Functional p53 is required for effective execution of telomerase inhibition in BCR-ABL-positive CML cells

Objective In chronic myeloid leukemia (CML), Increased cellular turnover of hematopoietic cells driven by the oncogene BCR-ABL leads to accelerated telomere shortening despite Increased telomerase activity It has been postulated that shortened telomeres, particularly in the context of increased telomerase activity, might facilitate accumulation of genetic aberrations and, consequently, disease progression from chronic phase to accelerated phase and blast crisis Therefore, inhibition of telomerase might be a promising approach in CML therapy Material and Methods To investigate the therapeutic potential of telomerase inhibition in this model disorder, we used a small molecule telomerase inhibitor, BIBR1532 as well as expression of a dominant-negative mutant of hTERT (DNhTERT IRES-GFP) in the p53-negative CML blast crisis cell line K562 and characterized the effects in long term culture Furthermore, we ex pressed an inducible p53 construct (vector pBabe p53ER(tam)) via retroviral transduction in cells with critically short telomeres and in cells with a normal telomere length to explain the role of the tumor suppressor in response to critical telomere shortening in BCR ABL-positive cells Results BIBR1532-treated bulk cultures did not show altered growth kinetics despite significant telomere shortening to a critical length of approximately 5 kb In comparison, DNhTERT expressing clones either lost telomere length, leading to a significant but transient slow down in proliferation but eventually all escaped senescence/crisis (group I) or, alternatively, remained virtually unaffected despite measurable telomerase inhibition (group II) Further analyses of group I clones revealed impaired DNA damage response and an accumulation of dicentric chromosomes However, upon restoration of p53 in telomerase-negative K562 clones with critically short telomeres, immediate reinduction of apoptosis and complete eradication of cells was observed, whereas vector control cells continued to escape from crisis Conclusions These results suggest that the success of strategies aimed at telomerase inhibition in CML is highly dependent on the presence of functional p53 and should be explored preferentially in chronic phase CML (C) 2011 ISEH - Society for Hematology and Stem Cells Published by Elsevier Inc