High Hemin Concentration Induces Escape from Senescence of Normoxic and Hypoxic Colon Cancer Cells.

Hemoglobin from either red meat or bowel bleeding may promote oxidative stress and increase the risk of colorectal cancer (CRC). Additionally, solid cancers or their metastases may be present with localized bruising. Escape from therapy-induced senescence (TIS) might be one of the mechanisms of tumor re-growth. Therefore, we sought to study whether hemin can cause escape from TIS in CRC. To induce senescence, human colon cancer cells were exposed to a chemotherapeutic agent irinotecan (IRINO). Cells treated with IRINO exhibited common hallmarks of TIS. To mimic bleeding, colon cancer cells were additionally treated with hemin. High hemin concentration activated heme oxygenase-1 (HO-1), induced escape from TIS and epithelial-to-mesenchymal transition, and augmented progeny production. The effect was even stronger in hypoxic conditions. Similar results were obtained when TIS cells were treated with another prooxidant agent, H2O2. Silencing of antioxidative enzymes such as catalase (CAT) or glutathione peroxidase-1 (GPx-1) maintained colon cancer cells in a senescent state. Our study demonstrates that a high hemin concentration combined with an increased activity of antioxidative enzymes, especially HO-1, leads to escape from the senescence of colon cancer cells. Therefore, our observations could be used in targeted anti-cancer therapy.

Polyploidy formation in cancer cells: How a Trojan horse is born.

Ploidy increase has been shown to occur in different type of tumors and participate in tumor initiation and resistance to the treatment. Polyploid giant cancer cells (PGCCs) are cells with multiple nuclei or a single giant nucleus containing multiple complete sets of chromosomes. The mechanism leading to formation of PGCCs may depend on: endoreplication, mitotic slippage, cytokinesis failure, cell fusion or cell cannibalism. Polyploidy formation might be triggered in response to various genotoxic stresses including: chemotherapeutics, radiation, hypoxia, oxidative stress or environmental factors like: air pollution, UV light or hyperthermia. A fundamental feature of polyploid cancer cells is the generation of progeny during the reversal of the polyploid state (depolyploidization) that may show high aggressiveness resulting in the formation of resistant disease and tumor recurrence. Therefore, we propose that modern anti-cancer therapies should be designed taking under consideration polyploidization/ depolyploidization processes, which confer the polyploidization a hidden potential similar to a Trojan horse delayed aggressiveness. Various mechanisms and stress factors leading to polyploidy formation in cancer cells are discussed in this review.

Pre-treatment or Post-treatment of Human Glioma Cells With BIX01294, the Inhibitor of Histone Methyltransferase G9a, Sensitizes Cells to Temozolomide.

Glioblastoma (GBM) is a malignant, primary brain tumor, highly resistant to conventional therapies. Temozolomide (TMZ) is a first line therapeutic agent in GBM patients, however, survival of such patients is poor. High level of DNA repair protein, O6-methylguanine-DNA-methyltransferase (MGMT) and occurrence of glioma stem-like cells contribute to GBM resistance to the drug. Here, we explored a possibility of epigenetic reprograming of glioma cells to increase sensitivity to TMZ and restore apoptosis competence. We combined TMZ treatment with BIX01294, an inhibitor of histone methyltransferase G9a, known to be involved in cancerogenesis. Two treatment combinations were tested: BIX01294 was administered to human LN18 and U251 glioma cell cultures 48 h before TMZ or 48 h after TMZ treatment. Despite their different status of the MGMT gene promoter, there was no correlation with the response to TMZ. The analyses of cell viability, appearance of apoptotic alterations in morphology of cells and nuclei, and markers of apoptosis, such as levels of cleaved caspase 3, caspase 7 and PARP, revealed that both pre-treatment and post-treatment with BIX01294 sensitize glioma cells to TMZ. The additive effect was stronger in LN18 cells. Moreover, BIX01294 enhanced the cytotoxic effect of TMZ on glioma stem-like cells, although it was not associated with modulation of the pluripotency markers (NANOG, SOX2, CD133) expression or methylation of NANOG and SOX2 gene promoters. Accordingly, knockdown of methyltransferase G9a augments TMZ-induced cell death in LN18 cells. We found the significant increases of the LC3-II levels in LN18 cells treated with BIX01294 alone and with drug combination that suggests involvement of autophagy in enhancement of anti-tumor effect of TMZ. Treatment with BIX01294 did not affect methylation of the MGMT gene promoter. Altogether, our results suggest that G9a is a potential therapeutic target in malignant glioma and the treatment with the G9a inhibitor reprograms glioma cells and glioma stem-like cells to increase sensitivity to TMZ and restore apoptosis competence.