Effective tumor targeting and enhanced anti-tumor effect of liposomes engrafted with peptides specific for tumor lymphatics and vasculature

Uptake Pathway of Styrene Maleic Acid Copolymer-Coated Lipid Emulsions Under Acidic Tumor Microenvironment

The purpose of this study was to elucidate and compare styrene maleic acid copolymer (SMA)-coated lipid emulsions (SMA emulsions) uptake pathway in vascular endothelial cells and surrounding cancer cells under not only neutral but also acidic pH, which is often observed in tumor microenvironment. DiI-labeled SMA emulsions were prepared using 1-palmitoyl-2-oleoyl-sn‑glycero-3-phosphocholine and triolein. In murine melanoma B16-BL6 (B16) cells and human umbilical vein endothelial cells (HUVEC), DiI-labeled SMA emulsions uptake under near-neutral (pH 7.4) and acidic (pH 6.0) conditions was determined by fluorescent analysis. SMA emulsions were taken up more efficiently into HUVEC than B16 cells under acidic condition in a temperature-dependent manner. Uptake study using endocytosis inhibitors showed that SMA emulsions were taken up by macropinocytosis and clathrin-mediated endocytosis in B16 cells. In HUVEC, however, they were taken up by clathrin- and caveolae-independent, but dynamin-dependent pathway. SMA emulsions would be internalized efficiently into vascular endothelial cells as well as cancer cells under acidic microenvironment via different endocytosis pathways. SMA emulsions could be a promising drug delivery carrier for anti-angiogenic drugs.

Advances in the Application of Nanomaterials to the Treatment of Melanoma

Melanoma can be divided into cutaneous melanoma, uveal melanoma, mucosal melanoma, etc. It is a very aggressive tumor that is prone to metastasis. Patients with metastatic melanoma have a poor prognosis and shorter survival. Although current melanoma treatments have been dramatically improved, there are still many problems such as systemic toxicity and the off-target effects of drugs. The use of nanoparticles may overcome some inadequacies of current melanoma treatments. In this review, we summarize the limitations of current therapies for cutaneous melanoma, uveal melanoma, and mucosal melanoma, as well as the adjunct role of nanoparticles in different treatment modalities. We suggest that nanomaterials may have an effective intervention in melanoma treatment in the future.

Using peptides to promote delivery and improve anti-tumour efficacy of liposomal drug

Liposomal drugs exhibit advantages for cancer therapy, but efficacy is often limited by their rapid clearance from blood by the reticuloendothelial system, and an inability to target and penetrate tumours. Interestingly, a 21-amino acid SIRP-α- (signal regulatory protein-α) interacting 'self' peptide is reported to inhibit uptake by phagocytes. Also, 'iRGD' a 9-amino acid cyclic peptide that binds αvβ3 integrins and neuropilin-1 (NRP-1), promotes targeting and penetration of drug into tumours. Here we explore the potential of nitrilotriacetic acid-ditetra-decylamine (NTA₃-DTDA)-containing liposomes (NTA-liposomes) engrafted with His-tagged forms of 'self' peptide (pCD47) to prolong circulation time in blood after iv administration, and of iRGD peptide (piRGD) to enhance treatment efficacy of doxorubicin-containing liposomes (Caelyx). Our results show that pre-incubation of murine phagocytic DC2.4 and RAW246.7 cells with pCD47 inhibits uptake of NTA-liposomes in vitro, but engraftment of pCD47 surprisingly reduces liposome lifetime in blood. Engraftment of piRGD promoted binding of NTA-liposomes to murine B16 melanoma and CT26 colorectal carcinoma cells in vitro. Importantly, iv administration of piRGD-engrafted Caelyx was found to significantly inhibit tumour growth and prolong survival in both B16 and CT26 murine tumour models. Our results show that engraftment of piRGD onto Caelyx is a convenient strategy to enhance treatment efficacy.

The Use of Alternative Strategies for Enhanced Nanoparticle Delivery to Solid Tumors

Nanomaterial (NM) delivery to solid tumors has been the focus of intense research for over a decade. Classically, scientists have tried to improve NM delivery by employing passive or active targeting strategies, making use of the so-called enhanced permeability and retention (EPR) effect. This phenomenon is made possible due to the leaky tumor vasculature through which NMs can leave the bloodstream, traverse through the gaps in the endothelial lining of the vessels, and enter the tumor. Recent studies have shown that despite many efforts to employ the EPR effect, this process remains very poor. Furthermore, the role of the EPR effect has been called into question, where it has been suggested that NMs enter the tumor via active mechanisms and not through the endothelial gaps. In this review, we provide a short overview of the EPR and mechanisms to enhance it, after which we focus on alternative delivery strategies that do not solely rely on EPR in itself but can offer interesting pharmacological, physical, and biological solutions for enhanced delivery. We discuss the strengths and shortcomings of these different strategies and suggest combinatorial approaches as the ideal path forward.

Development of Nanosome-Encapsulated Honokiol for Intravenous Therapy Against Experimental Autoimmune Encephalomyelitis

Background

Honokiol has been reported to possess anti-inflammatory and neuroprotective activities. However, the poor aqueous solubility of honokiol limits its clinical application for systemic administration.

Purpose

This study aims to develop a novel formulation of nanosome-encapsulated honokiol (NHNK) for intravenous therapy against mouse experimental autoimmune encephalomyelitis (EAE) that mimics human multiple sclerosis.

Methods

Nanosomes and NHNK were prepared by using an ultra-high pressure homogenization (UHPH) method. Mice were treated with NHNK or empty nanosomes during the peak phase of EAE symptoms. Symptoms of EAE were monitored and samples of the spinal cord were obtained for histopathological examinations.

Results

The stock of NHNK containing honokiol in the nanosome formulation, which showed the structure of single phospholipid bilayer membranes, was well formulated with the particle size of 48.0 ± 0.1 nm and the encapsulation efficiency 58.1 ± 4.2%. Intravenous administration of NHNK ameliorated the severity of EAE accompanied by a significant reduction of demyelination and inflammation in the spinal cord. Furthermore, NHNK decreased the number of IL-6⁺, Iba-1⁺TNF ⁺, Iba-1⁺IL-12 p40⁺, and CD3⁺IFN-γ⁺ cells infiltrating the spinal cord.

Conclusion

The UHPH method simplified the preparation of NHNK with uniformly distributed nanosize and high encapsulation efficiency. Intravenous administration of NHNK ameliorated the severity of EAE by suppressing the infiltration of activated microglia and Th1 cells into the spinal cord. Collectively, these results suggest that the formulation of NHNK is a prospective therapeutic approach for inflammatory CNS diseases, such as multiple sclerosis.

Recent progress in LyP-1-based strategies for targeted imaging and therapy

The identification of markers expressed by pathological cells or their microenvironment would help to distinguish such cells from the normal tissues. The strategies derived from this theory can be a promising modality for imaging and treating diseases. LyP-1, a tumor homing peptide, can selectively bind to its receptor p32 protein overexpressed in various tumor-associated cells and atherosclerotic plaque macrophages. During recent decades, multiple types of LyP-1-based imaging probes and drug delivery systems have been designed and developed for diagnostic and therapeutic applications. This review first introduces LyP-1 and its receptor p32, as well as its homing, internalization and proapoptotic properties. Next, we highlight recent studies focusing on the applications of LyP-1-based strategies in the diagnosis and treatment of tumors, metastatic lesions, and atherosclerotic plaques. Finally, several limitations in the clinical translation of LyP-1-based bioconjugates are summarized.

Efficacy of a novel LyP-1-containing self-microemulsifying drug delivery system (SMEDDS) for active targeting to breast cancer

An ideal cancer therapy targets the tumor cells selectively without damaging healthy tissues. Even though the tumor-specific markers are limited, these molecules can be used for the delivery of anti-cancer drugs as an active targeting strategy. Since the lymphatic system plays a critical role in the dissemination of cancer cells, the drugs directed through lymphatics can feasibly reach to the sites of metastasis. LyP-1 is a peptide that binds to the p32 receptor which is highly expressed not only on the lymphatic endothelium but also on the malignant cells; thus, making this peptide ligand a preferable candidate to mediate active targeting of lymphatics and cancer cells. In this study, different formulations of LyP-1 containing lipid-based nanopharmaceutics so-called self-microemulsifying drug delivery systems (SMEDDS) were developed and tested for their efficacy in targeting breast cancer. Following the selection of non-toxic formulation, doxorubicin hydrochloride and LyP-1 were co-administered in the SMEDDS, which resulted in a significant increase in in vitro cytotoxicity in p32-expressing breast cancer cells, 4T1 and MDA-MB-231. Accordingly, the uptake of LyP-1 in the SMEDDS by the cancer cells was demonstrated. The expression of p32 was detected in the 4T1 tumor tissues which were efficiently targeted with LyP-1 in the SMEDDS. When doxorubicin was co-administrated with LyP-1 in SMEDDS via intraperitonial administration, tumor growth and metastasis were significantly reduced. In conclusion, a novel and efficacious SMEDDS formulation containing LyP-1 with a droplet size less than 100 nm was developed for the lymphatic targeting of breast cancer.

Development of a novel albumin-based and maleimidopropionic acid-conjugated peptide with prolonged half-life and increased in vivo anti-tumor efficacy

Angiogenesis plays a critical role in tumor aggressiveness, and a lot of anti-angiogenic agents have been used in clinical therapy. The therapeutic efficacy of peptides are generally restricted by the short in vivo life-time, thus, we were interested in developing a novel albumin-based and maleimidopropionic acid-conjugated peptide to prolong the half-life and improve the anti-tumor effect.

Methods: We developed a peptide F56 with a maleimidopropionic acid (MPA) at the C-terminal (denoted as F56-CM), which allows immediate and irreversible conjugation with serum albumin. Biological property and anti-tumor activity of F56-CM were evaluated in vitro and in vivo.

Results: We showed that F56-CM reduced migration and tube formation of endothelial cells in vitro and inhibited the generation of subintestinal vessels (SIV) in zebrafish embryos in vivo. F56-CM inhibited vascular endothelial growth factor (VEGF) induced phosphorylation of VEGFR1 and activation of the PI3K-AKT axis. Furthermore, F56-CM rapidly conjugated with albumin upon intravenous injection and extended the biological half-life of F56 from 0.4249 h to 6.967 h in rats. Compared with F56, F56-CM exhibited stronger anti-tumor activity on both BGC-823 gastric cancer and HT-29 colon cancer xenografts in nude mice, and the statistical difference was remarkable. More significantly, the efficacy of F56-CM inhibiting lung metastasis of BGC-823 cells was also better than that of F56. The inhibition rates were 62.1% and 78.9% for F56 and F56-CM respectively when administrated every day, and 43.8% and 63.1% when administrated every four days at equal dose.

Conclusions: Taken together, our results demonstrated that F56-CM has considerable potential for cancer therapy.

Construction and Evaluation of the Tumor-Targeting, Cell-Penetrating Multifunctional Molecular Probe iCREKA

A novel tumor stroma targeting and membrane-penetrating cyclic peptide, named iCREKA, was designed and labeled by fluorescein isothiocyanate (FITC) and positron emitter ¹⁸F to build the tumor-targeting tracers. The FITC-iCREKA was proved to have significantly higher cellular uptake in the glioma U87 cells in the presence of activated MMP-2 than that in absence of activated MMP-2 by cells fluorescence test in vitro. The tumor tissue fluorescence microscope imaging demonstrated that FITC-iCREKA accumulated in the walls of the blood vessels and the surrounding stroma in the glioma tumor at 1 h after intravenous injection. While at 3 h after injection, FITC-iCREKA was found to be uptaken in the tumor cells. However, the control FITC-CREKA can only be found in the tumor stroma, not in the tumor cells, no matter at 1 h or 3 h after injection. The whole-animal fluorescence imaging showed that the glioma tumor could be visualized clearly with high fluorescence signal. The microPET/CT imaging further demonstrated that 18F-iCREKA could target U87MG tumor in vivo from 30 min to 2 h after injection. The present study indicated the iCREKA had the capacity of tumor stroma targeting and the membrane-penetrating. It was potential to be developed as the fluorescent and PET tracers for tumor imaging.

Vincristine liposomes with smaller particle size have stronger diffusion ability in tumor and improve tumor accumulation of vincristine significantly

The passive targeting is the premise of active targeting that could make nanocarrier detained in tumor tissue. The particle size is the most important factor that influences the diffusion and distribution of nanoparticle both in vivo and in vitro. In order to investigate the relationship between particle size and diffusion ability, two kinds of liposome loaded with Vincristine (VCR-Lip) were prepared. The diffusion behavior of VCR-Lip with different particle size and free VCR was compared through diffusion stability study. The diffusion ability from 12-well culture plate to Millipore transwell of each formulation reflected on HepG-2 cytotoxicity results. Different cell placement methods and drug adding positions were used to study the VCR-Lip diffusion behaviors, which influenced the apoptosis of HepG-2 cell. The different cell uptake of Nile red–Lip and free Nile red was compared when changed the adding way of fluorescent fluorescein. To study the penetration ability in HepG-2 tumor spheroids, we constructed 30 nm and 100 nm Cy5.5-Lip to compare with free Cy5.5. Then the anti-tumor effect, tissue distribution of free VCR injection, 30 nm and 100 nm VCR-Lip were further investigated on the HepG-2 tumor bearing nude mice. The results of these study showed that the diffusion ability of free drug and fluorescent fluorescein was remarkable stronger than which encapsulated in liposomes. Moreover, diffusion ability of smaller liposome was stronger than larger one. In this way, 30 nm liposome had not only faster and stronger tumor distribution than 100 nm liposome, but also higher tumor drug accumulation than free drug as well. Our study provided a new thinking to improve the targeting efficiency of nano drug delivery system, no matter passive or active targeting.

Peptide ligand-modified nanomedicines for targeting cells at the tumor microenvironment

Since their initial discovery more than 30years ago, tumor-homing peptides have become an increasingly useful tool for targeted delivery of therapeutic and diagnostic agents into tumors. Today, it is well accepted that cells at the tumor microenvironment (TME) contribute in many ways to cancer development and progression. Tumor-homing peptide-decorated nanomedicines can interact specifically with surface receptors expressed on cells in the TME, improve cellular uptake of nanomedicines by target cells, and impair tumor growth and progression. Moreover, peptide ligand-modified nanomedicines can potentially accumulate in the target tissue at higher concentrations than would small conjugates, thus increasing overall target tissue exposure to the therapeutic agent, enhance therapeutic efficacy and reduce side effects. This review describes the most studied peptide ligands aimed at targeting cells in the TME, discusses major obstacles and principles in the design of ligands for drug targeting and provides an overview of homing peptides in ligand-targeted nanomedicines that are currently in development for cancer therapy and diagnosis.

Molecular dynamics, thermodynamic, and mutational binding studies for tumor-specific LyP-1 in complex with p32

Recent studies in tumor homing peptides have shown the specificity of LyP-1 (CGNKRTRGC) to tumor lymphatics. In this present work, we evaluated the possible interactions between cyclic LyP-1 and its receptor, p32, with molecular dynamics and docking studies in order to lead the design of novel LyP-1 derivatives, which could bind to p32 more effectively and perform enhanced antitumor effect. The total binding enthalpy energies have been obtained by MM-PBSA thermodynamic computations and the favorability of p32.LyP-1 complex in water has been shown by explicit water MD computations. The last 30 ns of molecular dynamics trajectory have shown the strong interaction of LyP-1 with the inner surface chains of p32, especially with chains B and C. ALA-SCAN mutagenesis studies have indicated the considerable influence of Asn3, Lys4, Arg5, and Arg7 amino acid residues on the specific binding of LyP-1. Within the knowledge of the critical role of p32 receptor in cancer cell metabolism, this study can lead to further developments in anticancer therapy by targeting p32 with LyP-1 derivatives as active targeting moiety. This data can also be applied for the development of new drug delivery systems in which LyP-1 can be used for its targeting and anticancer properties.

Tumor Microenvironment Targeting and Responsive Peptide-Based Nanoformulations for Improved Tumor Therapy

The tumor microenvironment participates in all stages of tumor progression and has emerged as a promising therapeutic target for cancer therapy. Rapid progress in the field of molecular self-assembly using various biologic molecules has resulted in the fabrication of nanoformulations that specifically target and regulate microenvironment components to inhibit tumor growth. This inhibition process is based on differentiating between biophysicochemical cues guiding tumor and normal tissue microenvironments. Peptides and peptide derivatives, owing to their biocompatibility, chemical versatility, bioactivity, environmental sensitivity, and biologic recognition abilities, have been widely used as building blocks to construct multifunctional nanostructures for targeted drug delivery and controlled release. Several groups of peptides have been identified as having the ability to penetrate plasma membranes, regulate the essential signaling pathways of angiogenesis and immune reactions, and recognize key components in the tumor microenvironment (such as vascular systems, stromal cells, and abnormal tumor biophysicochemical features). Thus, using different modules, various functional peptides, and their derivatives can be integrated into nanoformulations specifically targeting the tumor microenvironment with increased selectivity, on-demand response, elevated cellular uptake, and improved tumor therapy. In this review, we introduce several groups of functional peptides and highlight peptide-based nanoformulations that specifically target the tumor microenvironment. We also provide our perspective on the development of smart drug-delivery systems with enhanced therapeutic efficacy.

Tumor-targeting peptides from combinatorial libraries

Cancer is one of the major and leading causes of death worldwide. Two of the greatest challenges in fighting cancer are early detection and effective treatments with no or minimum side effects. Widespread use of targeted therapies and molecular imaging in clinics requires high affinity, tumor-specific agents as effective targeting vehicles to deliver therapeutics and imaging probes to the primary or metastatic tumor sites. Combinatorial libraries such as phage-display and one-bead one-compound (OBOC) peptide libraries are powerful approaches in discovering tumor-targeting peptides. This review gives an overview of different combinatorial library technologies that have been used for the discovery of tumor-targeting peptides. Examples of tumor-targeting peptides identified from each combinatorial library method will be discussed. Published tumor-targeting peptide ligands and their applications will also be summarized by the combinatorial library methods and their corresponding binding receptors.

Assessing the therapeutic efficacy of VEGFR-1-targeted polymer drug conjugates in mouse tumor models

Polymer-drug conjugates that can actively target the tumor vasculature have emerged as an attractive technology for improving the therapeutic efficacy of cytotoxic drugs. We have recently provided, for the first time, in vivo evidence showing the significant advantage of the E-selectin-targeted N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer-doxorubicin conjugate, P-(Esbp)-DOX, in inhibiting primary tumor growth and preventing the formation and development of cancer metastases. Here, we describe the design of a vascular endothelial growth factor receptor (VEGFR)-1-targeted HPMA copolymer-DOX conjugate (P-(F56)-DOX) that can actively and simultaneously target different cell types in the tumor microenvironment, such as endothelial cells (ECs), bone marrow-derived cells and many human cancer cells of diverse tumor origin. The VEGFR-1-targeted copolymer was tested for its binding, internalization and in vitro cytotoxicity in ECs (bEnd.3 and cEND cells) and cancer cells (B16-F10, 3LL and HT29). The in vivo anti-cancer activity of P-(F56)-DOX was then tested in two tumor-bearing mice (TBM) models (i.e., primary Lewis lung carcinoma (3LL) tumors and B16-F10 melanoma pulmonary metastases), relative to that of the E-selectin-targeted system (P-(Esbp)-DOX) that solely targets ECs. Our results indicate that the binding and internalization profiles of the VEGFR-1-targeted copolymer were superior towards ECs as compared to cancer cells and correlated well to the level of VEGFR-1 expression in cells. Accordingly, the VEGFR-1-targeted copolymer (P-(F56)-DOX) was more toxic towards bEnd.3 cells than to cancer cells, and exhibited significantly higher cytotoxicity than did the non-targeted control copolymer. P-(F56)-DOX inhibited 3LL tumor growth and significantly prolonged the survival of mice with B16-F10 pulmonary metastases. When compared to a system that actively targets only tumor vascular ECs, P-(F56)-DOX and P-(Esbp)-DOX exhibited comparable efficacy in slowing the growth of primary 3LL tumors and prolonging the survival of these mice. Still, P-(Esbp)-DOX had more pronounced anti-tumor activity in mice bearing B16-F10 lung metastases after a single intravenous injection, at an equivalent DOX dose. Overall, our results indicate that the VEGFR-1- and E-selectin-targeted drug delivery systems evaluated here show enhanced anti-cancer activity, and prolonged the survival of mice after a single intravenous injection. This is thus the first study comparing the anti-tumor activity of VEGFR-1- and E-selectin-targeted polymer drug conjugates in the same TBM models at an equivalent drug dose.

Nanopreparations to overcome multidrug resistance in cancer

Multidrug resistance is the most widely exploited phenomenon by which cancer eludes chemotherapy. Broad variety of factors, ranging from the cellular ones, such as over-expression of efflux transporters, defective apoptotic machineries, and altered molecular targets, to the physiological factors such as higher interstitial fluid pressure, low extracellular pH, and formation of irregular tumor vasculature are responsible for multidrug resistance. A combination of various undesirable factors associated with biological surroundings together with poor solubility and instability of many potential therapeutic small & large molecules within the biological systems and systemic toxicity of chemotherapeutic agents has necessitated the need for nano-preparations to optimize drug delivery. The physiology of solid tumors presents numerous challenges for successful therapy. However, it also offers unique opportunities for the use of nanotechnology. Nanoparticles, up to 400 nm in size, have shown great promise for carrying, protecting and delivering potential therapeutic molecules with diverse physiological properties. In this review, various factors responsible for the MDR and the use of nanotechnology to overcome the MDR, the use of spheroid culture as well as the current technique of producing microtumor tissues in vitro are discussed in detail.

A liposomal drug platform overrides peptide ligand targeting to a cancer biomarker, irrespective of ligand affinity or density

One method for improving cancer treatment is the use of nanoparticle drugs functionalized with targeting ligands that recognize receptors expressed selectively by tumor cells. In theory such targeting ligands should specifically deliver the nanoparticle drug to the tumor, increasing drug concentration in the tumor and delivering the drug to its site of action within the tumor tissue. However, the leaky vasculature of tumors combined with a poor lymphatic system allows the passive accumulation, and subsequent retention, of nanosized materials in tumors. Furthermore, a large nanoparticle size may impede tumor penetration. As such, the role of active targeting in nanoparticle delivery is controversial, and it is difficult to predict how a targeted nanoparticle drug will behave in vivo. Here we report in vivo studies for α_vβ₆-specific H2009.1 peptide targeted liposomal doxorubicin, which increased liposomal delivery and toxicity to lung cancer cells in vitro. We systematically varied ligand affinity, ligand density, ligand stability, liposome dosage, and tumor models to assess the role of active targeting of liposomes to α_vβ₆. In direct contrast to the in vitro results, we demonstrate no difference in in vivo targeting or efficacy for H2009.1 tetrameric peptide liposomal doxorubicin, compared to control peptide and no peptide liposomes. Examining liposome accumulation and distribution within the tumor demonstrates that the liposome, and not the H2009.1 peptide, drives tumor accumulation, and that both targeted H2009.1 and untargeted liposomes remain in perivascular regions, with little tumor penetration. Thus H2009.1 targeted liposomes fail to improve drug efficacy because the liposome drug platform prevents the H2009.1 peptide from both actively targeting the tumor and binding to tumor cells throughout the tumor tissue. Therefore, using a high affinity and high specificity ligand targeting an over-expressed tumor biomarker does not guarantee enhanced efficacy of a liposomal drug. These results highlight the complexity of in vivo targeting.

Recent trends in multifunctional liposomal nanocarriers for enhanced tumor targeting

Liposomes are delivery systems that have been used to formulate a vast variety of therapeutic and imaging agents for the past several decades. They have significant advantages over their free forms in terms of pharmacokinetics, sensitivity for cancer diagnosis and therapeutic efficacy. The multifactorial nature of cancer and the complex physiology of the tumor microenvironment require the development of multifunctional nanocarriers. Multifunctional liposomal nanocarriers should combine long blood circulation to improve pharmacokinetics of the loaded agent and selective distribution to the tumor lesion relative to healthy tissues, remote-controlled or tumor stimuli-sensitive extravasation from blood at the tumor's vicinity, internalization motifs to move from tumor bounds and/or tumor intercellular space to the cytoplasm of cancer cells for effective tumor cell killing. This review will focus on current strategies used for cancer detection and therapy using liposomes with special attention to combination therapies.

Influence of PEGylation and RGD loading on the targeting properties of radiolabeled liposomal nanoparticles

Purpose

Liposomes have been proposed to be a means of selectively targeting cancer sites for diagnostic and therapeutic applications. The focus of this work was the evaluation of radiolabeled PEGylated liposomes derivatized with varying amounts of a cyclic arginyl–glycyl–aspartic acid (RGD) peptide. RGD peptides are known to bind to α_vβ₃ integrin receptors overexpressed during tumor-induced angiogenesis.

Methods

Several liposomal nanoparticles carrying the RGD peptide targeting sequence (RLPs) were synthesized using a combination of 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine, cholesterol, diethylenetriaminepentaacetic acid-derivatized lipids for radiolabeling, a polyethylene glycol (PEG) building block, and a lipid-based RGD building block. Relative amounts of RGD and PEG building blocks were varied. In vitro binding affinities were determined using isolated α_vβ₃ integrin receptors incubated with different concentrations of RLPs in competition with iodine-125-labeled cyclo-(-RGDyV-). Binding of the indium-111-labeled RLPs was also evaluated. Biodistribution and micro single photon emission computed tomography/computed tomography imaging studies were performed in nude mice using different tumor xenograft models.

Results

RLPs were labeled with indium-111 with high radiochemical yields. In vitro binding studies of RLPs with different RGD/PEG loading revealed good binding to isolated receptors, which was dependent on the extent of RGD and PEG loading. Binding increased with higher RGD loading, whereas reduced binding was found with higher PEG loading. Biodistribution showed increased circulating time for PEGylated RLPs, but no dependence on RGD loading. Both biodistribution and micro single photon emission computed tomography/computed tomography imaging studies revealed low, nonspecific tumor uptake values.

Conclusion

In this study, RLPs for targeting angiogenesis were described. Even though good binding to α_vβ₃ integrin receptors was found in vitro, the balance between PEGylation and RGD loading clearly requires optimization to achieve targeting in vivo. These data form the basis for future development and provide a platform for the investigation of multimodal approaches.

Peptide targeted lipid nanoparticles for anticancer drug delivery

Encapsulating anticancer drugs in nanoparticles has proven to be an effective mechanism to alter the pharmacokinetic and pharmacodynamic profiles of the drugs, leading to clinically useful cancer therapeutics like Doxil and DaunoXome. Underdeveloped tumor vasculature and lymphatics allow these first-generation nanoparticles to passively accumulate within the tumor, but work to create the next-generation nanoparticles that actively participate in the tumor targeting process is underway. Lipid nanoparticles functionalized with targeting peptides are among the most often studied. The goal of this article is to review the recently published literature of targeted nanoparticles to highlight successful designs that improved in vivo tumor therapy, and to discuss the current challenges of designing these nanoparticles for effective in vivo performance.

pDNA-lipoplexes engrafted with flagellin-related peptide induce potent immunity and anti-tumour effects

Complexes of cationic lipids and DNA (lipoplexes) are widely used for non-viral gene delivery and DNA vaccine development, but cationic lipids are toxic and promote non-specific interactions with cells, leading to poor efficacy. Near-neutral lipoplexes, on the other hand, can obviate toxicity, but a convenient means to target them to specific cells such as dendritic cells (DCs) has been lacking. Here, we show that a His-tagged flagellin-derived peptide (denoted 9Flg), previously reported to promote binding of liposomal antigen to TLR5-expressing cells, can be used to target near-neutral pDNA-lipoplexes incorporating the chelator lipid NTA(3)-DTDA (3(nitrilotriacetic acid)-ditetradecylamine) to DCs and other antigen-presenting cells (APCs). Thus, we show that pDNA-lipoplexes engrafted with 9Flg target pDNA to APCs in vitro and in vivo. Following i.v. administration, radiolabelled 9Flg-lipoplexes exhibited increased accumulation in spleen, lung and liver. Vaccination of C57BL/6 mice with 9Flg-lipoplexes containing either pcDNA3.1-SIIN (pSIIN) or a Kunjin virus replicon-based vector (pKUN), each encoding the epitope OVA(257-264) (SIINFEKL), induced Ag-specific T cell priming, and elicited strong cellular immunity as reflected by a marked increase in the number of Ag-responsive IFN-γ-producing CD8(+) T cells. Importantly, compared to i.m. injection of these SIINFEKL-encoding pDNAs in naked form, the i.v. administration of pSIIN or pKUN in 9Flg-lipoplexes to C57BL/6 mice induced a significantly more potent anti-tumour response in the B16-OVA melanoma tumour model. The targeting of near-neutral 9Flg-lipoplexes bearing pDNA encoding tumour antigens to TLR5 on APCs, therefore, is a powerful approach for developing more effective DNA vaccines and immunotherapies.