From whole monoclonal antibodies to single domain antibodies: think small

Innovations in cancer immunotherapy: A comprehensive overview of recent breakthroughs and future directions

A major advance in cancer treatment has been the development and refinement of cancer immunotherapy. The discovery of immunotherapies for a wide range of cancers has revolutionized cancer treatment paradigms. Despite relapse or refractory disease, immunotherapy approaches can prolong the life expectancy of metastatic cancer patients. Multiple therapeutic approaches and agents are currently being developed to manipulate various aspects of the immune system. Oncolytic viruses, cancer vaccines, adoptive cell therapies, monoclonal antibodies, cytokine therapies, and inhibitors of immune checkpoints have all proven successful in clinical trials. There are several types of immunotherapeutic approaches available for treating cancer, and others are being tested in preclinical and clinical settings. Immunotherapy has proven successful, and many agents and strategies have been developed to improve its effectiveness. The purpose of this article is to present a comprehensive overview of current immunotherapy approaches used to treat cancer. Cancer immunotherapy advancements, emerging patterns, constraints, and potential future breakthroughs are also discussed.

Characterization of Lactobacilli Phage Endolysins and Their Functional Domains-Potential Live Biotherapeutic Testing Reagents

Phage endolysin-specific binding characteristics and killing activity support their potential use in biotechnological applications, including potency and purity testing of live biotherapeutic products (LBPs). LBPs contain live organisms, such as lactic acid bacteria (LAB), and are intended for use as drugs. Our approach uses the endolysin cell wall binding domains (CBD) for LBP potency assays and the endolysin killing activity for purity assays. CBDs of the following five lactobacilli phage lysins were characterized: CL1, Jlb1, Lj965, LL-H, and ΦJB. They exhibited different bindings to 27 LAB strains and were found to bind peptidoglycan or surface polymers. Flow cytometry based on CBD binding was used to enumerate viable counts of two strains in the mixture. CL1-lys, jlb1-lys, and ΦJB-lys and their enzymatic domains (EADs) exhibited cell wall digestive activity and lytic activity against LAB. Jlb1-EAD and ΦJB-EAD were more sensitive than their respective hololysins to buffer pH and NaCl changes. The ΦJB-EAD exhibited stronger lytic activity than ΦJB-lys, possibly due to ΦJB-CBD-mediated sequestration of ΦJB-lys by cell debris. CBD multiplex assays indicate that these proteins may be useful LBP potency reagents, and the lytic activity suggests that CL1-lys, jlb1-lys, and ΦJB-lys and their EADs are good candidates for LBP purity reagent development.

Large-Scale Production of Anti-RNase A VHH Expressed in pyrG Auxotrophic Aspergillus oryzae

Nanobodies, also referred to as VHH antibodies, are the smallest fragments of naturally produced camelid antibodies and are ideal affinity reagents due to their remarkable properties. They are considered an alternative to monoclonal antibodies (mAbs) with potential utility in imaging, diagnostic, and other biotechnological applications given the difficulties associated with mAb expression. Aspergillus oryzae (A. oryzae) is a potential system for the large-scale expression and production of functional VHH antibodies that can be used to meet the demand for affinity reagents. In this study, anti-RNase A VHH was expressed under the control of the glucoamylase promoter in pyrG auxotrophic A. oryzae grown in a fermenter. The feature of pyrG auxotrophy, selected for the construction of a stable and efficient platform, was established using homologous recombination. Pull-down assay, size exclusion chromatography, and surface plasmon resonance were used to confirm the binding specificity of anti-RNase A VHH to RNase A. The affinity of anti-RNase A VHH was nearly 18.3-fold higher (1.9 nM) when expressed in pyrG auxotrophic A. oryzae rather than in Escherichia coli. This demonstrates that pyrG auxotrophic A. oryzae is a practical, industrially scalable, and promising biotechnological platform for the large-scale production of functional VHH antibodies with high binding activity.

Targeting tumor-associated macrophages in hepatocellular carcinoma: biology, strategy, and immunotherapy

Hepatocellular carcinoma (HCC), one of the most malignant tumors, is characterized by its stubborn immunosuppressive microenvironment. As one of the main members of the tumor microenvironment (TME) of HCC, tumor-associated macrophages (TAMs) play a critical role in its occurrence and development, including stimulating angiogenesis, enhancing immunosuppression, and promoting the drug resistance and cancer metastasis. This review describes the origin as well as phenotypic heterogeneity of TAMs and their potential effects on the occurrence and development of HCC and also discusses about various adjuvant therapy based strategies that can be used for targeting TAMs. In addition, we have highlighted different treatment modalities for TAMs based on immunotherapy, including small molecular inhibitors, immune checkpoint inhibitors, antibodies, tumor vaccines, adoptive cellular immunotherapy, and nanocarriers for drug delivery, to explore novel combination therapies and provide feasible therapeutic options for clinically improving the prognosis and quality of life of HCC patients.

CuS@BSA-NB2 Nanoparticles for HER2-Targeted Photothermal Therapy

Breast cancer is characterized by the uncontrolled proliferation of breast epithelial cells under the action of a variety of carcinogens. Although HER2-inhibitors were currently applied for HER2-positive breast cancer patients, they didn't work for patients with resistance to HER2-targeted anti-cancer drugs. In this work, we prepared novel CuS@BSA-NB2 nanoparticles (NPs) for breast cancer photothermal therapy (PTT). The NPs had good biocompatibility due to the Bovine Serum Albumin (BSA) encapsulating and excellent targeting to HER2 because of nanobody 2 (NB2). Under 808 nm laser irradiation, CuS@BSA-NB2 NPs had high photothermal conversion efficiency and photothermal stability. Meanwhile, we constructed a stable cell line of MDA-MB-231/HER2 with a high expression of HER2 protein. Immunofluorescence and ICP-MS assays showed that CuS@BSA-NB2 NPs can be specifically enriched and be ingested in MDA-MB-231/HER2 cells. Furthermore, CuS@BSA-NB2 NPs had shown a more significant photothermal treatment effect than CuS@BSA under certain treatment conditions for MDA-MB-231/HER2. In addition, the cytotoxicity assay demonstrated that CuS@BSA-NB2 NPs had a low toxicity for MDA-MB-231/HER2 cells. The above results suggested that CuS@BSA-NB2 NPs were great photothermal therapeutic agents to reduce the malignant proliferation of breast epithelial cells and have potential for breast cancer therapy.

Curcumin as an Adjuvant to Cancer Immunotherapy

The components of the immune system play a very sincere and crucial role in combating tumors. However, despite their firm efforts of elimination, tumor cells cleverly escape the surveillance process by adopting several immune evasion mechanisms. The conversion of immunogenicity of tumor microenvironment into tolerogenic is considered as a prime reason for tumor immune escape. Therapeutically, different immunotherapies have been adopted to block such immune escaping routes along with better clinical outcomes. Still, the therapies are haunted by several drawbacks. Over time, curcumin has been considered as a potential anti-cancer molecule. Its potentialities have been recorded against the standard hallmarks of cancer such as continuous proliferation, escaping apoptosis, continuous angiogenesis, insensitivity to growth inhibitors, tissue invasion, and metastasis. Hence, the diversity of curcumin functioning has already been established and exploration of its application with immunotherapies might open up a new avenue for scientists and clinicians. In this review, we briefly discuss the tumor's way of immune escaping, followed by various modern immunotherapies that have been used to encounter the escaping paths and their minute flaws. Finally, the conclusion has been drawn with the application of curcumin as a potential immune-adjuvant, which fearlessly could be used with immunotherapies for best outcomes.

Patented therapeutic approaches targeting LRP/LR for cancer treatment

Introduction: The ubiquitously expressed 37 kDa/67 kDa high-affinity laminin receptor (laminin receptor precursor/laminin receptor, LRP/LR) is a protein found to play several roles within cells. The receptor is located in the nucleus, cytosol and the cell surface. LRP/LR mediates cell proliferation, cell adhesion and cell differentiation. As a result, it is seen to enhance tumor angiogenesis as well as invasion and adhesion, key steps in the metastatic cascade of cancer. Recent findings have shown that LRP/LR is involved in the maintenance of cell viability through apoptotic evasion, allowing for tumor progression. Thus, several patented therapeutic approaches targeting the receptor for the prevention and treatment of cancer have emerged.Areas covered: The several roles that LRP/LR plays in cancer progression as well as an overview of the current therapeutic patented strategies targeting LRP/LR and cancer to date.Expert opinion: Small molecule inhibitors, monoclonal antibodies and small interfering RNAs might act used as powerful tools in preventing tumor angiogenesis and metastasis through the induction of apoptosis and telomere erosion in several cancers. This review offers an overview of the roles played by LRP/LR in cancer progression, while providing novel patented approaches targeting the receptor as potential therapeutic routes for the treatment of cancer as well as various other diseases.

Nanobody-horseradish peroxidase fusion protein as an ultrasensitive probe to detect antibodies against Newcastle disease virus in the immunoassay

BACKGROUND

Sensitive and specific antibodies can be used as essential probes to develop competitive enzyme-linked immunosorbent assay (cELISA). However, traditional antibodies are difficult to produce, only available in limited quantities, and ineffective as enzymatic labels. Nanobodies, which are single-domain antibodies (sdAbs), offer an alternative, more promising tool to circumvent these limitations. In the present work, a cELISA using nanobody-horseradish peroxidase (HRP) fusion protein firstly designed as a probe was developed for detecting anti-Newcastle disease virus (NDV) antibodies in chicken sera.

RESULTS

In the study, a platform for the rapid and simple production of nanobody-HRP fusion protein was constructed. First, a total of 9 anti-NDV-NP protein nanobodies were screened from a immunised Bactrian camel. Then, the Nb5-HRP fusions were produced with the platform and used for the first time as sensitive reagents for developing cELISA to detect anti-NDV antibodies. The cut-off value of the cELISA was 18%, and the sensitivity and specificity were respectively 100% and 98.6%. The HI test and commercial ELISA kit (IDEXX) separately agreed 97.83% and 98.1% with cELISA when testing clinical chicken sera and both agreed 100% when testing egg yolks. However, for detecting anti-NDV antibodies in the sequential sera from the challenged chickens, cELISA demonstrated to be more sensitive than the HI test and commercial ELISA kit. Moreover, a close correlation (R² = 0.914) was found between the percent competitive inhibition values of cELISA and HI titers.

CONCLUSIONS

A platform was successfully designed to easily and rapidly produce the nanobody-HRP fusion protein, which was the first time to be used as reagents for establishing cELISA. Results suggest that the platform supports the development of a cELISA with high sensitivity, simplicity, and rapid detection of anti-NDV antibodies. Overall, we believe that the platform based on nanobody-HRP fusions can be widely used for future investigations and treatment other diseases and viruses.

Monoclonal antibodies in cancer immunotherapy

Nowadays, in cancer treatments, immunotherapy which can be classified as a cancer type specific therapy is more popular than non-specific therapy methods such as surgery, radiotherapy and chemotherapy. The main aim of immunotherapy is to enable patients' immune system to target cancer cells and destroy them. The mainly used treatment methods in cancer immunotherapy are cancer vaccines, adoptive cell therapy, cytokines and monoclonal antibodies. In this review, we discuss the immunotherapy approaches, especially monoclonal antibodies which are mostly used in cancer immunotherapy in clinical applications.

Anti-EGFR-iRGD recombinant protein modified biomimetic nanoparticles loaded with gambogic acid to enhance targeting and antitumor ability in colorectal cancer treatment

Background

Red blood cell membrane-coated nanoparticle (RBCm-NP) platform, which consist of natural RBCm and synthetic polymeric core, can extend circulation time in vivo with an improved biocompatibility and stability of this biomimetic nanocarrier. To achieve better bioavailability of antitumor drugs that were loaded in RBCm-NPs, the functionalization of coated RBCm with specific targeting ability is essential. Bispecific recombinant protein anti-EGFR-iRGD, containing both tumor penetrating peptide (internalizing RGD peptide) and EGFR single-domain antibody (sdAb), seems to be an optimal targeting ligand for RBCm-NPs in the treatment of multiple tumors, especially colorectal cancer with high EGFR expression.

Materials and methods

We modified the anti-EGFR-iRGD recombinant protein on the surface of RBCm-NPs by lipid insertion method to construct iE-RBCm-PLGA NPs and confirmed the presentation of active tumor-targeting ability in colorectal cancer models with high EGFR expression when compared with RBCm-PLGA NPs. In addition, potential anti-tumor drug gambogic acid (GA) was loaded into the NPs to endow the antitumor efficiency of iE-RBCm-GA/PLGA NPs. It was simultaneously evaluated whether GA can reach better biocompatibility benefiting from the improved antitumor efficiency of iE-RBCm-GA/PLGA NPs in colorectal cancer models.

Results

We successfully modified anti-EGFR-iRGD proteins on the surface of biomimetic NPs with integrated and stable "shell-core" structure. iE-RBCm-PLGA NPs showed its improved targeting ability in vitro (multicellular spheroids [MCS]) and in vivo (nude mice bearing tumors). Besides, no matter on short-term cell apoptosis at tumor site (terminal deoxyribonucleotidyl transferase-mediated dUTP nick end labeling [TUNEL]) and long-term tumor inhibition, iE-RBCm-GA/PLGA NPs achieved better antitumor efficacy than free GA in spite of the similar effects of cytotoxicity and apoptosis to GA in vitro.

Conclusion

We expect that the bispecific biomimetic nanocarrier can extend the clinical application of many other potential antitumor drugs similar to GA and become a novel drug carrier in the colorectal cancer treatment.

Current status and future directions of cancer immunotherapy

In the past decades, our knowledge about the relationship between cancer and the immune system has increased considerably. Recent years' success of cancer immunotherapy including monoclonal antibodies (mAbs), cancer vaccines, adoptive cancer therapy and the immune checkpoint therapy has revolutionized traditional cancer treatment. However, challenges still exist in this field. Personalized combination therapies via new techniques will be the next promising strategies for the future cancer treatment direction.

Challenging tumour immunological techniques that help to track cancer stem cells in malignant melanomas and other solid tumours

Aim of the study

The arsenal of questions and answers about the minor cancer initiating cancer stem cell (CSC) population put responsible for cancer invasiveness and metastases, has left with an unsolved puzzle. Specific aims of a complex project were partly focused on revealing new biomarkers of cancer. We designed and set up novel techniques to facilitate the detection of cancerous cells.

Materials and methods

As a novel approach, we investigated B cells infiltrating breast carcinomas and melanomas (TIL-B) in terms of their tumour antigen binding potential. By developing the TIL-B phage display technology we provide here a new technology for the specific detection of highly tumour-associated antigens. Single chain Fv (scFv) antibody fragment phage ELISA, immunofluorescence (IF) FACS analysis, chamber slide technique with IF confocal laser microscopy and immunohistochemistry (IHC) in paraffin-embedded tissue sections were set up and standardized.

Results

We showed strong tumour-associated disialylated glycosphingolipid expression levels on various cancer cells using scFv antibody fragments, generated previously by uniquely invasive breast carcinoma TIL-B phage display library technology.

Conclusions

We report herein a novel strategy to obtain antibody fragments of human origin that recognise tumour-associated ganglioside antigens. Our investigations have the power to detect privileged molecules in cancer progression, invasiveness, and metastases. The technical achievements of this study are being harnessed for early diagnostics and effective cancer therapeutics.

Structural basis of nanobody-mediated blocking of BtuF, the cognate substrate-binding protein of the Escherichia coli vitamin B12 transporter BtuCD

Bacterial ABC importers catalyze the uptake of essential nutrients including transition metals and metal-containing co-factors. Recently, an IgG antibody targeting the external binding protein of the Staphylococcus aureus Mn(II) ABC importer was reported to inhibit transport activity and reduce bacterial cell growth. We here explored the possibility of using alpaca-derived nanobodies to inhibit the vitamin B12 transporter of Escherichia coli, BtuCD-F, as a model system by generating nanobodies against the periplasmic binding protein BtuF. We isolated six nanobodies that competed with B12 for binding to BtuF, with inhibition constants between 10⁻⁶ and 10⁻⁹ M. Kinetic characterization of the nanobody-BtuF interactions revealed dissociation half-lives between 1.6 and 6 minutes and fast association rates between 10⁴ and 10⁶ M⁻¹s⁻¹. For the tightest-binding nanobody, we observed a reduction of in vitro transport activity of BtuCD-F when an excess of nanobody over B12 was used. The structure of BtuF in complex with the most effective nanobody Nb9 revealed the molecular basis of its inhibitory function. The CDR3 loop of Nb9 reached into the substrate-binding pocket of BtuF, preventing both B12 binding and BtuCD-F complex formation. Our results suggest that nanobodies can mediate ABC importer inhibition, providing an opportunity for novel antibiotic strategies.

Identification and in vitro characterization of novel nanobodies against human granulocyte colony-stimulating factor receptor to provide inhibition of G-CSF function

It has been shown that Granulocyte colony-stimulating factor (G-CSF) has a higher expression in malignant tumors, and anti-G-CSF therapy considerably decreases tumor growth, tumor vascularization and metastasis. Thus, blocking the signaling pathway of G-CSF could be beneficial in cancer therapy. This study is aimed at designing and producing a monoclonal nanobody that could act as an antagonist of G-CSF receptor. Nanobodies are the antigen binding fragments of camelid single-chain antibodies, also known as VHH. These fragments have exceptional properties which makes them ideal for tumor imaging and therapeutic applications. We have used our previously built nanobody phage libraries to isolate specific nanobodies to the G-CSF receptor. After a series of cross-reactivity and affinity experiments, two unique nanobodies were selected for functional analysis. Proliferation assay, real-time PCR and immunofluorescence assays were used to characterize these nanobodies. Finally, VHH26 nanobody that was able to specifically bind G-CSF receptor (G-CSF-R) on the surface of NFS60 cells and efficiently block G-CSF-R downstream signaling pathway in a dose-dependent manner was selected. This nanobody could be further developed into a valuable tool in tumor therapy and it forms a basis for additional studies in preclinical animal models.

Single-Domain Antibodies As Versatile Affinity Reagents for Analytical and Diagnostic Applications

With just three CDRs in their variable domains, the antigen-binding site of camelid heavy-chain-only antibodies (HcAbs) has a more limited structural diversity than that of conventional antibodies. Even so, this does not seem to limit their specificity and high affinity as HcAbs against a broad range of structurally diverse antigens have been reported. The recombinant form of their variable domain [nanobody (Nb)] has outstanding properties that make Nbs, not just an alternative option to conventional antibodies, but in many cases, these properties allow them to reach analytical or diagnostic performances that cannot be accomplished with conventional antibodies. These attributes include comprehensive representation of the immune specificity in display libraries, easy adaptation to high-throughput screening, exceptional stability, minimal size, and versatility as affinity building block. Here, we critically reviewed each of these properties and highlight their relevance with regard to recent developments in different fields of immunosensing applications.

A camelid single-domain antibody neutralizes botulinum neurotoxin A by blocking host receptor binding

Antibody treatment is currently the only available countermeasure for botulism, a fatal illness caused by flaccid paralysis of muscles due to botulinum neurotoxin (BoNT) intoxication. Among the seven major serotypes of BoNT/A-G, BoNT/A poses the most serious threat to humans because of its high potency and long duration of action. Prior to entering neurons and blocking neurotransmitter release, BoNT/A recognizes motoneurons via a dual-receptor binding process in which it engages both the neuron surface polysialoganglioside (PSG) and synaptic vesicle glycoprotein 2 (SV2). Previously, we identified a potent neutralizing antitoxin against BoNT/A1 termed ciA-C2, derived from a camelid heavy-chain-only antibody (VHH). In this study, we demonstrate that ciA-C2 prevents BoNT/A1 intoxication by inhibiting its binding to neuronal receptor SV2. Furthermore, we determined the crystal structure of ciA-C2 in complex with the receptor-binding domain of BoNT/A1 (H_CA1) at 1.68 Å resolution. The structure revealed that ciA-C2 partially occupies the SV2-binding site on H_CA1, causing direct interference of H_CA1 interaction with both the N-glycan and peptide-moiety of SV2. Interestingly, this neutralization mechanism is similar to that of a monoclonal antibody in clinical trials, despite that ciA-C2 is more than 10-times smaller. Taken together, these results enlighten our understanding of BoNT/A1 interactions with its neuronal receptor, and further demonstrate that inhibiting toxin binding to the host receptor is an efficient countermeasure strategy.

Design and In Vitro Evaluation of a Cytotoxic Conjugate Based on the Anti-HER2 Affibody Fused to the Fc Fragment of IgG1

In our previous work we demonstrated that a small protein called affibody can be used for a cytotoxic conjugate development. The anti-HER2 affibody was armed with one moiety of a highly potent auristatin E and specifically killed HER2-positive cancer cells with a nanomolar IC₅₀. The aim of this study was to improve the anti-HER2 affibody conjugate by increasing its size and the number of conjugated auristatin molecules. The affibody was fused to the Fc fragment of IgG1 resulting in a dimeric construct with the molecular weight of 68 kDa, referred to as Z_HER2:2891-Fc, ensuring its prolonged half-life in the blood. Due to the presence of four interchain cysteines, the fusion protein could carry four drug molecules. Notably, the in vitro tests of the improved anti-HER2 conjugate revealed that it exhibits the IC₅₀ of 130 pM for the HER2-positive SK-BR-3 cells and 98 nM for the HER2-negative MDA-MB-231 cells. High efficacy and specificity of the auristatin conjugate based on Z_HER2:2891-Fc indicate that this construct is suitable for further in vivo evaluation.

Nanocell targeting using engineered bispecific antibodies

There are many design formats for bispecific antibodies (BsAbs), and the best design choice is highly dependent on the final application. Our aim was to engineer BsAbs to target a novel nanocell (EnGeneIC Delivery Vehicle or EDV^TMnanocell) to the epidermal growth factor receptor (EGFR). EDV^TMnanocells are coated with lipopolysaccharide (LPS), and BsAb designs incorporated single chain Fv (scFv) fragments derived from an anti-LPS antibody (1H10) and an anti-EGFR antibody, ABX-EGF. We engineered various BsAb formats with monovalent or bivalent binding arms and linked scFv fragments via either glycine-serine (G4S) or Fc-linkers. Binding analyses utilizing ELISA, surface plasmon resonance, bio-layer interferometry, flow cytometry and fluorescence microscopy showed that binding to LPS and to either soluble recombinant EGFR or MDA-MB-468 cells expressing EGFR, was conserved for all construct designs. However, the Fc-linked BsAbs led to nanocell clumping upon binding to EDV^TMnanocells. Clumping was eliminated when additional disulfide bonds were incorporated into the scFv components of the BsAbs, but this resulted in lower BsAb expression. The G4S-linked tandem scFv BsAb format was the optimal design with respect to EDV binding and expression yield. Doxorubicin-loaded EDV^TMnanocells actively targeted with tandem scFv BsAb in vivo to MDA-MB-468-derived tumors in mouse xenograft models enhanced tumor regression by 40% compared to passively targeted EDV^TMnanocells. BsAbs therefore provide a functional means to deliver EDV^TMnanocells to target cells.

Tumor-penetrating peptide fused EGFR single-domain antibody enhances cancer drug penetration into 3D multicellular spheroids and facilitates effective gastric cancer therapy

Human tumors, including gastric cancer, frequently express high levels of epidermal growth factor receptors (EGFRs), which are associated with a poor prognosis. Targeted delivery of anticancer drugs to cancerous tissues shows potential in sparing unaffected tissues. However, it has been a major challenge for drug penetration in solid tumor tissues due to the complicated tumor microenvironment. We have constructed a recombinant protein named anti-EGFR-iRGD consisting of an anti-EGFR VHH (the variable domain from the heavy chain of the antibody) fused to iRGD, a tumor-specific binding peptide with high permeability. Anti-EGFR-iRGD, which targets EGFR and αvβ3, spreads extensively throughout both the multicellular spheroids and the tumor mass. The recombinant protein anti-EGFR-iRGD also exhibited antitumor activity in tumor cell lines, multicellular spheroids, and mice. Moreover, anti-EGFR-iRGD could improve anticancer drugs, such as doxorubicin (DOX), bevacizumab, nanoparticle permeability and efficacy in multicellular spheroids. This study draws attention to the importance of iRGD peptide in the therapeutic approach of anti-EGFR-iRGD. As a consequence, anti-EGFR-iRGD could be a drug candidate for cancer treatment and a useful adjunct of other anticancer drugs.

Construction of a synthetic phage-displayed Nanobody library with CDR3 regions randomized by trinucleotide cassettes for diagnostic applications

Background

Nanobodies (Nbs) have proved their great value as therapeutic molecules and clinical diagnostic tools. Although the routine procedure to obtain Nbs is to immunize camels with antigens, it is unavailable to immunize a camel when the antigens are highly toxic, pathogenic or nonimmunogenic. A synthetic phage display library is an alternative to generate Nbs against such targets, besides all the other ones.

Methods

We constructed a large and diverse synthetic phage display Nanobody (Nb) library based on the conserved camel single-domain antibody fragment (VHH) framework of cAbBCII10. Diversity was introduced in the complementarity-determining region 3 (CDR3) by means of randomization of synthetic oligonucleotides. Then human prealbumin (PA) and neutrophil gelatinase-associated lipocalin (NGAL) were used to select specific Nbs from this library. Furthermore, a sandwich enzyme-linked immunosorbent assay (ELISA) was developed to detect PA based on horseradish peroxidase (HRP)-conjugated anti-PA Nb isolated from this study and another biotinylated anti-PA Nb obtained from an immune library, in our previous study.

Results

A large and diverse synthetic phage display Nb library with CDR3 regions randomized by trinucleotide cassettes was constructed. The library size was 1.65 × 10⁹ CFU/mL and the correct insertion ratio was nearly 100%. A Nb against human PA and against NGAL was successfully isolated from the synthetic library. The obtained anti-PA Nb was effectively used to develop a sandwich ELISA for PA detection and it demonstrated a working range from 50 to 1000 ng/mL, with a limit of detection (LOD) of 27.1 ng/mL.

Conclusion

This proposed novel synthetic library was a good source for obtaining some antigen-specific Nbs. This approach could provide crucial support to an immune library and a naïve library in the acquisition of specific Nbs, potentially functioning as a great resource for medical diagnostic applications. In addition, we have successfully developed a novel sandwich ELISA to detect PA, which could provide great assistance for clinical PA detection.

Molecular dynamics simulation of the crystallizable fragment of IgG1-insights for the design of Fcabs

An interesting format in the development of therapeutic monoclonal antibodies uses the crystallizable fragment of IgG1 as starting scaffold. Engineering of its structural loops allows generation of an antigen binding site. However, this might impair the molecule’s conformational stability, which can be overcome by introducing stabilizing point mutations in the CH3 domains. These point mutations often affect the stability and unfolding behavior of both the CH2 and CH3 domains. In order to understand this cross-talk, molecular dynamics simulations of the domains of the Fc fragment of human IgG1 are reported. The structure of human IgG1-Fc obtained from X-ray crystallography is used as a starting point for simulations of the wild-type protein at two different pH values. The stabilizing effect of a single point mutation in the CH3 domain as well as the impact of the hinge region and the glycan tree structure connected to the CH2 domains is investigated. Regions of high local flexibility were identified as potential sites for engineering antigen binding sites. Obtained data are discussed with respect to the available X-ray structure of IgG1-Fc, directed evolution approaches that screen for stability and use of the scaffold IgG1-Fc in the design of antigen binding Fc proteins.

The Effect of Molecular Weight, PK, and Valency on Tumor Biodistribution and Efficacy of Antibody-Based Drugs

Poor drug delivery and penetration of antibody-mediated therapies pose significant obstacles to effective treatment of solid tumors. This study explored the role of pharmacokinetics, valency, and molecular weight in maximizing drug delivery. Biodistribution of a fibroblast growth factor receptor 4 (FGFR4) targeting CovX-body (an FGFR4-binding peptide covalently linked to a nontargeting IgG scaffold; 150 kDa) and enzymatically generated FGFR4 targeting F(ab)2 (100 kDa) and Fab (50 kDa) fragments was measured. Peak tumor levels were achieved in 1 to 2 hours for Fab and F(ab)2 versus 8 hours for IgG, and the percentage injected dose in tumors was 0.45%, 0.5%, and 2.5%, respectively, compared to 0.3%, 2%, and 6% of their nontargeting controls. To explore the contribution of multivalent binding, homodimeric peptides were conjugated to the different sized scaffolds, creating FGFR4 targeting IgG and F(ab)2 with four peptides and Fab with two peptides. Increased valency resulted in an increase in cell surface binding of the bivalent constructs. There was an inverse relationship between valency and intratumoral drug concentration, consistent with targeted consumption. Immunohistochemical analysis demonstrated increased size and increased cell binding decreased tumor penetration. The binding site barrier hypothesis suggests that limited tumor penetration, as a result of high-affinity binding, could result in decreased efficacy. In our studies, increased target binding translated into superior efficacy of the IgG instead, because of superior inhibition of FGFR4 proliferation pathways and dosing through the binding site barrier. Increasing valency is therefore an effective way to increase the efficacy of antibody-based drugs.

Human antibodies targeting the C-type lectin-like domain of the tumor endothelial cell marker clec14a regulate angiogenic properties in vitro

It has been suggested that clec14a may be involved in tumor angiogenesis. However, a molecular mechanism has not been clearly identified. In this study, we show for the first time that C-type lectin-like domain (CTLD) of clec14a may be important for regulating cell migration and filopodia formation. Using phage display technology, recombinant human antibodies specific to the CTLDs of human and mouse clec14a (clec14a-CTLD (immunoglobulin G) IgG) were selected. Functional assays using the antibodies showed that clec14a-CTLD IgGs specifically blocked endothelial cell migration and tube formation without affecting cell viability or activation. Further, clec14a-CTLD IgGs inhibited clec14a-mediated cell–cell contact by blocking interaction between CTLDs. Finally, clec14a cross-linking by the clec14a-CTLD IgGs significantly downregulated clec14a expression on the surface of endothelial cells. These results strongly suggest that the clec14a-CTLD may be a key domain in angiogenesis, and that clec14a-CTLD IgGs specifically inhibit angiogenesis by modulating CTLD-mediated cell interactions and clec14a expression on the surface of endothelial cells.

Strategies to stabilize compact folding and minimize aggregation of antibody-based fragments

Monoclonal antibodies (mAbs) have proven to be useful for development of new therapeutic drugs and diagnostic techniques. To overcome the difficulties posed by their complex structure and folding, reduce undesired immunogenicity, and improve pharmacokinetic properties, a plethora of different Ab fragments have been developed. These include recombinant Fab and Fv segments that can display improved properties over those of the original mAbs upon which they are based. Antibody (Ab) fragments such as Fabs, scFvs, diabodies, and nanobodies, all contain the variable Ig domains responsible for binding to specific antigenic epitopes, allowing for specific targeting of pathological cells and/or molecules. These fragments can be easier to produce, purify and refold than a full Ab, and due to their smaller size they can be well absorbed and distributed into target tissues. However, the physicochemical and structural properties of the immunoglobulin (Ig) domain, upon which the folding and conformation of all these Ab fragments is based, can limit the stability of Ab-based drugs. The Ig domain is fairly sensitive to unfolding and aggregation when produced out of the structural context of an intact Ab molecule. When unfolded, Ab fragments may lose their specificity as well as establish non-native interactions leading to protein aggregation. Aggregated antibody fragments display altered pharmacokinetic and immunogenic properties that can augment their toxicity. Therefore, much effort has been placed in understanding the factors impacting the stability of Ig folding at two different levels: 1) intrinsically, by studying the effects of the amino acid sequence on Ig folding; 2) extrinsically, by determining the environmental conditions that may influence the stability of Ig folding. In this review we will describe the structure of the Ig domain, and the factors that impact its stability, to set the context for the different approaches currently used to achieve stable recombinant Ig domains when pursuing the development of Ab fragment-based biotechnologies.