A novel peptide enhances therapeutic efficacy of liposomal anti-cancer drugs in mice models of human lung cancer

Targeted drug delivery systems mediated by a novel Peptide in breast cancer therapy and imaging

Targeted delivery of drugs to tumors represents a significant advance in cancer diagnosis and therapy. Therefore, development of novel tumor-specific ligands or pharmaceutical nanocarriers is highly desirable. In this study, we utilized phage display to identify a new targeting peptide, SP90, which specifically binds to breast cancer cells, and recognizes tumor tissues from breast cancer patients. We used confocal and electron microscopy to reveal that conjugation of SP90 with liposomes enables efficient delivery of drugs into cancer cells through endocytosis. Furthermore, in vivo fluorescent imaging demonstrated that SP90-conjugated quantum dots possess tumor-targeting properties. In tumor xenograft and orthotopic models, SP90-conjugated liposomal doxorubicin was found to improve the therapeutic index of the chemotherapeutic drug by selectively increasing its accumulation in tumors. We conclude that the targeting peptide SP90 has significant potential in improving the clinical benefits of chemotherapy in the treatment and the diagnosis of breast cancer.

Supercritical fluid technology based large porous celecoxib-PLGA microparticles do not induce pulmonary fibrosis and sustain drug delivery and efficacy for several weeks following a single dose

Although pulmonary dosing of large porous particles has been shown to sustain drug delivery for a few days, there are no reports on safety or long term delivery. In this study we prepared large porous poly(lactide-co-glycolide) (PLGA) microparticles of celecoxib using supercritical fluid pressure-quench technology and demonstrated 4.8-, 15.7-, and 2.1-fold greater drug levels in lung, bronchoalveolar lavage fluid (BAL), and plasma compared to conventional microparticles on day 21 after a single intratracheal dosing of dry powders in A/J mice. Porous particle based delivery was 50.2-, 95.5-, and 7.7-fold higher compared to plain drug in the lung, BAL, and plasma, respectively. Toxicity of the formulations was assessed on day 21 following a fibrosis assessment protocol in A/J mice. There was no significant change in lactate dehydrogenase (LDH), total protein, and total cell counts in the BAL, and soluble collagen levels in the lung tissue following particle or drug treatments. Lung histology indicated no significant hyperplasia, granuloma, or collagen deposition in the treated groups. Chemopreventive potential of celecoxib porous particles was assessed in a benzo[a]pyrene (B[a]P) induced lung cancer model in A/J mice, on day 60 following a single intratracheal dose with or without single intravenous paclitaxel/carboplatin treatment. The combination group was more effective than individual groups, with the inhibition of tumor multiplicity and reduction of vascular endothelial growth factor in the BAL being 70 and 58%, respectively. Thus, large porous celecoxib-PLGA microparticles prepared using supercritical fluid technology exhibited sustained drug delivery and anti-tumor efficacy, without causing any significant toxicity.

Peptide modified polymeric micelles specific for breast cancer cells

The specific targeting ability of novel breast cancer targeting peptides as ligands coupled to polymeric micelles was evaluated in the present study. In this context, engineered breast cancer cell targeting peptides, denoted as peptide 11 (RGDPAYQGRFL) and peptide 18 (WXEAAYQRFL), were compared with the lead 12-mer p160 peptide and cyclic RGDfK peptide. All four peptides were conjugated individually to poly(ethylene oxide)-b-poly(caprolactone) (PEO-b-PCL) diblock polymeric micelles to obtain targeted carrier systems PM11, PM18, PM 160, and PM c-RGD. Physical blending of the peptides 11 and 18 with PEO-b-PCL was also done to yield combination micelles, comPM11 and comPM18. The structural confirmation of polymer was carried out using (1)H NMR and MALDI-TOF, and the size distribution and zeta potential of the micelles were determined using dynamic light scattering. Lipophilic cyanine fluorescent probe DiI was physically incorporated in the polymeric micelles to imitate the hydrophobic drug loaded in the micellar core. The cellular uptake of DiI-loaded peptide-containing polymeric micelles by MDA-MB-435, MDA-MB-231, and MCF7 breast cancer cell lines, as well as HUVEC and MCF10A noncancerous cells, were analyzed using flow cytometry and confocal microscopy techniques. Modification of polymeric micelles with peptide 11 or 18 led to an increase in micellar uptake specifically in breast cancer cells compared to p160, c-RGD modified, or naked micelles. The peptide-micelle combinations (comPM11 and comPM18) displayed better uptake by the cells compared to the covalently conjugated PM11 and PM18 micelles; however, the combinations were less selective toward cancer cells. The results point to a potential for peptides 11- and 18-micelle conjugates as attractive platforms for improved performance of a wide range of chemotherapeutic drugs and/or imaging agents in cancer therapy and diagnosis.

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.

Lipid-peptide vesicle nanoscale hybrids for triggered drug release by mild hyperthermia in vitro and in vivo

The present study describes leucine zipper peptide-lipid hybrid nanoscale vesicles engineered by self-assembled anchoring of the amphiphilic peptide within the lipid bilayer. These hybrid vesicles aim to combine the advantages of traditional temperature-sensitive liposomes (TSL) with the dissociative, unfolding properties of a temperature-sensitive peptide to optimize drug release under mild hyperthermia, while improving in vivo drug retention. The secondary structure of the peptide and its thermal responsiveness after anchoring onto liposomes were studied with circular dichroism. In addition, the lipid-peptide vesicles (Lp-peptide) showed a reduction in bilayer fluidity at the inner core, as observed with DPH anisotropy studies, while the opposite effect was observed with an ANS probe, indicating peptide interactions with both the headgroup region and the hydrophobic core. A model drug molecule, doxorubicin, was successfully encapsulated in the Lp-peptide vesicles at higher than 90% efficiency following the remote loading, pH-gradient methodology. The release of doxorubicin from Lp-peptide hybrids in vitro indicated superior serum stability at physiological temperatures compared to lysolipid-containing temperature-sensitive liposomes (LTSL) without affecting the overall thermo-responsive nature of the vesicles at 42 °C. A similar stabilizing effect was observed in vivo after intravenous administration of the Lp-peptide vesicles by measuring (14)C-doxorubicin blood kinetics that also led to increased tumor accumulation after 24 h. We conclude that Lp-peptide hybrid vesicles present a promising new class of TSL that can offer previously unexplored opportunities for the development of clinically relevant mild hyperthermia-triggered therapeutic modalities.

Phage display--a powerful technique for immunotherapy: 1. Introduction and potential of therapeutic applications

One of the most effective molecular diversity techniques is phage display. This technology is based on a direct linkage between phage phenotype and its encapsulated genotype, which leads to presentation of molecule libraries on the phage surface. Phage display is utilized in studying protein-ligand interactions, receptor binding sites and in improving or modifying the affinity of proteins for their binding partners. Generating monoclonal antibodies and improving their affinity, cloning antibodies from unstable hybridoma cells and identifying epitopes, mimotopes and functional or accessible sites from antigens are also important advantages of this technology. Techniques originating from phage display have been applied to transfusion medicine, neurological disorders, mapping vascular addresses and tissue homing of peptides. Phages have been applicable to immunization therapies, which may lead to development of new tools used for treating autoimmune and cancer diseases. This review describes the phage display technology and presents the recent advancements in therapeutic applications of phage display.

Nanoglue: an alternative way to display cell-internalizing peptide at the spikes of hepatitis B virus core nanoparticles for cell-targeting delivery

Cell-internalizing peptides (CIPs) can be used to mediate specific delivery of nanoparticles across cellular membrane. The objective of this study was to develop a display technique using hepatitis B virus (HBV) capsid-binding peptide as a "nanoglue" to present CIPs on HBV nanoparticles for cell-targeting delivery. A CIP was selected from a phage display library and cross-linked specifically at the tips of the spikes of the HBV capsid nanoparticle via the "nanoglue" by using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) and N-hydroxysulfosuccinimide (sulfo-NHS). Fluorescent oligonucleotides packaged in the nanoparticles and the fluorescein molecules conjugated on the nanoparticles were delivered to cells by using this display technique. This study demonstrated a proof of principle for cell-targeting delivery via "nanoglue" bioconjugation.

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.

Targeted polymeric therapeutic nanoparticles: design, development and clinical translation

Polymeric materials have been used in a range of pharmaceutical and biotechnology products for more than 40 years. These materials have evolved from their earlier use as biodegradable products such as resorbable sutures, orthopaedic implants, macroscale and microscale drug delivery systems such as microparticles and wafers used as controlled drug release depots, to multifunctional nanoparticles (NPs) capable of targeting, and controlled release of therapeutic and diagnostic agents. These newer generations of targeted and controlled release polymeric NPs are now engineered to navigate the complex in vivo environment, and incorporate functionalities for achieving target specificity, control of drug concentration and exposure kinetics at the tissue, cell, and subcellular levels. Indeed this optimization of drug pharmacology as aided by careful design of multifunctional NPs can lead to improved drug safety and efficacy, and may be complimentary to drug enhancements that are traditionally achieved by medicinal chemistry. In this regard, polymeric NPs have the potential to result in a highly differentiated new class of therapeutics, distinct from the original active drugs used in their composition, and distinct from first generation NPs that largely facilitated drug formulation. A greater flexibility in the design of drug molecules themselves may also be facilitated following their incorporation into NPs, as drug properties (solubility, metabolism, plasma binding, biodistribution, target tissue accumulation) will no longer be constrained to the same extent by drug chemical composition, but also become in-part the function of the physicochemical properties of the NP. The combination of optimally designed drugs with optimally engineered polymeric NPs opens up the possibility of improved clinical outcomes that may not be achievable with the administration of drugs in their conventional form. In this critical review, we aim to provide insights into the design and development of targeted polymeric NPs and to highlight the challenges associated with the engineering of this novel class of therapeutics, including considerations of NP design optimization, development and biophysicochemical properties. Additionally, we highlight some recent examples from the literature, which demonstrate current trends and novel concepts in both the design and utility of targeted polymeric NPs (444 references).

A novel mouse CD133 binding-peptide screened by phage display inhibits cancer cell motility in vitro

Increased expression of CD133 (Prominin-1), an important cancer stem cell-associated marker, has been observed in the cancer stem cells of a variety of human and mouse cancers. However, no natural ligand of CD133 has yet been identified and little is known about its function. In the present study, LS-7 (amino acid sequence: LQNAPRS), a specific binding peptide targeting mouse CD133, was screened and identified for the first time by phage-displayed peptide library technology. The in vitro and in vivo affinity and specificity of LS-7 were determined, and MTT, adhesion, and migration assays were performed to evaluate the effects of LS-7 on the biological behaviors of cancer cells. To determine which signaling pathways are affected by LS-7, HMGB1, S-100A4, CXCR7, uPAR, AMFR, STAT3, and c-Met gene and protein expression were evaluated by RT-PCR and Western blot. Flow cytometry and immunofluorescence assays showed specific, high-affinity binding of the peptide to mCD133 in vitro. Confocal microscopy confirmed the co-localization of LS-7 positive cells and CD133-positive cells. Migration and wound-healing assays showed that LS-7 significantly inhibited the migration of colon and breast cancer cells in a concentration-dependent manner. In vivo experiments also confirmed the high specificity and affinity of LS-7 to mCD133. RT-PCR and Western blot showed that the expressions of only c-Met and STAT3 decreased obviously in colon and breast cancer cells exposed to LS-7. These findings may provide a novel tool for anti-motility and anti-metastasis strategies in cancer research and cancer stem cell therapy.

Delivery of chimeric hepatitis B core particles into liver cells

AIMS

To display a liver-specific ligand on the hepatitis B virus core particles for cell-targeting delivery.

METHODS AND RESULTS

A liver cell-binding ligand (preS1) was fused at the N-terminal end of the hepatitis B core antigen (HBcAg), but the fusion protein (preS1His(6) HBcAg) was insoluble in Escherichia coli and did not form virus-like particles (VLPs). A method to display the preS1 on the HBcAg particle was established by incorporating an appropriate molar ratio of the truncated HBcAg (tHBcAg) to the preS1His(6) HBcAg. Gold immunomicroscopy showed that the subunit mixture reassembled into icosahedral particles, displaying the preS1 ligand on the surface of VLPs. Fluorescence microscopy revealed that the preS1 ligand delivered the fluorescein-labelled VLPs into the HepG2 cells efficiently.

CONCLUSIONS

Chimeric VLPs containing the insoluble preS1His(6) HBcAg and highly soluble tHBcAg were produced by a novel incorporation method. The preS1 ligand was exposed on the surface of the VLPs and was shown to deliver fluorescein molecules into liver cells.

SIGNIFICANCE AND IMPACT OF STUDY

The newly established incorporation method can be used in the development of chimeric VLPs that could serve as potential nanovehicles to target various cells specifically by substituting the preS1 ligand with different cell-specific ligands.

Identification of a LNCaP-specific binding peptide using phage display

PURPOSE

To identify a LNCaP-specific peptide using a phage display library and evaluate its potential applications in targeted drug delivery.

METHODS

Binding abilities of selected phages were evaluated by cell phage ELISA. The KYL peptide encoded by the most specific phage clone was synthesized, labeled with fluorescein, and assayed in various cell lines. A fusion peptide composed of the KYL peptide and a proapoptotic peptide ( D )(KLAKLAK)(2) was synthesized, and the cell death effect was evaluated on different cells. Moreover, the KYL peptide was conjugated to a cationic protein, protamine, to explore its potential application in siRNA delivery.

RESULTS

One phage clone with a high binding affinity to LNCaP cells was identified. Cell phage ELISA and immunostaining demonstrated high specificity of this phage to LNCaP cells. The fluorescein-labeled KYL peptide exhibited higher binding to LNCaP cells in comparison to other cells. The fusion peptide composed of the KYL peptide and the proapoptotic peptide induced cell death in LNCaP cells, but not in PC-3 cells. The KYL peptide-protamine conjugate also efficiently delivered a fluorescein-labeled siRNA into LNCaP cells.

CONCLUSION

We identified a LNCaP-specific peptide and demonstrated its potential applications in targeted drug delivery to LNCaP cells.

Delivery of siRNA into breast cancer cells via phage fusion protein-targeted liposomes

Efficacy of siRNAs as potential anticancer therapeutics can be increased by their targeted delivery into cancer cells via tumor-specific ligands. Phage display offers a unique approach to identify highly specific and selective ligands that can deliver nanocarriers to the site of disease. In this study, we proved a novel approach for intracellular delivery of siRNAs into breast cancer cells through their encapsulation into liposomes targeted to the tumor cells with preselected intact phage proteins. The targeted siRNA liposomes were obtained by a fusion of two parental liposomes containing spontaneously inserted siRNA and fusion phage proteins. The presence of pVIII coat protein fused to a MCF-7 cell-targeting peptide DMPGTVLP in the liposomes was confirmed by Western blotting. The novel phage-targeted siRNA-nanopharmaceuticals demonstrate significant down-regulation of PRDM14 gene expression and PRDM14 protein synthesis in the target MCF-7 cells. This approach offers the potential for development of new anticancer siRNA-based targeted nanomedicines.

FROM THE CLINICAL EDITOR

In this study, the authors report a novel approach for targeted intracellular delivery of siRNAs into breast cancer cells through encapsulation into liposomes targeted to the tumor cells with preselected intact phage proteins.

In vitro screening of ovarian tumor specific peptides from a phage display peptide library

To develop more biomarkers for diagnosis and therapy of ovarian cancer, a 12-mer phage display library was used to isolate peptides that bound specifically to the human ovarian tumor cell line SK-OV-3. After five rounds of in vitro screening, the recovery rate of phages showed a 69-fold increase over the first round of washings and a group of phage clones capable of binding to SK-OV-3 cells were obtained. A phage clone named Z1 with high affinity and specificity to SK-OV-3 cells was identified in vitro. More importantly, the synthetic biotin-labeled peptide, ZP1 (=SVSVGMKPSPRP), which corresponded to the sequence of the inserted fragment of Z1, demonstrated a high specificity to SK-OV-3 cells especially when compared to other cell lines (A2780 and 3T3). ZP1 might therefore be a biomarker for targeting drug delivery in ovarian cancer therapy.

Minicircle-oriP-IFNγ: a novel targeted gene therapeutic system for EBV positive human nasopharyngeal carcinoma

Background

Nonviral vectors are attractively used for gene therapy owing to their distinctive advantages. Our previous study has demonstrated that transfer of human IFNγ gene into nasopharyngeal carcinoma (NPC) by using a novel nonviral vector, minicircle (mc), under the control of cytomegalovirus (CMV) promoter was effective to inhibit tumor growth. However, therapies based on CMV promoter cannot express the targeted genes in cancer tissues. Previous studies indicated that the development of human NPC was closely associated with Epstein-Barr virus (EBV) and demonstrated the transcriptional enhancer function of oriP when bound by EBV protein. Therefore, the present study is to explore the targeted gene expression and the anti-tumor effect of a novel tumor-specific gene therapeutic system (mc-oriP-IFNγ) in which the transgene expression was under the transcriptional regulation of oriP promoter.

Methodology/Principal Findings

Dual-luciferase reporter assay and ELISA were used to assess the expression of luciferase and IFNγ. WST assay was used to assess the cell proliferation. RT-PCR was used to detect the mRNA level of EBNA1. RNAi was used to knockdown the expression of EBNA1. NPC xenograft models in nude mice were used to investigate the targeted antitumor efficacy of mc-oriP-IFNγ. Immunohistochemistry was used to detect the expression and the activity of the IFNγ in tumor sections. Our results demonstrated that mc-oriP vectors mediated comparable gene expression and anti-proliferative effect in the EBV-positive NPC cell line C666-1 compared to mc-CMV vectors. Furthermore, mc-oriP vectors exhibited much lower killing effects on EBV-negative cell lines compared to mc-CMV vectors. The targeted expression of mc-oriP vectors was inhibited by EBNA1-siRNA in C666-1. This selective expression was corroborated in EBV-positive and -negative tumor models.

Conclusions/Significance

This study demonstrates the feasibility of mc-oriP-IFNγ as a safe and highly effective targeted gene therapeutic system for the treatment of EBV positive NPC.

A novel peptide probe for imaging and targeted delivery of liposomal doxorubicin to lung tumor

Targeted delivery of imaging agents and therapeutics to tumors would provide early detection and increased therapeutic efficacy against cancer. Here we have screened a phage-displayed peptide library to identify peptides that selectively bind to lung tumor cells. Evaluation of individual phage clones after screening revealed that a phage clone displaying the CSNIDARAC peptide bound to H460 lung tumor cells at higher extent than other phage clones. The synthetic CSNIDARAC peptide strongly bound to H460 cells and was efficiently internalized into the cells, while little binding of a control peptide was seen. It also preferentially bound to other lung tumor cell lines as compared to cells of different tumor types. In vivo imaging of lung tumor was achieved by homing of fluorescence dye-labeled CSNIDARAC peptide to the tumor after intravenous injection into mice. Ex vivo imaging and microscopic analysis of isolated organs further demonstrated the targeting of CSNIDARAC peptide to tumor. The CSNIDARAC peptide-targeted and doxorubicin-loaded liposomes inhibited the tumor growth more efficiently than untargeted liposomes or free doxorubicin. In vivo imaging of fluorescence dye-labeled liposomes demonstrated selective homing of the CSNIDARAC-liposomes to tumor. In the same context, higher levels of doxorubicin and apoptosis in tumor tissue were observed when treated with the targeted liposomes than untargeted liposomes or free doxorubicin. These results suggest that the CSNIDARAC peptide is a promising targeting probe that is able to direct imaging agents and therapeutics to lung tumor.

Receptor-targeted nanocarriers for therapeutic delivery to cancer

Efficient and site-specific delivery of therapeutic drugs is a critical challenge in clinical treatment of cancer. Nano-sized carriers such as liposomes, micelles, and polymeric nanoparticles have been investigated for improving bioavailability and pharmacokinetic properties of therapeutics via various mechanisms, for example, the enhanced permeability and retention (EPR) effect. Further improvement can potentially be achieved by conjugation of targeting ligands onto nanocarriers to achieve selective delivery to the tumour cell or the tumour vasculature. Indeed, receptor-targeted nanocarrier delivery has been shown to improve therapeutic responses both in vitro and in vivo. A variety of ligands have been investigated including folate, transferrin, antibodies, peptides and aptamers. Multiple functionalities can be incorporated into the design of nanoparticles, e.g., to enable imaging and triggered intracellular drug release. In this review, we mainly focus on recent advances on the development of targeted nanocarriers and will introduce novel concepts such as multi-targeting and multi-functional nanoparticles.

In vivo imaging of tumor apoptosis using histone H1-targeting peptide

In vivo imaging of apoptosis could allow monitoring of tumor response to cancer treatments such as chemotherapy. Using phage display, we identified the CQRPPR peptide, named ApoPep-1(Apoptosis-targeting Peptide-1), that was able to home to apoptotic and necrotic cells in tumor tissue. ApoPep-1 also bound to apoptotic and necrotic cells in culture, while only little binding to live cells was observed. Its binding to apoptotic cells was not dependent on calcium ion and not competed by annexin V. The receptor for ApoPep-1 was identified to be histone H1 that was exposed on the surface of apoptotic cells. In necrotic cells, ApoPep-1 entered the cells and bound to histone H1 in the nucleus. The imaging signals produced during monitoring of tumor apoptosis in response to chemotherapy was enhanced by the homing of a fluorescent dye- or radioisotope-labeled ApoPep-1 to tumor treated with anti-cancer drugs, whereas its uptake of the liver and lung was minimal. These results suggest that ApoPep-1 holds great promise as a probe for in vivo imaging of apoptosis, while histone H1 is a unique molecular signature for this purpose.

Peptidic tumor targeting agents: the road from phage display peptide selections to clinical applications

Cancer has become the number one cause of death amongst Americans, killing approximately 1,600 people per day. Novel methods for early detection and the development of effective treatments are an eminent priority in medicine. For this reason, isolation of tumor-specific ligands is a growing area of research. Tumor-specific binding agents can be used to probe the tumor cell surface phenotype and to customize treatment accordingly by conjugating the appropriate cell-targeting ligand to an anticancer drug. This refines the molecular diagnosis of the tumor and creates guided drugs that can target the tumor while sparing healthy tissues. Additionally, these targeting agents can be used as in vivo imaging agents that allow for earlier detection of tumors and micrometastasis. Phage display is a powerful technique for the isolation of peptides that bind to a particular target with high affinity and specificity. The biopanning of intact cancer cells or tumors in animals can be used as the bait to isolate peptides that bind to cancer-specific cell surface biomarkers. Over the past 10 years, unbiased biopanning of phage-displayed peptide libraries has generated a suite of cancer targeting peptidic ligands. This review discusses the recent advances in the isolation of cancer-targeting peptides by unbiased biopanning methods and highlights the use of the isolated peptides in clinical applications.

Peptide-mediated liposomal drug delivery system targeting tumor blood vessels in anticancer therapy

Solid tumors are known to recruit new blood vessels to support their growth. Therefore, unique molecules expressed on tumor endothelial cells can function as targets for the antiangiogenic therapy of cancer. Current efforts are focusing on developing therapeutic agents capable of specifically targeting cancer cells and tumor-associated microenvironments including tumor blood vessels. These therapies hold the promise of high efficacy and low toxicity. One recognized strategy for improving the therapeutic effectiveness of conventional chemotherapeutics is to encapsulate anticancer drugs into targeting liposomes that bind to the cell surface receptors expressed on tumor-associated endothelial cells. These anti-angiogenic drug delivery systems could be used to target both tumor blood vessels as well as the tumor cells, themselves. This article reviews the mechanisms and advantages of various present and potential methods using peptide-conjugated liposomes to specifically destroy tumor blood vessels in anticancer therapy.

Targeting liposomes toward novel pediatric anticancer therapeutics

Although modern multimodal treatment of pediatric cancer has resulted in long-term cure of many patients, clinical success has come with significant acute and chronic morbidity. Targeted therapy using anticancer agents encapsulated in nanoparticles holds considerable promise in further improving efficacy and reducing toxic side effects. This review highlights the current strategies toward developing such therapeutic tools with an emphasis on using liposomes as flexible delivery vehicles. Potential strengths and technical difficulties encountered in advancing this platform are summarized. Critical functional determinants of nanoparticle delivery systems and future strategies to improve efficacy and specificity are described.

Isolation of peptide ligands that interact specifically with human glioma cells

Poor prognosis of high grade gliomas coupled with the difficulty of widespread delivery of therapeutic agents prompted the search into new molecular targets. Our aim is to isolate glioma-specific peptide sequences that can be used for targeted delivery of therapeutic drugs and imaging tracer to accurately demarcate tumor volume as a response to therapy. Herein, we describe the isolation and characterization of a glioma-specific peptide sequence, GL1, that interact exclusively with human glioma cells lines and primary glioma cells derived from human biopsy in vitro. Further analysis showed that the receptors for GL1 were located on the external side of the plasma membrane, where the GL1 peptides could bind stably up to a period of 180 min. More importantly, GL1 phages home specifically to human glioma xenograft when administered through tail vein, a phenomenon that was not observed when non-specific phages were used as control. Taken together, our results confirmed that GL1 could represent a novel peptide that target to tumor of glial origins, and could potentially be used as a targeting moiety for the conjugation of therapeutic drugs or diagnostic imaging radiolabels.

MiR-218 inhibits invasion and metastasis of gastric cancer by targeting the Robo1 receptor

MicroRNAs play key roles in tumor metastasis. Here, we describe the regulation and function of miR-218 in gastric cancer (GC) metastasis. miR-218 expression is decreased along with the expression of one of its host genes, Slit3 in metastatic GC. However, Robo1, one of several Slit receptors, is negatively regulated by miR-218, thus establishing a negative feedback loop. Decreased miR-218 levels eliminate Robo1 repression, which activates the Slit-Robo1 pathway through the interaction between Robo1 and Slit2, thus triggering tumor metastasis. The restoration of miR-218 suppresses Robo1 expression and inhibits tumor cell invasion and metastasis in vitro and in vivo. Taken together, our results describe a Slit-miR-218-Robo1 regulatory circuit whose disruption may contribute to GC metastasis. Targeting miR-218 may provide a strategy for blocking tumor metastasis.

Combined delivery and magnetic resonance imaging of neural cell adhesion molecule-targeted doxorubicin-containing liposomes in experimentally induced Kaposi's sarcoma

Specific targeting of tumors by combined delivery of drugs and of imaging agents represents an attractive strategy for treatment of cancer. The aim of the present study was to investigate whether neural cell adhesion molecule (NCAM)-targeted liposomes may enhance drug delivery and allow magnetic resonance imaging (MRI) in a severe combined immunodeficient mouse model of NCAM-positive Kaposi's sarcoma. NCAM-binding peptide-coated liposomes loaded with both doxorubicin and a lipophilic gadolinium (Gd) derivative were generated. NCAM-targeted liposomes induced an enhanced in vitro doxorubicin internalization within Kaposi's cells as detected by MRI with respect to untargeted polyethylene glycol liposomes. Internalization resulted in enhanced apoptosis. In vivo weekly administration of NCAM-targeted liposomes containing 5 mg/kg doxorubicin for 4 consecutive weeks induced a significant reduction of tumor mass and vascularization and enhanced cell necrosis and apoptosis with respect to untargeted liposomes. These effects were associated with an enhanced concentration of doxorubicin within the tumor and a reduced systemic toxicity of doxorubicin. By electron microscopy, NCAM-targeted liposomes were detected mainly within tumor cells whereas the untargeted liposomes were mainly accumulated in the extracellular space. Gd-labeled liposomes allowed the MRI visualization of drug delivery in the tumor region. The intensity of MRI signal was partially hampered by the "quenching" of the attainable relaxation enhancement on endosomal entrapment of the Gd-labeled liposomes. In conclusion, targeting NCAM may be a suitable strategy for specific drug delivery and imaging by liposomes in NCAM-expressing tumors. Moreover, treatment with NCAM-targeted liposomes showed enhanced therapeutic effect and reduced toxicity with respect to untargeted liposomes.

In vivo targeting of B-cell lymphoma with glycan ligands of CD22

Antibody-mediated cell depletion therapy has proven to provide significant clinical benefit in treatment of lymphomas and leukemias, driving the development of improved therapies with novel mechanisms of cell killing. A current clinical target for B-cell lymphoma is CD22, a B-cell-specific member of the sialic acid binding Ig-like lectin (siglec) family that recognizes alpha2-6-linked sialylated glycans as ligands. Here, we describe a novel approach for targeting B lymphoma cells with doxorubicin-loaded liposomal nanoparticles displaying high-affinity glycan ligands of CD22. The targeted liposomes are actively bound and endocytosed by CD22 on B cells, and significantly extend life in a xenograft model of human B-cell lymphoma. Moreover, they bind and kill malignant B cells from peripheral blood samples obtained from patients with hairy cell leukemia, marginal zone lymphoma, and chronic lymphocytic leukemia. The results demonstrate the potential for using a carbohydrate recognition-based approach for efficiently targeting B cells in vivo that can offer improved treatment options for patients with B-cell malignancies.

Molecular and magnetic resonance imaging: The value of immunoliposomes

Molecular imaging has the potential to transform the field of diagnostic imaging through enabling far more detailed investigation and characterisation of disease processes than is currently possible. Magnetic resonance imaging (MRI) is capable of three-dimensional non-invasive imaging of opaque tissues at near cellular resolution. Among the imaging techniques available today, MRI has, perhaps, the greatest potential to exploit the possibilities that molecular imaging presents. Nanoparticles are the focus of intense research, due to a wide variety of potential applications in the biomedical, optical, and electronic fields. In this article we examine the progress made in the development of nanoparticles as targeted contrast agents for molecular magnetic resonance imaging. In particular, we will examine the potential of antibody-targeted liposomes (immunoliposomes) as vehicles for delivering MRI contrast agents to cellular biomarkers, thus enabling visualisation of structures and processes at the molecular level. We will address some of the challenges that must be faced by researchers in this field before the progress made in the laboratory can be translated into improved clinical diagnostics and therapeutics.

Use of liposomes as drug delivery vehicles for treatment of melanoma

Melanoma is a progressive disease that claims many lives each year due to lack of therapeutics effective for the long-term treatment of patients. Currently, the best treatment option is early detection followed by surgical removal. Better melanoma therapies that are effectively delivered to tumors with minimal toxicity for patients are urgently needed. Nanotechnologies provide one approach to encapsulate therapeutic agents leading to improvements in circulation time, enhanced tumor uptake, avoidance of the reticulo-endothelial system, and minimization of toxicity. Liposomes in particular are a promising nanotechnology that can be used for more effective delivery of therapeutic agents to treat melanoma. Liposomes delivering chemotherapies, siRNA, asODNs, DNA, and radioactive particles are just some of the promising new nanotechnology based therapies under development for the treatment of melanoma that are discussed in this review.

Antiangiogenic targeting liposomes increase therapeutic efficacy for solid tumors

It is known that solid tumors recruit new blood vessels to support tumor growth, but the molecular diversity of receptors in tumor angiogenic vessels might also be used clinically to develop better targeted therapy. In vivo phage display was used to identify peptides that specifically target tumor blood vessels. Several novel peptides were identified as being able to recognize tumor vasculature but not normal blood vessels in severe combined immunodeficiency (SCID) mice bearing human tumors. These tumor-homing peptides also bound to blood vessels in surgical specimens of various human cancers. The peptide-linked liposomes containing fluorescent substance were capable of translocating across the plasma membrane through endocytosis. With the conjugation of peptides and liposomal doxorubicin, the targeted drug delivery systems enhanced the therapeutic efficacy of the chemotherapeutic agent against human cancer xenografts by decreasing tumor angiogenesis and increasing cancer cell apoptosis. Furthermore, the peptide-mediated targeting liposomes improved the pharmacokinetics and pharmacodynamics of the drug they delivered compared with nontargeting liposomes or free drugs. Our results indicate that the tumor-homing peptides can be used specifically target tumor vasculature and have the potential to improve the systemic treatment of patients with solid tumors.