Enhanced antitumor effect of novel dual-targeted paclitaxel liposomes

Advances in functional lipid nanoparticles: from drug delivery platforms to clinical applications

Since Doxil's first clinical approval in 1995, lipid nanoparticles have garnered great interest and shown exceptional therapeutic efficacy. It is clear from the licensure of two RNA treatments and the mRNA-COVID-19 vaccination that lipid nanoparticles have immense potential for delivering nucleic acids. The review begins with a list of lipid nanoparticle types, such as liposomes and solid lipid nanoparticles. Then it moves on to the earliest lipid nanoparticle forms, outlining how lipid is used in a variety of industries and how it is used as a versatile nanocarrier platform. Lipid nanoparticles must then be functionally modified. Various approaches have been proposed for the synthesis of lipid nanoparticles, such as High-Pressure Homogenization (HPH), microemulsion methods, solvent-based emulsification techniques, solvent injection, phase reversal, and membrane contractors. High-pressure homogenization is the most commonly used method. All of the methods listed above follow four basic steps, as depicted in the flowchart below. Out of these four steps, the process of dispersing lipids in an aqueous medium to produce liposomes is the most unpredictable step. A short outline of the characterization of lipid nanoparticles follows discussions of applications for the trapping and transporting of various small molecules. It highlights the use of rapamycin-coated lipid nanoparticles in glioblastoma and how lipid nanoparticles function as a conjugator in the delivery of anticancer-targeting nucleic acids. High biocompatibility, ease of production, scalability, non-toxicity, and tailored distribution are just a meager of the enticing allowances of using lipid nanoparticles as drug delivery vehicles. Due to the present constraints in drug delivery, more research is required to utterly realize the potential of lipid nanoparticles for possible clinical and therapeutic purposes.

Light-Responsive and Dual-Targeting Liposomes: From Mechanisms to Targeting Strategies

In recent years, nanocarriers have played an ever-increasing role in clinical and biomedical applications owing to their unique physicochemical properties and surface functionalities. Lately, much effort has been directed towards the development of smart, stimuli-responsive nanocarriers that are capable of releasing their cargos in response to specific stimuli. These intelligent-responsive nanocarriers can be further surface-functionalized so as to achieve active tumor targeting in a sequential manner, which can be simply modulated by the stimuli. By applying this methodological approach, these intelligent-responsive nanocarriers can be directed to different target-specific organs, tissues, or cells and exhibit on-demand controlled drug release that may enhance therapeutic effectiveness and reduce systemic toxicity. Light, an external stimulus, is one of the most promising triggers for use in nanomedicine to stimulate on-demand drug release from nanocarriers. Light-triggered drug release can be achieved through light irradiation at different wavelengths, either in the UV, visible, or even NIR region, depending on the photophysical properties of the photo-responsive molecule embedded in the nanocarrier system, the structural characteristics, and the material composition of the nanocarrier system. In this review, we highlighted the emerging functional role of light in nanocarriers, with an emphasis on light-responsive liposomes and dual-targeted stimuli-responsive liposomes. Moreover, we provided the most up-to-date photo-triggered targeting strategies and mechanisms of light-triggered drug release from liposomes and NIR-responsive nanocarriers. Lastly, we addressed the current challenges, advances, and future perspectives for the deployment of light-responsive liposomes in targeted drug delivery and therapy.

Liposomes: An emerging carrier for targeting Alzheimer's and Parkinson's diseases

The function of the brain can be affected by various factors that include infection, tumor, and stroke. The major disorders reported with altered brain function are Alzheimer's disease (AD), Parkinson's disease (PD), dementia, brain cancer, seizures, mental disorders, and other movement disorders. The major barrier in treating CNS disease is the blood-brain barrier (BBB), which protects the brain from toxic molecules, and the cerebrospinal fluid (CSF) barrier, which separates blood from CSF. Brain endothelial cells and perivascular elements provide an integrated cellular barrier, the BBB, which hamper the invasion of molecules from the blood to the brain. Even though many drugs are available to treat neurological disorders, it fails to reach the desired site with the required concentration. In this purview, liposomes can carry required concentrations of molecules intracellular by diverse routes such as carrier-mediated transport and receptor-mediated transcytosis. Surface modification of liposomes enables them to deliver drugs to various brain cells, including neurons, astrocytes, oligodendrocytes, and microglia. The research studies supported the role of liposomes in delivering drugs across BBB and in reducing the pathogenesis of AD and PD. The liposomes were surface-functionalized with various molecules to reach the cells intricated with the AD or PD pathogenesis. The targeted and sustained delivery of drugs by liposomes is disturbed due to the antibody formation, renal clearance, accelerated blood clearance, and complement activation-related pseudoallergy (CARPA). Hence, this review will focus on the characteristics, surface functionalization, drug loading, and biodistribution of liposomes respective to AD and PD. In addition, the alternative strategies to overcome immunogenicity are discussed briefly.

Forward Precision Medicine: Micelles for Active Targeting Driven by Peptides

Precision medicine is based on innovative administration methods of active principles. Drug delivery on tissue of interest allows improving the therapeutic index and reducing the side effects. Active targeting by means of drug-encapsulated micelles decorated with targeting bioactive moieties represents a new frontier. Between the bioactive moieties, peptides, for their versatility, easy synthesis and immunogenicity, can be selected to direct a drug toward a considerable number of molecular targets overexpressed on both cancer vasculature and cancer cells. Moreover, short peptide sequences can facilitate cellular intake. This review focuses on micelles achieved by self-assembling or mixing peptide-grafted surfactants or peptide-decorated amphiphilic copolymers. Nanovectors loaded with hydrophobic or hydrophilic cytotoxic drugs or with gene silence sequences and externally functionalized with natural or synthetic peptides are described based on their formulation and in vitro and in vivo behaviors.

Dual-Targeting and Stimuli-Triggered Liposomal Drug Delivery in Cancer Treatment

The delivery of chemotherapeutics to solid tumors using smart drug delivery systems (SDDSs) takes advantage of the unique physiology of tumors (i.e., disordered structure, leaky vasculature, abnormal extracellular matrix (ECM), and limited lymphatic drainage) to deliver anticancer drugs with reduced systemic side effects. Liposomes are the most promising of such SDDSs and have been well investigated for cancer therapy. To improve the specificity, bioavailability, and anticancer efficacy of liposomes at the diseased sites, other strategies such as targeting ligands and stimulus-sensitive liposomes have been developed. This review highlights relevant surface functionalization techniques and stimuli-mediated drug release for enhanced delivery of anticancer agents at tumor sites, with a special focus on dual functionalization and design of multistimuli responsive liposomes.

Integrin αvβ3-targeted liposomal drug delivery system for enhanced lung cancer therapy

Conventional chemotherapy for tumor treatment remains flawed because it fails to limit cytotoxicity to a small set of selectable tissues. Active targeting techniques for the delivery of drugs to specific sites are increasingly used to enhance drug accumulation at tumor sites with the aim of reducing side effects in vivo. Liposomes, modified with different targeting ligands, are considered to be one of the most promising targeted drug carriers. Herein, novel linear and cyclic arginine-glycine-aspartate (RGD) peptide-based lipids were synthesized to develop modified liposomal drug delivery systems with active targeting and pH-sensitivity. The RGD-modified liposomes showed excellent active targeting ability for integrin α_vβ₃ receptors, resulting in improved cellular uptake. The modified liposomes also enhanced intracellular doxorubicin (DOX) release because of their degradation in an acidic environment. Consequently, the RGD-modified, DOX-loaded liposomes exhibited significant antitumor efficacy and low toxicity in vitro and in vivo. In particular, 5% cRGD-lipid modified DOX-loaded liposome showed the greatest inhibition of tumor growth in mice among the tested formulations, and much less toxicity than free DOX. In conclusion, the DOX-loaded pH-sensitive liposome modified with 5% cRGD-lipid developed in the current study provides a potential approach for improved tumor therapy.

Opportunities and challenges of fatty acid conjugated therapeutics

Instability, poor cellular uptake and unfavorable pharmacokinetics and biodistribution of many therapeutic molecules require modification in their physicochemical properties. The conjugation of these APIs with fatty acids has demonstrated an enhancement in their lipophilicity and stability. The improvement in the formulations that resulted from the conjugation of a drug with a fatty acid includes increased half-life, enhanced cellular uptake and retention, targeted tumor delivery, reduced chemoresistance in cancer, and improved blood-brain-barrier (BBB) penetration. In this review, various therapeutic molecules, including small molecules, peptides and oligonucleotides, that have been conjugated with fatty acid have been thoroughly discussed along with various conjugation strategies. The application of nano-system based delivery is gaining a lot of attention due to its ability to provide controlled drug release, targeting and reducing the extent of side effects. This review also covers various nano-carriers that have been utilized for the delivery of fatty acid drug conjugates. The enhanced lipophilicity of the drug-fatty acid conjugate has shown to enhance the affinity of the drug towards these carriers, thereby increasing the entrapment efficiency and formulation performance.

Integrin-Targeting Peptides for the Design of Functional Cell-Responsive Biomaterials

Integrins are a family of cell surface receptors crucial to fundamental cellular functions such as adhesion, signaling, and viability, deeply involved in a variety of diseases, including the initiation and progression of cancer, of coronary, inflammatory, or autoimmune diseases. The natural ligands of integrins are glycoproteins expressed on the cell surface or proteins of the extracellular matrix. For this reason, short peptides or peptidomimetic sequences that reproduce the integrin-binding motives have attracted much attention as potential drugs. When challenged in clinical trials, these peptides/peptidomimetics let to contrasting and disappointing results. In the search for alternative utilizations, the integrin peptide ligands have been conjugated onto nanoparticles, materials, or drugs and drug carrier systems, for specific recognition or delivery of drugs to cells overexpressing the targeted integrins. Recent research in peptidic integrin ligands is exploring new opportunities, in particular for the design of nanostructured, micro-fabricated, cell-responsive, stimuli-responsive, smart materials.

Peptide-Based Drug-Delivery Systems in Biotechnological Applications: Recent Advances and Perspectives

Peptides of natural and synthetic sources are compounds operating in a wide range of biological interactions. They play a key role in biotechnological applications as both therapeutic and diagnostic tools. They are easily synthesized thanks to solid-phase peptide devices where the amino acid sequence can be exactly selected at molecular levels, by tuning the basic units. Recently, peptides achieved resounding success in drug delivery and in nanomedicine smart applications. These applications are the most significant challenge of recent decades: they can selectively deliver drugs to only pathological tissues whilst saving the other districts of the body. This specific feature allows a reduction in the drug side effects and increases the drug efficacy. In this context, peptide-based aggregates present many advantages, including biocompatibility, high drug loading capacities, chemical diversity, specific targeting, and stimuli responsive drug delivery. A dual behavior is observed: on the one hand they can fulfill a structural and bioactive role. In this review, we focus on the design and the characterization of drug delivery systems using peptide-based carriers; moreover, we will also highlight the peptide ability to self-assemble and to actively address nanosystems toward specific targets.

Dual integrin αvβ 3 and NRP-1-Targeting Paramagnetic Liposome for Tumor Early Detection in Magnetic Resonance Imaging

Enhanced MRI (magnetic resonance imaging) plays a vital role in the early detection of tumor but with low specificity. Molecular imaging of angiogenesis could efficiently deliver contrast agents to the tumor site by specific targeted carriers. We designed and synthesized dual-targeted paramagnetic liposomes functionalized with two angiogenesis-targeting ligands, the αVβ3 integrin-specific RGD (Arg-Gly-Asp) and the neuropilin-1 (NRP-1) receptor-specific ATWLPPR (Ala-Thr-Trp-Leu-Pro-Pro-Arg) (A7R). These liposomes were proved to be in the nanoparticle range and demonstrated to effectively encapsulate paramagnetic MRI contrast agents Gd-DTPA (gadolinium-diethylenetriamine pentaacetic acid). T1 relaxivity of various liposome formulations was lower than pure Gd-DTPA but with no statistically significant difference. In vitro cellular uptake and competitive inhibition assay showed the higher binding affinity of dual-targeted liposomes to HUVECs (human umbilical vein endothelial cells) and A549 cells compared with pure Gd-DTPA, non-targeted, and single-targeted liposomes, which was proved to be mediated by the binding of RGD/ανβ3-integrin and A7R/NRP1. For MR imaging of mice bearing A549 cells in vivo, dual-targeted liposomes reached the highest SER (signal enhancement rate) value with a significant difference at all experimental time points. It was about threefold increase compared to pure Gd-DTPA and non-targeted liposomes and was 1.5-fold of single-targeted liposomes at 2 h post injection. The SER was lowered gradually and decreased only by 40% of the peak value in 6 h. Dual-targeted liposomes were likely to exert a synergistic effect and the specificity of delivering Gd-DTPA to the tumor site. Therefore, dual-ανβ3-integrin-NRP1-targeting paramagnetic liposome with a RGD-ATWLPPR heterodimeric peptide might be a potent system for molecular imaging of tumor.

A dual-targeting reconstituted high density lipoprotein leveraging the synergy of sorafenib and antimiRNA21 for enhanced hepatocellular carcinoma therapy

Sorafenib (So) is a multi-target kinase inhibitor extensively used in clinic for hepatocellular carcinoma therapy. It demonstrated strong inhibition both in tumor proliferation and tumor angiogenesis, while hampered by associated cutaneous side-effect and drug resistance. The knockdown of miR-21 with antisense oligonucleotides (antimiRNA21) was regarded as an efficient strategy for increasing tumor sensibility to chemotherapy, which could be employed to appreciate the efficacy of So. Herein, we successfully formulated a dual-targeting delivery system for enhanced hepatocellular carcinoma therapy by encapsulating So and antimiRNA21 in RGD pentapeptide-modified reconstituted high-density lipoprotein (RGD-rHDL/So/antimiRNA21). The RGD and apolipoprotein A-I (ApoA-I) on nanoparticles (NPs) could drive the system simultaneously to tumor neovascular and parenchyma by binding to the overexpressed ανβ3-integrin and SR-B1 receptors, achieving precise delivery of therapeutics to maximize the efficacy. A series in vitro and in vivo experiments revealed that co-delivery of So and antimiRNA21 by RGD-rHDL significantly strengthened the anti-tumor and anti-angiogenic effect of So with negligible toxicity towards major organs, reversed drug-resistance and was capable of remodeling tumor environments. The constructed RGD-rHDL/So/antimiRNA21 with improved efficacy and excellent tumor targeting ability provided new idea for chemo-gene combined therapy in hepatocellular carcinoma.

STATEMENT OF SIGNIFICANCE

Sorafenib (So) is a multi-target kinase inhibitor which was approved by FDA as first-line drug for hepatocellular carcinoma (HCC) therapy. However, long term application of So in clinic was hampered by serious dermal toxicity and drug resistance. Although numerous researchers were devoted to finding alternatives or therapies as combination treatments with So to reach more desired therapeutic efficacy, the therapeutic options were still limited. The present study prepares RGD pentapeptide decorated biomimic reconstituted high-density lipoprotein (rHDL) loaded with So and antimiRNA21 (RGD-rHDL/So/antimiRNA21) for enhanced HCC therapy. The RGD-rHDL/So/antimiRNA21 NPs offer an effective platform for anti-tumor and anti-angiogenesis therapy in HCC and provide new approach to reverse drug-resistance of So for feasible clinical application.

Paclitaxel-Loaded pH-Sensitive Liposome: New Insights on Structural and Physicochemical Characterization

A long-circulating and pH-sensitive liposome containing paclitaxel (SpHL-PTX) was recently developed by our group. Once in an acidic environment, for example, tumors, these liposomes undergo destabilization, releasing the encapsulated drug. In this way, the aim of this study was to evaluate the molecular and supramolecular interactions between the lipid bilayer and PTX in similar biological environment conditions. High-sensitivity analyses of SpHL-PTX structures were obtained by the small-angle X-ray scattering technique combined with other techniques such as dynamic light scattering, asymmetric flow field-flow fractionation, transmission electron microscopy, and high-performance liquid chromatography. The results showed that PTX incorporation in the liposomal bilayer clearly leads to changes in supramolecular organization of dioleoylphosphatidylethanolamine (DOPE) molecules, inducing the formation of more ordered structures. Changes in supramolecular organization were observed at lower pH, indicating that pH sensitivity was preserved even in the presence of fetal bovine serum proteins. Furthermore, morphological and physicochemical characterization of SpHL-PTX evidenced the formation of nanosized dispersion suitable for intravenous administration. In conclusion, a stable nanosized dispersion of PTX was obtained at pH 7.4 with suitable parameters for intravenous administration. At lower pH conditions, the pH sensitivity of the system was clearly evidenced by changes in the supramolecular organization of DOPE molecules, which is crucial for the delivery of PTX into the cytoplasm of the targeted cells. In this way, the results obtained by different techniques confirm the feasibility of SpHL as a promising tool to PTX delivery in acidic environments, such as tumors.

Anticancer Efficacy of Targeted Shikonin Liposomes Modified with RGD in Breast Cancer Cells

Shikonin (SHK) has been proven to have a good anti-tumor effect. However, poor water solubility and low bioavailability limit its wide application in clinical practice. In this study, to overcome these drawbacks, RGD-modified shikonin-loaded liposomes (RGD-SSLs-SHK) were successfully prepared. It exhibited excellent physicochemical characteristics including particle size, zeta potential, encapsulation efficiency, and delayed release time. Meanwhile, the targeting activity of the RGD-modified liposomes was demonstrated by flow cytometry and confocal microscopy in the α_vβ₃-positive MDA-MB-231 cells. Besides exhibiting greater cytotoxicity in vitro, compared with non-targeted shikonin-loaded liposomes (SSLs-SHK), RGD-SSLs-SHK could also evidently induce apoptosis by decreasing the expression of Bcl-2 and increasing the expression of Bax. It could also inhibit cell proliferation, migration, invasion, and adhesion by reducing the expression of MMP-9 and the level of NF-κB p65, but did not affect the expression of MMP-2 in the MDA-MB-231 cells. Therefore, these findings indicated that the strategy to use RGD-modified liposomes as carriers for targeted delivery of shikonin is a very promising approach to achieve breast cancer targeted therapy.

Paclitaxel-loaded folate-coated long circulating and pH-sensitive liposomes as a potential drug delivery system: A biodistribution study

A range of antitumor agents for cancer treatment is available; however, they show low specificity, which often limit their use. Recently, we have reported the preparation of folate-coated long-circulating and pH-sensitive liposomes (SpHL-folate-PTX) loaded with paclitaxel (PTX), an effective drug for the treatment of solid tumors, including breast cancer. The purpose of this study was to prepare and characterize SpHL-PTX and SpHL-folate-PTX radiolabeled with technetium-99m (99mTc). Biodistribution studies and scintigraphic images were performed after intravenous administration of 99mTc-PTX, 99mTc-SpHL-PTX and 99mTc-SpHL-folate-PTX into healthy and tumor-bearing mice. High radiochemical purity (>98%) and in vitro stability (>90%) were achieved for both liposome formulations. The pharmacokinetic properties of 99mTc-SpHL-DTPA-PTX and 99mTc-SpHL-folate-DTPA-PTX decreased in a monophasic manner showing half-life of 400.1 and 541.8min, respectively. Scintigraphic images and biodistribution studies showed a significant uptake in liver, spleen and kidneys, demonstrating these routes as way for excretion. At 8h post-injection, the liposomal tumor uptake was higher than 99mTc-PTX. Interesting, 4h after administration, the liposome folate coated showed higher tumor-to-muscle ratio than 99mTc-SpHL-DTPA-PTX and 99mTc-PTX. In conclusion, the liposomal systems, showed high tumor uptake by scintigraphic images, especially the 99mTc-SpHL-folate-DTPA-PTX that showed a sustained and higher tumor-to-muscle ratio than non-functionalized liposome, which indicate its feasibility as a PTX delivery system to folate positive tumors.

Physicochemical characterization of chitosan-hyaluronan-coated solid lipid nanoparticles for the targeted delivery of paclitaxel: a proof-of-concept study in breast cancer cells

Aim: To investigate the potential of modified solid lipid nanoparticles (SLN) for the delivery of paclitaxel (PAX). Materials & methods: SLN loaded with PAX were prepared via modified high-pressure hot homogenization. Formulation parameters were optimized to obtain a high-quality delivery system. SLN cores were coated, layer-by-layer, with a chitosan and hyaluronan (HA) shell. Selectivity toward HA receptors was tested in a breast cancer cell line, MCF-7. Results: Stable and reproducible nano-sized and negatively charged nanoparticles resulted. Findings reveal that chitosan-HA-coated SLN facilitated the targeting, cellular uptake and the time-/dose-controlled delivery and release of PAX, enhancing intrinsic chemotherapeutic activities. Conclusion: SLN are suitable carrier candidates for nano-oncology given their localized, and potent cytotoxic potential overcoming multidrug-resistant cancer cells.

Paradigm shift in bacteriophage-mediated delivery of anticancer drugs: from targeted 'magic bullets' to self-navigated 'magic missiles'

INTRODUCTION

New phage-directed nanomedicines have emerged recently as a result of the in-depth study of the genetics and structure of filamentous phage and evolution of phage display and phage nanobiotechnology. This review focuses on the progress made in the development of the cancer-targeted nanomaterials and discusses the trends in using phage as a bioselectable molecular navigation system. Areas covered: The merging of phage display technologies with nanotechnology in recent years has proved promising in different areas of medicine and technology, such as medical diagnostics, molecular imaging, vaccine development and targeted drug/gene delivery, which is the focus of this review. The authors used data obtained from their research group and sourced using Science Citation Index (Web of Science) and NCBI PubMed search resources. Expert opinion: First attempts of adapting traditional concepts of direct targeting of tumor using phage-targeted nanomedicines has shown minimal improvements. With discovery and study of biological and technical barriers that prevent anti-tumor drug delivery, a paradigm shift from traditional drug targeting to nanomedicine navigation systems is required. The advanced bacteriophage-driven self-navigation systems are thought to overcome those barriers using more precise, localized phage selection methods, multi-targeting 'promiscuous' ligands and advanced multifunctional nanomedicine platforms.

Peptide-22 and Cyclic RGD Functionalized Liposomes for Glioma Targeting Drug Delivery Overcoming BBB and BBTB

Chemotherapy outcomes for the treatment of glioma remain unsatisfied due to the inefficient drug transport across BBB/BBTB and poor drug accumulation in the tumor site. Nanocarriers functionalized with different targeting ligands are considered as one of the most promising alternatives. However, few studies were reported to compare the targeting efficiency of the ligands and develop nanoparticles to realize BBB/BBTB crossing and brain tumor targeting simultaneously. In this study, six peptide-based ligands (Angiopep-2, T7, Peptide-22, c(RGDfK), D-SP5 and Pep-1), widely used for brain delivery, were selected to decorate liposomes, respectively, so as to compare their targeting ability to BBB or BBTB. Based on the in vitro cellular uptake results on BCECs and HUVECs, Peptide-22 and c(RGDfK) were picked to construct a BBB/BBTB dual-crossing, glioma-targeting liposomal drug delivery system c(RGDfK)/Pep-22-DOX-LP. In vitro cellular uptake demonstrated that the synergetic effect of c(RGDfK) and Peptide-22 could significantly increase the internalization of liposomes on U87 cells. In vivo imaging further verified that c(RGDfK)/Pep-22-LP exhibited higher brain tumor distribution than single ligand modified liposomes. The median survival time of glioma-bearing mice treated with c(RGDfK)/Pep-22-DOX-LP (39.5 days) was significantly prolonged than those treated with free doxorubicin or other controls. In conclusion, the c(RGDfK) and Peptide-22 dual-modified liposome was constructed based on the targeting ability screening of various ligands. The system could effectively overcome BBB/BBTB barriers, target to tumor cells and inhibit the growth of glioma, which proved its potential for improving the efficacy of chemotherapeutics for glioma therapy.

Implementation of Nanoparticles in Cancer Therapy

Cancer is a wide group of diseases and generally characterized by uncontrolled proliferation of cells whose metabolic activities are disrupted. Conventionally, chemotherapy, radiotherapy, and surgery are used in the treatment of cancer. However, in theory, even a single cancer cell may trigger recurrence. Therefore, these treatments cannot provide high survival rate for deadly types. Identification of alternative methods in treatment of cancers is inevitable because of adverse effects of conventional methods. In the last few decades, nanotechnology developed by scientists working in different disciplines—physics, chemistry, and biology—offers great opportunities. It is providing elimination of both circulating tumor cells and solid cancer cells by targeting cancer cells. In this chapter, inadequate parts of conventional treatment methods, nanoparticle types used in new treatment methods of cancer, and targeting methods of nanoparticles are summarized; furthermore, recommendations of future are provided.

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.

MRI-guided liposomes for targeted tandem chemotherapy and therapeutic response prediction

Liposomes are effective drug delivery systems that can be functionalized with imaging contrast agents, providing both diagnosis and monitoring of disease treatment. Here we describe the design of a theranostic liposomal drug delivery system whose biodistribution can be real time imaged by contrast enhanced MRI and can achieve tandem chemotherapy drug delivery. Because T1 relaxation of MRI depends upon the chemical structure of contrast agent as well as its interaction with neighbor environment, we rationally designed a functional liposome for in vivo T1 enhanced MRI. The liposome shows a 36-fold higher T1 relaxation rate over the commercial MRI contrast agent Omniscan® and a long circulation time up to 300min in vivo. Moreover, the multifunctional liposome carries both hydrophobic and hydrophilic chemotherapeutic drugs, can synergistically enhance therapeutic effects of multiple drugs and selectively deliver them to lung tumors, leading to lower doses, toxicity and sustained release. The nanoparticles, which exhibit favorable biodistributions to tumors, offer new possibilities for the simultaneous delivery of more than one drug and the evaluation of therapeutic response in vivo by T1 enhanced MRI.

STATEMENT OF SIGNIFICANCE

Cancer cells invoke different mechanisms to resist cancer therapies, particularly when delivering a single agent in a given therapy. The combination of two (or more) thermotherapy agents provides a promising way to circumvent such situations of drug resistance, due to a favorable synergistic effect that "tricks" the drug resistance mechanism. However, challenges to the simultaneous delivery of two drugs prevail, especially with regards to the simultaneous delivery of hydrophobic and hydrophobic drugs. Furthermore, non-invasive in vivo imaging of drug distribution enables the real-time monitoring and prediction of therapeutic responses to treatment. In this study, we rationally designed a theranostic liposomal drug delivery system whose biodistribution can be imaged via T1-weighted MRI in real-time and can achieve tandem chemotherapy drug delivery. This original study will be of considerable use to the wider drug delivery community.

Dual-functionalized liposomal delivery system for solid tumors based on RGD and a pH-responsive antimicrobial peptide

[D]-H₆L₉, as a pH-responsive anti-microbial peptide (AMP), has been evidenced by us to be an excellent choice in tumor microenvironment-responsive delivery as it could render liposomes responsive to the acidified tumor microenvironment. However, [D]-H₆L₉-modified liposomes could not actively target to tumor area. Therefore, integrin α_vβ₃-targeted peptide RGD was co-modified with [D]-H₆L₉ onto liposomes [(R + D)-Lip] for improved tumor delivery efficiency. Under pH 6.3, (R + D)-Lip could be taken up by C26 cells and C26 tumor spheroids (integrin α_vβ₃-positive) with significantly improved efficiency compared with other groups, which was contributed by both RGD and [D]-H₆L₉, while RGD did not increase the cellular uptake performance on MCF-7 cells (integrin α_vβ₃-negative). Results showed that RGD could decrease cellular uptake of (R + D)-Lip while [D]-H₆L₉ could increase it, implying the role of both RGD and [D]-H₆L₉ in cellular internalization of (R + D)-Lip. On the other hand, (R + D)-Lip could escape the entrapment of lysosomes. PTX-loaded (R + D)-Lip could further increase the cellular toxicity against C26 cells compared with liposomes modified only with RGD and [D]-H₆L₉ respectively, and achieve remarkable tumor inhibition effect on C26 tumor models.

Potential of CXCR4/CXCL12 Chemokine Axis in Cancer Drug Delivery

This review discusses the potential of CXCR4 chemokine receptor in the design of anticancer and antimetastatic drug delivery systems. The role of CXCR4 in cancer progression and metastasis is discussed in the context of the development of several types of drug delivery strategies. Overview of drug delivery systems targeted to cancers that overexpress CXCR4 is provided, together with the main types of CXCR4-binding ligands used in targeting applications. Drug delivery applications that take advantage of CXCR4 inhibition to achieve enhanced anticancer and antimetastatic activity of combination treatments are also discussed.

A dual functional liposome specifically targets melanoma cells through integrin and ephrin receptors

A novel bi-functional liposome delivers docetaxel specifically to melanoma cancer cells targeting integrin (α₄β₁) and ephrin (EphA2) receptors and enhances the efficacy of docetaxel.

Experimental design of a liposomal lipid system: A potential strategy for paclitaxel-based breast cancer treatment

Paclitaxel (PTX) is widely used as a first-line treatment for patients with metastatic breast cancer; however, its poor water solubility represents a major challenge for parenteral administration. The encapsulation of the PTX in drug-delivery systems with high affinity for tumor sites could improve the uptake and increase its therapeutic efficacy. In this work, long-circulating and pH-sensitive PEG-coated (SpHL-PTX) and PEG-folate-coated liposomes containing PTX (SpHL-FT-PTX) were prepared, and the physicochemical properties and in vitro cytotoxic activity were evaluated. Both formulations presented adequate physicochemical properties, including a mean diameter smaller than 200 nm, zeta potential values near the neutral range, and an encapsulation percentage higher than 93%. Moreover, SpHL-FT-PTX showed a good stability after storage for 100 days at 4 °C. The viability studies on breast cancer cell lines (MDA-MB-231 and MCF-7) demonstrated cytotoxic activity more pronounced for SpHL-FT-PTX than for SpHL-PTX or free drug for both tumor cell lines. This activity was reduced to a rate comparable to SpHL-PTX when the cells were previously treated with folic acid in order to saturate the receptors. In contrast, in the normal cell line (L929), cell viability was decreased only by free or liposomal PTX in the highest concentrations. A significantly higher selectivity index was obtained after SpHL-FT-PTX treatment compared to SpHL-PTX and free PTX. Therefore, the results of the present work suggest that SpHL-FT-PTX can be a promising formulation for the treatment of metastatic breast cancer.

A7RC peptide modified paclitaxel liposomes dually target breast cancer

A7R peptide (ATWLPPR), a ligand of the NRP-1 receptor, regulates the intracellular signal transduction related to tumor vascularization and tumor growth. Here, we designed A7R-cysteine peptide (A7RC) surface modified paclitaxel liposomes (A7RC-LIPs) to achieve targeting delivery and inhibition of tumor growth and angiogenesis simultaneously. The cytotoxicity, inhibiting angiogenesis, and internalization of various liposomes by cells were assessed in vitro to confirm the influence of the peptide modification. The accumulations of A7RC-LIPs in various xenografts in mice were tracked to further identify the function of the peptide on the liposomes' surface. The results confirmed that A7RC peptides could enhance the uptake of vesicles by MDA-MB-231 cells, leading to stronger cytotoxicity in vitro and higher accumulation of vesicles in MDA-MB-231 xenografts in vivo. In addition, A7RC peptides enhanced the inhibitory effects of LIPs on the HUVEC tubular formation on Matrigel. The A7RC-LIPs may be promising drug carriers for anticancer therapy.

Bioengineering strategies for designing targeted cancer therapies

The goals of bioengineering strategies for targeted cancer therapies are (1) to deliver a high dose of an anticancer drug directly to a cancer tumor, (2) to enhance drug uptake by malignant cells, and (3) to minimize drug uptake by nonmalignant cells. Effective cancer-targeting therapies will require both passive- and active-targeting strategies and a thorough understanding of physiologic barriers to targeted drug delivery. Designing a targeted therapy includes the selection and optimization of a nanoparticle delivery vehicle for passive accumulation in tumors, a targeting moiety for active receptor-mediated uptake, and stimuli-responsive polymers for control of drug release. The future direction of cancer targeting is a combinatorial approach, in which targeting therapies are designed to use multiple-targeting strategies. The combinatorial approach will enable combination therapy for delivery of multiple drugs and dual ligand targeting to improve targeting specificity. Targeted cancer treatments in development and the new combinatorial approaches show promise for improving targeted anticancer drug delivery and improving treatment outcomes.

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.

Liposomal paclitaxel formulations

Over the past three decades, taxanes represent one of the most important new classes of drugs approved in oncology. Paclitaxel (PTX), the prototype of this class, is an anti-cancer drug approved for the treatment of breast and ovarian cancer. However, notwithstanding a suitable premedication, present-day chemotherapy employing a commercial preparation of PTX (Taxol®) is associated with serious side effects and hypersensitivity reactions. Liposomes represent advanced and versatile delivery systems for drugs. Generally, both in vivo mice tumor models and human clinical trials demonstrated that liposomal PTX formulations significantly increase a maximum tolerated dose (MTD) of PTX which outperform that for Taxol®. Liposomal PTX formulations are in various stages of clinical trials. LEP-ETU (NeoPharm) and EndoTAG®-1 (Medigene) have reached the phase II of the clinical trials; Lipusu® (Luye Pharma Group) has already been commercialized. Present achievements in the preparation of various liposomal formulations of PTX, the development of targeted liposomal PTX systems and the progress in clinical testing of liposomal PTX are discussed in this review summarizing about 30 years of liposomal PTX development.

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.

Dual targeting strategies with bispecific antibodies

Monoclonal antibodies are widely used for the treatment of cancer, inflammatory and infectious diseases and other disorders. Most of the marketed antibodies are monospecific and therefore capable of interacting and interfering with a single target. However, complex diseases are often multifactorial in nature, and involve redundant or synergistic action of disease mediators or upregulation of different receptors, including crosstalk between their signaling networks. Consequently, blockade of multiple, different pathological factors and pathways may result in improved therapeutic efficacy. This result can be achieved by combining different drugs, or use of the dual targeting strategies applying bispecific antibodies that have emerged as an alternative to combination therapy. This review discusses the various dual targeting strategies for which bispecific antibodies have been developed and provides an overview of the established bispecific antibody formats.

Targeted anticancer prodrug with mesoporous silica nanoparticles as vehicles

A targeted anticancer prodrug system was fabricated with 180 nm mesoporous silica nanoparticles (MSNs) as carriers. The anticancer drug doxorubicin (DOX) was conjugated to the particles through an acid-sensitive carboxylic hydrazone linker which is cleavable under acidic conditions. Moreover, folic acid (FA) was covalently conjugated to the particle surface as the targeting ligand for folate receptors (FRs) overexpressed in some cancer cells. The in vitro release profiles of DOX from the MSN-based prodrug systems showed a strong dependence on the environmental pH values. The fluorescent dye FITC was incorporated in the MSNs so as to trace the cellular uptake on a fluorescence microscope. Cellular uptakes by HeLa, A549 and L929 cell lines were tested for FA-conjugated MSNs and plain MSNs respectively, and a much more efficient uptake by FR-positive cancer cells (HeLa) can be achieved by conjugation of folic acid onto the particles because of the folate-receptor-mediated endocytosis. The cytotoxicities for the FA-conjugated MSN prodrug, the plain MSN prodrug and free DOX against three cell lines were determined, and the result indicates that the FA-conjugated MSN prodrug exhibits higher cytotoxicity to FR-positive cells, and reduced cytotoxicity to FR-negative cells. Thus, with 180 nm MSNs as the carriers for the prodrug system, good drug loading, selective targeting and sustained release of drug molecules within targeted cancer cells can be realized. This study may provide useful insights for designing and improving the applicability of MSNs in targeted anticancer prodrug systems.