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Quercetin is a dietary flavonoid with known antitumor effects against several types of cancers by promoting apoptotic cell death and inducing cell cycle arrest. However, U373MG malignant glioma cells expressing mutant p53 are resistant to a 24 h quercetin treatment. In this study, the anticancer effect of quercetin was reevaluated in U373MG cells, and quercetin was found to be significantly effective in inhibiting proliferation of U373MG cells in a concentration-dependent manner after 48 and 72 h of incubation. Quercetin induced U373MG cell death through apoptosis, as evidenced by the increased number of cells in the sub-G1 phase, the appearance of fragmented nuclei, decreased mitochondrial membrane potential, proteolytic activation of caspase-3 and caspase-7, an increase in caspase-3 and 9 activities, and degradation of poly(ADP-ribose) polymerase protein. Furthermore, quercetin activated JNK and increased the expression of p53, which translocated to the mitochondria and simultaneously led to the release of cytochrome c from mitochondria to the cytosol. We also found that quercetin induced autophagy. Pretreatment with chloroquine, an autophagy inhibitor, strongly augmented apoptosis in U373MG cells, indicating that quercetin induced protective autopagy in U373MG cells.

Pitaya, commonly known as dragon fruit, has generated considerable consumer interest because of its attractive color and micronutrient content. The present study investigated the total polyphenol and flavonoid content, antioxidant activity against various free radicals, and antiproliferative effect on several cancer cell lines of extracts of flesh and peel of white and red pitayas, collected from Jeju Island, Korea. The total polyphenol and flavonoid contents of 80% methanol extracts of red pitaya peel (RPP) and white pitaya peel (WPP) were approximately 3- and 5-fold higher than those of red pitaya flesh (RPF) and white pitaya flesh (WPF), respectively. Overall, the total flavonoid and polyphenol contents of these extracts were RPP>WPP>RPF>WPF and WPP>RPP>RPF>WPF, respectively. In addition, a study involving nontargeted high-performance liquid chromatography coupled with a photodiode array and electrospray ionization mass spectrometry (HPLC-PDA-ESI-MS) of different pitaya extracts indicated the presence of phenolic, hydroxycinnamic acid derivatives, flavonol glycosides, betacyanin, and its derivatives with a few unknown compounds. Separately, peel extracts of both red and white pitayas showed higher 2,2-diphenyl-1-picrylhydrazyl, hydroxyl, and alkyl radical-scavenging activity than did the corresponding flesh extracts. Both peel extracts also showed stronger antiproliferative activity against AGS and MCF-7 cancer cells than either flesh extract. There was a direct correlation between the phenolic content and antioxidant effect, but no correlation observed between antioxidant activity and antiproliferative activity. These results suggest that the peel of white and red pitaya may be a valuable ingredient in foods and may also be useful in cosmetic, nutraceutical, and pharmaceutical applications.

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Resistance to both chemotherapy and radiation therapy is frequent in triple-negative breast cancer (TNBC) patients. We established treatment-resistant TNBC MDA-MB-231/IR cells by irradiating the parental MDA-MB-231 cells 25 times with 2 Gy irradiation and investigated the molecular mechanisms of acquired resistance. The resistant MDA-MB-231/IR cells were enhanced in migration, invasion, and stem cell-like characteristics. Pathway analysis by the Database for Annotation, Visualization and Integrated Discovery revealed that the NF-κB pathway, TNF signaling pathway, and Toll-like receptor pathway were enriched in MDA-MB-231/IR cells. Among 77 differentially expressed genes revealed by transcriptome analysis, 12 genes involved in drug and radiation resistance, including interferon-induced protein with tetratricopeptide repeats 2 (IFIT2), were identified. We found that baicalein effectively reversed the expression of IFIT2, which is reported to be associated with metastasis, recurrence, and poor prognosis in TNBC patients. Baicalein sensitized radio- and chemoresistant cells and induced apoptosis, while suppressing stem cell-like characteristics, such as mammosphere formation, side population, expression of Oct3/4 and ABCG2, and CD44highCD24low population in MDA-MB-231/IR cells. These findings improve our understanding of the genes implicated in radio- and chemoresistance in breast cancer, and indicate that baicalein can serve as a sensitizer that overcomes treatment resistance.

Saturated fatty acids possess few health benefits compared to unsaturated fatty acids. However, increasing experimental evidence demonstrates the nutritionally beneficial role of odd-chain saturated fatty acids in human health. In this study, the anti-cancer effects of pentadecanoic acid were evaluated in human breast carcinoma MCF-7/stem-like cells (SC), a cell line with greater mobility, invasiveness, and cancer stem cell properties compared to the parental MCF-7 cells. Pentadecanoic acid exerted selective cytotoxic effects in MCF-7/SC compared to in the parental cells. Moreover, pentadecanoic acid reduced the stemness of MCF-7/SC and suppressed the migratory and invasive ability of MCF-7/SC as evidenced by the results of flow cytometry, a mammosphere formation assay, an aldehyde dehydrogenase activity assay, and Western blot experiments conducted to analyze the expression of cancer stem cell markers—CD44, β-catenin, MDR1, and MRP1—and epithelial–mesenchymal transition (EMT) markers—snail, slug, MMP9, and MMP2. In addition, pentadecanoic acid suppressed interleukin-6 (IL-6)-induced JAK2/STAT3 signaling, induced cell cycle arrest at the sub-G1 phase, and promoted caspase-dependent apoptosis in MCF-7/SC. These findings indicate that pentadecanoic acid can serve as a novel JAK2/STAT3 signaling inhibitor in breast cancer cells and suggest the beneficial effects of pentadecanoic acid-rich food intake during breast cancer treatments.

Nobiletin, a major component of citrus fruits, is a polymethoxyflavone derivative that exhibits anticancer activity against several forms of cancer, including SNU-16 human gastric cancer cells. To explore the nobiletin-induced cell death mechanism, we examined the changes in protein expression caused by nobiletin in human gastric cancer SNU-16 cells by means of two-dimensional gel electrophoresis (2-DGE), followed by peptide mass fingerprinting (PMF) analysis. Seventeen of 20 selected protein spots were successfully identified, including nine upregulated and eight downregulated proteins. In nobiletin-treated SNU-16 cells the glucose-regulated protein 78 kDa (GRP78) mRNA level was induced most significantly among six proteins related to cell survival and death. Western blot analysis was used to confirm the expression of GRP78 protein. We detected increases in the levels of the ER-stress related proteins inositol requiring enzyme 1 alpha (IRE1-α), activating transcription factor 4 (ATF-4), and C/EBP homology protein (CHOP), as well as GRP78, in response to nobiletin in SNU-16 cells. Furthermore, the ER stress-mediated apoptotic protein caspase-4 was proteolytically activated by nobiletin. Pretreatment with chloroquine, an autophagy inhibitor, strongly augmented apoptosis in SNU-16 cells, as evidenced by decreased cell viability, an increased number of sub-G1 phase cells and increased levels of cleaved PARP. Our results suggest that nobiletin-induced apoptosis in SNU-16 cells is mediated by pathways involving intracellular ER stress-mediated protective autophagy. Thus, the combination of nobiletin and an autophagy inhibitor could be a promising treatment for gastric cancer patients.