Telomeres are DNA sequences found at the ends of chromosomes that play a key role in controlling the life span of cells. With every cell division, telomeres get a bit shorter until eventually they become so short that the enzymes that copy DNA for cell division no longer work properly and the cell stops dividing. In a sense, telomeres function as a kind of counting mechanism that regulates how many times a cell can divide.
In contrast to normal cells, cancer cells divide continuously and uncontrollably. Scientists know that cancer cells produce an enzyme, called telomerase, which prevents telomeres from getting too short so cells can keep dividing. Telomerase is not used by healthy cells, and has been identified as a logical target for anticancer therapeutics. However, recent studies indicate that for this therapy to be effective, telomeres must be in a critically short state, requiring an extended treatment duration that can lead to drug resistance and other problems.
Dr. Hiroyuki Seimiya from the Japanese Foundation for Cancer Research in Tokyo and colleagues examined what happens to cancer cells when telomerase inhibition is combined with inhibition of an enzyme called tankyrase 1 that is involved in making telomeres accessible to telomerase. The researchers found that both tankyrase 1 activity and telomere shortening decrease the effects of telomerase inhibitors. Importantly, tankyrase inhibition enhanced telomere shortening upon treatment with a telomerase inhibitor and accelerated cancer cell death.
"This study provides insight into strategies for telomere-based molecular cancer therapeutics. We expect that inhibition of tankyrase 1 will compensate for incomplete inhibition of telomerase. Consequently, this strategy would shorten the time period of drug treatment that is required for the onset of telomere crisis and reduce the potential risk of acquired drug resistance, " writes Dr. Seimiya.
Hiroyuki Seimiya, Yukiko Muramatsu, Tomokazu Ohishi, and Takashi Tsuruo: "Tankyrase 1 as a target for telomere-directed molecular cancer therapeutics"
The context and implications of this work are discussed in a Preview by Shay et al.
The other members of the research team include Yukiko Muramatsu of the Japanese Foundation for Cancer Research in Tokyo; and Tomokazu Ohishi and Takashi Tsuruo of the Japanese Foundation for Cancer Research and University of Tokyo in Tokyo.
This work was funded in part by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan, and grants of Japanese Foundation for Multidisciplinary Treatment of Cancer and the Virtual Research Institute of Aging of Nippon Boehringer Ingelheim.
Publishing in Cancer Cell, Volume 7, Number 1, January 2005. www.cancercell.org