Ursolic acid loaded tri-block copolymer nanoparticles based on triphenylphosphine for mitochondria-targeted cancer therapy

A novel biodegradable amphiphilic triblock copolymer, polyphosphate, polyethylene glycol, and polylactic acid (PAEEP-PEG-PLLA), was synthesized by twice ring-opening polymerization and triphenylphosphine (TPP) was grafted onto the block copolymer to synthesize a carrier material TPP-PAEEP-PEG-PLLA, which was identified by1H-nuclear magnetic resonance (1H-NMR) spectroscopy. The TPP-PAEEP-PEG-PLLA nanoparticles encapsulated with ursolic acid (UA) were prepared by the emulsion-solvent evaporation method and characterized by dynamic light scattering. The mitochondrial targeting ability of fluorescently labeled nanoparticles was evaluated by laser confocal microscopy. The average particle size and surface charge of the UA -loaded nanoparticle solution were 180.07 ± 1.67 nm and +15.57 ± 1.33 mV, respectively. The biocompatibility of nanoparticles was briefly evaluated by erythrocyte hemolysis assay.In vitrocell proliferation assay and scratch migration assay were performed to compare the difference in anti-tumor effect between UA and UA nanoparticles. The results showed that TPP-modified triblock copolymers had good mitochondrial targeting and improved the low bioavailability of UA, and UA nanoparticles exhibited more pronounced anti-tumor capabilities. In summary, the results suggested that our UA nanoparticles were a promising drug-targeted delivery system for the treatment of tumors.

A CD326 monoclonal antibody modified core cross-linked curcumin-polyphosphoester prodrug for targeted delivery and cancer treatment

Stimuli-responsive cross-linked micelles (SCMs) are ideal nanocarriers for anti-cancer drugs. Compared with non-cross-linked micelles, SCMs exhibit superior structural stability. At the same time, the introduction of an environmentally sensitive crosslinker into a drug delivery system allows SCMs to respond to single or multiple stimuli in the tumor microenvironment, which can minimize drug leakage during the blood circulation process. In this study, curcumin (CUR) was modified as the hydrophobic core crosslinker by utilizing the bisphenol structure, and redox sensitive disulfide bonds were introduced to prepare the glutathione (GSH) stimulated responsive core crosslinker (abbreviated as N3-ss-CUR-ss-N3). In addition, amphiphilic polymer APEG-b-PBYP was prepared through the ring opening reaction, and reacted with the crosslinker through the "click" reaction. After being dispersed in the aqueous phase, core cross-linked nanoparticles (CCL NPs) were obtained. Finally, monoclonal antibody CD326 (mAb-CD326) was reduced and coupled to the hydrophilic chain ends to obtain the nanoparticles with surface modified antibodies (R-mAb-CD326@CCL NPs) for further enhancing targeted drug delivery. The structures of the polymer and crosslinker were characterized by 1H NMR, UV-Vis, FT-IR, and GPC. The morphology, size and stability of CCL NPs and R-mAb-CD326@CCL NPs were investigated by DLS and TEM. The in vitro drug release behavior of CCL NPs was also studied. The results showed that the CCL NPs exhibited reduction-responsiveness and were able to release the original drug CUR under 10 mM GSH conditions. Additionally, the CCL NPs exhibited excellent stability in both the simulated body fluid environment and organic solvents. Especially, R-mAb-CD326@CCL NPs can actively target tumor cells and showed better therapeutic efficacy in in vivo experiments with a tumor suppression rate of 78.7%. This work provides a new idea for the design of nano-drugs targeting breast cancer.

Biodegradable nanomaterials for diagnosis and therapy of tumors

Although degradable nanomaterials have been widely designed and applied for cancer bioimaging and various cancer treatments, few reviews of biodegradable nanomaterials have been reported. Herein, we have summarized the representative research advances of biodegradable nanomaterials with respect to the mechanism of degradation and their application in tumor imaging and therapy. First, four kinds of tumor microenvironment (TME) responsive degradation are presented, including pH, glutathione (GSH), hypoxia and matrix metalloproteinase (MMP) responsive degradation. Second, external stimulation degradation is summarized briefly. Next, we have outlined the applications of nanomaterials in bioimaging. Finally, we have focused on some typical examples of biodegradable nanomaterials in radiotherapy (RT), photothermal therapy (PTT), starvation therapy, photodynamic therapy (PDT), chemotherapy, chemodynamic therapy (CDT), sonodynamic therapy (SDT), gene therapy, immunotherapy and combination therapy.

pH/redox-responsive core cross-linked based prodrug micelle for enhancing micellar stability and controlling delivery of chemo drugs: An effective combination drug delivery platform for cancer therapy

Core-crosslinking of micelles (CCMs) appears to be a favorable strategy to enhance micellar stability and sustained release of the loaded drug. In this study, the DOX-conjugated pH-sensitive polymeric prodrug Methoxy Poly (ethylene oxide)-b-Poly (Aspartate-Hydrazide) (mPEG-P [Asp-(Hyd-DOX)] was created using ring-opening polymerization. To further enhance the micellar system, 3,3'-diselanediyldipropanoic acid (DSeDPA) was applied to link the hydrophobic segment via click reaction to form pH/redox-responsive CCMs. Dual anti-cancer drugs, DOX as a pro-drug and SN-38 as a targeting drug, were used to enhance inhibition. DLS confirmed that the non-cross-linked micelle (NCMs) showed a higher (96.43 nm) particle size compared to the CCMs (72.63 nm). Due to micellar shrinkage after crosslinking, CCMs displayed SN-38 drug loading (7.32 %) and encapsulation efficiency (86.23 %). The mPEG-P(Asp-Hyd) copolymer's in vitro cytotoxicity on HeLa and HaCaT cell lines found that 84.52 % of the cells are alive, and zebrafish (Danio rerio) embryos and larvae are highly biocompatible. The DOX/SN-38@CCMs had a sustained discharge profile in vitro, unlike the DOX/SN-38@NCMs. In DOX/SN-38@CCMs, HeLa cells were inhibited 50.90 % more than HaCaT (14.25 %) at the maximum drug dose (10 μg/mL). The CCMs successfully targeted and supplied DOX/SN-38 in HeLa cells rather than HaCaT cells, based on cellular uptake of 2D cell culture. CCMs, unlike NCMs, inhibit the growth of spheroids for extended periods of time due to the prolonged release of the loaded drug. Overall, CCMs are good-looking for use as regulated delivery of DOX/SN-38 in cancer cells because of all of these appealing characteristics.

Hydrogen-bond super-amphiphile based drug delivery system: design, synthesis, and biological evaluation

Drug delivery systems (DDSs) show great application prospects in tumor therapy. So far, physical encapsulation and covalent grafting were the two most common strategies for the construction of DDSs. However, physical encapsulation-based DDSs usually suffered from low drug loading capacity and poor stability, and covalent grafting-based DDSs might reduce the activity of original drug, which greatly limited their clinical application. Therefore, it is of great research value to design a new DDS with high drug loading capacity, robust stability, and original drug activity. Herein, we report a super-amphiphile based drug delivery system (HBS-DDS) through self-assembly induced by hydrogen bonds between amino-substituted N-heterocycles of the 1,3,5-triazines and hydrophilic carmofur (HCFU). The resulting HBS-DDS had a high drug loading capacity (38.1%) and robust stability. In addition, the drug delivery system exhibited pH-triggered size change and release of drugs because of the pH responsiveness of hydrogen bonds. In particular, the anticancer ability test showed that the HBS-DDS could be efficiently ingested by tumor cells, and its half-maximal inhibitory concentration (IC50 = 3.53 μg mL-1) for HeLa cells was close to that of free HCFU (IC50 = 5.54 μg mL-1). The hydrogen bond-based DDS represents a potential drug delivery system in tumor therapy.

Amphiphilic copolymers in biomedical applications: Synthesis routes and property control

The request of new materials, matching strict requirements to be applied in precision and patient-specific medicine, is pushing for the synthesis of more and more complex block copolymers. Amphiphilic block copolymers are emerging in the biomedical field due to their great potential in terms of stimuli responsiveness, drug loading capabilities and reversible thermal gelation. Amphiphilicity guarantees self-assembly and thermoreversibility, while grafting polymers offers the possibility of combining blocks with various properties in one single material. These features make amphiphilic block copolymers excellent candidates for fine tuning drug delivery, gene therapy and for designing injectable hydrogels for tissue engineering. This manuscript revises the main techniques developed in the last decade for the synthesis of amphiphilic block copolymers for biomedical application. Strategies for fine tuning the properties of these novel materials during synthesis are discussed. A deep knowledge of the synthesis techniques and their effect on the performance and the biocompatibility of these polymers is the first step to move them from the lab to the bench. Current results predict a bright future for these materials in paving the way towards a smarter, less invasive, while more effective, medicine.

A PEGylated photosensitizer-core pH-responsive polymeric nanocarrier for imaging-guided combination chemotherapy and photodynamic therapy

A novel chemo-photodynamic combined therapeutic self-assembly polymeric platform (MPEG-Hyd-Br₂-BODIPY) was constructed which can encapsulate DOX and exhibited an accelerated release rate with decreasing pH value which results in considerable time/dose-dependent cytotoxicity.

A biodegradable CO2-based polymeric antitumor nanodrug via a one-pot surfactant- and solvent-free miniemulsion preparation

In the present study, low molecular weight poly(propylene carbonate) (PPC, Mn = 3500), a biodegradable liquid polymer easily prepared from carbon dioxide (CO2), was modified into poly(propylene carbonate)diacrylate (PPC-DA) by acylation, and methoxy poly(ethylene glycol) (mPEG) was modified into methoxy poly(ethylene glycol) acrylate (mPEG-A). Using PPC-DA as the dispersant to dissolve hydrophobic doxorubicin (DOX) and the initiator, and with mPEG-A as the co-monomer and polymerisable surfactant, a biodegradable nanodrug with excellent biocompatibility was prepared by shear emulsification polymerization without surfactants or organic solvent residues. The nanodrug can be efficiently endocytosed by tumor cells and can rapidly release doxorubicin triggered by the acidic endosomal pH. As evidenced by experiments in tumor-bearing mice, such a nanodrug is stealthy during blood circulation, and targets tumor sites with high efficiency. Moreover, this nanodrug is more effective and less toxic than free doxorubicin. This study provides a green and versatile approach for preparing biodegradable nanodrugs via a simple and efficient process. Moreover, this study extends the applications of CO2 based polymers in the biomedical field, promoting the development of CO2 polymerization fixation.

Highly-controllable drug release from core cross-linked singlet oxygen-responsive nanoparticles for cancer therapy

Highly-controllable release consisting of preventing unnecessary drug leakage at physiologically normal tissues and triggering sufficient drug release at tumor sites is the main aim of nanoparticle-based tumor therapy. Developing drug-conjugation strategies with covalent bonds in response to a characteristic stimulus, such as reactive oxygen species (ROS) generated by photodynamic therapy (PDT) has attracted much attention. ROS can not only cause cytotoxicity, but also trigger the cleavage of ROS-responsive linkers. Therefore, it is feasible to design a new model of controlled drug release via the breakage of ROS-responsive linkers and degradation of nanoparticles. The self-supply of the stimulus and highly-controllable drug release can be achieved by encapsulation of photosensitizer (PS) and chemotherapeutic drugs simultaneously without any support of tumor endogenous stimuli. Therefore, we used thioketal (TK) linkers as the responsive linkers due to their reaction with singlet oxygen (¹O₂, SO), a type of ROS. They were conjugated to the side groups of polyphosphoesters (PPE) via click chemistry to acquire the core cross-linked SO-responsive PPE nanoparticles poly(thioketal phosphoesters) (TK-PPE). TK-PPE coated with the photosensitizer chlorin e6 (Ce6) and chemotherapeutic drug doxorubicin (DOX) simultaneously were prepared and named as TK-PPE_Ce6&DOX. TK-PPE_Ce6&DOX kept stable due to the high stability of the TK-linkers in the normal physiological environment. With self-production of SO as the stimulating factor from the encapsulated Ce6, highly-controlled drug release was achieved. After incubation of tumor cells, 660 nm laser irradiation induced SO generation, resulting in the cleavage of TK-linkers and boosted-release of DOX. Highly-controllable drug release of TK-PPE_Ce6&DOX through self-production of stimulus increased antitumor efficacy, offering a promising avenue for clinical on-demand chemotherapy.

Core cross-linked singlet oxygen-responsive nanoparticle TK-PPE_Ce6&DOX could achieve highly-controllable drug release through self-production of SO as the stimulus to increase antitumor efficacy for cancer therapy.

Dynamic core crosslinked camptothecin prodrug micelles with reduction sensitivity and boronic acid-mediated enhanced endocytosis: An intelligent tumor-targeted delivery nanoplatform

The physicochemical properties of camptothecin (CPT) limit its clinical application. To maximize drug efficacy, a novel intelligent prodrug delivery nanoplatform with a tumor microenvironment-cleavable core crosslinking strategy was proposed based on a phenylboronic acid (PBA) modified polyethylene glycol (PEG)-polyglutamic acid (PGlu) polymer with disulfide-bonded CPT, called PBA-PEG-P(Glu-co-GlussCPT). The fabricated nanoplatform was a spherical micelle that could withstand dilution and carry a large number of therapeutic molecules to the tumor tissues, thereby minimizing premature drug release. Moreover, the nanoplatform release 6.2 ± 0.62, 12.4 ± 1.8, 46.7 ± 0.33, and 79.2 ± 1.58% of CPT after incubation in 0.02, 1, 5, and 10 mM dithiothreitol for 24 h, respectively, exhibiting good reduction-sensitivity. Moreover, the nanoplatform exhibited significant antiproliferative activity against tumor cells. In addition, with PBA modification, the nanoplatform demonstrated enhanced endocytosis efficiency. This prodrug nanoplatform also exhibited significant in vivo antitumor efficacy on both murine and human hepatoma xenograft models, without showing significant systemic toxicity but demonstrating good biocompatibility. In other words, this novel intelligent prodrug delivery nanoplatform with tumor microenvironment-cleavable core crosslinking strategy and active targeting strategy based on prodrug polymer PBA-PEG-P(Glu-co-GlussCPT) demonstrated multiple functions and significant potential for antitumor drug delivery.

GSH/pH dual-responsive biodegradable camptothecin polymeric prodrugs combined with doxorubicin for synergistic anticancer efficiency

GSH and pH dual-responsive camptothecin polymeric prodrugs combined doxorubicin for synergistic drug delivery to highly improved selectivity and synergy benefiting from good long-term stability, better internalization and sensitive dual-responsibility.

Recent advances in stimuli-responsive polymeric micelles via click chemistry

Stimuli-responsive polymeric micelles via click chemistry are divided into six major sections (temperature, light, ultrasound, pH, enzymes, and redox).

Chemoenzymatic synthesis of dual-responsive graft copolymers for drug delivery: long-term stability, high loading and cell selectivity

A series of amphiphilic graft copolymers, poly(N-propargyldiethanolamine 4,4'-dithiodibutyionate)-graft-monomethoxy poly(ethylene glycol) (PPD-g-mPEG), were designed via a chemoenzymatic method for pH and reduced glutathione (GSH) dual-responsive drug delivery. The effects of percent grafting and molecular weights of mPEG on critical micelle concentration (CMC) values, size of micelles, drug loading and dual-response were tested. The graft copolymers could easily form homogeneous spherical micelles with appropriate sizes and zeta-potentials. The micelles of PPD-g-mPEG copolymers loaded doxorubicin (DOX) in high efficiency, and showed excellent stability under physiological conditions and synergetic dual-response to weakly acidic pH and GSH. In vitro experiments confirmed that the DOX-loaded micelles could be internalized into cancer cells efficiently and release DOX over time. Furthermore, cell cytotoxicity assays indicated that the graft copolymers were non-cytotoxic to both cancerous and normal cells while the DOX-loaded micelles greatly improved the selectivity ratios between HeLa cells and HL-7702 cells. DOX-loaded micelles also avoided hemolysis of red blood cells (RBCs) effectively compared with commercialized doxorubicin hydrochloride. All these demonstrated the potential of PPD-g-mPEG as a model to create more functional dual-responsive nanocarriers for controlled drug delivery.

One-Pot Synthesis of pH/Redox Responsive Polymeric Prodrug and Fabrication of Shell Cross-Linked Prodrug Micelles for Antitumor Drug Transportation

Shell cross-linked (SCL) polymeric prodrug micelles have the advantages of good blood circulation stability and high drug content. Herein, we report on a new kind of pH/redox responsive dynamic covalent SCL micelle, which was fabricated by self-assembly of a multifunctional polymeric prodrug. At first, a macroinitiator PBYP- ss- iBuBr was prepared via ring-opening polymerization (ROP), wherein PBYP represents poly[2-(but-3-yn-1-yloxy)-2-oxo-1,3,2-dioxaphospholane]. Subsequently, PBYP- hyd-DOX- ss-P(DMAEMA- co-FBEMA) prodrug was synthesized by a one-pot method with a combination of atom transfer radical polymerization (ATRP) and a Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction using a doxorubicin (DOX) derivative containing an azide group to react with the alkynyl group of the side chain in the PBYP block, while DMAEMA and FBEMA are the abbriviations of N, N-(2-dimethylamino)ethyl methacrylate and 2-(4-formylbenzoyloxy)ethyl methacrylate, respectively. The chemical structures of the polymer precursors and the prodrugs have been fully characterized. The SCL prodrug micelles were obtained by self-assembly of the prodrug and adding cross-linker dithiol bis(propanoic dihydrazide) (DTP). Compared with the shell un-cross-linked prodrug micelles, the SCL prodrug micelles can enhance the stability and prevent the drug from leaking in the body during blood circulation. The average size and morphology of the SCL prodrug micelles were measured by dynamic light scattering (DLS) and transmission electron microscopy (TEM), respectively. The SCL micelles can be dissociated under a moderately acidic and/or reductive microenvironment, that is, endosomal/lysosomal pH medium or high GSH level in the tumorous cytosol. The results of DOX release also confirmed that the SCL prodrug micelles possessed pH/reduction responsive properties. Cytotoxicity and cellular uptake analyses further revealed that the SCL prodrug micelles could be rapidly internalized into tumor cells through endocytosis and efficiently release DOX into the HeLa and HepG2 cells, which could efficiently inhibit the cell proliferation. This study provides a fast and precise synthesis method for preparing multifunctional polymer prodrugs, which hold great potential for optimal antitumor therapy.

2,2'-Dithiodisuccinic acid-stabilized polyion complex micelles for pH and reduction dual-responsive drug delivery

In this work, a new kind of polyion complex (PIC) micelles with pH and reduction dual responsiveness was developed for effective intracellular drug delivery. The PIC micelles can be readily prepared by mixing a polycationic block polymer, methoxy poly(ethylene glycol)-b-poly(l-lysine) (mPEG-PLL), with a small molecule polyacid, 2, 2'-dithiodisuccinic acid (DTS) in aqueous media. The resultant PIC micelles are of uniform spherical shapes with hydrodynamic radii ranging from 65 to 75 nm based on different feeding ratios of mPEG-PLL and DTS. Interestingly, by using the small molecule polyacid DTS, the obtained PIC micelles show distinct pH-responsive disintegration in acid solution. Meanwhile, the PIC micelles were also assessed to be reduction-responsive due to the presence of disulfide bond in DTS. In view of these stimuli-responsive properties, the potential use of this PIC micelle as smart drug carrier was then investigated. Doxorubicin (DOX), a cationic anticancer drug, was loaded into the PIC micelles with high efficiency. In vitro drug release studies revealed that release of DOX from the PIC micelles was suppressed in neutral solutions due to the stable electrostatic interactions between PIC micelles and DOX, but could be accelerated in acidic solutions or under high GSH condition. Furthermore, flow cytometry and confocal laser scanning microscopy (CLSM) studies indicated that the DOX-loaded PIC micelles could be effectively internalized by MCF-7 human breast cancer cells and release the loaded DOX in intracellular environment. Consequently, the DOX-loaded PIC micelles were capable of inhibiting the proliferation of C26 murine colon cancer and MCF-7 human breast cancer cells in high efficiency, showing similar IC₅₀ values as free DOX. Thus, this biocompatible PIC micelle may be promising for intracellular 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.

Environment-stimulated nanocarriers enabling multi-active sites for high drug encapsulation as an “on demand” drug release system

Limited active sites in polyesters hinder fabrication of multifunctional biodegradable nanocarriers for successful clinical applications.