Parthenolide and DMAPT induce cell death in primitive CML cells through reactive oxygen species.

Tyrosine kinase inhibitors (TKI) have become a first-line treatment for chronic myeloid leuakemia (CML). TKIs efficiently target bulk CML cells; however, they are unable to eliminate the leukaemic stem cell (LSC) population that causes resistance and relapse in CML patients. In this study, we assessed the effects of parthenolide (PTL) and dimethyl amino parthenolide (DMAPT), two potent inhibitors of LSCs in acute myeloid leukaemia (AML), on CML bulk and CML primitive (CD34+ lin- ) cells. We found that both agents induced cell death in CML, while having little effect on the equivalent normal hematopoietic cells. PTL and DMAPT caused an increase in reactive oxygen species (ROS) levels and inhibited NF-κB activation. PTL and DMAPT inhibited cell proliferation and induced cell cycle arrest in G0 and G2 phases. Furthermore, we found cell cycle inhibition to correlate with down-regulation of cyclin D1 and cyclin A. In summary, our study shows that PTL and DMAPT have a strong inhibitory effect on CML cells. Given that cell cycle arrest was not dependent on ROS induction, we speculate that this effect could be a direct consequence of NF-κB inhibition and if this mechanism was to be evaded, PTL and DMAPT induced cell death would be potentiated.

[Tyrosine kinase inhibitors (TKI): a new revolution in the treatment of chronic myeloid leukemia (CML)]. / Inhibidores de cinasas de tirosina (ICT): la nueva revolución en el tratamiento de la leucemia mieloide crónica (LMC).

Chronic myeloid leukemia (CML) is a clonal myeloproliferative neoplasia associated with the t(9,22)(q34:q11) reciprocal translocation, also known as Philadelphia chromosome (Ph). As a result of such abnormality, a chimeric gene (bcr-abl) is produced that is translated into a chimeric protein (BCR-ABL), a constitutively activated tyrosine kinase. Major cell dysfunctions result from this abnormal kinase activity, including increased proliferation and reduced apoptosis. Based on the structure of BCR-ABL, several molecules have been designed that inhibit its kinase activity. Five such molecules have already been brought into the clinic for the treatment of Ph+ CML patients. Good results have been obtained in terms of patients' remission rates and quality of life. Some major problems, however, have been observed. Firstly, a significant proportion of patients develop resistance to the drugs; secondly, it is clear that such drugs affect most of the leukemic cells, but do not eliminate leukemia stem cells. Thus, important CML-related challenges remain to be solved in the near future.

Global gene expression profiles of hematopoietic stem and progenitor cells from patients with chronic myeloid leukemia: the effect of in vitro culture with or without imatinib.

In this study, we determined the gene expression profiles of bone marrow-derived cell fractions, obtained from normal subjects and Chronic Myeloid Leukemia (CML) patients, that were highly enriched for hematopoietic stem (HSCs) and progenitor (HPCs) cells. Our results indicate that the profiles of CML HSCs and HPCs were closer to that of normal progenitors, whereas normal HSCs showed the most different expression profile of all. We found that the expression profiles of HSCs and HPCs from CML marrow were closer to each other than those of HSCs and HPCs from normal marrow. The major biologic processes dysregulated in CML cells included DNA repair, cell cycle, chromosome condensation, cell adhesion, and the immune response. We also determined the genomic changes in both normal and CML progenitor cells under culture conditions, and found that several genes involved in cell cycle, steroid biosynthesis, and chromosome segregation were upregulated, whereas genes involved in transcription regulation and apoptosis were downregulated. Interestingly, these changes were the same, regardless of the addition of Imatinib (IM) to the culture. Finally, we identified three genes-PIEZO2, RXFP1, and MAMDC2- that are preferentially expressed by CML primitive cells and that encode for cell membrane proteins; thus, they could be used as biomarkers for CML stem cells.

Casiopeina III-Ea, a copper-containing small molecule, inhibits the in vitro growth of primitive hematopoietic cells from chronic myeloid leukemia.

Several novel compounds have been developed for the treatment of different types of leukemia. In the present study, we have assessed the in vitro effects of Casiopeina III-Ea, a copper-containing small molecule, on cells from patients with Chronic Myeloid Leukemia (CML). We included primary CD34+ Lineage-negative (Lin-) cells selected from CML bone marrow, as well as the K562 and MEG01 cell lines. Bone marrow cells obtained from normal individuals - both total mononuclear cells as well as CD34+ Lin- cells- were used as controls. IC50 corresponded to 0.5µM for K562 cells, 0.63µM for MEG01 cells, 0.38µM for CML CD34+ lin- cells, and 1.0µM for normal CD34+ lin- cells. Proliferation and expansion were also inhibited to significantly higher extents in cultures of CML cells as compared to their normal counterparts. All these effects seemed to occur via a bcr-abl transcription-independent mechanism that involved a delay in cell division, an increase in cell death, generation of Reactive Oxygen Species and changes in cell cycle. Our results demonstrate that Casiopeina III-Ea possesses strong antileukemic activity in vitro, and warrant further preclinical (animal) studies to assess such effects in vivo.

CDKIs p18(INK4c) and p57(Kip2) are involved in quiescence of CML leukemic stem cells after treatment with TKI.

Chronic Myeloid Leukemia (CML) is sustained by a small population of cells with stem cell characteristics known as Leukemic Stem Cells that are positive to BCR-ABL fusion protein, involved with several abnormalities in cell proliferation, expansion, apoptosis and cell cycle regulation. Current treatment options for CML involve the use of Tirosine Kinase Inhibitor (Imatinib, Nilotinib and Dasatinib), that efficiently reduce proliferation proliferative cells but do not kill non proliferating CML primitive cells that remain and contributes to the persistence of the disease. In order to understand the role of Cyclin Dependent Kinase Inhibitors in CML LSC permanence after TKI treatment, in this study we analyzed cell cycle status, the levels of several CDKIs and the subcellular localization of such molecules in different CML cell lines, as well as primary CD34(+)CD38(-)lin(-) LSC and HSC. Our results demonstrate that cellular location of p18(INK4c) and p57(Kip2) seems to be implicated in the antiproliferative activity of Imatinib and Dasatinib in CML cells and also suggest that the permanence of quiescent stem cells after TKI treatment could be associated with a decrease in p18(INK4c) and p57(Kip2) nuclear location. The differences in p18(INK4c)and p57(Kip2)activities in CML and normal stem cells suggest a different cell cycle regulation and provide a platform that could be considered in the development of new therapeutic options to eliminate LSC.