Involvement of caspase and MAPK activities in norcantharidin-induced colorectal cancer cell apoptosis

Norcantharidin exhibits cytotoxicity in many cancer cell lines, including colorectal cancer (CRC) cells. Its cytotoxic potency on primary CRC cells and other normal constituent cells of the human body remains elusive. This study investigates whether norcantharidin differentially exhibits cytotoxicity on primarily isolated CRC cells and dermal fibroblasts. The in vitro chemosensitivity of norcantharidin was measured using a MTT tetrazolium assay and compared with 73 primary tumor cells from surgically excised colorectal tumors, six human CRC cell lines and dermal fibroblasts. Observations of cytotoxicity to primary tumor cells reveal significant differences among genders and histological types; however, drug-induced chemosensitivity was not correlated with age or clinical stages of CRC patients. Norcantharidin had a similar cytotoxic effect on primary tumor cells and CRC cell lines in a dose-dependent manner. In contrast, normal fibroblasts were more resistant to norcantharidin-induced cytotoxicity than CRC cells. DAPI staining results demonstrated that norcantharidin caused CRC cell apoptosis by nuclear fragmentation and chromatin condensation. The release of cytochrome c and the triggering of caspase-3, -8 and -9 activation mediated apoptotic induction. Conversely, pretreatment with caspases or mitogen-activated protein kinase (MAPK) inhibitors significantly suppressed norcantharidin-induced CRC cytotoxicity. These in vitro results suggest that norcantharidin may be a safe and effective anti-cancer drug for CRC.