Proteasome inhibitors induce FLT3-ITD degradation through autophagy in AML cells

FLT3-Mutated Leukemic Stem Cells: Mechanisms of Resistance and New Therapeutic Targets

Despite the availability of target drugs in the first and second line, only 30% of FLT3mut AMLs are cured. Among the multiple mechanisms of resistance, those of FLT3mut LSC are the most difficult to eradicate because of their metabolic and genomic characteristics. Reactivation of glycogen synthesis, inhibition of the RAS/MAPK pathway, and degradation of FLT3 may be potential aids to fight the resistance of LSC to FLT3i. LSC is also characterized by the expression of a CD34+/CD25+/CD123+/CD99+ immunophenotype. The receptor and ligand of FLT3, the natural killer group 2 member D ligand (NKGD2L), and CD123 are some of the targets of chimeric antigen receptor T cells (CAR-T), bispecific T-cell engager molecules (BiTEs), CAR-NK and nanoparticles recently designed and reported here. The combination of these new therapeutic options, hopefully in a minimal residual disease (MRD)-driven approach, could provide the future answer to the challenge of treating FLT3mut AML.

MAPK/ERK and PI3K/AKT signaling pathways are activated in adolescent and adult acute lymphoblastic leukemia

BACKGROUND

The mitogen-activated protein kinase (MAPK)/ERK signaling cascade and the phosphoinosytol-3 phosphate/Akt (PI3K/Akt) pathways are involved in proliferation and differentiation of hematopoietic cells. The frequency of PI3K/Akt and MAPK pathway activation in adult acute lymphoblastic leukemia (ALL) still need to be elucidated.

AIMS

To assess the activity and prognostic implications of MAPK/ERK and PI3K/Akt pathways in adult (ALL).

METHODS

We examined 28 precursor-B-cell ALL and 6 T-cell primary ALL samples. Flow cytometry was employed to analyze the expression levels of phosphorylated ERK and phosphorylated Akt.

RESULTS

Ten out of 15 (67%) ALL fresh samples (7 B-cell, 3 T-cell) showed constitutive p-ERK expression. The p-ERK mean fluorescent index ratio (MFI (R)) showed a tendency to be higher in ALL than in normal T lymphocytes (1.26 [0.74-3.10] vs. 1.08 [1.02-1.21], respectively [p = .069]) and was significantly lower than in leukemic cell lines (median MFI (R) 3.83 [3.71-5.97] [p < .001]). Expression of p-Akt was found in 35% (12/34) (10 B-cell, 2 T-cell). The median MFI (R) expression for p-Akt in primary blast cell was 1.13 (0.48-9.90) compared to 1.01 (1.00-1.20) in normal T lymphocytes (p = ns) and lower than in leukemic cell lines (median MFI (R) 2.10 [1.77-3.40] [p = .037]). Moreover, expression of p-ERK was negatively associated with the expression of CD34 (1.22 [0.74-1.33] vs. 1.52 [1.15-3.10] for CD34(+) and CD34(-) group, respectively, p = .009).

CONCLUSION

Our findings suggest that both MAPK/ERK and PI3K/Akt are constitutively activated in adult ALL, indicating a targeted therapy potential for ALL by using inhibitors of these pathways.

Blockade of de novo pyrimidine biosynthesis triggers autophagic degradation of oncoprotein FLT3-ITD in acute myeloid leukemia

The internal tandem duplication of the FMS-like tyrosine kinase 3 (FLT3-ITD) is one of the most frequent genetic alterations in acute myeloid leukemia (AML). Limited and transient clinical benefit of FLT3 kinase inhibitors (FLT3i) emphasizes the need for alternative therapeutic options for this subset of myeloid malignancies. Herein, we showed that FLT3-ITD mutant (FLT3-ITD+) AML cells were susceptible toward inhibitors of DHODH, a rate-limiting enzyme of de novo pyrimidine biosynthesis. Genetic and pharmacological blockade of DHODH triggered downregulation of FLT3-ITD protein, subsequently suppressed activation of downstream ERK and STAT5, and promoted cell death of FLT3-ITD+ AML cells. Mechanistically, DHODH blockade triggered autophagy-mediated FLT3-ITD degradation via inactivating mTOR, a potent autophagy repressor. Notably, blockade of DHODH synergized with an FDA-approved FLT3i quizartinib in significantly impairing the growth of FLT3-ITD+ AML cells and improving tumor-bearing mice survival. We further demonstrated that DHODH blockade exhibited profound anti-proliferation effect on quizartinib-resistant cells in vitro and in vivo. In summary, this study demonstrates that the induction of degradation of FLT3-ITD protein by DHODH blockade may offer a promising therapeutic strategy for AML patients harboring FLT3-ITD mutation.

FLT3 inhibitors and novel therapeutic strategies to reverse AML resistance: An updated comprehensive review

FMS-like tyrosine kinase 3 (FLT3) mutations occur in almost 30% of acute myeloid leukemia (AML) patients. Despite the initial clinical efficacy of FLT3 inhibitors, many treated AML patients with mutated FLT3 eventually relapse. This review critically discusses the opportunities and challenges of FLT3-targeted therapies and sheds light on their drug interactions as well as potential biomarkers. Furthermore, we focus on the molecular mechanisms underlying the resistance of FLT3 internal tandem duplication (FLT3-ITD) AMLs to FLT3 inhibitors alongside novel therapeutic strategies to reverse resistance. Notably, dynamic heterogeneous patterns of clonal selection and evolution contribute to the resistance of FLT3-ITD AMLs to FLT3 inhibitors. Ongoing preclinical research and clinical trials are actively directed towards devising rational "personalized" or "patient-tailored" combinatorial therapeutic regimens to effectively treat patients with FLT3 mutated AML.

Multi-omics analysis of multiple myeloma patients with differential response to first-line treatment

The genome backgrounds of multiple myeloma (MM) would affect the efficacy of specific treatment. However, the mutational and transcriptional landscapes in MM patients with differential response to first-line treatment remains unclear. We collected paired whole-exome sequencing (WES) and transcriptomic data of over 200 MM cases from MMRF-COMPASS project. R package, maftools was applied to analyze the somatic mutations and mutational signatures across MM samples. Differential expressed genes (DEG) was calculated using R package, DESeq2. The feature selection of the predictive model was determined by LASSO regression. In silico analysis revealed newly discovered recurrent mutated genes such as TTN, MUC16. TP53 mutation was observed more frequent in nonCR (complete remission) group with poor prognosis. DNA repair-associated mutational signatures were enriched in CR patients. Transcriptomic profiling showed that the activity of NF-kappa B and TGF-β pathways was suppressed in CR patients. A transcriptome-based response predictive model was constructed and showed promising predictive accuracy in MM patients receiving first-line treatment. Our study delineated distinctive mutational and transcriptional landscapes in MM patients with differential response to first-line treatment. Furthermore, we constructed a 20-gene predictive model which showed promising accuracy in predicting treatment response in newly diagnosed MM patients.

PLM-101 is a novel and potent FLT3/RET inhibitor with less adverse effects in the treatment of acute myeloid leukemia

Acute myeloid leukemia (AML) is a prevalent form of leukemia in adults. As its survival rate is low, there is an urgent need for new therapeutic options. In AML, FMS-like tyrosine kinase 3 (FLT3) mutations are common and have negative outcomes. However, current FLT3-targeting agents, Midostaurin and Gilteritinib, face two significant issues, specifically the emergence of acquired resistance and drug-related adverse events leading to treatment failure. Rearranged during transfection (RET), meanwhile, is a proto-oncogene linked to various types of cancer, but its role in AML has been limited. A previous study showed that activation of RET kinase enhances FLT3 protein stability, leading to the promotion of AML cell proliferation. However, no drugs are currently available that target both FLT3 and RET. This study introduces PLM-101, a new therapeutic option derived from the traditional Chinese medicine indigo naturalis with potent in vitro and in vivo anti-leukemic activities. PLM-101 potently inhibits FLT3 kinase and induces its autophagic degradation via RET inhibition, providing a superior mechanism to that of FLT3 single-targeting agents. Single- and repeated-dose toxicity tests conducted in the present study showed no significant drug-related adverse effects. This study is the first to present a new FLT3/RET dual-targeting inhibitor, PLM-101, that shows potent anti-leukemic activity and fewer adverse effects. PLM-101, therefore, should be considered for use as a potential therapeutic agent for AML.

Effectiveness of chemotherapy using bortezomib combined with homoharringtonine and cytarabine in refractory or relapsed acute myeloid leukemia: a phase II, multicenter, prospective clinical trial

Background

Refractory/relapsed acute myeloid leukemia (R/R AML) has unsatisfactory outcomes even after allogeneic hematopoietic stem cell transplantation. Long-term survival is mainly influenced by complete remission (CR) rates after induction therapies.

Objectives

To investigate CR/CR with incomplete hematologic recovery (CRi) rates and adverse events with a new induction therapy (bortezomib, homoharringtonine, and cytarabine [BHA]) for patients with R/R AML.

Methods

We enrolled 21 patients with R/R AML (median age, 42 [range, 30-62] years), who received BHA for remission induction (bortezomib, 1.3 mg/m2/day on days 1 and 4; homoharringtonine, 4 mg/m2/day for 5 days, and cytarabine, 1.5 g/m2/day for 5 days). CR and adverse events were assessed.

Results

After one course of BHA, the CR/CRi and partial remission rates were 38.1% and 14.3%, respectively, with an overall response rate (ORR) of 52.4% in 21 patients. 9 of 21 patients harbored FLT3-ITD or FLT3-TKD mutations, and achieved either CR/CRi or ORR of 66.7% (P=0.03) by comparison with that in R/R AML without FLT3 mutation. After induction therapy, consolidation chemotherapy or allogeneic hematopoietic stem cell transplantation led to a one-year overall survival of 27.8% in all patients. One-year relapse-free survival was 50% in 8 patients who had achieved CR/CRi after one course of BHA. During induction, non-hematologic adverse events (grade 3/4) commonly were infection (90.5%), hypokalemia (14.4%), hypocalcemia (14.3%), and mucositis (9.5%). In patients achieving CR, the median time to neutrophil count >0.5×109/L and time to platelet count >20×109/L were 15 (13-17) days and 13 (13-18) days, respectively.

Conclusion

BHA chemotherapy regimen was safe and tolerable to serve as an induction therapy for R/R AML, particularly with FLT3 mutation. The higher CR/CRi rate will give a clue to determine a potentialeffectiveness of BHA for AML patients carrying FLT3 mutation in a further investigation.

Clinical trial registration

https://www.chictr.org.cn/, identifier ChiCTR2000029841.

Exogenous Antigen Upregulation Empowers Antibody Targeted Nanochemotherapy of Leukemia

Acute myeloid leukemia (AML) is afflicted by a high-mortality rate and few treatment options. The lack of specific surface antigens severely hampers the development of targeted therapeutics and cell therapy. Here, it is shown that exogenous all-trans retinoic acid (ATRA) mediates selective and transient CD38 upregulation on leukemia cells by up to 20-fold, which enables high-efficiency targeted nanochemotherapy of leukemia with daratumumab antibody-directed polymersomal vincristine sulfate (DPV). Strikingly, treatment of two CD38-low expressing AML orthotopic models with ATRA and DPV portfolio strategies effectively eliminates circulating leukemia cells and leukemia invasion into bone marrow and organs, leading to exceptional survival benefits with 20-40% of mice becoming leukemia-free. The combination of exogenous CD38 upregulation and antibody-directed nanotherapeutics provides a unique and powerful targeted therapy for leukemia.

The role of autophagy in acute myeloid leukemia development

INTRODUCTION

Autophagy is a highly conservative self-degradative process. It aims at elimination-impaired proteins and cellular organelles. Previous research confirmed the autophagy role in cancer pathogenesis.

AREAS COVERED

This article discusses the role of autophagy in the development of AML. Autophagy seems to be a 'double-sword' mechanism, hence, either its suppression or induction could promote neoplasm growth. This mechanism could also be the aim of the 'molecular targeted therapy.' Chemo- and radiotherapy induce cellular stress in neoplasm cells with subsequent autophagy suppression. Simultaneously, it is claimed that the autophagy suppression increases chemosensitivity 'in neoplastic cells. Some agents, like bortezomib, in turn could promote autophagy process, e.g. in AML (acute myeloid leukemia). However, currently there are not many studies focusing on the role of autophagy in patients suffering for AML. In this review, we summarize the research done so far on the role of autophagy in the development of AML.

EXPERT OPINION

The analysis of autophagy genes expression profiling in AML could be a relevant factor in the diagnostic process and treatment 'individualization.' Autophagy modulation seems to be a relevant target in the oncological therapy - it could limit disease progression and increase the effectiveness of treatment.

Therapeutic Targeting of FLT3 in Acute Myeloid Leukemia: Current Status and Novel Approaches

FMS-like tyrosine kinase 3 (FLT3) is mutated in approximately 30% of acute myeloid leukemia (AML) patients. The presence of FLT3-ITD (internal tandem duplication, 20-25%) mutation and, to a lesser extent, FLT3-TKD (tyrosine kinase domain, 5-10%) mutation is associated with poorer diagnosis and therapy response since the leukemic cells become hyperproliferative and resistant to apoptosis after continuous activation of FLT3 signaling. Targeting FLT3 has been the focus of many pre-clinical and clinical studies. Hence, many small-molecule FLT3 inhibitors (FLT3is) have been developed, some of which are approved such as midostaurin and gilteritinib to be used in different clinical settings, either in combination with chemotherapy or alone. However, many questions regarding the best treatment strategy remain to be answered. On the other hand, various FLT3-dependent and -independent resistance mechanisms could be evolved during FLT3i therapy which limit their clinical impact. Therefore, identifying molecular mechanisms of resistance and developing novel strategies to overcome this obstacle is a current interest in the field. In this review, recent studies of approved FLT3i and knowledge about major resistance mechanisms of clinically approved FLT3i's will be discussed together with novel treatment approaches such as designing novel FLT3i and dual FLT3i and combination strategies including approved FLT3i plus small-molecule agents targeting altered molecules in the resistant cells to abrogate resistance. Moreover, how to choose an appropriate FLT3i for the patients will be summarized based on what is currently known from available clinical data. In addition, strategies beyond FLT3i's including immunotherapeutics, small-molecule FLT3 degraders, and flavonoids will be summarized to highlight potential alternatives in FLT3-mutated AML therapy.

19S Proteasome Subunits as Oncogenes and Prognostic Biomarkers in FLT3-Mutated Acute Myeloid Leukemia (AML)

26S proteasome non-ATPase subunits 1 (PSMD1) and 3 (PSMD3) were recently identified as prognostic biomarkers and potential therapeutic targets in chronic myeloid leukemia (CML) and multiple solid tumors. In the present study, we analyzed the expression of 19S proteasome subunits in acute myeloid leukemia (AML) patients with mutations in the FMS-like tyrosine kinase 3 (FLT3) gene and assessed their impact on overall survival (OS). High levels of PSMD3 but not PSMD1 expression correlated with a worse OS in FLT3-mutated AML. Consistent with an oncogenic role for PSMD3 in AML, shRNA-mediated PSMD3 knockdown impaired colony formation of FLT3+ AML cell lines, which correlated with increased OS in xenograft models. While PSMD3 regulated nuclear factor-kappa B (NF-κB) transcriptional activity in CML, we did not observe similar effects in FLT3+ AML cells. Rather, proteomics analyses suggested a role for PSMD3 in neutrophil degranulation and energy metabolism. Finally, we identified additional PSMD subunits that are upregulated in AML patients with mutated versus wild-type FLT3, which correlated with worse outcomes. These findings suggest that different components of the 19S regulatory complex of the 26S proteasome can have indications for OS and may serve as prognostic biomarkers in AML and other types of cancers.

Autophagy inhibition impairs leukemia stem cell function in FLT3-ITD AML but has antagonistic interactions with tyrosine kinase inhibition

The FLT3-ITD mutation is associated with poor prognosis in acute myeloid leukemia (AML). FLT3 tyrosine kinase inhibitors (TKIs) demonstrate clinical efficacy but fail to target leukemia stem cells (LSC) and do not generate sustained responses. Autophagy is an important cellular stress response contributing to hematopoietic stem cells (HSC) maintenance and promoting leukemia development. Here we investigated the role of autophagy in regulating FLT3-ITD AML stem cell function and response to TKI treatment. We show that autophagy inhibition reduced quiescence and depleted repopulating potential of FLT3-ITD AML LSC, associated with mitochondrial accumulation and increased oxidative phosphorylation. However, TKI treatment reduced mitochondrial respiration and unexpectedly antagonized the effects of autophagy inhibition on LSC attrition. We further show that TKI-mediated targeting of AML LSC and committed progenitors was p53-dependent, and that autophagy inhibition enhanced p53 activity and increased TKI-mediated targeting of AML progenitors, but decreased p53 activity in LSC and reduced TKI-mediated LSC inhibition. These results provide new insights into the role of autophagy in differentially regulating AML stem and progenitor cells, reveal unexpected antagonistic effects of combined oncogenic tyrosine kinase inhibition and autophagy inhibition in AML LSC, and suggest an alternative approach to target AML LSC quiescence and regenerative potential.

Autophagy in Hematological Malignancies

Simple Summary

Autophagy is a dynamic and tightly regulated process that seems to have dual effects in cancer. In some contexts, it can induce carcinogenesis and promote cancer cell survival, whereas in others, it acts preventing tumor cell growth and tumor progression. Thus, autophagy functions seem to strictly depend on cancer ontogenesis, progression, and type. Here, we will dive into the current knowledge of autophagy in hematological malignancies and will highlight the main genetic components involved in each cancer type.

Abstract

Autophagy is a highly conserved metabolic pathway via which unwanted intracellular materials, such as unfolded proteins or damaged organelles, are digested. It is activated in response to conditions of oxidative stress or starvation, and is essential for the maintenance of cellular homeostasis and other vital functions, such as differentiation, cell death, and the cell cycle. Therefore, autophagy plays an important role in the initiation and progression of tumors, including hematological malignancies, where damaged autophagy during hematopoiesis can cause malignant transformation and increase cell proliferation. Over the last decade, the importance of autophagy in response to standard pharmacological treatment of hematological tumors has been observed, revealing completely opposite roles depending on the tumor type and stage. Thus, autophagy can promote tumor survival by attenuating the cellular damage caused by drugs and/or stabilizing oncogenic proteins, but can also have an antitumoral effect due to autophagic cell death. Therefore, autophagy-based strategies must depend on the context to create specific and safe combination therapies that could contribute to improved clinical outcomes. In this review, we describe the process of autophagy and its role on hematopoiesis, and we highlight recent research investigating its role as a potential therapeutic target in hematological malignancies. The findings suggest that genetic variants within autophagy-related genes modulate the risk of developing hemopathies, as well as patient survival.

Protein tyrosine kinase inhibitor resistance in malignant tumors: molecular mechanisms and future perspective

Protein tyrosine kinases (PTKs) are a class of proteins with tyrosine kinase activity that phosphorylate tyrosine residues of critical molecules in signaling pathways. Their basal function is essential for maintaining normal cell growth and differentiation. However, aberrant activation of PTKs caused by various factors can deviate cell function from the expected trajectory to an abnormal growth state, leading to carcinogenesis. Inhibiting the aberrant PTK function could inhibit tumor growth. Therefore, tyrosine kinase inhibitors (TKIs), target-specific inhibitors of PTKs, have been used in treating malignant tumors and play a significant role in targeted therapy of cancer. Currently, drug resistance is the main reason for limiting TKIs efficacy of cancer. The increasing studies indicated that tumor microenvironment, cell death resistance, tumor metabolism, epigenetic modification and abnormal metabolism of TKIs were deeply involved in tumor development and TKI resistance, besides the abnormal activation of PTK-related signaling pathways involved in gene mutations. Accordingly, it is of great significance to study the underlying mechanisms of TKIs resistance and find solutions to reverse TKIs resistance for improving TKIs efficacy of cancer. Herein, we reviewed the drug resistance mechanisms of TKIs and the potential approaches to overcome TKI resistance, aiming to provide a theoretical basis for improving the efficacy of TKIs.

Translatome proteomics identifies autophagy as a resistance mechanism to on-target FLT3 inhibitors in acute myeloid leukemia

Internal tandem duplications (ITD) in the receptor tyrosine kinase FLT3 occur in 25 % of acute myeloid leukemia (AML) patients, drive leukemia progression and confer a poor prognosis. Primary resistance to FLT3 kinase inhibitors (FLT3i) quizartinib, crenolanib and gilteritinib is a frequent clinical challenge and occurs in the absence of identifiable genetic causes. This suggests that adaptive cellular mechanisms mediate primary resistance to on-target FLT3i therapy. Here, we systematically investigated acute cellular responses to on-target therapy with multiple FLT3i in FLT3-ITD + AML using recently developed functional translatome proteomics (measuring changes in the nascent proteome) with phosphoproteomics. This pinpointed AKT-mTORC1-ULK1-dependent autophagy as a dominant resistance mechanism to on-target FLT3i therapy. FLT3i induced autophagy in a concentration- and time-dependent manner specifically in FLT3-ITD + cells in vitro and in primary human AML cells ex vivo. Pharmacological or genetic inhibition of autophagy increased the sensitivity to FLT3-targeted therapy in cell lines, patient-derived xenografts and primary AML cells ex vivo. In mice xenografted with FLT3-ITD + AML cells, co-treatment with oral FLT3 and autophagy inhibitors synergistically impaired leukemia progression and extended overall survival. Our findings identify a molecular mechanism responsible for primary FLT3i treatment resistance and demonstrate the pre-clinical efficacy of a rational combination treatment strategy targeting both FLT3 and autophagy induction.

A bavachinin analog, D36, induces cell death by targeting both autophagy and apoptosis pathway in acute myeloid leukemia cells

PURPOSE

Acute myeloid leukemia (AML) is an aggressive hematologic malignancy with high mortality, and it is urgent to find new and optimized treatment strategies for AML. In this study, bavachinin, isolated from Psoralea corylifolia L. exhibiting extensive anti-tumor activity in many solid tumors and a series of its synthesized analogs, were screened for their anti-cancer activity on AML cell lines.

METHODS

The cell viability of AML cells was measured using CCK-8 assays. Cell apoptosis and cell cycle were detected by flow cytometry. The expression of apoptosis-related protein and autophagy-related protein/gene was detected by western blot, immunofluorescence or RT-PCR. Subcutaneous mice tumor model was used to evaluate the anti-cancer activity of D36 in vivo.

RESULTS

D36 robustly induced AML cells death in a dose-dependent manner with the IC₅₀ value of 1.0 μM for HL-60 cells and 0.81 μM for MV4-11 cells at 24 h. D36 activated autophagy by inducing the accumulation of LC3B and promoting the autophagy flux. In addition, D36 triggered the extrinsic apoptosis by upregulating the protein level of FAS, cleaved-caspase 8, cleaved-caspase 3 and cleaved-PARP. D36 also blocked the cell cycle at S phase or G₂/M phase in AML cells. In addition, we find that activation of caspase cascade induced apoptosis and meanwhile activated autophagy, autophagy activation in turns contributes to apoptosis. Furthermore, D36 suppressed the tumor growth in HL-60 AML-bearing mice without obvious side effects.

CONCLUSION

This study suggests that D36 is a promising small-molecule for the treatment of acute myeloid leukemia.

The dual role of autophagy in acute myeloid leukemia

Acute myeloid leukemia (AML) is a severe hematologic malignancy prevalent in older patients, and the identification of potential therapeutic targets for AML is problematic. Autophagy is a lysosome-dependent catabolic pathway involved in the tumorigenesis and/or treatment of various cancers. Mounting evidence has suggested that autophagy plays a critical role in the initiation and progression of AML and anticancer responses. In this review, we describe recent updates on the multifaceted functions of autophagy linking to genetic alterations of AML. We also summarize the latest evidence for autophagy-related genes as potential prognostic predictors and drivers of AML tumorigenesis. We then discuss the crosstalk between autophagy and tumor cell metabolism into the impact on both AML progression and anti-leukemic treatment. Moreover, a series of autophagy regulators, i.e., the inhibitors and activators, are described as potential therapeutics for AML. Finally, we describe the translation of autophagy-modulating therapeutics into clinical practice. Autophagy in AML is a double-edged sword, necessitating a deeper understanding of how autophagy influences dual functions in AML tumorigenesis and anti-leukemic responses.

Small Molecule Induced FLT3 Degradation

Target protein degrader is a new paradigm in the small molecule drug discovery field and relates to the term ‘event-driven pharmacology’. Fms-like tyrosine kinase 3 (FLT3) is a significant target for treating acute myeloid leukemia (AML). A few FLT3 kinase inhibitors are currently used in the clinic for AML patients. However, resistance to current FLT3 inhibitors has emerged, and strategies to overcome this resistance are required. Small molecules downregulating FLT3 protein level are reported, exhibiting antileukemic effects against AML cell lines. Small molecules with various mechanisms such as Hsp90 inhibition, proteasome inhibition, RET inhibition, and USP10 inhibition are explained. In addition, reports of FLT3 as a client of Hsp90, current knowledge of the ubiquitin proteasome system for FLT3 degradation, the relationship with FLT3 phosphorylation status and susceptibility of FLT3 degradation are discussed.

Autophagy Targeting and Hematological Mobilization in FLT3-ITD Acute Myeloid Leukemia Decrease Repopulating Capacity and Relapse by Inducing Apoptosis of Committed Leukemic Cells

Targeting FLT3-ITD in AML using TKI against FLT3 cannot prevent relapse even in the presence of complete remission, suggesting the resistance and/or the persistence of leukemic-initiating cells in the hematopoietic niche. By mimicking the hematopoietic niche condition with cultures at low oxygen concentrations, we demonstrate in vitro that FLT3-ITD AML cells decrease their repopulating capacity when Vps34 is inhibited. Ex vivo, AML FLT3-ITD blasts treated with Vps34 inhibitors recovered proliferation more slowly due to an increase an apoptosis. In vivo, mice engrafted with FLT3-ITD AML MV4-11 cells have the invasion of the bone marrow and blood in 2 weeks. After 4 weeks of FLT3 TKI treatment with gilteritinib, the leukemic burden had strongly decreased and deep remission was observed. When treatment was discontinued, mice relapsed rapidly. In contrast, Vps34 inhibition strongly decreased the relapse rate, and even more so in association with mobilization by G-CSF and AMD3100. These results demonstrate that remission offers the therapeutic window for a regimen using Vps34 inhibition combined with mobilization to target persistent leukemic stem cells and thus decrease the relapse rate.

A unique role of p53 haploinsufficiency or loss in the development of acute myeloid leukemia with FLT3-ITD mutation

With an incidence of ~50%, the absence or reduced protein level of p53 is much more common than TP53 mutations in acute myeloid leukemia (AML). AML with FLT3-ITD (internal tandem duplication) mutations has an unfavorable prognosis and is highly associated with wt-p53 dysfunction. While TP53 mutation in the presence of FLT3-ITD does not induce AML in mice, it is not clear whether p53 haploinsufficiency or loss cooperates with FLT3-ITD in the induction of AML. Here, we generated FLT3-ITD knock-in; p53 knockout (heterozygous and homozygous) double-transgenic mice and found that both alterations strongly cooperated in the induction of cytogenetically normal AML without increasing the self-renewal potential. At the molecular level, we found the strong upregulation of Htra3 and the downregulation of Lin28a, leading to enhanced proliferation and the inhibition of apoptosis and differentiation. The co-occurrence of Htra3 overexpression and Lin28a knockdown, in the presence of FLT3-ITD, induced AML with similar morphology as leukemic cells from double-transgenic mice. These leukemic cells were highly sensitive to the proteasome inhibitor carfilzomib. Carfilzomib strongly enhanced the activity of targeting AXL (upstream of FLT3) against murine and human leukemic cells. Our results unravel a unique role of p53 haploinsufficiency or loss in the development of FLT3-ITD + AML.

Autophagy and cancer metabolism-The two-way interplay

Autophagy is an intracellular catabolic process that degrades cytoplasmic components for recycling in response to stressed conditions, such as nutrient deprivation. Dysregulation of autophagy is associated with various diseases, including cancer. Although autophagy plays dichotomous and context-dependent roles in cancer, evidence has emerged that cancer cells exploit autophagy for metabolic adaptation. Autophagy is upregulated in many cancer types through tumor cell-intrinsic proliferation demands and the hypoxic and nutrient-limited tumor microenvironment (TME). Autophagy-induced breakdown products then fuel into various metabolic pathways to supply tumor cells with energy and building blocks for biosynthesis and survival. This bidirectional regulation between autophagy and tumor constitutes a vicious cycle to potentiate tumor growth and therapy resistance. In addition, the pro-tumor functions of autophagy are expanded to host, including cells in TME and distant organs. Thus, inhibition of autophagy or autophagy-mediated metabolic reprogramming may be a promising strategy for anticancer therapy. Better understanding the metabolic rewiring mechanisms of autophagy for its pro-tumor effects will provide insights into patient treatment.

The Dual Role of Autophagy in Crizotinib-Treated ALK+ ALCL: From the Lymphoma Cells Drug Resistance to Their Demise

Autophagy has been described as harboring a dual role in cancer development and therapy. Depending on the context, it can exert either pro-survival or pro-death functions. Here, we review what is known about autophagy in crizotinib-treated ALK⁺ ALCL. We first present our main findings on the role and regulation of autophagy in these cells. Then, we provide literature-driven hypotheses that could explain mechanistically the pro-survival properties of autophagy in crizotinib-treated bulk and stem-like ALK⁺ ALCL cells. Finally, we discuss how the potentiation of autophagy, which occurs with combined therapies (ALK and BCL2 or ALK and RAF1 co-inhibition), could convert it from a survival mechanism to a pro-death process.

Autophagy in Hematological Malignancies: Molecular Aspects in Leukemia and Lymphoma

The organization of the hematopoietic system is dependent on hematopoietic stem cells (HSCs) that are capable of self-renewal and multilineage differentiation to produce different blood cell lines. Autophagy has a central role in energy production and metabolism of the cells during starvation, cellular stress adaption, and removing mechanisms for aged or damaged organelles. The role and importance of autophagy pathways are becoming increasingly recognized in the literature because these pathways can be useful in organizing intracellular circulation, molecular complexes, and organelles to meet the needs of various hematopoietic cells. There is supporting evidence in the literature that autophagy plays an emerging role in the regulation of normal cells and that it also has important features in malignant hematopoiesis. Understanding the molecular details of the autophagy pathway can provide novel methods for more effective treatment of patients with leukemia. Overall, our review will emphasize the role of autophagy and its different aspects in hematological malignant neoplasms.

Autophagy is a major metabolic regulator involved in cancer therapy resistance

Autophagy sustains cellular homeostasis and metabolism in numerous diseases. By regulating cancer metabolism, both tumor and microenvironmental autophagy promote tumor growth. However, autophagy can support cancer progression through other biological functions such as immune response regulation or cytokine/growth factor secretion. Moreover, autophagy is induced in numerous tumor types as a resistance mechanism following therapy, highlighting autophagy inhibition as a promising target for anti-cancer therapy. Thus, better understanding the mechanisms involved in tumor growth and resistance regulation through autophagy, which are not fully understood, will provide insights into patient treatment.

Reducing FASN expression sensitizes acute myeloid leukemia cells to differentiation therapy

Fatty acid synthase (FASN) is the only human lipogenic enzyme available for de novo fatty acid synthesis and is often highly expressed in cancer cells. We found that FASN mRNA levels were significantly higher in acute myeloid leukemia (AML) patients than in healthy granulocytes or CD34⁺ hematopoietic progenitors. Accordingly, FASN levels decreased during all-trans retinoic acid (ATRA)-mediated granulocytic differentiation of acute promyelocytic leukemia (APL) cells, partially via autophagic degradation. Furthermore, our data suggest that inhibition of FASN expression levels using RNAi or (-)-epigallocatechin-3-gallate (EGCG) accelerated the differentiation of APL cell lines and significantly re-sensitized ATRA refractory non-APL AML cells. FASN reduction promoted translocation of transcription factor EB (TFEB) to the nucleus, paralleled by activation of CLEAR network genes and lysosomal biogenesis. Together, our data demonstrate that inhibition of FASN expression in combination with ATRA treatment facilitates granulocytic differentiation of APL cells and may extend differentiation therapy to non-APL AML cells.

Proteasome inhibitors suppress MYB oncogenic activity in a p300-dependent manner

Studies of the role of MYB in human malignancies have highlighted MYB as a potential drug target for acute myeloid leukemia (AML) and adenoid cystic carcinoma (ACC). Although transcription factors are often considered un-druggable, recent work has demonstrated successful targeting of MYB by low molecular weight compounds. This has fueled the notion that inhibition of MYB has potential as a therapeutic approach against MYB-driven malignancies. Here, we have used a MYB reporter cell line to screen a library of FDA-approved drugs for novel MYB inhibitors. We demonstrate that proteasome inhibitors have significant MYB-inhibitory activity, prompting us to characterize the proteasome inhibitor oprozomib in more detail. Oprozomib was shown to interfere with the ability of the co-activator p300 to stimulate MYB activity and to exert anti-proliferative effects on human AML and ACC cells. Overall, our work demonstrated suppression of oncogenic MYB activity as a novel result of proteasome inhibition.

Autophagy a Close Relative of AML Biology

Simple Summary

Acute myeloid leukemia (AML) is the most common acute leukemia in adults. Despite a high rate of complete remission following conventional chemotherapy, the prognosis remains poor due to frequent relapses caused by relapse-initiating leukemic cells (RICs), which are resistant to chemotherapies. While the development of new targeted therapies holds great promise (e.g., molecules targeting IDH1/2, FLT3, BCL2), relapses still occur. Therefore, a paramount issue in the elimination of RICs is to decipher the AML resistance mechanisms. Thus, it has been recently shown that AML cells exhibit metabolic changes in response to chemotherapy or targeted therapies. Autophagy is a major regulator of cell metabolism, involved in maintaining cancer state, metastasis, and resistance to anticancer therapy. However, whether autophagy acts as a tumor suppressor or promoter in AML is still a matter of debate. Therefore, depending on molecular AML subtypes or treatments used, a better understanding of the role of autophagy is needed to determine whether its modulation could result in a clinical benefit.

Abstract

Autophagy, which literally means “eat yourself”, is more than just a lysosomal degradation pathway. It is a well-known regulator of cellular metabolism and a mechanism implicated in tumor initiation/progression and therapeutic resistance in many cancers. However, whether autophagy acts as a tumor suppressor or promoter is still a matter of debate. In acute myeloid leukemia (AML), it is now proven that autophagy supports cell proliferation in vitro and leukemic progression in vivo. Mitophagy, the specific degradation of mitochondria through autophagy, was recently shown to be required for leukemic stem cell functions and survival, highlighting the prominent role of this selective autophagy in leukemia initiation and progression. Moreover, autophagy in AML sustains fatty acid oxidation through lipophagy to support mitochondrial oxidative phosphorylation (OxPHOS), a hallmark of chemotherapy-resistant cells. Nevertheless, in the context of therapy, in AML, as well as in other cancers, autophagy could be either cytoprotective or cytotoxic, depending on the drugs used. This review summarizes the recent findings that mechanistically show how autophagy favors leukemic transformation of normal hematopoietic stem cells, as well as AML progression and also recapitulates its ambivalent role in resistance to chemotherapies and targeted therapies.

MiR-15a-5p Confers Chemoresistance in Acute Myeloid Leukemia by Inhibiting Autophagy Induced by Daunorubicin

Anthracyclines remain a cornerstone of induction chemotherapy for acute myeloid leukemia (AML). Refractory or relapsed disease due to chemotherapy resistance is a major obstacle in AML management. MicroRNAs (miRNAs) have been observed to be involved in chemoresistance. We previously observed that miR-15a-5p was overexpressed in a subgroup of chemoresistant cytogenetically normal AML patients compared with chemosensitive patients treated with daunorubicin and cytarabine. MiR-15a-5p overexpression in AML cells reduced apoptosis induced by both drugs in vitro. This study aimed to elucidate the mechanisms by which miR-15a-5p contributes to daunorubicin resistance. We showed that daunorubicin induced autophagy in myeloid cell lines. The inhibition of autophagy reduced cell sensitivity to daunorubicin. The overexpression of miR-15a-5p decreased daunorubicin-induced autophagy. Conversely, the downregulation of miR-15a-5p increased daunorubicin-induced autophagy. We found that miR-15a-5p targeted four genes involved in autophagy, namely ATG9a, ATG14, GABARAPL1 and SMPD1. Daunorubicin increased the expression of these four genes, and miR-15a-5p counteracted this regulation. Inhibition experiments with the four target genes showed the functional effect of miR-15a-5p on autophagy. In summary, our results indicated that miR-15a-5p induces chemoresistance in AML cells through the abrogation of daunorubicin-induced autophagy, suggesting that miR-15a-5p could be a promising therapeutic target for chemoresistant AML patients.

Abnormal saccharides affecting cancer multi-drug resistance (MDR) and the reversal strategies

Clinically, chemotherapy is the mainstay in the treatment of multiple cancers. However, highly adaptable and activated survival signaling pathways of cancer cells readily emerge after long exposure to chemotherapeutics drugs, resulting in multi-drug resistance (MDR) and treatment failure. Recently, growing evidences indicate that the molecular action mechanisms of cancer MDR are closely associated with abnormalities in saccharides. In this review, saccharides affecting cancer MDR development are elaborated and analyzed in terms of aberrant aerobic glycolysis and its related enzymes, abnormal glycan structures and their associated enzymes, and glycoproteins. The reversal strategies including depletion of ATP, circumventing the original MDR pathway, activation by or inhibition of sugar-related enzymes, combination therapy with traditional cytotoxic agents, and direct modification on the sugar moiety, are ultimately proposed. It follows that abnormal saccharides have a significant effect on cancer MDR development, providing a new perspective for overcoming MDR and improving the outcome of chemotherapy.

Wu-5, a novel USP10 inhibitor, enhances crenolanib-induced FLT3-ITD-positive AML cell death via inhibiting FLT3 and AMPK pathways

The kinase FLT3 internal tandem duplication (FLT3-ITD) is related to poor clinical outcomes of acute myeloid leukemia (AML). FLT3 inhibitors have provided novel strategies for the treatment of FLT3-ITD-positive AML. But they are limited by rapid development of acquired resistance and refractory in monotherapy. Recent evidence shows that inducing the degradation of FLT3-mutated protein is an attractive strategy for the treatment of FLT3-ITD-positive AML, especially those with FLT3 inhibitor resistance. In this study we identified Wu-5 as a novel USP10 inhibitor inducing the degradation of FLT3-mutated protein. We showed that Wu-5 selectively inhibited the viability of FLT3 inhibitor-sensitive (MV4-11, Molm13) and -resistant (MV4-11R) FLT3-ITD-positive AML cells with IC₅₀ of 3.794, 5.056, and 8.386 μM, respectively. Wu-5 (1-10 μM) dose-dependently induced apoptosis of MV4-11, Molm13, and MV4-11R cells through the proteasome-mediated degradation of FLT3-ITD. We further demonstrated that Wu-5 directly interacted with and inactivated USP10, the deubiquitinase for FLT3-ITD in vitro (IC₅₀ value = 8.3 µM) and in FLT3-ITD-positive AML cells. Overexpression of USP10 abrogated Wu-5-induced FLT3-ITD degradation and cell death. Also, the combined treatment of Wu-5 and crenolanib produced synergistic cell death in FLT3-ITD-positive cells via the reduction of both FLT3 and AMPKα proteins. In support of this, AMPKα inhibitor compound C synergistically enhanced the anti-leukemia effect of crenolanib, while AMPKα activator metformin inhibited the anti-leukemia effect of crenolanib. In summary, we demonstrate that Wu-5, a novel USP10 inhibitor, can overcome FLT3 inhibitor resistance and synergistically enhance the anti-AML effect of crenolanib through targeting FLT3 and AMPKα pathway.

FLT3 Inhibitors in Acute Myeloid Leukemia: Challenges and Recent Developments in Overcoming Resistance

Mutations in the FMS-like tyrosine kinase 3 (FLT3) gene are often present in newly diagnosed acute myeloid leukemia (AML) patients with an incidence rate of approximately 30%. Recently, many FLT3 inhibitors have been developed and exhibit positive preclinical and clinical effects against AML. However, patients develop resistance soon after undergoing FLT3 inhibitor treatment, resulting in short durable responses and poor clinical effects. This review will discuss the main mechanisms of resistance to clinical FLT3 inhibitors and summarize the emerging strategies that are utilized to overcome drug resistance. Basically, medicinal chemistry efforts to develop new small-molecule FLT3 inhibitors offer a direct solution to this problem. Other potential strategies include the combination of FLT3 inhibitors with other therapies and the development of multitarget inhibitors. It is hoped that this review will provide inspiring insights into the discovery of new AML therapies that can eventually overcome the resistance to current FLT3 inhibitors.

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.

Whole transcriptome sequencing and integrated network analysis elucidates the effects of 3,8-Di-O-methylellagic acid 2-O-glucoside derived from Sanguisorba offcinalis L., a novel differentiation inducer on erythroleukemia cells

Acute erythroid leukemia (AEL) is a rare and aggressive hematologic malignancy with no specific treatment. Sanguisorba officinalis L. (S. officinalis), a well-known traditional Chinese medicine, possesses potent anticancer activity. However, the active components of S. officinalis against AEL and the associated molecular mechanisms remain unknown. In this study, we predicted the anti-AML effect of S. officinalis based on network pharmacology. Through the identification of active components of S. officinalis, we found that 3,8-Di-O-methylellagic acid 2-O-glucoside (DMAG) not only significantly inhibited the proliferation of erythroleukemic cell line HEL, but also induced their differentiation to megakaryocytes. Furthermore, we demonstrated that DMAG could prolong the survival of AEL mice model. Whole-transcriptome sequencing was performed to elucidate the underlying molecular mechanisms associated with anti-AEL effect of DMAG. The results showed that the total of 68 miRNAs, 595 lncRNAs, 4030 mRNAs and 35 circRNAs were significantly differentially expressed during DMAG induced proliferation inhibition and differentiation of HEL cells. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analyses revealed that the differentially expressed miRNAs, lncRNAs, mRNAs and circRNAs were mainly involved in metabolic, HIF-1, MAPK, Notch pathway and apoptosis. The co-expression networks showed that miR-23a-5p, miR-92a-1-5p, miR-146b and miR-760 regulatory networks were crucial for megakaryocyte differentiation induced by DMAG. In conclusion, our results suggest that DMAG, derived from S. officinalis might be a potent differentiation inducer of AEL cells and provide important information on the underlying mechanisms associated with its anti-AEL activity.

FLT3 Mutations in Acute Myeloid Leukemia: Key Concepts and Emerging Controversies

The FLT3 receptor is overexpressed on the majority of acute myeloid leukemia (AML) blasts. Mutations in FLT3 are the most common genetic alteration in AML, identified in approximately one third of newly diagnosed patients. FLT3 internal tandem duplication mutations (FLT3-ITD) are associated with increased relapse and inferior overall survival. Multiple small molecule inhibitors of FLT3 signaling have been identified, two of which (midostaurin and gilteritinib) are currently approved in the United States, and many more of which are in clinical trials. Despite significant advances, resistance to FLT3 inhibitors through secondary FLT3 mutations, upregulation of parallel pathways, and extracellular signaling remains an ongoing challenge. Novel therapeutic strategies to overcome resistance, including combining FLT3 inhibitors with other antileukemic agents, development of new FLT3 inhibitors, and FLT3-directed immunotherapy are in active clinical development. Multiple questions regarding FLT3-mutated AML remain. In this review, we highlight several of the current most intriguing controversies in the field including the role of FLT3 inhibitors in maintenance therapy, the role of hematopoietic cell transplantation in FLT3-mutated AML, use of FLT3 inhibitors in FLT3 wild-type disease, significance of non-canonical FLT3 mutations, and finally, emerging concerns regarding clonal evolution.

Reductive regulation of BECN1 gene in adult Egyptian patients with do novo AML

Background

Acute myeloid leukaemia (AML) is a clonal haematopoietic disease characterized by the proliferation of immature blast cells in the bone marrow and peripheral blood. Autophagy is an inherent cellular route by which waste macromolecules are engulfed within autophagosomes prior to their fusion with cytoplasmic lysosomes for degradation. The BECN1 gene encodes the Beclin-1 protein, which regulates autophagy. Few reports have investigated BECN1 gene expression and its value in AML patients.

Results

This randomized case-control study included 50 newly diagnosed AML patients, in addition to 20 subjects as a control group. BECN1 gene expression was assessed using real-time quantitative polymerase chain reaction (qRT-PCR).

The median level of BECN1 gene expression in AML patients was 0.41 (IQR 0.29–1.03) in comparison to 1.12 (IQR 0.93–1.26) in the control group (P = 0.000). Seventy-two percent of AML patients showed reduced BECN1 gene expression, which was highly significantly associated with intermediate and adverse cytogenetic risk. Reduced BECN1 gene expression was associated with older age, higher total leukocyte counts, the presence of peripheral blood blast cells, a higher percentage of bone marrow blast cells, and higher expression of CD34 and CD117. FLT3-ITD mutation was detected in 14 patients (38.9%), all of whom showed reduced BECN1 gene expression (P = 0.006). BECN1 gene expression was also reduced in non-responder AML patients, with a highly statistically significant difference (P = 0.002).

Conclusion

A reduction in BECN1 gene expression might indicate a poor prognosis in adult Egyptian patients with de novo AML. Decreased BECN1 gene expression is associated with a higher risk of resistance to treatment. Targeting autophagy pathways may help in the treatment of AML patients.

Inhibition of the proteasome and proteaphagy enhances apoptosis in FLT3-ITD-driven acute myeloid leukemia

Acute myeloid leukaemia (AML) is a clonal disorder that affects hematopoietic stem cells or myeloid progenitors. One of the most common mutations that results in AML occurs in the gene encoding fms‐like tyrosine kinase 3 (FLT3). Previous studies have demonstrated that AML cells expressing FLT3‐internal tandem duplication (ITD) are more sensitive to the proteasome inhibitor bortezomib (Bz) than FLT3 wild‐type cells, with this cytotoxicity being mediated by autophagy (Atg). Here, we show that proteasome inhibition with Bz results in modest but consistent proteaphagy in MOLM‐14 leukemic cells expressing the FLT3‐ITD mutation, but not in OCI‐AML3 leukemic cells with wild‐type FLT3. Chemical inhibition of Atg with bafilomycin A simultaneously blocked proteaphagy and resulted in the accumulation of the p62 Atg receptor in Bz‐treated MOLM‐14 cells. The use of ubiquitin traps revealed that ubiquitin plays an important role in proteasome‐Atg cross‐talk. The p62 inhibitor verteporfin blocked proteaphagy and, importantly, resulted in accumulation of high molecular weight forms of p62 and FLT3‐ITD in Bz‐treated MOLM‐14 cells. Both Atg inhibitors enhanced Bz‐induced apoptosis in FLT3‐ITD‐driven leukemic cells, highlighting the therapeutic potential of these treatments.

Antileukemic activity of the VPS34-IN1 inhibitor in acute myeloid leukemia

Acute myeloid leukemia (AML) is an aggressive disease with a poor prognosis. Vacuolar protein sorting 34 (VPS34) is a member of the phosphatidylinositol-3-kinase lipid kinase family that controls the canonical autophagy pathway and vesicular trafficking. Using a recently developed specific inhibitor (VPS34-IN1), we found that VPS34 inhibition induces apoptosis in AML cells but not in normal CD34+ hematopoietic cells. Complete and acute inhibition of VPS34 was required for the antileukemic activity of VPS34-IN1. This inhibitor also has pleiotropic effects against various cellular functions related to class III PI3K in AML cells that may explain their survival impairment. VPS34-IN1 inhibits basal and L-asparaginase-induced autophagy in AML cells. A synergistic cell death activity of this drug was also demonstrated. VPS34-IN1 was additionally found to impair vesicular trafficking and mTORC1 signaling. From an unbiased approach based on phosphoproteomic analysis, we identified that VPS34-IN1 specifically inhibits STAT5 phosphorylation downstream of FLT3-ITD signaling in AML. The identification of the mechanisms controlling FLT3-ITD signaling by VPS34 represents an important insight into the oncogenesis of AML and could lead to new therapeutic strategies.

Dendrogenin A Enhances Anti-Leukemic Effect of Anthracycline in Acute Myeloid Leukemia

Simple Summary

Recently, several molecules have improved the clinical outcome of acute myeloid leukemia (AML) patients. Despite these recent advances, their prognosis remains poor and new strategies to improve the standard anthracycline and Ara-C-based chemotherapy are needed. We recently published that dendrogenin A (DDA), a mammalian cholesterol metabolite with tumor-suppressor properties, can potentiate the effect of Ara-C to kill AML cells. In this study, we find that DDA can also potentiate anthracycline against AML. The potentiation of Ara-C by DDA is due to a switch from a protective autophagy to a deadly autophagy. Regarding anthracyclines, the potentiation of daunorubicin is caused by the modulation of the efflux by the PgP pump, and that of idarubicin, to an increase in DNA damage and to the induction of a rapid and lethal autophagy. This is caused by rapid modulation of AKT/mTOR and JNK activity, two major pathways involved both in DNA repair and lethal autophagy.

Abstract

Dendrogenin A (DDA), a mammalian cholesterol metabolite with tumor suppressor properties, has recently been shown to exhibit strong anti-leukemic activity in acute myeloid leukemia (AML) cells by triggering lethal autophagy. Here, we demonstrated that DDA synergistically enhanced the toxicity of anthracyclines in AML cells but not in normal hematopoietic cells. Combination index of DDA treatment with either daunorubicin or idarubicin indicated a strong synergism in KG1a, KG1 and MV4-11 cell lines. This was confirmed in vivo using immunodeficient mice engrafted with MOLM-14 cells as well as in a panel of 20 genetically diverse AML patient samples. This effect was dependent on Liver X Receptor β, a major target of DDA. Furthermore, DDA plus idarubicin strongly increased p53BP1 expression and the number of DNA strand breaks in alkaline comet assays as compared to idarubicin alone, whereas DDA alone was non-genotoxic. Mechanistically, DDA induced JNK phosphorylation and the inhibition of AKT phosphorylation, thereby maximizing DNA damage induced by idarubicin and decreasing DNA repair. This activated autophagic cell death machinery in AML cells. Overall, this study shows that the combination of DDA and idarubicin is highly promising and supports clinical trials of dendrogenin A in AML patients.

Novel Approaches to Target Mutant FLT3 Leukaemia

Simple Summary

Acute myeloid leukemia (AML) is a haematologic disease in which oncogenic mutations in the receptor tyrosine kinase FLT3 frequently lead to leukaemic development. Potent treatment of AML patients is still hampered by inefficient targeting of leukemic stem cells expressing constitutive active FLT3 mutants. This review summarizes the current knowledge about the regulation of FLT3 activity at cellular level and discusses therapeutical options to affect the tumor cells and the microenvironment to impair the haematological aberrations.

Abstract

Fms-like tyrosine kinase 3 (FLT3) is a member of the class III receptor tyrosine kinases (RTK) and is involved in cell survival, proliferation, and differentiation of haematopoietic progenitors of lymphoid and myeloid lineages. Oncogenic mutations in the FLT3 gene resulting in constitutively active FLT3 variants are frequently found in acute myeloid leukaemia (AML) patients and correlate with patient’s poor survival. Targeting FLT3 mutant leukaemic stem cells (LSC) is a key to efficient treatment of patients with relapsed/refractory AML. It is therefore essential to understand how LSC escape current therapies in order to develop novel therapeutic strategies. Here, we summarize the current knowledge on mechanisms of FLT3 activity regulation and its cellular consequences. Furthermore, we discuss how aberrant FLT3 signalling cooperates with other oncogenic lesions and the microenvironment to drive haematopoietic malignancies and how this can be harnessed for therapeutical purposes.

The role of autophagy in targeted therapy for acute myeloid leukemia

Although molecular targeted therapies have recently displayed therapeutic effects in acute myeloid leukemia (AML), limited response and acquired resistance remain common problems. Numerous studies have associated autophagy, an essential degradation process involved in the cellular response to stress, with the development and therapeutic response of cancers including AML. Thus, we review studies on the role of autophagy in AML development and summarize the linkage between autophagy and several recurrent genetic abnormalities in AML, highlighting the potential of capitalizing on autophagy modulation in targeted therapy for AML.Abbreviations: AML: acute myeloid leukemia; AMPK: AMP-activated protein kinase; APL: acute promyelocytic leukemia; ATG: autophagy related; ATM: ATM serine/threonine kinase; ATO: arsenic trioxide; ATRA: all trans retinoic acid; BCL2: BCL2 apoptosis regulator; BECN1: beclin 1; BET proteins, bromodomain and extra-terminal domain family; CMA: chaperone-mediated autophagy; CQ: chloroquine; DNMT, DNA methyltransferase; DOT1L: DOT1 like histone lysine methyltransferase; FLT3: fms related receptor tyrosine kinase 3; FIS1: fission, mitochondrial 1; HCQ: hydroxychloroquine; HSC: hematopoietic stem cell; IDH: isocitrate dehydrogenase; ITD: internal tandem duplication; KMT2A/MLL: lysine methyltransferase 2A; LSC: leukemia stem cell; MDS: myelodysplastic syndromes; MTORC1: mechanistic target of rapamycin kinase complex 1; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; NPM1: nucleophosmin 1; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PML: PML nuclear body scaffold; ROS: reactive oxygen species; RB1CC1/FIP200: RB1 inducible coiled-coil 1; SAHA: vorinostat; SQSTM1: sequestosome 1; TET2: tet methylcytosine dioxygenase 2; TKD: tyrosine kinase domain; TKI: tyrosine kinase inhibitor; TP53/p53: tumor protein p53; ULK1: unc-51 like autophagy activating kinase 1; VPA: valproic acid; WDFY3/ALFY: WD repeat and FYVE domain containing 3.

Retinoic acid synergizes with the unfolded protein response and oxidative stress to induce cell death in FLT3-ITD+ AML

Acute myeloid leukemia (AML) is often characterized by the expression of fusion or mutant proteins that cause impaired differentiation and enhanced proliferation and survival. The presence of mutant proteins prone to misfolding can render the cells sensitive to endoplasmic reticulum (ER) stress and oxidative stress that could otherwise be overcome. Here, we show that the triple combination of the differentiating agent retinoic acid (RA), the ER stress-inducing drug tunicamycin (Tm), and arsenic trioxide (ATO), able to generate oxidative stress, leads to the death of AML cell lines expressing fusion proteins involving the gene MLL and the internal tandem duplication (ITD) in the FLT3 tyrosine kinase receptor. Importantly, the combination of RA, Tm, and ATO decreased the colony-forming capacity of primary leukemic blasts bearing the FLT-ITD mutation without affecting healthy hematopoietic progenitor cells. We demonstrate in cell lines that combination of these drugs generates ER and oxidative stresses and impairs maturation and causes accumulation of FLT3 protein in the ER. Our data provide a proof of concept that low amounts of drugs that generate ER and oxidative stresses combined with RA could be an effective targeted therapy to hit AML cells characterized by MLL fusion proteins and FLT3-ITD mutation.

Casein kinase 1α inhibits p53 downstream of MDM2‑mediated autophagy and apoptosis in acute myeloid leukemia

Enhancement of autophagy serves as a promising therapeutic strategy for cancer, including acute myeloid leukemia (AML). Casein kinase 1α (CK1α), encoded by CSNK1A1, regulates Wnt/β-catenin, p53 and other key signaling pathways, and is critically involved in tumor progression. However, the relationship and mechanism of CK1α with autophagy in AML still remain unclear. In the present study, it was found that AML patients had higher expression of CSNK1A1 mRNA than healthy donors. Furthermore, we analyzed 163 cases of AML patients in the LAML database of TCGA and found that AML patients with high CSNK1A1 had shorter overall survival than those with low or medium CSNK1A1 expression. Furthermore, we demonstrated that CK1α was a negative regulator of autophagy and apoptosis. Pharmacologic inhibition of CK1α using D4476 or CK1α knockdown via lentivirus-mediated shRNA suppressed proliferation and the clone formation by enhancing autophagic flux and apoptosis in AML cell lines as well as in patient blast cells. Intriguingly, D4476-induced cell death was aggravated in combination with an autophagy inhibitor, Spautin-1, suggesting that autophagy may be a pro-survival signaling. CK1α interacted with murine double minute 2 (MDM2) and p53, and CK1α inhibitor D4476 significantly upregulated p53 and phosphorylated 5′ AMP-activated protein kinase (AMPK), and substantially inhibited the phosphorylation of mammalian target of rapamycin (mTOR). Our findings indicate that CK1α promotes AML by suppressing p53 downstream of MDM2-mediated autophagy and apoptosis, suggesting that targeting CK1α provides a therapeutic opportunity to treat AML.

BRCA1/2 Mutation Status Impact on Autophagy and Immune Response: Unheralded Target

BRCA1 and possibly BRCA2 proteins may relate to the regulation of autophagy. Autophagy plays a key role in immune response from both a tumor and immune effector cell standpoint. In cells with BRCA mutations, increased autophagy leads to elevated expression of major histocompatibility complex class II but may cause subclonal neoantigen presentation, which may impair the immune response related to clonal neoantigen visibility. We review evidence of BRCA1/2 regulation of autophagy, immune response, and antigen presentation.

mTOR Inhibition Leads to Src-Mediated EGFR Internalisation and Degradation in Glioma Cells

Epidermal Growth Factor receptor (EGFR) is a tyrosine kinase receptor widely expressed on the surface of numerous cell types, which activates several downstream signalling pathways involved in cell proliferation, migration and survival. EGFR alterations, such as overexpression or mutations, have been frequently observed in several cancers, including glioblastoma (GBM), and are associated to uncontrolled cell proliferation. Here we show that the inhibition of mammalian target of Rapamycin (mTOR) mediates EGFR delivery to lysosomes for degradation in GBM cells, independently of autophagy activation. Coherently with EGFR internalisation and degradation, mTOR blockade negatively affects the mitogen activated protein/extracellular signal-regulated kinase (MAPK)/ERK pathway. Furthermore, we provide evidence that Src kinase activation is required for EGFR internaliation upon mTOR inhibition. Our results further support the hypothesis that mTOR targeting may represent an effective therapeutic strategy in GBM management, as its inhibition results in EGFR degradation and in proliferative signal alteration.

Apatinib induces apoptosis and autophagy via the PI3K/AKT/mTOR and MAPK/ERK signaling pathways in neuroblastoma

The clinical outcome of neuroblastoma (NB) has significantly improved in the last 30 years for patients with localized disease; however, the overall survival (OS) for patients with metastasis remains poor. Apatinib, a selective inhibitor of the vascular endothelial growth factor receptor-2 (VEGFR-2) tyrosine kinase, which was discovered to be highly associated with metastasis, has been reported to exert antitumor effects in numerous types of cancer. However, the effect of apatinib in NB remains relatively unknown. The present study aimed to investigate the antitumor effects of apatinib in NB cells in vitro. The results revealed that apatinib inhibited cell viability and colony formation, whilst inducing cell cycle arrest and the apoptosis of NB cells. Additionally, apatinib inhibited the migration and invasion of NB cells, in addition to promoting the autophagy of NB cells. Western blotting demonstrated that the protein expression levels of phosphorylated (p)-AKT, p-mTOR and p-P70S6K, and downstream molecules associated with the cell cycle and apoptosis, such as cyclin D1 and the Bcl-2/Bax ratio of NB cells, were significantly decreased following treatment with apatinib. In addition, western blotting and immunofluorescence assays identified that the expression level of microtubule-associated protein 1A/1B-light chain 3-II, which is expressed in autophagosomes, was upregulated following apatinib treatment. In conclusion, the findings of the present study suggested that apatinib may induce apoptosis and autophagy via the PI3K/AKT/mTOR and mitogen-activated protein kinase/ERK signaling pathways in NB cells. Thus, apatinib may be a potential antitumor agent for the clinical treatment of NB.

Mechanisms Underlying Resistance to FLT3 Inhibitors in Acute Myeloid Leukemia

FLT3-ITD and FLT3-TKD mutations were observed in approximately 20 and 10% of acute myeloid leukemia (AML) cases, respectively. FLT3 inhibitors such as midostaurin, gilteritinib and quizartinib show excellent response rates in patients with FLT3-mutated AML, but its duration of response may not be sufficient yet. The majority of cases gain secondary resistance either by on-target and off-target abnormalities. On-target mutations (i.e., FLT3-TKD) such as D835Y keep the TK domain in its active form, abrogating pharmacodynamics of type II FLT3 inhibitors (e.g., midostaurin and quizartinib). Second generation type I inhibitors such as gilteritinib are consistently active against FLT3-TKD as well as FLT3-ITD. However, a “gatekeeper” mutation F691L shows universal resistance to all currently available FLT3 inhibitors. Off-target abnormalities are consisted with a variety of somatic mutations such as NRAS, AXL and PIM1 that bypass or reinforce FLT3 signaling. Off-target mutations can occur just in the primary FLT3-mutated clone or be gained by the evolution of other clones. A small number of cases show primary resistance by an FL-dependent, FGF2-dependent, and stromal CYP3A4-mediated manner. To overcome these mechanisms, the development of novel agents such as covalently-coupling FLT3 inhibitor FF-10101 and the investigation of combination therapy with different class agents are now ongoing. Along with novel agents, gene sequencing may improve clinical approaches by detecting additional targetable mutations and determining individual patterns of clonal evolution.

Mislocalisation of Activated Receptor Tyrosine Kinases - Challenges for Cancer Therapy

Activating mutations in genes encoding receptor tyrosine kinases (RTKs) mediate proliferation, cell migration, and cell survival, and are therefore important drivers of oncogenesis. Numerous targeted cancer therapies are directed against activated RTKs, including small compound inhibitors, and immunotherapies. It has recently been discovered that not only certain RTK fusion proteins, but also many full-length RTKs harbouring activating mutations, notably RTKs of the class III family, are to a large extent mislocalised in intracellular membranes. Active kinases in these locations cause aberrant activation of signalling pathways. Moreover, low levels of activated RTKs at the cell surface present an obstacle for immunotherapy. We outline here why understanding of the mechanisms underlying mislocalisation will help in improving existing and developing novel therapeutic strategies.