Antitumor activity of synthetic oligonucleotides with sequences from cDNA encoding proteins of Mycobacterium bovis BCG

TLR9 Monotherapy in Immune-Competent Mice Suppresses Orthotopic Prostate Tumor Development

Prostate cancer is ranked second in the world for cancer-related deaths in men, highlighting the lack of effective therapies for advanced-stage disease. Toll-like receptors (TLRs) and immunity have a direct role in prostate cancer pathogenesis, but TLR9 has been reported to contribute to both the progression and inhibition of prostate tumorigenesis. To further understand this apparent disparity, we have investigated the effect of TLR9 stimulation on prostate cancer progression in an immune-competent, syngeneic orthotopic mouse model of prostate cancer. Here, we utilized the class B synthetic agonist CPG-1668 to provoke a TLR9-mediated systemic immune response and demonstrate a significant impairment of prostate tumorigenesis. Untreated tumors contained a high abundance of immune-cell infiltrates. However, pharmacological activation of TLR9 resulted in smaller tumors containing significantly fewer M1 macrophages and T cells. TLR9 stimulation of tumor cells in vitro had no effect on cell viability or its downstream transcriptional targets, whereas stimulation in macrophages suppressed cancer cell growth via type I IFN. This suggests that the antitumorigenic effects of CPG-1668 were predominantly mediated by an antitumor immune response. This study demonstrated that systemic TLR9 stimulation negatively regulates prostate cancer tumorigenesis and highlights TLR9 agonists as a useful therapeutic for the treatment of prostate cancer.

Immunotherapeutic potential of CpG oligodeoxynucleotides in veterinary species

Innate immunity plays a critical role in host defense against infectious diseases by discriminating between self and infectious non-self. The recognition of infectious non-self involves germ-line encoded pattern recognition receptors (PRRs) that recognize pathogen-associated molecular patterns (PAMPs). The PAMPs are the components of pathogenic microbes which include not only the cell wall constituents but also the unmethylated 2'-deoxy-ribo-cytosine-phosphate-guanosine (CpG) motifs. These CpG motifs present within bacterial and viral DNA are recognized by toll-like receptor 9 (TLR9), and signaling by this receptor triggers a proinflammatory cytokine response which, in turn, influences both innate and adaptive immune responses. The activation of TLR9 with synthetic CpG oligodeoxynucleotides (ODNs) induces powerful Th1-like immune responses. It has been shown to provide protection against infectious diseases, allergy and cancer in laboratory animal models and some domestic animal species. With better understanding of the basic biology and immune mechanisms, it would be possible to exploit the potential of CpG motifs for animal welfare. The research developments in the area of CpG and TLR9 and the potential applications in animal health have been reviewed in this article.

Treatment of recurrent metastatic head and neck cancer: focus on cetuximab

EGFR belongs to the ErbB family of receptor tyrosine kinases and is associated with worse prognosis in head and neck squamous cell carcinoma (HNSCC). Cetuximab is a monoclonal antibody to the extracellular domain of EGFR and inhibits its downstream actions via multiple mechanisms. Besides its proven efficacy in locally advanced and incurable HNSCC, cetuximab has the distinct advantage of having a relatively tolerable side effect profile and not potentiating radiation toxicity. Though therapies for advanced HNSCC are evolving, locoregional recurrence and/or distant metastases occur in a large percentage of patients. Though some patients can be salvaged with surgery or radiation therapy, the majority are incurable, and are treated palliatively with systemic therapy. In the setting of first line therapy for recurrent/metastatic HNSCC, the EXTREME trial provided level 1 evidence that cetuximab improves overall survival when combined with cisplatinum and 5 FU. Following progression on first line chemotherapy, several phase II trials suggest that cetuximab monotherapy is a reasonable choice in this setting. Future studies should concentrate on clinical and molecular markers that may allow more personalized approaches to treating HNSCC, and combining EGFR inhibitors with other agents in a synergistic approach.

Immunomodulatory oligonucleotides as novel therapy for breast cancer: pharmacokinetics, in vitro and in vivo anticancer activity, and potentiation of antibody therapy

Oligonucleotides containing CpG motifs and immunomodulatory oligonucleotides (IMO) containing a synthetic immunostimulatory dinucleotide and a novel DNA structure have been suggested to have potential for the treatment of various human diseases. In the present study, a newly designed IMO was evaluated in several models of human (MCF-7 and BT474 xenograft) and murine (4T1 syngeneic) breast cancer. Pharmacokinetics studies of the IMO administered by s.c., i.v., p.o., or i.p. routes were also accomplished. The IMO was widely distributed to various tissues by all four routes, with s.c. administration yielding the highest concentration in tumor tissue. The IMO inhibited the growth of tumors in all three models of breast cancer, with the lowest dose of the IMO inhibiting MCF-7 xenograft tumor growth by >40%. Combining the IMO with the anticancer antibody, Herceptin, led to potent antitumor effects, resulting in >96% inhibition of tumor growth. The IMO also exerted in vitro antitumor activity, as measured by cell growth, apoptosis, and proliferation assays in the presence of Lipofectin. This is the first report of the pharmacokinetics of this agent in normal and tumor-bearing mice. Based on the present results, we believe that the IMO is a good candidate for clinical development for breast cancer therapy used either alone or in combination with conventional cancer therapeutic agents.

Novel toll-like receptor 9 agonist induces epidermal growth factor receptor (EGFR) inhibition and synergistic antitumor activity with EGFR inhibitors

PURPOSE

Immunostimulating Toll-like receptor 9 (TLR9) agonists cause antitumor activity interfering also with cancer proliferation and angiogenesis by mechanisms still incompletely understood. We hypothesized that modified TLR9 agonists could impair epidermal growth factor receptor (EGFR) signaling and, by this means, greatly enhance EGFR inhibitors effect, acting on both the receptor targeting and the immunologic arm.

EXPERIMENTAL DESIGN

We used a novel second-generation, modified, immunomodulatory TLR9 agonist (IMO), alone and in combination with the anti-EGFR monoclonal antibody cetuximab or tyrosine kinase inhibitor gefitinib, on the growth of GEO and cetuximab-resistant derivatives GEO-CR colon cancer xenografts. We have also evaluated the expression of several proteins critical for cell proliferation, apoptosis, and angiogenesis, including EGFR, mitogen-activated protein kinase, Akt, bcl-2, cyclooxygenase-2, vascular endothelial growth factor, and nuclear factor-kappaB.

RESULTS

IMO inhibited GEO growth and signaling by EGFR and the other proteins critical for cell proliferation and angiogenesis. IMO plus the anti-EGFR antibody cetuximab synergistically inhibited tumor growth, signaling proteins, and microvessel formation. EGFR signaling inhibition by IMO is relevant because IMO cooperated also with EGFR tyrosine kinase inhibitor gefitinib in GEO tumors, while it was inactive against GEO-CR xenografts. On the other hand, IMO boosted the non-EGFR-dependent cetuximab activity, causing a cooperative antitumor effect in GEO-CR cells. Finally, combination of IMO, cetuximab and chemotherapeutic irinotecan eradicated the tumors in 90% of mice.

CONCLUSION

IMO interferes with EGFR-related signaling and angiogenesis and has a synergistic antitumor effect with EGFR inhibitors, especially with cetuximab, boosting both the EGFR dependent and independent activity of this agent. Moreover, this therapeutic strategy could be translated in patients affected by colorectal cancer.

Oral administration of second-generation immunomodulatory oligonucleotides induces mucosal Th1 immune responses and adjuvant activity

CpG DNA induces potent Th1 immune responses through Toll-like receptor 9. In the present study, we used oligonucleotides consisting of a novel 3'-3'-linked structure and synthetic stimulatory motifs, referred as second-generation immunomodulatory oligonucleotides (IMOs). The stimulatory motifs included: CpR, YpG, or R'pG (R = 2'-deoxy-7-deazaguanosine, Y = 2'-deoxy-5-hydroxy-cytidine, and R' = 1-[2'-deoxy-beta-d-ribofuranosyl]-2-oxo-7-deaza-8-methyl-purine). We evaluated the stability of orally administered IMOs in the gastrointestinal (GI) environment and their ability to induce mucosal immune responses in mice, and compared these characteristics with those of a conventional CpG DNA. The IMOs were significantly more stable than CpG DNA following oral administration, and IMOs induced stronger local and systemic immune responses as determined by MIP-1beta, MCP-1, IP-10, and IL-12 production. Mice orally immunized with ovalbumin (OVA) and IMO had higher levels of IgG2a antibodies in serum and IgA antibodies in intestinal mucosa than did mice immunized with OVA and CpG DNA. These studies demonstrate that IMOs are more stable than CpG DNA in the GI tract and can induce more potent mucosal Th1 adjuvant responses. IMOs may prove to be effective oral adjuvants, able to promote strong systemic and mucosal immune responses to oral vaccines and antigens for therapeutic and prophylactic applications.

Development of immunomodulatory six base-length non-CpG motif oligonucleotides for cancer vaccination

We have previously described a novel family of immunomodulatory synthetic oligonucleotides characterized by a phosphodiester backbone, a length of six bases and a 5'G3xG23' sequence, where x is A, C, G or T. In the present study, we have evaluated whether these 5'G3xG23' oligonucleotides possess additional activities essential for adequate cancer vaccination. Immunization for the treatment of cancer requires an adjuvant, a source of tumor-associated antigen(s), for example apoptotic cancer cells, and a way to overcome the escape of tumor cells from the immune system, for example the up-regulation of Fas ligand (FasL) on the surface of cancer cells. The results show that phosphodiester 5'G3AG23' and 5'G3TG23' oligonucleotides have a direct activity on a number of different cancer cells by inducing apoptosis (release of cytochrome C, activation of caspase-3, cleavage of poly [ADP-ribose] polymerase, degradation of nuclear mitotic apparatus protein and translocation of phophatidylserine at the cell surface). In addition, the 5'G3AG23', 5'G3CG23', and 5'G3TG23' oligonucleotides were found to down-regulate the levels of FasL on the surface of cancer cells. These immunomodulatory phosphodiester six base-length oligonucleotides, which are capable of inducing apoptosis in cancer cells as well as downregulating the expression of FasL at their cell surface, may have application as cancer cell vaccines.

Secondary structures in CpG oligonucleotides affect immunostimulatory activity

Oligodeoxynucleotides containing CpG dinucleotides in specific sequence contexts activate the vertebrate immune system. Our previous studies showed that the 5(')-end of a CpG oligonucleotide should be accessible for receptor recognition and subsequent immune stimulation. Activity is abrogated if this end is blocked by joining two CpG oligos through 5(')-5(') linkage. It was not known whether a similar effect would arise from secondary structures at either end of a CpG oligo, such as hairpin loops or terminal dimers. In the present study we found that 5(')-terminal secondary structures affect activity significantly more than those at the 3(')-end. The need for an open 5(')-end suggests that the receptor responsible for immune stimulation reads the DNA sequence from this end. These results may also provide insights to place CpG motifs appropriately in DNA vaccines to induce additional Th1 type responses.

Potent CpG oligonucleotides containing phosphodiester linkages: in vitro and in vivo immunostimulatory properties

Bacterial and synthetic DNAs, containing CpG dinucleotides in specific sequence contexts, activate the vertebrate immune system. Unlike phosphorothioate (PS) CpG DNAs, phosphodiester (PO) CpG DNAs require either palindromic sequences and/or poly(dG) sequences at the 3(')-end for activity. Here, we report 'PO-immunomers' having two PO-CpG DNA molecules joined through their 3(')-ends. These PO-imunomers permitted us, for the first time, to assess immunostimulatory properties of PO-CpG DNAs in vitro and in vivo without the need for palindromic and/or poly(dG) sequences. In medium containing 10% fetal bovine serum, PO-immunomers were more resistant than PO-CpG DNAs to nucleases. Compared to PS-CpG DNA in BALB/c and C3H/HeJ mice spleen cell culture assays, PO-immunomers showed increased IL-12 secretion and minimal amounts of IL-6 secretion. PO-immunomers activated NF-kappa B and induced cytokine secretion in J774 cell cultures. In addition, PO-immunomers showed antitumor activity in nude mice bearing human breast (MCF-7) and prostate (DU145) cancer xenografts.

CpG motifs in bacterial DNA and their immune effects

Unmethylated CpG motifs are prevalent in bacterial but not vertebrate genomic DNAs. Oligodeoxynucleotides (ODN) containing CpG motifs activate host defense mechanisms leading to innate and acquired immune responses. The recognition of CpG motifs requires Toll-like receptor (TLR) 9, which triggers alterations in cellular redox balance and the induction of cell signaling pathways including the mitogen activated protein kinases (MAPKs) and NF kappa B. Cells that express TLR-9, which include plasmacytoid dendritic cells (PDCs) and B cells, produce Th1-like proinflammatory cytokines, interferons, and chemokines. Certain CpG motifs (CpG-A) are especially potent at activating NK cells and inducing IFN-alpha production by PDCs, while other motifs (CpG-B) are especially potent B cell activators. CpG-induced activation of innate immunity protects against lethal challenge with a wide variety of pathogens, and has therapeutic activity in murine models of cancer and allergy. CpG ODN also enhance the development of acquired immune responses for prophylactic and therapeutic vaccination.

Site of chemical modifications in CpG containing phosphorothioate oligodeoxynucleotide modulates its immunostimulatory activity

Phosphorothioate oligodeoxynucleotides containing CpG motifs have immunostimulatory activity. Appropriate substitution of deoxynucleosides in the flanking region of CpG-containing phosphorothioate oligodeoxynucleotides with 2'-O-methylribonucleosides results in significant decreases or increases in their immunostimulatory activities. The results provide insights in how to chemically modify phosphorothioate oligodeoxynucleotides containing CpG motifs to suppress or enhance their immunostimulatory activity for different therapeutic uses.

The influence of lipofectin on the in vitro stimulation of murine spleen cells by bacterial DNA and plasmid DNA vectors

Lipofectin is a mixture of two cationic lipids, N-[1-(2,3-dioleyloxy)propyl]-n,n,n-trimethylammonium chloride (DOTMA) and dioleoyl phosphotidylethanolamine (DOPE), and has been commonly used to promote transfection of plasmid vectors in vitro and in vivo. In these experiments, the effect of lipofectin on in vitro immunostimulation by bacterial and plasmid DNA was tested to determine if these lipids can also influence immune properties of DNA. As a model, spleen cells from BALB/c and C3H/HeJ mice were cultured with DNA from either Escherichia coli DNA or the pEGFP-N1 plasmid at various ratios with lipofectin. As an index of immune stimulation, in vitro proliferation as well as production of interleukin-12 (IL-12) and interferon-gamma (IFN-gamma) were assessed. For both bacterial DNA and plasmid DNA, the presence of lipofectin led to a marked increase in the production of IFN-gamma under conditions in which increases in IL-12 production were limited. The IFN-gamma production was nevertheless dependent on IL-12, as shown by the effects of anti-IL-12 antibodies. Under these culture conditions, lipofectin did not significantly augment proliferation induced by DNA. These findings indicate that lipofectin can increase the in vitro immunostimulatory effects of bacterial and plasmid DNA, although the magnitude of the increase may vary among responses.

Oligodeoxynucleotides Containing Palindrome Sequences with Internal 5′-CpG-3′ Act Directly on Human NK and Activated T Cells to Induce IFN-γ Production In Vitro

Previous studies have shown that the action of bacterial or synthetic oligodeoxynucleotide (oligo-DNA) on mouse NK cells to produce IFN-γ is mediated mostly by monocytes/macrophages activated by olig-DNA. However, its action on human IFN-γ-producing cells has not been well investigated. In the present study, we examined the effect of oligo-DNAs on highly purified human NK and T cells. Bacillus Calmette-Guérin-derived or synthetic oligo-DNAs induced NK cells to produce IFN-γ with an increased CD69 expression, and the autocrine IFN-γ enhanced their cytotoxicity. The response of NK cells to oligo-DNAs was enhanced when the cells were activated with IL-2, IL-12, or anti-CD16 Ab. T cells did not produce IFN-γ in response to oligo-DNAs but did respond independently of IL-2 when they were stimulated with anti-CD3 Ab. In the action of oligo-DNAs, the palindrome sequence containing unmethylated 5′-CpG-3′ motif(s) appeared to play an important role in the IFN-γ-producing ability of NK cells. The changes of base composition inside or outside the palindrome sequence altered its activity: The homooligo-G-flanked GACGATCGTC was the most potent IFN-γ inducer for NK cells. The CG palindrome was also important for activated NK and T cells in their IFN-γ production, although certain nonpalindromes acted on them. Among the sequences tested, cell activation- or cell lineage-specific sequences were likely; i.e., palindrome ACCGGT and nonpalindrome AACGAT were favored by activated NK cells but not by unactivated NK cells or activated T cells. These results indicate that oligo-DNAs containing CG palindrome act directly on human NK cells and activated T cells to induce IFN-γ production.

The influence of susceptibility factors on the immune response to DNA

Susceptibility to autoimmune disease results from genetic factors that determine the pattern of immune responsiveness to self as well as foreign antigens. These factors may influence the immune response to DNA, a complex macromolecule that can induce antibody responses in normal as well as aberrant immunity. In systemic lupus erythematosus, anti-DNA antibodies target conserved sites present on all DNA and appear to arise by a T dependent mechanism. In contrast, in normal humans, anti-DNA antibodies react to non-conserved sites on certain bacterial DNA and have features suggesting induction by a T independent mechanism. The activity of bacterial DNA reflects the presence of base sequence motifs centering on an unmethylated CpG core. Because of susceptibility factors in patients with systemic lupus erythematosus, bacterial DNA may drive a response crossreactive with self DNA instead of a response specific for the foreign antigen.

Hexamer palindromic oligonucleotides with 5'-CG-3' motif(s) induce production of interferon

We have shown previously that 30-mer oligonucleotides containing hexamer palindromic sequences with 5'-CG-3' motif(s) induce interferon (IFN), activate natural killer (NK) cells, and thus exhibit tumor-regressing activity. The present study showed that a hexamer palindromic oligonucleotide (5'-AACGTT-3') alone induced IFN from mouse spleen cells when added with cationic liposomes. Accordingly, 32 kinds of hexamer palindromic oligonucleotides were tested for their ability to induce IFN in the presence of cationic liposomes. The results show that oligonucleotides with NACGTN and NTCGAN sequences exhibited the strongest activity. ACGCGT and TCGCGA also possessed moderate but significant activity. In contrast, palindromes without CG motif(s) were devoid of the activity. No hexamer oligonucleotides showed the activity when liposomes were absent. A complete palindromic sequence was essential as any single base substitution resulted in diminished activity. Among variety of palindromic oligonucleotides of different sizes with an ACGT sequence at the center, the tetramer oligonucleotide was without activity, whereas the activity of hexamer and longer oligonucleotides was almost equally high. These results strongly suggest that the minimal essential structure required for IFN induction is the hexamer palindromic sequence with CG motif(s).

Lymphocyte activation by CpG dinucleotide motifs in prokaryotic DNA

CpG dinucleotides are present at the expected frequency in prokaryotic DNA, but are underrepresented ('CpG suppression') and methylated in vertebrate DNA. The vertebrate immune system has apparently evolved the ability to recognize these unmethylated CpG motifs and respond with a rapid and coordinated cytokine response leading to the induction of humoral and cell-mediated immunity.

Synthetic oligonucleotides with certain palindromes stimulate interferon production of human peripheral blood lymphocytes in vitro

We studied the ability of synthetic single-stranded 30-mer oligodeoxyribonucleotides (oligoDNAs) with three different kinds of hexamer palindromic sequence to induce interferon (IFN) production of human peripheral blood lymphocytes (PBL). When PBL was cultured with oligoDNA having a palindrome of AACGTT or GACGTC, IFN activity was detected by bioassay in the culture fluid after 8 h, and the amount of IFN reached the maximum after 18 h. IFN-alpha was predominantly produced, and small amounts of IFN-beta and IFN-gamma were also found. OligoDNA with the palindrome ACCGGT had no effect.

Oligonucleotide sequences required for natural killer cell activation

Based on the previous finding that certain 30-mer single-stranded oligodeoxyribonucleotides (oligonucleotides) having particular 6-mer palindromic sequences could induce interferon-alpha and -gamma, and enhance natural killer activity, the present study was carried out to clarify the entire relationship between the activity and the sequence of 30-mer oligonucleotides. The results indicated that the activity depended critically on the presence of particular palindromic sequences including the 5'-CG-3' motif(s). The size and the number of palindromes as well as the extra-palindromic sequences also influenced the activity. An oligonucleotide with a 10-mer palindrome and extra-palindromic oligoguanylate sequences showed the strongest activity among the oligonucleotides tested.

DNA from bacteria, but not from vertebrates, induces interferons, activates natural killer cells and inhibits tumor growth

The nucleic acid fraction from cells of 6 species of bacterium and 2 kinds of vertebrate, calf and salmon, was extracted and purified by the same procedures as described previously. When the spleen cells from BALB/c mice were incubated with the nucleic acid fraction from either of the bacteria, natural killer (NK) activity of the cells was remarkably elevated and the cells produced factors to activate macrophages and to inhibit viral growth. It was shown that the factor to activate macrophages was interferon (IFN)-gamma and that to inhibit viral growth was IFN-alpha/beta. On the other hand, the nucleic acid fraction from either of the vertebrate cells did not show such activities. Pretreatment of the bacterial nucleic acid fraction with DNase, but not with RNase, abrogated completely the biological activities. The activities of the bacterial nucleic acid were not influenced by the presence of polymyxin B, an inhibitor of lipopolysaccharide (LPS), and the spleen cells from not only BALB/c mice but also LPS-insensitive C3H/HeJ mice were activated, indicating that the activities of the fraction were not ascribed to LPS contaminated possibly into the fraction, but to DNA itself. Intralesional injection with the bacterial DNA fraction caused regression of mouse IMC tumors, but the injection with the vertebrate DNA fraction did not. These findings prompted us to examine the biological activities of DNA samples from a variety of animals and plants, which were provided from other laboratories or purchased from manufacturers. All of the DNA samples from cells of 5 kinds of bacterium, 2 of virus and 4 of invertebrate augmented NK activity and induced IFN, more or less, in mouse spleen calls, while the DNA from 10 kinds of vertebrate, including 3 of fish and 5 of mammal, showed no such activities. The DNA from 2 species of plants, were also inactive. Possible mechanisms to explain the different biological activities of DNA from different cell sources were discussed based on our previous finding that the particular palindromic sequences with a G-C motif(s) are required for induction of IFNs and activation of NK cells with synthetic 30-mer oligonucleotides.