replacement studies using these systems demonstrated that bisphosphonates do not derive all their activity from sequestration of calcium ions from cells by chelation. Whereas calcium ion replacement abrogated the activity of EDTA, a nonbisphosphonate calcium chelator active in both systems, it failed to abrogate either the cytotoxic or the migration inhibitory effects of the bisphosphonates tested. Calcium ion replacement increased the migration inhibitory activity of all the bisphosphonates tested. Further, calcium ion replacement increased the cytotoxicity of HHBP and HOBP; however, it decreased the cytotoxicity of HEBP, HBBP, AHPrBP, and Cl2MBP.