Sun Nyoung Yu

Salinomycin-induced apoptosis of human prostate cancer cells due to accumulated reactive oxygen species and mitochondrial membrane depolarization

The anticancer activity of salinomycin has evoked excitement due to its recent identification as a selective inhibitor of breast cancer stem cells (CSCs) and its ability to reduce tumor growth and metastasis in vivo. In prostate cancer, similar to other cancer types, CSCs and/or progenitor cancer cells are believed to drive tumor recurrence and tumor growth. Thus salinomycin can potentially interfere with the end-stage progression of hormone-indifferent and chemotherapy-resistant prostate cancer. Androgen-responsive (LNCaP) and androgen-refractive (PC-3, DU-145) human prostate cancer cells showed dose- and time-dependent reduced viability upon salinomycin treatment; non-malignant RWPE-1 prostate cells were relatively less sensitive to drug-induced lethality. Salinomycin triggered apoptosis of PC-3 cells by elevating the intracellular ROS level, which was accompanied by decreased mitochondrial membrane potential, translocation of Bax protein to mitochondria, cytochrome c release to the cytoplasm, activation of the caspase-3 and cleavage of PARP-1, a caspase-3 substrate. Expression of the survival protein Bcl-2 declined. Pretreatment of PC-3 cells with the antioxidant N-acetylcysteine prevented escalation of oxidative stress, dissipation of the membrane polarity of mitochondria and changes in downstream molecular events. These results are the first to link elevated oxidative stress and mitochondrial membrane depolarization to salinomycin-mediated apoptosis of prostate cancer cells.

Interplay of reactive oxygen species, intracellular Ca2+ and mitochondrial homeostasis in the apoptosis of prostate cancer cells by deoxypodophyllotoxin

The limited treatment option for recurrent prostate cancer and the eventual resistance to conventional chemotherapy drugs has fueled continued interest in finding new anti‐neoplastic agents of natural product origin. We previously reported anti‐proliferative activity of deoxypodophyllotoxin (DPT) on human prostate cancer cells. Using the PC‐3 cell model of human prostate cancer, the present study reveals that DPT induced apoptosis via a caspase‐3‐dependent pathway that is activated due to dysregulated mitochondrial function. DPT‐treated cells showed accumulation of the reactive oxygen species (ROS), intracellular Ca  i2+ surge, increased mitochondrial membrane potential (MMP, ΔΨm), Bax protein translocation to mitochondria and cytochrome c release to the cytoplasm. This resulted in caspase‐3 activation, which in turn induced apoptosis. The antioxidant N‐acetylcysteine (NAC) reduced ROS accumulation, MMP and Ca  i2+ surge, on the other hand the Ca2+ chelator BAPTA inhibited the Ca  i2+ overload and MMP without affecting the increase of ROS, indicating that the generation of ROS occurred prior to Ca2+ flux. This suggested that both ROS and Ca  i2+ signaling play roles in the increased MMP via Ca  i2+ ‐dependent and/or ‐independent mechanisms, since ΔΨm elevation was reversed by NAC and BAPTA. This study provides the first evidence for the involvement of both ROS‐ and Ca  i2+ ‐activated signals in the disruption of mitochondrial homeostasis and the precedence of ROS production over the failure of Ca2+ flux homeostasis. J. Cell. Biochem. 114: 1124–1134, 2013.

Salinomycin enhances doxorubicin-induced cytotoxicity in multidrug resistant MCF-7/MDR human breast cancer cells via decreased efflux of doxorubicin

Salinomycin is a monocarboxylic polyether antibiotic, which is widely used as an anticoccidial agent. The anticancer property of salinomycin has been recognized and is based on its ability to induce apoptosis in human multidrug resistance (MDR). The present study investigated whether salinomycin reverses MDR towards chemotherapeutic agents in doxorubicin-resistant MCF-7/MDR human breast cancer cells. The results demonstrated that doxorubicin-mediated cytotoxicity was significantly enhanced by salinomycin in the MCF-7/MDR cells, and this occurred in a dose-dependent manner. This finding was consistent with subsequent observations made under a confocal microscope, in which the doxorubicin fluorescence signals of the salinomycin-treated cells were higher compared with the cells treated with doxorubicin alone. In addition, flow cytometric analysis revealed that salinomycin significantly increased the net cellular uptake and decreased the efflux of doxorubicin. The expression levels of MDR-1 and MRP-1 were not altered at either the mRNA or protein levels in the cells treated with salinomycin. These results indicated that salinomycin was mediated by its ability to increase the uptake and decrease the efflux of doxorubicin in MCF-7/MDR cells. Salinomycin reversed the resistance of doxorubicin, suggesting that chemotherapy in combination with salinomycin may benefit MDR cancer therapy.

Biological Activities of Mesembryanthemum crystallinum (Ice plant) Extract

This study analyzed the physiological quality of Mesembryanthemum crystallinum (ice plant) extract. M. crystallinum is a succulent plant found in Africa, southern Europe, North America, South America, and Australia. It has known antidiabetic, antioxidant, and activation of lipid metabolism effects. Extracts from M. crystallinum were prepared with methanol (MCM), ethanol (MCE), hot water (MCHW), and methanol after hot water (MCHM) extractions. The yields of MCM, MCE, MCHW, and MCHM were 0.37, 0.33, 0.50, and 0.07%, respectively. To determine the biological activities of the extracts, mushroom tyrosinase, pancreatic lipase, 1,1-diphenyl-2-picryl hydrazyl (DPPH) radical scavenging, nitric oxide (NO) production, and α-glucosidase assays were conducted. The DPPH radical scavenging activity of the MCHW extract was 62.9% at a concentration of 400 μg/ml, which was the highest of all the extracts. The MCM extract showed the highest inhibition activity of α-glucosidase and NO production (56.6 and 57.2%, respectively). The pancreatic lipase inhibition of the MCE extract was similar to that of the MCM extract, with significant inhibition of 90%. The mushroom tyrosinase inhibition of all the extracts was very low (approximately 30%). These results suggest that extracts from M. crystallinum have antioxidant, anti-inflammatory, antiobesity, and antidiabetic activities. Thus, it may have potential as a functional food product and therapeutic potential as an antidiabetic or antiobesity agent.

Anti-inflammatory Effect of Citrus unshiu Peels Fermented with Aspergillus niger

Citrus, yield of which is the highest among fruits produced in Korea, is extensively consumed for processed food items. The amount of by-products of citrus produced from the processing within a short period after the harvest is tremendous. These by-products are mostly dumped into land or neglected because of cost involved in processing them. The aim of the present study was to explore the usefulness of the by-products as a new material by examining the anti-inflammatory activity of fermented extracts of citrus peels. The peels of `unshu` (Citrus unshiu) was fermented with Aspergillus niger and their extracts before or after fermentation were analyzed using HPLC. The analysis showed that neohesperidin level considerably increased and the two new compounds were synthesized after fermentation. The anti-inflammatory activity of the fermented extracts was examined on RAW 264.7 murine macrophage cells stimulated with lipopolysaccharide. Fermented unshu extracts significantly enhanced the decrease of nitric oxide (NO) production, iNOS and COX-2 expression, comparing with those of unfermented extracts. Also TNF- and IL-6 production, both of which are pro-inflammatory cytokine, were more inhibited in fermented extracts. These results showed that the fermentation and promotion of the function of the by-products of citrus peels will help find a new application.

Biological Activities of Pharbitis nil and Partial Purification of Anticancer Agent from Its Extract

This study aimed to evaluate several biological activities of Pharbitis nil and to isolate an anticancer agent from its methanol extract. Pharbitis nil seeds were extracted with methanol (PNM). Then, PNM was fractionated into solvent layers such as ethyl acetate fraction (PNE), butanol fraction (PNB), and water fraction (PNW). The biological activities of the fractions were analyzed for tyrosinase inhibition, lipase inhibition, DPPH-free radical scavenging, and cell growth inhibition. PNM showed strong growth inhibition of prostate cancer PC-3 cells. PNM was subjected to Diaion HP-20 and eluted stepwise with 50%, 80%, and 100% methanol. Then, for activity-guided fraction, each fraction was analyzed for growth inhibition of prostate cancer PC-3 cells by using an MTT assay. Because the 100% fraction showed significantly strong inhibitory activity, the fraction was further separated in the reverse phase C18, which was eluted with 80% and 90% methanol. The 90% fraction was further subjected to Sephadex LH-20 using a mobile solvent of 100% methanol. Finally, the compound PN was partially purified for HPLC analysis. PN showed cell growth inhibitory activity and induced the apoptosis and cell cycle arrest of prostate cancer PC-3 cells, as measured by flow cytometry. The results together suggest that Pharbitis nil possesses various biological activities, especially the inhibitory activity for the proliferation of prostate cancer PC-3 cells, suggesting the possibility of its use as an anticancer agent.