Abemaciclib drives the therapeutic differentiation of acute myeloid leukaemia stem cells.

Self-renewal and differentiation arrest are two features of leukaemia stem cells (LSCs) responsible for the high relapse rate of acute myeloid leukaemia (AML). To screen drugs to overcome differentiation blockade for AML, we conducted screening of 2040 small molecules from a library of United States Food and Drug Administration-approved drugs and found that the cyclin-dependent kinase (CDK)4/6 inhibitor, abemaciclib, exerts high anti-leukaemic activity. Abemaciclib significantly suppressed proliferation and promoted the differentiation of LSCs in vitro. Abemaciclib also efficiently induced differentiation and impaired self-renewal of LSCs, thus reducing the leukaemic cell burden and improving survival in various preclinical animal models, including patient-derived xenografts. Importantly, abemaciclib strongly enhanced anti-tumour effects in combination with venetoclax, a B-cell lymphoma 2 (Bcl-2) inhibitor. This treatment combination led to a marked decrease in LSC-enriched populations and resulted in a synergistic anti-leukaemic effect. Target screening revealed that in addition to CDK4/6, abemaciclib bound to and inhibited CDK9, consequently attenuating the protein levels of global p-Ser2 RNA Polymerase II (Pol II) carboxy terminal domain (CTD), Myc, Bcl-2, and myeloid cell leukaemia-1 (Mcl-1), which was important for the anti-AML effect of abemaciclib. Collectively, these data provide a strong rationale for the clinical evaluation of abemaciclib to induce LSC differentiation and treat highly aggressive AML as well as other advanced haematological malignancies.

A three-gene leukaemic stem cell signature score is robustly prognostic in chronic myelomonocytic leukaemia.

Leukaemic stem cell (LSC) gene expression has recently been linked to prognosis in patients with acute myeloid leukaemia (17-gene LSC score, LSC-17) and myelodysplastic syndromes. Although chronic myelomonocytic leukaemia (CMML) is regarded as a stem cell disorder, the clinical and biological impact of LSCs on CMML patients remains elusive. Making use of multiple independent validation cohorts, we here describe a concise three-gene expression signature (LSC-3, derived from the LSC-17 score) as an independent and robust prognostic factor for leukaemia-free and overall survival in CMML. We propose that LSC-3 could be used to supplement existing risk stratification systems, to improve prognostic performance and guide management decisions.

Bortezomib suppresses self-renewal and leukemogenesis of leukemia stem cell by NF-ĸB-dependent inhibition of CDK6 in MLL-rearranged myeloid leukemia.

Acute myeloid leukaemia (AML) with chromosomal rearrangements involving the H3K4 methyltransferase mixed-lineage leukaemia (MLL) is an aggressive subtype with low overall survival. Bortezomib (Bort) is first applied in multiple myeloma. However, whether bort possesses anti-self-renewal and leukemogenesis of leukaemia stem cell (LSC) in AML with MLL rearrangements is still unclear. Here, we found that bort suppressed cell proliferation and decreased colony formation in human and murine leukaemic blasts. Besides, bort reduced the frequency and function of LSC, inhibited the progression, and extended the overall survival in MLL-AF9 (MF9) -transformed leukaemic mice. Furthermore, bort decreased the percentage of human LSC (CD34+ CD38- ) cells and extended the overall survival in AML blasts-xenografted NOD/SCID-IL2Rγ (NSG) mice. Mechanistically, cyclin dependent kinase 6 (CDK6) was identified as a bort target by RNA sequencing. Bort reduced the expressions of CDK6 by inhibiting NF ĸB recruitment to the promoter of CDK6, leading to the abolishment of NF ĸB DNA-binding activity for CDK6 promoter. Overexpression of CDK6 partially rescued bort-induced anti-leukemogenesis. Most importantly, bort had little side-effect against the normal haematological stem and progenitor cell (HSPC) and did not affect CDK6 expression in normal HSPC. In conclusion, our results suggest that bort selectively targets LSC in MLL rearrangements. Bort might be a prospective drug for AML patients bearing MLL rearrangements.

Propofol inhibits biological functions of leukaemia stem and differentiated cells through suppressing Wnt/ß-catenin and Akt/mTOR.

The biological roles of intravenous anaesthetic propofol in cancer have been shown by various studies using cancer cell lines that represent differentiated cancer cells. However, the activities of propofol in cancer stem cells have not been elucidated. In this work, we examined the effects and mechanisms of propofol on acute myeloid leukaemia (AML) differentiated and CD34+ CD38- stem cells. We found that propofol inhibited growth, differentiation and self-renewal capabilities of AML stem cells regardless of cellular origin and genetic profiling. In addition, propofol inhibited the growth of AML differentiated cells. Propofol significantly induced apoptosis of AML differentiated but not CD34+ CD38- stem cells. We further found that propofol significantly augmented the efficacy of AML standard therapeutic drugs. Consistent with the previous findings, we showed that propofol suppressed the Akt/mTOR pathway in AML cells. We also found that propofol inhibited pathways important for stem cell maintenance and self-renewal, such as Wnt/ß-catenin. Overexpression of constitutively active Akt partially reversed the inhibitory effects of propofol in AML differentiated cells. Stabilization of ß-catenin using genetic and pharmacological approaches also partially rescued the inhibitory effects of propofol in AML differentiated and stem cells. Our work shows that propofol targets leukaemia cells at all stages of development, in a cell type-specific manner. Inhibition of both Akt/mTOR and Wnt/ß-catenin is required for the action of propofol in AML. Our findings also highlight the activities of propofol on cancer stem cells.

Targeting miR-193a-AML1-ETO-ß-catenin axis by melatonin suppresses the self-renewal of leukaemia stem cells in leukaemia with t (8;21) translocation.

AML1-ETO, the most common fusion oncoprotein by t (8;21) in acute myeloid leukaemia (AML), enhances hematopoietic self-renewal and leukemogenesis. However, currently no specific therapies have been reported for t (8;21) AML patients as AML1-ETO is still intractable as a pharmacological target. For this purpose, leukaemia cells and AML1-ETO-induced murine leukaemia model were used to investigate the degradation of AML1-ETO by melatonin (MLT), synthesized and secreted by the pineal gland. MLT remarkedly decreased AML1-ETO protein in leukemic cells. Meanwhile, MLT induced apoptosis, decreased proliferation and reduced colony formation. Furthermore, MLT reduced the expansion of human leukemic cells and extended the overall survival in U937T-AML1-ETO-xenografted NSG mice. Most importantly, MLT reduced the infiltration of leukaemia blasts, decreased the frequency of leukaemia stem cells (LSCs) and prolonged the overall survival in AML1-ETO-induced murine leukaemia. Mechanistically, MLT increased the expression of miR-193a, which inhibited AML1-ETO expression via targeting its putative binding sites. Furthermore, MLT decreased the expression of ß-catenin, which is required for the self-renewal of LSC and is the downstream of AML1-ETO. Thus, MLT presents anti-self-renewal of LSC through miR-193a-AML1-ETO-ß-catenin axis. In conclusion, MLT might be a potential treatment for t (8;21) leukaemia by targeting AML1-ETO oncoprotein.

Contribution of Chronic Myeloid Leukaemia (CML) as a Disease Model to Define and Study Clonal Heterogeneity.

Although tumour cell intra-clonal heterogeneity has been known for many years, its application in the oncology clinical practice (patient management, prognosis, etc.) remains limited. For this, chronic myeloid leukaemia (CML) is a remarkable model. Basic research studies revealed the heterogeneity of the initial clone, and led to the hypothesis of the existence of leukemic stem cells. Nevertheless, the indisputable evidence of the intra-clonal heterogeneity role in the therapeutic response came from the outcomes of the treatment with tyrosine kinase inhibitors (the first targeted therapy in medicine) combined with the early and rigorous clinical and molecular monitoring of these patients. CML management already takes this heterogeneity into account for personalized patient follow-up. The adventure continues with the objectives of better tailoring the treatment and of curing the disease in most of the patients.

Synthesis and biological evaluation of dithiocarbamate esters of parthenolide as potential anti-acute myelogenous leukaemia agents.

A series of dithiocarbamate esters of parthenolide (PTL) was designed, synthesised, and evaluated for their anti- acute myelogenous leukaemia (AML) activities. The most promising compound 7l showed greatly improved potency against AML progenitor cell line KG1a with IC50 value of 0.7 µM, and the efficacy was 8.7-folds comparing to that of PTL (IC50 = 6.1 µM). Compound 7l induced apoptosis of total primary human AML cells and leukaemia stem cell (LSCs) of primary AML cells while sparing normal cells. Furthermore, 7l suppressed the colony formation of primary human leukaemia cells. Moreover, compound 12, the salt form of 7l, prolonged the lifespan of mice in two patient-derived xenograft models and had no observable toxicity. The preliminary molecular mechanism study revealed that 7l-mediated apoptosis is associated with mitogen-activated protein kinase signal pathway. On the basis of these investigations, we propose that 12 might be a promising drug candidate for ultimate discovery of anti-LSCs drug.

CD45RA, a specific marker for leukaemia stem cell sub-populations in acute myeloid leukaemia.

Chemotherapy resistant leukaemic stem cells (LSC) are thought to be responsible for relapses after therapy in acute myeloid leukaemia (AML). Flow cytometry can discriminate CD34(+) CD38(-) LSC and normal haematopoietic stem cells (HSC) by using aberrant expression of markers and scatter properties. However, not all LSC can be identified using currently available markers, so new markers are needed. CD45RA is expressed on leukaemic cells in the majority of AML patients. We investigated the potency of CD45RA to specifically identify LSC and HSC and improve LSC quantification. Compared to our best other markers (CLL-1, also termed CLEC12A, CD33 and CD123), CD45RA was the most reliable marker. Patients with high percentages (>90%) of CD45RA on CD34(+) CD38(-) LSC have 1·69-fold higher scatter values compared to HSC (P < 0·001), indicating a more mature CD34(+) CD38(-) phenotype. Patients with low (<10%) or intermediate (10-90%) CD45RA expression on LSC showed no significant differences to HSC (1·12- and 1·15-fold higher, P = 0·31 and P = 0·44, respectively). CD45RA-positive LSC tended to represent more favourable cytogenetic/molecular markers. In conclusion, CD45RA contributes to more accurate LSC detection and is recommended for inclusion in stem cell tracking panels. CD45RA may contribute to define new LSC-specific therapies and to monitor effects of anti-LSC treatment.

Cancer stem cells in haematological malignancies.

At least several types of human haematological malignancies can now be seen as 'stem-cell diseases'. The best-studied in this context is acute myeloid leukaemia (AML). It has been shown that these diseases are driven by a pool of 'leukaemia stem cells (LSC)', which remain in the quiescent state, have the capacity to survive and self-renew, and are responsible for the recurrence of cancer after classical chemotherapy. It has been understood that LSC must be eliminated in order to cure patients suffering from haematological cancers. Recent advances in LSC research have allowed for description of LSC phenotype and identification of potential targets for anti-LSC therapies. This concise review summarises the current view on LSC biology and targeted approaches against LSC.

Targeting BCR-ABL1-positive leukaemias: a review article.

Treatment and understanding of BCR::ABL1-positive leukaemias is a precision medicine success story. Our appreciation of the BCR::ABL1 gene and resulting BCR::ABL1 oncoprotein in chronic myeloid leukaemia (CML) and Philadelphia chromosome-positive (Ph+) acute leukaemias, has led to treatment advances associated with exceptional improvements in patient outcomes with normal life expectancy for many patients with chronic phase (CP-)CML. However, despite these major therapeutic advances, the management of Ph+ leukaemias remains complex, with development of specific resistance mutations on treatment, as well as the need for lifelong therapy in most patients due to the persistence of CML stem cells despite prolonged tyrosine kinase inhibitors (TKIs) treatment. BCR::ABL1-specific TKIs are associated with chronic toxicities affecting quality-of-life in many patients but can also result in more serious pulmonary and cardiovascular complications. Dose optimisation is increasingly being used to manage side effects and maintain molecular response in CML patients. Here, we review the development of BCR::ABL1-specific TKIs from the discovery of imatinib in 1996 to the more recent second- and third-generation TKIs and emerging specifically targeting the ABL myristoyl pocket (STAMP) inhibitors. We will also evaluate the current evidence for treatment of BCR::ABL1-positive leukaemias, including TKI discontinuation in optimally responding CP-CML patients.

What Does Chronic Myeloid Leukaemia Tell Us About Other Leukaemias?

PURPOSE OF REVIEW: Determine if therapy of chronic myeloid leukaemia (CML) is a model for treating other cancers. RECENT FINDINGS: CML has a relatively homogeneous phenotype and genotype and is caused by one mutation, BCRABL1, in every instance. In contrast, most other leukaemias, haematologic cancers and solid cancer have more heterogeneous phenotypes and extraordinarily greater genotypic diversity and mutational complexity. Lesions learned from treating CML have little applicability to other leukaemias, haematologic cancers or solid cancer.