Accumulating evidence suggests that exposures to elevated levels of either endogenous estrogen or environmental estrogenic chemicals are associated with breast cancer development and progression. ...These natural or synthetic estrogens are known to produce reactive oxygen species (ROS) and increased ROS has been implicated in both cellular apoptosis and carcinogenesis. Though there are several studies on direct involvement of ROS in cellular apoptosis using short-term exposure model, there is no experimental evidence to directly implicate chronic exposure to ROS in increased growth and tumorigenicity of breast cancer cells. Therefore, the objective of this study was to evaluate the effects of chronic oxidative stress on growth, survival and tumorigenic potential of MCF-7 breast cancer cells. MCF-7 cells were exposed to exogenous hydrogen peroxide (H2O2) as a source of ROS at doses of 25 µM and 250 µM for acute (24 hours) and chronic period (3 months) and their effects on cell growth/survival and tumorigenic potential were evaluated. The results of cell count, MTT and cell cycle analysis showed that while acute exposure inhibits the growth of MCF-7 cells in a dose-dependent manner, the chronic exposure to H2O2-induced ROS leads to increased cell growth and survival of MCF-7 cells. This was further confirmed by gene expression analysis of cell cycle and cell survival related genes. Significant increase in number of soft agar colonies, up-regulation of pro-metastatic genes VEGF, WNT1 and CD44, whereas down-regulation of anti-metastatic gene E-Cadherin in H2O2 treated MCF-7 cells observed in this study further suggests that persistent exposure to oxidative stress increases tumorigenic and metastatic potential of MCF-7 cells. Since many chemotherapeutic drugs are known to induce their cytotoxicity by increasing ROS levels, the results of this study are also highly significant in understanding the mechanism for adaptation to ROS-induced toxicity leading to acquired chemotherapeutic resistance in breast cancer cells.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Renal Cell Carcinoma (RCC) in humans is positively influenced by oxidative stress status in kidneys. We recently reported that adaptive response to low level of chronic oxidative stress induces ...malignant transformation of immortalized human renal tubular epithelial cells. Epigenetic alterations in human RCC are well documented, but its role in oxidative stress-induced malignant transformation of kidney cells is not known. Therefore, the objective of this study was to evaluate the potential role of epigenetic changes in chronic oxidative stress-induced malignant transformation of HK-2, human renal tubular epithelial cells. The results revealed aberrant expression of epigenetic regulatory genes involved in DNA methylation (DNMT1, DNMT3a and MBD4) and histone modifications (HDAC1, HMT1 and HAT1) in HK-2 cells malignantly transformed by chronic oxidative stress. Additionally, both in vitro soft agar assay and in vivo nude mice study showing decreased tumorigenic potential of malignantly transformed HK-2 cells following treatment with DNA de-methylating agent 5-aza 2' dC further confirmed the crucial role of DNA hypermethyaltion in oxidative stress-induced malignant transformation. Changes observed in global histone H3 acetylation (H3K9, H3K18, H3K27 and H3K14) and decrease in phospho-H2AX (Ser139) also suggest potential role of histone modifications in increased survival and malignant transformation of HK-2 cells by oxidative stress. In summary, the results of this study suggest that epigenetic reprogramming induced by low levels of oxidative stress act as driver for malignant transformation of kidney epithelial cells. Findings of this study are highly relevant in potential clinical application of epigenetic-based therapeutics for treatments of kidney cancers.
The role of chronic oxidative stress in the development and aggressive growth of estrogen receptor (ER)-positive breast cancer is well known; however, the mechanistic understanding is not clear. ...Estrogen-independent growth is one of the features of aggressive subtype of breast cancer. Therefore, the objective of this study was to evaluate the effect of oxidative stress on estrogen sensitivity and expression of nuclear estrogen receptors in ER-positive breast cancer cells. MCF-7 cells chronically exposed to hydrogen peroxide were used as a cell model in this study, and their growth in response to 17-β estradiol was evaluated by cell viability, cell cycle, and cell migration analysis. Results were further confirmed at molecular level by analysis of gene expressions at transcript and protein levels. Histone H3 modifications, expression of epigenetic regulatory genes, and the effect of DNA demethylation were also analyzed. Loss of growth in response to estrogen with a decrease in ERα expression was observed in MCF-7 cells adapted to chronic oxidative stress. Increases in
mtTFA
and
NRF1
in these cells further suggested the role of mitochondria-dependent redox-sensitive growth signaling as an alternative pathway to estrogen-dependent growth. Changes in expression of epigenetic regulatory genes, levels of histone H3 modifications as well as significant restorations of both ERα expression and estrogen response by 5-Aza-2′-deoxycytidine further confirmed the epigenetic basis for estrogen-independent growth in these cells. In conclusion, results of this study suggest that chronic oxidative stress can convert estrogen-dependent nonaggressive breast cancer cells into estrogen-independent aggressive form potentially by epigenetic mechanism.
Antibody-drug conjugates (ADCs) are a promising therapeutic modality for oncology indications. The concept of an ADC platform is to increase the therapeutic index (TI) of chemotherapeutics through ...more selective delivery of cytotoxic agents to tumor cells while limiting exposure to healthy normal cells. Despite the use of antibodies targeting antigens abundantly and/or exclusively expressed on cancer cells (i.e., target cells), dose limiting toxicities (DLTs) in normal cells/tissues are frequently reported even at suboptimal therapeutic doses. Although advancement of ADC technology has helped to optimize all three key components (i.e., mAb, linker, and payload), DLTs remain a key challenge for ADC development. Mechanisms of ADC toxicity in normal cells/tissues are not clearly understood, but the majority of DLTs are considered to be target-independent. In addition to linker-drug instability contributing to the premature release of cytotoxic drug (payload) in circulation, uptake/trafficking of intact ADCs by both receptor-dependent (FcγRs, FcRn and C-type lectin receptors), and-independent (non-specific endocytosis) mechanisms may contribute to off-target toxicity in normal cells. In this article, we review potential mechanisms of target-independent ADC uptake and toxicity in normal cells, as well as discuss components of ADCs which may influence these mechanisms. This information will provide a deeper understanding of the underlying mechanisms of ADC off-target toxicity and prove helpful toward improving the overall TI of the next generation of ADCs.
Epigenetic therapy by DNA demethylating agent 5-aza-2′-deoxycytidine (5-aza 2′dC) is clinically effective in acute myeloid leukemia; however, it has shown limited results in treatment of breast ...cancer and has significant toxicity to normal cells. Green tea polyphenol (−)-epigallocatechin-3-gallate (EGCG) has anti-cancer and DNA demethylating properties with no significant toxicity toward normal cells. Therefore, the objective of this study was to evaluate the therapeutic efficacy of a combination of non-toxic, low dose of 5-aza 2′ dC with EGCG, on growth inhibition of breast cancer cells. Human breast cancer cell lines (MCF-7, MDA-MB 231) and non-tumorigenic MCF-10A breast epithelial cells were treated with either 5-aza 2′ dC, EGCG, or their combination for 7 days. Cell growth inhibition was determined by cell count, cell viability, cell cycle, and soft agar assay, whereas genes expression changes were determined by quantitative real-time PCR and/or Western blot analysis. Histone modifications and global DNA methylation changes were determined by Western blot and RAPD-PCR, respectively. The results revealed significantly greater inhibition of growth of breast cancer cells by co-treatment with 5-aza 2′ dC and EGCG compared to individual treatments, whereas it has no significant toxicity to MCF-10A cells. This was further confirmed by gene expression analysis. Changes in DNA methylation and histone modifications were also greater in cells with combination treatment. Findings of this study suggest that potentiation of growth inhibition of breast cancer cells by 5-aza 2′ dC and EGCG combination treatment, at least in part, is mediated by epigenetic mechanism.
Breast cancer is the most common cancer in women for which doxorubicin is still the mainstay treatment. However, chemotherapy resistance is a major limitation in breast cancer treatment. Role of ...treatment schedule and estrogen receptor (ER) status in subtypes of breast cancers in acquired resistance development is not clear. Therefore, objective of this study was to evaluate whether the treatment schedule and ER status in breast cancer cells influence the doxorubicin resistance. To address these questions, ER-positive MCF-7 and triple-negative MDA-MB-231 breast cancer cell lines were given either continuous or intermittent exposure with clinically relevant concentration of doxorubicin and the influence of these two treatment strategies on resistance to drug sensitivity was evaluated. Results revealed that intermittent treatment but not the continuous treatment induced resistance in breast cancer cells against doxorubicin. MCF-7 cells developed relatively earlier and high level of resistance when compared to MDA-MB-231 cells. Acquisition of epithelial to mesenchymal transition (EMT) and cancer stem cell-like phenotype was also observed during resistance development in MCF-7 cells. Changes in the expression of selected marker genes including drug transporters confirmed doxorubicin resistance in these cells. In summary, this study suggests that acquisition of resistance against doxorubicin depends on the treatment schedule of this drug as well as the estrogen receptor-based subtypes of breast cancer. Additionally, acquisition of EMT and stem cell-like phenotype further provided a molecular basis for breast cancer subtype-dependent chemotherapeutic resistance development. Findings of this study will have significant clinical implications in optimizing the chemotherapy schedule to minimize chemoresistance in breast cancer patients.
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Renal cell carcinoma is the most common form of kidney cancer and is highly resistant to chemotherapy. Although the role of oxidative stress in kidney cancer is known, the chemotherapeutic response ...of cancer cells adapted to chronic oxidative stress is not clear. Hence, the effect of oxidative stress on sensitivity to doxorubicin-induced cytotoxicity was evaluated using an in vitro model of human kidney cancer cells adapted to chronic oxidative stress. Results of MTT- and anchorage-independent growth assays and cell cycle analysis revealed significant decrease in sensitivity to doxorubicin in Caki-1 cells adapted to oxidative stress. Changes in the expression of genes involved in drug transport, cell survival, and DNA repair-dependent apoptosis further confirmed increased resistance to doxorubicin-induced cytotoxicity in these cells. Decreased expression of mismatch repair (MMR) gene MSH2 in cells exposed to oxidative stress suggests that loss of MMR-dependent apoptosis could be a potential mechanism for increased resistance to doxorubicin-induced cytotoxicity. Additionally, downregulation of HDAC1, an increase in the level of histone H3 acetylation, and hypermethylation of MSH2 promoter were also observed in Caki-1 cells adapted to chronic oxidative stress. DNA-demethylating agent 5-Aza-2dC significantly restored the expression of MSH2 and doxorubicin-induced cytotoxicity in Caki-1 cells adapted to chronic oxidative stress, suggesting the role of DNA hypermethylation in inactivation of MSH2 expression and consequently MMR-dependent apoptosis in these cells. In summary, this study for the first time provides direct evidence for the role of oxidative stress in chemotherapeutic resistance in renal carcinoma cells potentially through epigenetic mechanism.
Acquired resistance against doxorubicin is a major limitation in clinical treatment of breast cancer. The molecular mechanism behind the aberrant expression of genes leading to doxorubicin resistance ...is not clear. Epigenetic changes play an important role in the regulation of gene expression. Therefore, the objective of this study was to identify the epigenetic mechanism underlying acquired doxorubicin resistance in breast cancer cells. Doxorubicin-resistant cells were selected by repeated exposure of MCF-7 and MDA-MB-231 breast cancer cell lines to clinically relevant doses of doxorubicin for 18 months. MTT assay, cell cycle analysis, colony formation, qRT-PCR, and Western blot analyses were used to characterize the epigenetic and molecular mechanism. Pyrosequencing was used to detect MSH2 promoter hypermethylation. Aberrant expression of epigenetic regulatory genes, a significant increase in H3 acetylation and methylation, as well as promoter hypermethylation-mediated inactivation of MSH2 gene were associated with the acquired resistant phenotype. Demethylating agent 5-Aza-deoxycytidine and HDAC inhibitor Trichostatin A significantly re-sensitized resistant cells to doxorubicin. Findings of this study revealed that epigenetic aberrations including promoter hypermethylation-mediated inactivation MSH2 contribute to the acquisition of doxorubicin resistance in breast cancer cells. Additionally, our data suggest that some of these epigenetic aberrations are progressive during resistance development and therefore can potentially be used as biomarkers for early detection of resistance. These epigenetic aberrations, being reversible, can also serve as targets for epigenetic therapy to re-sensitize doxorubicin-resistant breast cancer cells. Epigenetic inactivation of mismatch repair gene MSH2 further suggests that loss of MMR-dependent apoptotic potential could be a novel mechanistic basis for the acquisition of doxorubicin resistance in breast cancer cells.
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Chemotherapy is the most common clinical choice of treatment for cancer, however, acquired chemoresistance is a major challenge that limits the successful outcome of this option. Systematic review of ...in vitro, in vivo, preclinical and clinical studies suggests that acquired chemoresistance is polygenic, progressive, and involve both genetic and epigenetic heterogeneities and perturbations. Various mechanisms that confer resistance to chemotherapy are tightly controlled by epigenetic regulations. Poised epigenetic plasticity and temporal increase in epigenetic alterations upon chemotherapy make chemoresistance likely an epigenetic-driven process. The transient and reversible nature of epigenetic modulations enable ways to intervene the epigenetic re-programing associated with acquired chemoresistance via application of epigenetic modifying drugs. This review discusses recent understandings behind the various mechanisms of acquired chemoresistance that are under the control of epigenetic drivers, potential application of epigenetic-based drugs in resensitizing refractory cancers to chemotherapy, the limitations and future scope for clinical application of epigenetic therapeutics in successfully addressing chemoresistance.
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