Neutralization of the CD95 ligand by APG101 inhibits invasion of glioma cells in vitro.

Glioblastoma is a disease characterized by rapid invasive tumour growth. Studies on the proapoptotic CD95/CD95L signalling pathway recently suggested a significant contribution of CD95 signalling towards the high degree of motility in glioma cells. Apogenix has developed APG101, a clinical phase II compound designed to bind and neutralize CD95L, and thus to interfere with CD95/CD95L-based signalling. APG101 has shown clinical efficacy in a controlled randomized phase II trial in patients with recurrent glioma. Because APG101 is not cytotoxic to tumour cells in vitro, we postulated that the anti-invasive function of APG101 is the main mechanism of action for this compound. Using three-dimensional spheroid invasion assays in vitro and in murine brain tissue cultures, we found that knockdown of endogenous CD95L reduced the invasive phenotype in our two glioblastoma model cell lines U87-MG and U251-MG. Invasion was restored in CD95L knockdown cells upon the addition of soluble recombinant CD95L and this effect was inhibited by APG101. We conclude that CD95L from autocrine and paracrine sources contributes towards the invasive phenotype of glioblastoma cells and that APG101 acts as a suppressor of proinvasive signalling by the CD95/CD95L pathway in glioblastoma.

The CD40 agonist HERA-CD40L results in enhanced activation of antigen presenting cells, promoting an anti-tumor effect alone and in combination with radiotherapy.

Introduction: The ability to modulate and enhance the anti-tumor immune responses is critical in developing novel therapies in cancer. The Tumor Necrosis Factor (TNF) Receptor Super Family (TNFRSF) are potentially excellent targets for modulation which result in specific anti-tumor immune responses. CD40 is a member of the TNFRSF and several clinical therapies are under development. CD40 signaling plays a pivotal role in regulating the immune system from B cell responses to myeloid cell driven activation of T cells. The CD40 signaling axis is well characterized and here we compare next generation HERA-Ligands to conventional monoclonal antibody based immune modulation for the treatment of cancer. Methods & results: HERA-CD40L is a novel molecule that targets CD40 mediated signal transduction and demonstrates a clear mode of action in generating an activated receptor complex via recruitment of TRAFs, cIAP1, and HOIP, leading to TRAF2 phosphorylation and ultimately resulting in the enhanced activation of key inflammatory/survival pathway and transcription factors such asNFkB, AKT, p38, ERK1/2, JNK, and STAT1 in dendritic cells. Furthermore, HERA-CD40L demonstrated a strong modulation of the tumor microenvironment (TME) via the increase in intratumoral CD8+ T cells and the functional switch from pro-tumor macrophages (TAMs) to anti-tumor macrophages that together results in a significant reduction of tumor growth in a CT26 mouse model. Furthermore, radiotherapy which may have an immunosuppressive modulation of the TME, was shown to have an immunostimulatory effect in combination with HERA-CD40L. Radiotherapy in combination with HERA-CD40L treatment resulted in an increase in detected intratumoral CD4+/8+ T cells compared to RT alone and, additionally, the repolarization of TAMs was also observed, resulting in an inhibition of tumor growth in a TRAMP-C1 mouse model. Discussion: Taken together, HERA-CD40L resulted in activating signal transduction mechanisms in dendritic cells, resulting in an increase in intratumoral T cells and manipulation of the TME to be pro-inflammatory, repolarizing M2 macrophages to M1, enhancing tumor control.

CD95L and Anti-Tumor Immune Response: Current Understanding and New Evidence.

The ability of FasL/CD95L to induce apoptosis in various Fas/CD95-expressing cells has been described in the context of hematopoiesis or thymic elimination of self-reactive T cells and resolution of an acute immune response under physiological conditions. At the same time, non-apoptotic CD95 activation is widely described in cancer and shown to stimulate invasiveness of cancer cells, promote cancer progression as well as stemness of cancer cells. This paper puts emphasis on the evolving understanding of expression and the non-apoptotic activities of the CD95/CD95L signaling pathway on the function of tumor cells, tumor microenvironment and immune cells. The emerging evidence to support the role of CD95/CD95L signaling in the anti-tumor immune response will be presented in the context of various malignancies and the modalities of potential therapeutic interventions via selective CD95L inhibition in combination with traditional interventions such as RT, chemotherapy and immune checkpoint inhibitors.

Concepts for agonistic targeting of CD40 in immuno-oncology.

TNF Receptor Superfamily (TNF-R-SF) signaling is a structurally well-defined event that requires proper receptor clustering and trimerization. While the TNF-SF ligands naturally exist as trivalent functional units, the receptors are usually separated on the cell surface. Critically, receptor assembly into functional trimeric signaling complexes occurs through binding of the natural ligand unit. TNF-R-SF members, including CD40, have been key immunotherapeutic targets for over 20 years. CD40, expressed by antigen-presenting cells, endothelial cells, and many tumors, plays a fundamental role in connecting innate and adaptive immunity. The multiple investigated strategies to induce CD40 signaling can be broadly grouped into antibody-based or CD40L-based approaches. Currently, seven different antibodies and one CD40L-based hexavalent fusion protein are in active clinical trials. In this review, we describe the biology and structural properties of CD40, requirements for agonistic signal transduction through CD40 and summarize current attempts to exploit the CD40 signaling pathway for the treatment of cancer.

Correction: CD95 maintains stem cell-like and non-classical EMT programs in primary human glioblastoma cells.

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Asunercept as an innovative therapeutic approach for recurrent glioblastoma and other malignancies.

Glioblastoma is the most common and aggressive malignant tumor of the central nervous system. Despite the existing high unmet medical needs, the past few decades have seen no notable improvement in overall survival for glioblastoma patients. One active area of research to develop new therapeutic options for this disease is focusing on the CD95/Fas receptor and its ligand CD95L/FasL. It is now recognized that in addition to its role in programmed cell death, CD95/CD95L signaling is involved in a wide range of other apoptotic and non-apoptotic pathways directed toward T-effector cells and cells in the tumor microenvironment involved in tumor progression and invasiveness. Asunercept is a first-in-class recombinant glycosylated fusion protein, which has been designed to selectively bind to CD95L and therefore disrupt CD95/CD95L signaling. The current report provides a brief overview of the role of the CD95/CD95L signaling pathway in cancer pathogenesis and discusses how asunercept was designed to bind and neutralize CD95L and disrupt signaling thereby potentially improving outcomes in glioblastoma and other malignancies.

HERA-GITRL activates T cells and promotes anti-tumor efficacy independent of FcγR-binding functionality.

BACKGROUND: Glucocorticoid-induced TNFR-related protein (TNFRSF18, GITR, CD357), expressed by T cells, and its ligand (TNFSF18, GITRL), expressed by myeloid populations, provide co-stimulatory signals that boost T cell activity. Due to the important role that GITR plays in regulating immune functions, agonistic stimulation of GITR is a promising therapeutic concept. Multiple strategies to induce GITR signaling have been investigated. The limited clinical efficacy of antibody-based GITR agonists results from structural and functional characteristics of antibodies that are unsuitable for stimulating the well-defined trimeric members of the TNFRSF. METHODS: To overcome limitations of antibody-based TNFRSF agonists, we have developed HERA-GITRL, a fully human hexavalent TNF receptor agonist (HERA) targeting GITR and mimicking the natural signaling concept. HERA-GITRL is composed of a trivalent but single-chain GITRL-receptor-binding-domain (scGITRL-RBD) unit fused to an IgG1 derived silenced Fc-domain serving as dimerization scaffold. A specific mouse surrogate, mmHERA-GITRL, was also generated to examine in vivo activity in respective mouse tumor models. RESULTS: For functional characterization of HERA-GITRL in vitro, human immune cells were isolated from healthy-donor blood and stimulated with anti-CD3 antibody in the presence of HERA-GITRL. Consistently, HERA-GITRL increased the activity of T cells, including proliferation and differentiation, even in the presence of regulatory T cells. In line with these findings, mmHERA-GITRL enhanced antigen-specific clonal expansion of both CD4+ (OT-II) and CD8+ (OT-I) T cells in vivo while having no effect on non-specific T cells. In addition, mmHERA-GITRL showed single-agent anti-tumor activity in two subcutaneous syngeneic colon cancer models (CT26wt and MC38-CEA). Importantly, this activity is independent of its FcγR-binding functionality, as both mmHERA-GITRL with a functional Fc- and a silenced Fc-domain showed similar tumor growth inhibition. Finally, in a direct in vitro comparison to a bivalent clinical benchmark anti-GITR antibody and a trivalent GITRL, only the hexavalent HERA-GITRL showed full biological activity independent of additional crosslinking. CONCLUSION: In this manuscript, we describe the development of HERA-GITRL, a true GITR agonist with a clearly defined mechanism of action. By clustering six receptor chains in a spatially well-defined manner, HERA-GITRL induces potent agonistic activity without being dependent on additional FcγR-mediated crosslinking.

A Single-Chain-Based Hexavalent CD27 Agonist Enhances T Cell Activation and Induces Anti-Tumor Immunity.

Tumor necrosis factor receptor superfamily member 7 (TNFRSF7, CD27), expressed primarily by T cells, and its ligand CD27L (TNFSF7, CD70) provide co-stimulatory signals that boost T cell activation, differentiation, and survival. Agonistic stimulation of CD27 is therefore a promising therapeutic concept in immuno-oncology intended to boost and sustain T cell driven anti-tumor responses. Endogenous TNFSF/TNFRSF-based signal transmission is a structurally well-defined event that takes place during cell-to-cell-based contacts. It is well-established that the trimeric-trivalent TNFSF-receptor binding domain (TNFSF-RBD) exposed by the conducting cell and the resulting multi-trimer-based receptor clustering on the receiving cell are essential for agonistic signaling. Therefore, we have developed HERA-CD27L, a novel hexavalent TNF receptor agonist (HERA) targeting CD27 and mimicking the natural signaling concept. HERA-CD27L is composed of a trivalent but single-chain CD27L-receptor-binding-domain (scCD27L-RBD) fused to an IgG1 derived silenced Fc-domain serving as dimerization scaffold. The hexavalent agonist significantly boosted antigen-specific T cell responses while having no effect on non-specific T cells and was superior over stabilized recombinant trivalent CD27L. In addition, HERA-CD27L demonstrated potent single-agent anti-tumor efficacy in two different syngeneic tumor models, MC38-CEA and CT26wt. Furthermore, the combination of HERA-CD27L and an anti-PD-1 antibody showed additive anti-tumor effects highlighting the importance of both T cell activation and checkpoint inhibition in anti-tumor immunity. In this manuscript, we describe the development of HERA-CD27L, a true CD27 agonist with a clearly defined forward-signaling mechanism of action.

The Hexavalent CD40 Agonist HERA-CD40L Induces T-Cell-mediated Antitumor Immune Response Through Activation of Antigen-presenting Cells.

CD40 ligand (TNFSF5/CD154/CD40L), a member of the tumor necrosis factor (TNF) superfamily is a key regulator of the immune system. The cognate receptor CD40 (TNFRSF5) is expressed broadly on antigen-presenting cells and many tumor types, and has emerged as an attractive target for immunologic cancer treatment. Most of the CD40 targeting drugs in clinical development are antibodies which display some disadvantages: their activity typically depends on Fcγ receptor-mediated crosslinking, and depletion of CD40-expressing immune cells by antibody-dependent cellular cytotoxicity compromises an efficient antitumor response. To overcome the inadequacies of antibodies, we have developed the hexavalent receptor agonist (HERA) Technology. HERA compounds are fusion proteins composed of 3 receptor binding domains in a single chain arrangement, linked to an Fc-silenced human IgG1 thereby generating a hexavalent molecule. HERA-CD40L provides efficient receptor agonism on CD40-expressing cells and, importantly, does not require FcγR-mediated crosslinking. Strong activation of NFκB signaling was observed upon treatment of B cells with HERA-CD40L. Monocyte treatment with HERA-CD40L promoted differentiation towards the M1 spectrum and repolarization of M2 spectrum macrophages towards the M1 spectrum phenotype. Treatment of in vitro co-cultures of T and B cells with HERA-CD40L-triggered robust antitumor activation of T cells, which depended upon direct interaction with B cells. In contrast, bivalent anti-CD40 antibodies and trivalent soluble CD40L displayed weak activity which critically depended on crosslinking. In vivo, a murine surrogate of HERA-CD40L-stimulated clonal expansion of OT-I-specific murine CD8 T cells and showed single agent antitumor activity in the CD40 syngeneic MC38-CEA mouse model of colorectal cancer, suggesting an involvement of the immune system in controlling tumor growth. We conclude that HERA-CD40L is able to establish robust antitumor immune responses both in vitro and in vivo.

The novel TRAIL-receptor agonist APG350 exerts superior therapeutic activity in pancreatic cancer cells.

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has raised attention as a novel anticancer therapeutic as it induces apoptosis preferentially in tumor cells. However, first-generation TRAIL-receptor agonists (TRAs), comprising recombinant TRAIL and agonistic receptor-specific antibodies, have not demonstrated anticancer activity in clinical studies. In fact, cancer cells are often resistant to conventional TRAs. Therefore, in addition to TRAIL-sensitizing strategies, next-generation TRAs with superior apoptotic activity are warranted. APG350 is a novel, highly potent TRAIL-receptor agonist with a hexavalent binding mode allowing the clustering of six TRAIL-receptors per drug molecule. Here we report on preclinical in vitro and in vivo studies testing the activity of APG350 on pancreatic ductal adenocarcinoma (PDAC) cells. We found that APG350 potently induced apoptosis of Colo357, PancTuI and Panc89 cells in vitro. In addition, APG350 treatment activated non-canonical TRAIL signaling pathways (MAPK, p38, JNK, ERK1/ERK2 and NF-κB) and induced the secretion of IL-8. Stable overexpression of Bcl-xL inhibited APG350-induced cell death and augmented activation of non-canonical pathways. Intriguingly, pre-treatment of Bcl-xL-overexpressing cells with the BH3-mimic Navitoclax restored their sensitivity to APG350. To study the effects of APG350 on PDAC cells in vivo, we applied two different orthotopic xenotransplantation mouse models, with and without primary tumor resection, representing adjuvant and palliative treatment regimes, respectively. APG350 treatment of established tumors (palliative treatment) significantly reduced tumor burden. These effects, however, were not seen in tumors with enforced overexpression of Bcl-xL. Upon primary tumor resection and subsequent APG350 treatment (adjuvant therapy), APG350 limited recurrent tumor growth and metastases. Importantly, therapeutic efficacy of APG350 treatment was more effective compared with treatment with soluble TRAIL in both models. In conclusion, APG350 represents a promising next-generation TRA for the treatment of PDAC. Moreover, our results suggest that combining APG350 with Navitoclax might be a succesfull strategy for cancers harboring mitochondrial apoptosis resistance.

Inhibition of CD95/CD95L (FAS/FASLG) Signaling with APG101 Prevents Invasion and Enhances Radiation Therapy for Glioblastoma.

CD95 (Fas/APO-1), a death receptor family member, activity has been linked to tumorigenicity in multiple cancers, including glioblastoma multiforme (GBM). A phase II clinical trial on relapsed glioblastoma patients demonstrated that targeted inhibition of CD95 signaling via the CD95 ligand (CD95L) binding and neutralizing Fc-fusion protein APG101 (asunercept) prolonged patient survival. Although CD95 signaling may be relevant for multiple aspects of tumor growth, the mechanism of action of APG101 in glioblastoma is not clear. APG101 action was examined by in vitro proliferation, apoptosis, and invasion assays with human and murine glioma and human microglial cells, as well as in vivo therapy studies with orthotopic gliomas and clinical data. APG101 inhibits CD95L-mediated invasion of glioma cells. APG101 treatment was effective in glioma-bearing mice, independently of the presence or absence of CD4 and CD8 T lymphocytes, which should be sensitive to CD95L. Combined with radiotherapy, APG101 demonstrated a reduction of tumor growth, fewer tumor satellites, reduced activity of matrix metalloproteinases (MMP) as well as prolonged survival of tumor-bearing mice compared with radiotherapy alone. Inhibiting rather than inducing CD95 activity is a break-of-paradigm therapeutic approach for malignant gliomas. Evidence, both in vitro and in vivo, is provided that CD95L-binding fusion protein treatment enhanced the efficacy of radiotherapy and reduced unwanted proinfiltrative effects by reducing metalloproteinase activity by directly affecting the tumor cells.Implications: APG101 (asunercept) successfully used in a controlled phase II glioblastoma trial (NCT01071837) acts anti-invasively by inhibiting matrix metalloproteinase signaling, resulting in additive effects together with radiotherapy and helping to further develop a treatment for this devastating disease. Mol Cancer Res; 16(5); 767-76. ©2018 AACR.

TPR subunits of the anaphase-promoting complex mediate binding to the activator protein CDH1.

BACKGROUND: Chromosome segregation and mitotic exit depend on activation of the anaphase-promoting complex (APC) by the substrate adaptor proteins CDC20 and CDH1. The APC is a ubiquitin ligase composed of at least 11 subunits. The interaction of APC2 and APC11 with E2 enzymes is sufficient for ubiquitination reactions, but the functions of most other subunits are unknown. RESULTS: We have biochemically characterized subcomplexes of the human APC. One subcomplex, containing APC2/11, APC1, APC4, and APC5, can assemble multiubiquitin chains but is unable to bind CDH1 and to ubiquitinate substrates. The other subcomplex contains all known APC subunits except APC2/11. This subcomplex can recruit CDH1 but fails to support any ubiquitination reaction. In vitro, the C termini of CDC20 and CDH1 bind to the closely related TPR subunits APC3 and APC7. Homology modeling predicts that these proteins are similar in structure to the peroxisomal import receptor PEX5, which binds cargo proteins via their C termini. APC activation by CDH1 depends on a conserved C-terminal motif that is also found in CDC20 and APC10. CONCLUSIONS: APC1, APC4, and APC5 may connect APC2/11 with TPR subunits. TPR domains in APC3 and APC7 recruit CDH1 to the APC and may thereby bring substrates into close proximity of APC2/11 and E2 enzymes. In analogy to PEX5, the different TPR subunits of the APC might function as receptors that interact with the C termini of regulatory proteins such as CDH1, CDC20, and APC10.

APG350 induces superior clustering of TRAIL receptors and shows therapeutic antitumor efficacy independent of cross-linking via Fcγ receptors.

Cancer cells can be specifically driven into apoptosis by activating Death-receptor-4 (DR4; TRAIL-R1) and/or Death-receptor-5 (DR5; TRAIL-R2). Albeit showing promising preclinical efficacy, first-generation protein therapeutics addressing this pathway, especially agonistic anti-DR4/DR5-monoclonal antibodies, have not been clinically successful to date. Due to their bivalent binding mode, effective apoptosis induction by agonistic TRAIL-R antibodies is achieved only upon additional events leading to antibody-multimer formation. The binding of these multimers to their target subsequently leads to effective receptor-clustering on cancer cells. The research results presented here report on a new class of TRAIL-receptor agonists overcoming this intrinsic limitation observed for antibodies in general. The main feature of these agonists is a TRAIL-mimic consisting of three TRAIL-protomer subsequences combined in one polypeptide chain, termed the single-chain TRAIL-receptor-binding domain (scTRAIL-RBD). In the active compounds, two scTRAIL-RBDs with three receptor binding sites each are brought molecularly in close proximity resulting in a fusion protein with a hexavalent binding mode. In the case of APG350-the prototype of this engineering concept-this is achieved by fusing the Fc-part of a human immunoglobulin G1 (IgG1)-mutein C-terminally to the scTRAIL-RBD polypeptide, thereby creating six receptor binding sites per drug molecule. In vitro, APG350 is a potent inducer of apoptosis on human tumor cell lines and primary tumor cells. In vivo, treatment of mice bearing Colo205-xenograft tumors with APG350 showed a dose-dependent antitumor efficacy. By dedicated muteins, we confirmed that the observed in vivo efficacy of the hexavalent scTRAIL-RBD fusion proteins is-in contrast to agonistic antibodies-independent of FcγR-based cross-linking events.

The death receptor CD95 activates adult neural stem cells for working memory formation and brain repair.

Adult neurogenesis persists in the subventricular zone and the dentate gyrus and can be induced upon central nervous system injury. However, the final contribution of newborn neurons to neuronal networks is limited. Here we show that in neural stem cells, stimulation of the "death receptor" CD95 does not trigger apoptosis but unexpectedly leads to increased stem cell survival and neuronal specification. These effects are mediated via activation of the Src/PI3K/AKT/mTOR signaling pathway, ultimately leading to a global increase in protein translation. Induction of neurogenesis by CD95 was further confirmed in the ischemic CA1 region, in the naive dentate gyrus, and after forced expression of CD95L in the adult subventricular zone. Lack of hippocampal CD95 resulted in a reduction in neurogenesis and working memory deficits. Following global ischemia, CD95-mediated brain repair rescued behavioral impairment. Thus, we identify the CD95/CD95L system as an instructive signal for ongoing and injury-induced neurogenesis.

Yes and PI3K bind CD95 to signal invasion of glioblastoma.

Invasion of surrounding brain tissue by isolated tumor cells represents one of the main obstacles to a curative therapy of glioblastoma multiforme. Here we unravel a mechanism regulating glioma infiltration. Tumor interaction with the surrounding brain tissue induces CD95 Ligand expression. Binding of CD95 Ligand to CD95 on glioblastoma cells recruits the Src family member Yes and the p85 subunit of phosphatidylinositol 3-kinase to CD95, which signal invasion via the glycogen synthase kinase 3-beta pathway and subsequent expression of matrix metalloproteinases. In a murine syngeneic model of intracranial GBM, neutralization of CD95 activity dramatically reduced the number of invading cells. Our results uncover CD95 as an activator of PI3K and, most importantly, as a crucial trigger of basal invasion of glioblastoma in vivo.

Localization of the coactivator Cdh1 and the cullin subunit Apc2 in a cryo-electron microscopy model of vertebrate APC/C.

The anaphase-promoting complex/cyclosome (APC/C) is a ubiquitin ligase with essential functions in mitosis, meiosis, and G1 phase of the cell cycle. APC/C recognizes substrates via coactivator proteins such as Cdh1, and bound substrates are ubiquitinated by E2 enzymes that interact with a hetero-dimer of the RING subunit Apc11 and the cullin Apc2. We have obtained three-dimensional (3D) models of human and Xenopus APC/C by angular reconstitution and random conical tilt (RCT) analyses of negatively stained cryo-electron microscopy (cryo-EM) preparations, have determined the masses of these particles by scanning transmission electron microscopy (STEM), and have mapped the locations of Cdh1 and Apc2. These proteins are located on the same side of the asymmetric APC/C, implying that this is where substrates are ubiquitinated. We have further identified a large flexible domain in APC/C that adopts a different orientation upon Cdh1 binding. Cdh1 may thus activate APC/C both by recruiting substrates and by inducing conformational changes.

Mitotic regulation of the human anaphase-promoting complex by phosphorylation.

The anaphase-promoting complex (APC) or cyclosome is a ubiquitin ligase that initiates anaphase and mitotic exit. APC activation is thought to depend on APC phosphorylation and Cdc20 binding. We have identified 43 phospho-sites on APC of which at least 34 are mitosis specific. Of these, 32 sites are clustered in parts of Apc1 and the tetratricopeptide repeat (TPR) subunits Cdc27, Cdc16, Cdc23 and Apc7. In vitro, at least 15 of the mitotic phospho-sites can be generated by cyclin-dependent kinase 1 (Cdk1), and 3 by Polo-like kinase 1 (Plk1). APC phosphorylation by Cdk1, but not by Plk1, is sufficient for increased Cdc20 binding and APC activation. Immunofluorescence microscopy using phospho-antibodies indicates that APC phosphorylation is initiated in prophase during nuclear uptake of cyclin B1. In prometaphase phospho-APC accumulates on centrosomes where cyclin B ubiquitination is initiated, appears throughout the cytosol and disappears during mitotic exit. Plk1 depletion neither prevents APC phosphorylation nor cyclin A destruction in vivo. These observations imply that APC activation is initiated by Cdk1 already in the nuclei of late prophase cells.