Accelerated Blood Clearance of Nanoemulsions Modified with PEG-Cholesterol and PEG-Phospholipid Derivatives in Rats: The Effect of PEG-Lipid Linkages and PEG Molecular Weights

Zwitterionic Polymers for Biomedical Applications: Antimicrobial and Antifouling Strategies toward Implantable Medical Devices and Drug Delivery

Poly(ethylene glycol) (PEG) is extensively utilized in biomedical applications due to its biocompatibility; however, its thermal instability and susceptibility to oxidative degradation significantly constrain its long-term effectiveness. Zwitterionic polymers, characterized by their distinctive structure, enhanced stability, and superior biocompatibility, offer a more advantageous alternative. These polymers exhibit super hydrophilicity, resist nonspecific protein adsorption, and maintain stability in biological environments due to their charge-neutral ionic nature. Zwitterionic polymers enhance anticancer drug delivery by precisely targeting tumor cells and facilitating an efficient drug release. Their inherent antifouling properties and prolonged circulation within the bloodstream render them highly suitable for redox-sensitive drug carriers, thereby augmenting the antitumor efficacy. Moreover, zwitterionic polymers markedly mitigate biofouling in implants, biosensors, and wound dressings, thereby improving both their functionality and their therapeutic outcomes. These advantages arise from the formation of robust hydration layers, which significantly enhance the hemocompatibility and inhibit the adhesion of proteins, platelets, and bacteria. Zwitterionic polymers, including sulfobetaine (SB), phosphorylcholine (PC), and carboxybetaine (CB), are increasingly employed in blood-contacting devices and as effective coating materials for implantable devices. This mini-review paper aims to explore the recent diverse biomedical applications of zwitterionic polymers and highlight their advantageous properties compared with unmodified polymers. We will cover their use in drug delivery systems, tumor targeting nanocarriers, antibiofouling and antibacterial activities in implantable devices, tissue engineering, and diagnostic devices, demonstrating how their unique properties can translate into different applications. Through this exploration, this Perspective will display the potential of zwitterionic polymers as innovative polymer materials in the field of biomedical engineering and beyond.

Solubilization techniques used for poorly water-soluble drugs

About 40% of approved drugs and nearly 90% of drug candidates are poorly water-soluble drugs. Low solubility reduces the drugability. Effectively improving the solubility and bioavailability of poorly water-soluble drugs is a critical issue that needs to be urgently addressed in drug development and application. This review briefly introduces the conventional solubilization techniques such as solubilizers, hydrotropes, cosolvents, prodrugs, salt modification, micronization, cyclodextrin inclusion, solid dispersions, and details the crystallization strategies, ionic liquids, and polymer-based, lipid-based, and inorganic-based carriers in improving solubility and bioavailability. Some of the most commonly used approved carrier materials for solubilization techniques are presented. Several approved poorly water-soluble drugs using solubilization techniques are summarized. Furthermore, this review summarizes the solubilization mechanism of each solubilization technique, reviews the latest research advances and challenges, and evaluates the potential for clinical translation. This review could guide the selection of a solubilization approach, dosage form, and administration route for poorly water-soluble drugs. Moreover, we discuss several promising solubilization techniques attracting increasing attention worldwide.

Advances in the development of lipid nanoparticles for ophthalmic therapeutics

Previously, researchers have employed Lipid nanoparticles (LNPs) to directly encapsulate medicines. In the realm of gene therapy, researchers have begun to employ lipid nanoparticles to encapsulate nucleic acids such as messenger RNA, small interfering RNA, and plasmid DNA, which are known as nucleic acid lipid nanoparticles. Recent breakthroughs in LNP-based medicine have provided significant prospects for the treatment of ocular disorders, such as corneal, choroidal, and retinal diseases. The use of LNP as a delivery mechanism for medicines and therapeutic genes can increase their effectiveness while avoiding undesired immune reactions. However, LNP-based medicines may pose ocular concerns. In this review, we discuss the general framework of LNP. Additionally, we review adjustable approaches and evaluate their possible risks. In addition, we examine newly described ocular illnesses in which LNP was utilized as a delivery mechanism. Finally, we provide perspectives for solving these potential issues.

Impact of the Hydrophilicity of Poly(sarcosine) on Poly(ethylene glycol) (PEG) for the Suppression of Anti-PEG Antibody Binding

A method of poly(ethylene glycol) (PEG) conjugation is known as PEGylation, which has been employed to deliver therapeutic drugs, proteins, or nanoparticles by considering the intrinsic non- or very low immunogenic property of PEG. However, PEG has its weaknesses, and one major concern is the potential immunogenicity of PEGylated proteins. Because of its hydrophilicity, poly(sarcosine) (P(Sar)) may be an attractive-and superior-substitute for PEG. In the present study, we designed a double hydrophilic diblock copolymer, methoxy-PEG-b-P(Sar) m (m = 5-55) (mPEG-P(Sar) m ), and synthesized a triblock copolymer with hydrophobic poly(l-isoleucine) (P(Ile)). We validated that double hydrophilic mPEG-P(Sar) block copolymers suppressed the specific binding of three monoclonal anti-PEG antibodies (anti-PEG mAbs) to PEG. The results of our indirect ELISAs indicate that P(Sar) significantly helps to reduce the binding of anti-PEG mAbs to PEG. Importantly, the steady suppression of this binding was made possible, in part, thanks to the maximum number of sarcosine units in the triblock copolymer, as evidenced by sandwich ELISA and biolayer interferometry assay (BLI): the intrinsic hydrophilicity of P(Sar) had a clear supportive effect on PEG. Finally, because we used P(Ile) as a hydrophobic block, PEG-P(Sar) might be an attractive alternative to PEG in the search for protein shields that minimize the immunogenicity of PEGylated proteins.

Polyethylene glycol and immunology: aspects of allergic reactions and their mechanisms, as well as ways to prevent them in clinical practice

In modern medical practice, where polyethylene glycol is widely used as a component of various drugs, such as vaccines, chemotherapy drugs, and antibiotics, including vaccines, the issue of allergic reactions to this substance is becoming increasingly important. The purpose of this study is to review and systematise data on various aspects of allergic reactions to polyethylene glycol with the aim of better understanding their pathogenesis, clinical manifestations, diagnostic methods, and possible treatment approaches. The study analysed literature data in modern databases, such as MEDLINE, PubMed, and Scopus, on allergic reactions to polyethylene glycol, using the keywords: "PEG", "polyethylene glycol", "allergy", "side effect". The main aspects of allergy to this substance were highlighted, including mechanisms of development, diagnostic methods, and possible treatment strategies. The analysis found that allergic reactions to polyethylene glycol can manifest in a variety of ways, including anaphylaxis and systemic reactions. A possible role for the immune response has been identified, including the production of IgE and IgM antibodies, complement activation, and accelerated clearance in response to polyethylene glycol, in blood plasma. Data are also provided on how to diagnose an increased risk of an allergic reaction in patients who have previously received drugs with this type of drug transporter and in patients receiving high molecular weight types of polyethylene glycol. The results of this review contribute to a better understanding of allergic reactions to polyethylene glycol and provide information for the development of more effective diagnostic and treatment methods.

Surface-modified cationic liposomes with a matrix metalloproteinase-degradable polyethylene glycol derivative improved doxorubicin delivery in murine colon cancer

PEGylation is a commonly used approach to prolong the blood circulation time of cationic liposomes. However, PEGylation is associated with the "PEG dilemma", which hinders binding and uptake into tumor cells. The cleavable PEG products are a possible solution to this problem. In the current research, doxorubicin-loaded cationic liposomes (Dox-CLs) surface-conjugated with a matrix metalloproteinase-2 (MMP-2)-sensitive octapeptide linker-PEG derivative were prepared and compared to non-PEGylated and PEGylated CLs in terms of size, surface charge, drug encapsulation and release, uptake, in vivo pharmacokinetics, and anticancer efficacy. It was postulated that PEG deshielding in response to the overexpressed MMP-2 in the tumor microenvironment increases the interaction of protected CLs with cellular membranes and improves their uptake by tumor cells/vasculature. MMP2-responsive Dox-CLs had particle sizes of ∼115-140 nm, surface charges of ∼+25 mV, and encapsulation efficiencies of ∼85-95%. In vitro cytotoxicity assessments showed significantly enhanced uptake and cytotoxicity of PEG-cleavable CLs compared to their non-cleavable PEG-coated counterparts or Caelyx®. Also, the chick chorioallantoic membrane assay showed great antiangiogenesis ability of Dox-CLs leading to target and prevent tumor neovascularization. Besides, in vivo studies showed an effective therapeutic efficacy of PEG-cleavable Dox-CLs in murine colorectal cancer with negligible hematological and histopathological toxicity. Altogether, our results showed that MMP2-responsive Dox-CLs could be served as a promising approach to improve tumor drug delivery and uptake.

Microfluidic-assisted formulation of cell membrane-camouflaged anisotropic nanostructures

Anisotropic gold (Au) nanostructures have been widely explored for various nanomedicine applications. While these nanomaterials have shown great promise for disease theranostics, particularly for cancer diagnosis and treatment, the utilization and clinical translation of anisotropic Au nanostructures have been limited by their high phagocytic uptake and clearance and low cancer targeting specificity. Numerous efforts have thus been made toward mitigating these challenges. Many conventional strategies, however, rely on all-synthetic materials, involve complex chemical processes, or have low product throughput and reproducibility. Herein, by integrating cell membrane coating and microfluidic technologies, a high-throughput bioinspired approach for synthesizing biomimetic anisotropic Au nanostructures with minimized phagocytic uptake and improved cancer cell targeting is reported. Through continuous hydrodynamic flow focusing, mixing, and sonication, Au nanostructures are encapsulated within the macrophage and cancer cell membrane vesicles effectively. The fabricated nanostructures are uniform and highly stable in serum. Importantly, the macrophage membrane vesicle-encapsulated Au nanostructures can be preferentially internalized by breast cancer cells, but not by macrophages. Overall, this study has demonstrated the feasibility of employing an integrated microfluidic-sonication technique to formulate uniform and highly stable biomimetic anisotropic nanostructures for enhanced cancer theranostic applications.

Synergistic vesicle-vector systems for targeted delivery

With the immense progress in drug delivery systems (DDS) and the rise of nanotechnology, challenges such as target specificity remain. The vesicle-vector system (VVS) is a delivery system that uses lipid-based vesicles as vectors for a targeted drug delivery. When modified with target-probing materials, these vesicles become powerful vectors for drug delivery with high target specificity. In this review, we discuss three general types of VVS based on different modification strategies: (1) vesicle-probes; (2) vesicle-vesicles; and (3) genetically engineered vesicles. The synthesis of each VVS type and their corresponding properties that are advantageous for targeted drug delivery, are also highlighted. The applications, challenges, and limitations of VVS are briefly examined. Finally, we share a number of insights and perspectives regarding the future of VVS as a targeted drug delivery system at the nanoscale.

Targeting cancer with mRNA-lipid nanoparticles: key considerations and future prospects

Harnessing mRNA-lipid nanoparticles (LNPs) to treat patients with cancer has been an ongoing research area that started before these versatile nanoparticles were successfully used as COVID-19 vaccines. Currently, efforts are underway to harness this platform for oncology therapeutics, mainly focusing on cancer vaccines targeting multiple neoantigens or direct intratumoural injections of mRNA-LNPs encoding pro-inflammatory cytokines. In this Review, we describe the opportunities of using mRNA-LNPs in oncology applications and discuss the challenges for successfully translating the findings of preclinical studies of these nanoparticles into the clinic. We critically appraise the potential of various mRNA-LNP targeting and delivery strategies, considering physiological, technological and manufacturing challenges. We explore these approaches in the context of the potential clinical applications best suited to each approach and highlight the obstacles that currently need to be addressed to achieve these applications. Finally, we provide insights from preclinical and clinical studies that are leading to this powerful platform being considered the next frontier in oncology treatment.

Copolymer Micelles: A Focus on Recent Advances for Stimulus-Responsive Delivery of Proteins and Peptides

Historically used for the delivery of hydrophobic drugs through core encapsulation, amphiphilic copolymer micelles have also more recently appeared as potent nano-systems to deliver protein and peptide therapeutics. In addition to ease and reproducibility of preparation, micelles are chemically versatile as hydrophobic/hydrophilic segments can be tuned to afford protein immobilization through different approaches, including non-covalent interactions (e.g., electrostatic, hydrophobic) and covalent conjugation, while generally maintaining protein biological activity. Similar to many other drugs, protein/peptide delivery is increasingly focused on stimuli-responsive nano-systems able to afford triggered and controlled release in time and space, thereby improving therapeutic efficacy and limiting side effects. This short review discusses advances in the design of such micelles over the past decade, with an emphasis on stimuli-responsive properties for optimized protein/peptide delivery.

Persistent immune response: Twice tumor exfoliation induced by sialic acid-modified vincristine sulfate liposomes

Studies have shown that tumor-associated macrophages (TAMs) are crucial for the establishment and maintenance in immunosuppressive tumor immune microenvironment (TIME), which can help tumor cells to achieve immune escape and attenuate antitumor therapy. Siglecs, the receptors of sialic acid (SA), widely exist in TAMs, which could be targeted to disrupt TIME and inhibit tumor growth at the root. Therefore, a SA-modified VCR liposome was reported (VCR-SSAL). Cellular and pharmacodynamic experiments showed that VCR-SSAL exhibited strong TAMs targeting and tumor-killing ability. Interestingly, VCR-SSAL treatment induced a phenomenon in which the cancerous tissues were "fell off" from the growth site, after which the wound gradually healed. Three months after the wound healed, the mice whose tumors fell off were re-inoculated, and the tumor fell off again without treatment, with an exfoliation rate of 100%. We speculated that this special efficacy might be due to that VCR loaded in VCR-SSAL could activate adaptive immunity by inducing DNA damage, promoting cytotoxic T lymphocytes (CTLs) infiltration into tumor sites, and enhancing the antitumor immune response. Thus, this study might provide new insights into the application of traditional chemotherapeutic drugs.

Psychotropic drugs interaction with the lipid nanoparticle of COVID-19 mRNA therapeutics

The messenger RNA (mRNA) vaccines for COVID-19, Pfizer-BioNTech and Moderna, were authorized in the US on an emergency basis in December of 2020. The rapid distribution of these therapeutics around the country and the world led to millions of people being vaccinated in a short time span, an action that decreased hospitalization and death but also heightened the concerns about adverse effects and drug-vaccine interactions. The COVID-19 mRNA vaccines are of particular interest as they form the vanguard of a range of other mRNA therapeutics that are currently in the development pipeline, focusing both on infectious diseases as well as oncological applications. The Vaccine Adverse Event Reporting System (VAERS) has gained additional attention during the COVID-19 pandemic, specifically regarding the rollout of mRNA therapeutics. However, for VAERS, absence of a reporting platform for drug-vaccine interactions left these events poorly defined. For example, chemotherapy, anticonvulsants, and antimalarials were documented to interfere with the mRNA vaccines, but much less is known about the other drugs that could interact with these therapeutics, causing adverse events or decreased efficacy. In addition, SARS-CoV-2 exploitation of host cytochrome P450 enzymes, reported in COVID-19 critical illness, highlights viral interference with drug metabolism. For example, patients with severe psychiatric illness (SPI) in treatment with clozapine often displayed elevated drug levels, emphasizing drug-vaccine interaction.

Polymer-Modified Liposomes for Drug Delivery: From Fundamentals to Applications

Liposomes are highly advantageous platforms for drug delivery. To improve the colloidal stability and avoid rapid uptake by the mononuclear phagocytic system of conventional liposomes while controlling the release of encapsulated agents, modification of liposomes with well-designed polymers to modulate the physiological, particularly the interfacial properties of the drug carriers, has been intensively investigated. Briefly, polymers are incorporated into liposomes mainly using “grafting” or “coating”, defined according to the configuration of polymers at the surface. Polymer-modified liposomes preserve the advantages of liposomes as drug-delivery carriers and possess specific functionality from the polymers, such as long circulation, precise targeting, and stimulus-responsiveness, thereby resulting in improved pharmacokinetics, biodistribution, toxicity, and therapeutic efficacy. In this review, we summarize the progress in polymer-modified liposomes for drug delivery, focusing on the change in physiological properties of liposomes and factors influencing the overall therapeutic efficacy.

Branched PEG-modification: A new strategy for nanocarriers to evade of the accelerated blood clearance phenomenon and enhance anti-tumor efficacy

PEGylation is one of the most successful technologies for reducing immunogenicity, improving the stability and circulation time of nanocarriers, and has been applied in the clinic for over three decades. However, linear PEG-modified nanocarriers have been found to induce anti-PEG IgM at the first injection, which triggers the accelerated blood clearance (ABC) phenomenon upon repeated injections. Furthermore, clinical and research evidence has revealed that anti-PEG antibodies also cause serious complement activation-related pseudoallergies (CARPA), which greatly reduce the safety of linear PEGylated nanocarriers. In this study, as an alternative to linear PEG, branched PEG was selected owing to its low antigenicity. We pioneer the use of branched PEG lipid derivatives [DSPE-mPEG_2,n (n = 2, 10, and 20 kDa)] to modify nanoemulsions (PE_2,n) and liposomes (PL_2,n). Upon characterization, PE_2,n and PL_2,n showed similar physicochemical properties to linear DSPE-mPEG₂₀₀₀-modified nanocarriers in terms of size, polydispersity index (PDI), and zeta potential. However, our pharmacokinetics study surprisingly indicated that PE_2,n and PL_2,n did not induce the ABC phenomenon after repeated injection. This may be attributed to the fact that PE_2,n and PL_2,n induced noticeably lower levels of anti-PEG IgM than linear PEG-modified nanocarriers and did not activate the complement system. Furthermore, we are the first to investigate the anti-tumor efficacy of DSPE-mPEG_2,n-modified liposomal doxorubicin (DOX). The pharmacodynamic experiments showed that DSPE-mPEG_2,n-m-modified liposomal DOX had better in vivo anti-tumor effects than linear DSPE-mPEG₂₀₀₀-modified liposomes. Therefore, we speculate that DSPE-mPEG_2,n-modified nanocarriers possess promising prospects in avoiding the ABC phenomenon, reducing CARPA, and improving the anti-tumor efficacy of encapsulated drugs.

Evasion of the accelerated blood clearance phenomenon by branched PEG lipid derivative coating of nanoemulsions

PEGylation increases the circulation time of the nanocarrier, but also triggers accelerated blood clearance (ABC) phenomenon. It is well-known that the ABC phenomenon results in shortened blood circulation and aberrant increase in liver and spleen accumulation, which greatly limits the application of PEGylated nano-preparations. For many years, researchers have been working hard to find ways to reduce or eliminate the ABC phenomenon. Previous studies have focused on PEG molecular weight and PEG alternative materials, but there has never been any research on the effect of different PEG chain types on the ABC phenomenon. Therefore, 40 kDa molecular weight of linear PEG lipid derivatives (DSPE-mPEG_40k) and branched PEG lipid derivatives (DSPE-mPEG_2,40k) were selected to modify nanoemulsions to explore the influence of distinct PEG chain types on avoiding the ABC phenomenon for the first time. We pioneer the use of linear and branched PEG lipid derivatives (DSPE-mPEG_40k and DSPE-mPEG_2,40k) to modify nanoemulsions (PE_40k and PE_2,40k). Upon characterization, PE_40k and PE_2,40k showed good physicochemical properties in the aspect of size, polydispersity index (PDI value), and zeta potential. Surprisingly, the pharmacokinetics study indicated that repeated injection of PE_40k and PE_2,40k did not trigger the ABC phenomenon. More importantly, PE_2,40k possessed a long circulation time and did not cause ABC phenomenon after repeated injection. This may be attributed to the fact that PE_2,40k induced noticeably lower anti-PEG IgM levels compared to linear PEG-modified nanocarriers and did not activate the complement system. Therefore, we speculate that DSPE-mPEG_2,40k-modified nanocarriers possess promising prospects in avoiding the ABC phenomenon, which may improve the possibility of wide application of nanoformulations.

Biomimetically constructing a hypoxia-activated programmable phototheranostics at the molecular level

A programmable strategy at the molecular level to modulate the ratio of a catalyst and photosensitizer to maximize the collaborative efficiency of anti-angiogenesis and PDT.

A preliminary study of the innate immune memory of Kupffer cells induced by PEGylated nanoemulsions

The accelerated blood clearance (ABC) phenomenon describes a dilemma of polyethylene glycol (PEG) applied in drug delivery system (DDS) caused by its immunogenicity, that results in the enhanced blood clearance rate and increased hepatic and splenic accumulation after secondary injection of PEGylated nanocarriers. However, the ABC index, as the judgement of ABC phenomenon, only describes the accelerated blood clearance rate, but ignores the enhanced hepatic and splenic accumulation. Therefore, we proposed the hepatic accumulation (HA) index and the splenic accumulation (SA) index as supplements for assessing the ABC phenomenon, to emphasize the contribution of liver and spleen, especially the liver, possessing the most population of tissue resident macrophages. By altering the first injection site from the tail vein to the liver portal vein, there was no impact on anti-PEG IgM production, and the secondary hepatic accumulation of PEGylated nanoemulsions (PE) was observed to be proportionate to the first PE stimulation strength on the liver. We also determined that Kupffer cells (KCs) were the main contributor to this enhancement. On this basis, we revealed a definite phenomenon that PE could induce innate immune memory in KCs, by enhancing the phagocytosis of KCs toward PE during the secondary stimulation. The PE-stimulated KCs could carry this memory to the naïve rats through adoptive transfer, resulting in increased hepatic accumulation in the recipient rats without antibody production. Studies examining the phagocytosis of KCs in vivo, ex vivo and in vitro revealed that the memory of KCs against PE triggered by first-stimulated PE could be maintained independently of other cells or components until 21 days after the first stimulation, and possessing specificity to PEG, which was invalid to long-circulating GE (GM1 modified nanoemulsions). The discovery of immune memory in KCs induced by PE highlights the importance of focusing on the relationship between the innate immune system and PEGylated nanocarriers during the development of DDS to improve medication safety in the clinic.

Therapeutic and delivery strategies of phytoconstituents for renal fibrosis

Chronic kidney disease (CKD) is one of the most common diseases endangering human health and life. By 2030, 14 per 100,000 people may die from CKD. Renal fibrosis (RF) is an important intermediate link and the final pathological change during CKD progression to the terminal stage. Therefore, identifying safe and effective treatment methods for RF has become an important goal. In 2018, the World Health Organization introduced traditional Chinese medicine into its effective global medical program. Various phytoconstituents that affect the RF process have been extracted from different plants. Here, we review the potential therapeutic capabilities of active phytoconstituents in RF treatment and discuss how phytoconstituents can be structurally modified or combined with other ingredients to enhance efficiency and reduce toxicity. We also summarize phytoconstituent delivery strategies to overcome renal barriers and improve bioavailability and targeting.

Effects of polyethylene glycol on the surface of nanoparticles for targeted drug delivery

The rapid development of drug nanocarriers has benefited from the surface hydrophilic polymers of particles, which has improved the pharmacokinetics of the drugs. Polyethylene glycol (PEG) is a kind of polymeric material with unique hydrophilicity and electrical neutrality. PEG coating is a crucial factor to improve the biophysical and chemical properties of nanoparticles and is widely studied. Protein adherence and macrophage removal are effectively relieved due to the existence of PEG on the particles. This review discusses the PEGylation methods of nanoparticles and related techniques that have been used to detect the PEG coverage density and thickness on the surface of the nanoparticles in recent years. The molecular weight (MW) and coverage density of the PEG coating on the surface of nanoparticles are then described to explain the effects on the biophysical and chemical properties of nanoparticles.

Delivery technologies for in utero gene therapy

Advances in prenatal imaging, molecular diagnostic tools, and genetic screening have unlocked the possibility to treat congenital diseases in utero prior to the onset of clinical symptoms. While fetal surgery and in utero stem cell transplantation can be harnessed to treat specific structural birth defects and congenital hematological disorders, respectively, in utero gene therapy allows for phenotype correction of a wide range of genetic disorders within the womb. However, key challenges to realizing the broad potential of in utero gene therapy are biocompatibility and efficiency of intracellular delivery of transgenes. In this review, we outline the unique considerations to delivery of in utero gene therapy components and highlight advances in viral and non-viral delivery platforms that meet these challenges. We also discuss specialized delivery technologies for in utero gene editing and provide future directions to engineer novel delivery modalities for clinical translation of this promising therapeutic approach.

Monodispersity of Poly(ethylene glycol) Matters for Low-Fouling Coatings

Poly(ethylene glycol) (PEG) is the most used hydrophilic polymer for low-fouling coatings to minimize nonspecific interactions. The PEG molecular weight or its length as well as surface density are typically considered as the main impacts on the control over low-fouling properties. However, the influence of PEG monodispersity on such investigations is typically ignored and rarely reported. Herein, we report the assembly of PEGylated coatings on planar surfaces and Au nanorods (AuNRs) using a series of monodisperse PEG (Mono-PEG) with exact molecular weights and commonly used polydisperse PEG (Poly-PEG) to investigate the effect of the PEG molecular weight and monodispersity on the low-fouling properties. Nonspecific interactions with proteins or cells on PEGylated planar surfaces can be significantly reduced when Mono-PEG with a molecular weight of 752 Da and above is used, while a higher average molecular weight of 2000 Da is required for Poly-PEG-modified surfaces. Cell association of PEGylated AuNRs further confirms that a low molecular weight of Mono-PEG is sufficient to achieve low-fouling properties. This study provides an insight and general guidance into the engineering of low-fouling surfaces by the appropriate choice based on the PEG monodispersity and/or molecular weights.

PEG shedding-rate-dependent blood clearance of PEGylated lipid nanoparticles in mice: Faster PEG shedding attenuates anti-PEG IgM production

PEGylation-modification with polyethylene glycol (PEG)-is useful for stabilizing lipid nanoparticles (LNPs). However, such PEGylation can prevent small interfering RNA (siRNA) encapsulated in LNPs from exerting its gene-silencing effects by disrupting the interaction of LNPs with target cells and by inducing the accelerated blood clearance phenomenon via anti-PEG IgM. PEG-lipids with short acyl chains can be used to address these issues because they are quickly shed from LNPs after administration; however, there are few reports on the relationships among PEG shedding rate, anti-PEG IgM production, and the gene-silencing activity of siRNA upon repeated LNP administration. Here, in mice, we found that LNPs conjugated to a fast-shedding PEG-lipid (short acyl chain) induced less anti-PEG IgM compared with LNPs conjugated to a slow-shedding PEG-lipid (long acyl chain). Moreover, pretreatment of mice with LNPs conjugated to the slow-shedding PEG-lipid caused loss of RNA interference activity after subsequent LNP administration because the payload siRNA was delivered primarily to Kupffer cells rather than to hepatocytes. Together, these findings imply that manipulating PEG shedding rate and anti-PEG antibody production is enormously important in the development of RNA interference-based therapeutics utilizing LNP technology.