Bisphosphonates in cancer therapy.

Bisphosphonates inhibit osteoclast-mediated bone resorption in metastatic bone disease. A wealth of preclinical data have begun to shed light on the complex mechanisms by which bisphosphonates inhibit bone resorption and interfere with the formation and growth of bone metastases. Nitrogen-containing bisphosphonates inhibit the mevalonate pathway, which results in the inhibition of osteoclast function and the induction of apoptosis in osteoclasts and tumor cells alike. There is now extensive evidence that bisphosphonates have cytostatic activity against tumor cell lines and inhibit tumor cell adhesion and invasion of the extracellular matrix. These data are supported by a growing body of evidence from animal models demonstrating that bisphosphonates can reduce skeletal tumor burden. However, it remains unclear whether this reduction reflects a direct antitumor effect or an indirect effect via osteoclast inhibition and alteration of the bone microenvironment. Further preclinical studies are needed to elucidate these biochemical mechanisms fully; ultimately, well-controlled clinical trials will be required to investigate whether the antitumor potential of bisphosphonates translates into a significant clinical benefit for patients with cancer.