Inhibitory effects of epigenetic modulators and differentiation inducers on human medulloblastoma cell lines

Modulation of Stemness and Differentiation Regulators by Valproic Acid in Medulloblastoma Neurospheres

Changes in epigenetic processes such as histone acetylation are proposed as key events influencing cancer cell function and the initiation and progression of pediatric brain tumors. Valproic acid (VPA) is an antiepileptic drug that acts partially by inhibiting histone deacetylases (HDACs) and could be repurposed as an epigenetic anticancer therapy. Here, we show that VPA reduced medulloblastoma (MB) cell viability and led to cell cycle arrest. These effects were accompanied by enhanced H3K9 histone acetylation (H3K9ac) and decreased expression of the MYC oncogene. VPA impaired the expansion of MB neurospheres enriched in stemness markers and reduced MYC while increasing TP53 expression in these neurospheres. In addition, VPA induced morphological changes consistent with neuronal differentiation and the increased expression of differentiation marker genes TUBB3 and ENO2. The expression of stemness genes SOX2, NES, and PRTG was differentially affected by VPA in MB cells with different TP53 status. VPA increased H3K9 occupancy of the promoter region of TP53. Among the genes regulated by VPA, the stemness regulators MYC and NES showed an association with patient survival in specific MB subgroups. Our results indicate that VPA may exert antitumor effects in MB by influencing histone acetylation, which may result in the modulation of stemness, neuronal differentiation, and the expression of genes associated with patient prognosis in specific molecular subgroups. Importantly, the actions of VPA in MB cells and neurospheres include a reduction in the expression of MYC and an increase in TP53.

Human endogenous retrovirus K contributes to a stem cell niche in glioblastoma

Human endogenous retroviruses (HERVs) are ancestral viral relics that constitute nearly 8% of the human genome. Although normally silenced, the most recently integrated provirus HERV-K (HML-2) can be reactivated in certain cancers. Here, we report pathological expression of HML-2 in malignant gliomas in both cerebrospinal fluid and tumor tissue that was associated with a cancer stem cell phenotype and poor outcomes. Using single-cell RNA-Seq, we identified glioblastoma cellular populations with elevated HML-2 transcripts in neural progenitor-like cells (NPC-like) that drive cellular plasticity. Using CRISPR interference, we demonstrate that HML-2 critically maintained glioblastoma stemness and tumorigenesis in both glioblastoma neurospheres and intracranial orthotopic murine models. Additionally, we demonstrate that HML-2 critically regulated embryonic stem cell programs in NPC-derived astroglia and altered their 3D cellular morphology by activating the nuclear transcription factor OCT4, which binds to an HML-2-specific long-terminal repeat (LTR5Hs). Moreover, we discovered that some glioblastoma cells formed immature retroviral virions, and inhibiting HML-2 expression with antiretroviral drugs reduced reverse transcriptase activity in the extracellular compartment, tumor viability, and pluripotency. Our results suggest that HML-2 fundamentally contributes to the glioblastoma stem cell niche. Because persistence of glioblastoma stem cells is considered responsible for treatment resistance and recurrence, HML-2 may serve as a unique therapeutic target.

Imidazolyl Ethanamide Pentandioic Acid (IEPA) as Potential Radical Scavenger during Tumor Therapy in Human Hematopoietic Stem Cells

Radiochemotherapy-associated leuco- or thrombocytopenia is a common complication, e.g., in head and neck cancer (HNSCC) and glioblastoma (GBM) patients, often compromising treatments and outcomes. Currently, no sufficient prophylaxis for hematological toxicities is available. The antiviral compound imidazolyl ethanamide pentandioic acid (IEPA) has been shown to induce maturation and differentiation of hematopoietic stem and progenitor cells (HSPCs), resulting in reduced chemotherapy-associated cytopenia. In order for it to be a potential prophylaxis for radiochemotherapy-related hematologic toxicity in cancer patients, the tumor-protective effects of IEPA should be precluded. In this study, we investigated the combinatorial effects of IEPA with radio- and/or chemotherapy in human HNSCC and GBM tumor cell lines and HSPCs. Treatment with IEPA was followed by irradiation (IR) or chemotherapy (ChT; cisplatin, CIS; lomustine, CCNU; temozolomide, TMZ). Metabolic activity, apoptosis, proliferation, reactive oxygen species (ROS) induction, long-term survival, differentiation capacity, cytokine release, and DNA double-strand breaks (DSBs) were measured. In tumor cells, IEPA dose-dependently diminished IR-induced ROS induction but did not affect the IR-induced changes in metabolic activity, proliferation, apoptosis, or cytokine release. In addition, IEPA showed no protective effect on the long-term survival of tumor cells after radio- or chemotherapy. In HSPCs, IEPA alone slightly enhanced CFU-GEMM and CFU-GM colony counts (2/2 donors). The IR- or ChT-induced decline of early progenitors could not be reversed by IEPA. Our data indicate that IEPA is a potential candidate for the prevention of hematologic toxicity in cancer treatment without affecting therapeutic benefits.

Enhanced Survival of High-Risk Medulloblastoma-Bearing Mice after Multimodal Treatment with Radiotherapy, Decitabine, and Abacavir

Children with high-risk SHH/TP53-mut and Group 3 medulloblastoma (MB) have a 5-year overall survival of only 40%. Innovative approaches to enhance survival while preventing adverse effects are urgently needed. We investigated an innovative therapy approach combining irradiation (RT), decitabine (DEC), and abacavir (ABC) in a patient-derived orthotopic SHH/TP53-mut and Group 3 MB mouse model. MB-bearing mice were treated with DEC, ABC and RT. Mouse survival, tumor growth (BLI, MRT) tumor histology (H/E), proliferation (Ki-67), and endothelial (CD31) staining were analyzed. Gene expression was examined by microarray and RT-PCR (Ki-67, VEGF, CD31, CD15, CD133, nestin, CD68, IBA). The RT/DEC/ABC therapy inhibited tumor growth and enhanced mouse survival. Ki-67 decreased in SHH/TP53-mut MBs after RT, DEC, RT/ABC, and RT/DEC/ABC therapy. CD31 was higher in SHH/TP53-mut compared to Group 3 MBs and decreased after RT/DEC/ABC. Microarray analyses showed a therapy-induced downregulation of cell cycle genes. By RT-PCR, no therapy-induced effect on stem cell fraction or immune cell invasion/activation could be shown. We showed for the first time that RT/DEC/ABC therapy improves survival of orthotopic SHH/TP53-mut and Group 3 MB-bearing mice without inducing adverse effects suggesting the potential for an adjuvant application of this multimodal therapy approach in the human clinic.

Epigenetic-Based Therapy-A Prospective Chance for Medulloblastoma Patients' Recovery

Medulloblastoma (MB) is one of the most frequent and malignant brain tumors in children. The prognosis depends on the advancement of the disease and the patient's age. Current therapies, which include surgery, chemotherapy, and irradiation, despite being quite effective, cause significant side effects that influence the central nervous system's function and cause neurocognitive deficits. Therefore, they substantially lower the quality of life, which is especially severe in a developing organism. Thus, there is a need for new therapies that are less toxic and even more effective. Recently, knowledge about the epigenetic mechanisms that are responsible for medulloblastoma development has increased. Epigenetics is a phenomenon that influences gene expression but can be easily modified by external factors. The best known epigenetic mechanisms are histone modifications, DNA methylation, or noncoding RNAs actions. Epigenetic mechanisms comprehensively explain the complex phenomena of carcinogenesis. At the same time, they seem to be a potential key to treating medulloblastoma with fewer complications than past therapies. This review presents the currently known epigenetic mechanisms that are involved in medulloblastoma pathogenesis and the potential therapies that use epigenetic traits to cure medulloblastoma while maintaining a good quality of life and ensuring a higher median overall survival rate.

Specific Protein 1 and p53 Interplay Modulates the Expression of the KCTD-Containing Cullin3 Adaptor Suppressor of Hedgehog 2

The Hedgehog (Hh) signaling pathway plays a crucial role in normal embryonic development and adult tissue homeostasis. On the other end, dysregulated Hh signaling triggers a prolonged mitogenic response that may prompt abnormal cell proliferation, favoring tumorigenesis. Indeed, about 30% of medulloblastomas (MBs), the most common malignant childhood cerebellar tumors, exhibit improper activation of the Hh signaling. The oncosuppressor KCASH2 has been described as a suppressor of the Hh signaling pathway, and low KCASH2 expression was observed in Hh-dependent MB tumor. Therefore, the study of the modulation of KCASH2 expression may provide fundamental information for the development of new therapeutic approaches, aimed to restore physiological KCASH2 levels and Hh inhibition. To this end, we have analyzed the TATA-less KCASH2 proximal promoter and identified key transcriptional regulators of this gene: Sp1, a TF frequently overexpressed in tumors, and the tumor suppressor p53. Here, we show that in WT cells, Sp1 binds KCASH2 promoter on several putative binding sites, leading to increase in KCASH2 expression. On the other hand, p53 is involved in negative regulation of KCASH2. In this context, the balance between p53 and Sp1 expression, and the interplay between these two proteins determine whether Sp1 acts as an activator or a repressor of KCASH2 transcription. Indeed, in p53^–/– MEF and p53 mutated tumor cells, we hypothesize that Sp1 drives promoter methylation through increased expression of the DNA methyltransferase 1 (DNMT1) and reduces KCASH2 transcription, which can be reversed by Sp1 inhibition or use of demethylating agents. We suggest therefore that downregulation of KCASH2 expression in tumors could be mediated by gain of Sp1 activity and epigenetic silencing events in cells where p53 functionality is lost. This work may open new venues for novel therapeutic multidrug approaches in the treatment of Hh-dependent tumors carrying p53 deficiency.

Resveratrol Derivative, Trans-3, 5, 4'-Trimethoxystilbene Sensitizes Osteosarcoma Cells to Apoptosis via ROS-Induced Caspases Activation

Numerous studies have shown that resveratrol can induce apoptosis in cancer cells. Trans-3, 5, 4'-trimethoxystilbene (TMS), a novel derivative of resveratrol, is a more potent anticancer compound than resveratrol and can induce apoptosis in cancer cells. Herein, we examined the mechanisms involved in TMS-mediated sensitization of human osteosarcoma (143B) cells to TNF-related apoptosis-inducing ligand- (TRAIL-) induced apoptosis. Our results showed that cotreatment with TSM and TRAIL activated caspases and increased PARP-1 cleavage in 143B cells. Decreasing cellular ROS levels using NAC reversed TSM- and TRAIL-induced apoptosis in 143B cells. NAC abolished the upregulated expression of PUMA and p53 induced by treatment with TRAIL and TSM. Silencing the expression of p53 or PUMA using RNA interference attenuated TSM-mediated sensitization of 143B cells to TRAIL-induced apoptosis. Knockdown of Bax also reversed TSM-induced sensitization of 143B cell to TRAIL-mediated apoptotic cell death. These results indicate that cotreatment with TRAIL and TSM evaluated intracellular ROS level, promoted DNA damage, and activated the Bax/PUMA/p53 pathway, leading to activation of both mitochondrial and caspase-mediated apoptosis in 143B cells. Orthotopic implantation of 143B cells in mice also demonstrated that cotreatment with TRAIL and TSM reversed resistance to apoptosis in cells without obvious adverse effects in normal cells.

Abacavir induces the transcriptional activity of YY1 and other oncogenic transcription factors in gastric cancer cells

Yin Yang 1 (YY1) is a ubiquitous transcription factor with both transcriptional activating and repressing functions. Targeting YY1 is considered as a potential therapeutic strategy for several malignancies. Telomerase Reverse Transcriptase (TERT) is also considered as a potential target for cancer therapeutics. To enable the large-scale screening and identification of potential YY1 targeting drugs, a gastric cancer cell line-based drug screening assay was developed. In a YY1 targeted drug repurpose screen, abacavir sulfate, a nucleoside analog reverse transcriptase inhibitor, known to target TERT was identified to show the feature of activating YY1 mediated transcription. We further explored i) the molecular targets of abacavir, ii) activation pattern of pathways regulated by abacavir in gastric tumors, and iii) therapeutic potential of abacavir for gastric cancer cells. Oncogenic signaling pathways like MYC, HIF1-α, ERK, WNT, E2F, NFκB and NRF1/2 were also found to be highly activated by abacavir. Abacavir was found to have less impact on the viability of gastric cancer cells. Across gastric tumors, we observed the co-activation of TERT, alternative lengthening of telomere (ALT), DNA repair, and the oncogenic pathways MYC, E2F/DP1, ERK, YY1, HIF1α, and NFκB specific gene-sets, in a subset of gastric tumors. The observed connectivity among TERT, DNA repair, and multiple oncogenic pathways indicate the need for the development of combinatorial therapeutics for the gastric tumors with the activated TERT.

Radiosensitizing effects of trabectedin on human A549 lung cancer cells and HT-29 colon cancer cells

Background and Purpose Trabectedin is a unique alkylating agent with promising effects against a range of solid tumors. In this study, we aimed to examine the cytotoxic and radiosensitizing effects of trabectedin on two human epithelial tumor cell lines in vitro, and its effects on DNA repair capacity. Methods Cancer cells (A549: human lung cancer cells, HT-29: colon cancer cells) were treated with either trabectedin alone for the determination of their growth, or in combination with radiation for the determination of their metabolic activity, proliferation, and clonogenic survival. Besides, the γH2AX foci assay was performed for the assessment of ionizing radiation-induced DNA damage and to evaluate the influence of trabectedin on DNA damage repair. Results Treatment with trabectedin resulted in a growth-inhibiting effect on both cell lines, with the IC₅₀ values remaining within a low nanomolar range. Analyses of metabolic activity confirmed a cytotoxic influence of trabectedin and a BrdU assay demonstrated an antiproliferative effect. When combined with radiation, incubation with trabectedin was found to enhance the radiosensitivity of the tumor cells. The γH2AX foci assay resulted in an increased number of DNA double-strand breaks (DSBs) in cells treated with trabectedin. Conclusion The results of this study underline the antitumor activity of trabectedin at low nanomolar concentrations. We demonstrated that trabectedin enhanced radiation response in human lung (A549) cancer cells and colon (HT-29) cancer cells. Further studies are necessary to examine trabectedin as a potential candidate for future applications in radiotherapy.

Application of Small Epigenetic Modulators in Pediatric Medulloblastoma

Medulloblastoma is one of the most frequent among pediatric brain tumors, and it has been classified in various subgroups. Some of them already benefit from quite good therapeutic options, whereas others urgently need novel therapeutic approaches. Epigenetic modulators have long been studied in various types of cancer. Within this review, we summarize the main preclinical studies regarding epigenetic targets (such as HDAC, SIRT, BET, EZH2, G9a, LSD1, and DNMT) inhibitors in medulloblastoma. Furthermore, we shed light on the increasing number of applications of drug combinations as well as hybrid compounds involving epigenetic mechanisms. Nevertheless, in the studies published so far, mainly un-specific or old modulators have been used, and the PKs (brain permeability) have not been well-evaluated. Thus, these findings should be considered as a starting point for further improvement and not as a final result.

Regulation of USP37 Expression by REST-Associated G9a-Dependent Histone Methylation

The deubiquitylase (DUB) USP37 is a component of the ubiquitin system and controls cell proliferation by regulating the stability of the cyclin-dependent kinase inhibitor 1B, (CDKN1B/p27Kip1). The expression of USP37 is downregulated in human medulloblastoma tumor specimens. In the current study, we show that USP37 prevents medulloblastoma growth in mouse orthotopic models, suggesting that it has tumor-suppressive properties in this neural cancer. Here, we also report on the mechanism underlying USP37 loss in medulloblastoma. Previously, we observed that the expression of USP37 is transcriptionally repressed by the RE1 silencing transcription factor (REST), which requires chromatin remodeling factors for its activity. Genetic and pharmacologic approaches were employed to identify a specific role for G9a, a histone methyltransferase (HMT), in promoting methylation of histone H3 lysine-9 (H3K9) mono- and dimethylation, and surprisingly trimethylation, at the USP37 promoter to repress its gene expression. G9a inhibition also blocked the tumorigenic potential of medulloblastoma cells in vivo Using isogenic low- and high-REST medulloblastoma cells, we further showed a REST-dependent elevation in G9a activity, which further increased mono- and trimethylation of histone H3K9, accompanied by downregulation of USP37 expression. Together, these findings reveal a role for REST-associated G9a and histone H3K9 methylation in the repression of USP37 expression in medulloblastoma.Implications: Reactivation of USP37 by G9a inhibition has the potential for therapeutic applications in REST-expressing medulloblastomas. Mol Cancer Res; 15(8); 1073-84. ©2017 AACR.

Synergistic anti-cancer effects of epigenetic drugs on medulloblastoma cells

PURPOSE

Medulloblastomas are aggressive brain malignancies. While considerable progress has been made in the treatment of medulloblastoma patients with respect to overall survival, these patients are still at risk of developing neurologic and cognitive deficits as a result of anti-cancer therapies. It is hypothesized that targeted molecular therapies represent a better treatment option for medulloblastoma patients. Therefore, the aim of the present study was to test a panel of epigenetic drugs for their effect on medulloblastoma cells under mild hypoxic conditions that reflect the physiological concentrations of oxygen in the brain.

METHODS

Protein levels of histone deacetylase 1 (HDAC1) and DNA methyltransferase 1 (DNMT1) in medulloblastoma-derived cells (Daoy and D283 Med), as well as in developing and differentiated brain cells, were determined and compared. Class I and II histone deacetylase inhibitors (HDACi) and a DNMT inhibitor, 5-aza-2'-deoxycytidine (5-aza-dC), were applied to Daoy and D283 Med cells, and their effects were studied using viability, apoptosis and cancer sphere assays.

RESULTS

We found that in HDAC1 and DNMT1 overexpressing medulloblastoma-derived cells, cell death was induced under various epigenetic drug conditions tested. At low HDACi concentrations, however, a pro-proliferative effect was observed. Parthenolide, a drug that affects cancer stem cells, was found to be efficient in inducing cell death in both cell lines tested. In contrast, we found that Daoy cells were more resistant to 5-aza-dC than D283 Med cells. When suberoylanilide hydroxamic acid (SAHA) and parthenolide were individually applied to both cell lines in combination with 5-aza-dC, a synergistic effect on cell survival was observed.

CONCLUSIONS

Our current results suggest that the application of HDACi in combination with drugs that target DNMT may represent a promising option for the treatment of medulloblastoma.

Dose-dependent short- and long-term effects of ionizing irradiation on neural stem cells in murine hippocampal tissue cultures: neuroprotective potential of resveratrol

INTRODUCTION

Radiation therapy plays an essential role in the treatment of brain tumors, but neurocognitive deficits remain a significant risk, especially in pediatric patients. In recent trials, hippocampal sparing techniques are applied to reduce these adverse effects. Here, we investigate dose-dependent effects of ionizing radiation (IR) on juvenile hippocampal neurogenesis. Additionally, we evaluate the radioprotective potential of resveratrol, a plant polyphenol recognized for its bifunctional tumor-preventive and anticancer effects.

METHODS

Organotypic entorhinal-hippocampal slice cultures from transgenic nestin-CFPnuc C57BL/J6 mice, postnatal days 3-6, were irradiated on a X-ray machine (4.5, 8, 12, and 16 Gy, single doses) after about 2 weeks. Nestin-positive neural stem cells were counted at a confocal live imaging microscope 0, 2, 4, 14, 25, and 42 days after IR. Resveratrol (15 μmol/L) was added 2 hr before and 24 hr after IR. Proliferation and cell death were assessed by BrdU pulse label, 48 hr after and by propidium iodide staining 96 hr after IR. GFAP- and NeuN-positive cells were counted 42 days after IR in cryosectioned immunofluorescence-stained slices.

RESULTS

The observed age-related changes of nestin-positive stem cells in the organotypic slice culture model resembled the reduction of neural stem cells in vivo. IR (4.5-16 Gy) led to a dose-dependent damage of the neural stem cell pool in the dentate gyrus. No recovery was seen within 42 days after doses from 4.5 Gy onward. The decline of nestin-positive cells was paralleled by increased cell death and decreased proliferation. The number of GFAP-positive cells was significantly enhanced. No significant change was detected in the overall NeuN-positive cell population, whereas the number of newborn, NeuN/BrdU double-positive neurons was reduced. Resveratrol treatment reversed the irradiation-induced decline of neural stem cells.

CONCLUSION

The neuroprotective action of resveratrol on irradiated hippocampal tissue warrants further investigation as a possible supplement to hippocampal sparing procedures.

Enhanced inhibition of clonogenic survival of human medulloblastoma cells by multimodal treatment with ionizing irradiation, epigenetic modifiers, and differentiation-inducing drugs

Background

Medulloblastoma (MB) is the most common pediatric brain tumor. Current treatment regimes consisting of primary surgery followed by radio- and chemotherapy, achieve 5-year overall survival rates of only about 60 %. Therapy-induced endocrine and neurocognitive deficits are common late adverse effects. Thus, improved antitumor strategies are urgently needed. In this study, we combined irradiation (IR) together with epigenetic modifiers and differentiation inducers in a multimodal approach to enhance the efficiency of tumor therapy in MB and also assessed possible late adverse effects on neurogenesis.

Methods

In three human MB cell lines (DAOY, MEB-Med8a, D283-Med) short-time survival (trypan blue exclusion assay), apoptosis, autophagy, cell cycle distribution, formation of gH2AX foci, and long-term reproductive survival (clonogenic assay) were analyzed after treatment with 5-aza-2′-deoxycytidine (5-azadC), valproic acid (VPA), suberanilohydroxamic acid (SAHA), abacavir (ABC), all-trans retinoic acid (ATRA) and resveratrol (RES) alone or combined with 5-aza-dC and/or IR. Effects of combinatorial treatments on neurogenesis were evaluated in cultured murine hippocampal slices from transgenic nestin-CFPnuc C57BL/J6 mice. Life imaging of nestin-positive neural stem cells was conducted at distinct time points for up to 28 days after treatment start.

Results

All tested drugs showed a radiosynergistic action on overall clonogenic survival at least in two-outof-three MB cell lines. This effect was pronounced in multimodal treatments combining IR, 5-aza-dC and a second drug. Hereby, ABC and RES induced the strongest reduction of clongenic survival in all three MB cell lines and led to the induction of apoptosis (RES, ABC) and/or autophagy (ABC). Additionally, 5-aza-dC, RES, and ABC increased the S phase cell fraction and induced the formation of gH2AX foci at least in oneout-of-three cell lines. Thereby, the multimodal treatment with 5-aza-dC, IR, and RES or ABC did not change the number of normal neural progenitor cells in murine slice cultures.

Conclusion

In conclusion, the radiosensitizing capacities of epigenetic and differentiation-inducing drugs presented here suggest that their adjuvant administration might improve MB therapy. Thereby, the combination of 5-aza-dC/IR with ABC and RES seemed to be the most promising to enhance tumor control without affecting the normal neural precursor cells.

Resveratrol and Malignancies

Carcinogenesis is a multifactorial process, frequently encompassing 3 stages: initiation, promotion and progression. It is characterized by multiple deviations from normal both at the cell and organism levels. Although most people have a small number of cells that present deviations from normal, most of those cells will not cause cancer. However, some will. What tips the balance between normal and abnormal is the subject of intense scientific research as well as unfounded speculations. Chronic inflammation is one of the risk factors for cancer. Resveratrol is consumed by the population as a dietary supplement in the hope of decreasing the risk of inflammation and cancer and other chronic diseases such as diabetes and vascular diseases. There is a discrepancy between the doses used in the animal studies showing that resveratrol decreases all three stages of carcinogenesis, and the doses ingested by the population either as supplements or in the diet. While there is health benefit from using high resveratrol doses, it might be also of practical and scientific benefit to focus future effort in understanding the effects of normal dietary resveratrol levels.

Consequences of combining siRNA-mediated DNA methyltransferase 1 depletion with 5-aza-2'-deoxycytidine in human leukemic KG1 cells

5-azacytidine and 5-aza-2'-deoxycytidine are clinically used to treat patients with blood neoplasia. Their antileukemic property is mediated by the trapping and the subsequent degradation of a family of proteins, the DNA methyltransferases (DNMT1, DNMT3A, and DNMT3B) leading to DNA demethylation, tumor suppressor gene re-expression and DNA damage. Here we studied the respective role of each DNMT in the human leukemia KG1 cell line using a RNA interference approach. In addition we addressed the role of DNA damage formation in DNA demethylation by 5-aza-2'-deoxycytidine. Our data show that DNMT1 is the main DNMT involved in DNA methylation maintenance in KG1 cells and in mediating DNA damage formation upon exposure to 5-aza-2'-deoxycytidine. Moreover, KG1 cells express the DNMT1 protein at a level above the one required to ensure DNA methylation maintenance, and we identified a threshold for DNMT1 depletion that needs to be exceeded to achieve DNA demethylation. Most interestingly, by combining DNMT1 siRNA and treatment with low dose of 5-aza-2'-deoxycytidine, it is possible to uncouple DNA damage formation from DNA demethylation. This work strongly suggests that a direct pharmacological inhibition of DNMT1, unlike the use of 5-aza-2'-deoxycytidine, should lead to tumor suppressor gene hypomethylation and re-expression without inducing major DNA damage in leukemia.

Reverse chemomodulatory effects of the SIRT1 activators resveratrol and SRT1720 in Ewing's sarcoma cells: resveratrol suppresses and SRT1720 enhances etoposide- and vincristine-induced anticancer activity

PURPOSE

SIRT1-activating compounds (STACs) may have potential in the management of cancer. However, the best-studied STAC, the naturally occurring compound resveratrol, is reported to have contradictory effects in combination chemotherapy regimens: It has been shown both to increase and to decrease the action of anticancer agents. To shed more light on this issue, we comparatively investigated the impact of resveratrol and the synthetic STAC SRT1720 on the responsiveness of Ewing's sarcoma (ES) cells to the chemotherapeutic drugs etoposide and vincristine.

METHODS

Because the effects of STACs can depend on the functionality of the tumor suppressor protein p53, we used three ES cell lines differing in their p53 status, i.e., wild-type p53 WE-68 cells, mutant p53 SK-ES-1 cells and p53 null SK-N-MC cells. Single agent and combination therapy effects were assessed by flow cytometric analyses of propidium iodide uptake and mitochondrial depolarization, by measuring caspase 3/7 activity and by gene expression profiling.

RESULTS

When applied as single agents, both STACs were effective in ES cells irrespective of their p53 status. Strikingly, however, when applied in conjunction with cytostatic agents, the STACs displayed reverse effects: SRT1720 largely enhanced etoposide- and vincristine-induced cell death, while resveratrol inhibited it. Combination index analyses validated the antipodal impact of the STACs on the effectiveness of the chemotherapeutics.

CONCLUSION

These findings suggest that the synthetic STAC SRT1720 may be useful to enhance the efficacy of anticancer therapy in ES. But they also suggest that the dietary intake of the natural STAC resveratrol may be detrimental during chemotherapy of ES.

Deregulated proliferation and differentiation in brain tumors

Neurogenesis, the generation of new neurons, is deregulated in neural stem cell (NSC)- and progenitor-derived murine models of malignant medulloblastoma and glioma, the most common brain tumors of children and adults, respectively. Molecular characterization of human malignant brain tumors, and in particular brain tumor stem cells (BTSCs), has identified neurodevelopmental transcription factors, microRNAs, and epigenetic factors known to inhibit neuronal and glial differentiation. We are starting to understand how these factors are regulated by the major oncogenic drivers in malignant brain tumors. In this review, we will focus on the molecular switches that block normal neuronal differentiation and induce brain tumor formation. Genetic or pharmacological manipulation of these switches in BTSCs has been shown to restore the ability of tumor cells to differentiate. We will discuss potential brain tumor therapies that will promote differentiation in order to reduce treatment resistance, suppress tumor growth, and prevent recurrence in patients.