Suramin: Effectiveness of analogues reveals structural features that are important for the potent trypanocidal activity of the drug

Suramin was the first effective drug for the treatment of human African sleeping sickness. Structural analogues of the trypanocide have previously been shown to be potent inhibitors of several enzymes. Therefore, four suramin analogues lacking the methyl group on the intermediate rings and with different regiochemistry of the naphthalenetrisulphonic acid groups and the phenyl rings were tested to establish whether they exhibited improved antiproliferative activity against bloodstream forms of Trypanosomes brucei compared to the parent compound. The four analogues exhibited low trypanocidal activity and weak inhibition of the antitrypanosomal activity of suramin in competition experiments. This indicates that the strong trypanocidal activity of suramin is most likely due to the presence of methyl groups on its intermediate rings and to the specific regiochemistry of naphthalenetrisulphonic acid groups. These two structural features are also likely to be important for the inhibition mechanism of suramin because DNA distribution and nucleus/kinetoplast configuration analyses suggest that the analogues inhibit mitosis while suramin inhibits cytokinesis.

BCL-2 inhibition in haematological malignancies: Clinical application and complications

B-cell lymphoma-2 (BCL-2) family proteins are fundamental regulators of the intrinsic apoptotic pathway which modulate cellular fate. In many haematological malignancies, overexpression of anti-apoptotic factors (BCL-2, BCL-XL and MCL-1) circumvent apoptosis. To address this cancer hallmark, a concerted effort has been made to induce apoptosis by inhibiting BCL-2 family proteins. A series of highly selective BCL-2 homology 3 (BH3) domain mimetics are in clinical use and in ongoing clinical trials for acute myeloid leukaemia (AML), chronic myeloid leukaemia (CML), chronic lymphocytic leukaemia (CLL), and multiple myeloma (MM). These inhibitors serve as promising candidates, both as single agents or in combination therapy to improve patient outcomes. In other diseases such as follicular lymphoma, efficacy has been notably limited. There are also clinical problems with BCL-2 family inhibition, including drug resistance, disease relapse, tumour lysis syndrome, and clinically relevant cytopenias. Here, we provide a balanced view on both the clinical benefits of BCL-2 inhibition as well as the associated challenges.

Perlecan (HSPG2) promotes structural, contractile, and metabolic development of human cardiomyocytes

Perlecan (HSPG2), a heparan sulfate proteoglycan similar to agrin, is key for extracellular matrix (ECM) maturation and stabilization. Although crucial for cardiac development, its role remains elusive. We show that perlecan expression increases as cardiomyocytes mature in vivo and during human pluripotent stem cell differentiation to cardiomyocytes (hPSC-CMs). Perlecan-haploinsuffient hPSCs (HSPG2+/-) differentiate efficiently, but late-stage CMs have structural, contractile, metabolic, and ECM gene dysregulation. In keeping with this, late-stage HSPG2+/- hPSC-CMs have immature features, including reduced ⍺-actinin expression and increased glycolytic metabolism and proliferation. Moreover, perlecan-haploinsuffient engineered heart tissues have reduced tissue thickness and force generation. Conversely, hPSC-CMs grown on a perlecan-peptide substrate are enlarged and display increased nucleation, typical of hypertrophic growth. Together, perlecan appears to play the opposite role of agrin, promoting cellular maturation rather than hyperplasia and proliferation. Perlecan signaling is likely mediated via its binding to the dystroglycan complex. Targeting perlecan-dependent signaling may help reverse the phenotypic switch common to heart failure.

Panhematopoietic RNA barcoding enables kinetic measurements of nucleate and anucleate lineages and the activation of myeloid clones following acute platelet depletion

BACKGROUND

Platelets and erythrocytes constitute over 95% of all hematopoietic stem cell output. However, the clonal dynamics of HSC contribution to these lineages remains largely unexplored.

RESULTS

We use lentiviral genetic labeling of mouse hematopoietic stem cells to quantify output from all lineages, nucleate, and anucleate, simultaneously linking these with stem and progenitor cell transcriptomic phenotypes using single-cell RNA-sequencing. We observe dynamic shifts of clonal behaviors through time in same-animal peripheral blood and demonstrate that acute platelet depletion shifts the output of multipotent hematopoietic stem cells to the exclusive production of platelets. Additionally, we observe the emergence of new myeloid-biased clones, which support short- and long-term production of blood cells.

CONCLUSIONS

Our approach enables kinetic studies of multi-lineage output in the peripheral blood and transcriptional heterogeneity of individual hematopoietic stem cells. Our results give a unique insight into hematopoietic stem cell reactivation upon platelet depletion and of clonal dynamics in both steady state and under stress.

Plasma cell-derived mtDAMPs activate the macrophage STING pathway, promoting myeloma progression

Mitochondrial damage-associated molecular patterns (mtDAMPs) include proteins, lipids, metabolites, and DNA and have various context-specific immunoregulatory functions. Cell-free mitochondrial DNA (mtDNA) is recognized via pattern recognition receptors and is a potent activator of the innate immune system. Cell-free mtDNA is elevated in the circulation of trauma patients and patients with cancer; however, the functional consequences of elevated mtDNA are largely undefined. Multiple myeloma (MM) relies upon cellular interactions within the bone marrow (BM) microenvironment for survival and progression. Here, using in vivo models, we describe the role of MM cell-derived mtDAMPs in the protumoral BM microenvironment and the mechanism and functional consequence of mtDAMPs in myeloma disease progression. Initially, we identified elevated levels of mtDNA in the peripheral blood serum of patients with MM compared with those of healthy controls. Using the MM1S cells engrafted into nonobese diabetic severe combined immunodeficient gamma mice, we established that elevated mtDNA was derived from MM cells. We further show that BM macrophages sense and respond to mtDAMPs through the stimulator of interferon genes (STING) pathway, and inhibition of this pathway reduces MM tumor burden in the KaLwRij-5TGM1 mouse model. Moreover, we found that MM-derived mtDAMPs induced upregulation of chemokine signatures in BM macrophages, and inhibition of this signature resulted in egress of MM cells from the BM. Here, we demonstrate that malignant plasma cells release mtDNA, a form of mtDAMPs, into the myeloma BM microenvironment, which in turn activates macrophages via STING signaling. We establish the functional role of these mtDAMP-activated macrophages in promoting disease progression and retaining MM cells in the protumoral BM microenvironment.

Single-cell gene and isoform expression analysis reveals signatures of ageing in haematopoietic stem and progenitor cells

Single-cell approaches have revealed that the haematopoietic hierarchy is a continuum of differentiation, from stem cell to committed progenitor, marked by changes in gene expression. However, many of these approaches neglect isoform-level information and thus do not capture the extent of alternative splicing within the system. Here, we present an integrated short- and long-read single-cell RNA-seq analysis of haematopoietic stem and progenitor cells. We demonstrate that over half of genes detected in standard short-read single-cell analyses are expressed as multiple, often functionally distinct, isoforms, including many transcription factors and key cytokine receptors. We observe global and HSC-specific changes in gene expression with ageing but limited impact of ageing on isoform usage. Integrating single-cell and cell-type-specific isoform landscape in haematopoiesis thus provides a new reference for comprehensive molecular profiling of heterogeneous tissues, as well as novel insights into transcriptional complexity, cell-type-specific splicing events and consequences of ageing.

HSC-derived fatty acid oxidation in steady-state and stressed hematopoiesis

Metabolism impacts all cellular functions and plays a fundamental role in physiology. Metabolic regulation of hematopoiesis is dynamically regulated under steady-state and stress conditions. It is clear that hematopoietic stem cells (HSCs) impose different energy demands and flexibility during maintenance compared with stressed conditions. However, the cellular and molecular mechanisms underlying metabolic regulation in HSCs remain poorly understood. In this review, we focus on defining the role of fatty acid oxidation (FAO) in HSCs. We first review the existing literature describing FAO in HSCs under steady-state hematopoiesis. Next, we describe the models used to examine HSCs under stress conditions, and, finally, we describe how infection causes a shift toward FAO in HSCs and the impact of using this pathway on emergency hematopoiesis.

In Vivo Imaging of Bone Marrow Long-Chain Fatty Acid Uptake

In vivo imaging enables the detection and visualization of many different processes occurring within the body. Fatty acid uptake is a fundamental cellular process which is essential for the use of free fatty acids (FFAs) as a fuel source for metabolism. Detection and visualization of in vivo FFA uptake in the bone marrow has been relatively unknown. Here, we describe the process of non-invasive bioluminescent imaging of in vivo FFA uptake within the bone marrow.

PGC-1α induced mitochondrial biogenesis in stromal cells underpins mitochondrial transfer to melanoma

INTRODUCTION

Progress in the knowledge of metabolic interactions between cancer and its microenvironment is ongoing and may lead to novel therapeutic approaches. Until recently, melanoma was considered a glycolytic tumour due to mutations in mitochondrial-DNA, however, these malignant cells can regain OXPHOS capacity via the transfer of mitochondrial-DNA, a process that supports their proliferation in-vitro and in-vivo. Here we study how melanoma cells acquire mitochondria and how this process is facilitated from the tumour microenvironment.

METHODS

Primary melanoma cells, and MSCs derived from patients were obtained. Genes' expression and DNA quantification was analysed using Real-time PCR. MSC migration, melanoma proliferation and tumour volume, in a xenograft subcutaneous mouse model, were monitored through bioluminescent live animal imaging.

RESULTS

Human melanoma cells attract bone marrow-derived stromal cells (MSCs) to the primary tumour site where they stimulate mitochondrial biogenesis in the MSCs through upregulation of PGC1a. Mitochondria are transferred to the melanoma cells via direct contact with the MSCs. Moreover, inhibition of MSC-derived PGC1a was able to prevent mitochondrial transfer and improve NSG melanoma mouse tumour burden.

CONCLUSION

MSC mitochondrial biogenesis stimulated by melanoma cells is prerequisite for mitochondrial transfer and subsequent tumour growth, where targeting this pathway may provide an effective novel therapeutic approach in melanoma.

Acute Myeloid Leukaemia Drives Metabolic Changes in the Bone Marrow Niche

Acute myeloid leukaemia (AML) is a highly proliferative cancer characterised by infiltration of immature haematopoietic cells in the bone marrow (BM). AML predominantly affects older people and outcomes, particularly in this difficult to treat population remain poor, in part due to inadequate response to therapy, and treatment toxicity. Normal haematopoiesis is supported by numerous support cells within the BM microenvironment or niche, including adipocytes, stromal cells and endothelial cells. In steady state haematopoiesis, haematopoietic stem cells (HSCs) primarily acquire ATP through glycolysis. However, during stress-responses HSCs rapidly transition to oxidative phosphorylation, enabled by mitochondrial plasticity. Historically it was thought that cancer cells preferentially used glycolysis for ATP production, however recently it has become evident that many cancers, including AML primarily use the TCA cycle and oxidative phosphorylation for rapid proliferation. AML cells hijack the stress-response pathways of their non-malignant counterparts, utilising mitochondrial changes to drive expansion. In addition, amino acids are also utilised by leukaemic stem cells to aid their metabolic output. Together, these processes allow AML cells to maximise their ATP production, using multiple metabolites and fuelling rapid cell turnover which is a hallmark of the disease. This review of AML derived changes in the BM niche, which enable enhanced metabolism, will consider the important pathways and discuss future challenges with a view to understanding how AML cells are able to hijack metabolic pathways and how we may elucidate new targets for potential therapies.

LC3-associated phagocytosis in bone marrow macrophages suppresses acute myeloid leukemia progression through STING activation

The bone marrow (BM) microenvironment regulates acute myeloid leukemia (AML) initiation, proliferation, and chemotherapy resistance. Following cancer cell death, a growing body of evidence suggests an important role for remaining apoptotic debris in regulating the immunologic response to and growth of solid tumors. Here, we investigated the role of macrophage LC3–associated phagocytosis (LAP) within the BM microenvironment of AML. Depletion of BM macrophages (BMMs) increased AML growth in vivo. We show that LAP is the predominate method of BMM phagocytosis of dead and dying cells in the AML microenvironment. Targeted inhibition of LAP led to the accumulation of apoptotic cells (ACs) and apoptotic bodies (ABs), resulting in accelerated leukemia growth. Mechanistically, LAP of AML-derived ABs by BMMs resulted in stimulator of IFN genes (STING) pathway activation. We found that AML-derived mitochondrial damage–associated molecular patterns were processed by BMMs via LAP. Moreover, depletion of mitochondrial DNA (mtDNA) in AML-derived ABs showed that it was this mtDNA that was responsible for the induction of STING signaling in BMMs. Phenotypically, we found that STING activation suppressed AML growth through a mechanism related to increased phagocytosis. In summary, we report that macrophage LAP of apoptotic debris in the AML BM microenvironment suppressed tumor growth.

Metabolic Regulation of Macrophages by SIRT1 Determines Activation During Cholestatic Liver Disease in Mice

BACKGROUND & AIMS

Inflammation is the hallmark of chronic liver disease. Metabolism is a key determinant to regulate the activation of immune cells. Here, we define the role of sirtuin 1 (SIRT1), a main metabolic regulator, in controlling the activation of macrophages during cholestatic liver disease and in response to endotoxin.

METHODS

We have used mice overexpressing SIRT1, which we treated with intraperitoneal lipopolysaccharides or induced cholestasis by bile duct ligation. Bone marrow-derived macrophages were used for mechanistic in vitro studies. Finally, PEPC-Boy mice were used for adoptive transfer experiments to elucidate the impact of SIRT1-overexpressing macrophages in contributing to cholestatic liver disease.

RESULTS

We found that SIRT1 overexpression promotes increased liver inflammation and liver injury after lipopolysaccharide/GalN and bile duct ligation; this was associated with an increased activation of the inflammasome in macrophages. Mechanistically, SIRT1 overexpression associated with the activation of the mammalian target of rapamycin (mTOR) pathway that led to increased activation of macrophages, which showed metabolic rewiring with increased glycolysis and broken tricarboxylic acid cycle in response to endotoxin in vitro. Activation of the SIRT1/mTOR axis in macrophages associated with the activation of the inflammasome and the attenuation of autophagy. Ultimately, in an in vivo model of cholestatic disease, the transplantation of SIRT1-overexpressing myeloid cells contributed to liver injury and fibrosis.

CONCLUSIONS

Our study provides novel mechanistic insights into the regulation of macrophages during cholestatic disease and the response to endotoxin, in which the SIRT1/mTOR crosstalk regulates macrophage activation controlling the inflammasome, autophagy and metabolic rewiring.

Free fatty-acid transport via CD36 drives β-oxidation-mediated hematopoietic stem cell response to infection

Acute infection is known to induce rapid expansion of hematopoietic stem cells (HSCs), but the mechanisms supporting this expansion remain incomplete. Using mouse models, we show that inducible CD36 is required for free fatty acid uptake by HSCs during acute infection, allowing the metabolic transition from glycolysis towards β-oxidation. Mechanistically, high CD36 levels promote FFA uptake, which enables CPT1A to transport fatty acyl chains from the cytosol into the mitochondria. Without CD36-mediated FFA uptake, the HSCs are unable to enter the cell cycle, subsequently enhancing mortality in response to bacterial infection. These findings enhance our understanding of HSC metabolism in the bone marrow microenvironment, which supports the expansion of HSCs during pathogenic challenge.

Abstract 2799: Multiple myeloma derived mitochondrial DAMPs induce a pro-inflammatory signature in the bone marrow microenvironment to promote pro-tumoral expansion

Multiple myeloma (MM) is an incurable malignancy of antibody (Ig) secreting differentiated B cells (plasma cells) characterized by the accumulation and localization of tumor cells in the bone marrow microenvironment (BMM). Mitochondrial DNA (mtDNA) is a damage associated molecular pattern (DAMP), as the mitochondrial genome contains islands of unmethylated CpG nucleotide motifs that have been shown to activate and promote memory B cell proliferation and antibody secretion. Recent studies have indicated that mtDNA is elevated in the circulation of trauma and cancer patients. Here we investigate the functional purpose of elevated mtDNA within the BM microenvironment of MM.We hypothesize that multiple myeloma cells secrete mitochondrial DAMPs into the bone marrow microenvironment promoting a state of chronic inflammation that drives the progression and expansion of multiple myeloma. NSG immunocompromised mice engrafted with human MM1S myeloma cell line showed elevated levels of MM derived mtDNA in the serum, detected by real-time PCR. Next we engrafted C57BL/6 mice with murine 5TGM1 myeloma cell line to establish a syngeneic mouse model. Flow cytometry analysis of the haematopoietic stem and progenitor cell (HSPC) populations showed that 5TGM1 induced an inflammatory expansion of the stem cell niche To determine the role of mtDNA in HSPC expansion we treated C57BL/6 mice with multiple doses of CpG oligodeoxynucleotides to mimic mtDNA export by MM. Results showed similar expansion of haematopoietic stem and progenitor cell populations. To understand the effects of mtDAMPs on the inflammatory cells of the BMM, we show that bone marrow derived macrophages treated with mtDNA and CpG had increased expression of pro-inflammatory cytokines including IL-6. In vivo, isolated F4/80+ bone marrow macrophages from 5TGM1 and CpG treated mice also showed increased expression of pro-inflammatory cytokines. Finally, to understand the role of mtDAMPs in regulating HSPC expansion we used blocking antibodies to TLR9 (toll-like receptor 9 for mtDNA) and FPR1 (receptor for formylated mitochondrial proteins) in 5TGM1 engrafted animals. Blocking these receptors resulted in reduced myeloma tumor burden compared to control animals. Here we establish that MM releases mtDNA into the microenvironment and highlight the involvement of mtDAMPs in creating a pro-inflammatory BMM that aids in MM disease progression. This data suggests the potential for the targeting of TLR9 or FPR1 signaling pathways as a novel therapeutic approach for MM.

Citation Format: Aisha Jibril, Prakrit Kumar, Charlotte Hellmich, Jamie A. Moore, Jayna J. Mistry, Victoria Willimott, Kristian M. Bowles, Stuart A. Rushworth. Multiple myeloma derived mitochondrial DAMPs induce a pro-inflammatory signature in the bone marrow microenvironment to promote pro-tumoral expansion [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2799.

Abstract 2752: LC3-associated phagocytosis in bone marrow macrophages suppresses AML progression through TIM-4 mediated STING activation

Acute myeloid leukemia (AML) is a tumor dependent on its interactions within the bone marrow (BM) microenvironment. LC3-associated phagocytosis (LAP) maintains tissue homeostasis by regulating immune responses, including in tumor immunity. Here we investigate the function of LAP in the AML BM microenvironment.

We used two syngeneic leukemia models (HOXA9/Meis1 and MN1)to investigate the role of LAP on AML proliferation. AML cells were injected into LAP deficient (LAP-/-; ATG16E230-/-) and wild-type (WT) mice. LAP-/- mice had increased AML engraftment in the BM compared to WT mice, as well as reduced animal survival. Flow cytometry (Annexin+) of the BM microenvironment showed an increase in apoptosis in the BM compartment of mice engrafted with AML. This was further increased in LAP-/- mice with AML.

The number of BM macrophages (MØ) (CD45+, GR1-, F4/80+ CD115INT) did not differ between the WT and LAP-/- mice. Next, we quantified MØ numbers in the BM of WT and LAP-/- mice with AML. We found increased numbers of tumor associated CD206+ BM MØ in LAP-/- mice with AML compared to WT animals with AML. Gene expression analysis showed up-regulation of type I interferons (IFNs) relating to the STING pathway in the WT engrafted mice. Inhibition of the STING pathway reversed the LAP dependent AML suppression of inflammatory cytokines, suggesting LAP processing of apoptotic cells is important for STING activation.

AML has high mtDNA content compared to non-malignant cells, and as mtDNA can activate the STING pathway via cGAS we studied the effects of AML cells without mtDNA (AML ρ0) on STING pathway activation. Induction of apoptosis in AML ρ0 cells followed by co-culture with BM derived MØ (BMDM) for 24 hours did not activate the STING pathway in the MØ. In contrast, MØ co-culture with mitochondria containing apoptotic AML cells did activate the MØ STING pathway.

STING pathway activation via type I IFNs induces recruitment of cytotoxic T cells, but no increase in CD8+ T cell numbers or activation (Granzyme-B and IFN-γ) was observed in the BM between LAP-/- and WT animals engrafted with AML. Type I IFNs produced by MØ have been shown to act in an autocrine manner, we therefore investigated MØ phagocytic capacity in AML. Ex-vivo analysis showed enhanced phagocytosis and LAP processing of Zymosan fluorescent beads and LC3 association in MØ from AML engrafted mice compared to controls. Engulfment of apoptotic cells by MØ requires recognition of phosphatidylserine by surface TIM-4 which mediates LAP. We found TIM-4 inhibition increased AML proliferation in vivo. Finally, ex vivo analysis of TIM-4 inhibited MØ confirmed reduced LAP.

We report that BM MØ process apoptotic AML cells via LAP through TIM-4. Furthermore, AML apoptotic bodies containing mtDNA initiate MØ STING activation and inhibit AML proliferation.

Citation Format: Jamie Aaron Moore, Jayna J. Mistry, Charlotte Hellmich, Aisha Jibril, Tom Wileman, Angela Collins, Kristian M. Bowles, Stuart A. Rushworth. LC3-associated phagocytosis in bone marrow macrophages suppresses AML progression through TIM-4 mediated STING activation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2752.

Abstract 1048: Targeting BCL-2 and CD38 in models of acute myeloid leukemia reduces tumour burden

The prognosis for patients with acute myeloid leukemia (AML) remains poor with high mortality rates. It is often not possible to achieve complete remission with current therapy and relapse following treatment is common. New and more targeted treatment approaches are therefore needed to improve outcomes for patients. AML progression and treatment resistance has been associated with overexpression of BCL2. Venetoclax, a BH3 mimetic targeting BCL2, has been shown to effectively target AML cells and induce cell death. It has been approved for the treatment of AML but as with other AML treatments not all patients respond, and others develop treatment resistance. Research has therefore focussed on exploring combination therapies for Venetoclax. Our group has previously shown that mitochondrial transfer from mesenchymal stromal cells (MSC) to AML blasts promotes AML growth and is mediated by CD38. Daratumumab targets CD38 and inhibits this transfer, which results in impaired AML growth and improved animal survival. Here, we investigate the effect of inhibiting both CD38 with daratumumab and BCL2 with Venetoclax on the survival of AML. Primary AML blasts and MSC were isolated from patients' bone marrow in accordance with the Declaration of Helsinki. Flow cytometry was used to measure CD38 and BCL2 expression in AML blasts compared to normal CD34+ progenitor cells. BCL2 expression was significantly higher in AML blasts and CD38 expression was also increased. Cell viability was significantly reduced following treatment with Venetoclax alone, whilst Daratumumab alone or in combination with Venetoclax did not affect AML survival further. However, the action of daratumumab relies on the bone marrow microenvironment and AML blasts were therefore co-cultured with MSC and then treated with Venetoclax or daratumumab or in combination. After 24 hours cells were stained with Annexin V-FITC/PI and flow cytometry was used to assess levels of apoptosis. Combination treatment with Venetoclax and Daratumumab resulted in significantly more apoptosis in AML cells compared to AML cells treated with single agent. Finally, the effect of combination treatment with Venetoclax and Daratumumab was assessed in vivo using an NSG xenograft mouse model of AML. Mice were engrafted with MV411-luc or patient derived AML and then treated with vehicle control (PBS) or daratumumab alone (5mg/kg on day 7 and 14) or Venetoclax alone (100mg/kg/day) or both daratumumab and Venetoclax. Bioluminescence imaging was used to assess disease engraftment and progression before and after treatment. Combining treatment with Daratumumab and Venetoclax in vivo significantly reduced tumour burden and improved animal survival compared to control or single agent.

This data supports that combination treatment with Venetoclax and Daratumumab could have an important clinical application in the treatment of AML.

Citation Format: Charlotte Hellmich, Jayna J. Mistry, Amelia Lambert, Jamie A. Moore, Aisha Jibril, Angela Collins, Kristian M. Bowles, Stuart A. Rushworth. Targeting BCL-2 and CD38 in models of acute myeloid leukemia reduces tumour burden [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1048.

Venetoclax and Daratumumab combination treatment demonstrates pre-clinical efficacy in mouse models of Acute Myeloid Leukemia

Acute myeloid leukemia (AML) remains an incurable malignancy despite recent advances in treatment. Recently a number of new therapies have emerged for the treatment of AML which target BCL-2 or the membrane receptor CD38. Here, we show that treatment with Venetoclax and Daratumumab combination resulted in a slower tumor progression and a reduced leukemia growth both in vitro and in vivo. These data provide evidence for clinical evaluation of Venetoclax and Daratumumab combination in the treatment of AML.

Synthesis of Carboxamide-Containing Tranylcypromine Analogues as LSD1 (KDM1A) Inhibitors Targeting Acute Myeloid Leukemia

Lysine-specific demethylase 1 (LSD1/KDM1A) oxidatively removes methyl groups from histone proteins, and its aberrant activity has been correlated with cancers including acute myeloid leukemia (AML). We report a novel series of tranylcypromine analogues with a carboxamide at the 4-position of the aryl ring. These compounds, such as 5 a and 5 b with benzyl and phenethylamide substituents, respectively, had potent sub-micromolar IC50 values for the inhibition of LSD1 as well as cell proliferation in a panel of AML cell lines. The dose-dependent increase in cellular expression levels of H3K4me2, CD86, CD11b and CD14 supported a mechanism involving LSD1 inhibition. The tert-butyl and ethyl carbamate derivatives of these tranylcypromines, although inactive in LSD1 inhibition, were of similar potency in cell-based assays with a more rapid onset of action. This suggests that carbamates can act as metabolically labile tranylcypromine prodrugs with superior pharmacokinetics.

Mitochondrial oxidative phosphorylation in cutaneous melanoma

The Warburg effect in tumour cells is associated with the upregulation of glycolysis to generate ATP, even under normoxic conditions and the presence of fully functioning mitochondria. However, scientific advances made over the past 15 years have reformed this perspective, demonstrating the importance of oxidative phosphorylation (OXPHOS) as well as glycolysis in malignant cells. The metabolic phenotypes in melanoma display heterogeneic dynamism (metabolic plasticity) between glycolysis and OXPHOS, conferring a survival advantage to adapt to harsh conditions and pathways of chemoresistance. Furthermore, the simultaneous upregulation of both OXPHOS and glycolysis (metabolic symbiosis) has been shown to be vital for melanoma progression. The tumour microenvironment (TME) has an essential supporting role in promoting progression, invasion and metastasis of melanoma. Mesenchymal stromal cells (MSCs) in the TME show a symbiotic relationship with melanoma, protecting tumour cells from apoptosis and conferring chemoresistance. With the significant role of OXPHOS in metabolic plasticity and symbiosis, our review outlines how mitochondrial transfer from MSCs to melanoma tumour cells plays a key role in melanoma progression and is the mechanism by which melanoma cells regain OXPHOS capacity even in the presence of mitochondrial mutations. The studies outlined in this review indicate that targeting mitochondrial trafficking is a potential novel therapeutic approach for this highly refractory disease.

Abstract 2974: Targeting CD38 inhibits metabolic capacity of acute myeloid leukemia in the tumour microenvironment

Acute myeloid leukaemia (AML) causes 85,000 global deaths per year, which is estimated to double by 2040. AML has been shown to be highly dependent on the bone marrow (BM) microenvironment. Mesenchymal stromal cells (MSC) specifically, play an important pro-tumoral role. We previously demonstrated AML blasts rely on higher mitochondrial content and are more dependent on oxidative phosphorylation compared to non-malignant unstimulated CD34+ progenitor cells. To achieve this high metabolic demand, functional mitochondria are transferred from the MSC to the AML blasts. Mitochondrial transfer has also been demonstrated in myeloma in a pro-tumoral process regulated by CD38. Taken together, these data indicate that mitochondria are a biologically plausible and attractive drug target in the treatment of AML.We investigated the role mitochondrial transfer and the subsequent metabolic consequences of inhibiting CD38 using daratumumab on the AML BM microenvironment.Primary AML blasts and MSC were isolated from patient's BM. Mitochondrial transfer was assessed by coculture of AML and MSC in vitro using both qPCR DNA analysis and flow cytometry analysis. We used an NSG xenograft mouse model of AML, we transplanted OCI-AML3-luc, and treated the animals with either vehicle control (PBS) or daratumumab (5mg/kg) on day 9 and 16 followed by bioluminescence imaging. Post transplantation, AML mitochondrial transfer was assessed by murine mitochondrial DNA in human AML blasts by species specific PCR analysis. Post transplantation mitochondrial health and function was measured by TMRM and Seahorse analysis.Targeting CD38 using daratumumab inhibits the transfer of mitochondria from MSC to AML in vitro. In vivo, treatment with daratumumab significantly reduced tumor burden and improved survival compared to untreated controls. Additionally, we found two doses of daratumumab resulted in reduced mitochondrial potential, mitochondrial content and oxygen consumption rate in the AML cells sorted from the human xenograft mouse model. Finally, analysis of human AML cells sorted from NSG mouse BM showed reduced levels of mouse mitochondrial DNA in the human AML blasts from daratumumab treated mice compared to mice with AML treated with vehicle control.CD38 inhibition by daratumumab treatment inhibits mitochondrial transfer from MSC to AML blasts in the BM microenvironment. This results in a reduction in oxidative phosphorylation in AML blasts and subsequent reduced leukemia growth, which in turn results in improved NSG/AML animal survival. Whilst it is probable that daratumumab has a number of mechanisms of action, here we demonstrate inhibition of mitochondrial transfer is an addition to the list for this drug in AML. These data support the further clinical investigation of daratumumab based chemotherapeutic strategies as a therapeutic approach for the treatment AML.

Citation Format: Jayna J. Mistry, Jamie A. Moore, Christopher R. Marlein, Charlotte Hellmich, Genevra Pillinger, Federica Di Palma, Angela Collins, Kristian M. Bowles, Stuart A. Rushworth. Targeting CD38 inhibits metabolic capacity of acute myeloid leukemia in the tumour microenvironment [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 2974.

Autophagy Driven Extracellular Vesicles in the Leukaemic Microenvironment

The leukaemias are a heterogeneous group of blood cancers, which together, caused 310,000 deaths in 2016. Despite significant research into their biology and therapeutics, leukaemia is predicted to account for an increased 470,000 deaths in 2040. Many subtypes remain without targeted therapy, and therefore the mainstay of treatment remains generic cytotoxic drugs with bone marrow transplant the sole definitive option. In this review, we will focus on cellular mechanisms which have the potential for therapeutic exploitation to specifically target and treat this devastating disease. We will bring together the disciplines of autophagy and extracellular vesicles, exploring how the dysregulation of these mechanisms can lead to changes in the leukaemic microenvironment and the subsequent propagation of disease. The dual effect of these mechanisms in the disease microenvironment is not limited to leukaemia; therefore, we briefly explore their role in autoimmunity, inflammation and degenerative disease.

Bone Marrow Senescence and the Microenvironment of Hematological Malignancies

Senescence is the irreversible arrest of cell proliferation that has now been shown to play an important role in both health and disease. With increasing age senescent cells accumulate throughout the body, including the bone marrow and this has been associated with a number of age-related pathologies including malignancies. It has been shown that the senescence associated secretory phenotype (SASP) creates a pro-tumoural environment that supports proliferation and survival of malignant cells. Understanding the role of senescent cells in tumor development better may help us to identify new treatment targets to impair tumor survival and reduce treatment resistance. In this review, we will specifically discuss the role of senescence in the aging bone marrow (BM) microenvironment. Many BM disorders are age-related diseases and highly dependent on the BM microenvironment. Despite advances in drug development the prognosis particularly for older patients remains poor and new treatment approaches are needed to improve outcomes for patients. In this review, we will focus on the relationship of senescence and hematological malignancies, how senescence promotes cancer development and how malignant cells induce senescence.

CD38-Driven Mitochondrial Trafficking Promotes Bioenergetic Plasticity in Multiple Myeloma

Metabolic adjustments are necessary for the initiation, proliferation, and spread of cancer cells. Although mitochondria have been shown to move to cancer cells from their microenvironment, the metabolic consequences of this phenomenon have yet to be fully elucidated. Here, we report that multiple myeloma cells use mitochondrial-based metabolism as well as glycolysis when located within the bone marrow microenvironment. The reliance of multiple myeloma cells on oxidative phosphorylation was caused by intercellular mitochondrial transfer to multiple myeloma cells from neighboring nonmalignant bone marrow stromal cells. This mitochondrial transfer occurred through tumor-derived tunneling nanotubes (TNT). Moreover, shRNA-mediated knockdown of CD38 inhibits mitochondrial transfer and TNT formation in vitro and blocks mitochondrial transfer and improves animal survival in vivo. This study describes a potential treatment strategy to inhibit mitochondrial transfer for clinical benefit and scientifically expands the understanding of the functional effects of mitochondrial transfer on tumor metabolism. SIGNIFICANCE: Multiple myeloma relies on both oxidative phosphorylation and glycolysis following acquisition of mitochondria from its bone marrow microenvironment.See related commentary by Boise and Shanmugam, p. 2102.

Abstract 3131: Acute myeloid leukemia derived SDF1 repels tumor infiltrating lymphocytes in the bone marrow microenvironment

Introduction: Acute myeloid leukaemia (AML) is an age-related disease with a median age at diagnosis of 71. Combined with co-morbidities, survival of patients with AML above this age bracket is poor with 90% of older adults dying of their disease. Even in younger patients who achieve remission with chemotherapy, relapse is common and occurs from minimal residual disease sequestered in protective niches in the bone marrow microenvironment (BMM). AML as a disease is highly dependent on the bone marrow microenvironment and accordingly it is envisaged that improved outcomes will come from novel treatment strategies derived from an improved understanding of the biology of AML within the bone marrow and their interaction with the immune cells therein.

Objective: Here, we investigate a possible immune evasive mechanism imparted by AML blasts attributed to their localization within the BMM.

Methods and Results: Using RNA-seq data generated from bone marrow derived AML (BM-AML) compared to peripheral blood derived AML (PB-AML) (GEO ID: GSE49642, GSE48846) we identified SDF-1 as the most differentially expressed in favour of BM-AML. Further investigation using matched primary clinical samples (BM verses PB) by real-time PCR analysis and ELISA confirmed the in-silico findings. In addition, primary AML engrafted into NSG mice demonstrated high SDF-1 in the BM derived AML blasts compared to AML blasts derived from the spleen. Lentiviral knock-down of SDF-1 in the AML blasts impaired blast engraftment and prolonged survival of the animals. SDF1-mediated migration of T-cell subsets have been previously identified using varying concentrations of SDF1. We therefore, investigated the migration of CD8+ T cells when co-cultured with AML. We show that CD8+ T-cells migrate away from AML when in culture and this fugetaxis is reduced by the knock-down of SDF1 in the blasts.

Conclusion: We conclude that SDF-1 is secreted by the AML blasts within the BMM contributing to fugetaxis of CD8+ cells away from the blasts. Implications of these finding suggest a possible immune evasive mechanism by the blasts that can be manipulated to potentiate CD8+ infiltration into the AML bone marrow.

Citation Format: Manar S. Shafat, Amina A. Abdul-Aziz, Christopher Marlien, Rachel Piddock, Kristian M. Bowles, Stuart A. Rushworth. Acute myeloid leukemia derived SDF1 repels tumor infiltrating lymphocytes in the bone marrow microenvironment [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 3131.

Abstract 4970: Mitochondrial trafficking in the bone marrow microenvironment promotes bioenergetic flexibility in multiple myeloma

Multiple myeloma (MM) is an incurable malignancy of terminally differentiated plasma cells which is highly dependent on the bone marrow microenvironment (BMM). MM tumor survival, proliferation and drug resistance is reliant on ATP production however the mechanisms by which the malignant cells generate ATP are poorly defined. In this study, we investigate the contributions of oxidative phosphorylation and aerobic glycolysis to tumor cell ATP generation within BMM. Furthermore, we address whether ATP generation within tumor cells is enabled by the transfer of mitochondria from the non-malignant stromal cells of the BMM to the malignant plasma cell.

Bone marrow was obtained from patients under approval from the UK Health Research Authority. In-vivo experiments were performed with local Animal Welfare and Ethical Review Board approval and under license from the UK Home Office.

Using Seahorse extracellular flux analysis we show that primary MM cells have high baseline rates of mitochondrial respiration compared to MM cell lines. Furthermore, mitochondrial respiration rates increased ex-vivo after co-culture with non-malignant bone marrow stromal cells (BMSC). We engrafted the malignant MM1S cell line into NSG mice and examined the mitochondrial respiration rate from isolated tumor cells compared to MM1S cells cultured in-vitro. We found increased rates of mitochondrial respiration in MM1S cells isolated from mouse BM. To determine whether the increase in tumor oxidative phosphorylation observed in the presence of micro-environment cells was a result of mitochondrial transfer from BMSC to MM, we used three methods. Firstly we stained BMSC with the mitochondrial stain MitoTracker Green and cultured these with primary MM cells. Using a combination of flow cytometry and confocal microscopy we detected MitoTracker fluorescence in the MM cells after co-culture, showing that the stained mitochondria are transferred from BMSC to MM cells in-vitro. Secondly, mitochondrial transfer was directly observed between BMSC and MM cells, visualized by the acquisition of a mCherry labeled mitochondrial protein we transfected into BMSC. Finally, using a human MM cell line engrafted into an NSG mouse xenograft model, we detected murine mitochondrial DNA in sorted human MM1S and U266 tumor cells post-transplant. Through fixed cell confocal microscopy we found that mitochondria move through tunnelling nanotubes (TNTs), and inhibition of TNT formation by treatment with cytochalasin B resulted in reduced mitochondrial transfer and tumor cell oxidative phosphorylation.

Here we show that MM cellular metabolism favors oxidative phosphorylation over glycolysis, in the setting of the BMM. This is due to mitochondrial transfer occurring between non-malignant BMSC and malignant plasma cells. This process is necessary for optimum tumor growth in-vivo and forms part of the malignant phenotype of MM.

Citation Format: Christopher R. Marlein, Rachel E. Piddock, Charlotte Hellmich, Lyubov Zaitseva, Martin J. Auger, Kristian M. Bowles, Stuart A. Rushworth. Mitochondrial trafficking in the bone marrow microenvironment promotes bioenergetic flexibility in multiple myeloma [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 4970.

Abstract 2123: Myeloma derived macrophage inhibitory factor regulates BMSC IL6/8 via cMYC

Background

Multiple Myeloma (MM) is a plasma cell malignancy dependent on the bone marrow microenvironment. Macrophage inhibitory factor (MIF) acts directly on malignant plasma cells affecting homing and chemotherapy resistance, however the adaptive effect that MM derived MIF has on the tumor microenvironment is not yet defined. Here we investigate the function of MM derived MIF in the MM microenvironment by examining its effects on bone marrow mesenchymal stromal cells (BMSC).

Methods

Primary MM and BMSC were obtained from patient bone marrow. Proteome Profiler Human XL Cytokine Array was used. Inhibitors including JQ1 were

purchased from Merck. In-vivo experiments were performed using 8-10 week old NSG mice.

Results

First we injected 1 x 106 MM.1S MIF-knock down (KD) cells or MM.1S control-KD cells (containing the pCDH-luciferase-T2A-mCherry construct) into the tail vein of 6-8 week old NSG mice. MIF-KD in MM cells resulted in animals with significantly reduced tumor burden and improved overall survival. To further investigate the role of MIF in regulating the BM microenvironment we stimulated primary human BMSC with biologically appropriate doses of recombinant MIF and then used Human XL Cytokine Array and cytokine specific ELISA to assay the supernatant from these MIF stimulated BMSC. Results show that MIF induces IL-6 and IL-8 protein secretion from primary BMSC. To examine the mechanism of action of these observations we used a panel of inhibitors to screen for potential pathways responsible for MIF induced BMSC derived IL-6 and IL-8 expression. The c-Myc inhibitor JQ1 inhibited MIF induced IL-6 and IL-8 expression. Next, we looked at whether c-Myc regulates BMSC pro-tumoral interleukin production in-vivo. We injected NSG mice via the tail vein with human myeloma cell line U266 and then randomized animals to two groups; treating with either JQ1 (50mg/kg, IP) or alternatively vehicle control for 5 days, after which bloods were taken

to assess murine IL-6 levels (IL-8 is deleted from the mouse genome). Results show that murine IL-6 was significantly reduced in the JQ1 treated animals (carrying human MM) compared to vehicle control treated animals.

Summary

MM derived MIF is pro-tumoral through induction of c-Myc and downstream IL-6 and IL-8 in the BMSC of the tumor micro-environment. Identification of this novel pro-tumoral crosstalk mechanism which exists between MM and the bone marrow stroma provides scientific rationale for the clinical evaluation of new therapeutic targets in MM.

Citation Format: Rachel E. Piddock, Christopher R. Marlein, Amina Abdul-Aziz, Martin J. Auger, Kristian M. Bowles, Stuart A. Rushworth. Myeloma derived macrophage inhibitory factor regulates BMSC IL6/8 via cMYC [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 2123.

Myeloma-derived macrophage inhibitory factor regulates bone marrow stromal cell-derived IL-6 via c-MYC

Abstract

Multiple myeloma (MM) remains an incurable malignancy despite the recent advancements in its treatment. The protective effects of the niche in which it develops has been well documented; however, little has been done to investigate the MM cell’s ability to ‘re-program’ cells within its environment to benefit disease progression. Here, we show that MM-derived macrophage migratory inhibitory factor (MIF) stimulates bone marrow stromal cells to produce the disease critical cytokines IL-6 and IL-8, prior to any cell-cell contact. Furthermore, we provide evidence that this IL-6/8 production is mediated by the transcription factor cMYC. Pharmacological inhibition of cMYC in vivo using JQ1 led to significantly decreased levels of serum IL-6—a highly positive prognostic marker in MM patients.

Conclusions

Our presented findings show that MM-derived MIF causes BMSC secretion of IL-6 and IL-8 via BMSC cMYC. Furthermore, we show that the cMYC inhibitor JQ1 can reduce BMSC secreted IL-6 in vivo, irrespective of tumor burden. These data provide evidence for the clinical evaluation of both MIF and cMYC inhibitors in the treatment of MM.

Electronic supplementary material

The online version of this article (10.1186/s13045-018-0614-4) contains supplementary material, which is available to authorized users.

Targeting the KEAP1/NRF2 pathway to manipulate the expression of oncogenic and oncosuppressive miRNAs in human leukemia

The Kelch-like ECH-associated protein 1 (KEAP1)/nuclear factor E2-related factor 2 (NRF2L2, best known as NRF2) pathway plays a pivotal cytoprotective role in the regulation of cellular responses to oxidative stress. We report that NRF2 modulates the expression of microRNA-125B and microRNA-29B in acute myeloid leukemia. The regulation of microRNA in leukemia can now be added to the growing list of prosurvival functions of NRF2.

HIF1α drives chemokine factor pro-tumoral signaling pathways in acute myeloid leukemia

Approximately 80% of patients diagnosed with acute myeloid leukemia (AML) die as a consequence of failure to eradicate the tumor from the bone marrow microenvironment. We have recently shown that stroma-derived interleukin-8 (IL-8) promotes AML growth and survival in the bone marrow in response to AML-derived macrophage migration inhibitory factor (MIF). In the present study we show that high constitutive expression of MIF in AML blasts in the bone marrow is hypoxia-driven and, through knockdown of MIF, HIF1α and HIF2α, establish that hypoxia supports AML tumor proliferation through HIF1α signaling. In vivo targeting of leukemic cell HIF1α inhibits AML proliferation in the tumor microenvironment through transcriptional regulation of MIF, but inhibition of HIF2α had no measurable effect on AML blast survival. Functionally, targeted inhibition of MIF in vivo improves survival in models of AML. Here we present a mechanism linking HIF1α to a pro-tumoral chemokine factor signaling pathway and in doing so, we establish a potential strategy to target AML.

Targeting PI3Kδ and PI3Kγ signalling disrupts human AML survival and bone marrow stromal cell mediated protection

Phosphoinositide-3-kinase (PI3K) is an enzyme group, known to regulate key survival pathways in acute myeloid leukaemia (AML). It generates phosphatidylinositol-3,4,5-triphosphate, which provides a membrane docking site for protein kinaseB activation. PI3K catalytic p110 subunits are divided into 4 isoforms; α,β,δ and γ. The PI3Kδ isoform is always expressed in AML cells, whereas the frequency of PI3Kγ expression is highly variable. The functions of these individual catalytic enzymes have not been fully resolved in AML, therefore using the PI3K p110δ and p110γ-targeted inhibitor IPI-145 (duvelisib) and specific p110δ and p110γ shRNA, we analysed the role of these two p110 subunits in human AML blast survival. The results show that PI3Kδ and PI3Kγ inhibition with IPI-145 has anti-proliferative activity in primary AML cells by inhibiting the activity of AKT and MAPK. Pre-treatment of AML cells with IPI-145 inhibits both adhesion and migration of AML blasts to bone marrow stromal cells. Using shRNA targeted to the individual isoforms we demonstrated that p110δ-knockdown had a more significant anti-proliferative effect on AML cells, whereas targeting p110γ-knockdown significantly inhibited AML migration. The results demonstrate that targeting both PI3Kδ and PI3Kγ to inhibit AML-BMSC interactions provides a biologic rationale for the pre-clinical evaluation of IPI-145 in AML.

Inflammatory Differences in Plaque Erosion and Rupture in Patients With ST-Segment Elevation Myocardial Infarction

Background

Plaque erosion causes 30% of ST‐segment elevation myocardial infarctions, but the underlying cause is unknown. Inflammatory infiltrates are less abundant in erosion compared with rupture in autopsy studies. We hypothesized that erosion and rupture are associated with significant differences in intracoronary cytokines in vivo.

Methods and Results

Forty ST‐segment elevation myocardial infarction patients with <6 hours of chest pain were classified as ruptured fibrous cap (RFC) or intact fibrous cap (IFC) using optical coherence tomography. Plasma samples from the infarct‐related artery and a peripheral artery were analyzed for expression of 102 cytokines using arrays; results were confirmed with ELISA. Thrombectomy samples were analyzed for differential mRNA expression using quantitative real‐time polymerase chain reaction. Twenty‐three lesions were classified as RFC (58%), 15 as IFC (38%), and 2 were undefined (4%). In addition, 12% (12 of 102) of cytokines were differentially expressed in both coronary and peripheral plasma. I‐TAC was preferentially expressed in RFC (significance analysis of microarrays adjusted P<0.001; ELISA IFC 10.2 versus RFC 10.8 log₂ pg/mL; P=0.042). IFC was associated with preferential expression of epidermal growth factor (significance analysis of microarrays adjusted P<0.001; ELISA IFC 7.42 versus RFC 6.63 log₂ pg/mL, P=0.036) and thrombospondin 1 (significance analysis of microarrays adjusted P=0.03; ELISA IFC 10.4 versus RFC 8.65 log₂ ng/mL, P=0.0041). Thrombectomy mRNA showed elevated I‐TAC in RFC (P=0.0007) epidermal growth factor expression in IFC (P=0.0264) but no differences in expression of thrombospondin 1.

Conclusions

These results demonstrate differential intracoronary cytokine expression in RFC and IFC. Elevated thrombospondin 1 and epidermal growth factor may play an etiological role in erosion.

PI3Kδ and PI3Kγ isoforms have distinct functions in regulating pro-tumoural signalling in the multiple myeloma microenvironment

Phosphoinositide-3-kinase and protein kinase B (PI3K-AKT) is upregulated in multiple myeloma (MM). Using a combination of short hairpin RNA (shRNA) lentivirus-mediated knockdown and pharmacologic isoform-specific inhibition we investigated the role of the PI3K p110γ (PI3Kγ) subunit in regulating MM proliferation and bone marrow microenvironment-induced MM interactions. We compared this with inhibition of the PI3K p110δ (PI3kδ) subunit and with combined PI3kδ/γ dual inhibition. We found that MM cell adhesion and migration were PI3Kγ-specific functions, with PI3kδ inhibition having no effect in MM adhesion or migration assays. At concentration of the dual PI3Kδ/γ inhibitor duvelisib, which can be achieved in vivo we saw a decrease in AKT phosphorylation at s473 after tumour activation by bone marrow stromal cells (BMSC) and interleukin-6. Moreover, after drug treatment of BMSC/tumour co-culture activation assays only dual PI3kδ/γ inhibition was able to induce MM apoptosis. shRNA lentiviral-mediated targeting of either PI3Kδ or PI3Kγ alone, or both in combination, increased survival of NSG mice xeno-transplanted with MM cells. Moreover, treatment with duvelisib reduced MM tumour burden in vivo. We report that PI3Kδ and PI3Kγ isoforms have distinct functions in MM and that combined PI3kδ/γ isoform inhibition has anti-MM activity. Here we provide a scientific rationale for trials of dual PI3kδ/γ inhibition in patients with MM.

MIF-Induced Stromal PKCβ/IL8 Is Essential in Human Acute Myeloid Leukemia

Acute myeloid leukemia (AML) cells exhibit a high level of spontaneous apoptosis when cultured in vitro but have a prolonged survival time in vivo, indicating that tissue microenvironment plays a critical role in promoting AML cell survival. In vitro studies have shown that bone marrow mesenchymal stromal cells (BM-MSC) protect AML blasts from spontaneous and chemotherapy-induced apoptosis. Here, we report a novel interaction between AML blasts and BM-MSCs, which benefits AML proliferation and survival. We initially examined the cytokine profile in cultured human AML compared with AML cultured with BM-MSCs and found that macrophage migration inhibitory factor (MIF) was highly expressed by primary AML, and that IL8 was increased in AML/BM-MSC cocultures. Recombinant MIF increased IL8 expression in BM-MSCs via its receptor CD74. Moreover, the MIF inhibitor ISO-1 inhibited AML-induced IL8 expression by BM-MSCs as well as BM-MSC-induced AML survival. Protein kinase C β (PKCβ) regulated MIF-induced IL8 in BM-MSCs. Finally, targeted IL8 shRNA inhibited BM-MSC-induced AML survival. These results describe a novel, bidirectional, prosurvival mechanism between AML blasts and BM-MSCs. Furthermore, they provide biologic rationale for therapeutic strategies in AML targeting the microenvironment, specifically MIF and IL8. Cancer Res; 77(2); 303-11. ©2016 AACR.

Targeting BTK for the treatment of FLT3-ITD mutated acute myeloid leukemia

Approximately 20% of patients with acute myeloid leukaemia (AML) have a mutation in FMS-like-tyrosine-kinase-3 (FLT3). FLT3 is a trans-membrane receptor with a tyrosine kinase domain which, when activated, initiates a cascade of phosphorylated proteins including the SRC family of kinases. Recently our group and others have shown that pharmacologic inhibition and genetic knockdown of Bruton's tyrosine kinase (BTK) blocks AML blast proliferation, leukaemic cell adhesion to bone marrow stromal cells as well as migration of AML blasts. The anti-proliferative effects of BTK inhibition in human AML are mediated via inhibition of downstream NF-κB pro-survival signalling however the upstream drivers of BTK activation in human AML have yet to be fully characterised. Here we place the FLT3-ITD upstream of BTK in AML and show that the BTK inhibitor ibrutinib inhibits the survival and proliferation of FLT3-ITD primary AML blasts and AML cell lines. Furthermore ibrutinib inhibits the activation of downstream kinases including MAPK, AKT and STAT5. In addition we show that BTK RNAi inhibits proliferation of FLT3-ITD AML cells. Finally we report that ibrutinib reverses the cyto-protective role of BMSC on FLT3-ITD AML survival. These results argue for the evaluation of ibrutinib in patients with FLT3-ITD mutated AML.

Ibrutinib inhibits BTK-driven NF-κB p65 activity to overcome bortezomib-resistance in multiple myeloma

Multiple Myeloma (MM) is a haematologic malignancy characterized by the accumulation of clonal plasma cells in the bone marrow. Over the last 10-15 y the introduction of the proteasome-inhibitor bortezomib has improved MM prognosis, however relapse due to bortezomib-resistance is inevitable and the disease, at present, remains incurable. To model bortezomib-resistant MM we generated bortezomib-resistant MM cell lines (n = 4 ) and utilised primary malignant plasma cells from patients relapsing after bortezomib treatment (n = 6 ). We identified enhanced Bruton's tyrosine kinase (BTK) activity in bortezomib-resistant MM cells and found that inhibition of BTK, either pharmacologically with ibrutinib (0.5 μM) or via lenti-viral miRNA-targeted BTK interference, re-sensitized previously bortezomib-resistant MM cells to further bortezomib therapy at a physiologically relevant concentration (5 nM). Further analysis of pro-survival signaling revealed a role for the NF-κB p65 subunit in MM bortezomib-resistance, thus a combination of BTK and NF-κB p65 inhibition, either pharmacologically or via further lenti-viral miRNA NF-κB p65 interference, also restored sensitivity to bortezomib, significantly reducing cell viability (37.5 ± 6 .9 %, ANOVA P ≤ 0 .001). Accordingly, we propose the clinical evaluation of a bortezomib/ibrutinib combination therapy, including in patients resistant to single-agent bortezomib.

Ibrutinib inhibits SDF1/CXCR4 mediated migration in AML

Pharmacological targeting of BTK using ibrutinib has recently shown encouraging clinical activity in a range of lymphoid malignancies. Recently we reported that ibrutinib inhibits human acute myeloid leukemia (AML) blast proliferation and leukemic cell adhesion to the surrounding bone marrow stroma cells. Here we report that in human AML ibrutinib, in addition, functions to inhibit SDF1/CXCR4-mediated AML migration at concentrations achievable in vivo. It has previously been shown that SDF1/CXCR4-induced migration is dependent on activation of downstream BTK in chronic lymphocytic leukaemia (CLL) and multiple myeloma. Here we show that SDF-1 induces BTK phosphorylation and downstream MAPK signalling in primary AML blast. Furthermore, we show that ibrutinib can inhibit SDF1-induced AKT and MAPK activation. These results reported here provide a molecular mechanistic rationale for clinically evaluating BTK inhibition in AML patients and suggests that in some AML patients the blasts count may initially rise in response to ibrutinib therapy, analgous to similar clinical observations in CLL.

Attenuation of dexamethasone-induced cell death in multiple myeloma is mediated by miR-125b expression

Dexamethasone is a key front-line chemotherapeutic for B-cell malignant multiple myeloma (MM). Dexamethasone modulates MM cell survival signaling but fails to induce marked cytotoxicity when used as a monotherapy. We demonstrate here the mechanism behind this insufficient responsiveness of MM cells toward dexamethasone, revealing in MM a dramatic anti-apoptotic role for microRNA (miRNA)-125b in the insensitivity toward dexamethasone-induced apoptosis. MM cells responding to dexamethasone exhibited enhanced expression of oncogenic miR-125b. Dexamethasone also induced expression of miR-34a, which acts to suppress SIRT1 deacetylase, and thus allows maintained acetylation and inactivation of p53. p53 mRNA is also suppressed by miR-125b targeting. Reporter assays showed that both these dexamethasone-induced miRNAs act downstream of their target genes to prevent p53 tumor suppressor actions and, ultimately, resist cytotoxic responses in MM. Use of antisense miR-125b transcripts enhanced expression of pro-apoptotic p53, repressed expression of anti-apoptotic SIRT1 and, importantly, significantly enhanced dexamethasone-induced cell death responses in MM. Pharmacological manipulations showed that the key regulation enabling complete dexamethasone sensitivity in MM cells lies with miR-125b. In summary, dexamethasone-induced miR-125b induces cell death resistance mechanisms in MM cells via the p53/miR-34a/SIRT1 signaling network and provides these cells with an enhanced level of resistance to cytotoxic chemotherapeutics. Clearly, such anti-apoptotic mechanisms will need to be overcome to more effectively treat nascent, refractory and relapsed MM patients. These mechanisms provide insight into the role of miRNA regulation of apoptosis and their promotion of MM cell proliferative mechanisms.

Bortezomib induces heme oxygenase-1 expression in multiple myeloma

Multiple myeloma (MM) is a progressive malignant disorder characterized by accumulation of plasma cells in the bone marrow. MM remains an incurable disease with a 5-y survival rate of approximately 40%. While clinical response rates to first line chemotherapeutics are high, disease relapse is inevitable, and occurs because a small fraction of the original myeloma cells appear to be resistant to treatment. Heme oxygenase-1 (HO-1) is an Nrf2 transcription factor-regulated gene that is commonly induced following oxidative stress and cellular injury, functioning to decrease oxidative stress and inflammatory responses, protecting against apoptosis and altering the cell cycle. We and others have highlighted the role of HO-1 in providing cellular protection against chemotherapeutic drugs in a number of cancer cells, which we have highlighted here in this Extra View. Furthermore, we explored the expression of HO-1 in multiple myeloma cells in response to the key anti-myeloma drugs bortezomib and lenalidomide. We show here for the first time that bortezomib increases HO-1 expression in a time- and concentration-dependent manner. Moreover, we also observe that HO-1 is increased in lenalidomide-resistant MM cell lines. Altogether, we highlight a possible role for HO-1 in basal and acquired chemoresistance in MM.

Understanding the role of miRNA in regulating NF-κB in blood cancer

MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression by binding to complementary sequences in mRNAs encoding downstream target genes. A large variety of cellular processes, including differentiation, development, apoptosis and cell cycle progression, are dependent on miRNA-mediated suppression of gene expression for their regulation. As such, it is unsurprising that these small RNA molecules are associated with signaling networks that are often altered in various diseases, including many blood cancers. One such network is the nuclear factor-κB (NF-κB) pathways that universally stimulate transcription of proteins which generally promote cell survival, inhibit apoptosis, allow cellular growth, induce angiogenesis and generate many pro-inflammatory responses. The NF-κB signalling pathway is often constitutively activated in blood cell cancers including myelodysplastic syndrome (MDS), acute myeloid leukaemia (AML), acute lymphocytic leukaemia (ALL), chronic myeloid leukaemia (CML), chronic lymphocytic leukaemia (CLL), lymphomas and in multiple myeloma (MM). This review focuses on the function of miRNAs that directly target NF-κB signaling cascade. Recent findings that connect this pathway through various miRNA families to human blood cancers are reviewed, and support for using miRNA-based therapy as a novel method to counteract this tumour-promoting signalling event is discussed.

Micro RNAs as a new therapeutic target towards leukaemia signalling

Micro RNAs (miRNAs) have emerged as potentially useful and specific agents to regulate transcriptional control of many cellular genes. There is a real prospect that miRNA and other short-length RNA reagents could be useful in a therapeutic setting. Here we outline the control of miRNAs in acute myeloid leukaemia (AML) subtype of human leukaemia, and ask whether miRNA could be important either in the generation of an AML phenotype, or as a variety of agents to combat the disease in the clinic. The use of miRNAs as potential biomarkers of aberrant signalling pathways involved in AML oncogenesis is also discussed.

Targeting the oncogenic role of miRNA in human cancer using naturally occurring compounds

Micro-RNAs (miRNAs) are small RNA molecules that regulate the expression of genes involved in development, growth, proliferation and apoptosis. In cancer several miRNAs have been functionally classified as oncogenes or tumour suppressers or act to regulate transcription factors, like nuclear factor kappa B and NF-E2–related factor 2, in cancers such as leukaemia, breast and colorectal. Therefore, it has been proposed that manipulating miRNA regulation may be a novel avenue for developing efficient therapies against cancer. In this issue, Li and colleagues describe a novel way of targeting miRNA, by using a naturally occurring anti-cancer compound found in mistletoe which they showed to down-regulate miR-135a&b, which target the 3' untranslated region of adenomatous polyposis coli gene, the inactivation of which is a major initiating event in colorectal tumourigenesis. This commentary aims to discuss the regulatory mechanisms of miRNA synthesis and the potential outcomes for using naturally occurring compounds antioxidants or cellular antioxidant pathways to target miRNA for therapeutic intervention.