Michael W.Y. Chan

Identification and Characterization of Ovarian Cancer-Initiating Cells from Primary Human Tumors

The objective of this study was to identify and characterize a self-renewing subpopulation of human ovarian tumor cells (ovarian cancer-initiating cells, OCICs) fully capable of serial propagation of their original tumor phenotype in animals. Ovarian serous adenocarcinomas were disaggregated and subjected to growth conditions selective for self-renewing, nonadherent spheroids previously shown to derive from tissue stem cells. To affirm the existence of OCICs, xenoengraftment of as few as 100 dissociated spheroid cells allowed full recapitulation of the original tumor (grade 2/grade 3 serous adenocarcinoma), whereas >10(5) unselected cells remained nontumorigenic. Stemness properties of OCICs (under stem cell-selective conditions) were further established by cell proliferation assays and reverse transcription-PCR, demonstrating enhanced chemoresistance to the ovarian cancer chemotherapeutics cisplatin or paclitaxel and up-regulation of stem cell markers (Bmi-1, stem cell factor, Notch-1, Nanog, nestin, ABCG2, and Oct-4) compared with parental tumor cells or OCICs under differentiating conditions. To identify an OCIC cell surface phenotype, spheroid immunostaining showed significant up-regulation of the hyaluronate receptor CD44 and stem cell factor receptor CD117 (c-kit), a tyrosine kinase oncoprotein. Similar to sphere-forming OCICs, injection of only 100 CD44(+)CD117(+) cells could also serially propagate their original tumors, whereas 10(5) CD44(-)CD117(-) cells remained nontumorigenic. Based on these findings, we assert that epithelial ovarian cancers derive from a subpopulation of CD44(+)CD117(+) cells, thus representing a possible therapeutic target for this devastating disease.

Fibroblasts Isolated from Common Sites of Breast Cancer Metastasis Enhance Cancer Cell Growth Rates and Invasiveness in an Interleukin-6–Dependent Manner

Common sites of breast cancer metastasis include the lung, liver, and bone, and of these secondary metastatic sites, estrogen receptor alpha (ERalpha)-positive breast cancer often favors bone. Within secondary organs, cancer cells would predictably encounter tissue-specific fibroblasts or their soluble factors, yet our understanding of how tissue-specific fibroblasts directly affect cancer cell growth rates and survival remains largely unknown. Therefore, we tested the hypothesis that mesenchymal fibroblasts isolated from common sites of breast cancer metastasis provide a more favorable microenvironment with respect to tumor growth rates. We found a direct correlation between the ability of breast, lung, and bone fibroblasts to enhance ERalpha-positive breast cancer cell growth and the level of soluble interleukin-6 (IL-6) produced by each organ-specific fibroblast, and fibroblast-mediated growth enhancement was inhibited by the removal or inhibition of IL-6. Interestingly, mice coinjected with MCF-7 breast tumor cells and senescent skin fibroblasts, which secrete IL-6, developed tumors, whereas mice coinjected with presenescent skin fibroblasts that produce little to no IL-6 failed to form xenograft tumors. We subsequently determined that IL-6 promoted growth and invasion of breast cancer cells through signal transducer and activator of transcription 3-dependent up-regulation of Notch-3, Jagged-1, and carbonic anhydrase IX. These data suggest that tissue-specific fibroblasts and the factors they produce can promote breast cancer disease progression and may represent attractive targets for development of new therapeutics.

Identification of novel DNA methylation markers in cervical cancer

Testing for DNA methylation has potential in cancer screening. Most previous studies of DNA methylation in cervical cancer used a candidate gene approach. The aim our study was to identify novel genes that are methylated in cervical cancers and to test their potential in clinical applications. We did a differential methylation hybridization using a CpG island (CGI) microarray containing 8640 CGI tags to uncover methylated genes in squamous cell carcinomas (SCC) of the uterine cervix. Pooled DNA from cancer tissues and normal cervical swabs were used for comparison. Methylation‐specific polymerase chain reaction, bisulfite sequencing and reverse transcription polymerase chain reaction were used to confirm the methylation status in cell lines, normal cervices (n = 45), low‐grade lesions (n = 45), high‐grade lesions (HSIL; n = 58) and invasive squamous cell carcinomas (SCC; n = 22 from swabs and n = 109 from tissues). Human papillomavirus (HPV) was detected using reverse line blots. We reported 6 genes (SOX1, PAX1, LMX1A, NKX6‐1, WT1 and ONECUT1) more frequently methylated in SCC tissues (81.5, 94.4, 89.9, 80.4, 77.8 and 20.4%, respectively) than in their normal controls (2.2, 0, 6.7, 11.9, 11.1 and 0%, respectively; p < 0.0001). Parallel testing of HPV and PAX1 methylation in cervical swabs confers an improved sensitivity than HPV testing alone (80% vs. 66%) without compromising specificity (63% vs. 64%) for HSIL/SCC. Testing PAX1 methylation marker alone, the specificity for HSIL/SCC is 99%. The analysis of these novel DNA methylations may be a promising approach for the screening of cervical cancers.

Promoter hypermethylation of tumor-related genes in gastric intestinal metaplasia of patients with and without gastric cancer

Promoter hypermethylation is an alternative mechanism of gene silencing in human cancers including gastric cancer. While intestinal metaplasia (IM) is generally regarded as a precancerous lesion of the stomach, our study examines the presence of gene promoter hypermethylation in IM of patients with and without gastric cancer. We examined 31 samples of gastric cancer, 36 gastric IM (21 associated with gastric cancer and 15 from noncancer patients) and 10 normal gastric biopsies. Tissues containing foci of IM were carefully microdissected from paraffin‐embedded section. Bisulfite‐modifiedDNA was examined for gene promoter hypermethylation in DAP‐kinase, E‐cadherin, GSTP1, p14, p15, p16, RASSF1A and hMLH1 by methylation‐specific‐PCR. None of the control gastric tissues had hypermethylation detected, but gene promoter hypermethylation was frequently detected in gastric cancer and IM. The mean number of methylated genes in cancer and IM was 3.0 and 1.4, respectively (p < 0.0001). Methylation in IM from cancer patients was all associated with concurrent methylation in the corresponding tumor samples. The numbers of methylated genes were similar in IM obtained from cancer and noncancer patients. By examining the methylation patterns of these genes, 3 differential methylation patterns were recognized: hypermethylation was more frequent in cancer than in IM (DAP‐kinase, p14, p15 and p16); comparable frequencies of methylation in cancer and IM (E‐cadherin and hMLH1); and no methylation (GSTP1). Aberrant methylation in tumor‐related genes is frequently detected in gastric IM of both cancer and noncancer patients, suggesting their early involvement in the multistep progression of gastric carcinogenesis.

Epithelial progeny of estrogen-exposed breast progenitor cells display a cancer-like methylome.

Estrogen imprinting is used to describe a phenomenon in which early developmental exposure to endocrine disruptors increases breast cancer risk later in adult life. We propose that long-lived, self-regenerating stem and progenitor cells are more susceptible to the exposure injury than terminally differentiated epithelial cells in the breast duct. Mammospheres, containing enriched breast progenitors, were used as an exposure system to simulate this imprinting phenomenon in vitro. Using MeDIP-chip, a methylation microarray screening method, we found that 0.5% (120 loci) of human CpG islands were hypermethylated in epithelial cells derived from estrogen-exposed progenitors compared with the non-estrogen-exposed control cells. This epigenetic event may lead to progressive silencing of tumor suppressor genes, including RUNX3, in these epithelial cells, which also occurred in primary breast tumors. Furthermore, normal tissue in close proximity to the tumor site also displayed RUNX3 hypermethylation, suggesting that this aberrant event occurs in early breast carcinogenesis. The high prevalence of estrogen-induced epigenetic changes in primary tumors and the surrounding histologically normal tissues provides the first empirical link between estrogen injury of breast stem/progenitor cells and carcinogenesis. This finding also offers a mechanistic explanation as to why a tumor suppressor gene, such as RUNX3, can be heritably silenced by epigenetic mechanisms in breast cancer.

Quantitative Detection of Promoter Hypermethylation in Multiple Genes in the Serum of Patients with Colorectal Cancer

OBJECTIVES:While promoter hypermethylation is a common molecular alteration of human colorectal cancer that could be detected in the bloodstream, we tested the feasibility of quantitative detection of aberrant DNA methylation in multiple genes in the serum samples of colorectal cancer patients.METHODS:The pre-therapeutic serum samples of 49 colorectal cancer patients and 41 age-matched controls with normal colonoscopy were examined. The presence of methylated DNA in APC (adenomatous polyposis coli), hMLH1 (human MutL homolog 1), and HLTF (helicase-like transcription factor) was detected by quantitative methylation-specific PCR (MethyLight).RESULTS:There was a significant difference in the concentration of methylated serum DNA between cancer patients and controls for HLTF (p = 0.015) and hMLH1 (p = 0.0001) genes, but not for APC gene (p = 0.21). In total, 28 patients with colorectal cancer and 4 controls had methylated DNA detected in at least one marker, which gave a sensitivity of 57% and specificity of 90%. All patients with methylation in two methylation markers had advanced (stage III/IV) cancer (p = 0.006) and patients with methylation in at least one marker tended to have a lower probability of survival (p = 0.08).CONCLUSION:The quantitative detection of aberrant DNA methylation in serum may be a promising high-throughput approach for the noninvasive screening and monitoring of colorectal cancer.

Frequent hypermethylation of promoter region of RASSF1A in tumor tissues and voided urine of urinary bladder cancer patients

High frequency loss of 3p21.3 region where RASSF1A located was demonstrated in several tumors. We aimed to investigate the methylation status of RASSF1A and the frequency of LOH in 3p21.3 region in bladder cancer. Three bladder cancer cell lines, 40 cases of bladder TCC and 14 cases of paired voided urine samples were subjected to methylation analysis. By methylation specific PCR, complete methylation of promoter region of RASSF1A gene were detected in cell lines T24 and UMUC3. Demethylation treatment re‐expressed RASSF1A in these 2 cell lines. Methylation of RASSF1A was also detected in 47.5% (19/40) of the TCC cases but not in 6 carcinoma in situ (CIS) or 6 normal urothelium samples. For LOH study, loss of 3p21.3 region was detected in 57.9% (11/19) of our cases. Interestingly, methylation of RASSF1A was found in 72.7% (8/11) of the cases with LOH but only in 12.5% (1/8) of the cases without LOH. Methylation of RASSF1A was detected in 50% (7/14) of voided urine samples, but not in normal control. It showed a higher sensitivity than conventional urine cytology in detecting cancer cells, especially for low grade cases. In conclusion, our results demonstrated a high frequency of RASSF1A methylation with frequent LOH in 3p21.3 region in bladder cancer. It suggested that it may be a potential tumor suppressor gene in this chromosomal region and can be silenced by promoter hypermethylation. Detection of aberrant gene methylation in routine voided urine was feasible and may provide a non‐invasive and sensitive approach for cancer detection.

Expression of trefoil peptides (TFF1, TFF2, and TFF3) in gastric carcinomas, intestinal metaplasia, and non-neoplastic gastric tissues.

Trefoil factor family (TFF) domain peptides consist of three members that play a role in intestinal mucosal defence and repair, and in tumourigenesis. The role of the three TFF members in the gastric carcinogenesis cascade remains poorly defined. This study examined seven gastric cell lines, 50 gastric cancers and their adjacent non‐cancer tissues, and tissues from 40 non‐cancer patients, in order to elucidate the chronology of TFF expression in various stages of gastric carcinogenesis. TFF expression was determined by RT‐PCR, immunohistochemistry, and western blot. Aberrant expression of TFF1, TFF2, and TFF3 was frequently detected in gastric cell lines. Specifically, TFF1 was detected in all non‐cancer patients, but was detected in only 50% of gastric cancer and 66% of adjacent normal tissues. TFF2 expression was demonstrated in 87.5% of non‐cancer patients, 34% of gastric carcinomas, and 58% of adjacent non‐cancer tissues. There was a significant correlation between TFF1 and TFF2 expression in gastric cancer and adjacent non‐cancer tissues (p<0.001). By contrast, TFF3 was detected in 25% of non‐cancer patients and showed a predilection for areas with intestinal metaplasia (p=0.005). Sixty‐two per cent of gastric cancers and 24% of neighbouring non‐cancer tissues showed TFF3 expression. Immunoreactivity against TFF3 was demonstrated in goblet cells of intestinal metaplasia and within the cytoplasm and nuclei of tumour cells. Progressive loss of TFF1 and TFF2, together with the induction of TFF3, is likely to be involved in the early stage of the multi‐step gastric carcinogenesis pathway. Copyright

Hypermethylation of the TGF-β target, ABCA1 is associated with poor prognosis in ovarian cancer patients

BackgroundThe dysregulation of transforming growth factor-β (TGF-β) signaling plays a crucial role in ovarian carcinogenesis and in maintaining cancer stem cell properties. Classified as a member of the ATP-binding cassette (ABC) family, ABCA1 was previously identified by methylated DNA immunoprecipitation microarray (mDIP-Chip) to be methylated in ovarian cancer cell lines, A2780 and CP70. By microarray, it was also found to be upregulated in immortalized ovarian surface epithelial (IOSE) cells following TGF-β treatment. Thus, we hypothesized that ABCA1 may be involved in ovarian cancer and its initiation.ResultsWe first compared the expression level of ABCA1 in IOSE cells and a panel of ovarian cancer cell lines and found that ABCA1 was expressed in HeyC2, SKOV3, MCP3, and MCP2 ovarian cancer cell lines but downregulated in A2780 and CP70 ovarian cancer cell lines. The reduced expression of ABCA1 in A2780 and CP70 cells was associated with promoter hypermethylation, as demonstrated by bisulfite pyro-sequencing. We also found that knockdown of ABCA1 increased the cholesterol level and promoted cell growth in vitro and in vivo. Further analysis of ABCA1 methylation in 76 ovarian cancer patient samples demonstrated that patients with higher ABCA1 methylation are associated with high stage (P = 0.0131) and grade (P = 0.0137). Kaplan-Meier analysis also found that patients with higher levels of methylation of ABCA1 have shorter overall survival (P = 0.019). Furthermore, tissue microarray using 55 ovarian cancer patient samples revealed that patients with a lower level of ABCA1 expression are associated with shorter progress-free survival (P = 0.038).ConclusionsABCA1 may be a tumor suppressor and is hypermethylated in a subset of ovarian cancer patients. Hypermethylation of ABCA1 is associated with poor prognosis in these patients.

Helicobacter pylori Causes Epigenetic Dysregulation of FOXD3 to Promote Gastric Carcinogenesis

BACKGROUND & AIMS Deregulation of forkhead box (Fox) proteins, an evolutionarily conserved family of transcriptional regulators, leads to tumorigenesis. Little is known about their regulation or functions in the pathogenesis of gastric cancer. Promoter hypermethylation occurs during Helicobacter pylori-induced gastritis. We investigated whether the deregulated genes contribute to gastric tumorigenesis. METHODS We used integrative genome-wide scans to identify concomitant hypermethylated genes in mice infected with H pylori and human gastric cancer samples. We also analyzed epigenetic gene silencing in gastric tissues from patients with H pylori infection and gastritis, intestinal metaplasia, gastric tumors, or without disease (controls). Target genes were identified by chromatin immunoprecipitation microarrays and expression and luciferase reporter analyses. RESULTS Methylation profile analyses identified the promoter of FOXD3 as the only genomic region with increased methylation in mice and humans during progression of H pylori-associated gastric tumors. FOXD3 methylation also correlated with shorter survival times of patients with gastric cancer. Genome demethylation reactivated FOXD3 expression in gastric cancer cell lines. Transgenic overexpression of FOXD3 significantly inhibited gastric cancer cell proliferation and invasion, and reduced growth of xenograft tumors in mice, at least partially, by promoting tumor cell apoptosis. FOXD3 bound directly to the promoters of, and activated transcription of, genes encoding the cell death regulators CYFIP2 and RARB. Levels of FOXD3, CYFIP2, and RARB messenger RNAs were reduced in human gastric tumor samples, compared with control tissues. CONCLUSIONS FOXD3-mediated transcriptional control of tumor suppressors is deregulated by H pylori infection-induced hypermethylation; this could perturb the balance between cell death and survival. These findings identify a pathway by which epigenetic changes affect gastric tumor suppression.