Inhibition of Th1- and Enhancement of Th2-Initiating Cytokines and Chemokines in Trichosanthin- Treated Macrophages

Toxic proteins application in cancer therapy

Ribosome inactivating proteins (RIPs) as family of anti-cancer drugs recently received much attention due to their interesting anti-cancer mechanism. In spite of small drugs, RIPs use the large-size effect (LSE) to prevent the efflux process governed by drug resistance transporters (DRTs) which prevents inside of the cells against drug transfection. There are many clinical translation obstacles that severely restrict their applications especially their delivery approach to the tumor cells. As the main goal of this review, we will focus on trichosanthin (TCS) and gelonin (Gel) and other types, especially scorpion venom-derived RIPs to clarify that they are struggling with what types of bio-barriers and these challenges could be solved in cancer therapy science. Then, we will try to highlight recent state-of-the-arts in delivery of RIPs for cancer therapy.

Advances on Tumor-Targeting Delivery of Cytotoxic Proteins

Great attention has been paid to cytotoxic proteins (e.g., ribosome-inactivating proteins, RIPs) possessing high anticancer activities; unlike small drugs, cytotoxic proteins can effectively retain inside the cells and avoid drug efflux mediated by multidrug resistance transporters due to the large-size effect. However, the clinical translation of these proteins is severely limited because of various biobarriers that hamper their effective delivery to tumor cells. Hence, in order to overcome these barriers, many smart drug delivery systems (DDS) have been developed. In this review, we will introduce two representative type I RIPs, trichosanthin (TCS) and gelonin (Gel), and overview the major biobarriers for protein-based cancer therapy. Finally, we outline advances on the development of smart DDS for effective delivery of these cytotoxic proteins for various applications in cancer treatment.

Ribosome-Inactivating Protein α-Momorcharin Derived from Edible Plant Momordica charantia Induces Inflammatory Responses by Activating the NF-kappaB and JNK Pathways

Alpha-momorcharin (α-MMC), a member of the ribosome-inactivating protein (RIP) family, has been found in the seeds of Momordica charantia (bitter melon). α-MMC contributes a number of pharmacological activities; however, its inflammatory properties have not been well studied. Here, we aim to determine the inflammatory responses induced by recombinant α-MMC and identify the underlying mechanisms using cell culture and animal models. Recombinant α-MMC was generated in Rosetta™(DE3)pLysS and purified by the way of nitrilotriacetic acid (NTA) chromatography. Treatment of recombinant α-MMC at 40 μg/mL exerted sub-lethal cytotoxic effect on THP-1 monocytic cells. Transcriptional profiling revealed that various genes coding for cytokines and other proinflammatory proteins were upregulated upon recombinant α-MMC treatment in THP-1 cells, including MCP-1, IL-8, IL-1β, and TNF-α. Recombinant α-MMC was shown to activate IKK/NF-κB and JNK pathways and the α-MMC-induced inflammatory gene expression could be blocked by IKKβ and JNK inhibitors. Furthermore, murine inflammatory models further demonstrated that α-MMC induced inflammatory responses in vivo. We conclude that α-MMC stimulates inflammatory responses in human monocytes by activating of IKK/NF-κB and JNK pathways, raising the possibility that consumption of α-MMC-containing food may lead to inflammatory-related diseases.

A peptide tetramer Tk-tPN induces tolerance of cardiac allografting by conversion of type 1 to type 2 immune responses via the Toll-like receptor 2 signal-promoted activation of the MCP1 gene

The plant protein trichosanthin (Tk) and its derived peptide tetramer Tk-tPN have been shown to stimulate the type 2 immune responses for treating autoimmune disease. This work explores the possibility of using Tk-tPN as a non-toxic immunosuppressant to induce transplantation tolerance using the mechanisms by which T-cell-mediated immune responses are transferred from type 1 to type 2 through innate immunity-related pathways. Immunocytes and cytokine secretions involved in the mouse cardiac allografting model with Tk-tPN treatment were characterized. Identification of critical genes and analysis of their functions through Toll-like receptor (TLR) -initiated signalling and the possible epigenetic changes were performed. Mean survival times of the cardiac allografts were delayed from 7.7 ± 0.3 days (control) to 22.7 ± 3.9 days (P < 0.01) or 79.1 ± 19.2 days (P < 0.0001) when Tk-tPN was introduced into the recipients alone or together with rapamycin, respectively. The grafting tolerance was donor-specific. The secretion pattern of the type 1 cytokine/transcription factor (IL-2(+) IFN-γ(+) T-bet(+)), which is responsible for the acute graft rejection, was shifted to the type 2 factor (IL-4(+) IL-10(+) Gata3+), together with a selective expansion of the IL-4/IL-10-producing CD8+ CD28- regulatory T-cell subset. A TLR2-initiated high expression of chemokine gene MCP1 was detectable simultaneously. Epigenetically Tk/Tk-tPN could also acetylate the histone H3K9 of MCP1 promoter to skew the immunity towards T helper type 2 responses. Tk/Tk-tPN is therefore capable of down-regulating the type 1 response-dominant rejection of cardiac allografts by evoking type 2 immunity through the activation of a TLR2-initiated signalling pathway and MCP1 gene to expand the IL-4/IL-10-secreting CD8+ CD28- regulatory T cells. Tk-tPN could be a promising novel immunosuppressant to induce tolerance in allotransplantation.

A Trichosanthin-derived peptide suppresses type 1 immune responses by TLR2-dependent activation of CD8(+)CD28(-) Tregs

A group of 15-aa-long Trichosanthin-derived peptides was synthesized and screened based on their differential abilities to induce low-responsiveness in mouse strains with high and low susceptibility. One of them was conjugated to form a homo-tetramer Tk-tPN. At concentrations of 0.1-50 μg/ml, Tk-tPN activated CD8(+)CD28(-) Tregs in vitro to induce immune suppression as effectively as the native Trichosanthin but did not exhibit cytotoxicity. In EAE mice which were pre-treated with Tk-tPN or Tk-tPN-activated CD8(+) T cells, a marked attenuation of clinical scores was recorded together with an expansion of the CD8(+)CD28(-) Treg from 2.2% to 36.1% in vivo. A pull-down assay and signal transduction analyses indicated that the ability of Tk-tPN to convert the CD8(+)CD28(-) Treg-related cytokine secretion pattern from type 1 to type 2 depends on the TLR2-initiated signaling in macrophages. The high production of IL-4/IL-10 by the Tk-tPN-activated CD8(+)CD28(-) Treg suggests the value of using Tk-tPN as a therapeutic reagent for Th1-dominant immunological diseases.

Baicalin, a natural compound, promotes regulatory T cell differentiation

BACKGROUND

CD4(+)CD25(+)Foxp3(+) regulatory T (T(reg)) cells inhibit autoimmunity and protect against tissue injury. The development of these T(reg) cells is controlled by the regulator protein Foxp3, which can be enhanced by the in vitro activation of Foxp3 in the presence of transforming growth factor-beta. However, little is known about alternative methods, such as the use of natural products, for controlling Foxp3-mediated T(reg) cell differentiation.

METHOD

HEK 293 T cells were transfected with Foxp3 expression plasmid, and then treated with different compounds, Foxp3 mRNA expression was determined by real-time RT-PCR. CD4(+)CD25(-)T cells were stimulated with Baicalin, Foxp3 protein expression were analyzed by flow cytometry and confocal microscopy, the regulatory function of T cells stimulated with Baicalin was detected by the carboxyfluorescien succinimidyl ester.

RESULTS

We demonstrated that Baicalin, a compound isolated from the Chinese herb Huangqin, induced Foxp3 protein expression in cultured T cells, promoted T(reg) cell differentiation and regulatory activity. Our data also indicated that Baicalin restored Foxp3 expression following its initial interleukin-6-mediated inhibition and induced Foxp3 expression in vitro.

CONCLUSIONS

These data suggest that Baicalin may promote T(reg) cell differentiation and regulatory activity and may serve as a promising natural immunosuppressive compound for treating autoimmune inflammatory diseases.

A role for trichosanthin in the expansion of CD4CD25 regulatory T cells

CD4(+)CD25(+) regulatory T cells (Tregs) are critical for the peripheral immune tolerance. Understanding the signals for the generation of Tregs is important for the clinical immunotherapy, but only limited progress has been made on obtaining enough peripheral Tregs. The aim of this study was to evaluate the role of trichosanthin (Tk) extracted from Chinese medicinal herb Trichosanthes kirilowi on the function of Tregs in vitro and in vivo. We reported here that Tk is needed for the expansion of freshly isolated CD4(+)CD25(+)Tregs (nTregs) into Tk-expanded CD4(+)CD25(+)Tregs (Tk-Tregs) through up-regulating CD25 and Foxp3 expression. The dose-response analyses indicated that 100 ng/ml Tk was the most appropriate dose. The result of real-time PCR showed that Tk-Tregs expressed 1.5-fold higher levels of Foxp3 than those observed in nTregs. Tk-Tregs markedly suppressed activation of effector T cells at a suppressor/responder ratio of 1:1, 1:2, 1:4, 1:8 or 1:16, and their effect was dose dependent. Moreover, Tk-Tregs secreted more immunosuppressive cytokines interleukin (IL)-10 and transforming growth factor (TGF)-beta1 after stimulating with antigen and antigen-presenting cells (APC). Transwell experiments showed that not only cell-to-cell contact but also soluble cytokines were involved in suppressive mechanism of Tk-Tregs. And Tk-Tregs were more efficient in suppressing CD25(-)T cell response to specific antigen than to irrelative antigen. Most importantly, it was revealed for the first time that Tk-Tregs could prolong the survival duration of mice with acute graft-versus-host disease (aGVHD). In conclusion, the study suggests a possible therapeutic potential of Tk-Tregs for clinical treatment on aGVHD.

Blockade of alpha4 integrin signaling ameliorates the metabolic consequences of high-fat diet-induced obesity

OBJECTIVE

Many prevalent diseases of advanced societies, such as obesity-induced type 2 diabetes, are linked to indolent mononuclear cell-dependent inflammation. We previously proposed that blockade of alpha4 integrin signaling can inhibit inflammation while limiting mechanism-based toxicities of loss of alpha4 function. Thus, we hypothesized that mice bearing an alpha4(Y991A) mutation, which blocks signaling, would be protected from development of high-fat diet-induced insulin resistance.

RESEARCH DESIGN AND METHODS

Six- to eight-week-old wild-type and alpha4(Y991A) C57Bl/6 male mice were placed on either a high-fat diet that derived 60% calories from lipids or a chow diet. Metabolic testing was performed after 16-22 weeks of diet.

RESULTS

Alpha4(Y991A) mice were protected from development of high-fat diet-induced insulin resistance. This protection was conferred on wild-type mice by alpha4(Y991A) bone marrow transplantation. In the reverse experiment, wild-type bone marrow renders high-fat diet-fed alpha4(Y991A) acceptor animals insulin resistant. Furthermore, fat-fed alpha4(Y991A) mice showed a dramatic reduction of monocyte/macrophages in adipose tissue. This reduction was due to reduced monocyte/macrophage migration rather than reduced monocyte chemoattractant protein-1 production.

CONCLUSIONS

Alpha4 integrins contribute to the development of HFD-induced insulin resistance by mediating the trafficking of monocytes into adipose tissue; hence, blockade of alpha4 integrin signaling can prevent the development of obesity-induced insulin resistance.

Effect of site-directed PEGylation of trichosanthin on its biological activity, immunogenicity, and pharmacokinetics

Trichosanthin (TCS) is a type I ribosome-inactivating protein (RIP) with multiple biological and pharmacological activities. It has been approved effective in the clinical treatment of AIDS and tumor, but its strong immunogenicity and short plasma half-life have limited the clinical administration. To reduce the immunogenicity and prolong the plasma half-life of this compound, three TCS muteins (M(1), M(2) and M(3)) and two PEGylated TCS muteins (PM(1) and PM(2)) were constructed by site-directed mutagenesis and PEGylation, respectively. Compared with the unmodified TCS, both PEGylated TCS showed a 3- to 4-fold decrease in immunogenicity, a 0.5- to 0.8-fold decrease in non-specific toxicity, and a 4.5- to 6-fold increase in plasma half-life. But there is a problem of activity reduction. The increased circulating half-life in vivo may compensate for the reduced activity. Together with the other benefits of PEGylation such as reduced immunogenicity and toxicity, it is worthwhile to further explore the potential application of the PEGylated TCS as a better therapeutic agent for AIDS and tumor.

Recombined CC chemokine ligand 2 into B16 cells induces production of Th2-dominant [correction of dominanted] cytokines and inhibits melanoma metastasis

This study is aimed to verify whether CCL2 can induce Th2 polarization in vivo and subsequently inhibit tumor metastasis. B16 cells (a murine melanoma cell line) highly expressing CCL2 (CCL2-B16 cells) were obtained by transfection with recombinant plasmid CCL2-pcDNA3. Primary thymocytes were co-cultured with CCL2-B16 cells and STAT-6-mediated Th2 polarization was noticed after co-culture. Caudal vein injection of CCL2-B16 cells effectively inhibited pulmonary metastasis in C57BL/6 mice, but not in nude mice, indicating that T cells play a role in CCL2-induced inhibition of tumor metastasis. We found that high level of CCL2 up-regulated the expression of Th2-related cytokine (IL-4) in tumor microenvironment and increased CD4+, CD8+, and CD45RB+ cells in the peripheral blood and tumor tissues. We also demonstrated that inoculation of mice with CCL2-B16 cells prolonged mice survival time when they were reinjected with wildtype B16 cells, implying that CCL2 can activate immuno-memory in mice. It is concluded that high expression of CCL2 can induce Th2 polarization in tumor microenvironment and can effectively inhibit tumor metastasis, which casts new lights on the role of chemokines in reconstruction of immune surveillance in patients suffering from tumors.

Immune suppression via IL-4/IL-10-secreting T cells: A nontoxic property of anti-HIV agent Trichosanthin

The activity of Trichosanthin (Tk) has been attributed to its toxicity since this plant protein was used as an anti-HIV agent. However, in this study strong inhibition of human lymphoproliferation to soluble and allogeneic antigens was induced by Tk at 0.005-0.5 microg/ml without causing cell damages including apoptosis. The suppression was dependent on the presence of monocytes that are able to internalize and process Tk molecules as exogenous antigens. Among 39 Tk-primed T cell lines established, those with strong suppressive activity were CD8(+) TCRalphabeta(+) with type 2 cytokine secretion profile. Depletion of CD8 cells from total T cells or blocking expression of HLA-DQ molecules diminished Tk's inhibitory activity. In addition, healthy subjects with HLA haplotype DRB1*0301-DQA1*0501-DQB1*0201 were susceptible to the hyporeaction induced by Tk or a Tk-derived peptide. This indicates that Tk could induce an HLA-associated immune suppression via activating IL-4/IL-10-secreting T cells, which might belong to CD8 Tc2 subset.

Mapping the antigenic determinants and reducing the immunogenicity of trichosanthin by site-directed mutagenesis

Trichosanthin (TCS) is a type I ribosome-inactivating protein (RIP) possessing multiple pharmacological properties. One of its interesting properties is to inhibit human immunodeficiency virus (HIV) replication but its strong immunogenicity has limited the repeated clinical administration. To map the antigenic determinants and reduce the immunogenicity of TCS, two potential antigenic sites (YFF81-83 and KR173-174) were identified by computer modeling, and then three TCS mutants namely TCS(YFF81-83ACS), TCS(KR173-174CG), and TCS(YFF-KR) were constructed by site-directed mutagenesis. The RI activity and DNase-like activity of the three constructed TCS mutants were similar to natural TCS but with much lower immunogenicity. Results suggested that the two selected sites are all located at or near the antigenic determinants of TCS. In toxicity studies, the LD(50) of the three TCS mutants was not different from natural TCS. These findings would be useful in designing a better therapeutic agent for AIDS.

The Methylene Chloride Fraction of Trichosanthis Fructus Induces Apoptosis in U937 Cells through the Mitochondrial Pathway

Trichosanthis kirilowii MAXIM has been used as a folk remedy to treat diabetes, leukemia, and breast cancer. In the present study, the apoptotic mechanism of the methylene chloride fraction of Trichosanthis Fructus (MCTF) was investigated in human leukemic U937 cells. MCTF exhibited antiproliferative effectsagainst U937 cells (IC50=ca. 8 microg/ml). Apoptotic bodies were observed in MCTF-treated U937 cells in the TUNEL assay. We also confirmed that MCTF significantly increases annexin V(+)/propidium iodide-cells using FACS analysis. MCTF treatment activated caspase-8, -9 and -3, and led to cleaved poly (ADP-ribose) polymerase and release of cytochrome c into cytosol in a concentration-dependent manner, while MCTF did not affect Bax or Bcl-2 protein levels as shown by Western blot analysis. Taken together, these results indicate that MCTF can induce apoptosis in U937 cells chiefly via a mitochondrial-mediated pathway and suggest that Trichosanthis Fructus can be used in cancer treatment as a chemopreventive agent.

Prostaglandin E2 promotes degranulation-independent release of MCP-1 from mast cells

Mast cells (MCs) are common components of inflammatory infiltrates and a source of proangiogenic factors. Inflammation is often accompanied by vascular changes. However, little is known about modulation of MC-derived proangiogenic factors during inflammation. In this study, we evaluated the effects of the proinflammatory mediator prostaglandin E2 (PGE2) on MC expression and release of proangiogenic factors. We report that PGE2 dose-dependently induces primary MCs to release the proangiogenic chemokine monocyte chemoattractant protein-1 (MCP-1). This release of MCP-1 is complete by 2 h after PGE2 exposure, reaches levels of MCP-1 at least 15-fold higher than background, and is not accompanied by degranulation or increased MCP-1 gene expression. By immunoelectron microscopy, MCP-1 is detected within MCs at a cytoplasmic location distinct from the secretory granules. Dexamethasone and cyclosporine A inhibit PGE2-induced MCP-1 secretion by approximately 60%. Agonists of PGE2 receptor subtypes revealed that the EP1 and EP3 receptors can independently mediate MCP-1 release from MCs. These observations identify PGE2-induced MCP-1 release from MCs as a pathway underlying inflammation-associated angiogenesis and extend current understanding of the activities of PGE2.

Trichosanthin inhibits antigen-specific T cell expansion through nitric oxide-mediated apoptosis pathway

Trichosanthin (TCS) has been found to exhibit inflammation-suppressing effect but the underlying mechanisms are not clear. In this study, we found that TCS inhibited OVA-specific T cell proliferation in a dose-dependent manner. Such inhibition was correlated with enhanced cell death. At the same time, inducible nitric oxide synthase (iNOS) mRNA expression and protein levels were found increased in cells treated with TCS, and nitric oxide (NO) production by cells was elevated in the presence of TCS. When L-NIL, the specific inhibitor of iNOS, was added to suppress NO production induced by TCS, OVA-specific cell death was significantly inhibited, meanwhile, thymidine incorporation of cells was rescued towards normal levels. These results indicate that TCS could inhibit antigen-specific T cell activation via NO-mediated apoptosis pathway.

Identification of the amino acid residues in trichosanthin crucial for IgE response

Trichosanthin (TCS) is the major effective component from Chinese herb Trichosanthes kirilowii. TCS has been approved to be effective in clinical treatment of HIV infection and leukemia, but its allergenicity has limited its clinical usage. To identify amino acid residues in TCS with an important role in IgE induction, TCS-specific IgE mAb (TE1) was used to serve as a probe and TE1 epitope was determined by a random phage-peptide library. Based on phage peptide sequences, TE1 epitope was predicted at amino acid residues 169-174 (QQIGKR) of TCS protein. Based on modeling data, two amino acids (Lys173 and Arg174) on TCS were considered to have a crucial role in binding to TE1. After lysine 173 and arginine 174 were mutated to glycine, the mutant TCS protein specifically lost the binding activity to TE1 mAb and exhibited reduced IgE induction in the immunized mice. The data showed that the IgE epitope of TCS was determined and shown to play a critical role in induction of IgE, and the modification of IgE-epitope may be a useful strategy to reduce the allergenicity of an allergen.