Tetraspanins as therapeutic targets in hematological malignancy: a concise review

Transforming toxins into treatments: the revolutionary role of α-amanitin in cancer therapy

Amanita phalloides is the primary species responsible for fatal mushroom poisoning, as its main toxin, α-amanitin, irreversibly and potently inhibits eukaryotic RNA polymerase II (RNAP II), leading to cell death. There is no specific antidote for α-amanitin, which hinders its clinical application. However, with the advancement of precision medicine in oncology, including the development of antibody-drug conjugates (ADCs), the potential value of various toxic small molecules has been explored. These ADCs ingeniously combine the targeting precision of antibodies with the cytotoxicity of small-molecule payloads to precisely kill tumor cells. We searched PubMed for studies in this area using these MeSH terms "Amanitins, Alpha-Amanitin, Therapeutic use, Immunotherapy, Immunoconjugates, Antibodies" and did not limit the time interval. Recent studies have conducted preclinical experiments on ADCs based on α-amanitin, showing promising therapeutic effects and good tolerance in primates. The current challenges include the not fully understood toxicological mechanism of α-amanitin and the lack of clinical studies to evaluate the therapeutic efficacy of ADCs developed based on α-amanitin. In this article, we will discuss the role and therapeutic efficacy of α-amanitin as an effective payload in ADCs for the treatment of various cancers, providing background information for the research and application strategies of current and future drugs.

Cutting Edge: The Tetraspanin CD53 Promotes CXCR4 Signaling and Bone Marrow Homing in B Cells

B cell trafficking involves the coordinated activity of multiple adhesive and cytokine-receptor interactions, and the players in this process are not fully understood. In this study, we identified the tetraspanin CD53 as a critical regulator of both normal and malignant B cell trafficking. CXCL12 is a key chemokine in B cell homing to the bone marrow and secondary lymphoid organs, and both normal and malignant B cells from Cd53-/- mice have reduced migration toward CXCL12 in vitro, as well as impaired marrow homing in vivo. Using proximity ligation studies, we identified the CXCL12 receptor, CXCR4, as a novel, to our knowledge, CD53 binding partner. This interaction promotes receptor function, because Cd53-/- B cells display reduced signaling and internalization of CXCR4 in response to CXCL12. Together, our data suggest that CD53 interacts with CXCR4 on both normal and malignant B cells to promote CXCL12 signaling, receptor internalization, and marrow homing.

A novel tetraspanin-related gene signature for predicting prognosis and immune invasion status of lung adenocarcinoma

BACKGROUND

Lung adenocarcinoma (LUAD), the most common subtype of lung cancer, is the primary contributor to cancer-linked fatalities. Dysregulation in the proliferation of cells and death is primarily involved in its development. Recently, tetraspanins, a group of transmembrane proteins, have gained increasing attention for their potential role in the progression of LUAD. Hence, our endeavor involved the development of a novel tetraspanin-based model for the prognostication of lung cancer.

METHODS

A comprehensive set of bioinformatics tools was utilized to evaluate the expression of tetraspanin-related genes and assess their significance regarding prognosis. Hence, a robust risk signature was established through machine learning. The prognosis-predictive value of the signature was evaluated in terms of clinical application, functional enrichment, and the immune landscape.

RESULTS

The research first identified differential expression of tetraspanin genes in patients with LUAD via publicly available databases. The resulting data were indicative of the value that nine of them held regarding prognosis. Five distinct elements were utilized in the establishment of a tetraspanin-related model (TSPAN7, TSPAN11, TSPAN14, UPK1B, and UPK1A). Furthermore, as per the median risk scores, the participants were classified into high- and low-risk groups. The model was validated using inner and outer validation sets. Notably, consensus clustering and prognostic score grouping analysis revealed that tetraspanin-related features affect tumor prognosis by modulating tumor immunity. A nomogram based on the tetraspanin gene was constructed with the aim of enhancing the poor prognosis of high-risk groups and facilitating clinical application.

CONCLUSION

Through machine learning algorithms and in vitro experiments, a novel tetraspanin-associated signature was developed and validated for survival prediction in patients with LUAD that reflects tumor immune infiltration. This could potentially provide new and improved measures for diagnosis and therapeutic interventions for LUAD.

EWI2 and its relatives in Tetraspanin-enriched membrane domains regulate malignancy

Experimental studies on immunoglobulin superfamily (IgSF) member EWI2 reveal that it suppresses a variety of solid malignant tumors including brain, lung, skin, and prostate cancers in animal models and inhibits tumor cell movement and growth in vitro. While EWI2 appears to support myeloid leukemia in mouse models and maintain leukemia stem cells. Bioinformatics analyses suggest that EWI2 gene expression is downregulated in glioblastoma but upregulated in melanoma, pancreatic cancer, and liver cancer. The mechanism of action for EWI2 is linked to its inhibition of growth factor receptors and cell adhesion proteins through its associated tetraspanin-enriched membrane domains (TEMDs), by altering the cell surface clustering and endolysosome trafficking/turnover of these transmembrane proteins. Recent studies also show that EWI2 modulates the nuclear translocation of ERK and TFEB to change the activities of these gene expression regulators. For EWI2 relatives including FPRP, IgSF3, and CD101, although their roles in malignant diseases are not fully clear and remain to be determined experimentally, FPRP and IgSF3 likely promote the progression of solid malignant tumors while CD101 seems to modulate immune cells of tumor microenvironment. Distinctive from other tumor regulators, the impacts of EWI subfamily members on solid malignant tumors are likely to be context dependent. In other words, the effect of a given EWI subfamily member on a tumor probably depends on the molecular network and composition of TEMDs in that tumor. Collectively, EWI2 and its relatives are emerged as important regulators of malignant diseases with promising potentials to become anti-cancer therapeutics and cancer therapy targets.

Immunological Aspects of Richter Syndrome: From Immune Dysfunction to Immunotherapy

Richter Syndrome (RS) is defined as the development of an aggressive lymphoma in patients with a previous or simultaneous diagnosis of chronic lymphocytic leukemia (CLL). Two pathological variants of RS are recognized: diffuse large B-cell lymphoma (DLBCL)-type and Hodgkin lymphoma (HL)-type RS. Different molecular mechanisms may explain the pathogenesis of DLBCL-type RS, including genetic lesions, modifications of immune regulators, and B cell receptor (BCR) pathway hyperactivation. Limited data are available for HL-type RS, and its development has been reported to be similar to de novo HL. In this review, we focus on the immune-related pathogenesis and immune system dysfunction of RS, which are linked to BCR over-reactivity, altered function of the immune system due to the underlying CLL, and specific features of the RS tumor microenvironment. The standard of care of this disease consists in chemoimmunotherapy, eventually followed by stem cell transplantation, but limited possibilities are offered to chemo-resistant patients, who represent the majority of RS cases. In order to address this unmet clinical need, several immunotherapeutic approaches have been developed, namely T cell engagement obtained with bispecific antibodies, PD-1/PD-L1 immune checkpoint blockade by the use of monoclonal antibodies, selective drug delivery with antibody-drug conjugates, and targeting malignant cells with anti-CD19 chimeric antigen receptor-T cells.

Tetraspanin 7 promotes osteosarcoma cell invasion and metastasis by inducing EMT and activating the FAK-Src-Ras-ERK1/2 signaling pathway

Background

Tetraspanins are members of the 4-transmembrane protein superfamily (TM4SF) that function by recruiting many cell surface receptors and signaling proteins into tetraspanin-enriched microdomains (TEMs) that play vital roles in the regulation of key cellular processes including adhesion, motility, and proliferation. Tetraspanin7 (Tspan7) is a member of this superfamily that plays documented roles in hippocampal neurogenesis, synaptic transmission, and malignant transformation in certain tumor types. How Tspan7 influences the onset or progression of osteosarcoma (OS), however, remains to be defined. Herein, this study aimed to explore the relationship between Tspan7 and the malignant progression of OS, and its underlying mechanism of action.

Methods

In this study, the levels of Tspan7 expression in human OS cell lines were evaluated via qRT-PCR and western blotting. The effect of Tspan7 on proliferation was examined using CCK-8 and colony formation assays, while metastatic role of Tspan7 was assessed by functional assays both in vitro and in vivo. In addition, mass spectrometry and co-immunoprecipitation were performed to verify the interaction between Tspan7 and β1 integrin, and western blotting was used to explore the mechanisms of Tspan7 in OS progresses.

Results

We found that Tspan7 is highly expressed in primary OS tumors and OS cell lines. Downregulation of Tspan7 significantly suppressed OS growth, metastasis, and attenuated epithelial-mesenchymal transition (EMT), while its overexpression had the opposite effects in vitro. Furthermore, it exhibited reduced OS pulmonary metastases in Tspan7-deleted mice comparing control mice in vivo. Additionally, we proved that Tspan7 interacted with β1 integrin to facilitate OS metastasis through the activation of integrin-mediated downstream FAK-Src-Ras-ERK1/2 signaling pathway.

Conclusion

In summary, this study demonstrates for the first time that Tspan7 promotes OS metastasis via interacting with β1 integrin and activating the FAK-Src-Ras-ERK1/2 pathway, which could provide rationale for a new therapeutic strategy for OS.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12935-022-02591-1.

Acute myeloid leukemia: Therapy resistance and a potential role for tetraspanin membrane scaffolds

Acute myeloid leukemia (AML) is characterized by the disruption of myeloid differentiation and accumulation of blast cells in the bone marrow. While AML patients respond favorably to induction chemotherapy, long-term outcomes remain poor due to a high rate of chemoresistance. Advances with targeted therapies, which can be used in combination with conventional chemotherapy, have expanded therapeutic options for patients. However, remission is often short-lived and followed by disease relapse and drug resistance. Therefore, there is a substantial need to improve treatment options by identifying novel molecular and cellular targets that regulate AML chemosensitivity. Membrane scaffolds such as the tetraspanin family of proteins often serve as signaling mediators, translating extracellular signaling cues into intracellular signaling cascades. In this review, we discuss the conventional and targeted treatment strategies for AML and review chemoresistance mechanisms with a focus on the tetraspanin family of membrane scaffold proteins.

Spacer Length Modification Facilitates Discrimination between Normal and Neoplastic Cells and Provides Clinically Relevant CD37 CAR T Cells

Despite the remarkable initial efficacy of CD19 chimeric Ag receptor T (CAR-T) cell therapy, a high incidence of relapse has been observed. To further increase treatment efficacy and reduce the rate of escape of Ag-negative cells, we need to develop CAR-T cells that target other Ags. Given its restricted expression pattern, CD37 was considered a preferred novel target for immunotherapy in hematopoietic malignancies. Therefore, we designed a CD37-targeting CAR-T (CD37CAR-T) using the single-chain variable fragment of a humanized anti-CD37 Ab, transmembrane and intracellular domains of CD28, and CD3ζ signaling domains. High levels of CD37 expression were confirmed in B cells from human peripheral blood and bone marrow B cell precursors at late developmental stages; by contrast, more limited expression of CD37 was observed in early precursor B cells. Furthermore, we found that human CD37CAR-T cells with longer spacer lengths exhibited high gene transduction efficacy but reduced capacity to proliferate; this may be due to overactivation and fratricide. Spacer length optimization resulted in a modest transduction efficiency together with robust capacity to proliferate. CD37CAR-T cells with optimized spacer length efficiently targeted various CD37⁺ human tumor cell lines but had no impact on normal leukocytes both in vitro and in vivo. CD37CAR-T cells effectively eradicated Raji cells in xenograft model. Collectively, these results suggested that spacer-optimized CD37CAR-T cells could target CD37-high neoplastic B cells both in vitro and in vivo, with only limited interactions with their normal leukocyte lineages, thereby providing an additional promising therapeutic intervention for patients with B cell malignancies.

CD81 knockout promotes chemosensitivity and disrupts in vivo homing and engraftment in acute lymphoblastic leukemia

Relapse remains a major obstacle to achieving 100% overall survival rate in pediatric hematologic malignancies like acute lymphoblastic leukemia (ALL). Relapse often results from the development of chemoresistance. One of the mechanisms of chemoresistance involves ALL cell interactions with the bone marrow (BM) microenvironment, providing a sanctuary. This phenomenon is known as BM microenvironment-induced chemoprotection. Members of the transmembrane 4 superfamily (tetraspanins; TSPANs) are known to mediate microenvironmental interactions and have been extensively studied in solid tumors. Although the TSPAN family member CD81 is a minimal residual disease marker, its biological role in ALL is not well characterized. We show for the first time that CD81 knockout induces chemosensitivity, reduces cellular adhesion, and disrupts in vivo BM homing and engraftment in B-ALL. This chemosensitization is mediated through control of Bruton tyrosine kinase signaling and induction of p53-mediated cell death. We then show how CD81-related signaling can be disrupted by treatment with the epigenetic drug combination of DNA hypomethylating agent azacitidine (aza) and histone deacetylase inhibitor panobinostat (pano), which we previously used to sensitize ALL cells to chemotherapy under conditions that promote BM microenvironment-induced chemoprotection. Aza/pano-mediated modulation of CD81 surface expression is involved in decreasing BM load by promoting ALL cell mobilization from BM to peripheral blood and increasing response to chemotherapy in disseminated patient-derived xenograft models. This study identifies the novel role of CD81 in BM microenvironment-induced chemoprotection and delineates the mechanism by which aza/pano successfully sensitizes ALL cells via modulation of CD81.

CD37 in B Cell Derived Tumors-More than Just a Docking Point for Monoclonal Antibodies

CD37 is a tetraspanin expressed prominently on the surface of B cells. It is an attractive molecular target exploited in the immunotherapy of B cell-derived lymphomas and leukemia. Currently, several monoclonal antibodies targeting CD37 as well as chimeric antigen receptor-based immunotherapies are being developed and investigated in clinical trials. Given the unique role of CD37 in the biology of B cells, it seems that CD37 constitutes more than a docking point for monoclonal antibodies, and targeting this molecule may provide additional benefit to relapsed or refractory patients. In this review, we aimed to provide an extensive overview of the function of CD37 in B cell malignancies, providing a comprehensive view of recent therapeutic advances targeting CD37 and delineating future perspectives.

Extracellular Vesicles in Hematological Malignancies: From Biomarkers to Therapeutic Tools

Small extracellular vesicles (EVs) are a heterogenous group of lipid particles released by all cell types in physiological and pathological states. In hematological malignancies, tumor-derived EVs are critical players in mediating intercellular communications through the transfer of genetic materials and proteins between neoplastic cells themselves and to several components of the bone marrow microenvironment, rendering the latter a “stronger” niche supporting cancer cell proliferation, drug resistance, and escape from immune surveillance. In this context, the molecular cargoes of tumor-derived EVs reflect the nature and status of the cells of origin, making them specific therapeutic targets. Another important characteristic of EVs in hematological malignancies is their use as a potential “liquid biopsy” because of their high abundance in biofluids and their ability to protect their molecular cargoes from nuclease and protease degradation. Liquid biopsies are non-invasive blood tests that provide a molecular profiling clinical tool as an alternative method of disease stratification, especially in cancer patients where solid biopsies have limited accessibility. They offer accurate diagnoses and identify specific biomarkers for monitoring of disease progression and response to treatment. In this review, we will focus on the role of EVs in the most prevalent hematological malignancies, particularly on their prospective use as biomarkers in the context of liquid biopsies, as well as their molecular signature that identifies them as specific therapeutic targets for inhibiting cancer progression. We will also highlight their roles in modulating the immune response by acting as both immunosuppressors and activators of anti-tumor immunity.

A Proteomic Approach to Understand the Clinical Significance of Acute Myeloid Leukemia-Derived Extracellular Vesicles Reflecting Essential Characteristics of Leukemia

Extracellular vesicle (EV) proteins from acute myeloid leukemia (AML) cell lines were analyzed using mass spectrometry. The analyses identified 2450 proteins, including 461 differentially expressed proteins (290 upregulated and 171 downregulated). CD53 and CD47 were upregulated and were selected as candidate biomarkers. The association between survival of patients with AML and the expression levels of CD53 and CD47 at diagnosis was analyzed using mRNA expression data from The Cancer Genome Atlas database. Patients with higher expression levels showed significantly inferior survival than those with lower expression levels. ELISA results of the expression levels of CD53 and CD47 from EVs in the bone marrow of patients with AML at diagnosis and at the time of complete remission with induction chemotherapy revealed that patients with downregulated CD53 and CD47 expression appeared to relapse less frequently. Network model analysis of EV proteins revealed several upregulated kinases, including LYN, CSNK2A1, SYK, CSK, and PTK2B. The potential cytotoxicity of several clinically applicable drugs that inhibit these kinases was tested in AML cell lines. The drugs lowered the viability of AML cells. The collective data suggest that AML cell-derived EVs could reflect essential leukemia biology.

Communication between stromal and hematopoietic stem cell by exosomes in normal and malignant bone marrow niche

Extracellular vesicles (EVs) have been regarded as important tools for cell-cell communication. They act as carriers for the transfer of various molecules such as genes, proteins and miRNA. EVs shift and transfer their ingredients to target cells in an active form. These particles have prominent roles in modulation of bone marrow (BM) niche; therefore they can regulate proliferation, differentiation, and other properties of hematopoietic stem cells (HSCs) and hematopoietic progenitor cells (HPCs). This review discusses the different roles of EVs on BM niche; HPCs fate regulation and downstream effects of them on HSCs. Moreover, cellular and molecular mechanisms of BM microenvironment cross-talking are explained in healthy and malignant settings.

Open conformation of tetraspanins shapes interaction partner networks on cell membranes

Tetraspanins, including CD53 and CD81, regulate a multitude of cellular processes through organizing an interaction network on cell membranes. Here, we report the crystal structure of CD53 in an open conformation poised for partner interaction. The large extracellular domain (EC2) of CD53 protrudes away from the membrane surface and exposes a variable region, which is identified by hydrogen-deuterium exchange as the common interface for CD53 and CD81 to bind partners. The EC2 orientation in CD53 is supported by an extracellular loop (EC1). At the closed conformation of CD81, however, EC2 disengages from EC1 and rotates toward the membrane, thereby preventing partner interaction. Structural simulation shows that EC1-EC2 interaction also supports the open conformation of CD81. Disrupting this interaction in CD81 impairs the accurate glycosylation of its CD19 partner, the target for leukemia immunotherapies. Moreover, EC1 mutations in CD53 prevent the chemotaxis of pre-B cells toward a chemokine that supports B-cell trafficking and homing within the bone marrow, a major CD53 function identified here. Overall, an open conformation is required for tetraspanin-partner interactions to support myriad cellular processes.

Can short-term heart rate variability predict coronary artery disease in patients undergoing elective coronary angiography due to typical chest pain?

BACKGROUND

Presence of typical chest pain and normal coronary angiography suggests the possibility of microvascular ischemia of the myocardium as well as other non-cardiac causes that are also likely to decrease heart rate variability (HRV). This raises a question of whether poor HRV can predict abnormal elective coronary angiography (ECA).

AIM

The aim of this study was to compare HRV in patients with typical chest pain when they are classified according to ECA outcomes.

METHODS

The study enrolled 150 patients planned for ECA in the cardiac center of AlShaab Teaching Hospital, Khartoum, Sudan, due to typical chest pain. Following assessment of medical history and clinical examination, the Bluetooth electrocardiography (ECG) transmitter and receiver were used for ECG recording and evaluation of time and frequency domains HRV. ECA confirmed the diagnosis of coronary artery disease (CAD) in 108 patients, who were considered as the test group. The other 42 subjects were considered as a control group after the exclusion of CAD.

RESULTS

The Mean±SD of Ln(pNN10), Ln(pNN20), LnLF, and LnHF was significantly higher in subjects with normal angiography compared with CAD patients. However, these statistically significant differences disappeared when the comparison was adjusted for age, gender, BMI, and HR of the studied groups.

CONCLUSION

HRV is comparable in patients with typical chest pain regardless of ECA outcomes.

RELEVANCE FOR PATIENTS

The HRV differences between patients with normal and abnormal ECA are likely to be biased by CAD risk factors such as old age, male gender, and tachycardia that are known to disturb HRV. The possibility of microvascular ischemia in patients with normal ECA may have attenuated HRV in this group and make it comparable to those suffering from macrovascular ischemia due to CAD.

Expression and function of transmembrane 4 superfamily proteins in digestive system cancers

Background

Although the medical level is constantly improving, cancer is still a major disease that threatens human health, and very effective treatments have not been found. In recent years, studies have found that four-transmembrane superfamily proteins are involved in multiple stages of tumorigenesis and development, but their expression and function in tumors have not been systematically studied.

Methods

We used the Oncomine database to analyze the mRNA expression levels of TSPAN family in various cancers. Then differentially expressed genes were screened out and verified by liver cancer, colorectal cancer, and gastric cancer cells by q-PCR and Western blot analysis. CCK8 and EDU analysis are used to detect cell proliferation, Cell wound scrape assay and Cell invasion assay are used to analyze cell invasion and metastasis. Nude tumor formation test used to verify the tumor suppressive effect of TSPAN7 in vivo.

Results

Differential analysis of 33 TSPAN proteins revealed that a total of 11 proteins showed differential expression in 10% of independent analyses, namely TSPAN1, TSPAN3, TSPAN5, TSPAN6, TSPAN7, TSPAN8, TSPAN13, TSPAN25, TSPAN26, TSPAN29, TSPAN30. TSPAN7 is the only four-transmembrane protein with reduced expression in three types of digestive tract tumors, so we chose TSPAN7 to be selected for cellular and molecular level verification. We found that compared with normal cells, the expression of TSPAN7 in liver cancer cells was significantly reduced, while the expression of gastric and colon cancer was not significantly different from that of normal cells. In addition, we also found that the high expression of Tspan7 not only inhibited the proliferation of HCC-LM3 cells, but also inhibited its invasion and metastasis.

Conclusions

Our study evaluated the expression and function of the TSPANs family in digestive cancers and explored TSPAN7 in hepatoma cells in detail. We found some members of the TSPAN family show significant expression differences between cancer and normal tissues, of which TSPAN7 may be a potential biomarker for liver cancer.

Membrane Compartmentalization and Scaffold Proteins in Leukocyte Migration

Leukocyte migration across vessels into and within peripheral and lymphoid tissues is essential for host defense against invading pathogens. Leukocytes are specialized in sensing a variety of guidance cues and to integrate environmental stimuli to navigate in a timely and spatially controlled manner. These extracellular signals must be transmitted across the leukocyte’s plasma membrane in a way that intracellular signaling cascades enable directional cell movement. Therefore, the composition of the membrane in concert with proteins that influence the compartmentalization of the plasma membrane or contribute to delineate intracellular signaling molecules are key in controlling leukocyte navigation. This becomes evident by the fact that mislocalization of membrane proteins is known to deleteriously affect cellular functions that may cause diseases. In this review we summarize recent advances made in the understanding of how membrane cholesterol levels modulate chemokine receptor signaling and hence leukocyte trafficking. Moreover, we provide an overview on the role of membrane scaffold proteins, particularly tetraspanins, flotillins/reggies, and caveolins in controlling leukocyte migration both in vitro and in vivo.

Tetraspanin CD82 drives acute myeloid leukemia chemoresistance by modulating protein kinase C alpha and β1 integrin activation

A principal challenge in treating acute myeloid leukemia (AML) is chemotherapy refractory disease. As such, there remains a critical need to identify key regulators of chemotherapy resistance in AML. In this study, we demonstrate that the membrane scaffold, CD82, contributes to the chemoresistant phenotype of AML. Using an RNA-seq approach, we identified the increased expression of the tetraspanin family member, CD82, in response to the chemotherapeutic, daunorubicin. Analysis of the TARGET and BEAT AML databases identifies a correlation between CD82 expression and overall survival of AML patients. Moreover, using a combination of cell lines and patient samples, we find that CD82 overexpression results in significantly reduced cell death in response to chemotherapy. Investigation of the mechanism by which CD82 promotes AML survival in response to chemotherapy identified a crucial role for enhanced protein kinase c alpha (PKCα) signaling and downstream activation of the β1 integrin. In addition, analysis of β1 integrin clustering by super-resolution imaging demonstrates that CD82 expression promotes the formation of dense β1 integrin membrane clusters. Lastly, evaluation of survival signaling following daunorubicin treatment identified robust activation of p38 mitogen-activated protein kinase (MAPK) downstream of PKCα and β1 integrin signaling when CD82 is overexpressed. Together, these data propose a mechanism where CD82 promotes chemoresistance by increasing PKCα activation and downstream activation/clustering of β1 integrin, leading to AML cell survival via activation of p38 MAPK. These observations suggest that the CD82-PKCα signaling axis may be a potential therapeutic target for attenuating chemoresistance signaling in AML.

DuoHexaBody-CD37®, a novel biparatopic CD37 antibody with enhanced Fc-mediated hexamerization as a potential therapy for B-cell malignancies

Tetraspanin CD37 has recently received renewed interest as a therapeutic target for B-cell malignancies. Although complement-dependent cytotoxicity (CDC) is a powerful Fc-mediated effector function for killing hematological cancer cells, CD37-specific antibodies are generally poor inducers of CDC. To enhance CDC, the E430G mutation was introduced into humanized CD37 monoclonal IgG1 antibodies to drive more efficient IgG hexamer formation through intermolecular Fc-Fc interactions after cell surface antigen binding. DuoHexaBody-CD37, a bispecific CD37 antibody with the E430G hexamerization-enhancing mutation targeting two non-overlapping epitopes on CD37 (biparatopic), demonstrated potent and superior CDC activity compared to other CD37 antibody variants evaluated, in particular ex vivo in patient-derived chronic lymphocytic leukemia cells. The superior CDC potency was attributed to enhanced IgG hexamerization mediated by the E430G mutation in combination with dual epitope targeting. The mechanism of action of DuoHexaBody-CD37 was shown to be multifaceted, as it was additionally capable of inducing efficient antibody-dependent cellular cytotoxicity and antibody-dependent cellular phagocytosis in vitro. Finally, potent anti-tumor activity in vivo was observed in cell line- and patient-derived xenograft models from different B-cell malignancy subtypes. These encouraging preclinical results suggest that DuoHexaBody-CD37 (GEN3009) may serve as a potential therapeutic antibody for the treatment of human B-cell malignancies.

Tumour infiltrating lymphocytes and immune-related genes as predictors of outcome in pancreatic adenocarcinoma

BACKGROUND

We investigated the correlation between pancreatic ductal adenocarcinoma patient prognosis and the presence of tumour infiltrating lymphocytes and expression of 521 immune system genes.

METHODS

Intratumoural CD3+, CD8+, and CD20+ lymphocytes were examined by immunohistochemistry in 12 PDAC patients with different outcomes who underwent pancreaticoduodenectomy. The results were correlated with gene expression profile using the digital multiplexed NanoString nCounter analysis system (NanoString Technologies, Seattle, WA, USA).

RESULTS

Twenty immune system genes were significantly differentially expressed in patients with a good prognosis relative to patients with a worse prognosis: TLR2 and TLR7 (Toll-like receptor superfamily); CD4, CD37, FOXP3, PTPRC (B cell and T cell signalling); IRF5, IRF8, STAT1, TFE3 (transcription factors); ANP32B, CCND3 (cell cycle); BTK (B cell development); TNF, TNFRF1A (TNF superfamily); HCK (leukocyte function); C1QA (complement system); BAX, PNMA1 (apoptosis); IKBKE (NFκB pathway). Differential expression was more than twice log 2 for TLR7, TNF, C1QA, FOXP3, and CD37.

DISCUSSION

Tumour infiltrating lymphocytes were present at higher levels in samples from patients with better prognosis. Our findings indicate that tumour infiltrating lymphocyte levels and expression level of the immune system genes listed above influence pancreatic ductal adenocarcinoma prognosis. This information could be used to improve selection of best responders to immune inhibitors.

Deregulated expression of NKL homeobox genes in T-cell lymphomas

Recently, we have presented a scheme, termed "NKL-code", which describes physiological expression patterns of NKL homeobox genes in early hematopoiesis and in lymphopoiesis including main stages of T-, B- and NK-cell development. Aberrant activity of these genes underlies the generation of hematological malignancies notably T-cell leukemia. Here, we searched for deregulated NKL homeobox genes in main entities of T-cell lymphomas comprising angioimmunoblastic T-cell lymphoma (AITL), anaplastic large cell lymphoma (ALCL), adult T-cell leukemia/lymphoma (ATLL), hepatosplenic T-cell lymphoma (HSTL), NK/T-cell lymphoma (NKTL) and peripheral T-cell lymphoma (PTCL). Our data revealed altogether 19 aberrantly overexpressed genes in these types, demonstrating deregulated NKL homeobox genes involvement in T-cell lymphomas as well. For detailed analysis we focused on NKL homeobox gene MSX1 which is normally expressed in NK-cells. MSX1 was overexpressed in subsets of HSTL patients and HSTL-derived sister cell lines DERL-2 and DERL-7 which served as models to characterize mechanisms of deregulation. We performed karyotyping, genomic and expression profiling, and whole genome sequencing to reveal mutated and deregulated gene candidates, including the fusion gene CD53-PDGFRB. Subsequent knockdown experiments allowed the reconstruction of an aberrant network involved in MSX1 deregulation, including chromatin factors AUTS2 and mutated histone HIST1H3B(K27M). The gene encoding AUTS2 is located at chromosome 7q11 and may represent a basic target of the HSTL hallmark aberration i(7q). Taken together, our findings highlight an oncogenic role for deregulated NKL homeobox genes in T-cell lymphoma and identify MSX1 as a novel player in HSTL, implicated in aberrant NK- and T-cell differentiation.

Akt-ing Up Just About Everywhere: Compartment-Specific Akt Activation and Function in Receptor Tyrosine Kinase Signaling

The serine/threonine kinase Akt is a master regulator of many diverse cellular functions, including survival, growth, metabolism, migration, and differentiation. Receptor tyrosine kinases are critical regulators of Akt, as a result of activation of phosphatidylinositol-3-kinase (PI3K) signaling leading to Akt activation upon receptor stimulation. The signaling axis formed by receptor tyrosine kinases, PI3K and Akt, as well as the vast range of downstream substrates is thus central to control of cell physiology in many different contexts and tissues. This axis must be tightly regulated, as disruption of PI3K-Akt signaling underlies the pathology of many diseases such as cancer and diabetes. This sophisticated regulation of PI3K-Akt signaling is due in part to the spatial and temporal compartmentalization of Akt activation and function, including in specific nanoscale domains of the plasma membrane as well as in specific intracellular membrane compartments. Here, we review the evidence for localized activation of PI3K-Akt signaling by receptor tyrosine kinases in various specific cellular compartments, as well as that of compartment-specific functions of Akt leading to control of several fundamental cellular processes. This spatial and temporal control of Akt activation and function occurs by a large number of parallel molecular mechanisms that are central to regulation of cell physiology.

CD20 and CD37 antibodies synergize to activate complement by Fc-mediated clustering

CD20 monoclonal antibody therapies have significantly improved the outlook for patients with B-cell malignancies. However, many patients acquire resistance, demonstrating the need for new and improved drugs. We previously demonstrated that the natural process of antibody hexamer formation on targeted cells allows for optimal induction of complement-dependent cytotoxicity. Complement-dependent cytotoxicity can be potentiated by introducing a single point mutation such as E430G in the IgG Fc domain that enhances intermolecular Fc-Fc interactions between cell-bound IgG molecules, thereby facilitating IgG hexamer formation. Antibodies specific for CD37, a target that is abundantly expressed on healthy and malignant B cells, are generally poor inducers of complement-dependent cytotoxicity. Here we demonstrate that introduction of the hexamerization-enhancing mutation E430G in CD37-specific antibodies facilitates highly potent complement-dependent cytotoxicity in chronic lymphocytic leukemia cells ex vivo. Strikingly, we observed that combinations of hexamerization-enhanced CD20 and CD37 antibodies cooperated in C1q binding and induced superior and synergistic complement-dependent cytotoxicity in patient-derived cancer cells compared to the single agents. Furthermore, CD20 and CD37 antibodies colocalized on the cell membrane, an effect that was potentiated by the hexamerization-enhancing mutation. Moreover, upon cell surface binding, CD20 and CD37 antibodies were shown to form mixed hexameric antibody complexes consisting of both antibodies each bound to their own cognate target, so-called hetero-hexamers. These findings provide novel insights into the mechanisms of synergy in antibody-mediated complement-dependent cytotoxicity and provide a rationale to explore Fc-engineering and antibody hetero-hexamerization as a tool to enhance the cooperativity and therapeutic efficacy of antibody combinations.

Immune Targeting of Tetraspanins Involved in Cell Invasion and Metastasis

Metastasis is the ultimate consequence of cancer progression and the cause of patients’ death across different cancer types. Patients with initial diagnosis of distant disease have a worst 5-year survival compared to patients with localized disease. Therapies that target primary tumors fail to eradicate distant dissemination of cancer. Recently, immunotherapies have improved the survival of patients with metastatic disease, such as melanoma and lung cancer. However, only a fraction of patients responds to immunotherapy modalities that target the host immune system. The need to identify new druggable targets that inhibit or prevent metastasis is, therefore, much needed. Tetraspanins have emerged as key players in regulating cell migration, invasion, and metastasis. By serving as molecular adaptors that cluster adhesion receptors, signaling molecules, and cell surface receptors; tetraspanins are involved in all steps of the metastatic cascade. They regulate cell proliferation, participate in EMT transition, modulate integrin-mediated cell adhesion, and participate in angiogenesis and invasion processes. Tetraspanins have also been shown to modulate metastasis indirectly through exosomes and by regulating cellular interactions in the immune system. Importantly, targeting individual tetraspanin with antibodies has impacted tumor progression. This review will focus on the contribution of tetraspanins to the metastatic process and their potential as therapeutic tumor targets.

Antitumor Immunity Is Controlled by Tetraspanin Proteins

Antitumor immunity is shaped by the different types of immune cells that are present in the tumor microenvironment (TME). In particular, environmental signals (for instance, soluble factors or cell–cell contact) transmitted through the plasma membrane determine whether immune cells are activated or inhibited. Tetraspanin proteins are emerging as central building blocks of the plasma membrane by their capacity to cluster immune receptors, enzymes, and signaling molecules into the tetraspanin web. Whereas some tetraspanins (CD81, CD151, CD9) are widely and broadly expressed, others (CD53, CD37, Tssc6) have an expression pattern restricted to hematopoietic cells. Studies using genetic mouse models have identified important immunological functions of these tetraspanins on different leukocyte subsets, and as such, may be involved in the immune response against tumors. While multiple studies have been performed with regards to deciphering the function of tetraspanins on cancer cells, the effect of tetraspanins on immune cells in the antitumor response remains understudied. In this review, we will focus on tetraspanins expressed by immune cells and discuss their potential role in antitumor immunity. New insights in tetraspanin function in the TME and possible prognostic and therapeutic roles of tetraspanins will be discussed.

Interleukin-6 is essential for glomerular immunoglobulin A deposition and the development of renal pathology in Cd37-deficient mice

Immunoglobulin A (IgA) nephropathy (IgAN), the most common glomerulonephritis worldwide, is characterized by IgA depositions in the kidney. Deficiency of CD37, a leukocyte-specific tetraspanin, leads to spontaneous development of renal pathology resembling IgAN. However, the underlying molecular mechanism has not been resolved. Here we found that CD37 expression on B cells of patients with IgAN was significantly decreased compared to B cells of healthy donors. Circulating interleukin (IL)-6 levels, but not tumor necrosis factor-α or IL-10, were elevated in Cd37^-/- mice compared to wild-type mice after lipopolysaccharide treatment. Cd37^-/- mice displayed increased glomerular neutrophil influx, immune complex deposition, and worse renal function. To evaluate the role of IL-6 in the pathogenesis of accelerated renal pathology in Cd37^-/-mice, we generated Cd37xIl6 double-knockout mice. These double-knockout and Il6^-/- mice displayed no glomerular IgA deposition and were protected from exacerbated renal failure following lipopolysaccharide treatment. Moreover, kidneys of Cd37^-/- mice showed more mesangial proliferation, endothelial cell activation, podocyte activation, and segmental podocyte foot process effacement compared to the double-knockout mice, emphasizing that IL-6 mediates renal pathology in Cd37^-/- mice. Thus, our study indicates that CD37 may protect against IgA nephropathy by inhibition of the IL-6 pathway.

Extracellular vesicles in the hematopoietic microenvironment

Self-renewal and differentiation are defining characteristics of hematopoietic stem and progenitor cells, and their balanced regulation is central to lifelong function of both blood and immune systems. In addition to cell-intrinsic programs, hematopoietic stem and progenitor cell fate decisions are subject to extrinsic cues from within the bone marrow microenvironment and systemically. Yet, many of the paracrine and endocrine mediators that shape hematopoietic function remain to be discovered. Extracellular vesicles serve as evolutionarily conserved, constitutive regulators of cell and tissue homeostasis, with several recent reports supporting a role for extracellular vesicles in the regulation of hematopoiesis. We review the physiological and pathophysiological effects that extracellular vesicles have on bone marrow compartmental function while highlighting progress in understanding vesicle biogenesis, cargo incorporation, differential uptake, and downstream effects of vesicle internalization. This review also touches on the role of extracellular vesicles in hematopoietic stem and progenitor cell fate regulation and recent advances in therapeutic and diagnostic applications of extracellular vesicles in hematologic disorders.

Monoclonal Antibody Therapies for Hematological Malignancies: Not Just Lineage-Specific Targets

Today, monoclonal antibodies (mAbs) are a widespread and necessary tool for biomedical science. In the hematological cancer field, since rituximab became the first mAb approved by the Food and Drug Administration for the treatment of B-cell malignancies, a number of effective mAbs targeting lineage-specific antigens (LSAs) have been successfully developed. Non-LSAs (NLSAs) are molecules that are not restricted to specific leukocyte subsets or tissues but play relevant pathogenic roles in blood cancers including the development, proliferation, survival, and refractoriness to therapy of tumor cells. In consequence, efforts to target NLSAs have resulted in a plethora of mAbs-marketed or in development-to achieve different goals like neutralizing oncogenic pathways, blocking tumor-related chemotactic pathways, mobilizing malignant cells from tumor microenvironment to peripheral blood, modulating immune-checkpoints, or delivering cytotoxic drugs into tumor cells. Here, we extensively review several novel mAbs directed against NLSAs undergoing clinical evaluation for treating hematological malignancies. The review focuses on the structure of these antibodies, proposed mechanisms of action, efficacy and safety profile in clinical studies, and their potential applications in the treatment of hematological malignancies.

Upregulation of TSPAN12 is associated with the colorectal cancer growth and metastasis

Tetraspanin 12 (TSPAN12), as an earliest member of tetraspanin family, has been recently shown to be highly expressed in several malignant tumors, such as lung cancer and breast cancer, which plays an important role in regulating cell proliferation, migration and invasion. However, the functional roles of TSPAN12 in colorectal cancer (CRC) remain largely unclear. In this study, the expression of TSPAN12 was up-regulated compared to that in paracarcinoma tissues. Higher TSPAN12 expression was significantly correlated with TNM stage, tumor size and lymph node metastasis. The vitro functional analysis, including MTT, colony formation, flow cytometry and transwell assays indicated that lentivirus-mediated TSPAN12 knockdown significantly suppressed cell proliferation, migration and invasion, induced cell apoptosis of CRC cells. In addition, knockdown of TSPAN12 remarkably decreased the growth of subcutaneously inoculated tumors in nude mice. Our findings for the first time supported that TSPAN12 might play a positive role in the regulation of CRC cell proliferation, migration and invasion. The inhibition of TSPAN12 may serve as a novel promising therapeutic strategy against human CRC.

Assessment of CD37 B-cell antigen and cell of origin significantly improves risk prediction in diffuse large B-cell lymphoma

CD37 (tetraspanin TSPAN26) is a B-cell surface antigen widely expressed on mature B cells. CD37 is involved in immune regulation and tumor suppression but its function has not been fully elucidated. We assessed CD37 expression in de novo diffuse large B-cell lymphoma (DLBCL), and investigated its clinical and biologic significance in 773 patients treated with rituximab plus cyclophosphamide, doxorubicin, vincristine, and prednisone (R-CHOP) and 231 patients treated with CHOP. We found that CD37 loss (CD37^-) in ∼60% of DLBCL patients showed significantly decreased survival after R-CHOP treatment, independent of the International Prognostic Index (IPI), germinal center B-cell-like (GCB)/activated B-cell-like (ABC) cell of origin, nodal/extranodal primary origin, and the prognostic factors associated with CD37^-, including TP53 mutation, NF-κB^high, Myc^high, phosphorylated STAT3^high, survivin^high, p63^-, and BCL6 translocation. CD37 positivity predicted superior survival, abolishing the prognostic impact of high IPI and above biomarkers in GCB-DLBCL but not in ABC-DLBCL. Combining risk scores for CD37^- status and ABC cell of origin with the IPI, defined as molecularly adjusted IPI for R-CHOP (M-IPI-R), or IPI plus immunohistochemistry (IHC; IPI+IHC) for CD37, Myc, and Bcl-2, significantly improved risk prediction over IPI alone. Gene expression profiling suggested that decreased CD20 and increased PD-1 levels in CD37^- DLBCL, ICOSLG upregulation in CD37⁺ GCB-DLBCL, and CD37 functions during R-CHOP treatment underlie the pivotal role of CD37 status in clinical outcomes. In conclusion, CD37 is a critical determinant of R-CHOP outcome in DLBCL especially in GCB-DLBCL, representing its importance for optimal rituximab action and sustained immune responses. The combined molecular and clinical prognostic indices, M-IPI-R and IPI+IHC, have remarkable predictive values in R-CHOP-treated DLBCL.

Tetraspanin CD82 Regulates the Spatiotemporal Dynamics of PKCα in Acute Myeloid Leukemia

Patients with acute myeloid leukemia (AML) have increased myeloid cells within their bone marrow that exhibit aberrant signaling. Therefore, therapeutic targets that modulate disrupted signaling cascades are of significant interest. In this study, we demonstrate that the tetraspanin membrane scaffold, CD82, regulates protein kinase c alpha (PKCα)-mediated signaling critical for AML progression. Utilizing a palmitoylation mutant form of CD82 with disrupted membrane organization, we find that the CD82 scaffold controls PKCα expression and activation. Combining single molecule and ensemble imaging measurements, we determine that CD82 stabilizes PKCα activation at the membrane and regulates the size of PKCα membrane clusters. Further evaluation of downstream effector signaling identified robust and sustained activation of ERK1/2 upon CD82 overexpression that results in enhanced AML colony formation. Together, these data propose a mechanism where CD82 membrane organization regulates sustained PKCα signaling that results in an aggressive leukemia phenotype. These observations suggest that the CD82 scaffold may be a potential therapeutic target for attenuating aberrant signal transduction in AML.

Targeted therapies in gastric cancer and future perspectives

Advanced gastric cancer (AGC) is associated with a high mortality rate and, despite multiple new chemotherapy options, the survival rates of patients with AGC remains poor. After the discovery of targeted therapies, research has focused on the new treatment options for AGC. In the last two decades, many targeted molecules were developed against AGC. Currently, two targeted therapy molecules have been approved for patients with AGC. In 2010, trastuzumab was the first molecule shown to improve survival in patients with HER2-positive AGC as part of a first-line combination regimen. In 2014, ramucirumab was the second targeted molecule to improve survival rates and was suggested as treatment for patients with AGC who had progressed after first-line platinum plus fluoropyrimidine with or without anthracycline chemotherapy. Ramucirumab was the first targeted therapy acting as a single agent in patients with advanced gastroesophageal cancers. Although these two molecules were introduced into clinical use, many other promising molecules have been tested in phase I-II trials. It is obvious that in the near future many different targeted therapies will be in use for treatment of AGC. In this review, the current status of targeted therapies in the treatment of AGC and gastroesophageal junction tumors, including HER (2-3) inhibitors, epidermal growth factor receptor inhibitors, tyrosine kinase inhibitors, antiangiogenic agents, c-MET inhibitors, mammalian target of rapamycin inhibitors, agents against other molecular pathways fibroblast growth factor, Claudins, insulin-like growth factor, heat shock proteins, and immunotherapy, will be discussed.