Entwicklung einer Plattformtechnologie zur verstärkten endo/lysosomalen Freisetzung von zielgerichteten Toxinen mittels strukturspezifischer oleananer Saponine

Targeted toxins are protein-based therapeutics under investigation for their usage in targeted tumor therapies. They are composed of a toxic enzyme, such as the ribosome-inactivating protein (RIP) saporin, and a targeting ligand, such as growth factors or monoclonal antibodies. After specific binding to target cells and subsequent internalization, their efficacy is dramatically reduced by their accumulation and degradation in the lysosomes. Certain structurally specific oleanane saponins (a subclass of triterpenoidal saponins) that specifically augment the endo/lysosomal escape of particular RIPs may be of great help to circumvent this limiting step. The main objective of this work was the establishment of a platform technology for the enhanced endo/lysosomal escape of targeted toxins, in order to increase their efficacy and concomitantly reduce dosages, side effects and adverse immune reactions in patients. The platform technology was developed by constructing targeted toxins consisting of saporin and different therapeutic monoclonal antibodies. In this system, the ligand of the saporin-based targeted toxins can be exchanged depending on the target cell type, and the synergistic principle between saporin and oleanane saponins can be simultaneously exploited to achieve tremendous cytotoxicity augmentation effects. As a first step, the membrane permeabilizing effects of saponins were studied on different biological membranes. Saponins showed permeabilizing effects on cellular and lysosomal membranes at concentrations of 6 µM and higher and hemolysis at 3 µM and higher. The specific endo/lysosomal escape of targeted toxins is not based on these unspecific membrane permeabilizing effects of saponins and occurs at lower concentrations. To develop the platform technology, two immunotoxins were created by cross-linking the therapeutic antibodies Trastuzumab and Cetuximab to saporin. It was demonstrated that the immunotoxins deliver their toxic payload into the target cells and trigger the antibody-dependent cell- mediated cytotoxicity (ADCC). Immunotoxins preserved the advantages of the naked monoclonal antibodies while, most importantly, their direct cytotoxicity was drastically augmented in combination with saponins achieving death of all cells down to concentrations of 0.001 nM. The platform was validated by the analysis of three further immunotoxins consisting of saporin and the monoclonal antibodies Rituximab, anti-CD22 and anti-CD25. The cytotoxicity of the three immunotoxins was also augmented in the presence of saponins (150-, 19- and 26,000-fold, respectively). The present work opens up numerous vistas for exploiting the presented platform technology. The platform for the enhanced endo/lysosomal escape of targeted toxins may serve as a basis for the treatment of a variety of diseases and may help to achieve more efficient and successful treatments of solid tumors and hematologic malignances.Zielgerichtete Toxine sind proteinbasierte Therapeutika, die im Hinblick auf ihre Anwendung in der zielgerichteten Tumortherapie erforscht werden. Sie bestehen aus einem toxischen Enzym, zum Beispiel einem Ribosomen inaktivierenden Protein (RIP) wie Saporin, und einem Liganden, wie einem monoklonalen Antikörper. Nach spezifischer Bindung an die Zielzellen und anschließender Internalisierung wird ihre Effektivität aufgrund ihrer Akkumulation und Degradation in den Lysosomen dramatisch verringert. Bestimmte strukturspezifische oleanane Saponine (eine Subklasse von triterpenoiden Saponinen), welche spezifisch die endo/lysosomale Freisetzung von gewissen RIPs verstärken, können dabei helfen, diese limitierenden Schritte zu umgehen. Das Hauptziel dieser Arbeit war die Etablierung einer Plattformtechnologie zur verstärkten endo/lysosomalen Freisetzung von zielgerichteten Toxinen, um deren Effektivität zu erhöhen und gleichzeitig Dosis, Nebeneffekte und nachteilige Immunreaktionen am Patienten zu verringern. Die Plattformtechnologie wurde durch die Herstellung von zielgerichteten Toxinen, basierend auf Saporin und unterschiedlichen therapeutischen Antikörpern, entwickelt. In diesem System kann der Ligand der Saporin basierten, zielgerichteten Toxine je nach Zielzelltyp ausgetauscht werden. Das synergistische Prinzip zwischen Saporin und den oleananen Saponinen kann simultan genutzt werden, um eine deutliche Verstärkung der Zytotoxizität zu erreichen. Zunächst wurde der membranpermeabilisierende Effekt der Saponine auf unterschiedlichen biologischen Membranen evaluiert. Die Saponine zeigten bei Konzentrationen ab 6 µM einen permeabilisierenden Effekt auf zelluläre und lysosomale Membranen. Die spezifische endo/lysosomale Freisetzung von zielgerichteten Toxinen basiert nicht auf diesem unspezifischen, membranpermeabilisierenden Effekt der Saponine, sondern geschieht bereits bei niedrigeren, nicht lytischen Konzentrationen. Um die Plattformtechnologie zu entwickeln, wurden zwei Immunotoxine durch chemische Kopplung von Saporin mit den therapeutischen Antikörpern Trastuzumab bzw. Cetuximab konstruiert. Es konnte gezeigt werden, dass die Immuntoxine ihren toxischen Gehalt in die Zielzellen einbringen und die antikörperabhängige, zellvermittelte Zytotoxizität (ADCC) auslösen. Die Immuntoxine behielten die Vorteile des reinen monoklonalen Antikörpers bei, während die Zytotoxizität in Kombination mit Saponinen drastisch erhöht werden konnte und der Tod aller Zellen schon bei Konzentrationen von 0,001 nM eintrat. Die Plattformtechnologie wurde durch die Analyse von drei weiteren Immuntoxinen bestehend aus Saporin und den monoklonalen Antikörpern Rituximab, anti-CD22 und anti-CD25 validiert. Die vorliegende Arbeit eröffnet eine Vielzahl neuer Perspektiven, um die hier präsentierte Plattformtechnologie nutzen zu können. Die Plattformtechnologie könnte helfen, solide Tumorformen und leukämische Krebsformen effizienter und erfolgreicher zu behandeln

Liposomal Formulations to Modulate the Tumour Microenvironment and Antitumour Immune Response

Tumours are complex systems of genetically diverse malignant cells that proliferate in the presence of a heterogeneous microenvironment consisting of host derived microvasculature, stromal, and immune cells. The components of the tumour microenvironment (TME) communicate with each other and with cancer cells, to regulate cellular processes that can inhibit, as well as enhance, tumour growth. Therapeutic strategies have been developed to modulate the TME and cancer-associated immune response. However, modulating compounds are often insoluble (aqueous solubility of less than 1 mg/mL) and have suboptimal pharmacokinetics that prevent therapeutically relevant drug concentrations from reaching the appropriate sites within the tumour. Nanomedicines and, in particular, liposomal formulations of relevant drug candidates, define clinically meaningful drug delivery systems that have the potential to ensure that the right drug candidate is delivered to the right area within tumours at the right time. Following encapsulation in liposomes, drug candidates often display extended plasma half-lives, higher plasma concentrations and may accumulate directly in the tumour tissue. Liposomes can normalise the tumour blood vessel structure and enhance the immunogenicity of tumour cell death; relatively unrecognised impacts associated with using liposomal formulations. This review describes liposomal formulations that affect components of the TME. A focus is placed on formulations which are approved for use in the clinic. The concept of tumour immunogenicity, and how liposomes may enhance radiation and chemotherapy-induced immunogenic cell death (ICD), is discussed. Liposomes are currently an indispensable tool in the treatment of cancer, and their contribution to cancer therapy may gain even further importance by incorporating modulators of the TME and the cancer-associated immune response

An unusual type I ribosome-inactivating protein from Agrostemma githago L.

Agrostemma githago L. (corn cockle) is an herbaceous plant mainly growing in Europe. The seeds of the corn cockle are toxic and poisonings were widespread in the past by consuming contaminated flour. The toxic principle of Agrostemma seeds was attributed to triterpenoid secondary metabolites. Indeed, this is in part true. However Agrostemma githago L. is also a producer of ribosome-inactivating proteins (RIPs). RIPs are N-glycosylases that inactivate the ribosomal RNA, a process leading to an irreversible inhibition of protein synthesis and subsequent cell death. A widely known RIP is ricin from Ricinus communis L., which was used as a bioweapon in the past. In this study we isolated agrostin, a 27 kDa RIP from the seeds of Agrostemma githago L., and determined its full sequence. The toxicity of native agrostin was investigated by impedance-based live cell imaging. By RNAseq we identified 7 additional RIPs (agrostins) in the transcriptome of the corn cockle. Agrostin was recombinantly expressed in E. coli and characterized by MALDI-TOF-MS and adenine releasing assay. This study provides for the first time a comprehensive analysis of ribosome-inactivating proteins in the corn cockle and complements the current knowledge about the toxic principles of the plant

A simple passive equilibration method for loading carboplatin into pre-formed liposomes incubated with ethanol as a temperature dependent permeability enhancer.

A passive equilibration method which relies on addition of candidate drugs to pre-formed liposomes is described as an alternative method for preparing liposome encapsulated drugs. The method is simple, rapid and applicable to liposomes prepared with high (45mol%) or low (<20mol%) levels of cholesterol. Passive equilibration is performed in 4-steps: (i) formation of liposomes, (ii) addition of the candidate drug to the liposomes in combination with a permeability enhancing agent, (iii) incubation at a temperature that facilitates diffusion of the added compound across the lipid bilayer, and (iv) quenching the enhanced membrane permeability by reduction in temperature and/or removal of the permeabilization enhancer. The method is fully exemplified here using ethanol as the permeabilization enhancer and carboplatin (CBDCA) as the drug candidate. It is demonstrated that ethanol can be added to liposomes prepared with 1,2-distearoyl-sn-glycero-3-phosphocholine (DSPC) and Cholesterol (Chol) (55:45mol ratio) in amounts up to 30% (v/v) with no change in liposome size, even when incubated at temperatures>60°C. Super-saturated solutions of CBDCA (40mg/mL) can be prepared at 70°C and these are stable in the presence of ethanol even when the temperature is reduced to <30°C. maximum CBDCA encapsulation is achieved within 1h after the CBDCA solution is added to pre-formed DSPC/Chol liposomes in the presence of 30% (v/v) ethanol at 60°C. When the pre-formed liposomes are mixed with ethanol (30% v/v) at or below 40°C, the encapsulation efficiency is reduced by an order of magnitude. The method was also applied to liposomes prepared from other compositions include a cholesterol free formulations (containing 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[carboxy(polyethylene glycol)-2000] (DSPE-PEG2000)) and a low Chol (<20mol%) formulations prepared with the distearoyl-sn-glycero-3-phospho-(1'-rac-glycerol) DSPG)). The cytotoxic activity of CBDCA was unaffected when prepared in this manner and two of the resultant formulations exhibited good stability in vitro and in vivo. The cytotoxic activity of CBDCA was unaffected when prepared in this manner and the resultant formulations exhibited good stability in vitro and in vivo. Pharmacokinetics studies in CD-1 mice indicated that the resulting formulations increased the circulation half life of the associated CBDCA significantly (AUC0-24h of CBDCA=0.016μg·hr/mL; AUC0-24h of the DSPC/Chol CBDCA formulation=1014.0μg·hr/mL and AUC0-24h of the DSPC/DSPG/Chol CBDCA formulation=583.96μg·hr/mL). Preliminary efficacy studies in Rag-2M mice with established subcutaneous H1975 and U-251 tumors suggest that the therapeutic activity of CBDCA is improved when administered in liposomal formulations. The encapsulation method described here has not been disclosed previously and will have broad applications to drugs that would normally be encapsulated during liposome manufacturing

Modified Trastuzumab and Cetuximab Mediate Efficient Toxin Delivery While Retaining Antibody-Dependent Cell-Mediated Cytotoxicity in Target Cells

Monoclonal antibody-based therapy is one of the most successful strategies for treatment of cancer. However, the insufficient cell killing activity of monoclonal antibodies limits their therapeutic potential. These limitations can be overcome by the application of immunotoxins, which consist of a monoclonal antibody that specifically delivers a toxin into the cancer cell. An ideal immunotoxin combines the functionality of the monoclonal antibody (antagonistic binding to targeted receptors and interaction with the innate immune system) with the cell-killing activity of the toxic moiety. In addition, it should be sensitive for certain triterpenoid saponins that are known to lead to a tremendous augmentation of the antitumoral efficacy of the immunotoxin. In this study, the monoclonal antibodies trastuzumab (Herceptin) and cetuximab (Erbitux) were conjugated via cleavable disulfide bonds to the plant derived toxin saporin. The ability of the modified tumor-specific therapeutic antibodies to deliver their toxic payload into the target cells was investigated by impedance-based real-time viability assays and confocal live cell imaging. We further provide evidence that the immunotoxins retained their ability to trigger antibody-dependent cell-mediated cytotoxicity. They specifically bound to their target cell receptor, and their cell-killing activity was drastically augmented in the presence of triterpenoid saponins. Further mechanistic studies indicated a specific saponin-mediated endo/lysosomal release of the toxin moiety. These results open a promising avenue to overcome the present limitations of therapeutic antibodies and to achieve a higher antitumoral efficacy in cancer therapy

Augmenting the Efficacy of Immunotoxins and Other Targeted Protein Toxins by Endosomal Escape Enhancers

The toxic moiety of almost all protein-based targeted toxins must enter the cytosol of the target cell to mediate its fatal effect. Although more than 500 targeted toxins have been investigated in the past decades, no antibody-targeted protein toxin has been approved for tumor therapeutic applications by the authorities to date. Missing efficacy can be attributed in many cases to insufficient endosomal escape and therefore subsequent lysosomal degradation of the endocytosed toxins. To overcome this drawback, many strategies have been described to weaken the membrane integrity of endosomes. This comprises the use of lysosomotropic amines, carboxylic ionophores, calcium channel antagonists, various cell-penetrating peptides of viral, bacterial, plant, animal, human and synthetic origin, other organic molecules and light-induced techniques. Although the efficacy of the targeted toxins was typically augmented in cell culture hundred or thousand fold, in exceptional cases more than million fold, the combination of several substances harbors new problems including additional side effects, loss of target specificity, difficulties to determine the therapeutic window and cell type-dependent variations. This review critically scrutinizes the chances and challenges of endosomal escape enhancers and their potential role in future developments