An in vivo assay for assessing the metastatic potential of cancer cells has been developed. This is a functional assay that also allows for screening of compounds that are selective for metastatic cancer. Metastatic cancer is established in animals by intravenous injection of metastatic cancer cells before treatments are tested. This assay has been used to identify benzimidazoles for the treatment of metastatic prostate cancers. The benzimidazole(s) can be formulated for enteral or parenteral administration. In one embodiment, the compositions are formulated for parenteral administration. Compositions containing a benzimidazole exhibit greater cytotoxicity against cell lines prone to metastasis than against cells lines that are less prone to metastasis in vitro. The benzimidazoles described herein were effective at treating metastatic prostate cancer in bone. Administration of benzimidazoles in metastatic prostate cancer mouse models showed a significant increase in the survival times of the animals, even against paclitaxel resistant cancer cell lines.
