Influence of dose and animal species on accelerated blood clearance of PEGylated liposomal doxorubicin

Attenuated polyethylene glycol immunogenicity and overcoming accelerated blood clearance of a fully PEGylated dendrimer

Polyethylene glycol (PEG) is a popular biocompatible polymer and PEGylated nanoparticles passively accumulate in tumor tissues because of their enhanced permeability and retention effects. Recently, the anti-PEG immunity of PEGylated nanoparticles has become an issue that needs to be solved for their clinical applications. Dendrimers are highly branched and well-defined polymers with many terminal groups, which act as potent drug carriers. In this study, we examined the pharmacokinetics, biodistribution, anti-PEG immunity, and tumor accumulation of a fully PEGylated polyamidoamine (PAMAM) dendrimer after the first and second injections and compared them to those of a PEGylated liposome with the same lipid component as Doxil®. The PEGylated dendrimer showed greater blood circulation than that of the PEGylated liposome after the first and second injections in rats. In mice injected with the PEGylated dendrimer, much less anti-PEG immunoglobulin M (IgM) was generated than that in mice injected with the PEGylated liposome. The PEGylated dendrimer accumulated in the tumor after both the first and second injections. Our results indicated that the PEGylated dendrimer with a small size and high PEG density showed attenuated anti-PEG immunity and overcame the accelerated blood clearance phenomenon, which is useful for drug delivery systems for cancer treatment.

Frameworks for transformational breakthroughs in RNA-based medicines

RNA has sparked a revolution in modern medicine, with the potential to transform the way we treat diseases. Recent regulatory approvals, hundreds of new clinical trials, the emergence of CRISPR gene editing, and the effectiveness of mRNA vaccines in dramatic response to the COVID-19 pandemic have converged to create tremendous momentum and expectation. However, challenges with this relatively new class of drugs persist and require specialized knowledge and expertise to overcome. This Review explores shared strategies for developing RNA drug platforms, including layering technologies, addressing common biases and identifying gaps in understanding. It discusses the potential of RNA-based therapeutics to transform medicine, as well as the challenges associated with improving applicability, efficacy and safety profiles. Insights gained from RNA modalities such as antisense oligonucleotides (ASOs) and small interfering RNAs are used to identify important next steps for mRNA and gene editing technologies.

Treatment-induced and Pre-existing Anti-peg Antibodies: Prevalence, Clinical Implications, and Future Perspectives

Polyethylene glycol (PEG) is a versatile polymer that is used in numerous pharmaceutical applications like the food industry, a wide range of disinfectants, cosmetics, and many commonly used household products. PEGylation is the term used to describe the covalent attachment of PEG molecules to nanocarriers, proteins and peptides, and it is used to prolong the circulation half-life of the PEGylated products. Consequently, PEGylation improves the efficacy of PEGylated therapeutics. However, after four decades of research and more than two decades of clinical applications, an unappealing side of PEGylation has emerged. PEG immunogenicity and antigenicity are remarkable challenges that confound the widespread clinical application of PEGylated therapeutics - even those under clinical trials - as anti-PEG antibodies (Abs) are commonly reported following the systemic administration of PEGylated therapeutics. Furthermore, pre-existing anti-PEG Abs have also been reported in healthy individuals who have never been treated with PEGylated therapeutics. The circulating anti-PEG Abs, both treatment-induced and pre-existing, selectively bind to PEG molecules of the administered PEGylated therapeutics inducing activation of the complement system, which results in remarkable clinical implications with varying severity. These include increased blood clearance of the administered PEGylated therapeutics through what is known as the accelerated blood clearance (ABC) phenomenon and initiation of serious adverse effects through complement activation-related pseudoallergic reactions (CARPA). Therefore, the US FDA industry guidelines have recommended the screening of anti-PEG Abs, in addition to Abs against PEGylated proteins, in the clinical trials of PEGylated protein therapeutics. In addition, strategies revoking the immunogenic response against PEGylated therapeutics without compromising their therapeutic efficacy are important for the further development of advanced PEGylated therapeutics and drug-delivery systems.

Effects of PEG antibodies on in vivo performance of LNP-mRNA vaccines

Polyethylene glycol (PEG) plays important roles in stabilizing and lengthening circulation time of lipid nanoparticle (LNP) vaccines. Nowadays various levels of PEG antibodies have been detected in human blood, but the impact and mechanism of PEG antibodies on the in vivo performance of LNP vaccines has not been clarified thoroughly. By illustrating the distribution characteristics of PEG antibodies in human, the present study focused on the influence of PEG antibodies on the safety and efficacy of LNP-mRNA vaccine against COVID-19 in animal models. It was found that PEG antibodies led to shortened blood circulation duration, elevated accumulation and mRNA expression in liver and spleen, enhanced expression in macrophage and dendritic cells, while without affecting the production of anti-Spike protein antibodies of COVID-19 LNP vaccine. Noteworthily, PEG antibodies binding on the LNP vaccine increased probability of complement activation in animal as well as in human serum and led to lethal side effect in large dosage via intravenous injection of mice. Our data suggested that PEG antibodies in human was a risky factor of LNP-based vaccines for biosafety concerns but not efficacy.

In Vitro and Preclinical Antitumor Evaluation of Doxorubicin Liposomes Coated with a Cholesterol-Based Trimeric β-D-Glucopyranosyltriazole

The coating of liposomes with polyethyleneglycol (PEG) has been extensively discussed over the years as a strategy for enhancing the in vivo and in vitro stability of nanostructures, including doxorubicin-loaded liposomes. However, studies have shown some important disadvantages of the PEG molecule as a long-circulation agent, including the immunogenic role of PEG, which limits its clinical use in repeated doses. In this context, hydrophilic molecules as carbohydrates have been proposed as an alternative to coating liposomes. Thus, this work studied the cytotoxicity and preclinical antitumor activity of liposomes coated with a glycosyl triazole glucose (GlcL-DOX) derivative as a potential strategy against breast cancer. The glucose-coating of liposomes enhanced the storage stability compared to PEG-coated liposomes, with the suitable retention of DOX encapsulation. The antitumor activity, using a 4T1 breast cancer mouse model, shows that GlcL-DOX controlled the tumor growth in 58.5% versus 35.3% for PEG-coated liposomes (PegL-DOX). Additionally, in the preliminary analysis of the GlcL-DOX systemic toxicity, the glucose-coating liposomes reduced the body weight loss and hepatotoxicity compared to other DOX-treated groups. Therefore, GlcL-DOX could be a promising alternative for treating breast tumors. Further studies are required to elucidate the complete GlcL-DOX safety profile.

Activation of CYP3A by Accelerated Blood Clearance Phenomenon Potentiates the Hepatocellular Carcinoma-Targeting Therapeutic Effects of PEGylated Anticancer Prodrug Liposomes

Reduced enzyme activity in hepatocellular carcinoma (HCC) and poor targeting limit the application of enzyme-activating prodrugs, which is also detrimental to the effective treatment of HCC. Here, we investigated whether accelerated blood clearance (ABC) phenomenon occurs in HCC models following repeated injections of PEGylated liposomes (PEG-L), thus inducing prodrug accumulation and activation in the liver and exerting highly effective and low-toxicity therapeutic effects on HCC. First, PEGylated liposomal cyclophosphamide was prepared by solvent injection and characterized. Importantly, preinjection of PEG-L induced the ABC phenomenon and activation of CYP3A in both HCC rats and HCC mice by studying the effects of repeated injections of PEG-L on pharmacokinetics and tissue distribution. Next, the efficacy and toxicity of repeated injections of PEG-L in HCC mice were examined, and our data indicate that repeated injections are administered in a manner that significantly enhances the antitumor effect compared with controls, with little or no toxicity to other organs. To further reveal the pharmacokinetic mechanism of PEG-L repeated administration for the treatment of HCC, the protein expression of hepatic CYP3A and the concentration of cyclophosphamide in the liver and spleen of HCC mice by inhibiting CYP3A were analyzed. These results revealed that inducing CYP3A to accelerate the rapid conversion of prodrugs that accumulate significantly in the liver is a key mechanism for the treatment of HCC with repeated injections of PEG-L. Collectively, this work taps into the application potential of the ABC phenomenon and provides new insights into the clinical application of PEGylated nanoformulations. SIGNIFICANCE STATEMENT: This study revealed that repeated injections of PEGylated liposomes could induce the accelerated blood clearance (ABC) phenomenon characterized by hepatic accumulation and CYP3A activation based on hepatocellular carcinoma (HCC) rats and HCC mice. Furthermore, it was verified that induction of the ABC phenomenon dependent on hepatic accumulation and CYP3A activation could enhance the antihepatocellular carcinoma effects of PEGylated anticancer prodrugs in HCC mice. This elucidated the relevant pharmacokinetic mechanisms and unearthed new clues for solving the clinical application of PEGylated nanoparticles.

Regulation of the innate immune system by fragmented heparin-conjugated lipids on lipid bilayered membranes in vitro

Surface modification with heparin is a powerful biomaterial coating strategy that protects against innate immunity activation since heparin is a part of the proteoglycan heparan sulfate on cell surfaces in the body. We studied the heparinization of cellular and material surfaces via lipid conjugation to a heparin-binding peptide. In the present study, we synthesized fragmented heparin (fHep)-conjugated phospholipids and studied their regulation of the innate immune system on a lipid bilayered surface using liposomes. Liposomes have versatile applications, such as drug-delivery systems, due to their ability to carry a wide range of molecules. Owing to their morphological similarity to cell membranes, they can also be used to mimic a simple cell-membrane to study protein-lipid interactions. We investigated the interaction of complement-regulators, factor H and C4b-binding protein (C4BP), as well as the coagulation inhibitor antithrombin (AT), with fHep-lipids on the liposomal surface. Herein, we studied the ability of fHep-lipids to recruit factor H, C4BP, and AT using a quartz crystal microbalance with dissipation monitoring. With dynamic light scattering, we demonstrated that liposomes could be modified with fHep-lipids and were stable up to 60 days at 4 °C. Using a capillary western blot-based method (Wes), we showed that fHep-liposomes could recruit factor H in a model system using purified proteins and assist in the degradation of the active complement protein C3b to iC3b. Furthermore, we found that fHep-liposomes could recruit factor H and AT from human plasma. Therefore, the use of fHep-lipids could be a potential coating for liposomes and cell surfaces to regulate the immune system on the lipid surface.

The interplay between PEGylated nanoparticles and blood immune system

During the last two decades, an increasing number of reports have pointed out that the immunogenicity of polyethylene glycol (PEG) may trigger accelerated blood clearance (ABC) and hypersensitivity reaction (HSR) to PEGylated nanoparticles, which could make PEG modification counterproductive. These phenomena would be detrimental to the efficacy of the load and even life-threatening to patients. Consequently, further elucidation of the interplay between PEGylated nanoparticles and the blood immune system will be beneficial to developing and applying related formulations. Many groups have worked to unveil the relevance of structural factors, dosing schedule, and other factors to the ABC phenomenon and hypersensitivity reaction. Interestingly, the results of some reports seem to be difficult to interpret or contradict with other reports. In this review, we summarize the physiological mechanisms of PEG-specific immune response. Moreover, we speculate on the potential relationship between the induction phase and the effectuation phase to explain the divergent results in published reports. In addition, the role of nanoparticle-associated factors is discussed based on the classification of the action phase. This review may help researchers to develop PEGylated nanoparticles to avoid unfavorable immune responses based on the underlying mechanism.

Anti-PEG IgM production induced by PEGylated liposomes as a function of administration route

Modifying the surface of nanoparticles with polyethylene glycol (PEG) is a commonly used approach for improving the in vitro stability of nanoparticles such as liposomes and increasing their circulation half-lives. We have demonstrated that, in certain conditions, an intravenous (i.v.) injection of PEGylated liposomes (PEG-Lip) induced anti-PEG IgM antibodies, which led to rapid clearance of second doses in mice. SARS-CoV-2 vaccines, composed of mRNA-containing PEGylated lipid nanoparticles, have been widely administered as intramuscular (i.m.) injections, so it is important to determine if PEGylated formulations can induce anti-PEG antibodies. If the favorable properties that PEGylation imparts to therapeutic nanoparticles are to be widely applicable this should apply to various routes of administration. However, there are few reports on the effect of different administration routes on the in vivo production of anti-PEG IgM. In this study, we investigated anti-PEG IgM production in mice following i.m., intraperitoneal (i.p.) and subcutaneous (s.c.) administration of PEG-Lip. PEG-Lip appeared to induce anti-PEG IgM by all the tested routes of administration, although the lipid dose causing maximum responses varied. Splenectomy attenuated the anti-PEG IgM production for all routes of administration, suggesting that splenic immune cells may have contributed to anti-PEG IgM production. Interestingly, in vitro experiments indicated that not only splenic cells but also cells in the peritoneal cavity induced anti-PEG IgM following incubation with PEG-Lip. These observations confirm previous experiments that have shown that measurable amounts of PEG-Lip administered i.p., i.m. or s.c. are absorbed to some extent into the blood circulation, where they can be distributed to the spleen and/or peritoneal cavity, and are recognized by B cells, triggering anti-PEG IgM production. The results obtained in this study have important implications for developing efficient PEGylated nanoparticular delivery system.

Investigation of anti-PEG antibody response to PEG-containing cosmetic products in mice

Polyethylene glycol (PEG), a polyether compound, is available in molecular weights from ∼300 g/mol to ∼10,000,000 g/mol. In the molecular weight range of ∼750 to ∼5000, PEG is commonly used in bioconjugation technology and nano-formulations to improve the circulation half-life of the formulations and increase their stability. In cosmetics, lower molecular weight PEG compounds such as PEG 60 or PEG 100 are widely used as emulsifiers and skin penetration enhancers. PEG polymers are generally recognized as biologically inert and non-immunogenic. However, it is recently reported that the "pre-existing" anti-PEG antibodies have been detected in high percentages of healthy individuals who have never received treatment with parenteral PEGylated formulations. To the best of our knowledge, we are the first to attempt to find an explanation for the source of pre-existing anti-PEG antibodies in healthy individuals. In a murine study, we demonstrated that topically applied PEG derivatives, present in two commercially available cosmetic products, could efficiently penetrate the stratum corneum and reach the systemic circulation. The skin penetration of PEG derivatives was further enhanced in injured or otherwise compromised skin. Daily application of cosmetic PEG derivatives primed the immune system, inducing anti-PEG IgM production. Anti-PEG IgM was detected by Day 14 in mice with normal skin, while anti-PEG IgM was detected as early as day 7 in mice with compromised skin. In addition, in mice with pre-induced circulating levels of anti-PEG IgM, topically applied PEG derivatives from cosmetic products appeared to bind to the pre-induced anti-PEG IgM, lowering blood levels. Current results indicate that PEG derivatives in cosmetic products may be an important contributor to the source of the "pre-existing" anti-PEG antibodies that have been detected in healthy individuals.

Transferrin receptor-mediated liposomal drug delivery: recent trends in targeted therapy of cancer

INTRODUCTION

Compared to normal cells, malignant cancer cells require more iron for their growth and rapid proliferation, which can be supplied by a high expression level of transferrin receptor (TfR). It is well known that the expression of TfR on the tumor cells is considerably higher than that of normal cells, which makes TfR an attractive target in cancer therapy.

AREAS COVERED

In this review, the primary focus is on the role of TfR as a valuable tool for cancer-targeted drug delivery, followed by the full coverage of available TfR ligands and their conjugation chemistry to the surface of liposomes. Finally, the most recent studies investigating the potential of TfR-targeted liposomes as promising drug delivery vehicles to different cancer cells are highlighted with emphasis on their improvement possibilities to become a part of future cancer medicines.

EXPERT OPINION

Liposomes as a valuable class of nanocarriers have gained much attention toward cancer therapy. From all the studies that have exploited the therapeutic and diagnostic potential of TfR on cancer cells, it can be realized that the systematic assessment of TfR ligands applied for liposomal targeted delivery has yet to be entirely accomplished.

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.

To PEGylate or not to PEGylate: Immunological properties of nanomedicine's most popular component, polyethylene glycol and its alternatives

Polyethylene glycol or PEG has a long history of use in medicine. Many conventional formulations utilize PEG as either an active ingredient or an excipient. PEG found its use in biotechnology therapeutics as a tool to slow down drug clearance and shield protein therapeutics from undesirable immunogenicity. Nanotechnology field applies PEG to create stealth drug carriers with prolonged circulation time and decreased recognition and clearance by the mononuclear phagocyte system (MPS). Most nanomedicines approved for clinical use and experimental nanotherapeutics contain PEG. Among the most recent successful examples are two mRNA-based COVID-19 vaccines that are delivered by PEGylated lipid nanoparticles. The breadth of PEG use in a wide variety of over the counter (OTC) medications as well as in drug products and vaccines stimulated research which uncovered that PEG is not as immunologically inert as it was initially expected. Herein, we review the current understanding of PEG's immunological properties and discuss them in the context of synthesis, biodistribution, safety, efficacy, and characterization of PEGylated nanomedicines. We also review the current knowledge about immunological compatibility of other polymers that are being actively investigated as PEG alternatives.

Accelerated blood clearance and hypersensitivity by PEGylated liposomes containing TLR agonists

Systemic administration of toll-like receptor (TLR) agonists have demonstrated impressive preclinical results as an anti-cancer therapy due to their potent innate immune-stimulatory properties. The clinical advancement has, however, been hindered by severe adverse effects due to systemic activation of the immune system. Liposomal drug delivery systems may modify biodistribution, cellular uptake, and extend blood circulation, and thus, potentially enable systemic administration of TLR agonists at therapeutic doses. In this study, we investigated potential barriers for the administration of TLR agonists formulated in polyethylene glycosylated (PEGylated) liposomes with regards to liposome formulation, TLR agonist, administration route, administration schedule, biodistribution, blood clearance, and anti-PEG antibodies. We found that administration of TLR agonists formulated in PEGylated liposomes led to high anti-PEG antibody titers, which upon multiple intravenous administrations, resulted in accelerated blood clearance and acute hypersensitivity reactions. The latter was found to be associated with anti-PEG IgG antibody and not anti-PEG IgM antibody opsonization. This study highlights the need to carefully design and evaluate nanoparticle delivery systems for immunotherapy as anti-nanoparticle immune responses may challenge the therapeutic application.

Polyethylene Glycol Immunogenicity: Theoretical, Clinical, and Practical Aspects of Anti-Polyethylene Glycol Antibodies

Polyethylene glycol (PEG) is a flexible, hydrophilic simple polymer that is physically attached to peptides, proteins, nucleic acids, liposomes, and nanoparticles to reduce renal clearance, block antibody and protein binding sites, and enhance the half-life and efficacy of therapeutic molecules. Some naïve individuals have pre-existing antibodies that can bind to PEG, and some PEG-modified compounds induce additional antibodies against PEG, which can adversely impact drug efficacy and safety. Here we provide a framework to better understand PEG immunogenicity and how antibodies against PEG affect pegylated drug and nanoparticles. Analysis of published studies reveals rules for predicting accelerated blood clearance of pegylated medicine and therapeutic liposomes. Experimental studies of anti-PEG antibody binding to different forms, sizes, and immobilization states of PEG are also provided. The widespread use of SARS-CoV-2 RNA vaccines that incorporate PEG in lipid nanoparticles make understanding possible effects of anti-PEG antibodies on pegylated medicines even more critical.

Evaluation of antitumor efficacy of folate-poly(2-ethyl-2-oxazoline)-distearoyl phosphatidyl ethanolamine based liposome

This study aims to explore and evaluate the antitumor efficacy of doxorubicin (DOX)-loaded liposomes containing the novel tri-block polymer folate-poly (2-ethyl-2-oxazoline)-distearoyl phosphatidyl ethanolamine (F-PEOz-DSPE), compared with folate-polyethylene glycol-distearoyl phosphatidyl ethanolamine (F-PEG-DSPE) to offer an alternative for PEG decorated carriers. PEOz, a pH-sensitive polymer, exhibits similar solubility and segmental flexibility to PEG. In our previous study, PEOz was employed to an F-PEOz-DSPE which was segmentally similar to F-PEG-DSPE and exhibited selective targeting and pH-sensitivity in tumor cells. In this work, DOX-loaded liposomes containing F-PEOz-DSPE (F-PEOz liposome) or F-PEG-DSPE (F-PEG liposome) were prepared. In vivo/vitro antitumor efficacy and biodistribution were compared between the two liposomes. F-PEOz liposome showed higher in vitro antitumor activity and significantly stronger inhibition of tumor growth in HeLa tumor-bearing nude mice (tumor inhibition rate, 81.20 vs 52.99% with the treatment of 9 mg/kg DOX-loaded F-PEOz liposome/F-PEG liposome) and much less toxicity than free DOX. In vivo fluorescence imaging experiment confirmed that F-PEOz liposome accumulated much more than F-PEG liposome in tumor. Based on the above, F-PEOz liposome may be a promising carrier in tumor chemotherapy to achieve better therapeutic efficacy.

Blood retention and antigenicity of polycarboxybetaine-modified liposomes

Zwitterionic polycarboxybetaines (PCBs) have gained attention as alternative stealth polymers whose liposomal formulation and protein conjugates were reported not to elicit anti-polymer antibodies. Here, we studied the blood retention and antigenicity of liposomes modified with PCBs focusing on their chemical structures and doses. We compared PCBs with either 1 or 3 (PCB1 or PCB3) spacer carbons between the carboxylate and ammonium groups. PCB3-modified liposomes had a short blood retention, whereas PCB1-modified liposomes demonstrated extended blood retention that was somewhat superior to PEGylated liposome. This confirmed the excellent non-fouling nature of PCB1 reported previously. Interestingly, PCB1-liposome as well as PCB3-liposome elicited specific IgMs toward each PCB. The dose-dependent production of specific IgMs to PCB-liposomes was similar to that of PEGylated liposome, i.e., high doses of PCB-liposomes reduced the production of specific IgMs, termed immunological tolerance. These results indicate the importance of investigating the effect of dose to clarify the existence of antigenicity of stealth polymers.

Sensitization of drug resistant sarcoma tumors by membrane modulation via short chain sphingolipid-containing nanoparticles

Nanoparticles such as liposomes are able to overcome cancer treatment challenges such as multidrug resistance by increasing the bioavailability of the encapsulated drug, bypassing drug pumps or through targeting resistant cells. Here, we merge enhanced drug delivery by nanotechnology with tumor cell membrane modulation combined in a single formulation. This is achieved through the incorporation of Short chain sphingolipids (SCSs) in the liposomal composition, which permeabilizes cell membranes to amphiphilic drugs such as Doxorubicin (Dxr). To study the mechanism and capability of SCS-containing nanodevices to overcome Dxr resistance, a sensitive uterine sarcoma cell line, MES-SA, and a resistant derived cell line, MES-SA/MX2, were used. The mechanism of resistance was explored by lipidomics and flow cytometry, revealing significant differences in lipid composition and in P glycoprotein (Pgp) expression. In vitro assays show that SCS liposomes were able to reverse cell resistance, and importantly, display a higher net effect on resistant than sensitive cells. SCS lipids modulated the cell membrane of MES-SA/MX2 drug resistant cells, while Pgp expression was not affected. Furthermore, SCS-modified liposomes were evaluated in a sarcoma xenograft model on drug accumulation, pharmacokinetics and efficacy. SCS liposomes improved Dxr levels in tumor nuclei of MES-SA/MX2 tumor cells, which was accompanied by a delay in tumor growth of the resistant model. Here we show that Dxr accumulation in tumor cells by SCS-modified liposomes was especially improved in Dxr resistant cells, rendering Dxr as effective as in sensitive cells. Moreover, this phenomenon translated to improved efficacy when Dxr liposomes where modified with SCSs in the drug resistant tumor model, while no benefit was seen in the sensitive tumors.

Preclinical evaluation of liposome-supported peritoneal dialysis for the treatment of hyperammonemic crises

Liposome-supported peritoneal dialysis (LSPD) with transmembrane pH-gradient liposomes was previously shown to enhance ammonia removal in cirrhotic rats and holds promise for the treatment of hyperammonemic crises-associated disorders. The main objective of this work was to conduct the preclinical evaluation of LSPD in terms of pharmacokinetics, ammonia uptake, and toxicology to seek regulatory approval for a first-in-human study. The formulation containing citric acid-loaded liposomes was administered intraperitoneally at two different doses once daily for ten days to healthy minipigs. It was also tested in a domestic pig model of hyperammonemia. The pharmacokinetics of citric acid and 1,2-dipalmitoyl-sn-glycero-3-phosphocholine was linear following intraperitoneal administration of medium and high dose. There was no systemic accumulation following daily doses over ten days. The systemic exposure to phospholipids remained low. Furthermore, the liposome-containing peritoneal fluid contained significantly higher ammonia levels than the liposome-free control, demonstrating efficient ammonia sequestration in the peritoneal space. This was indeed confirmed by the ability of LSPD to decrease plasmatic ammonia levels in artificially induced hyperammonemic pigs. LSPD was well tolerated, and no complement activation-related pseudoallergy reactions were observed. The safety profile, the linear pharmacokinetics of citric acid following repeated administrations of LSPD as well as the linear dose-dependent ammonia sequestration in the peritoneal space provide a strong basis for the clinical investigation of LSPD.

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.

Pegylated liposomal doxorubicin-related palmar-plantar erythrodysesthesia: a literature review of pharmaceutical and clinical aspects

OBJECTIVES

The rate of dermal toxicity has been shown to increase in patients receiving pegylated liposomal doxorubicin (PLD), particularly palmar-plantar erythrodysesthesia (PPE). However, it is difficult to diagnose and treat PLD-related PPE due to its delayed dermal performance, unclear pathogenetic mechanism, and the lack of specific preventive measures. The aim of this study was to provide potential management strategies for PPE associated with PLD.

METHODS

The current article reviews the available data regarding the pharmacological and clinical aspects of PLD, including the formulation and pharmacokinetics of PLD, dose and schedule contribution to PPE, concomitant drugs affecting skin toxicity of PLD, the pathogenesis of PPE, and preventive measures and treatment of PLD-related PPE.

RESULTS

The long circulation structure of polyethylene glycol liposomes may be one of the reasons for PPE. PLD has radically different pharmacokinetic characteristics, including prolonged blood circulation time, decreased body distribution volume, and slow clearance. Altering the schedules and doses of PLD or combining it with platinum compounds can optimise clinical efficacy and minimise the occurrence of PPE. Doses of 150-200 mg of pyridoxine daily have been widely used for the prevention and treatment of PPE. Regional cooling and plasma filtration have been used for PPE prophylaxis.

CONCLUSIONS

To date, the mechanism of PPE induced by PLD remains unclear, and no complete preventive medication has been established. Further research and prospective randomised studies are needed to understand the management options in PLD-related PPE.

Anti-PEG antibodies: Properties, formation, testing and role in adverse immune reactions to PEGylated nano-biopharmaceuticals

Conjugation of polyethylene glycols (PEGs) to proteins or drug delivery nanosystems is a widely accepted method to increase the therapeutic index of complex nano-biopharmaceuticals. Nevertheless, these drugs and agents are often immunogenic, triggering the rise of anti-drug antibodies (ADAs). Among these ADAs, anti-PEG IgG and IgM were shown to account for efficacy loss due to accelerated blood clearance of the drug (ABC phenomenon) and hypersensitivity reactions (HSRs) entailing severe allergic symptoms with occasionally fatal anaphylaxis. In addition to recapitulating the basic information on PEG and its applications, this review expands on the physicochemical factors influencing its immunogenicity, the prevalence, features, mechanism of formation and detection of anti-PEG IgG and IgM and the mechanisms by which these antibodies (Abs) induce ABC and HSRs. In particular, we highlight the in vitro, animal and human data attesting to anti-PEG Ab-induced complement (C) activation as common underlying cause of both adverse effects. A main message is that correct measurement of anti-PEG Abs and individual proneness for C activation might predict the rise of adverse immune reactions to PEGylated drugs and thereby increase their efficacy and safety.

Doxebo (doxorubicin-free Doxil-like liposomes) is safe to use as a pre-treatment to prevent infusion reactions to PEGylated nanodrugs

The increasing use in the last decade of PEGylated nanodrugs such as Doxil® has seen a rise in the number of associated occurrences of hypersensitivity reactions (HSRs). These reactions (also called infusion reactions or IR), can range from harmless symptoms to life-threatening reactions. Current means to prevent IR include the prophylactic use of antihistamines and steroids, but they cannot ensure total prevention. We previously showed that an intravenous injection of doxorubicin-free Doxil-like PEGylated nano-liposomes (Doxebo) prior to Doxil treatment suppresses Doxil-induced complement activation-related pseudoallergy (CARPA) in pigs, a model of human hypersensitivity reactions to Doxil. However, in order to use Doxebo to prevent Doxil-induced IR, we have to prove its safety and that it does not affect Doxil's performance. Here we show that Doxebo itself does not have toxic effects on the host or tumor, and it does not interfere with Doxil's antitumor activity in mice. Blood, microscopic and macroscopic organ evaluation of rats after repeated administration confirm the lack of intrinsic adverse effect of Doxebo. Likewise, the repeated injection of Doxebo before Doxil did not impact Doxil's pharmacokinetics in plasma and therefore does not cause accelerated blood clearance (ABC). Taken together with our previous publications, these data suggest that the injection of Doxebo prior to Doxil administration can help protect against Doxil-induced IR without adversely affecting treatment efficacy and safety.

Exploiting Nanomaterial-mediated Autophagy for Cancer Therapy

Autophagy is a conserved process that is critical for sequestering and degrading proteins, damaged or aged organelles, and for maintaining cellular homeostasis under stress conditions. Despite its dichotomous role in health and diseases, autophagy usually promotes growth and progression of advanced cancers. In this context, clinical trials using chloroquine and hydroxychloroquine as autophagy inhibitors have suggested that autophagy inhibition is a promising approach for treating advanced malignancies and/or overcoming drug resistance of small molecule therapeutics (i.e., chemotherapy and molecularly targeted therapy). Efficient delivery of autophagy inhibitors may further enhance the therapeutic effect, reduce systemic toxicity, and prevent drug resistance. As such, nanocarriers-based drug delivery systems have several distinct advantages over free autophagy inhibitors that include increased circulation of the drugs, reduced off-target systemic toxicity, increased drug delivery efficiency, and increased solubility and stability of the encapsulated drugs. With their versatile drug encapsulation and surface-functionalization capabilities, nanocarriers can be engineered to deliver autophagy inhibitors to tumor sites in a context-specific and/or tissue-specific manner. This review focuses on the role of nanomaterials utilizing autophagy inhibitors for cancer therapy, with a focus on their applications in different cancer types.

Induction of Cytochrome P450 Involved in the Accelerated Blood Clearance Phenomenon Induced by PEGylated Liposomes In Vivo

Polyethylene glycol (PEG) is recognized as an attractive excipient to modify liposomes due to its extended-circulation properties. Nevertheless, intravenous injection of polyethylene glycol-coated liposomes (PEG-L) usually triggers a rapid systemic clearance of the subsequent dose from blood circulation, which is referred to as an accelerated blood clearance (ABC) phenomenon. Therefore, since the induction of cytochrome P450 (P450) activity may lead to enhanced drug clearance, it motivated us to investigate the possibility of P450 involvement in the ABC phenomenon. In this study, polyethylene glycol-coated liposomal docetaxel was prepared and used to evaluate the magnitude of the ABC phenomenon in rats induced by repeated injection of PEG-modified liposomes. Notably, the ABC phenomenon was observed when the time interval between two doses was from 1 to 7 days, and its magnitude reached the maximum level at 3 days before gradually decreasing the time. Meanwhile, increased activity of CYP3A1, CYP2C6, and CYP1A2 was detected when PEG-L was repeatedly injected in male rats at a 3-day interval. Consistently, the expression levels of hepatic CYP3A1, CYP2C6, and CYP1A2 were also significantly increased in the repeated injection groups and their levels were highest in the 3-day interval group. P450 selective inhibitors confirmed the inhibition of hepatic CYP3A1 was accompanied by an attenuated magnitude of the ABC phenomenon, which strongly suggests that P450s may be induced by repeated injection of PEG-L, thus favoring metabolic clearance of the second dose. Collectively, herein, for the first time we demonstrate that the contribution of P450s should not be ignored in the ABC phenomenon.

PEGylated liposomes: immunological responses

A commonly held view is that nanocarriers conjugated to polyethylene glycol (PEG) are non-immunogenic. However, many studies have reported that unexpected immune responses have occurred against PEG-conjugated nanocarriers. One unanticipated response is the rapid clearance of PEGylated nanocarriers upon repeat administration, called the accelerated blood clearance (ABC) phenomenon. ABC involves the production of antibodies toward nanocarrier components, including PEG, which reduces the safety and effectiveness of encapsulated therapeutic agents. Another immune response is the hypersensitivity or infusion reaction referred to as complement (C) activation-related pseudoallergy (CARPA). Such immunogenicity and adverse reactivities of PEGylated nanocarriers may be of potential concern for the clinical use of PEGylated therapeutics. Accordingly, screening of the immunogenicity and CARPA reactogenicity of nanocarrier-based therapeutics should be a prerequisite before they can proceed into clinical studies. This review presents PEGylated liposomes, immunogenicity of PEG, the ABC phenomenon, C activation and lipid-induced CARPA from a toxicological point of view, and also addresses the factors that influence these adverse interactions with the immune system.

Theranostic Imaging May Vaccinate against the Therapeutic Benefit of Long Circulating PEGylated Liposomes and Change Cargo Pharmacokinetics

The enhanced permeability and retention (EPR) effect increases tumor accumulation of liposomal chemotherapy and should, in theory, increase anticancer effects and lower toxicity. Unfortunately, liposomal chemotherapy has generally not met the expected potential, perhaps because the EPR effect is not ubiquitous. PET imaging using radiolabeled liposomes can identify cancers positive for the EPR effect. In the current study, we show in clinical canine cancer patients that repeated imaging with radiolabeled liposomes (⁶⁴Cu-liposome) induces the accelerated blood clearance (ABC) phenomenon. This was observed even with very long intervals between PEGylated liposome injections, which contradict previous reporting in experimental animal models. The induction of ABC may be devastating for the theranostic use of liposomal imaging, as this could vaccinate patients against therapeutic efficacy. To investigate and solve this important problem, an additional study part was designed in which rats were subjected to repeated liposomal administrations, including stealth ⁶⁴Cu-liposome PET imaging and Caelyx chemotherapy. Most importantly, it was found that, by increasing the lipid dose at the first injection or by supplying a small predose before the second ⁶⁴Cu-liposome injection, ABC could be prevented. Importantly, signs of liposome tracer breakdown with subsequent renal excretion were observed. These findings highlight the importance of the ABC phenomenon for liposomal predictive imaging in a clinically relevant setting and show that carefully planned application is central to avoid potential detrimental effects on patient benefit.

Improved Macaca fascicularis gene annotation reveals evolution of gene expression profiles in multiple tissues

Backgrounds

Macaca fascicularis (M. fascicularis) is a primate model organism that played important role in studying human health. It is vital to better understand the similarity and differences of gene regulation between M. fascicularis and human. Current comparative study of gene regulation between the two species are limited by low quality of gene annotation and lack of regulatory element data on M. fascicularis genome.

Results

In this study, we improved the M. fascicularis gene annotation with 57 gene expression data from multiple tissues and, more importantly, a manual curation procedure. The new annotation enabled us to map gene expression and identify gene location more accurately.

Conclusions

Comparing with human gene expression data from the same cell types, we characterized the evolution of expression patterns of homologous genes.

Electronic supplementary material

The online version of this article (10.1186/s12864-018-5183-y) contains supplementary material, which is available to authorized users.

Time Interval of Two Injections and First-Dose Dependent of Accelerated Blood Clearance Phenomenon Induced by PEGylated Liposomal Gambogenic Acid: The Contribution of PEG-Specific IgM

Repeated injection of PEGylated liposomes can cause the disappearance of long circulating property because of the induction of anti-PEG IgM antibody referred to as "accelerated blood clearance (ABC) phenomenon." Although ABC phenomenon typically occurs when entrapped drugs are chemotherapeutic agent with low cytotoxic, there is little evidence of accelerated blood clearance of PEGylated herbal-derived compound on repeated injection. Herein, we investigated the blood concentration of PEGylated liposomal gambogenic acid (PEG-GEA-L), a model PEGylated liposomal herbal extract, on its repeated injection to rats. We found time interval between injections had considerable impact on the magnitude of ABC phenomenon induced by PEG-GEA-L. When time interval was prolonged from 3 days to 7 days, ABC phenomenon could be attenuated. Furthermore, its magnitude was enhanced accompanied by a marked rise in the accumulation of PEG-GEA-L in the liver and spleen in a first-dose-dependent manner. Consistently, the level of anti-PEG IgM significantly increased with the first dose of PEG-GEA-L and decreased with the extended time interval between injections, which implies anti-PEG IgM is a major contributor to the ABC phenomenon. Notably, the increased expression of liver anti-PEG IgM was accompanied by an increased expression of efflux transporters in the induction process of the ABC phenomenon.

Block Copolymer Micelles in Nanomedicine Applications

Polymeric micelles are demonstrating high potential as nanomedicines capable of controlling the distribution and function of loaded bioactive agents in the body, effectively overcoming biological barriers, and various formulations are engaged in intensive preclinical and clinical testing. This Review focuses on polymeric micelles assembled through multimolecular interactions between block copolymers and the loaded drugs, proteins, or nucleic acids as translationable nanomedicines. The aspects involved in the design of successful micellar carriers are described in detail on the basis of the type of polymer/payload interaction, as well as the interplay of micelles with the biological interface, emphasizing on the chemistry and engineering of the block copolymers. By shaping these features, polymeric micelles have been propitious for delivering a wide range of therapeutics through effective sensing of targets in the body and adjustment of their properties in response to particular stimuli, modulating the activity of the loaded drugs at the targeted sites, even at the subcellular level. Finally, the future perspectives and imminent challenges for polymeric micelles as nanomedicines are discussed, anticipating to spur further innovations.

Towards clinical translation of ligand-functionalized liposomes in targeted cancer therapy: Challenges and opportunities

The development of therapeutic resistance to targeted anticancer therapies remains a significant clinical problem, with intratumoral heterogeneity playing a key role. In this context, improving the therapeutic outcome through simultaneous targeting of multiple tumor cell subtypes within a heterogeneous tumor is a promising approach. Liposomes have emerged as useful drug carriers that can reduce systemic toxicity and increase drug delivery to the tumor site. While clinically used liposomal drug formulations show marked therapeutic advantages over free drug formulations, ligand-functionalized liposomes that can target multiple tumor cell subtypes may further improve the therapeutic efficacy by facilitating drug delivery to a broader population of tumor cells making up the heterogeneous tumor tissue. Ligand-directed liposomes enable the so-called active targeting of cell receptors via surface-attached ligands that direct drug uptake into tumor cells or tumor-associated stromal cells, and so can increase the selectivity of drug delivery. Despite promising preclinical results demonstrating improved targeting and anti-tumor effects of ligand-directed liposomes, there has been limited translation of this approach to the clinic. Key challenges for translation include the lack of established methods to scale up production and comprehensively characterize ligand-functionalized liposome formulations, as well as the inadequate recapitulation of in vivo tumors in the preclinical models currently used to evaluate their performance. Herein, we discuss the utility of recent ligand-directed liposome approaches, with a focus on dual-ligand liposomes, for the treatment of solid tumors and examine the drawbacks limiting their progression to clinical adoption.

Polymeric Micelle of A₃B-Type Lactosome as a Vehicle for Targeting Meningeal Dissemination

Polymeric micelle of the A₃B-type lactosome comprising (poly(sarcosine))₃-b-poly(l-lactic acid) was labeled with ¹¹¹In. The ¹¹¹In-labeled A₃B-type lactosome was administered to the model mice bearing meningeal dissemination and bone metastasis at mandible. With single-photon emission computed tomography (SPECT) imaging, the meningeal dissemination was identified successfully by ¹¹¹In-labeled A₃B-type lactosome, which was superior to ²⁰¹TlCl in regard of the imaging contrast. The ¹¹¹In-labeled A₃B-type lactosome was also potential in imaging selectively of bone metastasis at mandible, whilst a nonspecific imaging of the whole bone was obtained by the SPECT imaging using ^99mTc-HMDP. The polymeric micelle of the A₃B-type lactosome was therefore found to be effective as a vehicle of ¹¹¹In to be targeted to meningeal dissemination and bone metastasis.

Metronomic chemotherapy and nanocarrier platforms

The therapeutic concept of administering chemotherapeutic agents continuously at lower doses, relative to the maximum tolerated dose (MTD) without drug-free breaks over extended periods -known as "metronomic chemotherapy"- is a promising approach for anti-angiogenic cancer therapy. In comparison with MTD chemotherapy regimens, metronomic chemotherapy has demonstrated reduced toxicity. However, as a monotherapy, metronomic chemotherapy has failed to provide convincing results in clinical trials. Therapeutic approaches including combining the anti-angiogenic "metronomic" therapy with conventional radio-/chemo-therapy and/or targeted delivery of chemotherapeutic agents to tumor tissues via their encapsulation with nanocarrier-based platforms have proven to potentiate the overall therapeutic outcomes. In this review, therefore, we focused on the mutual contribution made by nanoscale drug delivery platforms to the therapeutic efficacy of metronomic-based chemotherapy. In addition, the influence that the dosing schedule has on the overall therapeutic efficacy of metronomic chemotherapy is discussed.

Anti-PEG antibodies alter the mobility and biodistribution of densely PEGylated nanoparticles in mucus

Antibodies that specifically bind polyethylene glycol (PEG) can lead to rapid elimination of PEGylated therapeutics from the systemic circulation. We have recently shown that virus-binding IgG can immobilize viruses in mucus via multiple low-affinity crosslinks between IgG and mucins. However, it remains unclear whether anti-PEG antibodies in mucus may also alter the penetration and consequently biodistribution of PEGylated nanoparticles delivered to mucosal surfaces. We found that both anti-PEG IgG and IgM can readily bind nanoparticles that were densely coated with PEG polymer to minimize adhesive interactions with mucus constituents. Addition of anti-PEG IgG and IgM into mouse cervicovaginal mucus resulted in extensive trapping of mucus-penetrating PEGylated nanoparticles, with the fraction of mobile particles reduced from over 95% to only 34% and 7% with anti-PEG IgG and IgM, respectively. Surprisingly, we did not observe significant agglutination induced by either antibody, suggesting that particle immobilization is caused by adhesive crosslinks between mucin fibers and IgG or IgM bound to individual nanoparticles. Importantly, addition of corresponding control antibodies did not slow the PEGylated nanoparticles, confirming anti-PEG antibodies specifically bound to and trapped the PEGylated nanoparticles. Finally, we showed that trapped PEGylated nanoparticles remained largely in the luminal mucus layer of the mouse vagina even when delivered in hypotonic formulations that caused untrapped particles to be drawn by the flow of water (advection) through mucus all the way to the epithelial surface. These results underscore the potential importance of elucidating mucosal anti-PEG immune responses for PEGylated therapeutics and biomaterials applied to mucosal surfaces.

STATEMENT OF SIGNIFICANCE

PEG, generally considered a 'stealth' polymer, is broadly used to improve the circulation times and therapeutic efficacy of nanomedicines. Nevertheless, there is increasing scientific evidence that demonstrates both animals and humans can generate PEG-specific antibodies. Here, we show that anti-PEG IgG and IgM can specifically immobilize otherwise freely diffusing PEG-coated nanoparticles in fresh vaginal mucus gel ex vivo by crosslinking nanoparticles to the mucin mesh, and consequently prevent PEG-coated nanoparticles from accessing the vaginal epithelium in vivo. Given the increasing use of PEG coatings to enhance nanoparticle penetration of mucosal barriers, our findings demonstrate that anti-PEG immunity may be a potential concern not only for systemic drug delivery but also for mucosal drug delivery.

Multiple Administrations of Viral Nanoparticles Alter in Vivo Behavior-Insights from Intravital Microscopy

Multiple administrations of nanoparticle-based formulations are often a clinical requirement for drug delivery and diagnostic imaging applications. Steady pharmacokinetics of nanoparticles is desirable to achieve efficient therapeutic or diagnostic outcomes over such repeat administrations. While clearance through mononuclear phagocytic system is a key determinant of nanoparticle persistence in vivo, multiple administrations could potentially result in altered pharmacokinetics by evoking innate or adaptive immune responses. Plant viral nanoparticles (VNPs) represent an emerging class of programmable nanoparticle platform technologies that offer a highly organized proteinaceous architecture and multivalency for delivery of large payloads of drugs and molecular contrast agents. These very structural features also render them susceptible to immune recognition and subsequent accelerated systemic clearance that could potentially affect overall efficiency. While the biodistribution and pharmacokinetics of VNPs have been reported, the biological response following repeat administrations remains an understudied area of investigation. Here, we demonstrate that weekly administration of filamentous plant viruses results in the generation of increasing levels of circulating, carrier-specific IgM and IgG antibodies. Furthermore, PVX specific immunoglobulins from the serum of immunized animals quickly form aggregates when incubated with PVX in vitro. Such aggregates of VNP-immune complexes are also observed in the mouse vasculature in vivo following repeat injections when imaged in real time using intravital two-photon laser scanning microscopy (2P-LSM). The size of aggregates diminishes at later time points, coinciding with antibody class switching from IgM to IgG. Together, our results highlight the need for careful in vivo assessment of (viral) nanoparticle-based platform technologies, especially in studying their performance after repeat administration. We also demonstrate the utility of intravital microscopy to aid in this evaluation.

Design attributes of long-circulating polymeric drug delivery vehicles

Following systemic administration polymeric drug delivery vehicles allow for a controlled and targeted release of the encapsulated medication at the desired site of action. For an elevated and organ specific accumulation of their cargo, nanocarriers need to avoid opsonization, activation of the complement system and uptake by macrophages of the mononuclear phagocyte system. In this respect, camouflaged vehicles revealed a delayed elimination from systemic circulation and an improved target organ deposition. For instance, a steric shielding of the carrier surface by poly(ethylene glycol) substantially decreased interactions with the biological environment. However, recent studies disclosed possible deficits of this approach, where most notably, poly(ethylene glycol)-modified drug delivery vehicles caused significant immune responses. At present, identification of novel potential carrier coating strategies facilitating negligible immune reactions is an emerging field of interest in drug delivery research. Moreover, physical carrier properties including geometry and elasticity seem to be very promising design attributes to surpass numerous biological barriers, in order to improve the efficacy of the delivered medication.

Effect of Repeated Injections of Adenosine Diphosphate-Encapsulated Liposomes Coated with a Fibrinogen γ-Chain Dodecapeptide Developed as a Synthetic Platelet Substitute on Accelerated Blood Clearance in a Healthy and an Anticancer Drug-Induced Thrombocytopenia Rat Model

Adenosine diphosphate (ADP)-encapsulated liposomes coated with a fibrinogen γ-chain dodecapeptide [H12 (dodecapeptide ((400) HHLGGAKQAGDV(411) ))-(ADP)-liposome] is a synthetic platelet substitute, in which the surface is covered with polyethylene glycol (PEG). It has been reported that repeated injections of PEGylated liposomes induce an accelerated blood clearance (ABC) phenomenon, which involves a loss in the long-circulation half-life of the material when administered repeatedly to the same animals. The objective of this study was to determine whether the ABC phenomenon was induced by repeated injections of H12-(ADP)-liposome in healthy and anticancer drug-induced thrombocytopenia model rats. The findings show that the ABC phenomenon was induced by healthy rats that were repeatedly injected with H12-(ADP)-liposomes at the interval of 5 days at a dose of 10 mg lipids/kg. The ABC phenomenon involves the production of anti-H12-(ADP)-liposome immunoglobulin M (IgM) and complement activation. On the other hand, when thrombocytopenia model rats were repeatedly injected with H12-(ADP)-liposomes under the same conditions, no ABC phenomenon, nor was any suppression of anti-H12-(ADP)-liposome IgM-mediated complement activation observed. We thus conclude that the repeated injection of H12-(ADP)-liposome treatment in rat model with anticancer drug-induced thrombocytopenia did not induce the ABC phenomenon.