Targeted Delivery of Cargoes into a Murine Solid Tumor by a Cell-Penetrating Peptide and Cleavable Poly(ethylene glycol) Comodified Liposomal Delivery System via Systemic Administration

Research Advances of Lipid Nanoparticles in the Treatment of Colorectal Cancer

Colorectal cancer (CRC) is a common type of gastrointestinal tract (GIT) cancer and poses an enormous threat to human health. Current strategies for metastatic colorectal cancer (mCRC) therapy primarily focus on chemotherapy, targeted therapy, immunotherapy, and radiotherapy; however, their adverse reactions and drug resistance limit their clinical application. Advances in nanotechnology have rendered lipid nanoparticles (LNPs) a promising nanomaterial-based drug delivery system for CRC therapy. LNPs can adapt to the biological characteristics of CRC by modifying their formulation, enabling the selective delivery of drugs to cancer tissues. They overcome the limitations of traditional therapies, such as poor water solubility, nonspecific biodistribution, and limited bioavailability. Herein, we review the composition and targeting strategies of LNPs for CRC therapy. Subsequently, the applications of these nanoparticles in CRC treatment including drug delivery, thermal therapy, and nucleic acid-based gene therapy are summarized with examples provided. The last section provides a glimpse into the advantages, current limitations, and prospects of LNPs in the treatment of CRC.

Effect of TIMPs and Their Minimally Engineered Variants in Blocking Invasion and Migration of Brain Cancer Cells

Matrix metalloproteinases (MMPs) play a pivotal role in extracellular matrix (ECM) remodeling, influencing various aspects of cancer progression including migration, invasion, angiogenesis, and metastasis. Overexpression of MMPs, particularly MMP-2 and MMP-9, is notably pronounced in glioblastoma multiforme (GBM), a highly aggressive primary brain tumor characterized by diffuse and infiltrative behavior. Previous attempts to develop small molecule MMP inhibitors have failed in clinical trials, necessitating the exploration of more stable and selective alternatives. Tissue inhibitors of metalloproteinases (TIMPs), endogenous human proteins, offer promising potential due to their stability and broader interaction interfaces compared to small molecule inhibitors. In this study, we examined the effectiveness of wild-type human TIMP-1 and TIMP-3, alongside engineered minimal TIMP variants (mTC1 and mTC3), specifically designed for targeted MMP inhibition to reduce the migratory and invasive capabilities of GBM cells. Our investigation focused on these minimal TIMP variants, which provide enhanced tissue penetration and cellular uptake due to their small molecular weight, aiming to validate their potential as therapeutic agents. The results demonstrated that mTC1 and mTC3 effectively inhibit MMP activity, a critical factor in GBM aggressiveness, thereby highlighting their promise in controlling tumor spread. Given the lethality of GBM and the limited effectiveness of current treatments, the application of engineered TIMP variants represents a novel and potentially transformative therapeutic approach. By offering targeted MMP inhibition, these variants may significantly improve patient outcomes, providing new avenues for treatment and enhancing the survival and quality of life for patients with this devastating disease.

Role and application of CRISPR-Cas9 in the management of Alzheimer's disease

Alzheimer's disease (AD) is a serious health issue that has a significant social and economic impact worldwide. One of the key aetiological signs of the disease is a gradual reduction in cognitive function and irreversible neuronal death. According to a 2019 global report, more than 5.8 million people in the United States (USA) alone have received an AD diagnosis, with 45% of those people falling into the 75-84 years age range. According to the predictions, there will be 15 million affected people in the USA by 2050 due to the disease's steadily rising patient population. Cognitive function and memory formation steadily decline as a result of an irreversible neuron loss in AD, a chronic neurodegenerative illness. Amyloid-beta and phosphorylated Tau are produced and accumulate in large amounts, and glial cells are overactive. Additionally, weakened neurotrophin signalling and decreased synapse function are crucial aspects of AD. Memory loss, apathy, depression, and irritability are among the primary symptoms. The aetiology, pathophysiology, and causes of both cognitive decline and synaptic dysfunction are poorly understood despite extensive investigation. CRISPR/Cas9 is a promising gene-editing technique since it can fix certain gene sequences and has a lot of potential for treating AD and other human disorders. Regardless of hereditary considerations, an altered Aβ metabolism is frequently seen in familial and sporadic AD. Therefore, since mutations in the PSEN-1, PSEN-2 and APP genes are a contributing factor to familial AD, CRISPR/Cas9 technology could address excessive Aβ production or mutations in these genes. Overall, the potential of CRISPR-Cas9 technology outweighs it as currently the greatest gene-editing tool available for researching neurodegenerative diseases like AD.

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.

Integration of an LPAR1 Antagonist into Liposomes Enhances Their Internalization and Tumor Accumulation in an Animal Model of Human Metastatic Breast Cancer

Lysophosphatidic acid receptor 1 (LPAR1) is elevated in breast cancer. The deregulation of LPAR1, including the function and level of expression, is linked to cancer initiation, progression, and metastasis. LPAR1 antagonists, AM095 or Ki16425, may be effective therapeutic molecules, yet their limited water solubility hinders in vivo delivery. In this study, we report on the synthesis of two liposomal formulations incorporating AM095 or Ki16425, embedded within the lipid bilayer, as targeted nanocarriers for metastatic breast cancer (MBC). The data show that the Ki16425 liposomal formulation exhibited a 50% increase in internalization by MBC mouse epithelial cells (4T1) and a 100% increase in tumor accumulation in a mouse model of MBC compared with that of a blank liposomal formulation (control). At the same time, normal mouse epithelial cells (EpH-4Ev) internalized the Ki16425 liposomal formulation 25% lesser than the control formulation. Molecular dynamics simulations show that the integration of AM095 or Ki16425 modified the physical and mechanical properties of the lipid bilayer, making it more flexible in these liposomal formulations compared with liposomes without drug. The incorporation of an LPAR1 antagonist within a liposomal drug delivery system represents a viable therapeutic approach for targeting the LPA-LPAR1 axis, which may hinder the progression of MBC.

Multicompartment colloid systems with lipid and polymer membranes for biomedical applications

Multicompartment structures have the potential for biomedical applications because they can act as multifunctional systems and provide simultaneous delivery of drugs and diagnostics agents of different types. Moreover, some of them mimic biological cells to some extent with organelles as separate sub-compartments. This article analyses multicompartment colloidal structures with smaller sub-units covered with lipid or polymer membranes that provide additional protection for the encapsulated substances. Vesosomes with small vesicles encapsulated in the inner pools of larger liposomes are the most studied systems to date. Dendrimer molecules are enclosed by a lipid bilayer shell in dendrosomes. Capsosomes, polymersomes-in-polymer capsules, and cubosomes-in-polymer capsules are composed of sub-compartments encapsulated within closed multilayer polymer membranes. Janus or Cerberus emulsions contain droplets composed of two or three phases: immiscible oils in O/W emulsions and aqueous polymer or salt solutions that are separated into two or three phases and form connected droplets in W/O emulsions. In more cases, the external surface of engulfed droplets in Janus or Cerberus emulsions is covered with a lipid or polymer monolayer. eLiposomes with emulsion droplets encapsulated into a bilayer shell have been given little attention so far, but they have very great prospects. In addition to nanoemulsion droplets, solid lipid nanoparticles, nanostructured lipid carriers and inorganic nanoparticles can be loaded into eLiposomes. Molecular engineering of the external membrane allows the creation of ligand-targeted and stimuli-responsive multifunctional systems. As a result, the efficacy of drug delivery can be significantly enhanced.

Liposomes in Cancer Therapy: How Did We Start and Where Are We Now

Since their first discovery in the 1960s by Alec Bangham, liposomes have been shown to be effective drug delivery systems for treating various cancers. Several liposome-based formulations received approval by the U.S. Food and Drug Administration (FDA) and European Medicines Agency (EMA), with many others in clinical trials. Liposomes have several advantages, including improved pharmacokinetic properties of the encapsulated drug, reduced systemic toxicity, extended circulation time, and targeted disposition in tumor sites due to the enhanced permeability and retention (EPR) mechanism. However, it is worth noting that despite their efficacy in treating various cancers, liposomes still have some potential toxicity and lack specific targeting and disposition. This explains, in part, why their translation into the clinic has progressed only incrementally, which poses the need for more research to focus on addressing such translational limitations. This review summarizes the main properties of liposomes, their current status in cancer therapy, and their limitations and challenges to achieving maximal therapeutic efficacy.

Enhancing Methotrexate Delivery in the Brain by Mesoporous Silica Nanoparticles Functionalized with Cell-Penetrating Peptide using in Vivo and ex Vivo Monitoring

The blood-brain barrier (BBB) acts as a physical/biochemical barrier that protects brain parenchyma from potential hazards exerted by different xenobiotics found in the systemic circulation. This barrier is created by "a lipophilic gate" as well as a series of highly organized influx/efflux mechanisms. The BBB bottleneck adversely affects the efficacy of chemotherapeutic agents in treating different CNS malignancies such as glioblastoma, an aggressive type of cancer affecting the brain. In the present study, mesoporous silica nanoparticles (MSNs) were conjugated with the transactivator of transcription (TAT) peptide, a cell-penetrating peptide, to produce MSN-NH-TAT with the aim of improving methotrexate (MTX) penetration into the brain. The TAT-modified nanosystem was characterized by Fourier transform infrared spectrometry (FTIR), field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic light scattering (DLS), and N₂ adsorption-desorption analysis. In vitro hemolysis and cell viability studies confirmed the biocompatibility of the MSN-based nanocarriers. In addition, in vivo studies showed that the MTX-loaded MSN-NH-TAT improved brain-to-plasma concentration ratio, brain uptake clearance, and the drug's blood terminal half-life, compared with the use of free MTX. Taken together, the results of the present study indicate that MSN functionalization with TAT is crucial for delivery of MTX into the brain. The present nanosystem represents a promising alternative drug carrier to deliver MTX into the brain via overcoming the BBB.

Liposomes and liposome-like nanoparticles: From anti-fungal infection to the COVID-19 pandemic treatment

The liposome is the first nanomedicine transformed into the market and applied to human patients. Since then, such phospholipid bilayer vesicles have undergone technological advancements in delivering small molecular-weight compounds and biological drugs. Numerous investigations about liposome uses were conducted in different treatment fields, including anti-tumor, anti-fungal, anti-bacterial, and clinical analgesia, owing to liposome's ability to reduce drug cytotoxicity and improve the therapeutic efficacy and combinatorial delivery. In particular, two liposomal vaccines were approved in 2021 to combat COVID-19. Herein, the clinically used liposomes are reviewed by introducing various liposomal preparations in detail that are currently proceeding in the clinic or on the market. Finally, we discuss the challenges of developing liposomes and cutting-edge liposomal delivery for biological drugs and combination therapy.

Mitochondrial Targeting Probes, Drug Conjugates, and Gene Therapeutics

Mitochondria represent an important drug target for many phatology, including neurodegeneration, metabolic disease, heart failure, ischemia-reperfusion injury, and cancer. Mitochondrial dysfunctions are caused by mutation in mitochondrial DNA or in nuclear genes encoding mitochondrial proteins. Cell-penetrating peptides (CPPs) have been employed to overcome biological barriers, target this organelle, and therapeuticaly restore mitochondrial functions. Here, we describe recent methods used to deliver oligonucleotides targeting mitochondrial protein by using mitochondrial penetrating peptides. In particular, we highlight recent advances of formulated peptides/oligonucleotides nanocomplexes as a proof-of-principle for pharmaceutical form of peptide-based therapeutics.

Pharmacokinetic Analysis of Peptide-Modified Nanoparticles with Engineered Physicochemical Properties in a Mouse Model of Traumatic Brain Injury

Peptides are used to control the pharmacokinetic profiles of nanoparticles due to their ability to influence tissue accumulation and cellular interactions. However, beyond the study of specific peptides, there is a lack of understanding of how peptide physicochemical properties affect nanoparticle pharmacokinetics, particularly in the context of traumatic brain injury (TBI). We engineered nanoparticle surfaces with peptides that possess a range of physicochemical properties and evaluated their distribution after two routes of administration: direct injection into a healthy mouse brain and systemic delivery in a mouse model of TBI. In both administration routes, we found that peptide-modified nanoparticle pharmacokinetics were influenced by the charge characteristics of the peptide. When peptide-modified nanoparticles are delivered directly into the brain, nanoparticles modified with positively charged peptides displayed restricted distribution from the injection site compared to nanoparticles modified with neutral, zwitterionic, or negatively charged peptides. After intravenous administration in a TBI mouse model, positively charged peptide-modified nanoparticles accumulated more in off-target organs, including the heart, lung, and kidneys, than zwitterionic, neutral, or negatively charged peptide-modified nanoparticles. The increase in off-target organ accumulation of positively charged peptide-modified nanoparticles was concomitant with a relative decrease in accumulation in the injured brain compared to zwitterionic, neutral, or negatively charged peptide-modified nanoparticles. Understanding how nanoparticle pharmacokinetics are influenced by the physicochemical properties of peptides presented on the nanoparticle surface is relevant to the development of nanoparticle-based TBI therapeutics and broadly applicable to nanotherapeutic design, including synthetic nanoparticles and viruses.

CRISPR/Cas9 gene editing: New hope for Alzheimer's disease therapeutics

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Mutations in APP, PSEN1 and PSEN2 are known factors for AD pathobiology.

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CRISPR/Cas9 genome editing approach hold promises in AD management.

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CRISPR/Cas9 is utilized to help correct anomalous genetic functions.

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Off-target mutations may impair the functionality of edited cells.

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Non-viral vectors show better efficacy and safety than viral vectors.

Background

Alzheimer's disease (AD) is an insidious, irreversible, and progressive neurodegenerative health condition manifesting as cognitive deficits and amyloid beta (Aβ) plaques and neurofibrillary tangles. Approximately 50 million individuals are affected by AD, and the number is rapidly increasing globally. This review explores the role of CRISPR/Cas9 gene editing in the management of AD and its clinical manifestations.

Aim of Review

This review aims to provide a deep insight into the recent progress in CRISPR/Cas9-mediated genome editing and its use against neurodegenerative disorders, specifically AD. However, we have referred to its use against parkinsons’s disease (PD), Huntington’s disease (HD), and other human diseases, as is one of the most promising and emerging technologies for disease treatment.

Key Scientific Concepts of Review

The pathophysiology of AD is known to be linked with gene mutations, that is, presenilin (PSEN) and amyloid beta precursor protein (APP). However, clinical trials focused at the genetic level could not meet the desired efficiency. The CRISPR/Cas9 genome editing tool is one of the most powerful technologies for correcting inconsistent genetic signatures and now extensively used for AD management. It has significant potential for the correction of undesired gene mutations associated with AD. This technology has allowed the development of empirical AD models, therapeutic lines, and diagnostic approaches for better understanding the nervous system, from in vitro to in vivo models.

Stimulus-responsive liposomes for biomedical applications

Liposomes are amphipathic lipidic supramolecular aggregates that are able to encapsulate and carry molecules of both hydrophilic and hydrophobic nature. They have been widely used as in vivo drug delivery systems for some time because they offer features such as synthetic flexibility, biodegradability, biocompatibility, low immunogenicity, and negligible toxicity. In recent years, the chemical modification of liposomes has paved the way to the development of smart liposome-based drug delivery systems, which are characterized by even more tunable and disease-directed features. In this review, we highlight the different types of chemical modification introduced to date, with a particular focus on internal stimuli-responsive liposomes and prodrug activation.

PEGylation and Cell-Penetrating Peptides: Glimpse into the Past and Prospects in the Future

Several drug molecules have shown low bioavailability and pharmacokinetic profile due to metabolism by enzymes, excretion by the renal system, or due to other physiochemical properties of drug molecules. These problems have resulted in the loss of efficacy and the gain of side effects associated with drug molecules. PEGylation is one of the strategies to overcome these pharmacokinetic issues and has been successful in the clinic. Cell-penetrating Peptides (CPPs) help to deliver molecules across biological membranes and could be used to deliver cargo selectively to the intracellular site or to the drug target. Hence CPPs could be used to improve the efficacy and selectivity of the drug. However, due to the peptidic nature of CPPs, they have a low pharmacokinetic profile. Using PEGylation and CPPs together as a component of a drug delivery system, the and efficacy of drug molecules could be improved. The other important pharmacokinetic properties such as short half-life, solubility, stability, absorption, metabolism, and elimination could be also improved. Here in this review, we summarized PEGylated CPPs or PEGylation based formulations for CPPs used in a drug delivery system for several biomedical applications until August 2019.

CRISPR/Cas9 Delivery Potentials in Alzheimer's Disease Management: A Mini Review

Alzheimer’s disease (AD) is the most common dementia disorder. While genetic mutations account for only 1% of AD cases, sporadic AD resulting from a combination of genetic and risk factors constitutes >90% of the cases. Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)-associated protein (Cas9) is an impactful gene editing tool which identifies a targeted gene sequence, creating a double-stranded break followed by gene inactivation or correction. Although CRISPR/Cas9 can be utilized to irreversibly inactivate or correct faulty genes in AD, a safe and effective delivery system stands as a challenge against the translation of CRISPR therapeutics from bench to bedside. While viral vectors are efficient in CRISPR/Cas9 delivery, they might introduce fatal side effects and immune responses. As non-viral vectors offer a better safety profile, cost-effectiveness and versatility, they can be promising for the in vivo delivery of CRISPR/Cas9 therapeutics. In this minireview, we present an overview of viral and non-viral vector based CRISPR/Cas9 therapeutic strategies that are being evaluated on pre-clinical AD models. Other promising non-viral vectors that can be used for genome editing in AD, such as nanoparticles, nanoclews and microvesicles, are also discussed. Finally, we list the formulation and technical aspects that must be considered in order to develop a successful non-viral CRISPR/Cas9 delivery vehicle.

Cleavable PEGylation: a strategy for overcoming the "PEG dilemma" in efficient drug delivery

To prolong the circulation time of drug, PEGylation has been widely used via the enhanced permeability and retention (EPR) effect, thereby providing new hope for better treatment. However, PEGylation also brings the "PEG dilemma", which is difficult for the cellular absorption of drugs and subsequent endosomal escape. As a result, the activity of drugs is inevitably lost after PEG modification. To achieve successful drug delivery for effective treatment, the crucial issue associated with the use of PEG-lipids, that is, “PEG dilemma” must be addressed. In this paper, we introduced the development and application of nanocarriers with cleavable PEGylation, and discussed various strategies for overcoming the PEG dilemma. Compared to the traditional ones, the vehicle systems with different environmental-sensitive PEG-lipids were discussed, which cleavage can be achieved in response to the intracellular as well as the tumor microenvironment. This smart cleavable PEGylation provides us an efficient strategy to overcome “PEG dilemma”, thereby may be a good candidate for the cancer treatment in future.

Application of Light Scattering Techniques to Nanoparticle Characterization and Development

Over the years, the scientific importance of nanoparticles for biomedical applications has increased. The high stability and biocompatibility, together with the low toxicity of the nanoparticles developed lead to their use as targeted drug delivery systems, bioimaging systems, and biosensors. The wide range of nanoparticles size, from 10 nm to 1 μm, as well as their optical properties, allow them to be studied using microscopy and spectroscopy techniques. In order to be effectively used, the physicochemical properties of nanoparticle formulations need to be taken into account, namely, particle size, surface charge distribution, surface derivatization and/or loading capacity, and related interactions. These properties need to be optimized considering the final nanoparticle intended biodistribution and target. In this review, we cover light scattering based techniques, namely dynamic light scattering and zeta-potential, used for the physicochemical characterization of nanoparticles. Dynamic light scattering is used to measure nanoparticles size, but also to evaluate their stability over time in suspension, at different pH and temperature conditions. Zeta-potential is used to characterize nanoparticles surface charge, obtaining information about their stability and surface interaction with other molecules. In this review, we focus on nanoparticle characterization and application in infection, cancer and cardiovascular diseases.

Targeted multifunctional redox-sensitive micelle co-delivery of DNA and doxorubicin for the treatment of breast cancer

Drug/gene co-delivery carriers are a promising strategy for cancer treatment. Thus, herein, T7-conjugated redox-sensitive amphiphilic polyethylene glycol-polyethyleneimine-poly(caprolactone)-SS-poly(caprolactone)-polyethyleneimine-polyethylene glycol (PEG-PEI-PCL-SS-PCL-PEG) (PPPT) is designed to realize the co-delivery of pORF-hTRAIL and DOX efficiently into tumor cells. PPPT is synthesized via the ring opening polymerization (ROP) of ε-caprolactone followed by Michael addition polymerization and atom transfer radical polymerization (ATRP) of the maleic imide group of MAL-PEG-NHS. The PPPT micelles present a spherical or ellipsoidal geometry with a mean diameter of approximately 100-120 nm. Meanwhile, they also exhibit a redox-responsive drug release profile in vitro. The blood compatibility and complement activation tests reveal that the PPPT micelles do not induce blood hemolysis, blood clotting, or complement activation. The T7-modified co-delivery system shows a higher cellular uptake efficiency than the unmodified co-delivery system in human breast cancer MCF-7 cells and is accumulated in tumor more efficiently in vivo. These results suggest that the T7-targeted codelivery system of DOX and pORF-hTRAIL is a combined delivery platform that can significantly improve the treatment of breast cancer.

Non-viral delivery systems for CRISPR/Cas9-based genome editing: Challenges and opportunities

In recent years, CRISPR (clustered regularly interspaced short palindromic repeat)/Cas (CRISPR-associated) genome editing systems have become one of the most robust platforms in basic biomedical research and therapeutic applications. To date, efficient in vivo delivery of the CRISPR/Cas9 system to the targeted cells remains a challenge. Although viral vectors have been widely used in the delivery of the CRISPR/Cas9 system in vitro and in vivo, their fundamental shortcomings, such as the risk of carcinogenesis, limited insertion size, immune responses and difficulty in large-scale production, severely limit their further applications. Alternative non-viral delivery systems for CRISPR/Cas9 are urgently needed. With the rapid development of non-viral vectors, lipid- or polymer-based nanocarriers have shown great potential for CRISPR/Cas9 delivery. In this review, we analyze the pros and cons of delivering CRISPR/Cas9 systems in the form of plasmid, mRNA, or protein and then discuss the limitations and challenges of CRISPR/Cas9-based genome editing. Furthermore, current non-viral vectors that have been applied for CRISPR/Cas9 delivery in vitro and in vivo are outlined in details. Finally, critical obstacles for non-viral delivery of CRISPR/Cas9 system are highlighted and promising strategies to overcome these barriers are proposed.

Cell Penetrating Peptides as Molecular Carriers for Anti-Cancer Agents

Cell membranes with their selective permeability play important functions in the tight control of molecular exchanges between the cytosol and the extracellular environment as the intracellular membranes do within the internal compartments. For this reason the plasma membranes often represent a challenging obstacle to the intracellular delivery of many anti-cancer molecules. The active transport of drugs through such barrier often requires specific carriers able to cross the lipid bilayer. Cell penetrating peptides (CPPs) are generally 5–30 amino acids long which, for their ability to cross cell membranes, are widely used to deliver proteins, plasmid DNA, RNA, oligonucleotides, liposomes and anti-cancer drugs inside the cells. In this review, we describe the several types of CPPs, the chemical modifications to improve their cellular uptake, the different mechanisms to cross cell membranes and their biological properties upon conjugation with specific molecules. Special emphasis has been given to those with promising application in cancer therapy.

Cleavable Multifunctional Targeting Mixed Micelles with Sequential pH-Triggered TAT Peptide Activation for Improved Antihepatocellular Carcinoma Efficacy

Although tumor-targeting nanovehicles for hepatocellular carcinoma (HCC) chemotherapy have attracted great research and clinic interest, the poor cancer penetration, inefficient cellular uptake, and slow intracellular drug release greatly compromise their therapeutic outcomes. In this work, a multifunctional mixed micellar system, consisting of glycyrrhetinic acid (GA) for specific liver-targeting, trans-activator of transcription (TAT) peptide for potent cell penetration, and pH-sensitive poly(β-amino ester) polymers for acidic-triggered drug release, was developed to provide HCC-targeting delivery and pH-triggered release of doxorubicin (DOX). These micelles were hypothesized to efficaciously accumulate in HCC site by the guide of GA ligands, enter into cancer cells facilitated by the activated TAT peptide on the micellar surface, and finally rapidly release DOX in cytoplasm. To demonstrate this design, DOX was initially loaded in micelles modified with both GA and TAT (DOX/GA@TAT-M) with high drug loading efficiency and pH-sensitive drug release profiles. The HCC-targeting cellular uptake and synergetic anticancer efficacy were tested, indicating DOX/GA@TAT-M could be specifically and effectively internalized into HCC cells by the effect of GA targeting and TAT penetrating with enhanced cytotoxicity. In addition, the prolonged circulation time and enhanced accumulation in tumor facilitated its potent tumor growth inhibition activity in vivo. These results demonstrated that the cleavable multifunctional mixed micelles with tumor targeting, controlled TAT peptide activation, and sequential pH-sensitive drug release could be an efficient strategy for HCC treatment.

Synthetic high-density lipoprotein nanodisks for targeted withalongolide delivery to adrenocortical carcinoma

Adrenocortical carcinoma (ACC) is a rare endocrine malignancy and has a 5-year survival rate of <35%. ACC cells require cholesterol for steroid hormone production, and this requirement is met via expression on the cell surface of a high level of SRB1, responsible for the uptake of high-density lipoproteins (HDLs), which carry and transport cholesterol in vivo. Here, we describe how this natural lipid carrier function of SRB1 can be utilized to improve the tumor-targeted delivery of a novel natural product derivative - withalongolide A 4,19,27-triacetate (WGA-TA) - which has shown potent antitumor efficacy, but poor aqueous solubility. Our strategy was to use synthetic HDL (sHDL) nanodisks, which are effective in tumor-targeted delivery due to their smallness, long circulation half-life, documented safety, and ability to bind to SRB1. In this study, we prepared sHDL nanodisks using an optimized phospholipid composition combined with ApoA1 mimetic peptide (22A), which has previously been tested in clinical trials, to load WGA-TA. Following optimization, WGA-TA nanodisks showed drug encapsulation efficiency of 78%, a narrow particle size distribution (9.81±0.41 nm), discoid shape, and sustained drug release in phosphate buffered saline. WGA-TA-sHDL nanodisks exhibited higher cytotoxicity in the ACC cell line H295R half maximal inhibitory concentration ([IC50] 0.26±0.045 μM) than free WGA-TA (IC50 0.492±0.115 μM, P<0.05). Fluorescent dye-loaded sHDL nanodisks efficiently accumulated in H295R adrenal carcinoma xenografts 24 hours following dosing. Moreover, daily intraperitoneal administration of 7 mg/kg WGA-TA-loaded sHDL nanodisks significantly inhibited tumor growth during 21-day administration to H295R xenograft-bearing mice compared to placebo (P<0.01). Collectively, these results suggest that WGA-TA-loaded nanodisks may represent a novel and beneficial therapeutic strategy for the treatment of ACC.

Tandem Peptide Based on Structural Modification of Poly-Arginine for Enhancing Tumor Targeting Efficiency and Therapeutic Effect

The nonselectivity of cell penetrating peptides had greatly limited the application in systemic administration. By conjugating a dGR motif to the C-terminal of octa-arginine, the formed tandem peptide R8-dGR had been proved to specifically recognize both integrin α_vβ₃ and neuropilin-1 receptors. However, the positive charge of poly-arginine would still inevitably lead to rapid clearance in the circulation system. Therefore, in this study, we tried to reduce the positive charge of poly-arginine by decreasing the number of arginine, to thus achieve improved tumor targeting efficiency. We had designed several different Rx-dGR peptides (x = 4, 6, and 8) modified liposomes and investigated their tumor targeting and penetrating properties both in vitro and in vivo. Among all the liposomes, R6-dGR modified liposomes exhibited a long circulation time similar to that of PEGylated liposomes while they retained strong penetrating ability into both tumor cells and tumor tissues, and thus had displayed the most superior tumor targeting efficiency. Then, paclitaxel and indocyanine green coloaded liposomes were prepared, and R6-dGR modified coloaded liposomes also exhibited enhanced antitumor effect on C6 xenograft tumor bearing mice. Therefore, we suggest R6-dGR as a potential tumor targeting ligand with both strong penetrating ability and improved pharmacokinetic behavior, which could be further used for efficient antitumor therapy.

CPP-Assisted Intracellular Drug Delivery, What Is Next?

For the past 20 years, we have witnessed an unprecedented and, indeed, rather miraculous event of how cell-penetrating peptides (CPPs), the naturally originated penetrating enhancers, help overcome the membrane barrier that has hindered the access of bio-macromolecular compounds such as genes and proteins into cells, thereby denying their clinical potential to become potent anti-cancer drugs. By taking the advantage of the unique cell-translocation property of these short peptides, various payloads of proteins, nucleic acids, or even nanoparticle-based carriers were delivered into all cell types with unparalleled efficiency. However, non-specific CPP-mediated cell penetration into normal tissues can lead to widespread organ distribution of the payloads, thereby reducing the therapeutic efficacy of the drug and at the same time increasing the drug-induced toxic effects. In view of these challenges, we present herein a review of the new designs of CPP-linked vehicles and strategies to achieve highly effective yet less toxic chemotherapy in combating tumor oncology.

A branched TAT cell-penetrating peptide as a novel delivery carrier for the efficient gene transfection

Background

Cell penetrating peptides (CPPs) as one class of non-viral vectors, have been widely explored as a delivery tool due to their cell-penetrating capability with low cytotoxicity. However, CPPs have reported to have low gene transfection efficiency mainly due to the fact that DNA is larger than other biomolecules. On the other hand, the conventional linear CPPs are unstable for constructing the DNA complexes with it. Thus, here we designed a branched CPP using disulfide bridges based on the linear TAT peptide, to enhance the gene delivery efficiency in a better way.

Results

The branched TAT (BTAT) was synthesized by the DMSO oxidation method and showed high-molecular-weight about 294 kDa. The resulting BTAT was complexed with plasmid green fluorescence protein (pGFP) gene at various N/P ratios. The gene transfection efficiency was assessed on HeLa cells after treating with BTAT/pGFP complexes, showed high gene transfection efficiency as conformed by flowcytometry followed by confocal laser scanning microscopy (CLSM) visualization.

Conclusion

The novel BTAT/pGFP complex exhibited significantly higher stability and redox cleavability by reducing agent. In addition, BTAT showed higher transfection efficiency approximately 40-fold than those of the TAT and mTAT complexes. Our primary experiments demonstrated the potential of BTAT as a suitable candidate for gene delivery and it could be applied for various types of gene delivery platforms.

Redox and pH dual responsive poly(amidoamine) dendrimer-poly(ethylene glycol) conjugates for intracellular delivery of doxorubicin

To solve the contradiction between long circulation time and effective intracellular drug release, redox and pH-responsive drug delivery system was developed by incorporated redox-sensitive disulfide linkage between poly(amidoamine) dendrimers (PAMAM) and poly(ethylene glycol) (PEG). Doxorubicin (DOX) was loaded into the hydrophobic core of the conjugates to prepare PAMAM-SS-PEG/DOX complexes (PSSP/DOX). In vitro release studies suggested that DOX release from PSSP/DOX complexes followed an redox and acid-triggered manner and increased with increasing PEGylation degree. In vitro cytotoxicity of PSSP/DOX complexes against B16 tumor cells increased with, while cellular uptake decreased with increasing PEGylation degree. Further, intracellular DOX release observation and measurement indicate that the intracellular DOX release played a critical role for the cytotoxicity of DOX-loaded PSSP conjugates. In addition, cellular entry mechanism of the PSSP/DOX study demonstrated that both clathrin- and caveolae-mediated endocytosis were the primary pathways for cellular entry of PSSP/DOX. Finally, in vivo study of PSSP/DOX complexes in B16 tumor-bearing mice indicate that PSSP/DOX could significantly improve antitumor efficiency and present a good safety. The redox and pH-responsive drug delivery system has been demonstrated to be a promising candidate for solid tumor therapy.

STATEMENT OF SIGNIFICANCE

In previous research, pH-sensitive diblock polymer of poly(ethylene glycol)-poly(2,4,6-trimethoxybenzylidene-pentaerythritol carbonate) (PEG-PTMBPEC) was synthesized to facilitate the intracellular anticancer drug release. However, the nanoparticles based on PEG-PTMBPEC get into the tumor cells just relying on the EPR-mediated passive targeting resulting in the low drug accumulation. Therefore, cRGD peptide modified PEG-PTMBPEC polymeric micelles were developed for specific targeted delivery of doxorubicin (DOX) to neovascular cells and tumor cells simultaneously. The precise intracellular target site and effective drug concentration will contribute to enhancing the antitumor toxicity and reducing the systematic toxicity of DOX. The cRGD modified pH-sensitive micellar system is a promising vehicle for intracellular drug delivery to αvβ3 integrin receptor overexpressed tumor cells and neovascular cells.

Dual Receptor Recognizing Cell Penetrating Peptide for Selective Targeting, Efficient Intratumoral Diffusion and Synthesized Anti-Glioma Therapy

Cell penetrating peptides (CPPs) were widely used for drug delivery to tumor. However, the nonselective in vivo penetration greatly limited the application of CPPs-mediated drug delivery systems. And the treatment of malignant tumors is usually followed by poor prognosis and relapse due to the existence of extravascular core regions of tumor. Thus it is important to endue selective targeting and stronger intratumoral diffusion abilities to CPPs. In this study, an RGD reverse sequence dGR was conjugated to a CPP octa-arginine to form a CendR (R/KXXR/K) motif contained tandem peptide R8-dGR (RRRRRRRRdGR) which could bind to both integrin αvβ3 and neuropilin-1 receptors. The dual receptor recognizing peptide R8-dGR displayed increased cellular uptake and efficient penetration ability into glioma spheroids in vitro. The following in vivo studies indicated the active targeting and intratumoral diffusion capabilities of R8-dGR modified liposomes. When paclitaxel was loaded in the liposomes, PTX-R8-dGR-Lip induced the strongest anti-proliferation effect on both tumor cells and cancer stem cells, and inhibited the formation of vasculogenic mimicry channels in vitro. Finally, the R8-dGR liposomal drug delivery system prolonged the medium survival time of intracranial C6 bearing mice by 2.1-fold compared to the untreated group, and achieved an exhaustive anti-glioma therapy including anti-tumor cells, anti-vasculogenic mimicry and anti-brain cancer stem cells. To sum up, all the results demonstrated that R8-dGR was an ideal dual receptor recognizing CPP with selective glioma targeting and efficient intratumoral diffusion, which could be further used to equip drug delivery system for effective glioma therapy.

Effect of surface properties on liposomal siRNA delivery

Liposomes are one of the most widely investigated carriers for siRNA delivery. The surface properties of liposomal carriers, including the surface charge, PEGylation, and ligand modification can significantly affect the gene silencing efficiency. Three barriers of systemic siRNA delivery (long blood circulation, efficient tumor penetration and efficient cellular uptake/endosomal escape) are analyzed on liposomal carriers with different surface charges, PEGylations and ligand modifications. Cationic formulations dominate siRNA delivery and neutral formulations also have good performance while anionic formulations are generally not proper for siRNA delivery. The PEG dilemma (prolonged blood circulation vs. reduced cellular uptake/endosomal escape) and the side effect of repeated PEGylated formulation (accelerated blood clearance) were discussed. Effects of ligand modification on cationic and neutral formulations were analyzed. Finally, we summarized the achievements in liposomal siRNA delivery, outlined existing problems and provided some future perspectives.

A Copper-Mediated Disulfiram-Loaded pH-Triggered PEG-Shedding TAT Peptide-Modified Lipid Nanocapsules for Use in Tumor Therapy

Disulfiram, which exhibits marked tumor inhibition mediated by copper, was encapsulated in lipid nanocapsules modified with TAT peptide (TATp) and pH-triggered sheddable PEG to target cancer cells on the basis of tumor environmental specificity. PEG-shedding lipid nanocapsules (S-LNCs) were fabricated from LNCs by decorating short PEG chains with TATp (HS-PEG(1k)-TATp) to form TATp-LNCs and then covered by pH-sensitive graft copolymers of long PEG chains (PGA-g-PEG(2k)). The DSF-S-LNCs had sizes in the range of 60-90 nm and were stable in the presence of 50% plasma. DSF-S-LNCs exhibited higher intracellular uptake and antitumor activity at pH 6.5 than at pH 7.4. The preincubation of Cu showed that the DSF cytotoxicity was based on the accumulation of Cu in Hep G2 cells. Pharmacokinetic studies showed the markedly improved pharmacokinetic profiles of DSF-S-LNCs (AUC= 3921.391 μg/L·h, t(1/2z) = 1.294 h) compared with free DSF (AUC = 907.724 μg/L·h, t(1/2z) = 0.252 h). The in vivo distribution of S-LNCs was investigated using Cy5.5 as a fluorescent probe. In tumor-bearing mice, the delivery efficiency of S-LNCs was found to be 496.5% higher than that of free Cy5.5 and 74.5% higher than that of LNCs in tumors. In conclusion, DSF-S-LNCs increased both the stability and tumor internalization and further increased the cytotoxicity because of the higher copper content.

Targeted delivery of transferrin and TAT co-modified liposomes encapsulating both paclitaxel and doxorubicin for melanoma

The purpose of this study was to develop an efficient dual-ligand based liposomal drug delivery system with targeting specificity as well as properties that would kill melanoma cells. Liposomes modified with transferrin (Tf) and cell-penetrating peptide TAT was prepared, which encapsulated two kinds of chemotherapy drugs, paclitaxel and doxorubicin (Tf/TAT-PTX/DOX-LP). The Tf ligands specifically bind to the overexpressed Tf receptors on the surface of melanoma cells, while the TAT ligands functioned as a classical cell penetrating peptide, helping dual-ligand liposomes be internalized by melanoma cells. The effect of dual-targeting system and "double-drug" combination therapy were evaluated both in vitro and in vivo. In vitro, cellular uptake, intracellular distribution and tumor spheroids penetration studies demonstrated that the system could not only be selectively and efficiently penetrate melanoma cells. Besides, apoptosis staining assay and cytotoxicity showed effective anti-tumor capability and obvious synergistic effect of combination therapy of PTX and DOX. In vivo imaging and fluorescent images of tumor section further demonstrated that Tf/TAT-PTX/DOX-LP had the highest tumor distribution. The results of these experiments demonstrated that double-drug liposomal drug delivery systems (DDS) had both enhanced targeting efficiency and increased therapeutic efficacy.

Hybrid protein-synthetic polymer nanoparticles for drug delivery

Among the most common nanoparticulate systems, the polymeric nanocarriers have a number of key benefits, which give a great choice of delivery platforms. Nevertheless, polymeric nanoparticles possess some limitations that include use of toxic solvents in the production process, polymer degradation, drug leakage outside the diseased tissue, and polymer cytotoxicity. The combination of polymers of biological and synthetic origin is an appealing modern strategy for the production of novel nanocarriers with unprecedented properties. Proteins' interface can play an important role in determining bioactivity and toxicity and gives perspective for future development of the polymer-based nanoparticles. The design of hybrid constructs composed of synthetic polymer and biological molecules such as proteins can be considered as a straightforward tool to integrate a broad spectrum of properties and biofunctions into a single device. This review discusses hybrid protein-synthetic polymer nanoparticles with different structures and levels in complexity and functionality, in view of their applications as drug delivery systems.

Toward a magic or imaginary bullet? Ligands for drug targeting to cancer cells: principles, hopes, and challenges

There are many problems directly correlated with the systemic administration of drugs and how they reach their target site. Targeting promises to be a hopeful strategy as an improved means of drug delivery, with reduced toxicity and minimal adverse side effects. Targeting exploits the high affinity of cell-surface-targeted ligands, either directly or as carriers for a drug, for specific retention and uptake by the targeted diseased cells. One of the most important parameters which should be taken into consideration in the selection of an appropriate ligand for targeting is the binding affinity (K D). In this review we focus on the importance of binding affinities of monoclonal antibodies, antibody derivatives, peptides, aptamers, DARPins, and small targeting molecules in the process of selection of the most suitable ligand for targeting of nanoparticles. In order to provide a critical comparison between these various options, we have also assessed each technology format across a range of parameters such as molecular size, immunogenicity, costs of production, clinical profiles, and examples of the level of selectivity and toxicity of each. Wherever possible, we have also assessed how incorporating such a targeted approach compares with, or is superior to, original treatments.

Co-delivery of doxorubicin and P-gp inhibitor by a reduction-sensitive liposome to overcome multidrug resistance, enhance anti-tumor efficiency and reduce toxicity

To overcome multidrug resistance (MDR) in cancer chemotherapy with high efficiency and safety, a reduction-sensitive liposome (CL-R8-LP), which was co-modified with reduction-sensitive cleavable PEG and octaarginine (R8) to increase the tumor accumulation, cellular uptake and lysosome escape, was applied to co-encapsulate doxorubicin (DOX) and a P-glycoprotein (P-gp) inhibitor of verapamil (VER) in this study. The encapsulation efficiency (EE) of DOX and VER in the binary-drug loaded CL-R8-LP (DOX + VER) was about 95 and 70% (w/w), respectively. The uptake efficiencies, the cytotoxicity, and the apoptosis and necrosis-inducing efficiency of CL-R8-LP (DOX + VER) were much higher than those of DOX and the other control liposomes in MCF-7/ADR cells or tumor spheroids. Besides, CL-R8-LP (DOX + VER) was proven to be uptaken into MCF-7/ADR cells by clathrin-mediated and macropinocytosis-mediated endocytosis, followed by efficient lysosomal escape. In vivo, CL-R8-LP (DOX + VER) effectively inhibited the growth of MCF-7/ADR tumor and reduce the toxicity of DOX and VER, which could be ascribed to increased accumulation of drugs in drug-resistant tumor cells and reduced distribution in normal tissues. In summary, the co-delivery of chemotherapeutics and P-gp inhibitors by our reduction-sensitive liposome was a promising approach to overcome MDR, improve anti-tumor effect and reduce the toxicity of chemotherapy.

Surface modification of nonviral nanocarriers for enhanced gene delivery

Biomedical nanotechnology has given a new lease of life to gene therapy with the ever-developing and ever-diversifying nonviral gene delivery nanocarriers. These are designed to pass a series of barriers in order to bring their nucleic acid cargo to the right subcellular location of particular cells. For a given application, each barrier has its dedicated strategy, which translates into a physicochemical, biological and temporal identity of the nanocarrier surface. Different strategies have thus been explored to implement adequate surface identities on nanocarriers over time for systemic delivery. In that context, this review will mainly focus on organic nanocarriers, for which these strategies will be described and discussed.

Angiopep-2 and activatable cell penetrating peptide dual modified nanoparticles for enhanced tumor targeting and penetrating

Delivering chemotherapeutics by nanoparticles into tumor was influenced by at least two factors: specific targeting and highly efficient penetrating of the nanoparticles. In this study, two targeting ligands, angiopep-2 and activatable cell penetrating peptide (ACP), were functionalized onto nanoparticles for tumor targeting delivery. In this system, angiopep-2 is a ligand of low-density lipoprotein receptor-related protein-1 (LRP1) which was highly expressed on tumor cells, and the ACP was constructed by the conjugation of RRRRRRRR (R8) with EEEEEEEE through a matrix metalloproteinase-2 (MMP-2) sensitive linker, enabling the ACP with tumor microenvironment-responsive cell penetrating property. 4h incubation of ACP with MMP-2 leads to over 80% cleavage of ACP, demonstrating ACP indeed possessed MMP-2 responsive property. The constructed dual targeting nanoparticles (AnACNPs) were approximately 110 nm with a polydispersity index of 0.231. In vitro, ACP modification and angiopep-2 modification could both enhance the U-87 MG cell uptake because of the high expression of MMP-2 and LRP-1 on C6 cells. AnACNPs showed higher uptake level than the single ligand modified nanoparticles. The uptake of all particles was time- and concentration-dependent and endosomes were involved. In vivo, AnACNPs showed best tumor targeting efficiency. The distribution of AnACNPs in tumor was higher than all the other particles. After microvessel staining with anti-CD31 antibody, the fluorescent distribution demonstrated AnACNPs could distribute in the whole tumor with the highest intensity. In conclusion, a novel drug delivery system was developed for enhanced tumor dual targeting and elevated cell internalization.

Angiopep-2 and activatable cell-penetrating peptide dual-functionalized nanoparticles for systemic glioma-targeting delivery

Gliomas are hard to treat because of the two barriers involved: the blood-brain barrier and blood-tumor barrier. In this study, a dual-targeting ligand, angiopep-2, and an activatable cell-penetrating peptide (ACP) were functionalized onto nanoparticles for glioma-targeting delivery. The ACP was constructed by conjugating RRRRRRRR (R8) with EEEEEEEE through a matrix metalloproteinase-2 (MMP-2)-sensitive linker. ACP modification effectively enhanced the C6 cellular uptake because of the high expression of MMP-2 on C6 cells. The uptake was inhibited by batimastat, an MMP-2 inhibitor, suggesting that the cell-penetrating property of the ACP was activated by MMP-2. By combining the dual-targeting delivery effect of angiopep-2 and activatable cell-penetrating property of the ACP, the dual-modified nanoparticles (AnACNPs) displayed higher glioma localization than that of single ligand-modified nanoparticles. After loading with docetaxel, a common chemotherapeutic, AnACNPs showed the most favorable antiglioma effect both in vitro and in vivo. In conclusion, a novel drug delivery system was developed for glioma dual targeting and glioma penetrating. The results demonstrated that the system effectively targeted gliomas and provided the most favorable antiglioma effect.

Hybrid polymeric micelles based on bioactive polypeptides as pH-responsive delivery systems against melanoma

The bioactive polymer poly(L-glutamic acid)n-b-poly(D, L-lactic acid)m was synthesized and used to form doxorubicin-loaded hybrid polymeric micelles to treat melanoma. These polymers exhibited pH-responsive changes in conformation, which controlled the diverse functionalities of the micelles. During circulation, poly(L-glutamic acid)n-b-poly(D, L-lactic acid)m protected Tat peptides on the micelles from proteolysis. Under tumor-acidic conditions, polymers with shorter poly(l-glutamic acid) blocks underwent a conformational change to form channels that accelerated the release of doxorubicin. The conformational change also exposed the Tat peptides to tumor cells, thereby promoting cellular internalization of the micelles. Enhanced cellular uptake of the micelles induced significant apoptosis of A375 melanoma cells in tumor-acidic conditions. In vivo studies demonstrated that the micelles with shorter poly(L-glutamic acid) blocks could effectively accumulate in tumor tissues, suppress tumor growth and help maintain the body weight of tumor-bearing mice. However, micelles with longer poly(l-glutamic acid) blocks did not undergo a conformational change under acidic conditions and performed poorly in both in vitro and in vivo evaluations. Our work provides a strategy for applying bioactive polymers to the rational construction of pH-responsive delivery systems for solid tumors and lends insight into possible conformational effects on the bioactivity of drug carriers.

Novel serum-tolerant lipoplexes target the folate receptor efficiently

Gene transfer using non-viral vectors is a promising approach for the safe delivery of nucleic acid therapeutics. In this study, we investigate a lipid-based system for targeted gene delivery to malignant cells overexpressing the folate receptor (FR). Cationic liposomes were formulated with and without the targeting ligand folate conjugated to distearoylphosphatidyl ethanolamine polyethylene glycol 2000 (DSPE-PEG2000), the novel cytofectin 3β[N(N(1),N(1)-dimethlaminopropylsuccinamidoethane)-carbamoyl]cholesterol (SGO4), which contains a 13atom, 15Å spacer element, and the helper lipid, dioleoylphosphatidylethanolamine (DOPE). Physicochemical parameters of the liposomes and lipoplexes were obtained by zeta sizing, zeta potential measurement and cryo-TEM. DNA-binding and protection capabilities of liposomes were confirmed by gel retardation assays, EtBr intercalation and nuclease protection assays. The complexes were assessed in an in vitro system for their effect on cell viability using the MTT assay, and gene transfection activity using the luciferase assay in three cell lines; HEK293 (FR-negative), HeLa (FR(+)-positive), KB (FR(++)-positive). Low cytotoxicities were observed in all cell lines, while transgene activity promoted by folate-tagged lipoplexes in FR-positive lines was tenfold greater than that by untargeted constructs and cell entry by folate complexes was demonstrably by FR mediation. These liposome formulations have the design capacity for in vivo application and may therefore be promising candidates for further development.

Increased tumor targeted delivery using a multistage liposome system functionalized with RGD, TAT and cleavable PEG

Though PEGylation has been widely used to enhance the accumulation of liposomes in tumor tissues through enhanced permeability and retention (EPR) effects, it still inhibits cellular uptake and affects intracellular trafficking of carriers. Active targeting molecules displayed better cell selectivity but were shadowed by the poor tumor penetration effect. Cell penetrating peptides could increase the uptake of the carriers but were limited by their non-specificity. Dual-ligand system may possess a synergistic effect and create a more ideal drug delivery effect. Based on the above factors, we designed a multistage liposome system co-modified with RGD, TAT and cleavable PEG, which combined the advantages of PEG, specific ligand and penetrating peptide. The cleavable PEG could increase the stability and circulation time of liposomes during circulation. After the passive extravasation to tumor tissues, the previously hidden dual ligands on the liposomes were exposed in a controlled manner at the tumor site through exogenous administration of a safe reducing agent L-cysteine. The RGD specifically recognized the integrins overexpressed on various malignant tumors and mediated efficient internalization in the synergistic effect of the RGD and TAT. Invitro cellular uptake and 3D tumor spheroids penetration studies demonstrated that the system could not only be selectively and efficiently taken up by cells overexpress ingintegrins but also penetrate the tumor cells to reach the depths of the avascular tumor spheroids. In vivo imaging and fluorescent images of tumor section further demonstrated that this system achieved profoundly improved distribution within tumor tissues, and the RGD and TAT ligands on C-R/T liposomes produced a strong synergistic effect that promoted the uptake of liposomes into cells after the systemic administration of L-cysteine. The results of this study demonstrated a tremendous potential of this multistage liposomes for efficient delivery to tumor tissue and selective internalization into tumor cells.

A detachable coating of cholesterol-anchored PEG improves tumor targeting of cell-penetrating peptide-modified liposomes

Cell-penetrating peptides (CPPs) have been widely used to enhance the membrane translocation of various carriers for many years, but the non-specificity of CPPs seriously limits their utility in vivo. In this study, cholesterol-anchored, reduction-sensitive PEG (first synthesized by our laboratory) was applied to develop a co-modified liposome with improved tumor targeting. Following optimization of the formulation, the in vitro and in vivo properties of the co-modified liposome were evaluated. The co-modified liposome had a much lower cellular uptake and tumor spheroid uptake, but a much higher tumor accumulation compared to CPP-modified liposome, indicating the non-specific penetration of CPPs could be attenuated by the outer PEG coating. With the addition of exogenous reducing agent, both the in vitro and in vivo cellular uptake was markedly increased, demonstrating that the reduction-sensitive PEG coating achieved a controllable detachment from the surface of liposomes and did not affect the penetrating abilities of CPPs. The present results demonstrate that the combination of cholestervsitive PEG and CPPs is an ideal alternative for the application of CPP-modified carriers in vivo.

Liposomes co-modified with cholesterol anchored cleavable PEG and octaarginines for tumor targeted drug delivery

Tumor targeted drug delivery system with high efficiency of tumor accumulation, cell internalization and endosomal escape was considered ideal for cancer therapy. Herein, a cleavable polyethylene glycol (PEG) and octaarginines (R8) co-modified liposome (CL-R8-LP) was developed, in which the cholesterol was used as an alternative anchor to the commonest phospholipids for the diversified development of surface modification. The in vitro hemolysis assay and bio-distribution study demonstrated that CL-R8-LP improved biocompatibility and tumor accumulation compared with the single R8 modified liposomes (R8-LP), since the strong positive charges, toxicity and non-specificity of R8 were efficiently shielded by the outer cleavable PEG. And the cellular uptake, cytotoxicity and apoptosis of CL-R8-LP on C26 cells were much stronger than that of control liposomes in which R8 was not included or exposed. In addition, it was confirmed that CL-R8-LP entered cells via clathrin-mediated endocytosis and the macropinocytosis, and followed by a more efficient endosomal escape compared with R8-LP due to the topology change of R8. The enhanced in vivo delivery efficiency and anti-tumor efficacy were validated in C26 bearing mice. In conclusion, the results demonstrated that CL-R8-LP was a promising vehicle for enhancing the chemotherapy of solid cancers.