Phage-display selection of a human single-chain fv antibody highly specific for melanoma and breast cancer cells using a chemoenzymatically synthesized G(M3)-carbohydrate antigen

Recombinant antibodies by phage display for bioanalytical applications

Antibody phage display, aimed at preparing antibodies to defined antigens, is a useful replacement for hybridoma technology. The phage system replaces all work stages that follow animal immunization with simple procedures for manipulating DNA and bacteria. It enables the time needed to generate stable antibody-producing clones to be shortened considerably, making the process noticeably cheaper. Antibodies prepared by phage display undergo several affinity selection steps and can be used as selective receptors in biosensors. This article briefly describes the techniques used in the making of phage antibodies to various antigens. The possibilities and prospects are discussed of using phage antibodies as selective agents in analytical systems, including biosensors.

Pathogen-sugar interactions revealed by universal saturation transfer analysis

Many pathogens exploit host cell-surface glycans. However, precise analyses of glycan ligands binding with heavily modified pathogen proteins can be confounded by overlapping sugar signals and/or compounded with known experimental constraints. Universal saturation transfer analysis (uSTA) builds on existing nuclear magnetic resonance spectroscopy to provide an automated workflow for quantitating protein-ligand interactions. uSTA reveals that early-pandemic, B-origin-lineage severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike trimer binds sialoside sugars in an "end-on" manner. uSTA-guided modeling and a high-resolution cryo-electron microscopy structure implicate the spike N-terminal domain (NTD) and confirm end-on binding. This finding rationalizes the effect of NTD mutations that abolish sugar binding in SARS-CoV-2 variants of concern. Together with genetic variance analyses in early pandemic patient cohorts, this binding implicates a sialylated polylactosamine motif found on tetraantennary N-linked glycoproteins deep in the human lung as potentially relevant to virulence and/or zoonosis.

New Triazacycloalkane Derivatives as Cytotoxic Agents for CLL Treatment: From Proof of Concept to the Targeting Biomolecule

The 1,4,7-tris-(2-pyridinylmethyl)-1,4,7-triazacyclononane ligand (no3py) and its bifunctional analogue no3pyCOOK were synthesized to investigate their action toward zinc(II) depletion related to the apoptosis phenomenon in chronic lymphocytic leukemia (CLL) cells. no3py was used as the "free" ligand, while its "graftable" derivative was conjugated on a newly synthesized bifunctional sialoglycan, 6'-SL-NH₂, selected to specifically bind CD22 biomarker expressed on the B-CLL cell surface. Both compounds were produced with good yields thanks to a Sonogashira coupling reaction and an orthoester function, respectively, for the chelator and the targeting moiety. The newly reported bioconjugate 6'-SL-no3py was then obtained through a peptidic coupling reaction. Biological in vitro studies of no3py and 6'-SL-no3py consisting of real-time detection of cell health (cytotoxicity and proliferation) and caspases 3/7 activation (crucial enzymes whose activation triggers cell death signaling pathways) have been investigated. First, Ramos, Daudi, and Raji B-cell lines, which present different sensitivity to zinc(II) content variation, were incubated with no3py and 6'-SL-no3py. Then, a videomicroscope allowed the real-time monitoring of the morphological changes leading to cell death from the detection of the cytotoxicity, the antiproliferative effect, and the caspasic activity. In terms of mechanism, the Zn²⁺ chelator cytotoxic effect of no3py has been evidenced by a culture medium ion supplementation study and by the decrease of intracellular fluorescence of Zn-specific fluorophore zinquin in the presence of no3py and 6'-SL-no3py chelators. Finally, flow cytometry analysis with classical Annexin V staining was conducted to detect no3py- and 6'-SL-no3py-induced apoptotic cell death in B-CLL cells. Time-course analysis, using the Incucyte Live-Cell Analysis System, demonstrated that no3py induced cell death in a time- and dose-dependent manner with variability across cell lines. 6'-SL-no3py exhibited the same dose-dependent trend as no3py, showing the efficiency of the targeting moiety. In both cases, the chelators depicted proliferation curves that were inversely correlated with kinetic death. Morphological changes specific to apoptosis and caspase 3/7 activation were observed for the three cell lines treated with no3py and 6'-SL-no3py, highlighting their role as apoptotic agents. A higher concentration of 6'-SL-no3py is needed to reach 50% of the B-CLL mortality, confirming a targeting of the chelator to the cell membrane. Overall, our results proved that the biological properties of the triazamacrocyclic chelator still remain even after addition of the targeting moiety. The free chelator as well as the bioconjugate constitute promising cytotoxic agents for CLL therapy through apoptosis induction.

Synthesis of an Aminooxy Derivative of the GM3 Antigen and Its Application in Oxime Ligation

The anomeric aminooxy GM3 trisaccharide cancer antigen (Neu5Acα2,3Galβ1,4Glcβ-ONH2) has been chemically synthesized using a linear glycosylation approach. The key step involves a highly α(2,3)-stereoselective sialylation to a galactose acceptor. The Neu5Acα2,3Gal intermediate was functionalized as a donor for a [2 + 1] glycosylation, including a glucose acceptor that featured an O-succinimidyl group on the reducing end as an aminooxy precursor. The fully deprotected anomeric aminooxy GM3 trisaccharide was then conjugated to the immunologically relevant zwitterionic polysaccharide PS A1 via an oxime link.

Generation of a Fully Human scFv that binds Tumor-Specific Glycoforms

Tumor-specific glycosylation changes are an attractive target for the development of diagnostic and therapeutic applications. Periostin is a glycoprotein with high expression in many tumors of epithelial origin including ovarian cancer. Strategies to target the peptide portion of periostin as a diagnostic or therapeutic biomarker for cancer are limited due to increased expression of periostin in non-cancerous inflammatory conditions. Here, we have screened for antibody fragments that recognize the tumor-specific glycosylation present on glycoforms of periostin containing bisecting N-glycans in ovarian cancer using a yeast-display library of antibody fragments, while subtracting those that bind to the periostin protein with glycoforms found in non-malignant cell types. We generated a biotinylated form of a fully human scFv antibody (scFvC9) that targets the bisecting N-glycans expressed by cancer cells. Validation studies in vitro and in vivo using scFvC9 indicate this antibody can be useful for the development of diagnostic, imaging, and therapeutic applications for cancers that express the antigen.

Glycan-directed CAR-T cells

Cancer immunotherapy is rapidly advancing in the treatment of a variety of hematopoietic cancers, including pediatric acute lymphoblastic leukemia and diffuse large B cell lymphoma, with chimeric antigen receptor (CAR)-T cells. CARs are genetically encoded artificial T cell receptors that combine the antigen specificity of an antibody with the machinery of T cell activation. However, implementation of CAR technology in the treatment of solid tumors has been progressing much slower. Solid tumors are characterized by a number of challenges that need to be overcome, including cellular heterogeneity, immunosuppressive tumor microenvironment (TME), and, in particular, few known cancer-specific targets. Post-translational modifications that differentially occur in malignant cells generate valid cell surface, cancer-specific targets for CAR-T cells. We previously demonstrated that CAR-T cells targeting an aberrant O-glycosylation of MUC1, a common cancer marker associated with changes in cell adhesion, tumor growth and poor prognosis, could control malignant growth in mouse models. Here, we discuss the field of glycan-directed CAR-T cells and review the different classes of antibodies specific for glycan-targeting, including the generation of high affinity O-glycopeptide antibodies. Finally, we discuss historic and recently investigated glycan targets for CAR-T cells and provide our perspective on how targeting the tumor glycoproteome and/or glycome will improve CAR-T immunotherapy.

Sialyllactose-Modified Three-Way Junction DNA as Binding Inhibitor of Influenza Virus Hemagglutinin

Sialic acid present on the cell surface is recognized by hemagglutinin (HA) on the influenza virus in the first step of infection. Therefore, a compound that can efficiently interfere with the interaction between sialic acid and HA might inhibit infection and allow detection of the influenza virus. We focused on the spatial arrangement of sialic acid binding sites on HA and developed 2,3-sialyllactose (2,3-SL)-modified three-way junction (3WJ) DNA molecules with a topology similar to that of sialic acid binding sites. 3WJ DNA with three 2,3-SL residues on each DNA strand showed (8.0 × 10⁴)-fold higher binding affinity for influenza virus A/Puerto Rico/08/34 (H1N1) compared to the 2,3-SL. This result indicated that the glycocluster effect due to clustering on one DNA arm and optimal spatial arrangement of the 3WJ DNA improved the weak interactions between a sialic acid and its binding site on HA. This 3WJ DNA compound has possible application as an inhibitor of influenza infection and for virus sensing.

Targeting O-Acetyl-GD2 Ganglioside for Cancer Immunotherapy

Target selection is a key feature in cancer immunotherapy, a promising field in cancer research. In this respect, gangliosides, a broad family of structurally related glycolipids, were suggested as potential targets for cancer immunotherapy based on their higher abundance in tumors when compared with the matched normal tissues. GD2 is the first ganglioside proven to be an effective target antigen for cancer immunotherapy with the regulatory approval of dinutuximab, a chimeric anti-GD2 therapeutic antibody. Although the therapeutic efficacy of anti-GD2 monoclonal antibodies is well documented, neuropathic pain may limit its application. O-Acetyl-GD2, the O-acetylated-derivative of GD2, has recently received attention as novel antigen to target GD2-positive cancers. The present paper examines the role of O-acetyl-GD2 in tumor biology as well as the available preclinical data of anti-O-acetyl-GD2 monoclonal antibodies. A discussion on the relevance of O-acetyl-GD2 in chimeric antigen receptor T cell therapy development is also included.

Improvement of the immune efficacy of carbohydrate vaccines by chemical modification on the GM3 antigen

N-modified GM3 glycoconjugates improved the efficiency of the vaccination without the combination of metabolic oligosaccharide engineering technology.

BSA-boronic acid conjugate as lectin mimetics

We report bovine serum albumin (BSA)-boronic acid (BA) conjugates as lectin mimetics and their glyco-capturing capacity. The BSA-BA conjugates were synthesized by amidation of carboxylic acid groups in BSA with aminophenyl boronic acid in the presence of EDC, and were characterized by Alizarin Red S (ARS) assay and SDS-PAGE gel. The BSA-BA conjugates were immobilized onto maleimide-functionalized silica beads and their sugar capturing capacity and specificity were confirmed by ARS displacement assay. Further, surface plasmon resonance (SPR) analysis of the glyco-capturing activity of the BSA-BA conjugates was conducted by immobilizing BSA-BA onto SPR gold chip. Overall, we demonstrated a BSA-BA-based lectin mimetics for glyco-capturing applications. These lectin mimetics are expected to provide an important tool for glycomics and biosensor research and applications.

Production of a recombinant antibody specific for i blood group antigen, a mesenchymal stem cell marker

Multipotent mesenchymal stem/stromal cells (MSCs) offer great promise for future regenerative and anti-inflammatory therapies. Panels of functional and phenotypical markers are currently used in characterization of different therapeutic stem cell populations from various sources. The i antigen (linear poly-N-acetyllactosamine) from the Ii blood group system has been suggested as a marker for MSCs derived from umbilical cord blood (UCB). However, there are currently no commercially available antibodies recognizing the i antigen. In the present study, we describe the use of antibody phage display technology to produce recombinant antibodies recognizing a structure from the surface of mesenchymal stem cells. We constructed IgM phage display libraries from the lymphocytes of a donor with an elevated serum anti-i titer. Antibody phage display technology is not dependent on immunization and thus allows the generation of antibodies against poorly immunogenic molecules, such as carbohydrates. Agglutination assays utilizing i antigen–positive red blood cells (RBCs) from UCB revealed six promising single-chain variable fragment (scFv) antibodies, three of which recognized epitopes from the surface of UCB-MSCs in flow cytometric assays. The amino acid sequence of the V_H gene segment of B12.2 scFv was highly similar to the V_H4.21 gene segment required to encode anti-i specificities. Further characterization of binding properties revealed that the binding of B12.2 hyperphage was inhibited by soluble linear lactosamine oligosaccharide. Based on these findings, we suggest that the B12.2 scFv we have generated is a prominent anti-i antibody that recognizes i antigen on the surface of both UCB-MSCs and RBCs. This binder can thus be utilized in UCB-MSC detection and isolation as well as in blood group serology.

Engineering the binding site of an antibody against N-glycolyl GM3: from functional mapping to novel anti-ganglioside specificities

The structurally related gangliosides N-glycolyl GM3 and N-acetyl GM3 are potential targets for tumor immunotherapy. 14F7 is a monoclonal antibody able to discriminate the tumor-specific antigen N-glycolyl GM3 from the closely related N-acetyl GM3 on the basis of the presence of a single additional hydroxyl group in the former. A combinatorial phage display strategy, based on the screening of a large library followed by refined mutagenesis, allowed a thorough exploration of the binding chemistry of this unique antibody. Three essential features of the heavy chain variable region were identified: two aromatic rings (in positions 33 and 100D) contributing to the binding site architecture and an arginine residue (position 98) critical for recognition. Directed evolution of 14F7 resulted in novel variants that cross-react with the tumor-associated antigen N-acetyl GM3 and display recurrent replacements: the substitution W33Q and the appearance of additional arginine residues at several positions of CDR H1. Successful conversion of such engineered variable regions into whole cross-reactive anti-GM3 immunoglobulins validated our phage-based approach to study and modify the lead antibody 14F7. The resulting family of closely related antibodies offers new tools to study the mechanisms of cell death induced by antibodies targeting gangliosides. In vitro directed evolution was useful to overcome the technical limitations to obtain anti-ganglioside antibodies. The case of 14F7 illustrates the power of combining library screening with focused site-directed randomization for a comprehensive scanning of protein interactions.

Antibody phage display libraries: contributions to oncology

Since the advent of phage display technology, dating back to 1985, antibody libraries displayed on filamentous phage surfaces have been used to identify specific binders for many different purposes, including the recognition of tumors. Phage display represents a high-throughput technique for screening billions of random fusion antibodies against virtually any target on the surface or inside cancer cells, or even soluble markers found in patient serum. Many phage display derived binders targeting important tumor markers have been identified. Selection directed to tumoral cells’ surfaces lead to the identification of unknown tumoral markers. Also the improvement of methods that require smaller amounts of cells has opened the possibility to use this approach on patient samples. Robust techniques combining an antibody library displayed on the phage surface and protein microarray allowed the identification of auto antibodies recognized by patient sera. Many Ab molecules directly or indirectly targeting angiogenesis have been identified, and one of them, ramucirumab, has been tested in 27 phase I–III clinical trials in a broad array of cancers. Examples of such antibodies will be discussed here with emphasis on those used as probes for molecular imaging and other clinical trials.

Generation of antibodies recognizing an aberrant glycoform of human tissue inhibitor of metalloproteinase-1 (TIMP-1) using decoy immunization and phage display

Aberrant glycosylation of human tissue inhibitor of metalloproteinase-1 (TIMP-1) by N-acetylglucosaminyltransferase-V (GnT-V) was previously reported to be related to cancer progression. Here, we report on the antibodies recognizing the structural features initiated by an addition of N-linked β(1,6)-N-acetylglucosamine (GlcNAc) branch by GnT-V on TIMP-1. Two glycoforms of TIMP-1, TIMP1-L produced in Lec4 cells without GnT-V activity and TIMP1-B in GnT-V overexpressing transfectant cells, were purified from culture supernatant and used for generation of antibodies. TIMP1-L was injected in the left hind footpad of mice as decoy and TIMP1-B in the right hind footpad as immunogen. Phage-displayed scFv library was constructed from the B cells retrieved from the right popliteal lymph nodes and subjected to panning and screening. Phage ELISA of individual clones revealed the scFv clones with preferential binding activity to TIMP1-B, and they were converted into an scFv-Fc format for further characterization of binding specificity. Glycan binding assay of an antibody, 1-9F, revealed its differential specificity toward an extension of glycan structure initiated with β(1,6)-GlcNAc linkage and terminally decorated with a sialic acid. This study demonstrates feasibility of a new strategy combining decoy immunization with phage display for the efficient generation of antibodies tracking down structural features of different glycoforms.

Screening lectin-binding specificity of bacterium by lectin microarray with gold nanoparticle probes

To develop a novel high-throughput tool for monitoring specific affinity of microbes with lectins, a kind of lectin microarray has been fabricated by immobilizing lectins on epoxide-derivatized glass slides and used to capture microbes. The capturing events are marked by attachment of lectin-conjugated gold nanoparticles followed by silver deposition to enhance the resonance light scattering (RLS) of the particles. The interactions of 16 lectins with four bacteria and one fungus were profiled by this approach. We demonstrated that the gold-nanoparticle-labeled array was suitable for identifying the binding affinity of lectin with bacterium, as well as determining the bacterium with high sensitivity. More importantly, we found that the growth of microbial strains in different culture media resulted in significant changes in their binding affinities with lectins, which might be important to the pathogenesis of the organisms.

Production of anti-carbohydrate antibodies by phage display technologies: potential impairment of cell growth as a result of endogenous expression

Anti-mannotriose (Man3) antibodies were previously isolated from a Keio phage library displaying human single chain variable fragments (scFvs) using a neoglycolipid, Man3- dipalmitoylphosphatidylethanolamine. Of three genes constructed, the 5A3 clone was expressed in mouse myeloma NS0 cells as a conjugate with human IgG(1) Fc (scFv-Fc) and characterized (Sakai, K., Shimizu, Y., Chiba, T., Matsumoto-Takasaki, A., Kusada, Y., Zhang, W., Nakata, M., Kojima, N., Toma, K., Takayanagi, A., Shimizu, N., and Fujita-Yamaguchi, Y. (2007) Biochemistry 46, 253-262; Zhang, W., Matsumoto-Takasaki, A., Kusada, Y., Sakaue, H., Sakai, K., Nakata, M., and Fujita-Yamaguchi, Y. (2007) Biochemistry 46, 263-270). Similarly, anti-Le(x) phages were screened from the same library with lacto-N-fucopentaose III (LNFPIII; Le(x))-dipalmitoylphosphatidylethanolamine. Of five phage clones isolated, two scFv genes were constructed to express scFv-Fc proteins in NS0 cells. As was experienced with anti-Man3 scFv-Fc clones, only one anti-LNFPIII clone, 1F12, was successfully produced and purified as an scFv-Fc protein. Although anti-LNFPIII 1F12 and anti-Man3 5A3 scFv-Fc proteins were secreted into media, a decline in scFv-Fc production was observed with both stable clones during early passages. Transient expression of anti-LNFPIII and anti-Man3 scFv-Fc genes in COS-7 cells and subsequent analyses of scFv-Fc protein expression revealed accumulation of translated proteins in the endoplasmic reticulum for scFv-Fc proteins derived from clones that did not survive as stable clones. This report describes the following: (i) isolation of anti-LNFPIII scFv genes; (ii) purification of anti-LNFPIII scFv-Fc proteins from stably and transiently expressed cells; and (iii) extracellular or intracellular localization of two anti-LNFPIII and three anti-Man3 scFv-Fc proteins. The results suggest that expression of anti-Man3 and other anti-carbohydrate antibodies in mammalian cells is disadvantageous for cell growth.

Rewritable glycochips

We describe microarraying of carbohydrates for protein screening using either disulfide bridge or Schiff base imine immobilization chemistries on plasmachemical deposited functional nanolayers. The commonly observed issue of nonspecific background binding of proteins is overcome by spotting carbohydrates through a protein-resistant overlayer yielding spatially localized interaction with a reactive functional underlayer.

Phage-display selection of antibodies to the left end of CTX3C using synthetic fragments

Ciguatoxins (CTXs) are a family of toxins that contaminate a variety of fish and cause ciguatera seafood poisoning. The limited availability of CTXs from natural sources has hampered preparation of antibodies and, thus, the development of immunoassays for these toxins. In the current studies, we utilized synthetic fragments as haptens to prepare antibodies against CTX3C, a congener of CTXs, thereby avoiding the problem of its scarcity. Synthetic ABC-ring fragment (ABC) of CTX3C was conjugated with keyhole limpet hemocyanin (KLH) and immunized on mice. Phage-displayed antibodies were first screened based on affinity to a soluble biotin-linked ABC-ring fragment that was captured on streptavidin-linked magnetic beads. The beads were then eluted with the ABCD-ring fragment (ABCD), and recovered phages were amplified. This elution with a synthetic fragment allowed the preparation of antibodies to ABCD as well as to ABC. Three antibodies with affinities of K(d) approximately 10(-5) M for ABCD were selected and prepared as soluble recombinant Fabs (rFabs). One rFab, 1C49, bound to CTX3C itself, although the binding affinity for CTX3C was weaker than for ABCD.

Antibodies selected from combinatorial libraries block a tumor antigen that plays a key role in immunomodulation

We searched for cell-surface-associated proteins overexpressed on B cell chronic lymphocytic leukemia (CLL) to use as therapeutic antibody targets. Antibodies binding the immunosuppressive molecule CD200 were identified by cell panning of an antibody phage display library derived from rabbits immunized with primary CLL cells. B cells from 87 CLL patients exhibited 1.6- to 5.4-fold cell-surface up-regulation of CD200 relative to normal B cells. An effect of increased CD200 expression by CLL cells on the immune system was evaluated in mixed lymphocyte reactions. Addition of primary CLL but not normal B cells to macrophages and T cells downregulated the Th1 response, as seen by a 50-95% reduction in secreted IL-2 and IFN-gamma. Antibodies to CD200 prevented downregulation of the Th1 response in most B cell CLL samples evaluated, indicating abrogation of the CD200/CD200R interaction can be sufficient to restore the Th1 response. A disease-progression-associated shift of the immune response from Th1 to Th2 has been observed in numerous cancers. Because this cytokine shift is also believed to promote the induction of regulatory T cells, reverting the immune response to Th1 through direct targeting of the cancer cells may provide therapeutic benefits in CLL by encouraging a cytotoxic T cell response.

The Antitumor Effects of Angelica sinensis on Malignant Brain Tumors In vitro and In vivo

PURPOSE

In this study, we have examined the antitumor effects of chloroform extract of Angelica sinensis (AS-C), a traditional Chinese medicine, on glioblastoma multiforme (GBM) brain tumors in vitro and in vivo.

EXPERIMENTAL DESIGN

In vitro, GBM cells were treated with AS-C, and the cell proliferation, changes in distributions of cell cycle, and apoptosis were determined. In vivo, human DBTRG-05MG and rat RG2 GBM tumor cells were injected s.c. or i.c. and were treated with AS-C. Effects on tumor growth were determined by tumor volume, magnetic resonance imaging, survival, and histology analysis.

RESULTS

The AS-C displays potency in suppressing growth of malignant brain tumor cells without cytotoxicity to fibroblasts. Growth suppression of malignant brain tumor cells by AS-C results from cell cycle arrest and apoptosis. AS-C can up-regulate expression of cdk inhibitors, including p21, to decrease phosphorylation of Rb proteins resulting in cell arrest at the G0-G1 phase for DBTRG-05MG and RG2 cells. The apoptosis-associated proteins are dramatically increased and activated in DBTRG-05MG cells and RG2 cells by AS-C but RG2 cells without p53 protein expression. In vitro results showed AS-C triggered both p53-dependent and p53-independent pathways for apoptosis. In in vivo studies, AS-C not only can suppress growths of malignant brain tumors of rat and human origin but also shrink the volumes of in situ GBM, significantly prolonging survivals.

CONCLUSIONS

The in vitro and in vivo anticancer effects of AS-C indicate that it has sufficient potential to warrant further investigation and development as a new anti-brain tumor agent.

A survey of the year 2002 commercial optical biosensor literature

We have compiled 819 articles published in the year 2002 that involved commercial optical biosensor technology. The literature demonstrates that the technology's application continues to increase as biosensors are contributing to diverse scientific fields and are used to examine interactions ranging in size from small molecules to whole cells. Also, the variety of available commercial biosensor platforms is increasing and the expertise of users is improving. In this review, we use the literature to focus on the basic types of biosensor experiments, including kinetics, equilibrium analysis, solution competition, active concentration determination and screening. In addition, using examples of particularly well-performed analyses, we illustrate the high information content available in the primary response data and emphasize the impact of including figures in publications to support the results of biosensor analyses.

An adenoviral type 5 vector carrying a type 35 fiber as a vaccine vehicle: DC targeting, cross neutralization, and immunogenicity

Substituting the coat proteins of adenoviral vector serotype 5 (Ad5) can alter vector tropism and circumvent vector neutralization. Here we report that an Ad5 vector carrying a part of the fiber molecule of human subgroup B adenovirus serotype 35 (Ad5.Fib35) transduces cultured human dendritic cells (DC) and circulating myeloid derived DC with approximately 10-fold greater efficiency than Ad5 in vitro. The improved DC transduction results in increased T-cell activation ex vivo. In vivo however, immunogenicity of the vectors in mice and non-human primates did not correlate with in vitro DC tropism. Ad5.Fib35 was less immunogenic in monkeys than Ad5, despite the improved primate DC tropism of Ad5.Fib35. In mice with high Ad5 vector-specific immunity, Ad5.Fib35 showed no significant difference in anti-insert immunity over Ad5 indicating that fiber exchange alone does not evade pre-existing Ad5 immunity. We thus conclude that, for ex vivo vaccination, Ad5.Fib35 shows promise as vector for loading of DC but is unable to circumvent anti-Ad5 immunity limiting its in vivo utility.

Mapping Tumor Epitope Space by Direct Selection of Single-Chain Fv Antibody Libraries on Prostate Cancer Cells

The identification of tumor-specific cell surface antigens is a critical step toward the development of targeted therapeutics for cancer. The epitope space at the tumor cell surface is highly complex, composed of proteins, carbohydrates, and other membrane-associated determinants including post-translational modification products, which are difficult to probe by approaches based on gene expression. This epitope space can be efficiently mapped by complementary monoclonal antibodies. By selecting human antibody gene diversity libraries directly on the surface of prostate cancer cells, we have taken a functional approach to identifying fully human, tumor-specific monoclonal antibodies without prior knowledge of their target antigens. Selection conditions have been optimized to favor tumor-specific antibody binding and internalization. To date, we have discovered >90 monoclonal antibodies that specifically bind and enter prostate cancer cells, with little or no binding to control cells. These antibodies are able to efficiently deliver intracellular payloads when attached to nanoparticles such as liposomes. In addition, a subset of the antibodies displayed intrinsic antiproliferative activity. These tumor-specific internalizing antibodies are likely to be useful for targeted therapeutics either alone or in combination with effector molecules. The antigens they bind constitute a tumor-specific internalizing epitope space that is likely to play a significant role in cancer cell homeostasis. Targeting components of this epitope space may facilitate development of immunotherapeutic and small molecule-based strategies as well as the use of other therapeutic agents that rely upon delivery to the interior of the tumor cell.

Enabling ScFvs as multi-drug carriers: a dendritic approach

To enable scFvs as multi-drug carriers, we designed and synthesized dendritic linker molecules bearing up to nine chlorambucil residues at the branch ends. A maleimide group was used at the focal point of the dendron for easy linkage to the scFv. Originally designed molecules showed poor water solubility. To address this problem, a lysine residue with an unprotected carboxylic acid group was inserted into the dendron branches. The new molecules showed excellent water solubility and are now suitable for conjugation. Such dendritic molecules will allow studies to understand the relationship between the drug/antibody ratio and the potency of the immunoconjugates. The dendritic approach could also be applied to drugs other than chlorambucil and carriers other than scFvs to greatly increase the drug/carrier ratio.