Elongated PEO-based nanoparticles bind the high-density lipoprotein (HDL) receptor scavenger receptor class B I (SR-BI)

PEGylated nanoparticles interact with macrophages independently of immune response factors and trigger a non-phagocytic, low-inflammatory response

Poly-ethylene-glycol (PEG)-based nanoparticles (NPs) - including cylindrical micelles (CNPs), spherical micelles (SNPs), and PEGylated liposomes (PLs) - are hypothesized to be cleared in vivo by opsonization followed by liver macrophage phagocytosis. This hypothesis has been used to explain the rapid and significant localization of NPs to the liver after administration into the mammalian vasculature. Here, we show that the opsonization-phagocytosis nexus is not the major factor driving PEG-NP - macrophage interactions. First, mouse and human blood proteins had insignificant affinity for PEG-NPs. Second, PEG-NPs bound macrophages in the absence of serum proteins. Third, lipoproteins blocked PEG-NP binding to macrophages. Because of these findings, we tested the postulate that PEG-NPs bind (apo)lipoprotein receptors. Indeed, PEG-NPs triggered an in vitro macrophage transcription program that was similar to that triggered by lipoproteins and different from that triggered by lipopolysaccharide (LPS) and group A Streptococcus. Unlike LPS and pathogens, PLs did not increase transcripts involved in phagocytosis or inflammation. High-density lipoprotein (HDL) and SNPs triggered remarkably similar mouse bone-marrow-derived macrophage transcription programs. Unlike opsonized pathogens, CNPs, SNPs, and PLs lowered macrophage autophagosome levels and either reduced or did not increase the secretion of key macrophage pro-inflammatory cytokines and chemokines. Thus, the sequential opsonization and phagocytosis process is likely a minor aspect of PEG-NP - macrophage interactions. Instead, PEG-NP interactions with (apo)lipoprotein and scavenger receptors appear to be a strong driving force for PEG-NP - macrophage binding, entry, and downstream effects. We hypothesize that the high presence of these receptors on liver macrophages and on liver sinusoidal endothelial cells is the reason PEG-NPs localize rapidly and strongly to the liver.

Bionic lipoprotein loaded with chloroquine-mediated blocking immune escape improves antitumor immunotherapy

Tumor immunotherapy hold great promise for eradicating tumors. However, immune escape and the immunosuppressive microenvironment of tumor usually limit the efficiency of tumor immunotherapy. Therefore, simultaneously blocking immune escape and improving immunosuppressive microenvironment are the current problems to be solved urgently. Among them, CD47 on cancer cells membrane could bind to signal regulatory protein α (SIRPα) on macrophages membrane and sent out "don't eat me" signal, which was an important pathway of immune escape. The large number of M2-type macrophages in tumor microenvironment was a significant factor contributing to the immunosuppressive microenvironment. Here, we present a drug loading system for enhancing cancer immunotherapy, comprising CD47 antibody (aCD47) and chloroquine (CQ) with Bionic lipoprotein (BLP) carrier (BLP-CQ-aCD47). On the one hand, as drug delivery carrier, BLP could allow CQ to be preferentially taken up by M2-type macrophages, thereby efficiently polarized M2-type tumor-promoting cells into M1-type anti-tumor cells. On the other hand, blocking CD47 from binding to SIRPα could block the "don't eat me" signal, and improve the phagocytosis of macrophages to tumor cells. Taken together, BLP-CQ-aCD47 could block immune escape, improve immunosuppressive microenvironment of tumor, and induce a strong immune response without substantial systemic toxicity. Therefore, it provides a new idea for tumor immunotherapy.

Obesity and inflammation influence pharmacokinetic profiles of PEG-based nanoparticles

Most patients that will be treated with soft nanoparticles (NPs) will be obese. Yet, NP testing, which begins with pharmacokinetic (PK) and toxicity studies, is carried out almost exclusively in lean rodents having healthy livers and low inflammation. To address this knowledge gap, we determined the PK and toxicity of tail-vein-injected, PEG-based cylindrical nanoparticles (CNPs) and PEGylated liposomes (PLs) as a function of obesity, liver health, and inflammation in leptin-deficient ob/ob and wild-type C57BL/6 J mice. CNPs localized faster to obese livers than to healthy livers within 24 h of injection. PLs localized faster to obese livers than to healthy livers but only 30 min post-injection. Afterwards PL localization to lean livers was higher than localization to obese livers. Overall, PL liver signal peaked ∼6 h post-injection in lean mice, ∼24 h post-injection in heavy mice, and ∼ 48 h post-injection in obese mice. CNPs and PLs were non-toxic to mouse livers as assessed by histology; they reduced many cytokine and chemokine levels that were elevated by obesity. Liver macrophage depletion reduced CNP and PL liver localization as expected; liver sinusoidal endothelial cell (LSEC) depletion reduced PL liver localization but surprisingly increased CNP liver localization. The intensity of RAW264.7 macrophages was higher after CNP incubations than with PL incubations; conversely, the intensity of LSECs was higher after PL incubations than with CNP incubations. This shows the potential for key differences in NP-liver interactions. Triggering inflammation by administering lipopolysaccharide (LPS) to mice increased CNP liver localization but decreased PL liver localization. The results show that obesity and inflammation in a mouse model and in vitro affect soft PEG-based NP interaction with macrophages and LSECs, but also that these NPs can reduce pro-inflammatory pathways increased by obesity.

Interactions of Apolipoproteins with Lipid-Based Nanoparticles

Serum proteins bind and form a dynamic protein corona around nanoparticles (NPs) that have been injected into the mammalian vasculature. Several fundamental studies have shown that apolipoproteins are prominent components of the NP corona. Since apolipoproteins control the distribution of lipoproteins, they may also control the distribution of NPs. Indeed, apolipoprotein affinity for NPs has been recently taken advantage of to deliver CRISPR reagents encapsulated in NPs to cells that express particular lipoprotein receptors. In this scenario, an apolipoprotein binds an NP and the resulting apolipoprotein-NP complex binds a cell that expresses the (apo)lipoprotein receptor. But the NP will be diverted from the target cell if it does not express the (apo)lipoprotein receptor. This may hamper NP treatment of diseases. Therefore, we must understand the kinetics of apolipoprotein-NP affinity and how apolipoprotein-NP interactions affect NP biodistribution. In this Perspective, we discuss the evolving topic of apolipoprotein-NP interactions, which is of great interest for all NP-based disease treatments. Many properties of apolipoprotein-NP complexes are yet to be determined and will have a significant impact on NP efficacy for many NP-based treatments in animal models and in the clinic.

All-Atom Molecular Dynamics Simulations of Polyethylene Glycol (PEG) and LIMP-2 Reveal That PEG Penetrates Deep into the Proposed CD36 Cholesterol-Transport Tunnel

Polyethylene glycol (PEG) is the most prominent clinically administered synthetic polymer. For example, over 300 million people have been administered PEGylated liposome vaccines for SARS-CoV-2. PEG is used in mammals because it has low affinity for most proteins and vice versa. However, this makes it difficult to study the few interactions with proteins that PEG has. On the atomistic level, there are two PEG-protein structures: (1) PEG-LIMP-2 and (2) PEG-αPEG. In the first structure, two monomers of a 1.5 kDa PEG polymer (PEG2) had electron density deep in the postulated cholesterol transport tunnel of LIMP-2, a lysosomal cholesterol transport protein and member of the CD36 super family of proteins. It is unclear how PEG entered this tunnel. In the second structure, PEG wrapped around a surface-exposed tryptophan on its antibody. Since tryptophan is a rare residue, it is unclear if this PEG-Trp interaction is ubiquitous. To gain deeper mechanistic insight into PEG-protein interactions, we surrounded the LIMP-2 apo structure with 13 PEG chains of 10 monomers each (PEG10), water, and KCl and simulated the system using NAMD. One of the 13 chains penetrated LIMP-2 and came within 3 Å of PEG2. This was possible because of the strong hydrogen bonding between multiple oxygens along PEG10 and Arg192 but, most importantly, the clamping of the tertiary structure on PEG10. Clamping stabilized the movements of PEG10, and the leading oxygen of PEG10 was able to penetrate LIMP-2 and head toward to the position occupied by PEG2. Phe383 appears to act as a gate for objects to move through this cavity, which continues to the basal/membrane side of LIMP-2. Of all residues, PEG10 molecules had the most sustained interactions with lysine and arginine because of their strong hydrogen-bonding capabilities. These results show that the oxygens of PEG bind residues with high hydrogen bonding capabilities. However, the PEG-protein interaction is likely to be transient unless groups of resides can clamp down on PEG or a cavity that at least part of the PEG chain can enter is in close proximity to lower PEG's entropy.

Internalization and Transport of PEGylated Lipid-Based Mixed Micelles across Caco-2 Cells Mediated by Scavenger Receptor B1

The aim of this study was to get insight into the internalization and transport of PEGylat-ed mixed micelles loaded by vitamin K, as mediated by Scavenger Receptor B1 (SR-B1) that is abundantly expressed by intestinal epithelium cells as well as by differentiated Caco-2 cells. Inhibition of SR-B1 reduced endocytosis and transport of vitamin-K-loaded 0%, 30% and 50% PEGylated mixed micelles and decreased colocalization of the micelles with SR-B1. Confocal fluorescence microscopy, fluorescence-activated cell sorting (FACS) analysis, and surface plasmon resonance (SPR) were used to study the interaction between the mixed micelles of different compositions (varying vitamin K loading and PEG content) and SR-B1. Interaction of PEGylated micelles was independent of the vitamin K content, indicating that the PEG shell prevented vitamin K exposure at the surface of the micelles and binding with the receptor and that the PEG took over the micelles' ability to bind to the receptor. Molecular docking calculations corroborated the dual binding of both vita-min K and PEG with the binding domain of SR-B1. In conclusion, the improved colloidal stability of PEGylated mixed micelles did not compromise their cellular uptake and transport due to the affinity of PEG for SR-B1. SR-B1 is able to interact with PEGylated nanoparticles and mediates their subsequent internalization and transport.