Alendronate inhibits invasion of PC-3 prostate cancer cells by affecting the mevalonate pathway

Breast and prostate cancer preferentially metastasize in the skeleton, inducing locally increased bone resorption by osteoclasts. Bisphosphonates (BPs), potent inhibitors of osteoclasts and bone resorption, are able to reduce metastatic bone lesions, but the metastasis-related cellular target molecules for BPs have not yet been identified. In osteoclasts, nitrogen-containing BPs inhibit the function of the mevalonate pathway, impairing the prenylation and activation of small GTPases. In addition, direct effects of BPs on cancer cells have been suggested. In the present study, the effects of two clinically used BPs, the amino-BP alendronate and clodronate, on adhesion, invasion, and migration of human PC-3 prostate cancer cells were examined in vitro. We also studied the possible role of the mevalonate pathway in invasion and migration of PC-3 cells using the beta-hydroxy-beta-methylglutaryl-CoA reductase inhibitor mevastatin and the mevalonate pathway intermediates mevalonate (mevalonic acid lactone), geranylgeraniol, and trans-trans-farnesol. The results demonstrate that alendronate pretreatment very effectively inhibited in vitro invasion of prostate cancer cells in a dose-dependent manner, with an IC50 as low as approximately 1 pM. The inhibition was similar to that of mevastatin. Clodronate also inhibited invasion, but the IC50 was 0.1 microM. Importantly, geranylgeraniol and trans-trans-farnesol reversed the inhibitory effect of alendronate and mevastatin but not the clodronate-induced inhibition of invasion. Alendronate pretreatment also inhibited migration, which was partially reversed by geranylgeraniol and trans-trans-farnesol. Adhesion of PC-3 cells to various matrices was reduced, and their F-actin organization was changed. Alendronate pretreatment also inhibited invasion of human Du-145 prostate and MDA-MB-231 breast cancer cells. As a conclusion, the results demonstrate that the mevalonate pathway leading to protein prenylation is important for cancer cell invasion and migration in vitro. They further suggest that interference with this pathway is involved in inhibition of invasion and migration of prostate cancer cells by the amino-BP alendronate but that the mechanism of clodronate inhibition is different. It is possible that BPs have therapeutic potential in preventing the spread of prostate cancer.