Telomeres are repetitive DNA sequences located at the ends of chromosomes that serve as cap-like protective mechanisms that allow complete DNA replication and help keep the chromosome structure intact. With each cell division, a normal chromosome's overall telomere length (TL) continually shortens. Once telomeres become too short, the cell undergoes senescence or apoptosis. In order to avoid this biological fate in cancer, a tumor cell can activate telomerase, an enzyme that prevents further telomere shortening by adding the telomeric hexa-nucleotide repeat sequence (5′-TTAGGG) to the ends of the chromosomes. A smaller fraction of tumor cells can elongate their TL by initiating the alternative lengthening of telomeres (ALT) pathway.
Previously investigated as a biomarker for aging and general disease, TL has recently shown promise as a possible biomarker in cancer. A TL pattern between cancers might then provide valuable diagnostic or prognostic information to create a better understanding of the molecular or pathogenic characteristics of specific cancer types.
To measure TLs or more accurately telomere repeats, we based our assay on a Monochrome Multiplex Quantitative PCR (Cawthon 2009). This approach measures the signal generated from the telomere repeats against the signal from a single copy gene in the same DNA sample. The method is unique in that it measures both fluorescent signals using one DNA-intercalating dye within the same reaction tube. We compared the TLs of various cancer cell line DNAs (n=27) derived from organ specific tumors to explore a cancer-specific pattern. Seven transformed cell lines or normal DNA samples were used as controls.
Preliminary data show that pancreatic (n=9) and prostate cancers (n=3) produce cell lines with much shorter TLs than those derived from breast cancer (n=4) and osteosarcoma (n=8). Between the shortest and longest TLs, a 4-fold TL range was observed with pancreatic, a 6-fold range difference between breast cancer, and as much as a 9-fold difference within the osteosarcoma group. The osteosarcoma cell lines divided into two sub-classes of very short and very long TLs. The long TLs could possibly a product of the activation of the ALT pathway as indicated by prior C-circle test results. Control lymphoblastoid cell lines (n=3) in general presented longer TLs than cancerous cell lines, except for the proposed ALT-pathway osteosarcoma lines (n= 5 of 8). Only 6/29 cancer cell lines had TLs greater than the normal female Promega DNA control (#G1528). We plan to further investigate additional cell lines and to validate the utility of the assay on matched tumor/normal pairs derived from FFPE specimens.
Citation Format: Daniel C. Edelman, David Petersen, Allison Gomez, Gabriela Canales, Holly Stevenson, Paul S. Meltzer. Measurement of telomere repeats in human cancer cell lines and tissues using a monochrome multiplex quantitative PCR assay. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3508. doi:10.1158/1538-7445.AM2013-3508