The dichloromethane fraction of Stemona tuberosa Lour inhibits tumor cell growth and induces apoptosis of human medullary thyroid carcinoma cells

Medullary thyroid carcinoma (MTC), a neuroendocrine tumor arising from the thyroid gland, is known to be poorly responsive to conventional chemotherapy. The root of Stemona tuberosa Lour, also called Bai Bu, is a commonly used traditional Chinese anti-tussive medicine. The present study investigated this medicinal herb for the first time with respect to its anticancer activity in human medullary thyroid carcinoma cells. Four extracts of Stemona tuberosa Lour, including the n-hexane fraction, (ST-1), dichloromethane (DCM) fraction, (ST-2), ethyl acetate (EtOAc) fraction, (ST-3), and methanol fraction, (ST-4) were examined for antiproliferative effects in two MTC cell lines. We observed that only the DCM fraction ST-2 inhibited cell growth and viability in a dose-dependent manner. Furthermore, we found that ST-2 also induced the apoptosis of MTC-SK cells. Caspase-3/7 was activated, while caspase-9 was not, implying that at least a caspase-dependent apoptotic pathway was involved in this process. In addition, the multicellular spheroids of MTC-SK were destroyed and the cell morphology was changed by ST-2. Our results show the strong apoptotic effects of the DCM fraction of Stemona tuberosa Lour on human medullary thyroid carcinomas, so suggesting a new candidate for chemotherapy of the so far chemo-resistant medullary thyroid carcinoma.