Protein-bound Polysaccharide Research Articles

Randomized phase III clinical study comparing postoperative UFT/LV,UFT+LV/UFT and UFT+LV+PSK/UFT+PSK as adjuvant therapy for curatively resected stage III colorectal cancer HGCSG-CAD study.

3638 Background: Study showed that the oral anticancer agent UFT/LV is useful as postoperative adjuvant chemotherapy for stage III colorectal cancer. PSK, a protein-bound polysaccharide extracted from the mycelia of Coriolus versicolor, is an immunomodulator widely used in gastric, colorectal and lung cancers. Methods: Patients aged 20-80 years with stage III colorectal cancer registered in 35 facilities were randomized to: group A (UFT/LV 28 days/5 weeks for 6 months); group B (UFT+LV 28 days/5 weeks for 6 months, then UFT for 12 months); and group C (UFT+LV+PSK 28 days/5 weeks for 6 months, then UFT+PSK for 12 months). Treatment was started within 6 months after curative resection. Outcome measures were relapse-free survival (RFS), overall survival (OS), incidence and severity of adverse events, and QOL. Results: Of 342 patients registered, 340 eligible patients were analyzed (84 in group A, 85 in group B, and 171 in group C). At baseline, variation in QOL score was observed but histopathological parameters were not different among 3 groups. Median observation period was 36 months. 3-year RFS was 73.8%, 77.6% and 73.9% in groups A, B, and C [A vs C: hazard ratio (HR) 0.960, 95% confidence interval (CI) 0.575-1.601; B vs C: HR 0.837, CI 0.488-1.433; A vs B: HR 1.151, CI 0.623-2.126]. 3-year OS was 95.2%, 91.8% and 89.9% in groups A, B, and C (A vs C: HR 0.460, CI 0.155-1.367; B vs C: HR 0.814, CI 0.338-1.963 A vs B: HR 0.570, CI 0.167-1.947). Adverse events ≥grade 3 included gastrointestinal symptoms and general status. There was no treatment-related death. Excluding high fatigue score in QOL scale that showed pretreatment variation, stratification analysis showed interaction between family score and group, and efficacy was suggested especially in group C with high score (3-yesr RFS: 66.7%, 68.2% and 88.1% in groups A, B, and C. A vs C: HR 3.289, CI 0.951-11.375, B vs C: HR 3.070, CI 0.973-9.685, A vs B: HR 1.084, CI 0.344-3.417). Conclusions: A significant difference in primary endpoint was not detected. Variation in QOL at treatment initiation probably greatly affected outcome. Clinical trial information: NCT00209742.

Protein-bound polysaccharide activates dendritic cells and enhances OVA-specific T cell response as vaccine adjuvant

Protein-bound polysaccharide-K (PSK) is a hot water extract from Trametes versicolor mushroom. It has been used traditionally in Asian countries for its immune stimulating and anti-cancer effects. We have recently found that PSK can activate Toll-like receptor 2 (TLR2). TLR2 is highly expressed on dendritic cells (DC), so the current study was undertaken to evaluate the effect of PSK on DC activation and the potential of using PSK as a vaccine adjuvant. In vitro experiments using mouse bone marrow-derived DC (BMDC) demonstrated that PSK induces DC maturation as shown by dose-dependent increase in the expression of CD80, CD86, MHCII, and CD40. PSK also induces the production of multiple inflammatory cytokines by DC, including IL-12, TNF-α, and IL-6, at both mRNA and protein levels. In vivo experiments using PSK as an adjuvant to OVAp323–339 vaccine showed that PSK as adjuvant leads to enlarged draining lymph nodes with higher number of activated DC. PSK also stimulates proliferation of OVA-specific T cells, and induces T cells that produce multiple cytokines, IFN-γ, IL-2, and TNF-α. Altogether, these results demonstrate the ability of PSK to activate DC in vitro and in vivo and the potential of using PSK as a novel vaccine adjuvant.

Structural characterization and immunostimulatory activity of a novel protein-bound polysaccharide produced by Hirsutella sinensis Liu, Guo, Yu & Zeng

HS002-II, a novel protein-bound polysaccharide with 44kDa molecular weight, was fractionated from submerged cultures of Hirsutella sinensis Liu, Guo, Yu & Zeng by DEAE-Sepharose and Sephacryl S200 chromatography. Based on the results of infrared spectroscopy, high performance liquid chromatography, methylation, amino acid analysis, NMR spectroscopy and atomic force microscopy, the polysaccharide moieties of HS002-II mainly contained a long backbone of (1→3)-linked α-d-ribofuranosyl units (1→4)-linked α-d-xylopyranosyl units and (1→4)-linked β-d-glucopyranosyl units, which was substituted at C-6. The two branches were β-d-mannopyranosyl residues and β-d-galactopyranosyl residues terminated with α-l-arabinopyranosyl residues, respectively. HS002-II consisted of 57.9% polysaccharide and 42.1% protein with the existence of N-type carbohydrate–protein linkage. In terms of the pro-inflammatory cytokines assay (NO, TNF-α, IL-1β and NF-κB) using murine macrophages cell line (RAW264.7), HS002-II exhibited significant immunomodulatory activity by stimulating the IκB-NF-κB pathway.

Abstract 3986: Protein-bound polysaccharide induces IL-1β via NLRP3 inflammasome activation.

Abstract Protein-bound polysaccharide-K (PSK) is a hot water extract from Trametes Versicolor mushroom. It is widely used in Asian countries for its immune enhancing and anti-cancer potential. We have recently reported that PSK activates TLR2 and has CD8 T cell- and NK cell- dependent anti-tumor activity. PSK stimulates the production of multiple pro-inflammatory cytokines, including IL-1β, the production of which requires both TLR and inflammasome activation. The current study was undertaken to investigate the mechanism by which PSK activates inflammasome and induces IL-1β. RT-PCR and Western blot analyses showed that PSK induces pro-IL-1β in a dose- and time- dependent manner. PSK activates caspase-1 and pre-incubation with z-VAD-FMK, a caspase inhibitor, abolishes PSK-induced IL-1β. Comparison of THP-1 cells and THP-1 cells deficient for NLRP3 demonstrated that PSK-induced IL-1β production requires NLRP3 inflammasome. PSK also up-regulates the expression of NLRP3 mRNA. Further experiments were performed to investigate whether potassium efflux, reactive oxygen species (ROS) generation, or lysosomal perturbation was involved in PSK-induced NLRP3 inflammasome activation. Results showed that CA-074-Me, a cathepsin B inhibitor, significantly decreased PSK-induced IL-1β, while the production of TNF-α was not affected. Phagocytosis or ROS generation was not required for PSK-induced NLRP3 inflammasome activation. Altogether, our results suggest that PSK-induced IL-1β production is a two step process. Step 1 requires TLR2-dependent induction of pro-IL-1β and upregulation of NLRP3 expression; Step 2 involves NLRP3 inflammasome activation in a cathepsin B-dependent manner. These results provide novel insights into the mechanisms of the immune stimulatory and anti-tumor effects of PSK. Citation Format: Yi Yang, Carol Inatsuka, Mary L. Disis, Hailing Lu. Protein-bound polysaccharide induces IL-1β via NLRP3 inflammasome activation. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3986. doi:10.1158/1538-7445.AM2013-3986

Combined TLR2/4-Activated Dendritic/Tumor Cell Fusions Induce Augmented Cytotoxic T Lymphocytes

Induction of antitumor immunity by dendritic cell (DC)-tumor fusion cells (DC/tumor) can be modulated by their activation status. In this study, to address optimal status of DC/tumor to induce efficient antigen-specific cytotoxic T lymphocytes (CTLs), we have created various types of DC/tumor: 1) un-activated DC/tumor; 2) penicillin-killed Streptococcus pyogenes (OK-432; TLR4 agonist)-activated DC/tumor; 3) protein-bound polysaccharides isolated from Coriolus versicolor (PSK; TLR2 agonist)-activated DC/tumor; and 4) Combined OK-432- and PSK-activated DC/tumor. Moreover, we assessed the effects of TGF-β1 derived from DC/tumor on the induction of MUC1-specific CTLs. Combined TLR2- and TLR4-activated DC/tumor overcame immune-suppressive effect of TGF-β1 in comparison to those single activated or un-activated DC/tumor as demonstrated by: 1) up-regulation of MHC class II and CD86 expression on DC/tumor; 2) increased fusion efficiency; 3) increased production of fusions derived IL-12p70; 4) activation of CD4+ and CD8+ T cells that produce high levels of IFN-γ; 5) augmented induction of CTL activity specific for MUC1; and 6) superior efficacy in inhibiting CD4+CD25+Foxp3+ T cell generation. However, DC/tumor-derived TGF-β1 reduced the efficacy of DC/tumor vaccine in vitro. Incorporating combined TLRs-activation and TGF-β1-blockade of DC/tumor may enhance the effectiveness of DC/tumor-based cancer vaccines and have the potential applicability to the field of adoptive immunotherapy.

Protein-bound polysaccharide decreases invasiveness and proliferation in pancreatic cancer by inhibition of hedgehog signaling and HIF-1α pathways under hypoxia

To develop an effective therapeutic approach to pancreatic ductal adenocarcinoma (PDAC), we focused on the antitumor mechanism of protein-bound polysaccharide (PSK) under hypoxia. PSK decreased proliferation in PDAC cells under hypoxia but not normoxia. PSK also showed anti-tumor effects in vivo, inhibited invasiveness of PDAC cells, and decreased the expression of HIF-1α and hedgehog (Hh) signaling-related molecules under hypoxia. Inhibition of HIF-1α and Hh signaling reduced proliferation and invasiveness in PDAC cells under hypoxia. In conclusion, we found new PSK-related pathways in invasiveness and proliferation in PDAC under hypoxia. PSK may be a promising therapeutic drug to treat refractory PDAC.

The expression of integrins is decreased in colon cancer cells treated with polysaccharide K

Polysaccharide K (PSK), a protein-bound polysaccharide used as a non-specific immunotherapeutic agent, is said to improve the prognosis of malignant tumors such as colon cancer, but there have been few in‑depth investigations of its mechanism of action. In the present study, we investigated which genes in colon cancer cells themselves are regulated by PSK and what sort of action it exerts. Colon cancer cells were exposed to PSK in vitro and changes to their morphology and adhesive capacity were investigated, as were the changes in integrin expression that occurred. Exposure to PSK caused colon cancer cells to become spherical in morphology and investigation of their adhesion rate showed that it reduced adhesion to laminin, fibrinogen, collagen IV, collagen I and fibronectin. In terms of changes to molecules on the surface of cancer cells, there was reduced expression of integrin mRNA α and β, which are ligands for the proteins of basement membrane. An investigation of the adhesiveness of PSK-stimulated colon cancer cells to vascular endothelial cells also showed that the adhesion rate decreased significantly compared with cells not exposed to PSK. Suppression of integrin expression on the cell surface and reduced adhesion to vascular endothelial cells were observed as a novel mechanism of action of PSK on colon cancer cells.

Maturation of morphology, phenotype and functions of murine bone marrow-derived dendritic cells(DCs) induced by polysaccharide Kureha(PSK)

The aim of this work was to evaluate the influence of protein-bound polysaccharide Kureha(PSK) on murine dendritic cells (DCs). These impacts of PSK on DCs from bone marrow derived DCs(BMDCs) were assessed with inverted phase contrast microscope, conventional scanning electron microscopy (SEM), transmission electron microscopy (TEM) for morphology, fluorescence activated cell sorting (FACS) analysis, cytochemistry assay for key surface molecules, FITC-dextran for phagocytosis, bio-assay and enzyme linked immunosorbent assay (ELISA) for cytokine production. We found that under the influence of PSK, immature DCs changed into mature DCs with decrease of antigens up-taking, simultaneously high expression of key surface molecules of the MHC classII,CD40, CD80, CD86 and CD83 as well as more production of IL-12p70 and tumor necrosis factor α (TNF-α). These data indicate that PSK could markedly promote maturation of DCs and this adjuvant-like activity may have potential therapeutic value in vaccine preparation.

Polysaccharide K suppresses angiogenesis in colon cancer cells

The protein-bound polysaccharide K (PSK) is used as a non-specific immunotherapeutic agent for the treatment of colon cancer. Little research, however, has been conducted on its association with angiogenesis, which is a prognostic factor markedly correlated with hematogenous metastases. We therefore decided to investigate the action of PSK on angiogenic growth factors, angiogenesis inhibitors and angiogenesis in colon cancer cells. Reverse transcription-polymerase chain reaction (RT-PCR) was used to investigate changes in HIF-1α mRNA expression. PCR array was used to investigate changes in angiogenic growth factors and angiogenesis inhibitors, as well as the expression of related genes. Colon cancer cells were cultured with or without PSK for 48 h. The following day, cells were cultured for two days at 37°C in new complete media. The resulting culture medium was placed in the chamber of a tube formation system in order to investigate tube formation. Investigation of HIF-1α mRNA expression in colon cancer cell lines and in cells cultured under identical conditions with added PSK revealed a significant decrease in expression, as well as a decrease in angiogenic growth factors and related genes in PSK-treated colon cancer cell lines. By contrast, levels of angiogenesis inhibitors and related genes were higher in the PSK-treated colon cancer cell lines. Investigation of tube formation revealed that elongation was inhibited in the medium of the PSK-treated colon cancer cell lines in comparison to the medium of the non-treated colon cancer cell lines. PSK suppresses angiogenic growth factors and related genes, enhances angiogenesis inhibitors and related genes and ultimately suppresses angiogenesis in colon cancer cells.

차가버섯 균사체로부터 단백다당체의 추출 공정 확립

Inonotus obliquus mushroom, which is a fungus belonging to Hymenochaetaceae family, is known to grow on birth trees in colder northern climates and to be a fungal parasite that draws nutrients out of living trees rather than from the ground. For the separation of protein-bound polysaccharide (PBP) from the culture broth and mycelium of Inonotus obliquus, three well known extraction methods namely hot water, ultrasound and microwave were used. The best extraction conditions to separate the PBP (64.94 mg/g) from mycelium by microwave were found to be for 1 hour and <TEX>$150^{\circ}C$</TEX>. The possibility for concentration of extracted PBP solution by using membrane was also studied. The extracted PBP solution was concentrated effectively by using an ultrafiltration membrane and the molecular weight cut off (MWCO) is 30 KDa. It was observed that a concentration by the ultrafiltration membrane is essential not only for the development of clean separation technology but also for enhanced production of PBP. As a result, we have shown that PBP in the final concentrated solution showed approximately 10 times higher than that in the crude solution by application of the developed separation systems. The separation yield of PBP was about 89.79% by gel filtration of purification steps and the purified product was confirmed to be PBP by using FT-IR.

Structural characterization and immuno-modulating activities of a polysaccharide from Ganoderma sinense

A protein-bound polysaccharide (GSP-4) with a molecular weight of 8.3×105Da, was isolated from the water extract of the fruiting bodies of Ganoderma sinense. Chemical study revealed that this fraction was composed of mannose, glucose and galactose in the molar ratio of 4.7:27.1:1.0, with the sugar residues of t-, 1,3-, 1,4-, 1,6-, 1,3,4- and 1,3,6-linked Glcp, t-linked Galp, and 1,6-linked Manp. The immnomodulatory effects of GSP-4 were assessed using human peripheral blood mononuclear cells (PBMCs) and murine monocyte/macrophage cell line RAW 264.7. We found that GSP-4 could significantly stimulate the production of the immunomodulatory markers tumor necrosis factor α (TNF-α), interleukin (IL)-1β, IL-12, and granulocyte-macrophage colony-stimulating factor (GM-CSF) in PBMCs. This observation was further substantiated in RAW 264.7 cells, as indicated by the increase of nitric oxide (NO), TNF-α and IL-6 production. GSP-4 also enhanced the expression of inducible NO synthase mRNA in dose-dependent manner. Our current finding gives the first piece of evidence to support that GSP-4 possesses some promising immunomodulating effects and it could be a potential candidate to be further used in related cancer immunotherapy.

Extraction, purification and antitumor activity of a water-soluble polysaccharide from the roots of Polygala tenuifolia

One polysaccharide PTP was isolated and purified from the roots of Polygala tenuifolia. It consisted of galactose, glucose and galactose in the ratio of 3.1:3.7:2.5, and a small amount of rhamnose, mannose and xylose. 17 general amino acids were identified to be components of the protein-bound polysaccharide analyzed by automatic amino acid analyzer. In order to test the anti-cancer activity of PTP, we investigated its effect against the growth of human ovarian cancer cells SKOV3 in vitro and in ovarian cancer rats. The intracellular reactive oxygen species (ROS) and glutathione (GSH) in SKOV3 cells following PTP treatment were also quantified to explore the possible mechanism underlying the antitumor activity of the polysaccharide. The result showed that PTP is effective on inhibiting the proliferation of SKOV3 cells in a concentration-dependent manner. Furthermore, treatment with PTP caused a rapid depletion of intracellular GSH content and accumulation of intracellular ROS, thus resulting in the apoptosis, which may prove to be a pivotal mechanism for its cancer protection action. In addition, a significant tumor growth inhibition effect was observed in nude mice after PTP administration for 7 weeks. All above indicated PTP could be beneficial towards ovarian cancer therapy.

PSK induces apoptosis through the inhibition of activated STAT3 in human esophageal carcinoma cells

PSK, a protein-bound polysaccharide, is widely used in Japan as an immunopotentiating biological response modifier for cancer patients. PSK exerts antitumor activities through stimulation of the host's immune response; however, few studies have addressed the direct actions of PSK on tumor cells. Recently, it has been found that STAT3 is aberrantly activated in various types of malignancies, and plays a crucial role in tumor cell proliferation and survival. In the present study, STAT3 was constitutively activated in KYSE170 and TE13 esophageal carcinoma cells, and PSK inhibited proliferation and induced apoptosis in these cells in a dose-dependent manner. Based on these findings, the relationship between STAT3 and apoptosis in these cells was investigated. Results showed that PSK inhibited the expression of activated STAT3 and stimulated the expression of pro-apoptotic Bax in a dose-dependent manner, without affecting the expression of anti-apoptotic Bcl-xL and Mcl-1. These results indicate that PSK may induce apoptosis in esophageal carcinoma cells by inhibiting the expression of activated STAT3.

Abstract 523: γα T cells are activated by protein-bound polysaccharide krestin (PSK) and contribute to the antitumor effect of PSK

Abstract Gamma delta (γδ) T cells play an important role in anti-tumor immunity, and novel methods to augment γδ T cell function are highly desired. It has recently been shown that toll-like receptor (TLR) agonists may modulate the function of γδ T cells, so we questioned whether protein-bound polysaccharide krestin (PSK), a mushroom extract with TLR2 agonist activity, can activate γδ T cell. Using splenocytes from neu-transgenic mice, we found that γδ T cells produce IFN-γ after PSK treatment and have up-regulated expression of CD25 and CD69. The expression of CD107a in γδ T cells was also enhanced by PSK. To investigate whether the effect of PSK on γδ T cells is direct or indirect via activation of dendritic cells (DC), purified γδ T cells were cultured either alone or together with bone marrow derived DC (BMDC) in a co-culture or trans-well system and then stimulated with PSK. Results showed that direct cell-to-cell contact between γδ T cells and DC is required for optimal activation of γδ T cells. In the absence of DC, PSK can co-stimulate γδ T cells with anti-γδ TCR or anti-CD3 mAb. Oral administration of PSK in neu-transgenic mice with implanted breast tumors resulted in increased percentage of γδ T cells among splenocytes and increased expression of NKG2D on γδ T cells. Depleting γδ T cells during PSK treatment decreased the anti-tumor effect of PSK. All together, these results demonstrated that γδ T cells are activated by PSK and contribute to the anti-tumor effect of PSK. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 523. doi:1538-7445.AM2012-523

Correlation between efficacy of PSK postoperative adjuvant immunochemotherapy for gastric cancer and expression of MHC class I

Protein-bound polysaccharide K (PSK) is a glycoprotein that is purified from the mushroom Coriolus versicolor. In Japan, PSK is clinically used in combination with anticancer agents following gastric cancer surgery. Evaluation of the response is difficult, as efficacy is determined via antitumor immunoenhancing effects, and for that reason PSK has not become a standard therapy. The present study evaluated the expression of MHC class I in gastric cancer patients who received PSK postoperative adjuvant immunochemotherapy, and investigated the correlation between MHC class I expression and clinical outcomes. The subjects comprised 349 patients with stage II/III gastric cancer, who had received adjuvant therapy following curative resection between 1995 and 2008. MHC class I expression in the primary lesion was evaluated by immunohistochemical staining. Patients were divided into two treatment groups: one was only administered oral chemotherapy (chemotherapy-only group) and the other was administered chemotherapy plus PSK (PSK group). The clinical outcomes were compared between the two groups. The two groups did not differ in regard to their MHC class I expression. Expression-negative cases demonstrated 3-year recurrence-free survival (RFS) rates of 65% in the PSK group and 47% in the chemotherapy-only group. Therefore, the PSK group revealed a prolonged survival. For the 82 expression-negative cases with pN2 or greater, the RFS rates were 68% in the PSK group and 28% in the chemotherapy-only group, representing a significant difference. Thus, PSK adjuvant immunochemotherapy may be effective in MHC class I-negative patients, who are in a state of antitumor immunological tolerance, and patients with advanced lymph node metastasis of pN2 or greater.

Production, purification and characterisation of polysaccharides from Pleurotus ostreatus with antitumour activity

Mushroom polysaccharides play an important role in functional foods because they exhibit biological modulator properties such as antitumour, antiviral and antibacterial activities. The present study involved the production, purification and characterisation of intracellular and extracellular free and protein-bound polysaccharides from Pleurotus ostreatus and the investigation of their growth-inhibitory effect on human carcinoma cell lines. Several fermentation parameters were obtained: batch polysaccharide productivities of 0.013 ± 8.12 × 10⁻⁵ and 0.037 ± 0.0005 g L⁻¹ day⁻¹ for intracellular and extracellular polysaccharides respectively, a maximum biomass concentration of 9.35 ± 0.18 g L⁻¹ , P(max) = 0.935 ± 0.018 g L⁻¹ day⁻¹, µ(max) = 0.218 ± 0.02 day⁻¹, Y(EP/X) = 0.040 ± 0.0015 g g⁻¹ and Y(IP/X) = 0.014 ± 0.0003 g g⁻¹ . Some polysaccharides exhibited superoxide dismutase (SOD)-like activity of 50-200 units. Fourier transform infrared analysis of the polysaccharides revealed absorption bands characteristic of such biological macromolecules. Cytotoxicity assays showed that both intracellular and extracellular polysaccharides exhibited antitumour activity towards several tested human carcinoma cell lines in a dose-dependent manner. The polysaccharides of P. ostreatus exhibited high SOD-like activity, which strongly supports their biological effect on tumour cell lines. The extracellular polysaccharides presented the highest antitumour activity towards the RL95 carcinoma cell line and should be further investigated as an antitumour agent.

Antitumor Activity of a Polysaccharide−Protein Complex Isolated from a Wood-Rotting Polypore Macro Fungus Phellinus rimosus (Berk) Pilat

A protein-bound, water-soluble polysaccharide-protein complex was isolated from a medicinal mushroom, Phellinus rimosus (Berk) Pilat (PPC-Pr). The isolation was achieved by hot water extraction, filtration, solvent precipitation, dialysis, and freeze-drying. The proximate analysis showed that PPC-Pr comprised 54.8% polysaccharide and 28.6% protein. The molecular weight of the compound was determined by gel filtration using a Sephadex G 100. The molecular weight of PPC-Pr was approximately 1,200,000 D. The thin-layer chromatography analysis of PPC-Pr after acid hydrolysis with trifluroacetic acid showed that it was composed of glucose as the only monosaccharide unit. The amino acid profile analysis of PPC-Pr revealed that it contained large amounts of aspartic acid, glutamic acid, alanine, glycine, and serine. Thus, the results indicated that PPC-Pr is a glucan-protein complex. The PPC-Pr did not show in vitro cytotoxic activity against Dalton's lymphoma ascites and Ehrlich's ascites carcinoma cell lines. The PPC-Pr was found to be effective in increasing the life span of ascites tumors induced by Ehrlich's ascites carcinoma cell line in mice. PPC-Pr also was found to have significant preventive and curative effects on solid tumors induced by the Dalton's lymphoma ascites cell line. The experimental results thus indicated that protein-bound polysaccharide (PPC-Pr) isolated from P. rimosus possessed profound antitumor activity. The findings suggest the potential therapeutic use of this compound as an antitumor agent.

Polysaccharide-K (PSK) may suppress surgical stress-induced metastasis in rat colon cancer

We previously demonstrated that hepatic ischemia and reperfusion (I/R) injury increased liver metastasis and cancer growth of RCN-H4 cells. Using a rat model of hepatic I/R-induced liver metastasis, we investigated the metastasis-suppressing effect of polysaccharide-K (PSK), a biological response modifier composed of protein-bound polysaccharide. Fischer rats underwent 60 min of 70% partial hepatic ischemia. After 60 min of reperfusion, rat colon adenocarcinoma cells (RCN-H4) were inoculated intrasplenically. PSK was administered orally before I/R, after I/R, or before and after I/R. The weights of metastatic lesions of the liver or the numbers of liver metastatic nodules were determined on day 21. The effect of PSK on angiogenesis was studied by a rat cornea model using RCN-H4 cells or a vascular endothelial growth factor (VEGF)-containing pellet and an in vitro VEGF-induced endothelial cell migration assay. PSK administration significantly (p < 0.05) suppressed the I/R-induced increase in hepatic metastasis of RCN-H4 cells. The suppression of I/R-promoted metastasis was observed irrespective of the timing of administration. Furthermore, PSK significantly suppressed angiogenesis induced by RCN-H4 cells (p < 0.05) and the VEGF pellet (p < 0.01). PSK significantly suppressed the VEGF-induced migration of vascular endothelial cells (p < 0.05). PSK may suppress metastasis induced by hepatic I/R. The suppression of angiogenesis by PSK may be one of the mechanisms of the inhibition of hepatic metastasis.

Biological mechanism and clinical effect of protein-bound polysaccharide K (KRESTIN(®)): review of development and future perspectives.

The mechanism of action of protein-bound polysaccharide K (PSK; KRESTIN®) involves the following actions: (1) recovery from immunosuppression induced by humoral factors such as transforming growth factor (TGF)-β or as a result of surgery and chemotherapy; (2) activation of antitumor immune responses including maturation of dendritic cells, correction of Th1/Th2 imbalance, and promotion of interleukin-15 production by monocytes; and (3) enhancement of the antitumor effect of chemotherapy by induction of apoptosis and inhibition of metastasis through direct actions on tumor cells. The clinical effectiveness of PSK has been demonstrated for various cancers. In patients with gastric or colorectal cancer, combined use of PSK with postoperative adjuvant chemotherapy prolongs survival, and this effect has been confirmed in multiple meta-analyses. For small-cell lung carcinoma, PSK in conjunction with chemotherapy prolongs the remission period. In addition, PSK has been shown to be effective against various other cancers, reduce the adverse effects of chemotherapy, and improve quality of life. Future studies should examine the effects of PSK under different host immune conditions and tumor properties, elucidate the mechanism of action exhibited in each situation, and identify biomarkers.

Direct inhibition of the transforming growth factor‐β pathway by protein‐bound polysaccharide through inactivation of Smad2 signaling

Transforming growth factor-β (TGF-β) is involved in the regulation of cell proliferation, differentiation, and apoptosis and is associated with epithelial-mesenchymal transition (EMT). Inhibition of the TGF-β pathway is an attractive strategy for the treatment of cancer. We recently screened for novel TGF-β inhibitors among commercially available drugs and identified protein-bound polysaccharide (PSK) as a strong inhibitor of the TGF-β-induced reporter activity of 3TP-lux, a TGF-β1-responsive luciferase reporter. Protein-bound polysaccharide is used as a non-specific immunostimulant for the treatment of gastric and colorectal cancers in Japan. The anticancer activity of this agent may involve direct regulation of growth factor production and enzyme activity in tumors in addition to its immunomodulatory effect. Although several clinical studies have shown the beneficial therapeutic effects of PSK on various types of tumors, its mechanism of action is not clear. In the present study, Western blot analysis showed that PSK suppressed the phosphorylation and nuclear localization of the Smad2 protein, thereby suggesting that PSK inhibits the Smad and MAPK pathways. Quantitative PCR analysis showed that PSK decreased the expression of several TGF-β pathway target genes. E-cadherin and vimentin immunohistochemistry showed that PSK suppressed TGF-β1-induced EMT, and FACS analysis showed that PSK inhibited the EMT-mediated generation of CD44(+) /CD24(-) cells. These data provide new insights into the mechanisms mediating the TGF-β-inhibiting activity of PSK and suggest that PSK can effectively treat diseases associated with TGF-β signaling.