Effects of anti-CD44 monoclonal antibodies on differentiation and apoptosis of human myeloid leukemia cell lines

CD44: a cancer stem cell marker and therapeutic target in leukemia treatment

CD44 is a ubiquitous leukocyte adhesion molecule involved in cell-cell interaction, cell adhesion, migration, homing and differentiation. CD44 can mediate the interaction between leukemic stem cells and the surrounding extracellular matrix, thereby inducing a cascade of signaling pathways to regulate their various behaviors. In this review, we focus on the impact of CD44s/CD44v as biomarkers in leukemia development and discuss the current research and prospects for CD44-related interventions in clinical application.

Immunotherapy in leukaemia

Leukaemia is the common name for a group of malignant diseases of the haematopoietic system with complex classifications and characteristics. Remarkable progress has been made in basic research and preclinical studies for acute leukaemia compared to that of the many other types/subtypes of leukaemia, especially the exploration of the biological basis and application of immunotherapy in acute myeloid leukaemia (AML) and B-cell acute lymphoblastic leukaemia (B-ALL). In this review, we summarize the basic approaches to immunotherapy for leukaemia and focus on the research progress made in immunotherapy development for AML and ALL. Importantly, despite the advances made to date, big challenges still exist in the effectiveness of leukaemia immunotherapy, especially in AML. Therefore, we use AML as an example and summarize the mechanisms of tumour cell immune evasion, describe recently reported data and known therapeutic targets, and discuss the obstacles in finding suitable treatment targets and the results obtained in recent clinical trials for several types of single and combination immunotherapies, such as bispecific antibodies, cell therapies (CAR-T-cell treatment), and checkpoint blockade. Finally, we summarize novel immunotherapy strategies for treating lymphocytic leukaemia and clinical trial results.

CD44-fibrinogen binding promotes bleeding in acute promyelocytic leukemia by in situ fibrin(ogen) deposition

Early haemorrhagic death is still the main obstacle for the successful treatment of acute promyelocytic leukaemia (APL). However, the mechanisms underlying haemostatic perturbations in APL have not been fully elucidated. Here, we report that CD44 on the membrane of APL blasts and NB4 cells ligated bound fibrinogen, resulting in in situ deposition of fibrin and abnormal fibrin distribution. Clots formed by leukaemic cells in response to CD44 and fibrinogen interaction exhibited low permeability and resistance to fibrinolysis. Using flow cytometry and confocal microscopy, we found that CD44 was also involved in platelet and leukaemic cell adhesion. CD44 bound activated platelets but not resting platelets through interaction with P-selectin. APL cell-coated fibrinogen-activated platelets directly induce enhanced procoagulant activity of platelets. In vivo studies revealed that CD44 knockdown shortened bleeding time, increased the level of fibrinogen, and elevated the number of platelets by approximately 2-fold in an APL mouse model. Moreover, CD44 expression on leukaemic cells in an APL mouse model was not only associated with bleeding complications but was also related to the wound healing process and the survival time of APL mice. Collectively, our results suggest that CD44 may be a potential intervention target for preventing bleeding complications in APL.

Necrosulfonamide Selectively Induces DNA Double-Strand Breaks in Acute Myeloid Leukemia Cells

Acute myeloid leukemia (AML) is a heterogeneous hematologic malignancy that causes endless pain for patients and accounts for thousands of deaths worldwide. The development of an effective AML treatment is a topic of ongoing interest. Here, we demonstrated that a pyroptosis inhibitor necrosulfonamide (NSA) can selectively induce highly toxic double-strand breaks and kill AML cells. Mechanistically, reactive oxygen species (ROS) were the key effectors mediating the toxicity of NSA. These results probably indicate that NSA is a novel candidate for the treatment of AML.

CD44 engagement enhances acute myeloid leukemia cell adhesion to the bone marrow microenvironment by increasing VLA-4 avidity

Adhesive properties of leukemia cells shape the degree of organ infiltration and the extent of leukocytosis. CD44 and the integrin VLA-4, a CD49d/CD29 heterodimer, are important factors in progenitor cell adhesion in bone marrow. Here, we report their cooperation in acute myeloid leukemia (AML) by a novel non-classical CD44-mediated way of inside-out VLA-4 activation. In primary AML bone marrow samples from patients and the OCI-AML3 cell line, CD44 engagement by hyaluronan induced inside-out activation of VLA-4 resulting in enhanced leukemia cell adhesion on VCAM-1. This was independent of VLA-4 affinity regulation but based on ligand-induced integrin clustering on the cell surface. CD44-induced VLA-4 activation could be inhibited by the Src family kinase inhibitor PP2 and the multikinase inhibitor midostaurin. As a further consequence, the increased adhesion on VCAM-1 allowed AML cells to bind stromal cells strongly. Thereby, the VLA-4/VCAM-1 interaction promoted activation of Akt, MAPK, NF-kB and mTOR signaling and decreased AML cell apoptosis. Collectively, our investigations provide a mechanistic description of an unusual CD44 function in regulating VLA-4 avidity in AML, enhancing AML cell retention in the supportive bone marrow microenvironment.

Acute Myeloid Leukemia Stem Cells: The Challenges of Phenotypic Heterogeneity

Patients suffering from acute myeloid leukemia (AML) show highly heterogeneous clinical outcomes. Next to variabilities in patient-specific parameters influencing treatment decisions and outcome, this is due to differences in AML biology. In fact, different genetic drivers may transform variable cells of origin and co-exist with additional genetic lesions (e.g., as observed in clonal hematopoiesis) in a variety of leukemic (sub)clones. Moreover, AML cells are hierarchically organized and contain subpopulations of more immature cells called leukemic stem cells (LSC), which on the cellular level constitute the driver of the disease and may evolve during therapy. This genetic and hierarchical complexity results in a pronounced phenotypic variability, which is observed among AML cells of different patients as well as among the leukemic blasts of individual patients, at diagnosis and during the course of the disease. Here, we review the current knowledge on the heterogeneous landscape of AML surface markers with particular focus on those identifying LSC, and discuss why identification and targeting of this important cellular subpopulation in AML remains challenging.

Facts and Challenges in Immunotherapy for T-Cell Acute Lymphoblastic Leukemia

T-cell acute lymphoblastic leukemia (T-ALL), a T-cell malignant disease that mainly affects children, is still a medical challenge, especially for refractory patients for whom therapeutic options are scarce. Recent advances in immunotherapy for B-cell malignancies based on increasingly efficacious monoclonal antibodies (mAbs) and chimeric antigen receptors (CARs) have been encouraging for non-responding or relapsing patients suffering from other aggressive cancers like T-ALL. However, secondary life-threatening T-cell immunodeficiency due to shared expression of targeted antigens by healthy and malignant T cells is a main drawback of mAb—or CAR-based immunotherapies for T-ALL and other T-cell malignancies. This review provides a comprehensive update on the different immunotherapeutic strategies that are being currently applied to T-ALL. We highlight recent progress on the identification of new potential targets showing promising preclinical results and discuss current challenges and opportunities for developing novel safe and efficacious immunotherapies for T-ALL.

Location First: Targeting Acute Myeloid Leukemia Within Its Niche

Despite extensive research and development of new treatments, acute myeloid leukemia (AML)-backbone therapy has remained essentially unchanged over the last decades and is frequently associated with poor outcomes. Eradicating the leukemic stem cells (LSCs) is the ultimate challenge in the treatment of AML. Emerging evidence suggests that AML remodels the bone marrow (BM) niche into a leukemia-permissive microenvironment while suppressing normal hematopoiesis. The mechanism of stromal-mediated protection of leukemic cells in the BM is complex and involves many adhesion molecules, chemokines, and cytokines. Targeting these factors may represent a valuable approach to complement existing therapies and overcome microenvironment-mediated drug resistance. Some strategies for dislodging LSCs and leukemic blasts from their protective niche have already been tested in patients and are in different phases of the process of clinical development. Other strategies, such as targeting the stromal cells remodeling processes, remain at pre-clinical stages. Development of humanized xenograft mouse models, which overcome the mismatch between human leukemia cells and the mouse BM niche, is required to generate physiologically relevant, patient-specific human niches in mice that can be used to unravel the role of human AML microenvironment and to carry out preclinical studies for the development of new targeted therapies.

Anti-CD44 DNA Aptamers Selectively Target Cancer Cells

CD44 is a type I transmembrane glycoprotein interacting with a number of extracellular components, including hyaluronic acid (HA). CD44-HA axis is involved in a variety of processes, including adhesion, migration, differentiation, trafficking, and others. CD44 is overexpressed in several cancers where binding of HA induces signal transduction leading to activation of antiapoptotic proteins and factors linked to drug resistance. As such, CD44 has been implicated in cancer growth, progression, and metastasis. It has been convincingly demonstrated that blocking CD44-HA interaction decreases cancer cell survival and metastasis. In this study, using in vitro selection, we have developed DNA aptamers recognizing a HA-binding domain of CD44 with high affinity and specificity. The aptamers bind to CD44 with nanomolar affinities and efficiently inhibit the growth of leukemic cancer cells characterized by high expression of CD44. The selectivity is demonstrated by an irrelevant effect on cells characterized by low CD44 levels. The obtained aptamers broaden the existing landscape of potential approaches to the development of antitumor strategies based on inhibition of the CD44 axis.

Follistatin is a novel therapeutic target and biomarker in FLT3/ITD acute myeloid leukemia

Internal tandem duplication of Fms-like tyrosine kinase 3 (FLT3/ITD) occurs in about 30% of acute myeloid leukemia (AML) and is associated with poor response to conventional treatment and adverse outcome. Here, we reported that human FLT3/ITD expression led to axis duplication and dorsalization in about 50% of zebrafish embryos. The morphologic phenotype was accompanied by ectopic expression of a morphogen follistatin (fst) during early embryonic development. Increase in fst expression also occurred in adult FLT3/ITD-transgenic zebrafish, Flt3/ITD knock-in mice, and human FLT3/ITD AML cells. Overexpression of human FST317 and FST344 isoforms enhanced clonogenicity and leukemia engraftment in xenotransplantation model via RET, IL2RA, and CCL5 upregulation. Specific targeting of FST by shRNA, CRISPR/Cas9, or antisense oligo inhibited leukemic growth in vitro and in vivo. Importantly, serum FST positively correlated with leukemia engraftment in FLT3/ITD AML patient-derived xenograft mice and leukemia blast percentage in primary AML patients. In FLT3/ITD AML patients treated with FLT3 inhibitor quizartinib, serum FST levels correlated with clinical response. These observations supported FST as a novel therapeutic target and biomarker in FLT3/ITD AML.

The role of cell adhesion in hematopoiesis and leukemogenesis

The cells of the bone marrow microenvironment are emerging as important contributors and regulators of normal hematopoiesis. This microenvironment is perturbed during leukemogenesis, and evidence points toward a bidirectional communication between leukemia cells and the normal cells of the bone marrow, mediated by direct cell-cell contact as well as soluble factors. These interactions are increasingly appreciated to play a role in leukemogenesis and possibly in resistance to chemotherapy. In fact, several compounds that specifically target the bone marrow microenvironment, including inhibitors of cell adhesion, are being tested as adjuncts to leukemia therapy.

Immunotherapy in acute myeloid leukemia and myelodysplastic syndromes: The dawn of a new era?

Immunotherapy has revolutionized therapy in both solid and liquid malignancies. The ability to cure acute myeloid leukemia (AML) and myelodysplastic syndromes (MDS) with an allogeneic hematopoietic stem cell transplant (HSCT) is proof of concept for the application of immunotherapy in AML and MDS. However, outside of HSCT, only the anti-CD33 antibody drug conjugate gemtuzumab ozogamicin is currently approved as an antibody-targeted therapy for AML. Several avenues of immunotherapeutic drugs are currently in different stages of clinical development. Here, we review recent advances in antibody-based therapy, immune checkpoint inhibitors, vaccines and adoptive cell-based therapy for patients with AML and MDS. First, we discuss different antibody constructs. Immune checkpoint inhibitors targeting cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), programmed cell death protein-1 (PD-1) and CD47 as well as peptide, dendritic cell and dendritic/AML cell-based vaccines are reviewed next. Lastly, adoptive cell-based therapy including chimeric antigen receptor (CAR)-T cell and NK cell therapy is discussed.

CD44 is a RAS/STAT5-regulated invasion receptor that triggers disease expansion in advanced mastocytosis

The Hermes receptor CD44 is a multifunctional adhesion molecule that plays an essential role in the homing and invasion of neoplastic stem cells in various myeloid malignancies. Although mast cells (MCs) reportedly express CD44, little is known about the regulation and function of this receptor in neoplastic cells in systemic mastocytosis (SM). We found that clonal CD34⁺/CD38^- stem cells, CD34⁺/CD38⁺ progenitor cells, and CD117⁺⁺/CD34^- MCs invariably express CD44 in patients with indolent SM (ISM), SM with an associated hematologic neoplasm, aggressive SM, and MC leukemia (MCL). In addition, all human MCL-like cell lines examined (HMC-1, ROSA, and MCPV-1) displayed cytoplasmic and cell-surface CD44. We also found that expression of CD44 in neoplastic MCs depends on RAS-MEK and STAT5 signaling and increases with the aggressiveness of SM. Correspondingly, higher levels of soluble CD44 were measured in the sera of patients with advanced SM compared with ISM or cutaneous mastocytosis and were found to correlate with overall and progression-free survival. To investigate the functional role of CD44, a xenotransplantation model was employed using severe combined immunodeficient (SCID) mice, HMC-1.2 cells, and a short hairpin RNA (shRNA) against CD44. In this model, the shRNA-mediated knockdown of CD44 resulted in reduced MC expansion and tumor formation and prolonged survival in SCID mice compared with HMC-1.2 cells transduced with control shRNA. Together, our data show that CD44 is a RAS-MEK/STAT5-driven MC invasion receptor that correlates with the aggressiveness of SM. Whether CD44 can serve as therapeutic target in advanced SM remains to be determined in forthcoming studies.

New synergistic combinations of differentiation-inducing agents in the treatment of acute promyelocytic leukemia cells

Acute promyelocytic leukemia (APL) was considered to be one of the most lethal forms of leukemia in adults before the introduction of the vitamin A metabolite all-trans retinoic acid (ATRA). Surprisingly, it has been confirmed that FICZ (6-Formylindolo (3, 2-b) carbazole) enhances ATRA-induced differentiation. Moreover, a number of studies have demonstrated that anti CD44 monoclonal antibody (mAb) induces to bring back differentiation blockage the leukemic stem cells. The level of differentiation markers including CD11b and CD11c in NB4 cells was assessed by flow cytometry. The induction of apoptosis was also evaluated. We estimated the induction potential of a triple compound of ATRA-FICZ, anti-CD44 maps. The cells showed the gradually increased expression levels of CD11b and CD11c. A mixture of a "CD44 mAb, ATRA and FICZ effectively promoted granulocytic maturation resulting in increased rates of apoptosis. The differences in expression of CD11b and CD11c at 5 μg/ml and 10 μg/ml were significant. These phenomena were highest at 10 μg/ml CD44 mAb concentrations. Synergistic induction differentiation and apoptosis of APL cells by using a co-treatment with novel triple compound are more effective for eradicating blasts and controlling the metastasis. Our results show that the addition of anti-CD44 mAb improves "ATRA-FICZ"-induced differentiation and has potential to reduce usual chemotherapy based treatments. Taken together, this compound may lead to novel clinical applications of differentiation-based approaches for APL and other types of leukemia. Further clinical studies would be recommended to clarify the clinical efficacy.

Phase I clinical study of RG7356, an anti-CD44 humanized antibody, in patients with acute myeloid leukemia

RG7356, a recombinant anti-CD44 immunoglobulin G1 humanized monoclonal antibody, inhibits cell adhesion and has been associated with macrophage activation in preclinical models. We report results of a phase I dose-escalation study of RG7356 in relapsed/refractory acute myeloid leukemia (AML).Eligible patients with refractory AML, relapsed AML after induction chemotherapy, or previously untreated AML not eligible for intensive chemotherapy were enrolled and received intravenous RG7356 at dosages ≤ 2400 mg every other week or ≤ 1200 mg weekly or twice weekly; dose escalation started at 300 mg.Forty-four patients (median age, 69 years) were enrolled. One dose-limiting toxicity occurred (grade 3 hemolysis exacerbation) after one 1200 mg dose (twice-weekly cohort). The majority of adverse events were mild/moderate. Infusion-related reactions occurred in 64% of patients mainly during cycle 1. Two patients experienced grade 3 drug-induced aseptic meningitis. Pharmacokinetics increased supraproportionally, suggesting a target-mediated drug disposition (TMDD) at ≥ 1200 mg. Two patients achieved complete response with incomplete platelet recovery or partial response, respectively. One patient had stable disease with hematologic improvement.RG7356 was generally safe and well tolerated. Maximum tolerated dose was not reached, but saturation of TMDD was achieved. The recommended dose for future AML evaluations is 2400 mg every other week.

Therapeutic antibodies against cancer stem cells: a promising approach

Monoclonal antibodies have been extensively used to treat malignancy along with routine chemotherapeutic drugs. Chemotherapy for metastatic cancer has not been successful in securing long-term remission of disease. This is in part due to the resistance of cancer cells to drugs. One aspect of the drug resistance is the inability of conventional drugs to eliminate cancer stem cells (CSCs) which often constitute less than 1-2% of the whole tumor. In some tumor types, it is possible to identify these cells using surface markers. Monoclonal antibodies targeting these CSCs are an attractive option for a new therapeutic approach. Although administering antibodies has not been effective, when combined with chemotherapy they have proved synergistic. This review highlights the potential of improving treatment efficacy using functional antibodies against CSCs, which could be combined with chemotherapy in the future.

Opposing roles of ICAT and Wnt/β-catenin signaling in NSC67657-induced monocytic differentiation

NSC67657 is a new steroid drug that induces monocytic differentiation of acute myeloid leukemia cells. Here, we demonstrate that NSC67657 has opposing effects on expression of downstream targets of inhibitor of β-catenin and TCF (ICAT) and Wnt signaling in HL60 cells. ICAT binds to β-catenin, and this interaction is further increased in NSC67657-differentiated cells. ICAT overexpression decreases expression of Wnt downstream targets and increases sensitivity of HL60 cells to NSC67657, while ICAT silencing increases Wnt signaling and delays the NSC67657-induced cell differentiation. In addition, pharmacological inhibition of Wnt/β-catenin signaling increases the NSC67657-induced cell differentiation, while activation of Wnt/β-catenin signaling inhibits the differentiation, indicating Wnt/β-catenin signaling inhibits NSC67657-induced monocytic differentiation of HL60 cells. Our data demonstrate the opposing roles of ICAT and Wnt signaling in the NSC67657-induced monocytic differentiation, and suggest that ICAT and Wnt signaling may serve as therapeutic targets for leukemia chemotherapy.

Development of high-affinity monoclonal antibody using CD44 overexpressed cells as a candidate for targeted immunotherapy and diagnosis of acute myeloid leukemia

AIM

CD44s antigens have been suggested as an efficient biomarker for cancer stem cells. Current study aimed to develop a hybridoma that producing a high affinity murine anti-human CD44 monoclonal antibody for early diagnostic laboratory tests of some cancer.

MATERIALS AND METHODS

To make hybridoma against CD44, mice were immunized with MDA-MB-468 cells. Resulted hybridomas using three culture media were screened by indirect ELISA, then cloned by limiting dilution, and isotype was determined after obtaining ascitic fluid and antibody purification.

RESULTS

We obtained a stable secreting clone, capable of secreting a high-affinity monoclonal antibody against CD44 protein, IgG2a kappa, with the affinity of 5.4 × 10-8 M without cross-reactivity.

CONCLUSION

We could establish a hybridoma in a native form. This stable and high-affinity anti-CD44 mAb has a potential for diagnostic procedures and laboratory research. Thus, it could be exploited as a suitable tool for target-specific diagnosis and even treatment in several cancers.

Hyaluronan as a therapeutic target in human diseases

Accumulation and turnover of extracellular matrix is a hallmark of tissue injury, repair and remodeling in human diseases. Hyaluronan is a major component of the extracellular matrix and plays an important role in regulating tissue injury and repair, and controlling disease outcomes. The function of hyaluronan depends on its size, location, and interactions with binding partners. While fragmented hyaluronan stimulates the expression of an array of genes by a variety of cell types regulating inflammatory responses and tissue repair, cell surface hyaluronan provides protection against tissue damage from the environment and promotes regeneration and repair. The interactions of hyaluronan and its binding proteins participate in the pathogenesis of many human diseases. Thus, targeting hyaluronan and its interactions with cells and proteins may provide new approaches to developing therapeutics for inflammatory and fibrosing diseases. This review focuses on the role of hyaluronan in biological and pathological processes, and as a potential therapeutic target in human diseases.

Targeting CD44 as a novel therapeutic approach for treating pancreatic cancer recurrence

Pancreatic ductal adenocarcinoma (PDAC) is an extraordinarily lethal disease, which, despite a more or less efficient chemotherapeutic treatment, systematically displays a rapid and uncontrolled progression towards a fatal recurrence. Determining which cells give rise to such tumor recurrence is thus crucial before an improved therapeutics outcome can be envisaged for patients with PDAC. In this regard, we recently reported that following a standard chemotherapy for PDAC, a heterogeneous subpopulation of CD44+ cells proliferates and is responsible for tumor recurrence, as shown by almost all recurrent tumor cells becoming CD44+. We designed a strategy to eliminate these cells based on a weekly administration of an anti-CD44 monoclonal antibody to human PDAC-derived xenografts in mice. We demonstrate that xenografts, which were unresponsive to gemcitabine treatment, are however sensitive to this strategy. In conclusion, CD44 represents an efficient therapeutic target in patients with recurrent PDAC.

Monoclonal antibodies against human cancer stem cells

Cancer stem cells (CSCs) are a subpopulation of tumor cells that display self-renewal and tumor initiation capacity and the ability to give rise to the heterogenous lineages of cancer cells that comprise the tumor. CSCs exhibit intrinsic mechanisms of resistance to modern cancer therapeutics, allowing them to survive current cancer therapies and to initiate tumor recurrence and metastasis. Various cell surface and transmembrane proteins expressed by CSCs, including CD44, CD47, CD123, EpCAM (CD326), CD133, IGF receptor I, and proteins of the Notch and Wnt signaling pathways have been identified. Recently, monoclonal antibodies and antibody constructs raised against these CSC proteins have shown efficacy against CSCs in human cancer xenograft mice, and some of them have demonstrated antitumor activity in clinical studies. Since current cancer therapies fail to eliminate CSCs, leading to cancer recurrence and progression, selective targeting of CSCs with monoclonal antibodies and antibody constructs may represent a novel therapeutic strategy against cancer.

CD44 regulates pancreatic cancer invasion through MT1-MMP

Pancreatic cancer is one of the deadliest human malignancies due to its early metastatic spread and resistance to therapy. The mechanisms regulating pancreatic cancer metastasis are so far poorly understood. Here, using both in vitro and in vivo approaches, it is demonstrated that CD44, a transmembrane glycoprotein expressed on a subset of pancreatic cancer cells, is required for the induction of epithelial-mesenchymal transition (EMT) and the activation of an invasive program in pancreatic cancer. Mechanistically, the transcription factor Snail1 (SNAI1), a regulator of the EMT program, is a downstream target of CD44 in primary pancreatic cancer cells and regulates membrane bound metalloproteinase (MMP14/MT1-MMP) expression. In turn, MT1-MMP expression is required for pancreatic cancer invasion. Thus, these data establish the CD44-Snail-MMP axis as a key regulator of the EMT program and of invasion in pancreatic cancer.

IMPLICATIONS

This study sets the stage for CD44 and MT1-MMP as therapeutic targets in pancreatic cancer, for which small molecule or biologic inhibitors are available. Visual Overview: http://mcr.aacrjournals.org/content/early/2014/09/10/1541-7786.MCR-14-0076/F1.large.jpg.

MTI-101 (cyclized HYD1) binds a CD44 containing complex and induces necrotic cell death in multiple myeloma

Our laboratory recently reported that treatment with the d-amino acid containing peptide HYD1 induces necrotic cell death in multiple myeloma cell lines. Because of the intriguing biological activity and promising in vivo activity of HYD1, we pursued strategies for increasing the therapeutic efficacy of the linear peptide. These efforts led to a cyclized peptidomimetic, MTI-101, with increased in vitro activity and robust in vivo activity as a single agent using two myeloma models that consider the bone marrow microenvironment. MTI-101 treatment similar to HYD1 induced reactive oxygen species, depleted ATP levels, and failed to activate caspase-3. Moreover, MTI-101 is cross-resistant in H929 cells selected for acquired resistance to HYD1. Here, we pursued an unbiased chemical biology approach using biotinylated peptide affinity purification and liquid chromatography/tandem mass spectrometry analysis to identify binding partners of MTI-101. Using this approach, CD44 was identified as a predominant binding partner. Reducing the expression of CD44 was sufficient to induce cell death in multiple myeloma cell lines, indicating that multiple myeloma cells require CD44 expression for survival. Ectopic expression of CD44s correlated with increased binding of the FAM-conjugated peptide. However, ectopic expression of CD44s was not sufficient to increase the sensitivity to MTI-101-induced cell death. Mechanistically, we show that MTI-101-induced cell death occurs via a Rip1-, Rip3-, or Drp1-dependent and -independent pathway. Finally, we show that MTI-101 has robust activity as a single agent in the SCID-Hu bone implant and 5TGM1 in vivo model of multiple myeloma.

Functional polymorphisms in the CD44 gene and acute myeloid leukemia cancer risk in a Chinese population

CD44 is such one adhesion molecule that mediates interactions between acute myeloid leukemia (AML) cells and stromal. It has been demonstrated that CD4 plays a critical role in AML development. However, studies of functional single nucleotide polymorphisms (SNPs) in CD44 gene have not touched upon AML. This case-control study probed the contribution of functional SNPs in CD44 gene to AML susceptibility in eastern Chinese population. Five representative SNPs of CD44 (rs10836347C>T, rs13347C>T, rs1425802A>G, rs11821102G>A, rs713330T>C) were opted and genotyped in 421 AML patients and 461 healthy subjects and the association with risk of AML was estimated by logistic regression. Moreover, the potential role of rs13347C > T in AML was further explored. Compared with the rs13347CC genotype, CT carriers had a significant increase in AML susceptibility (adjusted odds ratio [OR] = 1.76; 95% confidence interval [CI] = 1.32-2.34), TT carriers had a further increased risk of AML (OR = 2.67; 95% CI = 1.69-4.21). Furthermore, our transient transfection assay and Western blot results demonstrated that the presence of rs13347T allele led to more CD44 expression. Yet, there exists no significant difference in genotype frequencies of the other four sites between cases and controls. Above findings suggest that rs13347C>T in 3'UTR of CD44 may be a genetic modifier for developing AML.

Development of a novel treatment for leukemia directed at tumor-associated mRNA splicing

This report describes a novel approach to cancer therapy that targets genes that are preferentially alternatively spliced and expressed in leukemia. We developed CD44v6 and CD44v8 splicing constructs fused with GFP or a humanized fragment of Pseudomonas aeruginosa exotoxin A (hPE24). Transfection of K562 leukemia cells with the GFP-linked splicing constructs led to subsequent production of detectable levels of GFP. Transfection of K562 cells with the hPE24-linked splicing constructs led to significant reduction of cell viability and an increase in the induction of apoptosis. Normal human PBMCs were unaffected by following transfection with these constructs.

CXCR4 chemokine receptor signaling induces apoptosis in acute myeloid leukemia cells via regulation of the Bcl-2 family members Bcl-XL, Noxa, and Bak

The CXCR4 chemokine receptor promotes survival of many different cell types. Here, we describe a previously unsuspected role for CXCR4 as a potent inducer of apoptosis in acute myeloid leukemia (AML) cell lines and a subset of clinical AML samples. We show that SDF-1, the sole ligand for CXCR4, induces the expected migration and ERK activation in the KG1a AML cell line transiently overexpressing CXCR4, but ERK activation did not lead to survival. Instead, SDF-1 treatment led via a CXCR4-dependent mechanism to apoptosis, as evidenced by increased annexin V staining, condensation of chromatin, and cleavage of both procaspase-3 and PARP. This SDF-1-induced death pathway was partially inhibited by hypoxia, which is often found in the bone marrow of AML patients. SDF-1-induced apoptosis was inhibited by dominant negative procaspase-9 but not by inhibition of caspase-8 activation, implicating the intrinsic apoptotic pathway. Further analysis showed that this pathway was activated by multiple mechanisms, including up-regulation of Bak at the level of mRNA and protein, stabilization of the Bak activator Noxa, and down-regulation of antiapoptotic Bcl-XL. Furthermore, adjusting expression levels of Bak, Bcl-XL, or Noxa individually altered the level of apoptosis in AML cells, suggesting that the combined modulation of these family members by SDF-1 coordinates their interplay to produce apoptosis. Thus, rather than mediating survival, SDF-1 may be a means to induce apoptosis of CXCR4-expressing AML cells directly in the SDF-1-rich bone marrow microenvironment if the survival cues of the bone marrow are disrupted.

Extranodal Nasal NK/T-Cell Lymphoma: A Rare Oral Presentation and FASN, CD44 and GLUT-1 Expression

Extranodal natural killer (NK)/T-cell lymphoma is an aggressive malignant tumor with distinctive clinicopathological features, characterized by vascular invasion and destruction, prominent necrosis, cytotoxic lymphocyte phenotype and a strong association with Epstein-Barr virus. Here is reported an extranodal nasal NK/T-cell lymphoma case, involving the maxillary sinus, floor of the orbit, and interestingly extending to the oral cavity through the alveolar bone and buccal mucosa, preserving the palate, leading to a primary misdiagnosis of aggressive periodontal disease. Moreover, this work investigated for the first time the immunohistochemical expression of fatty acid synthase (FASN) and glucose transporter 1 (GLUT-1) proteins in this neoplasia. FASN showed strong cytoplasmatic expression in the neoplastic cells, whereas GLUT-1 and CD44 were negative. These findings suggest that the expression of FASN and the loss of CD44 might be involved in the pathogenesis of the extranodal nasal NK/T-cell lymphoma, and that GLUT-1 may not participate in the survival adaptation of the tumor cells to the hypoxic environment. Further studies with larger series are required to confirm these initial results.

CD44 regulates the apoptotic response and promotes disease development in chronic lymphocytic leukemia

The cell-surface glycoprotein CD44 is expressed in chronic lymphocytic leukemia (CLL), but its functional role in this disease is poorly characterized. We therefore investigated the contribution of CD44 to CLL in a murine disease model, the Eµ-TCL1 transgenic mouse, and in CLL patients. Surface CD44 increased during murine CLL development. CD44 expression in human CLL was induced by stimulation with interleukin 4/soluble CD40 ligand and by stroma cell contact. Engagement of CD44 by its natural ligands, hyaluronic acid or chondroitin sulfate, protected CLL cells from apoptosis, while anti-CD44 small interfering RNAs impaired tumor cell viability. Deletion of CD44 during TCL1-driven murine leukemogenesis reduced the tumor burden in peripheral blood and spleen and led to a prolonged overall survival. The leukemic cells from these CD44 knockout animals revealed lower levels of antiapoptotic MCL1, a higher propensity to apoptosis, and a diminished B-cell receptor kinase response. The inhibitory anti-CD44 antibodies IM7 and A3D8 impaired the viability of CLL cells in suspension cultures, in stroma contact models, and in vivo via MCL1 reduction and by effector caspase activation. Taken together, CD44 expression in CLL is mediated by the tumor microenvironment. As a coreceptor, CD44 promotes leukemogenesis by regulating stimuli of MCL1 expression. Moreover, CD44 can be addressed therapeutically in CLL by specific antibodies.

Dengue virus enhances thrombomodulin and ICAM-1 expression through the macrophage migration inhibitory factor induction of the MAPK and PI3K signaling pathways

Dengue virus (DV) infections cause mild dengue fever (DF) or severe life-threatening dengue hemorrhagic fever (DHF). The mechanisms that cause hemorrhage in DV infections remain poorly understood. Thrombomodulin (TM) is a glycoprotein expressed on the surface of vascular endothelial cells that plays an important role in the thrombin-mediated activation of protein C. Prior studies have shown that the serum levels of soluble TM (sTM) and macrophage migration inhibitory factor (MIF) are significantly increased in DHF patients compared to levels in DF patients or normal controls. In this study, we investigated how MIF and sTM concentrations are enhanced in the plasma of DHF patients and the potential effect of MIF on coagulation through its influence on two factors: thrombomodulin (TM) and intercellular adhesion molecule-1 (ICAM-1) in endothelial cells and monocytes. Recombinant human macrophage migration inhibitory factor (rMIF) was used to treat monocytic THP-1 cells and endothelial HMEC-1 cells or primary HUVEC cells. The subsequent expression of TM and ICAM-1 was assessed by immunofluorescent staining and flow cytometry analysis. Additionally, the co-incubation of THP-1 cells with various cell signaling pathway inhibitors was used to determine the pathways through which MIF mediated its effect. The data provided evidence that severe DV infections induce MIF expression, which in turn stimulates monocytes or endothelial cells to express TM and ICAM-1 via the Erk, JNK MAPK and the PI3K signaling pathways, supporting the idea that MIF may play an important role as a regulator of coagulation.

CD44 ligation with A3D8 antibody induces apoptosis in acute myeloid leukemia cells through binding to CD44s and clustering lipid rafts

CD44 is a cell surface antigen expressed on acute myeloid leukemia cells and is used as a marker to isolate leukemia stem cells. CD44 ligation with the antibody A3D8 has been found to induce apoptosis in human acute promyelocytic leukemia (APL) cells via activation of caspase-8. The mechanism of A3D8-induced caspase-8 activation was studied in APL NB4 cells. A3D8 induces lipid raft clustering which causes Fas aggregation as determined with a confocal microscope. A3D8-induced apoptosis is abrogated by the lipid raft disrupting agent methyl-β-cyclodextrin and the caspase-8 inhibitor Z-IETD-fmk. Western blot analysis reveals that A3D8 binds to the standard form of CD44 (CD44s). HL-60 cells without detectable CD44s protein are not responsive to A3D8-induced apoptosis. SKNO-1 cells containing higher level of CD44s protein are more sensitive to A3D8-induced apoptosis than NB4 cells. These results indicate that A3D8 induces apoptosis in leukemia cells through caspase-8 activation by binding to CD44s protein and inducing lipid raft clustering.

Mobilization of hematopoietic stem and leukemia cells

HSC mobilization is an essential homeostatic process during inflammation and for the maintenance of hematopoietic progenitors. It has been exploited for the therapeutic application of HSC transplantation. Recent evidence suggests that leukemic cells share surface molecules in common with stem cells and may be mobilized under similar conditions. This effect could be used for therapeutic interventions. In this review, we will provide evidence showing that leukemia cells and stem cells traffic similarly and may share a common niche. Studies are discussed comparing and contrasting the mechanism of normal stem cells and leukemic cell mobilization through the CXCR4/CXCL12 axis and other key intermediaries.

Cancer stem cells: the development of new cancer therapeutics

INTRODUCTION

Cancer stem cells (CSCs) are a subpopulation of tumor cells with indefinite proliferative potential that drive the growth of tumors. CSCs seem to provide a suitable explanation for several intriguing aspects of cancer pathophysiology.

AREAS COVERED

An explosion of therapeutic options for cancer treatment that selectively target CSCs has been recorded in the recent years. These include the targeting of cell-surface proteins, various activated signalling pathways, different molecules of the stem cell niche and various drug resistance mechanisms. Importantly, approaching cancer research by investigating the pathogenesis of these intriguing cancer cells is increasing the knowledge of the pathophysiology of the disease, emphasizing certain molecular mechanisms that have been partially neglected.

EXPERT OPINION

The characterization of the molecular phenotype of these cancer stem-like cells, associated with an accurate definition of their typical derangement in cell differentiation, can represent a fundamental advance in terms of diagnosis and therapy of cancer. Preliminary results seem to be promising but further studies are required to define the therapeutic index of this new anticancer treatment. Moreover, understanding the pathogenetic mechanisms of CSCs can expand the therapeutic applications of normal adult stem cells by reducing the risk of uncontrolled tumorigenic stem cell differentiation.

CD44 in hematological neoplasias

The CD44 protein family spans a large group of transmembrane glycoproteins acquired by alternative splicing and post-translational modifications. The great heterogeneity in molecular structure is reflected in its various important functions: CD44 mediates (1) interaction between cell and extracellular matrix, (2) signal submission, e.g., by acting as co-receptor for membrane-spanning receptor tyrosine kinases or by association with intracellular molecules initiating several signaling pathways, and (3) anchor function connecting to the cytoskeleton via the ezrin-radixin-moesin protein family. The expression pattern of the different CD44 isoforms display strong variations dependent on cell type, state of activation, and differentiation stage. In hematopoietic cells, CD44 mediates interaction of progenitor cells and bone marrow stroma during hematopoiesis, regulates maturation, and activation-induced cell death in T cells, influences neutrophil and macrophage migration as well as cytokine production, and participates in lymphocyte extravasation and migration. CD44 is involved in development and progress of hematological neoplasias by enhancement of apoptotic resistance, invasiveness, as well as regulation of bone marrow homing, and mobilization of leukemia-initiating cells into the peripheral blood. Thereby altered CD44 expression functions as marker for worse prognosis in most hematological malignancies. Additionally, CD44 expression levels can be used to distinguish between different hematological neoplasias and subtypes. Concerning new treatment strategies, CD44 displays promising potential either by direct targeting of CD44 expressed on the malignant cells or reversing an acquired resistance to primary treatment mediated through altered CD44 expression. The former can be achieved by antibody or hyaluronan-based immunotherapy.

Amelioration of murine immune thrombocytopenia by CD44 antibodies: a potential therapy for ITP?

To explore the potential for monoclonal antibodies as a treatment for immune thrombocytopenia (ITP) and to further explore their mechanisms of action, we tested 8 monoclonal CD44 antibodies in murine ITP and found 4 antibodies that could successfully ameliorate ITP; 2 of these antibodies function at a full 3-log fold lower dosage compared with IVIg. Further characterization of the 2 most successful antibodies (5035–41.1D and KM114) demonstrated that, similar to IVIg: (1) the presence of the inhibitory IgG receptor FcγRIIB was required for their ameliorative function, (2) complement-deficient mice responded to anti-CD44 treatment, and (3) human transgenic FcγRIIA-expressing mice also responded to the CD44 therapeutic modality. Dissimilar to IVIg, the Fc portion of the CD44 antibody was not required. These data demonstrate that CD44 antibodies can function therapeutically in murine ITP and that they could potentially provide a very-low-dose recombinant therapy for the amelioration of human ITP.

Epigenetic regulation of CD44 in Hodgkin and non-Hodgkin lymphoma

Background

Epigenetic inactivation of tumor suppressor genes (TSG) by promoter CpG island hypermethylation is a hallmark of cancer. To assay its extent in human lymphoma, methylation of 24 TSG was analyzed in lymphoma-derived cell lines as well as in patient samples.

Methods

We screened for TSG methylation using methylation-specific multiplex ligation-dependent probe amplification (MS-MLPA) in 40 lymphoma-derived cell lines representing anaplastic large cell lymphoma, Burkitt lymphoma (BL), diffuse large B-cell lymphoma (DLBCL), follicular lymphoma (FL), Hodgkin lymphoma and mantle cell lymphoma (MCL) as well as in 50 primary lymphoma samples. The methylation status of differentially methylated CD44 was verified by methylation-specific PCR and bisulfite sequencing. Gene expression of CD44 and its reactivation by DNA demethylation was determined by quantitative real-time PCR and on the protein level by flow cytometry. Induction of apoptosis by anti-CD44 antibody was analyzed by annexin-V/PI staining and flow cytometry.

Results

On average 8 ± 2.8 of 24 TSG were methylated per lymphoma cell line and 2.4 ± 2 of 24 TSG in primary lymphomas, whereas 0/24 TSG were methylated in tonsils and blood mononuclear cells from healthy donors. Notably, we identified that CD44 was hypermethylated and transcriptionally silenced in all BL and most FL and DLBCL cell lines, but was usually unmethylated and expressed in MCL cell lines. Concordant results were obtained from primary lymphoma material: CD44 was not methylated in MCL patients (0/11) whereas CD44 was frequently hypermethylated in BL patients (18/29). In cell lines with CD44 hypermethylation, expression was re-inducible at mRNA and protein levels by treatment with the DNA demethylating agent 5-Aza-2'-deoxycytidine, confirming epigenetic regulation of CD44. CD44 ligation assays with a monoclonal anti-CD44 antibody showed that CD44 can mediate apoptosis in CD44⁺ lymphoma cells. CD44 hypermethylated, CD44^- lymphoma cell lines were consistently resistant towards anti-CD44 induced apoptosis.

Conclusion

Our data show that CD44 is epigenetically regulated in lymphoma and undergoes de novo methylation in distinct lymphoma subtypes like BL. Thus CD44 may be a promising new epigenetic marker for diagnosis and a potential therapeutic target for the treatment of specific lymphoma subtypes.