Hybrid polymer micelles capable of cRGD targeting and pH-triggered surface charge conversion for tumor selective accumulation and promoted uptake

Cyclic RGD modified dextran-quercetin polymer micelles for targeted therapy of breast cancer

Quercetin is a natural flavonoid found in many plants which has various pharmacological activities including antitumor effect. However, the poor water solubility and bioavailability limit the potential benefits of quercetin for patients. Thus, modifying quercetin structure and developing actively targeted drug delivery systems are extremely important for tumor precision therapy. Herein, polymer-drug conjugates dextran-quercetin (D-Q) and cRGD-dextran (R-D) were synthesized by grafting quercetin and polypeptide cRGDfk (Arg-Gly-Asp-(D-Phe)-Lys) to dextran. Then cRGD-modified dextran-quercetin polymer micelles (R-D-Q) were constructed by self-assembling of D-Q and R-D. R-D-Q micelles possessed appropriate particle size (133.4 nm), nearly neutral potential (8.14 mV) and excellent drug-loading efficiency (13.1 %) and achieved higher cytotoxicity, apoptosis induction and penetration to human breast cancer MCF-7 cells than the micelles unmodified with cRGD, which were ascribed to cRGD-integrin mediated transcytosis. R-D-Q micelles effectively suppressed tumor growth in tumor-bearing mice by delivering more quercetin throughout the tumor tissue. And R-D-Q micelles could promote the apoptosis of tumor cells by activating p38 and JNK signal pathways and suppressing ERK signal pathway. In addition, R-D-Q micelles had no damage to normal tissues of mice at therapeutic dose. These results indicate promising prospects for R-D-Q micelles as an effective drug delivery system against tumor.

Mitochondria-targeting nanostructures from enzymatically degradable fluorescent amphiphilic polyesters

Water-soluble π-conjugated luminescent bioprobes have been broadly used in biomedical research but are limited by the nonbiodegradability associated with their rigid C-C backbones. In the present work, we introduced three naphthalene monoimide (NMI)-functionalized amphiphilic fluorescent polyesters (P1, P2, and P3) prepared by transesterification of functional diols with an activated diester monomer of adipic acid. These polyesters featured a side-chain NMI fluorophore, imparting the required hydrophobicity for self-assembly in water and endowing the polymeric nanoassemblies with green fluorescence. Two polymers (P1 and P2) were intrinsically cationic at physiological pH (7.4), while neutral P3 exhibited pH-triggered (pH ∼6.2) cationic features due to the protonation of the tertiary amine groups present in its backbone. These biocompatible polymers revealed around 85% cellular uptake after 1 hour of incubation. However, the initial uptake for the cationic polymers (P1 and P2) within 15 minutes was significantly greater than that of the neutral P3 because of their stronger electrostatic interactions with the negatively charged cell membranes. Notably, cationic P1 and P2 could specifically target mitochondria in cancerous HeLa cells by escaping the initial endosome/lysosome trap. In contrast, neutral P3 exhibited cell-selective mitochondria targeting in cancerous (HeLa) cells over non-cancerous (NKE) cells. This is attributed to P3's protonation-induced positive charge accumulation in the acidic environment of cancer cells, unlike in the non-acidic environment of non-cancerous cells. This possibly causes P3 nanoassemblies to behave similarly to P1 and P2 in HeLa cells despite P3 being intrinsically neutral. The insights gained from this work may be relevant for future development of cell-specific, mitochondria-targeted drug delivery systems from enzymatically degradable polyester backbones.

Stimuli-Responsive Polymeric Nanocarriers Accelerate On-Demand Drug Release to Combat Glioblastoma

Glioblastoma multiforme (GBM) is a highly malignant brain tumor with a poor prognosis and limited treatment options. Drug delivery by stimuli-responsive nanocarriers holds great promise for improving the treatment modalities of GBM. At the beginning of the review, we highlighted the stimuli-active polymeric nanocarriers carrying therapies that potentially boost anti-GBM responses by employing endogenous (pH, redox, hypoxia, enzyme) or exogenous stimuli (light, ultrasonic, magnetic, temperature, radiation) as triggers for controlled drug release mainly via hydrophobic/hydrophilic transition, degradability, ionizability, etc. Modifying these nanocarriers with target ligands further enhanced their capacity to traverse the blood-brain barrier (BBB) and preferentially accumulate in glioma cells. These unique features potentially lead to more effective brain cancer treatment with minimal adverse reactions and superior therapeutic outcomes. Finally, the review summarizes the existing difficulties and future prospects in stimuli-responsive nanocarriers for treating GBM. Overall, this review offers theoretical guidelines for developing intelligent and versatile stimuli-responsive nanocarriers to facilitate precise drug delivery and treatment of GBM in clinical settings.

Design and synthesis of a star-like polymeric micelle modified with AS1411 aptamer for targeted delivery of camptothecin for cancer therapy

Improving of tumor targeting and decreasing side effects at normal cells of antitumor drugs are necessary to promote the cancer chemotherapy efficacy. Herein, we have synthesized a novel 21-arm star like diblock polymer of β-cyclodextrin-{poly(ε-caprolactone)-poly(2-aminoethylmethacrylate)}₂₁ which decorated with nucleolin aptamer (AS1411). The diblock polymer was prepared by combined ROP with electron transfer atom transfer radical polymerization (ARGET ATRP) methods followed camptothecin (CPT) encapsulation with high entrapment efficiency (65%). Subsequently, the attachment of AS1411 aptamer via covalent bond led to the formation of the final product β-CD-(PCL-PAEMA)₂₁/AS1411/CPT. In vitro drug release experiment demonstrated almost 50% of CPT was released in 72 h at acidic tumoral environment. The data of cellular toxicity (MTT) showed that the final product remarkably enhanced cell death in MCF-7 and 4T1 cells while normal cells (L929) showed high viability toward the prepared complex. Also, the finding of flow cytometry analysis and fluorescence imaging indicated successful internalization of complex into the target cells but not the nontarget cells. The in vivo experiments revealed the fact that β-CD-(PCL-PAEMA)₂₁/AS1411/CPT micelles showed high tumor inhibitory potential in comparison with free CPT. These findings exhibited the excellent ability of the novel star-like polymeric micelle with targeting agent for the targeted and effective delivery of CPT in cancer treatment.

Biomimetic smart nanoplatform for dual imaging-guided synergistic cancer therapy

A biomimetic nanoplatform for MRI and fluorescence imaging-guided synergetic cancer therapies has been constructed using a folate-functionalized erythrocyte membrane-coated metal–organic framework as both a photosensitizer and a nanocarrier.

A Small-Molecule Diketopyrrolopyrrole-Based Dye for in vivo NIR-IIa Fluorescence Bioimaging

Organic small-molecule fluorophores with near-infrared IIa (NIR-IIa) emission have great potential in pre-clinical detection and inoperative imaging due to the high-spatial resolution and deep penetration. However, developments of the NIR-IIa fluorophores are still facing considerable challenges. In this work, a series of diketopyrrolopyrrole (DPP)-based fluorophores were designed and synthesized. Subsequently, nanomaterial T25@F127 with significant NIR-IIa emission properties was rationally prepared by encapsulating DPP-based fluorophore T25, and was selected for fluorescence angiography and cerebral vascular microscopic imaging with nearly 800 μm penetrating depth and excellent signal-background ratio of 4.07 and 2.26 (at 250 and 400 μm), respectively. Furthermore, the nanomaterial T25@cRGD with tumor targeting ability can image tiny metastatic tumor on intestine with a small size of 0.3 mm×1.0 mm and high-spatial resolution (SBR=3.84). This study demonstrates that the nanomaterials which encapsulated T25 behave as excellent NIR-IIa fluorescence imaging agents and have a great potential for in vivo biological application.

In Situ Determination of Sialic Acid on Cell Surface with a pH-Regulated Polymer Enzyme Nanoreactor

Sialic acid (SA) is an important monosaccharide that is involved in incurable cancer immunotherapy. However, it is difficult to detect SA in situ using the existing strategy based on the SA-terminated glycopeptide extraction from the cell lysate. The countermeasures of the bottleneck caused by cell disruption and peptide extraction should be designed based on a "cell-surface attachment and controlled enzymolysis" protocol. Herein, a poly(styrene-co-maleic anhydride-acrylic acid-concanavalin A) (PSM-PAA-ConA) was synthesized and developed as a pH-regulated enzyme nanoreactor after being loaded with sialidase and myoglobin. The nanoreactor showed controllable biocatalysis induced by a cascade enzyme reaction and applied for the in situ detection of SA on a living cell surface. The addition of an acidic solution resulted in a decrease in the size of the nanoreactor and enhancement of its permeability, triggering an "on" state of the SA catalysis. Subsequent pH increase led to increased hydrophilicity of the nanoreactor, increasing its size and resulting in the catalytic "off" state. ConA assisted the cell-surface attachment of the enzyme reactor. Furthermore, SA on the surface of living cancer cells was successfully monitored by the pH-regulated enzyme nanoreactor, demonstrating the feasibility of high specificity in situ analysis for SA. This pH-induced catalytic efficiency control by the enzyme nanoreactor provides a potential platform for functional stimuli-responsive catalytic systems as well as a strategy for in situ analysis of biomolecules on the cell surface.

Elkasabgy N, Shao P, A. Farag M. Recent Advances in Tannic Acid (Gallotannin) Anticancer Activities and Drug Delivery Systems for Efficacy Improvement; A Comprehensive Review

Tannic acid is a chief gallo-tannin belonging to the hydrolysable tannins extracted from gall nuts and other plant sources. A myriad of pharmaceutical and biological applications in the medical field has been well recognized to tannic acid. Among these effects, potential anticancer activities against several solid malignancies such as liver, breast, lung, pancreatic, colorectal and ovarian cancers have been reported. Tannic acid was found to play a maestro-role in tuning several oncological signaling pathways including JAK/STAT, RAS/RAF/mTOR, TGF-β1/TGF-β1R axis, VEGF/VEGFR and CXCL12/CXCR4 axes. The combinational beneficial effects of tannic acid with other conventional chemotherapeutic drugs have been clearly demonstrated in literature such as a synergistic anticancer effect and enhancement of the chemo-sensitivity in several resistant cases. Yet, clinical applications of tannic acid have been limited owing to its poor lipid solubility, low bioavailability, off-taste, and short half-life. To overcome such obstacles, novel drug delivery systems have been employed to deliver tannic acid with the aim of improving its applications and/or efficacy against cancer cells. Among these drug delivery systems are several types of organic and metallic nanoparticles. In this review, the authors focus on the molecular mechanisms of tannic acid in tuning several neoplastic diseases as well as novel drug delivery systems that can be used for its clinical applications with an attempt to provide a systemic reference to promote the development of tannic acid as a cheap drug and/or drug delivery system in cancer management.

Sequential post-polymerization modification of a pentafluorophenyl ester-containing homopolymer: a convenient route to effective pH-responsive nanocarriers for anticancer drugs

Recently, pH-responsive polymeric micelles have gained significant attention as effective carriers for anti-cancer drug delivery. Herein, pH-responsive polymeric micelles were constructed by a simple post-polymerization modification of a single homopolymer, poly(pentafluorophenyl acrylate) (PPFPA). The PPFPA was first subjected to modification with 1-amino-2-propanol yielding the amphiphilic copolymer of poly(pentafluorophenyl acrylate)-ran-poly(N-(2-hydroxypropyl acrylamide)). A series of amphiphilic random copolymers of different compositions could self-assemble into spherical micelles with a unimodal size distribution in aqueous solution. Then, 1-(3-aminopropyl)imidazole (API), a reagent to introduce charge conversional entities, was reacted with the remaining PPFPA segment in the micellar core resulting in API-modified micelles which can encapsulate doxorubicin (DOX), a hydrophobic anti-cancer drug. As monitored by dynamic light scattering, the API-modified micelles underwent disintegration upon pH switching from 7.4 to 5.0, presumably due to imidazolyl group protonation. This pH-responsiveness of the API-modified micelles was responsible for the faster and greater in vitro DOX release in an acidic environment than neutral pH. Cellular uptake studies revealed that the developed carriers were internalized into MDA-MB-231 cells within 30 min via endocytosis and exhibited cytotoxicity in a dose-dependent manner.

Novel zwitterionic vectors: Multi-functional delivery systems for therapeutic genes and drugs

Zwitterions consist of equal molar cationic and anionic moieties and thus exhibit overall electroneutrality. Zwitterionic materials include phosphorylcholine, sulfobetaine, carboxybetaine, zwitterionic amino acids/peptides, and other mix-charged zwitterions that could form dense and stable hydration shells through the strong ion-dipole interaction among water molecules and zwitterions. As a result of their remarkable hydration capability and low interfacial energy, zwitterionic materials have become ideal choices for designing therapeutic vectors to prevent undesired biosorption especially nonspecific biomacromolecules during circulation, which was termed antifouling capability. And along with their great biocompatibility, low cytotoxicity, negligible immunogenicity, systematic stability and long circulation time, zwitterionic materials have been widely utilized for the delivery of drugs and therapeutic genes. In this review, we first summarized the possible antifouling mechanism of zwitterions briefly, and separately introduced the features and advantages of each type of zwitterionic materials. Then we highlighted their applications in stimuli-responsive "intelligent" drug delivery systems as well as tumor-targeting carriers and stressed the multifunctional role they played in therapeutic gene delivery.

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.

Folate-Conjugated Cell Membrane Mimetic Polymer Micelles for Tumor-Cell-Targeted Delivery of Doxorubicin

Tumor-targeting nano-drug-delivery systems hold great potential to improve the therapeutic efficacy and alleviate the side effects of cancer treatments. Herein, folic acid (FA)-decorated amphiphilic copolymer of FA-P(MPC- co-MaPCL) (MPC: 2-methacryloxoethyl phosphorylcholine, MaPCL: poly(ε-caprolactone) macromonomer) is synthesized and its micelles are fabricated for doxorubicin (DOX) delivery. And non-FA-decorated P(MPC- co-MaPCL) micelles are used as the control. Dynamic light scattering and scanning electron microscopy measurements reveal that FA-P(MPC- co-MaPCL) and P(MPC- co-MaPCL) micelles are spherical with average diameters of 140 and 90 nm, respectively. The evaluation in vitro demonstrates that the blank micelles are nontoxic, while DOX-loaded FA-P(MPC- co-MaPCL) micelles show significant cytotoxicity to HeLa cells and slight cytotoxicity to L929 cells. Moreover, the cellular uptake of DOX-loaded FA-P(MPC- co-MaPCL) micelles in HeLa cells are 4.3-fold and 1.7-fold higher than that of DOX-loaded P(MPC- co-MaPCL) micelles and free DOX after 6 h of incubation, respectively. These results indicate the great potential of this system in anticancer target drug-delivery applications.

Chemistry and engineering of cyclodextrins for molecular imaging

Cyclodextrins (CDs) are naturally occurring cyclic oligosaccharides bearing a basket-shaped topology with an "inner-outer" amphiphilic character. The abundance of hydroxyl groups enables CDs to be functionalized with multiple targeting ligands and imaging elements. The imaging time, and the payload of different imaging elements, can be tuned by taking advantage of the commercial availability of CDs with different sizes of the cavity. This review aims to offer an outlook of the chemistry and engineering of CDs for the development of molecular probes. Complexation thermodynamics of CDs, and the corresponding implications for probe design, are also presented with examples demonstrating the structural and physiochemical roles played by CDs in the full ambit of molecular imaging. We hope that this review not only offers a synopsis of the current development of CD-based molecular probes, but can also facilitate translation of the incremental advancements from the laboratory to real biomedical applications by illuminating opportunities and challenges for future research.

Fabrication of Charge-Conversion Nanoparticles for Cancer Imaging by Flash Nanoprecipitation

Traditional charge-conversion nanoparticles (NPs) need the breakage of acid-labile groups on the surface, which impedes the rapid response to the acidic microenvironment. Here, we developed novel rodlike charge-conversion NPs with amphiphilic dextran- b-poly(lactic- co-glycolic acid), poly(2-(dimethylamino) ethylmethylacrylate)- b-poly(ε-caprolactone), and an aggregation-induced emission-active probe through flash nanoprecipitation (FNP). These NPs exhibit reversible negative-to-positive charge transition at a slightly acidic pH relying on the rapid protonation/deprotonation of polymers. The size and the critical charge-conversion pH can be further tuned by varying the flow rate and polymer ratio. Consequently, the charge conversion endows NPs with resistance to protein adsorption at physiological pH and enhanced internalization to cancer cells under acidic conditions. Ex vivo imaging on harvest organs shows that charge-conversion NPs were predominantly distributed in tumors after intravenous administration to mice due to the robust response of NPs to the acidic microenvironment in tumor tissue, whereas control NPs or free probes were broadly accumulated in tumor, liver, kidney, and lung. These results suggest the great potential of the current FNP strategy in the facile and generic fabrication of charge-conversion NPs for tumor-targeting delivery of drugs or fluorescent probes.

Multifunctional hybrid micelles with tunable active targeting and acid/phosphatase-stimulated drug release for enhanced tumor suppression

Therapeutic efficacy of conventional single PEGylated polymeric micelles is significantly reduced by limited endocytosis and intracellular drug release. To improve drug delivery efficiency, poly (ethylene glycol)-block-poly (l-lactic acid)/(Arg-Gly-Asp-Phe)-poly (aminoethyl ethylene phosphate)-block-poly (l-lactic acid) (PEG-PLLA/RGDF-PAEEP-PLLA) hybrid micelles with tunable active targeting and acid/phosphatase-stimulated drug release are developed. The optimized hybrid micelles with 6 wt % of RGDF have favorable in vitro and in vivo activities. The hybrid micelles could temporarily shield the targeting efficacy of RGDF at pH 7.4 due to the steric effect exerted by concealment of RGDF peptides in the PEG corona, which strongly decreases the clearance by mononuclear phagocyte system and consequently improves the tumor accumulation. Inside the solid tumor with a lower acidic pH, the hybrid micelles restore the active tumor targeting property with exposed RGDF on the surface of the micelles because of the increased protonation and stretching degree of PAEEP blocks. RGDF-mediated endocytosis improves the tumor cell uptake. The hybrid micelles would also enhance intracellular drug release because of the hydrolysis of the acid/phosphatase-sensitivity of PAEEP blocks in endo/lysosome. Systemic administration of the hybrid micelles significantly inhibits tumor growth by 96% due to the integration of enhanced circulation time, tumor accumulation, cell uptake and intracellular drug release.

Charge Reversible and Mitochondria/Nucleus Dual Target Lipid Hybrid Nanoparticles To Enhance Antitumor Activity of Doxorubicin

The experiment aims to increase antitumor activity while decreasing the systemic toxicity of doxorubicin (DOX). Charge reversible and mitochondria/nucleus dual target lipid hybrid nanoparticles (LNPs) was prepared. The in vitro experimental results indicated that LNPs released more amount of DOX in acidic environment and delivered more amount of DOX to the mitochondria and nucleus of tumor cells than did free DOX, which resulted in the reduction of mitochondrial membrane potential and the enhancement of cytotoxicity of LNPs on tumor cells. Furthermore, the in vivo experimental results indicated that LNPs delivered more DOX to tumor tissue and significantly prolonged the retention time of DOX in tumor tissue as compared with free DOX, which consequently resulted in the high antitumor activity and low systemic toxicity of LNPs on tumor-bearing nude mice. The above results indicated that charge reversible mitochondria/nucleus dual targeted lipid hybrid nanoparticles greatly enhanced therapeutic efficacy of DOX for treating lung cancer.

A review: the trend of progress about pH probes in cell application in recent years

Intracellular pH values are some of the most important factors that govern biological processes and the acid-base homeostasis in cells, body fluids and organs sustains the normal operations of the body. Subcellular organelles including the acidic lysosomes and the alkalescent mitochondria undergo various processes such as intracellular digestion, ATP production and apoptosis. Due to their precise imaging capabilities, fluorescent probes have attracted great attention for the illustration of pH modulated processes. Furthermore, based on the unique acidic extracellular environment of acidic lysosomes, fluorescent probes can specifically be activated in cancer cells or tumors. In this review, recently reported lysosome and mitochondria specific pH imaging probes as well as pH-activatable cancer cell-targetable probes have been discussed.

Porphyrin-Based Carbon Dots for Photodynamic Therapy of Hepatoma

Porphyrin-containing carbon dots (CDs) possess ultrasmall size, excellent water solubility, and photostability. These CDs can effectively generate cytotoxic singlet oxygen upon irradiation, and induce the cell apoptosis. Photodynamic ability of CDs inhibits the growth of hepatoma. This work not only sheds light on developing functional carbon dots, but also highlights the importance of special-structure precursor molecules in synthesizing functional CDs.

Enhanced Cellular Internalization and On-Demand Intracellular Release of Doxorubicin by Stepwise pH-/Reduction-Responsive Nanoparticles

The efficient delivery of antitumor agents to tumor sites faces numerous obstacles, such as poor cellular uptake and slow intracellular drug release. In this regard, smart nanoparticles (NPs) that respond to the unique microenvironment of tumor tissues have been widely used for drug delivery. In this study, novel charge-reversal and reduction-responsive histidine-grafted chitosan-lipoic acid NPs (HCSL-NPs) were selected for efficient therapy of breast cancer by enhancing cell internalization and intracellular pH- and reduction-triggered doxorubicin (DOX) release. The surface charge of HCSL-NPs presented as negative at physiological pH and reversed to positive at the extracellular and intracellular pH of the tumor. In vitro release investigation revealed that DOX/HCSL-NPs demonstrated a sustained drug release under the physiological condition, whereas rapid DOX release was triggered by both endolysosome pH and high-concentration reducing glutathione (GSH). These NPs exhibited enhanced internalization at extracellular pH, rapid intracellular drug release, and improved cytotoxicity against 4T1 cells in vitro. Excellent tumor penetrating efficacy was also found in 4T1 tumor spheroids and solid tumor slices. In vivo experiments demonstrated that HCSL-NPs exhibited excellent tumor-targeting ability in tumor tissues as well as excellent antitumor efficacy and low systemic toxicity in breast tumor-bearing BALB/c mice. These results indicated that the novel charge-reversal and reduction-responsive HCSL-NPs have great potential for targeted and efficient delivery of chemotherapeutic drugs in cancer treatments.

Self-Assembled PAEEP-PLLA Micelles with Varied Hydrophilic Block Lengths for Tumor Cell Targeting

The properties of hydrophilic shell in micelles significantly affect the interaction between micelles and cells. Compared with frequently used polyethylene glycol (PEG) as the hydrophilic block, polyphosphoesters (PPEs) are superior in functionality, biocompatibility, and degradability. A series of amphiphilic poly(aminoethyl ethylene phosphate)/poly(l-lactide acid) (PAEEP-PLLA) copolymers were synthesized with hydrophilic PAEEP with different chain lengths. The corresponding self-assembled micelles were used for doxorubicin (Dox) entrapment. The length of hydrophilic PAEEP block on the shell affected the structure of micelles. PAEEPm-PLLA168 (m = 130 or 37) polymers formed vesicles, while PAEEPm-PLLA168 (m = 15 or 9) formed large compound micelles (LCMs), suggesting a difference in tumor cell uptake and intracellular trafficking. PAEEP15-PLLA168 polymer showed superiority on cellular uptake amount, intracellular drug release, and cell apoptosis. Lipid rafts and macropinocytosis are the leading endocytic pathways of PAEEP-PLLA micelles. The shape coupling between micelles and cell membrane facilitated cell surface features such as flattened protrusions (membrane protein) and inward-pointing hollows as well as efficient endocytosis. These results suggested that PAEEP-PLLA self-assembled block copolymer micelles may be an excellent drug delivery system for tumor treatment and that the hydrophilic chain length could regulate drug targeting to tumor cells.

pH-Activated Targeting Drug Delivery System Based on the Selective Binding of Phenylboronic Acid

Phenylboronic acid (PBA) is a tumor-targeting molecule, but its nonspecific interaction with normal cells or other components containing cis-diol residues undoubtedly limits its potential application in tumor-targeting drug delivery. Herein, we developed fructose-coated mixed micelles via PBA-terminated polyethylene glycol monostearate (PBA-PEG-C18) and Pluronic P123 (PEG20-PPG70-PEG20) to solve this problem, as the stability of borate formed by PBA and fructose was dramatically dependent on pH. The fluorescence spectroscopic results indicated that the borate formed by PBA and fructose decomposed at a decreased pH, and better binding between PBA and sialic acid (SA) was observed at a low pH. These results implied that the fructose groups decorated on the surface of the micelles could be out-competed by SA at a low pH. In vitro uptake and cytotoxicity studies demonstrated that the fructose coating on the mixed micelles improved the endocytosis and enhanced the cytotoxicity of drug-loaded mixed micelles in HepG2 cells but reduced the cytotoxicity in normal cells. These results demonstrate that a simple decorating strategy may facilitate PBA-targeted nanoparticles for tumor-specific drug delivery.

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.

A targeted nanoglobular contrast agent from host-guest self-assembly for MR cancer molecular imaging

The clinical application of nanoparticular Gd(III) based contrast agents for tumor molecular MRI has been hindered by safety concerns associated with prolonged tissue retention, although they can produce strong tumor enhancement. In this study, a targeted well-defined cyclodextrin-based nanoglobular contrast agent was developed through self-assembly driven by host-guest interactions for safe and effective cancer molecular MRI. Multiple β-cyclodextrins attached POSS (polyhedral oligomeric silsesquioxane) nanoglobule was used as host molecule. Adamantane-modified macrocyclic Gd(III) contrast agent, cRGD (cyclic RGDfK peptide) targeting ligand and fluorescent probe was used as guest molecules. The targeted host-guest nanoglobular contrast agent cRGD-POSS-βCD-(DOTA-Gd) specifically bond to αvβ3 integrin in malignant 4T1 breast tumor and provided greater contrast enhancement than the corresponding non-targeted agent. The agent also provided significant fluorescence signal in tumor tissue. The histological analysis of the tumor tissue confirmed its specific and effective targeting to αvβ3 integrin. The targeted imaging agent has a potential for specific cancer molecular MR and fluorescent imaging.

A facile way to fabricate pH-sensitive charge-conversion polymeric nanoparticles with tunable pH conversion point

pH-Sensitive charge-conversion polymeric nanoparticles could significantly enhance drug bioavailability due to improved tumor cell internalization.

Active Tumor Permeation and Uptake of Surface Charge-Switchable Theranostic Nanoparticles for Imaging-Guided Photothermal/Chemo Combinatorial Therapy

To significantly promote tumor uptake and penetration of therapeutics, a nanovehicle system comprising poly(lactic-co-glycolic acid) (PLGA) as the hydrophobic cores coated with pH-responsive N-acetyl histidine modified D-α-tocopheryl polyethylene glycol succinate (NAcHis-TPGS) is developed in this work. The nanocarriers with switchable surface charges in response to tumor extracellular acidity (pH_e) were capable of selectively co-delivering indocyanine green (ICG), a photothermal agent, and doxorubicin (DOX), a chemotherapy drug, to tumor sites. The in vitro cellular uptake of ICG/DOX-loaded nanoparticles by cancer cells and macrophages was significantly promoted in weak acidic environments due to the increased protonation of the NAcHis moieties. The results of in vivo and ex vivo biodistribution studies demonstrated that upon intravenous injection the theranostic nanoparticles were substantially accumulated in TRAMP-C1 solid tumor of tumor-bearing mice. Immunohistochemical examination of tumor sections confirmed the active permeation of the nanoparticles into deep tumor hypoxia due to their small size, pH_e-induced near neutral surface, and the additional hitchhiking transport via tumor-associated macrophages. The prominent imaging-guided photothermal therapy of ICG/DOX-loaded nanoparticles after tumor accumulation induced extensive tumor tissue/vessel ablation, which further promoted their extravasation and DOX tumor permeation, thus effectively suppressing tumor growth.

A tumor-targeting protein nanoparticle based on Tat peptide and enhanced green fluorescent protein

A protein-based nanoparticle containing cell penetrating peptides (CPPs) and enhanced green fluorescent protein (EGFP) was developed through a genetic engineering method.

Reduction-responsive fluorescence off–on BODIPY–camptothecin conjugates for self-reporting drug release

A reduction-responsive fluorescence off–on theranostic prodrug with self-reporting drug release was constructed based on boron dipyrromethene (BODIPY) and therapeutic drug camptothecin (CPT) with a long flexible disulfide linker.

Cyclic RGD targeting cisplatin micelles for near-infrared imaging-guided chemotherapy

Nowadays imaging-guided chemotherapy is of great importance for developing highly efficient nanomedicines for cancer therapy.

Acidity-triggered surface charge neutralization and aggregation of functionalized nanoparticles for promoted tumor uptake

A polymeric nanovehicle featured with histidine-rich surface was developed for tumor-targeted delivery of doxorubicin.

Glycyrrhetinic Acid-Mediated Polymeric Drug Delivery Targeting the Acidic Microenvironment of Hepatocellular Carcinoma

PURPOSE

The major hurdle of current drug carrier against hepatocellular carcinoma (HCC) is the lack of specific and selective drug delivery to HCC. In this study, a novel glycyrrhetinic acid (GA) and poly(L-Histidine) (PHIS) mediated polymeric drug delivery system was developed to target HCC that have GA binding receptors and release its encapsulated anticancer drug in the acidic microenvironment of HCC.

METHODS

Firstly, GA and PHIS were conjugated to form poly (ethylene glycol)-poly(lactic-co-glycolic acid) (GA-PEG-PHIS-PLGA, GA-PPP) micelles by grafting reaction between active terminal groups. Secondly, andrographolide (AGP) was encapsulated to GA-PPP to make AGP/GA-PPP using the solvent evaporation method. The pH-responsive property of AGP/GA-PPP micelles was validated by monitoring its stability and drug release behavior in different pH conditions. Furthermore, selective hepatocellular uptake of GA-PPP micelles in vitro, liver specific drug accumulation in vivo, as well as the enhanced antitumor effects of AGP/GA-PPP micelles confirmed the HCC targeting property of our novel drug delivery system.

RESULTS

Average size of AGP/GA-PPP micelles increased significantly and the encapsulated AGP released faster in vitro at pH 5.0, while micelles keeping stable in pH 7.4. AGP/GA-PPP micelles were uptaken more efficiently by human Hep3B liver cells than that by human MDA-MB-231 breast cancer cells. GA-PPP micelles accumulated specifically in the liver and possessed long retention time in vivo. AGP/GA-PPP micelles significantly inhibited tumor growth and provided better therapeutic outcomes compared to free AGP and AGP/PEG-PLGA(AGP/PP) micelles without GA and PHIS decoration.

CONCLUSIONS

This novel GA-PPP polymeric carrier is promising for targeted treatment of HCC.

pH-Responsive Poly(ethylene glycol)/Poly(L-lactide) Supramolecular Micelles Based on Host-Guest Interaction

pH-responsive supramolecular amphiphilic micelles based on benzimidazole-terminated poly(ethylene glycol) (PEG-BM) and β-cyclodextrin-modified poly(L-lactide) (CD-PLLA) were developed by exploiting the host-guest interaction between benzimidazole (BM) and β-cyclodextrin (β-CD). The dissociation of the supramolecular micelles was triggered in acidic environments. An antineoplastic drug, doxorubicin (DOX), was loaded into the supramolecular micelles as a model drug. The release of DOX from the supramolecular micelles was clearly accelerated as the pH was reduced from 7.4 to 5.5. The DOX-loaded PEG-BM/CD-PLLA supramolecular micelles displayed an enhanced intracellular drug-release rate in HepG2 cells compared to the pH-insensitive DOX-loaded PEG-b-PLLA counterpart. After intravenous injection into nude mice bearing HepG2 xenografts by the tail vein, the DOX-loaded supramolecular micelles exhibited significantly higher tumor inhibition efficacy and reduced systemic toxicity compared to free DOX. Furthermore, the DOX-loaded supramolecular micelles showed a blood clearance rate markedly lower than that of free DOX and comparable to that of the DOX-loaded PEG-b-PLLA micelles after intravenous injection into rats. Therefore, the pH-responsive PEG-BM/CD-PLLA supramolecular micelles hold potential as a smart nanocarrier for anticancer drug delivery.

Effects of hydrophobic core components in amphiphilic PDMAEMA nanoparticles on siRNA delivery

Due to their biodegradable character, polyesters such as polycaprolactone (PCL), poly(D,L-lactide) (PDLLA), and polylactic-co-glycolic acid (PLGA) were widely used as the hydrophobic cores of amphiphilic cationic nanoparticles (NPs) for siRNA delivery. However, fewer researches focused on facilitating siRNA delivery by adjusting the polyester composition of these nanoparticles. Herein, we investigated the contribution of polyester segments in siRNA delivery in vitro by introducing different ratio of DLLA moieties in PCL segments of mPEG-block-PCL-graft-poly(dimethylamino ethyl methacrylate)(PEG-b-PCL-g-PDMAEMA). It was noticed that compared with the other ratios of DLLA moieties, a certain molar ratio (about 70%) of the NPs, named mPEG45-P(CL21-co-DLLA48)-g-(PDMAEMA29)2 (PECLD-70), showed the highest gene knockdown efficiency but poorest cellular uptake ability in vitro. Further research revealed that NPs with various compositions of the polyester cores showed different physicochemical properties including particle size, zeta potential and stiffness, leading to different endocytosis mechanisms thus influencing the cellular uptake efficiency. Subsequently, we observed that the cells treated by PECLD-70 NPs/Cy5 siRNA complexes exhibited more diffuse Cy5 signal distribution than other NPs by confocal laser scanning microscope, which suggested that siRNA delivered by PECLD-70 NPs/Cy5 siRNA complexes possessed of stronger capabilities in escaping from endosome/lysosome, entering the RNA-induced silencing complex (RISC) and cutting the target mRNA efficiently. The different siRNA release profile was dominated by the degradation rate of polyester segments. Therefore, it could be concluded that the adjustment of hydrophobic core of cationic nanoparticles could significantly affect their transfection behavior and appropriate polyester composition should be concerned in designing of analogous siRNA vectors.

cRGD targeted and charge conversion-controlled release micelles for doxorubicin delivery

A biodegradable polymeric micelle with cRGD targeting and charge-conversional moiety could enhance the cellular uptake of pharmaceuticals and result in high cytotoxicity to tumor cells.

Functionalization of biodegradable hyperbranched poly(α,β-malic acid) as a nanocarrier platform for anticancer drug delivery

A facile strategy for fabricating hyperbranched poly(α,β-malic acid) nanoparticles with multiple functions was developed for anticancer drug delivery.

Small molecular nanomedicines made from a camptothecin dimer containing a disulfide bond

Small molecules camptothecin (CPT) dimer could self-assemble into stable nanoparticles in aqueous solution, which indicated high cellular proliferation inhibition toward HeLa and HepG2 cells.