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Highlights from the latest articles in nanomedicine
Spherical nucleic acids: crossing the uncrossable to drug the undruggable Evaluation of: Jensen SA, Day ES, Ko CH et al. Spherical nucleic acid nanoparticle conjugates as an RNAi-based therapy for glioblastoma. Sci. Transl. Med. 5, 209ra152 (2013). Glioblastoma multiforme is an aggressive and incurable type of brain cancer, with a current median survival time of approximately 14 months. Partially responsible for this low survival rate is the limited repertoire of druggable targets, and the tendency of glioblastoma multiforme to develop resistance to a small molecule inhibitor [1] . More complex treatment strategies are impeded by the existence of the blood–brain barrier, which can stop many nano-based strategies from distributing through to the cancerous tissue [2] . In a recent issue of Science Translational Medicine, Jensen et al. reported a nanostrategy that intrinsically addresses both these concerns. RNAi is a highly customizable method capable of downregulating the expression of any protein, including so-called ‘undruggable’ targets, by using highly charged siRNA. By conjugating many of the siRNAs to a gold nanoparticle core, a dense, negatively charged particle was formed [3] . The particles, termed spherical nucleic acids (SNAs) demonstrated intrinsic cellular uptake in both brain microendothelial cells, as well as glial cells, via interaction with the scavenger receptor class A. Most interestingly, the particles were capable of being transcytosed through a brain microendothelial cell monolayer and binding astrocytes when cultured in a trans-well system, indicating
10.2217/NMM.13.216 © 2014 Future Medicine Ltd
that the SNA might be capable of crossing the blood–brain barrier in vivo. Opening up the brain to oligonucleotide therapeutics allows researchers a greater repertoire of targets, including those deemed ‘undruggable’. In the article, researchers designed siRNA-laden SNA to target the oncogene Bcl2L12. SNAs accumulated tenfold higher in the tumor tissue than the surrounding healthy brain, allowing clear delineation of the tumor mass via MRI. Furthermore, the SNA decreased Bcl2L12 protein level by 40% in the tumor, significantly increased intratumoral apoptosis markers, and decreased tumor burden. The SNA strategy has yet to reach its full potential. More work is required to optimize to allow active targeting, to increase retention time, and to maximize siRNA efficacy. Nevertheless, the paper here describes an excellent starting point for SNA therapy of undruggable targets in brain cancers.
Benjamin M Luby1,2, Arash Farhadi1,3, Mojdeh Shakiba1,3, Danielle M Charron1,2, Áron Roxin1,4 & Gang Zheng*,1,2,3,4 Ontario Cancer Institute & Techna Institute, UHN, Toronto, Canada 2 Institute of Biomaterials & Biomedical Engineering, University of Toronto, ON, M5G 1L7, Canada 3 Department of Medical Biophysics, University of Toronto, ON, M5G 1L7, Canada 4 Department of Pharmaceutical Sciences, Leslie L Dan Faculty of Pharmacy, University of Toronto, ON, M5G 1L7, Canada *Author for correspondence: [email protected] 1
Nanoworms shed synthetic urinary biomarkers to aid the detection of thrombin activity Evaluation of: Lin KY, Kwong GA, Warren AD et al. Nanoparticles that sense thrombin activity as synthetic urinary biomarkers of thrombosis. ACS Nano 7, 9001–9009 (2013). Thrombi are an important pathophysiologic event for a number of disease states and disorders. Monitoring, detection, and management of thrombi are of clinical importance. Failure to do so dubbed deep vein thrombosis and pulmonary embolism as ‘silent killers’ for in-patient hospital care [4] . Techniques for detection and monitoring of thrombi typically entail assays that
Nanomedicine (2014) 9(4), 385–388
part of
ISSN 1743-5889
385
News & Views Research Highlights detect related serum analyte levels, such as D-dimer, a downstream protein from fibrin degradation [5] , or medical imaging techniques, such as angiography and ultrasound (with and without contrast) to monitor physiologic features, which indicate anatomical perversions or features such as stenosis, flow occlusion and abnormal flow patterns [6] . In a recent report in the journal of ACS Nano, Lin et al. described a technique to monitor systemic thrombin activity via circulating nanoparticles that release small molecule reporters through the renal system, which are noninvasively measured with standard ELISA assays. One important feature of this study is the conception of a technique that uses nanotechnology in conjunction with standard readout methods currently used in the medical profession. While numerous examples of long circulating nanoparticles have served as contrast agents for various medical imaging modes such as optical imaging, MRI and computed tomography [7] , this study has expanded their utility for urine assays which have remained largely unexplored for monitoring systemic thrombin activity. Iron oxide nanostructures (nanoworms) carry molecule reporters through a thrombin protease cleavable peptide linker. Upon interaction with thrombin proteases, reporter moieties are released in the blood and become rapidly cleared into the urine. The inability of the relatively large nanoworms to filter through renal fenestrations and the rapid clearance of the thrombin-cleaved reporter moieties through the kidney enable a high contrast for detection of thrombin activity. A standard sandwich ELISA technique was easily used to measure the content of the activated reporter in urine and the result correlated well with fibrinogen formation in vivo. The strategy of using smart nanoworms to survey the host blood to release the detectable reporter specifically in response to substrate cleavage by thrombin is innovative and promising, which opens a new direction to detect in vivo activity of vascular disease biomarkers from urine. Resolving the paradox of rapid clearance and effective tumor targeting Evaluation of: Liu J, Yu M, Ning X et al. PEGylation and zwitterionization: pros and cons in the renal clearance and tumor targeting of near-IR-emitting gold nanoparticles. Angew. Chem. Int. Ed. Engl. 52(48), 12572–12576 (2013). Effective tumor targeting of nanoparticles (NPs) has been generally believed to result from methods that prolong circulation in blood and prevent nonspecific uptake by the reticuloendothelial system (RES).
386
Nanomedicine (2014) 9(4)
PEGylation is perhaps the most commonly used and the most successful of such methods. Yet the majority of PEGylated NPs still accumulate in the RES, which is deemed a health hazard. In order for NPs to avoid the RES, Liu et al. previously used zwitterionic ligands (glutathione [GS]) to coat the surface of gold NPs (Au-NPs), resulting in GS-AuNPs with a smaller hydrodynamic diameter [8] . This method allowed for effective clearance of the GS-AuNPs through the renal system, but suffered from low tumor-targeting efficiency. To elucidate the paradox of renal clearance and tumor-targeting, as well as the factors involved, Liu et al. recently developed the first renal-clearable PEGylated near infrared-emitting Au-NPs (PEG‑AuNPs) with similar core size, physiological stability and photophysical properties to GS-AuNPs to allow for head-to-head comparison. The PEGAuNPs showed tumor-targeting efficiency threetimes more than that of GS-AuNPs (8.3 ± 0.9 vs 2.3%ID g-1 at 12 h postinjection), but a comparable accumulation in liver. In terms of the enhanced permeability and retention (EPR) effect, the PEGAuNPs were shown to have higher tumor/blood ratio at 24 h post injection, comparable with conventional PEG-AuNPs (nonrenal clearable) [9] , suggesting that PEGylation enhances accumulation via the EPR effect. This is unique in that high EPR effect is generally attributed to nonrenal-clearable NPs and, in light of these results, it can be concluded that tuning the surface chemistry of renal-clearable NPs can enhance their accumulation via the EPR effect. PEG-AuNPs showed much slower accumulation (5 h vs 40 min) and longer clearance half-life (4 h vs 43 min) compared with GS-AuNPs. The consistent slower renal clearance of PEG-AuNPs, together with the comparable NPs amount detected in urine for both PEG-AuNPs and GS-AuNPs, indicated that the slower clearance of PEG-AuNPs was due to a result of slow diffusion in the body rather than slow uptake by the RES. This study demonstrates an advantage in using PEGylated renal-clearable NPs for therapeutic purposes where high and prolonged accumulation is important, and using zwitterionic NPs for imaging where short detection time and rapid clearance is desirable. The fundamental study shows that surface chemistry has a significant impact on tumor targeting, such that renal-clearable NPs with PEGylated surfaces can have high tumor targeting as well – characteristics previously regarded as paradoxical. As such, it brings to light the importance of such fundamental studies on our understanding of NP behavior in vivo and means of improving them.
future science group
Research Highlights
Shaking up lipoprotein for nanocrystal‑based imaging and therapy Evaluation of: Allijn IE, Wie L, Tang J et al. Gold nanocrystal labeling allows low-density lipoprotein imaging from the subcellular to macroscopic level. ACS Nano 7, 9761–9770 (2013). Over the past 30 years, intracellular transport of lowdensity lipoprotein (LDL) via the LDL receptor has been exploited for efficient delivery of therapeutics and imaging agents using both native LDL and LDLmimicking nanoparticles [10] . Hydrophobic molecules are incorporated into the LDL core by reconstitution. However, efficient core-loading of LDL with nanocrystals has not been reported. Building on their previous work labeling high-density lipoprotein-mimicking particles [11] , Allijn and colleagues recently reported a robust method for core-loading a range of nanocrystals and molecular contrast agents in LDL, with minimal impact on biological function [12] . In this study, phospholipid-encapsulated gold nanocrystal (AuNC) was sonicated with native LDL in phosphate buffer saline. From this solution, 70% of the particles were isolated as AuNC-loaded LDL (Au-LDL), each particle loaded with on average 1.5 AuNC. In vitro and in vivo data suggest that AuNC core-loading using this method preserves the physicochemical properties and biological function of native LDL, including receptor specificity and biodistribution. Their experimental results highlight the advantages of Au-LDL for multimodal imaging. Au-LDL can be imaged from the subcellular level by transmission electron microscopy, to the anatomical level by computed tomography. Fluorescence imaging capability was also easily provided by incorporating phospholipid–fluorophore conjugates in the initial micelles encapsulating the AuNC, or by encapsulating fluorophores, such as BODIPY and DiR, in place of AuNC. In summary, this new method is a promising strategy for efficient core-loading of nanocrystals and molecules in LDL, with the potential to enhance our imaging capabilities and treatment strategies using lipoprotein nanoparticles The ‘GO chip’ goes beyond efficient circulating tumour cell capture Evaluation of: Yoon HJ, Kim TH, Zhang Z et al. Sensitive capture of circulating tumour cells by functionalized graphene oxide nanosheets. Nat. Nanotechnol. 8, 735–741 (2013). Patients with early-stage cancers may have very rare circulating tumour cells (CTCs) in their bloodstream that hold vital information about the identity and progression of the primary tumor. Owing to these low cell concentrations, however, successful CTC
future science group
News & Views
capture requires a device that can sequester even single-digit CTCs from patient blood samples for an accurate diagnosis [13] . Yoon and colleagues from the University of Michigan in Anne Arbor (MI, USA) solved the challenge with their antibody-functionalized graphene oxide (GO) nanosheet-based microfluidic device (GOchip), that offers more than efficient CTC capture. Their report clearly describes the fabrication and functionalization of the GO chip, which has a surface arranged with approximately 60,000 flowershaped gold patterns containing densely intercalated anti-EpCAM antibody-modified GO nanosheets. The GO chip efficiently recovered single-digit EpCAM-expressing cells spiked into human blood and has a surface capable of identifying and distinguishing CTCs from healthy leukocytes by fluorescence microscopy. The GO chip substrate was suitable for culturing captured cells and this report presents methods for re-culturing captured cells on conventional tissue culture plates for downstream biological ana-lysis. Even efficient CTC capture may only identify a few CTCs per ml of human blood [14] . Therefore, the ability to potentially amplify captured CTCs is a powerful advantage of the GO chip platform. As a proof of concept, this report showed that the GO chip efficiently identified CTCs from human blood samples of patients with either metastatic breast cancer, pancreatic cancer or early-stage lung cancer. Quantification of CTC recovery suggests that the GO chip may be a potential competitor of the US FDA-approved VeridexCellSearch platform, particularly for the capture of metastatic breast cancer CTCs [14] . Since the antibody-conjugation approach is based on biotin–avidin binding, this platform can be easily modified with different biotinylated antibodies to create GO chip-like devices adapted to detect circulating cells that overexpress other surface biomarkers. The high sensitivity, imaging compatibility, cell amplification potential and the adaptability of this platform makes the GO chip an attractive new development that should capture the attention of the CTC field. 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.
www.futuremedicine.com
387
News & Views Research Highlights retention and fast normal tissue clearance. J. Am. Chem. Soc. 135, 4978–4981 (2013).
References 1
Michiue H, Equchi A, Scadeng M et al. Induction of in vivo synthetic lethal RNAi responses to treat glioblastoma. Cancer Biol. Ther. 8, 2304–2311 (2009).
2
Hwang SR, Kim K. Nano-enabled delivery systems across the blood–brain barrier. Arch. Pharm. Res. 37(1), 24–30 (2013).
3
Cutler JI, Auyeung E, Mirkin CA. Spherical nucleic acids. J. Am. Chem. Soc. 134, 1376–1391 (2012).
4
Futterman LG, Lemberg L. A silent killer – often preventable. Am. J. Crit. Care 13, 431–436 (2004).
5
Stein PD, Hull RD, Patel KC et al. D-dimer for the exclusion of acute venous thrombosis and pulmonary embolism: a systematic review. Ann. Intern. Med. 140, 589–602 (2004).
6
Osborn E, Jaffer F. Imaging atherosclerosis and risk of paque rupture. Curr. Atheroscler. Rep. 15, 1–9 (2013).
7
McAteer MA, Choudhury RP. Targeted molecular imaging of vascular inflammation in cardiovascular disease using nano- and micro-sized agents. Vascul. Pharmacol. 58, 31–38 (2013).
8
388
Liu J, Yu M, Zhou C et al. Passive tumor targeting of renal-clearable luminescent gold nanoparticles: long tumor
Nanomedicine (2014) 9(4)
9
Zhang G, Yang Z, Liu W et al. Influence of anchoring ligands and particle size on the colloidal stability and in vivo biodistribution of polyethylene glycol-coated gold nanoparticles in tumor-xenografted mice. Biomaterials 30, 1928–1936 (2009).
10
Ng KK, Lovell JF, Zheng G. Lipoprotein-inspired nanoparticles for cancer theranostics. Acc. Chem. Res. 44, 1105–1113 (2011).
11
Cormode DP, Skajaa T, Schooneveld MM et al. Nanocrystal core high-density lipoproteins: a multimodality contrast agent platform. Nano Lett. 8, 3715–3723 (2008).
12
Allijn IE, Wie L, Tang J et al. Gold nanocrystal labeling allows low-density lipoprotein imaging from the subcellular to macroscopic level. ACS Nano 7, 9761–9770 (2013).
13
Pantel K, Brakenhoff RH, Brandt B. Detection, clinical relevance and specific biological properties of disseminating tumour cells. Nat. Rev. Cancer 8, 329–340 (2008).
14
Ozkumur E, Shah AM, Ciciliano JC et al. Inertial focusing for tumor antigen-dependent and -independent sorting of rare circulating tumor cells. Sci. Transl. Med. 5, 1–11 (2013).
future science group
Highlights from the latest articles in nanomedicine
Spherical nucleic acids: crossing the uncrossable to drug the undruggable Evaluation of: Jensen SA, Day ES, Ko CH et al. Spherical nucleic acid nanoparticle conjugates as an RNAi-based therapy for glioblastoma. Sci. Transl. Med. 5, 209ra152 (2013). Glioblastoma multiforme is an aggressive and incurable type of brain cancer, with a current median survival time of approximately 14 months. Partially responsible for this low survival rate is the limited repertoire of druggable targets, and the tendency of glioblastoma multiforme to develop resistance to a small molecule inhibitor [1] . More complex treatment strategies are impeded by the existence of the blood–brain barrier, which can stop many nano-based strategies from distributing through to the cancerous tissue [2] . In a recent issue of Science Translational Medicine, Jensen et al. reported a nanostrategy that intrinsically addresses both these concerns. RNAi is a highly customizable method capable of downregulating the expression of any protein, including so-called ‘undruggable’ targets, by using highly charged siRNA. By conjugating many of the siRNAs to a gold nanoparticle core, a dense, negatively charged particle was formed [3] . The particles, termed spherical nucleic acids (SNAs) demonstrated intrinsic cellular uptake in both brain microendothelial cells, as well as glial cells, via interaction with the scavenger receptor class A. Most interestingly, the particles were capable of being transcytosed through a brain microendothelial cell monolayer and binding astrocytes when cultured in a trans-well system, indicating
10.2217/NMM.13.216 © 2014 Future Medicine Ltd
that the SNA might be capable of crossing the blood–brain barrier in vivo. Opening up the brain to oligonucleotide therapeutics allows researchers a greater repertoire of targets, including those deemed ‘undruggable’. In the article, researchers designed siRNA-laden SNA to target the oncogene Bcl2L12. SNAs accumulated tenfold higher in the tumor tissue than the surrounding healthy brain, allowing clear delineation of the tumor mass via MRI. Furthermore, the SNA decreased Bcl2L12 protein level by 40% in the tumor, significantly increased intratumoral apoptosis markers, and decreased tumor burden. The SNA strategy has yet to reach its full potential. More work is required to optimize to allow active targeting, to increase retention time, and to maximize siRNA efficacy. Nevertheless, the paper here describes an excellent starting point for SNA therapy of undruggable targets in brain cancers.
Benjamin M Luby1,2, Arash Farhadi1,3, Mojdeh Shakiba1,3, Danielle M Charron1,2, Áron Roxin1,4 & Gang Zheng*,1,2,3,4 Ontario Cancer Institute & Techna Institute, UHN, Toronto, Canada 2 Institute of Biomaterials & Biomedical Engineering, University of Toronto, ON, M5G 1L7, Canada 3 Department of Medical Biophysics, University of Toronto, ON, M5G 1L7, Canada 4 Department of Pharmaceutical Sciences, Leslie L Dan Faculty of Pharmacy, University of Toronto, ON, M5G 1L7, Canada *Author for correspondence: [email protected] 1
Nanoworms shed synthetic urinary biomarkers to aid the detection of thrombin activity Evaluation of: Lin KY, Kwong GA, Warren AD et al. Nanoparticles that sense thrombin activity as synthetic urinary biomarkers of thrombosis. ACS Nano 7, 9001–9009 (2013). Thrombi are an important pathophysiologic event for a number of disease states and disorders. Monitoring, detection, and management of thrombi are of clinical importance. Failure to do so dubbed deep vein thrombosis and pulmonary embolism as ‘silent killers’ for in-patient hospital care [4] . Techniques for detection and monitoring of thrombi typically entail assays that
Nanomedicine (2014) 9(4), 385–388
part of
ISSN 1743-5889
385
News & Views Research Highlights detect related serum analyte levels, such as D-dimer, a downstream protein from fibrin degradation [5] , or medical imaging techniques, such as angiography and ultrasound (with and without contrast) to monitor physiologic features, which indicate anatomical perversions or features such as stenosis, flow occlusion and abnormal flow patterns [6] . In a recent report in the journal of ACS Nano, Lin et al. described a technique to monitor systemic thrombin activity via circulating nanoparticles that release small molecule reporters through the renal system, which are noninvasively measured with standard ELISA assays. One important feature of this study is the conception of a technique that uses nanotechnology in conjunction with standard readout methods currently used in the medical profession. While numerous examples of long circulating nanoparticles have served as contrast agents for various medical imaging modes such as optical imaging, MRI and computed tomography [7] , this study has expanded their utility for urine assays which have remained largely unexplored for monitoring systemic thrombin activity. Iron oxide nanostructures (nanoworms) carry molecule reporters through a thrombin protease cleavable peptide linker. Upon interaction with thrombin proteases, reporter moieties are released in the blood and become rapidly cleared into the urine. The inability of the relatively large nanoworms to filter through renal fenestrations and the rapid clearance of the thrombin-cleaved reporter moieties through the kidney enable a high contrast for detection of thrombin activity. A standard sandwich ELISA technique was easily used to measure the content of the activated reporter in urine and the result correlated well with fibrinogen formation in vivo. The strategy of using smart nanoworms to survey the host blood to release the detectable reporter specifically in response to substrate cleavage by thrombin is innovative and promising, which opens a new direction to detect in vivo activity of vascular disease biomarkers from urine. Resolving the paradox of rapid clearance and effective tumor targeting Evaluation of: Liu J, Yu M, Ning X et al. PEGylation and zwitterionization: pros and cons in the renal clearance and tumor targeting of near-IR-emitting gold nanoparticles. Angew. Chem. Int. Ed. Engl. 52(48), 12572–12576 (2013). Effective tumor targeting of nanoparticles (NPs) has been generally believed to result from methods that prolong circulation in blood and prevent nonspecific uptake by the reticuloendothelial system (RES).
386
Nanomedicine (2014) 9(4)
PEGylation is perhaps the most commonly used and the most successful of such methods. Yet the majority of PEGylated NPs still accumulate in the RES, which is deemed a health hazard. In order for NPs to avoid the RES, Liu et al. previously used zwitterionic ligands (glutathione [GS]) to coat the surface of gold NPs (Au-NPs), resulting in GS-AuNPs with a smaller hydrodynamic diameter [8] . This method allowed for effective clearance of the GS-AuNPs through the renal system, but suffered from low tumor-targeting efficiency. To elucidate the paradox of renal clearance and tumor-targeting, as well as the factors involved, Liu et al. recently developed the first renal-clearable PEGylated near infrared-emitting Au-NPs (PEG‑AuNPs) with similar core size, physiological stability and photophysical properties to GS-AuNPs to allow for head-to-head comparison. The PEGAuNPs showed tumor-targeting efficiency threetimes more than that of GS-AuNPs (8.3 ± 0.9 vs 2.3%ID g-1 at 12 h postinjection), but a comparable accumulation in liver. In terms of the enhanced permeability and retention (EPR) effect, the PEGAuNPs were shown to have higher tumor/blood ratio at 24 h post injection, comparable with conventional PEG-AuNPs (nonrenal clearable) [9] , suggesting that PEGylation enhances accumulation via the EPR effect. This is unique in that high EPR effect is generally attributed to nonrenal-clearable NPs and, in light of these results, it can be concluded that tuning the surface chemistry of renal-clearable NPs can enhance their accumulation via the EPR effect. PEG-AuNPs showed much slower accumulation (5 h vs 40 min) and longer clearance half-life (4 h vs 43 min) compared with GS-AuNPs. The consistent slower renal clearance of PEG-AuNPs, together with the comparable NPs amount detected in urine for both PEG-AuNPs and GS-AuNPs, indicated that the slower clearance of PEG-AuNPs was due to a result of slow diffusion in the body rather than slow uptake by the RES. This study demonstrates an advantage in using PEGylated renal-clearable NPs for therapeutic purposes where high and prolonged accumulation is important, and using zwitterionic NPs for imaging where short detection time and rapid clearance is desirable. The fundamental study shows that surface chemistry has a significant impact on tumor targeting, such that renal-clearable NPs with PEGylated surfaces can have high tumor targeting as well – characteristics previously regarded as paradoxical. As such, it brings to light the importance of such fundamental studies on our understanding of NP behavior in vivo and means of improving them.
future science group
Research Highlights
Shaking up lipoprotein for nanocrystal‑based imaging and therapy Evaluation of: Allijn IE, Wie L, Tang J et al. Gold nanocrystal labeling allows low-density lipoprotein imaging from the subcellular to macroscopic level. ACS Nano 7, 9761–9770 (2013). Over the past 30 years, intracellular transport of lowdensity lipoprotein (LDL) via the LDL receptor has been exploited for efficient delivery of therapeutics and imaging agents using both native LDL and LDLmimicking nanoparticles [10] . Hydrophobic molecules are incorporated into the LDL core by reconstitution. However, efficient core-loading of LDL with nanocrystals has not been reported. Building on their previous work labeling high-density lipoprotein-mimicking particles [11] , Allijn and colleagues recently reported a robust method for core-loading a range of nanocrystals and molecular contrast agents in LDL, with minimal impact on biological function [12] . In this study, phospholipid-encapsulated gold nanocrystal (AuNC) was sonicated with native LDL in phosphate buffer saline. From this solution, 70% of the particles were isolated as AuNC-loaded LDL (Au-LDL), each particle loaded with on average 1.5 AuNC. In vitro and in vivo data suggest that AuNC core-loading using this method preserves the physicochemical properties and biological function of native LDL, including receptor specificity and biodistribution. Their experimental results highlight the advantages of Au-LDL for multimodal imaging. Au-LDL can be imaged from the subcellular level by transmission electron microscopy, to the anatomical level by computed tomography. Fluorescence imaging capability was also easily provided by incorporating phospholipid–fluorophore conjugates in the initial micelles encapsulating the AuNC, or by encapsulating fluorophores, such as BODIPY and DiR, in place of AuNC. In summary, this new method is a promising strategy for efficient core-loading of nanocrystals and molecules in LDL, with the potential to enhance our imaging capabilities and treatment strategies using lipoprotein nanoparticles The ‘GO chip’ goes beyond efficient circulating tumour cell capture Evaluation of: Yoon HJ, Kim TH, Zhang Z et al. Sensitive capture of circulating tumour cells by functionalized graphene oxide nanosheets. Nat. Nanotechnol. 8, 735–741 (2013). Patients with early-stage cancers may have very rare circulating tumour cells (CTCs) in their bloodstream that hold vital information about the identity and progression of the primary tumor. Owing to these low cell concentrations, however, successful CTC
future science group
News & Views
capture requires a device that can sequester even single-digit CTCs from patient blood samples for an accurate diagnosis [13] . Yoon and colleagues from the University of Michigan in Anne Arbor (MI, USA) solved the challenge with their antibody-functionalized graphene oxide (GO) nanosheet-based microfluidic device (GOchip), that offers more than efficient CTC capture. Their report clearly describes the fabrication and functionalization of the GO chip, which has a surface arranged with approximately 60,000 flowershaped gold patterns containing densely intercalated anti-EpCAM antibody-modified GO nanosheets. The GO chip efficiently recovered single-digit EpCAM-expressing cells spiked into human blood and has a surface capable of identifying and distinguishing CTCs from healthy leukocytes by fluorescence microscopy. The GO chip substrate was suitable for culturing captured cells and this report presents methods for re-culturing captured cells on conventional tissue culture plates for downstream biological ana-lysis. Even efficient CTC capture may only identify a few CTCs per ml of human blood [14] . Therefore, the ability to potentially amplify captured CTCs is a powerful advantage of the GO chip platform. As a proof of concept, this report showed that the GO chip efficiently identified CTCs from human blood samples of patients with either metastatic breast cancer, pancreatic cancer or early-stage lung cancer. Quantification of CTC recovery suggests that the GO chip may be a potential competitor of the US FDA-approved VeridexCellSearch platform, particularly for the capture of metastatic breast cancer CTCs [14] . Since the antibody-conjugation approach is based on biotin–avidin binding, this platform can be easily modified with different biotinylated antibodies to create GO chip-like devices adapted to detect circulating cells that overexpress other surface biomarkers. The high sensitivity, imaging compatibility, cell amplification potential and the adaptability of this platform makes the GO chip an attractive new development that should capture the attention of the CTC field. 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.
www.futuremedicine.com
387
News & Views Research Highlights retention and fast normal tissue clearance. J. Am. Chem. Soc. 135, 4978–4981 (2013).
References 1
Michiue H, Equchi A, Scadeng M et al. Induction of in vivo synthetic lethal RNAi responses to treat glioblastoma. Cancer Biol. Ther. 8, 2304–2311 (2009).
2
Hwang SR, Kim K. Nano-enabled delivery systems across the blood–brain barrier. Arch. Pharm. Res. 37(1), 24–30 (2013).
3
Cutler JI, Auyeung E, Mirkin CA. Spherical nucleic acids. J. Am. Chem. Soc. 134, 1376–1391 (2012).
4
Futterman LG, Lemberg L. A silent killer – often preventable. Am. J. Crit. Care 13, 431–436 (2004).
5
Stein PD, Hull RD, Patel KC et al. D-dimer for the exclusion of acute venous thrombosis and pulmonary embolism: a systematic review. Ann. Intern. Med. 140, 589–602 (2004).
6
Osborn E, Jaffer F. Imaging atherosclerosis and risk of paque rupture. Curr. Atheroscler. Rep. 15, 1–9 (2013).
7
McAteer MA, Choudhury RP. Targeted molecular imaging of vascular inflammation in cardiovascular disease using nano- and micro-sized agents. Vascul. Pharmacol. 58, 31–38 (2013).
8
388
Liu J, Yu M, Zhou C et al. Passive tumor targeting of renal-clearable luminescent gold nanoparticles: long tumor
Nanomedicine (2014) 9(4)
9
Zhang G, Yang Z, Liu W et al. Influence of anchoring ligands and particle size on the colloidal stability and in vivo biodistribution of polyethylene glycol-coated gold nanoparticles in tumor-xenografted mice. Biomaterials 30, 1928–1936 (2009).
10
Ng KK, Lovell JF, Zheng G. Lipoprotein-inspired nanoparticles for cancer theranostics. Acc. Chem. Res. 44, 1105–1113 (2011).
11
Cormode DP, Skajaa T, Schooneveld MM et al. Nanocrystal core high-density lipoproteins: a multimodality contrast agent platform. Nano Lett. 8, 3715–3723 (2008).
12
Allijn IE, Wie L, Tang J et al. Gold nanocrystal labeling allows low-density lipoprotein imaging from the subcellular to macroscopic level. ACS Nano 7, 9761–9770 (2013).
13
Pantel K, Brakenhoff RH, Brandt B. Detection, clinical relevance and specific biological properties of disseminating tumour cells. Nat. Rev. Cancer 8, 329–340 (2008).
14
Ozkumur E, Shah AM, Ciciliano JC et al. Inertial focusing for tumor antigen-dependent and -independent sorting of rare circulating tumor cells. Sci. Transl. Med. 5, 1–11 (2013).
future science group
