Targeting lipid nanoparticles to the blood-brain barrier to ameliorate acute ischemic stroke.

Effective delivery of mRNA or small molecule drugs to the brain is a significant challenge in developing treatment for acute ischemic stroke (AIS). To address the problem, we have developed targeted nanomedicine to increase drug concentrations in endothelial cells of the blood-brain barrier (BBB) of the injured brain. Inflammation during ischemic stroke causes continuous neuronal death and an increase in the infarct volume. To enable targeted delivery to the inflamed BBB, we conjugated lipid nanocarriers (NCs) with antibodies that bind cell adhesion molecules expressed at the BBB. In the transient middle cerebral artery occlusion mouse model, NCs targeted to vascular cellular adhesion molecule-1 (VCAM) achieved the highest level of brain delivery, nearly two orders of magnitude higher than untargeted ones. VCAM-targeted lipid nanoparticles with luciferase-encoding mRNA and Cre-recombinase showed selective expression in the ischemic brain. Anti-inflammatory drugs administered intravenously after ischemic stroke reduced cerebral infarct volume by 62% (interleukin-10 mRNA) or 35% (dexamethasone) only when they were encapsulated in VCAM-targeted NCs. Thus, VCAM-targeted lipid NCs represent a new platform for strongly concentrating drugs within the compromised BBB of penumbra, thereby ameliorating AIS.

Combination of Physicochemical Tropism and Affinity Moiety Targeting of Lipid Nanoparticles Enhances Organ Targeting.

Two camps have emerged for targeting nanoparticles to specific organs and cell types: affinity moiety targeting and physicochemical tropism. Here we directly compare and combine both using intravenous (IV) lipid nanoparticles (LNPs) designed to target the lungs. We utilized PECAM antibodies as affinity moieties and cationic lipids for physicochemical tropism. These methods yield nearly identical lung uptake, but aPECAM LNPs show higher endothelial specificity. LNPs combining these targeting methods had >2-fold higher lung uptake than either method alone and markedly enhanced epithelial uptake. To determine if lung uptake is because the lungs are the first organ downstream of IV injection, we compared IV vs intra-arterial (IA) injection into the carotid artery, finding that IA combined-targeting LNPs achieve 35% of the injected dose per gram (%ID/g) in the first-pass organ, the brain, among the highest reported. Thus, combining the affinity moiety and physicochemical strategies provides benefits that neither targeting method achieves alone.

Effective Prevention of Arterial Thrombosis with Albumin-Thrombin Inhibitor Conjugates.

Thromboprophylaxis is indicated in patients at an elevated risk of developing thrombotic disorders, typically using direct oral anticoagulants or low-molecular-weight heparins. We postulated that transient thromboprophylaxis (days-weeks) could be provided by a single dose of an anticoagulant engineered for prolonged pharmacokinetics. In the present work, d-phenylalanyl-l-prolyl-l-arginine chloromethyl ketone (PPACK) was used as a model anticoagulant to test the hypothesis that conjugation of thrombin inhibitors to the surface of albumin would provide durable protection against thrombotic insults. Covalent conjugates were formed between albumin and PPACK using click chemistry, and they were tested in vitro using a thrombin activity assay and a clot formation assay. Thromboprophylactic efficacy was tested in mouse models of arterial thrombosis, both chemically induced (FeCl3) and following ischemia-reperfusion (transient middle cerebral artery occlusion; tMCAO). Albumin-PPACK conjugates were shown to have nanomolar potency in both in vitro assays, and following intravenous injection had prolonged circulation. Conjugates did not impact hemostasis (tail clipping) or systemic coagulation parameters in normal mice. Intravenous injection of conjugates prior to FeCl3-induced thrombosis provided significant protection against occlusion of the middle cerebral and common carotid arteries, and injection immediately following ischemia-reperfusion reduced stroke volume measured 3 days after injury by ∼40% in the tMCAO model. The data presented here provide support for the use of albumin-linked anticoagulants as an injectable, long-circulating, safe thromboprophylactic agent. In particular, albumin-PPACK provides significant protection against thrombosis induced by multiple mechanisms, without adversely affecting hemostasis.

Selective targeting of nanomedicine to inflamed cerebral vasculature to enhance the blood-brain barrier.

Drug targeting to inflammatory brain pathologies such as stroke and traumatic brain injury remains an elusive goal. Using a mouse model of acute brain inflammation induced by local tumor necrosis factor alpha (TNFα), we found that uptake of intravenously injected antibody to vascular cell adhesion molecule 1 (anti-VCAM) in the inflamed brain is >10-fold greater than antibodies to transferrin receptor-1 and intercellular adhesion molecule 1 (TfR-1 and ICAM-1). Furthermore, uptake of anti-VCAM/liposomes exceeded that of anti-TfR and anti-ICAM counterparts by ∼27- and ∼8-fold, respectively, achieving brain/blood ratio >300-fold higher than that of immunoglobulin G/liposomes. Single-photon emission computed tomography imaging affirmed specific anti-VCAM/liposome targeting to inflamed brain in mice. Intravital microscopy via cranial window and flow cytometry showed that in the inflamed brain anti-VCAM/liposomes bind to endothelium, not to leukocytes. Anti-VCAM/LNP selectively accumulated in the inflamed brain, providing de novo expression of proteins encoded by cargo messenger RNA (mRNA). Anti-VCAM/LNP-mRNA mediated expression of thrombomodulin (a natural endothelial inhibitor of thrombosis, inflammation, and vascular leakage) and alleviated TNFα-induced brain edema. Thus VCAM-directed nanocarriers provide a platform for cerebrovascular targeting to inflamed brain, with the goal of normalizing the integrity of the blood-brain barrier, thus benefiting numerous brain pathologies.

Targeted In Vivo Loading of Red Blood Cells Markedly Prolongs Nanocarrier Circulation.

Engineering drug delivery systems for prolonged pharmacokinetics (PK) has been an ongoing pursuit for nearly 50 years. The gold standard for PK enhancement is the coating of nanoparticles with polymers, namely polyethylene glycol (PEGylation), which has been applied in several clinically used products. In the present work, we utilize the longest circulating and most abundant component of blood─the erythrocyte─to improve the PK behavior of liposomes. Antibody-mediated coupling of liposomes to erythrocytes was tested in vitro to identify a loading dose that did not adversely impact the carrier cells. Injection of erythrocyte targeting liposomes into mice resulted in a ∼2-fold improvement in the area under the blood concentration versus time profile versus PEGylated liposomes and a redistribution from the plasma into the cellular fraction of blood. These results suggest that in vivo targeting of erythrocytes is a viable strategy to improve liposome PK relative to current, clinically viable strategies.

Copper Oxide Nanoparticle-Induced Acute Inflammatory Response and Injury in Murine Lung Is Ameliorated by Synthetic Secoisolariciresinol Diglucoside (LGM2605).

Metal-oxide nanoparticles (MO-NPs), such as the highly bioreactive copper-based nanoparticles (CuO-NPs), are widely used in manufacturing of hundreds of commercial products. Epidemiological studies correlated levels of nanoparticles in ambient air with a significant increase in lung disease. CuO-NPs, specifically, were among the most potent in a set of metal-oxides and carbons studied in parallel regarding DNA damage and cytotoxicity. Despite advances in nanotoxicology research and the characterization of their toxicity, the exact mechanism(s) of toxicity are yet to be defined. We identified chlorination toxicity as a damaging consequence of inflammation and myeloperoxidase (MPO) activation, resulting in macromolecular damage and cell damage/death. We hypothesized that the inhalation of CuO-NPs elicits an inflammatory response resulting in chlorination damage in cells and lung tissues. We further tested the protective action of LGM2605, a synthetic small molecule with known scavenging properties for reactive oxygen species (ROS), but most importantly, for active chlorine species (ACS) and an inhibitor of MPO. CuO-NPs (15 µg/bolus) were instilled intranasally in mice and the kinetics of the inflammatory response in lungs was evaluated 1, 3, and 7 days later. Evaluation of the protective action of LGM2605 was performed at 24 h post-challenge, which was selected as the peak acute inflammatory response to CuO-NP. LGM2605 was given daily via gavage to mice starting 2 days prior to the time of the insult (100 mg/kg). CuO-NPs induced a significant inflammatory influx, inflammasome-relevant cytokine release, and chlorination damage in mouse lungs, which was mitigated by the action of LGM2605. Preventive action of LGM2605 ameliorated the adverse effects of CuO-NP in lung.

Inhibition of Thrombin With PPACK-Nanoparticles Restores Disrupted Endothelial Barriers and Attenuates Thrombotic Risk in Experimental Atherosclerosis.

OBJECTIVE: A role for thrombin in the pathogenesis of atherosclerosis has been suggested through clinical and experimental studies revealing a critical link between the coagulation system and inflammation. Although approved drugs for inhibition of thrombin and thrombin-related signaling have demonstrated efficacy, their clinical application to this end may be limited because of significant potential for bleeding side effects. Thus, we sought to implement a plaque-localizing nanoparticle-based approach to interdict thrombin-induced inflammation and hypercoagulability in atherosclerosis. APPROACH AND RESULTS: We deployed a novel magnetic resonance spectroscopic method to quantify the severity of endothelial damage for correlation with traditional metrics of vessel procoagulant activity after dye-laser injury in fat-fed apolipoprotein E-null mice. We demonstrate that a 1-month course of treatment with antithrombin nanoparticles carrying the potent thrombin inhibitor PPACK (d-phenylalanyl-l-prolyl-l-arginyl chloromethylketone) nanoparticle (1) reduces the expression and secretion of proinflammatory and procoagulant molecules, (2) diminishes plaque procoagulant activity without the need for systemic anticoagulation, (3) rapidly restores disrupted vascular endothelial barriers, and (4) retards plaque progression in lesion-prone areas. CONCLUSIONS: These observations illustrate the role of thrombin as a pleiotropic atherogenic molecule under conditions of hypercholesterolemia and suggest the utility of its inhibition with locally acting antithrombin nanoparticle therapeutics as a rapid-acting anti-inflammatory strategy in atherosclerosis to reduce thrombotic risk.

Mechanisms that determine nanocarrier targeting to healthy versus inflamed lung regions.

Inflamed organs display marked spatial heterogeneity of inflammation, with patches of inflamed tissue adjacent to healthy tissue. To investigate how nanocarriers (NCs) distribute between such patches, we created a mouse model that recapitulates the spatial heterogeneity of the inflammatory lung disease ARDS. NCs targeting the epitope PECAM strongly accumulated in the lungs, but were shunted away from inflamed lung regions due to hypoxic vasoconstriction (HVC). In contrast, ICAM-targeted NCs, which had lower whole-lung uptake than PECAM/NCs in inflamed lungs, displayed markedly higher NC levels in inflamed regions than PECAM/NCs, due to increased regional ICAM. Regional HVC, epitope expression, and capillary leak were sufficient to predict intra-organ of distribution of NCs, antibodies, and drugs. Importantly, these effects were not observable with traditional spatially-uniform models of ARDS, nor when examining only whole-organ uptake. This study underscores how examining NCs' intra-organ distribution in spatially heterogeneous animal models can guide rational NC design.

Quantifying progression and regression of thrombotic risk in experimental atherosclerosis.

Currently, there are no generally applicable noninvasive methods for defining the relationship between atherosclerotic vascular damage and risk of focal thrombosis. Herein, we demonstrate methods to delineate the progression and regression of vascular damage in response to an atherogenic diet by quantifying the in vivo accumulation of semipermeable 200-300 nm perfluorocarbon core nanoparticles (PFC-NP) in ApoE null mouse plaques with [(19)F] magnetic resonance spectroscopy (MRS). Permeability to PFC-NP remained minimal until 12 weeks on diet, then increased rapidly following 12 weeks, but regressed to baseline within 8 weeks after diet normalization. Markedly accelerated clotting (53.3% decrease in clotting time) was observed in carotid artery preparations of fat-fed mice subjected to photochemical injury as defined by the time to flow cessation. For all mice on and off diet, an inverse linear relationship was observed between the permeability to PFC-NP and accelerated thrombosis (P = 0.02). Translational feasibility for quantifying plaque permeability and vascular damage in vivo was demonstrated with clinical 3 T MRI of PFC-NP accumulating in plaques of atherosclerotic rabbits. These observations suggest that excessive permeability to PFC-NP may indicate prothrombotic risk in damaged atherosclerotic vasculature, which resolves within weeks after dietary therapy.

Rapamycin nanoparticles target defective autophagy in muscular dystrophy to enhance both strength and cardiac function.

Duchenne muscular dystrophy in boys progresses rapidly to severe impairment of muscle function and death in the second or third decade of life. Current supportive therapy with corticosteroids results in a modest increase in strength as a consequence of a general reduction in inflammation, albeit with potential untoward long-term side effects and ultimate failure of the agent to maintain strength. Here, we demonstrate that alternative approaches that rescue defective autophagy in mdx mice, a model of Duchenne muscular dystrophy, with the use of rapamycin-loaded nanoparticles induce a reproducible increase in both skeletal muscle strength and cardiac contractile performance that is not achievable with conventional oral rapamycin, even in pharmacological doses. This increase in physical performance occurs in both young and adult mice, and, surprisingly, even in aged wild-type mice, which sets the stage for consideration of systemic therapies to facilitate improved cell function by autophagic disposal of toxic byproducts of cell death and regeneration.

Programmable nanoparticle functionalization for in vivo targeting.

The emerging demand for programmable functionalization of existing base nanocarriers necessitates development of an efficient approach for cargo loading that avoids nanoparticle redesign for each individual application. Herein, we demonstrate in vivo a postformulation strategy for lipidic nanocarrier functionalization with the use of a linker peptide, which rapidly and stably integrates cargos into lipidic membranes of nanocarriers after simple mixing through a self-assembling process. We exemplified this strategy by generating a VCAM-1-targeted perfluorocarbon nanoparticle for in vivo targeting in atherosclerosis (ApoE-deficient) and breast cancer (STAT-1-deficient) models. In the atherosclerotic model, a 4.1-fold augmentation in binding to affected aortas was observed for targeted vs. nontargeted nanoparticles (P<0.0298). Likewise, in the breast cancer model, a 4.9-fold increase in the nanoparticle signal from tumor vasculature was observed for targeted vs. nontargeted nanoparticles (P<0.0216). In each case, the nanoparticle was registered with fluorine ((19)F) magnetic resonance spectroscopy of the nanoparticle perfluorocarbon core, yielding a quantitative estimate of the number of tissue-bound nanoparticles. Because other common nanocarriers with lipid coatings (e.g., liposomes, micelles, etc.) can employ this strategy, this peptide linker postformulation approach is applicable to more than half of the available nanosystems currently in clinical trials or clinical uses.

Controlling spatial distribution of functional lipids in a supported lipid bilayer prepared from vesicles.

Conjugating biomolecules, such as antibodies, to bioconjugate moieties on lipid surfaces is a powerful tool for engineering the surface of diverse biomaterials, including cells and nanoparticles. We developed supported lipid bilayers (SLBs) presenting well-defined spatial distributions of functional moieties as models for precisely engineered functional biomolecular-lipid surfaces. We used quartz crystal microbalance with dissipation (QCM-D) and atomic force microscopy (AFM) to determine how vesicles containing a mixture of 1,2-dipalmitoyl-sn-glycero-3-phosphatidylcholine (DPPC) and 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[azido(polyethylene glycol)-2000] (DSPE-PEG-N3) form SLBs as a function of the lipid phase transition temperature (Tm). Above the DPPC Tm, DPPC/DSPE-PEG-N3 vesicles form SLBs with functional azide moieties on SiO2 substrates via vesicle fusion. Below this Tm, DPPC/DSPE-PEG-N3 vesicles attach to SiO2 intact. Intact DPPC/DSPE-PEG-N3 vesicles on the SiO2 surfaces fuse and rupture to form SLBs when temperature is brought above the DPPC Tm. AFM studies show uniform and complete DPPC/DSPE-PEG-N3 SLB coverage of SiO2 surfaces for different DSPE-PEG-N3 concentrations. As the DSPE-PEG-N3 concentration increases from 0.01 to 6 mol%, the intermolecular spacing of DSPE-PEG-N3 in the SLBs decreases from 4.6 to 1.0 nm. The PEG moiety undergoes a mushroom to brush transition as DSPE-PEG-N3 concentration varies from 0.1 to 2.0 mol%. Via copper-free click reaction, IgG was conjugated to SLB surfaces with 4.6 nm or 1.3 nm inter-DSPE-PEG-N3 spacing. QCM-D and AFM data show; 1) uniform and complete IgG layers of similar mass and thickness on the two types of SLB; 2) a higher-viscosity/less rigid IgG layer on the SLB with 4.6 nm inter-DSPE-PEG-N3 spacing. Our studies provide a blueprint for SLBs modeling spatial control of functional macromolecules on lipid surfaces, including surfaces of lipid nanoparticles and cells.

Nanocarriers' repartitioning of drugs between blood subcompartments as a mechanism of improving pharmacokinetics, safety, and efficacy.

For medical emergencies, such as acute ischemic stroke, rapid drug delivery to the target site is essential. For many small molecule drugs, this goal is unachievable due to poor solubility that prevents intravenous administration, and less obviously, by extensive partitioning to plasma proteins and red blood cells (RBCs), which greatly slows delivery to the target. Here we study these effects and how they can be solved by loading into nanoscale drug carriers. We focus on fingolimod, a small molecule drug that is FDA-approved for treatment of multiple sclerosis, which has also shown promise in the treatment of stroke. Unfortunately, fingolimod has poor solubility and very extensive partitioning to plasma proteins and RBCs (in whole blood, 86% partitions to RBCs, 13.96% to plasma proteins, and 0.04% is free). We develop a liposomal formulation that slows the partitioning of fingolimod to RBCs and plasma proteins, enables intravenous delivery, and additionally prevents fingolimod toxicity to RBCs. The liposomal formulation nearly completely prevented fingolimod adsorption to plasma proteins (association with plasma proteins was 98.4 ± 0.4% for the free drug vs. 5.6 ± 0.4% for liposome-loaded drug). When incubated with whole blood in vitro, the liposomal formulation greatly slowed partitioning of fingolimod to RBCs and also eliminated deleterious effects of fingolimod on RBC rigidity, morphology, and hemolysis. In vivo, the liposomal formulation delayed fingolimod partitioning to RBCs for over 30 min, a critical time window for stroke. Fingolimod-loaded liposomes showed improved efficacy in a mouse model of post-stroke neuroinflammation, completely sealing the leaky blood-brain barrier (114 ± 11.5% reduction in albumin leak into the brain for targeted liposomes vs. 38 ± 16.5% reduction for free drug). This effect was only seen for liposomes modified with antibodies to enable targeted delivery to the site of action, and not in unmodified, long-circulating liposomes. Thus, loading fingolimod into liposomes prevented partitioning to RBCs and associated toxicities and enabled targeted delivery. This paradigm can be used for tuning the blood distribution of small molecule drugs for the treatment of acute illnesses requiring rapid pharmacologic intervention.

A percolation-type criticality threshold controls immune protein coating of surfaces.

When a material enters the body, it is immediately attacked by hundreds of proteins, organized into complex networks of binding interactions and reactions. How do such complex systems interact with a material, "deciding" whether to attack? We focus on the "complement" system of ∼40 blood proteins that bind microbes, nanoparticles, and medical devices, initiating inflammation. We show a sharp threshold for complement activation upon varying a fundamental material parameter, the surface density of potential complement attachment points. This sharp threshold manifests at scales spanning single nanoparticles to macroscale pathologies, shown here for diverse engineered and living materials. Computational models show these behaviors arise from a minimal subnetwork of complement, manifesting percolation-type critical transitions in the complement response. This criticality switch explains the "decision" of a complex signaling network to interact with a material, and elucidates the evolution and engineering of materials interacting with the body.

Physicochemical Targeting of Lipid Nanoparticles to the Lungs Induces Clotting: Mechanisms and Solutions.

Lipid nanoparticles (LNPs) have become the dominant drug delivery technology in industry, holding the promise to deliver RNA to up or down-regulate any protein of interest. LNPs have mostly been targeted to specific cell types or organs by physicochemical targeting in which LNP's lipid compositions are adjusted to find mixtures with the desired tropism. Here lung-tropic LNPs are examined, whose organ tropism derives from containing either a cationic or ionizable lipid conferring a positive zeta potential. Surprisingly, these LNPs are found to induce massive thrombosis. Such thrombosis is shown in the lungs and other organs, and it is shown that it is greatly exacerbated by pre-existing inflammation. This clotting is induced by a variety of formulations with cationic lipids, including LNPs and non-LNP nanoparticles, and even by lung-tropic ionizable lipids that do not have a permanent cationic charge. The mechanism depends on the LNPs binding to and then changing the conformation of fibrinogen, which then activates platelets and thrombin. Based on these mechanisms, multiple solutions are engineered that enable positively charged LNPs to target the lungs while ameliorating thrombosis. The findings illustrate how physicochemical targeting approaches must be investigated early for risks and re-engineered with a careful understanding of biological mechanisms.

Lipid Nanoparticle-Associated Inflammation is Triggered by Sensing of Endosomal Damage: Engineering Endosomal Escape Without Side Effects.

Lipid nanoparticles (LNPs) have emerged as the dominant platform for RNA delivery, based on their success in the COVID-19 vaccines and late-stage clinical studies in other indications. However, we and others have shown that LNPs induce severe inflammation, and massively aggravate pre-existing inflammation. Here, using structure-function screening of lipids and analyses of signaling pathways, we elucidate the mechanisms of LNP-associated inflammation and demonstrate solutions. We show that LNPs' hallmark feature, endosomal escape, which is necessary for RNA expression, also directly triggers inflammation by causing endosomal membrane damage. Large, irreparable, endosomal holes are recognized by cytosolic proteins called galectins, which bind to sugars on the inner endosomal membrane and then regulate downstream inflammation. We find that inhibition of galectins abrogates LNP-associated inflammation, both in vitro and in vivo . We show that rapidly biodegradable ionizable lipids can preferentially create endosomal holes that are smaller in size and reparable by the endosomal sorting complex required for transport (ESCRT) pathway. Ionizable lipids producing such ESCRT-recruiting endosomal holes can produce high expression from cargo mRNA with minimal inflammation. Finally, we show that both routes to non-inflammatory LNPs, either galectin inhibition or ESCRT-recruiting ionizable lipids, are compatible with therapeutic mRNAs that ameliorate inflammation in disease models. LNPs without galectin inhibition or biodegradable ionizable lipids lead to severe exacerbation of inflammation in these models. In summary, endosomal escape induces endosomal membrane damage that can lead to inflammation. However, the inflammation can be controlled by inhibiting galectins (large hole detectors) or by using biodegradable lipids, which create smaller holes that are reparable by the ESCRT pathway. These strategies should lead to generally safer LNPs that can be used to treat inflammatory diseases.

Marginated Neutrophils in the Lungs Effectively Compete for Nanoparticles Targeted to the Endothelium, Serving as a Part of the Reticuloendothelial System.

Nanomedicine has long pursued the goal of targeted delivery to specific organs and cell types but has yet to achieve this goal with the vast majority of targets. One rare example of success in this pursuit has been the 25+ years of studies targeting the lung endothelium using nanoparticles conjugated to antibodies against endothelial surface molecules. However, here we show that such "endothelial-targeted" nanocarriers also effectively target the lungs' numerous marginated neutrophils, which reside in the pulmonary capillaries and patrol for pathogens. We show that marginated neutrophils' uptake of many of these "endothelial-targeted" nanocarriers is on par with endothelial uptake. This generalizes across diverse nanomaterials and targeting moieties and was even found with physicochemical lung tropism (i.e., without targeting moieties). Further, we observed this in ex vivo human lungs and in vivo healthy mice, with an increase in marginated neutrophil uptake of nanoparticles caused by local or distant inflammation. These findings have implications for nanomedicine development for lung diseases. These data also suggest that marginated neutrophils, especially in the lungs, should be considered a major part of the reticuloendothelial system (RES), with a special role in clearing nanoparticles that adhere to the lumenal surfaces of blood vessels.

Thrombin-targeted liposomes establish a sustained localized anticlotting barrier against acute thrombosis.

The goal of the present work was to design and test an acute-use nanoparticle-based antithrombotic agent that exhibits sustained local inhibition of thrombin without requiring a systemic anticoagulant effect to function against acute arterial thrombosis. To demonstrate proof of concept, we functionalized the surface of liposomes with multiple copies of the direct thrombin inhibitor, d-phenylalanyl-l-prolyl-l-arginyl-chloromethyl ketone (PPACK), which exhibits high affinity for thrombin as a free agent but manifests too rapid clearance in vivo to be effective alone. The PPACK-liposomes were formulated as single unilamellar vesicles, with a diameter of 170.78 ± 10.59 nm and a near neutral charge. In vitro models confirmed the inhibitory activity of PPACK-liposomes, demonstrating a KI' of 172.6 nM. In experimental clots in vitro, treatment of formed clots completely abrogated any further clotting upon exposure to human plasma. The liposomes were evaluated in vivo in a model of photochemical-induced carotid artery injury, resulting in significantly prolonged arterial occlusion time over that of controls (69.06 ± 5.65 min for saline treatment, N = 6, 71.33 ± 9.46 min for free PPACK treated; N = 4, 85.75 ± 18.24 min for precursor liposomes; N = 4, 139.75 ± 20.46 min for PPACK-liposomes; P = 0.0049, N = 6). Systemic anticoagulant profiles revealed a rapid return to control levels within 50 min, while still maintaining antithrombin activity at the injury site. The establishment of a potent and long-acting anticoagulant surface over a newly forming clot with the use of thrombin targeted nanoparticles that do not require systemic anticoagulation to be effective offers an alternative site-targeted approach to the management of acute thrombosis.

Meta-analysis of material properties influencing nanoparticle plasma pharmacokinetics.

Thorough characterization of the plasma pharmacokinetics (PK) is a critical step in clinical development of novel therapeutics and is routinely performed for small molecules and biologics. However, there is a paucity of even basic characterization of PK for nanoparticle-based drug delivery systems. This has led to untested generalizations about how nanoparticle properties govern PK. Here, we present a meta-analysis of 100 nanoparticle formulations following IV administration in mice to identify any correlations between four PK parameters derived by non-compartmental analysis (NCA) and four cardinal properties of nanoparticles: PEGylation, zeta potential, size, and material. There was a statistically significant difference between the PK of particles stratified by nanoparticle properties. However, single linear regression between these properties and PK parameters showed poor predictability (r2 < 0.10 for all analyses), while multivariate regressions showed improved predictability (r2 > 0.38, except for t1/2). This suggests that no single nanoparticle property alone is even moderately predictive of PK, while the combination of multiple nanoparticle features does provide moderate predictive power. Improved reporting of nanoparticle properties will enable more accurate comparison between nanoformulations and will enhance our ability to predict in vivo behavior and design optimal nanoparticles.

Targeted drug delivery to the brain endothelium dominates over passive delivery via vascular leak in experimental intracerebral hemorrhage.

Intracerebral hemorrhage (ICH) is one of the most common causes of fatal stroke, yet has no specific drug therapies. Many attempts at passive intravenous (IV) delivery in ICH have failed to deliver drugs to the salvageable area around the hemorrhage. The passive delivery method assumes vascular leak through the ruptured blood-brain barrier will allow drug accumulation in the brain. Here we tested this assumption using intrastriatal injection of collagenase, a well-established experimental model of ICH. Fitting with hematoma expansion in clinical ICH, we showed that collagenase-induced blood leak drops significantly by 4 h after ICH onset and is gone by 24 h. We observed passive-leak brain accumulation also declines rapidly over ∼4 h for 3 model IV therapeutics (non-targeted IgG; a protein therapeutic; PEGylated nanoparticles). We compared these passive leak results with targeted brain delivery by IV monoclonal antibodies (mAbs) that actively bind vascular endothelium (anti-VCAM, anti-PECAM, anti-ICAM). Even at early time points after ICH induction, where there is high vascular leak, brain accumulation via passive leak is dwarfed by brain accumulation of endothelial-targeted agents: At 4 h after injury, anti-PECAM mAbs accumulate at 8-fold higher levels in the brain vs. non-immune IgG; anti-VCAM nanoparticles (NPs) deliver a protein therapeutic (superoxide dismutase, SOD) at 4.5-fold higher levels than the carrier-free therapeutic at 24 h after injury. These data suggest that relying on passive vascular leak provides inefficient delivery of therapeutics even at early time points after ICH, and that a better strategy might be targeted delivery to the brain endothelium, which serves as the gateway for the immune attack on the peri-hemorrhage inflamed brain region.