Biosynthesized tumor acidity and MMP dual-responsive plant toxin gelonin for robust cancer therapy.

Among all kinds of anticancer agents, small molecule drugs produce an unsatisfactory therapeutic effect due to the lack of selectivity, notorious drug resistance and side effects. Therefore, researchers have begun to pay extensive attention to macromolecular drugs with high efficacy and specificity. As a plant toxin, gelonin exerts potent antitumor activity via inhibiting intracellular protein synthesis. However, gelonin lacks a translocation domain, and thus its poor cellular uptake leads to low outcomes of antitumor response. Here, tumor acidity and matrix metalloproteinase (MMP) dual-responsive functional gelonin (Trx-PVGLIG-pHLIP-gelonin, TPpG), composed of a thioredoxin (Trx) tag, a pH low insertion peptide (pHLIP), an MMP-responsive motif PVGLIG hexapeptide and gelonin, was innovatively proposed and biologically synthesized by a gene recombination technique. TPpG exhibited good thermal and serum stability, showed MMP responsiveness and could enter tumor cells under weakly acidic conditions, especially for MMP2-overexpressing HT1080 cells. Compared to low MMP2-expressing MCF-7 cells, TPpG displayed enhanced in vitro antitumor efficacy to HT1080 cells at pH 6.5 as determined by different methods. Likewise, TPpG was much more effective in triggering cell apoptosis and inhibiting protein synthesis in HT1080 cells than in MCF-7 cells. Intriguingly, with enhanced stability and pH/MMP dual responsiveness, TPpG notably inhibited subcutaneous HT1080 xenograft growth in mice and no noticeable off-target side effect was observed. This ingeniously designed strategy aims at providing new perspectives for the development of a smart platform that can intelligently respond to a tumor microenvironment for efficient protein delivery.

Sapovaccarin-S1 and -S2, Two Type I RIP Isoforms from the Seeds of Saponaria vaccaria L.

Type I ribosome-inactivating proteins (RIPs) are plant toxins that inhibit protein synthesis by exerting rRNA N-glycosylase activity (EC 3.2.2.22). Due to the lack of a cell-binding domain, type I RIPs are not target cell-specific. However once linked to antibodies, so called immunotoxins, they are promising candidates for targeted anti-cancer therapy. In this study, sapovaccarin-S1 and -S2, two newly identified type I RIP isoforms differing in only one amino acid, were isolated from the seeds of Saponaria vaccaria L. Sapovaccarin-S1 and -S2 were purified using ammonium sulfate precipitation and subsequent cation exchange chromatography. The determined molecular masses of 28,763 Da and 28,793 Da are in the mass range typical for type I RIPs and the identified amino acid sequences are homologous to known type I RIPs such as dianthin 30 and saporin-S6 (79% sequence identity each). Sapovaccarin-S1 and -S2 showed adenine-releasing activity and induced cell death in Huh-7 cells. In comparison to other type I RIPs, sapovaccarin-S1 and -S2 exhibited a higher thermostability as shown by nano-differential scanning calorimetry. These results suggest that sapovaccarin-S1 and -S2 would be optimal candidates for targeted anti-cancer therapy.

Curcin C inhibit osteosarcoma cell line U2OS proliferation by ROS induced apoptosis, autophagy and cell cycle arrest through activating JNK signal pathway.

Osteosarcoma is a kind of primary bone malignant tumors. Its cure rate has been stagnant in the past decade years. Curcin C belongs to type I ribosome inactivating proteins, extracted from the cotyledons of post-germinated Jatropha curcas seeds. It can inhibit the proliferation of several tumor lines including U2OS cells with extraordinary efficiency. The treated U2OS cells were arrested in both S and G2/M phase, showed typical apoptosis morphological characteristic, formed autophagosomes and increase the ratio of LC3II to LC3I. Meanwhile, the level of ROS in the treated cells was found increasing significantly, with the change of mitochondrial membrane potential and decreased antioxidant enzyme activities. The application of ROS scavenger NAC not only significantly inhibited the toxicity of Curcin C but also prevented the happen of apoptosis and autophagy to some extent. These results suggested that Curcin C may function through ROS pathway. In addition, the Curcin C treatment could activate JNK and inhibit ERK signal pathway. Sp600125, an inhibitor of JNK signaling pathway, can prevent subsequent apoptosis and autophagy events, suggesting that JNK pathway was at least one of the pathways of Curcin C action. Moreover, the relevant including antagonistic among autophagy, apoptosis and cell cycle arresting induced by Curcin C also was found. In summary, it can be speculated that Curcin C may induce S, G2/M phase arrest, apoptosis and autophagy of human osteosarcoma U2OS cells through activating JNK signal pathway and blocking ERK signal pathway by promoting ROS accumulation in cell, thus finally reflected in the effect of inhibiting tumor cell proliferation.

Novel Binding Mechanisms of Fusion Broad Range Anti-Infective Protein Ricin A Chain Mutant-Pokeweed Antiviral Protein 1 (RTAM-PAP1) against SARS-CoV-2 Key Proteins in Silico.

The deadly pandemic named COVID-19, caused by a new coronavirus (SARS-CoV-2), emerged in 2019 and is still spreading globally at a dangerous pace. As of today, there are no proven vaccines, therapies, or even strategies to fight off this virus. Here, we describe the in silico docking results of a novel broad range anti-infective fusion protein RTAM-PAP1 against the various key proteins of SARS-CoV-2 using the latest protein-ligand docking software. RTAM-PAP1 was compared against the SARS-CoV-2 B38 antibody, ricin A chain, a pokeweed antiviral protein from leaves, and the lectin griffithsin using the special CoDockPP COVID-19 version. These experiments revealed novel binding mechanisms of RTAM-PAP1 with a high affinity to numerous SARS-CoV-2 key proteins. RTAM-PAP1 was further characterized in a preliminary toxicity study in mice and was found to be a potential therapeutic candidate. These findings might lead to the discovery of novel SARS-CoV-2 targets and therapeutic protein structures with outstanding functions.

Analysis of Triterpenoid Saponins Reveals Insights into Structural Features Associated with Potent Protein Drug Enhancement Effects.

Plant-based saponins are amphipathic glycosides composed of a hydrophobic aglycone backbone covalently bound to one or more hydrophilic sugar moieties. Recently, the endosomal escape activity of triterpenoid saponins has been investigated as a potentially powerful tool for improved cytosolic penetration of protein drugs internalized by endocytic uptake, thereby greatly enhancing their pharmacological effects. However, only a few saponins have been studied, and the paucity in understanding the structure-activity relationship of saponins imposes significant limitations on their applications. To address this knowledge gap, 12 triterpenoid saponins with diverse structural side chains were screened for their utility as endosomolytic agents. These compounds were used in combination with a toxin (MAP30-HBP) comprising a type I ribosome-inactivating protein fused to a cell-penetrating peptide. Suitability of saponins as endosomolytic agents was assessed on the basis of cytotoxicity, endosomal escape promotion, and synergistic effects on toxins. Five saponins showed strong endosomal escape activity, enhancing MAP30-HBP cytotoxicity by more than 106 to 109 folds. These saponins also enhanced the apoptotic effect of MAP30-HBP in a pH-dependent manner. Additionally, growth inhibition of MAP30-HBP-treated SMMC-7721 cells was greater than that of similarly treated HeLa cells, suggesting that saponin-mediated endosomolytic effect is likely to be cell-specific. Furthermore, the structural features and hydrophobicity of the sugar side chains were analyzed to draw correlations with endosomal escape activity and derive predictive rules, thus providing new insights into structure-activity relationships of saponins. This study revealed new saponins that can potentially be exploited as efficient cytosolic delivery reagents for improved therapeutic drug effects.

A Spectroscopic Study on Secondary Structure and Thermal Unfolding of the Plant Toxin Gelonin Confirms Some Typical Structural Characteristics and Unravels the Sequence of Thermal Unfolding Events.

Gelonin from the Indian plant Gelonium multiflorum belongs to the type I ribosome-inactivating proteins (RIPs). Like other members of RIPs, this toxin glycoprotein inhibits protein synthesis of eukaryotic cells; hence, it is largely used in the construction of immunotoxins composed of cell-targeted antibodies. Lysosomal degradation is one of the main issues in targeted tumor therapies, especially for type I RIP-based toxins, as they lack the translocation domains. The result is an attenuated cytosolic delivery and a decrease of the antitumor efficacy of these plant-derived toxins; therefore, strategies to permit their release from endosomal vesicles or modifications of the toxins to make them resistant to degradation are necessary to improve their efficacy. Using infrared spectroscopy, we thoroughly analyzed both the secondary structure and the thermal unfolding of gelonin. Moreover, by the combination of two-dimensional correlation spectroscopy and phase diagram method, it was possible to deduce the sequence of events during the unfolding, confirming the typical characteristic of the RIP members to denature in two steps, as a sequential loss of tertiary and secondary structure was detected at 58 °C and at 65 °C, respectively. Additionally, some discrepancies in the unfolding process between gelonin and saporin-S6, another type I RIP protein, were detected.

Binding and structural studies of the complexes of type 1 ribosome inactivating protein from Momordica balsamina with uracil and uridine.

Ribosome inactivating protein (RIP) catalyzes the cleavage of glycosidic bond formed between adenine and ribose sugar of ribosomal RNA to inactivate ribosomes. Previous structural studies have shown that RNA bases, adenine, guanine, and cytosine tend to bind to RIP in the substrate binding site. However, the mode of binding of uracil with RIP was not yet known. Here, we report crystal structures of two complexes of type 1 RIP from Momordica balsamina (MbRIP1) with base, uracil and nucleoside, uridine. The binding studies of MbRIP1 with uracil and uridine as estimated using fluorescence spectroscopy showed that the equilibrium dissociation constants (KD ) were 1.2 × 10-6 M and 1.4 × 10-7 M respectively. The corresponding values obtained using surface plasmon resonance (SPR) were found to be 1.4 × 10-6 M and 1.1 × 10-7 M, respectively. Structures of the complexes of MbRIP1 with uracil (Structure-1) and uridine (Structure-2) were determined at 1.70 and 1.98 Å resolutions respectively. Structure-1 showed that uracil bound to MbRIP1 at the substrate binding site but its mode of binding was significantly different from those of adenine, guanine and cytosine. However, the mode of binding of uridine was found to be similar to those of cytidine. As a result of binding of uracil to MbRIP1 at the substrate binding site, three water molecules were expelled while eight water molecules were expelled when uridine bound to MbRIP1.

Self-Assembly of Extracellular Vesicle-like Metal-Organic Framework Nanoparticles for Protection and Intracellular Delivery of Biofunctional Proteins.

The intracellular delivery of biofunctional enzymes or therapeutic proteins through systemic administration is of great importance in therapeutic intervention of various diseases. However, current strategies face substantial challenges owing to various biological barriers, including susceptibility to protein degradation and denaturation, poor cellular uptake, and low transduction efficiency into the cytosol. Here, we developed a biomimetic nanoparticle platform for systemic and intracellular delivery of proteins. Through a biocompatible strategy, guest proteins are caged in the matrix of metal-organic frameworks (MOFs) with high efficiency (up to ∼94%) and high loading content up to ∼50 times those achieved by surface conjunction, and the nanoparticles were further decorated with the extracellular vesicle (EV) membrane with an efficiency as high as ∼97%. In vitro and in vivo study manifests that the EV-like nanoparticles can not only protect proteins against protease digestion and evade the immune system clearance but also selectively target homotypic tumor sites and promote tumor cell uptake and autonomous release of the guest protein after internalization. Assisted by biomimetic nanoparticles, intracellular delivery of the bioactive therapeutic protein gelonin significantly inhibits the tumor growth in vivo and increased 14-fold the therapeutic efficacy. Together, our work not only proposes a new concept to construct a biomimetic nanoplatform but also provides a new solution for systemic and intracellular delivery of protein.

Supramolecularly Engineered Circular Bivalent Aptamer for Enhanced Functional Protein Delivery.

Circular bivalent aptamers (cb-apt) comprise an emerging class of chemically engineered aptamers with substantially improved stability and molecular recognition ability. Its therapeutic application, however, is challenged by the lack of functional modules to control the interactions of cb-apt with therapeutics. We present the design of a ß-cyclodextrin-modified cb-apt (cb-apt-ßCD) and its supramolecular interaction with molecular therapeutics via host-guest chemistry for targeted intracellular delivery. The supramolecular ensemble exhibits high serum stability and enhanced intracellular delivery efficiency compared to a monomeric aptamer. The cb-apt-ßCD ensemble delivers green fluorescent protein into targeted cells with efficiency as high as 80%, or cytotoxic saporin to efficiently inhibit tumor cell growth. The strategy of conjugating ßCD to cb-apt, and subsequently modulating the supramolecular chemistry of cb-apt-ßCD, provides a general platform to expand and diversify the function of aptamers, enabling new biological and therapeutic applications.

Novel bioactive peptides from PD-L1/2, a type 1 ribosome inactivating protein from Phytolacca dioica L. Evaluation of their antimicrobial properties and anti-biofilm activities.

Antimicrobial peptides, also called Host Defence Peptides (HDPs), are effectors of innate immune response found in all living organisms. In a previous report, we have identified by chemical fragmentation, and characterized the first cryptic antimicrobial peptide in PD-L4, a type 1 ribosome inactivating protein (RIP) from leaves of Phytolacca dioica L. We applied a recently developed bioinformatic approach to a further member of the differently expressed pool of type 1 RIPs from P. dioica (PD-L1/2), and identified two novel putative cryptic HDPs in its N-terminal domain. These two peptides, here named IKY31 and IKY23, exhibit antibacterial activities against planktonic bacterial cells and, interestingly, significant anti-biofilm properties against two Gram-negative strains. Here, we describe that PD-L1/2 derived peptides are able to induce a strong dose-dependent reduction in biofilm biomass, affect biofilm thickness and, in the case of IKY31, interfere with cell-to-cell adhesion, likely by affecting biofilm structural components. In addition to these findings, we found that both PD-L1/2 derived peptides are able to assume stable helical conformations in the presence of membrane mimicking agents (SDS and TFE) and intriguingly beta structures when incubated with extracellular bacterial wall components (LPS and alginate). Overall, the data collected in this work provide further evidence of the importance of cryptic peptides derived from type 1 RIPs in host/pathogen interactions, especially under pathophysiological conditions induced by biofilm forming bacteria. This suggests a new possible role of RIPs as precursors of antimicrobial and anti-biofilm agents, likely released upon defensive proteolytic processes, which may be involved in plant homeostasis.

Targeting Receptor-Type Protein Tyrosine Phosphatases with Biotherapeutics: Is Outside-in Better than Inside-Out?

Protein tyrosine phosphatases (PTPs), of the receptor and non-receptor classes, are key signaling molecules that play critical roles in cellular regulation underlying diverse physiological events. Aberrant signaling as a result of genetic mutation or altered expression levels has been associated with several diseases and treatment via pharmacological intervention at the level of PTPs has been widely explored; however, the challenges associated with development of small molecule phosphatase inhibitors targeting the intracellular phosphatase domain (the "inside-out" approach) have been well documented and as yet there are no clinically approved drugs targeting these enzymes. The alternative approach of targeting receptor PTPs with biotherapeutic agents (such as monoclonal antibodies or engineered fusion proteins; the "outside-in" approach) that interact with the extracellular ectodomain offers many advantages, and there have been a number of exciting recent developments in this field. Here we provide a brief overview of the receptor PTP family and an update on the emerging area of receptor PTP-targeted biotherapeutics for CD148, vascular endothelial-protein tyrosine phosphatase (VE-PTP), receptor-type PTPs σ, γ, ζ (RPTPσ, RPTPγ, RPTPζ) and CD45, and discussion of future potential in this area.

Fusion of gelonin and anti-insulin-like growth factor-1 receptor (IGF-1R) affibody for enhanced brain cancer therapy.

Owing to the extraordinary potency in inhibiting protein translation that could eventually lead to apoptosis of tumor cells, ribosome-inactivating proteins (RIPs) such as gelonin have been considered attractive drug candidates for cancer therapy. However, due to several critical obstacles (e.g., severe toxicity issues caused by a lack of selectivity in their mode of action and the low cytotoxicity via poor cellular uptake, etc.), clinical application of RIPs is yet far from being accomplished. To overcome these challenges, in the present study, we engineered gelonin fusion proteins with anti-insulin-like growth factor-1 receptor (IGF-1R) affibody ("IAFF") via the genetic recombinant method and the SpyCatcher/SpyTag-mediated conjugation method. To this end, recombinant gelonin-anti-IGF-1R affibody (rGel-IAFF), gelonin-SpyCatcher (Gel-SpyCatcher) and SpyTag-IAFF fusion proteins were produced from the E. coli expression system, and gelonin-IAFF conjugate was synthesized by mixing Gel-SpyCatcher and SpyTag-IAFF. After preparation of both rGel-IAFF and Gel-IAFF conjugate, their components' functionality was characterized in vitro. Our assay results confirmed that, while both Gel-IAFF and Gel-SpyCatcher retained equipotent N-glycosidase activity to that of gelonin, IAFF was able to selectively bind to IGF-1R overexpressed U87 MG brain cancer cells over low expression LNCaP cells. The results of cellular analyses showed that rGel-IAFF and Gel-IAFF conjugate both exhibited a greater cell uptake in the U87 MG cells than gelonin, but not in the LNCaP cells, yielding a significantly augmented cytotoxicity only in the U87 MG cells. Remarkably, rGel-IAFF and Gel-IAFF conjugate displayed 22- and 5.6-fold lower IC50 values (avg. IC50: 180 and 720 nM, respectively) than gelonin (avg. IC50: 4000 nM) in the U87 MG cells. Overall, the results of the present research demonstrated that fusion of gelonin with IAFF could provide an effective way to enhance the anti-tumor activity, while reducing the associated toxicity of gelonin.

Curcin C, a novel type I ribosome-inactivating protein from the post-germinating cotyledons of Jatropha curcas.

A novel type I ribosome-inactivating protein (RIP), designated as curcin C, was purified from Jatropha curcas, an important feedback source of bio-fuel. Molecular mass and isoelectric point of curcin C were 31.398 kDa and 7.12 as detected by MALTI-TOF assay and capillary electrophoresis assay, respectively. N-terminal sequence and LC-MS/MS analyses confirmed that curcin C is a type I RIP having high homology, but not the exactly the same with curcin, another type 1 RIP isolated from the endosperm of J. curcas. It exhibited N-glycosidase activity and in vitro translation inhibition activity. Moreover, curcin C displayed a strong selectively anti-tumor activity on human cancer cells. Its cytotoxicity against osteosarcoma cell line U20S is even higher than that of Paclitaxel with IC50 of 0.019 µM. Purification and identification of curcin C not only suggested its potential in natural anticancer drug development, but also provide chance to understanding different cytotoxic action among different RIPs.

Two Saporin-Containing Immunotoxins Specific for CD20 and CD22 Show Different Behavior in Killing Lymphoma Cells.

Immunotoxins (ITs) are hybrid proteins combining the binding specificity of antibodies with the cytocidal properties of toxins. They represent a promising approach to lymphoma therapy. The cytotoxicity of two immunotoxins obtained by chemical conjugation of the plant toxin saporin-S6 with the anti-CD20 chimeric antibody rituximab and the anti-CD22 murine antibody OM124 were evaluated on the CD20-/CD22-positive cell line Raji. Both ITs showed strong cytotoxicity for Raji cells, but the anti-CD22 IT was two logs more efficient in killing, probably because of its faster internalization. The anti-CD22 IT gave slower but greater caspase activation than the anti-CD20 IT. The cytotoxic effect of both immunotoxins can be partially prevented by either the pan-caspase inhibitor Z-VAD or the necroptosis inhibitor necrostatin-1. Oxidative stress seems to be involved in the cell killing activity of anti-CD20 IT, as demonstrated by the protective role of the H2O2 scavenger catalase, but not in that of anti-CD22 IT. Moreover, the IT toxicity can be augmented by the contemporary administration of other chemotherapeutic drugs, such as PS-341, MG-132, and fludarabine. These results contribute to the understanding of the immunotoxin mechanism of action that is required for their clinical use, either alone or in combination with other drugs.

Molecular tumor targeting of gelonin by fusion with F3 peptide.

Therapeutically potent macromolecular drugs have shown great promise for overcoming the limitations of small-molecule anti-cancer drugs. But tumor cell-selective intracellular delivery of the macromolecules remains a major hurdle for their successful clinical application. To overcome this challenge, we engineered a novel genetic fusion protein (F3-Gel) that composed of F3 peptide, a tumor-homing peptide, and gelonin, a plant-derived ribosome-inactivating protein (RIP), and then evaluated its anti-cancer activity in vitro and in vivo. The F3-Gel-encoding gene was synthesized by genetic recombination, and F3-Gel was successfully expressed in E coli. The anti-cancer activity of the produced F3-Gel was evaluated by various in vitro assays, which revealed that F3-Gel maintained equipotent protein synthesis inhibition activity (IC50=11 pmol/L) as unmodified gelonin (IC50=10 pmol/L). Furthermore, F3-Gel displayed enhanced cellular uptake into cancer cells (U87 MG, HeLa, LnCaP and 9L) than noncancerous cells (293 HEK and SVGp12). Compared with gelonin, F3-Gel exerted significantly higher cytotoxicity against these cancer cells. F3-Gel displayed significantly greater inhibition of protein translation in U87 MG cells: F3-Gel (0.5 µmol/L) was able to reduce the protein level to less than 50%, while gelonin (1 µmol/L) did not affect the intracellular protein level. In a U87 MG xenograft tumor-bearing mouse model, F3-Gel was accumulated in the tumor site at much higher levels and maintained for a prolonged time compared with gelonin. Administration of F3-Gel (0.5, 0.75 mol/kg, iv) caused 36% and 66%, respectively, inhibition of tumor growth in U87 MG xenograft mice, suggesting that it is a promising candidate drug for cancer treatment. Furthermore, this study demonstrates that fusion of F3 peptide to a potent macromolecule could provides an effective method for targeting tumors and eventually could improve their druggability.

Cathepsin B-degradable, NIR-responsive nanoparticulate platform for target-specific cancer therapy.

Stimuli-responsive anticancer formulations can promote drug release and activation within the target tumour, facilitate cellular uptake, as well as improve the therapeutic efficacy of drugs and reduce off-target effects. In the present work, indocyanine green (ICG)-containing polyglutamate (PGA) nanoparticles were developed and characterized. Digestion of nanoparticles with cathepsin B, a matrix metalloproteinase overexpressed in the microenvironment of advanced tumours, decreased particle size and increased ICG cellular uptake. Incorporation of ICG in PGA nanoparticles provided the NIR-absorbing agent with time-dependent altered optical properties in the presence of cathepsin B. Having minimal dark toxicity, the formulation exhibited significant cytotoxicity upon NIR exposure. Combined use of the formulation with saporin, a ribosome-inactivating protein, resulted in synergistically enhanced cytotoxicity attributed to the photo-induced release of saporin from endo/lysosomes. The results suggest that this therapeutic approach can offer significant therapeutic benefit in the treatment of superficial malignancies, such as head and neck tumours.

Oligonucleotide transition state analogues of saporin L3.

Ribosome inactivating proteins (RIPs) are among the most toxic agents known. More than a dozen clinical trials against refractory cancers have been initiated using modified RIPs with impressive results. However, dose-limiting toxicity due to vascular leak syndrome limits success of the therapy. We have previously reported some tight-binding transition state analogues of Saporin L3 that mimic small oligonucleotide substrates in which the susceptible adenosine has been replaced by a 9-deazaadenyl hydroxypyrrolidinol derivative. They provide the first step in the development of rescue agents to prevent Saporin L3 toxicity on non-targeted cells. Here we report the synthesis, using solution phase chemistry, of these and a larger group of transition state analogues. They were tested for inhibition against Saporin L3 giving Ki values as low as 3.3 nM and indicating the structural requirements for inhibition.

Vectorization of biomacromolecules into cells using extracellular vesicles with enhanced internalization induced by macropinocytosis.

Extracellular vesicles (EVs, exosomes) are approximately 30- to 200-nm-long vesicles that have received increased attention due to their role in cell-to-cell communication. Although EVs are highly anticipated to be a next-generation intracellular delivery tool because of their pharmaceutical advantages, including non-immunogenicity, their cellular uptake efficacy is low because of the repulsion of EVs and negatively charged cell membranes and size limitations in endocytosis. Here, we demonstrate a methodology for achieving enhanced cellular EV uptake using arginine-rich cell-penetrating peptides (CPPs) to induce active macropinocytosis. The induction of macropinocytosis via a simple modification to the exosomal membrane using stearylated octaarginine, which is a representative CPP, significantly enhanced the cellular EV uptake efficacy. Consequently, effective EV-based intracellular delivery of an artificially encapsulated ribosome-inactivating protein, saporin, in EVs was attained.

Saponins from Saponaria officinalis L. Augment the Efficacy of a Rituximab-Immunotoxin.

Triterpenoidal saponins are synthesized in the roots of Saponaria officinalis L. The same plant is also a source for the toxin Saporin, which is a ribosome-inactivating protein. Triterpenoidal saponins are known to increase the cytotoxicity of Saporin by modulating its intracellular trafficking. Here, we investigated if the combinatorial effects elicited by purified saponins and Saporin can be applied to increase the therapeutic efficacy of the immunotoxin Saporin-Rituximab. First, saponins were purified by high-performance liquid chromatography. Thereafter, their intrinsic cytotoxicity was evaluated on Ramos cells with no observed effect up to 5 µg/mL, however, saponins increased the cytotoxicity of Saporin, while no influence was observed on its N-glycosidase activity. Saporin-Rituximab bound to CD20 in Ramos cells and, in the absence of saponins, had a GI50 (concentration inhibiting cell growth to 50 %) of 7 nM. However, in the presence of a nontoxic concentration of saponins, the GI50 of Saporin-Rituximab was 0.01 nM, a nearly 700-fold increase in efficacy. Moreover, two further immunotoxins, namely Saporin-anti-CD22 and Saporin-anti-CD25, were tested in combination with saponins yielding enhancement factors of 170-fold and 25-fold, respectively. All three receptors are present in Ramos cells and the differences in cytotoxicity enhancement may be explained by the differing expression levels of the cellular receptors. The application of purified saponins from S. officinalis L. is therefore a new strategy to potentially improve the cytotoxicity and therapeutic efficacy of Rituximab-immunotoxins for the treatment of B-cell lymphoma.

Preparation and Characterization of Gelonin-Melittin Fusion Biotoxin for Synergistically Enhanced Anti-Tumor Activity.

PURPOSE: To investigate the applicability of fusion biotoxins combining pore-forming toxins (PFTs) and ribosome-inactivating proteins (RIPs) for the anti-cancer treatment. METHODS: Membrane active PFTs tend to destabilize cell membranes of tumor cells, but lack a warhead inducing significant cause of cell death. Cell-impermeable RIPs possess a powerful warhead, yet not able to enter the tumor cells. To address these challenges for anti-tumor effects, we introduced a fusion strategy of conjugating melittin (a PFT) and gelonin (a type 1 RIP) via chemical and recombinant methods, followed by in vitro assays and in vivo animal studies. RESULTS: In vitro characterization results confirmed that the chimeric gelonin-melittin fusion proteins retained equivalent intrinsic activity to that of unmodified gelonin in inhibiting protein translation. However, chemically conjugated gelonin-melittin (cGel-Mel) and recombinant chimeric gelonin-melittin fusion (rGel-Mel) exhibited greater cell uptake, yielding a significantly enhanced cytotoxic activity over treatment of gelonin, melittin or physical mixture of gelonin and melittin. Remarkably, cGel-Mel and rGel-Mel displayed 32- and 10-fold lower IC50 than gelonin in the cell lines. The superior anti-tumor efficacy of multivalent cGel-Mel to monovalent rGel-Mel suggested that valency could be a crucial factor for the extent of melittin-mediated cell uptake. Tumoricidal effects observed from animal studies were in good accordance with our findings from the cellular assays. CONCLUSIONS: This study successfully demonstrated that fusion of biotoxins could provide a simple yet effective way to synergistically augment their anti-tumor activity.