Glycosylated Triterpenoids as Endosomal Escape Enhancers in Targeted Tumor Therapies

Abstract

Protein-based targeted toxins play an increasingly important role in targeted tumor therapies. In spite of their high intrinsic toxicity, their efficacy in animal models is low. A major reason for this is the limited entry of the toxin into the cytosol of the target cell, which is required to mediate the fatal effect. Target receptor bound and internalized toxins are mostly either recycled back to the cell surface or lysosomally degraded. This might explain why no antibody-targeted protein toxin has been approved for tumor therapeutic applications by the authorities to date although more than 500 targeted toxins have been developed within the last decades. To overcome the problem of insufficient endosomal escape, a number of strategies that make use of diverse chemicals, cell-penetrating or fusogenic peptides, and light-induced techniques were designed to weaken the membrane integrity of endosomes. This review focuses on glycosylated triterpenoids as endosomal escape enhancers and throws light on their structure, the mechanism of action, and on their efficacy in cell culture and animal models. Obstacles, challenges, opportunities, and future prospects are discussed.

A new liquid chromatography-high resolution Orbitrap mass spectrometry-based strategy to characterize Glucuronide Oleanane-type Triterpenoid Carboxylic Acid 3, 28-O-Bidesmosides (GOTCAB) saponins.A case study of Gypsophila glomerata Pall ex M. B. (Caryophyllaceae)

“…An aliquot of the crude extract (1 g) was fractionated by a low pressure liquid chromatography over a C18 column (310 × 25 mm,40-63 µm) (Merck, Germany) using a binary gradient of methanolwater (10:90 -100:0) to afford 20 fractions (each 25 ml). Fractions (10)(11)(12)(13) were separated by repeated semi-preparative HPLC on Kinetex C18 (150 x 10 mm, 5 µm) (Phenomenex, USA) and gave 18 fractions (each 5ml). Semi-preparative HPLC was performed on a chromatographic system Varian equipped with a ternary pump Model 9012, a Rheodyne injector with 200 µL loop and an UV/VIS detector Model 9050 set at 210 nm.…”

“…Gypsophila L. species (Caryophyllaceae) have been shown to accumulate GOTCAB saponins [2][3][4][5]. Gypsophila GOTCAB are known to possess various pharmaceutical properties such as cytostatic and cytotoxic effects on malignant tumor cells [6][7][8][9], synergistic enhancement of the immunotoxines activity [10], adjuvant properties for vaccines as immunostimulatory complexes [11]. Since GOTCAB saponins usually are a mixture of structurally related forms with very similar polarities, their separation remains a challenge [1].…”

“…The MS data and chromatographic behavior of 9 allowed us to deduce an isobar of 10. Their structural difference could be attributed to the pentose unit at C-3 trisaccharidexylose (9) and arabinose(10). Thus,9 could correspond to 3-O-β-D-galactopyranosyl-(1→2)-[β-D-xylopyranosyl-(1→3)]-β-Dglucuronopyranosyl gypsogenin 28-O-(β-D-glucopyranosyl-(1→3)-[β-D-xylopyranosyl-(1→4)]-α-L-rhamnopyranosyl-(1→2)-β-D-fucopyranosyl ester, previously isolated from the roots of G. paniculata L [30].…”

Critical Issues in the Development of Immunotoxins for Anticancer Therapy

“…116 One approach to facilitate and enhance the cytosolic delivery of ITs is the combination treatment with endosomal escape enhancers, such as chemicals, peptides, or proteins. 14,117,118 For instance, coadministration of bacterial pore-forming cytolysins and a gelonin-based IT, both of which have been designed to target the same antigen, potentiates the cytosolic delivery of gelonin by several orders of magnitude, resulting in a large increase in antitumor efficacy. 119 Chemical endosomal-escape enhancers, such as lysosomotropic amines and carboxylic ionophores, are membrane destabilizers (because they disrupt membrane integrity) or endosomolytic agents (because they inhibit the vesicular proton-ATPase pump) 14 ; therefore, they enhance the endosomal escape of coadministered ITs in in vitro settings.…”

“…Antibody-based ITs are mostly lysosomally degraded rather than released into the cytosol because the tight association of antibodies with the antigen (receptor) hampers the antibody dissociation from the antigen for the subsequent cytosolic release before lysosomal degradation. 117 As a solution to the problem, a cellular cytosol-penetrating antibody, known as cytotransmab technology, [126][127][128] could be utilized in the design of ITs as a targeting moiety because it has the capacity for endosomal escape by itself after cellular internalization. Cytotransmab in the intact human IgG1 format can reach the cytosol of cancer cells after tumor cellespecific endocytotic internalization after systemic administration in mouse models, thereby showing much higher endosomal-escape efficiency as compared to conventional cellpenetrating peptides.…”