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The lack of telomerase does not affect cell growth until the telomeres are short enough to cause cells to "die or undergo growth arrest". However, inhibiting telomerase alone is not enough to destroy large tumors. It must be combined with surgery, radiation, chemotherapy or immunotherapy. [57]
Two concerns with applying telomerase inhibitors in cancer treatment are that effective treatment requires continuous, long-term drug application and that off-target effects are common. [30] For example, the telomerase inhibitor imetelstat, first proposed in 2003, [31] [32] has been held up in clinical trials due to hematological toxicity. [30]
The cause of these barriers is primarily due to the DNA at the end of chromosomes, known as telomeres. Telomeric DNA shortens with every cell division, until it becomes so short it activates senescence, so the cell stops dividing. Cancer cells bypass this barrier by manipulating enzymes (telomerase) to increase the length of telomeres.
Human chromosomes (grey) capped by telomeres (white). A telomere (/ ˈ t ɛ l ə m ɪər, ˈ t iː l ə-/; from Ancient Greek τέλος (télos) 'end' and μέρος (méros) 'part') is a region of repetitive nucleotide sequences associated with specialized proteins at the ends of linear chromosomes (see Sequences).
Cancer cells have unique features that make them "immortal" according to some researchers. The enzyme telomerase is used to extend the cancer cell's life span. While the telomeres of most cells shorten after each division, eventually causing the cell to die, telomerase extends the cell's telomeres. This is a major reason that cancer cells can ...
Alternative Lengthening of Telomeres (also known as "ALT") is a telomerase-independent mechanism by which cancer cells avoid the degradation of telomeres.. At each end of the chromosomes of most eukaryotic cells, there is a telomere: a region of repetitive nucleotide sequences which protects the end of the chromosome from deterioration or from fusion with neighboring chromosomes.
Telomerase replicates the telomere head and does not require ATP. [17] In most multicellular eukaryotic organisms , telomerase is active only in germ cells , some types of stem cells such as embryonic stem cells , and certain white blood cells . [ 9 ]
In some cells, such as germ cells, stem cells and white blood cells, the withdrawal process do not occur. This is to ensure that these cells continue dividing for body growth or reproduction. Such phenomena is brought about by the presence of telomerase, which would catalyse the reaction of adding nucleotide sequences to the ends of telomeres ...