pH-sensitive polymeric nanoparticles for tumor-targeting doxorubicin delivery: concept and recent advances

Biconcave Carbon Nanodisks for Enhanced Drug Accumulation and Chemo-Photothermal Tumor Therapy

It is considered a significant challenge to construct nanocarriers that have high drug loading capacity and can overcome physiological barriers to deliver efficacious amounts of drugs to solid tumors. Here, the development of a safe, biconcave carbon nanodisk to address this challenge for treating breast cancer is reported. The nanodisk demonstrates fluorescent imaging capability, an exceedingly high loading capacity (947.8 mg g-1 , 94.78 wt%) for doxorubicin (DOX), and pH-responsive drug release. It exhibits a higher uptake rate by tumor cells and greater accumulation in tumors in a mouse model than its carbon nanosphere counterpart. In addition, the nanodisk absorbs and transforms near-infrared (NIR) light to heat, which enables simultaneous NIR-responsive drug release for chemotherapy and generation of thermal energy for tumor cell destruction. Notably, this NIR-activated dual therapy demonstrates a near complete suppression of tumor growth in a mouse model of triple-negative breast cancer when DOX-loaded nanodisks are administered systemically.

Thermally-responsive Virus-like Particle for Targeted Delivery of Cancer Drug

Multifunctional nanocarriers displaying specific ligands and simultaneously response to stimuli offer great potentials for targeted and controlled drug delivery. Several synthetic thermally-responsive nanocarriers have been studied extensively for hyperthermia incorporated chemotherapy. However, no information is available on the application of virus-like particle (VLP) in thermally-controlled drug delivery systems. Here, we describe the development of a novel multifunctional nanovehicle based on the VLP of Macrobrachium rosenbergii nodavirus (MrNVLP). Folic acid (FA) was covalently conjugated to lysine residues located on the surface of MrNVLP, while doxorubicin (Dox) was loaded inside the VLP using an infusion method. This thermally-responsive nanovehicle, namely FA-MrNVLP-Dox, released Dox in a sustained manner and the rate of drug release increased in response to a hyperthermia temperature at 43 °C. The FA-MrNVLP-Dox enhanced the delivery of Dox to HT29 cancer cells expressing high level of folate receptor (FR) as compared to CCD841CoN normal cells and HepG2 cancer cells, which express low levels of FR. As a result, FA-MrNVLP-Dox increased the cytotoxicity of Dox on HT29 cells, and decreased the drug's cytotoxicity on CCD841CoN and HepG2 cells. This study demonstrated the potential of FA-MrNVLP-Dox as a thermally-responsive nanovehicle for targeted delivery of Dox to cancer cells rich in FR.

The Pathway to Intelligence: Using Stimuli-Responsive Materials as Building Blocks for Constructing Smart and Functional Systems

Systems that are intelligent have the ability to sense their surroundings, analyze, and respond accordingly. In nature, many biological systems are considered intelligent (e.g., humans, animals, and cells). For man-made systems, artificial intelligence is achieved by massively sophisticated electronic machines (e.g., computers and robots operated by advanced algorithms). On the other hand, freestanding materials (i.e., not tethered to a power supply) are usually passive and static. Hence, herein, the question is asked: can materials be fabricated so that they are intelligent? One promising approach is to use stimuli-responsive materials; these "smart" materials use the energy supplied by a stimulus available from the surrounding for performing a corresponding action. After decades of research, many interesting stimuli-responsive materials that can sense and perform smart functions have been developed. Classes of functions discussed include practical functions (e.g., targeting and motion), regulatory functions (e.g., self-regulation and amplification), and analytical processing functions (e.g., memory and computing). The pathway toward creating truly intelligent materials can involve incorporating a combination of these different types of functions into a single integrated system by using stimuli-responsive materials as the basic building blocks.

Potentials of combining nanomaterials and stem cell therapy in myocardial repair

Cardiac diseases have become the leading cause of death worldwide. Developing efficient strategies to treat such diseases is of great urgency. Stem cell-based regeneration medicine offers a novel approach for heart repair. However, low retention and poor survival rate of engrafted cells limit its applications. Nanomaterials have shown great potentials in addressing above issues due to nanoparticles-bio interactions. Therefore, combining nanomaterials and stem cell therapy is of great interest and significance for heart repair. Herein, we provide a comprehensive understanding of the applications of four types of nanomaterials (nanogels, polymeric nanomaterials, inorganic nanomaterials and exosomes) in stem cell therapy for myocardial repair. In addition, we launch an initial discussion on current problems and more importantly, possible solutions for myocardial repair.

pH-Sensitive Poly(β-amino ester)s Nanocarriers Facilitate the Inhibition of Drug Resistance in Breast Cancer Cells

Multidrug resistance (MDR) remains an unmet challenge in chemotherapy. Stimuli-responsive nanocarriers emerge as a promising tool to overcome MDR. Herein, pH-sensitive poly(β-amino ester)s polymers (PHP)-based micellar nanoparticles were synthesized for enhanced doxorubicin (DOX) delivery in drug resistant breast cancer MCF-7/ADR cells. DOX-loaded PHP micelles showed rapid cell-internalization and lysosomal escape in MCF-7/ADR cells. The cytotoxicity assays showed relatively higher cell inhibition of DOX-loaded PHP micelles than that of free DOX against MCF-7/ADR cells. Further mechanistic studies showed that PHP micelles were able to inhibit P-glycoprotein (P-gp) activity by lowering mitochondrial membrane potentials and ATP levels. These results suggested that the enhanced antitumor effect might be attributed to PHP-mediated lysosomal escape and drug efflux inhibition. Therefore, PHP would be a promising pH-responsive nanocarrier for enhanced intracellular drug delivery and overcoming MDR in cancer cells.

Unique Energy Transfer in Fluorescein-Conjugated Au22 Nanoclusters Leading to 160-Fold pH-Contrasting Photoluminescence

Accurate measurements of intracellular pH are of crucial importance in understanding the cellular activities and in the development of intracellular drug delivery systems. Here we report a highly sensitive pH probe based on a fluorescein-conjugated Au₂₂ nanocluster. Steady-state photoluminescence (PL) measurements have shown that, when conjugated to Au₂₂, fluorescein exhibits more than 160-fold pH-contrasting PL in the pH range of 4.3-7.8. Transient absorption measurements show that there are two competing ultrafast processes in the fluorescein-conjugated Au₂₂ nanocluster: the intracore-state relaxation and the energy transfer from the nonthermalized states of Au₂₂ to fluorescein. The latter becomes predominant at a higher pH, leading to dramatic PL enhancement of fluorescein. In addition to the intrinsically low toxicity, fluorescein-conjugated Au₂₂ nanoclusters exhibit high pH sensitivity, wide dynamic range, and excellent photostability, providing a powerful tool for the study of intracellular processes.

Surface modification of doxorubicin-loaded nanoparticles based on polydopamine with pH-sensitive property for tumor targeting therapy

One major challenge of current surface modification of nanoparticles is the demand for chemical reactive polymeric layers, such modification is always complicated, inefficient, and may lead the polymer lose the ability to encapsulate drug. To overcome this limitation, we adopted a pH-sensitive platform using polydopamine (PDA) as a way of functionalizing nanoparticles (NPs) surfaces. All this method needed to be just a brief incubation in weak alkaline solution of dopamine, which was simple and applicable to a variety of polymer carriers regardless of their chemical reactivity. We successfully conjugated the doxorubicin (DOX)-PDA-poly (lactic-co-glycolic acid) (PLGA) NPs with two typical surface modifiers: folate (FA) and a peptide (Arg-Gly-Asp, RGD). The DOX-PDA-FA-NPs and DOX-PDA-RGD-NPs (targeting nanoparticles) were characterized by particle size, zeta potential, and surface morphology. They were quite stable in various physiological solutions and exhibited pH-sensitive property in drug release. Compared to DOX-NPs, the targeting nanoparticles possessed an excellent targeting ability against HeLa cells. In addition, the in vivo study demonstrated that targeting nanoparticles achieved a tumor inhibition rate over 70%, meanwhile prominently decreased the side effects of DOX and improve drug distribution in tumors. Our studies indicated that the DOX-PLGA-NPs modified with PDA and various functional ligands are promising nanocarriers for targeting tumor therapy.

Phospholipid-Block Copolymer Hybrid Vesicles with Lysosomal Escape Ability

The success of nanoparticulate formulations in drug delivery depends on various aspects including their toxicity, internalization, and intracellular location. Vesicular assemblies consisting of phospholipids and amphiphilic block copolymers are an emerging platform, which combines the benefits from liposomes and polymersomes while overcoming their challenges. We report the synthesis of poly(cholesteryl methacrylate)- block-poly(2-(dimethylamino) ethyl methacrylate) (pCMA- b-pDMAEMA) block copolymers and their assembly with phospholipids into hybrid vesicles. Their geometry, their ζ-potential, and their ability to adsorb onto polymer-coated surfaces were assessed. Giant unilamellar vesicles were employed to confirm the presence of both the phospholipids and the block copolymer in the same membrane. Furthermore, the cytotoxicity of selected hybrid vesicles was determined in RAW 264.7 mouse macrophages, primary rat Kupffer cells, and human macrophages. The internalization and lysosomal escape ability of the hybrid vesicles were confirmed using RAW 264.7 mouse macrophages. Taken together, our findings illustrate that the reported hybrid vesicles are a promising complementary drug delivery platform for existing liposomes and polymersomes.

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

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

Copolymer micelles function as pH-responsive nanocarriers to enhance the cytotoxicity of a HER2 aptamer in HER2-positive breast cancer cells

Efficient delivery of nucleic acids into target cells is crucial for nucleic acid-based therapies. Various nucleic acid delivery systems have been developed, each with its own advantages and limitations. We previously developed a nanoparticle-based delivery system for small chemical drugs using pH-responsive PEG₈-PDPA₁₀₀-PEG₈ polymer micelles as carriers. In this study, we extend the application of these pH-responsive micelle-like nanoparticles (MNPs) to deliver oligonucleotides. We demonstrate that the MNPs efficiently encapsulate and deliver oligonucleotides of different lengths (20-100 nt) into cells. The cargo oligonucleotides are rapidly released at pH 5.0. We prepared MNPs carrying a Texas red-fluorescently labeled anti-human epidermal growth factor receptor 2 (HER2) aptamer (HApt). Compared to free HApt, the HApt-MNPs resulted in significantly better cellular uptake, reduced cell viability, and increased apoptosis in SKBR3 breast cancer cells, which overexpress HER2. Moreover, HApt-MNPs were significantly less cytotoxic to MCF7 breast cancer cells, which express low levels of HER2. After cellular uptake, HApt-MNPs mainly accumulated in lysosomes; inhibition of lysosomal activity using bafilomycin A1 and LysoTracker Red staining confirmed that lysosomal activity and low pH were required for HApt-MNP accumulation and release. Furthermore, HER2 protein expression declined significantly following treatment with HApt-MNPs in SKBR3 cells, indicating that HApt-induced translocation of HER2 to lysosomes exerted a potent cytotoxic effect by altering signaling downstream of HER2. In conclusion, this pH-responsive and lysosome-targeting nanoparticle system can efficiently deliver oligonucleotides to specific target cells and has significant potential for nucleic acid-based cancer therapies.

A DOX-loaded polymer micelle for effectively inhibiting cancer cells

A novel triblock polymer is synthesized and self-assembled with doxorubicin to form DOX-loaded micelles. The synthetic process involves the ring-opening polymerization, carboxylation and amidation reactions, and the structures are characterized. The drug release test indicated that the micelles have the ability to control the release of drugs. The cell uptake results indicated that the DOX-loaded micelles could enter cancer cells easily, and the cytotoxicity and apoptosis test confirmed that DOX-loaded micelles have a strong killing effect on tumor cells, while the blank micelles do not have cytotoxicity. Therefore, the novel polymer micelles are a promising carrier for delivery of anticancer drugs to enhance cancer treatment.

A novel triblock polymer is synthesized and self-assembled with doxorubicin to form DOX-loaded micelles.

Computational approaches to cell-nanomaterial interactions: keeping balance between therapeutic efficiency and cytotoxicity

Owing to their unique properties, nanomaterials have been widely used in biomedicine since they have obvious inherent advantages over traditional ones. However, nanomaterials may also cause dysfunction in proteins, genes and cells, resulting in cytotoxic and genotoxic responses. Recently, more and more attention has been paid to these potential toxicities of nanomaterials, especially to the risks of nanomaterials to human health and safety. Therefore, when using nanomaterials for biomedical applications, it is of great importance to keep the balance between therapeutic efficiency and cytotoxicity (i.e., increase the therapeutic efficiency as well as decrease the potential toxicity). This requires a deeper understanding of the interactions between various types of nanomaterials and biological systems at the nano/bio interface. In this review, from the point of view of theoretical researchers, we will present the current status regarding the physical mechanism of cytotoxicity caused by nanomaterials, mainly based on recent simulation results. In addition, the strategies for minimizing the nanotoxicity naturally and artificially will also be discussed in detail. Furthermore, we should notice that toxicity is not always bad for clinical use since causing the death of specific cells is the main way of treating disease. Enhancing the targeting ability of nanomaterials to diseased cells and minimizing their side effects on normal cells will always be hugely challenging issues in nanomedicine. By combining the latest computational studies with some experimental verifications, we will provide special insights into recent advances regarding these problems, especially for the design of novel environment-responsive nanomaterials.

Nanomicelle drug with acid-triggered doxorubicin release and enhanced cellular uptake ability based on mPEG-graft-poly(N-(2-aminoethyl)-L-aspartamide)-hexahydrophthalic acid copolymers

In order to achieve the passive tumor targeting and acid-triggered drugs release in lysosomes, optimized delivery system for doxorubicin based on pH-sensitive complex nanomicelles with suitable particle size was developed in this research. Particularly, poly(L-succinimide) was thoroughly ring-opened by ethylenediamine to give the poly(N-(2-aminoethyl)-L-aspartamide). Then, graft copolymer mPEG-graft-poly(N-(2-aminoethyl)-L-aspartamide)-hexahydrophthalic acid (mPEG-g-P(ae-Asp)-Hap) was synthesized by grafting mPEG-2000 and hexahydrophthalic anhydride onto poly(N-(2-aminoethyl)-L-aspartamide). In vitro studies revealed that mPEG-g-P(ae-Asp)-Hap copolymer was stable in neutral solutions but tend to be hydrolyzed under acidic condition, which was attributed to the acid-sensitive properties of hexahydrophthalic amides (β-carboxylic amides). MPEG-g-P(ae-Asp)-Hap copolymer with critical aggregation concentration of 0.166 mg·mL^-1 could self-assemble into stable blank nanomicelles with an average particle hydrodynamic diameter of 98.1 nm, but the hydrodynamic diameter of doxorubicin-loaded nanomicelles (mPEG-g-P(ae-Asp)-Hap·Dox) was smaller and approximately 77.5 nm. MPEG-g-P(ae-Asp)-Hap·Dox nanomicelles showed sustained drug release profiles over 34 h, and the cumulative drug release showed a tendency to increase from 25% to 62% with the pH value decreasing from 7.4 to 5.0 due to the acid-triggered disassembly of nanomicelles. The cytotoxicity of mPEG-g-P(ae-Asp)-Hap·Dox nanomicelles against A549 treated with 40 mM NH₄Cl (lysosomotropic weak bases) was decreased significantly than that without NH₄Cl treatment, further confirmed the drug release from the nanomicelles was triggered by the low pH value of lysosome (pH 5.0). Compared with doxorubicin HCl, mPEG-g-P(ae-Asp)-Hap·Dox nanomicelle drug showed enhanced cellular uptake ability during 2 or 4 h of incubation due to the endocytosis mechanism of nanomicelle drug. In summary, the cleavage of pH-sensitive β-carboxylic amides bonds on the hydrophobic branch of mPEG-g-P(ae-Asp)-Hap copolymer triggered the disassembly of the nanomicelles and release of doxorubicin in the acidic lysosomal compartments of cancer cells. These nanomicelles exhibited excellent potential for drug delivery due to their smart properties-PEGylation, suitable size, and acid-triggered drug release.

Polymeric nanoparticles developed by vitamin E-modified aliphatic polycarbonate polymer to promote oral absorption of oleanolic acid

Oleanolic acid (OA) exhibited good pharmacological activities in the clinical treatment of hypoglycemia, immune regulation, acute jaundice and chronic toxic hepatitis. However, the oral delivery of OA is greatly limited by its inferior water solubility and poor intestinal mucosa permeability. Herein, we developed a novel polymeric nanoparticle (NP) delivery system based on vitamin E modified aliphatic polycarbonate (mPEG-PCC-VE) to facilitate oral absorption of OA. OA encapsulated mPEG-PCC-VE NPs (OA/mPEG-PCC-VE NPs) showed uniform particle size of about 170 nm with high drug loading capability (8.9%). Furthermore, the polymeric mPEG-PCC-VE NPs, with good colloidal stability and pH-sensitive drug release characteristics, significantly enhanced the in vitro dissolution of OA in the alkaline medium. The in situ single pass intestinal perfusion (SPIP) studies performed on rats demonstrated that the OA/mPEG-PCC-VE NPs showed significantly improved permeability in the whole intestinal tract when compared to OA solution, especially for duodenum and colon. As a result, the in vivo pharmacokinetics study indicated that the bioavailability of OA/mPEG-PCC-VE NPs showed 1.5-fold higher than commercially available OA tablets. These results suggest that mPEG-PCC-VE NPs are a promising platform to facilitate the oral delivery of OA.

Poly(N-(2-Hydroxypropyl) Methacrylamide)-Valproic Acid Conjugates as Block Copolymer Nanocarriers

We report nanoassemblies based on block copolymers of N-(2-hydroxypropyl) methacrylamide (HPMA) in which drug cleavage enhances the biological compatibility of the original polymer carrier by regeneration of HPMA units. Drug release via ester hydrolysis suggests this approach offers potential for stimuli-responsive drug delivery under acidic conditions.

Delivery of a chemotherapeutic drug using novel hollow carbon spheres for esophageal cancer treatment

Low toxicity and high efficacy are the key factors influencing the real-world clinical applications of nanomaterial-assisted drug delivery. In this study, novel hollow carbon spheres (HCSs) with narrow size distribution were developed. In addition to demonstrating their ease of synthesis for large-scale production, we also demonstrated in vitro that the HCSs possessed high drug-loading capacity, lower cell toxicity, and optimal drug release profile at low pH, similar to the pH in the tumor microenvironment. The HCSs also displayed excellent immunocompatibility and could rapidly distribute themselves in the cytoplasm to escape lysosomal clearance. More importantly, the HCSs could efficiently deliver doxorubicin (a representative chemotherapeutic drug) to tumor sites, which resulted in significant inhibition of tumor growth in an esophageal xenograft cancer model. This also prolonged the circulation time and altered the biodistribution of the drug. In conclusion, this study revealed a novel drug delivery system for targeted tumor therapy.

pH-sensitive polymeric nanoparticles for co-delivery of doxorubicin and curcumin to treat cancer via enhanced pro-apoptotic and anti-angiogenic activities

Co-delivery of multiple drugs with complementary anticancer mechanisms by nano-carriers offers an effective strategy to treat cancer. The combination of drugs with pro-apoptotic and anti-angiogenic activities is potentially effective in treating human hepatocellular carcinoma (HCC). Herein, we developed a co-delivery system for doxorubicin (Dox), a pro-apoptotic drug, and curcumin (Cur), a potent drug for antiangiogenesis, in pH-sensitive nanoparticles (NPs) constituted with amphiphilic poly(β-amino ester) copolymer. Dox & Cur co-loaded NPs ((D+C)/NPs) were prepared with optimized drug ratio, showing low polydispersity, high encapsulation efficiency, and enhanced release in the acidic environment of cancer cells. Furthermore, enhanced cellular internalization of cargoes delivered from (D+C)/NPs were observed in human liver cancer SMMC 7721 cells and human umbilical vein endothelial cells (HUVECs) compared to the use of free drugs. The (D+C)/NPs induced a high rate of apoptosis in SMMC 7721 cells through decreased mitochondrial membrane potential. Additionally, (D+C)/NPs exhibited stronger anti-angiogenic effects including inhibition of HUVEC proliferation, migration, invasion, and tube formation mediated VEGF pathway modulation in vitro and in vivo. Taken together, encapsulation of the pro-apoptotic drug Dox and antiangiogenic agent Cur in pH-sensitive NPs provides a promising strategy to effectively inhibit HCC progression in a synergistic manner.

STATEMENT OF SIGNIFICANCE

The combination of multiple drugs has been demonstrated to be more effective than single treatment. However, the different physicochemical and pharmacokinetic profiles of each drug render optimal delivery challenging. In view of the great delivery advantage of nanocarriers to unify the multiple drugs in vivo, stimulus-responsive nano-carriers are more crucial to increase efficacy and reduce toxicity from off-target exposure. Therefore, herein the pH-sensitive nanoparticles, composed by d-α-tocopheryl polyethylene glycol 1000-block-poly (β-amino ester) (TPGS-PAE) polymers, have been fabricated for doxorubicin (Dox) and curcumin (Cur) co-delivery, which exhibited diverse anticancer approaches, i.e. pro-apoptosis and antiangiogenesis. The precise intracellular target site and effective drug combination concentration result in the enhanced antitumor efficiency and the reduced systematic toxicity of Dox. The co-encapsulation of the pro-apoptotic drug and antiangiogenic agent in pH-sensitive NPs provides a promising strategy to effectively inhibit malignant neoplasm progression in a synergistic manner.

MDR in cancer: Addressing the underlying cellular alterations with the use of nanocarriers

Multidrug resistance (MDR) is associated with a wide range of pathological changes at different cellular and intracellular levels. Nanoparticles (NPs) have been extensively exploited as the carriers of MDR reversing payloads to resistant tumor cells. However, when properly formulated in terms of chemical composition and physicochemical properties, NPs can serve as beyond delivery systems and help overcome MDR even without carrying a load of chemosensitizers or MDR reversing molecular cargos. Whether serving as drug carriers or beyond, a wise design of the nanoparticulate systems to overcome the cellular and intracellular alterations underlying the resistance is imperative. Within the current review, we will initially discuss the cellular changes occurring in resistant cells and how such changes lead to chemotherapy failure and cancer cell survival. We will then focus on different mechanisms through which nanosystems with appropriate chemical composition and physicochemical properties can serve as MDR reversing units at different cellular and intracellular levels according to the changes that underlie the resistance. Finally, we will conclude by discussing logical grounds for a wise and rational design of MDR reversing nanoparticulate systems to improve the cancer therapeutic approaches.

Shear-responsive injectable supramolecular hydrogel releasing doxorubicin loaded micelles with pH-sensitivity for local tumor chemotherapy

In this study, glycol chitosan-Pluronic F127 conjugate (GC-PF127), produced by an amidation reaction between terminal-carboxylated PF127 and glycol chitosan (GC), was used to prepare doxorubicin (DOX)-loaded micelles. The DOX/GC-PF127 micelles produced at optimal conditions had sizes of about 150nm and pH-sensitive surface charges. DOX/GC-PF127 hydrogel formed after addition of α-cyclodextrin into DOX/GC-PF127 micelle solution. The hydrogel had good shear-responsive, injectable and rapid recovery properties. In vitro release experiment confirmed that the hydrogel could sustainedly release DOX/GC-PF127 micelles via the dissociation of the hydrogel. After peritumoral injection into H22 tumor-bearing mice, the hydrogel could greatly increase DOX accumulation in tumor tissue and synchronously avoid DOX accumulation in normal tissues including heart. At similar total DOX dose administrated, the tumors of free DOX treatment group grew slowly after thrice intravenous injections, the tumors of the micelle group did not grow after twice intravenous injections, and the tumors of the hydrogel group disappeared almost after once peritumoral injection. This study demonstrates that injectable DOX/GC-PF127 hydrogel, which can sustainedly release DOX-loaded micelles with tumor-targeting function, is a promising system for local tumor chemotherapy.

A Simple Add-and-Display Method for Immobilisation of Cancer Drug on His-tagged Virus-like Nanoparticles for Controlled Drug Delivery

pH-responsive virus-like nanoparticles (VLNPs) hold promising potential as drug delivery systems for cancer therapy. In the present study, hepatitis B virus (HBV) VLNPs harbouring His-tags were used to display doxorubicin (DOX) via nitrilotriacetic acid (NTA) conjugation. The His-tags served as pH-responsive nanojoints which released DOX from VLNPs in a controlled manner. The His-tagged VLNPs conjugated non-covalently with NTA-DOX, and cross-linked with folic acid (FA) were able to specifically target and deliver the DOX into ovarian cancer cells via folate receptor (FR)-mediated endocytosis. The cytotoxicity and cellular uptake results revealed that the His-tagged VLNPs significantly increased the accumulation of DOX in the ovarian cancer cells and enhanced the uptake of DOX, which improved anti-tumour effects. This study demonstrated that NTA-DOX can be easily displayed on His-tagged VLNPs by a simple Add-and-Display step with high coupling efficiency and the drug was only released at low pH in a controlled manner. This approach facilitates specific attachment of any drug molecule on His-tagged VLNPs at the very mild conditions without changing the biological structure and native conformation of the VLNPs.

Method validation and nanoparticle characterization assays for an innovative amphothericin B formulation to reach increased stability and safety in infectious diseases

Drug Delivery Systems (DDS) of known drugs are prominent candidates towards new and more-effective treatments of various infectious diseases as they may increase drug bioavailability, control drug delivery and target the site of action. In this sense, the encapsulation of Amphotericin B (AmB) in Nanostructured Lipid Carriers (NLCs) designed with pH-sensible phospholipids to target infectious tissues was proposed and suitable analytical methods were validated, as well as, proper nanoparticle characterization were conducted. Characterization assays by Dinamic Light Scattering (DLS) and Atomic Force Microscopy demonstrated spherical particles with nanometric size 268.0±11.8nm and Zeta Potential -42.5±1.5mV suggestive of important stability. DSC/TGA and FT-IR assessments suggested mechanical encapsulation of AmB. The AmB aggregation study indicated that the encapsulation provided AmB at the lowest cytotoxic form, polyaggregate. Analytical methods were developed and validated according to regulatory agencies in order to fast and assertively determine AmB in nanoparticle suspension and, in Drug Encapsulation Efficiency (EE%), release and stability studies. The quantification method for AmB in NLC suspension presented linearity in 5.05-60.60μgmL^-1 range (y=0.07659x+0.05344) and for AmB in receptor solution presented linearity in 0.15-10.00μgmL^-1 range (y=54609x+263.1), both with r≥0.999. EE% was approximately 100% and according to the release results, at pH 7.4, a sustained controlled profile was observed for up 46h. In the meantime, a micellar AmB solution demonstrated an instability pattern after 7h of contact with the medium. Degradation and release studies under acid conditions (infectious condition) firstly depicted a prominent degradation of AmB (raw-material), with 20.3±3.5% at the first hour, reaching 43.3±7.0% after 7h of study. Next, particles faster disruption in acid environment was evidenced by measuring the NLC size variation by DLS and by the loss of the bluish sheen, characteristic of the nanostructured system macroscopically observed. Finally, safety studies depicted that NLC-AmB presented reduced toxicity in fibroblast cells, corroborating with AmB aggregated form study. Therefore, an innovative AmB formulation was fully characterized and it is a new proposal for in vivo investigations.

Asymmetrical Polymer Vesicles for Drug delivery and Other Applications

Scientists have been attracted by polymersomes as versatile drug delivery systems since the last two decades. Polymersomes have the potential to be versatile drug delivery systems because of their tunable membrane formulations, stabilities in vivo, various physicochemical properties, controlled release mechanisms, targeting abilities, and capacities to encapsulate a wide range of drugs and other molecules. Asymmetrical polymersomes are nano- to micro-sized polymeric capsules with asymmetrical membranes, which means, they have different outer and inner coronas so that they can exhibit better endocytosis rate and endosomal escape ability than other polymeric systems with symmetrical membranes. Hence, asymmetrical polymersomes are highly promising as self-assembled nano-delivery systems in the future for in vivo therapeutics delivery and diagnostic imaging applications. In this review, we prepared a summary about recent research progresses of asymmetrical polymersomes in the following aspects: synthesis, preparation, applications in drug delivery and others.

Mussel-inspired poly(L-DOPA)-templated mineralization for calcium phosphate-assembled intracellular nanocarriers

We developed a calcium phosphate (CaP)-assembled polymer nanocarrier for intracellular doxorubicin (DOX) delivery based on a mussel-inspired mineralization approach. A DOX-loaded core-shell polymer nanoparticle (DOX-NP) consisting of a poly(3,4-dihydroxy-l-phenylalanine) (PDOPA) core and a poly (ethylene glycol) (PEG) shell was utilized as a nanotemplate for CaP mineralization. The mean hydrodynamic diameter of the DOX-loaded CaP-mineralized polymer nanoparticles (DOX-CaP-NPs) was 154.3nm. Energy-dispersive X-ray spectroscopy confirmed that the DOX-CaP-NPs contained substantial amounts of Ca and P, elements found only in the CaP mineral. The loading efficiency and content of DOX, estimated by fluorescence spectroscopy, were 54.0% and 10.8wt%, respectively. The CaP deposited in the PDOPA core domain enabled the DOX-CaP-NPs to maintain a robust structure and effectively inhibit DOX release at extracellular pH, whereas at endosomal pH, the CaP core dissolved to trigger a facilitated DOX release. The DOX-CaP-NPs may serve as robust nanocarriers with a high delivery efficacy for cancer chemotherapy.

A quantitative study of the intracellular fate of pH-responsive doxorubicin-polypeptide nanoparticles

Nanoscale carriers with an acid-labile linker between the carrier and drug are commonly used for drug delivery. However, their efficacy is potentially limited by inefficient linker cleavage, and lysosomal entrapment of drugs. To address these critical issues, we developed a new imaging method that spatially overlays the location of a nanoparticle and the released drug from the nanoparticle, on a map of the local intracellular pH that delineates individual endosomes and lysosomes, and the therapeutic intracellular target of the drug-the nucleus. We used this method to quantitatively map the intracellular fate of micelles of a recombinant polypeptide conjugated with doxorubicin via an acid-labile hydrazone linker as a function of local pH and time within live cells. We found that hydrolysis of the acid-labile linker is incomplete because the pH range of 4-7 in the endosomes and lysosomes does not provide complete cleavage of the drug from the nanoparticle, but that once cleaved, the drug escapes the acidic endo-lysosomal compartment into the cytosol and traffics to its therapeutic destination-the nucleus. This study also demonstrated that unlike free drug, which enters the cytosol directly through the cell membrane and then traffics into the nucleus, the nanoparticle-loaded drug almost exclusively traffics into endosomes and lysosomes upon intracellular uptake, and only reaches the nucleus after acid-triggered drug release in the endo-lysosomes. This methodology provides a better and more quantitative understanding of the intracellular behavior of drug-loaded nanoparticles, and provides insights for the design of the next-generation of nanoscale drug delivery systems.

pH-sensitive Au-BSA-DOX-FA nanocomposites for combined CT imaging and targeted drug delivery

Albumin-based nanoparticles (NPs) as a drug delivery system have attracted much attention owing to their nontoxicity, non-immunogenicity, great stability and ability to bind to many therapeutic drugs. Herein, bovine serum albumin (BSA) was utilized as a template to prepare Au–BSA core/shell NPs. The outer layer BSA was subsequently conjugated with cis-aconityl doxorubicin (DOX) and folic acid (FA) to create Au–BSA–DOX–FA nanocomposites. A list of characterizations was undertaken to identify the successful conjugation of drug molecules and targeted agents. In vitro cytotoxicity using a cell counting kit-8 (CCK-8) assay indicated that Au–BSA NPs did not display obvious cytotoxicity to MGC-803 and GES-1 cells in the concentration range of 0–100 μg/mL, which can therefore be used as a safe drug delivery carrier. Furthermore, compared with free DOX, Au–BSA–DOX–FA nanocomposites exhibited a pH-sensitive drug release ability and superior antitumor activity in a drug concentration-dependent manner. In vivo computed tomography (CT) imaging experiments showed that Au–BSA–DOX–FA nanocomposites could be used as an efficient and durable CT contrast agent for targeted CT imaging of the folate receptor (FR) overexpressed in cancer tissues. In vivo antitumor experiments demonstrated that Au–BSA–DOX–FA nanocomposites have selective antitumor activity effects on FR-overexpressing tumors and no adverse effects on normal tissues and organs. In conclusion, the Au–BSA–DOX–FA nanocomposite exhibits selective targeting activity, X-ray attenuation activity and pH-sensitive drug release activity. Therefore, it can enhance CT imaging and improve the targeting therapeutic efficacy of FR-overexpressing gastric cancers. Our findings suggest that Au–BSA–DOX–FA nanocomposite is a novel drug delivery carrier and a promising candidate for cancer theranostic applications.

Polyphosphoramidates That Undergo Acid-Triggered Backbone Degradation

The direct and facile synthesis of polyphosphoramidates (PPAs) with acid-labile phosphoramidate backbone linkages are reported, together with demonstration of their hydrolytic degradability, evaluated under acidic conditions. The introduction of acid-labile linkages along the polymer backbone led to rapid degradation of the polymer backbone dependent upon the environmental stimuli. An oxazaphospholidine monomer bearing a phosphoramidate linkage was designed and synthesized to afford the PPAs via organobase-catalyzed ring-opening polymerization in a controlled manner. The hydrolytic degradation of the PPAs was studied, revealing breakdown of the polymer backbone through cleavage of the phosphoramidate linkages under acidic conditions.

Synergistic chemotherapeutic effect of sorafenib-loaded pullulan-Dox conjugate nanoparticles against murine breast carcinoma

pH-Sensitive pullulan-doxorubicin conjugates encapsulating sorafenib (P-Dox/S) nanoparticles were developed as a synergistic combinatorial delivery system against murine breast carcinoma. The nanoparticles can encapsulate Dox and sorafenib with ultra-high loading capacity (65.34 wt%) through chemical conjugation and physical loading, whereas can remain stable under physiological conditions and gradually release Dox and sorafenib with the decreasing pH. These conjugates can be effectively internalized and clearly suppress 4T1 cell growth in vitro. Furthermore, research data of in vivo animal models revealed that the synergistic combinatorial P-Dox/S nanoparticles heavily accumulated in solid tumor tissue sites to maximize therapeutic efficacy; they also significantly inhibited solid tumor growth, even remarkably reduced solid tumor volume in comparison to the initial volume, and obviously diminished adverse effects. The anti-tumor therapeutic effect obviously outperformed the delivery of combinational chemotherapy of free drugs or single drug-loaded P-Dox nanoparticles at the same concentration. These promising results indicate the high-efficiency synergistic chemotherapeutic effects of these nanoparticles. Combinational chemotherapy using P-Dox/S nanoparticles has important potential in the clinical treatment of malignancy for overcoming drug resistance and heterogeneity.

Targeted delivery and release of doxorubicin using a pH-responsive and self-assembling copolymer

We developed a pH-response copolymer that entrapped DOX into its hydrophobic core and self-assembles into smart DOX-loaded nanoparticles, which could enhance cancer-targeting and effective drug release in tumors.

pH-responsive Virus-like Nanoparticles with Enhanced Tumour-targeting Ligands for Cancer Drug Delivery

Multifunctional nanocarriers harbouring specific targeting moieties and with pH-responsive properties offer great potential for targeted cancer therapy. Several synthetic drug carriers have been studied extensively as drug delivery systems but not much information is available on the application of virus-like nanoparticles (VLNPs) as multifunctional nanocarriers. Here, we describe the development of pH-responsive VLNPs, based on truncated hepatitis B virus core antigen (tHBcAg), displaying folic acid (FA) for controlled drug delivery. FA was conjugated to a pentadecapeptide containing nanoglue bound on tHBcAg nanoparticles to increase the specificity and efficacy of the drug delivery system. The tHBcAg nanoparticles loaded with doxorubicin (DOX) and polyacrylic acid (PAA) demonstrated a sustained drug release profile in vitro under tumour tissue conditions in a controlled manner and improved the uptake of DOX in colorectal cancer cells, leading to enhanced antitumour effects. This study demonstrated that DOX-PAA can be packaged into VLNPs without any modification of the DOX molecules, preserving the pharmacological activity of the loaded DOX. The nanoglue can easily be used to display a tumour-targeting molecule on the exterior surface of VLNPs and can bypass the laborious and time-consuming genetic engineering approaches.

Tumor microenvironment-responsive micelles for pinpointed intracellular release of doxorubicin and enhanced anti-cancer efficiency

Internal stimuli, such as intracellular lysosomal pH, enzyme, redox and reduction, can be applied to improve biological specificity of chemotherapeutic drugs for cancer therapy. Thus, functionalized copolymers based on their response to specific microenvironment of tumor regions have been designed as smart drug vesicles for enhanced anti-cancer efficiency and reduced side effects. Herein, we reported dually pH/reduction-responsive novel micelles based on self-assembly of carboxymethyl chitosan-cysteamine-N-acetyl histidine (CMCH-SS-NA) and doxorubicin (DOX). The tailor-made dually responsive micelles demonstrated favorable stability in normal physiological environment and triggered rapid drug release in acidic and/or reduction environment. Additionally, the nanocarriers responded to the intracellular environment in an ultra-fast manner within several minutes, which led to the pinpointed release of DOX in tumor cells effectively and ensured higher DOX concentrations within tumor areas with the aid of targeted delivery, thereby leading to enhanced tumor ablation. Thus, this approach with sharp drug release behavior represented a versatile strategy to provide a promising paradigm for cancer therapy.

Ammonium salt modified mesoporous silica nanoparticles for dual intracellular-responsive gene delivery

Effective gene delivery system plays an importmant role in the gene therapy. Mesoporous silica nanoparticle (MSN) has become one potential gene delivery vector because of its high stability, good biodegradability and low cytotoxicity. Herein, MSN-based dual intracellular responsive gene delivery system CMSN-A was designed and fabricated. Short chain ammonium group, which is modified with disulfide bond and amide bond simultaneously, is facilely grafted onto the mesoporous silica nanoparticles. As-synthesized CMSN-A is endowed with small size (80-110nm), large conical pores (15-23nm), and moderate Zeta potential (+25±2mV), which behaves high gene loading capacity, good stability and effectively gene transfection. Moreover, CMSN-A exhibits dual micro-environment responsive (lower pH, more reducing substances) due to the redox-sensitive disulfide bond and pH-sensitive amide bond in the short chain ammonium group. The cellular uptake study indicates that CMSN-A could transfer both plasmid DNA (pDNA) and siRNA into different kinds of tumour cells, which demonstrate the promising potential of CMSN-A as effective and safe gene-delivery vectors.

The Smart Drug Delivery System and Its Clinical Potential

With the unprecedented progresses of biomedical nanotechnology during the past few decades, conventional drug delivery systems (DDSs) have been involved into smart DDSs with stimuli-responsive characteristics. Benefiting from the response to specific internal or external triggers, those well-defined nanoplatforms can increase the drug targeting efficacy, in the meantime, reduce side effects/toxicities of payloads, which are key factors for improving patient compliance. In academic field, variety of smart DDSs have been abundantly demonstrated for various intriguing systems, such as stimuli-responsive polymeric nanoparticles, liposomes, metals/metal oxides, and exosomes. However, these nanoplatforms are lack of standardized manufacturing method, toxicity assessment experience, and clear relevance between the pre-clinical and clinical studies, resulting in the huge difficulties to obtain regulatory and ethics approval. Therefore, such relatively complex stimulus-sensitive nano-DDSs are not currently approved for clinical use. In this review, we highlight the recent advances of smart nanoplatforms for targeting drug delivery. Furthermore, the clinical translation obstacles faced by these smart nanoplatforms have been reviewed and discussed. We also present the future directions and perspectives of stimuli-sensitive DDS in clinical applications.

Phosphorus and Nitrogen Dual-Doped Hollow Carbon Dot as a Nanocarrier for Doxorubicin Delivery and Biological Imaging

Innovative phosphorus and nitrogen dual-doped hollow carbon dots (PNHCDs) have been fabricated for anticancer drug delivery and biological imaging. The functional groups of PNHCDs are introduced by simply mixing glucose, 1,2-ethylenediamine, and concentrated phosphoric acid. This is an automatic method without external heat treatment to rapidly produce large quantities of PNHCDs, which avoid high temperature, complicated operations, and long reaction times. The as-prepared PNHCDs possess small particle size, hollow structure, and abundant phosphate/hydroxyl/pyridinic/pyrrolic-like N groups, endowing PNHCDs with fluorescent properties, improving the accuracy of PNHCDs as an optical monitoring code both in vitro and in vivo. The investigation of PNHCDs as an anticancer drug nanocarrier for doxorubicin (DOX) indicates a better antitumor efficacy than free DOX owing to its enhanced nuclear delivery in vitro and tumor accumulation in vivo, which results in highly effective tumor growth inhibition and improved targeted therapy for cancer in clinical medicine.