Normalization of previously shortened telomere length under treatment with imatinib argues against a preexisting telomere length deficit in normal hematopoietic stem cells from patients with chronic myeloid leukemia

Cord blood telomere shortening associates with increased gestational age and birth weight in preterm neonates

Preterm birth is considered to be associated with premature cellular aging. To address this question, two hallmarks of aging were analyzed in cord blood cells, namely telomere length and age-associated DNA methylation. Cord blood samples from 35 preterm and 11 full-term neonates were enrolled in the present study. Furthermore, quantitative telomere fluorescence in situ hybridization and flow cytometry (flow-FISH) were applied to demonstrate that telomere shortening was strongly associated with advanced gestational age and increased birth weight (R²=0.267 for granulocytes and R²=0.307 for lymphocytes). The estimated rate of telomere attrition in newborns during gestation ranged from 126 base pairs (bp)/week and 186 bp/week for granulocytes and lymphocytes, respectively. In addition, neonates with longer telomeres at birth were characterized by increased weight gain during the first year of their life compared with that noted to neonates with shorter telomeres. By contrast, the epigenetic aging signature (EAS) revealed a negative correlation between epigenetic age and premature birth of unclear basis (R²=0.26). Pending prospective validation in a larger patient cohort, the present study suggested that telomere length may be a novel biomarker alone or in combination with traditional indicators for the prediction of weight development in preterm neonates.

An enhanced genetic model of relapsed IGH-translocated multiple myeloma evolutionary dynamics

Most patients with multiple myeloma (MM) die from progressive disease after relapse. To advance our understanding of MM evolution mechanisms, we performed whole-genome sequencing of 80 IGH-translocated tumour-normal newly diagnosed pairs and 24 matched relapsed tumours from the Myeloma XI trial. We identify multiple events as potentially important for survival and therapy-resistance at relapse including driver point mutations (e.g., TET2), translocations (MAP3K14), lengthened telomeres, and increased genomic instability (e.g., 17p deletions). Despite heterogeneous mutational processes contributing to relapsed mutations across MM subtypes, increased AID/APOBEC activity is particularly associated with shorter progression time to relapse, and contributes to higher mutational burden at relapse. In addition, we identify three enhanced major clonal evolution patterns of MM relapse, independent of treatment strategies and molecular karyotypes, questioning the viability of "evolutionary herding" approach in treating drug-resistant MM. Our data show that MM relapse is associated with acquisition of new mutations and clonal selection, and suggest APOBEC enzymes among potential targets for therapy-resistant MM.

Replicative cellular age distributions in compartmentalized tissues

The cellular age distribution of hierarchically organized tissues can reveal important insights into the dynamics of cell differentiation and self-renewal and associated cancer risks. Here, we examine the effect of progenitor compartments with varying differentiation and self-renewal capacities on the resulting observable distributions of replicative cellular ages. We find that strongly amplifying progenitor compartments, i.e. compartments with high self-renewal capacities, substantially broaden the age distributions which become skewed towards younger cells with a long tail of few old cells. For several of these strongly amplifying compartments, the age distribution becomes virtually independent of the influx from the stem cell compartment. By contrast, if tissues are organized into many downstream compartments with low self-renewal capacity, the shape of the replicative cell distribution in more differentiated compartments is dominated by stem cell dynamics with little added variation. In the limiting case of a strict binary differentiation tree without self-renewal, the shape of the output distribution becomes indistinguishable from that of the input distribution. Our results suggest that a comparison of cellular age distributions between healthy and cancerous tissues may inform about dynamical changes within the hierarchical tissue structure, i.e. an acquired increased self-renewal capacity in certain tumours. Furthermore, we compare our theoretical results to telomere length distributions in granulocyte populations of 10 healthy individuals across different ages, highlighting that our theoretical expectations agree with experimental observations.

The Effect of Cancer Treatments on Telomere Length: A Systematic Review of the Literature

Background

It has been hypothesized that cancer treatments cause accelerated aging through a mechanism involving the shortening of telomeres. However, the effect of cancer treatments on telomere length is unclear.

Methods

We systematically reviewed the epidemiological evidence evaluating the associations between cancer treatment and changes in telomere length. Searches were performed in PubMed for the period of January 1966 through November 2016 using the following search strategy: telomere AND (cancer OR tumor OR carcinoma OR neoplasm) AND (survivor OR patient). Data were extracted and the quality of studies was assessed.

Results

A total of 25 studies were included in this review. Ten were solid cancer studies, 11 were hematological malignancy studies, and 4 included a mixed sample of both solid and hematological cancers. Three of the 10 solid tumor studies reported a statistically significant association between cancer treatment and telomere length shortening, and one reported longer telomere length after treatment. Among the hematological cancer studies, three showed statistically significant decreases in telomere length with treatment, and two showed elongation. When these studies were rated using quality criteria, most of the studies were judged to be of moderate quality.

Conclusions

The findings from this review indicate that the effect of cancer treatment on telomere length may differ by cancer type and treatment as well as other factors. Definitive conclusions cannot be made based on the published literature, because sample sizes tended to be small; treatments, cancer types, and biospecimens were heterogenous; and the length of follow-up times differed greatly.

Telomere shortening correlates with leukemic stem cell burden at diagnosis of chronic myeloid leukemia

Telomere length (TL) in peripheral blood (PB) cells of patients with chronic myeloid leukemia (CML) has been shown to correlate with disease stage, prognostic scores, response to therapy, and disease progression. However, due to considerable genetic interindividual variability, TL varies substantially between individuals, limiting its use as a robust prognostic marker in individual patients. Here, we compared TL of BCR-ABL^-, nonleukemic CD34⁺CD38^- hematopoietic stem cells (HSC) in the bone marrow of CML patients at diagnosis to their individual BCR-ABL⁺ leukemic stem cell (LSC) counterparts. We observed significantly accelerated telomere shortening in LSC compared with nonleukemic HSC. Interestingly, the degree of LSC telomere shortening was found to correlate significantly with the leukemic clone size. To validate the diagnostic value of nonleukemic cells as internal controls and to rule out effects of tyrosine kinase inhibitor (TKI) treatment on these nontarget cells, we prospectively assessed TL in 134 PB samples collected in deep molecular remission after TKI treatment within the EURO-SKI study (NCT01596114). Here, no significant telomere shortening was observed in granulocytes compared with an age-adjusted control cohort. In conclusion, this study provides proof of principle for accelerated telomere shortening in LSC as opposed to HSC in CML patients at diagnosis. The fact that the degree of telomere shortening correlates with leukemic clone's size supports the use of TL in leukemic cells as a prognostic parameter pending prospective validation. TL in nonleukemic myeloid cells seems unaffected even by long-term TKI treatment arguing against a reduction of telomere-mediated replicative reserve in normal hematopoiesis under TKI treatment.

Telomere Biology of Human Hematopoietic Stem Cells

BACKGROUND

Telomeres are protein DNA structures present at the ends of chromosomes and are essential for genetic stability and cell replication. Telomerase is the enzyme complex that maintains telomere integrity. Hematopoietic stem cells express telomerase and contain long telomeres, which become shorter as cells differentiate and mature. The extent of telomere shortening and the level of telomerase activity often correlate with the presence and severity of some hematopoietic diseases.

METHODS

The fundamentals of telomeres and telomerase are reviewed, and the telomere biology of human hematopoietic cells is discussed.

RESULTS

Telomere length and telomerase activity are important in the self-renewal of hematopoietic stem cells. Changes within these compartments affect both normal hematopoietic cells and the generation of hematopoietic disease. Telomere length provides information pertaining to the proliferative history and potential of a hematopoietic cell.

CONCLUSIONS

The role of telomerase and telomeres within the hematopoietic compartment needs further clarification. Advances in our knowledge in this field may improve clinical outcomes for the treatment of hematologic disease.

Potential mechanisms of disease progression and management of advanced-phase chronic myeloid leukemia

Despite vast improvements in the treatment of Philadelphia chromosome-positive chronic myeloid leukemia (CML) in chronic phase (CP), advanced stages of CML, accelerated phase or blast crisis, remain notoriously difficult to treat. Treatments that are highly effective against CML-CP produce disappointing results against advanced disease. Therefore, a primary goal of therapy should be to maintain patients in CP for as long as possible, by (1) striving for deep, early molecular response to treatment; (2) using tyrosine kinase inhibitors that lower risk of disease progression; and (3) more closely observing patients who demonstrate cytogenetic risk factors at diagnosis or during treatment.

Evolutionary dynamics of chronic myeloid leukemia

Cancer is an evolutionary process that arises due to mutations and expands through the selection of clones with higher reproductive success that will outcompete their peers. Most tumors require many mutations to explain the cancer phenotype, making it difficult to identify the gene(s) that confer the reproductive fitness to the clone. Moreover, the impact of any oncogene is context dependent: it can increase the fitness of particular stages of cell differentiation but not other stages. In addition, the fitness advantage of an oncogene is not irreversible: sometimes it can be reversed with targeted therapy, for example. The understanding of these dynamical processes and their consequences may be greatly simplified when addressed from an evolutionary perspective. Using the dynamics of chronic myeloid leukemia-perhaps the best understood human neoplasm-as an example, we show how three fundamental evolutionary behaviors provide insights into the dynamics of this disease: (1) BCR-ABL does not affect the reproductive success of any cell within the stem cell pool (resulting therefore in neutral drift), (2) BCR-ABL expression gives a fitness (selective) advantage to progenitor cells, and (3) imatinib therapy reduces the fitness of progenitor cells expressing the oncogene (selective disadvantage) and consequently leads to significant reductions in disease burden. These three different evolutionary dynamics scenarios based on the interpretation of mutation and gene expression as potentially leading to a fitness imbalance of cell populations clearly explain the course of the disease, providing as such a better grasp of cancer dynamics and the role of related therapies.

Telomere biology in hematopoiesis and stem cell transplantation

Telomeres are long (TTAGGG)(n) nucleotide repeats and an associated protein complex located at the end of the chromosomes. They shorten with every cell division and, thus are markers for cellular aging, senescence, and replicative capacity. Telomere dysfunction is linked to several bone marrow disorders, including dyskeratosis congenita, aplastic anemia, myelodysplastic syndrome, and hematopoietic malignancies. Hematopoietic stem cell transplantation (HSCT) provides an opportunity in which to study telomere dynamics in a high cell proliferative environment. Rapid telomere shortening of donor cells occurs in the recipient shortly after HSCT; the degree of telomere attrition does not appear to differ by graft source. As expected, telomeres are longer in recipients of grafts with longer telomeres (e.g., cord blood). Telomere attrition may play a role in, or be a marker of, long term outcome after HSCT, but these data are limited. In this review, we discuss telomere biology in normal and abnormal hematopoiesis, including HSCT.

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 expressed 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.

Effect of imatinib on the signal transduction cascade regulating telomerase activity in K562 (BCR-ABL-positive) cells sensitive and resistant to imatinib

OBJECTIVE

Imatinib mesylate (IM) is a tyrosine kinase inhibitor selective for BCR-ABL and indicated for the treatment of chronic myeloid leukemia. It has recently been demonstrated that IM also targets other cellular components. Considering the significant role of telomerase in malignant transformation, we studied the effect of IM on telomerase activity (TA) and regulation in BCR-ABL-positive and -negative cells, sensitive and resistant to IM.

MATERIALS AND METHODS

Through combining telomeric repeat amplification protocol for detecting TA, reverse transcription polymerase chain reaction and Western blots for detecting RNA and protein levels of telomerase regulating proteins and fluorescence-activated cell sorting analysis, we showed that IM targets telomerase and the signal transduction cascade upstream of it.

RESULTS

IM significantly inhibited TA in BCR-ABL-positive and -negative cells and in chronic myeloid leukemia patients. TA inhibition was also observed in BCR-ABL positive cells resistant to IM at drug concentrations that did not lead to a reduction in BCR-ABL expression. In addition, a reduction in phosphorylated AKT and phosphorylated PDK-1 was also detected following IM incubation.

CONCLUSIONS

We demonstrate an inhibitory effect of IM on TA and on the AKT/PDK pathway. Because this effect was observed in cell expressing the BCR-ABL protein as well as cells not expressing it, and in cells sensitive as well as resistant to IM, it is reasonable to assume that the inhibitory effect of IM on TA is not mediated through known IM targets. The results of this study show that cells resistant to IM with regard to its effect on BCR-ABL could still be sensitive to IM treatment regarding other cellular components.

Tyrosine kinase inhibitor therapy can cure chronic myeloid leukemia without hitting leukemic stem cells

BACKGROUND

Tyrosine kinase inhibitors, such as imatinib, are not considered curative for chronic myeloid leukemia--regardless of the significant reduction of disease burden during treatment--since they do not affect the leukemic stem cells. However, the stochastic nature of hematopoiesis and recent clinical observations suggest that this view must be revisited.

DESIGN AND METHODS

We studied the natural history of a large cohort of virtual patients with chronic myeloid leukemia under tyrosine kinase inhibitor therapy using a computational model of hematopoiesis and chronic myeloid leukemia that takes into account stochastic dynamics within the hematopoietic stem and early progenitor cell pool.

RESULTS

We found that in the overwhelming majority of patients the leukemic stem cell population undergoes extinction before disease diagnosis. Hence leukemic progenitors, susceptible to tyrosine kinase inhibitor attack, are the natural target for chronic myeloid leukemia treatment. Response dynamics predicted by the model closely match data from clinical trials. We further predicted that early diagnosis together with administration of tyrosine kinase inhibitor opens the path to eradication of chronic myeloid leukemia, leading to the wash out of the aberrant progenitor cells, ameliorating the patient's condition while lowering the risk of blast transformation and drug resistance.

CONCLUSIONS

Tyrosine kinase inhibitor therapy can cure chronic myeloid leukemia, although it may have to be prolonged. The depth of response increases with time in the vast majority of patients. These results illustrate the importance of stochastic effects on the dynamics of acquired hematopoietic stem cell disorders and have direct relevance for other hematopoietic stem cell-derived diseases.

FISH glossary: an overview of the fluorescence in situ hybridization technique

The introduction of FISH (fluorescence in situ hybridization) marked the beginning of a new era for the study of chromosome structure and function. As a combined molecular and cytological approach, the major advantage of this visually appealing technique resides in its unique ability to provide an intermediate degree of resolution between DNA analysis and chromosomal investigations while retaining information at the single-cell level. Used to support large-scale mapping and sequencing efforts related to the human genome project, FISH accuracy and versatility were subsequently capitalized on in biological and medical research, providing a wealth of diverse applications and FISH-based diagnostic assays. The diversification of the original FISH protocol into the impressive number of procedures available these days has been promoted throughout the years by a number of interconnected factors: the improvement in sensitivity, specificity and resolution, together with the advances in the fields of fluorescence microscopy and digital imaging, and the growing availability of genomic and bioinformatic resources. By assembling in a glossary format many of the "acronymed" FISH applications published so far, this review intends to celebrate the ability of FISH to re-invent itself and thus remain at the forefront of biomedical research.

hTERT, the catalytic component of telomerase, is downregulated in the haematopoietic stem cells of patients with chronic myeloid leukaemia

Telomere shortening is associated with disease progression in chronic myeloid leukaemia (CML). To investigate the biology and regulation of telomerase in CML, we evaluated expression of the telomerase components, its regulators and several telomeric-associated proteins. Quantitative real-time-polymerase chain reaction (PCR) was used to compare gene expression in the CD34+/leukaemic blast cells of 22 CML patient samples to the CD34+ cell population of healthy individuals. hTERT, the catalytic component of telomerase, was downregulated in eight of 12 chronic phase (CP) patients (P = 0.0387). Furthermore, hTERT was significantly downregulated in two of three patients in accelerated phase (AP) and seven of seven patients in blast crisis (BC), P = 0.0017. Expression of hTR and telomeric-associated proteins TEP1, TRF1, TRF2, tankyrase and PinX1 was high in the majority of CP and AP patients. With the exceptions of TEP1 and hTR, expression of these factors was highest in CP and decreased during disease progression. Expression of c-Myc, a positive regulator of hTERT transcription, correlated with hTERT expression and decreased with disease progression, falling below control levels in BC. hTERT levels were increased in CP patients following successful treatment with imatinib, relative to untreated CP patients. We suggest that reduced hTERT expression directly causes the shortened telomeres observed in CML.

Telomere length dynamics in normal hematopoiesis and in disease states characterized by increased stem cell turnover

Telomeres both reflect and limit the replicative lifespan of normal somatic cells. Immature sub-populations of human CD34+38- hematopoietic stem cell (HSC) can be identified in vitro based on their growth kinetics and telomere length. Fluorescence in situ hybridization and flow cytometry (flow-FISH) has been used to characterize telomere length dynamics as a surrogate marker for HSC turnover in vivo. Investigations in normal steady-state hematopoiesis provided the basis for follow-up studies in model scenarios characterized by increased HSC turnover. Disorders with underlying malignant transformation of HSC (e.g., chronic myeloid leukemia (CML)) can be discriminated from disease states with increased HSC turnover rates secondary to depletion of the stem cell compartment, for example, as in defined bone marrow failure syndromes. In some of these model scenarios, the degree of telomere shortening can be correlated with disease duration, disease stage and severity as well as with response to disease-modifying treatment strategies. Whether increased telomere shortening represents a causal link between HSC turnover, replicative senescence and/or the induction of genetic instability in acquired HSC disorders remains to be shown. However, data from congenital disorders, like dyskeratosis congenita (DKC), suggest that disturbed telomere maintenance may play a role for replicative exhaustion of the HSC pool in vivo.

The importance of the telomere and telomerase system in hematological malignancies

Telomeres are specialized chromosomal end structures composed of repeat TTAGGG sequences in humans. They shorten with each cell division and thus serve as the "mitotic clock" of the cell. One of their main functions is the maintenance of chromosomal integrity and their excessive shortening is associated with DNA instability. Telomerase, a unique reverse transcriptase, is inactive in most somatic human cells and is up-regulated in most cancer cells. Recently, the biology of the telomere/telomerase system has attracted much attention because of its possible role in carcinogenesis and aging. In this article we review the biology of this system and its relevance to normal and malignant hematopoietic cells. The biological, diagnostic and prognostic value of telomere/telomerase biology is discussed, as well as its potential future applications in cancer therapeutics.

Telomere length and telomerase activity in the BCR-ABL-transformed murine Pro-B cell line BaF3 is unaffected by treatment with imatinib

OBJECTIVE

Imatinib mesylate is a novel tyrosine kinase inhibitor used for the treatment of Philadelphia chromosome positive (Ph+) leukemia and other malignancies. In previous studies, we found significant telomere shortening in Ph+ cells from patients with chronic myeloid leukemia (CML). Interestingly, imatinib treatment was found to lead to a normalization of previously shortened telomere length in CML patients. Based on recent reports demonstrating that c-ABL phosphorylates hTERT and thereby inhibits hTERT activity, a direct effect of imatinib on hTERT activity leading to telomere elongation in BCR-ABL-positive cells has been proposed by others. Such an effect could be of potential importance for telomere maintenance in Ph+ cells by facilitating clonal selection and progression of the disease to blast crisis.

METHODS

We investigated the impact of imatinib on telomere length and telomerase activity of the interleukin-3 (IL-3)-dependent murine pro-B cell line BaF3 and the BCR-ABL-positive, IL-3-independent transfectant BaF3p185 in vitro.

RESULTS

When BaF3 and BaF3p185 cells were treated with imatinib (the latter being rescued with IL-3), no effect on either telomerase activity or telomere length was observed. These findings can be explained by the cytoplasmatic localization of BCR-ABL found in BaF3p185 as compared to the nuclear localization of telomerase (and c-ABL).

CONCLUSION

As opposed to recent reports for c-ABL, we do not see evidence for a functional interaction between BCR-ABL and hTERT in this model system arguing against imatinib-mediated upregulation of hTERT as a crucial factor for clonal selection and disease progression of CML.

Shared phenotypes among segmental progeroid syndromes suggest underlying pathways of aging

Segmental progeroid syndromes are those whose phenotypes resemble accelerated aging. Here we analyze those phenotypes and hypothesize that short telomeres produce the same group of symptoms in a variety of otherwise unrelated progeroid syndromes. Specific findings are the following: (a) short telomeres in some progeroid syndromes cause an alopecia/osteoporosis/fingernail-atrophy group of symptoms; (b) fingernail atrophy in progeroid syndromes resembles the natural slowing of nail growth that occurs in normal aging and nail growth velocity, and may be a marker of replicative aging in keratinocyte stem cells; (c) alopecia and reduced hair diameter parallel the nail results; (d) osteoporosis in Dyskeratosis Congenita resembles age-related osteoporosis, but the same is not true of other progerias; and (e) gray hair is associated with short telomeres, but may also involve reactive oxygen species. On the basis of these results, we make several predictions and discuss how the segmental quality of progeroid syndromes may provide insight into normative aging.

Statins enhance migratory capacity by upregulation of the telomere repeat-binding factor TRF2 in endothelial progenitor cells

BACKGROUND

Cultivation of endothelial progenitor cells (EPCs) leads to premature replicative senescence, limiting ex vivo expansion for potential clinical cell therapy. Recent studies have linked senescence to the dysfunction of telomeres, the "ends" of chromosomes, via the so-called mitotic clock or culture-induced stress. The purpose of this study was to elucidate a possible role of telomere biology in the functional augmentation of EPCs by statins.

METHODS AND RESULTS

Human EPCs were isolated from peripheral blood. Using flow cytometry after fluorescence in situ hybridization with a telomere-specific (C3TA2)3 peptide nucleic acid probe (Flow-FISH), we found mean telomere length in untreated EPCs from healthy subjects to range between 8.5+/-0.2 and 11.1+/-0.5 kb with no change over 6 days of culture, excluding telomere erosion as one cause for premature senescence. Although mean telomere length did not differ between statin-treated and untreated EPCs, atorvastatin (0.1 micromol/L) and mevastatin (1.0 micromol/L) both led to a more than 3-fold increase in the expression of the telomere capping protein TRF2 (telomere repeat-binding factor), as shown by immunoblotting, whereas quantitative reverse transcription-polymerase chain reaction demonstrated no increase in TRF2 mRNA. Telomere dysfunction of EPCs was also paralleled by a 4-fold increase in the DNA damage checkpoint-kinase 2 (Chk2). Conversely, statin cotreatment or overexpression of TRF2 completely suppressed Chk2 induction. Finally, overexpression of a dominant negative mutant of the TRF2 protein abrogated statin-induced enhancement of migratory activity down to baseline values.

CONCLUSIONS

Ex vivo culturing of EPCs leads to "uncapping" of telomeres, indicated by the loss of TRF2. Statin cotreatment of EPCs prevents impairment of their functional capacity by a TRF2-dependent, posttranscriptional mechanism. This is the first time a beneficial effect of statins on telomere biology has been described.

Suppression of bcr-abl synthesis by siRNAs or tyrosine kinase activity by Glivec alters different oncogenes, apoptotic/antiapoptotic genes and cell proliferation factors (microarray study)

Short 21-mer double-stranded/small-interfering RNAs (ds/siRNAs) were designed to target bcr-abl mRNA in chronic myelogenous leukemia. The ds/siRNAs were transfected into bcr-abl-positive K-562 (derived from blast crisis chronic myelogenous leukemia), using lipofectamine. Penetrating of ds/siRNAs into the cells was detected by fluorescent confocal microscopy, using fluorescein-labeled ds/siRNAs. The cells were treated with mix of three siRNA sequences (3 x 60 nM) during 6 days with three repetitive transfections. The siRNA-treatment was accompanied with significant reduction of bcr-abl mRNA, p210, protein tyrosine kinase activity and cell proliferation index. Treatment of cells with Glivec (during 8 days with four repetitive doses, 180 nM single dose) resulted in analogous reduction of cell proliferation activity, stronger suppression of protein tyrosine kinase activity, and very low reduction of p210. siRNA-mix and Glivec did not affect significantly the viability of normal lymphocytes. Microarray analysis of siRNA- and Glivec-treated K-562 cells demonstrated that both pathways of bcr-abl suppression were accompanied with overexpression and suppression of many different oncogenes, apoptotic/antiapoptotic and cell proliferation factors. The following genes of interest were found to decrease in relatively equal degree in both siRNA- and Glivec-treated cells: Bcd orf1 and orf2 proto-oncogene, chromatin-specific transcription elongation factor FACT 140-kDa subunit mRNA, gene encoding splicing factor SF1, and mRNA for Tec protein tyrosine kinase. siRNA-mix and Glivec provoked overexpression of the following common genes: c-jun proto-oncogene, protein kinase C-alpha, pvt-1 oncogene homologue (myc activator), interleukin-6, 1-8D gene from interferon-inducible gene family, tumor necrosis factor receptor superfamily (10b), and STAT-induced STAT inhibitor.

Antisense inhibition of Bcr-Abl/c-Abl synthesis promotes telomerase activity and upregulates tankyrase in human leukemia cells

Clinical studies in chronic myelogenous leukemia demonstrate that the overexpression of Bcr-Abl tyrosine kinase is usually accompanied by relatively low telomerase activity in the chronic phase, which reverts to a high activity in blast crisis. The present study was designed to investigate the cross-talk between both enzymes, using Bcr-Abl-positive K-562 and Bcr-Abl-negative Jurkat cell lines, treated with antisense oligodeoxyribonucleotides (ODNs) against Bcr-Abl/c-Abl mRNA. The decreased amount and enzyme activity of Bcr-Abl/c-Abl provoked telomerase activation in both cell lines. After short-term treatment with anti-Bcr-Abl/c-Abl ODNs (6 days), no variations in hTERT and phospho-hTERT were detected. The decreased amount of Bcr-Abl/c-Abl was accompanied by: alterations in telomeric associated proteins-overexpression of tankyrase and decreased amount of TRF1/Tin2, cell growth arrest of K-562 cells, reaching a plateau after 6 days treatment, and increased proliferating activity of Jurkat cells. No changes in telomere length were detected after short-term treatment. In contrast, after long-term treatment with anti-Bcr-Abl/c-Abl ODNs (36 days), a significant elongation of telomeres and enhancement of hTERT were established, accompanied by an increased proliferating activity of both cell lines. These data provide evidence that the inhibition of Bcr-Abl or c-Abl synthesis keeps a potential to restore or induce cell proliferation through telomere lengthening control and telomerase activation.