Promoter Hypermethylation: A New Therapeutic Target Emerges in Urothelial Cancer Richard J. Cote, Peter W. Laird, and Ram H. Datar, Departments of Pathology and Urology; Biochemistry, Molecular Biology, and Surgery; and Pathology, University of Southern California Keck School of Medicine, Los Angeles, CA Significant changes in the global levels and regional patterns of DNA methylation are among the earliest and most frequent events known to occur in human cancers. 1 Alterations in DNA methylation have a direct impact on both the mutational and epigenetic components of neoplastic transformation. Important effects of DNA methylation on the genome include mutational burden of 5-methylcytosine, epigenetic effects of promoter methylation on gene tran- scription and potential gene activation, and induction of chromosomal instability by DNA hypomethylation. 2,3 Hy- permethylation of cytosine-guanine dinucleotide (CpG) is- lands is associated with transcriptional repression, whereas hypomethylation may lead to increased potential for gene activity or chromosomal instability. CpG islands located in tumor suppressor gene promoters are normally unmethyl- ated. Abnormal methylation of these regions may lead to progressive reduction in gene expression, thus transcrip- tionally silencing suppressor genes by a variety of mecha- nisms, including remodeling of local chromatin structure or inhibition of transcription factor binding, ultimately altering normal cellular growth properties. Application of novel molecular biologic techniques has increased our ap- preciation of the widespread changes in methylation pat- terns that occur during urinary bladder carcinogenesis. Epigenetic events, such as methylation, occur throughout all stages of tumorigenesis, including the early phases, and are increasingly recognized as major mechanisms involved in silencing tumor suppressor genes. A large number of genes have been reported to be hypermethylated in bladder cancer. The frequency of such events suggests that widespread alterations in the patterns of DNA methylation are common in bladder carcinogene- sis. Some examples include the p16 gene (at CDKN2A INK4a locus on chromosome 9p21), E-cadherin gene (CDH1, en- coding a transmembrane glycoprotein that modulates calcium-dependent intercellular adhesion), and RASSF1A gene (ras association domain family gene 1, isoform A). 4-6 Diminished CDH1 expression may lead to increase in beta- catenin activity and proliferation in urothelial carcinomas. 7 Aside from deletion and mutation, the p16 gene has been shown to be inactivated by promoter methylation. 8-11 Mu- tation or deletion of one p16 allele and hypermethylation of the remaining allele may be sufficient for loss of functional activity. Progressive inhibition of p16 expression by DNA methylation may result in loss of adequate growth regula- tory function. Methylation of p16 has been observed in 27% to 60% of primary urothelial carcinomas. 12,13 Both p16INKa and p14ARF hypermethylation may be involved in bladder carcinogenesis. 14 p14ARF promoter hypermethyl- ation in plasma DNA may also be an indicator of disease recurrence in bladder cancer patients. 15 A variety of techniques are available for assessment of DNA methylation. Methylation-specific polymerase chain reaction 16 and methylation-sensitive single nucleotide primer extension 17 are among the most widely used tech- niques for identification and characterization of novel methylation changes associated with bladder carcinogene- sis. This method has been used to detect methylation differ- ences between the genomes of normal and tumor bladder cancer tissues and cell lines. 18 The development of Methy- Light technology has further improved the ability to assess the methylation patterns in a high-throughput manner. 19 Gene expression microarray analysis has also been used to characterize methylation changes in bladder cancer cells after treatment with 5-aza-2'-deoxycytidine. 20 Given that DNA-based tumor markers can be characterized by unique specificity, they make an attractive target for molecular diagnosis of cancer in body fluids such as blood serum, plasma, and urine. Methylation changes in DNA isolated from body fluids such as urine or blood may serve as useful adjuncts to current techniques for disease detection or surveillance. The potential clinical value of DNA-based JOURNAL OF CLINICAL ONCOLOGY E D I T O R I A L VOLUME 23  NUMBER 13  MAY 1 2005 2879 Journal of Clinical Oncology, Vol 23, No 13 (May 1), 2005: pp 2879-2881 DOI: 10.1200/JCO.2005.11.923 Downloaded from ascopubs.org by 52.91.93.142 on December 18, 2022 from 052.091.093.142 Copyright © 2022 American Society of Clinical Oncology. All rights reserved.