Cucurbitacin B induces G2 arrest and apoptosis via a reactive oxygen species-dependent mechanism in human colon adenocarcinoma SW480 cells.

Cucurbitacin B (cucB) is a triterpenoid constituent of Cucurbitaceae vegetables and a promising phytochemical for cancer prevention. However, the mechanism of anti-tumor activity of cucB remains unknown, especially in colon cancers. Here, we demonstrate for the first time that cucB inhibited growth of human colon cancer SW480 cells through a reactive oxygen species (ROS)-dependent mechanism. CucB induced G(2) phase arrest and apoptosis in a dose-dependent manner. At the molecular level, cucB reduced the expression of cyclin B1 and cdc25C proteins and activated caspases in SW480 cells. On the other hand, the state of phosphorylation of signaling transducer and activator of transcription 3 (STAT3) was unchanged. We found that cucB increased intracellular ROS levels, and N-acetylcysteine, a well-known antioxidant, reduced the changes in expression of the molecules, and suppressed both G(2) arrest and apoptosis. These results suggested that cucB induced G(2) arrest and apoptosis through a STAT3-independent but ROS-dependent mechanism in SW480 cells.

A combination of indol-3-carbinol and genistein synergistically induces apoptosis in human colon cancer HT-29 cells by inhibiting Akt phosphorylation and progression of autophagy.

BACKGROUND: The chemopreventive effects of dietary phytochemicals on malignant tumors have been studied extensively because of a relative lack of toxicity. To achieve desirable effects, however, treatment with a single agent mostly requires high doses. Therefore, studies on effective combinations of phytochemicals at relatively low concentrations might contribute to chemopreventive strategies. RESULTS: Here we found for the first time that co-treatment with I3C and genistein, derived from cruciferous vegetables and soy, respectively, synergistically suppressed the viability of human colon cancer HT-29 cells at concentrations at which each agent alone was ineffective. The suppression of cell viability was due to the induction of a caspase-dependent apoptosis. Moreover, the combination effectively inhibited phosphorylation of Akt followed by dephosphorylation of caspase-9 or down-regulation of XIAP and survivin, which contribute to the induction of apoptosis. In addition, the co-treatment also enhanced the induction of autophagy mediated by the dephosphorylation of mTOR, one of the downstream targets of Akt, whereas the maturation of autophagosomes was inhibited. These results give rise to the possibility that co-treatment with I3C and genistein induces apoptosis through the simultaneous inhibition of Akt activity and progression of the autophagic process. This possibility was examined using inhibitors of Akt combined with inhibitors of autophagy. The combination effectively induced apoptosis, whereas the Akt inhibitor alone did not. CONCLUSION: Although in vivo study is further required to evaluate physiological efficacies and toxicity of the combination treatment, our findings might provide a new insight into the development of novel combination therapies/chemoprevention against malignant tumors using dietary phytochemicals.

A novel synthetic drug, LB-18, closely related to lembehyne-A derived from a marine sponge, induces caspase-independent cell death to human neuroblastoma cells.

Neuroblastoma is a common solid tumor of children that arises from the sympathetic nervous system. Much work has consequently focused on the possibility of inducing marked cell death in neuroblastoma, and the new effective drugs are required. We have newly synthesized LB-18, closely related to lembehyne A (LB-A), a polyacetylene derived from a kind of marine sponge. LB-A has been shown to induce p21/WAF1 and causes G1 phase arrest in mouse neuroblastoma Neuro2A cells; however, we show here that LB-18 causes cell death in human neuroblastoma KP-N-TK cells in a dose-dependent manner. TUNEL assay and flow cytometric analysis showed that the cell death caused by LB-18 was associated with the DNA damage but the pan-caspase inhibitor, zVAD-fmk, could not prevent the cell death. Western blot analysis and cleavage of the caspase-3 or -7 substrate assay showed that LB-18 could not activate caspases 3, 7, 8 and 9. These results suggest that LB-18 causes caspase-independent cell death in human neuroblastoma cells. In the future, LB-18 may be useful for cancer therapeutics, especially for neuroblastoma.