Saporin-S6: a useful tool in cancer therapy

Streptavidin-drug conjugates streamline optimization of antibody-based conditioning for hematopoietic stem cell transplantation

Hematopoietic stem cell transplantation (HSCT) conditioning using antibody-drug conjugates (ADC) is a promising alternative to conventional chemotherapy- and irradiation-based conditioning regimens. The drug payload bound to an ADC is a key contributor to its efficacy and potential toxicities; however, a comparison of HSCT conditioning ADCs produced with different toxic payloads has not been performed. Indeed, ADC optimization studies in general are hampered by the inability to produce and screen multiple combinations of antibody and drug payload in a rapid, cost-effective manner. Herein, we used Click chemistry to covalently conjugate four different small molecule payloads to streptavidin; these streptavidin-drug conjugates can then be joined to any biotinylated antibody to produce stable, indirectly conjugated ADCs. Evaluating CD45-targeted ADCs produced with this system, we found the pyrrolobenzodiazepine (PBD) dimer SGD-1882 was the most effective payload for targeting mouse and human hematopoietic stem cells (HSCs) and acute myeloid leukemia cells. In murine syngeneic HSCT studies, a single dose of CD45-PBD enabled near-complete conversion to donor hematopoiesis. Finally, human CD45-PBD provided significant antitumor benefit in a patient-derived xenograft model of acute myeloid leukemia. As our streptavidin-drug conjugates were generated in-house with readily accessible equipment, reagents, and routine molecular biology techniques, we anticipate this flexible platform will facilitate the evaluation and optimization of ADCs for myriad targeting applications.

Cell surface sculpting using logic-gated protein actuators

Cell differentiation and tissue specialization lead to unique cellular surface landscapes and exacerbated or loss of expression patterns can result in further heterogenicity distinctive of pathological phenotypes1-3. Immunotherapies and emerging protein therapeutics seek to exploit such differences by engaging cell populations selectively based on their surface markers. Since a single surface antigen rarely defines a specific cell type4,5, the development of programmable molecular systems that integrate multiple cell surface features to convert on-target inputs to user-defined outputs is highly desirable. Here, we describe an autonomous decision-making protein device driven by proximity-gated protein trans-splicing that allows local generation of an active protein from two otherwise inactive fragments. We show that this protein actuator platform can perform various Boolean logic operations on cell surfaces, allowing highly selective recruitment of enzymatic and cytotoxic activities to specific cells within mixed populations. Due to its intrinsic modularity and tunability, this technology is expected to be compatible with different types of inputs, targeting modalities and functional outputs, and as such will have broad application in the synthetic biology and biotechnology areas.

Hosts and Heterologous Expression Strategies of Recombinant Toxins for Therapeutic Purposes

The production of therapeutic recombinant toxins requires careful host cell selection. Bacteria, yeast, and mammalian cells are common choices, but no universal solution exists. Achieving the delicate balance in toxin production is crucial due to potential self-intoxication. Recombinant toxins from various sources find applications in antimicrobials, biotechnology, cancer drugs, and vaccines. "Toxin-based therapy" targets diseased cells using three strategies. Targeted cancer therapy, like antibody-toxin conjugates, fusion toxins, or "suicide gene therapy", can selectively eliminate cancer cells, leaving healthy cells unharmed. Notable toxins from various biological sources may be used as full-length toxins, as plant (saporin) or animal (melittin) toxins, or as isolated domains that are typical of bacterial toxins, including Pseudomonas Exotoxin A (PE) and diphtheria toxin (DT). This paper outlines toxin expression methods and system advantages and disadvantages, emphasizing host cell selection's critical role.

New Insights on Saporin Resistance to Chemical Derivatization with Heterobifunctional Reagents

Saporin is a type 1 ribosome-inactivating protein widely used as toxic payload in the construction of targeted toxins, chimeric molecules formed by a toxic portion linked to a carrier moiety. Among the most used carriers, there are large molecules (mainly antibodies) and small molecules (such as neurotransmitters, growth factors and peptides). Some saporin-containing targeted toxins have been used for the experimental treatment of several diseases, giving very promising results. In this context, one of the reasons for the successful use of saporin lies in its resistance to proteolytic enzymes and to conjugation procedures. In this paper, we evaluated the influence of derivatization on saporin using three heterobifunctional reagents, namely 2-iminothiolane (2-IT), N-succinimidyl 3-(2-pyridyldithio)propionate (SPDP) and 4-succinimidyloxycarbonyl-α-methyl-α-[2-pyridyldithio]toluene (SMPT). In order to obtain the highest number of inserted -SH groups with the lowest reduction of saporin biological activities, we assessed the residual ability of saporin to inhibit protein synthesis, to depurinate DNA and to induce cytotoxicity after derivatization. Our results demonstrate that saporin maintains an excellent resistance to derivatization processes, especially with SPDP, and permit us to define reaction conditions, in which saporin biological properties may not be altered. Therefore, these findings provide useful information for the construction of saporin-based targeted toxins, especially with small carriers.

Expanding role of ribosome-inactivating proteins: From toxins to therapeutics

Ribosome-inactivating proteins (RIPs) are toxic proteins with N-glycosidase activity. RIPs exert their action by removing a specific purine from 28S rRNA, thereby, irreversibly inhibiting the process of protein synthesis. RIPs can target both prokaryotic and eukaryotic cells. In bacteria, the production of RIPs aid in the process of pathogenesis whereas, in plants, the production of these toxins has been attributed to bolster defense against insects, viral, bacterial and fungal pathogens. In recent years, RIPs have been engineered to target a particular cell type, this has fueled various experiments testing the potential role of RIPs in many biomedical applications like anti-viral and anti-tumor therapies in animals as well as anti-pest agents in engineered plants. In this review, we present a comprehensive study of various RIPs, their mode of action, their significance in various fields involving plants and animals. Their potential as treatment options for plant infections and animal diseases is also discussed.

Polymersome-based protein drug delivery - quo vadis?

Protein-based therapeutics are an attractive alternative to established therapeutic approaches and represent one of the fastest growing families of drugs. While many of these proteins can be delivered using established formulations, the intrinsic sensitivity of proteins to denaturation sometimes calls for a protective carrier to allow administration. Historically, lipid-based self-assembled structures, notably liposomes, have performed this function. After the discovery of polymersome-based targeted drug-delivery systems, which offer manifold advantages over lipid-based structures, the scientific community expected that such systems would take the therapeutic world by storm. However, no polymersome formulations have been commercialised. In this review article, we discuss key obstacles for the sluggish translation of polymersome-based protein nanocarriers into approved pharmaceuticals, which include limitations imparted by the use of non-degradable polymers, the intricacies of polymersome production methods, and the complexity of the in vivo journey of polymersomes across various biological barriers. Considering this complex subject from a polymer chemist's point of view, we highlight key areas that are worthy to explore in order to advance polymersomes to a level at which clinical trials become worthwhile and translation into pharmaceutical and nanomedical applications is realistic.

Tumor-specific intracellular delivery: peptide-guided transport of a catalytic toxin

There continues to be a need for cancer-specific ligands that can deliver a wide variety of therapeutic cargos. Ligands demonstrating both tumor-specificity and the ability to mediate efficient cellular uptake of a therapeutic are critical to expand targeted therapies. We previously reported the selection of a peptide from a peptide library using a non-small cell lung cancer (NSCLC) cell line as the target. Here we optimize our lead peptide by a series of chemical modifications including truncations, N-terminal capping, and changes in valency. The resultant 10 amino acid peptide has an affinity of <40 nM on four different NSCLC cell lines as a monomer and is stable in human serum for >48 h. The peptide rapidly internalizes upon cell binding and traffics to the lysosome. The peptide homes to a tumor in an animal model and is retained up to 72 h. Importantly, we demonstrate that the peptide can deliver the cytotoxic protein saporin specifically to cancer cells in vitro and in vivo, resulting in an effective anticancer agent.

A Novel EGFR Targeted Immunotoxin Based on Cetuximab and Type 1 RIP Quinoin Overcomes the Cetuximab Resistance in Colorectal Cancer Cells

Cetuximab is a monoclonal antibody blocking the epidermal growth factor receptor (EGFR) in metastatic colorectal cancer (mCRC). However, cetuximab treatment has no clinical benefits in patients affected by mCRC with KRAS mutation or in the presence of constitutive activation of signalling pathways acting downstream of the EGFR. The aim of this study was to improve cetuximab's therapeutic action by conjugating cetuximab with the type 1 ribosome inactivating protein (RIP) quinoin isolated from quinoa seeds. A chemical conjugation strategy based on the use of heterobifunctional reagent succinimidyl 3-(2-pyridyldithio)propionate (SPDP) was applied to obtain the antibody-type 1 RIP chimeric immunoconjugate. The immunotoxin was then purified by chromatographic technique, and its enzymatic action was evaluated compared to quinoin alone. Functional assays were performed to test the cytotoxic action of the quinoin cetuximab immunoconjugate against the cetuximab-resistant GEO-CR cells. The novel quinoin cetuximab immunoconjugate showed a significant dose-dependent cytotoxicity towards GEO-CR cells, achieving IC50 values of 27.7 nM (~5.0 μg/mL) at 72 h compared to cetuximab (IC50 = 176.7 nM) or quinoin (IC50 = 149.3 nM) alone assayed in equimolar amounts. These results support the therapeutic potential of quinoin cetuximab immunoconjugate for the EGFR targeted therapy, providing a promising candidate for further development towards clinical use in the treatment of cetuximab-resistant metastatic colorectal cancer.

Biological Activities of Ribosome-Inactivating Proteins

After more than 50 years of research, studies on the structure and biological activities of ribosome-inactivating proteins (RIPs) continue to provide a field of great interest within the scientific community, both for the health risks they pose and their applications in medicine and biotechnology [...].

Recent Advances in the Biomedical Applications of Functionalized Nanogels

Nanomaterials have been extensively used in several applications in the past few decades related to biomedicine and healthcare. Among them, nanogels (NGs) have emerged as an important nanoplatform with the properties of both hydrogels and nanoparticles for the controlled/sustained delivery of chemo drugs, nucleic acids, or other bioactive molecules for therapeutic or diagnostic purposes. In the recent past, significant research efforts have been invested in synthesizing NGs through various synthetic methodologies such as free radical polymerization, reversible addition-fragmentation chain-transfer method (RAFT) and atom transfer radical polymerization (ATRP), as well as emulsion techniques. With further polymeric functionalizations using activated esters, thiol-ene/yne processes, imines/oximes formation, cycloadditions, nucleophilic addition reactions of isocyanates, ring-opening, and multicomponent reactions were used to obtain functionalized NGs for targeted delivery of drug and other compounds. NGs are particularly intriguing for use in the areas of diagnosis, analytics, and biomedicine due to their nanodimensionality, material characteristics, physiological stability, tunable multi-functionality, and biocompatibility. Numerous NGs with a wide range of functionalities and various external/internal stimuli-responsive modalities have been possible with novel synthetic reliable methodologies. Such continuous development of innovative, intelligent materials with novel characteristics is crucial for nanomedicine for next-generation biomedical applications. This paper reviews the synthesis and various functionalization strategies of NGs with a focus on the recent advances in different biomedical applications of these surface modified/functionalized single-/dual-/multi-responsive NGs, with various active targeting moieties, in the fields of cancer theranostics, immunotherapy, antimicrobial/antiviral, antigen presentation for the vaccine, sensing, wound healing, thrombolysis, tissue engineering, and regenerative medicine.

Virus-inspired strategies for cancer therapy

The intentional use of viruses for cancer therapy dates back over a century. As viruses are inherently immunogenic and naturally optimized delivery vehicles, repurposing viruses for drug delivery, tumor antigen presentation, or selective replication in cancer cells represents a simple and elegant approach to cancer treatment. While early virotherapy was fraught with harsh side effects and low response rates, virus-based therapies have recently seen a resurgence due to newfound abilities to engineer and tune oncolytic viruses, virus-like particles, and virus-mimicking nanoparticles for improved safety and efficacy. However, despite their great potential, very few virus-based therapies have made it through clinical trials. In this review, we present an overview of virus-inspired approaches for cancer therapy, discuss engineering strategies to enhance their mechanisms of action, and highlight their application for overcoming the challenges of traditional cancer therapies.

Saporin Toxin Delivered by Engineered Colloidal Nanoparticles Is Strongly Effective against Cancer Cells

Ribosome-inactivating proteins, including Saporin toxin, have found application in the search for innovative alternative cancer therapies to conventional chemo- and radiotherapy. Saporin’s main mechanism of action involves the inhibition of cytoplasmic protein synthesis. Its strong theoretical efficacy is counterbalanced by negligible cell uptake and diffusion into the cytosol. In this work, we demonstrate that by immobilizing Saporin on iron oxide nanoparticles coated with an amphiphilic polymer, which promotes nanoconjugate endosomal escape, a strong cytotoxic effect mediated by ribosomal functional inactivation can be achieved. Cancer cell death was mediated by apoptosis dependent on nanoparticle concentration but independent of surface ligand density. The cytotoxic activity of Saporin-conjugated colloidal nanoparticles proved to be selective against three different cancer cell lines in comparison with healthy fibroblasts.

RIPpore: A Novel Host-Derived Method for the Identification of Ricin Intoxication through Oxford Nanopore Direct RNA Sequencing

Ricin is a toxin which enters cells and depurinates an adenine base in the sarcin-ricin loop in the large ribosomal subunit, leading to the inhibition of protein translation and cell death. We postulated that this depurination event could be detected using Oxford Nanopore Technologies (ONT) direct RNA sequencing, detecting a change in charge in the ricin loop. In this study, A549 cells were exposed to ricin for 2–24 h in order to induce depurination. In addition, a novel software tool was developed termed RIPpore that could quantify the adenine modification of ribosomal RNA induced by ricin upon respiratory epithelial cells. We provided demonstrable evidence for the first time that this base change detected is specific to RIP activity using a neutralising antibody against ricin. We believe this represents the first detection of depurination in RNA achieved using ONT sequencers. Collectively, this work highlights the potential for ONT and direct RNA sequencing to detect and quantify depurination events caused by ribosome-inactivating proteins such as ricin. RIPpore could have utility in the evaluation of new treatments and/or in the diagnosis of exposure to ricin.

Spatio-temporal control of cell death by selective delivery of photo-activatable proteins

Protein therapeutics offer exquisite selectivity in targeting cellular processes and behaviors, but are rarely used against non‐cell surface targets due to their poor cellular uptake. While cell‐penetrating peptides can be used to deliver recombinant proteins to the cytosol, it is generally difficult to selectively deliver active proteins to target cells. Here, we report a recombinantly produced, intracellular protein delivery and targeting platform that uses a photocaged intein to regulate the spatio‐temporal activation of protein activity in selected cells upon irradiation with light. The platform was successfully demonstrated for two cytotoxic proteins to selectively kill cancer cells after photoactivation of intein splicing. This platform can generically be applied to any protein whose activity can be disrupted by a fused intein, allowing it to underpin a wide variety of future protein therapeutics.

Upregulation of p75NTR by Histone Deacetylase Inhibitors Sensitizes Human Neuroblastoma Cells to Targeted Immunotoxin-Induced Apoptosis

Histone deacetylase (HDAC) inhibitors are novel chemotherapy agents with potential utility in the treatment of neuroblastoma, the most frequent solid tumor of childhood. Previous studies have shown that the exposure of human neuroblastoma cells to some HDAC inhibitors enhanced the expression of the common neurotrophin receptor p75NTR. In the present study we investigated whether the upregulation of p75NTR could be exploited to render neuroblastoma cells susceptible to the cytotoxic action of an anti-p75NTR antibody conjugated to the toxin saporin-S6 (p75IgG-Sap). We found that two well-characterized HDAC inhibitors, valproic acid (VPA) and entinostat, were able to induce a strong expression of p75NTR in different human neuroblastoma cell lines but not in other cells, with entinostat, displaying a greater efficacy than VPA. Cell pretreatment with entinostat enhanced p75NTR internalization and intracellular saporin-S6 delivery following p75IgG-Sap exposure. The addition of p75IgG-Sap had no effect on vehicle-pretreated cells but potentiated the apoptotic cell death that was induced by entinostat. In three-dimensional neuroblastoma cell cultures, the subsequent treatment with p75IgG-Sap enhanced the inhibition of spheroid growth and the impairment of cell viability that was produced by entinostat. In athymic mice bearing neuroblastoma xenografts, chronic treatment with entinostat increased the expression of p75NTR in tumors but not in liver, kidney, heart, and cerebellum. The administration of p75IgG-Sap induced apoptosis only in tumors of mice that were pretreated with entinostat. These findings define a novel experimental strategy to selectively eliminate neuroblastoma cells based on the sequential treatment with entinostat and a toxin-conjugated anti-p75NTR antibody.

Carbamoylated Guanidine-Containing Polymers for Non-Covalent Functional Protein Delivery in Serum-Containing Media

Despite the high potential of controlling cellular processes and treating various diseases by intracellularly delivered proteins, current delivery systems exhibit poor efficiency due to poor serum stability, cellular entry, and cytosolic availability of proteins. Here, we report a novel functional group, phenyl carbamoylated guanidine (Ph-CG), that greatly enhances the delivery efficiency to various types of cells. Owing to the substantially lowered pK_a , the hydrophobic Ph-CG offers optimized inter-macromolecular interactions via enhanced hydrogen-bonding and hydrophobic interactions. The coplanarity of Ph-CG also leads to the better intracellular entry of protein complexes. Intracellularly delivered apoptosis-inducing enzymes and antibodies significantly induce cell viability inhibitions in a serum-containing medium. The newly developed Ph-CG can be introduced to various existing carriers, leading to the realization of future therapeutic protein delivery.

Saporin as a Commercial Reagent: Its Uses and Unexpected Impacts in the Biological Sciences—Tools from the Plant Kingdom

Saporin is a ribosome-inactivating protein that can cause inhibition of protein synthesis and causes cell death when delivered inside a cell. Development of commercial Saporin results in a technology termed ‘molecular surgery’, with Saporin as the scalpel. Its low toxicity (it has no efficient method of cell entry) and sturdy structure make Saporin a safe and simple molecule for many purposes. The most popular applications use experimental molecules that deliver Saporin via an add-on targeting molecule. These add-ons come in several forms: peptides, protein ligands, antibodies, even DNA fragments that mimic cell-binding ligands. Cells that do not express the targeted cell surface marker will not be affected. This review will highlight some newer efforts and discuss significant and unexpected impacts on science that molecular surgery has yielded over the last almost four decades. There are remarkable changes in fields such as the Neurosciences with models for Alzheimer’s Disease and epilepsy, and game-changing effects in the study of pain and itch. Many other uses are also discussed to record the wide-reaching impact of Saporin in research and drug development.

Suicide nanoplasmids coding for ribosome-inactivating proteins

Conventional eukaryotic expression plasmids contain a DNA backbone that is dispensable for the cellular expression of the transgene. In order to reduce the vector size, minicircle DNA technology was introduced. A drawback of the minicircle technology are considerable production costs. Nanoplasmids are a relatively new class of mini-DNA constructs that are of tremendous potential for pharmaceutical applications. In this study we have designed novel suicide nanoplasmid constructs coding for plant derived ribosome-inactivating proteins. The suicide-nanoplasmids were formulated with a targeted K16-lysine domain, analyzed for size, and characterized by electron microscopy. The anti-proliferative activity of the suicide-nanoplasmids was investigated in vitro by real time microscopy and the expression kinetic was determined using an enhanced green fluorescent protein nanoplasmid variant. In an aggressive in vivo neuroblastoma tumor model, treated mice showed a reduced tumor growth whereby the therapy was well tolerated.

Generation of nanobodies targeting the human, transcobalamin-mediated vitamin B12 uptake route

Cellular uptake of vitamin B₁₂ in humans is mediated by the endocytosis of the B₁₂ carrier protein transcobalamin (TC) via its cognate cell surface receptor TCblR, encoded by the CD320 gene. Because CD320 expression is associated with the cell cycle and upregulated in highly proliferating cells including cancer cells, this uptake route is a potential target for cancer therapy. We developed and characterized four camelid nanobodies that bind holo-TC (TC in complex with B₁₂ ) or the interface of the human holo-TC:TCblR complex with nanomolar affinities. We determined X-ray crystal structures of these nanobodies bound to holo-TC:TCblR, which enabled us to map their binding epitopes. When conjugated to the model toxin saporin, three of our nanobodies caused growth inhibition of HEK293T cells and therefore have the potential to inhibit the growth of human cancer cells. We visualized the cellular binding and endocytic uptake of the most potent nanobody (TC-Nb4) using fluorescent light microscopy. The co-crystal structure of holo-TC:TCblR with another nanobody (TC-Nb34) revealed novel features of the interface of TC and the LDLR-A1 domain of TCblR, rationalizing the decrease in the affinity of TC-B₁₂ binding caused by the Δ88 mutation in CD320.

Light-controlled elimination of PD-L1+ cells

The programmed death ligand-1 (PD-L1), also known as CD274 or B7-H1, is mainly expressed on cancer cells and/or immunosuppressive cells in the tumor microenvironment (TME) and plays an essential role in tumor progression and immune escape. Immune checkpoint inhibitors (ICIs) of the PD-1/PD-L1 axis have shown impressive clinical success, however, the majority of the patients do not respond to immune checkpoint therapy (ICT). Thus, to overcome ICT resistance there is a high need for potent and novel strategies that simultaneously target both tumor cells and immunosuppressive cells in the TME. In this study, we show that the intracellular light-controlled drug delivery method photochemical internalization (PCI) induce specific and strongly enhanced cytotoxic effects of the PD-L1-targeting immunotoxin, anti-PD-L1-saporin (Anti-PDL1-SAP), in the PD-L1+ triple-negative breast cancer MDA-MB-231 cell line, while no enhanced efficacy was obtained in the PD-L1 negative control cell line MDA-MB-453. Using fluorescence microscopy, we reveal that the anti-PD-L1 antibody binds to PD-L1 on the surface of the MDA-MD-231 cells and overnight accumulates in late endosomes and lysosomes where it co-localizes with the PCI photosensitizer fimaporfin (TPCS_2a). Moreover, light-controlled endosomal/lysosomal escape of the anti-PD-L1 antibody and fimaporfin into the cytosol was obtained. We also confirm that the breast MDA-MB-468 and the prostate PC-3 and DU-145 cancer cell lines have subpopulations with PD-L1 expression. In addition, we show that interferon-gamma strongly induce PD-L1 expression in the per se PD-L1 negative CT26.WT cells and enhance the PD-L1 expression in MC-38 cells, of which both are murine colon cancer cell lines. In conclusion, our work provides an in vitro proof-of-concept of PCI-enhanced targeting and eradication of PD-L1 positive immunosuppressive cells. This light-controlled combinatorial strategy has a potential to advance cancer immunotherapy and should be explored in preclinical studies.

The Urokinase Receptor (uPAR) as a "Trojan Horse" in Targeted Cancer Therapy: Challenges and Opportunities

Simple Summary

Discovered more than three decades ago, the urokinase-type plasminogen activator receptor (uPAR) has now firmly established itself as a versatile molecular target holding promise for the treatment of aggressive malignancies. The copious abundance of uPAR in virtually all human cancerous tissues versus their healthy counterparts has fostered a gradual shift in the therapeutic landscape targeting this receptor from function inhibition to cytotoxic approaches to selectively eradicate the uPAR-expressing cells by delivering a targeted cytotoxic insult. Multiple avenues are being explored in a preclinical setting, including the more innovative immune- or stroma targeting therapies. This review discusses the current state of these strategies, their potentialities, and challenges, along with future directions in the field of uPAR targeting.

Abstract

One of the largest challenges to the implementation of precision oncology is identifying and validating selective tumor-driving targets to enhance the therapeutic efficacy while limiting off-target toxicity. In this context, the urokinase-type plasminogen activator receptor (uPAR) has progressively emerged as a promising therapeutic target in the management of aggressive malignancies. By focalizing the plasminogen activation cascade and subsequent extracellular proteolysis on the cell surface of migrating cells, uPAR endows malignant cells with a high proteolytic and migratory potential to dissolve the restraining extracellular matrix (ECM) barriers and metastasize to distant sites. uPAR is also assumed to choreograph multiple other neoplastic stages via a complex molecular interplay with distinct cancer-associated signaling pathways. Accordingly, high uPAR expression is observed in virtually all human cancers and is frequently associated with poor patient prognosis and survival. The promising therapeutic potential unveiled by the pleiotropic nature of this receptor has prompted the development of distinct targeted intervention strategies. The present review will focus on recently emerged cytotoxic approaches emphasizing the novel technologies and related limits hindering their application in the clinical setting. Finally, future research directions and emerging opportunities in the field of uPAR targeting are also discussed.

Non-genotoxic conditioning facilitates hematopoietic stem cell gene therapy for hemophilia A using bioengineered factor VIII

Hematopoietic stem and progenitor cell (HSPC) lentiviral gene therapy is a promising strategy toward a lifelong cure for hemophilia A (HA). The primary risks associated with this approach center on the requirement for pre-transplantation conditioning necessary to make space for, and provide immune suppression against, stem cells and blood coagulation factor VIII, respectively. Traditional conditioning agents utilize genotoxic mechanisms of action, such as DNA alkylation, that increase risk of sterility, infection, and developing secondary malignancies. In the current study, we describe a non-genotoxic conditioning protocol using an immunotoxin targeting CD117 (c-kit) to achieve endogenous hematopoietic stem cell depletion and a cocktail of monoclonal antibodies to provide transient immune suppression against the transgene product in a murine HA gene therapy model. This strategy provides high-level engraftment of hematopoietic stem cells genetically modified ex vivo using recombinant lentiviral vector (LV) encoding a bioengineered high-expression factor VIII variant, termed ET3. Factor VIII procoagulant activity levels were durably elevated into the normal range and phenotypic correction achieved. Furthermore, no immunological rejection or development of anti-ET3 immunity was observed. These preclinical data support clinical translation of non-genotoxic antibody-based conditioning in HSPC LV gene therapy for HA.

Aptamer-Driven Toxin Gene Delivery in U87 Model Glioblastoma Cells

A novel suicide gene therapy approach was tested in U87 MG glioblastoma multiforme cells. A 26nt G-rich double-stranded DNA aptamer (AS1411) was integrated into a vector at the 5' of a mammalian codon-optimized saporin gene, under CMV promoter. With this plasmid termed "APTSAP", the gene encoding ribosome-inactivating protein saporin is driven intracellularly by the glioma-specific aptamer that binds to cell surface-exposed nucleolin and efficiently kills target cells, more effectively as a polyethyleneimine (PEI)-polyplex. Cells that do not expose nucleolin at the cell surface such as 3T3 cells, used as a control, remain unaffected. Suicide gene-induced cell killing was not observed when the inactive saporin mutant SAPKQ DNA was used in the (PEI)-polyplex, indicating that saporin catalytic activity mediates the cytotoxic effect. Rather than apoptosis, cell death has features resembling autophagic or methuosis-like mechanisms. These main findings support the proof-of-concept of using PEI-polyplexed APTSAP for local delivery in rat glioblastoma models.

The Effect of Small Molecule Pharmacological Agents on the Triterpenoid Saponin Induced Endolysosomal Escape of Saporin and a Saporin-Based Immunotoxin in Target Human Lymphoma Cells

Triterpenoid saponins augment the cytotoxicity of saporin based immunotoxins. It is postulated that this results from a saponin-mediated increase in the endolysosomal escape of the toxin to the cytosol, but this remains to be confirmed. To address this issue, we used a number of pharmacological inhibitors of endocytic processes as probes to investigate the role played by saponin in the endolysosomal escape of fluorescently labeled saporin and a saporin based immunotoxin targeted against CD38 on human lymphoma and leukemia cell lines. Endolysosomal escape of the toxin was measured by flow cytometric pulse shape analysis. These results were compared to the effects of the various inhibitors on the saponin-mediated augmentation of toxin and immunotoxin cytotoxicity. Inhibitors of clathrin-mediated endocytosis, micropinocytosis, and endosomal acidification abrogated the saponin-induced increase in the endolysosomal escape of the toxin into the cytosol, suggesting that these processes may be involved in the internalization of saponin to the same endolysosomal vesicle as the toxin. Alternatively, these processes may play a direct role in the mechanism by which saponin promotes toxin escape from the endolysosomal compartment to the cytosol. Correlation with the effects of these inhibitors on the augmentation of cytotoxicity provides additional evidence that endolysosomal escape is involved in driving augmentation.

Mucoricin is a ricin-like toxin that is critical for the pathogenesis of mucormycosis

Fungi of the order Mucorales cause mucormycosis, a lethal infection with an incompletely understood pathogenesis. We demonstrate that Mucorales fungi produce a toxin, which plays a central role in virulence. Polyclonal antibodies against this toxin inhibit its ability to damage human cells in vitro and prevent hypovolemic shock, organ necrosis and death in mice with mucormycosis. Inhibition of the toxin in Rhizopus delemar through RNA interference compromises the ability of the fungus to damage host cells and attenuates virulence in mice. This 17 kDa toxin has structural and functional features of the plant toxin ricin, including the ability to inhibit protein synthesis through its N-glycosylase activity, the existence of a motif that mediates vascular leak and a lectin sequence. Antibodies against the toxin inhibit R. delemar- or toxin-mediated vascular permeability in vitro and cross react with ricin. A monoclonal anti-ricin B chain antibody binds to the toxin and also inhibits its ability to cause vascular permeability. Therefore, we propose the name 'mucoricin' for this toxin. Not only is mucoricin important in the pathogenesis of mucormycosis but our data suggest that a ricin-like toxin is produced by organisms beyond the plant and bacterial kingdoms. Importantly, mucoricin should be a promising therapeutic target.

Nanoencapsulated rituximab mediates superior cellular immunity against metastatic B-cell lymphoma in a complement competent humanized mouse model

BACKGROUND

Despite the numerous applications of monoclonal antibodies (mAbs) in cancer therapeutics, animal models available to test the therapeutic efficacy of new mAbs are limited. NOD.Cg-Prkdc^scid Il2rg ^tm1Wjl /SzJ (NSG) mice are one of the most highly immunodeficient strains and are universally used as a model for testing cancer-targeting mAbs. However, this strain lacks several factors necessary to fully support antibody-mediated effector functions-including antibody-dependent cellular cytotoxicity, antibody-dependent cellular phagocytosis, and complement-dependent cytotoxicity (CDC)-due to the absence of immune cells as well as a mutation in the Hc gene, which is needed for a functional complement system.

METHODS

We have developed a humanized mouse model using a novel NSG strain, NOD.Cg^-Hc1 Prkdc^scid Il2rgtm1Wjl/SzJ (NSG^-Hc1), which contains the corrected mutation in the Hc gene to support CDC in addition to other mechanisms endowed by humanization. With this model, we reevaluated the anticancer efficacies of nanoencapsulated rituximab after xenograft of the human Burkitt lymphoma cell line 2F7-BR44.

RESULTS

As expected, xenografted humanized NSG^-Hc1 mice supported superior lymphoma clearance of native rituximab compared with the parental NSG strain. Nanoencapsulated rituximab with CXCL13 conjugation as a targeting ligand for lymphomas further enhanced antilymphoma activity in NSG^-Hc1 mice and, more importantly, mediated antilymphoma cellular responses.

CONCLUSIONS

These results indicate that NSG^-Hc1 mice can serve as a feasible model for both studying antitumor treatment using cancer targeting as well as understanding induction mechanisms of antitumor cellular immune response.

Kirkiin: A New Toxic Type 2 Ribosome-Inactivating Protein from the Caudex of Adenia kirkii

Ribosome-inactivating proteins (RIPs) are plant toxins that irreversibly damage ribosomes and other substrates, thus causing cell death. RIPs are classified in type 1 RIPs, single-chain enzymatic proteins, and type 2 RIPs, consisting of active A chains, similar to type 1 RIPs, linked to lectin B chains, which enable the rapid internalization of the toxin into the cell. For this reason, many type 2 RIPs are very cytotoxic, ricin, volkensin and stenodactylin being the most toxic ones. From the caudex of Adenia kirkii (Mast.) Engl., a new type 2 RIP, named kirkiin, was purified by affinity chromatography on acid-treated Sepharose CL-6B and gel filtration. The lectin, with molecular weight of about 58 kDa, agglutinated erythrocytes and inhibited protein synthesis in a cell-free system at very low concentrations. Moreover, kirkiin was able to depurinate mammalian and yeast ribosomes, but it showed little or no activity on other nucleotide substrates. In neuroblastoma cells, kirkiin inhibited protein synthesis and induced apoptosis at doses in the pM range. The biological characteristics of kirkiin make this protein a potential candidate for several experimental pharmacological applications both alone for local treatments and as component of immunoconjugates for systemic targeting in neurodegenerative studies and cancer therapy.

Innovative Cell-Based Therapies and Conditioning to Cure RAG Deficiency

Genetic defects in recombination activating genes (RAG) 1 and 2 cause a broad spectrum of severe immune defects ranging from early severe and repeated infections to inflammation and autoimmune manifestations. A correlation between in vitro recombination activity and immune phenotype has been described. Hematopoietic cell transplantation is the treatment of care; however, the availability of next generation sequencing and whole genome sequencing has allowed the identification of novel genetic RAG variants in immunodeficient patients at various ages, raising therapeutic questions. This review addresses the recent advances of novel therapeutic approaches for RAG deficiency. As conventional myeloablative conditioning regimens are associated with acute toxicities and transplanted-related mortality, innovative minimal conditioning regimens based on the use of monoclonal antibodies are now emerging and show promising results. To overcome shortage of compatible donors, gene therapy has been developed in various RAG preclinical models. Overall, the transplantation of autologous gene corrected hematopoietic precursors and the use of non-genotoxic conditioning will open a new era, offering a cure to an increasing number of RAG patients regardless of donor availability and severity of clinical conditions.

Saporin from Saponaria officinalis as a Tool for Experimental Research, Modeling, and Therapy in Neuroscience

Saporin, which is extracted from Saponaria officinalis, is a protein toxin that inactivates ribosomes. Saporin itself is non-selective toxin but acquires high specificity after conjugation with different ligands such as signaling peptides or antibodies to some surface proteins expressed in a chosen cell subpopulation. The saporin-based conjugated toxins were widely adopted in neuroscience as a convenient tool to induce highly selective degeneration of desired cell subpopulation. Induction of selective cell death is one of approaches used to model neurodegenerative diseases, study functions of certain cell subpopulations in the brain, and therapy. Here, we review studies where saporin-based conjugates were used to analyze cell mechanisms of sleep, general anesthesia, epilepsy, pain, and development of Parkinson’s and Alzheimer’s diseases. Limitations and future perspectives of use of saporin-based toxins in neuroscience are discussed.

Nongenotoxic antibody-drug conjugate conditioning enables safe and effective platelet gene therapy of hemophilia A mice

Gene therapy offers the potential to cure hemophilia A (HA). We have shown that hematopoietic stem cell (HSC)-based platelet-specific factor VIII (FVIII) (2bF8) gene therapy can produce therapeutic protein and induce antigen-specific immune tolerance in HA mice, even in the presence of inhibitory antibodies. For HSC-based gene therapy, traditional preconditioning using cytotoxic chemotherapy or total body irradiation (TBI) has been required. The potential toxicity associated with TBI or chemotherapy is a deterrent that may prevent patients with HA, a nonmalignant disease, from agreeing to such a protocol. Here, we describe targeted nongenotoxic preconditioning for 2bF8 gene therapy utilizing a hematopoietic cell-specific antibody-drug conjugate (ADC), which consists of saporin conjugated to CD45.2- and CD117-targeting antibodies. We found that a combination of CD45.2- and CD117-targeting ADC preconditioning was effective for engrafting 2bF8-transduced HSCs and was favorable for platelet lineage reconstitution. Two thirds of HA mice that received 2bF8 lentivirus-transduced HSCs under (CD45.2+CD117)-targeting ADC conditioning maintained sustained therapeutic levels of platelet FVIII expression. When CD8-targeting ADC was supplemented, chimerism and platelet FVIII expression were significantly increased, with long-term sustained platelet FVIII expression in all primary and secondary recipients. Importantly, immune tolerance was induced and hemostasis was restored in a tail-bleeding test, and joint bleeding also was effectively prevented in a needle-induced knee joint injury model in HA mice after 2bF8 gene therapy. In summary, we show for the first time efficient engraftment of gene-modified HSCs without genotoxic conditioning. The combined cocktail ADC-mediated hematopoietic cell-targeted nongenotoxic preconditioning that we developed is highly effective and favorable for platelet-specific gene therapy in HA mice.

Transcriptional network inference and master regulator analysis of the response to ribosome-inactivating proteins in leukemia cells

Gene-regulatory networks reconstruction has become a very popular approach in applied biology to infer and dissect functional interactions of Transcription Factors (TFs) driving a defined phenotypic state, termed as Master Regulators (MRs). In the present work, cutting-edge bioinformatic methods were applied to re-analyze experimental data on leukemia cells (human myelogenous leukemia cell line THP-1 and acute myeloid leukemia MOLM-13 cells) treated for 6 h with two different Ribosome-Inactivating Proteins (RIPs), namely Shiga toxin type 1 (400 ng/mL) produced by Escherichia coli strains and the plant toxin stenodactylin (60 ng/mL), purified from the caudex of Adenia stenodactyla Harms. This analysis allowed us to identify the common early transcriptional response to 28S rRNA damage based on gene-regulatory network inference and Master Regulator Analysis (MRA). Both toxins induce a common response at 6 h which involves inflammatory mediators triggered by AP-1 family transcriptional factors and ATF3 in leukemia cells. We describe for the first time the involvement of MAFF, KLF2 and KLF6 in regulating RIP-induced apoptotic cell death, while receptor-mediated downstream signaling through ANXA1 and TLR4 is suggested for both toxins.

Early Response to the Plant Toxin Stenodactylin in Acute Myeloid Leukemia Cells Involves Inflammatory and Apoptotic Signaling

Stenodactylin, a highly toxic type 2 ribosome-inactivating protein purified from the caudex of Adenia stenodactyla Harms, is a potential anticancer drug candidate. Previous studies demonstrated that stenodactylin induces apoptosis and necroptosis in treated cells, involving the production of reactive oxygen species. We analyzed the effect of stenodactylin on Raji and Ramos (Human Burkitt’s lymphoma cells) and MOLM-13 (acute myeloid leukemia cells). Moreover, we focused on the early events in MOLM-13 cells that characterize the cellular response to the toxin by whole-genome microarray analysis of gene expression. Treatment with stenodactylin induced the depurination of 28S rRNA within 4 h and increased the phosphorylation of p38 and JNK. A time-dependent activation of caspase 1, 2, 8, 9, 3/7 was also observed. Genome-wide gene expression microarray analysis revealed early changes in the expression of genes involved in the regulation of cell death, inflammation and stress response. After 4 h, a significant increase of transcript level was detectable for ATF3, BTG2, DUSP1, EGR1, and JUN. Increased upstream JUN signaling was also confirmed at protein level. The early response to stenodactylin treatment involves inflammatory and apoptotic signaling compatible with the activation of multiple cell death pathways. Because of the above described properties toward acute myeloid leukemia cells, stenodactylin may be a promising candidate for the design of new immunoconjugates for experimental cancer treatment.

Efficacy and safety of anti-CD45-saporin as conditioning agent for RAG deficiency

Background:

Mutations in the recombinase-activating genes cause severe immunodeficiency, with a spectrum of phenotypes ranging from severe combined immunodeficiency to immune dysregulation. Hematopoietic stem cell transplantation is the only curative option, but a high risk of graft failure and poor immune reconstitution have been observed in the absence of myeloablation.

Objectives:

Our aim was to improve multilineage engraftment; we tested nongenotoxic conditioning with anti-CD45 mAbs conjugated with saporin CD45 (CD45-SAP).

Methods:

Rag1-KO and Rag1-F971L mice, which represent models of severe combined immune deficiency and combined immune deficiency with immune dysregulation, respectively, were conditioned with CD45-SAP, CD45-SAP plus 2 Gy of total body irradiation (TBI), 2 Gy of TBI, 8 Gy of TBI, or no conditioning and treated by using transplantation with lineage-negative bone marrow cells from wild-type mice. Flow cytometry and immunohistochemistry were used to assess engraftment and immune reconstitution. Antibody responses to 2,4,6-trinitrophenyl–conjugated keyhole limpet hemocyanin were measured by ELISA, and presence of autoantibody was detected by microarray.

Results:

Conditioning with CD45-SAP enabled high levels of multilineage engraftment in both Rag1 mutant models, allowed overcoming of B- and T-cell differentiation blocks and thymic epithelial cell defects, and induced robust cellular and humoral immunity in the periphery.

Conclusions:

Conditioning with CD45-SAP allows multilineage engraftment and robust immune reconstitution in mice with either null or hypomorphic Rag mutations while preserving thymic epithelial cell homeostasis.

A Novel Antibody-Drug Conjugate (ADC) Delivering a DNA Mono-Alkylating Payload to Chondroitin Sulfate Proteoglycan (CSPG4)-Expressing Melanoma

Despite emerging targeted and immunotherapy treatments, no monoclonal antibodies or antibody-drug conjugates (ADCs) directly targeting tumor cells are currently approved for melanoma therapy. The tumor-associated antigen chondroitin sulphate proteoglycan 4 (CSPG4), a neural crest glycoprotein over-expressed on 70% of melanomas, contributes to proliferative signaling pathways, but despite highly tumor-selective expression it has not yet been targeted using ADCs. We developed a novel ADC comprising an anti-CSPG4 antibody linked to a DNA minor groove-binding agent belonging to the novel pyrridinobenzodiazepine (PDD) class. Unlike conventional DNA-interactive pyrrolobenzodiazepine (PBD) dimer payloads that cross-link DNA, PDD-based payloads are mono-alkylating agents but have similar efficacy and substantially enhanced tolerability profiles compared to PBD-based cross-linkers. We investigated the anti-tumor activity and safety of the anti-CSPG4-(PDD) ADC in vitro and in human melanoma xenografts. Anti-CSPG4-(PDD) inhibited CSPG4-expressing melanoma cell growth and colony formation and triggered apoptosis in vitro at low nanomolar to picomolar concentrations without off-target Fab-mediated or Fc-mediated toxicity. Anti-CSPG4-(PDD) restricted xenograft growth in vivo at 2 mg/kg doses. One 5 mg/kg injection triggered tumor regression in the absence of overt toxic effects or of acquired residual tumor cell resistance. This anti-CSPG4-(PDD) can deliver a highly cytotoxic DNA mono-alkylating payload to CSPG4-expressing tumors at doses tolerated in vivo.

Exploiting the internalization feature of an antibody against the glycosphingolipid SSEA-4 to deliver immunotoxins in breast cancer cells

The stage-specific embryonic antigen-4 (SSEA-4) is a cell surface glycosphingolipid antigen expressed in early stages of human development. This surface marker is downregulated during the differentiation process but is found re-expressed in several types of tumors, including breast cancer. This feature makes SSEA-4 an attractive target for the development of therapeutic antibodies against tumors. In this work, we first studied the binding and intracellular fate of the monoclonal antibody MC-813-70 directed against SSEA-4. MC-813-70 was found to be rapidly internalized into triple-negative breast cancer cells following binding to its target at the plasma membrane, and to accumulate in acidic organelles, most likely lysosomes. Given the internalization feature of MC-813-70, we next tested whether the antibody was able to selectively deliver the saporin toxin inside SSEA-4-expressing cells. Results show that the immunotoxin complex was properly endocytosed and able to reduce cell viability of breast cancer cells in vitro, either alone or in combination with chemotherapeutic drugs. Our findings indicate that the MC-813-70 antibody has the potential to be developed as an alternative targeted therapeutic agent for cancer cells expressing the SSEA-4 glycolipid.

Lipid-Saporin Nanoparticles for the Intracellular Delivery of Cytotoxic Protein to Overcome ABC Transporter-Mediated Multidrug Resistance In Vitro and In Vivo

Although the judicious use of anticancer drugs that target one or more receptor tyrosine kinases constitutes an effective strategy to attenuate tumor growth, drug resistance is commonly encountered in cancer patients. The ATP-binding cassette transporters are one of the major contributors to the development of multidrug resistance as their overexpression significantly decreases the intracellular concentration and thus, the efficacy of certain anticancer drugs. Therefore, the development of treatment strategies that would not be susceptible to efflux or excretion by specific ABC transporters could overcome resistance to treatment. Here, we investigated the anticancer efficacy of saporin, a ribosome-inactivating protein. Since saporin has poor permeability across the cell membrane, it was encapsulated in a lipid-based nanoparticle system (EC16-1) that effectively delivered the formulation (EC16-1/saporin) intracellularly and produced anti-cancer efficacy. EC16-1/saporin, at nanomolar concentrations, significantly inhibited the cellular proliferation of parental and ABCB1- and ABCG2-overexpressing cancer cells. EC16-1/saporin did not significantly alter the subcellular localization of ABCB1 and ABCG2. In addition, EC16-1/saporin induced apoptosis in parental and ABCB1- and ABCG2-overexpressing cancer cells. In a murine model system, EC16-1/saporin significantly inhibited the tumor growth in mice xenografted with parental and ABCB1- and ABCG2-overexpressing cancer cells. Our findings suggest that the EC16-1/saporin combination could potentially be a novel therapeutic treatment in patients with parental or ABCB1- and ABCG2-positive drug-resistant cancers.

A Flow Cytometric Method to Quantify the Endosomal Escape of a Protein Toxin to the Cytosol of Target Cells

Purpose

The aim of this work was to develop a quantitative, flow cytometric method for tracking the endolysosomal escape of a fluorescently labelled saporin toxin.

Methods

Flow cytometric measurements of fluorescent pulse width and height were used to track the endocytic uptake into Daudi cells of a fluorescently labelled saporin toxin and the saporin based immunotoxin, OKT10-SAP. Subsequently, measurement of changes in pulse width were used to investigate the effect of a triterpenoid saponin on the endolysosomal escape of internalised toxin into the cytosol. Live cell confocal microscopy was used to validate the flow cytometry data.

Results

Increased endolysosomal escape of saporin and OKT10-SAP was observed by confocal microscopy in cells treated with saponin. Fluorescent pulse width measurements were also able to detect and quantify escape more sensitively than confocal microscopy. Saponin induced endolysosomal escape could be abrogated by treatment with chloroquine, an inhibitor of endolysosomal acidification. Chloroquine abrogation of escape was also mirrored by a concomitant abrogation of cytotoxicity.

Conclusions

Poor endolysosomal escape is often a rate limiting step for the cytosolic delivery of protein toxins and other macromolecules. Pulse width analysis offers a simple method to semi-quantify the endolysosomal escape of this and similar molecules into the cytosol.

Electronic supplementary material

The online version of this article (10.1007/s11095-019-2725-1) contains supplementary material, which is available to authorized users.

Dianthin and Its Potential in Targeted Tumor Therapies

Dianthin enzymes belong to ribosome-inactivating proteins (RIPs) of type 1, i.e., they only consist of a catalytic domain and do not have a cell binding moiety. Dianthin-30 is very similar to saporin-S3 and saporin-S6, two RIPs often used to design targeted toxins for tumor therapy and already tested in some clinical trials. Nevertheless, dianthin enzymes also exhibit differences to saporin with regard to structure, efficacy, toxicity, immunogenicity and production by heterologous expression. Some of the distinctions might make dianthin more suitable for targeted tumor therapies than other RIPs. The present review provides an overview of the history of dianthin discovery and illuminates its structure, function and role in targeted toxins. It further discusses the option to increase the efficacy of dianthin by endosomal escape enhancers.

Synthesis of saporin-antibody conjugates for targeting EpCAM positive tumour cells

Epithelial cell adhesion molecule (EpCAM) is a transmembrane glycoprotein involved in cell proliferation and differentiation. Ribosomal inactivating proteins derived from plants specifically target ribosomes and irreversibly inhibit protein synthesis. EpCAM antibody and saporin were conjugated using 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide hydrochloride/N-hydroxysuccinimide chemistry. The mass of the conjugates were characterised using matrix-assisted laser desorption ionisation (MALDI). The saporin-EpCAM (SAP-EpAB) conjugates were tested in-vitro against MCF-7 (breast cancer cells), WERI-Rb1 (retinoblastoma) cells. The flow cytometry and fluorescence microscopy were performed to show the binding efficiency of SAP-EpAB conjugate. Whole transcriptome changes of sap-conjugate treated cells were studied using affymetrix microarrays. MALDI-TOF analysis and polyacrylamide gel electrophoresis confirmed the conjugation of SAP with EpCAM antibody. Flow cytometry and fluorescent microscopy analysis revealed the binding of SAP-EpAB conjugates to the MCF-7, WERI-Rb1 cells. Apoptosis assay by annexin-V has shown an increased apoptotic and necrotic population in conjugate treated cells. MTT assay confirmed the tumour cell death and had shown the IC₅₀ value of 0.8 µg for conjugate in MCF-7 (breast cancer cells), and 1 µg for WERI-Rb1 (retinoblastoma) cells. The microarray analysis revealed downregulation of the tumourigenic genes and upregulation of pro-apoptotic genes leading to apoptosis of tumour cells.

Lipid-peptide bioconjugation through pyridyl disulfide reaction chemistry and its application in cell targeting and drug delivery

Background

The design of efficient drug delivery vectors requires versatile formulations able to simultaneously direct a multitude of molecular targets and to bypass the endosomal recycling pathway of cells. Liposomal-based vectors need the decoration of the lipid surface with specific peptides to fulfill the functional requirements. The unspecific binding of peptides to the lipid surface is often accompanied with uncontrolled formulations and thus preventing the molecular mechanisms of a successful therapy.

Results

We present a simple synthesis pathway to anchor cysteine-terminal peptides to thiol-reactive lipids for adequate and quantitative liposomal formulations. As a proof of concept, we have synthesized two different lipopeptides based on (a) the truncated Fibroblast Growth Factor (tbFGF) for cell targeting and (b) the pH sensitive and fusogenic GALA peptide for endosomal scape.

Conclusions

The incorporation of these two lipopeptides in the liposomal formulation improves the fibroblast cell targeting and promotes the direct delivery of cargo molecules to the cytoplasm of the cell.

Electronic supplementary material

The online version of this article (10.1186/s12951-019-0509-8) contains supplementary material, which is available to authorized users.

Cloning, expression and characterization of a HER2-alpha luffin fusion protein in Escherichia coli

In recent decades, immunotoxins have attracted significant attention in treatment of a wide range of diseases including cancers due to their natural origins and their role in blocking crucial pathways within the cells. Ribosome inactivating proteins (RIPs) are efficient molecules in blocking protein synthesis through interactions with ribosomal rRNA molecules. cDNA molecule encoding HER2 scFv antibody fragment originated from trastuzumab attached to the mature alpha luffin gene fragment was subcloned into pET28a expression vector and expressed in different E. coli expression hosts. Identity of the expressed recombinant protein was investigated through western blotting and the fusion protein was purified using Ni-NTA affinity chromatography. The biological activity (toxicity) of the protein was investigated on DNA and RNA samples. A 58 kDa protein was expressed in E. coli. The best protein expression level was achieved in 0.2 mM IPTG at 30 °C in TB medium using E. coli BL21 (DE3) host strain. The fusion protein showed RNase and DNA glycosylase activity on tested RNA and DNA samples. DNA glycosylase activity of the recombinant fusion protein showed that alpha luffin part of this protein is active in conjugation to the scFv molecule and the expressed protein can be further studied in targeted biological in vitro assays.

Integrin α10, a Novel Therapeutic Target in Glioblastoma, Regulates Cell Migration, Proliferation, and Survival

New, effective treatment strategies for glioblastomas (GBMs), the most malignant and invasive brain tumors in adults, are highly needed. In this study, we investigated the potential of integrin α10β1 as a therapeutic target in GBMs. Expression levels and the role of integrin α10β1 were studied in patient-derived GBM tissues and cell lines. The effect of an antibody–drug conjugate (ADC), an integrin α10 antibody conjugated to saporin, on GBM cells and in a xenograft mouse model was studied. We found that integrin α10β1 was strongly expressed in both GBM tissues and cells, whereas morphologically unaffected brain tissues showed only minor expression. Partial or no overlap was seen with integrins α3, α6, and α7, known to be expressed in GBM. Further analysis of a subpopulation of GBM cells selected for high integrin α10 expression demonstrated increased proliferation and sphere formation. Additionally, siRNA-mediated knockdown of integrin α10 in GBM cells led to decreased migration and increased cell death. Furthermore, the ADC reduced viability and sphere formation of GBM cells and induced cell death both in vitro and in vivo. Our results demonstrate that integrin α10β1 has a functional role in GBM cells and is a novel, potential therapeutic target for the treatment of GBM.

Selective Cytotoxicity to HER2 Positive Breast Cancer Cells by Saporin-Loaded Nanobody-Targeted Polymeric Nanoparticles in Combination with Photochemical Internalization

In cancer treatment, polymeric nanoparticles (NPs) can serve as a vehicle for the delivery of cytotoxic proteins that have intracellular targets but that lack well-defined mechanisms for cellular internalization, such as saporin. In this work, we have prepared PEGylated poly(lactic acid- co-glycolic acid- co-hydroxymethyl glycolic acid) (PLGHMGA) NPs for the selective delivery of saporin in the cytosol of HER2 positive cancer cells. This selective uptake was achieved by decorating the surface of the NPs with the 11A4 nanobody that is specific for the HER2 receptor. Confocal microscopy observations showed rapid and extensive uptake of the targeted NPs (11A4-NPs) by HER2 positive cells (SkBr3) but not by HER2 negative cells (MDA-MB-231). This selective uptake was blocked upon preincubation of the cells with an excess of nanobody. Nontargeted NPs (Cys-NPs) were not taken up by either type of cells. Importantly, a dose-dependent cytotoxic effect was only observed on SkBr3 cells when these were treated with saporin-loaded 11A4-NPs in combination with photochemical internalization (PCI), a technique that uses a photosensitizer and local light exposure to facilitate endosomal escape of entrapped nanocarriers and biomolecules. The combined use of saporin-loaded 11A4-NPs and PCI strongly inhibited cell proliferation and decreased cell viability through induction of apoptosis. Also the cytotoxic effect could be reduced by an excess of nanobody, reinforcing the selectivity of this system. These results suggest that the combination of the targeting nanobody on the NPs with PCI are effective means to achieve selective uptake and cytotoxicity of saporin-loaded NPs.

Augmentation of Saporin-Based Immunotoxins for Human Leukaemia and Lymphoma Cells by Triterpenoid Saponins: The Modifying Effects of Small Molecule Pharmacological Agents

Triterpenoid saponins from Saponinum album (SA) significantly augment the cytotoxicity of saporin-based immunotoxins but the mechanism of augmentation is not fully understood. We investigated the effects of six small molecule pharmacological agents, which interfere with endocytic and other processes, on SA-mediated augmentation of saporin and saporin-based immunotoxins (ITs) directed against CD7, CD19, CD22 and CD38 on human lymphoma and leukaemia cell lines. Inhibition of clathrin-mediated endocytosis or endosomal acidification abolished the SA augmentation of saporin and of all four immunotoxins tested but the cytotoxicity of each IT or saporin alone was largely unaffected. The data support the hypothesis that endocytic processes are involved in the augmentative action of SA for saporin ITs targeted against a range of antigens expressed by leukaemia and lymphoma cells. In addition, the reactive oxygen species (ROS) scavenger tiron reduced the cytotoxicity of BU12-SAP and OKT10-SAP but had no effect on 4KB128-SAP or saporin cytotoxicity. Tiron also had no effect on SA-mediated augmentation of the saporin-based ITs or unconjugated saporin. These results suggest that ROS are not involved in the augmentation of saporin ITs and that ROS induction is target antigen-dependent and not directly due to the cytotoxic action of the toxin moiety.

A new type 1 ribosome-inactivating protein from the seeds of Gypsophila elegans M.Bieb

Ribosome-inactivating proteins (RIPs) are enzymes with N-glycosylase activity that remove adenine bases from the ribosomal RNA. In theory, one single RIP molecule internalized into a cell is sufficient to induce cell death. For this reason, RIPs are of high potential as toxic payload for anti-tumor therapy. A considerable number of RIPs are synthesized by plants that belong to the carnation family (Caryophyllaceae). Prominent examples are the RIPs saporin from Saponaria officinalis L. or dianthin from Dianthus caryophyllus L. In this study, we have isolated and characterized a novel RIP (termed gypsophilin-S) from the tiny seeds of Gypsophila elegans M. Bieb. (Caryophyllaceae). It is noteworthy that this is the first study presenting the complete amino acid sequence of a RIP from a Gypsophila species. Gypsophilin-S was isolated from the defatted seed material following ammonium sulphate precipitation and HPLC-based ion exchange chromatography. Gypsophilin-S-containing fractions were analysed by SDS-PAGE and mass spectrometry. The full amino acid sequence of gypsophilin-S was assembled by MALDI-TOF-MS-MS and PCR. Gypsophilin-S exhibited strong adenine releasing activity and its cytotoxicity in human glioblastoma cells was investigated using an impedance-based real-time assay in comparison with recombinant saporin and dianthin.

Human anti-NKp46 antibody for studies of NKp46-dependent NK cell function and its applications for type 1 diabetes and cancer research

Natural killer (NK) cells are innate lymphocytes that efficiently eliminate cancerous and infected cells. NKp46 is an important NK activating receptor shown to participate in recognition and activation of NK cells against pathogens, tumor cells, virally infected cells, and self-cells in autoimmune conditions, including type I and II diabetes. However, some of the NKp46 ligands are unknown and therefore investigating human NKp46 activity and its critical role in NK cell biology is problematic. We developed a unique anti-human NKp46 monocloncal antibody, denoted hNKp46.02 (02). The 02 mAb can induce receptor internalization and degradation. By binding to a unique epitope on a particular domain of NKp46, 02 lead NKp46 to lysosomal degradation. This downregulation therefore enables the investigation of all NKp46 activities. Indeed, using the 02 mAb we determined NK cell targets which are critically dependent on NKp46 activity, including certain tumor cells lines and human pancreatic beta cells. Most importantly, we showed that a toxin-conjugated 02 inhibits the growth of NKp46-positive cells; thus, exemplifying the potential of 02 in becoming an immunotherapeutic drug to treat NKp46-dependent diseases, such as, type I diabetes and NK and T cell related malignancies.