Epigenetic modulation of endogenous tumor suppressor expression in lung cancer xenografts suppresses tumorigenicity

Epigenetic changes involved in cancer development, unlike genetic changes, are reversible. DNA methyltransferase and histone deacetylase inhibitors show antiproliferative effects in vitro, through tumor suppressor reactivation and induction of apoptosis. Such inhibitors have shown activity in the treatment of hematologic disorders but there is little data concerning their effectiveness in treatment of solid tumors. FHIT, WWOX and other tumor suppressor genes are frequently epigenetically inactivated in lung cancers. Lung cancer cell clones carrying conditional FHIT or WWOX transgenes showed significant suppression of xenograft tumor growth after induction of expression of the FHIT or WWOX transgene, suggesting that treatments to restore endogenous Fhit and Wwox expression in lung cancers would result in decreased tumorigenicity. H1299 lung cancer cells, lacking Fhit, Wwox, p16(INK4a) and Rassf1a expression due to epigenetic modifications, were used to assess efficacy of epigenetically targeted protocols in suppressing growth of lung tumors, by injection of 5-aza-2-deoxycytidine (AZA) and trichostatin A (TSA) in nude mice with established H1299 tumors. High doses of intraperitoneal AZA/TSA suppressed growth of small tumors but did not affect large tumors (200 mm(3)); lower AZA doses, administered intraperitoneally or intratumorally, suppressed growth of small tumors without apparent toxicity. Responding tumors showed restoration of Fhit, Wwox, p16(INKa), Rassf1a expression, low mitotic activity, high apoptotic fraction and activation of caspase 3. These preclinical studies show the therapeutic potential of restoration of tumor suppressor expression through epigenetic modulation and the promise of re-expressed tumor suppressors as markers and effectors of the responses.     

Epigenetic silencing of PEG3 gene expression in human glioma cell lines

Genomic imprinting, the phenomenon in which alleles of genes are expressed differentially depending on their parental origins, has important consequences for mammalian development, and disturbance of normal imprinting leads to abnormal embryogenesis and some inherited diseases and is also associated with various cancers. In the context of screening for novel imprinted genes on human chromosome 19q13.4 with mouse A9 hybrids, we identified a maternal allele-specific methylated CpG island in exon 1 of paternally expressed imprinted gene 3 (PEG3), a gene that exhibits paternal allele-specific expression. Because PEG3 expression is downregulated in some gliomas and glioma cell lines, despite high-level expression in normal brain tissues, we investigated whether the loss of PEG3 expression is related to epigenetic modifications involving DNA methylation. We found monoallelic expression of PEG3 in all normal brain tissues examined and five of nine glioma cell lines that had both unmethylated and methylated alleles; the remaining four glioma cell lines exhibited gain of imprinting with hypermethylated alleles. In addition, treatment of glioma cell lines with the DNA demethylating agent 5-aza-2'-deoxycytidine reversed the silencing of PEG3 biallelically. In this article, we report that the epigenetic silencing of PEG3 expression in glioma cell lines depends on aberrant DNA methylation of an exonic CpG island, suggesting that PEG3 contributes to glioma carcinogenesis in certain cases.     

5-Aza-2'-deoxycytidine induces p21WAF expression by demethylation of p73 leading to p53-independent apoptosis in myeloid leukemia

The DNA methylation inhibitor 5-Aza-2'-deoxycytidine (5-Aza-CdR) has significant therapeutic value for the treatment of patients with myelodysplastic syndrome (MDS), acute myeloid leukemia (AML) and chronic myeloid leukemia (CML). The demethylating effect of 5-Aza-CdR has been well characterized. In contrast, less is known about the molecular events downstream of the methylation inhibition. Here, 5-Aza-CdR induced apoptosis in AML cells (both p53 mutant and wild-type) but not in epithelial or normal PBMCs. Cell death was accompanied by activation of the mitochondrial apoptosis pathway, as shown by release of cytochrome c and AIF and loss of mitochondrial membrane potential (DeltaPsim). Activation of caspase-3 (but not -6 and -8) was detectable using Western blot analysis and measurement of caspase enzymatic activity. 5-Aza-CdR treatment resulted in the induction of p21, which correlated with the arrest of AML cells in the G1 cell cycle phase. Induction of p21 expression was independent of its promoter methylation status but mediated by 5-Aza-CdR-induced reexpression of the tumor-suppressor p73, a known upstream regulator of p21. The p73 promoter was hypermethylated in AML cell lines and in primary AML cells but not in epithelial cells, which were resistant toward 5-Aza-CdR. Therefore, 5-Aza-CdR-mediated specific killing of myeloid cells might be dependent on its ability to revert p73 promoter methylation and to reexpress p73 mRNA. In addition, exogenous expression of p73 rendered epithelial cells sensitive to apoptosis induced by 5-Aza-CdR or other cytostatic drugs. We therefore conclude that p73 is a relevant target for methylation-dependent efficacy of 5-Aza-CdR in AML cells.     

A histone deacetylase inhibitor enhances expression of genes inhibiting Wnt pathway and augments activity of DNA demethylation reagent against nonsmall‐cell lung cancer

Development of new inhibitors targeting histone deacetylases (HDACs) with improved efficacy for solid tumor therapy is urgently needed. Here, we report the development of a novel HDAC inhibitor TMU‐35435 and verify it as a single agent and in combination treatment with DNA demethylation reagent 5‐aza‐2′‐deoxycytidine (5‐aza‐dC) in lung cancer preclinical models. TMU‐35435 exerted cancer‐specific cytotoxicity via mitochondria‐mediated apoptosis. Expression microarrays revealed a unique TMU‐35435‐induced gene networks enriched in biological processes, including “negative regulation of cell proliferation” and “Wnt receptor signaling pathway” compared to FDA‐approved HDAC inhibitor SAHA. TMU‐35435 inhibited tumor growth with good pharmacokinetic properties and safety features in lung orthotopic and subcutaneously implanted xenograft models. TMU‐35435 and 5‐aza‐dC showed synergistic antitumor effects through reactivation of tumor suppressor genes and those genes encoding negative regulators of Wnt signaling pathway in vitro and in vivo. Some genes showed additive inhibition of DNA methylation upon TMU‐35435 and 5‐aza‐dC combined treatment. Our findings suggested that TMU‐35435 is a potential HDAC inhibitor for lung cancer treatment as a single agent and in combination with 5‐aza‐dC.     

2'-5' oligoadenylate synthetase 1 polymorphism is associated with prostate cancer

BACKGROUND:

The antiviral, proapoptotic, antiproliferative gene 2′‐5′ oligoadenylate synthetase (2‐5OAS1) converts adenosine triphosphate into a series of 2′‐5′ oligoadenylates (2‐5A). In turn, 2‐5A activates latent ribonuclease (RNaseL), a candidate hereditary prostate cancer gene. OAS1 polymorphism (reference single nucleotide polymorphism [SNP] 2660 [rs2660]) has been associated with increased susceptibility to infections and various diseases. In general, the low‐enzyme‐activity adenine‐adenine (AA) genotype promotes susceptibility, whereas the high‐enzyme‐activity guanosine‐guanosine (GG) genotype confers protection. In this study, the authors investigated the association of this functional OAS1 polymorphism (rs2660) with prostate cancer.

METHODS:

Sample size and power were calculated using a power calculation software program for case‐control genetic association analyses. Genomic DNA samples from a control group (n = 140) and from a case group of patients with prostate cancer (n = 164) were used for genotyping SNPs rs2660, rs1131454, and rs34137742 in all samples. Statistical analyses were performed using a logistic regression model.

RESULTS:

A significant association was observed between the rs2660 genotype (A/G) and prostate cancer. Genotype AA increased the risk, whereas genotype GG decreased the risk of prostate cancer. The GG genotype was not observed in the African American samples. The AA genotype also increased the risk of prostate cancer with age.

CONCLUSIONS:

The OAS1 SNP rs2660 AA genotype was associated significantly with prostate cancer, whereas the GG genotype protected against prostate cancer. OAS1 rs2660 may be a prostate cancer susceptibility polymorphism, which is a significant observation, especially in a context of the OAS1‐RNaseL pathway. Thus, a functional defect in OAS1 because of the rs2660 SNP not only can attenuate RNaseL function but also can alter cell growth and apoptosis independent of RNaseL. Cancer 2011;. © 2011 American Cancer Society.     

Suppression of murine mammary carcinoma metastasis by the murine ortholog of breast cancer metastasis suppressor 1 (Brms1)

The murine ortholog (Brms1) of human breast cancer metastasis suppressor 1 shares 95% identity to the human metastasis suppressor, BRMS1, in amino acid structure. We tested Brms1 for suppression of metastasis of mouse mammary carcinoma cell line 4T1 in syngenic BALB/c mice, using orthotopic (mammary fat pad) injection as well as intravenous injection. As observed for BRMS1, transfection with Brms1 did not inhibit 4T1 primary tumor formation, but significantly suppressed lung colonization. We also show that Brms1 protein interacts with histone deacetylases, indicating involvement of Brms1 in murine Sin3-HDAC complex, like its human counterpart. Thus, because of similarities with its human ortholog, the results suggest that Brms1 will be useful as a model for studying mechanism of action of BRMS1.     

P53 is a regulator of the metastasis suppressor gene Nm23-H1

p53, a tumor suppressor gene involved in the G1 cell cycle checkpoint, is also the most frequently mutated gene in human cancer. In addition, p53 modifies the ability of tumor cells to metastasize. The metastasis-associated gene Nm23-H1, which encodes an 18-kDa nucleoside diphosphate kinase, was previously identified in cells with low metastatic potential. Although p53 and Nm23-H1 proteins play an important part in regulating the progression of cancer, any functional relationship between these two proteins is currently unknown. Here we report an association between p53 levels and expression of the Nm23-H1 gene. Our data indicate that wild-type (wt) p53 upregulated the expression of Nm23-H1 at protein and mRNA levels in MCF-7 and J7B cells. This capacity of wt p53 to regulate expression of Nm23-H1 was not only dependent on the endogenous but also the exogenous origin of p53, and could not be reproduced with mutant p53. Subsequently, the invasive ability of MCF-7 and J7B cells was suppressed upon induction of the Nm23-H1 protein by p53. In contrast, increased levels of p53 downregulated the expression of Nm23-H1 at the protein and mRNA levels in RKO and H1299 cells and, as a consequence, increased the invasive ability of both cell types. Thus, our results implicated the differential regulation of Nm23-H1 by p53 in different cell types as an important component in the molecular mechanisms of tumor metastasis.     

Synergistic antineoplastic action of DNA methylation inhibitor 5-AZA-2'-deoxycytidine and histone deacetylase inhibitor depsipeptide on human breast carcinoma cells

During tumorigenesis, cancer-related genes can be silenced by aberrant DNA methylation and by changes in chromatin structure. It has been reported that 5-aza-2'-deoxycytidine, a potent inhibitor of DNA methylation, in combination with histone deacetylase inhibitors, can produce a synergistic reactivation of these genes. The aim of our study was to investigate the in vitro antineoplastic activity of 5-aza-2'-deoxycytidine in combination with depsipeptide, a potent histone deacetylase inhibitor, against MDA-MB-231 and MDA-MB-435 human breast carcinoma cell lines. We observed that the combination of 5-aza-2'-deoxycytidine and depsipeptide produced a synergistic antineoplastic effect against these tumor cells as compared to either agent administered alone. We also investigated the effect of this drug combination on the activation of maspin and gelsolin expression. These 2 genes whose function is to suppress tumor metastasis have been reported to be silenced by epigenetic events in breast cancer. Using semi-quantitative RT-PCR, we observed that 5-aza-2'-deoxycytidine in combination with depsipeptide produced a greater reactivation of both maspin and gelsolin as compared to each agent alone. The synergistic interaction between 5-aza-2'-deoxycytidine and depsipeptide on breast carcinoma cell lines provides a rationale to investigate this interesting drug combination in future clinical trials on patients with advanced breast cancer.     

Peperomin E reactivates silenced tumor suppressor genes in lung cancer cells by inhibition of DNA methyltransferase

Advanced lung cancer has poor prognosis owing to its low sensitivity to current chemotherapy agents. Therefore, discovery of new therapeutic agents is urgently needed. In this study, we investigated the antitumor effects of peperomin E, a secolignan isolated from Peperomia dindygulensis, a frequently used Chinese folk medicine for lung cancer treatment. The results indicate that peperomin E has antiproliferative effects, promoting apoptosis and cell cycle arrest in non‐small‐cell lung cancer (NSCLC) cell lines in a dose‐dependent manner, while showing lower toxicity against normal human lung epidermal cells. Peperomin E inhibited tumor growth in A549 xenograft BALB/c nude mice without significant secondary adverse effects, indicating that it may be safely used to treat NSCLC. Furthermore, the mechanisms underlying the anticancer effects of peperomin E have been investigated. Using an in silico target fishing method, we observed that peperomin E directly interacts with the active domain of DNA methyltransferase 1 (DNMT1), potentially affecting its genome methylation activity. Subsequent experiments verified that peperomin E decreased DNMT1 activity and expression, thereby decreasing global methylation and reactivating the epigenetically silenced tumor suppressor genes including RASSF1A, APC, RUNX3, and p16INK4, which in turn activates their mediated pro‐apoptotic and cell cycle regulatory signaling pathways in lung cancer cells. The observations herein report for the first time that peperomin E is a potential chemotherapeutic agent for NSCLC. The anticancer effects of peperomin E may be partly attributable to its ability to demethylate and reactivate methylation‐silenced tumor suppressor genes through direct inhibition of the activity and expression of DNMT1.     

MUC2 expression is regulated by histone H3 modification and DNA methylation in pancreatic cancer

Mucins are highly glycosylated proteins that play important roles in carcinogenesis. In pancreatic neoplasia, MUC2 mucin has been demonstrated as a tumor suppressor and we have reported that MUC2 is a favorable prognostic factor. Regulation of MUC2 gene expression is known to be controlled by DNA methylation, but the role of histone modification for MUC2 gene expression has yet to be clarified. Herein, we provide the first report that the histone H3 modification of the MUC2 promoter region regulates MUC2 gene expression. To investigate the histone modification and DNA methylation of the promoter region of the MUC2 gene, we treated 2 human pancreatic cancer cell lines, PANC1 (MUC2-negative) and BxPC3 (MUC2-positive) with the DNA methyltransferase inhibitor 5-azacytidine (5-aza), the histone deacetylase inhibitor trichostatin A (TSA), and a combination of these agents. The DNA methylation level of PANC1 cells was decreased by all 3 treatments, whereas histone H3-K4/K9 methylation and H3-K9/K27 acetylation in PANC1 cells was changed to the level in BxPC3 cells by treatment with TSA alone and with the 5-aza/TSA combination. The expression level of MUC2 mRNA in PANC1 cells exhibited a definite increase when treated with TSA and 5-aza/TSA, whereas 5-aza alone induced only a slight increase. Our results suggest that histone H3 modification in the 5' flanking region play an important role in MUC2 gene expression, possibly affecting DNA methylation. An understanding of these intimately correlated epigenetic changes may be of importance for predicting the outcome of patients with pancreatic neoplasms.     

Blockade of MEK signaling potentiates 5‐Aza‐2′‐deoxycytidine‐induced apoptosis and upregulation of p21waf1 in acute myelogenous leukemia cells

We have recently reported that the mitogen‐activated protein kinase/ERK kinase (MEK) inhibitor AZD6244 (ARRY‐142886) strikingly potentiated the effects of histone deacetylase inhibitor to induce growth arrest and apoptosis of acute myelogeneous leukemia (AML) cells in association with enhanced upregulation of p21^waf1. This study examined the effects of the MEK inhibitor on the action of DNA methyltransferase inhibitor 5‐Aza‐2′‐deoxycytidine (5‐AzadC), another epigenetic agent in AML cells. AZD6244 significantly potentiated the ability of 5‐AzadC to induce growth arrest and apoptosis of NB4, and freshly isolated AML cells. In parallel, 5‐AzadC induced expression of p21^waf1 in AML cells, which was potently enhanced in the presence of AZD6244. Further studies explored the molecular mechanisms by which 5‐AzadC induced expression of p21^waf1 and found that a low dose of 5‐AzadC (1 μM) induced acetylation of histone H3 on the p21^waf1 gene promoter; however, higher dose of this compound (3 or 5 μM) potently induced DNA damage as assessed by expression of γH2AX, in NB4 cells. These effects were strikingly enhanced by concomitant blockade of MEK signaling. Furthermore, knock‐down of p21^waf1 by the siRNA rescued NB4 cells from 5‐AzadC‐mediated growth inhibition. Taken together, combination of 5‐AzadC and the MEK inhibitor may be useful for treatment of individuals with a subset of AML. © 2009 UICC     

Aberrant methylation of HIN-1 (high in normal-1) is a frequent event in many human malignancies

HIN-1 (high in normal-1) is a putative cytokine with growth inhibitory activities and is downregulated by aberrant methylation in breast cancers. We studied HIN-1 methylation status in many types of adult and pediatric malignancies and cell lines. We examined the expression of HIN-1 mRNA in 52 cell lines and the promoter methylation status in the cell lines and in over 800 primary tumors representing 17 tumor types using methylation specific PCR. Promoter methylation was observed in 73% of breast cancer, 67% of nonsmall cell lung cancer (NSCLC), 30% of small cell lung cancer (SCLC) and 57% of malignant mesothelioma (MM) cell lines, and methylation was completely correlated with loss of expression. Expression negative cell lines restored HIN-1 expression after treatment with 5-aza-2'-deoxycytidine. Promoter methylation of HIN-1 was found in 90% of retinoblastomas, 73% of Wilms' tumors, 61% of rhabdomyosarcomas, 57% of breast cancers, 52% of prostate cancers, 40% of MMs, 28% of NSCLCs and 27% of lymphomas. Methylation frequencies in colorectal cancers, cervical cancers, bronchial carcinoids, SCLCs, neuroblastomas, osteosarcomas, leukemia, medulloblastomas and bladder cancers were lower (4-21%), while hepatoblastomas lacked methylation. HIN-1 methylation was rarely detected in nonmalignant tissues (8 of 165, 5%). Aberrant methylation of HIN-1 with loss of expression is a common event and may contribute to the pathogenesis of many types of human malignancies.     

Anti-tumor efficacy of the nucleoside analog 1-(2-deoxy-2-fluoro-4-thio-beta-D-arabinofuranosyl) cytosine (4'-thio-FAC) in human pancreatic and ovarian tumor xenograft models

1-(2-deoxy-2-fluoro-4-thio-beta-D-arabinofuranosyl) cytosine (4'-thio-FAC) is a deoxycytidine analog that has been shown previously to have impressive anti-proliferative and cytotoxic effects in vitro and in vivo toward colorectal and gastric tumors. In our present studies, the pharmacokinetic behavior in nude mice and the effectiveness of 4'-thio-FAC against human pancreatic and ovarian tumor growth were assessed in comparison with standard chemotherapeutic agents. Potent in vitro anti-proliferative effects were observed against pancreatic (Capan-1, MIA-PaCa-2, BxPC-3) and ovarian (SK-OV-3, OVCAR-3, ES-2) cancer cell lines with IC(50) of 0.01-0.2 microM. In vivo anti-tumor activity was evaluated in nude mice bearing subcutaneously (s.c.) implanted human pancreatic tumor xenografts or intraperitoneally (i.p.) disseminated human ovarian xenografted tumors. Oral daily administration of 4'-thio-FAC for 8-10 days significantly inhibited the growth of gemcitabine-resistant BxPC-3 pancreatic tumors and induced regression of gemcitabine-refractory Capan-1 tumors. 4'-Thio-FAC was also a highly effective inhibitor of ovarian peritoneal carcinomatosis. In the SK-OV-3 and ES-2 ovarian cancer models, 4'-thio-FAC prolonged survival to a greater extent than that observed with gemcitabine. Furthermore, the superiority of 4'-thio-FAC to carboplatin and paclitaxel was demonstrated in the ES-2 clear cell ovarian carcinoma model. Studies provide evidence that 4'-thio-FAC is a promising new alternative to gemcitabine and other chemotherapeutic drugs in the treatment of a variety of tumor indications, including pancreatic and ovarian carcinoma.     

抑癌基因p16和转移抑制基因nm 23在卵巢上皮性肿瘤中的表达

目的:探讨抑癌基因p16及转移抑制基因nm23与卵巢上皮性肿瘤病理特点及生物学行为的关系。方法:免疫组化SP法检测30例正常卵巢,50例卵巢上皮性良性肿瘤及50例卵巢癌组织中P16蛋白和nm23蛋白,并分析其阳性表达与肿瘤的关系。结果:nm23蛋白在卵巢癌组织中的阳性率(70.0%)明显高于正常卵巢(43.3%)及良性肿瘤组(44.0%)(P<0.05);在浆液性癌(87.5%)和粘液性癌(47.8%)中的阳性差率也有显著差异(P<0.05);特别是在有淋巴结转移(39.1%)和无淋巴结转移(92.6%)的中检出率相非常显著(P<0.01),而与卵巢癌的临床分期及病理分级无明显相关性。p16蛋白在卵巢癌中的检出率(26.0%)明显低于正常卵巢(80.0%)和良性上皮性肿瘤(52.0%)(P<0.01),在晚期肿瘤中的表达率(20.5%)也远低于早期肿瘤(63.6%),而且在高度恶性组织中表达水平(11.1%)与中低度恶性组织的表达水平(43.5%)也有显著差异(P<0.05)。结论:nm23基因的表达与卵巢癌的淋巴结转移等生物学行为有关,p16基因可作为临床判断预后的重要指标之一。nm23、p16基因与卵巢上皮性肿瘤的发生、发展密切相关。     

MTS1及E-cadherin的表达与乳腺癌转移的关系

背景与目的:乳腺癌患者主要死于远处转移,目前还没有一种预测和早期诊断乳腺癌转移的方法。本研究旨在观察多肿瘤抑制基因(multipletumorsuppressor1,MTS1/p16)及上皮型钙粘附素(E-cadherin)的表达与乳腺癌转移的关系。方法:应用免疫组化S-P法,检测54例乳腺癌组织中的MTS1、E-cadherin的表达。结果:MTS1在远处转移组和多于4枚局部淋巴结转移组的表达率(分别为40.7%、38.1%)均低于相应对照组(74.1%、69.7%)(P<0.05);在组织学分级Ⅰ、Ⅱ、Ⅲ级三组中的表达率分别为76.2%、58.8%、31.3%,三组间差异有显著性(P<0.01)。E-cadherin在远处转移组和多于4枚局部淋巴结转移组的表达率(分别为37%、23.8%)均低于相应对照组(70.4%、66.7%)(P<0.05);在组织学分级Ⅰ、Ⅱ、Ⅲ级三组中的表达率分别为80.9%、47.1%、25.0%,三组间差异有显著性(P<0.01)。结论:MTS1及E-cadherin与乳腺癌的浸润和转移相关。     

Elevation of breast carcinoma Nm23-H1 metastasis suppressor gene expression and reduced motility by DNA methylation inhibition

We hypothesize that elevation of Nm23-H1 expression in micrometastatic breast cancer cells may inhibit their metastatic colonization and further invasion, and induce differentiation, thus resulting in a clinical benefit. The current study investigated the possible contribution of DNA methylation to the regulation of Nm23-H1 expression, based on the observation that two CpG islands are present in its promoter. 5-Aza-2'-deoxycytidine (5-Aza-CdR), a DNA methylation inhibitor, increased the Nm23-H1 expression of 5 of 11 human breast carcinoma cell lines in vitro, including 3 of 3 metastatically competent lines. Increased Nm23-H1 expression was accompanied by a reduction in motility in vitro, with minimal effect on proliferation. Both increased Nm23-H1 expression and decreased motility were observed using low (75 nM) concentrations of 5-Aza-CdR. Array analysis of MDA-MB-231 breast carcinoma cells treated with 5-Aza-CdR confirmed the elevation of nm23-H1 mRNA, whereas relatively few other genes exhibited altered expression. Bisulfite sequencing of the two CpG islands in a panel of cell lines and in 20 infiltrating ductal carcinomas revealed that one island (-3090 bp to -3922 bp) exhibited infrequent differential methylation. The data indicate that DNA methylation inhibitors can directly or indirectly cause both elevation of Nm23-H1 expression and decreased function in one aspect of metastasis, motility.