Synthetic ligands of death receptor 5 display a cell-selective agonistic effect at different oligomerization levels

Target receptor identification and subsequent treatment of resected brain tumors with encapsulated and engineered allogeneic stem cells

Cellular therapies offer a promising therapeutic strategy for the highly malignant brain tumor, glioblastoma (GBM). However, their clinical translation is limited by the lack of effective target identification and stringent testing in pre-clinical models that replicate standard treatment in GBM patients. In this study, we show the detection of cell surface death receptor (DR) target on CD146-enriched circulating tumor cells (CTC) captured from the blood of mice bearing GBM and patients diagnosed with GBM. Next, we developed allogeneic "off-the-shelf" clinical-grade bifunctional mesenchymal stem cells (MSCBif) expressing DR-targeted ligand and a safety kill switch. We show that biodegradable hydrogel encapsulated MSCBif (EnMSCBif) has a profound therapeutic efficacy in mice bearing patient-derived invasive, primary and recurrent GBM tumors following surgical resection. Activation of the kill switch enhances the efficacy of MSCBif and results in their elimination post-tumor treatment which can be tracked by positron emission tomography (PET) imaging. This study establishes a foundation towards a clinical trial of EnMSCBif in primary and recurrent GBM patients.

Lipid Phase Separation in Vesicles Enhances TRAIL-Mediated Cytotoxicity

Ligand spatial presentation and density play important roles in signaling pathways mediated by cell receptors and are critical parameters when designing protein-conjugated therapeutic nanoparticles. Here, we harness lipid phase separation to spatially control the protein presentation on lipid vesicles. We use this system to improve the cytotoxicity of TNF-related apoptosis inducing ligand (TRAIL), a therapeutic anticancer protein. Vesicles with phase-separated TRAIL presentation induce more cell death in Jurkat cancer cells than vesicles with uniformly presented TRAIL, and cytotoxicity is dependent on TRAIL density. We assess this relationship in other cancer cell lines and demonstrate that phase-separated vesicles with TRAIL only enhance cytotoxicity through one TRAIL receptor, DR5, while another TRAIL receptor, DR4, is less sensitive to TRAIL density. This work demonstrates a rapid and accessible method to control protein conjugation and density on vesicles that can be adopted to other nanoparticle systems to improve receptor signaling by nanoparticles.

Say no to drugs: Bioactive macromolecular therapeutics without conventional drugs

The vast majority of nanomedicines (NM) investigated today consists of a macromolecular carrier and a drug payload (conjugated or encapsulated), with a purpose of preferential delivery of the drug to the desired site of action, either through passive accumulation, or by active targeting via ligand-receptor interaction. Several drug delivery systems (DDS) have already been approved for clinical use. However, recent reports are corroborating the notion that NM do not necessarily need to include a drug payload, but can exert biological effects through specific binding/blocking of important target proteins at the site of action. The seminal work of Kopeček et al. on N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers containing biorecognition motifs (peptides or oligonucleotides) for crosslinking cell surface non-internalizing receptors of malignant cells and inducing their apoptosis, without containing any low molecular weight drug, led to the definition of a special group of NM, termed Drug-Free Macromolecular Therapeutics (DFMT). Systems utilizing this approach are typically designed to employ pendant targeting-ligands on the same macromolecule to facilitate multivalent interactions with receptors. The lack of conventional small molecule drugs reduces toxicity and adverse effects at off-target sites. In this review, we describe different types of DFMT that possess biological activity without attached low molecular weight drugs. We classified the relevant research into several groups by their mechanisms of action, and compare the advantages and disadvantages of these different approaches. We show that identification of target sites, specificity of attached targeting ligands, binding affinity and the synthesis of carriers of defined size and ligand spacing are crucial aspects of DFMT development. We further discuss how knowledge in the field of NM accumulated in the past few decades can help in the design of a successful DFMT to speed up the translation into clinical practice.

Nongenetic engineering strategies for regulating receptor oligomerization in living cells

Nongenetic strategies for regulating receptor oligomerization in living cells based on DNA, protein, small molecules and physical stimuli.

TRAIL-R1 and TRAIL-R2 Mediate TRAIL-Dependent Apoptosis in Activated Primary Human B Lymphocytes

The maintenance of B cell homeostasis requires a tight control of B cell generation, survival, activation, and maturation. In lymphocytes upon activation, increased sensitivity to apoptotic signals helps controlling differentiation and proliferation. The death receptor Fas is important in this context because genetic Fas mutations in humans lead to an autoimmune lymphoproliferative syndrome that is similar to lymphoproliferation observed in Fas-deficient mice. In contrast, the physiological role of TNF-related apoptosis-inducing ligand receptors (TRAIL-Rs) in humans has been poorly studied so far. Indeed, most studies have focused on tumor cell lines and on mouse models whose results are difficult to transpose to primary human B cells. In the present work, the expression of apoptosis-inducing TRAIL-R1 and TRAIL-R2 and of the decoy receptors TRAIL-R3 and TRAIL-R4 was systematically studied in all developmental stages of peripheral B cells isolated from the blood and secondary lymphoid organs. Expression of TRAIL-Rs is modulated along development, with highest levels observed in germinal center B cells. In addition, T-dependent and T-independent signals elicited induction of TRAIL-Rs with distinct kinetics, which differed among B cell subpopulations: switched memory cells rapidly upregulated TRAIL-R1 and -2 upon activation while naïve B cells only reached similar expression levels at later time points in culture. Increased expression of TRAIL-R1 and -2 coincided with a caspase-3-dependent sensitivity to TRAIL-induced apoptosis in activated B cells but not in freshly isolated resting B cells. Finally, both TRAIL-R1 and TRAIL-R2 could signal actively and both contributed to TRAIL-induced apoptosis. In conclusion, this study provides a systematic analysis of the expression of TRAIL-Rs in human primary B cells and of their capacity to signal and induce apoptosis. This dataset forms a basis to further study and understand the dysregulation of TRAIL-Rs and TRAIL expression observed in autoimmune diseases. Additionally, it will be important to foresee potential bystander immunomodulation when TRAIL-R agonists are used in cancer treatment.

Morniga-G, a T/Tn-Specific Lectin, Induces Leukemic Cell Death via Caspase and DR5 Receptor-Dependent Pathways

Morniga-G, the Gal-specific black mulberry (Morus nigra) lectin, displays high affinity for T (CD176) and Tn (CD175) antigens, frequently expressed at the cancer cell surface. The effects of Morniga-G were investigated on a Tn-positive leukemic Jurkat cell line. The lectin, used in a concentration range between 5⁻20 μg/mL, induced cell death in leukemic Jurkat cells. Microscopic and cytofluorometric analyses indicated that Jurkat cell death was essentially apoptotic, associated with an increase in the ceramide content and a depolarization of the mitochondrial transmembrane potential. This lectin-mediated cell death was inhibited by the pan caspase-inhibitor zVAD. In addition, cleavage of caspases 8, 9, and 3 was observed in Morniga-G-treated Jurkat cells whereas Jurkat cell lines that are deficient in caspase 8⁻10, caspase 9, or FADD, survived to the lectin-mediated toxicity. Furthermore, in the presence of TRAIL- or DR5-blocking mononoclonal antibodies, Jurkat cells became resistant to Morniga-G, suggesting that the lectin triggers cell death via the TRAIL/DR5 pathway. In silico computer simulations suggest that Morniga-G might facilitate both the DR5 dimerization and the building of TRAIL/DR5 complexes. Finally, upon treatment of Jurkat cells with benzyl-GalNAc, an O-glycosylation inhibitor, a decrease in Tn antigen expression associating with a reduced Morniga-G toxicity, was observed. Taken together, these results suggest that Morniga-G induces the cell death of Tn-positive leukemic cells via concomitant O-glycosylation-, caspase-, and TRAIL/DR5-dependent pathways.

Biorecognition: A key to drug-free macromolecular therapeutics

This review highlights a new paradigm in macromolecular nanomedicine - drug-free macromolecular therapeutics (DFMT). The effectiveness of the new system is based on biorecognition events without the participation of low molecular weight drugs. Apoptosis of cells can be initiated by the biorecognition of complementary peptide/oligonucleotide motifs at the cell surface resulting in the crosslinking of slowly internalizing receptors. B-cell CD20 receptors and Non-Hodgkin lymphoma (NHL) were chosen as the first target. Exposing cells to a conjugate of one motif with a targeting ligand decorates the cells with this motif. Further exposure of decorated cells to a macromolecule (synthetic polymer or human serum albumin) containing multiple copies of the complementary motif as grafts results in receptor crosslinking and apoptosis induction in vitro and in vivo. The review focuses on recent developments and explores the mechanism of action of DFMT. The altered molecular signaling pathways demonstrated the great potential of DFMT to overcome rituximab resistance resulting from either down-regulation of CD20 or endocytosis and trogocytosis of rituximab/CD20 complexes. The suitability of this approach for the treatment of blood borne cancers is confirmed. In addition, the widespread applicability of DFMT as a new concept in macromolecular therapeutics for numerous diseases is exposed.

1H, 13C, 15N NMR resonance assignments and secondary structure determination of the extra-cellular domain from the human proapoptotic TRAIL-R2 death receptor 5 (DR5-ECD)

Death receptors (DR) selectively drive cancer cells to apoptosis upon binding to the Tumor necrosis factor-a-Related Apoptosis-Inducing Ligand (TRAIL). Complex formation induces the oligomerization of the death receptors DR4 (TRAIL-R1) and DR5 (TRAIL-R2) and transduces the apoptogenic signal to their respective death domains, leading to Death Inducing Signaling Complex (DISC) formation, caspase activation and ultimately cell death. Several crystal structures of the ExtraCellular Domain from Death Receptor 5 (DR5-ECD) have been reported in complex with the TRAIL ligand or anti-DR5 antibodies, but none for the isolated protein. In order to fill this gap and to perform binding experiments with TRAIL peptidomimetics, we have produced isotopically labelled DR5-ECD and started a conformational analysis by using high-field 3D NMR spectroscopy. Herein, we present the first resonance assignment of a TRAIL receptor in solution and the determination of its secondary structure from NMR chemical shifts.

Relationship between the agonist activity of synthetic ligands of TRAIL-R2 and their cell surface binding modes

Tumor Necrosis Factor Receptor Apoptosis Inducing Ligand (TRAIL) appears as an interesting candidate for targeted cancer therapy as it induces apoptosis in cancer cells without toxicity to normal cells. TRAIL elicits apoptosis through agonist death receptor TRAIL-R1 and TRAIL-R2 engagement. Nevertheless, recombinant soluble TRAIL and monoclonal antibodies against these receptors demonstrated insufficient efficacy in clinical trials. This may be explained by the cell-type dependency of the apoptotic response, itself influenced by the effect on ligand binding mode of factors such as the level of receptor oligomerization or glycosylation. To investigate the relation between binding mode and signaling, we used previously described synthetic divalent and monovalent peptides specific for TRAIL-R2. We measured their pro-apoptotic activity on three cancer cell lines sensitive to rhTRAIL induced-apoptosis and monitored their cell-surface binding kinetics. The two divalent peptides bound with strong affinity to TRAIL-R2 expressed on B lymphoma BJAB cells and induced a high degree of apoptosis. By contrast, the same peptides bound weakly to TRAIL-R2 expressed at the surface of the human colon cancer HCT116 or T lymphoma Jurkat cell lines and did not induce their apoptosis. Cross-linking experiments suggest that these differences could be afforded by variations in the TRAIL-R2 oligomerization state at cell surface before ligand addition. Moreover divalent peptides showed a different efficiency in BJAB apoptosis induction, and kinetic distribution analysis of the BJAB binding curves suggested subtle differences in binding mechanisms. Thus our data support a relation between the cell-surface binding mode of the peptides and their pro-apoptotic activity. In this case the precise characterization of ligand binding to the surface of living cells would be predictive of the therapeutic potential of TRAIL-R2 synthetic ligands prior to clinical trials.

Superior Properties of Fc-comprising scTRAIL Fusion Proteins

The TNF-related apoptosis-inducing ligand (TRAIL) has been considered as a promising molecule for cancer treatment. However, clinical studies with soluble TRAIL failed to show therapeutic activity, which resulted in subsequent development of more potent TRAIL-based therapeutics. In this study, we applied defined oligomerization and tumor targeting as strategies to further improve the activity of a single-chain version of TRAIL (scTRAIL). We compared three different formats of EGF receptor (EGFR)-targeting dimeric scTRAIL fusion proteins [Diabody (Db)-scTRAIL, scFv-IgE heavy chain domain 2 (EHD2)-scTRAIL, scFv-Fc-scTRAIL] as well as two nontargeted dimeric scTRAIL molecules (EHD2-scTRAIL, Fc-scTRAIL) to reveal the influence of targeting and protein format on antitumor activity. All EGFR-targeted dimeric scTRAIL molecules showed similar binding properties and comparable cell death induction in vitro, exceeding the activity of the respective nontargeted dimeric format and monomeric scTRAIL. Superior properties were observed for the Fc fusion proteins with respect to production and in vivo half-life. In vivo studies using a Colo205 xenograft model revealed potent antitumor activity of all EGFR-targeting formats and Fc-scTRAIL and furthermore highlighted the higher efficacy of fusion proteins comprising an Fc part. Despite enhanced in vitro cell death induction of targeted scTRAIL molecules, however, comparable antitumor activities were found for the EGFR-targeting scFv-Fc-scTRAIL and the nontargeting Fc-scTRAIL in vivoMol Cancer Ther; 16(12); 2792-802. ©2017 AACR.