ABSTRACT
Bufadienolides are constituents of the traditional Chinese medicine Chan Su and are found in toad venom. Cardiovascular side-effects are one of the limiting factors towards developing bufadienolides as chemotherapeutic agents. Thus, in the present study, low doses of bufalin and cinobufotalin, prominent members of the bufadienolides, were investigated for their cytotoxic activity in combination with hyperthermia (HT) or radiation (Rad) therapy. In addition, the underlying mechanism involved was investigated. A DNA fragmentation assay, viability assay and microscopic observation were primarily used to assess the effect of low doses of the two drugs in human lymphoma U937 cells. Furthermore, the effects of these drugs on the mitochondrial membrane potential (MMP) and apoptotic-associated protein activation were investigated. HT/bufadienolide- and RT/bufadienolide-treated samples significantly increased the DNA fragmentation percentile and decreased the MMP, as well as increasing the apoptotic features observed microscopically within a relatively short time (6 h) after treatment. The two combinations affected the expression of important apoptotic markers, including caspase-3 and BH3 interacting domain death agonist. The findings of the current study confirm the additive effect of HT with this group of drugs, directing a novel therapeutic avenue for the clinical use of bufadienolides at lower doses with more restrained cardio toxic side-effects.
ABSTRACT
It was previously reported that berberine (BBR) and tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) exhibited a synergistic apoptotic effect on triple negative breast cancer (TNBC) cells. In addition, the BBR/TRAIL combination treatment sensitized TRAIL-resistant TNBC cells to TRAIL. The aim of the present study was to investigate a novel pathway for enhancing the apoptotic effect of BBR/TRAIL through mitogen-activated protein kinases (MAPKs). Selective inhibitors and small interfering RNAs were utilized to understand the role of p38 MAPK in this pathway. The results demonstrated that p38 MAPK was activated in response to the combination therapy in TRAIL-resistant TNBC cells. In addition, it was revealed that the inhibition of p38 enhanced apoptosis in epidermal growth factor receptor (EGFR)-overexpressing MDA-MB-468 TNBC cells and EGFR-mutant PC-9 non-small-cell lung carcinoma cells, which was associated with the downregulation of EGFR serine phosphorylation. Viability assays for these two cell lines also confirmed the significant reduction of cell viability following p38 inhibition in BBR/TRAIL-treated cells. In conclusion, the present study provided novel evidence for the role of p38 in suppressing BBR/TRAIL-mediated apoptosis and its association with EGFR, which may explain the mechanism of treatment resistance in certain types of cancer.
ABSTRACT
Cinobufotalin (CB), one of the bufadienolides prepared from toad venom, was investigated for its cytotoxicity, and the underneath mechanism involved. We primarily utilized DNA fragmentation assay and microscopic observation to assess the effect of various doses of CB in human lymphoma U937 cells. Following that, we investigated other parameters involved in cell death mechanism such as reactive oxygen species (ROS), mitochondrial membrane potential (MMP), and apoptotic proteins activation. HeLa cells were concomitantly used to generalize the data observed. Our results show that CB caused significant DNA fragmentation, decrease of MMP, and an increase in the intracellular Ca(2+) ion and ROS production. In addition, CB induced upregulation of Fas protein, proteolytic activation of cytochrome c, caspase-2, -3, -8 and -9 together with the activation of Bid and Bax. Our findings were further validated using either Fas/FasL antagonist or pan-caspase inhibitor to significantly inhibit CB-induced DNA fragmentation. In our study, we suggest that CB induces caspase dependent cell death in U937 cells, and that Fas plays a role in CB-induced apoptosis. Altogether, our data provides novel insights of the mechanism of action of CB and its potential as a future chemotherapeutic agent.