CpG oligonucleotides elicit antitumor responses in a human melanoma NOD/SCID xenotransplantation model

CpG Oligodeoxynucleotides for Anticancer Monotherapy from Preclinical Stages to Clinical Trials

CpG oligodeoxynucleotides (CpG ODNs), the artificial versions of unmethylated CpG motifs that were originally discovered in bacterial DNA, are demonstrated not only as potent immunoadjuvants but also as anticancer agents by triggering toll-like receptor 9 (TLR9) activation in immune cells. TLR9 activation triggered by CpG ODN has been shown to activate plasmacytoid dendritic cells (pDCs) and cytotoxic T lymphocytes (CTLs), enhancing T cell-mediated antitumor immunity. However, the extent of antitumor immunity carried by TLR agonists has not been optimized individually or in combinations with cancer vaccines, resulting in a decreased preference for TLR agonists as adjuvants in clinical trials. Although various combination therapies involving CpG ODNs have been applied in clinical trials, none of the CpG ODN-based drugs have been approved by the FDA, owing to the short half-life of CpG ODNs in serum that leads to low activation of natural killer cells (NK cells) and CTLs, along with increases of pro-inflammatory cytokine productions. This review summarized the current innovation on CpG ODNs that are under clinical investigation and explored the future direction for CpG ODN-based nanomedicine as an anticancer monotherapy.

Intestinal epithelial glucocorticoid receptor promotes chronic inflammation-associated colorectal cancer

Synthetic immunosuppressive glucocorticoids (GCs) are widely used to control inflammatory bowel disease (IBD). However, the impact of GC signaling on intestinal tumorigenesis remains controversial. Here, we report that intestinal epithelial GC receptor (GR), but not whole intestinal tissue GR, promoted chronic intestinal inflammation-associated colorectal cancer in both humans and mice. In patients with colorectal cancer, GR was enriched in intestinal epithelial cells and high epithelial cell GR levels were associated with poor prognosis. Consistently, intestinal epithelium–specific deletion of GR (GR iKO) in mice increased macrophage infiltration, improved tissue recovery, and enhanced antitumor response in a chronic inflammation–associated colorectal cancer model. Consequently, GR iKO mice developed fewer and less advanced tumors than control mice. Furthermore, oral GC administration in the early phase of tissue injury delayed recovery and accelerated the formation of aggressive colorectal cancers. Our study reveals that intestinal epithelial GR signaling repressed acute colitis but promoted chronic inflammation–associated colorectal cancer. Our study suggests that colorectal epithelial GR could serve as a predictive marker for colorectal cancer risk and prognosis. Our findings further suggest that, although synthetic GC treatment for IBD should be used with caution, there is a therapeutic window for GC therapy during colorectal cancer development in immunocompetent patients.

Gliotoxin Targets Nuclear NOTCH2 in Human Solid Tumor Derived Cell Lines In Vitro and Inhibits Melanoma Growth in Xenograft Mouse Model

Deregulation of NOTCH2 signaling is implicated in a wide variety of human neoplasias. The current concept of targeting NOTCH is based on using gamma secretase inhibitors (GSI) to regulate the release of the active NOTCH intracellular domain. However, the clinical outcome of GSI remains unsatisfactory. Therefore we analyzed human solid tumor derived cell lines for their nuclear NOTCH activity and evaluated the therapeutic potential of the NOTCH2 transactivation inhibitor gliotoxin in comparison to the representative GSI DAPT. Electrophoretic mobility shift assays (EMSA) were used as a surrogate method for the detection of NOTCH/CSL transcription factor complexes. The effect of gliotoxin on cell viability and its clinical relevance was evaluated in vitro and in a melanoma xenograft mouse model. Cell lines derived from melanoma (518A2), hepatocellular carcinoma (SNU398, HCC-3, Hep3B), and pancreas carcinoma (PANC1) express high amounts of nuclear NOTCH2. Gliotoxin efficiently induced apoptosis in these cell lines whereas the GSI DAPT was ineffective. The specificity of gliotoxin was demonstrated in the well differentiated nuclear NOTCH negative cell line Huh7, which was resistant to gliotoxin treatment in vitro. In xenotransplanted 518A2 melanomas, a single day dosing schedule of gliotoxin was well tolerated without any study limiting side effects. Gliotoxin significantly reduced the tumor volume in early (83 mm³ vs. 115 mm³, p = 0.008) as well as in late stage (218 mm³ vs. 576 mm³, p = 0.005) tumor models. In conclusion, NOTCH2 appears to be a key target of gliotoxin in human neoplasias and gliotoxin deserves further evaluation as a potential therapeutic agent in cancer management.

c-Src Suppresses Dendritic Cell Antitumor Activity via T Cell Ig and Mucin Protein-3 Receptor

The enhanced expression of T cell Ig and mucin protein-3 (TIM-3) on tumor-associated dendritic cells (DCs) attenuates antitumor effects of DNA vaccines. To identify a potential target (or targets) for reducing TIM-3 expression on tumor-associated DCs, we explored the molecular mechanisms regulating TIM-3 expression. In this study, we have identified a novel signaling pathway (c-Src→Bruton's tyrosine kinase→transcription factors Ets1, Ets2, USF1, and USF2) necessary for TIM-3 upregulation on DCs. Both IL-10 and TGF-β, which are produced in the tumor microenvironment, upregulated TIM-3 expression on DCs via this pathway. Suppressed expression of c-Src or downstream Bruton's tyrosine kinase, Ets1, Ets2, USF1, or USF2 blocked IL-10- and TGF-β-induced TIM-3 upregulation on DCs. Notably, in vivo knockdown of c-Src in mice reduced TIM-3 expression on tumor-associated DCs. Furthermore, adoptive transfer of c-Src-silenced DCs in mouse tumors enhanced the in vivo antitumor effects of immunostimulatory CpG DNA; however, TIM-3 overexpression in c-Src-silenced DCs blocked this effect. Collectively, our data reveal the molecular mechanism regulating TIM-3 expression in DCs and identify c-Src as a target for improving the efficacy of nucleic acid-mediated anticancer therapy.

CpG oligodeoxynucleotide-loaded PAMAM dendrimer-coated magnetic nanoparticles promote apoptosis in breast cancer cells

One major application of nanotechnology in cancer treatment involves designing nanoparticles to deliver drugs, oligonucleotides, and genes to cancer cells. Nanoparticles should be engineered so that they could target and destroy tumor cells with minimal damage to healthy tissues. This research aims to develop an appropriate and efficient nanocarrier, having the ability of interacting with and delivering CpG-oligodeoxynucleotides (CpG-ODNs) to tumor cells. CpG-ODNs activate Toll-like receptor 9 (TLR9), which can generate a signal cascade for cell death. In our study, we utilized three-layer magnetic nanoparticles composed of a Fe3O4 magnetic core, an aminosilane (APTS) interlayer and a cationic poly(amidoamine) (PAMAM) dendrimer. This will be a novel targeted delivery system to enhance the accumulation of CpG-ODN molecules in tumor cells. The validation of CpG-ODN binding to DcMNPs was performed using agarose gel electrophoresis, UV-spectrophotometer, XPS analyses. Cytotoxicity of conjugates was assessed in MDA-MB231 and SKBR3 cancer cells based on cell viability by XTT assay and flow cytometric analysis. Our results indicated that the synthesized DcMNPs having high positive charges on their surface could attach to CpG-ODN molecules via electrostatic means. These nanoparticles with the average sizes of 40±10nm bind to CpG-ODN molecules efficiently and induce cell death in MDA-MB231 and SKBR3 tumor cells and could be considered a suitable targeted delivery system for CpG-ODN in biomedical applications. The magnetic core of these nanoparticles represents a promising option for selective drug targeting as they can be concentrated and held in position by means of an external magnetic field.

Combining miR-10b-Targeted Nanotherapy with Low-Dose Doxorubicin Elicits Durable Regressions of Metastatic Breast Cancer

The therapeutic promise of microRNA (miRNA) in cancer has yet to be realized. In this study, we identified and therapeutically exploited a new role for miR-10b at the metastatic site, which links its overexpression to tumor cell viability and proliferation. In the protocol developed, we combined a miR-10b-inhibitory nanodrug with low-dose anthracycline to achieve complete durable regressions of metastatic disease in a murine model of metastatic breast cancer. Mechanistic investigations suggested a potent antiproliferative, proapoptotic effect of the nanodrug in the metastatic cells, potentiated by a cell-cycle arrest produced by administration of the low-dose anthracycline. miR-10b was overexpressed specifically in cells with high metastatic potential, suggesting a role for this miRNA as a metastasis-specific therapeutic target. Taken together, our results implied the existence of pathways that regulate the viability and proliferation of tumor cells only after they have acquired the ability to grow at distant metastatic sites. As illustrated by miR-10b targeting, such metastasis-dependent apoptotic pathways would offer attractive targets for further therapeutic exploration.

Glutathione and Bcl-2 targeting facilitates elimination by chemoradiotherapy of human A375 melanoma xenografts overexpressing bcl-xl, bcl-2, and mcl-1

BACKGROUND

Bcl-2 is believed to contribute to melanoma chemoresistance. However, expression of Bcl-2 proteins may be different among melanomas. Thus correlations among expression of Bcl-2-related proteins and in vivo melanoma progression, and resistance to combination therapies, was investigated.

METHODS

Human A375 melanoma was injected s.c. into immunodeficient nude mice. Protein expression was studied in tumor samples obtained by laser microdisection. Transfection of siRNA or ectopic overexpression were applied to manipulate proteins which are up- or down-regulated, preferentially, during melanoma progression. Anti-bcl-2 antisense oligonucleotides and chemoradiotherapy (glutathione-depleting agents, paclitaxel protein-binding particles, daunorubicin, X rays) were administered in combination.

RESULTS

In vivo A375 cells down-regulated pro-apoptotic bax expression; and up-regulated anti-apoptotic bcl-2, bcl-xl, and mcl-1, however only Bcl-2 appeared critical for long-term tumor cell survival and progression in vivo. Reduction of Bcl-2, combined with partial therapies, decreased melanoma growth. But only Bcl-2 targeting plus the full combination of chemoradiotherapy eradicated A375 melanoma, and led to long-term survival (> 120 days) without recurrence in 80% of mice. Tumor regression was not due to immune stimulation. Hematology and clinical chemistry data were within accepted clinical toxicities.

CONCLUSION

Strategies to target Bcl-2, may increase the effectiveness of antitumor therapies against melanomas overexpressing Bcl-2 and likely other Bcl-2-related antiapoptotic proteins.

NK1.1+ cells mediate the antitumor effects of a dual Toll-like receptor 7/8 agonist in the disseminated B16-F10 melanoma model

Innate immune stimulation with Toll-like receptor (TLR) agonists is a proposed modality for immunotherapy of melanoma. Here, a TLR7/8 agonist, 3M-011, was used effectively as a single systemic agent against disseminated mouse B16-F10 melanoma. The investigation of the mechanism of antitumor action revealed that the agonist had no direct cytotoxic effects on tumor cells tested in vitro. In addition, 3M-011 retained its effectiveness in scid/B6 mice and scid/NOD mice, eliminating the requirement for T and B cells, but lost its activity in beige (bg/bg) and NK1.1-immunodepleted mice, suggesting a critical role for natural killer (NK) cells in the antitumor response. NK cytotoxicity was enhanced in vivo by the TLR7/8 agonist; this activation was long lasting, as determined by sustained expression of the activation marker CD69. Also, in human in vitro studies, 3M-011 potentiated NK cytotoxicity. TLR7/8-mediated NK-dependent antitumor activity was retained in IFN-alpha/beta receptor-deficient as well as perforin-deficient mice, while depletion of IFN-gamma significantly decreased the ability of 3M-011 to delay tumor growth. Thus, IFN-gamma-dependent functions of NK cell populations appear essential for cancer immunotherapy with TLR7/8 agonists.

Therapeutic applications of synthetic CpG oligodeoxynucleotides as TLR9 agonists for immune modulation

Vertebrate toll-like receptors (TLRs) sense invading pathogens by recognizing bacterial and viral structures and, as a result, activate innate and adaptive immune responses. Ten human functional TLRs have been reported so far; three of these (TLR7, 8, and 9) are expressed in intracellular compartments and respond to single-stranded nucleic acids as natural ligands. The pathogen structure selectively recognized by TLR9 in bacterial or viral DNA was identified to be CpG dinucleotides in specific sequence contexts (CpG motifs). Short phosphorothioate-stabilized oligodeoxynucleotides (ODNs) containing such motifs are used as synthetic TLR9 agonists, and different classes of ODN TLR9 agonists have been identified with distinct immune modulatory profiles. The TLR9-mediated activation of the vertebrate immune system suggests using such TLR9 agonists as effective vaccine adjuvants for infectious disease, and for the treatment of cancer and asthma/allergy. Immune activation by CpG ODNs has been demonstrated to be beneficial in animal models as a vaccine adjuvant and for the treatment of a variety of viral, bacterial, and parasitic diseases. Antitumor activity of CpG ODNs has also been established in numerous mouse models. In clinical vaccine trials in healthy human volunteers or in immunocompromised HIV-infected patients, CpG ODNs strongly enhanced vaccination efficiency. Most encouraging results in the treatment of cancers have come from human phase I and II clinical trials using CpG ODNs as a tumor vaccine adjuvant, monotherapy, or in combination with chemotherapy. Therefore, CpG ODNs represent targeted immune modulatory drugs with a broad range of potential applications.

Macrophages are essential for antitumour effects against weakly immunogenic murine tumours induced by class B CpG-oligodeoxynucleotides

We explored the mechanisms of class B CpG-oligodeoxynucleotide-induced antitumour effects against weakly immunogenic tumours. Treatment with CpG-oligodeoxynucleotide 1826 (CpG) induced similar antitumour effects in B16 melanoma-bearing immunocompetent C57BL/6 mice and T-cell-deficient severe combined immunodeficient (SCID) mice, and NXS2 neuroblastoma-bearing T-cell-depleted A/J mice. Both macrophages (Mphi) and natural killer (NK) cells from CpG-treated C57BL/6 mice could mediate cytotoxicity in vitro, suggesting that these cell types might control tumour growth in vivo. However, CpG treatment of SCID/beige mice or T-cell-depleted and NK-cell-depleted A/J mice still induced antitumour effects in vivo, arguing against a major role of NK cells in the antitumour effects of CpG in the absence of T cells. In contrast, CpG treatment of interferon-gamma knockout (IFN-gamma(-/-)) C57BL/6 mice resulted in no antitumour effects in vivo and no Mphi-mediated tumoristasis in vitro despite unaltered cytolytic function of NK cells in vitro. Moreover, Mphi inactivation by silica substantially reduced CpG-induced suppression of tumour growth in vivo, revealing an important role of Mphi in CpG-induced antitumour effects. The in vitro tumouritoxicity by CpG-stimulated Mphi (CpG-Mphi) correlated with tumour cell mitochondria dysfunction and involved nitric oxide (NO), tumour necrosis factor-alpha (TNF-alpha) and IFN-gamma, whereas interleukin-1alpha (IL-1alpha), IL-1beta, IFN-alpha, TNF-related apoptosis-inducing ligand and Fas ligand played insignificant roles in CpG-Mphi tumouritoxicity. Taken together, our results indicate that the growth control of weakly immunogenic tumours during CpG-immunotherapy is mediated predominantly by Mphi, rather than T cells or NK cells.

In vivo control of acute lymphoblastic leukemia by immunostimulatory CpG oligonucleotides

Despite considerable success in treating newly diagnosed childhood acute lymphoblastic leukemia (ALL), relapsed disease remains a significant clinical challenge. Using a NOD/SCID mouse xenograft model, we report that immunostimulatory DNA oligonucleotides containing CpG motifs (CpG ODNs) stimulate significant immune activity against primary human ALL cells in vivo. The administration of CpG ODNs induced a significant reduction in systemic leukemia burden, mediated continued disease control, and significantly improved survival of mice with established human ALL. The death of leukemia cells in vivo was independent of the ability of ALL cells to respond directly to CpG ODNs and correlated with the production of IL-12p70, IFN-α, and IFN-γ by the host. In addition, depletion of natural killer cells by anti–asialo-GM1 treatment significantly reduced the in vivo antileukemic activity of CpG ODN. This antileukemia effect was not limited to the xenograft model because natural killer cell–dependent killing of ALL by human peripheral blood mononuclear cells (PBMCs) was also increased by CpG ODN stimulation. These results suggest that CpG ODNs have potential as therapeutic agents for the treatment of ALL.

Systemic Bcl-2 antisense oligodeoxynucleotide in combination with cisplatin cures EBV+ nasopharyngeal carcinoma xenografts in SCID mice

Nasopharyngeal carcinoma (NPC) is causally linked to Epstein-Barr virus (EBV), and the EBV oncoprotein, latent membrane protein 1 (LMP-1), is expressed in the majority of NPCs. LMP-1 upregulates antiapoptotic genes, including bcl-2, and Bcl-2 protein is overexpressed in NPC. Given the antiapoptotic and chemoprotective effects of Bcl-2, it represents a rational therapeutic target in NPC. We have investigated the antitumor and chemosensitizing effects of the Bcl-2 antisense oligodeoxynucleotide G3139 (oblimersen, Genasense) in NPC. For these studies, we used the C666-1 line, a stably infected NPC-derived line that co-expresses LMP-1 and Bcl-2. We have shown that G3139 treatment of C666-1 in vitro caused sequence-dependent suppression of Bcl-2 protein, inhibition of cell growth and enhanced sensitivity to cisplatin (CDDP), as measured by increased antiproliferative and apoptotic effects. In vivo, G3139 treatment (25 mg/kg every 3 days x 5 doses) delayed engraftment and significantly inhibited growth of established C666-1 xenografts in SCID mice compared to control oligo-treated animals. However, G3139 alone did not prevent engraftment or cure established tumors in any animals. In contrast, G3139 treatment (25 mg/kg every 3 days x 5 starting on day 7) in combination with CDDP (8 mg/kg on day 14) completely abrogated tumor engraftment in 80% of animals compared to CDDP (0%) or CDDP + control oligo (0%). When treatment was delayed until tumor was established, G3139 in combination with CDDP significantly inhibited tumor growth compared to CDDP or CDDP + control oligo, and cured 69% animals with established tumors. No animals treated with G3139, CDDP or CDDP + control oligo were cured. Tumor burden and response to treatment correlated with EBV DNA load in serum, measured by real-time PCR. Western blots of tumor extracts obtained during oligo treatment showed that Bcl-2 levels were significantly decreased in G3139-treated animals. Our studies have demonstrated that the Bcl-2 antisense oligodeoxynucleotide, G3139, has proapoptotic effects in C666-1, and in combination with CDDP, is curative in C666-1 NPC xenograft tumors in vivo. The sequence-dependency of these effects is consistent with an antisense mechanism. These studies suggest that Bcl-2 may represent a biologically relevant target for the development of novel combinatorial therapies for NPC.

Anticancer drug development based on modulation of the Bcl-2 family core apoptosis mechanism

Cancer cells generally maintain their survival by suppressing apoptosis. Mitochondrial mechanisms are involved in most forms of apoptosis (referred to as mitochondrial apoptosis), and the Bcl-2 family controls apoptosis at the mitochondrion via a balance of the effects of pro- and antiapoptotic members. Antiapoptotic molecules such as Bcl-2 and Bcl-x(L) are often overexpressed in cancer cells and their inhibition is an attractive target for selective killing of tumor cells via induction of apoptosis. Reduction of the levels of these proteins with antisense molecules has shown encouraging experimental and clinical results and there has been some success in developing small-molecule inhibitors. These are likely to be the most productive drug development approaches in the near future. However, growing understanding of the molecular mechanisms involved has identified other potential targets. Cardiolipin is important for the proapoptotic activity of Bcl-2 family members such as Bid, Bax and Bak, and modulation of its metabolism and translocation in mitochondrial membranes could potentially have a strong influence on apoptosis. Post-translational modifications strongly influence the activity of Bcl-2 family members. Several molecules have been identified that bind to Bcl-2 family members and could be intracellular control mechanisms. These mechanisms may yield several drug development targets for the induction of apoptosis. Further research will qualify these targets and, in the longer term, could lead to a more specific means of inducing apoptosis in cancer cells.

CD4- plasmacytoid dendritic cells (pDCs) migrate in lymph nodes by CpG inoculation and represent a potent functional subset of pDCs

We have recently identified two groups of plasmacytoid dendritic cells (pDCs) isolated from murine liver based on the expression of CD4 and other cell surface markers uniquely expressed by pDCs. Herein, we describe the identification of both CD4+ and CD4- pDCs that clearly exist in lymph nodes (LNs), spleen, liver, thymus, bone marrow, and lung. Normally, CD4+ pDCs are enriched in LNs. However, after in vivo systemic injection with bacterial CpG, a larger number of CD4- pDCs are recruited to the LNs and local inoculation by CpG drives CD4- pDCs migrating into local sentinel LNs, suggesting that CD4- pDCs are the main subpopulation migrating to the peripheral LNs. Furthermore, although both freshly isolated CD4+ pDCs and CD4- pDCs appear as an immature plasmacytoid cell and develop into a DC morphology following activation, the two subsets have strikingly different immune features, including differences in the production pattern of cytokines stimulated with CpG and in T cell activation.

Activation of dendritic cells that cross-present tumor-derived antigen licenses CD8+ CTL to cause tumor eradication

The fate of naive CD8(+) T cells is determined by the environment in which they encounter MHC class I presented peptide Ags. The manner in which tumor Ags are presented is a longstanding matter of debate. Ag presentation might be mediated by tumor cells in tumor draining lymph nodes or via cross-presentation by professional APC. Either pathway is insufficient to elicit protective antitumor immunity. We now demonstrate using a syngeneic mouse tumor model, expressing an Ag derived from the early region 1A of human adenovirus type 5, that the inadequate nature of the antitumor CTL response is not due to direct Ag presentation by the tumor cells, but results from presentation of tumor-derived Ag by nonactivated CD11c(+) APC. Although this event results in division of naive CTL in tumor draining lymph nodes, it does not establish a productive immune response. Treatment of tumor-bearing mice with dendritic cell-stimulating agonistic anti-CD40 mAb resulted in systemic efflux of CTL with robust effector function capable to eradicate established tumors. For efficacy of anti-CD40 treatment, CD40 ligation of host APC is required because adoptive transfer of CD40-proficient tumor-specific TCR transgenic CTL into CD40-deficient tumor-bearing mice did not lead to productive antitumor immunity after CD40 triggering in vivo. CpG and detoxified LPS (MPL) acted similarly as agonistic anti-CD40 mAb with respect to CD8(+) CTL efflux and tumor eradication. Together these results indicate that dendritic cells, depending on their activation state, orchestrate the outcome of CTL-mediated immunity against tumors, leading either to an ineffective immune response or potent antitumor immunity.