Telomere shortening and apoptosis in telomerase-inhibited human tumor cells

Abstract

Despite a strong correlation between telomerase activity and malignancy, the outcome of telomerase inhibition in human tumor cells has not been examined. Here, we have addressed the role of telomerase activity in the proliferation of human tumor and immortal cells by inhibiting TERT function. Inducible dominant-negative mutants of hTERT dramatically reduced the level of endogenous telomerase activity in tumor cell lines. Clones with short telomeres continued to divide, then exhibited an increase in abnormal mitoses followed by massive apoptosis leading to the loss of the entire population. This cell death was telomere-length dependent, as cells with long telomeres were viable but exhibited telomere shortening at a rate similar to that of mortal cells. It appears that telomerase inhibition in cells with short telomeres lead to chromosomal damage, which in turn trigger apoptotic cell death. These results provide the first direct evidence that telomerase is required for the maintenance of human tumor and immortal cell viability, and suggest that tumors with short telomeres may be effectively and rapidly killed following telomerase inhibition.

Mutated telomeres sensitize tumor cells to anticancer drugs independently of telomere shortening and mechanisms of telomere maintenance

“…The major limitation of telomerase inhibition is the time necessary for the telomeres to become critically short before the antiproliferative effects are observed. Several reports have shown, in fact, that inhibition of telomerase by either a dominant-negative protein or antisense oligonucleotides against hTR results effectively in death of tumor cells with short but not long telomeres (Hahn et al, 1999;Herbert et al, 1999;Zhang et al, 1999). A complementary strategy to block tumor cell growth is to use telomerase inhibition as a means to sensitize cancer cells to chemotherapeutic drugs or angiogenesis inhibitors (Kondo et al, 1998;Ludwig et al, 2001;Misawa et al, 2002;Chen et al, 2003;Tentori et al, 2003).…”

Combination therapy of malignant glioma cells with 2-5A-antisense telomerase RNA and recombinant adenovirus p53

“…More recently, it has been demonstrated that the complete inhibition of telomerase using a dominant-negative mutant of hTERT resulted in reduction in telomere length and apoptotic death of tumor cells. [26][27][28] Inhibition of hTERT function is expected to be particularly effective for tumors with short telomere because its antitumor effect was telomere lengthdependent.…”

“…These facts strongly support the idea that telomerase inhibition may represent a novel targeting approach for the treatment of malignant gliomas. Recently, it has been demonstrated that targeting the RNA template of telomerase (hTR) with antisense RNA [22][23][24][25] or inhibiting the function of a catalytic protein subunit of telomerase (hTERT) with a dominant-negative mutant [26][27][28] showed a significant antitumor effect. We have recently synthesized a 19-mer antisense oligonucleotide against hTR linked 2-5A (5′-phosphorylated 2′-5′-linked oligoadenylate) (2-5A-anti-hTR) and demonstrated its cytotoxic effect on malignant glioma cells 29,30 or prostate cancer cells.…”

Treatment of bladder cancer cells in vitro and in vivo with 2–5A antisense telomerase RNA

“…More recently, it has been demonstrated that the complete inhibition of telomerase using a dominant-negative mutant of hTERT resulted in reduction in telomere length and apoptotic cell death of tumor cells. 24,36,37 When the tumors with short telomere are treated, inhibition of hTERT function may be effective. On the other hand, 2-5A-anti-hTR induced caspase-dependent apoptosis in tumor cells.…”