PEGylated nanomedicines: recent progress and remaining concerns.

Review

PEGylated nanomedicines: recent progress and remaining concerns Driton Vllasaliu†, Robyn Fowler & Snow Stolnik 1.

Introduction: the emerging field of nanomedicine

2.

Nanomedicines for targeted drug delivery: the role of surface ‘decorated’

Expert Opin. Drug Deliv. Downloaded from informahealthcare.com by University of Queensland on 10/11/14 For personal use only.

nanocarriers 3.

Performance of nanocarriers in biological systems

4.

PEGylated nanomedicines: drug delivery benefits

5.

PEGylated nanomedicine products

6.

PEGylated nanomedicines: remaining concerns

7.

Expert opinion

†

University of Lincoln, School of Pharmacy, Brayford Pool, Lincoln, UK

Introduction: Recent biopharma deals related to nanocarrier drug delivery technologies highlight the emergence of nanomedicine. This is perhaps an expected culmination of many years of research demonstrating the potential of nanomedicine as the next generation of therapeutics with improved performance. PEGylated nanocarriers play a key role within this field. Areas covered: The drug delivery advantages of nanomedicines in general are discussed, focusing on nanocarriers and PEGylated nanomedicines, including products under current development/clinical evaluation. Well-established drug delivery benefits of PEGylation (e.g., prolonged circulation) are only briefly covered. Instead, attention is deliberately made to less commonly reported advantages of PEGylation, including mucosal delivery of nanomedicines. Finally, some of the issues related to the safety of PEGylated nanomedicines in clinical application are discussed. Expert opinion: The advent of nanomedicine providing therapeutic options of refined performance continues. Although PEGylation as a tool to improve the pharmacokinetics of nanomedicines is well established and is used clinically, other benefits of ‘PEGnology’, including enhancement of physicochemical properties and/or biocompatibility of actives and/or drug carriers, as well as mucosal delivery, have attracted less attention. While concerns regarding the clinical use of PEGylated nanomedicines remain, evidence suggests that at least some safety issues may be controlled by adequate designs of nanosystems. Keywords: drug delivery, liposomes, nanomedicines, nanoparticles, polyethylene glycol, PEGylated nanomedicines Expert Opin. Drug Deliv. (2014) 11(1):139-154

1.

Introduction: the emerging field of nanomedicine

The application of nanoscale materials in drug delivery and diagnostics has now become established, extending beyond academic quests to commercial success and clinical application. This is demonstrated by the existence of a number of nanomedicines in the market and the recent commercial success of BIND Therapeutics, securing a series of deals with Amgen Inc., AstraZeneca and Pfizer [1] for their Nanoengineering nanocarrier development platform. This progress has showed no signs of slowing, with a recent literature analysis identifying nearly 247 nanomedicine products that are approved or in various stages of clinical study [2]. Nanosized therapeutic carriers have been explored for delivery of a wide range of actives -- from small anticancer drug molecules to biomacromolecules -- to various sites of the body in a broad spectrum of disease states. The appeal of using nanocarriers to ferry the therapeutic to its site of action lies in the potential manifold benefits offered by these systems, mostly related to the characteristics conferred by their sub-micron dimension. Some of these benefits relate to the ability of nanocarriers to overcome the biological barriers, including epithelial and endothelial barriers, as well as cell membranes, the latter being important for delivery of drugs to intracellular sites of action. Nanocarriers might also be employed to deliver multiple 10.1517/17425247.2014.866651 © 2014 Informa UK, Ltd. ISSN 1742-5247, e-ISSN 1744-7593 All rights reserved: reproduction in whole or in part not permitted

139

D. Vllasaliu et al.

Article highlights. . .


.

.

.

Application of nanomedicine in cancer and biotherapeutic delivery offers tremendous potential. A broad range of targeting ligands has been investigated for selective delivery of nanotherapeutics to target sites; however, the RES presents a major obstacle in achieving active targeting. Incorporation of PEG into drug delivery systems is a useful strategy to enhance the pharmacokinetic profile of particulate formulations and macromolecular therapeutics. However, other less well-reported benefits of PEGylation include facilitated nanoparticle diffusion in biological environments, such as mucus and brain extracellular space, as well as improvement of physicochemical (e.g., solubility) and biocompatibility profiles (reduction of toxicity) of drug delivery systems. One of the key benefits of PEGylated nanosystems in mucosal drug delivery is a reported improvement of nanoparticle diffusion across mucus following PEGylation. PEGylated nanomedicinal products on the market are mostly PEGylated proteins without a nanocarrier. However, a range of PEGylated, nanocarrier-delivered therapeutics is being currently clinically evaluated. Some of these systems include BIND’s Accurins, Genexol-PM and Aurimune (based on polymers, micelles and gold nanoparticles, respectively). Compromised uptake by target cells, immunogenicity, as well as biodegradability and potential accumulation within lysosomes following chronic administration remain a concern with PEGylated nanomedicines.

This box summarises key points contained in the article.

that this class of medicines could significantly benefit from some of the drug delivery advantages offered by nanocarriers, including protection of the therapeutic and facilitated permeation across the biological barriers. There has been a remarkable proliferation of biotherapeutics in the recent years, increasing from 633 products in clinical trials or under FDA review in 2008 to 907 in 2011 [9]. These encompass a range of products, as depicted in Figure 1. With the current challenges associated with the delivery of biotherapeutics, nanomedicine likely to become an increasingly important tool for effective delivery of this class of medicines, with the possibility of offering alternative non-invasive delivery routes [10,11]. PEGylated nanocarriers have a central role in the area of nanomedicine. The tremendous opportunities that PEGylation offers in terms of improvement of the performance of nanomedicines have been widely reported for some time now. This review will consider some of the currently studied PEGylated nanomedicines and will discuss the drug delivery advantages of PEGylation, with a focus on nanocarriers rather than soluble PEGylated macromolecules. Further, Sections 2 and 3 will cover nanomedicines for targeted therapy and will discuss the performance of nanocarriers (which may not necessarily be PEGylated) in biological systems, respectively. It must be noted that the term ‘nanomedicines’ is used here to denote nanopharmaceuticals, defined by the European Science Foundation Forward Look as drug delivery systems or biologically active drug products encompassing ‘nanometre size scale complex systems, consisting of at least two components, one of which is the active ingredient’ [12].

Nanomedicines for targeted drug delivery: the role of surface ‘decorated’ nanocarriers

2.

therapeutics (having similar or different physicochemical properties), or a combination of imaging and therapeutic agents. By manipulating the characteristics of the carrier, further important drug delivery advantages can be achieved, such as targeted delivery, controlled or stimuli-responsive delivery and protection of the of therapeutic from biological milieus. Application of nanomedicine in cancer for both drug delivery and diagnostic purposes has, in particular, demonstrated considerable potential. Nanoparticles extravasate from the leaky tumour vasculature and remain in the tumour area to a higher extent than healthy tissue due to the enhanced permeability and retention (EPR) effect [3-5]. This ‘passive’ mode of drug targeting is different to ‘active targeting’ whereby therapeutic or diagnostic nanocarriers are targeted to specific tissue usually by means of ligands present on the nanoparticle surface. The biomedical applications of nanomedicines are also being explored in other disease areas, including chronic inflammatory disease (such as atherosclerosis) [6] and infections [7], as well as in disease diagnosis or as tools offering a combination of disease diagnosis and therapy (‘nanotheranostics’) [8]. Nanomedicine also offers tremendous potential in the area of biotherapeutic delivery. The use of nanosized carriers for delivery of bioactives is particularly interesting, considering 140

Biological processes of receptor-mediated cellular uptake and transport have received considerable attention in the field of nanodrug/gene delivery in the past several years. These processes can potentially be exploited for designing site-specific and target-oriented delivery systems. In fact, several targeted nanomedicines in development have already reached the clinical testing stage in humans [13,14]. Active delivery of therapeutics to tissue(s) of interest usually involves linking the active or the carrier, such as nanoparticles, to a targeting moiety that is recognised and interacts with receptors expressed specifically by the target. A broad range of targeting ligands has been investigated for selective delivery of nanotherapeutics. The usual suspects are ligands with overexpressed biological uptake systems in cancerous tissue. These include folate [15-19], transferrin (Tf) [20-23], prostate-specific membrane antigen (PSMA) [24-26], epidermal growth factor [27-29], antibodies [30,31], peptides [32-34], and aptamers [35-37]. Of these, folate-guided delivery in cancer therapy has been particularly well explored. This is perhaps not surprising given some of the advantages associated with the use of this ligand (folate is stable, inexpensive and non-immunogenic compared to proteins such as monoclonal antibodies [38]) and the clear

Expert Opin. Drug Deliv. (2014) 11(1)


Re M com on b o c in lo an na t h l a or RN nt m A G i o G Ce en row I bod ne inte An ll e th nte ie s/p r V tis the the fa rfe s ( ro fer acc O en ra ra ct ro mA te en in th se py py ors ns b) ins ce es er

PEGylated nanomedicines

45 298 13 78 300 20 10 50 64 23 0

100 200 300 400 Number of medicines in development

Figure 1. The number of actives of different classes of ‘biologics’ under development in 2011 is shown. Data taken from [178]

overexpression of folate receptors in cancerous tissue [39]. This biological ‘window of opportunity’ for targeted delivery in cancer therapy has been exploited by nanomedicine researchers, typically by way of folate ligand-displaying nanovehicles of various sorts, incorporating anti-cancer actives [19,39-49]. Folate has been covalently attached to a diverse range of nanocarriers, including liposomes [50], nanoparticulates [51-53], and polymer conjugates [54], as well as biological macromolecules, such as plasmid DNA [55,56] and proteins [57]. The expression levels of the receptor for Tf, TfR1 (also known as CD71), on malignant cells are many times higher compared to normal cells and the extent of expression can be correlated with tumour stage or cancer progression [58-63]. This receptor is, therefore, an attractive target for selective delivery of anti-cancer therapy. TfR1 is located on the outer cell membrane and cycles into acidic endosomes, followed by recycling back to the cell surface [64]. Despite this constitutive recycling under normal circumstances, its use as a gateway for intracellular therapeutic delivery is possible and has been achieved. This is possibly due to modification of intracellular trafficking of the receptor, which can be caused by the therapeutic or nanocarrier, as our group has recently shown to occur with the vitamin B12 receptor [65], or through endosomal escape induced by the therapeutic agent or nanosystem. A Phase I clinical trial outcome showed that a Tf-containing nanoparticle formulation used in delivering siRNA to cancer patients delivers functional siRNA to melanoma tumours in a dose-dependent manner [66]. For more comprehensive reviews on nanosystems designed for cancer targeting, the readers are directed to previously published comprehensive reviews, such as those by Peer et al. [67], Ferrari [68], Riehemann [69] and Moghimi et al. [70].

Performance of nanocarriers in biological systems

3.

The fact that the reticuloendothelial system (RES) presents a major obstacle to achieve active targeting via microparticulate

and nanoparticulate drug carrier systems has been known for about 40 years [71]. Briefly, RES is an immune system component that serves to remove foreign material, including bacteria and viruses, from the body and comprises circulating macrophages and monocytes, liver Kupffer cells, spleen and other lymphatic vessels [72]. This system rapidly shuttles nanoparticles -- especially hydrophobic particles [73] -- out of circulation resulting in its accumulation in the liver, spleen or bone marrow. The process starts with nanoparticle surface being coated with plasma opsonin proteins (typically occurring to ‘mark’ the bacteria and viruses for engulfment by phagocytic cells), followed by transport to the liver or spleen for degradation and excretion [74]. RES functioning and the barrier it presents to drug delivery have been reviewed previously [71,74-76]. Surface decoration of nanocarriers with one or more materials that confer beneficial therapeutic delivery behaviour (e.g., targeted delivery, controlled drug release, prolonged circulation or a combination of these) is a common sense approach in the design of sophisticated drug delivery systems. However, despite the advances in fabrication of nanocarriers, relatively little is known about their behaviour in complex biological systems [77]. Changes in the surface of nanocarriers on exposure to biological fluids arise due to the formation of the protein corona. This consists of plasma proteins, with albumin being a major component [77-80] and may alter the overall nanomedicine characteristics (including size, surface charge, resistance to aggregation and hydrodynamic size) to a significant extent. This, in turn, may markedly influence not only their biocompatibility and biodistribution [71,81] but also their targeting capacity [82], making this an important point to consider when designing ‘smart’ nanomedicines. Elegant formulation techniques and chemistries have been used to fabricate nanocarriers displaying controlled arrangement of one or more targeting moieties on their surface, with literature examples ranging from ‘patchy’ folate ligand-clustered micelles [83-85] to nanocarriers with variable surface densities of mannose targeting ligands [86]. However, what is the fate of such ‘designer’ nanocarrier surfaces in complex biological media? Recently, Salvati et al. [82] showed that the targeting ability of Tf-functionalised nanoparticles disappears in a biological environment, with functionalised nanoparticles losing their targeting capability due to biological media-originating surface-adsorbed protein corona. This corona shields the Tf from binding to its targeted receptors, diminishing its targeting specificity, as shown in Figure 2, thus leading to cell entry through other (non-targeted) biological pathways. The performance of targeted nanosystems seen in simple dispersions (e.g., phosphate-buffered saline [PBS] or other ‘biological’ solutions, such as Hanks’ balanced salt solution, which are often employed in cell culture studies) can, therefore, be lost in relevant physiological conditions, which may result in loss of specificity and therapeutic accumulation in non-pathological tissues. Researchers conducting these studies should, therefore, consider whether the evaluation of their nanosystems is being


141

D. Vllasaliu et al.

B.

A. Relative Mw

100

100

Relative Mw

80 60

98 96 0.05

0.06 Dapp (mm)

0.07

40

No receptor (in PBS)

20

With TfR in PBS With TfR in 10% With TfR in 55%

serum serum

0 .4 0 .5 0 .6

0 .3

0 .2

0 .0 0 .0 6 0. 7 0.008 0 .1 9 0

3 0 .0 4

0 .0

TfR

Dapp (mm)

SiO2-PEG8-Tf Different serum proteins

10% serum 1 2 3

PBS 1 2 3

55% serum 1 2 3

D.

C. Cell fluorescence intensity (x103)


0

0% neg siRNA 0% siTFRC

21

10% neg siRNA

18

10% siTFRC 55% neg siRNA

15

55% siTFRC

12 9 6 3 0 0

60

120 180 240 300 360 420 480 Exposure time (min)

Figure 2. A. Differential centrifugal sedimentation assessment of TfR binding to PEGylated human Tf particles in the presence of foetal bovine serum (FBS) proteins is shown. A reduction in apparent diameter, Dapp, is observed with increasing amount of serum, indicating loss of TfR-binding when a protein corona is formed on the nanoparticle surface, ‘shielding’ the active binding sites from recognition by TfR. The apparent diameter of bare nanoparticles and nanoparticles incubated with TfR in PBS is shown for reference. Bottom panels show the immunological detection of SiO2--PEG8--Tf/TfR complexes using anti-TfR antibody. The dot blot confirms the reduction of TfR binding at increasing bovine serum content. B. Schematic representation of blocked Tf--TfR interaction in the presence of FBS proteins. C. A549 cells are silenced for 72 h with a negative silencer control (neg siRNA) and for the Tf receptor (siTFRC), before exposure to nanoparticles. Median cell fluorescence intensity obtained by flow cytometry from A549 cells exposed to 50 µg ml-1 PEGylated human Tf particles (SiO2--PEG8--Tf) in serum-free MEM (0%), complete medium (10%) and MEM supplemented with 55% serum (55%) is shown. At increasing serum content the uptake decreases and the effect of TfR is also lost. D. Schematic representation of loss of TfR targeting for Tf-conjugated nanoparticles in the presence of FBS proteins (endogenous Tf, where present, could also compete for TfR). Reproduced with permission from [82].

conducted under physiologically relevant conditions reflecting the local biological environment of the system. For example, injectable, targeted nanocarriers should be tested in the presence of serum proteins, whereas those designed for mucosal delivery should be examined using biorelevant media mimicking mucous and gastric juices. 142

Since the protein corona could dictate the cellular interactions with nanomaterials, based on observations that the corona constitutes the primary contact to the cells [87,88], an important consideration is the dependence of such protein interactions on nanomaterial composition. The nature of the particle surface will control which biomolecules interact with




the particles [89]. Here, several aspects of surface chemistry play important roles, including hydrophobicity, charge and surface coating, size, radius of curvature. This topic is covered comprehensively by Mahmoudi et al. [88]. Safe and effective use of nanomedicines for therapeutic and/or diagnostic effects (or both) requires an understanding of the biophysicochemical interactions occurring at the nano--bio interface and an ability to predict the behaviour of nanomaterials in biological environments. This includes an understanding of the binding properties of proteins (and other molecules) that associate with the particles, including binding affinities, stoichiometries, rates of binding and dissociation for different combinations of proteins and nanoparticles as critical parameters determining the biological effects of nanomedicines [90]. In this regard, interestingly, it has been shown that although there are thousands of proteins in human biological fluids, the protein corona is usually populated with about 10 -- 50 proteins that have the highest affinity for the surface [88].

PEGylated nanomedicines: drug delivery benefits

4.

The concept of surface modification of drug carriers to control the opsonisation process, as well as specific and nonspecific interactions with blood components, has been introduced in the 1970s [91]. In terms of the materials used for surface modification, researchers have focused on hydrophilic macromolecules and polymers with the capacity to form a hydrophilic, hydrated steric barrier on the particle surface [71]. Polyethylene glycol (PEG) has been extensively employed to enhance the drug delivery performance of therapeutics and/or therapeutic micro-carriers and nanocarriers. Incorporation of PEG into drug delivery systems has been used as a strategy to enhance the pharmacokinetic profile of particulate formulations, as well as macromolecular therapeutics. Many other beneficial features have been observed following PEGylation of therapeutics and/or drug delivery systems, which include improvement of the stability of nanoparticles as systems with high surface energy having a tendency to aggregate, improvements in nanoparticle diffusion in biological environments, such as mucus and brain extracellular space, and improvement of physicochemical (e.g., solubility) and biocompatibility profiles (reduction of toxicity) of drug delivery systems. Improved pharmacokinetics Early evidence of the beneficial drug delivery properties of PEG originated from a study in 1977 showing modification of immunological properties of bovine serum albumin following covalent attachment of PEG [91]. PEGylation then became a popular approach to enhance drug delivery, with notable contribution to the field by the Langer [92], Kataoka [93], Torchilin [94] and Davis [71] laboratories among others. Since then, a plethora of PEGylated nanotherapeutic systems have 4.1

been reported in the literature. The flexible polymer chains of PEG have a high hydration capacity (3 to 4 molecules of water per 1 ethylene oxide oxygen [95]), which leads to an increase in the PEG moiety’s volume and bulkiness. This underpins the well-documented phenomenon of ‘steric stabilisation’, which reduces non-specific interaction with proteins (and cells), reducing plasma protein adsorption into the surface of nanocarriers and thereby the uptake by the RES. By reducing the opsonisation process and recognition and uptake activity of monocytes and macrophages, surface decoration of nanocarriers with PEG affords a ‘stealth’ behaviour and increased circulation time, with the overall impact of reduced dosage and frequency of its administration (and, therefore, a potential reduction in drug side effects/toxicity). The benefits of PEGylation in terms of increased circulation time have been demonstrated with a broad range of nanocarriers, including liposomes [96,97] and polymeric nanoparticles [73,98]. These effects are highly dependent on the molecular weight of PEG, polymer chain architecture and surface density of the PEG coating, which dictates PEG conformations at the surface [79,99,100]. It is generally accepted that stealth properties can be achieved following high density coating with PEG having molecular weights ranging from 2000 to 10,000 Da [71,101,102]. There is a consensus that an increase in the density of PEG on the surface of nanoparticles decreases protein adsorption [103-105] and that an increase in PEG surface coverage decreases macrophage association [80,105]. Attenuated protein adsorption and macrophage interaction are typically observed when PEG grafts are in the dense brush conformation [79,104-107], although a recent study by Perry et al. [108] has demonstrated that these properties can be achieved for both PEG mushroom and PEG brush. PEGylation effect on pharmacokinetics has been the subject of several reviews over the years [73,74,93,109-112] but would not be pursued in further detail here. In addition to improved pharmacokinetic outcomes by PEGylation, surface decoration of nanosystems with PEG may also be an important strategy to preserve the targeting capacity of nanocarriers functionalised with groups targeting receptors that are specifically expressed or overexpressed in diseased tissue. Recent work demonstrating the loss of targeting ability of Tf-functionalised silica nanoparticles in biological media had been discussed above. The same study [82] also employed PEGylated and PEGylated Tf-decorated nanoparticles and reported that the adsorption of serum proteins (from biological media) on nanoparticles is reduced considerably compared to non-PEGylated particles, although their targeting specificity is also lost following exposure to biological serum. Other useful drug delivery effects of PEGylation are discussed below. Mucosal delivery The drug delivery advantages offered by nanocarriers have been widely studied for mucosal delivery of biotherapeutics [113-115], with the view of enhancing drug delivery 4.2


143


D. Vllasaliu et al.

efficiency (absorption and bioavailability) to therapeutically relevant levels. The necessity to explore nanocarrier delivery strategies for non-invasive delivery of therapeutically active macromolecules stems from poor absorption of these molecules across the mucosal surfaces [116] coupled with their instability within the biological milieu of the mucosae. To exemplify, in vivo studies with native insulin in a murine model have shown bioavailabilities of < 1% following administration via the oral route (in the absence of ‘absorption enhancers’) [117]. The use of nanocarriers to augment mucosal delivery of bioactives is predominantly based on the potential of nanosized drug carriers to target the cell internalisation pathways of epithelial cells. However, mucosal surfaces present a barrier to the movement of nanoparticulates [118] due to the existence of a number of barriers, including mucus and the almost continuous ‘sheet’ of membranes of closely associated epithelial cells. Other barriers are also important. For example, in the nasal mucosa, the mucociliary mechanism clears 50% of the administered dose (applied as a spray) from its ciliated respiratory mucosa within 15 -- 20 min [119]. The presence of proteases is also an important barrier limiting the availability of nanocarrier-delivered peptides and proteins therapeutics at the mucosal surface and thereby their absorption [120]. Epithelial tight junctions ensure that macromolecules ~ > 1000 Da, and therefore most nanomedicines, are excluded from the paracellular space [121,122]. The mucus barrier is essential in protecting vulnerable surfaces in the respiratory, intestinal, eye and reproductive tissues from invasion by foreign agents, including bacteria, viruses, allergens and irritants. Mucus gel is mainly composed of linear, glycosylated mucin fibres entangled into a dense network [123,124]. The combination of mucin fibre composition and its architecture results in strong interactions between mucus and foreign molecules, severely inhibiting or hindering their movement through the gel [125,126]. Mucus presents a considerable barrier to the movement of nanoparticles [118,127] and one of the key benefits of PEGylated nanosystems in mucosal drug delivery is a reported improvement of nanoparticle diffusion across mucus following PEGylation [127-130]. Enhancement in particle diffusion in mucus has been reported to be dependent on the molecular weight of PEG and the coating density [128,129], with coating of short-length PEG at high density providing a more efficient nanoparticle diffusion in mucus gel [128]. This is related to the nature of the interaction of PEGylated nanocarrier surface with mucus, which is thought to be different depending on the size of PEG, as shown in Figure 3. Additionally, the effect of PEGylation on nanoparticle movement in mucus is also probably influenced by the characteristics of the entity to which it is attached (e.g., size and shape of nanoparticles). However, even if the nanotherapeutics successfully traverses the mucus layer and reaches the level of the epithelial cells, the transport of most nanocarriers across the epithelium is highly inefficient. Epithelial tight junctions can be transiently 144

widened [10] and this could offer a temporary corridor for nanomedicine absorption via the paracellular space. However, this approach is probably not feasible for transepithelial delivery of nanocarriers larger than about 10 -- 20 nm, based on the findings that epithelial absorption exponentially decreases with increasing molecular weight of macromolecules following tight junction opening [118,131]. Most nanomedicines will, therefore, have to traverse the epithelium by travelling transcellularly (across the cells). In this regard, a number of transcytotic pathways operate at the epithelial surfaces, with the potential to ‘shuttle’ material across the epithelium [132]. These potential entry points of nanomedicines might be exploited by surface functionalisation of nanocarriers with specific ligands that direct the system towards the biological transport pathways. Proof-of-concept studies by our group have demonstrated that transepithelial delivery of nanocarriers is possible following surface functionalisation (or adsorption) of model nanoparticles with different ligands known to traverse the epithelial barriers via receptor-mediated transcytosis, including immunoglobulin (Ig)G (airway epithelium) [133], vitamin B12 (intestinal and airway epithelium [65,134], respectively) and folate (airway epithelium) [85]. Although nanomedicine potentially offers exciting new possibilities for non-invasive delivery of biotherapeutics with the likely help of PEGylation, this area is somewhat lagging behind. This is demonstrated by recently published data, presented in Figure 4, which shows that the nanomedicines currently in clinical studies are predominantly designed for invasive delivery.

Enhancement of delivery of non-carrierassociated biotherapeutics

4.3

PEGylation as a drug delivery-enhancing tool is also popular with non-carrier-associated macromolecular therapeutics. Covalent attachment of PEG to peptides and proteins was introduced as early as 1970s [135]. For this therapeutics, relatively large PEG polymers of > 5000 Da were mainly used [96] and PEGylation was reported to improve their safety and efficacy, as well as reduce the immunogenicity [136,137]. With soluble therapeutic macromolecules, PEGylation modifies the physicochemical properties of the molecule in terms of size, hydration, conformation, electrostatic binding and hydrophobicity/hydrophilicity balance. These physical and chemical changes increase systemic retention of the therapeutic agent. The steric stabilisation offered by PEG-grafting is employed to provide a shield for conjugates from recognition by the patient’s immune system due to reduced non-specific protein--protein and protein--cell interactions and to increase the size of the therapeutic [138]. The net result is a prolonged drug circulation half-life and reduced renal clearance of the therapeutic [12]. Discussion of soluble PEGylated biotherapeutics is beyond the scope of this review and for an overview of pharmacokinetic



A.

B.

is being currently clinically evaluated and this drug delivery market is likely to be populated in the coming years. Some of the systems currently being investigated are considered below. Lipid-based nanomedicines Liposomal drug carriers are currently the most common products of nanotechnology reaching the market. Liposomes are composed of one or more lipid bilayers encapsulating an inner aqueous core. The outer lipid layer of liposomes, which is amenable to functionalisation to improve targeting or the pharmacokinetic profile, offers protection of the encapsulated drug from the biological milieu. Liposomal nanodrugs approved by the FDA include Doxil (Doxorubicin; Johnson & Johnson), DaunoXome (Daunorubicin; Gilead) and Mepact (Muramyl tripeptide; IDM Pharma SAS), while Myocet (Doxorubicin; Enzon) is approved in Europe and Canada [141]. As an example of a PEGylated liposomal drug formulation, Doxil/Caelyx was approved by the FDA in 1995 [142] for recurrent ovarian cancer, relapsed/refractory multiple myeloma and AIDS-related Kaposi’s sarcoma. Doxil’s PEGdecorated liposomal carrier, which encapsulates the active pharmaceutical agent doxorubicin, increases the blood circulation time of the drug, thus resulting in passive drug accumulation at the tumour site due to the EPR effect. Considering the formulation of the PEGylated nanovehicle of Doxil, a 2000 Da PEG residue was selected based on testing of PEG chains having a range of molecular weights (from 350 to 15,000 Da), in addition to other considerations such as the metabolism of the PEGylated lipids and the rate of secretion via the kidneys [96]. The success of Doxil highlights the importance of nanomedicine as a discipline in general and nanoPEGylation. Clinical usefulness of its therapeutic agent, doxorubicin, is limited by toxicity, including cardiotoxicity, myelosuppression, alopecia, severe acute nausea and vomiting, and mucositis. The pharmacokinetics of Doxil has been the subject of previous reviews [143], but to summarise, Doxil has a circulation halflife of ~ 73.9 h, which is many times larger compared to doxorubicin half-life of < 10 min [144]. The resulting prolonged circulation facilitates greater uptake of the therapeutic by tumour tissue. Accumulation of PEGylated liposomal doxorubicin in metastatic breast carcinoma tissue is also remarkably enhanced, with a 10-fold higher intracellular drug concentrations compared with adjacent normal tissue [145]. Further, PEGylated liposomal formulation reduces plasma levels of free doxorubicin and therefore drug delivery to normal tissue, which may be responsible for some of the reduced toxic effects of Doxil [146].

Figure 3. Steric stabilisation of nanoparticles versus entanglement in mucus is depicted. A. Shorter, denser graft layers of PEG (pink) tend to sterically stabilise the nanoparticle surface. B. Longer, sparser PEG grafts allow interpenetration of the grafted chains and the mucous network (green), leading to adhesion to the mucus. Reproduced with permission from [179].

140 120 100 80 60 40

ic

l

lm

sa O

pt

ha

Na

Ae

ro

so

ra

l

l

l O

pi To

rs

tit

ca

ia

us

te

an ut

m

tra

In

bc

v

tra

In

ar

ul

c us

eo

us

o en

In

0

l

20

Su


5.1

Figure 4. Route of administration for confirmed and likely nanomedicine applications and products identified in a recent publication is shown. Intravenous, intramuscular, subcutaneous and interstitial routes constitute invasive drug delivery, whereas topical and mucosal (oral, aerosol, nasal and ophthalmic) represent non-invasive therapeutic delivery. Reproduced with permission from [2].

benefits of recently developed PEGylated biologics, the readers are referred to an earlier publication [139]. 5.

PEGylated nanomedicine products

Thus far, PEGylated nanomedicinal products on the market appear mostly in the form of PEGylated protein therapeutics without a nanocarrier. Of notable exception are Doxil and Abraxane (albumin-stabilised, nanoparticle-based paclitaxel, approved in 2005). These products achieved sales of US $402 million and US$386 million in 2011, respectively, with Celgene Corp. targeting Abraxane sales of US$1 billion to US$1.25 billion in 2015, according to Reuters [140]. However, a range of PEGylated, nanocarrier-delivered therapeutics

Polymer-based nanomedicines Various synthetic and natural polymers have been actively investigated for potential applications in nanomedicine fabrication, including polylactide (PLA), polyglycolide (PGA), 5.2


145


D. Vllasaliu et al.

polyacrylates, poly(alkyl cyanoacrylates) (PACA), polycaprolactone, polyethylenimine and their derivatives [147]. However, PEG, PLA and poly(D,L-lactide-co-glycolide) (PLGA) and their copolymers PEG-PLA, PEG-PGA, PLGA and PEG-PLGA are probably the most extensively investigated synthetic polymers for drug and gene delivery. Unlike liposomal drugs, there are currently no polymer-based nanocarrier-associated nanomedicines approved by the FDA, which is perhaps surprising when considering the significant amount of research within the field. This imbalance also appears in clinical trials when comparing polymers to liposomes. The generation of new molecular entities through covalent attachment of therapeutic to the drug carrier in the case of many polymers (as opposed to liposomal formulations which are often fabricated without generating new molecular entities) is thought to be at least partially responsible for this phenomenon [141]. An example of a targeted and PEG-surface displaying polymeric nanocarrier-incorporating system is the technology platform of BIND Therapeutics. BIND’s Accurins are fabricated from relatively established materials and methods, though perhaps the combinatorial library approach taken in their design, which offers the identification of optimal delivery systems from a large number of nanoparticle formulations [143], is a reason for the success of this technology. The parameters optimised in the process include particle size, targeting ligand density, surface properties, drug loading and drug release profile. BIND’s first clinical-stage product candidate, BIND-014, contains the chemotherapeutic agent docetaxel and targets PSMA -- a transmembrane protein expressed in prostate cancer as well as in the neo-vasculature of non-prostatic solid tumours. Pharmacokinetic and tissue distribution studies in rats showed that nanoparticles had a blood circulation halflife of about 20 h, with minimal liver accumulation. Tumour accumulation at 12 h was markedly enhanced and tumour growth suppression prolonged compared to a solvent-based docetaxel in tumour-bearing mice. In tumour-bearing mice, rats and non-human primates, docetaxel-encapsulating targeted nanoparticles displayed prolonged circulation and controlled drug release, with total docetaxel plasma concentrations remaining at least 100-fold higher than solvent-based docetaxel for more than 24 h. This preclinical pharmacokinetic profile was also apparent in clinical data in patients with advanced solid tumours. Further, the nanoparticledelivered docetaxel displayed a different pharmacological profile with cases of tumour shrinkage at doses below those of solvent-based docetaxel [148]. Many other PEGylated polymeric nanoparticle systems have been investigated in the nanomedicine laboratories across the world. Nanoparticles of PACA and PLA (co)polymers are currently undergoing clinical evaluations for the treatment of multidrug resistance hepatocarcinoma (Phase III) and prostate cancer (Phase I) [149,150]. Interestingly, it has been demonstrated that the PEG corona of PACA 146

nanoparticles favours selective adsorption of apolipoprotein E [151,152], as well as amyloid-b (Ab)1--42 peptide, from serum and transport to the hepatic macrophages for destruction [153]. This adsorption occurred through a combination of hydrophilic and hydrophobic interactions between the PEG shell and Ab1--42 peptide. The authors hypothesise that these nanoparticles could act as ‘LDL-like’ structures which can increase in vivo the clearance of Ab peptide from the biological fluids by capturing its soluble forms redirecting the peptide to the hepatic macrophages for destruction. This capture could prevent the Ab aggregation process and its subsequent toxic effects on neuronal cells. Other PEGylated polymer-based nanosystems for drug delivery include polymeric micelles as nanoscopic aggregates of amphiphilic copolymers dispersed in aqueous media, characterised by a core-shell structure. They are generally fabricated from two or more polymers with different physicochemical properties and usually have a hydrophilic shell responsible for colloidal stability and a hydrophobic core enabling hydrophobic drug loading [154]. One such product is Genexol-PM (Samyang Corp.), a PEG-PLA micelle formulation (20 to 50 nm in size) of paclitaxel, which aims to reduce the toxicity of Cremophor EL as synthetic surfactant excipient used in dissolving paclitaxel in Taxol and to increase the therapeutic efficacy [155]. This product is currently approved and marketed in South Korea for metastatic breast cancer, non-small-cell lung cancer and ovarian cancer. The same formulation (under the name Cynviloq) is currently being clinically evaluated in the United States and has just completed Phase II studies [156]. PEGylated micellar nanosystems as drug delivery vehicles are also currently being clinically evaluated by NanoCarrier. Systems incorporating cisplatin derivatives (NC-6004 Nanoplatin) show sustained release, as well as accumulation in cancer cells and decreased nephrotoxicity and neurotoxicity. These are indicated for pancreatic cancer, solid cancer and non-small-cell lung cancer and are currently in Phase III clinical trials [156]. Another PEGylated micellar nanosystem encapsulating paclitaxel, code-named NK105, is currently in Phase II and Phase III clinical trials for stomach and breast cancers, respectively [156]. Other PEGylated nanomedicine platforms Aurimune (Cytimmune Sciences Inc.) is an anti-cancer nanomedicine in clinical development as recombinant human TNF-a-carrying colloidal gold particles (27 nm in size) with surface-conjugated PEG [157]. According to its developer, Aurimune ‘primarily and preferentially exits the circulation through leaky, newly formed vasculature at tumor sites, selectively passing through gaps in blood vessel walls’. The increase in vascular permeability associated with TNF-a and alteration of permeability in tumour tissue with TNF-a-gold nanoparticles [158] are thought to provide possibilities to enhance the EPR-mediated targeting using this system [159]. Phase I clinical data demonstrated that this product achieved ‘safe and 5.3



systemic delivery of TNF-a in humans in far beyond concentrations attained in previous human studies’, fever side effects and accumulation ‘in and around tumor sites, avoiding uptake by healthy tissues and immune system detection’ [160]. Other PEGylated inorganic nanoparticles have been researched/developed for biomedical applications (including drug delivery); these have been reviewed previously [159,161].

PEGylated nanomedicines: remaining concerns


6.

An often-cited disadvantage seen after PEGylation of drug delivery nanocarriers is a trade-off between the increased stability/improved pharmacokinetics and a compromised uptake by target cells [162]. This trade-off can have significant consequences in the performance of the drug delivery formulation as cell uptake is very often a necessary step for nanomedicineassociated therapeutic benefit. Any attenuation of nanodrug uptake by targeted cells, therefore, potentially hampers the therapeutic benefit. This problem is perhaps more important for actively targeted nanocarriers that rely on ligand--receptor interaction to achieve clinical benefit. The presence of PEG on nanocarrier surface may hinder the interaction of ligand(s) coexisting on the carrier surface with the biological target. This trade-off has been called the ‘PEG dilemma’ [163] and is an important point to consider when designing therapeutic or diagnostic nanocarriers. One way of circumventing the issue of PEGylation-mediated compromised cell uptake of the delivery system is to fabricate guided nanosystems that detach or ‘shed’ the PEG coat prior to their interaction with the receptors on the target site [164,165]. Another concern with PEGylated nanomedicines is immunogenicity. Moghimi et al. have shown that liposomes consisting of anionic phospholipid--PEG conjugates cause complement activation-related pseudoallergy (CARPA). While complement activation was, in this instance, at least partly attributed to electrostatic interaction-mediated binding of the highly cationic region of the globular C1q protein with the anionic charge on the phosphate oxygen of the lipid--PEG conjugate [166], another study has reported PEG-induced activation of complement, which occurs in a concentration and molecular weight-dependent fashion through classical (C1q-dependent), lectin, or alternative pathways [167]. PEG is also capable of eliciting anti-PEG antibody responses. PEGylated liposomes have been shown to elicit IgM antibodies, leading to accelerated blood clearance (ABC) phenomena post-repeat dosing. Rapid blood clearance of PEGylated liposomes on repeated injections was demonstrated in multiple studies [168-171]. ABC of the second dose of PEGylated liposomes was shown to be a cause of the binding of anti-PEG IgM, produced by the first dose of liposomes and the subsequent activation of the complement system [163]. Both complement activation and production of anti-PEG IgM depend on the density of PEG on a nanoparticle surface. Surface optimisation of PEG density and molecular weight

are, therefore, critical in dictating and avoiding unwanted immune (non-IgE) hypersensitivity reactions. Further, production of anti-PEG IgM appears to be dependent on other nanomedicine characteristics, including nanoparticle charge and type of drug encapsulated. Therefore, strategies to attenuate the anti-PEG immune response would include manipulation of the dose, PEG molecular weight and surface density and nanoparticle surface charge. Incorporating an agent that attenuates macrophage function would also be beneficial [14]. Some of the other worries with regard to the safety of PEGylated nanomedicines include biodegradability and potential accumulation within lysosomes following chronic administration [159]. The usual target organ is the kidney, given that renal excretion is the predominant clearance route for PEG [172]. Some preclinical studies reported an organspecific formation of PEG-containing intracellular vesicles (‘vacuolation’) in kidneys of animal models, which was linked to the clearance mechanism of PEGylated proteins [173]. Moreover, long circulation of PEGylated nanomedicines, as rendered by PEG presence on the surface, may increase normal tissue exposure, which in turn could lead to unexpected side effects (believed to be the case with the ‘hand and foot syndrome’ following Doxil administration [174]). As clinical data with PEGylated nanomedicines accumulates over time, it would be interesting to see whether these new issues arise and whether these are worrying enough as to encourage alternative, non-PEGylated approaches to improve the drug delivery profile of nanomedicines. Non-PEGylated methods to improve the pharmacokinetic profile of nanomedicines exist, which typically involve the use of nonbioadhesive hydrophilic polymers, such as polysaccharides (usually dextran or chitosan), polyvinyl alcohol, poly(Nvinyl-2-pyrrolidone) and N-(2-hydroxypropyl)methacrylamide copolymers [175]. The selection of coating materials for nanomedicines is also inspired from the body’s innate stealthing of circulating materials. For example, design cues (such as surface proteins) to devise long-circulating nanocarriers are taken from the properties of red blood cells as nature’s longcirculating delivery vehicles [176]. Another unusual approach of notable significance is reported in a recently published paper that utilised ‘self’ peptides that bind and signal to phagocytes to inhibit clearance of opsonised nanoparticles [177], which is depicted in Figure 5. Interestingly, the authors were able to calculate that a nanoparticle of 60 nm radius would require only one molecule to inhibit uptake, whereas PEG densities of > 1 PEG/20 nm2 are needed to enhance nanoparticle circulation via delayed opsonisation. 7.

Expert opinion

The recent multimillion dollar deals attracted by the nanotechnology drug delivery platform of BIND Therapeutics cement the increasingly important role of nanomedicine in offering the next-generation medicines with refined


147

D. Vllasaliu et al.

‘Don’t eat me’ ‘Self’ passivation ‘Eat me’ CD47 or Minimal peptide ‘passport’ SIRPα

Phagocytic activation Cytokine release Nanoparticles Oxidative burst

IgG-particle Myosin IIA P


P

P

P

P

F-actin SHP-1

P

Figure 5. A new way of shuttling nanoparticles past the body’s immune system is shown. A macrophage cell recognises the specific ‘don’t eat me’ signal, mediated by the ‘self’ protein, present on the surface of the nanoparticles. Unlike the unmodified nanoparticle (which is rapidly taken up), the uptake of self protein-decorated nanoparticle is prevented. Art: Mary Leonard, Biomedical Art & Design, Perelman School of Medicine, University of Pennsylvania. Figure based on publication from [177]. Reproduced with permission of Prof Dennis Discher, University of Pennsylvania.

therapeutic performance. The use of nanoscale carriers to deliver therapeutics specifically to their site of action is a key aspect of nanomedicine and significant advances have been made over the past decades in the engineering of various nanocarriers, as well as characterisation and optimisation of their performance. It is interesting that there has been a recent renaissance in the study of nanomedicine behaviour in complex biological milieus. This is probably triggered by realisation that intricately surface-decorated drug nanocarriers designed for targeted therapy, which is the usual strategy for achieving guided delivery of actives via nanomedicines, will morph into different systems in the complex biological environments. Neatly formulated and characterised nanomedicines may change in size, shape and surface features and with that so will the biological effects such as interaction with the components of the immune system and their target sites/receptors. PEGylation as a strategy to improve the pharmacokinetic profile of macromolecules and nanomedicines and to enhance their stability has been a successful drug delivery tool, the products of which have been in the market for a number of years. Additional benefits offered by PEGylation have attracted less attention, but include, and are not limited to, reduction in drug/drug formulation toxicity, improvement of physicochemical properties of actives, preservation of targeting capability of ligand-decorated nanocarriers and facilitated diffusion across mucus. These are all important outcomes of PEGylation that perhaps deserve more consideration. Some of the areas of concern still remaining for PEGylated nanomedicines include immunogenicity, lysosomal accumulation and compromised interaction with the biological targets. Many, if not all, of these potentially negative drug

148

delivery outcomes depend on the nature of PEGylation and may be controlled by an adequate design of nanosystems. Moreover, as our understanding of the mechanisms of antiPEG immune response improves so will the development of effective strategies to attenuate it. The existing evidence does suggest that the immune response is a problem that needs special consideration, but it may be possible to address it through appropriate formulation strategies. Nanomedicines that successfully reach the market will have to fulfil obvious key criteria, such as non-toxicity, non-immunogenicity, target selectivity and biodegradability. As the only existing PEGylated liposomal product on the market, Doxil has enjoyed considerable success. So perhaps it is surprising that other PEGylated nanocarrier-associated therapeutics have not reached the market in the past 10 -- 15 years. However, a number of such nanomedicine products are currently being clinically evaluated, with many more in early development stage. The importance of nanomedicine has been recognised for some time now, but it has only very recently begun to make a transition from the academic world into the clinic via the key players within the pharmaceutical industry. And the recent explosion in development of biologics as complex therapeutics with demanding drug delivery needs has undoubtedly boosted the progress in this area. PEGylation is a key formulation ‘trick’ in nanomedicine, helping to achieve the ‘magic bullet’ potential of nanomedicines as therapeutics fit for an aging population in a climate of increasing strains on healthcare.

Declaration of interest The authors state no conflict of interest and have received no payment in preparation of this manuscript.




Bibliography Papers of special note have been highlighted as either of interest () or of considerable interest () to readers.

12.

Davis FF. Commentary - the origin of pegnology. Adv Drug Deliv Rev 2002;54:457-8

1.

Bind Therapeutics. Available from: http://bindtherapeutics.com/newsevents/ releases/2013 0403 BINDPfizer.html [Cited 02 July 2013]

13.

Davis ME, Chen ZG, Shin DM. Nanoparticle therapeutics: an emerging treatment modality for cancer. Nat Rev Drug Discov 2008;7:771-82

2.

Etheridge ML, Campbell SA, Erdman AG, et al. The big picture on nanomedicine: the state of investigational and approved nanomedicine products. Nanomedicine 2013;9:1-14 This review publication is of interest as it presents a detailed analysis of different types of nanomedicines currently under investigation.

14.

..

3.

Maeda H, Wu J, Sawa T, et al. Tumor vascular permeability and the EPR effect in macromolecular therapeutics: a review. J Control Release 2000;65:271-84

4.

Brannon-Peppas L, Blanchette JO. Nanoparticle and targeted systems for cancer therapy. Adv Drug Deliv Rev 2004;56:1649-59

5.

6.

7.

Jain RK, Stylianopoulos T. Delivering nanomedicine to solid tumors. Nat Rev Clin Oncol 2010;7:653-64 Kamaly N, Fredman G, Subramanian M, et al. Development and in vivo efficacy of targeted polymeric inflammationresolving nanoparticles. Proc Natl Acad Sci USA 2013;110:6506-11 Radovic-Moreno AF, Lu TK, Puscasu VA, et al. Surface chargeswitching polymeric nanoparticles for bacterial cell wall-targeted delivery of antibiotics. ACS Nano 2012;6:4279-87

8.

Lammers T, Aime S, Hennink WE, et al. Theranostic nanomedicine. Acc Chem Res 2011;44:1029-38

9.

Medicines in Development: Biotechnology: Pharmaceutical Research and Manufacturers of America; 2013

10.

Vllasaliu D, Casettari L, Fowler R, et al. Absorption-promoting effects of chitosan in airway and intestinal cell lines: a comparative study. Int J Pharm 2012;430:151-60

11.

Vllasaliu D, Shubber S, Garnett M, et al. Evaluation of calcium depletion as a strategy for enhancement of mucosal absorption of macromolecules. Biochem Biophys Res Commun 2012;418:128-33

chimeras. Nat Biotechnol 2006;24:1005-15 26.

Gu F, Zhang L, Teply BA, et al. Precise engineering of targeted nanoparticles by using self-assembled biointegrated block copolymers. Proc Natl Acad Sci USA 2008;105:2586-91

Kamaly N, Xiao Z, Valencia PM, et al. Targeted polymeric therapeutic nanoparticles: design, development and clinical translation. Chem Soc Rev 2012;41:2971-3010

27.

Mackowiak SA, Schmidt A, Weiss V, et al. Targeted drug delivery in cancer cells with red-light photoactivated mesoporous silica nanoparticles. Nano Lett 2013;13:2576-83

15.

Hughes JA, Rao GA. Targeted polymers for gene delivery. Expert Opin Drug Deliv 2005;2:145-57

28.

16.

Salazar MD, Ratnam M. The folate receptor: what does it promise in tissuetargeted therapeutics? Cancer Metastasis Rev 2007;26:141-52

Sadhukha T, Wiedmann TS, Panyam J. Inhalable magnetic nanoparticles for targeted hyperthermia in lung cancer therapy. Biomaterials 2013;34:5163-71

29.

Master A, Malamas A, Solanki R, et al. A cell-targeted photodynamic nanomedicine strategy for head and neck cancers. Mol Pharm 2013;10:1988-97

30.

Wang Y, Liu P, Du J, et al. Targeted siRNA delivery by anti-HER2 antibodymodified nanoparticles of mPEGchitosan diblock copolymer. J Biomater Sci Polym Ed 2013;24:1219-32

31.

Kolhar P, Anselmo AC, Gupta V, et al. Using shape effects to target antibodycoated nanoparticles to lung and brain endothelium. Proc Natl Acad Sci USA 2013;110:10753-8

32.

Bai F, Wang C, Lu Q, et al. Nanoparticle-mediated drug delivery to tumor neovasculature to combat P-gp expressing multidrug resistant cancer. Biomaterials 2013;34:6163-74

33.

Shahin M, Soudy R, El-Sikhry H, et al. Engineered peptides for the development of actively tumor targeted liposomal carriers of doxorubicin. Cancer Lett 2013;334:284-92

34.

Koivistoinen A, Ilonen II, Punakivi K, et al. A novel peptide (Thx) homing to non-small cell lung cancer identified by ex vivo phage display. Clin Transl Oncol 2013;15:492-8

35.

Sa LT, Simmons S, Missailidis S, et al. Aptamer-based nanoparticles for cancer targeting. J Drug Target 2013;21:427-34

36.

Xiao ZY, Levy-Nissenbaum E, Alexis F, et al. Engineering of targeted nanoparticles for cancer therapy using internalizing aptamers isolated by cell-uptake selection. ACS Nano 2012;6:696-704

17.

Mehra NK, Mishra V, Jain NK. Receptor-based targeting of therapeutics. Ther Deliv 2013;4:369-94

18.

Sudimack J, Lee RJ. Targeted drug delivery via the folate receptor. Adv Drug Deliv Rev 2000;41:147-62

19.

Leamon CP, Reddy JA. Folate-targeted chemotherapy. Adv Drug Deliv Rev 2004;56:1127-41

20.

Daniels TR, Bernabeu E, Rodriguez JA, et al. The transferrin receptor and the targeted delivery of therapeutic agents against cancer. Biochim Biophys Acta 2012;1820:291-317

21.

Allen TM. Ligand-targeted therapeutics in anticancer therapy. Nat Rev Cancer 2002;2:750-63

22.

Weaver M, Laske DW. Transferrin receptor ligand-targeted toxin conjugate (Tf-CRM107) for therapy of malignant gliomas. J Neurooncol 2003;65:3-13

23.

Xu L, Pirollo KF, Tang WH, et al. Transferrin-liposome-mediated systemic p53 gene therapy in combination with radiation results in regression of human head and neck cancer xenografts. Hum Gene Ther 1999;10:2941-52

24.

25.

Cheng J, Teply BA, Sherifi I, et al. Formulation of functionalized PLGAPEG nanoparticles for in vivo targeted drug delivery. Biomaterials 2007;28:869-76 McNamara JO II, Andrechek ER, Wang Y, et al. Cell type-specific delivery of siRNAs with aptamer-siRNA


149

D. Vllasaliu et al.

37.

38.


39.

40.

41.

42.

43.

44.

45.

46.

47.

48.

49.

150

Li ZH, Liu Z, Yin ML, et al. Aptamer-capped multifunctional mesoporous strontium hydroxyapatite nanovehicle for cancer-cell-responsive drug delivery and imaging. Biomacromolecules 2012;13:4257-63 Vllasaliu D, Casettari L, Bonacucina G, et al. Folic acid conjugated chitosan nanoparticles for tumor targeting of therapeutic and imaging agents. Pharm Nanotechnol 2013;1:184-203

50.

51.

52.

Wang S, Low PS. Folate-mediated targeting of antineoplastic drugs, imaging agents, and nucleic acids to cancer cells. J Control Release 1998;53:39-48 Stella B, Arpicco S, Peracchia MT, et al. Design of folic acid-conjugated nanoparticles for drug targeting. J Pharm Sci 2000;89:1452-64 Quintana A, Raczka E, Piehler L, et al. Design and function of a dendrimerbased therapeutic nanodevice targeted to tumor cells through the folate receptor. Pharm Res 2002;19:1310-16 Saeed AO, Magnusson JP, Moradi E, et al. Modular construction of multifunctional bioresponsive celltargeted nanoparticles for gene delivery. Bioconjug Chem 2011;22:156-68 Lu Y, Low PS. Folate-mediated delivery of macromolecular anticancer therapeutic agents. Adv Drug Deliv Rev 2002;54:675-93

Park TG, Yoo HS. Folate receptor targeted biodegradable polymeric doxorubicin micelles. J Control Release 2004;96:273-83 Choi H, Sr C, Zhou R, et al. Iron oxide nanoparticles as magnetic resonance contrast agent for tumor imaging via folate receptor-targeted delivery. Acad Radiol 2004;11:996-1004 Dixit V, Van den Bossche J, Sherman DM, et al. Synthesis and grafting of thioctic acid-PEG-folate conjugates onto Au nanoparticles for selective targeting of folate receptorpositive tumor cells. Bioconjug Chem 2006;17:603-9

53.

Oyewumi MO, Mumper RJ. Influence of formulation parameters on gadolinium entrapment and tumor cell uptake using folate-coated nanoparticles. Int J Pharm 2003;251:85-97

54.

Jing XB, Lu TC, Sun J, et al. Folate-conjugated micelles and their folate-receptor-mediated endocytosis. Macromol Biosci 2009;9:1059-68

55.

56.

Kelemen LE. The role of folate receptor alpha in cancer development, progression and treatment: cause, consequence or innocent bystander? Int J Cancer 2006;119:243-50 Lam JK, Armes SP, Lewis AL, Stolnik S. Folate conjugated phosphorylcholinebased polycations for specific targeting in nucleic acids delivery. J Drug Target 2009;17:512-23

Lee D, Lockey R, Mohapatra S. Folate receptor-mediated cancer cell specific gene delivery using folic acid-conjugated oligochitosans. J Nanosci Nanotechnol 2006;6:2860-6

57.

Torchilin VP. Multifunctional nanocarriers. Adv Drug Deliv Rev 2006;58:1532-55

Low PS, Antony AC. Folate receptortargeted drugs for cancer and inflammatory diseases - Preface. Adv Drug Deliv Rev 2004;56:1055-8

58.

Yang DC, Wang F, Elliott RL, Head JF. Expression of transferrin receptor and ferritin H-chain mRNA are associated with clinical and histopathological prognostic indicators in breast cancer. Anticancer Res 2001;21:541-9

Lu Y, Sega E, Leamon CP, Low PS. Folate receptor-targeted immunotherapy of cancer: mechanism and therapeutic potential. Adv Drug Deliv Rev 2004;56:1161-76

59.

Pan D, Turner JL, Wooley KL. Folic acid-conjugated nanostructured materials designed for cancer cell targeting. Chem Commun 2003;9:2400-1 Sudimack J, Lee RJ. Targeted drug delivery via the folate receptor. Adv Drug Deliv Rev 2000;41:147-62 Xia W, Low PS. Folate-targeted therapies for cancer. J Med Chem 2010;53:6811-24

60.

Prior R, Reifenberger G, Wechsler W. Transferrin receptor expression in tumours of the human nervous system: relation to tumour type, grading and tumour growth fraction. Virchows Arch A Pathol Anat Histopathol 1990;416:491-6 Das Gupta A, Shah VI. Correlation of transferrin receptor expression with histologic grade and immunophenotype in chronic lymphocytic leukemia and


non-Hodgkin’s lymphoma. Hematol Pathol 1990;4:37-41 61.

Habeshaw JA, Lister TA, Stansfeld AG, Greaves MF. Correlation of transferrin receptor expression with histological class and outcome in non-Hodgkin lymphoma. Lancet 1983;1:498-501

62.

Kondo K, Noguchi M, Mukai K, et al. Transferrin receptor expression in adenocarcinoma of the lung as a histopathologic indicator of prognosis. Chest 1990;97:1367-71

63.

Seymour GJ, Walsh MD, Lavin MF, et al. Transferrin receptor expression by human bladder transitional cell carcinomas. Urol Res 1987;15:341-4

64.

Ciechanover A, Schwartz AL, Lodish HF. Sorting and recycling of cell surface receptors and endocytosed ligands: the asialoglycoprotein and transferrin receptors. J Cell Biochem 1983;23:107-30

65.

Fowler R, Vllasaliu D, Trillo FF, et al. Nanoparticle transport in epithelial cells: pathway switching through bioconjugation. Small 2013;9:3282-94

66.

Davis ME, Zuckerman JE, Choi CH, et al. Evidence of RNAi in humans from systemically administered siRNA via targeted nanoparticles. Nature 2010;464:1067-70

67.

Peer D, Karp JM, Hong S, et al. Nanocarriers as an emerging platform for cancer therapy. Nat Nanotechnol 2007;2:751-60

68.

Ferrari M. Cancer nanotechnology: opportunities and challenges. Nat Rev Cancer 2005;5:161-71

69.

Riehemann K, Schneider SW, Luger TA, et al. Nanomedicine--challenge and perspectives. Angew Chem Int Ed Engl 2009;48:872-97

70.

Moghimi SM, Hunter AC, Murray JC. Nanomedicine: current status and future prospects. FASEB J 2005;19:311-30

71.

Stolnik S, Illum L, Davis SS. Long circulating microparticulate drug carriers. Adv Drug Deliv Rev 1995;16:195-214

72.

Saba TM. Physiology and physiopathology of reticuloendothelial system. Arch Intern Med 1970;126:1031-52

73.

Owens DE III, Peppas NA. Opsonization, biodistribution, and pharmacokinetics of polymeric


nanoparticles. Int J Pharm 2006;307:93-102 74.

Jokerst JV, Lobovkina T, Zare RN, Gambhir SS. Nanoparticle PEGylation for imaging and therapy. Nanomedicine 2011;6:715-28

75.

Allen TM, Hansen C, Rutledge J. Liposomes with prolonged circulation times: factors affecting uptake by reticuloendothelial and other tissues. Biochim Biophys Acta 1989;981:27-35


76.

Moghimi SM, Porter CJ, Muir IS, et al. Non-phagocytic uptake of intravenously injected microspheres in rat spleen: influence of particle size and hydrophilic coating. Biochem Biophys Res Commun 1991;177:861-6

77.

Casals E, Pfaller T, Duschl A, et al. Time evolution of the nanoparticle protein corona. ACS Nano 2010;4:3623-32

78.

Ehrenberg MS, Friedman AE, Finkelstein JN, et al. The influence of protein adsorption on nanoparticle association with cultured endothelial cells. Biomaterials 2009;30:603-10

79.

.

Gref R, Luck M, Quellec P, et al. ‘Stealth’ corona-core nanoparticles surface modified by polyethylene glycol (PEG): influences of the corona (PEG chain length and surface density) and of the core composition on phagocytic uptake and plasma protein adsorption. Colloid Surf B 2000;18:301-13 The publication is of interest as it studies the influences of the PEG corona thickness and density, as well as the influence of the particle core on competitive plasma protein adsorption, surface charge and uptake by polymorphonuclear leucocytes. It shows PEG molecular weight and surface content for optimal protein resistance.

..

lose their targeting capabilities when a biomolecule corona adsorbs on the surface. Nat Nanotechnol 2013;8:137-43 This publication demonstrates that when nanoparticles are placed in a complex biological environment, its interaction with other proteins, which leads to the formation of a protein corona, can ‘screen’ the targeting molecules on the surface of nanoparticles, resulting in loss of targeting specificity.

83.

Poon Z, Lee JA, Huang S, et al. Highly stable, ligand-clustered “patchy” micelle nanocarriers for systemic tumor targeting. Nanomedicine 2011;7:201-9

84.

Poon Z, Chen S, Engler AC, et al. Ligand-clustered “patchy” nanoparticles for modulated cellular uptake and in vivo tumor targeting. Angew Chem Int Ed Engl 2010;49:7266-70

85.

Moradi E, Vllasaliu D, Garnett M, et al. Ligand density and clustering effects on endocytosis of folate modified nanoparticles. Rsc Adv 2012;2:3025-33

86.

D’Addio SM, Baldassano S, Shi L, et al. Optimization of cell receptor-specific targeting through multivalent surface decoration of polymeric nanocarriers. J Control Release 2013;168:41-9

87.

Mahmoudi M, Sant S, Wang B, et al. Superparamagnetic iron oxide nanoparticles (SPIONs): development, surface modification and applications in chemotherapy. Adv Drug Deliv Rev 2011;63:24-46

..

polymeric nanospheres. Science 1994;263:1600-3 This paper shows that PEG-coated polymeric nanospheres exhibited dramatically increased blood circulation time and reduced liver accumulation in mice compared to non-coated nanoparticles.

93.

Otsuka H, Nagasaki Y, Kataoka K. PEGylated nanoparticles for biological and pharmaceutical applications. Adv Drug Deliv Rev 2003;55:403-19

94.

Klibanov AL, Maruyama K, Torchilin VP, Huang L. Amphipathic polyethyleneglycols effectively prolong the circulation time of liposomes. FEBS Lett 1990;268:235-7

95.

Tirosh O, Barenholz Y, Katzhendler J, Priev A. Hydration of polyethylene glycol-grafted liposomes. Biophys J 1998;74:1371-9

96.

Barenholz Y. Doxil (R) - The first FDAapproved nano-drug: lessons learned. J Control Release 2012;160:117-34

97.

Immordino ML, Dosio F, Cattel L. Stealth liposomes: review of the basic science, rationale, and clinical applications, existing and potential. Int J Nanomedicine 2006;1:297-315

98.

Kumari A, Yadav SK, Yadav SC. Biodegradable polymeric nanoparticles based drug delivery systems. Colloids Surf B Biointerfaces 2010;75:1-18

99.

Malmsten M, Emoto K, Van Alstine JM. Effect of chain density on inhibition of protein adsorption by poly(ethylene glycol) based coatings. J Colloid Interface Sci 1998;202:507-17

88.

Mahmoudi M, Lynch I, Ejtehadi MR, et al. Protein-nanoparticle interactions: opportunities and challenges. Chem Rev 2011;111:5610-37

89.

Nel AE, Madler L, Velegol D, et al. Understanding biophysicochemical interactions at the nano-bio interface. Nat Mater 2009;8:543-57

100. Mosqueira VCF, Legrand P, Morgat JL, et al. Biodistribution of long-circulating PEG-grafted nanocapsules in mice: effects of PEG chain length and density. Pharm Res 2001;18:1411-19

80.

Lundqvist M, Stigler J, Elia G, et al. Nanoparticle size and surface properties determine the protein corona with possible implications for biological impacts. Proc Natl Acad Sci USA 2008;105:14265-70

90.

Cedervall T, Lynch I, Lindman S, et al. Understanding the nanoparticle-protein corona using methods to quantify exchange rates and affinities of proteins for nanoparticles. Proc Natl Acad Sci USA 2007;104:2050-5

101. Benhabbour SR, Sheardown H, Adronov A, Protein resistance of PEGfunctionalized dendronized surfaces: effect of PEG molecular weight and dendron generation. Macromolecules 2008;41:4817-23

81.

Leroux JC, Dejaeghere F, Anner B, et al. An investigation on the role of plasma and serum opsonins on the internalization of biodegradable poly(D, L-Lactic Acid) nanoparticles by human monocytes. Life Sci 1995;57:695-703

91.

Abuchowski A, van Es T, Palczuk NC, Davis FF. Alteration of immunological properties of bovine serum albumin by covalent attachment of polyethylene glycol. J Biol Chem 1977;252:3578-81

102. Zahr AS, Davis CA, Pishko MV. Macrophage uptake of core-shell nanoparticles surface modified with poly (ethylene glycol). Langmuir 2006;22:8178-85

92.

82.

Salvati A, Pitek AS, Monopoli MP, et al. Transferrin-functionalized nanoparticles

Gref R, Minamitake Y, Peracchia MT, et al. Biodegradable long-circulating

103. Damodaran VB, Fee CJ, Popat KC. Prediction of protein interaction


151

D. Vllasaliu et al.

behaviour with PEG-grafted matrices using X-ray photoelectron spectroscopy. Appl Surf Sci 2010;256:4894-901 104. Meng FH, Engbers GHM, Feijen J. Polyethylene glycol-grafted polystyrene particles. J Biomed Mater Res A 2004;70A:49-58


105. Walkey CD, Olsen JB, Guo HB, et al. Nanoparticle size and surface chemistry determine serum protein adsorption and macrophage uptake. J Am Chem Soc 2012;134:2139-47 106. Fang C, Shi B, Pei YY, et al. In vivo tumor targeting of tumor necrosis factor-alpha-loaded stealth nanoparticles: effect of MePEG molecular weight and particle size. Eur J Pharm Sci 2006;27:27-36 107. Li SD, Huang L. Nanoparticles evading the reticuloendothelial system: role of the supported bilayer. Biochim Biophys Acta 2009;1788:2259-66

115. Jung T, Kamm W, Breitenbach A, et al. Biodegradable nanoparticles for oral delivery of peptides: is there a role for polymers to affect mucosal uptake? Eur J Pharm Biopharm 2000;50:147-60 116. Morishita M, Peppas NA. Is the oral route possible for peptide and protein drug delivery? Drug Discov Today 2006;11:905-10 117. Perakslis E, Tuesca A, Lowman A. Complexation hydrogels for oral protein delivery: an in vitro assessment of the insulin transport-enhancing effects following dissolution in simulated digestive fluids. J Biomater Sci Polym Ed 2007;18:1475-90 118. Vllasaliu D, Fowler R, Garnett M, et al. Barrier characteristics of epithelial cultures modelling the airway and intestinal mucosa: a comparison. Biochem Biophys Res Commun 2011;415:579-85

108. Perry JL, Reuter KG, Kai MP, et al. PEGylated PRINT nanoparticles: the impact of PEG density on protein binding, macrophage association, biodistribution, and pharmacokinetics. Nano Lett 2012;12:5304-10 . The publication suggests that the density of PEGylation necessary to promote a long-circulating particle is dramatically lower than previously thought/reported.

119. Merkus FW, Verhoef JC, Schipper NG, Marttin E. Nasal mucociliary clearance as a factor in nasal drug delivery. Adv Drug Deliv Rev 1998;29:13-38

109. Avgoustakis K. Pegylated poly(lactide) and poly(lactide-co-glycolide) nanoparticles: preparation, properties and possible applications in drug delivery. Curr Drug Deliv 2004;1:321-33

122. Stolnik S, Shakesheff K. Formulations for delivery of therapeutic proteins. Biotechnol Lett 2009;31:1-11

110. Bhadra D, Bhadra S, Jain P, Jain NK. Pegnology: a review of PEG-ylated systems. Pharmazie 2002;57:5-29 111. Howard MD, Jay M, Dziublal TD, Lu XL. PEGylation of nanocarrier drug delivery systems: state of the art. J Biomed Nanotechnol 2008;4:133-48 112. Woodle MC. Sterically Stabilized Liposome Therapeutics. Adv Drug Deliv Rev 1995;16:249-65 113. Fowler R, Vllasaliu D, Falcone FH, et al. Uptake and transport of B-conjugated nanoparticles in airway epithelium. J Control Release 2013;172:374-81 114. Mrsny RJ. Lessons from nature: "Pathogen-Mimetic" systems for mucosal nano-medicines. Adv Drug Deliv Rev 2009;61:172-92

152

120. Lee VH. Protease inhibitors and penetration enhancers as approaches to modify peptide absorption. J Control Release 1990;13:213-23 121. Illum L. Transport of drugs from the nasal cavity to the central nervous system. Eur J Pharm Sci 2000;11:1-18

123. Bansil R, Turner BS. Mucin structure, aggregation, physiological functions and biomedical applications. Curr Opin Colloid Interface Sci 2006;11:164-70 124. Thornton DJ, Sheehan JK. From mucins to mucus: toward a more coherent understanding of this essential barrier. Proc Am Thorac Soc 2004;1:54-61 125. Lafitte G, Thuresson K, Soderman O. Mixtures of mucin and oppositely charged surfactant aggregates with varying charge density. Phase behavior, association, and dynamics. Langmuir 2005;21:7097-104 126. Albanese CT, Cardona M, Smith SD, et al. Role of intestinal mucus in transepithelial passage of bacteria across the intact ileum in vitro. Surgery 1994;116:76-82 127. Lai SK, O’Hanlon DE, Harrold S, et al. Rapid transport of large polymeric Expert Opin. Drug Deliv. (2014) 11(1)

.

nanoparticles in fresh undiluted human mucus. Proc Natl Acad Sci USA 2007;104:1482-7 This study shows that large nanoparticles, if properly coated with PEG, can rapidly penetrate physiological human mucus, thus suggesting that relatively large, PEGylated nanoparticles can be used for mucosal drug delivery.

128. Wang YY, Lai SK, Suk JS, et al. Addressing the PEG mucoadhesivity paradox to engineer nanoparticles that "slip" through the human mucus barrier. Angew Chem Int Ed Engl 2008;47:9726-9 129. Cu Y, Saltzman WM. Controlled surface modification with poly(ethylene)glycol enhances diffusion of PLGA nanoparticles in human cervical mucus. Mol Pharm 2009;6:173-81 130. Ensign LM, Henning A, Schneider CS, et al. Ex vivo characterization of particle transport in mucus secretions coating freshly excised mucosal tissues. Mol Pharm 2013;10:2176-82 131. Miyamoto M, Natsume H, Satoh I, et al. Effect of poly-L-arginine on the nasal absorption of FITC-dextran of different molecular weights and recombinant human granulocyte colonystimulating factor (rhG-CSF) in rats. Int J Pharm 2001;226:127-38 132. Tuma P, Hubbard AL. Transcytosis: crossing cellular barriers. Physiol Rev 2003;83:871-932 133. Vllasaliu D, Alexander C, Garnett M, et al. Fc-mediated transport of nanoparticles across airway epithelial cell layers. J Control Release 2012;158:479-86 134. Fowler R, Vllasaliu D, Falcone FH, et al. Uptake and transport of B-conjugated nanoparticles in airway epithelium. J Control Release 2013;172:374-81 135. Alconcel SNS, Baas AS, Maynard HD. FDA-approved poly(ethylene glycol)protein conjugate drugs. Polym Chem 2011;2:1442-8 136. Veronese FM, Harris JM. Preface introduction and overview of peptide and protein pegylation. Adv Drug Deliv Rev 2002;54:453-6 137. Veronese FM, Pasut G. PEGylation, successful approach to drug delivery. Drug Discov Today 2005;10:1451-8



138.

Roberts MJ, Bentley MD, Harris JM. Chemistry for peptide and protein PEGylation. Adv Drug Deliv Rev 2002;54:459-76

139.

Fishburn CS. The pharmacology of PEGylation: balancing PD with PK to generate novel therapeutics. J Pharm Sci 2008;97:4167-83

140.

Berkrot B. Celgene’s Abraxane increases survival in pancreatic cancer. Available from: http://www.reuters.com/article/ 2013/01/22/us-celgene-canceridUSBRE90L14O20130122 [Cited 18 July 2013]

141.

Venditto VJ, Szoka FC Jr. Cancer nanomedicines: so many papers and so few drugs!. Adv Drug Deliv Rev 2013;65:80-8

142.

Drugs@FDA. Available from: http:// www.accessdata.fda.gov/scripts/cder/ drugsatfda/index.cfm?fuseaction=Search. DrugDetails

143.

Gabizon A, Shmeeda H, Barenholz Y. Pharmacokinetics of pegylated liposomal doxorubicin - Review of animal and human studies. Clin Pharmacokinet 2003;42:419-36

144.

O’Brien MER, Wigler N, Inbar M, et al. Reduced cardiotoxicity and comparable efficacy in a phase III trial of pegylated liposomal doxorubicin HCl (CAELYX (TM)/Doxil (R)) versus conventional doxorubicin for first-line treatment of metastatic breast cancer. Ann Oncol 2004;15:440-9

145.

Symon Z, Peyser A, Tzemach D, et al. Selective delivery of doxorubicin to patients with breast carcinoma metastases by stealth liposomes. Cancer 1999;86:72-8

149.

Reddy LH, Couvreur P. Nanotechnology for therapy and imaging of liver diseases. J Hepatol 2011;55:1461-6

150.

Service RF. Nanotechnology. Nanoparticle Trojan horses gallop from the lab into the clinic. Science 2010;330:314-15

151.

152.

Kim HR, Andrieux K, Gil S, et al. Translocation of poly(ethylene glycol-cohexadecyl)cyanoacrylate nanoparticles into rat brain endothelial cells: role of apolipoproteins in receptor-mediated endocytosis. Biomacromolecules 2007;8:793-9 Peracchia MT, Harnisch S, Pinto-Alphandary H, et al. Visualization of in vitro protein-rejecting properties of PEGylated stealth polycyanoacrylate nanoparticles. Biomaterials 1999;20:1269-75

161. Karakoti AS, Das S, Thevuthasan S, Seal S. PEGylated inorganic nanoparticles. Angew Chem Int Ed 2011;50:1980-94 162. Hong RL, Huang CJ, Tseng YL, et al. Direct comparison of liposomal doxorubicin with or without polyethylene glycol coating in C-26 tumor-bearing mice: is surface coating with polyethylene glycol beneficial? Clin Cancer Res 1999;5:3645-52 163. Amoozgar Z, Yeo Y. Recent advances in stealth coating of nanoparticle drug delivery systems. Wiley Interdiscip Rev Nanomed Nanobiotechnol 2012;4:219-33

Brambilla D, Verpillot R, Le Droumaguet B, et al. PEGylated nanoparticles bind to and alter amyloidbeta peptide conformation: toward engineering of functional nanomedicines for Alzheimer’s disease. ACS Nano 2012;6:5897-908

164. Zalipsky S, Qazen M, Walker JA II, et al. New detachable poly(ethylene glycol) conjugates: cysteine-cleavable lipopolymers regenerating natural phospholipid, diacyl phosphatidylethanolamine. Bioconjug Chem 1999;10:703-7

154.

Talelli M, Rijcken CJF, van Nostrum CF, et al. Micelles based on HPMA copolymers. Adv Drug Deliv Rev 2010;62:231-9

155.

Lee KS, Chung HC, Im SA, et al. Multicenter phase II trial of GenexolPM, a Cremophor-free, polymeric micelle formulation of paclitaxel, in patients with metastatic breast cancer. Breast Cancer Res Treat 2008;108:241-50

165. Takae S, Miyata K, Oba M, et al. PEG-detachable polyplex micelles based on disulfide-linked block catiomers as bioresponsive nonviral gene vectors. J Am Chem Soc 2008;130:6001-9

156.

Available from: http:// sorrentotherapeutics.com/cynviloq/

Plosker GL. Pegylated liposomal doxorubicin a review of its use in the treatment of relapsed or refractory multiple myeloma. Drugs 2008;68:2535-51

157.

Libutti SK, Paciotti GF, Byrnes AA, et al. Phase I and pharmacokinetic studies of CYT-6091, a novel PEGylated colloidal Gold-rhTNF nanomedicine. Clin Cancer Res 2010;16:6139-49

147.

Karra N, Benita S. The ligand nanoparticle conjugation approach for targeted cancer therapy. Curr Drug Metab 2012;13:22-41

158.

Farma JM, Puhlmann M, Soriano PA, et al. Direct evidence for rapid and selective induction of tumor neovascular permeability by tumor necrosis factor and a novel derivative, colloidal gold bound tumor necrosis factor. Int J Cancer 2007;120:2474-80

Hrkach J, Von Hoff D, Mukkaram Ali M, et al. Preclinical development and clinical translation of a PSMA-targeted docetaxel nanoparticle with a differentiated pharmacological profile. Sci Transl Med 2012;4:128ra39

160. Available from: http://www.cytimmune. com/go.cfm?do=page.view&pid=26

153.

146.

148.

discussing their potential and limitations.

159.

.

Duncan R, Gaspar R. Nanomedicine(s) under the microscope. Mol Pharm 2011;8:2101-41 This is a very comprehensive and informative review of nanomedicines,


166. Moghimi SM, Hamad I, Andresen TL, et al. Methylation of the phosphate oxygen moiety of phospholipid-methoxy (polyethylene glycol) conjugate prevents PEGylated liposome-mediated complement activation and anaphylatoxin production. Faseb J 2006;20:2591-3 167. Hamad I, Hunter AC, Szebeni J, Moghimi SM. Poly(ethylene glycol)s generate complement activation products in human serum through increased alternative pathway turnover and a MASP-2-dependent process. Mol Immunol 2008;46:225-32 168. Ishida T, Ichihara M, Wang X, et al. Injection of PEGylated liposomes in rats elicits PEG-specific IgM, which is responsible for rapid elimination of a second dose of PEGylated liposomes. J Control Release 2006;112:15-25 . The publication is of interest as it demonstrates the occurrence of unexpected immune reactions on intravenous administration of PEGylated liposomes.

153

D. Vllasaliu et al.


169. Ishida T, Masuda K, Ichikawa T, et al. Accelerated clearance of a second injection of PEGylated liposomes in mice. Int J Pharm 2003;255:167-74

therapies in the management of advanced breast cancer. Semin Oncol 2004;31:106-46

170. Ishida T, Maeda R, Ichihara M, et al. Accelerated clearance of PEGylated liposomes in rats after repeated injections. J Control Release 2003;88:35-42

175. Jager E, Jager A, Etrych T, et al. Self-assembly of biodegradable copolyester and reactive HPMA-based polymers into nanoparticles as an alternative stealth drug delivery system. Soft Mater 2012;8:9563-75

171. Dams ET, Laverman P, Oyen WJ, et al. Accelerated blood clearance and altered biodistribution of repeated injections of sterically stabilized liposomes. J Pharmacol Exp Ther 2000;292:1071-9

176. Hu CM, Zhang L, Aryal S, et al. Erythrocyte membrane-camouflaged polymeric nanoparticles as a biomimetic delivery platform. Proc Natl Acad Sci USA 2011;108:10980-5

172. Webster R, Didier E, Harris P, et al. PEGylated proteins: evaluation of their safety in the absence of definitive metabolism studies. Drug Metab Dispos 2007;35:9-16

177. Rodriguez PL, Harada T, Christian DA, et al. Minimal "Self" peptides that inhibit phagocytic clearance and enhance delivery of nanoparticles. Science 2013;339:971-5 . This publication shows a non-PEG alternative for protecting nanoparticles from the immune system. A synthetic ‘self’ peptide attached to nanoparticles acts like a passport, preventing particle uptake by macrophage cells.

173. Markovsky E, Baabur-Cohen H, Eldar-Boock A, et al. Administration, distribution, metabolism and elimination of polymer therapeutics. J Control Release 2012;161:446-60 174. Robert NJ, Vogel CL, Henderson IC, et al. The role of the liposomal anthracyclines and other systemic

154

178. Medicines in Development Biotechnology 2011 report. Available


from: http://www.phrma.org/sites/ default/files/pdf/biotech2011.pdf 179. Hubbell JA, Thomas SN, Swartz MA. Materials engineering for immunomodulation. Nature 2009;462:449-60

Affiliation

Driton Vllasaliu†1 PhD, Robyn Fowler2 PhD & Snow Stolnik3 PhD † Author for correspondence 1 Senior Lecturer in Drug Delivery, University of Lincoln, School of Pharmacy, MHT Building MC3111, Brayford Pool, Lincoln, LN6 7TS, UK Tel: +44 152 283 7657; Fax: +44 152 288 6974; E-mail: [email protected] 2 Analyst (Market Access), GfK Bridgehead Limited, Pera Innovation Park, Nottingham Road, Melton Mowbray, LE13 0PB, UK 3 Associate Professor, University of Nottingham, School of Pharmacy, Division of Drug Delivery and Tissue Engineering, Boots Science Building, University Park, Nottingham, NG7 2RD, UK

High drug-loading nanomedicines: progress, current status, and prospects.

Noninvasive Imaging of Nanomedicines and Nanotheranostics: Principles, Progress, and Prospects.

The Cardio-PadTM project: progress and remaining challenges.

Serotonin antagonist antiemetics: progress and concerns.

Oncolytic viruses as immunotherapy: progress and remaining challenges.

Mammalian gonocyte and spermatogonia differentiation: recent advances and remaining challenges.

Recent progress in autophagy.

Conditional internalization of PEGylated nanomedicines by PEG engagers for triple negative breast cancer therapy.

Stronger Brønsted Acids: Recent Progress.

Recent progress in osteocyte research.

Recent progress in intestinal transplantation.

Alkaline phosphatase isozymes: recent progress.

Progress and Design Concerns of Nanostructured Solar Energy Harvesting Devices.

Recent progress in cancer therapeutics.

Recent progress in schizophrenia research.

Prescription-event monitoring: methodology and recent progress.

Recent progress in transdermal sonophoresis.

Recent progress in osteoarthritis research.

Recent Progress of Microfluidics in Translational Applications.

Recent Progress in Presolar Grain Studies.

Animal models of scleroderma: recent progress.

Recent progress in perceptual learning research.

Recent progress in hemorrhagic moyamoya disease.

Recent progress in Glinus oppositifolius research.