New chemotherapy-enhancing strategies are needed for better cancer therapy. Previous studies suggest that exogenous cell-permeable C6 ceramide may be a useful adjunct to the anti-tumor effects of chemotherapeutic agents (such as Taxol) against multiple cancers. Here we demonstrate that exogenous cell-permeable C6 ceramide largely sensitizes multiple progressive cancer cell lines to Doxorubicin-induced cell death and apoptosis. We found for the first time that Doxorubicin induces AMP-activated protein kinase (AMPK) activation in a reactive oxygen species-dependent manner. Activation of AMPK contributes to Doxorubicin-induced cancer cell death and apoptosis. Inhibition of AMPK by small interfering RNA knockdown or a pharmacological inhibitor reduces Doxorubicin-induced cancer cell apoptosis, whereas AMPK activator AICAR enhances it. Importantly, we found that C6 ceramide largely enhances Doxorubicin-induced activation of AMPK, which leads to mTOR complex 1 inhibition and chemo-sensitization. Our data suggest that the combination of C6 ceramide with traditional chemotherapy drugs such as Doxorubicin may have the potential to be used as a new therapeutic intervention against multiple cancers.

BackgroundThe exposure of skin keratinocytes to Ultraviolet (UV) irradiation leads to Akt phosphorylation at Ser-473, which is important for the carcinogenic effects of excessive sun exposure. The present study investigated the underlying mechanism of Akt Ser-473 phosphorylation by UVB radiation.ResultsWe found that DNA-dependent protein kinase catalytic subunit (DNA-PKcs) and mammalian target of rapamycin (mTOR) complex 2 (mTORC2) were both required for UVB-induced Akt Ser-473 phosphorylation in keratinocytes. Inhibition of DNA-PKcs activity via its inhibitor NU7026, a dominant-negative kinase-dead mutation, RNA interference (RNAi) or gene depletion led to the attenuation of UVB-induced Akt Ser-473 phosphorylation. Meanwhile, siRNA silencing or gene depletion of SIN1, a key component of mTORC2, abolished Akt Ser-473 phosphorylation by UVB. Significantly, we discovered that DNA-PKcs was associated with SIN1 in cytosol upon UVB radiation, and this complexation appeared required for Akt Ser-473 phosphorylation. Meanwhile, this DNA-PKcs-SIN1 complexation by UVB was dependent on epidermal growth factor receptor (EGFR) activation, and was disrupted by an EGFR inhibitor (AG1478) or by EGFR depletion. UVB-induced complexation between DNA-PKcs and mTORC2 components was also abolished by NU7026 and DNA-PKcs mutation. Finally, we found that both DNA-PKcs and SIN1 were associated with apoptosis resistance of UVB radiation, and inhibition of them by NU7026 or genetic depletion significantly enhanced UVB-induced cell death and apoptosis.ConclusionTaken together, these results strongly suggest that DNA-PKcs-mTORC2 association is required for UVB-induced Akt Ser-473 phosphorylation and cell survival, and might be important for tumor cell transformation.

Abstract. Pancreatic cancer remains a challenging disease worldwide. Cryptotanshinone (CPT) is one of the active constituents of Salvia miltiorrhiza Bunge and exhibits significant antitumor activities in several human cancer cells. However, the efficacy and molecular mechanism of CPT in pancreatic cancer remains to be elucidated. In the present study, the effect of CPT on the proliferation, apoptosis and cell cycle of human pancreatic cancer cell BxPC-3 cells was evaluated. The results demonstrated that CPT inhibited proliferation of the BxPC-3 cells in a concentration-dependent manner, and significantly induced cell apoptosis and cell cycle arrest. The protein levels of cleaved caspase-3, caspase-9 and poly ADP ribose polymerase were upregulated, while the levels of c-myc, survivin and cyclin D1 were downregulated following treatment with CPT. In addition, CPT decreased the activities of signal transducer and activator of transcription 3 (STAT3) and several upstream regulatory signaling pathways after 24 h. However, CPT only inhibited the phosphorylation of STAT3 Tyr705 within 30 min, without marked effects on the phosphorylation of the other proteins. These results suggested that the inhibition of STAT3 activity by CPT was directly and independent of the upstream regulators in human pancreatic cancer. The present study demonstrated that CPT exerts anticancer effects by inducing apoptosis and cell cycle arrest via inhibition of the STAT3 signaling pathway in human BxPC-3 cells.

Sesquiterpene lactones (SLs) are plant-derived constituents that have been proved to have potential antitumour activity. However, the intracellular molecular targets of SLs and the underlying molecular mechanisms have not been well elucidated. Here, we report that F1012-2, a novel SL active fraction, isolated from Eupatorium lindleyanum DC., can significantly inhibit the growth of triple-negative breast cancer (TNBC) cells (MDA-MB-231 and MDA-MB-468) but has no obvious inhibitory effect on the growth of human mammary epithelial cells (MCF-10A). The related mechanisms on cell growth inhibition of F1012-2 were demonstrated by inducing apoptosis in a caspase-dependent manner through the intrinsic pathway and extrinsic pathway. F1012-2 could also activate autophagy in TNBC cells. Simultaneously, we found that F1012-2-induced apoptosis was enhanced by inhibition of autophagy. Furthermore, F1012-2 could induce cell cycle arrest at G2/M phase with decreasing expression of cyclin B1, cdc2, and upregulating p21, p-cdc2. Also, F1012-2 activated Akt and p38 signalling pathways. In vivo, F1012-2 exhibited a potential antitumour effect in MDA-MB-231 xenografts without apparent toxicity. Taken together, our results identified that F1012-2 inhibited cell growth via multiple signalling pathways in vitro and in vivo. These data suggest that F1012-2 may be a potential natural active fraction for the treatment of TNBC.