Ribosome–Inactivating Proteins from Plants: Present Status and Future Prospects

Design, optimization, production and activity testing of recombinant immunotoxins expressed in plants and plant cells for the treatment of monocytic leukemia

Antibody-drug conjugates (ADCs) can improve therapeutic indices compared to plain monoclonal antibodies (mAbs). However, ADC synthesis is complex because the components are produced separately in CHO cells (mAb) and often by chemical synthesis (drug). They are individually purified, coupled, and then the ADC is purified, increasing production costs compared to regular mAbs. In contrast, it is easier to produce recombinant fusion proteins consisting of an antibody derivative, linker and proteinaceous toxin, i.e. a recombinant immunotoxin (RIT). Plants are capable of the post-translational modifications needed for functional antibodies and can also express active protein toxins such as the recombinant mistletoe lectin viscumin, which is not possible in prokaryotes and mammalian cells respectively. Here, we used Nicotiana benthamiana and N. tabacum plants as well as tobacco BY-2 cell-based plant cell packs (PCPs) to produce effective RITs targeting CD64 as required for the treatment of myelomonocytic leukemia. We compared RITs with different subcellular targeting signals, linkers, and proteinaceous toxins. The accumulation of selected candidates was improved to ~ 40 mg kg-1 wet biomass using a design of experiments approach, and corresponding proteins were isolated with a purity of ~ 80% using an optimized affinity chromatography method with an overall yield of ~ 84%. One anti-CD64 targeted viscumin-based drug candidate was characterized in terms of storage stability and cytotoxicity test in vitro using human myelomonocytic leukemia cell lines. We identified bottlenecks in the plant-based expression platform that require further improvement and assessed critical process parameters that should be considered during process development for plant-made RITs.

Guanidyl-Rich Poly(β Amino Ester)s for Universal Functional Cytosolic Protein Delivery and Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) Cas9 Ribonucleoprotein Based Gene Editing

Protein therapeutics are highly promising for complex disease treatment. However, the lack of ideal delivery vectors impedes their clinical use, especially the carriers for in vivo delivery of functional cytosolic protein. In this study, we modified poly(β amino ester)s (PAEs) with a phenyl guanidine (PG) group to enhance their suitability for cytosolic protein delivery. The effects of the PG group on protein binding, cell internalization, protein function protection, and endo/lysosomal escape were systematically evaluated. Compared to the unmodified PAEs (L3), guanidyl rich PAEs (L3PG) presented superior efficiency of protein binding and protein internalization, mainly via clathrin-mediated endocytosis. In addition, both PAEs showed robust capabilities to deliver cytosolic proteins with different molecular weight (ranging from 30 to 464 kDa) and isoelectric points (ranging from 4.3 to 9), which were significantly improved in comparison with the commercial reagents of PULsin and Pierce Protein Transection Reagent. Moreover, L3PG successfully delivered Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) Cas9 ribonucleoprotein (RNP) into HeLa cells expressing green fluorescent protein (GFP) and achieved more than 80% GFP expression knockout. These results demonstrated that guanidyl modification on PAEs can enhance its capabilities for intracellular delivery of cytosolic functional proteins and CRISPR/Cas9 ribonucleoprotein. The guanidyl-rich PAEs are promising nonviral vectors for functional protein delivery and potential use in protein and nuclease-based gene editing therapies.

MAP30 and luffin-α: Novel ribosome-inactivating proteins induce plant systemic resistance against plant viruses

Ribosome-inactivating proteins (RIPs) are toxic N-glycosylase that act on eukaryotic and prokaryotic rRNAs, resulting in arrest protein synthesis. RIPs are widely found in higher plant species and display strong antiviral activity. Previous studies have shown that PAP and α-MMC have antiviral activity against TMV. However, the localization of RIPs in plant cells and the mechanism by which RIPs activate plant defense against several plant viruses remain unclear. In this study, we obtained four RIPs (the C-terminal deletion mutant of pokeweed antiviral proteins (PAP-c), alpha-momorcharin (α-MMC), momordica anti-HIV protein of 30 kDa (MAP30) and luffin-α). The subcellular localization results indicated that these four RIPs were located on the plant cell membrane. Heterologous expression of RIPs (PAP-c, α-MMC, MAP30, luffin-α) enhanced tobacco mosaic virus (TMV) resistance in N. benthamiana. Compared with the control treatment, these RIPs significantly reduced the TMV content (149-357 fold) and altered the movement of TMV in the leaves of N. benthamiana. At the same time, heterologous expression of RIPs (MAP30 and luffin-α) could relieve TMV-induced oxidative damage, significantly inducing the expression of plant defense genes including PR1 and PR2. Furthermore, application of these RIPs could inhibit the infection of turnip mosaic virus (TuMV) and potato virus x (PVX). Therefore, this study demonstrated that MAP30 and luffin-α could be considered as new, effective RIPs for controlling plant viruses by activating plant systemic defense.

Articulatin B chain induced dendritic cells maturation and driven type I T helper cells and cytotoxic T cells activation

AIMS

Articulatin (AT), purified from the Chinese mistletoe (Viscum articulatum), belongs to the family of type II ribosome-inactivating proteins (RIPs) that contain two subunits, the A and B chains. The B chain of AT is believed to function by means of interacting with the galactose moiety of glycoproteins or glycolipids on the cell membrane and is internalized into cells through endocytosis. In the study, we aim to investigate the immunomodulatory effects of recombinant articulatin B chain (rATB) on mouse bone marrow-derived dendritic cells (BM-DCs).

MAIN METHODS

Detection of surface markers expression on BM-DCs by flow cytometry. Analysis of RNA and protein expression by RNAseq and Western blotting assays. Assessment of the adaptive immune responses using an in vivo mouse model.

KEY FINDING

Our study presents novel results showing the activation of mouse BM-DCs by rATB, which leads to the induction of CD80, CD86, and MHC II expression as well as primed type I CD4+ T cell differentiation and CD8+ T cell activation. RNAseq and Western blotting assays revealed rATB-induced BM-DC activation to be dependent on the MAPK and NF-κB signaling pathways. In a mouse model, rATB was observed to have adjuvant effects that induced an antigen-specific Th1 immune response.

SIGNIFICANCE

Based on in vitro and in vivo assays, this study shows rATB acting as a potential adjuvant that induces BM-DC activation and antigen-specific Th1 related immune response. rATB might have potential applicability in the development of vaccines against pathogens and tumors.

Saporin as a Commercial Reagent: Its Uses and Unexpected Impacts in the Biological Sciences—Tools from the Plant Kingdom

Saporin is a ribosome-inactivating protein that can cause inhibition of protein synthesis and causes cell death when delivered inside a cell. Development of commercial Saporin results in a technology termed ‘molecular surgery’, with Saporin as the scalpel. Its low toxicity (it has no efficient method of cell entry) and sturdy structure make Saporin a safe and simple molecule for many purposes. The most popular applications use experimental molecules that deliver Saporin via an add-on targeting molecule. These add-ons come in several forms: peptides, protein ligands, antibodies, even DNA fragments that mimic cell-binding ligands. Cells that do not express the targeted cell surface marker will not be affected. This review will highlight some newer efforts and discuss significant and unexpected impacts on science that molecular surgery has yielded over the last almost four decades. There are remarkable changes in fields such as the Neurosciences with models for Alzheimer’s Disease and epilepsy, and game-changing effects in the study of pain and itch. Many other uses are also discussed to record the wide-reaching impact of Saporin in research and drug development.

Neutralizing Monoclonal Antibody, mAb 10D8, Is an Effective Detoxicant against Abrin-a Both In Vitro and In Vivo

Abrin is a types II ribosome-inactivating protein (RIP) isolated from Abrus precatorious seeds, which comprises a catalytically active A chain and a lectin-like B chain linked by a disulfide bond. Four isotoxins of abrin have been reported with similar amino-acid composition but different cytotoxicity, of which abrin-a is the most potent toxin. High lethality and easy availability make abrin a potential bioterrorism agent. However, there are no antidotes available for managing abrin poisoning, and treatment is only symptomatic. Currently, neutralizing antibodies remain the most effective therapy against biotoxin poisoning. In this study, we prepared, identified, and acquired a high-affinity neutralizing monoclonal antibody (mAb) 10D8 with a potent pre- and post-exposure protective effect against cytotoxicity and animal toxicity induced by abrin-a or abrin crude extract. The mAb 10D8 could rescue the mouse injected intraperitoneally with a 25 × LD₅₀ dose of abrin-a from lethality and prevent tissue damages. Results indicated that 10D8 does not prevent the binding and internalization of abrin-a to cells but inhibits the enzymatic activity of abrin-a and reduces protein synthesis inhibition of cells. The high affinity, good specificity, and potent antitoxic efficiency of 10D8 make it a promising candidate for therapeutic antibodies against abrin.

A Novel Humanized Anti-Abrin A Chain Antibody Inhibits Abrin Toxicity In Vitro and In Vivo

Abrin, a type-II ribosome inactivating protein from the seed of Abrus precatorius, is classified as a Category B bioterrorism warfare agent. Due to its high toxicity, ingestion by animals or humans will lead to death from multiple organ failure. Currently, no effective agents have been reported to treat abrin poisoning. In this study, a novel anti-abrin neutralizing antibody (S008) was humanized using computer-aided design, which possessed lower immunogenicity. Similar to the parent antibody, a mouse anti-abrin monoclonal antibody, S008 possessed high affinity and showed a protective effect against abrin both in vitro and in vivo, and protected mice that S008 was administered 6 hours after abrin. S008 was found that it did not inhibit entry of abrin into cells, suggesting an intracellular blockade capacity against the toxin. In conclusion, this work demonstrates that S008 is a high affinity anti-abrin antibody with both a neutralizing and protective effect and may be an excellent candidate for clinical treatment of abrin poisoning.

Oxytocin-conjugated saporin injected into the substantia nigra of male rats alters the activity of the nigrostriatal dopaminergic system: A behavioral and neurochemical study

Saporin conjugated to oxytocin (OXY-SAP) destroys neurons expressing oxytocinergic receptors. When injected unilaterally in the substantia nigra of male rats, OXY-SAP causes a dose-dependent decrease up to 55 % in nigral Tyrosine Hydroxylase (TH)-immunoreactivity compared to control mock peptide BLANK-SAP- and PBS-treated rats or the contralateral substantia nigra. TH decrease was parallel to a dopamine content decrease in the ipsilateral striatum compared to BLANK-SAP- or PBS-treated rats or the contralateral striatum. OXY-SAP-treated rats showed a small but significant increase of locomotor activity 28 days after intranigral injection in the Open field test compared to BLANK-SAP- or PBS-treated rats, in line with an inhibitory role of nigral oxytocin on locomotor activity. OXY-SAP-, but not BLANK-SAP- or PBS-treated rats, also showed marked dose-dependent rotational turning ipsilateral to the injected substantia nigra when challenged with d-amphetamine, but not with apomorphine. Under isoflurane anesthesia OXY-SAP-treated rats showed levels of extracellular dopamine in the dialysate from the ipsilateral striatum only half those of BLANK-SAP- or PBS-treated rats or the contralateral striatum. When treated with d-amphetamine, OXY-SAP_60/120 rats showed increased extracellular dopamine levels in the dialysate from the ipsilateral striatum two third/one third only of those found in BLANK-SAP- or PBS-treated rats or the contralateral striatum, respectively. These results show that OXY-SAP destroys nigrostriatal dopaminergic neurons expressing oxytocin receptors leading to a reduced striatal dopamine function.

Therapeutic Potential of Medicinal Plant Proteins: Present Status and Future Perspectives

Biologically active molecules obtained from plant sources, mostly including secondary metabolites, have been considered to be of immense value with respect to the treatment of various human diseases. However, some inevitable limitations associated with these secondary metabolites like high cytotoxicity, low bioavailability, poor absorption, low abundance, improper metabolism, etc., have forced the scientific community to explore medicinal plants for alternate biologically active molecules. In this context, therapeutically active proteins/peptides from medicinal plants have been promoted as a promising therapeutic intervention for various human diseases. A large number of proteins isolated from the medicinal plants have been shown to exhibit anti-microbial, anti-oxidant, anti-HIV, anticancerous, ribosome-inactivating and neuro-modulatory activities. Moreover, with advanced technological developments in the medicinal plant research, medicinal plant proteins such as Bowman-Birk protease inhibitor and Mistletoe Lectin-I are presently under clinical trials against prostate cancer, oral carcinomas and malignant melanoma. Despite these developments and proteins being potential drug candidates, to date, not a single systematic review article has documented the therapeutical potential of the available biologically active medicinal plant proteome. The present article was therefore designed to describe the current status of the therapeutically active medicinal plant proteins/peptides vis-à-vis their potential as future protein-based drugs for various human diseases. Future insights in this direction have also been highlighted.

Exercise is neuroprotective on the morphology of somatic motoneurons following the death of neighboring motoneurons via androgen action at the target muscle

Motoneuron loss is a severe medical problem that can result in loss of motor control and eventually death. We have previously demonstrated that partial motoneuron loss can result in dendritic atrophy and functional deficits in nearby surviving motoneurons, and that an androgen-dependent effect of exercise following injury can be neuroprotective against this dendritic atrophy. In this study, we explored where the necessary site of androgen action is for exercise-driven neuroprotective effects on induced dendritic atrophy. Motoneurons innervating the vastus medialis muscles of adult male rats were selectively killed by intramuscular injection of cholera toxin-conjugated saporin. Simultaneously, some saporin-injected animals were given implants of the androgen receptor antagonist hydroxyflutamide, either directly at the adjacent vastus lateralis musculature ipsilateral to the saporin-injected vastus medialis or interscapularly as a systemic control. Following saporin injections, some animals were allowed free access to a running wheel attached to their home cages. Four weeks later, motoneurons innervating the same vastus lateralis muscle were labeled with cholera toxin-conjugated horseradish peroxidase, and dendritic arbors were reconstructed in three dimensions. Dendritic arbor lengths of saporin-injected animals allowed to exercise were significantly longer than those not allowed to exercise. Androgen receptor blockade locally at the vastus lateralis muscle prevented the protective effect of exercise. These findings indicate that exercise following neural injury exerts a protective effect on motoneuron dendrites, which acts via androgen receptor action at the target muscle.

ALPPL2 Is a Highly Specific and Targetable Tumor Cell Surface Antigen

Identification of tumor-specific cell surface antigens has proven challenging, as the vast majority of tumor-associated antigens are also expressed in normal tissues. In mesothelioma, we identified a highly specific tumor cell surface antigen that can be targeted for therapy development. Mesothelioma is caused by malignant transformation of the mesothelium, is incurable, and can be categorized into three histologic subtypes: epithelioid, biphasic, and sarcomatoid. To identity novel mesothelioma cell surface antigens with broad subtype coverage and high tissue specificity, we have previously selected phage antibody display libraries on live mesothelioma cells and tissues following counterselection on normal cells and identified a panel of human antibodies that bind all subtypes of mesothelioma, but not normal mesothelium. One of the antibodies, M25, showed high specificity against an antigen we identify here as ALPPL2. IHC on normal human tissues found that ALPPL2 is expressed only on placental trophoblasts, but not on any other normal tissues. This significant tissue specificity and broad tumor type coverage suggest that ALPPL2 could be an excellent cell surface target for therapeutic development against mesothelioma. To evaluate therapeutic potential of ALPPL2 targeting, an ALPPL2-targeted antibody-drug conjugate was developed and demonstrated potent and specific tumor killing in vitro and in vivo against both epithelioid and sarcomatoid mesothelioma. Thus, ALPPL2 belongs to a rare class of cell surface antigens classified as truly tumor specific and is well suited for therapy development against ALPPL2-expressing tumors. SIGNIFICANCE: These findings identify ALPP2 as a true tumor-specific cell surface antigen whose tissue specificity enables the development of novel therapies.

Saporin from Saponaria officinalis as a Tool for Experimental Research, Modeling, and Therapy in Neuroscience

Saporin, which is extracted from Saponaria officinalis, is a protein toxin that inactivates ribosomes. Saporin itself is non-selective toxin but acquires high specificity after conjugation with different ligands such as signaling peptides or antibodies to some surface proteins expressed in a chosen cell subpopulation. The saporin-based conjugated toxins were widely adopted in neuroscience as a convenient tool to induce highly selective degeneration of desired cell subpopulation. Induction of selective cell death is one of approaches used to model neurodegenerative diseases, study functions of certain cell subpopulations in the brain, and therapy. Here, we review studies where saporin-based conjugates were used to analyze cell mechanisms of sleep, general anesthesia, epilepsy, pain, and development of Parkinson’s and Alzheimer’s diseases. Limitations and future perspectives of use of saporin-based toxins in neuroscience are discussed.

Dissecting the Role of Subtypes of Gastrointestinal Vagal Afferents

Gastrointestinal (GI) vagal afferents convey sensory signals from the GI tract to the brain. Numerous subtypes of GI vagal afferent have been identified but their individual roles in gut function and feeding regulation are unclear. In the past decade, technical approaches to selectively target vagal afferent subtypes and to assess their function has significantly progressed. This review examines the classification of GI vagal afferent subtypes and discusses the current available techniques to study vagal afferents. Investigating the distribution of GI vagal afferent subtypes and understanding how to access and modulate individual populations are essential to dissect their fundamental roles in the gut-brain axis.

Molecular cloning and in-depth bioinformatics analysis of type II ribosome-inactivating protein isolated from Sambucus ebulus

Plant ribosome-inactivating proteins (RIPs) are N-glycosidases which inhibit protein synthesis through depurination of the ribosomal RNA sequence. Type II RIPs are heterodimer proteins which can bind to cell surfaces. The cytotoxicity of these RIPs is different. Sambucus spp. are a rich source of RIP proteins with different properties. In the present study, a type II RIP was isolated from S. ebulus plant that grows widely in the north of Iran, and different bioinformatics tools were used for the evaluation of physicochemical, functional and 3D protein characteristics. The results showed significant differences among isolated RIP and other Sambucus RIP proteins. The study of these differences can not only expand our insight into the functioning mechanisms of plant RIPs but also provide information about a novel RIP protein with potential biological applications.

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.

Neuroprotective Effects of Exercise on the Morphology of Somatic Motoneurons Following the Death of Neighboring Motoneurons

Background. Motoneuron loss is a severe medical problem that can result in loss of motor control and eventually death. We have previously demonstrated that partial motoneuron loss can result in dendritic atrophy and functional deficits in nearby surviving motoneurons, and that treatment with androgens can be neuroprotective against this dendritic atrophy. Exercise has also been shown to be protective following a variety of neural injury models and, in some cases, is dependent on androgen action. Objective. In this study, we explored whether exercise shows the same neuroprotective effect on induced dendritic atrophy as that seen with androgen treatment. Methods. Motoneurons innervating the vastus medialis muscles of adult male rats were selectively killed by intramuscular injection of cholera toxin-conjugated saporin. Following saporin injections, some animals were allowed free access to a running wheel attached to their home cages. Four weeks later, motoneurons innervating the ipsilateral vastus lateralis muscle were labeled with cholera toxin-conjugated horseradish peroxidase, and dendritic arbors were reconstructed in 3 dimensions. Results. Dendritic arbor lengths of animals allowed to exercise were significantly longer than those not allowed to exercise. Conclusions. These findings indicate that exercise following neural injury exerts a protective effect on motoneuron dendrites comparable to that seen with exogenous androgen treatment.

Antiproliferative potential from aqueous Viscum album L. preparations and their main constituents in comparison with ricin and purothionin on human cancer cells

ETHNOPHARMACOLOGICAL RELEVANCE

Mistletoe has been used since ancient times in Europe mostly for medicinal purposes. Since 1917, mistletoe preparations have been applied in cancer therapy and today are the most frequently used complementary medicine in tumor treatment. The main cytotoxic constituents of Viscum album are lectins and viscotoxins.

AIM OF THE STUDY

The aim of this in vitro study was to investigate the antiproliferative potential of Viscum album preparations from different host trees and to assess the impact of mistletoe lectin 1 (ML-1) and viscotoxin A (VT-A) in comparison to a structurally similar lectin and thionin.

MATERIALS AND METHODS

By means of widely accepted 2D Alamar Blue Assay, based on population counting of living cells using a fluorescent cell viability dye, the potential impact to inhibit tumor cell of the mistletoe preparations (Iscucin^®) and their single compounds (ML-1 and VT-A) on the cell growth of six human cancer cell lines were evaluated. Also the mixture of ML-1 and VT-A corresponding to the contents in the specific mistletoe preparations were monitored. Ricin and purothionin were used as reference lectin and reference thionin, respectively.

RESULTS

The lung carcinoma cell line HCC827 was very sensitive to the Iscucin^® preparations. Very strong antiproliferative effects were found with Iscucin^®Salicis and Tiliae and a strong with Iscucin^®Crataegi, Mali and Populi. The IC₅₀ concentrations of the Iscucin^® preparations correlated with their respective ML-1 contents, but the ML-1 levels were much lower than the IC₅₀ concentration of isolated ML-1 (1 ng/ml - 56 ng/ml). ML-1 was much more effective than ricin. Iscucin^® preparations, ML-1 and ricin showed antiproliferative activity on human tumor cells. VT-A and purothionin had no effect on cell viability in the concentration ranges tested.

CONCLUSION

The complete mistletoe extract is more potent to inhibit tumor cell proliferation than isolated ML-1 at an equivalent concentration level. Phenolic compounds found in all Iscucin^® preparations might contribute to uphold the cytotoxic activity of ML-1 by antioxidative action. However, further studies are necessary to evaluate the role of VT-A and possible synergistic actions to the antiproliferative effect of aqueous mistletoe extracts.

Whole-Cell Multiparameter Assay for Ricin and Abrin Activity-Based Digital Holographic Microscopy

Ricin and abrin are ribosome-inactivating proteins leading to inhibition of protein synthesis and cell death. These toxins are considered some of the most potent and lethal toxins against which there is no available antidote. Digital holographic microscopy (DHM) is a time-lapse, label-free, and noninvasive imaging technique that can provide phase information on morphological features of cells. In this study, we employed DHM to evaluate the morphological changes of cell lines during ricin and abrin intoxication. We showed that the effect of these toxins is characterized by a decrease in cell confluence and changes in morphological parameters such as cell area, perimeter, irregularity, and roughness. In addition, changes in optical parameters such as phase-shift, optical thickness, and effective-calculated volume were observed. These effects were completely inhibited by specific neutralizing antibodies. An enhanced intoxication effect was observed for preadherent compared to adherent cells, as was detected in early morphology changes and confirmed by annexin V/propidium iodide (PI) apoptosis assay. Detection of the dynamic changes in cell morphology at initial stages of cell intoxication by DHM emphasizes the highly sensitive and rapid nature of this method, allowing the early detection of active toxins.

Neuroprotective Effects on the Morphology of Somatic Motoneurons Following the Death of Neighboring Motoneurons: A Role for Microglia?

Partial depletion of spinal motoneuron populations induces dendritic atrophy in neighboring motoneurons, and treatment with testosterone protects motoneurons from induced dendritic atrophy. We explored a potential mechanism for this induced atrophy and protection by testosterone, examining the microglial response to partial depletion of motoneurons. Motoneurons innervating the vastus medialis muscles of adult male rats were killed by intramuscular injection of cholera toxin-conjugated saporin; some saporin-injected rats were treated with testosterone. Microglia were later visualized via immunohistochemical staining, classified as monitoring or activated, and counted stereologically. Partial motoneuron depletion increased the number of activated microglia in the quadriceps motor pool, and this increase was attenuated with testosterone treatment. The attenuation in microglial response could reflect an effect of testosterone on suppressing microglia activation, potentially sparing motoneuron dendrites. Alternatively, testosterone could be neuroprotective, sparing motoneuron dendrites, secondarily resulting in reduced microglial activation. To discriminate between these hypotheses, following partial motoneuron depletion, rats were treated with minocycline to inhibit microglial activation. Motoneurons innervating the ipsilateral vastus lateralis muscle were later labeled with cholera toxin-conjugated horseradish peroxidase, and dendritic arbors were reconstructed. Reduction of microglial activation by minocycline did not prevent induced dendritic atrophy following partial motoneuron depletion. Further, reduction of microglial activation by minocycline treatment resulted in dendritic atrophy in intact animals. Together, these findings indicate that the neuroprotective effect of testosterone on dendrites following motoneuron death is not due to inhibiting microglial activation, and that microglial activity contributes to the normal maintenance of dendritic arbors.

Correlation of abrin-mediated inhibition of protein synthesis and apoptosis

The plant toxin, abrin, a type-II ribosome inactivating protein, is extremely lethal, the human fatal dose being ~1 μg/kg body weight. Abrin has been classified as an agent for bioterrorism, which is of concern. Conversely, the high toxic property of abrin has been employed in generating immunotoxins, whereas its toxin moiety is conjugated to cell surface marker-specific antibodies for cell-targeted killing. Different cell types exhibit variable levels of sensitivity to abrin toxicity; therefore, adequate knowledge of the molecular mechanism that governs the activity of the protein would be a safeguard. To gain insights into this, two cell lines requiring strikingly different concentrations of abrin for inactivating ribosomes were studied. Employing conjugates of the wild-type and active site mutant of abrin A chain with the ricin B chain, it was found that abrin-induced apoptosis was dependent on inhibition of protein synthesis (PSI) leading to ER-stress in Ovcar-3 cells, but not in KB cells. Abrin was also observed to cause direct DNA damage in KB cells, while in Ovcar-3 cells abrin-induced DNA damage was found to be dependent on caspases. Overall, the study demonstrates that the correlation of abrin-mediated PSI and apoptosis is cell-specific and abrin can induce more than one pathway to cause cell death. © 2018 IUBMB Life, 71(3):357-363, 2019.

Targeting CD46 for both adenocarcinoma and neuroendocrine prostate cancer

Although initially responsive to androgen signaling inhibitors (ASIs), metastatic castration-resistant prostate cancer (mCRPC) inevitably develops and is incurable. In addition to adenocarcinoma (adeno), neuroendocrine prostate cancer (NEPC) emerges to confer ASI resistance. We have previously combined laser capture microdissection and phage antibody display library selection on human cancer specimens and identified novel internalizing antibodies binding to tumor cells residing in their tissue microenvironment. We identified the target antigen for one of these antibodies as CD46, a multifunctional protein that is best known for negatively regulating the innate immune system. CD46 is overexpressed in primary tumor tissue and CRPC (localized and metastatic; adeno and NEPC), but expressed at low levels on normal tissues except for placental trophoblasts and prostate epithelium. Abiraterone- and enzalutamide-treated mCRPC cells upregulate cell surface CD46 expression. Genomic analysis showed that the CD46 gene is gained in 45% abiraterone-resistant mCRPC patients. We conjugated a tubulin inhibitor to our macropinocytosing anti-CD46 antibody and showed that the resulting antibody-drug conjugate (ADC) potently and selectively kills both adeno and NEPC cell lines in vitro (sub-nM EC50) but not normal cells. CD46 ADC regressed and eliminated an mCRPC cell line xenograft in vivo in both subcutaneous and intrafemoral models. Exploratory toxicology studies of the CD46 ADC in non-human primates demonstrated an acceptable safety profile. Thus, CD46 is an excellent target for antibody-based therapy development, which has potential to be applicable to both adenocarcinoma and neuroendocrine types of mCRPC that are resistant to current treatment.

Prophylactic efficacy of some chemoprotectants against abrin induced lethality

Abrin is a highly toxic protein produced by Abrus precatorius. Exposure to abrin, either through accident or by act of terrorism, poses a significant risk to human health and safety. Abrin functions as a ribosome-inactivating protein by depurinating the 28S rRNA and inhibits protein synthesis. It is a potent toxin warfare agent. There are no antidotes available for abrin intoxication. Supportive care is the only option for treatment of abrin exposure. It is becoming increasingly important to develop countermeasures for abrin by developing pre- and post-exposure therapy. The aim of this study is to screen certain pharmaceutical compounds for their chemoprotective properties against abrin toxicity in vivo in BALB/c male mice. Twenty-one compounds having either antioxidant, anti-inflammatory and cyto-protective properties or combination of them, were screened and administered as 1h pre-treatment followed by exposure of lethal dose (2×LD₅₀, intraperitoneally) of abrin. To assess the protective efficacy of the compounds, survival and body weight was monitored. Fifteen compounds extended the survival time of animals significantly, as compared to abrin. The following five of these compounds, namely: Epicatechin-3-gallate, Gallic Acid, Lipoic Acid, GSH and Indomethacin extended the life time ranging from 6 to 9 days. These compounds also attenuated the abrin induced inflammation and enzymes associated with liver function, but none of them could prevent abrin induced lethality. The compounds offering extension of life could be useful to provide a time-window for other supportive treatment and could also be used as combinatorial therapy with other medical countermeasures against abrin induced lethality.

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 β-cyclodextrin-modified cb-apt (cb-apt-βCD) 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-βCD 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 βCD to cb-apt, and subsequently modulating the supramolecular chemistry of cb-apt-βCD, provides a general platform to expand and diversify the function of aptamers, enabling new biological and therapeutic applications.

Targeting prostate cancer: Prostate-specific membrane antigen based diagnosis and therapy

The high incidence rates of prostate cancer (PCa) raise demand for improved therapeutic strategies. Prostate tumors specifically express the prostate-specific membrane antigen (PSMA), a membrane-bound protease. As PSMA is highly overexpressed on malignant prostate tumor cells and as its expression rate correlates with the aggressiveness of the disease, this tumor-associated biomarker provides the possibility to develop new strategies for diagnostics and therapy of PCa. Major advances have been made in PSMA targeting, ranging from immunotherapeutic approaches to therapeutic small molecules. This review elaborates the diversity of PSMA targeting agents while focusing on the radioactively labeled tracers for diagnosis and endoradiotherapy. A variety of radionuclides have been shown to either enable precise diagnosis or efficiently treat the tumor with minimal effects to nontargeted organs. Most small molecules with affinity for PSMA are based on either a phosphonate or a urea-based binding motif. Based on these pharmacophores, major effort has been made to identify modifications to achieve ideal pharmacokinetics while retaining the specific targeting of the PSMA binding pocket. Several tracers have now shown excellent clinical usability in particular for molecular imaging and therapy as proven by the efficiency of theranostic approaches in current studies. The archetypal expression profile of PSMA may be exploited for the treatment with alpha emitters to break radioresistance and thus to bring the power of systemic therapy to higher levels.

A Monoclonal-Monoclonal Antibody Based Capture ELISA for Abrin

Abrin, one of the most highly potent toxins in the world, is derived from the plant, Abrus precatorius. Because of its high toxicity, it poses potential bioterror risks. Therefore, a need exists for new reagents and technologies that would be able to rapidly detect abrin contamination as well as lead to new therapeutics. We report here a group of abrin-specific monoclonal antibodies (mAbs) that recognize abrin A-chain, intact A–B chain toxin, and agglutinin by Western blot. Additionally, these mAbs were evaluated for their ability to serve as capture antibodies for a sandwich (capture) ELISA. All possible capture–detector pairs were evaluated and the best antibody pair identified and optimized for a capture ELISA. The capture ELISA based on this capture–detector mAb pair had a limit of detection (L.O.D) of ≈1 ng/mL measured using three independent experiments. The assay did not reveal any false positives with extracts containing other potential ribosome-inactivating proteins (RIPs). Thus, this new capture ELISA uses mAbs for both capture and detection; has no cross-reactivity against other plant RIPs; and has a sensitivity comparable to other reported capture ELISAs using polyclonal antibodies as either capture or detector.

Abrin Toxicity and Bioavailability after Temperature and pH Treatment

Abrin, one of most potent toxins known to man, is derived from the rosary pea (jequirity pea), Abrus precatorius and is a potential bioterror weapon. The temperature and pH stability of abrin was evaluated with an in vitro cell free translation (CFT) assay, a Vero cell culture cytotoxicity assay, and an in vivo mouse bioassay. pH treatment of abrin had no detrimental effect on its stability and toxicity as seen either in vitro or in vivo. Abrin exposure to increasing temperatures did not completely abrogate protein translation. In both the cell culture cytotoxicity model and the mouse bioassay, abrin’s toxic effects were completely abrogated if the toxin was exposed to temperatures of 74 °C or higher. In the cell culture model, 63 °C-treated abrin had a 30% reduction in cytotoxicity which was validated in the in vivo mouse bioassay with all mice dying but with a slight time-to-death delay as compared to the non-treated abrin control. Since temperature inactivation did not affect abrin’s ability to inhibit protein synthesis (A-chain), we hypothesize that high temperature treatment affected abrin’s ability to bind to cellular receptors (affecting B-chain). Our results confirm the absolute need to validate in vitro cytotoxicity assays with in vivo mouse bioassays.

Viscum album neutralizes tumor-induced immunosuppression in a human in vitro cell model

Tumor cells have the capacity to secrete immunosuppressive substances in order to diminish dendritic cell (DC) activity and thereby escape from immune responses. The impact of mistletoe (Viscum album) extracts (VAE), which are frequently used as an additive anti-cancer therapy to stimulate the immune response, is still unknown. Using a human cellular system, the impact of two different VAE (VAEA + VAEI) on the maturation of human dendritic cells and on T cell function has been investigated using flow cytometry, automated fluorescence microscopy and cytokine bead array assays. Furthermore, we examined whether VAEI was able to counteract tumor-induced immunosuppression within this cellular system using a renal cancer cell model. The role of mistletoe lectin (ML) was analyzed using ML-specific antibodies and ML-depleted VAEI. VAEI and VAEA augmented the maturation of dendritic cells. VAEI abrogated tumor-induced immunosuppression of dendritic cells and both processes were partially mediated by ML since ML-depleted VAEI and ML-specific antibodies almost neutralized the rehabilitative effects of VAEI on DC maturation. Using these settings, co-culture experiments with purified CD4⁺ T cells had no influence on T cell proliferation and activation but did have an impact on IFN-γ secretion. The study provides a potential mode-of-action of VAE as an additive cancer therapy based on immunomodulatory effects. However, the impact on the in vivo situation has to be evaluated in further studies.

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.

Effect of Momordica charantia protein on proliferation, apoptosis and the AKT signal transduction pathway in the human endometrial carcinoma Ishikawa H cell line in vitro

Endometrial carcinoma (EC) is one of the most common female malignancies, and there is an urgent requirement to explore new therapeutic strategies. In the present study, Ishikawa H cells were treated with Momordica charantia protein (MCP30). The cell morphology, growth inhibition rate, cell cycle distribution, and expression of phosphate and tensin homolog, P-AKT and AKT were measured. DNA fragmentation analysis and Annexin V-fluorescein isothiocyanate/propidium iodide double staining assay were used to analyze cell apoptosis. MCP30 decreased the viability of Ishikawa H cells in a dose- and time-dependent manner. The early apoptotic rates of Ishikawa H cells treated with MCP30 at 666.67 pM reached to 16.07±0.15%, following 72 h of treatment. DNA ladder was observed in cells treated with 333.33 and 666.67 pM MCP30 following 72 h of treatment. MCP30 blocks Ishikawa H cells from progressing between the S-phase and the G2/M-phase in a time- and concentration-dependent manner. Western blotting revealed that MCP30 treatment decreased the levels of P-AKT in a dose-dependent manner. It was revealed that MCP30 decreases cell proliferation, and induces apoptosis and S-phase cell cycle arrest through the AKT signaling pathway in Ishikawa H cells.

A chimeric protein of abrin and Abrus precatorius agglutinin that neutralizes abrin mediated lethality in mice

Abrin, a type II ribosome inactivating protein from the Abrus precatorius plant, is extremely toxic. It has been shown to be 75 times more potent than its infamous sister toxin, ricin and their potential use in bio-warfare is a cause of major concern. Although several vaccine candidates are under clinical trials for ricin, none are available against abrin. The present study proposes a chimeric protein, comprising of 1-123 amino acids taken from the A chain of abrin and 124-175 amino acids from Abrus precatorius agglutinin A chain, as a vaccine candidate against abrin intoxication. The design was based on the inclusion of the immunogenic region of the full length protein and the minimal essential folding domains required for inducing neutralizing antibody response. The chimera also contains the epitope for the only two neutralizing antibodies; D6F10 and A7C4, reported against abrin till now. Active immunization with the chimera protected all the mice challenged with 45 X LD₅₀ of abrin. Also, passive transfer of antibodies raised against the chimera rescued all mice challenged with 50 X LD₅₀ of toxin. Hence the chimeric protein appears to be a promising vaccine candidate against abrin induced lethality.

Mono-PEGylation of Alpha-MMC and MAP30 from Momordica charantia L.: Production, Identification and Anti-Tumor Activity

PEGylation is a well-established and effective strategy to decrease immunogenicity, which can increase the stability and in vivo half-life time. However, the generation of multi-site modified products is inevitable due to the lysine chemistry, which will bring difficulties in subsequent research, such as purification and quantification. Site-specific modification by mPEG-succinimidyl carbonate (mPEG-SC) is a widely used method for N-terminal conjugation. In this study, we used it for site-directed modification on two ribosome-inactivating proteins (RIPs), alpha-momorcharin (α-MMC) and momordica anti-HIV protein (MAP30), from Momordica charantia L. According to the optimization of previous modification conditions, we compared Macro-Cap SP with SP-Sepharose FF chromatography for separating the final mPEGylated RIPs. Two kinds of methods both can obtain homogenous mPEGylated RIPs which were identified by sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE), isoelectric focusing electrophoresis (IEF), and matrix-assisted laser desorption ionization-time of flight/time of flight (MALDI-TOF/TOF) analysis. We also used iodine staining method to detect the amount of unmodified PEG. Furthermore, the inhibition activity of both mPEGylated and non-PEGylated RIPs against human lung adenocarcinoma epithelial A549 cells was detected. All of the results suggested that the mPEGylated α-MMC/MAP30 might be potentially developed as new anti-tumor drugs.

Neuroprotective effects of testosterone metabolites and dependency on receptor action on the morphology of somatic motoneurons following the death of neighboring motoneurons

Partial depletion of spinal motoneuron populations induces dendritic atrophy in neighboring motoneurons, and treatment with testosterone is neuroprotective, attenuating induced dendritic atrophy. In this study we examined whether the protective effects of testosterone could be mediated via its androgenic or estrogenic metabolites. Furthermore, to assess whether these neuroprotective effects were mediated through steroid hormone receptors, we used receptor antagonists to attempt to prevent the neuroprotective effects of hormones after partial motoneuron depletion. Motoneurons innervating the vastus medialis muscles of adult male rats were selectively killed by intramuscular injection of cholera toxin-conjugated saporin. Simultaneously, some saporin-injected rats were treated with either dihydrotestosterone or estradiol, alone or in combination with their respective receptor antagonists, or left untreated. Four weeks later, motoneurons innervating the ipsilateral vastus lateralis muscle were labeled with cholera toxin-conjugated horseradish peroxidase, and dendritic arbors were reconstructed in three dimensions. Compared with intact normal animals, partial motoneuron depletion resulted in decreased dendritic length in remaining quadriceps motoneurons. Dendritic atrophy was attenuated with both dihydrotestosterone and estradiol treatment to a degree similar to that seen with testosterone, and attenuation of atrophy was prevented by receptor blockade. Together, these findings suggest that neuroprotective effects on motoneurons can be mediated by either androgenic or estrogenic hormones and require action via steroid hormone receptors, further supporting a role for hormones as neurotherapeutic agents in the injured nervous system. © 2016 Wiley Periodicals, Inc. Develop Neurobiol 77: 691-707, 2017.

Functional Analysis of a Type-I Ribosome Inactivating Protein Balsamin from Momordica balsamina with Anti-Microbial and DNase Activity

Ribosome inactivating proteins (RIPs) have received considerable attention in biomedical research because of their unique activities towards tumor and virus-infected cells. We extracted balsamin, a type-I RIP, from Momordica balsamina. In the present study, a detailed investigation on DNase activity, antioxidant capacity and antibacterial activity was conducted using purified balsamin. DNase-like activity of balsamin towards plasmid DNA was pH, incubation time and temperature dependent. Moreover, the presence of Mg(2+) (10-50 mM) influenced the DNA cleavage activity. Balsamin also demonstrated reducing power and a capacity to scavenge free radicals in a dose dependent manner. Furthermore, the protein exhibited antibacterial activity against Staphylococcus aureus, Salmonella enterica, Staphylococcus epidermidis and Escherichia coli, which suggests potential utility of balsamin as a nutraceutical.

Differential Effects of Viscum album Preparations on the Maturation and Activation of Human Dendritic Cells and CD4⁺ T Cell Responses

Extracts of Viscum album (VA); a semi-parasitic plant, are frequently used in the complementary therapy of cancer and other immunological disorders. Various reports show that VA modulates immune system and exerts immune-adjuvant activities that might influence tumor regression. Currently, several therapeutic preparations of VA are available and hence an insight into the mechanisms of action of different VA preparations is necessary. In the present study, we performed a comparative study of five different preparations of VA on maturation and activation of human dendritic cells (DCs) and ensuing CD4⁺ T cell responses. Monocyte-derived human DCs were treated with VA Qu Spez, VA Qu Frf, VA M Spez, VA P and VA A. Among the five VA preparations tested VA Qu Spez, a fermented extract with a high level of lectins, significantly induced DC maturation markers CD83, CD40, HLA-DR and CD86, and secretion of pro-inflammatory cytokines such as IL-6, IL-8, IL-12 and TNF-α. Furthermore, analysis of T cell cytokines in DC-T cell co-culture revealed that VA Qu Spez significantly stimulated IFN-γ secretion without modulating regulatory T cells and other CD4⁺ T cytokines IL-4, IL-13 and IL-17A. Our study thus delineates differential effects of VA preparations on DC maturation; function and T cell responses.

Near-Infrared Light Activation of Proteins Inside Living Cells Enabled by Carbon Nanotube-Mediated Intracellular Delivery

Light-responsive proteins have been delivered into the cells for controlling intracellular events with high spatial and temporal resolution. However, the choice of wavelength is limited to the UV and visible range; activation of proteins inside the cells using near-infrared (NIR) light, which has better tissue penetration and biocompatibility, remains elusive. Here, we report the development of a single-walled carbon nanotube (SWCNT)-based bifunctional system that enables protein intracellular delivery, followed by NIR activation of the delivered proteins inside the cells. Proteins of interest are conjugated onto SWCNTs via a streptavidin-desthiobiotin (SA-DTB) linkage, where the protein activity is blocked. SWCNTs serve as both a nanocarrier for carrying proteins into the cells and subsequently a NIR sensitizer to photothermally cleave the linkage and release the proteins. The released proteins become active and exert their functions inside the cells. We demonstrated this strategy by intracellular delivery and NIR-triggered nuclear translocation of enhanced green fluorescent protein, and by intracellular delivery and NIR-activation of a therapeutic protein, saporin, in living cells. Furthermore, we showed that proteins conjugated onto SWCNTs via the SA-DTB linkage could be delivered to the tumors, and optically released and activated by using NIR light in living mice.

Sprouting Buds of Zebrafish Research in Malaysia: First Malaysia Zebrafish Disease Model Workshop

Zebrafish is gaining prominence as an important vertebrate model for investigating various human diseases. Zebrafish provides unique advantages such as optical clarity of embryos, high fecundity rate, and low cost of maintenance, making it a perfect complement to the murine model equivalent in biomedical research. Due to these advantages, researchers in Malaysia are starting to take notice and incorporate the zebrafish model into their research activities. However, zebrafish research in Malaysia is still in its infancy stage and many researchers still remain unaware of the full potential of the zebrafish model or have limited access to related tools and techniques that are widely utilized in many zebrafish laboratories worldwide. To overcome this, we organized the First Malaysia Zebrafish Disease Model Workshop in Malaysia that took place on 11th and 12th of November 2015. In this workshop, we showcased how the zebrafish model is being utilized in the biomedical field in international settings as well as in Malaysia. For this, notable international speakers and those from local universities known to be carrying out impactful research using zebrafish were invited to share some of the cutting edge techniques that are used in their laboratories that may one day be incorporated in the Malaysian scientific community.

Neuroplasticity and Repair in Rodent Neurotoxic Models of Spinal Motoneuron Disease

Retrogradely transported toxins are widely used to set up protocols for selective lesioning of the nervous system. These methods could be collectively named "molecular neurosurgery" because they are able to destroy specific types of neurons by using targeted neurotoxins. Lectins such as ricin, volkensin, or modeccin and neuropeptide- or antibody-conjugated saporin represent the most effective toxins used for neuronal lesioning. Some of these specific neurotoxins could be used to induce selective depletion of spinal motoneurons. In this review, we extensively describe two rodent models of motoneuron degeneration induced by volkensin or cholera toxin-B saporin. In particular, we focus on the possible experimental use of these models to mimic neurodegenerative diseases, to dissect the molecular mechanisms of neuroplastic changes underlying the spontaneous functional recovery after motoneuron death, and finally to test different strategies of neural repair. The potential clinical applications of these approaches are also discussed.

Dorsal Horn Parvalbumin Neurons Are Gate-Keepers of Touch-Evoked Pain after Nerve Injury

Neuropathic pain is a chronic debilitating disease that results from nerve damage, persists long after the injury has subsided, and is characterized by spontaneous pain and mechanical hypersensitivity. Although loss of inhibitory tone in the dorsal horn of the spinal cord is a major contributor to neuropathic pain, the molecular and cellular mechanisms underlying this disinhibition are unclear. Here, we combined pharmacogenetic activation and selective ablation approaches in mice to define the contribution of spinal cord parvalbumin (PV)-expressing inhibitory interneurons in naive and neuropathic pain conditions. Ablating PV neurons in naive mice produce neuropathic pain-like mechanical allodynia via disinhibition of PKCγ excitatory interneurons. Conversely, activating PV neurons in nerve-injured mice alleviates mechanical hypersensitivity. These findings indicate that PV interneurons are modality-specific filters that gate mechanical but not thermal inputs to the dorsal horn and that increasing PV inter-neuron activity can ameliorate the mechanical hypersensitivity that develops following nerve injury.

Biological activities of ribosome-inactivating proteins and their possible applications as antimicrobial, anticancer, and anti-pest agents and in neuroscience research

Ribosome-inactivating proteins (RIPs) are enzymes which depurinate ribosomal RNA (rRNA), thus impeding the process of translation resulting in inhibition of protein synthesis. They are produced by various organisms including plants, fungi and bacteria. RIPs from plants are linked to plant defense due to their antiviral, antifungal, antibacterial, and insecticidal activities in which they can be applied in agriculture to combat microbial pathogens and pests. Their anticancer, antiviral, embryotoxic, and abortifacient properties may find medicinal applications. Besides, conjugation of RIPs with antibodies or other carriers to form immunotoxins has been found useful to research in neuroscience and anticancer therapy.

A monoclonal antibody to an abrin chimera recognizing a unique epitope on abrin A chain confers protection from abrin-induced lethality

Abrin, obtained from the seeds of Abrus precatorius plant, is a potent toxin belonging to the family of type II ribosome-inactivating proteins. Recently, a recombinant vaccine consisting of the A subunits of abrin and its homolog Abrus precatorius agglutinin (APA) was demonstrated to protect mice from abrin lethality. Toward identifying neutralizing epitopes recognized during this response, we generated monoclonal antibodies against the proposed vaccine candidate. One antibody, namely A7C4, the corresponding epitope of which was found to be distal to the active site of the enzymatic A chain, prevented abrin-mediated toxicity on cells and abrin-induced lethality in mice but did not inhibit the catalytic activity of the A chain. The in vivo protection conferred by monoclonal antibody A7C4 highlights the potential use of this antibody as a promising immunotherapeutic.

Plasmodium cellular effector mechanisms and the hepatic microenvironment

Plasmodium falciparum malaria remains one of the most serious health problems globally. Immunization with attenuated parasites elicits multiple cellular effector mechanisms capable of eliminating Plasmodium liver stages. However, malaria liver stage (LS) immunity is complex and the mechanisms effector T cells use to locate the few infected hepatocytes in the large liver in order to kill the intracellular LS parasites remain a mystery to date. Here, we review our current knowledge on the behavior of CD8 effector T cells in the hepatic microvasculature, in malaria and other hepatic infections. Taking into account the unique immunological and lymphogenic properties of the liver, we discuss whether classical granule-mediated cytotoxicity might eliminate infected hepatocytes via direct cell contact or whether cytokines might operate without cell–cell contact and kill Plasmodium LSs at a distance. A thorough understanding of the cellular effector mechanisms that lead to parasite death hence sterile protection is a prerequisite for the development of a successful malaria vaccine to protect the 40% of the world’s population currently at risk of Plasmodium infection.

Plant antifungal proteins and their applications in agriculture

Fungi are far more complex organisms than viruses or bacteria and can develop numerous diseases in plants that cause loss of a substantial portion of the crop every year. Plants have developed various mechanisms to defend themselves against these fungi which include the production of low-molecular-weight secondary metabolites and proteins and peptides with antifungal activity. In this review, families of plant antifungal proteins (AFPs) including defensins, lectins, and several others will be summarized. Moreover, the application of AFPs in agriculture will also be analyzed.

A combination of targeted toxin technology and the piggyBac-mediated gene transfer system enables efficient isolation of stable transfectants in nonhuman mammalian cells

Isolation of cells harboring exogenous DNA is typically achieved by the introduction of plasmids, but its efficiency remains still low. In this study, we developed a novel strategy to obtain stable transfectants efficiently. Porcine embryonic fibroblasts were transfected with two plasmids: (i) pTransIEnd, which comprises the ubiquitous promoter, the piggyBac (PB) transposase gene, an internal ribosomal entry site, the Clostridium perfringens-derived endo-β-galactosidase C (EndoGalC) gene, and a poly(A) tail and (ii) a PB-based plasmid, termed pT-EGFP, which contains enhanced green fluorescent protein (EGFP) expression unit flanked by PB acceptor sites. The PB transposase can accelerate the chromosomal integration of transposon vectors. EndoGalC expression results in removal of a cell surface α-Gal epitope, which is specifically recognized by Bandeiraea simplicifolia isolectin-B4 (IB4). Four days after transfection, cells were treated with IB4SAP (IB4 conjugated to saporin, which eliminates any α-Gal epitope-expressing cells) for a short period, followed by standard culture for approximately 10 days. Several colonies emerged, most of which were positive for EGFP expression and lacked TransIEnd. These results indicated that the proposed approach is useful and efficient for obtaining stable transfectants without the use of drug-resistance genes, and offers a novel route for gene manipulation in cultured nonhuman mammalian cells.

Efficient elimination of CD103-expressing cells by anti-CD103 antibody drug conjugates in immunocompetent mice

CD103 plays an important role in the destruction of islet allografts, and previous studies found that a CD103 immunotoxin (M290-Saporin, or M290-SAP) promoted the long-term survival of pancreatic islet allografts. However, systemic toxicity to the host and the bystander effects of M290-SAP obscure the underlying mechanisms of action and restrict its clinical applications. To overcome these shortcomings, anti-CD103 M290 was conjugated to different cytotoxic agents through cleavable or uncleavable linkages to form three distinct antibody-drug conjugates (ADCs): M290-MC-vc-PAB-MMAE, M290-MC-MMAF, and M290-MCC-DM1. The drug-to-antibody ratio (DAR) and the purity of the ADCs were determined by HIC-HPLC and SEC-HPLC, respectively. The binding characteristics, internalization and cytotoxicity of M290 and the corresponding ADCs were evaluated in vitro. The cell depletion efficacies of the various M290-ADCs against CD103-positive cells were then evaluated in vivo. The M290-ADCs maintained the initial binding affinity for the CD103-positive cell surface antigen and then quickly internalized the CD103-positive cell. Surprisingly, all M290-ADCs potently depleted CD103-positive cells in vivo, with high specificity and reduced toxicity. Our findings show that M290-ADCs have potent and selective depletion effects on CD103-expressing cells in immunocompetent mice. These data indicate that M290-ADCs could potentially serve as a therapeutic intervention to block the CD103/E-cadherin pathway.

Combination of antibody targeting and PTD-mediated intracellular toxin delivery for colorectal cancer therapy

The bottlenecks of current chemotherapy in the treatment of colorectal cancer lie in the ineffectiveness of the existing anti-cancer small molecule drugs as well as the dose-limiting toxicity caused by the nonselective action on normal tissues by such drugs. To address these problems, we introduce a novel therapeutic strategy based on tumor targeting using a non-internalizing anti-carcinoembryonic antigen (CEA) monoclonal antibody (mAb) and intracellular delivery of the extremely potent yet cell-impermeable protein toxin gelonin via the aid of a cell-penetrating peptide (also termed as protein transduction domain; PTD). A chimeric TAT-gelonin fusion protein was genetically engineered, and it displayed remarkably enhanced anti-cancer activity against human colorectal cancer cells, with IC50 values being several orders of magnitude lower than the unmodified gelonin. On the other hand, a chemically synthesized conjugate of heparin and a murine anti-CEA mAb, T84.66 (termed T84.66-Hep) was found able to bind highly specifically to CEA over-expressing LS174T colorectal cancer cells. When mixing together, TAT-gelonin and T84.66-Hep could associate tightly and automatically through an electrostatic interaction between the cationic TAT and anionic heparin. In preliminary in vivo studies using LS174T s.c. xenograft tumor bearing mouse, selective and significantly augmented (58-fold) delivery of TAT-gelonin to the tumor target was observed, when compared with administration of TAT-gelonin alone. More importantly, efficacy studies also revealed that only the TAT-gelonin/T84.66-Hep complex yielded a significant inhibition of tumor growth (46%) without causing gelonin-induced systemic toxicity. Overall, this study suggested a generic strategy to effectively yet safely deliver potent PTD-modified protein toxins to the tumor.