DNA demethylation in the PTEN gene promoter induced by 5-azacytidine activates PTEN expression in the MG-63 human osteosarcoma cell line

Blue light photobiomodulation induced apoptosis by increasing ROS level and regulating SOCS3 and PTEN/PI3K/AKT pathway in osteosarcoma cells

Blue light photobiomodulation (PBM) has attracted great attention in diminishing proliferation and inducing death of cancer cells recently. Osteosarcoma (OS) primarily occurring in children and adolescents, the limitations of drug resistance and limb salvage make it urgent to develop and identify new adjuvant therapeutic strategies. In this work, we attempted to research the anticancer effects and biological mechanisms of blue light PBM in human OS MG63 cells. The effects of various blue light parameters on MG63 cells indicated that suppressed cell proliferation and cell migration, induced cell apoptosis which are experimentally assessed using multiple assays including CCK, LDH, wound healing assay and Hoechst staining. Concurrently, the increases of ROS level and the inhibition of PI3K and AKT expression were identified under high-dose blue light PBM in MG63 cells. Meanwhile, SOCS3 is a major inducible anti-tumor molecule, we also found that blue light LED substantially promoted its expression. Thus, this study proposed that bule light PBM may be a hopeful therapeutic approach in OS clinical treatment in the future.

New emerging targets in osteosarcoma therapy: PTEN and PI3K/Akt crosstalk in carcinogenesis

Osteosarcoma (OS) is a malignant bone carcinoma that affects people in childhood and adulthood. The heterogeneous nature and chromosomal instability represent certain characteristics of OS cells. These cancer cells grow and migrate abnormally, making the prognosis undesirable for patients. Conventional and current treatments fail to completely eradicate tumor cells, so new therapeutics targeting genes may be considered. PI3K/Akt is a regulator of events such as growth, cell death, migration, and differentiation, and its expression changes during cancer progression. PTEN reduces PI3K/Akt expression, and its mutations and depletions have been reported in various tumors. Experimental evidence shows that there is upregulation of PI3K/Akt and downregulation of PTEN in OS. Increasing PTEN expression may suppress PI3K/Akt to minimize tumorigenesis. In addition, PI3K/Akt shows a positive association with growth, metastasis, EMT and metabolism of OS cells and inhibits apoptosis. Importantly, overexpression of PI3K/Akt causes drug resistance and radio-resistance and its level can be modulated by miRNAs, lncRNAs and circRNAs. Silencing PI3K/Akt by compounds and drugs can suppress OS. Here, we review in detail the function of the PTEN/PI3K/Akt in OS, revealing its biological function, function in tumor progression, resistance to therapy, and pharmacological significance.

Understanding and targeting anoikis in metastasis for cancer therapies

The development of effective treatments for cancers requires investigations for a more detailed and comprehensive understanding of the basic cellular mechanisms involved in carcinogenesis, cancer progression, and metastasis. One of those driving mechanisms is anoikis, a special type of apoptosis, which is induced by losing anchorage from the extracellular matrix (ECM). In other words, resisting death in detached cells (cells without ECM) forms an anoikis-resistant phenotype. Since the anoikis-resistance state compensates for the initial steps of cancer metastasis, this review aimed to discuss mechanisms of gaining anoikis/anoikis resistance phenotype in tumor cells. Finally, we highlighted the significance of anoikis in malignancies so as to provide clear insight into cancer diagnosis and therapy development.

Epigenetic Small-Molecule Modulators Targeting Metabolic Pathways in Cancer

Metabolic deregulation is a key factor in cancer progression. Epigenetic changes and metabolic rewiring are intertwined in cancer. Deregulated epigenetic modifiers cause metabolic aberrations by targeting the expression of metabolic enzymes. Conversely, metabolites and cofactors affect the expression and activity of epigenetic regulators. Small molecules are promising therapeutic approaches to target the epigenetic-metabolomic crosstalk in cancer. Here, we focus on the interplay between metabolic rewiring and epigenetic landscape in the context of tumourigenesis and highlight recent advances in the use of small-molecule drug targets for therapy.

HDAC6 inhibitor WT161 performs anti-tumor effect on osteosarcoma and synergistically interacts with 5-FU

BACKGROUND

WT161, as a selective HDAC6 inhibitor, has been shown to play anti-tumor effects on several kinds of cancers. The aim of the present study is to explore the roles of WT161 in osteosarcoma and its underlying mechanisms.

METHODS

The anti-proliferative effect of WT161 on osteosarcoma cells was examined using MTT assay and colony formation assay. Cell apoptosis was analyzed using flow cytometer. The synergistic effect was evaluated by isobologram analysis using CompuSyn software. The osteosarcoma xenograft models were established to evaluate the anti-proliferative effect of WT161 in vivo.

RESULTS

WT161 suppressed the cell growth and induced apoptosis of osteosarcoma cells in a dose- and time-dependent manner. Mechanistically, we found that WT161 treatment obviously increased the protein level of PTEN and decreased the phosphorylation level of protein kinase-B (AKT). More importantly, WT161 showed synergistic inhibition with 5-FU on osteosarcoma cells in vitro and in vivo.

CONCLUSIONS

These results indicate that WT161 inhibits the growth of osteosarcoma through PTEN and has a synergistic efficiency with 5-FU.

PTEN in osteosarcoma: Recent advances and the therapeutic potential

Osteosarcoma is the most common primary malignant bone tumor, predominantly occurring in children and adolescents. Despite treated with surgery and neoadjuvant chemotherapy, osteosarcoma has a high potential of local recurrence and lung metastasis. Overall survival rates for osteosarcoma have plateaued in the past four decades, therefore, identification of novel targets and development of more effective treatment strategies are urgent. Phosphatase and tensin homolog (PTEN) is a tumor suppressor gene that negatively regulates the phosphatidylinositol 3-kinase (PI3K)/ protein kinase B (AKT)/ mammalian target of rapamycin (mTOR) pathway. Over half of clinical osteosarcoma samples presented loss or low expression of PTEN, which usually indicated an advanced stage of tumor and a poor prognosis. The expression of PTEN is regulated by epigenetic silence, transcription regulation, post-translational modifications, and protein interactions in osteosarcoma. Therefore, explicating regulations to restore the anti-tumor function of PTEN might provide novel targeted therapies for osteosarcoma. Preclinical evidence suggested directly targeting the altered PTEN in osteosarcoma was promising. Current clinical application of PTEN related therapies in osteosarcoma are PI3K/mTOR inhibitors, and these drugs have shown the favorable efficacy in patients with advanced osteosarcoma.

High Throughput Screen Identifies the DNMT1 (DNA Methyltransferase-1) Inhibitor, 5-Azacytidine, as a Potent Inducer of PTEN (Phosphatase and Tensin Homolog): Central Role for PTEN in 5-Azacytidine Protection Against Pathological Vascular Remodeling

OBJECTIVE

Our recent work demonstrates that PTEN (phosphatase and tensin homolog) is an important regulator of smooth muscle cell (SMC) phenotype. SMC-specific PTEN deletion promotes spontaneous vascular remodeling and PTEN loss correlates with increased atherosclerotic lesion severity in human coronary arteries. In mice, PTEN overexpression reduces plaque area and preserves SMC contractile protein expression in atherosclerosis and blunts Ang II (angiotensin II)-induced pathological vascular remodeling, suggesting that pharmacological PTEN upregulation could be a novel therapeutic approach to treat vascular disease. Approach and Results: To identify novel PTEN activators, we conducted a high-throughput screen using a fluorescence based PTEN promoter-reporter assay. After screening ≈3400 compounds, 11 hit compounds were chosen based on level of activity and mechanism of action. Following in vitro confirmation, we focused on 5-azacytidine, a DNMT1 (DNA methyltransferase-1) inhibitor, for further analysis. In addition to PTEN upregulation, 5-azacytidine treatment increased expression of genes associated with a differentiated SMC phenotype. 5-Azacytidine treatment also maintained contractile gene expression and reduced inflammatory cytokine expression after PDGF (platelet-derived growth factor) stimulation, suggesting 5-azacytidine blocks PDGF-induced SMC de-differentiation. However, these protective effects were lost in PTEN-deficient SMCs. These findings were confirmed in vivo using carotid ligation in SMC-specific PTEN knockout mice treated with 5-azacytidine. In wild type controls, 5-azacytidine reduced neointimal formation and inflammation while maintaining contractile protein expression. In contrast, 5-azacytidine was ineffective in PTEN knockout mice, indicating that the protective effects of 5-azacytidine are mediated through SMC PTEN upregulation.

CONCLUSIONS

Our data indicates 5-azacytidine upregulates PTEN expression in SMCs, promoting maintenance of SMC differentiation and reducing pathological vascular remodeling in a PTEN-dependent manner.

Epigenetic reprogramming underlies efficacy of DNA demethylation therapy in osteosarcomas

Osteosarcoma (OS) patients with metastasis or recurrent tumors still suffer from poor prognosis. Studies have indicated the efficacy of DNA demethylation therapy for OS, but the underlying mechanism is still unclear. Here, we aimed to clarify the mechanism of how epigenetic therapy has therapeutic efficacy in OS. Treatment of four OS cell lines with a DNA demethylating agent, 5-aza-2′-deoxycytidine (5-aza-dC) treatment, markedly suppressed their growth, and in vivo efficacy was further confirmed using two OS xenografts. Genome-wide DNA methylation analysis showed that 10 of 28 primary OS had large numbers of methylated CpG islands while the remaining 18 OS did not, clustering together with normal tissue samples and Ewing sarcoma samples. Among the genes aberrantly methylated in primary OS, genes involved in skeletal system morphogenesis were present. Searching for methylation-silenced genes by expression microarray screening of two OS cell lines after 5-aza-dC treatment revealed that multiple tumor-suppressor and osteo/chondrogenesis-related genes were re-activated by 5-aza-dC treatment of OS cells. Simultaneous activation of multiple genes related to osteogenesis and cell proliferation, namely epigenetic reprogramming, was considered to underlie the efficacy of DNA demethylation therapy in OS.

The correlation between the methylation of PTEN gene and the apoptosis of osteosarcoma cells mediated by SeHA nanoparticles

The invasive spreading of residual osteosarcoma cells becomes a serious threat to human health, urgently needing new bone regenerative biomaterials for orthopedic therapy. Thus, in this work, selenite-substituted hydroxyapatite (SeHA) nanoparticles were prepared for both inhibiting the recurrence of the tumor and accelerating the regenerative repair of bone defect. Physicochemical characterization showed these synthetic nanoparticles were spherical poly-crystals with the shape of snowflakes. Such structure benefited them to inhibit the cellular viability of osteosarcoma cells by about (58.90 ± 14.37)% during 24 h co-culturing. The expression level of cell growth-related genes such as PTEN, MMP-9, Cyclin D1, Cyclin A2, Annexin A2 and CDC2 decreased. Bisulfite Sequence PCR of PTEN gene exhibited about (22.40 ± 5.39)%, (45.91 ± 6.36)% and (25.90 ± 5.36)% promoter methylation in control, HA and SeHA group. Animal experiment also proved the similar effects. Almost no recurrence were observed in SeHA group. Oppositely, the slowly recurrent growth of the remnant tumor appeared in purely surgical group. The overall survival and toxicity analysis showed that, in the usage dose of 0-0.1 g, the SeHA-0.01 exhibited higher inhibitory recurrence and metastasis potentials, lower renal toxicity and better anti-inflammation function. Immunohistochemistry stain showed the reduced expression of PTEN, MMP-9, Ki-67 and Annexin A2, but slightly increased expression of DNMT1 and BMP-2. Compared the methylation status of PTEN gene in each group, it was confirming that SeHA nanoparticles hardly possessed the de-methylation effect, but the pure HA strikingly increased the methylation level of such gene. It seemed the dopant selenite ions possessed de-methylation effect onto PTEN gene. Therefore, from the viewpoint of inhibiting metastatic potentials, the SeHA-0.01 might be a feasible biomaterial to inhibit the relapse of the tumor post-surgery.

Expression of NF-κB and PTEN in osteosarcoma and its clinical significance

We investigated the role of nuclear factor-κB (NF-κB) and phosphatase and tensin homolog deleted in chromosome 10 (PTEN) in the pathogenesis of osteosarcoma and its relationship with prognosis. Immunohistochemical method was used to detect the expression of NF-κB and PTEN in osteosarcoma and adjacent tissues. RT-PCR was used to detect the expression of NF-κB and PTEN mRNA in osteosarcoma and adjacent tissues. Western blotting was used to detect the expression of NF-κB and PTEN in osteosarcoma and adjacent tissues and compare their differences. The expression of NF-κB and PTEN was detected in osteosarcoma and adjacent tissues. The positive rate of NF-κB was 75.3 and 32.9%, respectively; while the positive rate of PTEN was 67.1 and 90.4%, respectively. The positive expression of NF-κB and PTEN was statistically significant. There was a negative correlation between NF-κB and PTEN expression (r=-0.502, p<0.05). The positive and negative expression of NF-κB and PTEN was statistically significant for the five-year survival (p<0.05). At gene and protein level, osteosarcoma tissues had higher expression of NF-κB, and lower expression of PTEN, which was significantly different from the adjacent tissues. In osteosarcoma, NF-κB is highly expressed, but PTEN is expressed at low level, and the two are negatively correlated. This is of great significance for the early diagnosis of osteosarcoma and prognosis.

Oxymatrine suppresses the growth and invasion of MG63 cells by up-regulating PTEN and promoting its nuclear translocation

Studies demonstrated that reduced PTEN levels are associated with poor prognoses of osteosarcoma. The nuclear localization of PTEN is important for its tumor suppressive function. Equally importantly, PTEN is the most significant negative regulator of PI3K/Akt signaling cascade, the constitutively activated pathway in osteosarcoma. In our study MG63 cells and U2OS cells were treated with the indicated concentrations of oxymatrine, in order to find the inhibition of oxymatrine to cells. We found the functions of oxymatrine on proliferation, apoptosis and invasion in cells. Oxymatrine could increase the expression of PTEN and promote its nuclear translocation in MG63 cells. In addition, oxymatrine could induce cell cycle arrest in G1 phase and apoptosis of MG63 cells. The migration and invasion potential of MG63 cells were also markedly inhibited by oxymatrine. Oxymatrine could suppress the growth and invasion of MG63 human osteosarcoma cells by up-regulating PTEN and promoting its nuclear translocation and inhibiting PI3K/Akt signaling pathway.

Epigenetic DNA Demethylation Causes Inner Ear Stem Cell Differentiation into Hair Cell-Like Cells

The DNA methyltransferase (DNMT) inhibitor 5-azacytidine (5-aza) causes genomic demethylation to regulate gene expression. However, it remains unclear whether 5-aza affects gene expression and cell fate determination of stem cells. In this study, 5-aza was applied to mouse utricle sensory epithelia-derived progenitor cells (MUCs) to investigate whether 5-aza stimulated MUCs to become sensory hair cells. After treatment, MUCs increased expression of hair cell genes and proteins. The DNA methylation level (indicated by percentage of 5-methylcytosine) showed a 28.57% decrease after treatment, which causes significantly repressed DNMT1 protein expression and DNMT activity. Additionally, FM1-43 permeation assays indicated that the permeability of 5-aza-treated MUCs was similar to that of sensory hair cells, which may result from mechanotransduction channels. This study not only demonstrates a possible epigenetic approach to induce tissue specific stem/progenitor cells to become sensory hair cell-like cells, but also provides a cell model to epigenetically modulate stem cell fate determination.

Concerted changes in transcriptional regulation of genes involved in DNA methylation, demethylation, and folate-mediated one-carbon metabolism pathways in the NCI-60 cancer cell line panel in response to cancer drug treatment

BACKGROUND

Aberrant patterns of DNA methylation are abundant in cancer, and epigenetic pathways are increasingly being targeted in cancer drug treatment. Genetic components of the folate-mediated one-carbon metabolism pathway can affect DNA methylation and other vital cell functions, including DNA synthesis, amino acid biosynthesis, and cell growth.

RESULTS

We used a bioinformatics tool, the Transcriptional Pharmacology Workbench, to analyze temporal changes in gene expression among epigenetic regulators of DNA methylation and demethylation, and one-carbon metabolism genes in response to cancer drug treatment. We analyzed gene expression information from the NCI-60 cancer cell line panel after treatment with five antitumor agents, 5-azacytidine, doxorubicin, vorinostat, paclitaxel, and cisplatin. Each antitumor agent elicited concerted changes in gene expression of multiple pathway components across the cell lines. Expression changes of FOLR2, SMUG1, GART, GADD45A, MBD1, MTR, MTHFD1, and CTH were significantly correlated with chemosensitivity to some of the agents. Among many genes with concerted expression response to individual antitumor agents were genes encoding DNA methyltransferases DNMT1, DNMT3A, and DNMT3B, epigenetic and DNA repair factors MGMT, GADD45A, and MBD1, and one-carbon metabolism pathway members MTHFD1, TYMS, DHFR, MTR, MAT2A, SLC19A1, ATIC, and GART.

CONCLUSIONS

These transcriptional changes are likely to influence vital cellular functions of DNA methylation and demethylation, cellular growth, DNA biosynthesis, and DNA repair, and some of them may contribute to cytotoxic and apoptotic action of the drugs. This concerted molecular response was observed in a time-dependent manner, which may provide future guidelines for temporal selection of genetic drug targets for combination drug therapy treatment regimens.

Low concentrations of 5-aza-2'-deoxycytidine induce breast cancer stem cell differentiation by triggering tumor suppressor gene expression

Background

Breast cancer stem cells (BCSCs) are considered the cause of tumor growth, multidrug resistance, metastasis, and recurrence. Therefore, differentiation therapy to reduce self-renewal of BCSCs is a promising approach. We have examined the effects of 5-aza-2′-deoxycytidine (DAC) on BCSC differentiation.

Materials and methods

BCSCs were treated with a range of DAC concentrations from 0.625 to 100 µM. The differentiation status of DAC-treated BCSCs was graded by changes in cell proliferation, CD44⁺CD24⁻ phenotype, expression of tumor suppressor genes, including BRCA1, BRCA2, p15, p16, p53, and PTEN, and antitumor drug resistance.

Results

DAC treatment caused significant BCSC differentiation. BCSCs showed a 15%–23% reduction in proliferation capacity, 3.0%–21.3% decrease in the expression of BCSC marker CD44⁺/CD24⁻, activation of p53 expression, and increased p15, p16, BRCA1, and BRCA2 expression. Concentrations of DAC ranging from 0.625 to 40 µM efficiently induce cell cycle arrest in S-phase. ABCG2, highly expressed in BCSCs, also decreased with DAC exposure. Of particular note, drug-sensitivity of BCSCs to doxorubicin, verapamil, and tamoxifen also increased 1.5-, 2.0-, and 3.7-fold, respectively, after pretreatment with DAC.

Conclusion

DAC reduced breast cancer cell survival and induced differentiation through reexpression of tumor suppressor genes. These results indicate the potential of DAC in targeting specific chemotherapy-resistant cells within a tumor.

MicroRNA-1908 is upregulated in human osteosarcoma and regulates cell proliferation and migration by repressing PTEN expression

Osteosarcoma is a high-grade malignant bone neoplasm. Although the introduction of chemotherapy has reduced its mortality, >50% of patients develop chemoresistance and have an extremely poor prognosis due to pulmonary metastasis. Several molecular pathways contributing to osteosarcoma development and progression have recently been identified. Various studies have addressed the genes involved in the metastasis of osteosarcoma. However, the highly complex molecular mechanisms of metastasis remain to be elucidated. Recent studies have emphasized causative links between aberrant microRNA expression patterns and osteosarcoma progression. miR-1908 is dysregulated in certain human types of cancer. The expression pattern, clinical significance and biological role of miR-1908 in osteosarcoma, however, remain largely undefined. In the present study, we showed that miR-1908 was markedly upregulated in osteosarcoma cells and tissues compared with normal bone tissues using RT-qPCR. miR-1908 upregulation in osteosarcoma tissues was significantly associated with cell proliferation, invasion, advanced TNM stage and tumor growth. Both gain- and loss-of-function studies showed that miR-1908 markedly increased the ability of osteosarcoma cells to proliferate and to invade through Matrigel in vitro. Analyses using mouse xenograft model revealed that xenografts of miR-1908 stable-expressing osteosarcoma cells exhibited a significant increase in tumor volume and weight, compared with the control group. Subsequent investigations revealed that miR-1908 directly inhibited the expression of phosphatase and tensin homolog deleted on chromosome ten (PTEN). Using a luciferase reporter carrying the 3'-untranslated region (3'-UTR) of PTEN, we identified PTEN as a direct target of miR-1908. Collectively, the results showed that, miR-1908 promotes proliferation and invasion of osteosarcoma cells by repressing PTEN expression.

Anoikis-resistant subpopulations of human osteosarcoma display significant chemoresistance and are sensitive to targeted epigenetic therapies predicted by expression profiling

Background

Osteosarcoma (OS) is the most common type of solid bone cancer, with latent metastasis being a typical mode of disease progression and a major contributor to poor prognosis. For this to occur, cells must resist anoikis and be able to recapitulate tumorigenesis in a foreign microenvironment. Finding novel approaches to treat osteosarcoma and target those cell subpopulations that possess the ability to resist anoikis and contribute to metastatic disease is imperative. Here we investigate anchorage-independent (AI) cell growth as a model to better characterize anoikis resistance in human osteosarcoma while using an expression profiling approach to identify and test targetable signaling pathways.

Methods

Established human OS cell lines and patient-derived human OS cell isolates were subjected to growth in either adherent or AI conditions using Ultra-Low Attachment plates in identical media conditions. Growth rate was assessed using cell doubling times and chemoresistance was assessed by determining cell viability in response to a serial dilution of either doxorubicin or cisplatin. Gene expression differences were examined using quantitative reverse-transcription PCR and microarray with principal component and pathway analysis. In-vivo OS xenografts were generated by either subcutaneous or intratibial injection of adherent or AI human OS cells into athymic nude mice. Statistical significance was determined using student’s t-tests with significance set at α = 0.05.

Results

We show that AI growth results in a global gene expression profile change accompanied by significant chemoresistance (up to 75 fold, p < 0.05). AI cells demonstrate alteration of key mediators of mesenchymal differentiation (β-catenin, Runx2), stemness (Sox2), proliferation (c-myc, Akt), and epigenetic regulation (HDAC class 1). AI cells were equally tumorigenic as their adherent counterparts, but showed a significantly decreased rate of growth in-vitro and in-vivo (p < 0.05). Treatment with the pan-histone deacetylase inhibitor vorinostat and the DNA methyltransferase inhibitor 5-azacytidine mitigated AI growth, while 5-azacytidine sensitized anoikis-resistant cells to doxorubicin (p < 0.05).

Conclusions

These data demonstrate remarkable plasticity in anoikis-resistant human osteosarcoma subpopulations accompanied by a rapid development of chemoresistance and altered growth rates mirroring the early stages of latent metastasis. Targeting epigenetic regulation of this process may be a viable therapeutic strategy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12967-015-0466-4) contains supplementary material, which is available to authorized users.

PI3K/Akt signaling in osteosarcoma

Osteosarcoma (OS) is the most common nonhematologic bone malignancy in children and adolescents. Despite the advances of adjuvant chemotherapy and significant improvement of survival, the prognosis remains generally poor. As such, the search for more effective anti-OS agents is urgent. The phosphatidylinositol 3-kinase (PI3K)/Akt pathway is thought to be one of the most important oncogenic pathways in human cancer. An increasing body of evidence has shown that this pathway is frequently hyperactivated in OS and contributes to disease initiation and development, including tumorigenesis, proliferation, invasion, cell cycle progression, inhibition of apoptosis, angiogenesis, metastasis and chemoresistance. Inhibition of this pathway through small molecule compounds represents an attractive potential therapeutic approach for OS. The aim of this review is to summarize the roles of the PI3K/Akt pathway in the development and progression of OS, and to highlight the therapeutic potential of targeting this signaling pathway. Knowledge obtained from the application of these compounds will help in further understanding the pathogenesis of OS and designing subsequent treatment strategies.