Leukemic Stem Cells: A Review

Uncovering BRD4 hyperphosphorylation associated with cellular transformation in NUT midline carcinoma

The epigenetic reader BRD4 plays a vital role in transcriptional regulation, cellular growth control, and cell-cycle progression. Dysregulation of BRD4 function has been implicated in the pathogenesis of a wide range of cancers. However, how BRD4 is regulated to maintain its normal function in healthy cells and how alteration of this process leads to cancer remain poorly understood. In this study, we discovered that BRD4 is hyperphosphorylated in NUT midline carcinoma and identified CDK9 as a potential kinase mediating BRD4 hyperphosphorylation. Disruption of BRD4 hyperphosphorylation using both chemical and molecular inhibitors led to the repression of BRD4 downstream oncogenes and abrogation of cellular transformation. BRD4 hyperphosphorylation is also observed in other cancers displaying enhanced BRD4 oncogenic activity. Our study revealed a mechanism that may regulate BRD4 biological function through phosphorylation, which, when dysregulated, could lead to oncogenesis. Our finding points to strategies to target the aberrant BRD4 signaling specifically for cancer intervention.

Live kinase B1 maintains CD34+CD38- AML cell proliferation and self-renewal

Live kinase B1 (LKB1) has been recognized as a tumor suppressor in many human cancers; however, LKB1 maintains self-renewal of hematopoietic stem cells (HSCs). The existence of leukemia stem cells (LSCs) is responsible for drug resistance and leukemia relapse. In acute myeloid leukemia (AML), CD34⁺CD38^- fraction is the most enriched compartment for LSCs. We found that LKB1 was upregulated in CD34⁺CD38^- AML cells. LKB1 downregulation suppressed the long-term proliferation of CD34⁺CD38^- AML cells, induced CD34⁺CD38^- AML cells into G2/M phase, and enhanced the sensitivity of CD34⁺CD38^- AML cells to chemotherapy. Furthermore, LKB1 downregulation in CD34⁺CD38^- AML cells inhibited tumor formation in NOD-SCID mice. Downregulation of LKB1 gene makes LSCs partly loose the characters as stem cells. Gene expression microarray showed that MAPK/ERK pathway was implicated in the regulation of CD34⁺CD38^- AML cell proliferation by LKB1. Together, these findings demonstrate that LKB1 plays an important role in the maintenance of LSCs, which may be responsible for drug resistance and AML relapse.

Human natural killer cells: news in the therapy of solid tumors and high-risk leukemias

It is well established that natural killer (NK) cells play an important role in the immunity against cancer, while the involvement of other recently identified, NK-related innate lymphoid cells is still poorly defined. In the haploidentical hematopoietic stem cell transplantation for the therapy of high-risk leukemias, NK cells have been shown to exert a key role in killing leukemic blasts residual after conditioning. While the clinical results in the cure of leukemias are excellent, the exploitation of NK cells in the therapy of solid tumors is still limited and unsatisfactory. In solid tumors, NK cell function may be inhibited via different mechanisms, occurring primarily at the tumor site. The cellular interactions in the tumor microenvironment involve tumor cells, stromal cells and resident or recruited leukocytes and may favor tumor evasion from the host's defenses. In this context, a number of cytokines, growth factors and enzymes synthesized by tumor cells, stromal cells, suppressive/regulatory myeloid and lymphoid cells may substantially impair the function of different tumor-reactive effector cells, including NK cells. The identification and characterization of such mechanisms may offer clues for the development of new immunotherapeutic strategies to restore effective anti-tumor responses. In order to harness NK cell-based immunotherapies, several approaches have been proposed, including reinforcement of NK cell cytotoxicity by means of specific cytokines, antibodies or drugs. These new tools may improve NK cell function and/or increase tumor susceptibility to NK-mediated killing. Hence, the integration of NK-based immunotherapies with conventional anti-tumor therapies may increase chances of successful cancer treatment.

The novel structure make LDM effectively remove CD123+ AML stem cells in combination with interleukin 3

CD123 became a therapeutic target for acute myelocytic leukemia(AML) because of its overexpression only on AML stem cells. It is α subunit of interleukin-3 (multi-CSF, IL3) receptor. Lidamycin(LDM) is a novel antibiotic composed of an apoprotein (LDP) and a chromophore (AE). We cloned, expressed and isolated IL3LDP fusion protein first then assembled with AE in vitro. We found that131/132 amino acids of IL3 were the key factors for IL3 fusion protein stability and I131L/F132L mutation effectively improved the IL3 fusion protein stability. The toxicity of IL3LDM to CD123+ tumor cells was 2-10 times compared to LDM alone and 10000 times compared to ADR. Meanwhile, IL3LDM impaired the colony-forming ability of CD123+ stem-like cells but not to CD123 negative normal cord blood cells. Three drug delivery methods in vivo were adopted: prophylactic treatment and single/multiple-dosing administration. The tumor-free survival extended to 120 d and cancer cell invasion significantly decreased after IL3LDM continuous multiple treated. Moreover, IL3LDM had been shown to modulate apoptosis by arrested cell cycle in G2/M phase. Therefore, IL3LDM is expected to be a new drug for leukemia target therapy.

Glioma stem cells: turpis omen in nomen? (The evil in the name?)

High-grade gliomas remain incurable and lethal. Through the availability of the stem-like cells responsible for glioblastoma (GB) formation, expansion, resilience and recurrence, the discovery of glioma cancer stem cells (GCSCs) is revolutionizing this field. GCSCs provide an unprecedented opportunity to reproduce and study GB pathophysiology more accurately. This critically emphasizes our ability to unambiguously identify, isolate and investigate cells that do qualify as GCSCs, to use them as a potential model that is truly predictive of GBs and of their regulation and response to therapeutic agents. We review this concept against the background of key findings on somatic, neural and solid tumour stem cells (SCs), also taking into account the emerging phenomenon of phenotypic SC plasticity. We suggest that basic approaches in these areas can be imported into the GCSC field, so that the same functional method used to identify normal somatic SCs becomes the most appropriate to define GCSCs. This, combined with knowledge of the cellular and molecular basis of normal adult neurogenesis, promises to improve the identification of GCSCs and of selective markers, as well as the development of innovative, more specific and efficacious antiglioma strategies.