News & Views
Research Highlights Highlights from the last year in nanomedicine
Ins and outs of lipid nanoparticle-mediated siRNA delivery Evaluation of: Sahay G, Querbes W, Alabi C et al. Efficiency of siRNA delivery by lipid nanoparticles is limited by endocytic recycling. Nat. Biotechnol. 31(7), 653–658 (2013).
To prevent translation of disease-causing proteins, specific siRNAs have to be delivered into the cytosol of target cells. In a recent study, Sahay et al. evaluated the delivery of siRNA using lipid nano particles (LNPs) formed by complexation of siRNA with the cationic lipid C12–200 [1]. Using automated high-throughput confocal microscopy to screen a library of small-molecule inhibitors, the authors were able to identify Cdc42-dependent macropinocytosis as the main internalization pathway for LNPs. Sahay et al. further employed fluorescence resonance energy transfer to quantify the kinetics of LNP disassembly and recycling, and found that LNPs disassembled rapidly within the first hour of entry into cells, followed by degradation or recycling of siRNA within 24 h. Most siRNAs remained trapped inside endosomes after the disassembly of LNPs. Notably, a significant fraction (~70%) of the internalized siRNAs underwent exocytosis from cells through egress of LNPs from late endosomes/lysosomes. This previously unrecognized mechanism suggests that approaches for retaining siRNAs inside cells are needed. In addition, studies are warranted to determine whether any bystander effects are elicited by the unscheduled extracellular release of siRNA. The subcellular trafficking of lipids, such as cholesterol from late endosomes and lysosomes to the extracellular milieu, depends on NPC1. To 10.2217/NNM.13.188 © 2014 Future Medicine Ltd
further investigate the recycling pathways of LNP-delivered siRNA, Sahay et al. compared the retention of LNPs in mouse embryonic fibroblasts devoid of NPC1 with their wild-type counterparts. Enhanced cellular retention was noted in cells deficient of NPC1 and this translated into improved gene silencing. In a related study, Gilleron et al. showed that LNPs enter cells through both macropinoc ytosis and clathrin-mediated endoc ytosis [2]. By directly detecting colloidal gold particles conjugated to siRNAs, the authors could show that escape of siRNAs from endosomes into the cytosol occurred at a low efficiency (1–2%) and only when the LNPs resided in a specific compartment with characteristics of both early and late endosomes. It is noted that the cationic lipids used to formulate the LNPs differed between the two studies while the same cancer cell model (HeLa) was employed [1,2]. In conclusion, Sahay et al. have provided new insights into the fate of LNP-delivered siRNAs and their study offers a potential screening strategy for the optimization of siRNA delivery using lipid carriers; understanding biology is the key to harnessing the emerging nanotechnologies for clinical benefit.
Táňa Brzicová1, Neus Feliu1 & Bengt Fadeel*1 Division of Molecular Toxicology, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden *Author for correspondence: [email protected] 1
Financial & competing interests disclosure The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties. No writing assistance was utilized in the production of this manuscript.
References 1
2
Sahay G, Querbes W, Alabi C et al. Efficiency of siRNA delivery by lipid nanoparticles is limited by endocytic recycling. Nat. Biotechnol. 31(7), 653–658 (2013). Gilleron J, Querbes W, Zeigerer A et al. Image-based analysis of lipid nanoparticle-mediated siRNA delivery, intracellular trafficking and endosomal escape. Nat. Biotechnol. 31(7), 638–646 (2013). Nanomedicine (2014) 9(1), 17–20
part of
ISSN 1743-5889
17
Research Highlights News & Views – News
Of mice and men: global immune status determines nanoparticle clearance Evaluation of: Jones SW, Roberts RA, Robbins GR et al. Nanoparticle clearance is governed by Th1/Th2 immunity and strain background. J. Clin. Invest. 123(7), 3061–3073 (2013).
Nanoparticles that are administered intravenously are rapidly cleared by cells of the reticuloendothelial system in the blood, liver and spleen. In a recent publication, Jones et al. showed that the rate of nanoparticle clearance depends on the global status of the immune system [1]. Using Th1- (C57BL/6) and Th2-biased (BALB/c) mouse strains, the authors found that mice that are prone to Th1type immune responses clear nano particles at a slower rate than Th2-prone mice. The particle replication in nonwetting templates (PRINT) technique was used to generate 300-nm cylindrical PEG hydrogel nanoparticles containing far-red
fluorescent dyes for in vivo imaging in live animals. Evidence of particle clearance in peripheral vasculature, as well as in the spleen, was provided. Notably, there were no differences in macrophage uptake in the spleen between the different mouse strains; instead, uptake of nanoparticles by granulocytes was significantly lower in both the blood and spleen in C57BL/6 mice. The study points to a poorly recognized role of granulocytes (mainly neutrophils) for nanoparticle clearance and suggests that these cells need to be considered when designing nanomedicines that are in circulation for extended periods of time. The differences in clearance could also be due, in part, to differences in the repertoire of receptors expressed on phagocytic cells in Th1- versus Th2-prone mice. The authors noted that microparticles (6-µm disks made of the same PEG hydrogel material as the 300-nm cylindrical PRINT hydrogels) were cleared at a similar rate in BALB/c and C57BL/6
mice. However, differences in shape may also impact particle clearance, as shown in a recent in vitro study in which spherical, rod- and disk-shaped polystyrene nanoand micro-particles were evaluated for uptake in human cancer cell lines [2]. The study by Jones et al. serves to highlight the importance of choosing appropriate in vivo models for preclinical evaluation of nanomedicines. The implications for patients are yet to be understood, but it can be speculated that pre-existing conditions such as infections or allergies could impact on the rate of nanoparticle clearance in humans [1].
References 1
2
Jones SW, Roberts RA, Robbins GR et al. Nanoparticle clearance is governed by Th1/Th2 immunity and strain background. J. Clin. Invest. 123(7), 3061–3073 (2013). Barua S, Yoo JW, Kolhar P et al. Particle shape enhances specificity of antibody-displaying nanoparticles. Proc. Natl Acad. Sci. USA 110(9), 3270–3275 (2013).
Flying under the radar: functionalization of nanoparticles with ‘marker of self’ peptides Evaluation of: Rodriguez PL, Harada T, Christian DA et al. Minimal ‘self’ peptides that inhibit phagocytic clearance and enhance delivery of nanoparticles. Science 339(6122), 971–975 (2013).
Macrophages and other phagocytes engulf micro-organisms and they also participate in the clearance of dying cells. These clearance mechanisms may hamper delivery of therapeutic and imaging agents, and considerable efforts have been devoted to extending the residence time of nano particles in the blood stream through surface modification of the nanoparticles. In an elegant proof-of-principle study, 18
Rodriguez et al. demonstrated that polystyrene nanoparticles (160 nm) coated with a ‘marker-of-self ’ peptide derived from the human CD47 protein displayed delayed macrophage-mediated clearance and enhanced drug delivery to tumors in mice. CD47 is a protein that is expressed on all cell membranes in mice and humans and its interaction with the receptor CD172a (also known as SIRPa) on phagocytes actively inhibits phagocytic uptake of viable cells. In other words, CD47 acts as a ‘don’t-eat-me-signal’ for macrophages. Using the NOD/SCID-IL2Rgnull mouse strain, a severely immunodeficient mouse strain whose macrophages express a SIRPa receptor compatible with human CD47, the authors could show that the attachment Nanomedicine (2014) 9(1)
of a 21-amino acid peptide derived from CD47 to polystyrene particles allowed for a prolonged circulation time. Preinjection of a SIRPa-specific antibody, which blocks CD47 binding, eliminated the enhanced circulation of CD47 peptide-functionalized nanoparticles, thus confirming interaction specificity in the in vivo setting. Using NOD/SCID-IL2Rgnull mice with flank tumors of human A549-derived lung adenocarcinoma cells, Rodriguez et al. demonstrated greater tumor accumulation of nanoparticles functionalized with CD47 peptides than the control nanoparticles. In addition, experiments performed in tumor-bearing mice showed that paclitaxel-loaded nanoparticles that displayed the CD47 peptide plus PEG future science group
Research Highlights News – and a CD47-targeting antibody (to target the tumor cells) shrank tumors more efficiently than nanoparticles lacking the CD47-derived peptide. However, whether or not a targeting antibody is required for accumulation of the nanoparticles and their cargo in the tumor warrants further
News & Views
study. In conclusion, the use of self-derived peptides alone or in combination with a targeting ligand provides inspiration for the further development of nanomedicines that are able to avoid immune clearance, yet at the same time can deliver therapeutic or imaging agents to tissues of interest.
Now you see it, now you don’t: serum proteins prevent specific targeting of nanoparticles Evaluation of: Salvati A, Pitek AS, Monopoli MP et al. Transferrinfunctionalized nanoparticles lose their targeting capabilities when a biomolecule corona adsorbs on the surface. Nat. Nanotechnol. 8(2), 137–143 (2013).
Nanoparticle-based delivery systems are being developed to improve the efficacy and reduce the systemic toxicity of a wide range of drugs. However, while the potential of targeted nanomedicines has already been demonstrated [1], it remains to be fully understood which parameters dictate the successful targeting of nanomedicines under realistic in vivo conditions. Notably, when nanoparticles are introduced into a biological system the surface is coated with proteins and other biomolecules to form a so-called ‘biocorona’, the identity of which depends on the specific bio logical milieu. In a key paper published last year, Salvati et al. studied the impact of the biocorona, which is formed in fetal
bovine or human serum, on the targeting ability of nanoparticles [2]. To this end, the authors used fluorescent silica nano particles (50 nm) coated with PEG and functionalized with human transferrin modified with a thiol–PEG linker through conjugation to the PEGylated particle. The human lung adenocarcinoma cell line A549, with or without silencing of the gene encoding the transferrin receptor, was used in order to assess specific uptake of nanoparticles. Salvati et al. found that transferrin receptor-dependent uptake occurred under serum-free conditions. Surprisingly, uptake of the PEGylated particles without functionalization was higher than that of the transferrin-coated particles, but occurred independently of the expression of the receptor. In the presence of serum, however, the overall uptake decreased, as well as the fraction of uptake that depended on the transferrin receptor, thus demonstrating that the specific targeting ability was lost. Using established protocols, the authors also confirmed that a corona of proteins was indeed formed
on the transferrin-functionalized nano particles, although much less than for non-PEGylated particles. While the study focused on a single model nanoparticle, and a single ligand–receptor interaction, and was based on experiments conducted in a single human cancer cell line, the work by Salvati et al. is of considerable relevance for nanomedicine as it highlights the importance of testing targeted nanoparticles in the biological fluid(s) in which the nanoparticles will be applied, and also as it offers an approach for the screening of nanoparticles in vitro prior to embarking on animal studies [2].
References 1
2
Davis ME, Zuckerman JE, Choi CH et al. Evidence of RNAi in humans from systemically administered siRNA via targeted nanoparticles. Nature 464(7291), 1067–1070 (2010). Salvati A, Pitek AS, Monopoli MP et al. Transferrin-functionalized nanoparticles lose their targeting capabilities when a biomolecule corona adsorbs on the surface. Nat. Nanotechnol. 8(2), 137–143 (2013).
Biomimetic camouflage: nanoporous particles cloaked in cellular membranes Evaluation of: Parodi A, Quattrocchi N, van de Ven AL et al. Synthetic nanoparticles functionalized with biomimetic leukocyte membranes possess cell-like functions. Nat. Nanotechnol. 8(1), 61–68 (2013).
future science group
Biomimetic approaches are aimed at imitating natural structures and processes at the cellular or subcellular level. In particular, strategies whereby opsonization and nonspecific clearance by phagocytic cells of the immune system are avoided are attracting considerable interest. In a study published last year, Parodi et al. www.futuremedicine.com
coated nanoporous silicon particles (NSPs; 3.2 µm) with cellular membranes to confer cellular functions, including ‘stealth’ [1]. The cellular membranes were derived from murine and human leukemia or lymphoma cell lines (J774, Jurkat and THP-1). The membrane coating was found to reduce in vitro opsonization by 19
Research Highlights News & Views – News
using albumin and IgG, two highly abundant serum proteins, and the membrane coating of NSPs significantly decreased particle uptake in vitro, particularly when the donor membrane matched that of the host phagocytic cell. Furthermore, Parodi et al. demonstrated that the membranecoated NSPs could interact with and pass through an endothelial cell barrier under inflamed conditions, and that they were able to deliver the anticancer drug doxorubicin through an endothelial layer and release it to kill human breast cancer cells while maintaining the viability of the endothelial layer (comprised of human umbilical vein endothelial cells).
20
In addition, using intravital microscopy the authors found that the membranedisguised NSPs showed delayed accumulation in the liver, and that the accumulation of the particles in murine B16 melanoma tumors in mice was enhanced compared with that of ‘naked’ NSPs. In a related study, Hu et al. employed erythroc yte (red blood cell) membranes from mice to camouflage polymeric nano particles (70 nm) [2]. However, as pointed out by the latter authors, to optimize such entities for use in the clinical setting, the particles would first need to be crossmatched to the patient’s own blood or, alternatively, the erythrocyte membranes would need to be selectively depleted from immunogenic proteins before fusing them with nanoparticles. The work by Parodi et al. suggests that biomimetic ‘camouflage’ can be achieved using cellular membranes and that this may allow synthetic
Nanomedicine (2014) 9(1)
particles to successfully negotiate vascular barriers. It would be of interest to learn whether membranes derived from normal white blood cells (leukocytes) also confer such properties, and to determine which protein and/or lipid signal(s) in these membranes are responsible for the observed biological effects. Further research on natural–synthetic hybrid structures may yield novel drug delivery and imaging platforms in nanomedicine.
References 1
2
Parodi A, Quattrocchi N, van de Ven AL et al. Synthetic nanoparticles functionalized with biomimetic leukocyte membranes possess cell-like functions. Nat. Nanotechnol. 8(1), 61–68 (2013). Hu CM, Zhang L, Aryal S et al. Erythrocyte membrane-camouflaged polymeric nanoparticles as a biomimetic delivery platform. Proc. Natl Acad. Sci. USA 108(27), 10980–10985 (2011).
future science group
Research Highlights Highlights from the last year in nanomedicine
Ins and outs of lipid nanoparticle-mediated siRNA delivery Evaluation of: Sahay G, Querbes W, Alabi C et al. Efficiency of siRNA delivery by lipid nanoparticles is limited by endocytic recycling. Nat. Biotechnol. 31(7), 653–658 (2013).
To prevent translation of disease-causing proteins, specific siRNAs have to be delivered into the cytosol of target cells. In a recent study, Sahay et al. evaluated the delivery of siRNA using lipid nano particles (LNPs) formed by complexation of siRNA with the cationic lipid C12–200 [1]. Using automated high-throughput confocal microscopy to screen a library of small-molecule inhibitors, the authors were able to identify Cdc42-dependent macropinocytosis as the main internalization pathway for LNPs. Sahay et al. further employed fluorescence resonance energy transfer to quantify the kinetics of LNP disassembly and recycling, and found that LNPs disassembled rapidly within the first hour of entry into cells, followed by degradation or recycling of siRNA within 24 h. Most siRNAs remained trapped inside endosomes after the disassembly of LNPs. Notably, a significant fraction (~70%) of the internalized siRNAs underwent exocytosis from cells through egress of LNPs from late endosomes/lysosomes. This previously unrecognized mechanism suggests that approaches for retaining siRNAs inside cells are needed. In addition, studies are warranted to determine whether any bystander effects are elicited by the unscheduled extracellular release of siRNA. The subcellular trafficking of lipids, such as cholesterol from late endosomes and lysosomes to the extracellular milieu, depends on NPC1. To 10.2217/NNM.13.188 © 2014 Future Medicine Ltd
further investigate the recycling pathways of LNP-delivered siRNA, Sahay et al. compared the retention of LNPs in mouse embryonic fibroblasts devoid of NPC1 with their wild-type counterparts. Enhanced cellular retention was noted in cells deficient of NPC1 and this translated into improved gene silencing. In a related study, Gilleron et al. showed that LNPs enter cells through both macropinoc ytosis and clathrin-mediated endoc ytosis [2]. By directly detecting colloidal gold particles conjugated to siRNAs, the authors could show that escape of siRNAs from endosomes into the cytosol occurred at a low efficiency (1–2%) and only when the LNPs resided in a specific compartment with characteristics of both early and late endosomes. It is noted that the cationic lipids used to formulate the LNPs differed between the two studies while the same cancer cell model (HeLa) was employed [1,2]. In conclusion, Sahay et al. have provided new insights into the fate of LNP-delivered siRNAs and their study offers a potential screening strategy for the optimization of siRNA delivery using lipid carriers; understanding biology is the key to harnessing the emerging nanotechnologies for clinical benefit.
Táňa Brzicová1, Neus Feliu1 & Bengt Fadeel*1 Division of Molecular Toxicology, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden *Author for correspondence: [email protected] 1
Financial & competing interests disclosure The authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties. No writing assistance was utilized in the production of this manuscript.
References 1
2
Sahay G, Querbes W, Alabi C et al. Efficiency of siRNA delivery by lipid nanoparticles is limited by endocytic recycling. Nat. Biotechnol. 31(7), 653–658 (2013). Gilleron J, Querbes W, Zeigerer A et al. Image-based analysis of lipid nanoparticle-mediated siRNA delivery, intracellular trafficking and endosomal escape. Nat. Biotechnol. 31(7), 638–646 (2013). Nanomedicine (2014) 9(1), 17–20
part of
ISSN 1743-5889
17
Research Highlights News & Views – News
Of mice and men: global immune status determines nanoparticle clearance Evaluation of: Jones SW, Roberts RA, Robbins GR et al. Nanoparticle clearance is governed by Th1/Th2 immunity and strain background. J. Clin. Invest. 123(7), 3061–3073 (2013).
Nanoparticles that are administered intravenously are rapidly cleared by cells of the reticuloendothelial system in the blood, liver and spleen. In a recent publication, Jones et al. showed that the rate of nanoparticle clearance depends on the global status of the immune system [1]. Using Th1- (C57BL/6) and Th2-biased (BALB/c) mouse strains, the authors found that mice that are prone to Th1type immune responses clear nano particles at a slower rate than Th2-prone mice. The particle replication in nonwetting templates (PRINT) technique was used to generate 300-nm cylindrical PEG hydrogel nanoparticles containing far-red
fluorescent dyes for in vivo imaging in live animals. Evidence of particle clearance in peripheral vasculature, as well as in the spleen, was provided. Notably, there were no differences in macrophage uptake in the spleen between the different mouse strains; instead, uptake of nanoparticles by granulocytes was significantly lower in both the blood and spleen in C57BL/6 mice. The study points to a poorly recognized role of granulocytes (mainly neutrophils) for nanoparticle clearance and suggests that these cells need to be considered when designing nanomedicines that are in circulation for extended periods of time. The differences in clearance could also be due, in part, to differences in the repertoire of receptors expressed on phagocytic cells in Th1- versus Th2-prone mice. The authors noted that microparticles (6-µm disks made of the same PEG hydrogel material as the 300-nm cylindrical PRINT hydrogels) were cleared at a similar rate in BALB/c and C57BL/6
mice. However, differences in shape may also impact particle clearance, as shown in a recent in vitro study in which spherical, rod- and disk-shaped polystyrene nanoand micro-particles were evaluated for uptake in human cancer cell lines [2]. The study by Jones et al. serves to highlight the importance of choosing appropriate in vivo models for preclinical evaluation of nanomedicines. The implications for patients are yet to be understood, but it can be speculated that pre-existing conditions such as infections or allergies could impact on the rate of nanoparticle clearance in humans [1].
References 1
2
Jones SW, Roberts RA, Robbins GR et al. Nanoparticle clearance is governed by Th1/Th2 immunity and strain background. J. Clin. Invest. 123(7), 3061–3073 (2013). Barua S, Yoo JW, Kolhar P et al. Particle shape enhances specificity of antibody-displaying nanoparticles. Proc. Natl Acad. Sci. USA 110(9), 3270–3275 (2013).
Flying under the radar: functionalization of nanoparticles with ‘marker of self’ peptides Evaluation of: Rodriguez PL, Harada T, Christian DA et al. Minimal ‘self’ peptides that inhibit phagocytic clearance and enhance delivery of nanoparticles. Science 339(6122), 971–975 (2013).
Macrophages and other phagocytes engulf micro-organisms and they also participate in the clearance of dying cells. These clearance mechanisms may hamper delivery of therapeutic and imaging agents, and considerable efforts have been devoted to extending the residence time of nano particles in the blood stream through surface modification of the nanoparticles. In an elegant proof-of-principle study, 18
Rodriguez et al. demonstrated that polystyrene nanoparticles (160 nm) coated with a ‘marker-of-self ’ peptide derived from the human CD47 protein displayed delayed macrophage-mediated clearance and enhanced drug delivery to tumors in mice. CD47 is a protein that is expressed on all cell membranes in mice and humans and its interaction with the receptor CD172a (also known as SIRPa) on phagocytes actively inhibits phagocytic uptake of viable cells. In other words, CD47 acts as a ‘don’t-eat-me-signal’ for macrophages. Using the NOD/SCID-IL2Rgnull mouse strain, a severely immunodeficient mouse strain whose macrophages express a SIRPa receptor compatible with human CD47, the authors could show that the attachment Nanomedicine (2014) 9(1)
of a 21-amino acid peptide derived from CD47 to polystyrene particles allowed for a prolonged circulation time. Preinjection of a SIRPa-specific antibody, which blocks CD47 binding, eliminated the enhanced circulation of CD47 peptide-functionalized nanoparticles, thus confirming interaction specificity in the in vivo setting. Using NOD/SCID-IL2Rgnull mice with flank tumors of human A549-derived lung adenocarcinoma cells, Rodriguez et al. demonstrated greater tumor accumulation of nanoparticles functionalized with CD47 peptides than the control nanoparticles. In addition, experiments performed in tumor-bearing mice showed that paclitaxel-loaded nanoparticles that displayed the CD47 peptide plus PEG future science group
Research Highlights News – and a CD47-targeting antibody (to target the tumor cells) shrank tumors more efficiently than nanoparticles lacking the CD47-derived peptide. However, whether or not a targeting antibody is required for accumulation of the nanoparticles and their cargo in the tumor warrants further
News & Views
study. In conclusion, the use of self-derived peptides alone or in combination with a targeting ligand provides inspiration for the further development of nanomedicines that are able to avoid immune clearance, yet at the same time can deliver therapeutic or imaging agents to tissues of interest.
Now you see it, now you don’t: serum proteins prevent specific targeting of nanoparticles Evaluation of: Salvati A, Pitek AS, Monopoli MP et al. Transferrinfunctionalized nanoparticles lose their targeting capabilities when a biomolecule corona adsorbs on the surface. Nat. Nanotechnol. 8(2), 137–143 (2013).
Nanoparticle-based delivery systems are being developed to improve the efficacy and reduce the systemic toxicity of a wide range of drugs. However, while the potential of targeted nanomedicines has already been demonstrated [1], it remains to be fully understood which parameters dictate the successful targeting of nanomedicines under realistic in vivo conditions. Notably, when nanoparticles are introduced into a biological system the surface is coated with proteins and other biomolecules to form a so-called ‘biocorona’, the identity of which depends on the specific bio logical milieu. In a key paper published last year, Salvati et al. studied the impact of the biocorona, which is formed in fetal
bovine or human serum, on the targeting ability of nanoparticles [2]. To this end, the authors used fluorescent silica nano particles (50 nm) coated with PEG and functionalized with human transferrin modified with a thiol–PEG linker through conjugation to the PEGylated particle. The human lung adenocarcinoma cell line A549, with or without silencing of the gene encoding the transferrin receptor, was used in order to assess specific uptake of nanoparticles. Salvati et al. found that transferrin receptor-dependent uptake occurred under serum-free conditions. Surprisingly, uptake of the PEGylated particles without functionalization was higher than that of the transferrin-coated particles, but occurred independently of the expression of the receptor. In the presence of serum, however, the overall uptake decreased, as well as the fraction of uptake that depended on the transferrin receptor, thus demonstrating that the specific targeting ability was lost. Using established protocols, the authors also confirmed that a corona of proteins was indeed formed
on the transferrin-functionalized nano particles, although much less than for non-PEGylated particles. While the study focused on a single model nanoparticle, and a single ligand–receptor interaction, and was based on experiments conducted in a single human cancer cell line, the work by Salvati et al. is of considerable relevance for nanomedicine as it highlights the importance of testing targeted nanoparticles in the biological fluid(s) in which the nanoparticles will be applied, and also as it offers an approach for the screening of nanoparticles in vitro prior to embarking on animal studies [2].
References 1
2
Davis ME, Zuckerman JE, Choi CH et al. Evidence of RNAi in humans from systemically administered siRNA via targeted nanoparticles. Nature 464(7291), 1067–1070 (2010). Salvati A, Pitek AS, Monopoli MP et al. Transferrin-functionalized nanoparticles lose their targeting capabilities when a biomolecule corona adsorbs on the surface. Nat. Nanotechnol. 8(2), 137–143 (2013).
Biomimetic camouflage: nanoporous particles cloaked in cellular membranes Evaluation of: Parodi A, Quattrocchi N, van de Ven AL et al. Synthetic nanoparticles functionalized with biomimetic leukocyte membranes possess cell-like functions. Nat. Nanotechnol. 8(1), 61–68 (2013).
future science group
Biomimetic approaches are aimed at imitating natural structures and processes at the cellular or subcellular level. In particular, strategies whereby opsonization and nonspecific clearance by phagocytic cells of the immune system are avoided are attracting considerable interest. In a study published last year, Parodi et al. www.futuremedicine.com
coated nanoporous silicon particles (NSPs; 3.2 µm) with cellular membranes to confer cellular functions, including ‘stealth’ [1]. The cellular membranes were derived from murine and human leukemia or lymphoma cell lines (J774, Jurkat and THP-1). The membrane coating was found to reduce in vitro opsonization by 19
Research Highlights News & Views – News
using albumin and IgG, two highly abundant serum proteins, and the membrane coating of NSPs significantly decreased particle uptake in vitro, particularly when the donor membrane matched that of the host phagocytic cell. Furthermore, Parodi et al. demonstrated that the membranecoated NSPs could interact with and pass through an endothelial cell barrier under inflamed conditions, and that they were able to deliver the anticancer drug doxorubicin through an endothelial layer and release it to kill human breast cancer cells while maintaining the viability of the endothelial layer (comprised of human umbilical vein endothelial cells).
20
In addition, using intravital microscopy the authors found that the membranedisguised NSPs showed delayed accumulation in the liver, and that the accumulation of the particles in murine B16 melanoma tumors in mice was enhanced compared with that of ‘naked’ NSPs. In a related study, Hu et al. employed erythroc yte (red blood cell) membranes from mice to camouflage polymeric nano particles (70 nm) [2]. However, as pointed out by the latter authors, to optimize such entities for use in the clinical setting, the particles would first need to be crossmatched to the patient’s own blood or, alternatively, the erythrocyte membranes would need to be selectively depleted from immunogenic proteins before fusing them with nanoparticles. The work by Parodi et al. suggests that biomimetic ‘camouflage’ can be achieved using cellular membranes and that this may allow synthetic
Nanomedicine (2014) 9(1)
particles to successfully negotiate vascular barriers. It would be of interest to learn whether membranes derived from normal white blood cells (leukocytes) also confer such properties, and to determine which protein and/or lipid signal(s) in these membranes are responsible for the observed biological effects. Further research on natural–synthetic hybrid structures may yield novel drug delivery and imaging platforms in nanomedicine.
References 1
2
Parodi A, Quattrocchi N, van de Ven AL et al. Synthetic nanoparticles functionalized with biomimetic leukocyte membranes possess cell-like functions. Nat. Nanotechnol. 8(1), 61–68 (2013). Hu CM, Zhang L, Aryal S et al. Erythrocyte membrane-camouflaged polymeric nanoparticles as a biomimetic delivery platform. Proc. Natl Acad. Sci. USA 108(27), 10980–10985 (2011).
future science group
