Abstract
Abstract 4877
Chronic Myeloid Leukemia (CML) is a clonal myeloproliferative disorder characterized by the reciprocal chromosomal translocation between chromosome 9 and 22, t(9;22)(q34;q11), known as Philadelphia chromosome. At molecular level, this cytogenetic aberration associates with a chimeric BCR-ABL fusion gene responsible for the pathogenesis of the disease. Targeting BCR-ABL with tyrosine kinase inhibitors (TKIs) has led to a rapid clinical response in most CML cases; however, harboring of point mutations within the kinase domain (KD) of BCR-ABL is the most common mechanism responsible for acquired resistance to therapy.
The objective of this work was to evaluate the expression profiles of 4 different genes involved in proliferation, differentiation or cell survival, in order to study their association with acquired missense mutations within the KD of BCR-ABL.
Due to its clear involvement in cell proliferation and apotosis the following genes were analyzed. CAMKIIγ (Ca2+ /calmodulin dependent protein kinase IIγ) is a critical regulator of multiple signalling networks regulating the proliferation in myeloid leukaemia. HSP70 (Heat Shock protein 70) is a chaperone protein that protects cells from apoptotic and necrotic stimuli. HSP90 (Heat Shock protein 90) is a chaperone that facilitates folding of client proteins such as BCR-ABL. Ki-67 is a nuclear antigen associated with cellular proliferation and ribosomal RNA transcription.
Total RNA was extracted from 50 TKI-resistant CML-patient's PBMC samples; by quantitative real time-PCR (QRT-PCR) (SybrGreen method, melting analysis and β2-microglobulin as an endogenous control reference gene) we measured the gene expression of CaMKIIγ, Ki67, HSP70, HSP90 and BCR-ABL. All patients were treated with TKIs (26 imatinib, 13 nilotinib, 11 dasatinib) and showed primary lack or loss of haematological and/or cytogenetic response according to the ELN (European Leukaemia Net) criteria.
To characterize TKI-resistant mutations within the KD of the chimeric BCR-ABL gene, ABL exons 4, 5, 6 and 7 were subjected to automated DNA sequencing following a nested- BCR-ABL-specific PCR. Mutations were observed in 27/50 cases at 15 different residues: 1 L248V, 1 G250E, 1 Y253H, 5 E255K/V, 1 E279K, 1 V289F, 4 T315I, 2 F317L, 1 L348M, 3 M351T, 1 E355G, 1 N358S, 2 F359V/C, 2 L387M and 1 L389V. Remaining 23 CML cases did not show mutations (detection limit 10–20%).
Our results showed a significant increase in the expression of CaMKIIγ and HSP70 and decrease of HSP90 in mutated patients (MT) with respect to cases without mutations (WT) (p<0.01). On the contrary, transcript levels of Ki67 and BCR-ABL did not show significant differences between MT and WT, likely due to the resistant status of both groups.
Taking into account these results we design a score (TKI-MT) to estimate the likelihoods for a patient to harbor TKI-resistance mutations using the transcript normalised expression of CaMKIIγ, HSP70 and HSP90 as follows: [Log10(CaMKIIγ) + Log10(HSP70) – Log10(HSP90)]. TKI-MT scores from 27 and 23 patients from the MT and WT groups respectively were analysed by use of ROC curves in order to find an optimal cut-off value to classify new unstudied cases. We found that patients with TKI-MT scores over a cut-off value of −0.79 showed 4.8 times more probabilities to present TKI-resistance mutations than those below −0.79 (OR 4.8, CI95% 1.3–17.6, P<0.02).
We concluded that the expression of CaMKIIγ, HSP70 and HSP90 allowed prediction of mutations in the ABL tyrosine kinase domain with 82% of specificity in CML patients treated with TKIs and associated with lack or loss of response.
Disclosures:
No relevant conflicts of interest to declare.
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