The role of the tumor microenvironment in hematological malignancies and implication for therapy

The tumor microenvironment is essential for tumor cell proliferation, angiogenesis, invasion, and metastasis by providing survival signals and a sanctuary site for tumor cells, by secretion of growth factors, pro-angiogenesis factors and direct adhesion molecule interactions. Our knowledge of microenvironment is only now beginning to unfold. In this review, the morphological and molecular characteristics of microenvironment in various hematological malignancies including acute lymphoblastic leukemia, acute myeloid leukemia, myelodysplastic syndrome, lymphoma, chronic lymphocytic leukemia, and multiple myeloma are summarized and the molecular mechanisms of microenvironment contributing to leukemogenesis are elucidated. We also aim to discuss the encouraging preclinical and clinical trials for treatment of hematological malignancies by targeting the tumor microenvironment. Further understanding of the signal transduction pathways between tumor cells and microenvironment will lead to the development of novel targeted therapeutic agents and more effective combination of current drugs for fighting hematological malignancies.

Tumor-derived exosomes in colorectal cancer progression and their clinical applications

Colorectal cancer (CRC) ranks as the third leading cause of cancer mortality in both of men and women worldwide due to its metastatic properties and resistance to current treatment. Recent studies have shown that tumor-derived exosomes play emerging roles in the development of cancer. Exosomes are nano-sized extracellular vesicles (EVs) that contain lipids, proteins, DNAs, and RNA species (mRNA, miRNA, long non-coding RNA). These exosomal cargos can be transferred locally and systemically, after taken by recipient cells, so exosomes represent a new form of intercellular communication. There is increasing evidence demonstrating that exosomes control a wide range of pathways bolstering tumor development, metastasis and drug resistance. This review provides an in-depth and timely summary of the role of exosomes in CRC. We first describe the common features and biogenesis of exosomes. We then highlight important findings that support the emerging roles of exosomes in CRC cell growth, invasion and metastasis, as well as resistance to treatment. Finally, we discuss the clinical application of exosomes as diagnostic biomarkers, in vivo drug delivery system and the potential of novel exosome-based immunotherapy for CRC.

Oncogenic roles of PRL-3 in FLT3-ITD induced acute myeloid leukaemia

FLT3-ITD mutations are prevalent mutations in acute myeloid leukaemia (AML). PRL-3, a metastasis-associated phosphatase, is a downstream target of FLT3-ITD. This study investigates the regulation and function of PRL-3 in leukaemia cell lines and AML patients associated with FLT3-ITD mutations. PRL-3 expression is upregulated by the FLT3-STAT5 signalling pathway in leukaemia cells, leading an activation of AP-1 transcription factors via ERK and JNK pathways. PRL-3-depleted AML cells showed a significant decrease in cell growth. Clinically, high PRL-3 mRNA expression was associated with FLT3-ITD mutations in four independent AML datasets with 1158 patients. Multivariable Cox-regression analysis on our Cohort 1 with 221 patients identified PRL-3 as a novel prognostic marker independent of other clinical parameters. Kaplan-Meier analysis showed high PRL-3 mRNA expression was significantly associated with poorer survival among 491 patients with normal karyotype. Targeting PRL-3 reversed the oncogenic effects in FLT3-ITD AML models in vitro and in vivo. Herein, we suggest that PRL-3 could serve as a prognostic marker to predict poorer survival and as a promising novel therapeutic target for AML patients.

Genome-wide pharmacologic unmasking identifies tumor suppressive microRNAs in multiple myeloma

Epigenetic alterations have emerged as an important cause of microRNA (miRNA) deregulation. In Multiple Myeloma (MM), a few tumor suppressive miRNAs silenced by DNA hypermethylation have been reported, but so far there are few systemic investigations on epigenetically silenced miRNAs. We conducted genome-wide screening for tumor suppressive miRNAs epigenetically silenced in MM. Four Human MM Cell lines were treated with demethylating agent 5'azacytidine (5'aza). Consistently upregulated miRNAs include miR-155, miR-198, miR-135a*, miR-200c, miR-125a-3p, miR-188-5p, miR-483-5p, miR-663, and miR-630. Methylation array analysis revealed increased methylation at or near miRNA-associated CpG islands in MM patients. Ectopic restoration of miR-155, miR-198, miR-135a*, miR-200c, miR-663 and miR-483-5p significantly repressed MM cell proliferation, migration and colony formation. Furthermore, we derived a 33-gene signature from predicted miRNA target genes that were also upregulated in MM patients and associated with patient survival in three independent myeloma datasets. In summary, we have revealed important, epigenetically silenced tumor suppressive miRNAs by pharmacologic reversal of epigenetic silencing.

Immunoglobulin gene segment usage, location and immunogenicity in mutated and unmutated chronic lymphocytic leukaemia

The mutational status of the variable region of the immunoglobulin heavy chain gene (IgV(H)) is an important prognostic marker in B-cell chronic lymphocytic leukaemia (B-CLL), with mutated patients having improved outcome. To examine the impact of mutational status on V(H), D(H), and J(H) gene segment location and immunogenicity, we analysed 375 IgH sequences from 356 patients with B-CLL. Although V(H) and D(H) gene usage was different in mutated compared to unmutated patients, there was no impact of gene location on frequency of use or clinical outcome. Surprisingly, somatic mutations did not increase the immunogenicity of the Ig, as assessed by predicted binding affinity of Ig-derived peptides to major histocompatibility Class I and Class II molecules. Even excluding patients using V(H)1-69, cases using the V(H)1 gene family had a poor outcome. Both mutated and unmutated CLL patients demonstrated evidence of antigen selection. The worst outcome was seen in the subset of 14 unmutated patients with similar HCDR3 amino acid sequence using V(H)1-69, D(H)3-3 and J(H)6, suggesting an antigen-driven process modulating the clinical course.

Inhibition of CD44 expression in hepatocellular carcinoma cells enhances apoptosis, chemosensitivity, and reduces tumorigenesis and invasion

PURPOSE

CD44 is overexpressed in various tumors including hepatocellular carcinoma (HCC). The purpose of this study was to examine the effects of CD44 antisense oligonucleotide (ASO) alone or combination with doxorubicin on HCC cells in vitro.

METHODS

Cytotoxicity was measured by use of a cell viability assay in HCC cell line SNU-449. Tumorigenesis and invasion were accessed by colony formation, growth in soft agar and ECMatrix invasion assay. Apoptosis and necrosis were evaluated by using double staining with Hoechst 33342 and propidium iodide. Protein expression and mRNA level were detected by Western blot and RT-PCR.

RESULTS

We have designed novel CD44 ASO, which can effectively down-regulate CD44 expression in SNU-449. Colony formation, growth in soft agar and invasion were significantly impaired after CD44 ASO treatment in SNU-499. In company with CD44 down-regulated by CD44 ASO, MDR-1 and Bcl-2 expression were also greatly reduced. CD44 ASO also increased chemosensitivity to doxorubicin significantly, lowered IC(50 )by one order of magnitude. Apoptosis and necrosis were also induced by CD44 ASO alone or in combination treatment with doxorubicin.

CONCLUSIONS

Inhibition of CD44 expression by CD44 ASO significantly induced apoptosis, decreased tumorigenesis and invasion, and increased chemosensitivity. Thus, CD44 ASO is potentially a therapy that is worth investigating in the clinical setting.

PRIMA-1met (APR-246) inhibits growth of colorectal cancer cells with different p53 status through distinct mechanisms

PRIMA-1met (APR-246) is a methylated derivative and structural analog of PRIMA-1 (p53 re-activation and induction of massive apoptosis). PRIMA-1met has been reported to restore both the wild type (wt) structure and function of mutant p53. Here, we show that PRIMA-1met is highly effective at limiting the growth of CRC cells regardless of p53 status. However, PRIMA-1met induces robust apoptosis only in CRC cells with mutant p53. Upregulation of Noxa, a proapoptotic molecule, is crucial for PRIMA-1met mediated activity. In human xenograft model of disease, PRIMA-1met effectively suppresses CRC tumor growth. Our results uncover distinct mechanisms of PRIMA-1met in CRC with different p53 status, thus providing a mechanistic rationale to evaluate the clinical efficacy of PRIMA-1met in CRC patients with different p53 status.

Engineering the first chimeric antibody in targeting intracellular PRL-3 oncoprotein for cancer therapy in mice

Antibodies are considered as 'magic bullets' because of their high specificity. It is believed that antibodies are too large to routinely enter the cytosol, thus antibody therapeutic approach has been limited to extracellular or secreted proteins expressed by cancer cells. However, many oncogenic proteins are localized within the cell. To explore the possibility of antibody therapies against intracellular targets, we generated a chimeric antibody targeting the intracellular PRL-3 oncoprotein to assess its antitumor activities in mice. Remarkably, we observed that the PRL-3 chimeric antibody could efficiently and specifically reduce the formation of PRL-3 expressing metastatic tumors. We further found that natural killer (NK) cells were important in mediating the therapeutic effect, which was only observed in a nude mouse model (T-cell deficient), but not in a Severe Combined Immunodeficiency' (scid ) mouse model (B- and T-cell deficient), indicating the anticancer effect also depends on host B-cell activity. Our study involving 377 nude and scid mice suggest that antibodies targeting intracellular proteins can be developed to treat cancer.

PRL3-zumab as an immunotherapy to inhibit tumors expressing PRL3 oncoprotein

Tumor-specific antibody drugs can serve as cancer therapy with minimal side effects. A humanized antibody, PRL3-zumab, specifically binds to an intracellular oncogenic phosphatase PRL3, which is frequently expressed in several cancers. Here we show that PRL3-zumab specifically inhibits PRL3+ cancer cells in vivo, but not in vitro. PRL3 antigens are detected on the cell surface and outer exosomal membranes, implying an 'inside-out' externalization of PRL3. PRL3-zumab binds to surface PRL3 in a manner consistent with that in classical antibody-dependent cell-mediated cytotoxicity or antibody-dependent cellular phagocytosis tumor elimination pathways, as PRL3-zumab requires an intact Fc region and host FcγII/III receptor engagement to recruit B cells, NK cells and macrophages to PRL3+ tumor microenvironments. PRL3 is overexpressed in 80.6% of 151 fresh-frozen tumor samples across 11 common cancers examined, but not in patient-matched normal tissues, thereby implicating PRL3 as a tumor-associated antigen. Targeting externalized PRL3 antigens with PRL3-zumab may represent a feasible approach for anti-tumor immunotherapy.

Utilization of Ig heavy chain variable, diversity, and joining gene segments in children with B-lineage acute lymphoblastic leukemia: implications for the mechanisms of VDJ recombination and for pathogenesis

Sequence analysis of the immunoglobulin heavy chain genes (IgH) has demonstrated preferential usage of specific variable (V), diversity (D), and joining (J) genes at different stages of B-cell development and in B-cell malignancies, and this has provided insight into B-cell maturation and selection. Knowledge of the association between rearrangement patterns based on updated databases and clinical characteristics of pediatric acute lymphoblastic leukemia (ALL) is limited. We analyzed 381 IgH sequences identified at presentation in 317 children with B-lineage ALL and assessed the V(H)D(H)J(H) gene utilization profiles. The D(H)J(H)-proximal V(H) segments and the D(H)2 gene family were significantly overrepresented. Only 21% of V(H)-J(H) joinings were potentially productive, a finding associated with a trend toward an increased risk of relapse. These results suggest that physical location at the V(H) locus is involved in preferential usage of D(H)J(H)-proximal V(H) segments whereas D(H) and J(H) segment usage is governed by position-independent molecular mechanisms. Molecular pathophysiology appears relevant to clinical outcome in patients who have only productive rearrangements, and specific rearrangement patterns are associated with differences in the tumor biology of childhood ALL.

LIN28B Activation by PRL-3 Promotes Leukemogenesis and a Stem Cell-like Transcriptional Program in AML

PRL-3 (PTP4A3), a metastasis-associated phosphatase, is also upregulated in patients with acute myeloid leukemia (AML) and is associated with poor prognosis, but the underlying molecular mechanism is unknown. Here, constitutive expression of PRL-3 in human AML cells sustains leukemogenesis in vitro and in vivo Furthermore, PRL-3 phosphatase activity dependently upregulates LIN28B, a stem cell reprogramming factor, which in turn represses the let-7 mRNA family, inducing a stem cell-like transcriptional program. Notably, elevated levels of LIN28B protein independently associate with worse survival in AML patients. Thus, these results establish a novel signaling axis involving PRL-3/LIN28B/let-7, which confers stem cell-like properties to leukemia cells that is important for leukemogenesis.Implications: The current study offers a rationale for targeting PRL-3 as a therapeutic approach for a subset of AML patients with poor prognosis. Mol Cancer Res; 15(3); 294-303. ©2016 AACR.

The emerging roles of exosomes in leukemogeneis

Communication between leukemia cells and their environment is essential for the development and progression of leukemia. Exosomes are microvesicles secreted by many types of cells that contain protein and RNA and mediate intercellular communication. The involvement of exosomes has been demonstrated in the crosstalk between leukemic cells, stromal cells and endothelial cells, consequently promoting the survival of leukemic cells, protection of leukemic cells from the cytotoxic effects of chemotherapeutic drugs, angiogenesis and cell migration. At the same time, exosomes can be used for the detection and monitoring of leukemia, with some advantage over current methods of detection and surveillance. As they are involved in immune response towards leukemic cells, exosomes can also potentially be exploited to augment immunotherapy in leukemia. In this review, we first describe the general characteristics of exosomes and biogenesis of exosomes. We then highlight the emerging role of exosomes in different types of leukemia. Finally, the clinical value of exosomes as biomarkers, in vivo drug carriers and novel exosome-based immunotherapy are discussed.

The pro-metastasis tyrosine phosphatase, PRL-3 (PTP4A3), is a novel mediator of oncogenic function of BCR-ABL in human chronic myeloid leukemia

BACKGROUND

Resistance to tyrosine kinase inhibitors (TKIs) remains a challenge in management of patients with chronic myeloid leukemia (CML). A better understanding of the BCR-ABL signalling network may lead to better therapy.

FINDINGS

Here we report the discovery of a novel downstream target of BCR-ABL signalling, PRL-3 (PTP4A3), an oncogenic tyrosine phosphatase. Analysis of CML cancer cell lines and CML patient samples reveals the upregulation of PRL-3. Inhibition of BCR-ABL signalling either by Imatinib or by RNAi silencing BCR-ABL reduces PRL-3 and increases cleavage of PARP. In contrast, the amount of PRL-3 protein remains constant or even increased in response to Imatinib treatment in drug resistant cells expressing P210 T315I. Finally, analysis with specific shRNA shows PRL-3 involvement in the proliferation and self-renewal of CML cells.

CONCLUSIONS

These data support a role for PRL-3 in BCR-ABL signalling and CML biology and may be a potential therapeutic target downstream of BCR-ABL in TKI resistant mutant cells.

ABT-869, a multi-targeted tyrosine kinase inhibitor, in combination with rapamycin is effective for subcutaneous hepatocellular carcinoma xenograft

BACKGROUND/AIMS

Receptor tyrosine kinase inhibitors (RTKIs) and mTOR inhibitors are potential novel anticancer therapies for HCC. We hypothesized that combination targeted on distinctive signal pathways would provide synergistic therapeutics.

METHODS

ABT-869, a novel RTKI, and rapamycin were investigated in HCC pre-clinical models.

RESULTS

Rapamycin, but not ABT-869, inhibited in vitro growth of Huh7 and SK-HEP-1 HCC cells in a dose dependant manner. However, in subcutaneous Huh7 and SK-HEP-1 xenograft models, either ABT-869 or rapamycin can significantly reduce tumor burden. Combination treatment reduced the tumors to the lowest volume (95+/-20mm(3)), and was significantly better than single agent treatment (p<0.05). Immunohistochemical staining of tumor shows that ABT-869 potently inhibits VEGF in HCC in vivo. In addition, the MAPK signaling pathway has been inhibited by significant inhibition of phosphorylation of p44/42 MAP kinase by ABT-869 in vivo. Rapamycin inhibits phosphorylation of p70 S6 kinase and 4E-BP-1, downstream targets of mTOR, and decreases VEGF. Combination treatment showed synergistic effect on expression levels of p27 in vivo. Dramatic inhibition of neo-angiogenesis by ABT-869 was also demonstrated.

CONCLUSIONS

HCC could potentially be treated with the combination treatment of ABT-869 and rapamycin. Clinical trials on combination therapy are warranted.

Determinants of sensitivity to DZNep induced apoptosis in multiple myeloma cells

The 3-Deazaneplanocin A (DZNep), one of S-adenosylhomocysteine (AdoHcy) hydrolase inhibitors, has shown antitumor activities in a broad range of solid tumors and acute myeloid leukemia. Here, we examined its effects on multiple myeloma (MM) cells and found that, at 500 nM, it potently inhibited growth and induced apoptosis in 2 of 8 MM cell lines. RNA from un-treated and DZNep treated cells was profiled by Affymetrix HG-U133 Plus 2.0 microarray and genes with a significant change in gene expression were determined by significance analysis of microarray (SAM) testing. ALOX5 was the most down-regulated gene (5.8-fold) in sensitive cells and was expressed at low level in resistant cells. The results were corroborated by quantitative RT-PCR. Western-blot analysis indicated ALOX5 was highly expressed only in sensitive cell line H929 and greatly decreased upon DZNep treatment. Ectopic expression of ALOX5 reduced sensitivity to DZNep in H929 cells. Furthermore, down-regulation of ALOX5 by RNA interference could also induce apoptosis in H929. Gene expression analysis on MM patient dataset indicated ALOX5 expression was significantly higher in MM patients compared to normal plasma cells. We also found that Bcl-2 was overexpressed in DZNep insensitive cells, and cotreatment with DZNep and ABT-737, a Bcl-2 family inhibitor, synergistically inhibited growth and induced apoptosis of DZNep insensitive MM cells. Taken together, this study shows one of mechanisms of the DZNep efficacy on MM correlates with its ability to down-regulate the ALOX5 levels. In addition, DZNep insensitivity might be associated with overexpression of Bcl-2, and the combination of ABT-737 and DZNep could synergistically induced apoptosis. These results suggest that DZNep may be exploited therapeutically for a subset of MM.

LEO1 is regulated by PRL-3 and mediates its oncogenic properties in acute myelogenous leukemia

PRL-3, an oncogenic dual-specificity phosphatase, is overexpressed in 50% of acute myelogenous leukemia (AML) and associated with poor survival. We found that stable expression of PRL-3 confers cytokine independence and growth advantage of AML cells. However, how PRL-3 mediates these functions in AML is not known. To comprehensively screen for PRL3-regulated proteins in AML, we performed SILAC-based quantitative proteomics analysis and discovered 398 significantly perturbed proteins after PRL-3 overexpression. We show that Leo1, a component of RNA polymerase II-associated factor (PAF) complex, is a novel and important mediator of PRL-3 oncogenic activities in AML. We described a novel mechanism where elevated PRL-3 protein increases JMJD2C histone demethylase occupancy on Leo1 promoter, thereby reducing the H3K9me3 repressive signals and promoting Leo1 gene expression. Furthermore, PRL-3 and Leo1 levels were positively associated in AML patient samples (N=24; P<0.01). On the other hand, inhibition of Leo1 reverses PRL-3 oncogenic phenotypes in AML. Loss of Leo1 leads to destabilization of the PAF complex and downregulation of SOX2 and SOX4, potent oncogenes in myeloid transformation. In conclusion, we identify an important and novel mechanism by which PRL-3 mediates its oncogenic function in AML.

Synergistic antileukemic effects between ABT-869 and chemotherapy involve downregulation of cell cycle-regulated genes and c-Mos-mediated MAPK pathway

Internal tandem duplications (ITDs) of fms-like tyrosine kinase 3 (FLT3) receptor play an important role in the pathogenesis of acute myeloid leukemia (AML) and represent an attractive therapeutic target. ABT-869 has demonstrated potent effects in AML cells with FLT3-ITDs. Here, we provide further evidence that ABT-869 treatment significantly downregulates cyclins D and E but increases the expression of p21 and p27. ABT-869 induces apoptosis through downregulation of Bcl-xL and upregulation of BAK, BID and BAD. We also evaluate the combinations of ABT-869 and chemotherapy. ABT-869 demonstrates significant sequence-dependent synergism with cytarabine and doxorubicin in cell lines and primary leukemia samples. The optimal combination was validated in MV4-11 xenografts. Low-density array analysis revealed the synergistic interaction involved in downregulation of cell cycle and mitogen-activated protein kinase pathway genes. CCND1 and c-Mos were the most significantly inhibited targets on both transcriptional and translational levels. Treatment with short hairpin RNAs targeting either CCND1 or c-Mos further sensitized MV4-11 cells to ABT-869. These findings suggest that specific pathway genes were further targeted by adding chemotherapy and support the rationale of combination therapy. Thus, a clinical trial using sequence-dependent combination therapy with ABT-869 in AML is warranted.

Aberrant RNA splicing and mutations in spliceosome complex in acute myeloid leukemia

The spliceosome, the cellular splicing machinery, regulates RNA splicing of messenger RNA precursors (pre-mRNAs) into maturation of protein coding RNAs. Recurrent mutations and copy number changes in genes encoding spliceosomal proteins and splicing regulatory factors have tumor promoting or suppressive functions in hematological malignancies, as well as some other cancers. Leukemia stem cell (LSC) populations, although rare, are essential contributors of treatment failure and relapse. Recent researches have provided the compelling evidence that link the erratic spicing activity to the LSC phenotype in acute myeloid leukemia (AML). In this article, we describe the diverse roles of aberrant splicing in hematological malignancies, particularly in AML and their contributions to the characteristics of LSC. We review these promising strategies to exploit the addiction of aberrant spliceosomal machinery for anti-leukemic therapy with aim to eradicate LSC. However, given the complexity and plasticity of spliceosome and not fully known functions of splicing in cancer, the challenges facing the development of the therapeutic strategies targeting RAN splicing are highlighted and future directions are discussed too.

Super Enhancer-Mediated Upregulation of HJURP Promotes Growth and Survival of t(4;14)-Positive Multiple Myeloma

Multiple myeloma is an incurable malignancy with marked clinical and genetic heterogeneity. The cytogenetic abnormality t(4;14) (p16.3;q32.3) confers aggressive behavior in multiple myeloma. Recently, essential oncogenic drivers in a wide range of cancers have been shown to be controlled by super-enhancers (SE). We used chromatin immunoprecipitation sequencing of the active enhancer marker histone H3 lysine 27 acetylation (H3K27ac) to profile unique SEs in t(4;14)-translocated multiple myeloma. The histone chaperone HJURP was aberrantly overexpressed in t(4;14)-positive multiple myeloma due to transcriptional activation by a distal SE induced by the histone lysine methyltransferase NSD2. Silencing of HJURP with short hairpin RNA or CRISPR interference of SE function impaired cell viability and led to apoptosis. Conversely, HJURP overexpression promoted cell proliferation and abrogated apoptosis. Mechanistically, the NSD2/BRD4 complex positively coregulated HJURP transcription by binding the promoter and active elements of its SE. In summary, this study introduces SE profiling as an efficient approach to identify new targets and understand molecular pathogenesis in specific subtypes of cancer. Moreover, HJURP could be a valuable therapeutic target in patients with t(4;14)-positive myeloma. SIGNIFICANCE: A super-enhancer screen in t(4;14) multiple myeloma serves to identify genes that promote growth and survival of myeloma cells, which may be evaluated in future studies as therapeutic targets.

Super-enhancer-driven TOX2 mediates oncogenesis in Natural Killer/T Cell Lymphoma

BACKGROUND

Extranodal natural killer/T-cell lymphoma (NKTL) is an aggressive type of non-Hodgkin lymphoma with dismal outcome. A better understanding of disease biology and key oncogenic process is necessary for the development of targeted therapy. Super-enhancers (SEs) have been shown to drive pivotal oncogenes in various malignancies. However, the landscape of SEs and SE-associated oncogenes remain elusive in NKTL.

METHODS

We used Nano-ChIP-seq of the active enhancer marker histone H3 lysine 27 acetylation (H3K27ac) to profile unique SEs NKTL primary tumor samples. Integrative analysis of RNA-seq and survival data further pinned down high value, novel SE oncogenes. We utilized shRNA knockdown, CRISPR-dCas9, luciferase reporter assay, ChIP-PCR to investigate the regulation of transcription factor (TF) on SE oncogenes. Multi-color immunofluorescence (mIF) staining was performed on an independent cohort of clinical samples. Various function experiments were performed to evaluate the effects of TOX2 on the malignancy of NKTL in vitro and in vivo.

RESULTS

SE landscape was substantially different in NKTL samples in comparison with normal tonsils. Several SEs at key transcriptional factor (TF) genes, including TOX2, TBX21(T-bet), EOMES, RUNX2, and ID2, were identified. We confirmed that TOX2 was aberrantly overexpressed in NKTL relative to normal NK cells and high expression of TOX2 was associated with worse survival. Modulation of TOX2 expression by shRNA, CRISPR-dCas9 interference of SE function impacted on cell proliferation, survival and colony formation ability of NKTL cells. Mechanistically, we found that RUNX3 regulates TOX2 transcription by binding to the active elements of its SE. Silencing TOX2 also impaired tumor formation of NKTL cells in vivo. Metastasis-associated phosphatase PRL-3 has been identified and validated as a key downstream effector of TOX2-mediated oncogenesis.

CONCLUSIONS

Our integrative SE profiling strategy revealed the landscape of SEs, novel targets and insights into molecular pathogenesis of NKTL. The RUNX3-TOX2-SE-TOX2-PRL-3 regulatory pathway may represent a hallmark of NKTL biology. Targeting TOX2 could be a valuable therapeutic intervene for NKTL patients and warrants further study in clinic.

Phosphatase of regenerating liver-3 is regulated by signal transducer and activator of transcription 3 in acute myeloid leukemia

Overexpression of protein-tyrosine phosphatase of regenerating liver 3 (PRL-3) has been identified in about 50% of patients with acute myeloid leukemia (AML). The mechanism of regulation of PRL-3 remains obscure. Signal transducer and activator of transcription 3 (STAT3), a latent transcriptional factor, has also been often found to be activated in AML. We first identified STAT3-consensus-binding sites in the promoter of PRL-3 genes. Then we experimentally validated the direct binding and transcriptional activation. We applied shRNA-mediated knockdown and overexpression approaches in STAT3(-/-) liver cells and leukemic cells to validate the functional regulation of PRL-3 by STAT3. A STAT3 core signature, derived through data mining from publicly available gene expression data, was employed to correlate PRL-3 expression in large AML patient samples. We discovered that STAT3 binds to the -201 to -210 region of PRL-3, which was conserved between human and mouse. Importantly, PRL-3 protein was significantly reduced in mouse STAT3-knockout liver cells compared with STAT3-wild type counterparts, and ectopic expression of STAT3 in these cells led to a pronounced increase in PRL-3 protein. We demonstrated that STAT3 functionally regulated PRL-3, and STAT3 core signature was enriched in AML with high PRL-3 expression. Targeting either STAT3 or PRL-3 reduced leukemic cell viability. Silencing PRL-3 impaired invasiveness and induced leukemic cell differentiation. In conclusion, PRL-3 was transcriptionally regulated by STAT3. The STAT3/PRL-3 regulatory loop contributes to the pathogenesis of AML, and it might represent an attractive therapeutic target for antileukemic therapy.

Synergistic antileukemia effect of genistein and chemotherapy in mouse xenograft model and potential mechanism through MAPK signaling

We investigated the antiproliferative effect of genistein, and its antileukemia effect in combination with cytosine arabinoside (ara-C) in acute myeloid leukemia (AML). Optimal dosage of genistein as single agent and in combination with ara-C was first determined in vitro. Genistein demonstrated a dose- and time-dependent inhibition of cell proliferation, induction of apoptosis, and cell-cycle arrest at G(2)/M phase. Gene-expression profiles revealed mitogen-activated protein kinase (MAPK) signaling as one of the most affected biological pathways. Phosphatidylinositol 3 kinase, protein kinase A, protein kinase C, MAPK kinase 4, KIT, PIM1, and transforming growth factor-beta receptor 1, were significantly downregulated by genistein. To test whether genistein could augment the antiproliferation activity of ara-C, two groups of severe combined immunodeficient mice were inoculated with NB4 and HL-60 cells, respectively, followed by treatment with either genistein or combination of genistein and ara-C. The combination treatment significantly inhibited tumor growth, and improved survival of NB4 (p = 0.0031) and HL-60 (p = 0.0007) xenograft mice. Our present study highlighted the schedule-dependent synergistic antileukemia effect of genistein with chemotherapy in both in vitro and in vivo models. This novel combination could potentially be a promising regimen for treatment of AML.

Myeloma-specific superenhancers affect genes of biological and clinical relevance in myeloma

Multiple myeloma (MM) is an aggressive plasma cell neoplasm characterized by genomic heterogeneity. Superenhancers (SEs) are defined as large clusters of enhancers in close genomic proximity, which regulate genes for maintaining cellular identity and promote oncogenic transcription to which cancer cells highly addicted. Here, we analyzed cis-regulatory elements in MM samples with H3K27ac ChIP-seq, to identify novel SE-associated genes involved in the myeloma pathogenesis. SEs and their associated genes in cancerous tissue were compared with the control samples, and we found SE analysis alone uncovered cell-lineage-specific transcription factors and well-known oncogenes ST3GAL6 and ADM. Using a transcriptional CDK7 inhibitor, THZ1, coupled with H3K27ac ChlP-seq, we identified MAGI2 as a novel SE-associated gene of myeloma cells. Elevated MAGI2 was related to myelomagenesis with gradual increased expression from MGUS, SMM to newly diagnosed and relapsed MM. High prevalence of MAGI2 was also associated with poor survival of MM patients. Importantly, inhibition of the SE activity associated with MAGI2 decreased MAGI2 expression, inhibited cell growth and induced cell apoptosis. Mechanistically, we revealed that the oncogenic transcription factor, MAF, directly bound to the SE region and activated gene transcription. In summary, the discoveries of these acquired SEs-associated genes and the novel mechanism by which they are regulated provide new insights into MM biology and MAGI2-MAF-SE regulatory circuit offer potential novel targets for disease treatment.

In vivo activity of ABT-869, a multi-target kinase inhibitor, against acute myeloid leukemia with wild-type FLT3 receptor

Neoangiogenesis plays an important role in leukemogenesis. We investigated the in vivo anti-leukemic effect of ABT-869 against AML with wild-type FLT3 using RFP transfected HL60 cells with in vivo imaging technology on both the subcutaneous and systemic leukemia xenograft models. ABT-869 showed a five-fold inhibition of tumor growth in comparison with vehicle control. IHC analysis revealed that ABT-869 decreased p-VEGFR1, Ki-67 labeling index, VEGF and remarkably increased apoptotic cells in the xenograft models. ABT-869 also reduced the leukemia burden and prolonged survival. Our study supports the rationale for clinically testing an anti-angiogenesis agent in AML with wild-type FLT3.

Integrative epigenome analysis identifies a Polycomb-targeted differentiation program as a tumor-suppressor event epigenetically inactivated in colorectal cancer

Aberrant DNA hypermethylation in human cancer has been associated with Polycomb target genes in embryonic stem (ES) cells, but a functional link of the Polycomb-targeted differentiation program to tumorigenesis remains to be established. Here, through epigenome analysis correlating DNA hypermethylation in colon cancer with ES cell pluripotency and differentiation, we identified a set of DNA hypermethylated genes in cancer cells that are Polycomb targets strongly associated with ES cell differentiation, including HAND1, a developmental regulator. Intriguingly, HAND1 is silenced in over 90% of human primary colorectal tumors, and re-expression of HAND1 in colon cancer cells induces terminal differentiation, inhibits proliferation and prevents xenograft tumor formation. Moreover, hypermethylated HAND1 has a minimum enrichment of EZH2-H3K27me3 in cancer cells, but becomes EZH2 bound and bivalent upon the loss of DNA methylation, suggesting a sequential gene silencing event during oncogenesis. These findings established a functional role of Polycomb-targeted differentiation program as a tumor-suppressor event epigenetically inactivated in human cancer.