Shin Kan

Mechanism of anticancer host response induced by OK-432, a streptococcal preparation, mediated by phagocytosis and Toll-like receptor 4 signaling

It has previously been reported by our group that Toll-like receptor (TLR) 4 is involved in anticancer immunity induced by OK-432, a Streptococcus-derived immunotherapeutic agent. However the detailed mechanism of the OK-432-induced immune response via TLR4 remained uncertain, because it may not be possible for OK-432, which consists of whole bacterial bodies, to bind directly to TLR4. In the current study, we conducted in vitro and in vivo experiments to investigate the hypothesis that OK-432 may first be captured and dissolved by phagocytes and that the active components released by the cells may then induce host responses via TLR4. TS-2 monoclonal antibody, which recognizes an active component of OK-432 designated OK-PSA was used in the current study. First, it was observed that OK-432-induced cytokine production by dendritic cells (DCs) and macrophages was significantly inhibited in vitro by cytochalasin B, a phagocytosis inhibitor. Immunofluorescence staining using TS-2 demonstrated that OK-432 was captured and dissolved by phagocytes. OK-PSA was detected in the supernatants derived from OK-432-treated DC culture by enzyme-linked immunosorbent assay using TS-2. Supernatants from OK-432-treated DC culture increased nuclear factor (NF)-κB activity in TLR4-expressing cells, and the increased activity was inhibited by TS-2 antibody. OK-432 itself did not activate NF-κB in these cells. In in vivo experiments, the anticancer effect of OK-432 was significantly inhibited by suppression of phagocytosis activity by cytochalasin B. In this case, the amount of OK-PSA, an active component of OK-432, in the sera was also reduced by cytochalasin B. These findings elucidated the mechanism mediated by phagocytosis and TLR4 signaling in the immune effect of OK-432.

Anti-tumor effect of an intratumoral administration of dendritic cells in combination with TS-1, an oral fluoropyrimidine anti-cancer drug, and OK-432, a streptococcal immunopotentiator: Involvement of toll-like receptor 4

The authors investigated the in vivo anti-tumor effect of intratumoral administration of bone marrow-derived dendritic cells (DCs) after chemotherapy using an oral fluoropyrimidine anti-cancer drug TS-1, and followed by immunotherapeutic agent OK-432, in two syngeneic tumor-bearing mouse models. Both in Meth-A fibrosarcoma-bearing BALB/c mice and in SCCVII-bearing C3H/HeN mice, 1 week of oral administration of TS-1 effected partial eradication of established tumors. Intratumoral injection of DCs and OK-432 caused only slight inhibition of the tumor growth. However, TS-1 administration followed by DCs and OK-432 resulted in a marked inhibition in the tumor growth and also contributed to a greater prolongation of survival. By the injection of DCs and OK-432 after TS-1 administration, a significant infiltration of immune cells, especially CD8+ T cells, was observed. Furthermore, the cytotoxic activities of tumor-infiltrating lymphocytes and draining lymph node cells against inoculated tumor cells were significantly increased by the therapy, while activities against nonspecific target cells were not. Cytotoxic memory T cells were also induced; the main effectors were MHC class I-restricted, CD8+ T cells. The same therapy was also applied to SCCVII-bearing C3H/HeJ mice in which the Toll-like receptor (TLR) 4 is mutated and its function impaired; no immunotherapeutic effect was observed in the TLR4-deficient mouse model. These findings suggest that the local DC therapy in combination with TS-1 and OK-432 may be a useful strategy for the treatment of solid tumors, and that TLR4 signaling is involved in the success of this therapy.

Fusions between dendritic cells and whole tumor cells as anticancer vaccines

Various strategies have been developed to deliver tumor-associated antigens (TAAs) to dendritic cells (DCs). Among these, the fusion of DCs and whole cancer cells can process a broad array of TAAs, including hitherto unidentified molecules, and present them in complex with MHC Class I and II molecules and in the context of co-stimulatory signals. DC-cancer cell fusions have been shown to stimulate potent antitumor immune responses in animal models. In early clinical trials, however, the antitumor effects of DC-cancer cell fusions are not as vigorous as in preclinical settings. This mini-review summarizes recent advances in anticancer vaccines based on DC-cancer cell fusions.

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.

Antitumor effect of OK-432-derived DNA: one of the active constituents of OK-432, a streptococcal immunotherapeutic agent.

OK-432 is a Streptococcus-derived immunotherapeutic agent for malignancies. Our group has tried to identify the effective components of OK-432 and has succeeded in isolating a lipoteichoic acid–related preparation designated as OK-PSA, which is a strong inducer of T helper 1 (TH1) cells, and elicits an anticancer effect via Toll-like receptor (TLR) 4. Conversely, bacterial DNA with unmethylated CpG motifs can stimulate a TH1-type host response via TLR9. The unmethylated CpG DNA contained in OK-432 may play a role in its anticancer effect. In the current study, we investigated the effect of OK-432–derived DNA (OK-DNA) in augmenting the anticancer immune response. Analysis of OK-DNA with the restriction enzymes Hpa II and MspI revealed that OK-DNA contained unmethylated CpG motifs. OK-DNA induced TH1-type cytokines such as interferon-γ, tumor necrosis factor-α, interleukin (IL)-12, and IL-18 and augmented killer cell activities in vitro on human peripheral blood mononuclear cells, whereas the methylated OK-DNA did not. Cytokines were also produced by OK-DNA–stimulated splenocytes derived from wild-type mice but not from TLR9-deficient mice. In the in vivo study, peritumoral administration of OK-DNA resulted in a significant inhibition of tumor growth in syngeneic tumor-bearing wild-type and TLR4-deficient mice but not in TLR9-deficient mice. The antitumor effect of OK-432 in TLR9-deficient mice was significantly but partially reduced compared with that in wild-type mice, whereas the effect of OK-432 was almost completely eliminated in TLR4-deficient mice. These findings suggest that unmethylated CpG DNA in OK-432 functions as an active component in OK-432–induced anticancer immunity via TLR9.

Strategies to improve the immunogenicity of anticancer vaccines based on dendritic cell/malignant cell fusions.

The rationale for fusing dendritic cells (DCs) with whole tumor cells to generate anticancer vaccines resides in the fact that the former operate as potent antigen-presenting cells, whereas the latter express a constellation of tumor-associated antigens (TAAs). Although the administration of DC/malignant cell fusions to cancer patients is safe and this immunotherapeutic intervention triggers efficient tumor-specific T-cell responses in vitro, a limited number of objective clinical responses to DC/cancer cell fusions has been reported thus far. This review discusses novel approaches to improve the immunogenicity of DC/malignant cell fusions as anticancer vaccines.

Augmentation of Antitumor Immunity by Fusions of Ethanol-Treated Tumor Cells and Dendritic Cells Stimulated via Dual TLRs through TGF-β1 Blockade and IL-12p70 Production

The therapeutic efficacy of fusion cell (FC)-based cancer vaccine generated with whole tumor cells and dendritic cells (DCs) requires the improved immunogenicity of both cells. Treatment of whole tumor cells with ethanol resulted in blockade of immune-suppressive soluble factors such as transforming growth factor (TGF)-β1, vascular endothelial growth factor, and IL-10 without decreased expression of major histocompatibility complex (MHC) class I and the MUC1 tumor-associated antigen. Moreover, the ethanol-treated tumor cells expressed “eat-me” signals such as calreticulin (CRT) on the cell surface and released immunostimulatory factors such as heat shock protein (HSP)90α and high-mobility group box 1 (HMGB1). A dual stimulation of protein-bound polysaccharides isolated from Coriolus versicolor (TLR2 agonist) and penicillin-inactivated Streptococcus pyogenes (TLR4 agonist) led human monocyte-derived DCs to produce HSP90α and multiple cytokines such as IL-12p70 and IL-10. Interestingly, incorporating ethanol-treated tumor cells and TLRs-stimulated DCs during the fusion process promoted fusion efficiency and up-regulated MHC class II molecules on a per fusion basis. Moreover, fusions of ethanol-treated tumor cells and dual TLRs-stimulated DCs (E-tumor/FCs) inhibited the production of multiple immune-suppressive soluble factors including TGF-β1 and up-regulated the production of IL-12p70 and HSP90α. Most importantly, E-tumor/FCs activated T cells capable of producing high levels of IFN-γ, resulting in augmented MUC1-specific CTL induction. Collectively, our results illustrate the synergy between ethanol-treated whole tumor cells and dual TLRs-stimulated DCs in inducing augmented CTL responses in vitro by FC preparations. The alternative system is simple and may provide a platform for adoptive immunotherapy.

Production of corticotropin-releasing factor and urocortin from human monocyte-derived dendritic cells is stimulated by commensal bacteria in intestine

AIM To examine whether commensal bacteria are a contributing cause of stress-related mucosal inflammation. METHODS Human peripheral blood monocyte-derived dendritic cells (MoDCs) were stimulated by commensal bacterial strains, including Escherichia coli, Clostridium clostridioforme, Bacteroides vulgatus (B. vulgatus), Fusobacterium varium (F. varium), and Lactobacillus delbrueckii subsp. bulgaricus. After incubation, corticotropin-releasing factor (CRF) and urocortin 1 (UCN1) mRNA in the cells was examined by real-time reverse transcription polymerase chain reaction. Supernatants from the cells were tested for CRF and UCN1 using an enzyme-linked immunosorbent assay. RESULTS Both CRF and UCN1 were significantly augmented by B. vulgatus and F. varium at both the mRNA and protein levels. In particular, B. vulgatus stimulated human MoDCs, resulting in extremely high levels of CRF and UCN1. CONCLUSION Stimulation of MoDCs by B. vulgatus and F. varium may be associated with CRF/UCN1-related intestinal disorders, such as irritable bowel syndrome and inflammatory bowel disease.

Gemcitabine enhances rituximab‐mediated complement‐dependent cytotoxicity to B cell lymphoma by CD20 upregulation

Although rituximab, a chimeric monoclonal antibody that specifically binds to CD20, has significantly improved the prognosis for diffuse large B cell lymphoma (DLBCL), one‐third of DLBCL patients demonstrate resistance to rituximab or relapse after rituximab treatment. Thus, a novel approach to rituximab‐based treatment is likely to be required to improve the efficacy of DLBCL treatment. As complement dependent cytotoxicity (CDC) is a key mechanism mediating rituximabs tumoricidal activity, rituximab binding to CD20 on tumor cells is a critical factor for effective rituximab‐based treatments against DLBCL. We found that gemcitabine (GEM), but not lenalidomide (LEN) or azacitidine (AZA), can upregulate CD20 expression in TK and KML‐1 cells, two human DLBCL cell lines. Treatment of TK and KML‐1 cells with GEM enhanced CD20 expression at both the mRNA and protein levels. CD20 upregulation by GEM treatment was accompanied by increased rituximab binding to CD20. In TK cells, GEM treatment synergistically increased rituximab‐mediated CDC activity in a dose‐dependent manner. In KML cells, GEM treatment also induced upregulation of complement regulatory proteins, possibly leading to resistance to CDC. Treatment with LEN, a drug that did not upregulate CD20, did not enhance rituximab‐mediated CDC activity. GEM treatment activated nuclear factor‐kappa B (NF‐kB) signaling in these cells. Furthermore, a specific inhibitor to NF‐kB suppressed GEM‐induced CD20 upregulation, indicating that GEM‐induced NF‐kB activation is closely associated with CD20 upregulation. These results suggest that when used in combination, GEM might enhance the antitumor efficacy of rituximab against DLBCL due to its unique ability to upregulate CD20.

Up-regulation of HER2 by gemcitabine enhances the antitumor effect of combined gemcitabine and trastuzumab emtansine treatment on pancreatic ductal adenocarcinoma cells

BackgroundAlthough pancreatic ductal adenocarcinomas (PDAs) widely express HER2, the expression level is generally low. If HER2 expression in PDA cells could be enhanced by treatment with a given agent, then combination therapy with that agent and trastuzumab emtansine (T-DM1), a chemotherapeutic agent that is a conjugate of trastuzumab, might lead to significant antitumor effects against PDA.MethodsCell proliferation was examined by spectrophotometry. HER2 expression was examined by flow cytometry, immunoblot and quantitative reverse transcription polymerase chain reaction. T-DM1 binding to cells was examined by flow cytometry and enzyme-linked immunosorbent assay.ResultsOut of 5 tested human PDA cell lines, including MIA PaCa-2, three showed increases in HER2 expression after gemcitabine (GEM) treatment. The binding of T-DM1 to GEM-treated MIA PaCa-2 cells was higher than to untreated MIA PaCa-2 cells. Treatment with GEM and T-DM1 showed synergic cytotoxic effects on MIA PaCa-2 cells in vitro. Cells in the G2M phase of the cell cycle were retained after GEM treatment and showed higher levels of HER2 expression, possibly contributing to the synergic effect of GEM and T-DM1.ConclusionsCombined treatment with GEM and T-DM1 might confer a potent therapeutic modality against PDA as a result of GEM-mediated HER2 up-regulation.