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Becker L, Plückthun A. DARPins bind their cytosolic targets after having been translocated through the protective antigen pore of anthrax toxin. Sci Rep 2023; 13:8048. [PMID: 37198284 DOI: 10.1038/s41598-023-34647-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2022] [Accepted: 05/04/2023] [Indexed: 05/19/2023] Open
Abstract
Intracellular protein-protein interactions in aberrant signaling pathways have emerged as a prime target in several diseases, particularly cancer. Since many protein-protein interactions are mediated by rather flat surfaces, they can typically not be interrupted by small molecules as they require cavities for binding. Therefore, protein drugs might be developed to compete with undesired interactions. However, proteins in general are not able to translocate from the extracellular side to the cytosolic target site by themselves, and thus an efficient protein translocation system, ideally combining efficient translocation with receptor specificity, is in high demand. Anthrax toxin, the tripartite holotoxin of Bacillus anthracis, is one of the best studied bacterial protein toxins and has proven to be a suitable candidate for cell-specific translocation of cargoes in vitro and in vivo. Our group recently developed a retargeted protective antigen (PA) variant fused to different Designed Ankyrin Repeat Proteins (DARPins) to achieve receptor specificity, and we incorporated a receptor domain to stabilize the prepore and prevent cell lysis. This strategy had been shown to deliver high amounts of cargo DARPins fused behind the N-terminal 254 amino acids of Lethal Factor (LFN). Here, we established a cytosolic binding assay, demonstrating the ability of DARPins to refold in the cytosol and bind their target after been translocated by PA.
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Affiliation(s)
- Lukas Becker
- Department of Biochemistry, University of Zurich, Winterthurerstr. 190, 8057, Zurich, Switzerland
| | - Andreas Plückthun
- Department of Biochemistry, University of Zurich, Winterthurerstr. 190, 8057, Zurich, Switzerland.
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Griffiths G, Gruenberg J, Marsh M, Wohlmann J, Jones AT, Parton RG. Nanoparticle entry into cells; the cell biology weak link. Adv Drug Deliv Rev 2022; 188:114403. [PMID: 35777667 DOI: 10.1016/j.addr.2022.114403] [Citation(s) in RCA: 26] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Revised: 06/22/2022] [Accepted: 06/23/2022] [Indexed: 12/22/2022]
Abstract
Nanoparticles (NP) are attractive options for the therapeutic delivery of active pharmaceutical drugs, proteins and nucleic acids into cells, tissues and organs. Research into the development and application of NP most often starts with a diverse group of scientists, including chemists, bioengineers and material and pharmaceutical scientists, who design, fabricate and characterize NP in vitro (Stage 1). The next step (Stage 2) generally investigates cell toxicity as well as the processes by which NP bind, are internalized and deliver their cargo to appropriate model tissue culture cells. Subsequently, in Stage 3, selected NP are tested in animal systems, mostly mouse. Whereas the chemistry-based development and analysis in Stage 1 is increasingly sophisticated, the investigations in Stage 2 are not what could be regarded as 'state-of-the-art' for the cell biology field and the quality of research into NP interactions with cells is often sub-standard. In this review we describe our current understanding of the mechanisms by which particles gain entry into mammalian cells via endocytosis. We summarize the most important areas for concern, highlight some of the most common mis-conceptions, and identify areas where NP scientists could engage with trained cell biologists. Our survey of the different mechanisms of uptake into cells makes us suspect that claims for roles for caveolae, as well as macropinocytosis, in NP uptake into cells have been exaggerated, whereas phagocytosis has been under-appreciated.
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Affiliation(s)
- Gareth Griffiths
- Department Biosciences, University of Oslo, Blindernveien 31, PO Box 1041, 0316 Oslo, Norway.
| | - Jean Gruenberg
- Department of Biochemistry, University of Geneva, 30 quai E. Ansermet, 1211-Geneva-4, Switzerland
| | - Mark Marsh
- Laboratory for Molecular Cell Biology, University College London, Gower Street, London, WC1E 6BT, UK
| | - Jens Wohlmann
- Department Biosciences, University of Oslo, Blindernveien 31, PO Box 1041, 0316 Oslo, Norway
| | - Arwyn T Jones
- School of Pharmacy and Pharmaceutical Sciences, Cardiff University, Redwood Building, Cardiff, Wales CF103NB, UK
| | - Robert G Parton
- Institute for Molecular Bioscience and Centre for Microscopy and Microanalysis, The University of Queensland, Qld 4072, Australia
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Becker L, Singh Badwal J, Brandl F, Verdurmen WPR, Plückthun A. Thermodynamic Stability Is a Strong Predictor for the Delivery of DARPins to the Cytosol via Anthrax Toxin. Pharmaceutics 2021; 13:pharmaceutics13081285. [PMID: 34452246 PMCID: PMC8401532 DOI: 10.3390/pharmaceutics13081285] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Accepted: 08/05/2021] [Indexed: 11/16/2022] Open
Abstract
Anthrax toxin has evolved to translocate its toxic cargo proteins to the cytosol of cells carrying its cognate receptor. Cargo molecules need to unfold to penetrate the narrow pore formed by its membrane-spanning subunit, protective antigen (PA). Various alternative cargo molecules have previously been tested, with some showing only limited translocation efficiency, and it may be assumed that these were too stable to be unfolded before passing through the anthrax pore. In this study, we systematically and quantitatively analyzed the correlation between the translocation of various designed ankyrin repeat proteins (DARPins) and their different sizes and thermodynamic stabilities. To measure cytosolic uptake, we used biotinylation of the cargo by cytosolic BirA, and we measured cargo equilibrium stability via denaturant-induced unfolding, monitored by circular dichroism (CD). Most of the tested DARPin cargoes, including target-binding ones, were translocated to the cytosol. Those DARPins, which remained trapped in the endosome, were confirmed by CD to show a high equilibrium stability. We could pinpoint a stability threshold up to which cargo DARPins still get translocated to the cytosol. These experiments have outlined the requirements for translocatable binding proteins, relevant stability measurements to assess translocatable candidates, and guidelines to further engineer this property if needed.
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Affiliation(s)
- Lukas Becker
- Department of Biochemistry, University of Zurich, Winterthurerstr. 190, 8057 Zurich, Switzerland; (L.B.); (J.S.B.); (F.B.)
| | - Jasleen Singh Badwal
- Department of Biochemistry, University of Zurich, Winterthurerstr. 190, 8057 Zurich, Switzerland; (L.B.); (J.S.B.); (F.B.)
| | - Fabian Brandl
- Department of Biochemistry, University of Zurich, Winterthurerstr. 190, 8057 Zurich, Switzerland; (L.B.); (J.S.B.); (F.B.)
| | - Wouter P. R. Verdurmen
- Department of Biochemistry, Radboud Institute for Molecular Life Sciences (RIMLS), Radboud University Medical Center, Geert Grooteplein 28, 6525 GA Nijmegen, The Netherlands;
| | - Andreas Plückthun
- Department of Biochemistry, University of Zurich, Winterthurerstr. 190, 8057 Zurich, Switzerland; (L.B.); (J.S.B.); (F.B.)
- Correspondence:
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Sánchez-Navarro M. Advances in peptide-mediated cytosolic delivery of proteins. Adv Drug Deliv Rev 2021; 171:187-198. [PMID: 33561452 DOI: 10.1016/j.addr.2021.02.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2020] [Revised: 01/26/2021] [Accepted: 02/03/2021] [Indexed: 02/06/2023]
Abstract
The number of protein-based drugs is exponentially increasing. However, development of protein therapeutics against intracellular targets is hampered by the lack of efficient cytosolic delivery strategies. In recent years, the use of cell-penetrating peptides has been proposed as a strategy to promote protein internalization. In this article, we provide the reader with a succinct update on the strategies exploited to enable peptide-mediated cytosolic delivery of proteins. First, we analyse the various methods available for delivery. We then describe the most popular and the in vitro assays designed to assess the intracellular distribution of protein cargo.
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Becker L, Verdurmen WPR, Plückthun A. Reengineering anthrax toxin protective antigen for improved receptor-specific protein delivery. BMC Biol 2020; 18:100. [PMID: 32792013 PMCID: PMC7427085 DOI: 10.1186/s12915-020-00827-y] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2020] [Accepted: 07/10/2020] [Indexed: 01/27/2023] Open
Abstract
Background To increase the size of the druggable proteome, it would be highly desirable to devise efficient methods to translocate designed binding proteins to the cytosol, as they could specifically target flat and hydrophobic protein-protein interfaces. If this could be done in a manner dependent on a cell surface receptor, two layers of specificity would be obtained: one for the cell type and the other for the cytosolic target. Bacterial protein toxins have naturally evolved such systems. Anthrax toxin consists of a pore-forming translocation unit (protective antigen (PA)) and a separate protein payload. When engineering PA to ablate binding to its own receptor and instead binding to a receptor of choice, by fusing a designed ankyrin repeat protein (DARPin), uptake in new cell types can be achieved. Results Prepore-to-pore conversion of redirected PA already occurs at the cell surface, limiting the amount of PA that can be administered and thus limiting the amount of delivered payload. We hypothesized that the reason is a lack of a stabilizing interaction with wild-type PA receptor. We have now reengineered PA to incorporate the binding domain of the anthrax receptor CMG2, followed by a DARPin, binding to the receptor of choice. This construct is indeed stabilized, undergoes prepore-to-pore conversion only in late endosomes, can be administered to much higher concentrations without showing toxicity, and consequently delivers much higher amounts of payload to the cytosol. Conclusion We believe that this reengineered system is an important step forward to addressing efficient cell-specific delivery of proteins to the cytosol.
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Affiliation(s)
- Lukas Becker
- Department of Biochemistry, University of Zurich, Winterthurerstr. 190, 8057, Zurich, Switzerland
| | - Wouter P R Verdurmen
- Department of Biochemistry, Radboud Institute for Molecular Life Sciences (RIMLS), Radboud University Medical Center, Geert Grooteplein 28, 6525 GA, Nijmegen, The Netherlands
| | - Andreas Plückthun
- Department of Biochemistry, University of Zurich, Winterthurerstr. 190, 8057, Zurich, Switzerland.
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In Vitro Assays: Friends or Foes of Cell-Penetrating Peptides. Int J Mol Sci 2020; 21:ijms21134719. [PMID: 32630650 PMCID: PMC7369778 DOI: 10.3390/ijms21134719] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2020] [Revised: 06/24/2020] [Accepted: 07/01/2020] [Indexed: 12/20/2022] Open
Abstract
The cell membrane is a complex and highly regulated system that is composed of lipid bilayer and proteins. One of the main functions of the cell membrane is the regulation of cell entry. Cell-penetrating peptides (CPPs) are defined as peptides that can cross the plasma membrane and deliver their cargo inside the cell. The uptake of a peptide is determined by its sequence and biophysicochemical properties. At the same time, the uptake mechanism and efficiency are shown to be dependent on local peptide concentration, cell membrane lipid composition, characteristics of the cargo, and experimental methodology, suggesting that a highly efficient CPP in one system might not be as productive in another. To better understand the dependence of CPPs on the experimental system, we present a review of the in vitro assays that have been employed in the literature to evaluate CPPs and CPP-cargos. Our comprehensive review suggests that utilization of orthogonal assays will be more effective for deciphering the true ability of CPPs to translocate through the membrane and enter the cell cytoplasm.
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Deprey K, Becker L, Kritzer J, Plückthun A. Trapped! A Critical Evaluation of Methods for Measuring Total Cellular Uptake versus Cytosolic Localization. Bioconjug Chem 2019; 30:1006-1027. [PMID: 30882208 PMCID: PMC6527423 DOI: 10.1021/acs.bioconjchem.9b00112] [Citation(s) in RCA: 56] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Biomolecules have many properties that make them promising for intracellular therapeutic applications, but delivery remains a key challenge because large biomolecules cannot easily enter the cytosol. Furthermore, quantification of total intracellular versus cytosolic concentrations remains demanding, and the determination of delivery efficiency is thus not straightforward. In this review, we discuss strategies for delivering biomolecules into the cytosol and briefly summarize the mechanisms of uptake for these systems. We then describe commonly used methods to measure total cellular uptake and, more selectively, cytosolic localization, and discuss the major advantages and drawbacks of each method. We critically evaluate methods of measuring "cell penetration" that do not adequately distinguish total cellular uptake and cytosolic localization, which often lead to inaccurate interpretations of a molecule's cytosolic localization. Finally, we summarize the properties and components of each method, including the main caveats of each, to allow for informed decisions about method selection for specific applications. When applied correctly and interpreted carefully, methods for quantifying cytosolic localization offer valuable insight into the bioactivity of biomolecules and potentially the prospects for their eventual development into therapeutics.
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Affiliation(s)
- Kirsten Deprey
- Department of Chemistry, Tufts University, 62 Talbot Avenue, Medford, Massachusetts 02155, United States
| | - Lukas Becker
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
| | - Joshua Kritzer
- Department of Chemistry, Tufts University, 62 Talbot Avenue, Medford, Massachusetts 02155, United States
| | - Andreas Plückthun
- Department of Biochemistry, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
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Verdurmen WPR, Mazlami M, Plückthun A. A quantitative comparison of cytosolic delivery via different protein uptake systems. Sci Rep 2017; 7:13194. [PMID: 29038564 PMCID: PMC5643320 DOI: 10.1038/s41598-017-13469-y] [Citation(s) in RCA: 61] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2017] [Accepted: 09/25/2017] [Indexed: 01/27/2023] Open
Abstract
Over many years, a variety of delivery systems have been investigated that have the capacity to shuttle macromolecular cargoes, especially proteins, into the cytosol. Due to the lack of an objective way to quantify cytosolic delivery, relative delivery efficiencies of the various transport systems have remained unclear. Here, we demonstrate the use of the biotin ligase assay for a quantitative comparison of protein transport to the cytosol via cell-penetrating peptides, supercharged proteins and bacterial toxins in four different cell lines. The data illustrate large differences in both the total cellular internalization, which denotes any intracellular location including endosomes, and in the cytosolic uptake of the transport systems, with little correlation between the two. Also, we found significant differences between the cell lines. In general, protein transport systems based on cell-penetrating peptides show a modest total uptake, and mostly do not deliver cargo to the cytosol. Systems based on bacterial toxins show a modest receptor-mediated internalization but an efficient delivery to the cytosol. Supercharged proteins, on the contrary, are not receptor-specific and lead to massive total internalization into endosomes, but only low amounts end up in the cytosol.
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Affiliation(s)
- Wouter P R Verdurmen
- Department of Biochemistry, University of Zurich, Winterthurerstr. 190, 8057, Zurich, Switzerland.,Department of Biochemistry, Radboud Institute for Molecular Life Sciences (RIMLS), Radboud university medical center, Geert Grooteplein 28, 6525 GA, Nijmegen, The Netherlands
| | - Marigona Mazlami
- Department of Biochemistry, University of Zurich, Winterthurerstr. 190, 8057, Zurich, Switzerland
| | - Andreas Plückthun
- Department of Biochemistry, University of Zurich, Winterthurerstr. 190, 8057, Zurich, Switzerland.
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