Idiopathic pulmonary fibrosis (IPF) is a progressive fibrotic lung disease where invasive pulmonary myofibroblasts secrete collagen and destroy lung integrity. Here, we show that interleukin-11 (IL11) is up-regulated in the lung of patients with IPF, associated with disease severity, and IL-11 is secreted from IPF fibroblasts. In vitro, IL-11 stimulates lung fibroblasts to become invasive actin alpha 2, smooth muscle–positive (ACTA2+), collagen-secreting myofibroblasts in an extracellular signal–regulated kinase (ERK)–dependent, posttranscriptional manner. In mice, fibroblast-specific transgenic expression or administration of murine IL-11 induces lung myofibroblasts and causes lung fibrosis. IL-11 receptor subunit alpha-1 (Il11ra1)–deleted mice, whose lung fibroblasts are unresponsive to profibrotic stimulation, are protected from fibrosis in the bleomycin mouse model of pulmonary fibrosis. We generated an IL-11–neutralizing antibody that blocks lung fibroblast activation downstream of multiple stimuli and reverses myofibroblast activation. In therapeutic studies, anti–IL-11 treatment diminished lung inflammation and reversed lung fibrosis while inhibiting ERK and SMAD activation in mice. These data prioritize IL-11 as a drug target for lung fibrosis and IPF.

The treatment of central nervous system (CNS) disease has long been difficult due to the ineffectiveness of drug delivery across the blood-brain barrier (BBB). This review summarizes important concepts of the BBB in normal versus pathophysiology and how this physical, enzymatic, and efflux barrier provides necessary protection to the CNS during drug delivery, and consequently treatment challenging. Small molecules account for the vast majority of available CNS drugs primarily due to their ability to penetrate the phospholipid membrane of the BBB by passive or carrier-mediated mechanisms. Physiochemical and biological factors relevant for designing small molecules with optimal capabilities for BBB permeability are discussed, as well as the most promising classes of transporters suitable for small-molecule drug delivery. Clinically translatable imaging methodologies for detecting and quantifying drug uptake and targeting in the brain are discussed as a means of further understanding and refining delivery parameters for both drugs and imaging probes in preclinical and clinical domains. This information can be used as a guide to design drugs with preserved drug action and better delivery profiles for improved treatment outcomes over existing therapeutic approaches.

The use of targeted therapeutics to replenish pathologically deficient proteins on the luminal endothelial membrane has the potential to revolutionize emergency and cardiovascular medicine. Untargeted recombinant proteins, like activated protein C (APC) and thrombomodulin (TM), have demonstrated beneficial effects in acute vascular disorders, but have failed to have a major impact on clinical care. We recently reported that TM fused with an scFv antibody fragment to platelet endothelial cell adhesion molecule-1 (PECAM-1) exerts therapeutic effects superior to untargeted TM. PECAM-1 is localized to cell-cell junctions, however, whereas the endothelial protein C receptor (EPCR), the key co-factor of TM/APC, is exposed in the apical membrane. Here we tested whether anchoring TM to the intercellular adhesion molecule (ICAM-1) favors scFv/TM collaboration with EPCR. Indeed: i) endothelial targeting scFv/TM to ICAM-1 provides ∼15-fold greater activation of protein C than its PECAM-targeted counterpart; ii) blocking EPCR reduces protein C activation by scFv/TM anchored to endothelial ICAM-1, but not PECAM-1; and iii) anti-ICAM scFv/TM fusion provides more profound anti-inflammatory effects than anti-PECAM scFv/TM in a mouse model of acute lung injury. These findings, obtained using new translational constructs, emphasize the importance of targeting protein therapeutics to the proper surface determinant, in order to optimize their microenvironment and beneficial effects.

Targeting nanoparticles (NPs) loaded with drugs and probes to precise locations in the body may improve the treatment and detection of many diseases. Generally, to achieve targeting, affinity ligands are introduced on the surface of NPs that can bind to molecules present on the cell of interest. Optimization of ligand density is a critical parameter in controlling NP binding to target cells and a higher ligand density is not always the most effective. In this study, we investigated how NP avidity affects targeting to the pulmonary vasculature, using NPs targeted to ICAM-1. This cell adhesion molecule is expressed by quiescent endothelium at modest levels and is upregulated in a variety of pathological settings. NP avidity was controlled by ligand density, with the expected result that higher avidity NPs demonstrated greater pulmonary uptake than lower avidity NPs in both naïve and pathological mice. However, in comparison with high avidity NPs, low avidity NPs exhibited several-fold higher selectivity of targeting to pathological endothelium. This finding was translated into a PET imaging platform that was more effective in detecting pulmonary vascular inflammation using low avidity NPs. Furthermore, computational modeling revealed that elevated expression of ICAM-1 on the endothelium is critical for multivalent anchoring of NPs with low avidity, while high avidity NPs anchor effectively to both quiescent and activated endothelium. These results provide a paradigm that can be used to optimize NP targeting by manipulating ligand density, and may find biomedical utility for increasing detection of pathological vasculature.

Targeting of therapeutics or imaging agents to the endothelium has the potential to improve specificity and effectiveness of treatment for many diseases. One strategy to achieve this goal is the use of nanoparticles (NPs) targeted to the endothelium by ligands of protein determinants present on this tissue, including cell adhesion molecules, peptidases, and cell receptors. However, detachment of the radiolabel probes from NPs poses a significant problem. In this study, we devised polymeric NPs directly labeled with radioiodine isotopes including the position emission tomography (PET) isotope 124I, and characterized their targeting to specific endothelial determinants. This approach provided sizable, targetable probes for specific detection of endothelial surface determinants non-invasively in live animals. Direct conjugation of radiolabel to NPs allowed for stable longitudinal tracking of tissue distribution without label detachment even in an aggressive proteolytic environment. Further, this approach permits tracking of NP pharmacokinetics in real-time and non-invasive imaging of the lung in mice using micro-PET imaging. The use of this strategy will considerably improve investigation of NP interactions with target cells and PET imaging in small animals, which ultimately can aid in the optimization of targeted drug delivery.

Vascular inflammation is a common, complex mechanism involved in pathogenesis of a plethora of disease conditions including ischemia-reperfusion, atherosclerosis, restenosis and stroke. Specific targeting of imaging probes and drugs to endothelial cells in inflammation sites holds promise to improve management of these conditions. Nanocarriers of diverse compositions and geometries, targeted with ligands to endothelial adhesion molecules exposed in inflammation foci are devised for this goal. Imaging modalities that employ these nanoparticle probes include radioisotope imaging, MRI and ultrasound that are translatable from animal to human studies, as well as optical imaging modalities that at the present time are more confined to animal studies. Therapeutic cargoes for these drug delivery systems include diverse anti-inflammatory agents, anti-proliferative drugs for prevention of restenosis, and antioxidants. This article reviews recent advances in the area of image-guided translation of targeted nanocarrier diagnostics and therapeutics in nanomedicine.

Antibodies to platelet endothelial cell adhesion molecule-1 (PECAM-1) facilitate targeted drug delivery to endothelial cells by “vascular immunotargeting.” To define the targeting quantitatively, we investigated the endothelial binding of monoclonal antibodies (mAbs) to extracellular epitopes of PECAM-1. Surprisingly, we have found in human and mouse cell culture models that the endothelial binding of PECAM-directed mAbs and scFv therapeutic fusion protein is increased by co-administration of a paired mAb directed to an adjacent, yet distinct PECAM-1 epitope. This results in significant enhancement of functional activity of a PECAM-1-targeted scFv-thrombomodulin fusion protein generating therapeutic activated Protein C. The “collaborative enhancement” of mAb binding is affirmed in vivo, as manifested by enhanced pulmonary accumulation of intravenously administered radiolabeled PECAM-1 mAb when co-injected with an unlabeled paired mAb in mice. This is the first demonstration of a positive modulatory effect of endothelial binding and vascular immunotargeting provided by the simultaneous binding a paired mAb to adjacent distinct epitopes. The “collaborative enhancement” phenomenon provides a novel paradigm for optimizing the endothelial-targeted delivery of therapeutic agents.

Introduction Brain tumors are inherently difficult to treat in large part due to the cellular blood-brain barriers (BBB) that limit the delivery of therapeutics to the tumor tissue from the systemic circulation. Virtually no large-molecules, including antibody-based proteins, can penetrate the BBB. With antibodies fast becoming attractive ligands for highly specific molecular targeting to tumor antigens, a variety of methods are being investigated to enhance the access of these agents to intracranial tumors for imaging or therapeutic applications. Areas covered This review describes the characteristics of the BBB and the vasculature in brain tumors, described as the blood-brain tumor barrier (BBTB). Antibodies targeted to molecular markers of CNS tumors will be highlighted, and current strategies for enhancing the delivery of antibodies across these cellular barriers into the brain parenchyma to the tumor will be discussed. Non-invasive imaging approaches to assess BBB/BBTB permeability and/or antibody targeting will be presented as a means of guiding the optimal delivery of targeted agents to brain tumors. Expert Opinion Pre-clinical and clinical studies highlight the potential of several approaches in increasing brain tumor delivery across the blood-brain barrier divide. However, each carries its own risks and challenges. There is tremendous potential in using neuroimaging strategies to assist in understanding and defining the challenges to translating and optimizing molecularly-targeted antibody delivery to CNS tumors to improve clinical outcomes.