Molecular engineering of high affinity single-chain antibody fragment for endothelial targeting of proteins and nanocarriers in rodents and humans

Targeted Nanoparticles for the Binding of Injured Vascular Endothelium after Percutaneous Coronary Intervention

Percutaneous coronary intervention (PCI) is a common procedure for the management of coronary artery obstruction. However, it usually causes vascular wall injury leading to restenosis that limits the long-term success of the PCI endeavor. The ultimate objective of this study was to develop the targeting nanoparticles (NPs) that were destined for the injured subendothelium and attract endothelial progenitor cells (EPCs) to the damaged location for endothelium regeneration. Biodegradable poly(lactic-co-glycolic acid) (PLGA) NPs were conjugated with double targeting moieties, which are glycoprotein Ib alpha chain (GPIbα) and human single-chain antibody variable fragment (HuscFv) specific to the cluster of differentiation 34 (CD34). GPIb is a platelet receptor that interacts with the von Willebrand factor (vWF), highly deposited on the damaged subendothelial surface, while CD34 is a surface marker of EPCs. A candidate anti-CD34 HuscFv was successfully constructed using a phage display biopanning technique. The HuscFv could be purified and showed binding affinity to the CD34-positive cells. The GPIb-conjugated NPs (GPIb-NPs) could target vWF and prevent platelet adherence to vWF in vitro. Furthermore, the HuscFv-conjugated NPs (HuscFv-NPs) could capture CD34-positive cells. The bispecific NPs have high potential to locate at the damaged subendothelial surface and capture EPCs for accelerating the vessel repair.

AbSE Workflow: Rapid Identification of the Coding Sequence and Linear Epitope of the Monoclonal Antibody at the Single-cell Level

Monoclonal antibody (mAb) has been widely used in immunity research and disease diagnosis and therapy. Antibody sequence and epitope are the prerequisites and basis of mAb applications, which determine the properties of antibodies and make the preparation of antibody-based molecules controllable and reliable. Here, we present the antibody sequence and epitope identification (AbSE) workflow, a time-saving and cost-effective route for rapid determination of antibody sequence and linear epitope of mAb even at the single-cell level. The feasibility and accuracy of the AbSE workflow were demonstrated through the identification and validation of the coding sequence and epitope of antihuman serum albumin (antiHSA) mAb. It can be inferred that the AbSE workflow is a powerful and universal approach for paired antibody-epitope sequence identification. It may characterize antibodies not only on a single hybridoma cell but also on any other antibody-secreting cells.

Expanding the arsenal against pulmonary diseases using surface-functionalized polymeric micelles: breakthroughs and bottlenecks

Pulmonary diseases such as lung cancer, asthma and tuberculosis have remained one of the common challenges globally. Polymeric micelles (PMs) have emerged as an effective technique for achieving targeted drug delivery for a local as well as a systemic effect. These PMs encapsulate and protect hydrophobic drugs, increase pulmonary targeting, decrease side effects and enhance drug efficacy through the inhalation route. In the current review, emphasis has been placed on the different barriers encountered by the drugs given via the pulmonary route and the mechanism of PMs in achieving drug targeting. The applications of PMs in different pulmonary diseases have also been discussed in detail.

A hybridoma-derived monoclonal antibody with high homology to the aberrant myeloma light chain

The identification of antibody variable regions in the heavy (V_H) and light (V_L) chains from hybridomas is necessary for the production of recombinant, sequence-defined monoclonal antibodies (mAbs) and antibody derivatives. This process has received renewed attention in light of recent reports of hybridomas having unintended specificities due to the production of non-antigen specific heavy and/or light chains for the intended antigen. Here we report a surprising finding and potential pitfall in variable domain sequencing of an anti-human CD63 hybridoma. We amplified multiple V_L genes from the hybridoma cDNA, including the well-known aberrant Sp2/0 myeloma V_K and a unique, full-length V_L. After finding that the unique V_L failed to yield a functional antibody, we discovered an additional full-length sequence with surprising similarity (~95% sequence identify) to the non-translated myeloma kappa chain but with a correction of its key frameshift mutation. Expression of the recombinant mAb confirmed that this highly homologous sequence is the antigen-specific light chain. Our results highlight the complexity of PCR-based cloning of antibody genes and strategies useful for identification of correct sequences.

Site-Specific Modification of Single-Chain Affinity Ligands for Fluorescence Labeling, Radiolabeling, and Bioconjugation

Single-chain protein affinity ligands are recombinant polypeptides that recreate the antigen-binding site of parental, monoclonal antibodies (mAbs) or present unique binding surfaces derived from display technologies, computational design, or other approaches. These diverse ligands have several advantages over full-length mAbs as agents for delivery of small molecule, protein, and nanoparticle cargoes to desired sites in the body. However, they present unique challenges for modification and bioconjugation. Fusion of a LPXTGG motif, or "sortag," and a 5-amino acid, flexible linker to the C-terminus of these affinity ligands enables high-efficiency transpeptidation by the bacterial enzyme, Sortase A, and site-specific addition of fluorophores, radiolabels, or functional groups for oriented and stoichiometrically controlled bioconjugation. We describe in detail this method and address several challenges and pitfalls in the purification and characterization of modified single-chain affinity ligands.

Endothelial Targeted Strategies to Combat Oxidative Stress: Improving Outcomes in Traumatic Brain Injury

The endothelium is a thin monolayer of specialized cells that lines the luminal wall of blood vessels and constitutes the critical innermost portion of the physical barrier between the blood and the brain termed the blood-brain barrier (BBB). Aberrant changes in the endothelium occur in many neuropathological states, including those with high morbidity and mortality that lack targeted therapeutic interventions, such as traumatic brain injury (TBI). Utilizing ligands of surface determinants expressed on brain endothelium to target and combat injury mechanisms at damaged endothelium offers a new approach to the study of TBI and new avenues for clinical advancement. Many factors influence the targets that are expressed on endothelium. Therefore, the optimization of binding sites and ideal design features of nanocarriers are controllable factors that permit the engineering of nanotherapeutic agents with applicability that is specific to a known disease state. Following TBI, damaged endothelial cells upregulate cell adhesion molecules, including ICAM-1, and are key sites of reactive oxygen species (ROS) generation, including hydrogen peroxide. Reactive oxygen species along with pro-inflammatory mediators are known to contribute to endothelial damage and loss of BBB integrity. The use of targeted endothelial nanomedicine, with conjugates of the antioxidant enzyme catalase linked to anti-ICAM-1 antibodies, has recently been demonstrated to minimize oxidative stress at the BBB and reduce neuropathological outcomes following TBI. Here, we discuss targeted endothelial nanomedicine and its potential to provide benefits in TBI outcomes and future directions of this approach.

Role of Noncoding RNAs in the Pathogenesis of Abdominal Aortic Aneurysm

Abdominal aortic aneurysm (AAA) is a local dilatation of the abdominal aortic vessel wall and is among the most challenging cardiovascular diseases as without urgent surgical intervention, ruptured AAA has a mortality rate of >80%. Most patients present acutely after aneurysm rupture or dissection from a previously asymptomatic condition and are managed by either surgery or endovascular repair. Patients usually are old and have other concurrent diseases and conditions, such as diabetes mellitus, obesity, and hypercholesterolemia making surgical intervention more difficult. Collectively, these issues have driven the search for alternative methods of diagnosing, monitoring, and treating AAA using therapeutics and less invasive approaches. Noncoding RNAs-short noncoding RNAs (microRNAs) and long-noncoding RNAs-are emerging as new fundamental regulators of gene expression. Researchers and clinicians are aiming at targeting these microRNAs and long noncoding RNAs and exploit their potential as clinical biomarkers and new therapeutic targets for AAAs. While the role of miRNAs in AAA is established, studies on long-noncoding RNAs are only beginning to emerge, suggesting their important yet unexplored role in vascular physiology and disease. Here, we review the role of noncoding RNAs and their target genes focusing on their role in AAA. We also discuss the animal models used for mechanistic understanding of AAA. Furthermore, we discuss the potential role of microRNAs and long noncoding RNAs as clinical biomarkers and therapeutics.

Cancer cell membrane-cloaked mesoporous silica nanoparticles with a pH-sensitive gatekeeper for cancer treatment

Nanoparticular drug delivery system (NDDS) has great potential for enhancing the efficacy of traditional chemotherapeutic drugs. However, it is still a great challenge to fabricate a biocompatible NDDS with simple structure capable of optimizing therapeutic efficacy, such as high tumor accumulation, suitable drug release profile (e.g. no premature drug leakage in normal physiological conditions while having a rapid release in cancer cells), low immunogenicity, as well as good biocompatibility. In this work, a simple core/shell structured nanoparticle was fabricated for prostate cancer treatment, in which a mesoporous silica nanoparticle core was applied as a container to high-efficiently encapsulate drugs (doxorubicin, DOX), CaCO₃ interlayer was designed to act as sheddable pH-sensitive gatekeepers for controlling drug release, and cancer cell membrane wrapped outlayer could improve the colloid stability and tumor accumulation capacity. In vitro cell experiments demonstrated that the as-prepared nanovehicles (denoted as DOX/MSN@CaCO₃@CM) could be efficiently uptaken by LNCaP-AI prostate cancer cells and even exhibited a better anti-tumor efficiency than free DOX. In addition, Live/Dead cell detection and apoptosis experiment demonstrated that MSN/DOX@CaCO₃@CM could effectively induce apoptosis-related death in prostate cancer cells. In vivo antitumor results demonstrated that DOX/MSN@CaCO₃@CM administration could remarkably suppress the tumor growth. Compared with other tedious approaches to optimize the therapeutic efficacy, this study provides an effective drug targeting system only using naturally biomaterials for the treatment of prostate cancer, which might have great potential in clinic usage.

Targeting therapeutics to endothelium: are we there yet?

Vascular endothelial cells represent an important therapeutic target in many pathologies, including inflammation, oxidative stress, and thrombosis; however, delivery of drugs to this site is often limited by the lack of specific affinity of therapeutics for these cells. Selective delivery of both small molecule drugs and therapeutic proteins to the endothelium has been achieved through the use of targeting ligands, such as monoclonal antibodies, directed against endothelial cell surface markers, particularly cell adhesion molecules (CAMs). Careful selection of target molecules and targeting agents allows for precise delivery to sites of inflammation, thereby maximizing therapeutic drug concentrations at the site of injury. A good understanding of the physiological and pathological determinants of drug and drug carrier pharmacokinetics and biodistribution may allow for a priori identification of optimal properties of drug carrier and targeting agent. Targeted delivery of therapeutics such as antioxidants and antithrombotic agents to the injured endothelium has shown efficacy in preclinical models, suggesting the potential for translation into clinical practice. As with all therapeutics, demonstration of both efficacy and safety are required for successful clinical implementation, which must be considered not only for the individual components (drug, targeting agent, etc.) but also for the sum of the parts (e.g., the drug delivery system), as unexpected toxicities may arise with complex delivery systems. While the use of endothelial targeting has not been translated into the clinic to date, the preclinical results summarized here suggest that there is hope for successful implementation of these agents in the years to come.

Vascular Targeting of Radiolabeled Liposomes with Bio-Orthogonally Conjugated Ligands: Single Chain Fragments Provide Higher Specificity than Antibodies

Liposomes are a proven, versatile, and clinically viable technology platform for vascular delivery of drugs and imaging probes. Although targeted liposomes have the potential to advance these applications, complex formulations and the need for optimal affinity ligands and conjugation strategies challenge their translation. Herein, we employed copper-free click chemistry functionalized liposomes to target platelet-endothelial cell adhesion molecule (PECAM-1) and intracellular adhesion molecule (ICAM-1) by conjugating clickable monoclonal antibodies (Ab) or their single chain variable fragments (scFv). For direct, quantitative tracing, liposomes were surface chelated with ¹¹¹In to a >90% radiochemical yield and purity. Particle size and distribution, stability, ligand surface density, and specific binding to target cells were characterized in vitro. Biodistribution of liposomes after IV injection was characterized in mice using isotope detection in organs and by noninvasive imaging (single-photon emission computed tomography/computed tomography, SPECT/CT). As much as 20-25% of injected dose of liposomes carrying PECAM and ICAM ligands, but not control IgG accumulated in the pulmonary vasculature. The immunospecificity of pulmonary targeting of scFv/liposomes to PECAM-1 and ICAM-1, respectively, was 10-fold and 2.5-fold higher than of Ab/liposomes. Therefore, the combination of optimal ligands, benign conjugation, and labeling yields liposomal formulations that may be used for highly effective and specific vascular targeting.

Focus on Fundamentals: Achieving Effective Nanoparticle Targeting

Successful molecular targeting of nanoparticle drug carriers can enhance therapeutic specificity and reduce systemic toxicity. Typically, ligands specific for cognate receptors expressed on the intended target cell type are conjugated to the nanoparticle surface. This approach, often called active targeting, seems to imply that the conjugated ligand imbues the nanoparticle with homing capacity. However, ligand-receptor interactions are mediated by short-range forces and cannot produce magnetic-like attraction over larger distances. Successful targeting actually involves two key characteristics: contact of the nanoparticle with the intended target cell and subsequent ligand-mediated retention at the site. Here we propose a conceptual framework, based on recent literature combined with basic principles of molecular interactions, to guide rational design of nanoparticle targeting strategies.

Nanomedicine: An effective tool in cancer therapy

Various types of nanoparticles (NPs) have been used in delivering anticancer drugs to the site of action. This area has become more attractive in recent years due to optimal size and negligible undesirable side effects caused by the NPs. The focus of this review is to explore various types of NPs and their surface/chemical modifications as well as attachment of targeting ligands for tuning their properties in order to facilitate targeted delivery to the cancer sites in a rate-controlled manner. Heme compatibility, biodistribution, longer circulation time, hydrophilic lipophilic balance for high bioavailability, prevention of drug degradation and leakage are important in transporting drugs to the targeted cancer sites. The review discusses advantages of polymeric, magnetic, gold, and mesoporous silica NPs in delivering chemotherapeutic agents over the conventional dosage formulations along with their shortcomings/risks and possible solutions/alternatives.

Site-Specific Modification of Single-Chain Antibody Fragments for Bioconjugation and Vascular Immunotargeting

The conjugation of antibodies to drugs and drug carriers improves delivery to target tissues. Widespread implementation and effective translation of this pharmacologic strategy awaits the development of affinity ligands capable of a defined degree of modification and highly efficient bioconjugation without loss of affinity. To date, such ligands are lacking for the targeting of therapeutics to vascular endothelial cells. To enable site-specific, click-chemistry conjugation to therapeutic cargo, we used the bacterial transpeptidase, sortase A, to attach short azidolysine containing peptides to three endothelial-specific single chain antibody fragments (scFv). While direct fusion of a recognition motif (sortag) to the scFv C-terminus generally resulted in low levels of sortase-mediated modification, improved reaction efficiency was observed for one protein, in which two amino acids had been introduced during cloning. This prompted insertion of a short, semi-rigid linker between scFv and sortag. The linker significantly enhanced modification of all three proteins, to the extent that unmodified scFv could no longer be detected. As proof of principle, purified, azide-modified scFv was conjugated to the antioxidant enzyme, catalase, resulting in robust endothelial targeting of functional cargo in vitro and in vivo.

The new frontiers of the targeted interventions in the pulmonary vasculature: precision and safety (2017 Grover Conference Series)

The pulmonary vasculature plays an important role in many lung pathologies, such as pulmonary arterial hypertension, primary graft dysfunction of lung transplant, and acute respiratory distress syndrome. Therapy for these diseases is quite limited, largely due to dose-limiting side effects of numerous drugs that have been trialed or approved. High doses of drugs targeting the pulmonary vasculature are needed due to the lack of specific affinity of therapeutic compounds to the vasculature. To overcome this problem, the field of targeted drug delivery aims to target drugs to the pulmonary endothelial cells, especially those in pathological regions. The field uses a variety of drug delivery systems (DDSs), ranging from nano-scale drug carriers, such as liposomes, to methods of conjugating drugs to affinity moieites, such as antibodies. These DDSs can deliver small molecule drugs, protein therapeutics, and imaging agents. Here we review targeted drug delivery to the pulmonary endothelium for the treatment of pulmonary diseases. Cautionary notes are made of the risk–benefit ratio and safety—parameters one should keep in mind when developing a translational therapeutic.

ICAM-1-targeted thrombomodulin mitigates tissue factor-driven inflammatory thrombosis in a human endothelialized microfluidic model

Diverse human illnesses are characterized by loss or inactivation of endothelial thrombomodulin (TM), predisposing to microvascular inflammation, activation of coagulation, and tissue ischemia. Single-chain antibody fragment (scFv)/TM) fusion proteins, previously protective against end-organ injury in murine models of inflammation, are attractive candidates to treat inflammatory thrombosis. However, animal models have inherent differences in TM and coagulation biology, are limited in their ability to resolve and control endothelial biology, and do not allow in-depth testing of "humanized" scFv/TM fusion proteins, which are necessary for translation to the clinical domain. To address these challenges, we developed a human whole-blood, microfluidic model of inflammatory, tissue factor (TF)-driven coagulation that features a multichannel format for head-to-head comparison of therapeutic approaches. In this model, fibrin deposition, leukocyte adhesion, and platelet adhesion and aggregation showed a dose-dependent response to tumor necrosis factor-α activation and could be quantified via real-time microscopy. We used this model to compare hTM/R6.5, a humanized, intracellular adhesion molecule 1 (ICAM-1)-targeted scFv/TM biotherapeutic, to untargeted antithrombotic agents, including soluble human TM (shTM), anti-TF antibodies, and hirudin. The targeted hTM/R6.5 more effectively inhibited TF-driven coagulation in a protein C (PC)-dependent manner and demonstrated synergy with supplemental PC. These results support the translational prospects of ICAM-targeted scFv/TM and illustrate the utility of the microfluidic system as a platform to study humanized therapeutics at the interface of endothelium and whole blood under flow.

Therapeutic targeting in nanomedicine: the future lies in recombinant antibodies

The unique chemical and functional properties of nanoparticles can be harnessed for the delivery of large quantities of various therapeutic biomolecules. Active targeting of nanoparticles by conjugating ligands that bind to target cells strongly facilitates accumulation, internalization into target cells and longer retention at the target site, with consequent enhanced therapeutic effects. Recombinant antibodies with high selectivity and availability for a vast range of targets will dominate the future. In this review, we systematically outline the tremendous progress in the conjugation of antibodies to nanoparticles and the clear advantages that recombinant antibodies offer in the therapeutic targeting of nanoparticles. The demonstrated flexibility of recombinant antibody coupling to nanoparticles highlights the bright future of this technology for modern therapeutic nanomedicine.

Endothelial antigen assembly leads to thrombotic complications in heparin-induced thrombocytopenia

Heparin-induced thrombocytopenia (HIT) is a prothrombotic disorder initiated by antibodies against complexes between human platelet factor 4 (hPF4) and heparin. A better understanding of the events that initiate the prothrombotic state may improve approaches to antithrombotic management. Here, we visualized thrombus formation in an in vivo murine model and an endothelialized microfluidic system that simulate the pathogenesis of HIT. hPF4 released from platelets predominantly bound to peri-injury endothelium and formed HIT antigenic complexes that were dissociated by heparin. In mice expressing both hPF4+ and human platelet IgG Fc receptor IIA (FcγRIIA), infusion of the HIT-like monoclonal antibody KKO increased fibrin and platelet deposition at sites of injury, followed immediately by antigen formation on proximate endothelial cells. After a few minutes, HIT antigen was detected within the thrombus itself at the interface between the platelet core and the surrounding shell. We observed similar results in the humanized, endothelialized microfluidic system. hPF4 and KKO selectively bound to photochemically injured endothelium at sites where surface glycocalyx was reduced. These studies support the concept that the perithrombus endothelium is the predominant site of HIT antigen assembly. This suggests that disrupting antigen formation along the endothelium or protecting the endothelium may provide a therapeutic opportunity to prevent thrombotic complications of HIT, while sparing systemic hemostatic pathways.