Tumor-acidity activated surface charge-conversion of polymeric nanocarriers for enhanced cell adhesion and targeted drug release

A Descriptive Review on the Potential Use of Diatom Biosilica as a Powerful Functional Biomaterial: A Natural Drug Delivery System

Although various chemically synthesized materials are essential in medicine, food, and agriculture, they can exert unexpected side effects on the environment and human health by releasing certain toxic chemicals. Therefore, eco-friendly and biocompatible biomaterials based on natural resources are being actively explored. Recently, biosilica derived from diatoms has attracted attention in various biomedical fields, including drug delivery systems (DDS), due to its uniform porous nano-pattern, hierarchical structure, and abundant silanol functional groups. Importantly, the structural characteristics of diatom biosilica improve the solubility of poorly soluble substances and enable sustained release of loaded drugs. Additionally, diatom biosilica predominantly comprises SiO2, has high biocompatibility, and can easily hybridize with other DDS platforms, including hydrogels and cationic DDS, owing to its strong negative charge and abundant silanol groups. This review explores the potential applications of various diatom biosilica-based DDS in various biomedical fields, with a particular focus on hybrid DDS utilizing them.

Internal stimuli-responsive nanocarriers for controlled anti-cancer drug release: a review

Cancer disease is one of the most frequent life-threatening, with a high fatality rate worldwide. However, recent immunotherapy studies in various tumours have yielded unsatisfactory outcomes, with just a few individuals experiencing long-term responses. To overcome these issues, nowadays internal stimuli-responsive nanocarriers have been widely exploited to transport a wide range of active substances, including peptides, genes and medicines. These nanosystems could be chemically adjusted to produce target-based drug release at the target location, minimizing pathological and physiological difficulties while increasing therapeutic efficiency. This review highlights the various types of internal stimuli-responsive nanocarriers and applications in cancer diagnosis. This study can provide inspiration and impetus for exploiting more promising internal stimuli-responsive nanosystems for drug delivery.

Biomimetic nanoparticles to enhance the reverse cholesterol transport for selectively inhibiting development into foam cell in atherosclerosis

A disorder of cholesterol homeostasis is one of the main initiating factors in the progression of atherosclerosis (AS). Metabolism and removal of excess cholesterol facilitates the prevention of foam cell formation. However, the failure of treatment with drugs (e.g. methotrexate, MTX) to effectively regulate progression of disease may be related to the limited drug bioavailability and rapid clearance by immune system. Thus, based on the inflammatory lesion "recruitment" properties of macrophages, MTX nanoparticles (MTX NPs) camouflaged with macrophage membranes (MM@MTX NPs) were constructed for the target to AS plaques. MM@MTX NPs exhibited a uniform hydrodynamic size around ~ 360 nm and controlled drug release properties (~ 72% at 12 h). After the macrophage membranes (MM) functionalized "homing" target delivery to AS plaques, MM@MTX NPs improved the solubility of cholesterol by the functionalized β-cyclodextrin (β-CD) component and significantly elevate cholesterol efflux by the loaded MTX mediated the increased expression levels of ABCA1, SR-B1, CYP27A1, resulting in efficiently inhibiting the formation of foam cells. Furthermore, MM@MTX NPs could significantly reduce the area of plaque, aortic plaque and cholesterol crystals deposition in ApoE-/- mice and exhibited biocompatibility. It is suggested that MM@MTX NPs were a safe and efficient therapeutic platform for AS.

Charge-Convertible and Reduction-Sensitive Cholesterol-Containing Amphiphilic Copolymers for Improved Doxorubicin Delivery

For achieving successful chemotherapy against cancer, designing biocompatible drug delivery systems (DDSs) with long circulation times, high cellular endocytosis efficiency, and targeted drug release is of upmost importance. Herein, a well-defined PEG-b-P(MASSChol-co-MANBoc) block copolymer bearing redox-sensitive cholesteryl-side group was prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization (with non-redox PEG-b-P(MACCChol-co-MAN-DCA) as the reference), and 1,2-dicarboxylic-cyclohexene acid (DCA) was then grafted onto the hydrophobic block to endow it with charge-convertible characteristics under a tumor microenvironment. The amphiphilic copolymer could be assembled into polymeric spherical micelles (SSMCs) with polyethylene glycol (PEG) as the corona/shell, and anti-cancer drug doxorubicin (DOX) was successfully encapsulated into the micellar core via strong hydrophobic and electrostatic interactions. This nanocarrier showed high stability in the physiological environment and demonstrated "smart" surface charge conversion from negative to positive in the slightly acidic environment of tumor tissues (pH 6.5~6.8), as determined by dynamic light scattering (DLS). Moreover, the cleavage of a disulfide bond linking the cholesterol grafts under an intracellular redox environment (10 mM GSH) resulted in micellar dissociation and accelerated drug release, with the non-redox-responsive micelles (CCMCs) as the control. Additionally, a cellular endocytosis and tumor proliferation inhibition study against MCF-7 tumor cells demonstrated the enhanced endocytosis and tumor cell inhibitory efficiency of dual-responsive SSMCs/DOX nanomedicines, revealing potentials as multifunctional nanoplatforms for effective oncology treatment.

Design of Smart Size-, Surface-, and Shape-Switching Nanoparticles to Improve Therapeutic Efficacy

Multiple biological barriers must be considered in the design of nanomedicines, including prolonged blood circulation, efficient accumulation at the target site, effective penetration into the target tissue, selective uptake of the nanoparticles into target cells, and successful endosomal escape. However, different particle sizes, surface chemistries, and sometimes shapes are required to achieve the desired transport properties at each step of the delivery process. In response, this review highlights recent developments in the design of switchable nanoparticles whose size, surface chemistry, shape, or a combination thereof can be altered as a function of time, a disease-specific microenvironment, and/or via an externally applied stimulus to enable improved optimization of nanoparticle properties in each step of the delivery process. The practical use of such nanoparticles in chemotherapy, bioimaging, photothermal therapy, and other applications is also discussed.

Formulation of Nano/Micro-Carriers Loaded with an Enriched Extract of Coffee Silverskin: Physicochemical Properties, In Vitro Release Mechanism and In Silico Molecular Modeling

Designing strategies for an effective transformation of food waste into high-value products is a priority to address environmental sustainability concerns. Coffee silverskin is the major by-product of the coffee roasting industry, being rich in compounds with health benefits. Such composition gives it the potential to be transformed into high-value products. In this study, coffee silverskin extracts were enriched, regarding caffeine and chlorogenic acid contents, by adsorbent column chromatography. The compounds content increased 3.08- and 2.75-fold, respectively, compared to the original extract. The enriched fractions were loaded into nano-phytosomes or cholesterol-incorporated nano-phytosomes (first coating layers) to improve the physiochemical properties and permeation rate. These nano-lipid carriers were also subjected to a secondary coating with different natural polymers to improve protection and stability against degradation. In parallel, and for comparison, different natural polymers were also used as first coating layers. The produced particles were evaluated regarding product yield, encapsulation efficiency, loading capacity, particle size, surface charge, and in vitro release simulating gastrointestinal conditions. All samples exhibited anionic surface charge. FTIR and molecular docking confirmed interactions between the phytoconstituents and lipid bilayers. The best docking score was observed for 5-caffeoylquinic acid (chlorogenic acid) exhibiting a stronger hydrogen binding to the lipid bilayer. Among several kinetic models tested, the particle release mechanism fitted well with the First-order, Korsmeyer-Peppas, and Higuchi models. Moreover, most of the formulated particles followed the diffusion-Fick law and anomalous transport.

The reversed intra- and extracellular pH in tumors as a unified strategy to chemotherapeutic delivery using targeted nanocarriers

Solid tumors are complex entities, comprising a wide variety of malignancies with very different molecular alterations. Despite this, they share a set of characteristics known as "hallmarks of cancer" that can be used as common therapeutic targets. Thus, every tumor needs to change its metabolism in order to obtain the energy levels required for its high proliferative rates, and these adaptations lead to alterations in extra- and intracellular pH. These changes in pH are common to all solid tumors, and can be used either as therapeutic targets, blocking the cell proton transporters and reversing the pH changes, or as means to specifically deliver anticancer drugs. In this review we will describe how proton transport inhibitors in association with nanocarriers have been designed to block the pH changes that are needed for cancer cells to survive after their metabolic adaptations. We will also describe studies aiming to decrease intracellular pH in cancer using nanoparticles as molecular cages for protons which will be released upon UV or IR light exposure. Finally, we will comment on several studies that have used the extracellular pH in cancer for an enhanced cell internalization and tumor penetration of nanocarriers and a controlled drug delivery, describing how nanocarriers are being used to increase drug stability and specificity.

Tumor Acid Microenvironment-Triggered Self-Assembly of ESIONPs for T1/T2 Switchable Magnetic Resonance Imaging

Smart magnetic resonance imaging (MRI) contrast agents (CAs), whose MRI contrasting enhancement is variable in response to the specific stimulus from tumor tissues, possess great potential in precise tumor diagnosis. Herein, we design a type of extremely small iron oxide nanoparticle (ESIONP)-based pH-responsive system for activatable T₂ MRI in the tumor acid microenvironment. The ESIONP system is composed of ESIONP-PEG-PGA and ESIONP-PEG-PDC, which were respectively constructed through the surface modification with poly (l-glutamic acid) (PGA) and poly(N-{N'-[N″-(2-carbox aminoethyl)]-2-aminoethyl}glutamide) (PDC) on the surface of ESIONP. The pH-responsive system exhibits the dispersed state under the neutral condition, and when it is exposed to the weakly acid environment, ESIONP-PEG-PDC switches from the neutral to positive charge, finally leading to the aggregation by the electrostatic interaction between the positively charged ESIONP-PEG-PDC and negatively charged ESIONP-PEG-PGA. On the basis of the aggregation, the T₁ contrasting effect of the pH-responsive system switches to a T₂ contrasting effect, which can be employed to realize the selective enhancement of imaging contrast at the tumor location owing to the weakly acid microenvironment. Moreover, on the basis of size increase originated from the aggregation effect, the residence time of extremely small iron oxide nanoparticles (ESIONPs) in the tumor site is effectively prolonged, which is beneficial for the MRI of tumors. Therefore, the pH-responsive system based on the ESIONPs is a potential smart MRI contrast agent for accurate tumor diagnosis.

Advanced drug-delivery systems: mechanoresponsive nanoplatforms applicable in atherosclerosis management

Nanoplatforms have been used extensively as advanced carriers to enhance the effectiveness of drug delivery, mostly through passive aggregation provided by the enhanced permeability and retention effect. Mechanical stimuli provide a robust strategy to bolster drug delivery performance by increasing the accumulation of nanoplatforms at the lesion sites, facilitating on-demand cargo release and providing theranostic aims. In this review, we focus on recent advances of mechanoresponsive nanoplatforms that can accomplish targeted drug delivery, and subsequent drug release, under specific stimuli, either endogenous (shear stress) or exogenous (magnetic field and ultrasound), to synergistically combat atherosclerosis at the molecular level.

Advances in refunctionalization of erythrocyte-based nanomedicine for enhancing cancer-targeted drug delivery

Cancer remains a daunting and cureless disease, which is responsible for one-sixth of human deaths worldwide. These mortality rates have been expected to rise in the future due to the side effects of conventional treatments (chemotherapy, radiotherapy, and surgery), which can be addressed by applying nanomedicine. In order to escape from biological barriers, such nanomedicine should be mimicked and designed to be stealthy while navigating in the bloodstream. To achieve this, scientists take advantage of erythrocytes (red blood cells; RBCs) as drug carriers and develop RBC membrane (RBCm) coating nanotechnology. Thanks to the significant advances in nanoengineering, various facile surface functionalization methods can be applied to arm RBCm with not only targeting moieties, but also imaging agents, therapeutic agents, and nanoparticles, which are useful for theranostic nanomedicine. This review focuses on refunctionalization of erythrocyte-based nanomedicine for enhancing cancer-targeted drug delivery.

Nanomaterials multifunctional behavior for enlightened cancer therapeutics

Cancer is an outrageous disease with uncontrolled differentiation, growth, and migration to the other parts of the body. It is the second-most common cause of death both in the U.S. and worldwide. Current conventional therapies, though much improved and with better prognosis, have several limitations. Chemotherapeutic agents, for instance, are cytotoxic to both tumor and healthy cells, and the non-specific distribution of drugs at tumor sites limits the dose administered. Nanotechnology, which evolved from the coalescence and union of varied scientific disciplines, is a novel science that has been the focus of much research. This technology is generating more effective cancer therapies to overcome biomedical and biophysical barriers against standard interventions in the body; its unique magnetic, electrical, and structural properties make it a promising tool. This article reviews endogenous- and exogenous-based stimulus-responsive drug delivery systems designed to overcome the limitations of conventional therapies. The article also summarizes the study of nanomaterials, including polymeric, gold, silver, magnetic, and quantum dot nanoparticles. Though an array of drug delivery systems has so far been proposed, there remain many challenges and concerns that should be addressed in order to fill the gaps in the field. Prominence is given to drug delivery systems that employ external- and internal-based stimuli and that are emerging as promising tools for cancer therapeutics in clinical settings.

Transforming stealthy to sticky nanocarriers: a potential application for tumor therapy

Nanomedicine has shown remarkable progress in preclinical studies of tumor treatment. Over the past decade, scientists have developed various nanocarriers (NCs) for delivering drugs into the tumor area. However, the average amount of accumulated drugs in tumor sites is far from satisfactory. This limitation is strongly related to the corona formation during blood circulation. To overcome this issue, NCs should be designed to become highly stealthy by modifying their surface charge. However, at the same time, stealthy effects not only prevent protein formation but also alleviate the cellular uptake of NCs. Therefore, it is necessary to develop NCs with switchable properties, which are stealthy in the circulation system and sticky when arriving at tumor sites. In this review, we discuss the recent strategies to develop passive and active charge-switchable NCs, known as chameleon-like drug delivery systems, which can reversibly transform their surface from stealthy to sticky and have various designs.

Atherosclerosis Treatment with Stimuli-Responsive Nanoagents: Recent Advances and Future Perspectives

Atherosclerosis is the root of approximately one-third of global mortalities. Nanotechnology exhibits splendid prospects to combat atherosclerosis at the molecular level by engineering smart nanoagents with versatile functionalizations. Significant advances in nanoengineering enable nanoagents to autonomously navigate in the bloodstream, escape from biological barriers, and assemble with their nanocohort at the targeted lesion. The assembly of nanoagents with endogenous and exogenous stimuli breaks down their shells, facilitates intracellular delivery, releases their cargo to kill the corrupt cells, and gives imaging reports. All these improvements pave the way toward personalized medicine for atherosclerosis. This review systematically summarizes the recent advances in stimuli-responsive nanoagents for atherosclerosis management and its progress in clinical trials.

Translational Multi-Disciplinary Approach for the Drug and Gene Delivery Systems for Cancer Treatment

Over the last several decades, nanoparticulate delivery systems have emerged as advanced drug and gene delivery tools for cancer therapy. However, their translation into clinical use still poses major challenges. Even though many innovative nanoparticulate approaches have shown very positive results both in vitro and in vivo, few of them have found a place in clinical practice. Possible factors responsible for the existing gap in the translation of nanomedicine to clinical practice may include oversimplification of enhanced permeability and retention effect, lack of correlation between the in vivo animal data vs their translation in human, and challenging multiple biological steps experienced during systemic delivery of nanomedicine. Understanding these challenges and coming up with solutions to overcome them is an important step in effective translation of nanomedicine into clinical practice. This review focuses on advancements in the field of nanomedicine used for anti-cancer therapy, including passive targeting, active targeting, and stimuli-controlled delivery. The review further reveals some of the challenges that are currently faced by pharmaceutical scientists in translation of nanomedicine; these include lack of adequate models for preclinical testing that can predict efficacy in humans, absence of appropriate regulatory guidelines for their approval processes, and difficulty in scale-up of the manufacturing of nanodrug delivery systems. A better understanding of these challenges will help us in filling the gap between the bench and bedside in cancer therapy.

Targeted polyethylenimine/(p53 plasmid) nanocomplexes for potential antitumor applications

The development of the tumor-targeting ability of nanocarriers is of paramount importance for gene delivery into tumor lesions as well as to avoid biotoxicity. Here we report the synthesis of the polyethyleneimine-fluorescein isothiocyanate-folic acid (PEI-FITC-FA) polymer, which could condense the tumor suppressor pp53 to form nanocomplexes. These targeted nanocomplexes exhibited favorable physical properties including a small size of <100 nm, exploiting the enhanced permeability and retention effect and tumor-targeting ability by binding to the overexpressed FA receptors on tumor cell surfaces. In addition, once the nanocomplexes are accumulating in the tumor tissue, the target functional ligand, FA, can selectively recognize the over-expressed FA receptor and subsequently remain on the tumor cell surface, which can significantly promote the tumor cell uptake because of the time- and concentration-dependent internalization caused by the enhanced interaction between nanocomplex and tumor cell. Our results indicated that PEI-FITC-FA/pp53 nanocomplexes could be efficiently delivered into tumor cells, and subsequently induce tumor cell apoptosis. Thus, the targeted cationic polymer PEI-FITC-FA could be used as an advanced nanocarrier for gene delivery.

Acid-Activated Melittin for Targeted and Safe Antitumor Therapy

Melittin (MLT), as a natural active biomolecule, can penetrate the tumor cell membrane to play a role in cancer treatment and will attract more attention in future development of antitumor drugs. The main component of natural bee venom MLT was modified by introducing a pH-sensitive amide bond between the 2,3-dimethyl maleimide (DMMA) and the lysine (Lys) of MLT (MLT-DMMA). MLT and its corresponding modified peptide MLT-DMMA were used for antitumor and biocompatibility validation. The biomaterial characteristics were tested by MALDI-TOF MS, ¹H NMR, IUPAC and HPLC, cell viability, hemolytic and animal experiment safety evaluation. Compared with the primary melittin, the modified peptide showed decreased surface charge and low cytotoxicity in physiological conditions. Moreover, cell assays confirmed the acid-activated conversion of amide bond resulting in adequate safety during delivery and timely antitumor activity in tumor lesions. Thus, MLT-DMMA provided a feasible platform to improve the targeted and safe antitumor applications.

Endogenous pH-responsive nanoparticles with programmable size changes for targeted tumor therapy and imaging applications

Nanotechnology-based antitumor drug delivery systems, known as nanocarriers, have demonstrated their efficacy in recent years. Typically, the size of the nanocarriers is around 100 nm. It is imperative to achieve an optimum size of these nanocarriers which must be designed uniquely for each type of delivery process. For pH-responsive nanocarriers with programmable size, changes in pH (~6.5 for tumor tissue, ~5.5 for endosomes, and ~5.0 for lysosomes) may serve as an endogenous stimulus improving the safety and therapeutic efficacy of antitumor drugs. This review focuses on current advanced pH-responsive nanocarriers with programmable size changes for anticancer drug delivery. In particular, pH-responsive mechanisms for nanocarrier retention at tumor sites, size reduction for penetrating into tumor parenchyma, escaping from endo/lysosomes, and swelling or disassembly for drug release will be highlighted. Additional trends and challenges of employing these nanocarriers in future clinical applications are also addressed.

Dual tumor-targeted poly(lactic-co-glycolic acid)-polyethylene glycol-folic acid nanoparticles: a novel biodegradable nanocarrier for secure and efficient antitumor drug delivery

Further specific target-ability development of biodegradable nanocarriers is extremely important to promote their security and efficiency in antitumor drug-delivery applications. In this study, a facilely prepared poly(lactic-co-glycolic acid) (PLGA)-polyethylene glycol (PEG)-folic acid (FA) copolymer was able to self-assemble into nanoparticles with favorable hydrodynamic diameters of around 100 nm and negative surface charge in aqueous solution, which was expected to enhance intracellular antitumor drug delivery by advanced dual tumor-target effects, ie, enhanced permeability and retention induced the passive target, and FA mediated the positive target. Fluorescence-activated cell-sorting and confocal laser-scanning microscopy results confirmed that doxorubicin (model drug) loaded into PLGA-PEG-FA nanoparticles was able to be delivered efficiently into tumor cells and accumulated at nuclei. In addition, all hemolysis, 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, and zebrafish-development experiments demonstrated that PLGA-PEG-FA nanoparticles were biocompatible and secure for biomedical applications, even at high polymer concentration (0.1 mg/mL), both in vitro and in vivo. Therefore, PLGA-PEG-FA nanoparticles provide a feasible controlled-release platform for secure and efficient antitumor drug delivery.

Co-delivery of all-trans-retinoic acid enhances the anti-metastasis effect of albumin-bound paclitaxel nanoparticles

Co-delivery of all-trans-retinoic acid and paclitaxel using albumin-bound nanoparticles demonstrated a significantly improved anti-metastatic effect to breast cancer both in vitro and in vivo. Notably, the co-delivery nanoparticles exhibited more pronounced therapeutic effects than the combination of two free drugs or two HSA loaded single drugs.

Surface Modified Multifunctional and Stimuli Responsive Nanoparticles for Drug Targeting: Current Status and Uses

Nanocarriers, due to their unique features, are of increased interest among researchers working with pharmaceutical formulations. Polymeric nanoparticles and nanocapsules, involving non-toxic biodegradable polymers, liposomes, solid lipid nanoparticles, and inorganic-organic nanomaterials, are among the most used carriers for drugs for a broad spectrum of targeted diseases. In fact, oral, injectable, transdermal-dermal and ocular formulations mainly consist of the aforementioned nanomaterials demonstrating promising characteristics such as long circulation, specific targeting, high drug loading capacity, enhanced intracellular penetration, and so on. Over the last decade, huge advances in the development of novel, safer and less toxic nanocarriers with amended properties have been made. In addition, multifunctional nanocarriers combining chemical substances, vitamins and peptides via coupling chemistry, inorganic particles coated by biocompatible materials seem to play a key role considering that functionalization can enhance characteristics such as biocompatibility, targetability, environmental friendliness, and intracellular penetration while also have limited side effects. This review aims to summarize the "state of the art" of drug delivery carriers in nanosize, paying attention to their surface functionalization with ligands and other small or polymeric compounds so as to upgrade active and passive targeting, different release patterns as well as cell targeting and stimuli responsibility. Lastly, future aspects and potential uses of nanoparticulated drug systems are outlined.

Hierarchical mesoporous silica nanoparticles for tailorable drug release

In order to modulate the drug release profiles, the hierarchical mesoporous silica nanoparticles (HMSNs) are fabricated by a two-step synthetic process. The HMSNs exhibit uniform spherical morphology with nanoscaled size, well mono-dispersed size distribution, and smooth surface. Because of the hierarchical pore structures with different mesoporous sizes and morphologies (partial open and partial blocked pores), the HMSNs can release the loaded drug in a controlled manner. The hierarchical mesoporous structures directed drug release profiles suggest a feasible strategy to tailor drug release behaviors. Meanwhile, the HMSNs exhibit good biocompatibility. Therefore, the HMSNs having tailorable drug release capacity would be a potential candidate to improve their therapeutic efficiency for drug delivery systems.

Charge-Convertible Carbon Dots for Imaging-Guided Drug Delivery with Enhanced in Vivo Cancer Therapeutic Efficiency

Carbon dots (CDs) are remarkable nanocarriers due to their promising optical and biocompatible capabilities. However, their practical applicability in cancer therapeutics is limited by their insensitive surface properties to complicated tumor microenvironment in vivo. Herein, a tumor extracellular microenvironment-responsive drug nanocarrier based on cisplatin(IV) prodrug-loaded charge-convertible CDs (CDs-Pt(IV)@PEG-(PAH/DMMA)) was developed for imaging-guided drug delivery. An anionic polymer with dimethylmaleic acid (PEG-(PAH/DMMA)) on the fabricated CDs-Pt(IV)@PEG-(PAH/DMMA) could undergo intriguing charge conversion to a cationic polymer in mildly acidic tumor extracellular microenvironment (pH ∼ 6.8), leading to strong electrostatic repulsion and release of positive CDs-Pt(IV). Importantly, positively charged nanocarrier displays high affinity to negatively charged cancer cell membrane, which results in enhanced internalization and effective activation of cisplatin(IV) prodrug in the reductive cytosol. The in vitro experimental results confirmed that this promising charge-convertible nanocarrier possesses better therapeutic efficiency under tumor extracellular microenvironment than normal physiological condition and noncharge-convertible nanocarrier. The in vivo experiments further demonstrated high tumor-inhibition efficacy and low side effects of the charge-convertible CDs, proving its capability as a smart drug nanocarrier with enhanced therapeutic effects. The present work provides a strategy to promote potential clinical application of CDs in the cancer treatment.

Activated Charge-Reversal Polymeric Nano-System: The Promising Strategy in Drug Delivery for Cancer Therapy

Various polymeric nanoparticles (NPs) with optimal size, tumor-targeting functionalization, or microenvironment sensitive characteristics have been designed to solve several limitations of conventional chemotherapy. Nano-sized polymeric drug carrier systems have remarkably great advantages in drug delivery and cancer therapy, which are still plagued with severe deficiencies, especially insufficient cellular uptake. Recently, surface charge of medical NPs has been demonstrated to play an important role in cellular uptake. NPs with positive charge show higher affinity to anionic cell membranes such that with more efficient cellular internalization, but otherwise cause severe aggregation and fast clearance in circulation. Thus, surface charge-reversal NPs, specifically activated at the tumor site, have shown to elegantly resolve the enhanced cellular uptake in cancer cells vs. non-specific protein adsorption dilemma. Herein, this review mainly focuses on the effect of tumor-site activated surface charge reversal NPs on tumor treatment, including the activated mechanisms and various applications in suppressing cancer cells, killing cancer stem cell and overcoming multidrug resistance, with the emphasis on recent research in these fields. With the comprehensive and in-depth understanding of the activated surface charge reversal NPs, this approach might arouse great interest of scientific research on enhanced efficient polymeric nano-carriers in cancer therapy.

Synergetic enhancement of antitumor efficacy with charge-reversal and reduction-sensitive polymer micelles

An amphiphilic block copolymer PLA-SS-PAEMA/DMMA was used to encapsulate and deliver Doxorubicin for synergetic enhancement of antitumor efficacy by the combinational effect of charge-reversal on cellular uptake and reduction-sensitivity on intracellular DOX release.

Tumor therapy: targeted drug delivery systems

The review highlights the main targeted drug delivery systems for tumor therapy, including the targeting sites, strategies, mechanisms and preclinical/clinical trials.

Albumin–polymer conjugate nanoparticles and their interactions with prostate cancer cells in 2D and 3D culture: comparison between PMMA and PCL

Using proteins as the hydrophilic moiety can dramatically improve the biodegradability and biocompatibility of self-assembled amphiphilic nanoparticles in the field of nanomedicine.

A drug release switch based on protein-inhibitor supramolecular interaction

The cargo release can be triggered by the specific interaction between the protein and its inhibitor.

Zwitterionic pH/redox nanoparticles based on dextran as drug carriers for enhancing tumor intercellular uptake of doxorubicin

Zwitterionic nanoparticles have excellent serum stability. In this study, pH/redox responsive polymer was synthesized through a modification of dextran using succinic acid, followed by crosslinking with cystamine. The polymer could self-assemble into stable nanoparticles (NPs) in aqueous solution. The NPs carried certain amount of free carboxyl and amino groups on the surface, which endowed the NPs excellent anti-protein adsorption ability. The surface charge was negative at pH7.4 and was converted to positive at pH5.0. It was revealed that the NPs showed little non-specific protein adsorption and had excellent serum stability, and the NPs could be internalized in Hela cells rapidly. This result was ascribed to the charge reversible feature of the NPs. Doxorubicin (DOX) was loaded in the NPs for release studies in vitro. The DOX-loaded NPs exhibited obvious pH and reduction sensitivities in response to the environment in tumor cells due to the introduction of carboxyl groups, amino groups and disulfide bonds in the NPs. The NPs were biocompatible, biodegradable, and could be potentially applied as anticancer drug carriers for enhancement of tumor intercellular uptake of doxorubicin.

Fabrication and Characterization of a Novel Anticancer Drug Delivery System: Salecan/Poly(methacrylic acid) Semi-interpenetrating Polymer Network Hydrogel

Salecan is a novel linear extracellular polysaccharide with a linear backbone of 1-3-linked glucopyranosyl units. Salecan is suitable for preparing hydrogels for biomedical applications due to its prominent physicochemical and biological profiles. In this contribution, a variety of innovative semi-interpenetrating polymer network (semi-IPN) hydrogels consisting of Salecan and poly(methacrylic acid) (PMAA) were developed via free radical polymerization for controlled drug delivery. The successful fabrication of the semi-IPNs was verified by Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), and thermogravimetric (TGA) measurements. Scanning electron microscopy (SEM) and rheology analyses demonstrated that the morphological and mechanical behaviors of the resultant hydrogels were strongly affected by the contents of Salecan and cross-linker N,N'-methylenebis(acrylamide) (BIS). Moreover, the swelling properties of these hydrogels were systematically investigated, and the results indicated that they exhibited pH sensitivity. The drug delivery applications of such fabricated hydrogels were further evaluated from which doxorubicin (Dox) was chosen as a model drug for in vitro release and cell viability studies. It was found that the Dox release from the Dox-loaded hydrogels was significantly accelerated when the pH of the release media decreased from 7.4 to 5.0. Toxicity assays confirmed that the blank hydrogels had negligible toxicity to normal cells, whereas the Dox-loaded hydrogels remained high in cytotoxicity for A549 and HepG2 cancer cells. All of these attributes implied that the new proposed semi-IPNs serve as potential drug delivery platforms for cancer therapy.

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.

Enhancement of cancer specific delivery using ultrasound active bio-originated particles

A bio-available microbubble, liposome, and Fe³⁺ chelated melanin nanoparticle complex with a dual ultrasound and T₁-w magnetic resonance imaging modality has been synthesized for the specific targeting of cancer cells.