Mitochondria inside acute myeloid leukemia cells hydrolyze ATP to resist chemotherapy

Despite early optimism, therapeutics targeting oxidative phosphorylation (OxPhos) have faced clinical setbacks, stemming from their inability to distinguish healthy from cancerous mitochondria. Herein, we describe an actionable bioenergetic mechanism unique to cancerous mitochondria inside acute myeloid leukemia (AML) cells. Unlike healthy cells which couple respiration to the synthesis of ATP, AML mitochondria were discovered to support inner membrane polarization by consuming ATP. Because matrix ATP consumption allows cells to survive bioenergetic stress, we hypothesized that AML cells may resist cell death induced by OxPhos damaging chemotherapy by reversing the ATP synthase reaction. In support of this, targeted inhibition of BCL-2 with venetoclax abolished OxPhos flux without impacting mitochondrial membrane potential. In surviving AML cells, sustained polarization of the mitochondrial inner membrane was dependent on matrix ATP consumption. Mitochondrial ATP consumption was further enhanced in AML cells made refractory to venetoclax, consequential to downregulations in both the proton-pumping respiratory complexes, as well as the endogenous F1-ATPase inhibitor ATP5IF1. In treatment-naive AML, ATP5IF1 knockdown was sufficient to drive venetoclax resistance, while ATP5IF1 overexpression impaired F1-ATPase activity and heightened sensitivity to venetoclax. Collectively, our data identify matrix ATP consumption as a cancer-cell intrinsic bioenergetic vulnerability actionable in the context of mitochondrial damaging chemotherapy.

A fluorogenic substrate for the detection of lipid amidases in intact cells

Lipid amidases of therapeutic relevance include acid ceramidase (AC), N-acylethanolamine-hydrolyzing acid amidase, and fatty acid amide hydrolase (FAAH). Although fluorogenic substrates have been developed for the three enzymes and high-throughput methods for screening have been reported, a platform for the specific detection of these enzyme activities in intact cells is lacking. In this article, we report on the coumarinic 1-deoxydihydroceramide RBM1-151, a 1-deoxy derivative and vinilog of RBM14-C12, as a novel substrate of amidases. This compound is hydrolyzed by AC (appKm = 7.0 μM; appVmax = 99.3 nM/min), N-acylethanolamine-hydrolyzing acid amidase (appKm = 0.73 μM; appVmax = 0.24 nM/min), and FAAH (appKm = 3.6 μM; appVmax = 7.6 nM/min) but not by other ceramidases. We provide proof of concept that the use of RBM1-151 in combination with reported irreversible inhibitors of AC and FAAH allows the determination in parallel of the three amidase activities in single experiments in intact cells.

KLRG1 Cell Depletion As A Novel Therapeutic Strategy In Patients With Mature T-cell lymphoma Subtypes

PURPOSE

Develop a novel therapeutic strategy for patients with subtypes of mature T-cell and NK-cell neoplasms.

EXPERIMENTAL DESIGN

Primary specimens, cell lines, patient-derived xenograft models, commercially available and proprietary anti-KLRG1 antibodies were used for screening, target, and functional validation.

RESULTS

Here we demonstrate that surface KLRG1 is highly expressed on tumor cells in subsets of patients with extranodal NK/T-cell lymphoma (ENKTCL), T-prolymphocytic leukemia (T-PLL) and gamma/delta T-cell lymphoma (G/D TCL). The majority of the CD8+/CD57+ or CD3-/CD56+ leukemic cells derived from patients with T- and NK-large granular lymphocytic leukemia (T-LGLL and NK-LGLL) respectively expressed surface KLRG1. The humanized afucosylated anti-KLRG1 monoclonal antibody (mAb208) optimized for mouse in vivo use depleted KLRG1+ TCL cells by mechanisms of ADCC, ADCP and CDC rather than apoptosis. mAb208 induced ADCC and ADCP of T-LGLL patient-derived CD8+/CD57+ cells ex vivo. mAb208 effected ADCC of subsets of healthy donor-derived KLRG1+ NK, CD4+, CD8+ Tem and TemRA cells while sparing KLRG1- naive and CD8+ Tcm cells. Treatment of cell line and TCL patient-derived xenografts with mAb208 or anti-CD47 mAb alone and in combination with the PI3K-δ/γ inhibitor, duvelisib extended survival. The depletion of macrophages in vivo antagonized mAb208 efficacy.

CONCLUSIONS

Our findings suggest the potential benefit of a broader treatment strategy combining therapeutic antibodies with PI3Ki for the treatment of patients with mature T-cell and NK-cell neoplasms.

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.

Acute myeloid leukemia stratifies as two clinically relevant sphingolipidomic subtypes

Acute myeloid leukemia (AML) is an aggressive disease with complex and heterogeneous biology. Although several genomic classifications have been proposed, there is a growing interest in going beyond genomics to stratify AML. In this study, we profile the sphingolipid family of bioactive molecules in 213 primary AML samples and 30 common human AML cell lines. Using an integrative approach, we identify two distinct sphingolipid subtypes in AML characterized by a reciprocal abundance of hexosylceramide (Hex) and sphingomyelin (SM) species. The two Hex-SM clusters organize diverse samples more robustly than known AML driver mutations and are coupled to latent transcriptional states. Using transcriptomic data, we develop a machine-learning classifier to infer the Hex-SM status of AML cases in TCGA and BeatAML clinical repositories. The analyses show that the sphingolipid subtype with deficient Hex and abundant SM is enriched for leukemic stemness transcriptional programs and comprises an unappreciated high-risk subgroup with poor clinical outcomes. Our sphingolipid-focused examination of AML identifies patients least likely to benefit from standard of care and raises the possibility that sphingolipidomic interventions could switch the subtype of AML patients who otherwise lack targetable alternatives.

Simultaneous Inhibition of Ceramide Hydrolysis and Glycosylation Synergizes to Corrupt Mitochondrial Respiration and Signal Caspase Driven Cell Death in Drug-Resistant Acute Myeloid Leukemia

Acute myelogenous leukemia (AML), the most prevalent acute and aggressive leukemia diagnosed in adults, often recurs as a difficult-to-treat, chemotherapy-resistant disease. Because chemotherapy resistance is a major obstacle to successful treatment, novel therapeutic intervention is needed. Upregulated ceramide clearance via accelerated hydrolysis and glycosylation has been shown to be an element in chemotherapy-resistant AML, a problem considering the crucial role ceramide plays in eliciting apoptosis. Herein we employed agents that block ceramide clearance to determine if such a "reset" would be of therapeutic benefit. SACLAC was utilized to limit ceramide hydrolysis, and D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (D-threo-PDMP) was used to block the glycosylation route. The SACLAC D-threo-PDMP inhibitor combination was synergistically cytotoxic in drug-resistant, P-glycoprotein-expressing (P-gp) AML but not in wt, P-gp-poor cells. Interestingly, P-gp antagonists that can limit ceramide glycosylation via depression of glucosylceramide transit also synergized with SACLAC, suggesting a paradoxical role for P-gp in the implementation of cell death. Mechanistically, cell death was accompanied by a complete drop in ceramide glycosylation, concomitant, striking increases in all molecular species of ceramide, diminished sphingosine 1-phosphate levels, resounding declines in mitochondrial respiratory kinetics, altered Akt, pGSK-3β, and Mcl-1 expression, and caspase activation. Although ceramide was generated in wt cells upon inhibitor exposure, mitochondrial respiration was not corrupted, suggestive of mitochondrial vulnerability in the drug-resistant phenotype, a potential therapeutic avenue. The inhibitor regimen showed efficacy in an in vivo model and in primary AML cells from patients. These results support the implementation of SL enzyme targeting to limit ceramide clearance as a therapeutic strategy in chemotherapy-resistant AML, inclusive of a novel indication for the use of P-gp antagonists.

Tγδ LGLL identifies a subset with more symptomatic disease: analysis of an international cohort of 137 patients

Tγδ large granular lymphocyte leukemia (LGLL) is a rare variant of T-cell LGLL (T-LGLL) that has been less investigated as compared with the more frequent Tαβ LGLL, particularly in terms of frequency of STAT3 and STAT5b mutations. In this study, we characterized the clinical and biological features of 137 patients affected by Tγδ LGLL; data were retrospectively collected from 1997 to 2020 at 8 referral centers. Neutropenia and anemia were the most relevant clinical features, being present in 54.2% and 49.6% of cases, respectively, including severe neutropenia and anemia in ∼20% of cases each. Among the various treatments, cyclosporine A was shown to provide the best response rates. DNA samples of 97 and 94 cases were available for STAT3 and STAT5b mutation analysis, with 38.1% and 4.2% of cases being mutated, respectively. Clinical and biological features of our series of Tγδ cases were also compared with a recently published Tαβ cohort including 129 cases. Though no differences in STAT3 and STAT5b mutational frequency were found, Tγδ cases more frequently presented with neutropenia (P = .0161), anemia (P < .0001), severe anemia (P = .0065), and thrombocytopenia (P = .0187). Moreover, Vδ2- cases displayed higher frequency of symptomatic disease. Overall, Tγδ cases displayed reduced survival with respect to Tαβ cases (P = .0017). Although there was no difference in STAT3 mutation frequency, our results showed that Tγδ LGLL represents a subset of T-LGLL characterized by more frequent symptoms and reduced survival as compared with Tαβ LGLL.

Cancer Prevention from the Viewpoint of UVA Comprehensive Cancer Center

Prevention is a cornerstone of the guiding mission of the University of Virginia Comprehensive Cancer Center, which is "to reduce the burden of cancer for the patients of today, through skilled, integrated, and compassionate care and to eliminate the threat of cancer for the patients of tomorrow, through research and education in an environment that promotes diversity, equity, and inclusion." We find it useful to conceptualize different opportunities for cancer prevention using NCI's Health Behaviors Research Branch's multilevel translational framework. The latter considers three intersecting continuums: cancer control-from prevention through survivorship; translation-from basic sciences to dissemination and implementation; and level of influence or impact-from genetics to policy. An advantage of this heuristic is that "prevention" is inherently defined as an inter-programmatic concept cutting across basic, clinical, and population science research rather than solely as a programmatic domain of Population Sciences. Through the UVA community outreach and engagement, we apply this multilevel framework to mitigate the social determinants of cancer risk and outcomes that drive cancer inequities in our catchment area. Below, we provide examples of our prevention research and translation along the model continuums and focus on equity.

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.

Harnessing the power of sphingolipids: Prospects for acute myeloid leukemia

Acute myeloid leukemia (AML) is an aggressive, heterogenous malignancy characterized by clonal expansion of bone marrow-derived myeloid progenitor cells. While our current understanding of the molecular and genomic landscape of AML has evolved dramatically and opened avenues for molecularly targeted therapeutics to improve upon standard intensive induction chemotherapy, curative treatments are elusive, particularly in older patients. Responses to current AML treatments are transient and incomplete, necessitating the development of novel treatment strategies to improve outcomes. To this end, harnessing the power of bioactive sphingolipids to treat cancer shows great promise. Sphingolipids are involved in many hallmarks of cancer of paramount importance in AML. Leukemic blast survival is influenced by cellular levels of ceramide, a bona fide pro-death molecule, and its conversion to signaling molecules such as sphingosine-1-phosphate and glycosphingolipids. Preclinical studies demonstrate the efficacy of therapeutics that target dysregulated sphingolipid metabolism as well as their combinatorial synergy with clinically-relevant therapeutics. Thus, increased understanding of sphingolipid dysregulation may be exploited to improve AML patient care and outcomes. This review summarizes the current knowledge of dysregulated sphingolipid metabolism in AML, evaluates how pro-survival sphingolipids promote AML pathogenesis, and discusses the therapeutic potential of targeting these dysregulated sphingolipid pathways.

Combined epigenetic and immunotherapy for blastic and classical mantle cell lymphoma

Classical MCL (cMCL) constitutes 6-8% of all B cell NHL. Despite recent advances, MCL is incurable except with allogeneic stem cell transplant. Blastic mantle cell lymphoma (bMCL) is a rarer subtype of cMCL associated with an aggressive clinical course and poor treatment response, frequent relapse and poor outcomes. We treated 13 bMCL patients with combined epigenetic and immunotherapy treatment consisting of vorinostat, cladribine and rituximab (SCR). We report an increased OS greater than 40 months with several patients maintaining durable remissions without relapse for longer than 5 years. This is remarkably better then current treatment regimens which in bMCL range from 14.5-24 months with conventional chemotherapy regimens. We demonstrate that the G/A870 CCND1 polymorphism is predictive of blastic disease, nuclear localization of cyclinD1 and response to SCR therapy. The major resistance mechanisms to SCR therapy are loss of CD20 expression and evasion of treatment by sanctuary in the CNS. These data indicate that administration of epigenetic agents improves efficacy of anti-CD20 immunotherapies. This approach is promising in the treatment of MCL and potentially other previously treatment refractory cancers.

Allogeneic Bone Marrow Transplant as a Cure for Refractory T-Cell Large Granular Lymphocytic Leukemia in an Adolescent

T-cell large granular lymphocytic (T-LGL) leukemia is a rare, typically indolent neoplasm with a median age of onset above 60 years. Pathogenesis involves clonal T-cell expansion, and nearly all reported pediatric cases have been associated with concurrent autoimmune disease. Immunosuppressive therapy often mitigates sequelae, but definitive cure is not routinely achieved. Here we present an otherwise healthy 13-year-old with T-LGL leukemia refractory to all standard treatments. Our patient ultimately underwent allogeneic bone marrow transplant (BMT) and is now stable in remission 3 years post-BMT. BMT may offer a viable definitive cure for refractory T-LGL leukemia in very young patients.

LGL leukemia patients exhibit substantial protective humoral responses following SARS-CoV-2 vaccination

Large granular lymphocyte leukemia is a rare chronic lymphoproliferative disorder of cytotoxic cells. Other hematological malignancies such as CLL and multiple myeloma have been associated with poor vaccination response and markedly increased severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) mortality rates, specifically in patients who have undergone immunosuppressive therapy. Given the immunosuppressive therapies often used to treat the disease, large granular lymphocytic (LGL) patients may be especially vulnerable to SARS-CoV-2 infection. A questionnaire was sent to all patients in the LGL Leukemia Registry at the University of Virginia (UVA) to obtain information on vaccination status, type of vaccine received, side effects of vaccination, patient treatment status before, during, and after vaccination, antibody testing, history of coronavirus disease 2019 (COVID-19) infection, and presence or absence of booster vaccination. Antibody testing of 27 patients who had quantitative SARS-CoV-2 Spike Protein IgG levels determined by University of Virginia medical laboratories via the Abbott Architect SARS-CoV-2 IgG II assay were collected. The assay was scored as reactive at a threshold of ≥50.0 AU/mL or nonreactive with a threshold of <50.0 AU/mL. LGL patients without treatment as well as patients who held treatment prior to their vaccination have a robust humoral response to SARS-CoV-2 vaccines. Patients who did not hold their immunosuppressive treatments have signifigantly diminished vaccine response compared to those who held their immunosuppressive treatment. Our findings support a dual strategy of pausing immunotherapy during the vaccination window and administration of the SARS-CoV-2 booster to all LGL leukemia patients to maximize protective antibodies.

Genomic landscape of TCRαβ and TCRγδ T-large granular lymphocyte leukemia

Large granular lymphocyte (LGL) leukemia comprises a group of rare lymphoproliferative disorders whose molecular landscape is incompletely defined. We leveraged paired whole-exome and transcriptome sequencing in the largest LGL leukemia cohort to date, which included 105 patients (93 T-cell receptor αβ [TCRαβ] T-LGL and 12 TCRγδ T-LGL). Seventy-six mutations were observed in 3 or more patients in the cohort, and out of those, STAT3, KMT2D, PIK3R1, TTN, EYS, and SULF1 mutations were shared between both subtypes. We identified ARHGAP25, ABCC9, PCDHA11, SULF1, SLC6A15, DDX59, DNMT3A, FAS, KDM6A, KMT2D, PIK3R1, STAT3, STAT5B, TET2, and TNFAIP3 as recurrently mutated putative drivers using an unbiased driver analysis approach leveraging our whole-exome cohort. Hotspot mutations in STAT3, PIK3R1, and FAS were detected, whereas truncating mutations in epigenetic modifying enzymes such as KMT2D and TET2 were observed. Moreover, STAT3 mutations co-occurred with mutations in chromatin and epigenetic modifying genes, especially KMT2D and SETD1B (P < .01 and P < .05, respectively). STAT3 was mutated in 50.5% of the patients. Most common Y640F STAT3 mutation was associated with lower absolute neutrophil count values, and N647I mutation was associated with lower hemoglobin values. Somatic activating mutations (Q160P, D170Y, L287F) in the STAT3 coiled-coil domain were characterized. STAT3-mutant patients exhibited increased mutational burden and enrichment of a mutational signature associated with increased spontaneous deamination of 5-methylcytosine. Finally, gene expression analysis revealed enrichment of interferon-γ signaling and decreased phosphatidylinositol 3-kinase-Akt signaling for STAT3-mutant patients. These findings highlight the clinical and molecular heterogeneity of this rare disorder.

Intersection Between Large Granular Lymphocyte Leukemia and Rheumatoid Arthritis

Large granular lymphocyte (LGL) leukemia, a rare hematologic malignancy, has long been associated with rheumatoid arthritis (RA), and the diseases share numerous common features. This review aims to outline the parallels and comparisons between the diseases as well as discuss the potential mechanisms for the relationship between LGL leukemia and RA. RA alone and in conjunction with LGL leukemia exhibits cytotoxic T-cell (CTL) expansions, HLA-DR4 enrichment, RA-associated autoantibodies, female bias, and unknown antigen specificity of associated T-cell expansions. Three possible mechanistic links between the pathogenesis of LGL leukemia and RA have been proposed, including LGL leukemia a) as a result of longstanding RA, b) as a consequence of RA treatment, or c) as a driver of RA. Several lines of evidence point towards LGL as a driver of RA. CTL involvement in RA pathogenesis is evidenced by citrullination and granzyme B cleavage that modifies the repertoire of self-protein antigens in target cells, particularly neutrophils, killed by the CTLs. Further investigations of the relationship between LGL leukemia and RA are warranted to better understand causal pathways and target antigens in order to improve the mechanistic understanding and to devise targeted therapeutic approaches for both disorders.

Identification and targeting of the developmental blockade in extranodal natural killer/T cell lymphoma

Extranodal natural killer/T-cell lymphoma (ENKTL) is an aggressive, rare lymphoma of natural killer (NK) cell origin with poor clinical outcomes. Here we used phenotypic and molecular profiling, including epigenetic analyses, to investigate how ENKTL ontogeny relates to normal NK-cell development. We demonstrate that neoplastic NK cells are stably, but reversibly, arrested at earlier stages of NK-cell maturation. Genes downregulated in the most epigenetic immature tumors were associated with polycomb silencing along with genomic gain and overexpression of EZH2. ENKTL cells exhibited genome-wide DNA hypermethylation. Tumor-specific DNA methylation gains were associated with polycomb-marked regions, involving extensive gene silencing and loss of transcription factor binding. To investigate therapeutic targeting, we treated novel patient-derived xenograft (PDX) models of ENKTL with the DNA hypomethylating agent, 5-azacytidine. Treatment led to reexpression of NK-cell developmental genes, phenotypic NK-cell differentiation, and prolongation of survival. These studies lay the foundation for epigenetic-directed therapy in ENKTL.

SIGNIFICANCE

Through epigenetic and transcriptomic analyses of ENKTL, a rare, aggressive malignancy, along with normal NK-cell developmental intermediates, we identified that extreme DNA hypermethylation targets genes required for NK-cell development. Disrupting this epigenetic blockade in novel PDX models led to ENKTL differentiation and improved survival. This article is highlighted in the In This Issue feature, p. 85.

Alterations in sphingolipid composition and mitochondrial bioenergetics represent synergistic therapeutic vulnerabilities linked to multidrug resistance in leukemia

Modifications in sphingolipid (SL) metabolism and mitochondrial bioenergetics are key factors implicated in cancer cell response to chemotherapy, including chemotherapy resistance. In the present work, we utilized acute myeloid leukemia (AML) cell lines, selected to be refractory to various chemotherapeutics, to explore the interplay between SL metabolism and mitochondrial biology supportive of multidrug resistance (MDR). In agreement with previous findings in cytarabine or daunorubicin resistant AML cells, relative to chemosensitive wildtype controls, HL-60 cells refractory to vincristine (HL60/VCR) presented with alterations in SL enzyme expression and lipidome composition. Such changes were typified by upregulated expression of various ceramide detoxifying enzymes, as well as corresponding shifts in ceramide, glucosylceramide, and sphingomyelin (SM) molecular species. With respect to mitochondria, despite consistent increases in both basal respiration and maximal respiratory capacity, direct interrogation of the oxidative phosphorylation (OXPHOS) system revealed intrinsic deficiencies in HL60/VCR, as well as across multiple MDR model systems. Based on the apparent requirement for augmented SL and mitochondrial flux to support the MDR phenotype, we explored a combinatorial therapeutic paradigm designed to target each pathway. Remarkably, despite minimal cytotoxicity in peripheral blood mononuclear cells (PBMC), co-targeting SL metabolism, and respiratory complex I (CI) induced synergistic cytotoxicity consistently across multiple MDR leukemia models. Together, these data underscore the intimate connection between cellular sphingolipids and mitochondrial metabolism and suggest that pharmacological intervention across both pathways may represent a novel treatment strategy against MDR.

miR-181a is a novel player in the STAT3-mediated survival network of TCRαβ+ CD8+ T large granular lymphocyte leukemia

T-LGL cells arise as a consequence of chronic antigenic stimulation and inflammation and thrive because of constitutive activation of the STAT3 and ERK pathway. Notably, in 40% of patients, constitutive STAT3 activation is due to STAT3 activating mutations, whereas in 60% this is unknown. As miRNAs are amongst the most potent regulators in health and disease, we hypothesized that aberrant miRNA expression could contribute to dysregulation of these pathways. miRNA sequencing in T-LGL leukemia cases and aged-matched healthy control TEMRA cells revealed overexpression of miR-181a. Furthermore, geneset enrichment analysis (GSEA) of downregulated targets of miR-181a implicated involvement in regulating STAT3 and ERK1/2 pathways. Flow cytometric analyses showed increased SOCS3+ and DUSP6+ T-LGL cells upon miR-181a inhibition. In addition, miR-181a-transfected human CD8+ T cells showed increased basal STAT3 and ERK1/2 phosphorylation. By using TL1, a human T-LGL cell line, we could show that miR-181a is an actor in T-LGL leukemia, driving STAT3 activation by SOCS3 inhibition and ERK1/2 phosphorylation by DUSP6 inhibition and verified this mechanism in an independent cell line. In addition, miR-181a inhibition resulted in a higher sensitivity to FAS-mediated apoptosis. Collectively, our data show that miR-181a could be the missing link to explain why STAT3-unmutated patients show hyperactive STAT3.

DJ4 Targets the Rho-Associated Protein Kinase Pathway and Attenuates Disease Progression in Preclinical Murine Models of Acute Myeloid Leukemia

The poor prognosis of acute myeloid leukemia (AML) and the highly heterogenous nature of the disease motivates targeted gene therapeutic investigations. Rho-associated protein kinases (ROCKs) are crucial for various actin cytoskeletal changes, which have established malignant consequences in various cancers, yet are still not being successfully utilized clinically towards cancer treatment. This work establishes the therapeutic activity of ROCK inhibitor (5Z)-2-5-(1H-pyrrolo[2,3-b]pyridine-3-ylmethylene)-1,3-thiazol-4(5H)-one (DJ4) in both in vitro and in vivo preclinical models of AML to highlight the potential of this class of inhibitors. Herein, DJ4 induced cytotoxic and proapoptotic effects in a dose-dependent manner in human AML cell lines (IC50: 0.05-1.68 μM) and primary patient cells (IC50: 0.264-13.43 μM); however, normal hematopoietic cells were largely spared. ROCK inhibition by DJ4 disrupts the phosphorylation of downstream targets, myosin light chain (MLC2) and myosin-binding subunit of MLC phosphatase (MYPT), yielding a potent yet selective treatment response at micromolar concentrations, from 0.02 to 1 μM. Murine models injected with luciferase-expressing leukemia cell lines subcutaneously or intravenously and treated with DJ4 exhibited an increase in overall survival and reduction in disease progression relative to the vehicle-treated control mice. Overall, DJ4 is a promising candidate to utilize in future investigations to advance the current AML therapy.

Frequent somatic TET2 mutations in chronic NK-LGL leukemia with distinct patterns of cytopenias

Chronic natural killer large granular lymphocyte (NK-LGL) leukemia, also referred to as chronic lymphoproliferative disorder of NK cells, is a rare disorder defined by prolonged expansion of clonal NK cells. Similar prevalence of STAT3 mutations in chronic T-LGL and NK-LGL leukemia is suggestive of common pathogenesis. We undertook whole-genome sequencing to identify mutations unique to NK-LGL leukemia. The results were analyzed to develop a resequencing panel that was applied to 58 patients. Phosphatidylinositol 3-kinase pathway gene mutations (PIK3CD/PIK3AP1) and TNFAIP3 mutations were seen in 5% and 10% of patients, respectively. TET2 was exceptional in that mutations were present in 16 (28%) of 58 patient samples, with evidence that TET2 mutations can be dominant and exclusive to the NK compartment. Reduced-representation bisulfite sequencing revealed that methylation patterns were significantly altered in TET2 mutant samples. The promoter of TET2 and that of PTPRD, a negative regulator of STAT3, were found to be methylated in additional cohort samples, largely confined to the TET2 mutant group. Mutations in STAT3 were observed in 19 (33%) of 58 patient samples, 7 of which had concurrent TET2 mutations. Thrombocytopenia and resistance to immunosuppressive agents were uniquely observed in those patients with only TET2 mutation (Games-Howell post hoc test, P = .0074; Fisher's exact test, P = .00466). Patients with STAT3 mutation, inclusive of those with TET2 comutation, had lower hematocrit, hemoglobin, and absolute neutrophil count compared with STAT3 wild-type patients (Welch's t test, P ≤ .015). We present the discovery of TET2 mutations in chronic NK-LGL leukemia and evidence that it identifies a unique molecular subtype.

Large granular lymphocyte leukemia serum and corresponding hematological parameters reveal unique cytokine and sphingolipid biomarkers and associations with STAT3 mutations

Large granular lymphocyte (LGL) leukemia is a rare hematological disorder with expansion of the T-cell or natural killer (NK) cell lineage. Signal transducer and activator of transcription 3 (STAT3) exhibits somatic activating mutations in 30%-40% of LGL leukemia cases. Transcriptional targets of STAT3 include inflammatory cytokines, thus previous studies have measured cytokine levels of LGL leukemia patients compared to normal donors. Sphingolipid metabolism is a growing area of cancer research, with efforts focused on drug discovery. To date, no studies have examined serum sphingolipids in LGL leukemia patients, and only one study compared a subset of cytokines between the T-LGL and NK-LGL subtypes. Therefore, here, we included both LGL leukemia subtypes with the goals of (a) measuring serum sphingolipids for the first time, (b) measuring cytokines to find distinctions between the subtypes, and (c) establishing relationships with STAT3 mutations and clinical data. The serum analyses identified cytokines (EGF, IP-10, G-CSF) and sphingolipids (SMC22, SMC24, SMC20, LysoSM) significantly different in the LGL leukemia group compared to normal donors. In a mixed STAT3 mutation group, D661Y samples exhibited the highest mean corpuscular volume (MCV) values. We explored this further by expanding the cohort to include larger groups of single STAT3 mutations. Male D661Y STAT3 samples had lower Hgb and higher MCV compared to wild type (WT) or Y640F counterparts. This is the first report examining large groups of individual STAT3 mutations. Overall, our results revealed novel serum biomarkers and evidence that D661Y mutation may show different clinical manifestation compared to WT or Y640F STAT3.

The PI3K/AKT Pathway Inhibitor ISC-4 Induces Apoptosis and Inhibits Growth of Leukemia in Preclinical Models of Acute Myeloid Leukemia

Acute myeloid leukemia is a heterogeneous disease with a 5-year survival rate of 28.3%, and current treatment options constrained by dose-limiting toxicities. One of the key signaling pathways known to be frequently activated and dysregulated in AML is PI3K/AKT. Its dysregulation is associated with aggressive cell growth and drug resistance. We investigated the activity of Phenybutyl isoselenocyanate (ISC-4) in primary cells obtained from newly diagnosed AML patients, diverse AML cell lines, and normal cord blood cells. ISC-4 significantly inhibited survival and clonogenicity of primary human AML cells without affecting normal cells. We demonstrated that ISC-4-mediated p-Akt inhibition caused apoptosis in primary AML (CD34⁺) stem cells and enhanced efficacy of cytarabine. ISC-4 impeded leukemia progression with improved overall survival in a syngeneic C1498 mouse model with no obvious toxic effects on normal myelopoiesis. In U937 xenograft model, bone marrow cells exhibited significant reduction in human CD45⁺ cells in ISC-4 (~87%) or AraC (~89%) monotherapy groups compared to control. Notably, combination treatment suppressed the leukemic infiltration significantly higher than the single-drug treatments (~94%). Together, the present findings suggest that ISC-4 might be a promising agent for AML treatment.

Advances in the Diagnosis and Treatment of Large Granular Lymphocytic Leukemia

PURPOSE OF REVIEW

The past decade in LGL leukemia research has seen increased pairing of clinical data with molecular markers, shedding new insights on LGL leukemia pathogenesis and heterogeneity. This review summarizes the current standard of care of LGL leukemia, updates from clinical trials, and our congruent improved understanding of LGL pathogenesis.

RECENT FINDINGS

Various clinical reports have identified associations between stem, bone marrow, and solid organ transplants and incidence of LGL leukemia. There is also a potential for underdiagnosis of LGL leukemia within the rheumatoid arthritis patient population, emphasizing our need for continued study. Preliminary results from the BNZ-1 clinical trial, which targets IL-15 along with IL-2 and IL-9 signaling pathways, show some evidence of clinical response. With advances in our understanding of LGL pathogenesis from both the bench and the clinic, exciting avenues for investigations lie ahead for LGL leukemia.

Sphingosine kinase-2 is overexpressed in large granular lymphocyte leukaemia and promotes survival through Mcl-1

Sphingolipid metabolism is increasingly recognised as a therapeutic target in cancer due to its regulation of cell proliferation and apoptosis. The sphingolipid rheostat is proposed to control cell fate through maintaining balance between pro-apoptotic and pro-survival sphingolipids. This balance is regulated by metabolising enzymes involved in sphingolipid production. One such enzyme, sphingosine kinase-2 (SPHK2), produces pro-survival sphingosine 1-phosphate (S1P) by phosphorylation of pro-apoptotic sphingosine. Elevated SPHK2 has been found in multiple cancer types and contributes to cell survival, chemotherapeutic resistance and apoptosis resistance. We have previously shown elevation of S1P in large granular lymphocyte (LGL) leukaemia serum and cells isolated from patients. Here, we examined SPHK2 expression in LGL leukaemia and found SPHK2 mRNA and protein upregulation in a majority of LGL leukaemia patient samples. Knockdown of SPHK2 with siRNA in LGL leukaemia cell lines decreased proliferation. Additionally, the use of ABC294640 or K145, both SPHK2-specific inhibitors, decreased viability of LGL leukaemia cell lines. ABC294640 selectively induced apoptosis in LGL cell lines and freshly isolated LGL leukaemia patient cells compared to normal controls. Mechanistically, SPHK2 inhibition downregulated pro-survival myeloid cell leukaemia-1 (Mcl-1) protein through proteasomal degradation. Targeting of SPHK2 therefore provides a novel therapeutic approach for the treatment of LGL leukaemia.

Whole Genome Sequencing of Spontaneously Occurring Rat Natural Killer Large Granular Lymphocyte Leukemia Identifies JAK1 Somatic Activating Mutation

Large granular lymphocyte (LGL) leukemia arises spontaneously in elderly Fischer (F344) rats. This rodent model has been shown to emulate many aspects of the natural killer (NK) variant of human LGL leukemia. Previous transplantation of leukemic material into young F344 rats resulted in several strains of rat NK (RNK) primary leukemic cells. One strain, RNK-16, was adapted into the RNK-16 cell line and established as an aggressive NK-LGL leukemia model. Whole genome sequencing of the RNK-16 cell line identified 255,838 locations where the RNK16 had an alternate allele that was different from F334, including a mutation in Jak1. Functional studies showed Jak1 Y1034C to be a somatic activating mutation that mediated increased STAT signaling, as assessed by phosphoprotein levels. Sanger sequencing of Jak1 in RNK-1, -3, -7, and -16 found only RNK-16 to harbor the Y1034C Jak1 mutation. In vivo studies revealed that rats engrafted with RNK-16 primary material developed leukemia more rapidly than those engrafted with RNK-1, -3, and -7. Additionally, ex vivo RNK-16 spleen cells from leukemic rats exhibited increased STAT1, STAT3, and STAT5 phosphorylation compared to other RNK strains. Therefore, we report and characterize a novel gain-of-function Jak1 mutation in a spontaneous LGL leukemia model that results in increased downstream STAT signaling.

Ceramide Analogue SACLAC Modulates Sphingolipid Levels and MCL-1 Splicing to Induce Apoptosis in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) is a disease characterized by uncontrolled proliferation of immature myeloid cells in the blood and bone marrow. The 5-year survival rate is approximately 25%, and recent therapeutic developments have yielded little survival benefit. Therefore, there is an urgent need to identify novel therapeutic targets. We previously demonstrated that acid ceramidase (ASAH1, referred to as AC) is upregulated in AML and high AC activity correlates with poor patient survival. Here, we characterized a novel AC inhibitor, SACLAC, that significantly reduced the viability of AML cells with an EC₅₀ of approximately 3 μmol/L across 30 human AML cell lines. Treatment of AML cell lines with SACLAC effectively blocked AC activity and induced a decrease in sphingosine 1-phosphate and a 2.5-fold increase in total ceramide levels. Mechanistically, we showed that SACLAC treatment led to reduced levels of splicing factor SF3B1 and alternative MCL-1 mRNA splicing in multiple human AML cell lines. This increased proapoptotic MCL-1S levels and contributed to SACLAC-induced apoptosis in AML cells. The apoptotic effects of SACLAC were attenuated by SF3B1 or MCL-1 overexpression and by selective knockdown of MCL-1S. Furthermore, AC knockdown and exogenous C16-ceramide supplementation induced similar changes in SF3B1 level and MCL-1S/L ratio. Finally, we demonstrated that SACLAC treatment leads to a 37% to 75% reduction in leukemic burden in two human AML xenograft mouse models. IMPLICATIONS: These data further emphasize AC as a therapeutic target in AML and define SACLAC as a potent inhibitor to be further optimized for future clinical development.

Retroviral sero-reactivity in LGL leukaemia patients and family members

T-cell large granular lymphocyte (T-LGL) leukaemia is characterized by a clonal proliferation of cytotoxic T cells and is frequently associated with rheumatoid arthritis. Sera from some LGL leukaemia patients react to a portion of the human T-cell leukaemia virus (HTLV-1/2) transmembrane envelope protein, BA21, although HTLV-1/2 infection is rare in LGL leukaemia patients. Here we show that family members, including spouses, of an LGL leukaemia patient had elevated LGL counts, BA21 reactivity and, additionally, recognition of HIV-1 gp41. Thus, both LGL leukaemia patients and clinically normal contacts sharing the same environment have evidence of exposure to a retrovirus.

Chemotherapy selection pressure alters sphingolipid composition and mitochondrial bioenergetics in resistant HL-60 cells

The combination of daunorubicin (dnr) and cytarabine (Ara-C) is a cornerstone of treatment for acute myelogenous leukemia (AML); resistance to these drugs is a major cause of treatment failure. Ceramide, a sphingolipid (SL), plays a critical role in cancer cell apoptosis in response to chemotherapy. Here, we investigated the effects of chemotherapy selection pressure with Ara-C and dnr on SL composition and enzyme activity in the AML cell line HL-60. Resistant cells, those selected for growth in Ara-C- and dnr-containing medium (HL-60/Ara-C and HL-60/dnr, respectively), demonstrated upregulated expression and activity of glucosylceramide synthase, acid ceramidase (AC), and sphingosine kinase 1 (SPHK1); were more resistant to ceramide than parental cells; and displayed sensitivity to inhibitors of SL metabolism. Lipidomic analysis revealed a general ceramide deficit and a profound upswing in levels of sphingosine 1-phosphate (S1P) and ceramide 1-phosphate (C1P) in HL-60/dnr cells versus parental and HL-60/Ara-C cells. Both chemotherapy-selected cells also exhibited comprehensive upregulations in mitochondrial biogenesis consistent with heightened reliance on oxidative phosphorylation, a property that was partially reversed by exposure to AC and SPHK1 inhibitors and that supports a role for the phosphorylation system in resistance. In summary, dnr and Ara-C selection pressure induces acute reductions in ceramide levels and large increases in S1P and C1P, concomitant with cell resilience bolstered by enhanced mitochondrial remodeling. Thus, strategic control of ceramide metabolism and further research to define mitochondrial perturbations that accompany the drug-resistant phenotype offer new opportunities for developing therapies that regulate cancer growth.

Genomics of LGL leukemia and select other rare leukemia/lymphomas

Genomic analysis of cancer offers the hope of identifying new treatments or aiding in the selection of existing treatments. Rare leukemias pose additional challenges in this regard as samples may be hard to acquire and when found the underlying pathway may not be attractive to drug development since so few individuals are affected. In this case, it can be useful to identify common mutational overlap among subsets of rare leukemias to increase the number of individuals that may benefit from a targeted therapy. This chapter examines the current mutational landscape of large granular lymphocyte (LGL) leukemia with a focus on STAT3 mutations, the most common mutation in LGL leukemia to date. We examined the linkage between these mutations and autoimmune symptoms and disorders, in cases of obvious and suspected LGL leukemia. We then summarized and compared mutations in a set of other rare leukemias that also have JAK/STAT signaling pathway activation brought about by genomic changes. These include T-cell acute lymphoblastic leukemia (T-ALL), T-cell prolymphocytic leukemia (T-PLL), cutaneous T-cell lymphoma (CTCL), select peripheral T-cell lymphoma (PTCL), and adult T-cell leukemia/lymphoma (ATLL). Though STAT3 activation is common in these leukemias, the way in which it is achieved, such as the activating cytokine pathway and/or the co-mutational background, is quite diverse.

Retrovirus insertion site analysis of LGL leukemia patient genomes

Background

Large granular lymphocyte (LGL) leukemia is an uncommon cancer characterized by sustained clonal proliferation of LGL cells. Antibodies reactive to retroviruses have been documented in the serum of patients with LGL leukemia. Culture or molecular approaches have to date not been successful in identifying a retrovirus.

Methods

Because a retrovirus must integrate into the genome of an infected cell, we focused our efforts on detecting a novel retrovirus integration site in the clonally expanded LGL cells. We present a new computational tool that uses long-insert mate pair sequence data to search the genome of LGL leukemia cells for retrovirus integration sites. We also utilize recently published methods to interrogate the status of polymorphic human endogenous retrovirus type K (HERV-K) provirus in patient genomes.

Results

Our data show that there are no new retrovirus insertions in LGL genomes of LGL leukemia patients. However, our insertion call tool did detect four HERV-K provirus integration sites that are polymorphic in the human population but absent from the human reference genome, hg19. To determine if the prevalence of these or other polymorphic proviral HERV-Ks differed between LGL leukemia patients and the general population, we used a recently developed tool that reports sites in the human genome occupied by a known proviral HERV-K. We report that there are significant differences in the number of polymorphic HERV-Ks in the genomes of LGL leukemia patients of European origin compared to individuals with European ancestry in the 1000 genomes (KGP) data.

Conclusions

Our study confirms that the clonal expansion of LGL cells in LGL leukemia is not driven by the integration of a new infectious or endogenous retrovirus, although we do not rule out that these cells are responding to retroviral antigens produced in other cell types. However, our computational analyses revealed that the genomes of LGL leukemia patients carry a higher burden of polymorphic HERV-K proviruses compare to individuals from KGP of European ancestry. Our research emphasizes the merits of comprehensive genomic assessment of HERV-K in cancer samples and suggests that further analyses to determine contributions of HERV-K to LGL leukemia are warranted.

Electronic supplementary material

The online version of this article (10.1186/s12920-019-0549-9) contains supplementary material, which is available to authorized users.

The novel Isatin analog KS99 targets stemness markers in acute myeloid leukemia

Leukemic stem cells are multipotent, self-renewing, highly proliferative cells that can withstand drug treatments. Although currently available treatments potentially destroy blast cells, they fail to eradicate leukemic progenitor cells completely. Aldehyde dehydrogenase and STAT3 are frequently up-regulated in pre-leukemic stem cells as well as in acute myeloid leukemia (AML) expressing the CD34⁺CD38⁻ phenotype. The Isatin analog, KS99 has shown anticancer activity against multiple myeloma which may, in part, be mediated by inhibition of Bruton’s tyrosine kinase activation. Here we demonstrate that KS99 selectively targets leukemic stem cells with high aldehyde dehydrogenase activity and inhibits phosphorylation of STAT3. KS99 targeted cells co-expressing CD34, CD38, CD123, TIM-3, or CD96 immunophenotypes in AML, alone or in combination with the standard therapeutic agent cytarabine. AML with myelodysplastic-related changes was more sensitive than de novo AML with or without NPM1 mutation. KS99 treatment reduced the clonogenicity of primary human AML cells as compared to normal cord blood mononuclear cells. Downregulation of phosphorylated Bruton’s tyrosine kinase, STAT3, and aldehyde dehydrogenase was observed, suggesting interaction with KS99 as predicted through docking. KS99 with or without cytarabine showed in vivo preclinical efficacy in human and mouse AML animal models and prolonged survival. KS99 was well tolerated with overall negligible adverse effects. In conclusion, KS99 inhibits aldehyde dehydrogenase and STAT3 activities and causes cell death of leukemic stem cells, but not normal hematopoietic stem and progenitor cells.

IL-2 and IL-15 blockade by BNZ-1, an inhibitor of selective γ-chain cytokines, decreases leukemic T-cell viability

Interleukin-15 (IL-15) and IL-2 drive T-cell malignancies including T-cell large granular lymphocyte leukemia (T-LGLL) and HTLV-1 driven adult T-cell leukemia (ATL). Both cytokines share common γ-chain receptors and downstream signaling pathways. T-LGLL is characterized by clonal expansion of cytotoxic T cells and is associated with abnormal JAK/STAT signaling. ATL is an aggressive CD4+ T-cell neoplasm associated with HTLV-1. T-LGLL and ATL share dependence on IL-2 and IL-15 for survival and both diseases lack effective therapies. BNZ-1 is a pegylated peptide designed to specifically bind the γc receptor to selectively block IL-2, IL-15, and IL-9 signaling. We hypothesized that treatment with BNZ-1 would reduce cytokine-mediated proliferation and viability. Our results demonstrated that in vitro treatment of a T-LGLL cell line and ex vivo treatment of T-LGLL patient cells with BNZ-1 inhibited cytokine-mediated viability. Furthermore, BNZ-1 blocked downstream signaling and increased apoptosis. These results were mirrored in an ATL cell line and in ex vivo ATL patient cells. Lastly, BNZ-1 drastically reduced leukemic burden in an IL-15-driven human ATL mouse xenograft model. Thus, BNZ-1 shows great promise as a novel therapy for T-LGLL, ATL, and other IL-2 or IL-15 driven hematopoietic malignancies.

Acid ceramidase promotes drug resistance in acute myeloid leukemia through NF-κB-dependent P-glycoprotein upregulation

Acute myeloid leukemia (AML) is the most common acute leukemia in adults. More than half of older AML patients fail to respond to cytotoxic chemotherapy, and most responders relapse with drug-resistant disease. Failure to achieve complete remission can be partly attributed to the drug resistance advantage of AML blasts that frequently express P-glycoprotein (P-gp), an ATP-binding cassette transporter. Our previous work showed that elevated acid ceramidase (AC) levels in AML contribute to blast survival. Here, we investigated P-gp expression levels in AML relative to AC. Using parental HL-60 cells and drug-resistant derivatives as our model, we found that P-gp expression and efflux activity were highly upregulated in resistant derivatives. AC overexpression in HL-60 conferred resistance to the AML chemotherapeutic drugs, cytarabine, mitoxantrone, and daunorubicin, and was linked to P-gp upregulation. Furthermore, targeting AC through pharmacologic or genetic approaches decreased P-gp levels and increased sensitivity to chemotherapeutic drugs. Mechanistically, AC overexpression increased NF-κB activation whereas NF-kB inhibitors reduced P-gp levels, indicating that the NF-kappaB pathway contributes to AC-mediated modulation of P-gp expression. Hence, our data support an important role for AC in drug resistance as well as survival and suggest that sphingolipid targeting approaches may also impact drug resistance in AML.

Vitamin D pathway activation selectively deactivates signal transducer and activator of transcription (STAT) proteins and inflammatory cytokine production in natural killer leukemic large granular lymphocytes

Calcitriol, the active form of vitamin D, has been well documented to act directly on immune cells and malignant cells. Activated T cells are one of the best characterized targets of calcitriol, with effects including decreasing inflammatory cytokine output and promoting anti-inflammatory cytokine production. However, the effects of calcitriol on natural killer (NK) cells are less clear. Reports suggest that only immature NK cell populations are affected by calcitriol treatment resulting in impaired cytotoxic function and cytokine production, while mature NK cells may have little or no response. NK cell large granular lymphocyte leukemia (NK-LGLL) is a rare leukemia with CD3-CD16+CD56+NK cell clonal expansion. The current standard treatments are immunosuppressant therapies, which are not curative. The Janus kinase (JAK) - signal transducer and activator of transcription (STAT) pathway is hyperactivated in LGLL and is one pathway of interest in new drug target investigations. We previously demonstrated the ability of calcitriol to decrease STAT1 tyrosine 701 (p-STAT1) and STAT3 tyrosine 705 (p-STAT3) phosphorylation as well as inflammatory cytokine output of T cell large granular lymphocyte leukemia cells, but did not determine the effects of calcitriol on NK-LGLL. Therefore, in the present study, we investigated whether NKL cells, a model of NK-LGLL, and NK-LGLL patient peripheral blood mononuclear cells (PBMCs) are susceptible to treatment with calcitriol or seocalcitol (EB1089), a potent analog of calcitriol. NKL cells are dependent on interleukin (IL)-2 for survival and we show here for the first time that treatment with IL-2 induced tyrosine phosphorylation of STATs 1 through 6. Both calcitriol and EB1089 caused significant upregulation of the vitamin D receptor (VDR). IL-2 induction of p-STAT1 and p-STAT3 phosphorylation was significantly decreased after calcitriol or EB1089 treatment. Additionally, IL-10, interferon (IFN)-γ, and FMS-like tyrosine kinase 3 ligand (Flt-3L) extracellular output was significantly decreased at 100 nM EB1089 and intracellular IL-10 was decreased with either calcitriol or EB1089 treatment. We treated NK-LGLL patient PBMCs with calcitriol or EB1089 and found decreased p-STAT1 and p-STAT3 while VDR increased, which matched the NKL cell line data. We then measured 75 serum cytokines in NK-LGLL patients (n = 8) vs. age- and sex-matched normal healthy donors (n = 8), which is the first serum cytokine study for this LGLL subtype. We identified 15 cytokines, including IL-10 and Flt-3L, which were significantly different between normal donors and NK-LGLL patients. Overall, our results suggest that activating the vitamin D pathway could be a mechanism to decrease STAT1 and 3 activation and inflammatory cytokine output in NK-LGLL patients.

Abstract 5832: Sphingolipid metabolism determines the efficacy of nanoliposomal ceramide in acute myeloid leukemia

Therapeutic advances for the treatment of acute myeloid leukemia (AML) have been limited in part due to the heterogeneity and complexity of the disease and a poor understanding of its underlying biology. The leukemia stem cell (LSC) arguably resists current therapy resulting in relapses for most initially treatment sensitive patients. AML with myelodysplastic syndrome related changes (AML-MRC) highlights this challenge, representing a very poor outlook subset. The present study sought to understand the underlying sphingolipid biology in and AML, and to evaluate the efficacy of nanoliposomal ceramide (Lip-C6). Sphingolipids play essential roles in cell survival and proliferation, as well as stress and death. Lip-C6, which delivers a short-chain analog of the pro-apoptotic sphingolipid ceramide, has been in development as an anticancer therapeutic. The efficacy of Lip-C6 therapy was evaluated in both in vitro and in vivo models using primary AML cells and AML cell lines. Evaluation and characterization of the effect of treatment with Lip-C6 was done through lipidomic, short term assays such as apoptosis, autophagy and colony formation assays. Efficacy of Lip-C6 and vinblastine was tested in patient derived xenograft models and mouse - human cell line xenograft MV-411. NOD SCID gamma (NSG) mice were injected with luciferase/YFP labeled cells and monitored by bioluminescence imaging (BLI) for the leukemia progression and efficacy. Sphingolipid metabolism was observed to be elevated in patient samples with De Novo AML but not those with AML-MRC. Apoptosis induced by Lip-C6 in CD34+ve/CD38-ve “LSCs” was robust in AML-MRC, but limited in De Novo AMLs. Similarly, AML colonies forming cells were more sensitive to Lip-C6 in AML- MRC than in De Novo cases. It was hypothesized that elevated sphingolipid metabolism and the upregulation of pro-survival pathways such as autophagy contributed to Lip-C6 resistance in De Novo AML. Vinblastine, when combined with Lip-C6, focused sphingolipid metabolism towards pro-apoptotic metabolites and blocked autophagy. In-vivo combination of Lip-C6 and vinblastine uniquely yielded long term control of leukemia progression without systemic toxicity, translating in to prolonged overall leukemia free survival compared to single agents. Altogether, this study shows fundamental biological differences in sphingolipid metabolism between De Novo AML and AML-MRC. The combination of Vinblastine and Lip-C6 targets the LSC and yields apparent cure of lethal human xenograft AML.

Citation Format: Charyguly Annageldiyev, Arati Sharma, Brian M. Barth, Todd E. Fox, Tye Deering, Viola Devine, Nicole R. Keasey, Stephan T. Stern, Megan M. Young, Hong-Gang Wan Wang, Jason Liao, Junjia Zhu, Aaron D. Viny, Ross L. Levine, Thomas P. Loughran, Mark Kester, David F. Claxton. Sphingolipid metabolism determines the efficacy of nanoliposomal ceramide in acute myeloid leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5832.

Aggressive natural killer-cell leukemia mutational landscape and drug profiling highlight JAK-STAT signaling as therapeutic target

Aggressive natural killer-cell (NK-cell) leukemia (ANKL) is an extremely aggressive malignancy with dismal prognosis and lack of targeted therapies. Here, we elucidate the molecular pathogenesis of ANKL using a combination of genomic and drug sensitivity profiling. We study 14 ANKL patients using whole-exome sequencing (WES) and identify mutations in STAT3 (21%) and RAS-MAPK pathway genes (21%) as well as in DDX3X (29%) and epigenetic modifiers (50%). Additional alterations include JAK-STAT copy gains and tyrosine phosphatase mutations, which we show recurrent also in extranodal NK/T-cell lymphoma, nasal type (NKTCL) through integration of public genomic data. Drug sensitivity profiling further demonstrates the role of the JAK-STAT pathway in the pathogenesis of NK-cell malignancies, identifying NK cells to be highly sensitive to JAK and BCL2 inhibition compared to other hematopoietic cell lineages. Our results provide insight into ANKL genetics and a framework for application of targeted therapies in NK-cell malignancies.

Aggressive natural killer-cell leukemia (ANKL) has few targeted therapies. Here ANKL patients are reported to harbor STAT3, RAS-MAPK pathway, DDX3X and epigenetic modifier mutations; and drug sensitivity profiling uncovers the importance of the JAK-STAT pathway, revealing potential ANKL therapeutic targets.

Calcitriol-mediated reduction in IFN-γ output in T cell large granular lymphocytic leukemia requires vitamin D receptor upregulation

Constitutively activated STAT1 and elevated IFN-γ are both characteristic of T cell large granular lymphocytic leukemia (T-LGLL), a rare incurable leukemia with clonal expansion of cytotoxic T cells due to defective apoptosis. Interferon gamma (IFN-γ) is an inflammatory cytokine that correlates with worse progression and symptomology in multiple autoimmune diseases and cancers. In canonical IFN-γ-STAT1 signaling, IFN-γ activates STAT1, a transcription factor, via phosphorylation of tyrosine residue 701 (p-STAT1). p-STAT1 then promotes transcription of IFN-γ, creating a positive feedback loop. We previously found that calcitriol treatment of the TL-1 cell line, a model of T-LGLL, significantly decreased IFN-γ secretion and p-STAT1 while increasing the vitamin D receptor (VDR) protein. Here we further explore these observations. Using TL-1 cells, IFN-γ decreased starting at 4h following calcitriol treatment, with a reduction in the intracellular and secreted protein levels as well as the mRNA content. A similar reduction in IFN-γ transcript levels was observed in primary T-LGLL patient peripheral blood mononuclear cells (PBMCs). p-STAT1 inhibition followed a similar temporal pattern and VDR upregulation inversely correlated with IFN-γ levels. Using EB1089 and 25(OH)D₃, which have high or low affinity for VDR, respectively, we found that the decrease in IFN-γ correlated with the ability of EB1089, but not 25(OH)D₃, to upregulate VDR. However, both compounds inhibited p-STAT1; thus the reduction of p-STAT1 is not solely responsible for IFN-γ inhibition. Conversely, cells treated with VDR siRNA exhibited decreased basal IFN-γ production upon VDR knockdown in a dose-dependent manner. Calcitriol treatment upregulated VDR and decreased IFN-γ regardless of initial VDR knockdown efficiency, strengthening the connection between VDR upregulation and IFN-γ reduction. Our findings suggest multiple opportunities to further explore the clinical relevance of the vitamin D pathway and the potential role for vitamin D supplementation in T-LGLL.

Dysregulation of the IFN-γ-STAT1 signaling pathway in a cell line model of large granular lymphocyte leukemia

T cell large granular lymphocyte leukemia (T-LGLL) is a rare incurable disease that is characterized by defective apoptosis of cytotoxic CD8+ T cells. Chronic activation of the Janus Kinase-Signal Transducer and Activator of Transcription (JAK-STAT) pathway is a hallmark of T-LGLL. One manifestation is the constitutive phosphorylation of tyrosine 701 of STAT1 (p-STAT1). T-LGLL patients also exhibit elevated serum levels of the STAT1 activator, interferon-γ (IFN-γ), thus contributing to an inflammatory environment. In normal cells, IFN-γ production is tightly controlled through induction of IFN-γ negative regulators. However, in T-LGLL, IFN-γ signaling lacks this negative feedback mechanism as evidenced by excessive IFN-γ production and decreased levels of suppressors of cytokine signaling 1 (SOCS1), a negative regulator of IFN-γ. Here we characterize the IFN-γ-STAT1 pathway in TL-1 cells, a cell line model of T-LGLL. TL-1 cells exhibited lower IFN-γ receptor protein and mRNA expression compared to an IFN-γ responsive cell line. Furthermore, IFN-γ treatment did not induce JAK2 or STAT1 activation or transcription of IFN-γ-inducible gene targets. However, IFN-β induced p-STAT1 and subsequent STAT1 gene transcription, demonstrating a specific IFN-γ signaling defect in TL-1 cells. We utilized siRNA targeting of STAT1, STAT3, and STAT5b to probe their role in IL-2-mediated IFN-γ regulation. These studies identified STAT5b as a positive regulator of IFN-γ production. We also characterized the relationship between STAT1, STAT3, and STAT5b proteins. Surprisingly, p-STAT1 was positively correlated with STAT3 levels while STAT5b suppressed the activation of both STAT1 and STAT3. Taken together, these results suggest that the dysregulation of the IFN-γ-STAT1 signaling pathway in TL-1 cells likely results from low levels of the IFN-γ receptor. The resulting inability to induce negative feedback regulators explains the observed elevated IL-2 driven IFN-γ production. Future work will elucidate the best way to target this pathway, with the ultimate goal to find a better therapeutic for T-LGLL.

Acid ceramidase is upregulated in AML and represents a novel therapeutic target

There is an urgent unmet need for new therapeutics in acute myeloid leukemia (AML) as standard therapy has not changed in the past three decades and outcome remains poor for most patients. Sphingolipid dysregulation through decreased ceramide levels and elevated sphingosine 1-phosphate (S1P) promotes cancer cell growth and survival. Acid ceramidase (AC) catalyzes ceramide breakdown to sphingosine, the precursor for S1P. We report for the first time that AC is required for AML blast survival. Transcriptome analysis and enzymatic assay show that primary AML cells have high levels of AC expression and activity. Treatment of patient samples and cell lines with AC inhibitor LCL204 reduced viability and induced apoptosis. AC overexpression increased the expression of anti-apoptotic Mcl-1, significantly increased S1P and decreased ceramide. Conversely, LCL204 induced ceramide accumulation and decreased Mcl-1 through post-translational mechanisms. LCL204 treatment significantly increased overall survival of C57BL/6 mice engrafted with leukemic C1498 cells and significantly decreased leukemic burden in NSG mice engrafted with primary human AML cells. Collectively, these studies demonstrate that AC plays a critical role in AML survival through regulation of both sphingolipid levels and Mcl-1. We propose that AC warrants further exploration as a novel therapeutic target in AML.

Abstract 48: Acid ceramidase inhibition: A targeted therapy for acute myeloid leukemia

Acute myeloid leukemia (AML) is a disease characterized by uncontrolled proliferation of immature myeloid cells in the blood and bone marrow. Patient 5-year survival rate is only 26%, and there have been no significant treatment advances for decades. Therefore, there is an urgent need to identify novel therapeutic targets. We have previously shown that acid ceramidase (AC) is upregulated in AML and high AC activity correlates with poor patient survival. We continue to validate AC as a potential therapeutic target in AML through inhibitor screening and characterization. We utilize viability assays, enzyme activity assays, Western blotting, qPCR, lipidomics, and flow cytometry to examine the effects of inhibitors on AML cell lines, patient samples, and normal controls. We have found that a newly developed selective AC inhibitor, SACLAC, significantly reduces viability of AML cells with an EC50 of approximately 3 μM, with limited effect on normal cells at an EC50 of approximately 13 μM. Treatment of AML cell lines with SACLAC effectively blocks AC activity, induces a drastic decrease of sphingosine 1-phosphate, and a 2.5-fold increase in total ceramide levels. Ongoing studies continue to explore the mechanistic basis for the loss of viability. These data support the investigation of AC as a therapeutic target in AML and define SACLAC as a potent and selective inhibitor that presents promise for preclinical studies and future clinical development.

Citation Format: Jennifer M. Pearson, Su-Fern Tan, Arati Sharma, Todd E. Fox, Jose Luis Abad, Gemma Fabrias, David F. Claxton, David J. Feith, Mark Kester, Thomas P. Loughran, Jr.. Acid ceramidase inhibition: A targeted therapy for acute myeloid leukemia [abstract]. In: Proceedings of the Second AACR Conference on Hematologic Malignancies: Translating Discoveries to Novel Therapies; May 6-9, 2017; Boston, MA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(24_Suppl):Abstract nr 48.

Chronic neutropenia in LGL leukemia and rheumatoid arthritis

This section reviews the diagnostic criteria and pathogenesis of large granular lymphocyte (LGL) leukemia. There is a particular focus on the overlap of LGL leukemia and rheumatoid arthritis (Felty's syndrome). Current understanding of the mechanisms of neutropenia in these disorders is discussed. Finally, treatment indications and therapeutic recommendations are outlined.

Somatic STAT3 mutations in Felty syndrome: an implication for a common pathogenesis with large granular lymphocyte leukemia

Felty syndrome is a rare disease defined by neutropenia, splenomegaly, and rheumatoid arthritis. Sometimes the differential diagnosis between Felty syndrome and large granular lymphocyte leukemia is problematic. Recently, somatic STAT3 and STAT5B mutations were discovered in 30–40% of patients with large granular lymphocyte leukemia. Herein, we aimed to study whether these mutations can also be detected in Felty syndrome, which would imply the existence of a common pathogenic mechanism between these two disease entities. We collected samples and clinical information from 14 Felty syndrome patients who were monitored at the rheumatology outpatient clinic for Felty syndrome. Somatic STAT3 mutations were discovered in 43% (6/14) of Felty syndrome patients with deep amplicon sequencing targeting all STAT3 exons. Mutations were located in the SH2 domain of STAT3, which is a known mutational hotspot. No STAT5B mutations were found. In blood smears, overrepresentation of large granular lymphocytes was observed, and in the majority of cases the CD8⁺ T-cell receptor repertoire was skewed when analyzed by flow cytometry. In bone marrow biopsies, an increased amount of phospho-STAT3 positive cells was discovered. Plasma cytokine profiling showed that ten of the 92 assayed cytokines were elevated both in Felty syndrome and large granular lymphocyte leukemia, and three of these cytokines were also increased in patients with uncomplicated rheumatoid arthritis. In conclusion, somatic STAT3 mutations and STAT3 activation are as frequent in Felty syndrome as they are in large granular lymphocyte leukemia. Considering that the symptoms and treatment modalities are also similar, a unified reclassification of these two syndromes is warranted.

SKI-178: A Multitargeted Inhibitor of Sphingosine Kinase and Microtubule Dynamics Demonstrating Therapeutic Efficacy in Acute Myeloid Leukemia Models

AIM

To further characterize the selectivity, mechanism-of-action and therapeutic efficacy of the novel small molecule inhibitor, SKI-178.

METHODS

Using the state-of-the-art Cellular Thermal Shift Assay (CETSA) technique to detect "direct target engagement" of proteins intact cells, in vitro and in vivo assays, pharmacological assays and multiple mouse models of acute myeloid leukemia (AML).

RESULTS

Herein, we demonstrate that SKI-178 directly target engages both Sphingosine Kinase 1 and 2. We also present evidence that, in addition to its actions as a Sphingosine Kinase Inhibitor, SKI-178 functions as a microtubule network disrupting agent both in vitro and in intact cells. Interestingly, we separately demonstrate that simultaneous SphK inhibition and microtubule disruption synergistically induces apoptosis in AML cell lines. Furthermore, we demonstrate that SKI-178 is well tolerated in normal healthy mice. Most importantly, we demonstrate that SKI-178 has therapeutic efficacy in several mouse models of AML.

CONCLUSION

SKI-178 is a multi-targeted agent that functions both as an inhibitor of the SphKs as well as a disruptor of the microtubule network. SKI-178 induced apoptosis arises from a synergistic interaction of these two activities. SKI-178 is safe and effective in mouse models of AML, supporting its further development as a multi-targeted anti-cancer therapeutic agent.