Stealth properties to improve therapeutic efficacy of drug nanocarriers

Zwitterionic nanoparticles constructed from bioreducible RAFT-ROP double head agent for shell shedding triggered intracellular drug delivery

Nanomedicines have emerged as indispensable platforms for cancer theranostics, however, the therapeutic outcomes were often compromised not only by the multiple biological barriers during the itinerary from the initial injection site to the intracellular action site but also the insufficient drug release at the pathological site. Herein, novel bioreducible double head agent, combining reversible addition-fragmentation chain transfer agent and ring opening polymerization initiator through disulfide linkage, was firstly prepared. Well-defined cRGDfK-polycarboxybetaine methacrylate-SS-polycaprolactone block copolymers (termed as cRGD-PCSSL) were facilely synthesized using this initiator. Subsequently, shell sheddable and drug-encapsulated zwitterionic nanoparticles were constructed by one-step self-assembly with doxorubicin (DOX) (termed as cRGD-PCSSL/DOX NPs). The reduction-responsive shedding of PCB shells resulted in the rapid loss of cRGD-PCSSL/DOX NPs stability in the presence of glutathione, facilitating the rapid DOX release. Results of flow cytometry and fluorescence microscopy demonstrated that cRGD-PCSSL/DOX NPs could be internalized by HepG2 cells via receptor-mediated endocytosis with fast intracellular drug release, leading to considerable cytotoxicity in comparison with free DOX. Importantly, the low protein adsorption and excellent serum stability properties of cRGD-PCSSL/DOX NPs translated into prolonged systemic circulation and enhanced tumor accumulation. Furthermore, intravenous injection of cRGD-PCSSL/DOX NPs in tumor-bearing mice exhibited significantly higher antitumor efficiency and lower systemic toxicity compared to free DOX. Consequently, the novel zwitterionic NPs, which facilely overcome the dilemma between multifunctionality and complexity by programmatically circumventing the multiple biological barriers, would represent a promising platform for enhanced anticancer drug delivery.

STATEMENT OF SIGNIFICANCE

Herein, novel bioreducible RAFT and ROP double-head agent was first reported for the synthesis of cRGDfK-polycarboxybetaine methacrylate-SS-polycaprolactone zwitterionic block copolymers (cRGD-PCB-SS-PCL, termed as cRGD-PCSSL) through controllable polymerization methods. Firstly, this synthetic route surmounted the major disadvantage of most current used methods, which required thiol exchange reaction between active disulfide bond and free thiol groups at the chain ends. Secondly, the prepared cRGD-PCSSL/DOX NPs reasonably integrated cRGD for active tumor targeting and receptor-mediated endocytosis, zwitterionic PCB with nonfouling property for prolonged systemic circulation, disulfide linkage for reduction-responsive drug release, biodegradable PCL for hydrophobic anticancer drug loading. Finally, the systematic evaluation fully verified that the in vitro optimized cRGD-PCSSL/DOX NPs translated into significantly better therapeutic efficiency with reduced side effects in vivo.

A pH-sensitive stearoyl-PEG-poly(methacryloyl sulfadimethoxine)-decorated liposome system for protein delivery: An application for bladder cancer treatment

Stealth pH-responsive liposomes for the delivery of therapeutic proteins to the bladder epithelium were prepared using methoxy-poly(ethylene glycol)5kDa-1,2-distearoyl-sn-glycero-3-phosphoethanolamine (mPEG5kDa-DSPE) and stearoyl-poly(ethylene glycol)-poly(methacryloyl sulfadimethoxine) copolymer (stearoyl-PEG-polySDM), which possesses an apparent pKa of 7.2. Liposomes of 0.2:0.6:100, 0.5:1.5:100 and 1:3:100 mPEG5kDa-DSPE/stearoyl-PEG-polySDM/(soybean phosphatidylcholine+cholesterol) molar ratios were loaded with bovine serum albumin (BSA) as a protein model. The loading capacity was 1.3% w/w BSA/lipid. At pH7.4, all liposome formulations displayed a negative zeta-potential and were stable for several days. By pH decrease or addition to mouse urine, the zeta potential strongly decreased, and the liposomes underwent a rapid size increase and aggregation. Photon correlation spectroscopy (PCS) and transmission electron microscopy (TEM) analyses showed that the extent of the aggregation depended on the stearoyl-PEG-polySDM/lipid molar ratio. Cytofluorimetric analysis and confocal microscopy showed that at pH6.5, the incubation of MB49 mouse bladder cancer cells and macrophages with fluorescein isothiocyanate-labelled-BSA (FITC-BSA) loaded and N-(Lissamine Rhodamine B sulfonyl)-1, 2-dihexadecanoyl-sn-glycero-3-phosphoethanolamine triethylammonium salt (rhodamine-DHPE) labelled 1:3:100 mPEG5kDa-DSPE/stearoyl-PEG-polySDM/lipid molar ratio liposomes resulted in a time-dependent liposome association with the cells. At pH7.4, the association of BSA-loaded liposomes with the MB49 cells and macrophages was remarkably lower than at pH6.5. Confocal images of bladder sections revealed that 2h after the instillation, liposomes at pH7.4 and control non-responsive liposomes at pH7.4 or 6.5 did not associate nor delivered FITC-BSA to the bladder epithelium. On the contrary, the pH-responsive liposome formulation set at pH6.5 and soon administered to mice by bladder instillation showed that, 2h after administration, the pH-responsive liposomes efficiently delivered the loaded FITC-BSA to the bladder epithelium.

Probing adsorption of DSPE-PEG2000 and DSPE-PEG5000 to the surface of felodipine and griseofulvin nanocrystals

Nanosized formulations of poorly water-soluble drugs show great potential due to improved bioavailability. In order to retain colloidal stability, the nanocrystals need to be stabilized. Here we explore the use of the poly(ethylene glycol) (PEG) conjugated phospholipids DSPE-PEG2000 and DSPE-PEG5000 as stabilizers of felodipine and griseofulvin nanocrystals. Nanocrystal stability and physicochemical properties were examined and the interaction between the PEGylated lipids and the nanocrystal surface as well as a macroscopic model surface was investigated. Using quartz crystal microbalance with dissipation monitoring both mass adsorption and the thickness of the adsorbed layer were estimated. The results indicate that the PEGylated lipids are adsorbed as flat layers of around 1-3nm, and that DSPE-PEG5000 forms a thicker layer compared with DSPE-PEG2000. In addition, the mass adsorption to the drug crystals and the model surface are seemingly comparable. Furthermore, both DSPE-PEG2000 and DSPE-PEG5000 rendered stable drug nanocrystals, with a somewhat higher surface binding and stability seen for DSPE-PEG2000. These results suggest DSPE-PEG2000 and DSPE-PEG5000 as efficient nanocrystal stabilizers, with DSPE-PEG2000 giving a somewhat higher surface coverage and superior colloidal stability, whereas DSPE-PEG5000 shows a more extended structure that may have advantages for prolongation of circulation time in vivo and facilitation for targeting modifications.

Receptor-targeted drug delivery: current perspective and challenges

Receptor-targeted drug delivery has been extensively explored for active targeting. However, the scarce clinical applications of such delivery systems highlight the implicit hurdles in development of such systems. These hurdles begin with lack of knowledge of differential expression of receptors, their accessibility and identification of newer receptors. Similarly, ligand-specific challenges range from proper choice of ligand and conjugation chemistry, to release of drug/delivery system from ligand. Finally, nanocarrier systems, which offer improved loading, biocompatibility and reduced premature degradation, also face multiple challenges. This review focuses on understanding these challenges, and means to overcome such challenges to develop efficient, targeted drug-delivery systems.

Micelle Mixtures for Coadministration of Gemcitabine and GDC-0449 To Treat Pancreatic Cancer

Hedgehog (Hh) signaling plays an important role in the development and metastasis of pancreatic ductal adenocarcinoma (PDAC). Although gemcitabine (GEM) has been used as a first-line therapy for PDAC, its rapid metabolism and short plasma half-life restrict its use as a single chemotherapy. Combination therapy with more than one drug is a promising approach for treating cancer. Herein, we report the use of methoxy poly(ethylene glycol)-block-poly(2-methyl-2-carboxyl-propylene carbonate)-graft-dodecanol (mPEG-b-PCC-g-DC) copolymer for conjugating GEM and encapsulating a Hh inhibitor, vismodegib (GDC-0449), into its hydrophobic core for treating PDAC. Our objective was to determine whether the micelle mixtures of these two drugs could show better response in inhibiting Hh signaling pathway and restraining the proliferation and metastasis of pancreatic cancer. The in vivo stability of GEM significantly increased after conjugation, which resulted in its increased antitumor efficacy. Almost 80% of encapsulated GDC-0449 and 19% conjugated GEM were released in vitro at pH 5.5 in 48 h in a sustained manner. The invasion, migration, and colony forming features of MIA PaCa-2 cells were significantly inhibited by micelle mixture carrying GEM and GDC-0449. Remarkable increase in PARP cleavage and Bax proved increased apoptosis by this combination formulation compared to individual micelles. This combination therapy efficiently inhibited tumor growth, increased apoptosis, reduced Hh ligands PTCH-1 and Gli-1, and lowered EMT-activator ZEB-1 when injected to athymic nude mice bearing subcutaneous tumor generated using MIA PaCa-2 cells compared to monotherapy as observed from immunohistochemical analysis. In conclusion, micelle mixtures carrying GEM and GDC-0449 have the potential to treat pancreatic cancer.

Enhanced uptake and transport of PLGA-modified nanoparticles in cervical cancer

BACKGROUND

Uncoordinated cellular proliferation and dysregulated angiogenesis in solid tumors are coupled with inadequate tissue, blood, and lymphatic vascularization. Consequently, tumors are often characterized by hypoxic regions with limited access to vascular-borne substances. In particular, systemically administered nanoparticles (NPs) targeting tumor cells and relying on vascular access to reach tumor tissue can suffer from limited therapeutic efficacy due to inhomogeneous intra-tumor distribution and insufficient cellular internalization of NPs. To circumvent these challenges, NP surfaces can be modified to facilitate tumor interstitial transport and cellular uptake.

RESULTS

We create poly(lactic-co-glycolic) acid NPs modified with MPG, polyethylene glycol (PEG), MPG/PEG, and Vimentin (VIM), and evaluate their cellular uptake in 2D (monolayer) cell culture of human cervical carcinoma (HeLa). We compare NP performance by evaluating uptake by non-cancerous vaginal (VK2) cells. We further assess NP interstitial transport in hypo-vascularized lesions by evaluating the effect of the various modifications on NP penetration in 3D cell culture of the HeLa cells. Results show that after 24 h incubation with HeLa cells in monolayer, MPG, MPG/PEG, PEG, and VIM NPs were internalized at 66×, 24×, 30×, and 15× that of unmodified NPs, respectively. In contrast, incubation with VK2 cells in monolayer showed that MPG , MPG/PEG , PEG , and VIM NPs internalized at 6.3×, 4.3×, 12.4×, and 3.0× that of unmodified NPs, respectively. Uptake was significantly enhanced in tumorigenic vs. normal cells, with internalization of MPG NPs by HeLa cells being twice that of PEG NPs by VK2 cells. After 24 h incubation in HeLa 3D cell culture, MPG and MPG/PEGNPs were internalized 2× and 3× compared to PEG and VIM NPs, respectively. Whereas MPG NPs were internalized mostly in the cell culture periphery (1.2×, 1.4×, and 2.7× that of PEG, MPG/PEG, and VIM NPs, respectively), PEG NPs at 250 μm penetrated 2× farther into the tissue culture than MPG NPs. For all NP types, cellular internalization was severely hindered in 3D compared to monolayer.

CONCLUSIONS

Although MPG surface modification enhances internalization and uptake in hypo-vascularized cervical tissue culture, coating with PEG reduces this internalization while enhancing penetration. A delivery strategy combining NPs with either modification may balance cellular internalization vs. tissue penetration in hypo-vascularized cervical cancer lesions.

iRGD decorated lipid-polymer hybrid nanoparticles for targeted co-delivery of doxorubicin and sorafenib to enhance anti-hepatocellular carcinoma efficacy

The combination of doxorubicin (DOX) with sorafenib (SOR) has proven an effective strategy to enhance anti-hepatocellular carcinoma (HCC) efficacy. However, respective in vivo pharmacokinetic profiles and different endocytosis capacities of these two drugs greatly hinder their current application. Herein, the tumor-targeting peptide iRGD decorated lipid-polymer hybrid nanoparticles (NPs) with a shell-core structure were developed for co-delivery of DOX and SOR (DOX+SOR/iRGD NPs). After the drug ratio was optimized, the stabilized DOX+SOR/iRGD NPs were prepared. Through the iRGD-integrin recognition, DOX+SOR/iRGD NPs showed synergistic cytotoxicity, pro-apoptotic ability and enhanced internalization rate in human liver cancer HepG2 cells. In vivo pharmacokinetic result demonstrated that an extended circulation and bioavailability of DOX+SOR/iRGD NPs than free drugs. More importantly, DOX+SOR/iRGD NPs significantly enhanced antitumor efficiency in HCC xenograft mouse models. Overall, this study describes a promising nanoparticulate drug co-delivery strategy to combine clinical anticancer drugs and enhance anti-HCC efficacy.

Current development of targeted oligonucleotide-based cancer therapies: Perspective on HER2-positive breast cancer treatment

This Review discusses the various types of non-coding oligonucleotides, which have garnered extensive interest as new alternatives for targeted cancer therapies over small molecule inhibitors and monoclonal antibodies. These oligonucleotides can target any hallmark of cancer, no longer limited to so-called "druggable" targets. Thus, any identified gene that plays a key role in cancer progression or drug resistance can be exploited with oligonucleotides. Among them, small-interfering RNAs (siRNAs) are frequently utilized for gene silencing due to the robust and well established mechanism of RNA interference. Despite promising advantages, clinical translation of siRNAs is hindered by the lack of effective delivery platforms. This Review provides general criteria and consideration of nanoparticle development for systemic siRNA delivery. Different classes of nanoparticle candidates for siRNA delivery are discussed, and the progress in clinical trials for systemic cancer treatment is reviewed. Lastly, this Review presents HER2 (human epidermal growth factor receptor type 2)-positive breast cancer as one example that could benefit significantly from siRNA technology. How siRNA-based therapeutics can overcome cancer resistance to such therapies is discussed.

A peptide-lipid nanoparticle assembly platform with integrated functions for targeted cell delivery

Liposomes are extensively used as drug carriers because of their biocompatibility, low toxicity, and controlled release properties, however challenges exist in the control of their particle size, surface properties and targeting functionality. In this work, we report a peptide-lipid nanoparticle platform that can achieve nanoparticle formation, surface functionalization and hydrophobic drug loading in an integrated assembly process. A designer peptide that harbors bivalent amphipathic α-helices linked by a central loop (ALA peptide) was used to encapsulate lipid nanoparticles (LNPs). The bivalency design affords higher peptide helicity and lipid-packaging efficiency, and allows encapsulated hydrophobic molecules for more stability under long-term storage. The central loop structure displays sufficient surface exposure as demonstrated by the interaction between penta-histidine installed LNPs and Ni-NTA agarose. RGD-inserted and cytotoxic iridium complex-encapsulated LNPs showed preferential entry and selective cytotoxicity to integrin high expression cancer cells, while showing reduced toxicity to non-cancer cells. Further study indicates that a constrained cyclic conformation of RGD is required to fully exert targeting capability, suggesting an intact structural exposure on the LNP surface. In summary, we demonstrate a simple yet effective method of peptide-based LNP surface modification with potential for various targeted deliveries of hydrophobic drugs.

Challenges in preclinical to clinical translation for anticancer carrier-mediated agents

Major advances in carrier-mediated agents (CMAs), which include nanoparticles and conjugates, have revolutionized drug delivery capabilities over the past decade. While providing numerous advantages over their small-molecule counterparts, there is substantial variability in how individual CMA formulations and patient characteristics affect the pharmacology, pharmacokinetics (PK), and pharmacodynamics (PD) (efficacy and toxicity) of these agents. Development or selection of animal models is used to predict the effects within a particular human disease. A breadth of studies have begun to emphasize the importance of preclinical animal models in understanding and evaluating the interaction between CMAs and the immune system and tumor matrix, which ultimately influences CMA PK (clearance and distribution) and PD (efficacy and toxicity). It is fundamental to study representative preclinical tumor models that recapitulate patients with diseases (e.g., cancer) and evaluate the interplay between CMAs and the immune system, including the mononuclear phagocyte system (MPS), chemokines, hormones, and other immune modulators. Furthermore, standard allometric scaling using body weight does not accurately predict drug clearance in humans. Future studies are warranted to better understand the complex pharmacology and interaction of CMA carriers within individual preclinical models and their biological systems, such as the MPS and tumor microenvironment, and their application to allometric scaling across species. WIREs Nanomed Nanobiotechnol 2016, 8:642-653. doi: 10.1002/wnan.1394 For further resources related to this article, please visit the WIREs website.

Zwitterionic-Modified Starch-Based Stealth Micelles for Prolonging Circulation Time and Reducing Macrophage Response

Over the last few decades, nanoparticles have been emerging as useful means to improve the therapeutic efficacy of drug delivery and medical diagnoses. However, the heterogeneity and complexity of blood as a medium is a fundamental problem; large amounts of protein can be adsorbed onto the surface of nanoparticles and cause their rapid clearance before reaching their target sites, resulting in the failure of drug delivery. To overcome this challenge, we present a rationally designed starch derivative (SB-ST-OC) with both a superhydrophilic moiety of zwitterionic sulfobetaine (SB) and a hydrophobic segment of octane (OC) as functional groups, which can self-assemble into "stealth" micelles (SSO micelles). The superhydrophilic SB kept the micelles stable against aggregation in complex media and imbued them with "stealth" properties, eventually extending their circulation time in blood. In stability and hemolysis tests the SSO micelles showed excellent protein resistance properties and hemocompatibility. Moreover, a phagocytosis test and cytokine secretion assay confirmed that the SSO micelles had less potential to trigger the activation of macrophages and were more suitable as a drug delivery candidate in vivo. On the basis of these results, doxorubicin (DOX), a hydrophobic drug, was used to investigate the potential application of this novel starch derivative in vivo. The results of the pharmacokinetic study showed that the values of the plasma area under the concentration curve (AUC) and elimination half-life (T1/2) of the SSO micelles were higher than those of micelles without SB modifications. In conclusion, the combination of excellent protein resistance, lower macrophage activation, and longer circulation time in vivo makes this synthesized novel starch derivative a promising candidate as a hydrophobic drug carrier for long-term circulation in vivo.

Nanomedicine concepts in the general medical curriculum: initiating a discussion

Various applications of nanoscale science to the field of medicine have resulted in the ongoing development of the subfield of nanomedicine. Within the past several years, there has been a concurrent proliferation of academic journals, textbooks, and other professional literature addressing fundamental basic science research and seminal clinical developments in nanomedicine. Additionally, there is now broad consensus among medical researchers and practitioners that along with personalized medicine and regenerative medicine, nanomedicine is likely to revolutionize our definitions of what constitutes human disease and its treatment. In light of these developments, incorporation of key nanomedicine concepts into the general medical curriculum ought to be considered. Here, I offer for consideration five key nanomedicine concepts, along with suggestions regarding the manner in which they might be incorporated effectively into the general medical curriculum. Related curricular issues and implications for medical education also are presented.

Addressing challenges of heterogeneous tumor treatment through bispecific protein-mediated pretargeted drug delivery

Tumors are frequently characterized by genomically and phenotypically distinct cancer cell subpopulations within the same tumor or between tumor lesions, a phenomenon termed tumor heterogeneity. These diverse cancer cell populations pose a major challenge to targeted delivery of diagnostic and/or therapeutic agents, as the conventional approach of conjugating individual ligands to nanoparticles is often unable to facilitate intracellular delivery to the full spectrum of cancer cells present in a given tumor lesion or patient. As a result, many cancers are only partially suppressed, leading to eventual tumor regrowth and/or the development of drug-resistant tumors. Pretargeting (multistep targeting) approaches involving the administration of 1) a cocktail of bispecific proteins that can collectively bind to the entirety of a mixed tumor population followed by 2) nanoparticles containing therapeutic and/or diagnostic agents that can bind to the bispecific proteins accumulated on the surface of target cells offer the potential to overcome many of the challenges associated with drug delivery to heterogeneous tumors. Despite its considerable success in improving the efficacy of radioimmunotherapy, the pretargeting strategy remains underexplored for a majority of nanoparticle therapeutic applications, especially for targeted delivery to heterogeneous tumors. In this review, we will present concepts in tumor heterogeneity, the shortcomings of conventional targeted systems, lessons learned from pretargeted radioimmunotherapy, and important considerations for harnessing the pretargeting strategy to improve nanoparticle delivery to heterogeneous tumors.

Zwitterionic Amphiphilic Homopolymer Assemblies

Zwitterionic amphiphilic homopolymers can be conveniently prepared in one-pot using activated ester-based polymer precursors. We show that these zwitterionic polymers can (i) spontaneously self-assemble to form micelle-like and inverse micelle-like assemblies depending on the solvent environment; (ii) act as hydrophilic and hydrophobic nanocontainers in apolar and polar solvents respectively; (iii) undergo pH-responsive surface charge and size variations; (iv) exhibit least cytotoxicity compared to structurally analogous amphiphilic homopolymers.

NaCl-triggered self-assembly of hydrophilic poloxamine block copolymers

Tetronic 1307 (T1307) is a hydrophilic poloxamine (HLB>24) with a high molecular mass owing to its long PEO and PPO blocks. In spite of good biocompatibility, its use as a component of drug delivery systems is limited by its high critical micelle concentration (CMC) and temperature (CMT). The aim of this work was to elucidate whether the addition of NaCl or the combination of salts and temperature may bring T1307 micellization and gelling features into more practically useful values. Increasing NaCl concentration in the 0.154 M (isotonic) to 2M (hypertonic) range made the copolymer more hydrophobic and more prone to self-assemble into unimodal micelles, as observed by means of π-A isotherms, (1)H NMR, dynamic light scattering (DLS), small-angle neutron scattering (SANS), and pyrene fluorescence. The decrease in CMC and CMT observed for T1307 in 0.5 M NaCl medium (tolerable hypertonic solution), compared to water, notably favored the solubility of hydrophobic drugs such as curcumin and quercetin. Moreover, phase diagram, intrinsic viscosity and sol-to-gel transition were markedly affected by NaCl concentration. Overall, the strong dependence of T1307 self-assembly features on NaCl opens interesting possibilities for tuning the performance of T1307 as a component of nanocarriers and in situ gelling systems.

Formulation and physiologic factors affecting the pharmacology of carrier-mediated anticancer agents

INTRODUCTION

Major advances in carrier-mediated agents (CMAs), which include nanoparticles and conjugates, have revolutionized drug delivery capabilities over the past decade. While providing numerous advantages such as increased exposure duration, greater solubility and delivery to tumor sites over their small molecule counterparts, there is substantial variability in how individual CMA formulations affect the pharmacology, pharmacokinetics and pharmacodynamics (efficacy and toxicity) of these agents.

AREAS COVERED

CMA formulations are complex in nature compared to their small molecule counterparts and consist of multiple components and variables that can affect the pharmacological profile. This review provides an overview of factors that affect the pharmacologic profiles observed in CMA-formulated chemotherapy, primarily in liposomal formulations, that are currently in preclinical or early clinical development.

EXPERT OPINION

Despite the numerous advantages that CMA formulations provide, their clinical use is still in its infancy. It is critical that we understand the mechanisms and effects of CMAs in navigating biological barriers and how these factors affect their biodistribution and delivery to tumors. Future studies are warranted to better understand the complex pharmacology and interaction between CMA carriers and biological systems, such as the mononuclear phagocyte system and tumor microenvironment.

Development of nanotoxicology: implications for drug delivery and medical devices

Current nanotoxicology research suffers from suboptimal in vitro models, lack of in vitro–in vivo correlations, variability within in vitro protocols, deficits in both material purity and physicochemical characterization. Reliable nanomaterial toxicity and mechanistic insights are required for health and toxicity risk assessments. Much in vitro toxicological data is inconclusive in designating whether nanomaterials for drug delivery and medical device implants are truly safe. A critique is presented to analyze the interface between toxicology and nanopharmaceuticals. Deficiencies of existing practices in toxicology are reviewed and useful emerging techniques (e.g., lab-on-a-chip, tissue engineering, atomic force microscopy, high-content analysis) are highlighted. Cross-fertilization between disciplines will aid development of biocompatible delivery and implant platforms while improvements are being suggested for better translation of nanotoxicology.

Therapeutic and safety considerations of nanoparticle-mediated drug delivery in pregnancy

Advances in nanotechnology have resulted in the design of effective, safe and tissue-selective nanocarriers for delivering therapeutics to treat malignancies, infections and other diseases. In pregnancy, nanoparticle-based drug formulations could have the potential to selectively target either the placenta and/or fetus, enabling ‘fetal-friendly’ drugs to be administered in pregnancy with minimal risk of off-target effects. A considerable amount of research has been carried out on maternal-placental-fetal nanoparticle uptake, transfer and toxicity using rodent and ex vivo models. However, the development of placental targeting strategies and the therapeutic evaluation of nanoformulations in pregnancy remains in its infancy. While some promising avenues are currently under investigation, much work is needed to bring the advantages of nanoparticle-based drug therapy in pregnancy to clinical reality.

S-layer fusion protein as a tool functionalizing emulsomes and CurcuEmulsomes for antibody binding and targeting

Selective targeting of tumor cells by nanoparticle-based drug delivery systems is highly desirable because it maximizes the drug concentration at the desired target while simultaneously protecting the surrounding healthy tissues. Here, we show a design for smart nanocarriers based on a biomimetic approach that utilizes the building principle of virus envelope structures. Emulsomes and CurcuEmulsomes comprising a tripalmitin solid core surrounded by phospholipid layers are modified by S-layer proteins that self-assemble into a two-dimensional array to form a surface layer. One significant advantage of this nanoformulation is that it increases the solubility of the lipophilic anti-cancer agent curcumin in the CurcuEmulsomes by a factor of 2700. In order to make the emulsomes specific for IgG, the S-layer protein is fused with two protein G domains. This S-layer fusion protein preserves its recrystallization characteristics, forming an ordered surface layer (square lattice with 13 nm unit-by-unit distance). The GG domains are presented in a predicted orientation and exhibit a selective binding affinity for IgG.

Management of retinoblastoma: opportunities and challenges

Nano-delivery systems have significantly evolved over the last decade for the treatment of cancer by enabling site-specific delivery and improved bioavailability. The widely investigated nanoparticle systems are biodegradable polyesters, dendrimers, liposomes, mesoporous silica and gold nanoparticles. These particles when conjugated with different targeting motifs enhance the therapeutic efficiency of the drug molecules and biocompatibility. However, the application of such systems towards the treatment of retinoblastoma (RB), a rapidly spreading childhood eye cancer, still remains in its infancy. Nanoparticle-based systems that have been investigated for RB therapy have displayed improved drug delivery to the most restricted posterior segment of the eyes and have increased intra-vitreal half-life of the chemotherapy agents highlighting its potential in treatment of this form of cancer. This review focuses on the challenges involved in the treatment of RB and highlights the attempts made to develop nano-dimensional systems for the treatment of RB.

Codelivery of small molecule hedgehog inhibitor and miRNA for treating pancreatic cancer

Successful treatment of pancreatic ductal adenocarcinoma (PDAC) remains a challenge due to the desmoplastic microenvironment that promotes both tumor growth and metastasis and forms a barrier to chemotherapy. Hedgehog (Hh) signaling is implicated in initiation and progression of PDAC and also contributes to desmoplasia. While Hh levels are increased in pancreatic cancer cells, levels of tumor suppressor miR-let7b, which targets several genes involved in PDAC pathogenesis, is downregulated. Therefore, our overall objective was to inhibit Hh pathway and restore miR-let7b simultaneously for synergistically treating PDAC. miR-let7b and Hh inhibitor GDC-0449 could inhibit the proliferation of human pancreatic cancer cells (Capan-1, HPAF-II, T3M4, and MIA PaCa-2), and there was synergistic effect when miR-let7b and GDC-0449 were coformulated into micelles using methoxy poly(ethylene glycol)-block-poly(2-methyl- 2-carboxyl-propylenecarbonate-graft-dodecanol-graft-tetraethylene-pentamine) (mPEG-b-PCC-g-DC-g-TEPA). This copolymer self-assembled into micelles of <100 nm and encapsulated hydrophobic GDC-0449 into its core with 5% w/w drug loading and allowed complex formation between miR-let7b and its cationic pendant chains. Complete polyplex formation with miRNA was observed at the N/P ratio of 16/1. Almost 80% of GDC-0449 was released from the polyplex in a sustained manner in 2 days. miRNA in the micelle formulation was stable for up to 24 h in the presence of serum and high uptake efficiency was achieved with low cytotoxicity. This combination therapy effectively inhibited tumor growth when injected to athymic nude mice bearing ectopic tumor generated using MIA PaCa-2 cells compared to micelles carrying GDC-0449 or miR-let7b alone. Immunohistochemical analysis revealed decreased tumor cell proliferation with increased apoptosis in the animals treated with miR-let7b and GDC-0449 combination.

Zwitterionic nanoparticles constructed with well-defined reduction-responsive shell and pH-sensitive core for "spatiotemporally pinpointed" drug delivery

Enabling nanocarriers to complete the sophisticated journey from the initial injection site to the targeted tumor cells and achieve "spatiotemporally pinpointed" drug release intracellularly is a challenging task in anticancer drug delivery. Herein, versatile shell-cross-linked nanoparticles (SCNPs) were prepared by one-step assembly of triblock zwitterionic copolymers, polycarboxybetaine methacrylate-block-poly(N-(2-(2-pyridyl disulde) ethyl methacrylamide-block-poly(2-(diisopropylamino) ethyl methacrylate) (PCB-b-PDS-b-PDPA, termed as PCSSD), which was well-defined via reversible additive fragment transfer (RAFT) polymerization, followed by functionalization with Arg-Gly-Asp (RGD). Thus, the RGD-PCSSD SCNPs cooperatively combine the ultra pH-sensitive PDPA core for efficient drug loading and pH-responsive drug release, the disulfide-cross-linked PDS shell that prevents premature drug release, the zwitterionic PCB corona to stabilize the SCNPs and prolong its systemic circulation, the RGD ligand for active tumor targeting and receptor-mediated endocytosis. Doxorubicin (DOX) was loaded as a model medicine (termed as RGD-PCSSD/DOX SCNPs). The dual-sensitivity studies showed that the pH-sensitivity of PDPA core could be adjusted by the shell-cross-linking density, accompanied by better control over premature drug release. Furthermore, results obtained by flow cytometry and fluorescence microscopy analysis demonstrated that once the RGD-PCSS10D/DOX SCNPs were internalized into tumor cells via receptor-mediated endocytosis, boost drug release was observed with considerable cytotoxicity in vitro. The results of ex vivo imaging studies further confirmed the successful drug delivery from the injection site to the tumor tissue. In summary, the well-constructed RGD-PCSS10D/DOX SCNPs with cooperative multifunctionality showed great potential as novel nanocarriers for tumor targeted anticancer drug delivery.

pH-sensitive stearoyl-PEG-poly(methacryloyl sulfadimethoxine) decorated liposomes for the delivery of gemcitabine to cancer cells

Novel, acid-sensitive liposomes that respond to physiopathological pH for tumour targeting applications were obtained by surface decoration with 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)] (mPEG-DSPE) and stearoyl-poly(ethylene glycol)-poly(methacryloyl sulfadimethoxine) copolymer (stearoyl-PEG-polySDM). The pH-sensitive stearoyl-PEG-polySDM copolymer contained an average of seven methacryloyl sulfadimethoxines per molecule and was found to possess an apparent pKa of 7.2. Preliminary cloud point studies showed that the hydrophilic/hydrophobic copolymer conversion occurred at pH 7.0. The copolymer was soluble above pH 7.0 and underwent aggregation at lower pH. Liposome formulations were prepared with 0.2:0.6:100, 0.5:1.5:100 and 1:3:100 mPEG-DSPE/stearoyl-PEG-polySDM/lipids molar ratios. All of the liposome formulations were stable at pH 7.4, even in the presence of foetal bovine serum, but they underwent rapid size increase at pH 6.5. TEM analysis showed that, at pH 6.5, the formulations coated with a stearoyl-PEG-polySDM/lipids molar ratio greater than 1:100 underwent aggregation. At pH 7.4, the liposomes showed negative zeta potential that significantly decreased after incubation at pH 6.5. Cell-culture studies indicated that the liposomes were not toxic up to 10mg/mL. Fluorescence spectroscopy, cytofluorimetry and confocal microscopy showed that at pH 6.5, the incubation of MCF-7 tumour cells with fluorescein-labelled 1:3:100 mPEG-DSPE/stearoyl-PEG-polySDM/lipids molar ratio liposomes resulted in time-dependent cell association, while at pH 7.4 the cell interaction was significantly lower. The same pH-responsive liposome formulation loaded with gemcitabine (98.2±4.7nmol gemcitabine/lipid μmol loading capacity) was stable at pH 7.4 for several hours, while at pH 6.5 it rapidly aggregated. At pH 6.5, these liposomes displayed higher cytotoxicity than at pH 7.4 or compared to non-responsive control liposomes at both incubation pH. Notably, treatment with free gemcitabine did not yield cytotoxic effects, indicating that the carrier can efficiently deliver the anticancer drug to the cytosolic compartment.

The effect of hyperbranched polyglycerol coatings on drug delivery using degradable polymer nanoparticles

A key attribute for nanoparticles (NPs) that are used in medicine is the ability to avoid rapid uptake by phagocytic cells in the liver and other tissues. Poly(ethylene glycol) (PEG) coatings has been the gold standard in this regard for several decades. Here, we examined hyperbranched polyglycerols (HPG) as an alternate coating on NPs. In earlier work, HPG was modified with amines and subsequently conjugated to poly(lactic acid) (PLA), but that approach compromised the ability of HPG to resist non-specific adsorption of biomolecules. Instead, we synthesized a copolymer of PLA-HPG by a one-step esterification. NPs were produced from a single emulsion using PLA-HPG: fluorescent dye or the anti-tumor agent camptothecin (CPT) were encapsulated at high efficiency in the NPs. PLA-HPG NPs were quantitatively compared to PLA-PEG NPs, produced using approaches that have been extensively optimized for drug delivery in humans. Despite being similar in size, drug release profile and in vitro cytotoxicity, the PLA-HPG NPs showed significantly longer blood circulation and significantly less liver accumulation than PLA-PEG. CPT-loaded PLA-HPG NPs showed higher stability in suspension and better therapeutic effectiveness against tumors in vivo than CPT-loaded PLA-PEG NPs. Our results suggest that HPG is superior to PEG as a surface coating for NPs in drug delivery.

Receptor binding peptides for target-selective delivery of nanoparticles encapsulated drugs

Active targeting by means of drug encapsulated nanoparticles decorated with targeting bioactive moieties represents the next frontier in drug delivery; it reduces drug side effects and increases the therapeutic index. Peptides, based on their chemical and biological properties, could have a prevalent role to direct drug encapsulated nanoparticles, such as liposomes, micelles, or hard nanoparticles, toward the tumor tissues. A considerable number of molecular targets for peptides are either exclusively expressed or overexpressed on both cancer vasculature and cancer cells. They can be classified into three wide categories: integrins; growth factor receptors (GFRs); and G-protein coupled receptors (GPCRs). Therapeutic agents based on nanovectors decorated with peptides targeting membrane receptors belonging to the GPCR family overexpressed by cancer cells are reviewed in this article. The most studied targeting membrane receptors are considered: somatostatin receptors; cholecystokinin receptors; receptors associated with the Bombesin like peptides family; luteinizing hormone-releasing hormone receptors; and neurotensin receptors. Nanovectors of different sizes and shapes (micelles, liposomes, or hard nanoparticles) loaded with doxorubicin or other cytotoxic drugs and externally functionalized with natural or synthetic peptides are able to target the overexpressed receptors and are described based on their formulation and in vitro and in vivo behaviors.

An emerging platform for drug delivery: aerogel based systems

Over the past few decades, advances in "aerogel science" have provoked an increasing interest for these materials in pharmaceutical sciences for drug delivery applications. Because of their high surface areas, high porosities and open pore structures which can be tuned and controlled by manipulation of synthesis conditions, nanostructured aerogels represent a promising class of materials for delivery of various drugs as well as enzymes and proteins. Along with biocompatible inorganic aerogels and biodegradable organic aerogels, more complex systems such as surface functionalized aerogels, composite aerogels and layered aerogels have also been under development and possess huge potential. Emphasis is given to the details of the aerogel synthesis and drug loading methods as well as the influence of synthesis parameters and loading methods on the adsorption and release of the drugs. Owing to their ability to increase the bioavailability of low solubility drugs, to improve both their stability and their release kinetics, there are an increasing number of research articles concerning aerogels in different drug delivery applications. This review presents an up to date overview of the advances in all kinds of aerogel based drug delivery systems which are currently under investigation.

In vitro performance of lipid-PLGA hybrid nanoparticles as an antigen delivery system: lipid composition matters

Due to the many beneficial properties combined from both poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) and liposomes, lipid-PLGA hybrid NPs have been intensively studied as cancer drug delivery systems, bio-imaging agent carriers, as well as antigen delivery vehicles. However, the impact of lipid composition on the performance of lipid-PLGA hybrid NPs as a delivery system has not been well investigated. In this study, the influence of lipid composition on the stability of the hybrid NPs and in vitro antigen release from NPs under different conditions was examined. The uptake of hybrid NPs with various surface charges by dendritic cells (DCs) was carefully studied. The results showed that PLGA NPs enveloped by a lipid shell with more positive surface charges could improve the stability of the hybrid NPs, enable better controlled release of antigens encapsulated in PLGA NPs, as well as enhance uptake of NPs by DC.

Liposome-like Nanostructures for Drug Delivery

Liposomes are a class of well-established drug carriers that have found numerous therapeutic applications. The success of liposomes, together with recent advancements in nanotechnology, has motivated the development of various novel liposome-like nanostructures with improved drug delivery performance. These nanostructures can be categorized into five major varieties, namely: (1) polymer-stabilized liposomes, (2) nanoparticle-stabilized liposomes, (3) core-shell lipid-polymer hybrid nanoparticles, (4) natural membrane-derived vesicles, and (5) natural membrane coated nanoparticles. They have received significant attention and have become popular drug delivery platforms. Herein, we discuss the unique strengths of these liposome-like platforms in drug delivery, with a particular emphasis on how liposome-inspired novel designs have led to improved therapeutic efficacy, and review recent progress made by each platform in advancing healthcare.

Emerging targets and novel approaches to Ebola virus prophylaxis and treatment

Ebola is a highly virulent pathogen causing severe hemorrhagic fever with a high case fatality rate in humans and non-human primates (NHPs). Although safe and effective vaccines or other medicinal agents to block Ebola infection are currently unavailable, a significant effort has been put forth to identify several promising candidates for the treatment and prevention of Ebola hemorrhagic fever. Among these, recombinant adenovirus-based vectors have been identified as potent vaccine candidates, with some affording both pre- and post-exposure protection from the virus. Recently, Investigational New Drug (IND) applications have been approved by the US Food and Drug Administration (FDA) and phase I clinical trials have been initiated for two small-molecule therapeutics: anti-sense phosphorodiamidate morpholino oligomers (PMOs: AVI-6002, AVI-6003) and lipid nanoparticle/small interfering RNA (LNP/siRNA: TKM-Ebola). These potential alternatives to vector-based vaccines require multiple doses to achieve therapeutic efficacy, which is not ideal with regard to patient compliance and outbreak scenarios. These concerns have fueled a quest for even better vaccination and treatment strategies. Here, we summarize recent advances in vaccines or post-exposure therapeutics for prevention of Ebola hemorrhagic fever. The utility of novel pharmaceutical approaches to refine and overcome barriers associated with the most promising therapeutic platforms are also discussed.