Natural tripeptide capped pH-sensitive gold nanoparticles for efficacious doxorubicin delivery both in vitro and in vivo

Nanobiotechnology has been gaining ever-increasing interest for the successful implementation of chemotherapy based treatment of cancer. Gold nanoparticles (AuNPs) capped with a natural pH-responsive short tripeptide (Lys-Phe-Gly or KFG) sequence are presented herein for significant intracellular delivery of an anti-cancer drug, doxorubicin (DOX). A particularly increased apoptotic response has been observed for DOX treatments mediated by KFG-AuNPs when compared with drug alone treatments in various cell lines (BT-474, HeLa, HEK 293 T and U251). Furthermore, KFG-AuNP mediated DOX treatment significantly decreases cell proliferation and tumor growth in a BT-474 cell xenograft model in nude mice. In addition, KFG-AuNPs demonstrate efficacious drug delivery in DOX-resistant HeLa cells (HeLa-DOXR).

Controlled Drug Delivery Systems for Oral Cancer Treatment-Current Status and Future Perspectives

Oral squamous cell carcinoma (OSCC), which encompasses the oral cavity-derived malignancies, is a devastating disease causing substantial morbidity and mortality in both men and women. It is the most common subtype of the head and neck squamous cell carcinoma (HNSCC), which is ranked the sixth most common malignancy worldwide. Despite promising advancements in the conventional therapeutic approaches currently available for patients with oral cancer, many drawbacks are still to be addressed; surgical resection leads to permanent disfigurement, altered sense of self and debilitating physiological consequences, while chemo- and radio-therapies result in significant toxicities, all affecting patient wellbeing and quality of life. Thus, the development of novel therapeutic approaches or modifications of current strategies is paramount to improve individual health outcomes and survival, while early tumour detection remains a priority and significant challenge. In recent years, drug delivery systems and chronotherapy have been developed as alternative methods aiming to enhance the benefits of the current anticancer therapies, while minimizing their undesirable toxic effects on the healthy non-cancerous cells. Targeted drug delivery systems have the potential to increase drug bioavailability and bio-distribution at the site of the primary tumour. This review confers current knowledge on the diverse drug delivery methods, potential carriers (e.g., polymeric, inorganic, and combinational nanoparticles; nanolipids; hydrogels; exosomes) and anticancer targeted approaches for oral squamous cell carcinoma treatment, with an emphasis on their clinical relevance in the era of precision medicine, circadian chronobiology and patient-centred health care.

The synthesis and co-micellization of PCL-P(HEMA/HEMA-LA) and PCL-P(HEMA/HEMA-FA) as shell cross-linked drug carriers with target/redox properties

In order to obtain target/redox shell cross-linked micelles (TCM), copolymers poly(ε-caprolactone)-poly(2-hydroxyethyl methacrylate/methacrylate-alpha lipoic acid) and poly(ε-caprolactone)-poly(2-hydroxyethyl methacrylate/methacrylate-folate, PCL-P(HEMA/HEMA-LA) and PCL-P(HEMA/HEMA-FA) were designed and synthesized. The copolymers PCL-P(HEMA/HEMA-LA) could form reduction-sensitive cross-linked micelles (CM) by using a catalytic amount of DTT. The micelles maintained high stability against dilution but were destroyed in 10 mM dithiothreitol (DTT). The drug loaded content (DLC) of CM was 8.9%, which was almost twice as much as non-cross-linked micelle (NCM). In vitro drug release at pH 7.4 showed that the cumulative release rate of CM in 36 h was less than 30%, while it was about 50% for NCM. When PCL-P(HEMA/HEMA-LA) and PCL-P(HEMA/HEMA-FA) (FA 1%, 3% and 5%) formed target/redox micelles, IC50 of TCM with FA 3% was the lowest (1.4 µg/mL) to Hela cells with excessive expression folate receptors. The cell uptake of TCM by Hela cells is higher than target non-cross-linked micelles (TNCM), while there was not much difference between both micelles uptaken by A549 cells, which are lack of folate receptors. Therefore, the drug carriers of TCM have potential to be explored as shell cross-linked target/redox drug carriers to the cancer cells on the surface with excessive folate receptors.

Degradable redox-responsive disulfide-based nanogel drug carriers via dithiol oxidation polymerization

Stimuli-responsive nanogels are important drug and gene carriers that mediate the controlled release of therapeutic molecules. Herein, we report the synthesis of fully degradable disulfide cross-linked nanogel drug carriers formed by oxidative radical polymerization of 2,2'-(ethylenedioxy)diethanethiol (EDDET) as a monomer with different cross-linkers, including pentaerythritol tetramercaptoacetate (PETMA). Because the poly(EDDET) backbone repeat structure and cross-linking junctions are composed entirely of disulfide bonds, these nanogels specifically degrade to small molecule dithiols intracellularly in response to the reducing agent glutathione present inside of cells. Cross-linked nanogels were synthesized using controlled microfluidic mixing in the presence of a nonionic Pluronic surfactant PLU-127 to increase the nanogel stability. Adjusting the monomer to cross-linker ratio from 5 : 1 to 100 : 1 (mol/mol) tuned the cross-linking density, resulting in swelling ratios from 1.65 to >3. Increasing the amount of stabilizing Pluronic surfactant resulted in a decrease of nanogel diameter, as expected due to increased surface area of the resulting nanogels. The monomer to cross-linker ratio in the feed had no effect on the formed nanogel diameter, providing a way to control cross-linking density with constant nanogel size but tunable drug release kinetics. Nanogels exhibited an entrapment efficiency of up to 75% for loading of Rhodamine B dye. In vitro studies showed low cytotoxicity, quick uptake, and fast degradation kinetics. Due to the ease of synthesis, rapid gelation times, and tunable functionality, these non-toxic and fully degradable nanogels offer potential for use in a variety of drug delivery applications.

Nanoparticle Binding to Urokinase Receptor on Cancer Cell Surface Triggers Nanoparticle Disintegration and Cargo Release

Cancer cell expresses abundant surface receptors. These receptors are important targets for cancer treatment and imaging applications. Our goal here is to develop nanoparticles with cargo loading and tumor targeting capability.

Methods: A peptide targeting at cancer cell surface receptor (urokinase receptor, uPAR) was expressed in fusion with albumin (diameter of ~7 nm), and the fusion protein was assembled into nanoparticles with diameter of 40 nm, either in the presence or absence of cargo molecules, by a novel preparation method. An important feature of this method is that the nanoparticles were stabilized by hydrophobic interaction of the fusion protein and no covalent linking agent was used in the preparation. The stability, the cargo release, in vitro and in vivo properties of such formed nanoparticles were characterized by transmission electron microscopy, dynamic light scattering, gel shift assay, laser scanning confocal microscopy and 3D fluorescent molecular tomography.

Results: The nanoparticles were stable for more than two weeks in aqueous buffer, even in the buffer containing 10% fetal bovine serum. Interestingly, in the presence of urokinase receptor, the uPAR-targeting nanoparticle disintegrated into 7.5 nm fragments and released its cargo, but not the non-targeting nanoparticles made from albumin by the same preparation method. Such nanoparticles also showed higher uptake and cytotoxicity to the receptor-expressing cancer cells in vitro and higher tumor accumulation in xenografted tumor-bearing mice in vivo compared to the non-targeting nanoparticles.

Conclusion: Our results demonstrate a new function of cell surface receptor as a responsive trigger to disassemble nanoparticles, besides its common use to enrich targeting agents. Such nanoparticles were thus named receptor-responsive nanoparticles (RRNP).

Polymeric nanogels as drug delivery systems

The present review focuses on the description of the design, synthesis and physico-chemical and biological evaluation of polymer nanogels. Nanogels are robust swollen cross-linked polymer nanoparticles that can be used as highly efficient and biodegradable carriers for the transport of drugs in controlled drug delivery. In this article, various types of nanogels are described and methods for their preparation discussed. The possibility of using synthesized nanosystems for targeting are reviewed to show the potential of tailored structures to reach either solid tumor tissue or direct tumor cells. Finally, the methods for encapsulation or attachment of biologically active molecules, e.g. drugs, proteins, are described and compared.

Logical design and application of prodrug platforms

This review summarizes the current state of prodrugs and elaborates the logical design and future development of the prodrug platform.

Degradable pH and redox dual responsive nanoparticles for efficient covalent drug delivery

Hydrophobic drug paclitaxel was modified into a polymerizable monomer and subsequently copolymerized with pH-sensitive monomers and redox-sensitive disulfide-based cyclic monomers.

Inhibition of proliferation and migration of tumor cells through lipoic acid-modified oligoethylenimine-mediated p53 gene delivery

Inhibition of proliferation and migration of tumor cells through lipoic acid-modified oligoethylenimine-mediated p53 gene delivery.

Self-assembly of folic acid dextran conjugates for cancer chemotherapy

Folic acid (FA) has long been used as a specific targeting agent since many cancer cells overexpress folate receptors (FRs). Herein, novel functionalities of FA will be explored: directed self-assembly of nanoparticles for drug delivery together with pH responsive release. By conjugating with dextran (DEX), DEX-FA exerts a pH dependent self-assembly behavior: it self-associates into nanoparticles (NPs) around physiological pH (pH 7) and disassembles at higher pH (pH > 9). Doxorubicin (DOX), a model antitumor drug, has been successfully encapsulated via electrostatic interactions between DOX and FA. Moreover, the pH responsive release behaviors of DOX are controlled by FA. The DOX@DEX-FA NPs exhibit typical FA-FRs-mediated endocytosis in vitro and targeted delivery in vivo, altogether contributing to an enhanced antitumor efficacy, alleviated side effects, and elongated overall survival in a 4T1 subcutaneous tumor-bearing mouse model. The DOX@DEX-FA NPs have been demonstrated to be a simple, safe and efficient nanoplatform, holding significant translation potential for treating FR-overexpressing cancers. This study may present novel functionalities of FA in cancer-targeted nanotherapeutics.

Thiol-Mediated Chemoselective Strategies for In Situ Formation of Hydrogels

Hydrogels are three-dimensional networks composed of hydrated polymer chains and have been a material of choice for many biomedical applications such as drug delivery, biosensing, and tissue engineering due to their unique biocompatibility, tunable physical characteristics, flexible methods of synthesis, and range of constituents. In many cases, methods for crosslinking polymer precursors to form hydrogels would benefit from being highly selective in order to avoid cross-reactivity with components of biological systems leading to adverse effects. Crosslinking reactions involving the thiol group (SH) offer unique opportunities to construct hydrogel materials of diverse properties under mild conditions. This article reviews and comments on thiol-mediated chemoselective and biocompatible strategies for crosslinking natural and synthetic macromolecules to form injectable hydrogels for applications in drug delivery and cell encapsulation.

Construction of Small-Sized, Robust, and Reduction-Responsive Polypeptide Micelles for High Loading and Targeted Delivery of Chemotherapeutics

Polypeptide micelles, though having been proved to be an appealing nanoplatform for cancer chemotherapy, are met with issues like inefficient drug encapsulation, gradual drug release, and low tumor cell selectivity and uptake. Here, we report on cRGD-decorated, small-sized, robust, and reduction-responsive polytyrosine micelles (cRGD-rPTM) based on poly(ethylene glycol)- b-poly(l-tyrosine)-lipoic acid (PEG- b-PTyr-LA) conjugate for high loading and targeted delivery of doxorubicin (Dox). Notably, cRGD-rPTM exhibited efficient loading of Dox, giving cRGD-rPTM-Dox with a drug loading content (DLC) of 18.5 wt % and a small size of 45 nm at a theoretical DLC of 20 wt %. cRGD-rPTM-Dox displayed reduction-triggered drug release, high selectivity and superior antiproliferative activity toward α_vβ₃ integrin positive MDA-MB-231 breast cancer cells (IC₅₀ = 1.5 μg/mL) to both nontargeted rPTM-Dox and clinical liposomal formulation (LP-Dox). cRGD-rPTM-Dox demonstrated a prolonged circulation time compared with the noncrosslinked cRGD-PTM-Dox control and significantly better accumulation in MDA-MB-231 breast tumor xenografts than nontargeted rPTM-Dox. Moreover, cRGD-rPTM-Dox at 6 mg Dox equiv/kg could remarkably suppress growth of MDA-MB-231 human breast tumor without inducing obvious side effects, outperforming both rPTM-Dox and LP-Dox. These reduction-responsive multifunctional polytyrosine micelles appear to be a viable and versatile nanoplatform for targeted chemotherapy.

Unlockable Nanocomplexes with Self-Accelerating Nucleic Acid Release for Effective Staged Gene Therapy of Cardiovascular Diseases

Nucleic acid (NA)-based therapy is proposed to address serious diseases such as cardiovascular diseases (CVDs). Powerful NA delivery vehicles are essential for effective gene therapy. Herein, a novel type of delivery vehicle, an unlockable core-shell nanocomplex (Hep@PGEA) with self-accelerating NA release, is structurally designed. Hep@PGEA is composed of disulfide-bridged heparin nanoparticle (HepNP) core and low-toxicity PGEA cationic shell. In comparison with NA, heparin, a negatively charged polysaccharide macromolecule, exhibits stronger interactions with cationic species. Upon the breakdown of redox-responsive HepNP cores, unlocked heparin would interact with the outer cationic shells and replace the condensed NA to facilitate NA release. Such unique Hep@PGEA is successfully explored for effective miRNA-pDNA staged gene therapy of myocardial infarction (MI), one of the most serious CVDs. With the progression of MI, glutathione amounts in heart tissues increase. MiR-499 (for the inhibition of cardiomyocyte apoptosis) and plasmid encoding vascular endothelial growth factor (for the promotion of angiogenesis) are sequentially delivered for systemic treatment of MI. Such treatment produces impressive results in restoring heart function and suppressing cardiac hypertrophy. Due to the wide existence of redox agents in cells, the proposed unlockable delivery nanovehicle and staged therapy strategy can provide new methods to effectively treat different serious diseases.

Bioresponsive functional nanogels as an emerging platform for cancer therapy

INTRODUCTION

Bioresponsive nanogels with a crosslinked three-dimensional structure and an aqueous environment that undergo physical or chemical changes including swelling and dissociation in response to biological signals such as mild acidity, hyperthermia, enzymes, reducing agents, reactive oxygen species (ROS), and adenosine-5'-triphosphate (ATP) present in tumor microenvironments or inside cancer cells have emerged as an appealing platform for targeted drug delivery and cancer therapy.

AREAS COVERED

This review highlights recent designs and development of bioresponsive nanogels for facile loading and triggered release of chemotherapeutics and biotherapeutics. The in vitro and in vivo antitumor performances of drug-loaded nanogels are discussed.

EXPERT OPINION

Bioresponsive nanogels with an excellent stability and safety profile as well as fast response to biological signals are unique systems that mediate efficient and site-specific delivery of anticancer drugs, in particular macromolecular drugs like proteins, siRNA and DNA, leading to significantly enhanced tumor therapy compared with the non-responsive counterparts. Future research has to be directed to the development of simple, tumor-targeted and bioresponsive multifunctional nanogels, which can be either constructed from natural polymers with intrinsic targeting ability or functionalized with targeting ligands. We anticipate that rationally designed nanotherapeutics based on bioresponsive nanogels will become available for future clinical cancer treatment.

ABBREVIATIONS

AIE, aggregation-induced emission; ATP, adenosine-5'-triphosphate; ATRP, atom transfer radical polymerization; BSA, bovine serum albumin; CBA, cystamine bisacrylamide; CC, Cytochrome C; CDDP, cisplatin; CT, computed tomography; DC, dendritic cell; DiI, 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate; DOX, doxorubicin; dPG, dendritic polyglycerol; DTT, dithiothreitol; EAMA, 2-(N,N-diethylamino)ethyl methacrylate; EPR, enhanced permeability and retention; GrB, granzyme B; GSH, glutathione tripeptide; HA, hyaluronic acid; HAase, hyaluronidases; HCPT, 10-Hydroxycamptothecin; HEP, heparin; HPMC, hydroxypropylmethylcellulose; LBL, layer-by-layer; MTX, methotrexate; NCA, N-carboxyanhydride; OVA, ovalbumin; PAH, poly(allyl amine hydrochloride); PBA, phenylboronic acid; PCL, polycaprolactone; PDEAEMA, poly(2-diethylaminoethyl methacrylate); PDGF, platelet derived growth factor; PDPA, poly(2-(diisopropylamino)ethyl methacrylate); PDS, pyridyldisulfide; PEG, poly(ethylene glycol); PEGMA, polyethyleneglycol methacrylate; PEI, polyethyleneimine; PHEA, poly(hydroxyethyl acrylate); PHEMA, poly(2-(hydroxyethyl) methacrylate; PNIPAM, poly(N-isopropylacrylamide); PMAA, poly(methacrylic acid); PPDSMA, poly(2-(pyridyldisulfide)ethyl methacrylate); PTX, paclitaxel; PVA, poly(vinyl alcohol); QD, quantum dot; RAFT, reversible addition-fragmentation chain transfer; RGD, Arg-Gly-Asp peptide; ROP, ring-opening polymerization; ROS, reactive oxygen species; TMZ, temozolomide; TRAIL, tumor necrosis factor-related apoptosis inducing ligand; VEGF, vascular endothelial growth factor.

Biotin-Tagged Polysaccharide Vesicular Nanocarriers for Receptor-Mediated Anticancer Drug Delivery in Cancer Cells

Biotin-conjugated multistimuli-responsive polysaccharide vesicular nanocarriers are designed and developed, for the first time, to accomplish receptor-mediated endocytosis in cancer cells and to deliver anticancer drugs to intracellular compartments. For this purpose, a new renewable hydrophobic unit was custom designed with redox-degradable disulfide and enzyme-biodegradable aliphatic ester chemical linkages, and it was conjugated along with biotin on the dextran backbone. The dextran derivative self-assembled into nanovesicles of <200 nm in size, which were characterized by dynamic and static light scattering, electron, and atomic force microscopes. Avidin-HABA assay established the high affinity of biotin-tagged dextran vesicles toward membrane-receptors up to 25 nM concentration. Doxorubicin-hydrochloride (DOX.HCl)-loaded dextran vesicles exhibited stable formulation in phosphate-buffered saline (PBS) and fetal bovine serum (FBS). Redox-degradation by glutathione (GSH) showed 60% drug release, whereas lysosomal esterase enzyme enabled >98% drug release in 12 h. Confocal microscope and flow cytometry-assisted time-dependent cellular uptake studies revealed that the biotin-receptors overexpressed in cervical cancer cells (HeLa) exhibited larger drug accumulation through the receptor-assisted endocytosis process. This process enabled the delivery of higher amount of DOX and significantly enhanced the killing in cancer cells (HeLa) compared to wild-type mouse embryonic fibroblast cells (WT-MEF, normal cells). Control experiments such as biotin pretreatment in cancer cells and energy-suppressed cellular uptake at 4 °C further supported the occurrence of receptor-mediated endocytosis by the biotin-tagged polymer vesicles. This report provides first insights into the targeted polysaccharide vesicle platform, and the proof-of-concept is successfully demonstrated in biotin receptor-overexpressed cervical cancer cells.

Cytosolic Uptake of Large Monofunctionalized Dextrans

Dextrans are a versatile class of polysaccharides with applications that span medicine, cell biology, food science, and consumer goods. Here, we report on a new type of large monofunctionalized dextran that exhibits unusual properties: efficient cytosolic and nuclear uptake. This dextran permeates various human cell types without the use of transfection agents, electroporation, or membrane perturbation. Cellular uptake occurs primarily through active transport via receptor-mediated processes. These monofunctionalized dextrans could serve as intracellular delivery platforms for drugs or other cargos.

Preparation of pH/redox dual responsive polymeric micelles with enhanced stability and drug controlled release

Stimuli-responsive polymeric micelles were prepared through self-assembly of amphiphilic copolymers poly(ethylene glycol)-poly(γ-benzyl l-glutamate), followed by a core-crosslinking reaction using cystamine as the crosslinking agent. The crosslinked micelles with spherical morphologies in nanometer size showed enhanced stability against dilution and concentrated salt solutions compared to the micelles before crosslinking. Doxorubicin (DOX) as a model drug was encapsulated into the core of micelles through electrostatic interactions between carboxylic acid and DOX. In vitro drug release under pH and redox conditions was investigated. Furthermore, the cytotoxicity of micelles was evaluated before and after drug loading. The endocytosis of DOX-loaded micelles and the intracellular drug release were studied. DOX-loaded micelles exhibited accelerated drug release behaviors in an acidic and reductive environment, and showed an inhibited premature release behavior as compared to the noncrosslinked micelles. Considering their enhanced stability, pH and redox dual triggered responsive characteristics, the polymeric micelles can serve as potential systems for controlled drug delivery.

Glutathione-triggered dual release of doxorubicin and camptothecin for highly efficient synergistic anticancer therapy

An amphiphilic biodegradable prodrug (PLG-g-mPEG/CPT) was synthesized by conjugating disulfide-containing camptothecin (CPT) to poly(L-glutamic acid)-graft-methoxy poly(ethylene glycol) (PLG-g-mPEG) through esterification reaction. The amphiphilic prodrugs could self-assemble into micellar nanoparticles and encapsulate doxorubicin (DOX) in aqueous solution at pH 7.4. The treatment of the nanoparticles with reducing glutathione (GSH) at cytosolic concentration (10 mM) significantly promoted the in vitro dual release of DOX and CPT from the micelles. The results of flow cytometry (FCM) and confocal laser scanning microscopy (CLSM) manifested that the intracellular release of DOX and CPT from the micelles was enhanced by increasing the intracellular GSH level. Consistently, the MCF-7 cell killing mediated by the micelles was also intracellular GSH concentration-dependent. The low combination index (CI) value of < 0.3 demonstrated the high synergistic effect of DOX and CPT co-delivered by the nanoparticles in tumor cell killing. Therefore, this GSH-triggered dual release drug delivery system is a promising strategy for combination cancer therapy.

pH and redox dual-sensitive polysaccharide nanoparticles for the efficient delivery of doxorubicin

A pH and redox dual-sensitive biodegradable polysaccharide, succinic acid-decorated dextran-g-phenylalanine ethyl ester-g-cysteine ethyl ester (Dex-SA-l-Phe-l-Cys), was synthesized to load doxorubicin hydrochloride (DOX·HCl). The DOX-loaded nanoparticles, which were prepared in aqueous solution and free of organic solvent, could spontaneously self-assemble into uniform sizes. When loading DOX·HCl, mercapto Dex-SA-l-Phe-l-Cys was oxidized into a crosslinked disulfide linkage to form pH and redox dual-sensitive nanoparticles (DOX-S-NPs). The amphiphilic polymer loaded DOX·HCl into the core through electrostatic and hydrophobic interactions, meanwhile the crosslinked disulfide bond could stabilize the drug loaded nanoparticles. As a control with similar polymer structure, succinic acid decorated dextran-g-phenylalanine ethyl ester (Dex-SA-l-Phe) was prepared to obtain pH-sensitive DOX-loaded micelles (DOX-N-NPs). The controlled pH and redox-dependent release profiles of the DOX-S-NPs in vitro were certified in different releasing mediums. Furthermore, the cellular uptake of the DOX-S-NPs was comparable with that of free DOX·HCl, determined by confocal laser scanning microscopy (CLSM) and flow cytometry. Cytotoxicity assay in vitro showed that the DOX-S-NPs and free DOX·HCl were similar in inhibiting the proliferation of non-small cell lung carcinoma A549 and breast cancer MCF-7 cell lines. DOX-S-NPs displayed similar antitumor efficiency compared with free DOX·HCl, but lower toxicity by body weight. These dual-sensitive DOX-S-NPs provide a useful strategy for anti-tumor therapy.

Enhanced bioreduction-responsive biodegradable diselenide-containing poly(ester urethane) nanocarriers

Stimuli-responsive nanocarriers have been limited for bench-to-bedside translation mainly because the stimuli sensitivity and responsive rate are not high enough to ensure sufficient drug concentration at the target sites for superior therapeutic benefits. Herein, we reported an enhanced bioreduction-responsive and biodegradable nanocarrier based on the amphiphilic poly(ester urethane) copolymers (PAUR-SeSe) bearing multiple diselenide groups on the backbone. The copolymer could spontaneously self-assemble into stable micelles in aqueous medium with an average diameter of 68 nm, which could be rapidly disassembled in a reductive environment as a result of the reduction-triggered cleavage of diselenide groups. Furthermore, the PAUR-SeSe micelles showed an enhanced drug release profile and cellular uptake compared with the disulfide-containing analogue (PAUR-SS). CCK8 assays revealed that the antitumor activity of DOX-loaded PAUR-SeSe micelles was much higher than that of DOX-loaded PAUR-SS micelles. Besides, the blank micelles and degradation products were nontoxic up to a tested concentration of 50 μg mL^-1. Therefore, the enhanced therapeutic efficacy and good biocompatibility demonstrated that this drug nanocarrier had great potential for smart antitumor drug delivery applications.

Lipoyl Ester Terminated Star PLGA as a Simple and Smart Material for Controlled Drug Delivery Application

PLGA, a copolymer of lactide and glycolide, is one of the most used biodegradable polymers that find a wide range of biomedical applications including drug delivery and tissue engineering. However, in spite of remarkable advancement, nanotherapeutics based on PLGA might have drawbacks of inadequate stability, drug leakage, and slow drug release at the tumor site, which reduces its targeting ability and therapeutic efficacy. Here, we report that direct modification of star PLGA ends with lipoic acid, a natural antioxidant present in our human body, affords a smart material (sPLGA-LA) that forms reversibly crosslinked and bioresponsive multifunctional nanoparticles (sPLGA XNPs). Interestingly, sPLGA XNPs obtained in the presence of 23.0 wt % PEG-PDLLA displayed a small hydrodynamic size of 73 ± 1.2 nm, high stability against dilution and 10% serum, while fast destabilization under a reductive environment. Moreover, sPLGA XNPs achieved efficient loading of lipophilic anticancer drug model, doxorubicin (DOX), at a theoretical drug loading content of 13.3 wt %, giving DOX-loaded sPLGA XNPs with reduced drug leakage under physiological conditions as well as significantly accelerated drug release under 10 mM glutathione condition compared with both linear and star PLGA controls (denoted as lPLGA NPs and sPLGA NPs, respectively). Confocal microscopy and flow cytometry displayed obviously stronger DOX fluorescence in B16F10 melanoma cells treated with DOX-loaded sPLGA XNPs than with lPLGA and sPLGA counterparts. MTT assays revealed that DOX-sPLGA XNPs caused 2.4- and 4.2-fold higher antitumor activity toward B16F10 cells than DOX-sPLGA NPs and DOX-lPLGA NPs, respectively. Notably, in vivo pharmacokinetics studies showed prolonged circulation time and significantly improved AUC for DOX-sPLGA XNPs over lPLGA NPs control. Hence, lipoyl ester terminated star PLGA emerges as a simple and smart material for better-controlled anticancer drug delivery.

Folate-Conjugated Polyphosphoester with Reversible Cross-Linkage and Reduction Sensitivity for Drug Delivery

To improve the therapeutic efficacy and circulation stability in vivo, we synthesized a new kind of drug delivery carrier based on folic acid conjugated polyphosphoester via the combined reactions of Michael addition polymerization and esterification. The produced amphiphilic polymer, abbreviated as P(EAEP-AP)-LA-FA, could self-assemble into nanoparticles (NPs) with core-shell structure in water and reversible core cross-linked by lipoyl groups. Using the core cross-linked FA-conjugated nanoparticles (CCL-FA NPs) to encapsulate hydrophobic anticancer drug doxorubicin (DOX), we studied the stability of NPs, in vitro drug release, cellular uptake, and targeting intracellular release compared with both un-cross-linked FA-conjugated nanoparticles (UCL-FA NPs) and core cross-linked nanoparticles without FA conjugation (CCL NPs). The results showed that under the condition of pH 7.4, the DOX-loaded CCL-FA NPs could maintain stable over 72 h, and only a little DOX release (∼15%) was observed. However, under the reductive condition (pH 7.4 containing 10 mM GSH), the disulfide-cross-linked core would be broken up and resulted in 90% of DOX release at the same incubation period. The study of methyl thiazolyl tetrazolium (MTT) assay indicated that the DOX-loaded CCL-FA NPs exhibited higher cytotoxicity (IC₅₀: 0.33 mg L^-1) against HeLa cells than the DOX-loaded CCL NPs without FA. These results indicate that the core cross-linked FA-conjugated nanoparticles have unique stability and targetability.

Integrated Multifunctional Micelles Co-Self-Assembled from Polypeptides Conjugated with Natural Ferulic Acid and Lipoic Acid for Doxorubicin Delivery

The development of safe, easily accessible, and multifunctional nanocarriers is a big topic in nanomedicine research. Here, integrated multifunctional micelles (IMM) were developed by co-self-assembly of poly(ethylene glycol)-b-poly(l-lysine) derivatives with natural ferulic acid (FA) or lipoic acid (LA). FA confers IMM with intrinsic antitumor activity, improved loading of doxorubicin (DOX) through π-π stacking, and reduced DOX cardiotoxicity. LA provides IMM with reversible crosslinking property, which leads to a high colloidal stability with inhibited drug leakage and triggered intracellular DOX release. Notably, our results showed that cRGD-decorated IMM (cRGD-IMM) had a small size (≈56 nm) and superior loading of DOX (27.1 wt. %). Blank cRGD-IMM, though nontoxic to normal cells, exhibited obvious antiproliferative activity against cancer cells including B16F10 and HCT-116 cells at 150 μg FA equiv. mL^-1 . DOX-loaded cRGD-IMM displayed enhanced growth inhibition of α_v β₃ -positive B16F10 and HCT-116 cells, a long elimination half-life of 3.85 h, and a high maximum-tolerated dose of over 100 mg DOX equiv. kg^-1 . Histological analysis revealed that DOX-loaded cRGD-IMM at 100 mg DOX equiv. kg^-1 caused negligible cardiotoxicity, which is a major issue for the clinical use of DOX. These integrated multifunctional micelles with excellent safety and accessibility have emerged as a new platform for targeted cancer chemotherapy.

Redox-Responsive Core-Cross-Linked Block Copolymer Micelles for Overcoming Multidrug Resistance in Cancer Cells

Success of chemotherapy as a treatment for cancer has been often inhibited by multidrug resistance (MDR) of the cancer cells. There is a clear need to generate strategies to overcome this resistance. In this work, we have developed redox-responsive and core-cross-linked micellar nanocarriers using poly(ethylene glycol)-block-poly(2-(methacryloyloxy)ethyl 5-(1,2-dithiolan-3-yl)pentanoate) diblock copolymers (PEG-b-PLAHEMA) with tunable swelling properties for the delivery of drugs toward drug-sensitive MDA-MB-231 and drug-resistant MDA-MB-231 (231R) cancer cells. PEG-b-PLAHEMA containing varying number of 2-(methacryloyloxy)ethyl 5-(1,2-dithiolan-3-yl)pentanoate (LAHEMA) units were synthesized by employing the reversible addition-fragmentation chain transfer polymerization technique. The block copolymer self-assembly, cross-linking induced by reduction, and de-cross-linking triggered time-dependent controlled swelling of micelles were studied using dynamic light scattering, fluorescence spectroscopy, and transmission electron microscopy. In vitro cytotoxicity, cellular uptake efficiency, and glutathione-responsive anticancer activity of doxorubicin (DOX) encapsulated in core-cross-linked block copolymer micelles (CCMs) toward both drug-sensitive and drug-resistant cancer cell lines were evaluated. Significant reduction in IC₅₀ was observed by DOX-loaded CCMs toward drug-resistant 231R cancer cell lines, which was further improved by coencapsulating DOX and verapamil (a P-glycoprotein inhibitor) in CCMs. Thus, these reduction-sensitive biocompatible CCMs with tunable swelling property are very promising in overcoming MDR in cancer cells.

Inulin based glutathione-responsive delivery system for colon cancer treatment

Colorectal cancer is one of the most common types of tumor in the world. Here we developed a lipoic acid esterified polysaccharide (inulin) delivery system for tanshinone IIA to treat colorectal cancer in vitro. The release of tanshinone IIA in the system was highly responsive to glutathione, which is commonly abundant in cancer cells. In addition, this drug delivery system was proliferative to Bifidobacterium longum, the common inhabitant of human intestine. Thus, this strategy might be useful to improve colon cancer therapy efficacy of anticancer drugs and meanwhile promote the growth of beneficial commensal flora in the gut.

Low molecular weight heparin-based reduction-sensitive nanoparticles for antitumor and anti-metastasis of orthotopic breast cancer

Tumor metastasis has become a major obstacle for the clinical treatment of malignant breast cancer.

A hyperbranched amphiphilic acetal polymer for pH-sensitive drug delivery

In this study, a novel hyperbranched amphiphilic block copolymer was synthesized using deactivation-enhanced atom transfer radical polymerization (DE-ATRP) for smart drug delivery.