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Single-Cell Transcription Site Activation Predicts Chemotherapy Response in Human Colorectal Tumors

¹ Department of Anatomy and Structural Biology, Albert Einstein College of Medicine and ² Departments of Medicine and Cell Biology, Albert Einstein Cancer Center, Bronx, New York; ³ Department of Surgery, Thomas Jefferson University; and ⁴ Department of Cancer Biology, Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania

Requests for reprints: Robert H. Singer, Albert Einstein College of Medicine, Golding Building Room 601BA, 1300 Morris Park Avenue, Bronx, NY 10461. Phone: 718-430-8646; Fax: 718-430-8697; E-mail: rhsinger{at}aecom.yu.edu.

Key Words: FISH • transcription site • single-cell gene expression profiling • 5-Fluorouracil • colorectal cancer

Candidate gene and pathway approaches, and unbiased gene expression profiling, have identified marker signatures predictive of tumor phenotypes, such as drug sensitivity and invasive or metastatic potential. However, application of such information to evaluation of tumors in the clinic is limited by cell heterogeneity in the tumor. We have developed a novel method of fluorescence in situ hybridization (FISH) that can detect transcriptional activation of individual genes at their site in single cells in the interphase nucleus. A major obstacle in the treatment of colorectal cancer is relative insensitivity to the chemotherapeutic agent 5-Fluorouracil (5-FU). Here, we have developed a sensitive approach to predict relative sensitivity of colorectal cancer cells to 5-FU, using FISH with probes targeted to nascent mRNAs to measure the number of individual cells with active transcription sites for a panel of candidate genes. These results reveal that the transcriptional status of four key genes, thymidylate synthase (TYMS), MORF-related gene X (MRGX), Bcl2-antagonist/killer (BAK), and ATPase, Cu²⁺ transporting β polypeptide (ATP7B), can accurately predict response to 5-FU. As proof of principle, we show that this transcriptional profile is predictive of response to 5-FU in a small number of patient colon tumor tissues. This approach provides a novel ability to identify and characterize unique minor cell populations in the tumor that may exhibit relative resistance to chemotherapy. [Cancer Res 2008;68(13):4977–82]