Ten tandem repeats of beta-hCG 109-118 enhance immunogenicity and anti-tumor effects of beta-hCG C-terminal peptide carried by mycobacterial heat-shock protein HSP65

Unconventional Actions of Glycoprotein Hormone Subunits: A Comprehensive Review

The glycoprotein hormones (GPH) are heterodimers composed of a common α subunit and a specific β subunit. They act by activating specific leucine-rich repeat G protein-coupled receptors. However, individual subunits have been shown to elicit responses in cells devoid of the receptor for the dimeric hormones. The α subunit is involved in prolactin production from different tissues. The human chorionic gonadotropin β subunit (βhCG) plays determinant roles in placentation and in cancer development and metastasis. A truncated form of the thyrotropin (TSH) β subunit is also reported to have biological effects. The GPH α- and β subunits are derived from precursor genes (gpa and gpb, respectively), which are expressed in most invertebrate species and are still represented in vertebrates as GPH subunit paralogs (gpa2 and gpb5, respectively). No specific receptor has been found for the vertebrate GPA2 and GPB5 even if their heterodimeric form is able to activate the TSH receptor in mammals. Interestingly, GPA and GPB are phylogenetically and structurally related to cysteine-knot growth factors (CKGF) and particularly to a group of antagonists that act independently on any receptor. This review article summarizes the observed actions of individual GPH subunits and presents the current hypotheses of how these actions might be induced. New approaches are also proposed in light of the evolutionary relatedness with antagonists of the CKGF family of proteins.

Overcoming Physiological Barriers to Nanoparticle Delivery-Are We There Yet?

The exploitation of nanosized materials for the delivery of therapeutic agents is already a clinical reality and still holds unrealized potential for the treatment of a variety of diseases. This review discusses physiological barriers a nanocarrier must overcome in order to reach its target, with an emphasis on cancer nanomedicine. Stages of delivery include residence in the blood stream, passive accumulation by virtue of the enhanced permeability and retention effect, diffusion within the tumor lesion, cellular uptake, and arrival at the site of action. We also briefly outline strategies for engineering nanoparticles to more efficiently overcome these challenges: Increasing circulation half-life by shielding with hydrophilic polymers, such as PEG, the limitations of PEG and potential alternatives, targeting and controlled activation approaches. Future developments in these areas will allow us to harness the full potential of nanomedicine.

Gonadotropin and tumorigenesis: Direct and indirect effects on inflammatory and immunosuppressive mediators and invasion

Human chorionic gonadotropin (hCG), a hormone essential for pregnancy, is also ectopically expressed by a variety of cancers and is associated with poor prognosis; molecular mechanisms which may contribute to tumor progression remain ill-defined. Exogenous hCG enhanced the viability of human colorectal and lung cancer cells and promoted the growth of syngeneic tumors in mice. It induced the synthesis of VEGF, IL-8, matrix metalloprotease (MMP)-2 and MMP-9, and increased invasiveness in an MMP-dependent manner. While inducing the secretion of the tumor-associated extra-cellular matrix proteoglycan versican from tumor cells, hCG consequently caused the TLR-2-mediated generation of the inflammatory, tumor-associated cytokines TNF-α and IL-6 from peripheral blood adherent cells. The molecule up-modulated the Treg-associated transcription factor FOXP3 in tumor cells and increased the secretion of TGFβ and IL-10, thereby inhibiting T cell proliferation and inducing the differentiation FOXP3^- CD4⁺ CD25^- cells into functional FOXP3⁺ CD4⁺ CD25⁺ suppressor cells. Co-culture of hCG-treated tumor cells with mature bone-marrow derived dendritic cells induced the generation of active indoleamine deoxygenase. While anti-hCG antibodies restricted the growth of implanted tumor cells in nude mice, immunization of immune competent mice with a βhCG-TT conjugate supplemented with Mycobacterium indicus pranii provided synergistic survival benefit in animals implanted with syngeneic, hCG-responsive tumor cells. These studies elucidate the pathways by which hCG can promote tumorigenesis, providing further rationale for anti-hCG vaccination in the treatment of gonadotropin-sensitive tumors. © 2016 Wiley Periodicals, Inc.

Gonadotropin-mediated chemoresistance: Delineation of molecular pathways and targets

Background

Human chorionic gonadotropin (hCG) has essential roles in pregnancy. Reports linking hCG in non-trophoblastic tumors with poor patient prognosis has spurred interest in patho-physiological roles the hormone might play.

Methods

The ability of hCG to prevent tumor cell death and sustain viability in the presence of chemotherapeutic drugs was assessed and potential synergies with TLR ligands explored. hCG-induced up-modulation of genes involved in chemoresistance was documented and targets validated by siRNA knock-down. Whether hCG could drive collaboration between tumor cells and macrophages in the production of IL-6 and consequent chemoresistance was assessed. The effects of concurrent anti-hCG immunization and chemotherapy on the growth of syngeneic murine tumors were evaluated.

Results

hCG maintained basal levels of cytokine secretion by tumor cells exposed to chemotherapeutic drugs, and enhanced viability and proliferation; pre-treatment with hCG also decreased apoptosis, as assessed by Annexin-V binding and the cleavage of caspase 3. While co-incubation with hCG along with several TLR ligands mediated heightened chemo-resistance, TLR-2/6 and TLR-9 ligands increased the phosphorylation of JNK, and TLR-2 and TLR-8 ligands the phosphorylation of ERK in presence of hCG and curcumin, providing evidence of tri-molecular synergy. The hormone increased the transcription and/or expression of molecular intermediates (SURVIVIN, HIF-1α, PARP-1, Bcl-2, c-FLIP, KLK-10, XIAP, c-IAP-1) associated with chemo-resistance and increased levels of stress modulators (PON2, HO-1, HSP27 and NRF-2). siRNAs to SURVIVIN, NRF-2, HO-1 and HIF-1α attenuated hCG-mediated chemo-resistance. hCG-conditioned tumor cell supernatants induced heightened secretion of IL-6 and TNF-α from peripheral blood adherent cells and secreted IL-6 imparted chemo-resistance to naïve tumor cells. Co-administration of curcumin along with an anti-hCG vaccine (hCGβ conjugated to Tetanus Toxoid (TT)) to mice carrying syngeneic tumors resulted in significantly enhanced benefits on animal survival; synergy was demonstrated between anti-hCG antibodies and curcumin in the reduction of tumor cell viability.

Conclusions

The data suggest that hCG, via direct as well as collaborative effects with TLR ligands and accessory cell-secreted cytokines, mediates chemo-resistance in gonadotropin-sensitive tumors and outlines the potential benefits of combination therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1938-x) contains supplementary material, which is available to authorized users.

Immunopreventive effects against murine H22 hepatocellular carcinoma in vivo by a DNA vaccine targeting a gastrin- releasing peptide

There is a continuing need for innovative alternative therapies for liver cancer. DNA vaccines for hormone/ growth factor immune deprivation represent a feasible and attractive approach for cancer treatment. We reported a preventive effect of a DNA vaccine based on six copies of the B cell epitope GRP18-27 with optimized adjuvants against H22 hepatocarcinoma. Vaccination with pCR3.1-VS-HSP65-TP-GRP6-M2 (vaccine) elicited much higher level of anti-GRP antibodies and proved efficacious in preventing growth of transplanted hepatocarcinoma cells. The tumor size and weight were significantly lower (p<0.05) in the vaccine subgroup than in the control pCR3.1-VS-TP-HSP65-TP-GRP6, pCR3.1-VS-TP-HSP65-TP-M2 or saline subgroups. In addition, significant reduction of tumor-induced angiogenesis associated with intradermal tumors of H22 cells was observed. These potent effects may open ways towards the development of new immunotherapeutic approaches in the treatment of liver cancer.

Detection of antibodies against customized epitope: use of a coating antigen employing VEGF as fusion partner

Diagnosis of many infectious, autoimmune diseases and cancers depends on the detection of specific antibodies against peptide epitope by enzyme-linked immunosorbent assay (ELISA). However, small peptides are difficult to be coated on the plate surfaces. In this study, we selected GnRH as a model hapten to evaluate whether VEGF121 would be suitable as an irrelevant hapten-carrier to develop a universal platform for specific antibodies detection. Firstly, GnRH was fused to the C terminus of VEGF121 and the resultant fusion protein VEGF-GnRH expressed effectively as inclusion bodies in Escherichia coli. Thereafter, VEGF-GnRH was easily purified to near homogeneity with a yield of about 235 mg from 2.1 L induced culture. At last, VEGF-GnRH was used to perform ELISA and western blot, and our results suggested that VEGF-GnRH was capable of detecting anti-GnRH antibodies in sera both qualitatively and quantitatively. Indeed, previous studies of our laboratory had demonstrated that other fusion proteins such as VEGF-Aβ10, VEGF-GRP, VEGF-CETPC, and VEGF-βhCGCTP37 were able to detect their corresponding antibodies specifically. Therefore, VEGF121 may be a suitable irrelevant fusion partner of important diagnostic peptide markers. Our works would shed some light on the development of a universal platform for detection of specific antibodies.

High-density sub-100-nm peptide-gold nanoparticle complexes improve vaccine presentation by dendritic cells in vitro

Nanocarriers have been explored to improve the delivery of tumor antigens to dendritic cells (DCs). Gold nanoparticles are attractive nanocarriers because they are inert, non-toxic, and can be readily endocytosed by DCs. Here, we designed novel gold-based nanovaccines (AuNVs) using a simple self-assembling bottom-up conjugation method to generate high-peptide density delivery and effective immune responses with limited toxicity. AuNVs were synthesized using a self-assembling conjugation method and optimized using DC-to-splenocyte interferon-γ enzyme-linked immunosorbent spot assays. The AuNV design has shown successful peptide conjugation with approximately 90% yield while remaining smaller than 80 nm in diameter. DCs uptake AuNVs with minimal toxicity and are able to process the vaccine peptides on the particles to stimulate cytotoxic T lymphocytes (CTLs). These high-peptide density AuNVs can stimulate CTLs better than free peptides and have great potential as carriers for various vaccine types.

Diagnostic peptide discovery: prioritization of pathogen diagnostic markers using multiple features

The availability of complete pathogen genomes has renewed interest in the development of diagnostics for infectious diseases. Synthetic peptide microarrays provide a rapid, high-throughput platform for immunological testing of potential B-cell epitopes. However, their current capacity prevent the experimental screening of complete “peptidomes”. Therefore, computational approaches for prediction and/or prioritization of diagnostically relevant peptides are required. In this work we describe a computational method to assess a defined set of molecular properties for each potential diagnostic target in a reference genome. Properties such as sub-cellular localization or expression level were evaluated for the whole protein. At a higher resolution (short peptides), we assessed a set of local properties, such as repetitive motifs, disorder (structured vs natively unstructured regions), trans-membrane spans, genetic polymorphisms (conserved vs. divergent regions), predicted B-cell epitopes, and sequence similarity against human proteins and other potential cross-reacting species (e.g. other pathogens endemic in overlapping geographical locations). A scoring function based on these different features was developed, and used to rank all peptides from a large eukaryotic pathogen proteome. We applied this method to the identification of candidate diagnostic peptides in the protozoan Trypanosoma cruzi, the causative agent of Chagas disease. We measured the performance of the method by analyzing the enrichment of validated antigens in the high-scoring top of the ranking. Based on this measure, our integrative method outperformed alternative prioritizations based on individual properties (such as B-cell epitope predictors alone). Using this method we ranked 10 million 12-mer overlapping peptides derived from the complete T. cruzi proteome. Experimental screening of 190 high-scoring peptides allowed the identification of 37 novel epitopes with diagnostic potential, while none of the low scoring peptides showed significant reactivity. Many of the metrics employed are dependent on standard bioinformatic tools and data, so the method can be easily extended to other pathogen genomes.

A novel synthetic bipartite carrier protein for developing glycotope-based vaccines

Development of successful vaccines against glycotopes remains a major challenge. In the current studies, we have successfully developed a novel carrier protein for glycotopes based on the concept of antigen clustering and specific stimulation of T helper cells to mount strong antibody response to glycotopes. The bipartite carrier protein consists of a tandem repeat of a cysteine-rich peptide for docking of clustered glycotopes to effectively activate B cells and an Fc domain for antigen delivery to antigen presenting cells (APCs). To demonstrate its utility, we conjugated the tumor-specific monosaccharide antigen Tn to this novel carrier protein and successfully developed a Tn vaccine against cancer in animal models. The Tn vaccine effectively elicited high-titer IgG1 antibodies against Tn in immunized mice, and effectively suppressed the development of prostate cancer in Transgenic Adenocarcinoma of the Mouse Prostate (TRAMP) mice. Our results suggest that this novel bipartite carrier protein could be effectively used for developing anti-glycotope vaccines such as the anticancer Tn vaccine.

Transgenesis-mediated reproductive dysfunction and tumorigenesis: effects of immunological neutralization

Human chorionic gonadotropin (hCG) was initially thought to be made only during pregnancy, but is now known to also be synthesized by a variety of cancers and is associated with poor patient prognosis. Transgenic expression of βhCG in mice causes hyper-luteinized ovaries, a loss in estrous cyclicity and infertility, increased body weight, prolactinomas and mammary gland tumors. Strategies were devised to generate antibody responses against hCG to investigate whether reversal of the molecular processes driving tumorigenesis would follow. hCG-immunized transgenic mice did not exhibit increases in body weight or serum prolactin levels, and gross ovarian and pituitary morphology remained normal. While non-immunized transgenic animals demonstrated heightened levels of transcripts associated with pituitary tumorigenesis (HMG2A, E2F1, CCND1, PRL, GH, GAL, PTTG1, BMP4) and decreased levels of CDK inhibitors CDKN1B (p27), CDKN2A (p16) and CDKN2c (p18), immunization led to a reversal to levels found in non-transgenic animals. Serum derived from transgenic (but not non-transgenic) mice led to enhanced transcription as well as expression of VEGF, IL-8, KC (murine IL-8) and MMP-9 in tumor cells, effects not seen when sera derived from hCG-immunized transgenic mice was employed. As the definitive indication of the restoration of the reproductive axis, immunization led to the resumption of estrous cyclicity as well as fertility in transgenic mice. These results indicate that hCG may influence cancer pathogenesis and progression via several distinct mechanisms. Using a stringent in vivo system in which βhCG acts both a “self” antigen and a tumor-promoting moiety (putatively akin to the situation in humans), the data builds a case for anti-gonadotropin vaccination strategies in the treatment of gonadotropin-dependent or secreting malignancies that frequently acquire resistance to conventional therapy.

Production of double repeated B subunit of Shiga toxin 2e at high levels in transgenic lettuce plants as vaccine material for porcine edema disease

Pig edema disease is a bacterial disease caused by enterohemorrhagic Escherichia coli. E. coli produces Shiga toxin 2e (Stx2e), which is composed of one A subunit (Stx2eA) and five B subunits (Stx2eB). We previously reported production of Stx2eB in lettuce plants as a potential edible vaccine (Matsui et al. in Biosci Biotechnol Biochem 73:1628-1634, 2009). However, the accumulation level was very low, and it was necessary to improve expression of Stx2eB for potential use of this plant-based vaccine. Therefore, in this study, we optimized the Stx2eB expression cassette and found that a double repeated Stx2eB (2× Stx2eB) accumulates to higher levels than a single Stx2eB in cultured tobacco cells. Furthermore, a linker peptide between the two Stx2eB moieties played an important role in maximizing the effects of the double repeat. Finally, we generated transgenic lettuce plants expressing 2× Stx2eB with a suitable linker peptide that accumulate as much as 80 mg per 100 g fresh weight, a level that will allow us to use these transgenic lettuce plants practically to generate vaccine material.

Effect of repetitiveness on the immunogenicity and antigenicity of Trypanosoma cruzi FRA protein

Repetitive proteins (RP) of Trypanosoma cruzi are highly present in the parasite and are strongly recognized by sera from Chagas' disease patients. Flagelar Repetitive Antigen (FRA), which is expressed in all steps of the parasite life cycle, is the RP that displays the greatest number of aminoacids per repeat and has been indicated as one of the most suitable candidate for diagnostic test because of its high performance in immunoassays. Here we analyzed the influence of the number of repeats on the immunogenic and antigenic properties of the antigen. Recombinant proteins containing one, two, and four tandem repeats of FRA (FRA1, FRA2, and FRA4, respectively) were obtained and the immune response induced by an equal amount of repeats was evaluated in a mouse model. The reactivity of specific antibodies present in sera from patients naturally infected with T. cruzi was also assessed against FRA1, FRA2, and FRA4 proteins, and the relative avidity was analyzed. We determined that the number of repeats did not increase the humoral response against the antigen and this result was reproduced when the repeated motifs were alone or fused to a non-repetitive protein. By contrast, the binding affinity of specific human antibodies increases with the number of repeated motifs in FRA antigen. We then concluded that the high ability of FRA to be recognized by specific antibodies from infected individuals is mainly due to a favorable polyvalent interaction between the antigen and the antibodies. In accordance with experimental results, a 3D model was proposed and B epitope in FRA1, FRA2, and FRA4 were predicted.

A novel virus-like particle based on hepatitis B core antigen and substrate-binding domain of bacterial molecular chaperone DnaK

Hepatitis B virus core (HBc) protein has been proved to be an attractive carrier for foreign epitopes, and can display green fluorescent protein (GFP) on its surface. The structure of substrate-binding domain of DnaK [DnaK (394-504 aa), DnaK SBD] is similar to GFP, we therefore reasoned that DnaK SBD might also be tolerated. Electron microscopic observations suggested that the chimeric proteins containing the truncated HBc (HBcDelta) and DnaK SBD could self-assemble into virus-like particle (VLP). Then the accessibility of DnaK SBD and the adjuvanticity of VLP HBcDelta-SBD were demonstrated by two recombinant peptide vaccines against gonadotropin-releasing hormone (GnRH), GhM and GhMNR. The latter carries in addition the peptide motif NRLLLTG which is known to bind to DnaK and DnaK SBD. The combination of VLP HBcDelta-SBD and GhMNR elicited stronger humoral responses and caused further testicular atrophy than the combinations of VLP HBcDelta and GhMNR or VLP HBcDelta-SBD and GhM in Balb/c mice. These findings indicate VLP HBcDelta-SBD might serve as an excellent carrier for GhMNR and some other peptide vaccines.

Improved efficacy of DNA vaccination against prostate carcinoma by boosting with recombinant protein vaccine and by introduction of a novel adjuvant epitope

DNA vaccine represents an attractive approach for cancer treatment by inducing active immune-deprivation of gastrin-releasing peptide (GRP) from tumor cells, the growth of which is dependent on the stimulation of GRP. In this study, we developed a DNA vaccine using a plasmid vector to deliver the immunogen of six copies of the B cell epitope GRP(18-27) (GRP6). In order to increase the potency of this DNA vaccine, multiple strategies have been applied including DNA-prime protein-boost immunization and introduction of a foreign T-helper epitope into DNA vaccine. Mice vaccinated DNA vaccine boosting with HSP65-GRP6 protein induced high titer and relatively high avidity of anti-GRP antibodies as well as inhibition effect on the growth of murine prostate carcinoma, superior to the treatment using DNA alone or BCG priming HSP65-GRP6 protein boosting. Furthermore, the introduction of a novel foreign T-helper epitope into the GRP DNA vaccine showed a markedly stronger humoral immune response against GRP and tumor rejection even than the DNA-prime protein-boost strategy. No further stronger immunogenicity of this foreign T-helper epitope modified DNA vaccine was observed even using the strategy of modified DNA vaccine-priming and HSP65-GRP6 boosting method. The data presented demonstrate that improvement of potency of anti-GRP DNA vaccine with the above two feasible approaches should offer useful methods in the development of new DNA vaccine against growth factors for cancer immunotherapy.

Specific antibodies elicited by a novel DNA vaccine targeting gastrin-releasing peptide inhibit murine melanoma growth in vivo

The elevated expression and receptor binding of gastrin-releasing peptide (GRP) in various types of cancer, especially in malignant melanoma of the skin, suggest that GRP might be a putative target for immunotherapy in neoplastic diseases. We have therefore constructed a novel DNA vaccine coding for six tandem repeats of a fragment of GRP from amino acids 18 to 27 (GRP6) flanked by helper T-cell epitopes for increased immunogenicity, including HSP65, a tetanus toxoid fragment from amino acids 830 to 844 (T), pan-HLA-DR-binding epitope (PADRE) (P), and two repeats of a mycobacterial HSP70 fragment from amino acids 407 to 426 (M). The anti-GRP DNA vaccine (pCR3.1-VS-HSP65-TP-GRP6-M2) was constructed on a backbone of a pCR3.1 plasmid vector with eight 5'-GACGTT-3' CpG motifs and the VEGF183 signal peptide (VS). Intramuscular (IM) injections of anti-GRP vaccine in mice stimulated the production of high titers of specific antibodies against GRP and suppressed the growth of subcutaneous tumors of B16-F10 melanoma cells. Parallel results were obtained in vitro, showing inhibition of B16-F10 cell proliferation by GRP antisera. IM injections of the DNA vaccine also significantly attenuated tumor-induced angiogenesis associated with intradermal tumors of B16-F10 cells. In addition, lung invasion of intravenously injected cells was highly diminished, suggesting potent antimetastatic activity of the DNA vaccine. These findings support the highly immunogenic and potent antitumorigenic activity of specific anti-GRP antibodies elicited by the anti-GRP DNA vaccine.

Single intranasal immunization with recombinant adenovirus-based vaccine induces protective immunity against respiratory syncytial virus infection

Respiratory syncytial virus (RSV) is a major cause of severe lower respiratory tract disease in infancy and early childhood. Despite its importance as a pathogen, there is no licensed vaccine against RSV. The G glycoprotein of RSV, a major attachment protein, is a potentially important target for protective antiviral immune responses. Here, a recombinant replication-deficient adenovirus-based vaccine, rAd/3xG, expressing the soluble core domain of G glycoprotein (amino acids 130 to 230) engineered by codon optimization and tandem repetition for higher-level expression, was constructed and evaluated for its potential as an RSV vaccine in a murine model. A single intranasal immunization with rAd/3xG provided potent protection against RSV challenge which lasted for more than 10 weeks. Strong mucosal immunoglobulin A responses were also induced by a single intranasal immunization but not by intramuscular or oral administration of rAd/3xG. Interestingly, neither gamma interferon- nor interleukin-4-producing CD4 T cells directed to I-E(d)-restricted epitope were detected in the lungs of rAd/3xG-immune mice upon challenge, whereas priming with vaccinia virus expressing RSV G (vvG) elicited strong Th1/Th2 mixed CD4 T-cell responses. Lung eosinophilia and vaccine-induced weight loss were significantly lower in the rAd/3xG-immune group than in the vvG-primed group. Together, our data demonstrate that a single intranasal administration of rAd/3xG elicits beneficial protective immunity and represents a promising vaccine regimen against RSV infection.

CTA1-M2e-DD: a novel mucosal adjuvant targeted influenza vaccine

At present few vaccine candidates exists against potentially pandemic influenza virus infections. We provide compelling evidence that a targeted fusion protein based on the CTA1-DD adjuvant and containing tandem repeats of the matrix protein 2 (M2e) ectodomain epitope, CTA1-3M2e-DD, confers strong protective immunity against a potentially lethal challenge infection with influenza virus in mice. The formulation was highly effective for mucosal immunizations and promoted high M2e-specific serum IgG and mucosal IgA antibody titers and an hitherto unknown anti-M2e CD4 T cell immunity. This novel CTA1-3M2e-DD fusion protein combines adjuvant and a conserved influenza A antigen in a promising candidate for a universal anti-influenza vaccine.