Recent studies suggest that TJ-41, a herbal drug, possesses chemotherapeutic effects. Accordingly, this study was undertaken to investigate the anticarcinogenic effects of TJ-41 on human breast cancer cells lines. TJ-41 inhibited the proliferation of human breast cancer cell lines dose dependently. Flow cytometric analysis showed that this decrease in DNA synthesis is to be associated with induction of apoptosis. In both cell lines, apoptosis was abolished by caspase-9 inhibitor Z-LEHD-fmk but was weakly inhibited by caspase-8 inhibitor Z-IETD-fmk, indicating that caspase-9 activation was involved in TJ-41 induced apoptosis. Additionally, TJ-41 stimulated phosphorylation of c-Jun NH2-terminal kinase (JNK) and pretreatment of breast cancer cells with JNK inhibitor SP600125 completely abolished TJ-41 induced apoptosis. Our data also demonstrate that combined treatment of TJ-41 and 5-FU significantly potentiates the apoptotic effects of 5-FU in both breast cancer cell lines. Taken together, these data suggest that TJ-41 might provide a novel chemotherapeutic treatment for breast cancer. Copyright © 2009 Suresh Volate et al.