Simvastatin enhances the radiosensitivity of p53­deficient cells via inhibition of mouse double minute 2 homolog.

Simvastatin exhibits anticancer activities, but its molecular mechanisms and radiosensitizing effects relative to p53 status remain unclear. In this study, we investigated whether the combination of simvastatin and ionizing radiation (IR) would enhance the antitumor effects of IR alone in HCT116 p53+/+ and p53­/- colon cancer cells. Using colony formation assays and a xenograft mouse model, we found that simvastatin potently stimulated radiosensitization of HCT116 p53­/- cells and xenograft tumors. The combination of simvastatin with IR decreased G2/M arrest and delayed the repair of IR-induced DNA damage; however, no differences between the HCT116 p53+/+ and p53­/- cells were evident. A further analysis revealed that simvastatin exhibited a novel function, namely, MDM2 suppression, regardless of p53 status. Interestingly, simvastatin induced radiosensitization by enhancing MDM2 suppression and elevating IR-induced p­ATM foci formation compared with IR alone in HCT116 p53­/- cells. Furthermore, simvastatin caused accumulations of the FOXO3a, E-cadherin, and p21 tumor suppressor proteins, which are downstream factors of MDM2, in HCT116 p53­/- cells. In conclusion, simvastatin enhanced radiosensitivity by inducing MDM2 inhibition and increasing tumor suppressor protein levels in radioresistant HCT116 p53­/- cells and xenografts. Overall, our novel findings suggest a scientific rationale for the clinical use of simvastatin as an MDM2 inhibitor and radiosensitizer for p53­deficient colorectal tumor treatments.

Enhanced anticancer effects of a mixture of low-dose mushrooms and Panax ginseng root extracts in human colorectal cancer cells.

Worldwide, colorectal cancer is the third most common cancer in men and the second most common in women. As conventional colorectal cancer therapies result in various side effects, there is a need for adjuvant therapy that can enhance the conventional therapies without complications. In this study, we investigated the anticancer effects of combined mixture of the several medicinal mushrooms and Panax ginseng root extracts (also called Amex7) as an adjuvant compound in the treatment of human colorectal cancer. We observed the in vivo inhibitory effect of Amex7 (1.25, 6.25, and 12.5 ml/kg, oral administration, twice daily) on tumor growth in a mouse model xenografted with HT-29 human colorectal cancer cells. In vitro, at 6, 12, and 24 h after 4% Amex7 treatment, we analyzed cell cycle by flow cytometry and the expression levels of cell cycle progression, apoptosis, and DNA damage repair-related proteins using immunoblotting and immunofluorescence staining in HT-29 cell line. As a result, Amex7 significantly suppressed tumor growth in HT-29 human colorectal cancer cells and xenografts. In vitro, Amex7 induced G2/M arrest through the regulation of cell cycle proteins and cell death by apoptosis and autophagy. Additionally, Amex7 consistently induced DNA damage and delayed the repair of Amex7-induced DNA damage by reducing the level of HR repair proteins. In conclusion, Amex7 enhanced anticancer effects through the induction of G2/M arrest and cell death, including apoptosis and autophagy. Furthermore, Amex7 impaired DNA damage repair. The present study provides a scientific rationale for the clinical use of a combined mixture of medicinal mushrooms and P. ginseng root extracts as an adjuvant treatment in human colorectal cancer.

Digoxin enhances radiation response in radioresistant A549 cells by reducing protein phosphatase 2A.

Protein phosphatase 2A (PP2A) is a ubiquitous multifunctional enzyme usually known as a tumor suppressor. Recent studies have reported that although inhibition of PP2A leads to acceleration of cell growth, it also induces damaged cells to pass through the cell cycle and renders them sensitive to radiotherapy. Here, we investigated the radiosensitizing effects of digoxin as a PP2A inhibitor in two non-small-cell lung cancer (NSCLC) cell types (H460 and A549) with differential sensitivity to radiation. Digoxin inhibited the proliferation of H460 and A549 cells in a dose-dependent fashion and was especially effective on radioresistant A549 cells. Interestingly, the radiosensitizing effect of digoxin was only present in the radioresistant A549 cells and xenografts. The combination of digoxin and ionizing radiation (IR) significantly reduced clonogenic survival and xenograft tumor growth (P<0.001), compared with IR alone. Digoxin suppressed PP2A protein expression and prevented IR-induced PP2A expression in A549 cells. Digoxin treatment combined with IR allowed the damaged cell to progress through the cell cycle via suppression of cell cycle-related proteins (p53, cyclin D1, cyclin B1, CDK4, and p-cdc2). Moreover, digoxin enhanced IR-induced DNA damage through reduction in levels of repair proteins and elevation of p-ATM foci formation up to 24 h (P<0.001). In conclusion, digoxin has a novel function as a PP2A inhibitor, and combined with IR produces a synergistic effect on radiosensitizing cells, thereby indicating a potentially promising therapeutic approach to radioresistant lung cancer treatment.

Rod-shaped iron oxide nanoparticles are more toxic than sphere-shaped nanoparticles to murine macrophage cells.

Variable sizes of nanoparticles, ranging from nano to micro scale, are of toxicological interest. In the present study, the authors hypothesized that, in addition to the size, the shape of iron oxide (Fe2O3) nanoparticles is a major factor that contributes to particle cytotoxicity. Cytotoxicity to mouse macrophage cells (RAW 264.7) was investigated using 3 different particles: micro-sized Fe2 O3 (M-Fe2O3), nano-sized Fe2O3 (N-Fe2O3), and rod-shaped Fe2O3 (R-Fe2O3). Whereas M-Fe2O3 and N-Fe2O3 were located in the vacuole as aggregates, R-Fe2 O3 was often spread throughout the cytoplasm. The extent of cytotoxicity measured by the water soluble tetrazolium (WST-1) assay was in the order R-Fe2O3 ≈ N-Fe2O3 > M-Fe2O3, whereas the extent revealed by the lactate dehydrogenase assay was in the order R-Fe2O3 >> N-Fe2O3 ≈ M-Fe2 O3. In addition, the degree of tumor necrosis factor-α and reactive oxygen species (ROS) production was in the order of R-Fe2O3 > N-Fe2 O3 > M-Fe2O3. In addition, a much higher extent of necrosis was associated with the presence of R-Fe2O3. These results suggest that the higher degree of necrosis due to R-Fe2O3 is correlated with both the higher degree of membrane damage and ROS production by R-Fe2O3 compared with the results of the other Fe2O3 particles. These results also showed that the degree of cytotoxicity of nanoparticles should be evaluated based on shape as well as size, because changes in shape and size are accompanied by alterations in surface area, which relate closely to cytotoxicity.

Silver wire amplifies the signaling mechanism for IL-1beta production more than silver submicroparticles in human monocytic THP-1 cells.

Silver materials have been widely used in diverse fields. However, their toxicity and their mechanism, especially in different forms, have not been studied sufficiently. Thus, cytotoxicity, apoptosis, and interleukin-1beta (IL-1ß) production were investigated using macrophage-like THP-1 cells in the presence of Ag microparticles (AgMPs, 2.7 µm), Ag submicroparticles (AgSMPs, 150 nm), and Ag wires (AgWs, 274 nm×5.3 µm). The levels of cytotoxicity, apoptosis, and IL-1ß production by AgWs were higher than those by the other two AgSMPs and AgMPs. This trend was also observed with each step of the signaling mechanism for IL-1ß production, which is a single pathway affiliated with ROS generation or lysosomal rupture or both, cathepsin B, caspase-1 (NALP3 inflammasome), and finally IL-1ß production in THP-1 cells. All these results suggest that, for development of safe and effective silver materials, the shape or form of silver materials should be considered, especially for macrophage cell lines because epithelial cell lines are not overly sensitive to silver materials.