Diving through Membranes: Molecular Cunning to Enforce the Endosomal Escape of Antibody-Targeted Anti-Tumor Toxins

Abstract

Membranes are vital barriers by which cells control the flux of molecules and energy between their exterior and interior and also between their various intracellular compartments. While numerous transport systems exist for ions and small molecules, the cytosolic uptake of larger biological molecules and in particular antibody-targeted drugs, is a big challenge. Inducing leakage of the plasma membrane is unfavorable since the target cell specificity mediated by the antibody would likely be lost in this case. After binding and internalization, the antibody drug conjugates reach the endosomes. Thus, enforcing the endosomal escape of anti-tumor toxins without affecting the integrity of other cellular membranes is of paramount importance. Different strategies have been developed in the last decades to overcome endosomal accumulation and subsequent lysosomal degradation of targeted protein-based drugs. In this review we summarize the various efforts made to establish efficient techniques to disrupt the endosomal membrane barrier including the use of molecular ferries such as cell penetrating peptides or viral membrane fusion proteins, endosomal leakage inducing molecules such as saponins or monensin and physicochemical methods as represented by photochemical internalization.

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

“…The large size and resulting poor bioavailability of these molecules often requires the use of a delivery system to facilitate their endocytic uptake into the cell. The rate limiting step in this delivery process is often endolysosomal escape into the cytosol and overcoming this remains a major challenge [32]. The use of pulse shape analysis to quantify endolysosomal escape may represent a useful tool in the development of escape enhancers.…”

Human Cytolytic Fusion Proteins: Modified Versions of Human Granzyme B and Angiogenin Have the Potential to Replace Bacterial Toxins in Targeted Therapies against CD64+ Diseases

“…One strategy to address the endosomal release of effector molecules lacking endogenous translocation domains has been the insertion of PTDs between the binding and effector domains [122,139]. In 2001 the concept of a multifunctional adapter flanking a MTP with a cytosolic cleavable peptide (CCP) and an endosomal cleavable peptide (ECP) was described for the first time by Keller et al [24].…”

“…The use of optimized adapter compositions based on alternative protease cleavage sites increasing the half-life of systemically applied hCFPs might offer suitable approaches to meeting this challenge. Further strategies include the induction of endosomal leakage and disruption by pH alteration or the use of membrane-destabilizing agents, and photochemical internalization (PCI) by light-induced activation of co-administered photosensitizers and have recently been reviewed [122].…”

“…The maturation of endosomes involves acidification, fusion to lysosomes and subsequent enzymatic degradation (endosomal/lysosomal degradation pathway), and this represents one of the major bottlenecks limiting the biological activity of receptor-targeting protein drugs. Research has, therefore, focused on strategies to promote the release of biopharmaceuticals from early endosomes [122,123]. Various strategies have been developed, including the use of carrier systems, such as liposomes, cationic polymers and nanoparticles, or the linkage of protein-based drugs to short peptides that facilitate membrane translocation [122,124,125].…”

Germline mutagenesis ofNasonia vitripennisthrough ovarian delivery of CRISPR-Cas9 ribonucleoprotein

“…In mosquitoes, an endosomal escape reagent like chloroquine or saponin is necessary to achieve efficient gene editing (Chaverra-Rodriguez et al, 2018;Macias et al, 2020). Endosomal escape reagents help the release of the ribonucleoprotein once delivered into the ovary (Fuchs et al, 2013). However, in the whitefly the use of saponin was unnecessary, and even detrimental for viability (Heu et al, 2020).…”