Abnormalities related to telomere organization has been described in many cases of cancer [8, 32, 28, 10, 33]. On the other, hand few investigations have explored the telomere organization in CML, regarding its dynamics during the disease progression. For the first time, we compare the telomere organization in two distinct phases of the disease, whose samples became from the same patient. By using 3D nuclear telomeric analysis, it was possible to determine the telomere numbers, the presence of telomere aggregates, telomere signal intensities, nuclear volumes, and nuclear telomere distribution in CML cells. In addition, at the gene expression level, we demonstrated differences in both CML groups, by comparing the expressions of AURKA and AURKB genes. These parameters, independently, became possible subdivide the CML cells into distinct subgroups. Thus, our results are compatible with the “thesis” that telomere abnormalities generate genomic instability, leading to the CML cells transformation, during the evolution of the disease.
Samassekou et al. (2013)  identified abnormal telomere nuclear organization profile on twelve patients diagnosed with CML in chronic phase. According to their analysis the samples were characterized by a high number of telomeric aggregates, and changes in telomeric position. Despite of the absence of correlation with clinical data, Samassekou et al. (2013)  confirmed that the telomeres abnormalities observed in CML samples manifested in an early stage of malignancy. Some studies have pointed that telomere from CML cells are shorter than those from healthy leukocytes and are also associated with poor prognostic [34–36]. A high number of telomeric aggregates is closely associated to genomic instability .
According to our results the number of telomeric aggregates increases when the disease progress from chronic to accelerated/blastic phase. Therefore, some factors have been proposed to be responsible for telomere abnormalities in CML. The rapid proliferation rate of leukemic cells may represent the force underlying telomere abnormalities. From a not yet clear way, during the disease evolution, telomere abnormalities might be able to induce cell proliferation in one cell lineage, and apoptosis in another cell population, at the same time. In the first situation, the genomic instability gives the cells a proliferative advantage. For the second ones, the genomic instability leads to cell death. This imbalance could explain the clonal expansion and the selective apoptosis in the bone marrow of CML patients . In addition, the elevated activity of tyrosine kinase can generate reactive oxygen species, which are prone to cause damage on telomeres. The occurrence of these events over the course of the disease corroborates for the increase level of genomic instability, making treatment strategies less effective .
Previous studies have pointed out that the 3D nuclear telomere abnormalities act as reliable biomarker to predict disease evolution [10, 11, 28, 32]. Our investigation has demonstrated that is possible to distinguish between “cellular status” of lower/elevated level of genomic instability, considering the presence and frequency of telomere aggregates. We found telomere aggregates in all samples. However, significant difference between was observed between chronic and accelerated/blastic phase (Table 2; p < 0.001). This evidence makes the nuclear telomere analysis an indicator of disease progression and become the CML an important model to clarify molecular mechanisms underlying tumorigenesis.
Some studies have pointed out that telomere positions, in the nuclei, may act as an important factor beyond chromosome territory. Thus, disruptions in this dynamic process can produce as consequence a differential gene expression pattern, induce chromosomal abnormalities, and disrupt cell function [27, 39–42]. It is possible that in CML, the differential positioning of telomeres may be a consequence of BCR::ABL1 activity, additional chromosomal abnormalities, as seen in different stages of the disease, and gene expression. AURKA and AURKB mRNA were expressed at significantly higher levels in both CML subgroups, when compared to healthy donors.
The relative expression of AURKA and AURKB genes, by adopting the mean value from ΔCt, identified two distinct subgroups of CML patients, based on clinical and cytogenetic evidence. Gene amplification may be one, but not the main mechanism leading to overexpression of aurora genes. It´s possible that telomere disruption, in some way, may be related to aurora kinase overexpression and, therefore, to induce mitotic abnormalities. Few years ago, we have demonstrated that AURKA and AURKB overexpression were associated with genomic instability in cytogenetically stratified group (Normal vs. Abnormal karyotype) of hematopoietic cells and bone marrow derived mesenchymal stem cells (MSCs) of myelodysplastic syndrome patients . However, the regulation of AURKA during DNA damage remains most of the time to be well elucidated .
Overexpression and amplification of the Aurora kinase genes, particularly AURKA, have been documented for many types of neoplasia, with some data evidencing association with clinical parameters, survival, and cancer risk . In human breast cancer, overexpression of these kinases induced aneuploidy, centrosome amplification and tumorigenic transformation. Altered expression of these genes was also reported to correlate with the invasiveness and chromosomal instability of the disease . In agreement, our results suggest that overexpression of AURKA and AURKB are associated with genomic instability and markers of poor prognosis during CML evolution.
This study demonstrates that 3D telomere organization and the expression levels of aurora kinase genes can be used to subgroup CML patients. Classifying CML patients based on these characteristics might represent an important strategy to define better therapeutic strategies. Our results also suggest an association between progressive telomeric dysfunction and elevated aurora kinase expression, as important components for the evolution of CML. Like previous studies, we found telomere profiles in CML to correlate with distinct clinical phases of the disease [10, 11, 27, 28, 32]. Thus, we propose that 3D telomere organization may be a novel prognostic marker in hematological disorders with define stages driven by genomic instability. However, our study has one limitation, the cohort of patients was relatively small, and we did not determine sorted myeloid cells from bone marrow for all telomere investigations, although previous studies showed that no significant differences in CML telomere lengths are observed when comparing peripheral mononuclear blood cells, fractionated peripheral neutrophils, and non-fractionated bone marrow mononuclear cells .