Protein-bound polysaccharide (PSK) induces cytotoxic activity in the NKL human natural killer cell line

Dose matters: Direct killing or immunoregulatory effects of natural polysaccharides in cancer treatment

Polysaccharides from natural resources possess anti-tumor activities for decades, but the efficacy of polysaccharides as the adjuvant drugs for cancer treatment at prescribed doses remains open for debate. In this review, molecular mechanisms involved in direct killing effects of polysaccharides, including apoptosis, cell cycle arrest and mitochondria/DNA damage were described. However, the concentrations/doses used to reach the direct killing effects are too high to be applicable. Polysaccharides can also exert anti-tumor effects through immunoregulation at lower doses, and the effects of polysaccharides on natural killer cells, dendritic cells and other lymphocytes for tumor destruction, along with the receptor recognition and downstream signaling pathways, were delineated. Unfortunately, the prescribed doses of polysaccharides are too low to stimulate immunoresponse, resulting in the failure of some clinical trials. Therefore, understanding the sophisticated mechanisms of the immunoregulatory function of natural polysaccharides with refined doses for clinical use will help the standardization of traditional medicine.

NK cell-based immunotherapy for malignant diseases

Natural killer (NK) cells play critical roles in host immunity against cancer. In response, cancers develop mechanisms to escape NK cell attack or induce defective NK cells. Current NK cell-based cancer immunotherapy aims to overcome NK cell paralysis using several approaches. One approach uses expanded allogeneic NK cells, which are not inhibited by self histocompatibility antigens like autologous NK cells, for adoptive cellular immunotherapy. Another adoptive transfer approach uses stable allogeneic NK cell lines, which is more practical for quality control and large-scale production. A third approach is genetic modification of fresh NK cells or NK cell lines to highly express cytokines, Fc receptors and/or chimeric tumor-antigen receptors. Therapeutic NK cells can be derived from various sources, including peripheral or cord blood cells, stem cells or even induced pluripotent stem cells (iPSCs), and a variety of stimulators can be used for large-scale production in laboratories or good manufacturing practice (GMP) facilities, including soluble growth factors, immobilized molecules or antibodies, and other cellular activators. A list of NK cell therapies to treat several types of cancer in clinical trials is reviewed here. Several different approaches to NK-based immunotherapy, such as tissue-specific NK cells, killer receptor-oriented NK cells and chemically treated NK cells, are discussed. A few new techniques or strategies to monitor NK cell therapy by non-invasive imaging, predetermine the efficiency of NK cell therapy by in vivo experiments and evaluate NK cell therapy approaches in clinical trials are also introduced.

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.

Natural killer cell lines in tumor immunotherapy

Natural killer (NK) cells are considered to be critical players in anticancer immunity. However, cancers are able to develop mechanisms to escape NK cell attack or to induce defective NK cells. Current NK cell-based cancer immunotherapy is aimed at overcoming NK cell paralysis through several potential approaches, including activating autologous NK cells, expanding allogeneic NK cells, usage of stable allogeneic NK cell lines and genetically modifying fresh NK cells or NK cell lines. The stable allogeneic NK cell line approach is more practical for quality-control and large-scale production. Additionally, genetically modifying NK cell lines by increasing their expression of cytokines and engineering chimeric tumor antigen receptors could improve their specificity and cytotoxicity. In this review, NK cells in tumor immunotherapy are discussed, and a list of therapeutic NK cell lines currently undergoing preclinical and clinical trials of several kinds of tumors are reviewed.

Immunomodulatory Polysaccharide from Chlorophytum borivilianum Roots

Chlorophytum borivilianum Santapau & Fernandes (Liliaceae) is an ayurvedic Rasayana herb with immunostimulating properties. The polysaccharide fraction (CBP) derived from hot water extraction of C. borivilianum (CB), comprising of ∼31% inulin-type fructans and ∼25% acetylated mannans (of hot water-soluble extract), was evaluated for its effect on natural killer (NK) cell activity (in vitro). Human peripheral blood mononuclear cells (PBMCs), isolated from whole blood on a Ficoll-Hypaque density gradient, were tested in the presence or absence of varying concentrations of each C. borivilianum fraction for modulation of NK cell cytotoxic activity toward K562 cells. Preliminary cytotoxicity evaluation against P388 cells was performed to establish non-cytotoxic concentrations of the different fractions. Testing showed the observed significant stimulation of NK cell activity to be due to the CBP of C. borivilianum. Furthermore, in vivo evaluation carried out on Wistar strain albino rats for humoral response to sheep red blood cells (SRBCs) and immunoglobulin-level determination using enzyme-linked immunosorbent assay (ELISA), exhibited an effectiveness of C. borivilianum aqueous extract in improving immune function. Present results provide useful information for understanding the role of CBP in modulating immune function.

The impact of redox and thiol status on the bone marrow: Pharmacological intervention strategies

Imbalances in cancer cell redox homeostasis provide a platform for new opportunities in the development of anticancer drugs. The control of severe dose-limiting toxicities associated with redox regulation, including myelosuppression and immunosuppression, remains a challenge. Recent evidence implicates a critical role for redox regulation and thiol balance in pathways that control myeloproliferation, hematopoietic progenitor cell mobilization, and immune response. Hematopoietic stem cell (HSC) self-renewal and differentiation are dependent upon levels of intracellular reactive oxygen species (ROS) and niche microenvironments. Redox status and the equilibrium of free thiol:disulfide couples are important in modulating immune response and lymphocyte activation, proliferation and differentiation. This subject matter is the focus of the present review. The potential of redox modulating chemotherapeutics as myeloproliferative and immunomodulatory agents is also covered.

Protein-bound polysaccharide-K (PSK) directly enhanced IgM production in the human B cell line BALL-1

Protein-bound polysaccharide-K (PSK) prepared from the basidiomycete Coriolus versicolor has been used as a biological response modifier for the treatment of cancer patients. Many studies describing the immunomodulatory effects and direct anti-cancer effects of PSK have been reported. Most of studies describing the immunomodulatory effects focused on cellular immunity, although there were several studies which focused on humoral immunity where PSK was shown to be able to induce antibody production in vivo. However, even in these humoral immunity studies, it is thought that the enhancement of antibody production was due to the activation of cellular immunity. In this study, we investigated the direct effect of PSK on B cells and discovered that PSK was able to enhance IgM production in the human B cell line BALL-1. Furthermore, BALL-1 was shown to have the characteristic features of B-1a cells, which are independently involved in the primary immune response. These results show that there is a possibility that PSK directly acts on B cells and simultaneously enhances both humoral immunity and cellular immunity.

The immunomodulator PSK induces in vitro cytotoxic activity in tumour cell lines via arrest of cell cycle and induction of apoptosis

BACKGROUND

Protein-bound polysaccharide (PSK) is derived from the CM-101 strain of the fungus Coriolus versicolor and has shown anticancer activity in vitro and in in vivo experimental models and human cancers. Several randomized clinical trials have demonstrated that PSK has great potential in adjuvant cancer therapy, with positive results in the adjuvant treatment of gastric, esophageal, colorectal, breast and lung cancers. These studies have suggested the efficacy of PSK as an immunomodulator of biological responses. The precise molecular mechanisms responsible for its biological activity have yet to be fully elucidated.

METHODS

The in vitro cytotoxic anti-tumour activity of PSK has been evaluated in various tumour cell lines derived from leukaemias, melanomas, fibrosarcomas and cervix, lung, pancreas and gastric cancers. Tumour cell proliferation in vitro was measured by BrdU incorporation and viable cell count. Effect of PSK on human peripheral blood lymphocyte (PBL) proliferation in vitro was also analyzed. Studies of cell cycle and apoptosis were performed in PSK-treated cells.

RESULTS

PSK showed in vitro inhibition of tumour cell proliferation as measured by BrdU incorporation and viable cell count. The inhibition ranged from 22 to 84%. Inhibition mechanisms were identified as cell cycle arrest, with cell accumulation in G0/G1 phase and increase in apoptosis and caspase-3 expression. These results indicate that PSK has a direct cytotoxic activity in vitro, inhibiting tumour cell proliferation. In contrast, PSK shows a synergistic effect with IL-2 that increases PBL proliferation.

CONCLUSION

These results indicate that PSK has cytotoxic activity in vitro on tumour cell lines. This new cytotoxic activity of PSK on tumour cells is independent of its previously described immunomodulatory activity on NK cells.

Efficacy of adjuvant immunochemotherapy with polysaccharide K for patients with curative resections of gastric cancer

Non-specific immunopotentiators, such as polysaccharide K (PSK), also known as OK-432, induce anti-tumor effects via immunological responses. The efficacy of combination immunochemotherapy using these immunopotentiators has been examined by multiple previous studies. The survival benefits of immunochemotherapy for patients with curative resections of gastric cancers are not widely accepted. To clarify this issue, we performed a meta-analysis to evaluate the effect of immunochemotherapy on survival in patients with curative resections of gastric cancer. For this study, we compared the results of chemotherapy and immunotherapy using the biological response modifier PSK as an immunopotentiator. The meta-analysis included 8,009 patients from eight randomized controlled trials after central randomization. The overall hazard ratio for eligible patients was 0.88 (95% confidence interval, 0.79-0.98; P = 0.018) with no significant heterogeneity [chi (2)(8) for heterogeneity = 11.7; P = 0.16]. The results of this meta-analysis suggest that adjuvant immunochemotherapy with PSK improves the survival of patients after curative gastric cancer resection.

Efficacy of adjuvant immunochemotherapy with polysaccharide K for patients with curatively resected colorectal cancer: a meta-analysis of centrally randomized controlled clinical trials

The benefits of immunochemotherapy employing the biological response modifier polysaccharide K (PSK) for patients with curatively resected colorectal cancer was reassessed by means of a meta-analysis of data with center randomization from 1,094 patients enrolled in three clinical trials. In all three trials, patients were followed up for at least 5 years after surgery and enrollment of the last patient and outcomes for standard chemotherapy were compared with those for chemotherapy plus PSK. The endpoints were overall survival and disease-free survival; and intent-to-treat analysis was performed without patient exclusion. Data were analyzed using the weighted average of the individual log hazard ratios. The overall survival risk ratio for all eligible patients was 0.71 (95% confidence interval (CI) : 0.55-0.90; P=0.006), and the disease-free survival risk ratio was 0.72 (95% CI: 0.58-0.90; P=0.003). The results of this meta-analysis suggest that adjuvant immunochemotherapy with PSK can improve both survival and disease-free survival of patients with curatively resected colorectal cancer.

Identification of the protein components of protein-bound polysaccharide (PSK) that interact with NKL cells

We identified the protein components of a protein-bound polysaccharide (PSK) that are responsible for the biological function of this immunomodulator in its interaction with NKL cells, an NK-derived cell line previously known to be activated by this extract, obtained from the basidiomycete Coriolus versiocolor. In addition, we show that PSK protein interacts with NKL cells through a different receptor from that used by IL-2. This was deduced from the different molecular weights of the PSK/NKL and IL-2/NKL receptor complexes. We show that PSK is composed of a highly glycosylated 12-kDa protein. Protein-bound polysaccharide interacts in vitro with an NKL receptor of approximately 48 kDa, whereas IL-2 shows a similar interaction with NKL receptor proteins of approximately 64 and 75 kDa. Our results may explain why PSK and IL-2 use completely different intracellular routes for their biological activities in NKL cells-i.e., regulating different PKC isozymes, mitogen-activated protein kinases, and nuclear transcription factors.

Protein-bound polysaccharide K induced apoptosis of the human Burkitt lymphoma cell line, Namalwa

Protein-bound polysaccharide K (PSK), which is derived from mushrooms belonging to the Basidiomycetes genus, has been clinically used as a biological response modifier (BRM) for the treatment of epithelial cancer patients in Japan and other Asian countries. There are a large number of studies on the biological activities of PSK as regards the activation of immunocompetent cells and the potential cytotoxic effects on epithelial cancer cells. However, only a few studies have been conducted to see the direct cytotoxic effects of PSK on hematological malignant cells. In this study, we investigated whether or not PSK was able to induce cellular apoptosis in hematological malignant cells. PSK was found to inhibit cell growth, and induced subsequent cellular apoptosis in the Burkkit lymphoma cell line (Namalwa), out of 33 hematological malignant cell lines tested. This PSK-induced apoptosis was neutralized by the addition of galactose to the culture medium, whereas apoptosis was augmented by treatment with beta-galactosidase, indicating the inhibitory involvement of galactose in the mechanism of action. These results provide initial evidence of the direct cytotoxic activity of PSK in a hematological malignant cell line, thus encouraging further molecular-level study of PSK-mediated apoptosis in malignant hematological cells.

Adjuvant immunochemotherapy with oral Tegafur/Uracil plus PSK in patients with stage II or III colorectal cancer: a randomised controlled study

Intravenous fluorouracil and leucovorin is the standard adjuvant treatment for stage III colon cancer. However, oral adjuvant chemotherapy is attractive because it has low toxicity and greater convenience. We investigated the benefits of oral protein-bound polysaccharide K (PSK) with tegafur/uracil (UFT) as an adjuvant in stage II and III colorectal cancer. Patients were assigned to groups that received either 3 g PSK plus 300 mg UFT, or 300 mg UFT alone orally each day for a 2-year period following intravenous mitomycin C. Of 207 registered patients, 205 with stage II (n=123) or III (n=82) were analysed. The 5-year disease-free survival was 73.0% (95% CI 65.6-80.4%) with PSK (n=137) and 58.8% (95% CI 47.1-70.5%) in the controls (n=68) (P=0.016). Polysaccharide K reduced the recurrence by 43.6% (95% CI 4.5-66.7%) and mortality by 40.2% (95% CI -12.5 to 68.3%). The 5-year survival was 81.8% (95% CI 75.3-88.2%) in the PSK group and 72.1% (95% CI 61.4-82.7%) in the control group (P=0.056). In stage III patients, disease-free and overall survivals in patients receiving PSK were increased significantly: 60.0% (95% CI 47.1-72.9%) and 74.6% (95% CI 63.0-86.1%) in the PSK group as compared with 32.1% (95% CI 14.8-49.4%) and 46.4% (95% CI 28.0-64.9%) in the controls (P=0.002 and 0.003, respectively). Polysaccharide K prevented recurrence, particularly lung metastases (P=0.02; odds ratio 0.27; 95% CI 0.09-0.77). In the models, the presence of regional metastases (relative risk, 2.973; 95% CI 1.712-5.165; P<0.001), omission of PSK (relative risk, 2.106; 95% CI 1.221-3.633; P=0.007), and higher primary tumour (relative risk, 4.398; 95% CI 1.017-19.014; P=0.047) were each significant indicators of recurrence. Adverse effects were mild and compliance was good. Oral PSK with UFT reduced recurrence in stage II and III colorectal cancer, and increased survival in stage III.

Regulation of perioperative immunological changes following laparotomy: effects of biological response modifier (BRM) on surgical stress

Immune responses have been reported to decline following surgical stress, leading to an increased susceptibility to infection or to the growth of tumors. In this study, we report that pre-operative treatment with the biological response modifier (BRM) polysaccharide Kureha (PSK) can inhibit the decline of immunocompetence during the perioperative period. BALB/c mice were laparotomized, the intestinal tracts were exposed to room air for 1.5 h, and then the abdomens were closed. Six hours after the operation, the spleen and serum were collected. The concentrations of IL-6 in the serum and of IFNgamma and IL-4 in the supernatant of splenocyte cultures were measured. In the surgical stress group that received surgical stress and the PSK treatment, the serum IL-6 concentration was significantly elevated in the group with surgical stress. PSK treatment controlled the stress-induced elevation. IFNgamma concentrations were measured in the supernatant of Concanavalin A (Con A) stimulated splenocyte cultures. It was lower in the group with surgical stress than in the cultures derived from the non-treated group. The IFNgamma concentration in the group with surgical stress plus PSK treatment was significantly higher than the level in the group with surgical stress alone. The IL-4 concentration was significantly lower in the surgical stress group than in the control group, however, the concentration tended to be higher in the surgical stress plus PSK treatment group than in the group with surgical stress alone. The IFNgamma/IL-4 ratio in the group with surgical stress was lower than the ratio in the non-treated group. The ratio in the group with surgical stress plus PSK treatment was significantly higher than the ratio in the group with surgical stress alone. These results suggest that PSK restores the abnormality of the biological responses induced by surgical stress and corrects the reduced Th1/Th2 cytokine balance to a normal level.