Telomeres and
telomerase have been subjects to a tremendous attention from scientists and oncologists during the past 5 years. This interest has been motivated by the potential of
telomerase as a
tumor marker for the diagnosis and the prognosis of
cancer. The possible use of
telomerase or telomeres as new targets for anticancer drugs also triggered investigations. The expression of
telomerase was found in overall 85% of
cancers.
Telomerase is early expressed during
oncogenesis with a gradient indicating that a high level of
telomerase expression could be associated with a bad prognosis. Therefore, drugs targeting
telomerase and telomeres might be useful in many human
tumors with little restrictions regarding the
tumor type or on the stage of the disease. Moreover, since
telomerase is not or slightly expressed in normal cells, it has been postulated that drugs targeting
telomerase would induce low toxicity. The race for the discovery of
telomerase inhibitors has started while the identification of the components controlling
telomerase, telomeres, cell survival, senescence, and apoptosis was still in progress. The recent identification of components regulating telomere length and
telomerase expression (TRF1, TRF2, and
tankyrase) opened a variety of new opportunities to control
telomerase/telomere interactions. Meanwhile, a proof of principle was provided that changing telomere interactions with
telomere binding proteins by chemical or
biological means can induce
cancer cell death. Interestingly, recent data challenge the old paradigm which suggested that a long exposure to
telomerase and telomere inhibitors is necessary to induce anticancer effects. In this paper, we review the most recent information concerning the regulation of telomere length and
telomerase expression, with emphasis on mechanisms that might translate into new
drug discovery.