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Anti-Tumorigenic Activity of Chrysin from Oroxylum indicum via Non-Genotoxic p53 Activation through the ATM-Chk2 Pathway.

ABSTRACT: The p53 tumor suppressor plays critical roles in cell cycle regulation and apoptotic cell death in response to various cellular stresses, thereby preventing cancer development. Therefore, the activation of p53 through small molecules is an attractive therapeutic strategy for the treatment of cancers retaining wild-type p53. We used a library of 700 Myanmar wild plant extracts to identify small molecules that induce p53 transcriptional activity. A cell-based screening method with a p53-responsive luciferase-reporter assay system revealed that an ethanol extract of Oroxylum indicum bark increased p53 transcriptional activity. Chrysin was isolated and identified as the active ingredient in the O. indicum bark extract. A treatment with chrysin increased p53 protein expression and the p53-mediated expression of downstream target genes, and decreased cell viability in MCF7 cells, but not in p53-knockdown MCF7 cells. We also found that chrysin activated the ATM-Chk2 pathway in the absence of DNA damage. Hence, the inactivation of the ATM-Chk2 pathway suppressed p53 activation induced by chrysin. These results suggest the potential of chrysin as an anti-cancer drug through the activation of p53 without DNA damage.

SUBMITTER: Nagasaka M

PROVIDER: S-EPMC6099937 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:BackgroundOptimizing the safety and efficacy of standard chemotherapeutic agents such as cisplatin (CDDP) is of clinical relevance. Serum starvation in vitro and short-term food starvation in vivo both stress cells by the sudden depletion of paracrine growth stimulation.MethodsThe effects of serum starvation on CDDP toxicity were investigated in normal and cancer cells by assessing proliferation, cell cycle distribution and activation of DNA-damage response and of AMPK, and were compared to effects observed in cells grown in serum-containing medium. The effects of short-term food starvation on CDDP chemotherapy were assessed in xenografts-bearing mice and were compared to effects on tumor growth and/or regression determined in mice with no diet alteration.ResultsWe observed that serum starvation in vitro sensitizes cancer cells to CDDP while protecting normal cells. In detail, in normal cells, serum starvation resulted in a complete arrest of cellular proliferation, i.e. depletion of BrdU-incorporation during S-phase and accumulation of the cells in the G0/G1-phase of the cell cycle. Further analysis revealed that proliferation arrest in normal cells is due to p53/p21 activation, which is AMPK-dependent and ATM-independent. In cancer cells, serum starvation also decreased the fraction of S-phase cells but to a minor extent. In contrast to normal cells, serum starvation-induced p53 activation in cancer cells is both AMPK- and ATM-dependent. Combination of CDDP with serum starvation in vitro increased the activation of ATM/Chk2/p53 signaling pathway compared to either treatment alone resulting in an enhanced sensitization of cancer cells to CDDP. Finally, short-term food starvation dramatically increased the sensitivity of human tumor xenografts to cisplatin as indicated not only by a significant growth delay, but also by the induction of complete remission in 60% of the animals bearing mesothelioma xenografts, and in 40% of the animals with lung carcinoma xenografts.ConclusionIn normal cells, serum starvation in vitro induces a cell cycle arrest and protects from CDDP induced toxicity. In contrast, proliferation of cancer cells is only moderately reduced by serum starvation whereas CDDP toxicity is enhanced. The combination of CDDP treatment with short term food starvation improved outcome in vivo. Therefore, starvation has the potential to enhance the therapeutic index of cisplatin-based therapy.

Project description:BackgroundOroxylum indicum fruit extract (OIE) has been reported to inhibit the development of adipocytes. However, the exact mechanism of its metabolic activity is not clearly defined. This study attempted to investigate whether OIE was involved in disrupting the cell cycle, glucose metabolism, and mitochondrial function in 3 T3-L1 cells.MethodsThe effect of the OIE on cell cycle progression was measured by flow cytometry along with observing the expression of the cycle regulator by immunoblotting. The effect of the OIE on glucose metabolism was investigated. The amount of glucose uptake (2-NBDG) influenced by insulin was determined as well as the protein tyrosine phosphorylation (PY20), and glucose transporter4 (GLUT4) expression was determined by immunoblotting assay. Mitochondria are also essential to metabolic processes. This study investigated mitochondrial activity using fluorescent lipophilic carbocyanine dye (JC-1) and mitochondria mass by MitoTracker Green (MTG) staining fluorescence dyes. Finally, cellular ATP concentration was measured using an ATP chemiluminescence assay.ResultsTreatment with OIE plus adipogenic stimulators for 24 h arrested cell cycle progression in the G2/M phase. Moreover, 200 μg/mL of OIE significantly diminished the expression of the insulin receptor (IR) and GLUT4 protein compared to the untreated-adipocytes (P < 0.05). The mitochondrial membrane potential (MMP) was significantly reduced (24 h) and increased (day 12) by OIE compared to untreated-adipocytes (P < 0.05). However, OIE maintained MMP and ATP at a similar level compared to the pre-adipocytes (day 12). Transmission electron microscope (TEM) results demonstrated that OIE could protect mitochondria deformation compared to the untreated-adipocytes.ConclusionThese results suggest that the inhibitory effect of the OIE on adipogenesis may potentially inhibit the cell cycle and phosphorylation of IR, leading to a decrease in glucose uptake to the cells. The OIE also slows down the mitochondrial activity of the early phase of cell differentiation, which can also inhibit the development of fat cells.

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Anti-Tumorigenic Activity of Chrysin from Oroxylum indicum via Non-Genotoxic p53 Activation through the ATM-Chk2 Pathway.

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