Ceramide-induced integrated stress response overcomes Bcl-2 inhibitor resistance in acute myeloid leukemia

BCL-2 inhibition in acute myeloid leukemia: resistance and combinations

INTRODUCTION

The introduction of venetoclax has revolutionized the treatment landscape of acute myeloid leukemia, offering new therapeutic opportunities. However, the clinical response to venetoclax varies significantly between patients, with many experiencing limited duration of response.

AREAS COVERED

Identified resistance mechanisms include both intrinsic and acquired resistance to VEN. The former is associated with cell lineage and differentiation state. The latter includes dependency on alternative BCL-2 family anti-apoptotic protein(s) mediated by genetic, epigenetic, or post-translational mechanisms, mitochondrial and metabolic involvement, as well as microenvironment. Understanding these mechanisms is crucial for optimizing venetoclax-based therapies and enhancing treatment outcomes for patients with acute myeloid leukemia. This review aims to elucidate the primary mechanisms underlying resistance to venetoclax and explore current therapeutic strategies to overcome this challenge.

EXPERT OPINION

In patients with venetoclax resistance, alternative options include targeted combination therapies tailored to individual cases based on cytogenetics and prior treatments. Many of these therapies require further clinical investigation to validate their safety and efficacy.

Integrated stress response activation induced by usnic acid alleviates BCL-2 inhibitor ABT-199 resistance in acute myeloid leukemia

INTRODUCTION

ABT-199 (venetoclax) is a BCL-2 suppressor with pronounced effects on acute myeloid leukemia (AML). However, its usefulness as a monotherapy or in combination with hypomethylating medicines like azacitidine is debatable due to acquired resistance. Usnic acid, a dibenzofuran extracted from lichen Usnea diffracta Vain, exhibits anticancer properties and may counteract multidrug resistance in leukemia cells.

OBJECTIVE

This study investigated whether usnic acid at low-cytotoxicity level could enhance sensitivity of AML cells with acquired resistance to ABT-199 by targeting the integrated stress response pathways.

METHODS

To investigate the combined effects on AML cells, we used a cell viability test, flow cytometry to quantify apoptosis, cell cycle analysis, and mitochondrial membrane potential measurement. RNA-seq and immunoblot were used to determine the potential mechanisms of ABT-199 + usnic acid combination.

RESULTS

Usnic acid, at a low cytotoxicity level, successfully restored ABT-199 sensitivity in AML cell lines that had developed ABT-199 resistance and increased ABT-199's antileukemic activity in a xenograft model. Mechanistically, the combination of usnic acid and ABT-199 cooperated to boost the expression of the integrated stress response (ISR)-associated genes ATF4, CHOP, and NOXA through the heme-regulated inhibitor kinase (HRI), while also promoting the degradation of the anti-apoptotic protein MCL-1. ISRIB, a compound that blocks the ISR, was able to reverse the growth suppression and cell death, the increase in expression of genes related with the ISR, and the inhibition of MCL-1 protein caused by combination therapy. Additionally, the downregulation of MCL-1 was linked to an increase in MCL-1 phosphorylation at serine 159 and subsequent destruction by the proteasome.

CONCLUSION

In summary, usnic acid improves chemosensitivity to ABT-199 by triggering the integrated stress response, leading to decreased levels of MCL-1 protein, suggesting a potential treatment for AML cases resistant to Bcl-2 inhibitors.

Influences on the Hematopoietic Stem Cell Niche

Hematopoietic stem cells (HSCs) are supported by the bone marrow microenvironment to maintain normal production of blood cells. The niche may be considered an "ecosystem" that support the function of HSCs and other supportive cells. Alterations in the bone marrow niche are commonly observed in hematologic malignancies. Here, we review recent insights into the location and the molecular and cellular components of the bone marrow niche. Moreover, we discuss how the niche interacts with HSCs to drive the pathogenesis of hematopoietic malignancies. Overall, a better understanding of the influences on the HSC niche may drive therapeutic development targeting defective and aberrant hematopoiesis.

Targeting YTHDF2 inhibits tumorigenesis of diffuse large B-cell lymphoma through ACER2-mediated ceramide catabolism

INTRODUCTION

Epigenetic alterations play crucial roles in diffuse large B-cell lymphoma (DLBCL). Disturbances in lipid metabolism contribute to tumor progression. However, studies in epigenetics, especially its critical regulator YTH N6-methyladenosine RNA binding protein 2 (YTHDF2), on lipid metabolism regulation in DLBCL are unidentified.

OBJECTIVES

Elucidate the prognostic value and biological functions of YTHDF2 in DLBCL and illuminate the underlying epigenetic regulation mechanism of lipid metabolism by YTHDF2 in DLBCL development.

METHODS

The expression and clinical value of YTHDF2 in DLBCL were performed in public databases and clinical specimens. The biological functions of YTHDF2 in DLBCL were determined in vivo and in vitro through overexpression and CRISPR/Cas9-mediated knockout of YTHDF2. RNA sequencing, lipidomics, methylated RNA immunoprecipitation sequencing, RNA immunoprecipitation-qPCR, luciferase activity assay, and RNA stability experiments were used to explore the potential mechanism by which YTHDF2 contributed to DLBCL progression.

RESULTS

YTHDF2 was highly expressed in DLBCL, and related to poor prognosis. YTHDF2 overexpression exerted a tumor-promoting effect in DLBCL, and knockdown of YTHDF2 restricted DLBCL cell proliferation, arrested cell cycle in the G2/M phase, facilitated apoptosis, and enhanced drug sensitivity to ibrutinib and venetoclax. In addition, YTHDF2 knockout drastically suppressed tumor growth in xenograft DLBCL models. Furthermore, a regulatory role of YTHDF2 in ceramide metabolism was identified in DLBCL cells. Exogenous ceramide effectively inhibited the malignant phenotype of DLBCL cells in vitro. The binding of YTHDF2 to m6A sites on alkaline ceramidase 2 (ACER2) mRNA promoted its stability and expression. Enhanced ACER2 expression hydrolyzed ceramides, disrupting the balance between ceramide and sphingosine-1-phosphate (S1P), activating the ERK and PI3K/AKT pathways, and leading to DLBCL tumorigenesis.

CONCLUSION

This study demonstrated that YTHDF2 contributed to the progression of DLBCL by regulating ACER2-mediated ceramide metabolism in an m6A-dependent manner, providing novel insights into targeted therapies.

Leveraging altered lipid metabolism in treating B cell malignancies

B cell malignancies, comprising over 80 heterogeneous blood cancers, pose significant prognostic challenges due to intricate oncogenic signaling. Emerging evidence emphasizes the pivotal role of disrupted lipid metabolism in the development of these malignancies. Variations in lipid species, such as phospholipids, cholesterol, sphingolipids, and fatty acids, are widespread across B cell malignancies, contributing to uncontrolled cell proliferation and survival. Phospholipids play a crucial role in initial signaling cascades leading to B cell activation and malignant transformation through constitutive B cell receptor (BCR) signaling. Dysregulated cholesterol and sphingolipid homeostasis support lipid raft integrity, crucial for propagating oncogenic signals. Sphingolipids impact malignant B cell stemness, proliferation, and survival, while glycosphingolipids in lipid rafts modulate BCR activation. Additionally, cancer cells enhance fatty acid-related processes to meet heightened metabolic demands. In obese individuals, the obesity-derived lipids and adipokines surrounding adipocytes rewire lipid metabolism in malignant B cells, evading cytotoxic therapies. Genetic drivers such as MYC translocations also intrinsically alter lipid metabolism in malignant B cells. In summary, intrinsic and extrinsic factors converge to reprogram lipid metabolism, fostering aggressive phenotypes in B cell malignancies. Therefore, targeting altered lipid metabolism has translational potential for improving risk stratification and clinical management of diverse B cell malignancy subtypes.

Cycloastragenol induces apoptosis and protective autophagy through AMPK/ULK1/mTOR axis in human non-small cell lung cancer cell lines

OBJECTIVE

Studies have demonstrated that cycloastragenol induces antitumor effects in prostate, colorectal and gastric cancers; however, its efficacy for inhibiting the proliferation of lung cancer cells is largely unexplored. This study explores the efficacy of cycloastragenol for inhibiting non-small cell lung cancer (NSCLC) and elucidates the underlying molecular mechanisms.

METHODS

The effects of cycloastragenol on lung cancer cell proliferation were assessed using an adenosine triphosphate monitoring system based on firefly luciferase and clonogenic formation assays. Cycloastragenol-induced apoptosis in lung cancer cells was evaluated using dual staining flow cytometry with an annexin V-fluorescein isothiocyanate/propidium iodide kit. To elucidate the role of cycloastragenol in the induction of apoptosis, apoptosis-related proteins were examined using Western blots. Immunofluorescence and Western blotting were used to determine whether cycloastragenol could induce autophagy in lung cancer cells. Genetic techniques, including small interfering RNA technology, were used to investigate the underlying mechanisms. The effects against lung cancer and biosafety of cycloastragenol were evaluated using a mouse subcutaneous tumor model.

RESULTS

Cycloastragenol triggered both autophagy and apoptosis. Specifically, cycloastragenol promoted apoptosis by facilitating the accumulation of phorbol-12-myristate-13-acetate-induced protein 1 (NOXA), a critical apoptosis-related protein. Moreover, cycloastragenol induced a protective autophagy response through modulation of the adenosine 5'-monophosphate-activated protein kinase (AMPK)/unc-51-like autophagy-activating kinase (ULK1)/mammalian target of rapamycin (mTOR) pathway.

CONCLUSION

Our study sheds new light on the antitumor efficacy and mechanism of action of cycloastragenol in NSCLC. This insight provides a scientific basis for exploring combination therapies that use cycloastragenol and inhibiting the AMPK/ULK1/mTOR pathway as a promising approach to combating lung cancer. Please cite this article as follows: Zhu LH, Liang YP, Yang L, Zhu F, Jia LJ, Li HG. Cycloastragenolinduces apoptosis and protective autophagy through AMPK/ULK1/mTOR axis in human non-small celllung cancer cell lines. J Integr Med. 2024; 22(4): 504-515.

Venetoclax therapy and emerging resistance mechanisms in acute myeloid leukaemia

Acute myeloid leukaemia (AML) is a highly aggressive and devastating malignancy of the bone marrow and blood. For decades, intensive chemotherapy has been the frontline treatment for AML but has yielded only poor patient outcomes as exemplified by a 5-year survival rate of < 30%, even in younger adults. As knowledge of the molecular underpinnings of AML has advanced, so too has the development new strategies with potential to improve the treatment of AML patients. To date the most promising of these targeted agents is the BH3-mimetic venetoclax which in combination with standard of care therapies, has manageable non-haematological toxicity and exhibits impressive efficacy. However, approximately 30% of AML patients fail to respond to venetoclax-based regimens and almost all treatment responders eventually relapse. Here, we review the emerging mechanisms of intrinsic and acquired venetoclax resistance in AML and highlight recent efforts to identify novel strategies to overcome resistance to venetoclax.

Comprehensive review of Bcl-2 family proteins in cancer apoptosis: Therapeutic strategies and promising updates of natural bioactive compounds and small molecules

Cancer has a considerably higher fatality rate than other diseases globally and is one of the most lethal and profoundly disruptive ailments. The increasing incidence of cancer among humans is one of the greatest challenges in the field of healthcare. A significant factor in the initiation and progression of tumorigenesis is the dysregulation of physiological processes governing cell death, which results in the survival of cancerous cells. B-cell lymphoma 2 (Bcl-2) family members play important roles in several cancer-related processes. Drug research and development have identified various promising natural compounds that demonstrate potent anticancer effects by specifically targeting Bcl-2 family proteins and their associated signaling pathways. This comprehensive review highlights the substantial roles of Bcl-2 family proteins in regulating apoptosis, including the intricate signaling pathways governing the activity of these proteins, the impact of reactive oxygen species, and the crucial involvement of proteasome degradation and the stress response. Furthermore, this review discusses advances in the exploration and potential therapeutic applications of natural compounds and small molecules targeting Bcl-2 family proteins and thus provides substantial scientific information and therapeutic strategies for cancer management.

Roles and therapeutic targeting of ceramide metabolism in cancer

BACKGROUND

Ceramides are sphingolipids that act as signaling molecules involved in regulating cellular processes including apoptosis, proliferation, and metabolism. Deregulation of ceramide metabolism contributes to cancer development and progression. Therefore, regulation of ceramide levels in cancer cells is being explored as a new approach for cancer therapy.

SCOPE OF THE REVIEW

This review discusses the multiple roles of ceramides in cancer cells and strategies to modulate ceramide levels for cancer therapy. Ceramides attenuate cell survival signaling and metabolic pathways, while activating apoptotic mechanisms, making them tumor-suppressive. Approaches to increase ceramide levels in cancer cells include using synthetic analogs, inhibiting ceramide degradation, and activating ceramide synthesis. We also highlight combination therapies such as use of ceramide modulators with chemotherapies, immunotherapies, apoptosis inducers, and anti-angiogenics, which offer synergistic antitumor effects. Additionally, we also describe ongoing clinical trials evaluating ceramide nanoliposomes and analogs. Finally, we discuss the challenges of these therapeutic approaches including the complexity of ceramide metabolism, targeted delivery, cancer heterogeneity, resistance mechanisms, and long-term safety.

MAJOR CONCLUSIONS

Ceramide-based therapy is a potentially promising approach for cancer therapy. However, overcoming hurdles in pharmacokinetics, specificity, and resistance is needed to optimize its efficacy and safety. This requires comprehensive preclinical/clinical studies into ceramide signaling, formulations, and combination therapies. Ceramide modulation offers opportunities for developing novel cancer treatments, but a deeper understanding of ceramide biology is vital to advance its clinical applications.

Sublethal engagement of apoptotic pathways in residual cancer

Cytotoxic chemo-, radio-, and targeted therapies frequently elicit apoptotic cancer cell death. Mitochondrial outer membrane permeabilization (MOMP) is a critical, regulated step in this apoptotic pathway. The residual cancer cells that survive treatment serve as the seeds of eventual relapse and are often functionally characterized by their transient tolerance of multiple therapeutic treatments. New studies suggest that, in these cells, a sublethal degree of MOMP, reflective of incomplete apoptotic commitment, is widely observed. Here, we review recent evidence that this sublethal MOMP drives the aggressive features of residual cancer cells while templating a host of unique vulnerabilities, highlighting how failed apoptosis may counterintuitively enable new therapeutic strategies to target residual disease (RD).

Fanning the Flames of Endoplasmic Reticulum (ER) Stress: Can Sphingolipid Metabolism Be Targeted to Enhance ER Stress-Associated Immunogenic Cell Death in Cancer?

The three arms of the unfolded protein response (UPR) surveil the luminal environment of the endoplasmic reticulum (ER) and transmit information through the lipid bilayer to the cytoplasm to alert the cell of stress conditions within the ER lumen. That same lipid bilayer is the site of de novo synthesis of phospholipids and sphingolipids. Thus, it is no surprise that lipids are modulated by and are modulators of ER stress. Given that sphingolipids have both prosurvival and proapoptotic effects, they also exert opposing effects on life/death decisions in the face of prolonged ER stress detected by the UPR. In this review, we will focus on several recent studies that demonstrate how sphingolipids affect each arm of the UPR. We will also discuss the role of sphingolipids in the process of immunogenic cell death downstream of the protein kinase RNA-like endoplasmic reticulum kinase (PERK)/eukaryotic initiating factor 2α (eIF2α) arm of the UPR. Furthermore, we will discuss strategies to target the sphingolipid metabolic pathway that could potentially act synergistically with agents that induce ER stress as novel anticancer treatments. SIGNIFICANCE STATEMENT: This review provides the readers with a brief discussion of the sphingolipid metabolic pathway and the unfolded protein response. The primary focus of the review is the mechanism(s) by which sphingolipids modulate the endoplasmic reticulum (ER) stress response pathways and the critical role of sphingolipids in the process of immunogenic cell death associated with the ER stress response.

Combating Acute Myeloid Leukemia via Sphingosine Kinase 1 Inhibitor-Nanomedicine Combination Therapy with Cytarabine or Venetoclax

MP-A08 is a novel sphingosine kinase 1 (SPHK1) inhibitor with activity against acute myeloid leukemia (AML). A rationally designed liposome-based encapsulation and delivery system has been shown to overcome the physicochemical challenges of MP-A08 and enable its effective delivery for improved efficacy and survival of mice engrafted with human AML in preclinical models. To establish therapies that overcome AML's heterogeneous nature, here we explored the combination of MP-A08-loaded liposomes with both the standard chemotherapy, cytarabine, and the targeted therapy, venetoclax, against human AML cell lines. Cytarabine (over the dose range of 0.1-0.5 µM) in combination with MP-A08 liposomes showed significant synergistic effects (as confirmed by the Chou-Talalay Combination Index) against the chemosensitised human AML cell lines MV4-11 and OCI-AML3. Venetoclax (over the dose range of 0.5-250 nM) in combination with MP-A08 liposomes showed significant synergistic effects against the chemosensitised human AML cell lines, particularly in venetoclax-resistant human AML cells. This strong synergistic effect is due to multiple mechanisms of action, i.e., inhibiting MCL-1 through SPHK1 inhibition, leading to ceramide accumulation, activation of protein kinase R, ATF4 upregulation, and NOXA activation, ultimately resulting in MCL-1 degradation. These combination therapies warrant further consideration and investigation in the search for a more comprehensive treatment strategy for AML.

Associations between genetic variants in sphingolipid metabolism pathway genes and hepatitis B virus-related hepatocellular carcinoma survival

Background

Although the sphingolipid metabolism pathway is known to play a significant role in tumor progression, there have been few studies on how genetic variants in the sphingolipid metabolism pathway genes affect the survival of patients with hepatitis B virus (HBV)-related hepatocellular carcinoma (HCC).

Methods

We utilized available genotyping data to conduct multivariate Cox proportional hazards regression model analysis, examining the associations of 12,188 single nucleotide polymorphisms (SNPs) in 86 sphingolipid metabolism pathway genes on the survival of 866 HBV-HCC patients, and the model was also used in additive interaction analysis. We used bioinformatics functional prediction and expression quantitative trait locus (eQTL) analysis to explore the potential functions of SNPs and to evaluate the association of SNPs with the corresponding mRNA expression, respectively. We also used the online database TIMER2.0 (http://timer.comp-genomics.org/) to analyze the relationship between the corresponding mRNA expression levels and immune cell infiltration.

Results

Our study found that GBA2 rs1570247 G>A was significantly associated with elevated survival of HBV-HCC patients [(hazards ratio (HR)=0.74, 95% confidence interval (CI)=0.64-0.86, P<0.001)]. And on an additive scale, a synergistic effect was observed between the GG genotype of rs1570247 and advanced BCLC stage. Among HBV-HCC patients with advanced BCLC stage, those carrying the GBA2 rs1570247 GG genotype exhibited a significantly elevated risk of mortality (HR=3.32, 95%CI=2.45-4.50). Further functional prediction and eQTL analysis revealed that rs1570247 were located in the 5' untranslated region of the GBA2, the A allele of SNP rs1570247 was associated with higher mRNA expression levels of GBA2 in normal liver tissues (P=0.009). Moreover, we observed a positive correlation between GBA2 mRNA expression and the infiltration level of B lymphocytes cell (R=0.331, P<0.001), while a negative correlation was noted between GBA2 mRNA expression and the infiltration level of macrophage M2 in HCC (R=-0.383, P<0.001).

Conclusion

Our findings suggest that GBA2 rs1570247 G>A in sphingolipid metabolism pathway may be a key factor for survival of HBV-HCC patients by regulating the expression of corresponding genes and affecting the infiltration level of immune cells.

Acid Ceramidase Inhibitor LCL-805 Antagonizes Akt Signaling and Promotes Iron-Dependent Cell Death in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is an aggressive hematologic malignancy requiring urgent treatment advancements. Ceramide is a cell-death-promoting signaling lipid that plays a central role in therapy-induced cell death. We previously determined that acid ceramidase (AC), a ceramide-depleting enzyme, is overexpressed in AML and promotes leukemic survival and drug resistance. The ceramidase inhibitor B-13 and next-generation lysosomal-localizing derivatives termed dimethylglycine (DMG)-B-13 prodrugs have been developed but remain untested in AML. Here, we report the in vitro anti-leukemic efficacy and mechanism of DMG-B-13 prodrug LCL-805 across AML cell lines and primary patient samples. LCL-805 inhibited AC enzymatic activity, increased total ceramides, and reduced sphingosine levels. A median EC50 value of 11.7 μM was achieved for LCL-805 in cell viability assays across 32 human AML cell lines. As a single agent tested across a panel of 71 primary AML patient samples, a median EC50 value of 15.8 μM was achieved. Exogenous ceramide supplementation with C6-ceramide nanoliposomes, which is entering phase I/II clinical trial for relapsed/refractory AML, significantly enhanced LCL-805 killing. Mechanistically, LCL-805 antagonized Akt signaling and led to iron-dependent cell death distinct from canonical ferroptosis. These findings elucidated key factors involved in LCL-805 cytotoxicity and demonstrated the potency of combining AC inhibition with exogenous ceramide.

Acid Ceramidase Inhibitor LCL-805 Antagonizes Akt Signaling and Promotes Iron-Dependent Cell Death in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is an aggressive hematologic malignancy requiring urgent treatment advancements. Ceramide is a cell death-promoting signaling lipid that plays a central role in therapy-induced cell death. Acid ceramidase (AC), a ceramide-depleting enzyme, is overexpressed in AML and promotes leukemic survival and drug resistance. The ceramidase inhibitor B-13 and next-generation lysosomal-localizing derivatives termed dimethylglycine (DMG)-B-13 prodrugs have been developed but remain untested in AML. Here, we report the in vitro anti-leukemic efficacy and mechanism of DMG-B-13 prodrug, LCL-805, across AML cell lines and primary patient samples. LCL-805 inhibited AC enzymatic activity, increased total ceramides, and reduced sphingosine levels. A median EC50 value of 11.7 μM was achieved for LCL-805 in cell viability assays across 32 human AML cell lines. As a single agent tested across a panel of 71 primary AML patient samples, a median EC50 value of 15.8 μM was achieved. Exogenous ceramide supplementation with C6-ceramide nanoliposomes, which is entering phase I/II clinical trial for relapsed/refractory AML, significantly enhanced LCL-805 killing. Mechanistically, LCL-805 antagonized Akt signaling and led to iron-dependent cell death distinct from canonical ferroptosis. These findings elucidated key factors involved in LCL-805 cytotoxicity and demonstrated the potency of combining AC inhibition with exogenous ceramide.

Targeting Acute Myeloid Leukemia Using Sphingosine Kinase 1 Inhibitor-Loaded Liposomes

Acute myeloid leukemia (AML) kills 75% of patients and represents a major clinical challenge with a need to improve on current treatment approaches. Targeting sphingosine kinase 1 with a novel ATP-competitive-inhibitor, MP-A08, induces cell death in AML. However, limitations in MP-A08's "drug-like properties" (solubility, biodistribution, and potency) hinder its pathway to the clinic. This study demonstrates a liposome-based delivery system of MP-A08 that exhibits enhanced MP-A08 potency against AML cells. MP-A08-liposomes increased MP-A08 efficacy against patient AML cells (>140-fold) and significantly prolonged overall survival of mice with human AML disease (P = 0.03). The significant antileukemic property of MP-A08-liposomes could be attributed to its enhanced specificity, bioaccessibility, and delivery to the bone marrow, as demonstrated in the pharmacokinetic and biodistribution studies. Our findings indicate that MP-A08-liposomes have potential as a novel treatment for AML.

Targeting BET Proteins Downregulates miR-33a To Promote Synergy with PIM Inhibitors in CMML

PURPOSE

Preclinical studies in myeloid neoplasms have demonstrated efficacy of bromodomain and extra-terminal protein inhibitors (BETi). However, BETi demonstrates poor single-agent activity in clinical trials. Several studies suggest that combination with other anticancer inhibitors may enhance the efficacy of BETi.

EXPERIMENTAL DESIGN

To nominate BETi combination therapies for myeloid neoplasms, we used a chemical screen with therapies currently in clinical cancer development and validated this screen using a panel of myeloid cell line, heterotopic cell line models, and patient-derived xenograft models of disease. We used standard protein and RNA assays to determine the mechanism responsible for synergy in our disease models.

RESULTS

We identified PIM inhibitors (PIMi) as therapeutically synergistic with BETi in myeloid leukemia models. Mechanistically, we show that PIM kinase is increased after BETi treatment, and that PIM kinase upregulation is sufficient to induce persistence to BETi and sensitize cells to PIMi. Furthermore, we demonstrate that miR-33a downregulation is the underlying mechanism driving PIM1 upregulation. We also show that GM-CSF hypersensitivity, a hallmark of chronic myelomonocytic leukemia (CMML), represents a molecular signature for sensitivity to combination therapy.

CONCLUSIONS

Inhibition of PIM kinases is a potential novel strategy for overcoming BETi persistence in myeloid neoplasms. Our data support further clinical investigation of this combination.

Activation of the PP2A-B56α heterocomplex synergizes with venetoclax therapies in AML through BCL2 and MCL1 modulation

Venetoclax combination therapies are becoming the standard of care in acute myeloid leukemia (AML). However, the therapeutic benefit of these drugs in older/unfit patients is limited to only a few months, highlighting the need for more effective therapies. Protein phosphatase 2A (PP2A) is a tumor suppressor phosphatase with pleiotropic functions that becomes inactivated in ∼70% of AML cases. PP2A promotes cancer cell death by modulating the phosphorylation state in a variety of proteins along the mitochondrial apoptotic pathway. We therefore hypothesized that pharmacological PP2A reactivation could increase BCL2 dependency in AML cells and, thus, potentiate venetoclax-induced cell death. Here, by using 3 structurally distinct PP2A-activating drugs, we show that PP2A reactivation synergistically enhances venetoclax activity in AML cell lines, primary cells, and xenograft models. Through the use of gene editing tools and pharmacological approaches, we demonstrate that the observed therapeutic synergy relies on PP2A complexes containing the B56α regulatory subunit, of which expression dictates response to the combination therapy. Mechanistically, PP2A reactivation enhances venetoclax-driven apoptosis through simultaneous inhibition of antiapoptotic BCL2 and extracellular signal-regulated kinase signaling, with the latter decreasing MCL1 protein stability. Finally, PP2A targeting increases the efficacy of the clinically approved venetoclax and azacitidine combination in vitro, in primary cells, and in an AML patient-derived xenograft model. These preclinical results provide a scientific rationale for testing PP2A-activating drugs with venetoclax combinations in AML.

Targeting the integrated stress response in hematologic malignancies

While numerous targeted therapies have been recently adopted to improve the treatment of hematologic malignancies, acquired or intrinsic resistance poses a significant obstacle to their efficacy. Thus, there is increasing need to identify novel, targetable pathways to further improve therapy for these diseases. The integrated stress response is a signaling pathway activated in cancer cells in response to both dysregulated growth and metabolism, and also following exposure to many therapies that appears one such targetable pathway for improved treatment of these diseases. In this review, we discuss the role of the integrated stress response in the biology of hematologic malignancies, its critical involvement in the mechanism of action of targeted therapies, and as a target for pharmacologic modulation as a novel strategy for the treatment of hematologic malignancies.

Advancements on the Multifaceted Roles of Sphingolipids in Hematological Malignancies

Dysregulation of sphingolipid metabolism plays a complex role in hematological malignancies, beginning with the first historical link between sphingolipids and apoptosis discovered in HL-60 leukemic cells. Numerous manuscripts have reviewed the field including the early discoveries that jumpstarted the studies. Many studies discussed here support a role for sphingolipids, such as ceramide, in combinatorial therapeutic regimens to enhance anti-leukemic effects and reduce resistance to standard therapies. Additionally, inhibitors of specific nodes of the sphingolipid pathway, such as sphingosine kinase inhibitors, significantly reduce leukemic cell survival in various types of leukemias. Acid ceramidase inhibitors have also shown promising results in acute myeloid leukemia. As the field moves rapidly, here we aim to expand the body of literature discussed in previously published reviews by focusing on advances reported in the latter part of the last decade.

Mechanisms of venetoclax resistance and solutions

The BCL-2 inhibitor venetoclax is currently approved for treatment of hematologic diseases and is widely used either as monotherapy or in combination strategies. It has produced promising results in the treatment of refractory or relapsed (R/R) and aged malignant hematologic diseases. However, with clinical use, resistance to venetoclax has emerged. We review the mechanism of reduced dependence on BCL-2 mediated by the upregulation of antiapoptotic proteins other than BCL-2, such as MCL-1 and BCL-XL, which is the primary mechanism of venetoclax resistance, and find that this mechanism is achieved through different pathways in different hematologic diseases. Additionally, this paper also summarizes the current investigations of the mechanisms of venetoclax resistance in terms of altered cellular metabolism, changes in the mitochondrial structure, altered or modified BCL-2 binding domains, and some other aspects; this article also reviews relevant strategies to address these resistance mechanisms.

Ceramide nanoliposomes augment the efficacy of venetoclax and cytarabine in models of acute myeloid leukemia

Despite several new therapeutic options for acute myeloid leukemia (AML), disease relapse remains a significant challenge. We have previously demonstrated that augmenting ceramides can counter various drug-resistance mechanisms, leading to enhanced cell death in cancer cells and extended survival in animal models. Using a nanoscale delivery system for ceramide (ceramide nanoliposomes, CNL), we investigated the effect of CNL within a standard of care venetoclax/cytarabine (Ara-C) regimen. We demonstrate that CNL augmented the efficacy of venetoclax/cytarabine in in vitro, ex vivo, and in vivo models of AML. CNL treatment induced non-apoptotic cytotoxicity, and augmented cell death induced by Ara-C and venetoclax. Mechanistically, CNL reduced both venetoclax (Mcl-1) and cytarabine (Chk1) drug-resistant signaling pathways. Moreover, venetoclax and Ara-C augmented the generation of endogenous pro-death ceramide species, which was intensified with CNL. Taken together, CNL has the potential to be utilized as an adjuvant therapy to improve outcomes, potentially extending survival, in patients with AML.

Construction and validation model of necroptosis-related gene signature associates with immunity for osteosarcoma patients

Osteosarcoma is the most common malignant tumor in children and adolescents and its diagnosis and treatment still need to be improved. Necroptosis has been associated with many malignancies, but its significance in diagnosing and treating osteosarcoma remains unclear. The objective is to establish a predictive model of necroptosis-related genes (NRGs) in osteosarcoma for evaluating the tumor microenvironment and new targets for immunotherapy. In this study, we download the osteosarcoma data from the TARGET and GEO websites and the average muscle tissue data from GTEx. NRGs were screened by Cox regression analysis. We constructed a prediction model through nonnegative matrix factorization (NMF) clustering and the least absolute shrinkage and selection operator (LASSO) algorithm and verified it with a validation cohort. Kaplan–Meier survival time, ROC curve, tumor invasion microenvironment and CIBERSORT were assessed. In addition, we establish nomograms for clinical indicators and verify them by calibration evaluation. The underlying mechanism was explored through the functional enrichment analysis. Eight NRGs were screened for predictive model modeling. NRGs prediction model through NMF clustering and LASSO algorithm was established. The survival, ROC and tumor microenvironment scores showed significant statistical differences among subgroups (P < 0.05). The validation model further verifies it. By nomogram and calibration, we found that metastasis and risk score were independent risk factors for the poor prognosis of osteosarcoma. GO and KEGG analyses demonstrate that the genes of osteosarcoma cluster in inflammatory, apoptotic and necroptosis signaling pathways. The significant role of the correlation between necroptosis and immunity in promoting osteosarcoma may provide a novel insight into detecting molecular mechanisms and targeted therapy.

Activation of the integrated stress response is a vulnerability for multidrug-resistant FBXW7-deficient cells

FBXW7 is one of the most frequently mutated tumor suppressors, deficiency of which has been associated with resistance to some anticancer therapies. Through bioinformatics and genome‐wide CRISPR screens, we here reveal that FBXW7 deficiency leads to multidrug resistance (MDR). Proteomic analyses found an upregulation of mitochondrial factors as a hallmark of FBXW7 deficiency, which has been previously linked to chemotherapy resistance. Despite this increased expression of mitochondrial factors, functional analyses revealed that mitochondria are under stress, and genetic or chemical targeting of mitochondria is preferentially toxic for FBXW7‐deficient cells. Mechanistically, the toxicity of therapies targeting mitochondrial translation such as the antibiotic tigecycline relates to the activation of the integrated stress response (ISR) in a GCN2 kinase‐dependent manner. Furthermore, the discovery of additional drugs that are toxic for FBXW7‐deficient cells showed that all of them unexpectedly activate a GCN2‐dependent ISR regardless of their accepted mechanism of action. Our study reveals that while one of the most frequent mutations in cancer reduces the sensitivity to the vast majority of available therapies, it renders cells vulnerable to ISR‐activating drugs.