Leukemia stem cells: Old concepts and new perspectives

Immunophenotypic clustering in paediatric acute myeloid leukaemia

Acute myeloid leukaemia (AML) is a highly heterogeneous disease, exhibiting diverse subtypes according to the characteristics of tumour cells. The immunophenotype is one of the aspects acquired routinely through flow cytometry in the diagnosis of AML. Here, we characterized the antigen expression in paediatric AML cases across both morphological and molecular genetic subgroups. We discovered a subgroup of patients with unfavourable prognosis that can be immunologically characterized, irrespective of morphological FAB results or genetic aberrations. Cox regression analysis unveiled key antigens influencing the prognosis of AML patients. In terms of underlying genotypes, we observed that the antigenic profiles and outcomes of one specific group, primarily composed of CBFA2T3::GLIS2 and FUS::ERG, were analogous to the reported RAM phenotype. Overall, our data highlight the significance of immunophenotype to tailor treatment for paediatric AML.

Therapeutic targeting of leukemia stem cells in acute myeloid leukemia

One of the distinguishing properties of hematopoietic stem cells is their ability to self-renew. Since self-renewal is important for the continuous replenishment of the hematopoietic stem cell pool, this property is often hijacked in blood cancers. Acute myeloid leukemia (AML) is believed to be arranged in a hierarchy, with self-renewing leukemia stem cells (LSCs) giving rise to the bulk tumor. Some of the earliest characterizations of LSCs were made in seminal studies that assessed the ability of prospectively isolated candidate AML stem cells to repopulate the entire heterogeneity of the tumor in mice. Further studies indicated that LSCs may be responsible for chemotherapy resistance and therefore act as a reservoir for secondary disease and leukemia relapse. In recent years, a number of studies have helped illuminate the complexity of clonality in bone marrow pathologies, including leukemias. Many features distinguishing LSCs from normal hematopoietic stem cells have been identified, and these studies have opened up diverse avenues for targeting LSCs, with an impact on the clinical management of AML patients. This review will discuss the role of self-renewal in AML and its implications, distinguishing characteristics between normal and leukemia stem cells, and opportunities for therapeutic targeting of AML LSCs.

MICONIDINE acetate, a new selective and cytotoxic compound with synergic potential, induces cell cycle arrest and apoptosis in leukemia cells

Plants are important sources of biologically active compounds and they provide unlimited opportunities for the discovery and development of new drug leads, including new chemotherapeutics. Miconidin acetate (MA) is a hydroquinone derivative isolated from E. hiemalis. In this study we demonstrated that MA was cytotoxic against acute leukemia (AL), solid tumor cells and cancer stem cells, with the strongest effect exhibited against AL. Furthermore, it was non-cytotoxic against non-tumor cells and did not cause significant hemolysis. MA blocks the G2/M phase and causes cytostatic effects, acting in a similar way to dexamethasone by increasing PML expression. The compound also triggered intrinsic and extrinsic apoptosis by modulating Bax, FasR and survivin expression. This led to an extensive mitochondrial damage that resulted in AIF, cytochrome c and endonuclease G release, caspase-3 and PARP cleavage and DNA fragmentation. We have further demonstrated that MA was strongly cytotoxic against neoplastic cells collected from patients with different AL subtypes. Interestingly, MA increased the cytotoxic effect of chemotherapeutics cytarabine and vincristine. This study indicates that MA may be a new agent for AL and highlights its potential as a new source of anticancer drugs. Graphical abstract MA blocks G2/M phase with PML expression and KI67 inhibition, ROS generation and intrinsic and extrinsic apoptosis, leading to mitochondrial damage, caspase 3 and PARP cleavage and DNA fragmentation.

Emerging role of exosome signalling in maintaining cancer stem cell dynamic equilibrium

Cancer stem cells (CSCs) are a small subset of heterogeneous cells existed in tumour tissues or cancer cell lines with self-renewal and differentiation potentials. CSCs were considered to be responsible for the failure of conventional therapy and tumour recurrence. However, CSCs are not a static cell population, CSCs and non-CSCs are maintained in dynamic interconversion state by their self-differentiation and dedifferentiation. Therefore, targeting CSCs for cancer therapy is still not enough,exploring the mechanism of dynamic interconversion between CSCs and non-CSCs and blocking the interconversion seems to be imperative. Exosomes are 30-100 nm size in diameter extracellular vesicles (EVs) secreted by multiple living cells into the extracellular space. They contain cell-state-specific bioactive materials, including DNA, mRNA, ncRNA, proteins, lipids, etc. with their specific surface markers, such as, CD63, CD81, Alix, Tsg101, etc. Exosomes have been considered as information carriers in cell communication between cancer cells and non-cancer cells, which affect gene expressions and cellular signalling pathways of recipient cells by delivering their contents. Now that exosomes acted as information carriers, whether they played role in maintaining dynamic equilibrium state between CSCs and non-CSCs and their mechanism of activity are unknown. This review summarized the current research advance of exosomes' role in maintaining CSC dynamic interconversion state and their possible mechanism of action, which will provide a better understanding the contribution of exosomes to dedifferentiation and stemness acquisition of non-CSCs, and highlight that exosomes might be taken as the attractive target approaches for cancer therapeutics.

EpCAM Inhibition Sensitizes Chemoresistant Leukemia to Immune Surveillance

The lack of effective tumor-associated antigens restricts the development of targeted therapies against myeloid leukemia. In this study, we compared gene expression patterns of acute myeloid leukemia (AML) and normal bone marrow samples and found that epithelial cell adhesion molecule (EpCAM) is frequently overexpressed in patients with AML, with EpCAM⁺ leukemic cells exhibiting enhanced chemoresistance and oncogenesis. The chemotherapeutic resistance of EpCAM-positive leukemic cells is a consequence of increased WNT5B signaling. Furthermore, we generated EpCAM antibodies that enabled phagocytosis or cytotoxicity of AML cells by macrophage or natural killer cells, respectively. Finally, EpCAM antibody treatment depleted AML in subcutaneous, disseminated, and intramedullary engrafted mice. In summary, EpCAM exhibits promise as a novel target for the treatment of leukemia. Cancer Res; 77(2); 482-93. ©2016 AACR.

Effect of Compound Zhebei Granule () combined with chemotherapy on surface markers of leukemia stem cell in patients with acute myeloid leukemia

OBJECTIVE

To observe the effects of Compound Zhebei Granule (, CZBG) combined with chemotherapy on surface markers of leukemia stem cell (LSC) in the bone marrow of patients with acute myeloid leukemia (AML).

METHODS

Seventy-eight patients with AML received bone marrow aspiration and the percentages of CD34(+) CD123(+) and CD33(+) CD123(+) cells were tested using flow cytometry method. A total of 24 refractory or relapsed AML patients were enrolled and treated with one cycle of standard chemotherapy combined with CZBG. Bone marrow samples were obtained before and after treatment, and the percentages of CD34(+) CD123(+) and CD33(+) CD123(+) cells were examined by flflow cytometry.

RESULTS

Compared with refractory or relapsed AML patients, patients achieved remission had a significant lower percentage of CD34(+) CD123(+) cells(P<0.01) and CD33(+) CD123(+) cells (P<0.01), indicating that controlling the LSC percentage may be important for patients with AML to achieve sustainable remission. Compared with those before treatment, the expression levels of CD34(+) CD123(+) were significantly decreased after CZBG combined with chemotherapy treatment (P<0.01). The percentages of CD34(+) CD123(+) cells and CD33(+) CD123(+) in patients achieving complete remission after CZBG combined with chemotherapy treatment were both significantly lower than those in patients with nonremission (P<0.01).

CONCLUSION

CZBG combining chemotherapy could reduce the percentages of CD34(+) CD123(+) and CD33(+) CD123(+) LSC, which might improve the clinical efficacy of refractory or relapsed AML.