Bcl-2 family members as prognostic indicators in AML

MDS and AML show elevated fractions of CD34-positive blast cell populations with a high anti-apoptotic versus proliferation ratio

This study investigates the intertwined processes of (anti-)apoptosis and cell proliferation in myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). Utilizing antibodies to Bcl-2 and Ki-67, the CD34-positive blast cell compartments in bone marrow aspirates from 50 non-malignant cases, 25 MDS patients, and 25 AML patients were analyzed for their anti-apoptotic and proliferative cell fractions through ten-color flow cytometry. MDS patients exhibited a significantly increased anti-apoptotic (p=0.0014) and reduced proliferative cell fraction (p=0.0030) in their blast cell population as compared to non-malignant cases. AML patients showed an even more exacerbated trend than MDS patients. The resulting Bcl-2:Ki-67 cell fraction ratios in MDS and AML were significantly increased as compared to the non-malignant cases (p=0.0004 and p<0.0001, respectively). AML patients displayed, however, a high degree of variability in their anti-apoptotic and proliferation index, attributed to heterogeneity in maturation stage and severity of the disease at diagnosis. Using double-labeling for Bcl-2 and Ki-67 it could be shown that besides blast cells with a mutually exclusive Ki-67 and Bcl-2 expression, also blast cells concurrently exhibiting anti-apoptotic and proliferative marker expression were found. Integrating these two dynamic markers into MDS and AML diagnostic workups may enable informed conclusions about their biological behavior, facilitating individualized therapy decisions for patients.

BCL2 overexpression: clinical implication and biological insights in acute myeloid leukemia

Background

BCL2 protein inhibitor venetoclax (ABT-199) has been authorized by Food and Drug Administration for relapsed/refractory chronic lymphoid leukemia with 17p deletion. Although venetoclax/ABT-199 also caused cell death in acute myeloid leukemia (AML), whether it could be applied to clinical treatment needs further studies. Here, we revealed clinical implication of BCL2 overexpression in de novo adult AML, and may provide theoretical basis for targeted therapy using venetoclax.

Methods

BCL2 expression was analyzed in adult AML patients from public datasets The Cancer Genome Atlas (TCGA) and confirmed by another independent cohort from our own data.

Results

BCL2 expression showed up-regulated in AML patients among TCGA data and confirmed by our own data. BCL2 overexpression was correlated with FAB-M0/M1, whereas BCL2 under-expression was related to FAB-M5. However, BCL2 expression has no effect on overall survival (OS) and leukemia-free survival (LFS) of AML patients (determined in BCL2^low and BCL2^high groups). Interestingly, in the BCL2^low group, patients undergoing autologous or allogeneic hematopoietic stem cell transplantation (auto/allo-HSCT) had significantly better OS and LFS compared with patients only received chemotherapy, whereas, no significant difference was found in OS and LFS between chemotherapy and auto/allo-HSCT patients in the BCL2^high group. BCL2 expression was found positively correlated with HOX family gene, and negatively correlated with tumor suppressor microRNA such as miR-195, miR-497, and miR-193b.

Conclusions

BCL2 overexpression identified specific FAB subtypes of AML, but it did not affect prognosis. Patients with BCL2 overexpression did not benefit from auto/allo-HSCT among whole-cohort-AML and cytogenetically normal AML.

Electronic supplementary material

The online version of this article (10.1186/s13000-019-0841-1) contains supplementary material, which is available to authorized users.

Salvianolic acid A, a novel PI3K/Akt inhibitor, induces cell apoptosis and suppresses tumor growth in acute myeloid leukemia

Salvianolic acid A (SAA), one of the main derivatives of Salvia miltiorrhiza, has been shown to possess anti-inflammatory and anti-thrombotic activities. Its role in inhibiting tumor growth, however, remains elusive. The aim of this study was to investigate the effect of SAA on acute myeloid leukemia (AML). Here, SAA showed a dose-dependent cell viability inhibition and apoptosis induction in AML cells. At the molecular level, SAA increased the expression of Bak and decreased the expression of Bcl-xL, following by PARP cleavage and caspase-3 activation. SAA also markedly attenuated Akt phosphorylation in AML cells. In a xenograft mouse model, SAA significantly suppressed the growth of AML tumors in vivo. Furthermore, SAA exhibited a more profound pro-apoptotic effect on primary AML cells than on bone marrow mononuclear cells from patients with benign diseases. Therefore, the pro-apoptotic and anti-tumor properties of SAA suggested its promising therapeutic value for AML.

Histone deacetylase inhibitor (HDACI) mechanisms of action: emerging insights

Initially regarded as "epigenetic modifiers" acting predominantly through chromatin remodeling via histone acetylation, HDACIs, alternatively referred to as lysine deacetylase or simply deacetylase inhibitors, have since been recognized to exert multiple cytotoxic actions in cancer cells, often through acetylation of non-histone proteins. Some well-recognized mechanisms of HDACI lethality include, in addition to relaxation of DNA and de-repression of gene transcription, interference with chaperone protein function, free radical generation, induction of DNA damage, up-regulation of endogenous inhibitors of cell cycle progression, e.g., p21, and promotion of apoptosis. Intriguingly, this class of agents is relatively selective for transformed cells, at least in pre-clinical studies. In recent years, additional mechanisms of action of these agents have been uncovered. For example, HDACIs interfere with multiple DNA repair processes, as well as disrupt cell cycle checkpoints, critical to the maintenance of genomic integrity in the face of diverse genotoxic insults. Despite their pre-clinical potential, the clinical use of HDACIs remains restricted to certain subsets of T-cell lymphoma. Currently, it appears likely that the ultimate role of these agents will lie in rational combinations, only a few of which have been pursued in the clinic to date. This review focuses on relatively recently identified mechanisms of action of HDACIs, with particular emphasis on those that relate to the DNA damage response (DDR), and discusses synergistic strategies combining HDACIs with several novel targeted agents that disrupt the DDR or antagonize anti-apoptotic proteins that could have implications for the future use of HDACIs in patients with cancer.

Synergistic effect of inhibiting translation initiation in combination with cytotoxic agents in acute myelogenous leukemia cells

We have previously shown that inhibition of translation initiation, using the small molecule inhibitor silvestrol, induces apoptosis in a pre-clinical murine lymphoma model when combined with daunorubicin. Silvestrol blocks ribosome recruitment by targeting the RNA helicase, eIF4A, which is required for this process. Here we investigate the sensitivity of acute myelogenous leukemia (AML) cell lines to protein synthesis inhibition in combination with the standard cytotoxic agents daunorubicin, etoposide, and cytarabine. Silvestrol shows synergy with standard-of-care agents in AML cell lines and synergizes with ABT-737, a small molecule inhibitor of Bcl-X(L) and Bcl-2. The in vitro synergy between silvestrol and the cytotoxic drugs used in AML therapy provides a basis for in vivo evaluation of these combinations.

FLT3-ITD-TKD dual mutants associated with AML confer resistance to FLT3 PTK inhibitors and cytotoxic agents by overexpression of Bcl-x(L)

FLT3 (fms-like tyrosine kinase 3) is constitutively activated in about 30% of patients with acute myeloid leukemia (AML) and represents a disease-specific molecular marker. Although FLT3-LM (length mutation) and TKD (tyrosine kinase domain) mutations have been considered to be mutually exclusive, 1% to 2% of patients carry both mutations. However, the functional and clinical significance of this observation is unclear. We demonstrate that FLT3-ITD-TKD dual mutants induce drug resistance toward PTK inhibitors and cytotoxic agents in in vitro model systems. As molecular mechanisms of resistance, we found that FLT3-ITD-TKD mutants cause hyperactivation of STAT5 (signal transducer and activator of transcription-5), leading to upregulation of Bcl-x(L) and RAD51 and arrest in the G(2)M phase of the cell cycle. Overexpression of Bcl-x(L) was identified as the critical mediator of drug resistance and recapitulates the PTK inhibitor and daunorubicin-resistant phenotype in FLT3-ITD cells. The combination of rapamycin, a selective mTOR inhibitor, and FLT3 PTK inhibitors restored the drug sensitivity in FLT3 dual mutant-expressing cells. Our data provide the molecular basis for understanding clinical FLT3 PTK inhibitor resistance and point to therapeutical strategies to overcome drug resistance in patients with AML.