BACKGROUND: A major issue in Chronic Myeloid Leukemia (CML) is the persistence of quiescent leukemia stem cells (LSCs) in the hematopoietic niche under tyrosine kinase inhibitor (TKI) treatment.
RESULTS: Here, using CFSE sorting, we show that low-proliferating CD34+ cells from CML patients in 3D co-culture hide under HS27A stromal cells during TKI treatment-a behavior less observed in untreated cells. Under the same conditions, Ba/F3p210 cells lose their spontaneous motility. In CML CD34+ and Ba/F3p210 cells, while Rac1 is completely inhibited by TKI, RhoA remains activated but is unable to signal to ROCK. Co-incubation of Ba/F3p210 cells with TKI, SKF-96365 (a calcium channel inhibitor), and EGF restores myosin II activation and amoeboid motility to levels comparable to untreated cells, sustaining the activation of ROCK. In CFSE+ CD34+ cells containing quiescent leukemic stem cells, co-incubation of TKI with SKF-96365 induced the expulsion of these cells from the HS27A niche.
CONCLUSIONS: This study underscores the role of RhoA in LSC behavior under TKI treatment and suggests that SKF-96365 could remobilize quiescent CML LSCs through reactivation of the RhoA/ROCK pathway.

Acute myeloid leukemia (AML) is a common type of leukemia that has a high mortality rate. The reasons for high mortality in patients with AML are therapeutic resistance, limited ability to predict duration of response, and likelihood of cancer relapse. Biomarkers, such as leukemic stem cell biomarkers, circulatory biomarkers, measurable residual disease biomarkers, and molecular biomarkers, are used for prognosis, diagnosis, and targeted killing to selectively eliminate AML cells. They also play an indispensable role in providing therapeutic resistance to patients with AML. Therefore, targeting these biomarkers will improve the outcome of AML patients. However, identifying biomarkers that can differentiate between treatment-responsive and non-responsive AML patients remains a challenge. This review discusses recent advancements in AML biomarkers, promising therapeutics, and associated challenges in the treatment of AML.

The most important reason for dismal outcomes in acute myeloid leukemia (AML) is the development of relapse. Leukemia stem cells (LSCs) are hypothesized to initiate relapse, and high CD34+CD38- LSC load is associated with poor prognosis. In 10% of AML patients, CD34 is not or is low expressed on the leukemic cells (<1%), and CD34+CD38- LSCs are absent. These patients are classified as CD34-negative. We aimed to determine whether the primitive marker CD133 can detect LSCs in CD34-negative AML. We retrospectively quantified 148 CD34-negative patients for proportions of CD34-CD133+ and CD133+CD38- cell fractions in the diagnostic samples of CD34-negative patients in the HOVON102 and HOVON132 trials. No prognostic difference was found between patients with high or low proportions of CD34-CD133+, which is found to be aberrantly expressed in AML. A high level of CD133+CD38- cells was not associated with poor overall survival, and expression in AML was similar to normal bone marrow. To conclude, CD133 is useful as an additional primitive marker for the detection of leukemic blast cells in CD34-negative AML. However, CD133+CD38 alone is not suitable for the detection of LSCs at diagnosis.

Acute myeloid leukemia (AML) arises from leukemia stem cells (LSCs) and is maintained by cells which have acquired features of stemness. We compared transcription profiles of AML cells with/without stem cell features defined as in vitro clonogenicity and serial engraftment in immune-deficient mice xenograft model. We used multi-parameter flow cytometry (MPFC) to separate CD34+ bone marrow-derived leukemia cells into sphingosine-1 phosphate receptor 1 (S1PR1)+ and S1PR1- fractions. Cells in the S1PR1+ fraction demonstrated significantly higher clonogenicity and higher engraftment potential compared with those in the S1PR1- fraction. In contrast, CD34+ bone marrow cells from normal samples showed reduced clonogenicity in the S1PR1+ fraction compared with the S1PR1- fraction. Inhibition of S1PR1 expression in an AML cell line reduced the colony-forming potential of KG1 cells. Transcriptomic analyses and rescue experiments indicated PI3K/AKT pathway and MYBL2 are downstream mediators of S1PR1-associated stemness. These findings implicate S1PR1 as a functional biomarker of LSCs and suggest its potential as a therapeutic target in AML treatment.

Cure rates for acute myeloid leukemia (AML) remain suboptimal; thus, new treatment strategies are needed for this deadly disease. Artemisia campestris leaves hold significant value in traditional medicine. Despite extensive research conducted on this plant globally, the specific anti-AML properties of the leaves have received limited investigation. This study aims to explore the potential anti-leukemic activities of the ethyl acetate extract derived from Artemisia campestris (EAEAC), using mononuclear cells from bone marrow of thirteen AML patients. To this end, cytotoxic effects were evaluated using the MTT assay, and the mechanisms of cell death were investigated through various methods, including propidium iodide staining, annexin V/propidium iodide double staining, mitochondrial depolarization, and caspase-3/7 activation assays. Results demonstrated that EAEAC induced cell apoptosis by increasing DNA fragmentation, causing mitochondrial depolarization, and activating caspases 3/7. On the other hand, we assessed EAEAC\'s effect on two leukemia stem cell subpopulations, with results suggesting a potential decrease in their frequencies (three/five patients).

Immunotherapy remains underexploited in acute myeloid leukemia (AML) compared to other hematological malignancies. Currently, gemtuzumab ozogamicin is the only therapeutic antibody approved for this disease. Here, to identify potential targets for immunotherapeutic intervention, we analyze the surface proteome of 100 genetically diverse primary human AML specimens for the identification of cell surface proteins and conduct single-cell transcriptome analyses on a subset of these specimens to assess antigen expression at the sub-population level. Through this comprehensive effort, we successfully identify numerous antigens and markers preferentially expressed by primitive AML cells. Many identified antigens are targeted by therapeutic antibodies currently under clinical evaluation for various cancer types, highlighting the potential therapeutic value of the approach. Importantly, this initiative uncovers AML heterogeneity at the surfaceome level, identifies several antigens and potential primitive cell markers characterizing AML subgroups, and positions immunotherapy as a promising approach to target AML subgroup specificities.

Acute myeloid leukemia is the second most frequent type of leukemia in adults. Due to a high risk of development of chemoresistance to first-line chemotherapy, the survival rate of patients in a 5-year period is below 30%. One of the reasons is that the AML population is heterogeneous, with cell populations partly composed of very primitive CD34+CD38- hematopoietic stem/progenitor cells, which are often resistant to chemotherapy. First-line treatment with cytarabine and idarubicin fails to inhibit the proliferation of CD34+CD38- cells. In this study, we investigated Metformin\'s effect with or without first-line conventional chemotherapy, or with other drugs like venetoclax and S63845, on primitive and undifferentiated CD34+ AML cells in order to explore the potential of Metformin or S63845 to serve as adjuvant therapy for AML. We found that first-line conventional chemotherapy treatment inhibited the growth of cells and arrested the cells in the S phase of the cell cycle; however, metformin affected the accumulation of cells in the G2/M phase. We observed that CD34+ KG1a cells respond better to lower doses of cytarabine or idarubicin in combination with metformin. Also, we determined that treatment with cytarabine, venetoclax, and S63845 downregulated the strong tendency of CD34+ KG1a cells to form cell aggregates in culture due to the downregulation of leukemic stem cell markers like CD34 and CD44, as well as adhesion markers. Also, we found that idarubicin slightly upregulated myeloid differentiation markers, CD11b and CD14. Treatment with cytarabine, idarubicin, venetoclax, metformin, and S63845 upregulated some cell surface markers like HLA-DR expression, and metformin upregulated CD9, CD31, and CD105 cell surface marker expression. In conclusion, we believe that metformin has the potential to be used as an adjuvant in the treatment of resistant-to-first-line-chemotherapy AML cells. Also, we believe that the results of our study will stimulate further research and the potential use of changes in the expression of cell surface markers in the development of new therapeutic strategies.

BACKGROUND: Leukemia stem cells (LSCs) are found to be one of the main factors contributing to poor therapeutic effects in acute myeloid leukemia (AML), as they are protected by the bone marrow microenvironment (BMM) against conventional therapies. Gossypol acetic acid (GAA), which is extracted from the seeds of cotton plants, exerts anti-tumor roles in several types of cancer and has been reported to induce apoptosis of LSCs by inhibiting Bcl2.
OBJECTIVE: To investigate the exact roles of GAA in regulating LSCs under different microenvironments and the exact mechanism.
METHODS: In this study, LSCs were magnetically sorted from AML cell lines and the CD34+CD38- population was obtained. The expression of leucine-rich pentatricopeptide repeat-containing protein (LRPPRC) and forkhead box M1 (FOXM1) was evaluated in LSCs, and the effects of GAA on malignancies and mitochondrial function were measured.
RESULTS: LRPPRC was found to be upregulated, and GAA inhibited cell proliferation by degrading LRPPRC. GAA induced LRPPRC degradation and inhibited the activation of interleukin 6 (IL-6)/janus kinase (JAK) 1/signal transducer and activator of transcription (STAT) 3 signaling, enhancing chemosensitivity in LSCs against conventional chemotherapies, including L-Asparaginase, Dexamethasone, and cytarabine. GAA was also found to downregulate FOXM1 indirectly by regulating LRPPRC. Furthermore, GAA induced reactive oxygen species accumulation, disturbed mitochondrial homeostasis, and caused mitochondrial dysfunction. By inhibiting IL-6/JAK1/STAT3 signaling via degrading LRPPRC, GAA resulted in the elimination of LSCs. Meanwhile, GAA induced oxidative stress and subsequent cell damage by causing mitochondrial damage.
CONCLUSIONS: Taken together, the results indicate that GAA might overcome the BMM protective effect and be considered as a novel and effective combination therapy for AML.

Despite most acute myeloid leukemia (AML) patients entering remission following chemotherapy, outcomes remain poor due to surviving leukemic cells that contribute to relapse. The nature of these enduring cells is poorly understood. Here, through temporal single-cell transcriptomic characterization of AML hierarchical regeneration in response to chemotherapy, we reveal a cell population: AML regeneration enriched cells (RECs). RECs are defined by CD74/CD68 expression, and although derived from leukemic stem cells (LSCs), are devoid of stem/progenitor capacity. Based on REC in situ proximity to CD34-expressing cells identified using spatial transcriptomics on AML patient bone marrow samples, RECs demonstrate the ability to augment or reduce leukemic regeneration in vivo based on transfusion or depletion, respectively. Furthermore, RECs are prognostic for patient survival as well as predictive of treatment failure in AML cohorts. Our study reveals RECs as a previously unknown functional catalyst of LSC-driven regeneration contributing to the non-canonical framework of AML regeneration.

UNASSIGNED: Despite the notable success of tyrosine kinase inhibitors (TKIs) in treating chronic myeloid leukemia (CML), a subset of patients experiences resistance, or relapse after discontinuation. This challenge is attributed to the Ph+ leukemia stem cells (LSCs) pool not fully involved in the inhibition process due to the current therapeutic approach.
UNASSIGNED: Current pharmacological advancements in CML therapy focus on targeting LSCs, intervening in self-renewal pathways, and exploiting biological vulnerabilities. Beyond BCR::ABL1 inhibition, innovative approaches include immunotherapy, epigenetic modulation, and interference with microenvironmental mechanisms.
UNASSIGNED: Diverse therapeutic strategies beyond TKIs are under investigation. Immunotherapy with interferon-α (IFN-α) shows some biological effects, although further research is needed for optimal application in enhancing discontinuation rates. Other compounds were able to mobilize Ph+ LSCs from the bone marrow niche (DPP-IV inhibitor vildagliptin or PAI-1 inhibitor TM5614) increasing the LSC clearance or target the CD26, a Ph+ specific surface receptor. It is noteworthy that the majority of these alternative strategies still incorporate TKIs. In conclusion, novel therapeutic perspectives are emerging for CML, holding the potential for substantial advancements in disease treatment.