Glycopeptide dendrimers, part III: a review. Use of glycopeptide dendrimers in immunotherapy and diagnosis of cancer and viral diseases

Dendrimers for cancer immunotherapy: Avidity-based drug delivery vehicles for effective anti-tumor immune response

Cancer immunotherapy, or the utilization of a patient's own immune system to treat cancer, has shifted the paradigm of cancer treatment. Despite meaningful responses being observed in multiple studies, currently available immunotherapy platforms have only proven effective to a small subset of patients. To address this, nanoparticles have been utilized as a novel carrier for immunotherapeutic drugs, achieving robust anti-tumor effects with increased adaptive and durable responses. Specifically, dendrimer nanoparticles have attracted a great deal of scientific interest due to their versatility in various therapeutic applications, resulting from their unique physicochemical properties and chemically well-defined architecture. This review offers a comprehensive overview of dendrimer-based immunotherapy technologies, including their formulations, biological functionalities, and therapeutic applications. Common formulations include: (1) modulators of cytokine secretion of immune cells (adjuvants); (2) facilitators of the recognition of tumorous antigens (vaccines); (3) stimulators of immune effectors to selectively attack cells expressing specific antigens (antibodies); and (4) inhibitors of immune-suppressive responses (immune checkpoint inhibitors). On-going works and prospects of dendrimer-based immunotherapies are also discussed. Overall, this review provides a critical overview on rapidly growing dendrimer-based immunotherapy technologies and serves as a guideline for researchers and clinicians who are interested in this field. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Materials for Immunotherapy

Breakthroughs in materials engineering have accelerated the progress of immunotherapy in preclinical studies. The interplay of chemistry and materials has resulted in improved loading, targeting, and release of immunomodulatory agents. An overview of the materials that are used to enable or improve the success of immunotherapies in preclinical studies is presented, from immunosuppressive to proinflammatory strategies, with particular emphasis on technologies poised for clinical translation. The materials are organized based on their characteristic length scale, whereby the enabling feature of each technology is organized by the structure of that material. For example, the mechanisms by which i) nanoscale materials can improve targeting and infiltration of immunomodulatory payloads into tissues and cells, ii) microscale materials can facilitate cell-mediated transport and serve as artificial antigen-presenting cells, and iii) macroscale materials can form the basis of artificial microenvironments to promote cell infiltration and reprogramming are discussed. As a step toward establishing a set of design rules for future immunotherapies, materials that intrinsically activate or suppress the immune system are reviewed. Finally, a brief outlook on the trajectory of these systems and how they may be improved to address unsolved challenges in cancer, infectious diseases, and autoimmunity is presented.

Click inspired synthesis of hexa and octadecavalent peripheral galactosylated glycodendrimers and their possible therapeutic applications

Click inspired glycodendrimers comprising a rigid hexapropargyloxy benzene core with peripheral β-d-galactopyranosidic units were developed and evaluated for their therapeutic potential.

Peptide dendrimers: drug/gene delivery and other approaches

Dendrimers are versatile hyperbranched molecules, which have deserved attention especially for their potential in many applications, including biological. Peptide dendrimers comprise interesting classes of dendrimers, and their use has been emphasized as a drug/bioactive compound delivery system, mostly in the antineoplastic area. The bioactive molecules can be covalently linked or entrapped inside the peptide derivative. Self-assembled nanocarriers are a recent trend in the design of potential delivery systems, and pH-sensitive carriers, one of their methods, have been designed to control their systems. In addition, the use of targeting peptides or other specific groups that direct the drug/bioactive compounds to specific organs is an important trend in the search for better drug delivery systems. Recent examples have been given in the literature, showing that gene delivery as another important peptide dendrimer application. It is worth emphasizing that some peptide dendrimers show activity per se, without bioactive compounds. Immune compounds and vaccines are presented herein, as well as uses of other peptide dendrimers are briefly discussed in this review, which encompasses around 10 years of work.

Large-scale synthesis and structural analysis of a synthetic glycopeptide dendrimer as an anti-cancer vaccine candidate

A complex glycopeptide was obtained in multigram as a fully synthetic anti-cancer vaccine for human use.

Synthesis of G0 aminopolyol and aminosugar dendrimers, controlled by NMR and MALDI TOF mass spectrometry

Organic compounds designed to serve as stable dendrimer cores were developed. A series of aminosugar and amino polyol containing G0 dendrimers were synthesized. The reaction mixture composition was checked by MALDI TOF mass spectrometry, while that of purified products – by ¹H and ¹³C NMR combined with 2D NMR spectroscopy as well as MALDI TOF MSMS mass spectra. Mass spectrometric fragmentation experiments were performed in positive ion mode in order to determine common fragmentation patterns of [M+H]⁺ ions.

Glycosylation-Based Serum Biomarkers for Cancer Diagnostics and Prognostics

Cancer is the second most common cause of death in developed countries with approximately 14 million newly diagnosed individuals and over 6 million cancer-related deaths in 2012. Many cancers are discovered at a more advanced stage but better survival rates are correlated with earlier detection. Current clinically approved cancer biomarkers are most effective when applied to patients with widespread cancer. Single biomarkers with satisfactory sensitivity and specificity have not been identified for the most common cancers and some biomarkers are ineffective for the detection of early stage cancers. Thus, novel biomarkers with better diagnostic and prognostic performance are required. Aberrant protein glycosylation is well known hallmark of cancer and represents a promising source of potential biomarkers. Glycoproteins enter circulation from tissues or blood cells through active secretion or leakage and patient serum is an attractive option as a source for biomarkers from a clinical and diagnostic perspective. A plethora of technical approaches have been developed to address the challenges of glycosylation structure detection and determination. This review summarises currently utilised glycoprotein biomarkers and novel glycosylation-based biomarkers from the serum glycoproteome under investigation as cancer diagnostics and for monitoring and prognostics and includes details of recent high throughput and other emerging glycoanalytical techniques.

Dendrimers for theranostic applications

Recently, there have been tremendous advances in the development of various nanotechnology-based platforms for diagnosis and therapy. These nanoplatforms, which include liposomes, micelles, polymers, and dendrimers, comprise highly integrated nanoparticles that provide multiple functions, such as targeting, imaging, and therapy. This review focuses on dendrimer-based nanocarriers that have recently been developed for 'theranostics (or theragnosis)', a combination of therapy and diagnostics. We discuss the in vitro and in vivo applications of these nanocarriers in strategies against diseases including cancer. We also explore the use of dendrimers as imaging agents for fluorescence imaging, magnetic resonance imaging, X-ray computed tomography, and nuclear medical imaging.

Dendritic glycopolymers based on dendritic polyamine scaffolds: view on their synthetic approaches, characteristics and potential for biomedical applications

The potential of dendritic glycopolymers based on dendritic polyamine scaffolds for biomedical applications is presented and compared with that of the structurally related anti-adhesive dendritic glycoconjugates.

Cancer immunotherapy: nanodelivery approaches for immune cell targeting and tracking

Cancer is one of the most common diseases afflicting people globally. New therapeutic approaches are needed due to the complexity of cancer as a disease. Many current treatments are very toxic and have modest efficacy at best. Increased understanding of tumor biology and immunology has allowed the development of specific immunotherapies with minimal toxicity. It is important to highlight the performance of monoclonal antibodies, immune adjuvants, vaccines and cell-based treatments. Although these approaches have shown varying degrees of clinical efficacy, they illustrate the potential to develop new strategies. Targeted immunotherapy is being explored to overcome the heterogeneity of malignant cells and the immune suppression induced by both the tumor and its microenvironment. Nanodelivery strategies seek to minimize systemic exposure to target therapy to malignant tissue and cells. Intracellular penetration has been examined through the use of functionalized particulates. These nano-particulate associated medicines are being developed for use in imaging, diagnostics and cancer targeting. Although nano-particulates are inherently complex medicines, the ability to confer, at least in principle, different types of functionality allows for the plausible consideration these nanodelivery strategies can be exploited for use as combination medicines. The development of targeted nanodelivery systems in which therapeutic and imaging agents are merged into a single platform is an attractive strategy. Currently, several nanoplatform-based formulations, such as polymeric nanoparticles, micelles, liposomes and dendrimers are in preclinical and clinical stages of development. Herein, nanodelivery strategies presently investigated for cancer immunotherapy, cancer targeting mechanisms and nanocarrier functionalization methods will be described. We also intend to discuss the emerging nano-based approaches suitable to be used as imaging techniques and as cancer treatment options.

Sialyl Tn-expressing bladder cancer cells induce a tolerogenic phenotype in innate and adaptive immune cells

Despite the wide acceptance that glycans are centrally implicated in immunity, exactly how they contribute to the tilt immune response remains poorly defined. In this study, we sought to evaluate the impact of the malignant phenotype-associated glycan, sialyl-Tn (STn) in the function of the key orchestrators of the immune response, the dendritic cells (DCs). In high grade bladder cancer tissue, the STn antigen is significantly overexpressed and correlated with the increased expression of ST6GALNAC1 sialyltransferase. Bladder cancer tissue presenting elevated expression of ST6GALNAC1 showed a correlation with increased expression of CD1a, a marker for bladder immature DCs and showed concomitant low levels of Th1-inducing cytokines IL-12 and TNF-α. In vitro, human DCs co-incubated with STn(+) bladder cancer cells, had an immature phenotype (MHC-II(low), CD80(low) and CD86(low)) and were unresponsive to further maturation stimuli. When contacting with STn(+) cancer cells, DCs expressed significantly less IL-12 and TNF-α. Consistent with a tolerogenic DC profile, T cells that were primed by DCs pulsed with antigens derived from STn(+) cancer cells were not activated and showed a FoxP3(high) IFN-γ(low) phenotype. Blockade of STn antigens and of STn(+) glycoprotein, CD44 and MUC1, in STn(+) cancer cells was able to lower the induction of tolerance and DCs become more mature. Overall, our data suggest that STn-expressing cancer cells impair DC maturation and endow DCs with a tolerogenic function, limiting their capacity to trigger protective anti-tumour T cell responses. STn antigens and, in particular, STn(+) glycoproteins are potential targets for circumventing tumour-induced tolerogenic mechanisms.

Sugar-appended polyamidoamine dendrimer conjugates with cyclodextrins as cell-specific non-viral vectors

The widespread use of various cyclodextrin (CyD)-appended polymers and polyrotaxanes as gene carriers has been reported. Among the various polyamidoamine dendrimer (dendrimer) conjugates with CyDs (CDE), the dendrimer (G3) conjugate with α-CyD having an average degree of substitution (DS) of 2.4 (α-CDE (G3, DS 2)) displayed remarkable properties as DNA carriers. In an attempt to develop cell-specific gene transfer carriers, we prepared some sugar-appended α-CDEs, e.g. mannosylated, galactosylated, and lactosylated α-CDEs. In addition, PEGylated Lac-α-CDEs (G3) were prepared and evaluated as a hepatocyte-selective and serum-resistant gene transfer carrier. Moreover, PEGylated-α-CDE/CyD polypseudorotaxane systems for novel sustained DNA release system have been developed. Interestingly, glucronylglucosyl-β-cyclodextrin (GUG-β-CyD) conjugates with dendrimer (G2) (GUG-β-CDE (G2)) had superior gene transfer activity to α-CDE (G2), expecting a development of new series of sugar-appended CDEs over α-CDEs (G2). Collectively, sugar-appended α-CDEs have the potential as novel cell-specific and safe carriers for DNA.

Sialyl-tn in cancer: (how) did we miss the target?

Sialyl-Tn antigen (STn) is a short O-glycan containing a sialic acid residue α2,6-linked to GalNAcα-O-Ser/Thr. The biosynthesis of STn is mediated by a specific sialyltransferase termed ST6GalNAc I, which competes with O-glycans elongating glycosyltransferases and prevents cancer cells from exhibiting longer O-glycans. While weakly expressed by fetal and normal adult tissues, STn is expressed by more than 80% of human carcinomas and in all cases, STn detection is associated with adverse outcome and decreased overall survival for the patients. Because of its pan-carcinoma expression associated with an adverse outcome, an anti-cancer vaccine, named Theratope, has been designed towards the STn epitope. In spite of the great enthusiasm around this immunotherapy, Theratope failed on Phase III clinical trial. However, in lieu of missing this target, one should consider to revise the Theratope design and the actual facts. In this review, we highlight the many lessons that can be learned from this failure from the immunological standpoint, as well as from the drug design and formulation and patient selection. Moreover, an irrefutable knowledge is arising from novel immunotherapies targeting other carbohydrate antigens and STn carrier proteins, such as MUC1, that will warrantee the future development of more successful anti-STn immunotherapy strategies.

Design and synthesis of multifunctional gold nanoparticles bearing tumor-associated glycopeptide antigens as potential cancer vaccines

The development of vaccines against specific types of cancers will offer new modalities for therapeutic intervention. Here, we describe the synthesis of a novel vaccine construction prepared from spherical gold nanoparticles of 3-5 nm core diameters. The particles were coated with both the tumor-associated glycopeptides antigens containing the cell-surface mucin MUC4 with Thomsen Friedenreich (TF) antigen attached at different sites and a 28-residue peptide from the complement derived protein C3d to act as a B-cell activating "molecular adjuvant". The synthesis entailed solid-phase glycopeptide synthesis, design of appropriate linkers, and attachment chemistry of the various molecules to the particles. Attachment to the gold surface was mediated by a novel thiol-containing 33 atom linker which was further modified to be included as a third "spacer" component in the synthesis of several three-component vaccine platforms. Groups of mice were vaccinated either with one of the nanoplatform constructs or with control particles without antigen coating. Evaluation of sera from the immunized animals in enzyme immunoassays (EIA) against each glycopeptide antigen showed a small but statistically significant immune response with production of both IgM and IgG isotypes. Vaccines with one carbohydrate antigen (B, C, and E) gave more robust responses than the one with two contiguous disaccharides (D), and vaccine E with a TF antigen attached to threonine at the 10th position of the peptide was selected for IgG over IgM suggesting isotype switching. The data suggested that this platform may be a viable delivery system for tumor-associated glycopeptide antigens.

Design of fully synthetic, self-adjuvanting vaccine incorporating the tumor-associated carbohydrate Tn antigen and lipoamino acid-based Toll-like receptor 2 ligand

Overexpression of certain tumor-associated carbohydrate antigens (TACA) caused by malignant transformation offers promising targets to develop novel antitumor vaccines, provided the ability to break their inherent low immunogenicity and overcome the tolerance of the immune system. We designed, synthesized, and immunologically evaluated a number of fully synthetic new chimeric constructs incorporating a cluster of the most common TACA (known as Tn antigen) covalently attached to T-cell peptide epitopes derived from polio virus and ovalbumin and included a synthetic built-in adjuvant consisting of two 16-carbon lipoamino acids. Vaccine candidates were able to induce significantly strong antibody responses in mice without the need for any additional adjuvant, carrier protein, or special pharmaceutical preparation (e.g., liposomes). Vaccine constructs were assembled either in a linear or in a branched architecture, which demonstrated the intervening effects of the incorporation and arrangement of T-cell epitopes on antibody recognition.

Design of biocompatible dendrimers for cancer diagnosis and therapy: current status and future perspectives

In the past decade, nanomedicine with its promise of improved therapy and diagnostics has revolutionized conventional health care and medical technology. Dendrimers and dendrimer-based therapeutics are outstanding candidates in this exciting field as more and more biological systems have benefited from these starburst molecules. Anticancer agents can be either encapsulated in or conjugated to dendrimer and be delivered to the tumour via enhanced permeability and retention (EPR) effect of the nanoparticle and/or with the help of a targeting moiety such as antibody, peptides, vitamins, and hormones. Imaging agents including MRI contrast agents, radionuclide probes, computed tomography contrast agents, and fluorescent dyes are combined with the multifunctional nanomedicine for targeted therapy with simultaneous cancer diagnosis. However, an important question reported with dendrimer-based therapeutics as well as other nanomedicines to date is the long-term viability and biocompatibility of the nanotherapeutics. This critical review focuses on the design of biocompatible dendrimers for cancer diagnosis and therapy. The biocompatibility aspects of dendrimers such as nanotoxicity, long-term circulation, and degradation are discussed. The construction of novel dendrimers with biocompatible components, and the surface modification of commercially available dendrimers by PEGylation, acetylation, glycosylation, and amino acid functionalization have been proposed as available strategies to solve the safety problem of dendrimer-based nanotherapeutics. Also, exciting opportunities and challenges on the development of dendrimer-based nanoplatforms for targeted cancer diagnosis and therapy are reviewed (404 references).

Immunotherapy of MHC class I-deficient tumors

MHC class I downregulation is a general mechanism by which tumor cells can escape from T-cell-mediated immunity. This downregulation also represents a serious obstacle to the development of effective antitumor immunotherapy or vaccination. Therefore, successful immunotherapeutic and vaccination protocols should be optimized against tumors with distinct cell surface expression of the MHC class I molecules. Mechanisms leading to protective immunity may vary in different models with respect to the particular tumors (e.g., in their levels of residual expression of the MHC class I molecules on tumor cells or inducibility of MHC class I expression). Notably, both CD8+ cell-mediated immunity and MHC class I-unrestricted mechanisms can take place against MHC class I-deficient tumors. Since MHC class I downregulation is frequently reversible by cytokines and also by the activation of epigenetically silenced genes, an attractive strategy is to elicit specific cell-mediated immunity combined with restoration of MHC class I expression on tumor cells.

Perfluoroalkylated amphiphilic MUC1 glycopeptide antigens as tools for cancer immunotherapy

The synthesis of perfluoroalkylated glycopeptide antigens and their specific binding to anti-MUC1 mouse antibodies is reported.

Advances in the design and delivery of peptide subunit vaccines with a focus on toll-like receptor agonists

Considerable success has been made with many peptide antigen formulations, and peptide-based vaccines are emerging as the next generation of prophylactic and remedial immunotherapy. However, finding an optimal platform balancing all of the requirements for an effective, specific and safe immune response remains a major challenge for many infectious and chronic diseases. This review outlines how peptide immunogenicity is influenced by the way in which peptides are presented to the immune system, underscoring the need for multifunctional delivery systems that couple antigen and adjuvant into a single construct. Particular attention is given to the ability of Toll-like receptor agonists to act as adjuvants. A survey of recent approaches to developing peptide antigen delivery systems is given, many of which incorporate Toll-like receptor agonists into the design.

Consequences of the expression of sialylated antigens in breast cancer

Changes in cell surface glycosylation are common modifications that occur during oncogenesis, leading to the over-expression of tumour-associated carbohydrate antigens (TACA). Most of these antigens are sialylated and the increase of sialylation is a well-known feature of transformed cells. In breast cancer, expression of TACA such as sialyl-Lewis(x) or sialyl-Tn is usually associated with a poor prognosis and a decreased overall survival of patients. However, the specific role of these sialylated antigens in breast tumour development and aggressiveness is not clearly understood. These glycosylation changes result from the modification of the expression of genes encoding specific glycosyltransferases involved in glycan biosynthesis and the level of expression of sialyltransferase genes has been proposed to be a prognostic marker for the follow-up of breast cancer patients. Several human cellular models have been developed in order to explain the mechanisms by which carbohydrate antigens can reinforce breast cancer progression and aggressiveness. TACA expression is associated with changes in cell adhesion, migration, proliferation and tumour growth. In addition, recent data on glycolipid biosynthesis indicate an important role of G(D3) synthase expression in breast cancer progression. The aim of this review is to summarize our current knowledge of sialylation changes that occur in breast cancer and to describe the cellular models developed to analyze the consequences of these changes on disease progression and aggressiveness.

Design and creativity in synthesis of multivalent neoglycoconjugates

From the authors' opinion, this chapter constitutes a modest extension of the seminal and inspiring contribution of Stowell and Lee on neoglycoconjugates published in this series [C. P. Stowell and Y. C. Lee, Adv. Carbohydr. Chem. Biochem., 37 (1980) 225-281]. The outstanding progresses achieved since then in the field of the "glycoside cluster effect" has witnessed considerable creativity in the design and synthetic strategies toward a vast array of novel carbohydrate structures and reflects the dynamic activity in the field even since the recent chapter by the Nicotra group in this series [F. Nicotra, L. Cipolla, F. Peri, B. La Ferla, and C. Radaelli, Adv. Carbohydr. Chem. Biochem., 61 (2007) 353-398]. Beyond the more classical neoglycoproteins and glycopolymers (not covered in this work) a wide range of unprecedented and often artistically beautiful multivalent and monodisperse nanostructures, termed glycodendrimers for the first time in 1993, has been created. This chapter briefly surveys the concept of multivalency involved in carbohydrate-protein interactions. The topic is also discussed in regard to recent steps undertaken in glycobiology toward identification of lead candidates using microarrays and modern analytical tools. A systematic description of glycocluster and glycodendrimer synthesis follows, starting from the simplest architectures and ending in the most complex ones. Presentation of multivalent glycostructures of intermediate size and comprising, calix[n]arene, porphyrin, cyclodextrin, peptide, and carbohydrate scaffolds, has also been intercalated to better appreciate the growing synthetic complexity involved. A subsection describing novel all-carbon-based glycoconjugates such as fullerenes and carbon nanotubes is inserted, followed by a promising strategy involving dendrons self-assembling around metal chelates. The chapter then ends with those glycodendrimers that have been prepared using commercially available dendrimers possessing varied functionalities, or systematically synthesized using either divergent or convergent strategies.

MAP dendrimer elicits antibodies for detecting rat and mouse GH-binding proteins

The membrane-bound rat GH-R and an alternatively spliced isoform, the soluble rat GH-BP, are comprised of identical N-terminal GH-binding domains; however, their C-terminal sequences differ. Immunological reagents are needed to distinguish between the two isoforms in order to understand their respective roles in mediating the actions of GH. Accordingly, a tetravalent MAP dendrimer with four identical branches of a C-terminal peptide sequence of the rat GH-BP (GH-BP(263-279)) was synthesized and used as an immunogen in rabbits. Solid-phase peptide synthesis of four GH-BP(263-279) segments onto a tetravalent Lys(2)-Lys-beta-Ala-OH core peptide was carried out using Fmoc chemistry. The mass of the RP-HPLC-purified synthetic product, 8398 Da, determined by ESI-MS, was identical to expected mass. Three anti-rat GH-BP(263-279) MAP antisera, BETO-8039, BETO-8040, and BETO-8041, at dilutions of 10(-3), recognized both the rat GH-BP(263-279) MAP and recombinant mouse GH-BP with ED(50)s within a range of 5-10 fmol, but did not cross-react with BSA in dot blot analyses. BETO-8041 antisera (10(-3) dilution) recognized GH-BPs of rat serum and liver having M(r)s ranging from 35 to 130 kDa, but did not recognize full-length rat GH-Rs. The antisera also detected recombinant mouse GH-BPs. In summary, the tetravalent rat GH-BP(263-279) MAP dendrimer served as an effective immunogenic antigen in eliciting high titer antisera specific for the C-termini of both rat and mouse GH-BPs. The antisera will facilitate studies aimed at improving our understanding of the biology of GH-BPs.

Synthesis of MUC1 Peptide and Glycopeptide Dendrimers

Several dendrimers possessing multiple copies of peptides and glycopeptides belonging to the MUC1 eicosapeptide tandem repeat sequence have been prepared. Fmoc-strategy solid-phase peptide synthesis was used to construct the peptides and glycopeptides, which were conjugated to suitably functionalized dendrimer cores using the copper-catalyzed azide-alkyne cycloaddition reaction to produce multivalent peptide and glycopeptide dendrimers.