Extensive analysis of the T315I substitution and detection of additional ABL mutations in progenitors and primitive stem cell compartment in a patient with tyrosine kinase inhibitor-resistant chronic myeloid leukemia

Antitumor efficacy of arsenic/interferon in preclinical models of chronic myeloid leukemia resistant to tyrosine kinase inhibitors

BACKGROUND

Tyrosine kinase inhibitors (TKIs) are the standard treatment for chronic myeloid leukemia (CML). Despite their clinical success, TKIs are faced with challenges such as treatment resistance, which may be driven by kinase domain mutations, and frequent disease relapse upon the cessation of treatment. The combination of arsenic trioxide (ATO) and interferon-α (IFN) was previously demonstrated to inhibit proliferation and induce apoptosis in CML cell lines, prolong the survival of primary wild-type CML mice, and dramatically decrease the activity of leukemia-initiating cells (LICs).

METHODS

The ATO/IFN combination was tested in vitro on imatinib (IMN)-resistant K562-R and Ar230-R cells. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assays were used to evaluate proliferation and apoptosis, respectively. The acridine orange assay was used to assess autophagy, and quantitative reverse transcription-polymerase chain reaction was used to assess the involvement of the hedgehog (Hh) pathway. In vivo, a retroviral transduction/transplantation T315I BCR-ABL CML mouse model was used to assay the effect of the treatment on survival, tumor burden (histopathology and blood counts), and LIC activity (secondary transplantation).

RESULTS

In vitro, ATO/IFN synergized to inhibit proliferation and induce apoptosis of IMN-resistant cells with variant modes of resistance. Furthermore, the preclinical effects of ATO/IFN were associated with induction of autophagy along with inhibition of the Hh pathway. Most remarkably, ATO/IFN significantly prolonged the survival of primary T315I-CML mice and displayed a dramatic impairment of disease engraftment in secondary mice, which reflected decreased LIC activity.

CONCLUSIONS

Collectively, the ATO/IFN strategy has been demonstrated to have the potential to lead to durable remissions in TKI-resistant CML preclinical models and to overcome various TKI-specific mechanisms of resistance.

Direct and rapid identification of T315I-Mutated BCR-ABL expressing leukemic cells using infrared microspectroscopy

Despite the major success obtained by the use of tyrosine kinase inhibitors (TKI) in chronic myeloid leukemia (CML), resistances to therapies occur due to mutations in the ABL-kinase domain of the BCR-ABL oncogene. Amongst these mutations, the "gatekeeper" T315I is a major concern as it renders leukemic cells resistant to all licenced TKI except Ponatinib. We report here that Fourier transform infrared (FTIR) microspectroscopy is a powerful methodology allowing rapid and direct identification of a spectral signature in single cells expressing T315I-mutated BCR-ABL. The specificity of this spectral signature is confirmed using a Dox-inducible T315I-mutated BCR-ABL-expressing human UT-7 cells as well as in murine embryonic stem cells. Transcriptome analysis of UT-7 cells expressing BCR-ABL as compared to BCR-ABL T315I clearly identified a molecular signature which could be at the origin of the generation of metabolic changes giving rise to the spectral signature. Thus, these results suggest that this new methodology can be applied to the identification of leukemic cells harbouring the T315I mutation at the single cell level and could represent a novel early detection tool of mutant clones. It could also be applied to drug screening strategies to target T315I-mutated leukemic cells.

Biological effects of T315I-mutated BCR-ABL in an embryonic stem cell-derived hematopoiesis model

The occurrence of T315I mutation during the course of targeted therapies of chronic myeloid leukemia is a major concern because it confers resistance to all currently approved tyrosine kinase inhibitors. The exact phenotype of the hematopoietic stem cell and the hierarchical level of the occurrence of this mutation in leukemic hematopoiesis has not been determined. To study the effects of T315I-mutated breakpoint cluster region-abelson (BCR-ABL) in a primitive hematopoietic stem cell, we have used the murine embryonic stem cell (mESC)-derived hematopoiesis model. Native and T315I-mutated BCR-ABL were introduced retrovirally in mESC-derived embryonic bodies followed by induction of hematopoiesis. In several experiments, T315I-mutated and nonmutated BCR-ABL-transduced embryonic bodies rapidly generated hematopoietic cells on OP-9 feeders, with evidence of hematopoietic stem cell markers. After injection into NOD/SCID mice, these cells induced myeloid and lymphoid leukemias, whereas transplantation of control (nontransduced) hematopoietic cells failed to produce any hematopoietic reconstitution in vivo. Moreover, the expression of native and T315I-mutated BCR-ABL conferred to mESC-derived hematopoietic cells a self-renewal capacity demonstrated by the generation of leukemias after secondary transplantations. Secondary leukemias were more aggressive with evidence of extramedullary tumors. The expression of stem cell regulator Musashi-2 was found to be increased in bone marrow of leukemic mice. These data show that T315I-mutated BCR-ABL is functional at the stem cell level, conferring to mESC-derived leukemic cells a long-term hematopoietic repopulation ability. This model could be of interest to test the efficiency of drugs at the stem cell level in leukemias with T315I mutation.

Analysis of mutations in the BCR-ABL1 kinase domain, using direct sequencing: detection of the T315I mutation in bone marrow CD34+ cells of a patient with chronic myelogenous leukemia 6 months prior to its emergence in peripheral blood

BACKGROUND AND OBJECTIVE

It has been shown that the occurrence of the BCR-ABL1 T315I mutation leads to a very poor therapeutic outcome in chronic myelogenous leukemia (CML) patients treated with tyrosine kinase inhibitors. Therefore, early detection of this mutation could potentially lead to early therapeutic intervention and a better prognosis with the ongoing treatment regimen.

METHODS

The detection of BCR-ABL1 kinase domain (KD) mutations was performed by direct sequencing of peripheral blood (PB), total bone marrow (BM), and BM CD34+ cells from a reported CML patient.

RESULTS

In this patient, the T315I mutation was detected in BM CD34+ cells 6 months prior to its emergence in PB, suggesting evolution and expansion of the T315I mutation clone, which most likely originated from more primitive CML cells.

CONCLUSION

Our finding reflects the natural development of a T315I mutation within the hematopoietic system of the reported patient and indicates the importance of BCR-ABL1 mutation monitoring in more primitive cell populations. Considering the natural history of T315I development in this reported CML case, we hypothesize that BCR-ABL1 KD mutations may be pre-concentrated in more primitive CML cells, which subsequently expand into the PB. These findings may have future implications for the strategy used for detecting BCR-ABL1 mutations.

Chronic myeloid leukemia stem cells in the era of targeted therapies: resistance, persistence and long-term dormancy

Targeted therapies of chronic myeloid leukemia (CML) using tyrosine kinase inhibitors (TKI) have profoundly changed the natural history of the disease with a major impact on survival. Molecular monitoring with BCR-ABL quantification shows that a status of undetectable molecular residual disease (UMRD) is obtained in a significant minority of patients. However, it remains unclear whether these patients are definitively cured of their leukemia. Imatinib mesylate withdrawal trials have demonstrated the rapid appearance of the malignant clone in the majority of the patients whereas some patients remain in a state of UMRD. It has clearly been demonstrated that the most primitive stem cells are refractory to all TKIs used in clinical practice. In addition, long-term dormancy is one of the most fundamental characteristics of hematopoietic stem cells. In this context, we have recently undertaken a systematic analysis of the bone marrow stem cell compartment in several patients in durable UMRD. We have demonstrated the long-term persistence of a considerable amount of BCR-ABL-expressing stem cells, even in the absence of relapse. The phenomenon of long-term leukemic stem cell dormancy is of major importance in CML and one of the key questions in cancer biology in general. We discuss, here, the potential mechanisms, including intrinsic and microenvironmental factors, that control the response of leukemic stem cells (LSCs) to targeted therapies and potential novel strategies currently in progress with a curative intent. Moreover, we propose a molecular evaluation of the residual LSC compartment in selected patients in order to develop rational TKI-cessation strategies in CML.