Doxorubicin in TAT peptide-modified multifunctional immunoliposomes demonstrates increased activity against both drug-sensitive and drug-resistant ovarian cancer models

Surface modification strategies in translocating nano-vesicles across different barriers and the role of bio-vesicles in improving anticancer therapy

Nanovesicles and bio-vesicles (BVs) have emerged as promising tools to achieve targeted cancer therapy due to their ability to overcome many of the key challenges currently being faced with conventional chemotherapy. These challenges include the diverse and often complex pathophysiology involving the progression of cancer, as well as the various biological barriers that circumvent therapeutic molecules reaching their target site in optimum concentration. The scientific evidence suggests that surface-functionalized nanovesicles and BVs camouflaged nano-carriers (NCs) both can bypass the established biological barriers and facilitate fourth-generation targeting for the improved regimen of treatment. In this review, we intend to emphasize the role of surface-functionalized nanovesicles and BVs camouflaged NCs through various approaches that lead to an improved internalization to achieve improved and targeted oncotherapy. We have explored various strategies that have been employed to surface-functionalize and biologically modify these vesicles, including the use of biomolecule functionalized target ligands such as peptides, antibodies, and aptamers, as well as the targeting of specific receptors on cancer cells. Further, the utility of BVs, which are made from the membranes of cells such as mesenchymal stem cells (MSCs), white blood cells (WBCs), red blood cells (RBCs), platelets (PLTs) as well as cancer cells also been investigated. Lastly, we have discussed the translational challenges and limitations that these NCs can encounter and still need to be overcome in order to fully realize the potential of nanovesicles and BVs for targeted cancer therapy. The fundamental challenges that currently prevent successful cancer therapy and the necessity of novel delivery systems are in the offing.

Stimuli-responsive liposomal nanoformulations in cancer therapy: Pre-clinical & clinical approaches

The site-specific delivery of antitumor agents is of importance for providing effective cancer suppression. Poor bioavailability of anticancer compounds and the presence of biological barriers prevent their accumulation in tumor sites. These obstacles can be overcome using liposomal nanostructures. The challenges in cancer chemotherapy and stimuli-responsive nanocarriers are first described in the current review. Then, stimuli-responsive liposomes including pH-, redox-, enzyme-, light-, thermo- and magneto-sensitive nanoparticles are discussed and their potential for delivery of anticancer drugs is emphasized. The pH- or redox-sensitive liposomes are based on internal stimulus and release drug in response to a mildly acidic pH and GSH, respectively. The pH-sensitive liposomes can mediate endosomal escape via proton sponge. The multifunctional liposomes responsive to both redox and pH have more capacity in drug release at tumor site compared to pH- or redox-sensitive alone. The magnetic field and NIR irradiation can be exploited for external stimulation of liposomes. The light-responsive liposomes release drugs when they are exposed to irradiation; thermosensitive-liposomes release drugs at a temperature of >40 °C when there is hyperthermia; magneto-responsive liposomes release drugs in presence of magnetic field. These smart nanoliposomes also mediate co-delivery of drugs and genes in synergistic cancer therapy. Due to lack of long-term toxicity of liposomes, they can be utilized in near future for treatment of cancer patients.

Peptide-based delivery of therapeutics in cancer treatment

Current delivery strategies for cancer therapeutics commonly cause significant systemic side effects due to required high doses of therapeutic, inefficient cellular uptake of drug, and poor cell selectivity. Peptide-based delivery systems have shown the ability to alleviate these issues and can significantly enhance therapeutic loading, delivery, and cancer targetability. Peptide systems can be tailor-made for specific cancer applications. This review describes three peptide classes, targeting, cell penetrating, and fusogenic peptides, as stand-alone nanoparticle systems, conjugations to nanoparticle systems, or as the therapeutic modality. Peptide nanoparticle design, characteristics, and applications are discussed as well as peptide applications in the clinical space.

Delivery of Various Cargos into Cancer Cells and Tissues via Cell-Penetrating Peptides: A Review of the Last Decade

Cell-penetrating peptides (CPPs), also known as protein transduction domains, are a class of diverse amino acid sequences with the ability to cross cellular membranes. CPPs can deliver several bioactive cargos, including proteins, peptides, nucleic acids and chemotherapeutics, into cells. Ever since their discovery, synthetic and natural CPPs have been utilized in therapeutics delivery, gene editing and cell imaging in fundamental research and clinical experiments. Over the years, CPPs have gained significant attention due to their low cytotoxicity and high transduction efficacy. In the last decade, multiple investigations demonstrated the potential of CPPs as carriers for the delivery of therapeutics to treat various types of cancer. Besides their remarkable efficacy owing to fast and efficient delivery, a crucial benefit of CPP-based cancer treatments is delivering anticancer agents selectively, rather than mediating toxicities toward normal tissues. To obtain a higher therapeutic index and to improve cell and tissue selectivity, CPP-cargo constructions can also be complexed with other agents such as nanocarriers and liposomes to obtain encouraging outcomes. This review summarizes various types of CPPs conjugated to anticancer cargos. Furthermore, we present a brief history of CPP utilization as delivery systems for anticancer agents in the last decade and evaluate several reports on the applications of CPPs in basic research and preclinical studies.

Molecular docking studies of HIV TAT and sitagliptin nano-formula as potential therapeutic targeting SARS-CoV2 protease

The outbreak of COVID-19 pandemic regarded as a major health/economic hazard. The importance of coming up with mechanisms for preventing or treating SARS-CoV-2infection has been felt across the world. This work aimed at examining the efficiency of Sitagliptin (SIT) and human immunodeficiency virus type 1 (HIV-1) trans-activator transcription peptide (TAT) against SARS-CoV-2 virus. 3CL-protease inhibition activity and docking studies were examined. According to the results, the prepared complex's formula was as follows 1: 1 SIT: TAT molar ratio, whereas zeta potential and particle size values were at 34.17 ​mV and 97.19 ​nm, respectively. This combination did exhibit its antiviral potentiality against SARS-CoV-2 via IC50 values of 9.083 5.415, and 16.14 ​μM for TAT, SIT-TAT, and SIT, respectively. In addition, the complex SIT-TAT showed a significant (P ​< ​0.001) viral-3CL-protease inhibitory effect. This was further confirmed via in silico study. Molecular docking investigation has shown promising binding affinity of the formula components towards SARS-CoV-2 main protease (3-CL).

pH-Sensitive PEGylated Liposomal Silybin: Synthesis, In Vitro and In Vivo Anti-Tumor Evaluation

The drug delivery systems improve the efficacy of chemotherapeutics through enhanced targeting and controlled release however, biological barriers of tumor microenvironment greatly impede the penetration of nanomedicine within the tumor. We report herein the fabrication of a PEG-detachable silybin (SLB) pH-sensitive liposome decorated with TAT-peptide. For this, Acyl hydrazide-activated PEG₂₀₀₀ was prepared and linked with ketone-derivatized DPPE via an acid-labile hydrazone bond to form mPEG₂₀₀₀-HZ-DPPE. TAT peptide was conjugated with a shorter -PEG₁₀₀₀-DSPE spacer and post-inserted into PEGylated liposome (DPPC: mPEG₂₀₀₀-DSPE: Chol). To prepare nanoliposomes (around 100 nm), first, a novel method was used to prepare SLB-Soya PC (SLB-SPC) complex, then this complex was incorporated into nanoliposomes. The pH-sensitivity and shielding effect of long PEG chain on TAT peptide was investigated using DiI liposome and FACS analysis. Pre-treatment to the lowered pH enhanced cellular association of TAT-modified pH-sensitive liposome due to the cleavage of hydrazone bond and TAT exposure. Besides, TAT-modified pH-sensitive liposomes significantly reduced cell viability compared to the plain liposome. In vivo results were very promising with pH-sensitive liposome by detaching PEG moieties upon exposure to the acidic tumor microenvironment, enhancing cellular uptake, retarding tumor growth, and prolonging the survival of 4T1 breast tumor-bearing BALB/c mice. TAT modification of pH-sensitive liposome improved cancer cell association and cytotoxicity and demonstrated potential intracellular delivery upon exposure to acidic pH. However, in in vivo studies, TAT as a targeting ligand significantly decreased the therapeutic efficacy of the formulation attributed to an inefficient tumor accumulation and higher release rate in the circulation. The results of this study indicated that pH-sensitive liposome containing SLB, which was prepared with a novel method with a significant SLB loading efficiency, is very effective in the treatment of 4T1 breast tumor-bearing BALB/c mice and merits further investigation.

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.

Liposomal doxorubicin as targeted delivery platform: Current trends in surface functionalization

Liposomal delivery systems have significantly enhanced the efficacy and safety of chemotherapeutic agents compared to free (non-liposomal) formulations. Liposomes are vesicles made up of lipophilic bilayer and a hydrophilic core which provides perfect opportunity for their application as transport vehicle for various therapeutic and diagnostic agents. Doxorubicin is the most exploited chemotherapeutic agent for evaluation of different liposomal applications, as its physicochemical properties permit high drug entrapment and easy remote loading in pre-formulated liposomes. Pegylated liposomal doxorubicin clinically approved and, on the market, Doxil®, exemplifies the benefits offered upon the surface modification of liposome with polyethylene glycol. This unique formulation prolonged the drug residence time in the circulation and increased accumulation of doxorubicin in tumor tissue via passive targeting (enhanced permeability and retention effect). However, there is ample scope for further improvement in the efficiency of targeting tumors by coupling biological active ligands onto the liposome surface to generate intelligent drug delivery systems. Small biomolecules such as peptides, fraction of antibodies and carbohydrates have the potential to target receptors present on the surface of the malignant cells. Hence, active targeting of malignant cells using functionalised nanocarrier (liposomes encapsulated with doxorubicin) have been attempted which is reviewed in this article.

Liposomes for Enhanced Cellular Uptake of Anticancer Agents

Cancers are life threatening diseases and their traditional treatment strategies have numerous limitations which include poor pharmacokinetic profiles, non-specific drug distribution in the body tissues and organs and deprived tumor cells penetration. This attracted the attention of researchers to tailor efficient drug delivery system for anticancer agents to overcome these limitations. Liposomes are one of the newly developed delivery systems for anticancer agents. They are vesicular structures, which were fabricated to enhance drug targeting to tumor tissues either via active or passive targeting. They can be tailored to penetrate tumor cells membrane which is considered the main rate limiting step in antineoplastic therapy. This resulted in enhancing drug cellular uptake and internalization and increasing drug cytotoxic effect. These modifications were achieved via various approaches which included the use of cell-penetrating peptides, the use of lipid substances that can increase liposome fusogenic properties or increase the cell membrane permeability toward amphiphilic drugs, surface modification or ligand targeted liposomes and immuno-liposomes. The modified liposomes were able to enhance anticancer agent's cellular uptake and this was reflected in their ability to destroy tumor tissues. This review outlines different approaches employed for liposomes modification for enhancing anticancer agent's cellular uptake.

Cell-penetrating peptides in oncologic pharmacotherapy: A review

Cancer is the second leading cause of death in the world and its treatment is extremely challenging, mainly due to its complexity. Cell-Penetrating Peptides (CPPs) are peptides that can transport into the cell a wide variety of biologically active conjugates (or cargoes), and are, therefore, promising in the treatment and in the diagnosis of several types of cancer. Some notable examples are TAT and Penetratin, capable of penetrating the central nervous system (CNS) and, therefore, acting in cancers of this system, such as Glioblastoma Multiforme (GBM). These above-mentioned peptides, conjugated with traditional chemotherapeutic such as Doxorubicin (DOX) and Paclitaxel (PTX), have also been shown to induce apoptosis of breast and liver cancer cells, as well as in lung cancer cells, respectively. In other cancers, such as esophageal cancer, the attachment of Magainin 2 (MG2) to Bombesin (MG2B), another CPP, led to pronounced anticancer effects. Other examples are CopA3, that selectively decreased the viability of gastric cancer cells, and the CPP p28. Furthermore, in preclinical tests, the anti-tumor efficacy of this peptide was evaluated on human breast cancer, prostate cancer, ovarian cancer, and melanoma cells in vitro, leading to high expression of p53 and promoting cell cycle arrest. Despite the numerous in vitro and in vivo studies with promising results, and the increasing number of clinical trials using CPPs, few treatments reach the expected clinical efficacy. Usually, their clinical application is limited by its poor aqueous solubility, immunogenicity issues and dose-limiting toxicity. This review describes the most recent advances and innovations in the use of CPPs in several types of cancer, highlighting their crucial importance for various purposes, from therapeutic to diagnosis. Further clinical trials with these peptides are warranted to examine its effects on various types of cancer.

Nanoparticle delivery systems to combat drug resistance in ovarian cancer

Due to the lack of early symptoms and difficulty of accurate diagnosis, ovarian cancer is the most lethal gynecological cancer faced by women. First-line therapy includes a combination of tumor resection surgery and chemotherapy regimen. However, treatment becomes more complex upon recurrence due to development of drug resistance. Drug resistance has been linked to many mechanisms, including efflux transporters, apoptosis dysregulation, autophagy, cancer stem cells, epigenetics, and the epithelial-mesenchymal transition. Thus, developing and choosing effective therapies is exceptionally complex. There is a need for increased specificity and efficacy in therapies for drug-resistant ovarian cancer, and research in targeted nanoparticle delivery systems aims to fulfill this challenge. Although recent research has focused on targeted nanoparticle-based therapies, few of these therapies have been clinically translated. In this review, non-viral nanoparticle delivery systems developed to overcome drug-resistance in ovarian cancer were analyzed, including their structural components, surface modifications, and drug-resistance targeted mechanisms.

Optimized Conjugation of Fluvastatin to HIV-1 TAT Displays Enhanced Pro-Apoptotic Activity in HepG2 Cells

Accumulating evidence indicates that statins reduce the risk of different cancers and inhibit the proliferation of liver cancer cells. This study aims to explore whether the electrostatic conjugation of optimized fluvastatin (FLV) to human immunodeficiency virus type 1 (HIV-1) trans-activator transcription peptide (TAT) would enhance the anti-proliferative activity against HepG2 cells. FLV-TAT conjugation was optimized to achieve the lowest size with highest zeta potential. Nine formulae were constructed, using a factorial design with three factors-FLV concentration, TAT concentration, and pH of the medium-while the responses were zeta potential and size. The optimized formula showed a particle size of 199.24 nm and 29.14 mV zeta potential. Data indicates that conjugation of FLV to TAT (optimized formula) significantly enhances anti-proliferative activity and uptake by HepG2 cells when compared to raw FLV. Flow cytometry showed significant accumulation of cells in the pre-G phase, which highlights higher apoptotic activity. Annexin V staining indicated a significant increase in total cell death in early and late apoptosis. This was confirmed by significantly elevated caspase 3 in cells exposed to FLV-TAT preparation. In conclusion, the FLV-TAT optimized formula exhibited improved anti-proliferative action against HepG2. This is partially attributed to the enhanced apoptotic effects and cellular uptake of FLV.

Stimuli-Sensitive Cell Penetrating Peptide-Modified Nanocarriers

The integration of drugs into nanocarriers favorably altered their pharmacodynamics and pharmacokinetics compared to free drugs, and increased their therapeutic index. However, selective cellular internalization in diseased tissues rather than normal tissues still presents a formidable challenge. In this chapter I will cover solutions involving environment-responsive cell-penetrating peptides (CPPs). I will discuss properties of CPPs as universal cellular uptake enhancers, and the modifications imparted to CPP-modified nanocarriers to confine CPP activation to diseased tissues.

Neutral Lipopolyplexes for In Vivo Delivery of Conventional and Replicative RNA Vaccine

Nucleic acid vaccination relies on injecting DNA or RNA coding antigen(s) to induce a protective immune response. RNA vaccination is being increasingly used in preclinical and clinical studies. However, few delivery systems have been reported for in vivo delivery of RNA of different sizes. Using a tripartite formulation with RNA, cationic polymer, and anionic liposomes, we were able to encapsulate RNA into neutral lipopolyplexes (LPPs). LPPs were stable in vitro and successfully delivered conventional RNA and replicative RNA to dendritic cells in cellulo. Their injection led to reporter gene expression in mice. Finally, administration of LPP-Replicon RNA (RepRNA) led to an adaptive immune response against the antigen coded by the RepRNA. Accordingly, LPPs may represent a universal formulation for RNA delivery.

Cardiolipin-Based Lipopolyplex Platform for the Delivery of Diverse Nucleic Acids into Gram-Negative Bacteria

Antibiotic resistance is a growing public health concern. Because only a few novel classes of antibiotics have been developed in the last 40 years, such as the class of oxazolidinones, new antibacterial strategies are urgently needed [1]. Nucleic acid-based antibiotics are a new type of antimicrobials. However, free nucleic acids cannot spontaneously cross the bacterial cell wall and membrane;consequently, their intracellular delivery into bacteria needs to be assisted. Here, we introduce an original lipopolyplex system named liposome polymer nucleic acid (LPN), capable of versatile nucleic acid delivery into bacteria. We characterized LPN formed with significant therapeutic nucleic acids: 11 nt antisense single-stranded (ss) DNA and double-stranded (ds) DNA of 15 and 95 base pairs (bp), 9 kbp plasmid DNA (pDNA), and 1,000 nt ssRNA. All these complexes were efficiently internalized by two different bacterial species, i.e., Escherichia coli and Pseudomonas aeruginosa, as shown by flow cytometry. Consistent with intracellular delivery, LPN prepared with an antisense oligonucleotide and directed against an essential gene, induced specific and important bacterial growth inhibition likely leading to a bactericidal effect. Our findings indicate that LPN is a versatile platform for efficient delivery of diverse nucleic acids into Gram-negative bacteria.

DePEGylation strategies to increase cancer nanomedicine efficacy

To maximize drug targeting to solid tumors, cancer nanomedicines with prolonged circulation times are required. To this end, poly(ethylene glycol) (PEG) has been widely used as a steric shield of nanomedicine surfaces to minimize serum protein absorption (opsonisation) and subsequent recognition and clearance by cells of the mononuclear phagocyte system (MPS). However, PEG also inhibits interactions of nanomedicines with target cancer cells, limiting the effective drug dose that can be reached within the target tumor. To overcome this dilemma, nanomedicines with stimuli-responsive cleavable PEG functionality have been developed. These benefit from both long circulation lifetimes en route to the targeted tumor as well as efficient drug delivery to target cancer cells. In this review, various stimuli-responsive strategies to dePEGylate nanomedicines within the tumor microenvironment will be critically reviewed.

Stimuli-Responsive Nano-Architecture Drug-Delivery Systems to Solid Tumor Micromilieu: Past, Present, and Future Perspectives

The microenvironment characteristics of solid tumors, renowned as barriers that harshly impeded many drug-delivery approaches, were precisely studied, investigated, categorized, divided, and subdivided into a complex diverse of barriers. These categories were further studied with a particular perspective, which makes all barriers found in solid-tumor micromilieu turn into different types of stimuli, and were considered triggers that can increase and hasten drug-release targeting efficacy. This review gathers data concerning the nature of solid-tumor micromilieu. Past research focused on the treatment of such tumors, the recent efforts employed for engineering smart nanoarchitectures with the utilization of the specified stimuli categories, the possibility of combining more than one stimuli for much-greater targeting enhancement, examples of the approved nanoarchitectures that already translated clinically as well as the obstacles faced by the use of these nanostructures, and, finally, an overview of the possible future implementations of smart-chemical engineering for the design of more-efficient drug delivery and theranostic systems and for making nanosystems with a much-higher level of specificity and penetrability features.

Transferrin and octaarginine modified dual-functional liposomes with improved cancer cell targeting and enhanced intracellular delivery for the treatment of ovarian cancer

Off-target effects of drugs severely limit cancer therapy. Targeted nanocarriers are promising to enhance the delivery of therapeutics to tumors. Among many approaches for active tumor-targeting, arginine-rich cell penetrating peptides (AR-CPP) and ligands specific to target over-expressed receptors on cancer-cell surfaces, are popular. Earlier, we showed that the attachment of an AR-CPP octaarginine (R8) to the surface of DOXIL^® (Doxorubicin encapsulated PEGylated liposomes) improved cytoplasmic and nuclear DOX delivery that enhanced the cytotoxic effect in vitro and improved therapeutic efficacy in vivo. Here, we report on DOX-loaded liposomes, surface-modified with, R8 and transferrin (Tf) (Dual DOX-L), to improve targeting of A2780 ovarian carcinoma cells via the over-expressed transferrin receptors (TfRs) with R8-mediated intracellular DOX delivery. Flow cytometry analysis with fluorescently labeled DualL (without DOX) showed two-fold higher cancer-cell association than other treatments after 4 h treatment. Blocking entry pathways of R8 (macropinocytosis) and Tf (receptor-mediated endocytosis, RME) resulted in a decreased cancer-cell association of DualL. Confocal microscopy confirmed involvement of both entry pathways and cytoplasmic liposome accumulation with nuclear DOX delivery for Dual DOX-L. Dual DOX-L exhibited enhanced cytotoxicity in vitro and was most effective in controlling tumor growth in vivo in an A2780 ovarian xenograft model compared to other treatments. A pilot biodistribution study showed improved DOX accumulation in tumors after Dual DOX-L treatment. All results collectively presented a clear advantage of the R8 and Tf combination to elevate the therapeutic potential of DOX-L by exploiting TfR over-expression imparting specificity followed by endosomal escape and intracellular delivery via R8.

Salubrinal Enhances Doxorubicin Sensitivity in Human Cholangiocarcinoma Cells Through Promoting DNA Damage

Cholangiocarcinoma (CCA) is a highly malignant and aggressive tumor of the bile duct that arises from epithelial cells. Chemotherapy is an important treatment strategy for CCA patients, but its efficacy remains limited due to drug resistance. Salubrinal, an inhibitor of eukaryotic translation initiation factor 2 alpha (eIF2α), has been reported to affect antitumor activities in cancer chemotherapy. In this study, the authors investigated the effect of salubrinal on the chemosensitivity of doxorubicin in CCA cells. They showed that doxorubicin induces CCA cell death in a dose- and time-dependent manner. Doxorubicin triggers reactive oxygen species (ROS) generation and induces DNA damage in CCA cells. In addition, ROS inhibitor N-acetylcysteine (NAC) pretreatment inhibits doxorubicin-induced CCA cell death. Importantly, these data demonstrate a synergistic death induction effect contributed by the combination of salubrinal and doxorubicin in CCA cells. It is notable that salubrinal promotes doxorubicin-induced ROS production and DNA damage in CCA cells. Taken together, these data suggest that salubrinal enhances the sensitivity of doxorubicin in CCA cells through promoting ROS-mediated DNA damage.

Nanotechnology and Glycosaminoglycans: Paving the Way Forward for Ovarian Cancer Intervention

Ovarian cancer (OC) has gained a great deal of attention due to its aggressive proliferative capabilities, high death rates and poor treatment outcomes, rendering the disease the ultimate lethal gynaecological cancer. Nanotechnology provides a promising avenue to combat this malignancy by the niche fabrication of optimally-structured nanomedicines that ensure potent delivery of chemotherapeutics to OC, employing nanocarriers to act as "intelligent" drug delivery vehicles, functionalized with active targeting approaches for precision delivery of chemotherapeutics to overexpressed biomarkers on cancer cells. Recently, much focus has been implemented to optimize these active targeting mechanisms for treatment/diagnostic purposes employing nanocarriers. This two-part article aims to review the latest advances in active target-based OC interventions, where the impact of the newest antibody, aptamer and folate functionalization on OC detection and treatment is discussed in contrast to the limitations of this targeting mechanism. Furthermore, we discuss the latest advances in nanocarrier based drug delivery in OC, highlighting their commercial/clinical viability of these systems beyond the realms of research. Lastly, in the second section of this review, we comprehensively discussed a focus shift in OC targeting from the well-studied OC cells to the vastly neglected extracellular matrix and motivate the potential for glycosaminoglycans (GAGs) as a more focused extracellular molecular target.

Enhancing siRNA-based cancer therapy using a new pH-responsive activatable cell-penetrating peptide-modified liposomal system

As a potent therapeutic agent, small interfering RNA (siRNA) has been exploited to silence critical genes involved in tumor initiation and progression. However, development of a desirable delivery system is required to overcome the unfavorable properties of siRNA such as its high degradability, molecular size, and negative charge to help increase its accumulation in tumor tissues and promote efficient cellular uptake and endosomal/lysosomal escape of the nucleic acids. In this study, we developed a new activatable cell-penetrating peptide (ACPP) that is responsive to an acidic tumor microenvironment, which was then used to modify the surfaces of siRNA-loaded liposomes. The ACPP is composed of a cell-penetrating peptide (CPP), an acid-labile linker (hydrazone), and a polyanionic domain, including glutamic acid and histidine. In the systemic circulation (pH 7.4), the surface polycationic moieties of the CPP (polyarginine) are "shielded" by the intramolecular electrostatic interaction of the inhibitory domain. When exposed to a lower pH, a common property of solid tumors, the ACPP undergoes acid-catalyzed breakage at the hydrazone site, and the consequent protonation of histidine residues promotes detachment of the inhibitory peptide. Subsequently, the unshielded CPP would facilitate the cellular membrane penetration and efficient endosomal/lysosomal evasion of liposomal siRNA. A series of investigations demonstrated that once exposed to an acidic pH, the ACPP-modified liposomes showed elevated cellular uptake, downregulated expression of polo-like kinase 1, and augmented cell apoptosis. In addition, favorable siRNA avoidance of the endosome/lysosome was observed in both MCF-7 and A549 cells, followed by effective cytoplasmic release. In view of its acid sensitivity and therapeutic potency, this newly developed pH-responsive and ACPP-mediated liposome system represents a potential platform for siRNA-based cancer treatment.

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.

Strategies of polymeric nanoparticles for enhanced internalization in cancer therapy

In order to achieve long circulation time and high drug accumulation in the tumor sites via the EPR effects, anticancer drugs have to be protected by non-fouling polymers such as poly(ethylene glycol) (PEG), poly(ethylene oxide) (PEO), dextran, and poly(acrylic acid) (PAA). However, the dense layer of stealth polymer also prohibits efficient uptake of anticancer drugs by target cancer cells. For cancer therapy, it is often more desirable to accomplish rapid cellular uptake after anticancer drugs arriving at the pathological site, which could on one hand maximize the therapeutic efficacy and on the other hand reduce probability of drug resistance in cells. In this review, special attention will be focused on the recent potential strategies that can enable drug-loaded polymeric nanoparticles to rapidly recognize cancer cells, leading to enhanced internalization.

Doxorubicin liposomes as an investigative model to study the skin permeation of nanocarriers

The objectives of this study were to develop an innovative investigative model using doxorubicin as a fluorophore to evaluate the skin permeation of nanocarriers and the impact of size and surface characteristics on their permeability. Different doxorubicin-loaded liposomes with mean particle size <130 nm and different surface chemistry were prepared by ammonium acetate gradient method using DPPC, DOPE, Cholesterol, DSPE-PEG 2000 and 1,1-Di-((Z)-octadec-9-en-1-yl) pyrrolidin-1-ium chloride (CY5)/DOTAP/1,2-dioleoyl-sn-glycero-3-phosphate (DOPA) as the charge modifier. There was minimal release of doxorubicin from the liposomes up to 8h; indicating that fluorescence observed within the skin layers was due to the intact liposomes. Liposomes with particle sizes >600 nm were restricted within the stratum corneum. DOTAP (p<0.01) and CY5 (p<0.05) liposomes demonstrated significant permeation into the skin than DOPA and PEG liposomes. Tape stripping significantly (p<0.01) enhanced the skin permeation of doxorubicin liposomes but TAT-decorated doxorubicin liposomes permeated better (p<0.005). Blockage of the hair follicles resulted in significant reduction in the extent and intensity of fluorescence observed within the skin layers. Overall, doxorubicin liposomes proved to be an ideal fluorophore-based model. The hair follicles were the major route utilized by the liposomes to permeate skin. Surface charge and particle size played vital roles in the extent of permeation.

Modifications of natural peptides for nanoparticle and drug design

Natural products serve as an important source of novel compounds for drug development. Recently, peptides have emerged as a new class of therapeutic agents due to their versatility and specificity for biological targets. Yet, their effective application often requires use of a nanoparticle delivery system. In this chapter, we review the role of natural peptides in the design and creation of nanomedicines, with a particular focus on cell-penetrating peptides, antimicrobial peptides, and peptide toxins. The use of natural peptides in conjunction with nanoparticle delivery systems holds great promise for the development of new therapeutic formulations as well as novel platforms for the delivery of various cargoes.

Intracellular Delivery of Nanoparticles with Cell Penetrating Peptides

The functionalization of nanoparticles (NPs) with cell penetrating peptides (CPPs) constitutes a breakthrough for the intracellular delivery of therapeutic and diagnostic payloads. In late 1998, a significant cellular uptake of a small protein from the HIV-1 virus, namely TAT peptide (TATp), was observed. Thereafter, research began on design of similarly acting peptides, and the coupling of NPs with these novel CPPs. Here, we describe recent methods used to modify the surface of NPs with CPPs and the in vitro and in vivo effects of such functionalization on the intracellular delivery of various cargos. In particular, we highlight recent advances aimed at reducing the non-selectivity of CPPs and the prevention of their enzymatic cleavage en route to target tissues.

Multifunctional, stimuli-sensitive nanoparticulate systems for drug delivery

The use of nanoparticulate pharmaceutical drug delivery systems (NDDSs) to enhance the in vivo effectiveness of drugs is now well established. The development of multifunctional and stimulus-sensitive NDDSs is an active area of current research. Such NDDSs can have long circulation times, target the site of the disease and enhance the intracellular delivery of a drug. This type of NDDS can also respond to local stimuli that are characteristic of the pathological site by, for example, releasing an entrapped drug or shedding a protective coating, thus facilitating the interaction between drug-loaded nanocarriers and target cells or tissues. In addition, imaging contrast moieties can be attached to these carriers to track their real-time biodistribution and accumulation in target cells or tissues. Here, I highlight recent developments with multifunctional and stimuli-sensitive NDDSs and their therapeutic potential for diseases including cancer, cardiovascular diseases and infectious diseases.

Multifunctional, stimuli-sensitive nanoparticulate systems for drug delivery

The use of nanoparticulate pharmaceutical drug delivery systems (NDDSs) to enhance the in vivo effectiveness of drugs is now well established. The development of multifunctional and stimulus-sensitive NDDSs is an active area of current research. Such NDDSs can have long circulation times, target the site of the disease and enhance the intracellular delivery of a drug. This type of NDDS can also respond to local stimuli that are characteristic of the pathological site by, for example, releasing an entrapped drug or shedding a protective coating, thus facilitating the interaction between drug-loaded nanocarriers and target cells or tissues. In addition, imaging contrast moieties can be attached to these carriers to track their real-time biodistribution and accumulation in target cells or tissues. Here, I highlight recent developments with multifunctional and stimuli-sensitive NDDSs and their therapeutic potential for diseases including cancer, cardiovascular diseases and infectious diseases.

Barriers to drug delivery in solid tumors

Over the last decade, significant progress has been made in the field of drug delivery. The advent of engineered nanoparticles has allowed us to circumvent the initial limitations to drug delivery such as pharmacokinetics and solubility. However, in spite of significant advances to tumor targeting, an effective treatment strategy for malignant tumors still remains elusive. Tumors possess distinct physiological features which allow them to resist traditional treatment approaches. This combined with the complexity of the biological system presents significant hurdles to the site-specific delivery of therapeutic drugs. One of the key features of engineered nanoparticles is that these can be tailored to execute specific functions. With this review, we hope to provide the reader with a clear understanding and knowledge of biological barriers and the methods to exploit these characteristics to design multifunctional nanocarriers, effect useful dosing regimens and subsequently improve therapeutic outcomes in the clinic.