Showing papers by "William G. Nelson published in 2003"

Hypermethylation of the Human Glutathione S-Transferase-π Gene (GSTP1) CpG Island Is Present in a Subset of Proliferative Inflammatory Atrophy Lesions but Not in Normal or Hyperplastic Epithelium of the Prostate : A Detailed Study Using Laser-Capture Microdissection

Abstract: Somatic inactivation of the glutathione S-transferase-π gene (GSTP1) via CpG island hypermethylation occurs early during prostate carcinogenesis, present in ∼70% of high-grade prostatic intraepithelial neoplasia (high-grade PIN) lesions and more than 90% of adenocarcinomas. Recently, there has been a resurgence of the concept that foci of prostatic atrophy (referred to as proliferative inflammatory atrophy or PIA) may be precursor lesions for the development of prostate cancer and/or high-grade PIN. Many of the cells within PIA lesions contain elevated levels of GSTP1, glutathione S-transferase-α (GSTA1), and cyclooxygenase-II proteins, suggesting a stress response. Because not all PIA cells are positive for GSTP1 protein, we hypothesized that some of the cells within these regions acquire GSTP1 CpG island hypermethylation, increasing the chance of progression to high-grade PIN and/or adenocarcinoma. Separate regions (n =199) from 27 formalin-fixed paraffin-embedded prostates were microdissected by laser-capture microdissection (Arcturus PixCell II). These regions included normal epithelium (n = 48), hyperplasticepithelium from benign prostatic hyperplasia nodules (n = 22), PIA (n = 64), high-grade PIN (n = 32), and adenocarcinoma (n = 33). Genomic DNA was isolated and assessed for GSTP1 CpG island hypermethylation by methylation-specific polymerase chain reaction. GSTP1 CpG island hypermethylation was not detected in normal epithelium (0 of 48) or in hyperplastic epithelium (0 of 22), but was found in 4 of 64 (6.3%) PIA lesions. The difference in the frequency of GSTP1 CpG island hypermethylation between normal or hyperplastic epithelium and PIA was statistically significant (P = 0.049). Similar to studies using nonmicrodissected cases, hypermethylation was found in 22 of 32 (68.8%) high-grade PIN lesions and in 30 of 33 (90.9%) adenocarcinoma lesions. Unlike normal or hyperplastic epithelium, GSTP1 CpG island hypermethylation can be detected in some PIA lesions. These data support the hypothesis that atrophic epithelium in a subset of PIA lesions may lead to high-grade PIN and/or adenocarcinoma. Because these atrophic lesions are so prevalent and extensive, even though only a small subset contains this somatic DNA alteration, the clinical impact may be substantial.

Prostate Cancer Detection by GSTP1 Methylation Analysis of Postbiopsy Urine Specimens

Abstract: Purpose: We assess the feasibility of a urinary test for prostate cancer detection in a high-risk patient cohort based on methylation-specific PCR analysis of the π class glutathione S -transferase ( GSTP1 ) gene promoter. Experimental Design: A total of 45 men underwent transrectal ultrasound-guided biopsy of the prostate for suspected malignancy. Clean-catch voided urine specimens were prospectively collected from each patient immediately after biopsy. Genomic DNA was isolated from urine specimens and subjected to sodium bisulfite modification. Methylation of the GSTP1 promoter was examined in a blinded manner by methylation-specific PCR analysis and correlated with pathology results, and clinical information was obtained from the patient record. Results: Methylation of GSTP1 in the urine was detected in a total of 18 of 36 (50%) informative cases. A total of 7 of 18 (39%) patients with prostate adenocarcinoma identified on their initial biopsy had detectable urinary GSTP1 methylation (58% sensitivity among informative cases). Abnormal urinary GSTP1 methylation was also detected in 7 of 21 (33%) patients without evidence of cancer on biopsy and in 4 of 6 (67%) patients diagnosed with atypia or high-grade prostatic intraepithelial neoplasia. Conclusions: We have demonstrated the feasibility of a novel, noninvasive molecular approach for the detection of epigenetic changes associated with prostate cancer. A screening test based on GSTP1 methylation in the urine specimens of patients with suspected prostate malignancy may be a useful adjunct to serum screening tests and digital rectal examination findings for identification of men at increased risk of harboring cancer despite a negative biopsy. This molecular assay has potential application for stratification of patients into low- and high-risk groups for surveillance versus repeat biopsy.

Enhanced radiation and chemotherapy-mediated cell killing of human cancer cells by small inhibitory RNA silencing of DNA repair factors

Abstract: Recent developments in the use of small inhibitory RNA molecules (siRNAs) to inhibit specific protein expression have highlighted the potential use of siRNA as a therapeutic agent. The double-strand break signaling/repair proteins ATM, ATR, and DNA-dependent protein kinase catalytic subunit (DNA-PK(cs)) are attractive targets to confer enhanced radio and chemosensitivity to tumor cells. We have designed and exogenously delivered plasmids encoding siRNAs targeting these critical kinases to human cancer cells to assess the feasibility of this concept as a clinically translatable experimental therapeutic. siRNA led to a approximately 90% reduction in target protein expression. siRNAs targeting ATM and DNA-PK(cs) gave rise to a dose-reduction factor of approximately 1.4 compared with untransfected and control vector-transfected cells at the clinically relevant radiation doses. This was greater than the radiosensitivity achieved using the phosphatidylinositol 3'-kinase inhibitor Wortmannin or DNA-PK(cs) competitive inhibitor LY294002. A similar increased sensitivity to the alkylating agent methyl methanesulfonate (MMS) was also observed for siRNA-mediated ATR silencing. Together, these data provide strong evidence for the potential use of siRNA as a novel radiation/chemotherapy-sensitizing agent.

Methyl-CpG-binding Domain Protein-2 Mediates Transcriptional Repression Associated with Hypermethylated GSTP1 CpG Islands in MCF-7 Breast Cancer Cells

Abstract: GSTP1, encoding the pi-class glutathione S-transferase, is commonly inactivated by somatic CpGisland hypermethylation in cancers of the prostate, liver, and breast. We report here thathypermethylation of CpG dinucleotides at the 5' transcriptional regulatory region was sufficient to inhibit GSTP1 transcription in MCF-7 breast cancer cells and that repression of GSTP1 transcription was mediated in part by the methyl-CpG-binding domain (MBD) protein MBD2. MCF-7 breast cancer cells contained only hypermethylated GSTP1 CpG island alleles and failed to express GSTP1 mRNA or GSTP1 polypeptides. In contrast, MCF-7/ADR cells contained only unmethylated GSTP1 CpG island alleles and exhibited abundant GSTP1 expression. Chromatin immunoprecipitation analysis detected the presence of MBD2 and DNMT1 at the GSTP1 promoter in MCF-7 breast cancer cells but not in MCF-7/ADR breast cancer cells. In a test of the contribution of MBD2 to GSTP1 repression in MCF-7 breast cancer cells, transfection of small interference RNA complementary to MBD2 mRNA into MCF-7 cells both reduced MBD2 polypeptide levels and stimulated GSTP1 mRNA expression. These findings implicate MBD2 in GSTP1 silencing associated with somatic GSTP1 CpG island hypermethylation in breast cancer cells.

Specific inhibition of DNMT1 by antisense oligonucleotides induces re-expression of estrogen receptor-alpha (ER) in ER-negative human breast cancer cell lines

Abstract: Recent studies have shown that changes in epigenetic regulation, such as DNA methylation and histone acetylation, are associated with silencing of the estrogen receptor a (ER) gene in ER-negative human breast cancer cells. Treatment of these cells with the general DNMT inhibitor, 5-aza-2'deoxycytidine, led to reactivation of functional ER protein. This study addresses the hypothesis that specific inhibition of the maintenance DNA methyltransferase, DNMT1, by antisense oligonucleotides (DNMT1 ASO) is sufficient to re-express the ER gene in ER-negative human breast cancer cell lines. MDA-MB-231 and Hs578t cells were transfected with 100 nM and 150 nM DNMT1 ASO respectively for three consecutive days and evidence of DNMT1 downregulation and functional ER re-expression was sought. Significant growth reduction was observed within 48 hr and persisted after 96 hr. DNMT1 expression was blocked after exposure to DNMT1 ASO as detected by RT-PCR, Western blot and enzymatic assay whereas a mutant DNMT1 ASO had little effect. This was associated with enhanced ER mRNA and protein expression and restoration of estrogen responsiveness in MDA-MB-231 cells as demonstrated by the ability of the induced ER protein to elicit ERE-regulated reporter activity from a luciferase reporter construct. Methylation specific PCR showed that the ER CpG island was minimally demethylated, suggesting that other epigenetic events, introduced by specific DNMT1 inhibition, might also be involved in ER re-expression. Our results suggest that specific inhibition of DNMT1 expression alone is sufficient to re-express ERa in human breast cancer cell lines.

Expression of the DNA-PK binding protein E4-34K fails to confer radiation sensitivity to mammalian cells.

Abstract: Purpose : The adenovirus E4orf6 34 kDa protein (E4-34k) is known to disrupt V(D)J recombination as a result of its interaction with the catalytic subunit of cellular DNA-dependent protein kinase (DNA-PK cs) , a major participant in the repair of DNA double-strand breaks (DSB). Previous studies have shown that cells with disrupted DSB repair and V(D)J recombination due to attenuation of DNA-PK cs activity exhibit a radiation-sensitive phenotype. It is not known at present whether the E4-34k protein can also modify cellular response to ionizing radiation. In an attempt to develop a novel gene therapy strategy to modify cellular radiation response, we sought to determine if expression of the adenovirus E4-34k protein resulted in sensitization to clinically relevant doses of ionizing radiation. Materials and methods : In order to minimize potential bias resulting from selection procedures, we performed clonogenic survival assays on DU 145 prostate cancer cells, RKO colorectal cancer cells and 293 kidney cells...

ENGINEERED RNAi ADENOVIRUS SILENCING EXPRESSION (ERASE) OF DNA REPAIR PROTEINS

Abstract: The present invention relates to compositions and methods for killing cancer cells and treating subjects having cancer comprising administering small inhibitory RNAs (siRNA) specific for DNA repair proteins in conjunction with administration of conventional DNA-damaging agents such as radiation and chemotherapeutic agents.