Ridaifen-B (RID-B) is a novel tamoxifen (TAM) analog that significantly augments apoptosis-inducing effect of TAM in estrogen receptor (ER)-negatives cells. Ridaifen-B induces mitochondria-involved apoptosis in Jurkat cells, as evidenced by chromatin-condensed cells as well as downstream activation of caspases (caspase-3, -8 and -9) in a dose- and time-dependent manner. At 4 hours of incubation, IC50 for RID-B is 4 muM (30 muM for TAM). And at prolonged treatment of 48 hours, IC50 for RID-B is 0.1 muM. In a related report on the global anti-tumor activity, RID-B strongly inhibits 39 human cancer cells (JFCR 39), both ER-+ or ER-- at concentrations of equal or less than 1muM (e.g., at 0.38muM for SF-539 [central nervous system], at 0.58muM for HT-29 [colon], at 0.20muM for DMS114 [lung], at 0.21muM for LOX-IMVI [melanoma], and at 0.23muM for MKN74 [stomach]. The binding protein of RID-B that exerts the apoptosis events is currently under investigation.