One-pot conversion of RAFT-generated multifunctional block copolymers of HPMA to doxorubicin conjugated acid- and reductant-sensitive crosslinked micelles

ThermOxshield ion pair self assembly unleashing suppressed release

Poly (acrylic acid) (PAA), an anionic polymer was used to prepare ion pair self-assembly (IPSAM) with 4-(methylthio)aniline (MTA), a hydrophobic counter ion, which is responsive to temperature and oxidation. The IPSAM was formed when the carboxylic to amino group molar ratio was 7/3-5/5. The structure of the IPSAM nanoparticle was spherical whose diameter was 30-40 nm on the TEM images. The PAA/MTA ion pair showed the upper critical solution temperature (UCST) that hiked with increasing MTA content. When the MTA of the ion pair was oxidized by H2O2, the UCST was also increased. The amphiphilic property of the ion pair was responsible for interface activity which declined upon the oxidation of the MTA. The surface tension was low for the ratio of PAA/MTA (5/5), which made the 5/5 ratio suitable for further studies. The interaction between PAA and MTA, which was ionic, and the oxidation of MTA was confirmed by FT-IR spectroscopy. The release of payload (i.e. Nile red) in IPSAM was restrained below the UCST but it was triggered above the phase transition temperature possibly due to the disintegration of the IPSAM whereas on MTA oxidation the release was shielded due to more hydrophobicity. The release was found to be higher in tumor environment temperature which could be controlled with the input concentration of H2O2 giving a stable IPSAM. The cell viability results showed that IPSAM has no significant cytotoxicity and can serve as a drug carrier for stimulus-response.

Drug Delivery Approaches to Improve Tendon Healing

Tendon injuries disrupt the transmission of forces from muscle to bone, leading to chronic pain, disability, and a large socioeconomic burden. Tendon injuries are prevalent; there are over 300,000 tendon repair procedures a year in the United States to address acute trauma or chronic tendinopathy. Successful restoration of function after tendon injury remains challenging clinically. Despite improvements in surgical and physical therapy techniques, the high complication rate of tendon repair procedures motivates the use of therapeutic interventions to augment healing. While many biological and tissue engineering approaches have attempted to promote scarless tendon healing, there is currently no standard clinical treatment to improve tendon healing. Moreover, the limited efficacy of systemic delivery of several promising therapeutic candidates highlights the need for tendon-specific drug delivery approaches to facilitate translation. This review article will synthesize the current state-of-the-art methods that have been used for tendon-targeted delivery through both systemic and local treatments, highlight emerging technologies used for tissue-specific drug delivery in other tissue systems, and outline future challenges and opportunities to enhance tendon healing through targeted drug delivery.

Synthesis of Degradable Polyolefins Bearing Disulfide Units via Metathesis Copolymerization

Disulfide bonds are dynamic covalent bonds, which are easy to cleave and reform upon chemical stimulus. Various methods including the oxidative coupling of thiols and polymerization of disulfide-containing monomers have been developed for the synthesis of poly(disulfide)s. However, installing small amounts of disulfide units in the main chain of polyolefins has received much less attention. Herein, we report a novel strategy for incorporating cleavable disulfide units into the backbone of polyolefins using commercially available diallyl disulfide (DADS) as a comonomer via metathesis copolymerization. The copolymerization of diallyl disulfide with cyclooctene occurred using the second-generation Grubbs catalyst under mild conditions, allowing for the synthesis of copolymers with adjustable disulfide content ranging from 0.7 to 8.5 mol%, and the molecular weight of the obtained copolymers ranged from 5.8 kg·mol^-1 to 42.8 kg·mol^-1. The resulting polyolefins with disulfide insertion retained excellent thermal processability and exhibited degradability. Treatment of the copolymer (8.5 mol% disulfide content) with tri-n-butylphosphine resulted in a significant reduction in molecular weight from 5.8 kg·mol^-1 to 1.6 kg·mol^-1. Successful copolymerization with diallyl disulfide provides a convenient and effective method for obtaining degradable polyolefins.

Core-crosslinked, temperature- and pH-responsive micelles: design, physicochemical characterization, and gene delivery application

Stimuli-responsive block copolymer micelles can provide tailored properties for the efficient delivery of genetic material. In particular, temperature- and pH-responsive materials are of interest, since their physicochemical properties can be easily tailored to meet the requirements for successful gene delivery. Within this study, a stimuli-responsive micelle system for gene delivery was designed based on a diblock copolymer consisting of poly(N,N-diethylacrylamide) (PDEAm) as a temperature-responsive segment combined with poly(aminoethyl acrylamide) (PAEAm) as a pH-responsive, cationic segment. Upon temperature increase, the PDEAm block becomes hydrophobic due to its lower critical solution temperature (LCST), leading to micelle formation. Furthermore, the monomer 2-(pyridin-2-yldisulfanyl)ethyl acrylate (PDSAc) was incorporated into the temperature-responsive PDEAm building block enabling disulfide crosslinking of the formed micelle core to stabilize its structure regardless of temperature and dilution. The cloud points of the PDEAm block and the diblock copolymer were investigated by turbidimetry and fluorescence spectroscopy. The temperature-dependent formation of micelles was analyzed by dynamic light scattering (DLS) and elucidated in detail by an analytical ultracentrifuge (AUC), which provided detailed insights into the solution dynamics between polymers and assembled micelles as a function of temperature. Finally, the micelles were investigated for their applicability as gene delivery vectors by evaluation of cytotoxicity, pDNA binding, and transfection efficiency using HEK293T cells. The investigations showed that core-crosslinking resulted in a 13-fold increase in observed transfection efficiency. Our study presents a comprehensive investigation from polymer synthesis to an in-depth physicochemical characterization and biological application of a crosslinked micelle system including stimuli-responsive behavior.

Nanomedicine from amphiphilizedprodrugs: Concept and clinical translation

Nanomedicines generally consisting of carrier materials with small fractions of active pharmaceutical ingredients (API) have long been used to improve the pharmacokinetics and biodistributions, augment the therapeutic efficacies and mitigate the side effects. Amphiphilizing hydrophobic/hydrophilic drugs to prodrugs capable of self-assembly into well-defined nanostructures has emerged as a facile approach to fabricating nanomedicines because this amphiphilized prodrug (APD) strategy presents many advantages, including minimized use of inert carrier materials, well-characterized prodrug structures, fixed and high drug loading contents, 100% loading efficiency, and burst-free but controlled drug release. This review comprehensively summarizes recent advances in APDs and their nanomedicines, from the rationale and the stimuli-responsive linker chemistry for on-demand drug release to their progress to the clinics, clinical performance of APDs, as well as the challenges and perspective on future development.

HER2-Targeted, Degradable Core Cross-Linked Micelles for Specific and Dual pH-Sensitive DOX Release

Here, a targeted, dual-pH responsive, and stable micelle nanocarrier is designed, which specifically selects an HER2 receptor on breast cancer cells. Intracellularly degradable and stabilized micelles are prepared by core cross-linking via reversible addition-fragmentation chain-transfer (RAFT) polymerization with an acid-sensitive cross-linker followed by the conjugation of maleimide-doxorubicin to the pyridyl disulfide-modified micelles. Multifunctional nanocarriers are obtained by coupling HER2-specific peptide. Formation of micelles, addition of peptide and doxorubicin (DOX) are confirmed structurally by spectroscopical techniques. Size and morphological characterization are performed by Zetasizer and transmission electron microscope (TEM). For the physicochemical verification of the synergistic acid-triggered degradation induced by acetal and hydrazone bond degradation, Infrared spectroscopy and particle size measurements are used. Drug release studies show that DOX release is accelerated at acidic pH. DOX-conjugated HER2-specific peptide-carrying nanocarriers significantly enhance cytotoxicity toward SKBR-3 cells. More importantly, no selectivity toward MCF-10A cells is observed compared to HER2(+) SKBR-3 cells. Formulations cause apoptosis depending on Bax and Caspase-3 and cell cycle arrest in G2 phase. This study shows a novel system for HER2-targeted therapy of breast cancer with a multifunctional nanocarrier, which has higher stability, dual pH-sensitivity, selectivity, and it can be an efficient way of targeted anticancer drug delivery.

HPMA Copolymer-Based Nanomedicines in Controlled Drug Delivery

Recently, numerous polymer materials have been employed as drug carrier systems in medicinal research, and their detailed properties have been thoroughly evaluated. Water-soluble polymer carriers play a significant role between these studied polymer systems as they are advantageously applied as carriers of low-molecular-weight drugs and compounds, e.g., cytostatic agents, anti-inflammatory drugs, antimicrobial molecules, or multidrug resistance inhibitors. Covalent attachment of carried molecules using a biodegradable spacer is strongly preferred, as such design ensures the controlled release of the drug in the place of a desired pharmacological effect in a reasonable time-dependent manner. Importantly, the synthetic polymer biomaterials based on N-(2-hydroxypropyl) methacrylamide (HPMA) copolymers are recognized drug carriers with unique properties that nominate them among the most serious nanomedicines candidates for human clinical trials. This review focuses on advances in the development of HPMA copolymer-based nanomedicines within the passive and active targeting into the place of desired pharmacological effect, tumors, inflammation or bacterial infection sites. Specifically, this review highlights the safety issues of HPMA polymer-based drug carriers concerning the structure of nanomedicines. The main impact consists of the improvement of targeting ability, especially concerning the enhanced and permeability retention (EPR) effect.

Therapeutic Delivery of Polymeric Tadpole Nanostructures with High Selectivity to Triple Negative Breast Cancer Cells

Targeted delivery of therapeutic drugs using nanoparticles to the highly aggressive triple negative breast cancer cells has the potential to reduce side effects and drug resistance. Cell entry into triple negative cells can be enhanced by incorporating cell binding receptor molecules on the surface of the nanoparticles to enhance receptor-mediated entry pathways, including clatherin or caveolae endocytosis. However, for highly aggressive cancer cells, these pathways may not be effective, with the more rapid and high volume uptake from macropinocytosis or phagocytosis being significantly more advantageous. Here we show, in the absence of attached cell binding receptor molecules, that asymmetric polymer tadpole nanostructure coated with a thermoresponsive poly(N-isopropylacrylamide) polymer with approximately 50% of this polymer in a globular conformation resulted in both high selectivity and rapid uptake into the triple breast cancer cell line MDA-MB-231. We found that the poly(N-isopropylacrylamide) surface coating in combination with the tadpole's unique shape had an almost 15-fold increase in cell uptake compared to spherical particles with the same polymer coating, and that the mode of entry was most likely through phagocytosis. Delivery of the tadpole attached with doxorubicin (a prodrug, which can be released at pHs < 6) showed a remarkable 10-fold decrease in the IC₅₀ compared to free doxorubicin. It was further observed that cell death was primarily through late apoptosis, which may allow further protection from the body's own immune system. Our results demonstrate that by tuning the chemical composition, polymer conformation and using an asymmetric-shaped nanoparticle, both selectivity and effective delivery and release of therapeutics can be achieved, and such insights will allow the design of nanoparticles for optimal cancer outcomes.

Dual Reduction/Acid-Responsive Disassembly and Thermoresponsive Tunability of Degradable Double Hydrophilic Block Copolymer

We report a thermoresponsive double hydrophilic block copolymer degradable in response to dual reduction and acidic pH at dual locations. The copolymer consists of a poly(ethylene oxide) block covalently connected through an acid-labile acetal linkage with a thermoresponsive polymethacrylate block containing pendant oligo(ethylene oxide) and disulfide groups. The copolymer undergoes temperature-driven self-assembly in water to form nanoassemblies with acetal linkages at the core/corona interface and disulfide pendants in the core, exhibiting dual reduction/acid responses at dual locations. The physically assembled nanoaggregates are converted to disulfide-core-crosslinked nanogels through disulfide-thiol exchange reaction, retaining enhanced colloidal stability, yet degraded to water-soluble unimers upon reduction/acid-responsive degradation. Further, the copolymer exhibits improved tunability of thermoresponsive property upon the cleavage of junction acetal and pendant disulfide linkages individually and in combined manner. This work suggests that dual location dual reduction/acid-responsive degradation is a versatile strategy toward effective drug delivery exhibiting disulfide-core-crosslinking capability and disassembly as well as improved thermoresponsive tunability.

Pyridyl disulfide-based thiol–disulfide exchange reaction: shaping the design of redox-responsive polymeric materials

This review provides an overview of synthetic approaches utilized to incorporate the thiol-reactive pyridyl-disulfide motif into various polymeric materials, and briefly highlights its utilization to obtain functional materials.

Low density lipoprotein-inspired nanostructured lipid nanoparticles containing pro-doxorubicin to enhance tumor-targeted therapeutic efficiency

Inefficient tumor accumulation and controlling drug release at the tumor site are two major obstacles limiting the antitumor efficacy of nanoparticle delivery systems. Inspired by the biological structure and function of low-density lipoprotein (LDL), a pH-sensitive ApoB-100/Oleic acid-DOX/NLC (AODN) nanoparticle based on nanostructured lipid carrier (NLC) was prepared in this study. The biological composition of ApoB-containing NLC nanoparticles is similar to that of LDL, which can effectively increase the cycle time and targeting efficiency of nanoparticles. Meantime, the doxorubicin prodrug strategy was used to increase the drug loading of the nanoparticles and achieve drug-sensitive release. In vitro results indicated that AODN nanoparticles can cause more drugs to be phagocytosed by LDL receptor-mediated endocytosis, thus showing high cytotoxicity in 4T1 cells. In vivo experiments have shown that pH-sensitive AODN nanoparticles can cause more drugs to accumulate in the tumor site, reducing systemic toxicity and effectively inhibiting orthotopic breast cancer. These data provide strong evidence that the strategy of combining bionics and prodrug technology provides a new approach to improving the efficiency of chemotherapy drugs in cancer treatment. STATEMENT OF SIGNIFICANCE: Inefficient tumor accumulation and controlling drug release at the tumor site are two major obstacles limiting the antitumor efficacy of nanoparticle delivery systems. Inspired by low density lipoprotein, a pH-sensitive ApoB-100/oleic acid-DOX/NLC (AODN) nanoparticle based on nanostructured lipid carrier (NLC) was prepared. Its biological composition is similar to that of LDL, which can effectively increase the cycle time and targeting efficiency of drugs. Then, the doxorubicin prodrug strategy was used to increase the drug loading of the nanoparticles and achieve drug-sensitive release. AODN nanoparticles can effectively inhibit tumor by effectively accumulating at tumor site and controlling release. The strategy of combining bionics and prodrug technology provides a new approach to improving the efficiency of chemotherapy drugs in cancer treatment.

Enhanced intracellular and intranuclear drug delivery mediated by biomimetic peptide SVS-1 for anticancer therapy

Tumor cell nucleus is the ultimate target of many first-line chemotherapeutics and therapeutic genes. However, nuclear drug delivery is always hampered by multiple intracellular obstacles especially low efficiency of cellular uptake and insufficient nuclear trafficking. It is urgent to establish novel nuclear drug delivery systems to simultaneously overcome barriers including cell membranes and nuclear envelope. Herein, an N-(2-hydroxypropyl) methacrylamide (HPMA) polymer-based drug delivery system was designed to achieve enhanced intracellular and intranuclear drug delivery. A biomimetic peptide (SVS-1), derived from antimicrobial peptides, which was reported to efficiently penetrate cell membranes and translocate rapidly into nucleus without decreasing cell viability, was conjugated to the HPMA copolymer backbone. The in vitro studies showed that SVS-1 could enhance the uptake and nuclei accumulation of HPMA copolymer by 4.1 and 7.0-fold on human cervical cancer cells (HeLa) separately compared with corresponding non-SVS-1 modified HPMA copolymers (P-DOX). This also transferred to greater DNA damage, more apoptosis and superior cytotoxicity (2.4-fold) of doxorubicin which was chosen as the model drug and attached to SVS-1 modified HPMA copolymer (SVS-1-P-DOX). Furthermore, the in vivo investigation revealed that compared with free doxorubicin, SVS-1-P-DOX not only showed prolonged blood circulation and preferential tumor accumulation, but also suppressed tumor growth more efficiently with tumor growth inhibition of 78.7% in HeLa tumor-bearing BALB/c nude mice without causing noticeable physiological change in major organs. These results demonstrated that the SVS-1 modification was a promising strategy for contemporaneously overcome cell membranes and nuclear envelope, which might provide new opportunities for constructing nucleus-targeted anticancer therapy.

Block copolymer prodrugs: Synthesis, self-assembly, and applications for cancer therapy

Block copolymer prodrugs (BCPs) have emerged as one of the most promising anticancer drug delivery strategies, which can self-assemble into nanoparticles with optimal physicochemical properties including sizes, morphologies, surface properties, and integration of multifunction for improved in vivo applications. Moreover, the utility of stimuli-responsive linkages to conjugate drugs onto the polymer backbones can achieve efficient and targeting drug release. Several BCP micellar delivery systems have been pushed ahead into the clinical trials, which showed great promising potentials for cancer therapy. In recent years, various novel and more efficient BCP systems have been developed for better in vivo performance. In this focus article, we focus on the recent advances of BCPs including the synthesis, self-assembly, and applications for cancer therapy. The synthetic methods are first introduced, and the self-assembly of BCPs for in vivo anticancer applications is discussed along the line of varying endogenous stimuli-responsive linkages including amide or ester bonds, pH, reduction, and oxidation-responsive linkages. Finally, conclusions along with the brief future perspectives are presented. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Nanotechnology Approaches to Biology > Nanoscale Systems in Biology.

Disassembly and tumor-targeting drug delivery of reduction-responsive degradable block copolymer nanoassemblies

Review on recent strategies to synthesize novel disulfide-containing reductively-degradable block copolymers and their nanoassemblies as being classified with the number, position, and location of the disulfide linkages toward effective tumor-targeting intracellular drug delivery exhibiting enhanced release of encapsulated drugs.

Designing Smart Polymer Conjugates for Controlled Release of Payloads

Incorporating labile bonds inside polymer backbone and side chains yields interesting polymer materials that are responsive to change of environmental stimuli. Drugs can be conjugated to various polymers through different conjugation linkages and spacers. One of the key factors influencing the release profile of conjugated drugs is the hydrolytic stability of the conjugated linkage. Generally, the hydrolysis of acid-labile linkages, including acetal, imine, hydrazone, and to some extent β-thiopropionate, are relatively fast and the conjugated drug can be completely released in the range of several hours to a few days. The cleavage of ester linkages are usually slow, which is beneficial for continuous and prolonged release. Another key structural factor is the water solubility of polymer-drug conjugates. Generally, the release rate from highly water-soluble prodrugs is fast. In prodrugs with large hydrophobic segments, the hydrophobic drugs are usually located in the hydrophobic core of micelles and nanoparticles, which limits the access to the water, hence lowering significantly the hydrolysis rate. Finally, self-immolative polymers are also an intriguing new class of materials. New synthetic pathways are needed to overcome the fact that much of the small molecules produced upon degradation are not active molecules useful for biomedical applications.

Dendrons and Multiarm Polymers with Thiol-Exchangeable Cores: A Reversible Conjugation Platform for Delivery

Disulfide exchange reaction has emerged as a powerful tool for reversible conjugation of proteins, peptides and thiol containing molecules to polymeric supports. In particular, the pyridyl disulfide group provides an efficient handle for the site-specific conjugation of therapeutic peptides and proteins bearing cysteine moieties. In this study, novel biodegradable dendritic platforms containing a pyridyl disulfide unit at their focal point were designed. Presence of hydroxyl groups at the periphery of these dendrons allows their elaboration to multivalent initiators that yield poly(ethylene glycol) based multiarm star polymers via controlled radical polymerization. The pyridyl disulfide unit at the core of these star polymers undergoes efficient reaction with thiol functional group containing molecules such as a hydrophobic dye, namely, Bodipy-SH, glutathione, and KLAK sequence containing peptide. While conjugation of the hydrophobic fluorescent dye to the PEG-based multiarm polymer renders it water-soluble, it can be cleaved off the construct through thiol-disulfide exchange in the presence of an external thiol such as dithiothreitol. The multiarm polymer was conjugated with a thiol group containing apoptotic peptide to increase its solubility and cellular transport. In vitro cytotoxicity and apoptosis assays demonstrated that the resultant peptide-polymer conjugate had almost five times more apoptotic potential primarily through triggering apoptosis by disrupting mitochondrial membranes of human breast cancer cell line (MDA-MB-231) compared to naked peptide. The novel dendritic platform disclosed here offers an attractive template that can be modified to multiarm polymeric constructs bearing a "tag and release" characteristic.

Legumain-cleavable 4-arm poly(ethylene glycol)-doxorubicin conjugate for tumor specific delivery and release

Traditional chemotherapy strategy exists undesirable toxic side-effects to normal tissues due to the low selectively to cancer cells of micromolecule cytotoxic drugs. One considered method to realizing the targeted delivery and increasing the specificity to tumor tissues of the cytotoxic drug is to transporting and discharging it through an environment-sensitive mechanism. In this study, a novel enzyme-sensitive polymer-doxorubicin conjugate was designed to delivery chemotherapeutic drug in a tumor-specific behavior and selectively activated in tumor tissue. Briefly, doxorubicin (DOX) was conjugated to carboxyl-terminated 4-arm poly(ethylene glycol) through a tetrapeptide linker, alanine-alanine-asparagine-leucine (AANL), which was one of the substrates of legumain, an asparaginyl endopeptidase that was found presented in plants, mammals and also highly expressed in human tumor tissues. Hereinafter, the polymer-DOX conjugate was termed as 4-arm PEG-AANL-DOX. Dynamic laser scattering (DLS) and transmission electron microscopy (TEM) measurements indicated that the 4-arm PEG-AANL-DOX could self-assemble into micelles in aqueous solution. Drug release and in vitro cytotoxicity studies revealed that the 4-arm PEG-AANL-DOX could be cleaved by legumain. Ex vivo DOX fluorescence imaging measurements demonstrated that the 4-arm PEG-AANL-DOX had an improved tumor-targeting delivery as compared with the free DOX·HCl. In vivo studies on nude mice bearing MDA-MB-435 tumors revealed that the 4-arm PEG-AANL-DOX had a comparable anticancer efficacy with the free DOX·HCl but without DOX-related toxicities to normal tissues as measured by body weight change and histological assessments, indicating that the 4-arm PEG-AANL-DOX had an improved therapeutic index for cancer therapy.

STATEMENT OF SIGNIFICANCE

Herein we describe the construction of a novel tumor environment-sensitive delivery system through the instruction of a legumain-cleavable linkage to a polymer-DOX conjugate (4-arm PEG-AANL-DOX). This particular design strategy allows for polymer-DOX conjugates to be delivered in a tumor-specific manner and selectively activable in tumor microenvironment so that it can combine the advantages of tumor-specific delivery and tumor intracellular microenvironment-triggered release systems.

A multi-stimuli responsive nanoparticulate SN38 prodrug for cancer chemotherapy

Modification of drug delivery systems (DDSs) with stimuli-responsive elements could significantly increase the tumor-specific delivery of anticancer drugs.

Lysosome-oriented, dual-stage pH-responsive polymeric micelles for β-Lapachone delivery

β-Lapachone (β-lap), a novel anticancer agent, is bioactivated by NADP(H):quinone oxidoreductase 1 (NQO1), an enzyme over-expressed in numerous tumors, including lung, pancreas, breast, and prostate cancers. Fast renal clearance and methemaglobinemia / hemolytic side-effects from the clinical formulation (β-lap-hydroxyl propyl-β-cyclodextrin complex) hindered its clinical translation. Here, we investigated a dual model pH responsive polymers for β-lap delivery. Three pH-sensitive linkages, including acylhydrazone, ketal and imine bonds for β-lap prodrug syntheses result in an aryl imine linkage the most optimal linkage. The conversion to β-lap was 2.8%, 4.5% and 100% at pH 7.4, 6.5 and 5.0 in 8 h, respectively. β-lap aryl imine prodrug conjugated ultra pH-sensitive (UPS) polymer reached high β-lap loading density (8.3%) and exhibited dual-stages responsiveness to pH variation. In pHs under pHt, at stage I, micelle immediately dissociation and subsequently entering stage II, micelles start quickly release β-lap. In vitro release study showed that the micelles constantly release β-lap (14.9 ± 0.1%) at pHs above pHt in 72 h, whereas boosted release of β-lap (79.4 ± 1.2%) at pH 5.0. Micelle intracellular distribution predominantly in the lysosome organelle guaranteed their pH responsive dissociation and subsequently β-lap controlled release. The M-P micelles retained NQO1-dependent cytotoxicity in A549 lung cancer cells, similar to free drug in both efficacy and mechanism of cell death. The lysosome-oriented dual-stage ultra pH responsive β-lap prodrug micelles potentially offer an alternative nanotherapeutic strategy for lung, as well as other NQO1+ cancer therapies.

Recent Developments in Active Tumor Targeted Multifunctional Nanoparticles for Combination Chemotherapy in Cancer Treatment and Imaging

Nanotechnology and combination therapy are two major fields that show great promise in the treatment of cancer. The delivery of drugs via nanoparticles helps to improve drug's therapeutic effectiveness while reducing adverse side effects associated wifh high dosage by improving their pharmacokinetics. Taking advantage of molecular markers over-expressing on tumor tissues compared to normal cells, an "active" molecular marker targeted approach would be-beneficial for cancer therapy. These actively targeted nanoparticles would increase drug concentration at the tumor site, improving efficacy while further reducing chemo-resistance. The multidisciplinary approach may help to improve the overall efficacy in cancer therapy. This review article summarizes recent developments of targeted multifunctional nanoparticles in the delivery, of various drugs for a combinational chemotherapy approach to cancer treatment and imaging.

Facile construction of dual-bioresponsive biodegradable micelles with superior extracellular stability and activated intracellular drug release

It is still a major challenge for targeted cancer chemotherapy to design stable biodegradable micellar drug delivery systems which show a rapid and complete intracellular drug release. Here, reversibly core-crosslinked pH-responsive biodegradable micelles were developed based on poly(ethylene glycol)-poly(2,4,6-trimethoxybenzylidene-pentaerythritol carbonate-co-pyridyl disulfide carbonate) [PEG-P(TMBPEC-co-PDSC)] copolymers and investigated for intracellular doxorubicin (DOX) release. PEG-P(TMBPEC-co-PDSC) copolymers formed micelles with a small size of 58.6nm were readily crosslinked by the addition of dithiothreitol (DTT). Notably, in vitro release studies showed that under physiological conditions only ca. 19.9% of DOX was released from the reversibly crosslinked micelles in 24h at a low micelle concentration of 40μg/mL. The release of DOX was accelerated at pH5.0 or in the presence of 10mM glutathione (GSH) at pH7.4, in which 64.2% and 44.1% of DOX was released, respectively, in 24h. The drug release was further boosted at pH5.0 and 10mM GSH, with 98.8% of DOX released in 12h. Moreover, DOX release was also facilitated by a 4h incubation at pH5.0 followed by incubation at pH7.4 with 10mM GSH. Confocal microscopy indicated that DOX was delivered and released into the nuclei of RAW 264.7 cells following a 12h incubation with DOX-loaded reversibly crosslinked micelles. MTT assays revealed that DOX-loaded reversibly crosslinked micelles had much higher antitumor activity than irreversibly crosslinked controls, with low IC50 values of 1.65 and 1.14μg/mL for HeLa and RAW 264.7 cells, respectively, following a 48h incubation. The blank crosslinked micelles had a low cytotoxicity of up to a concentration of 0.8mg/mL. These reversibly crosslinked pH-sensitive biodegradable micelles with superior extracellular stability but activated intracellular drug release provide a novel platform for tumor-targeting drug delivery.

Polymeric micelles with stimuli-triggering systems for advanced cancer drug targeting

Since the 1990s, nanoscale drug carriers have played a pivotal role in cancer chemotherapy, acting through passive drug delivery mechanisms and subsequent pharmaceutical action at tumor tissues with reduction of adverse effects. Polymeric micelles, as supramolecular assemblies of amphiphilic polymers, have been considerably developed as promising drug carrier candidates, and a number of clinical studies of anticancer drug-loaded polymeric micelle carriers for cancer chemotherapy applications are now in progress. However, these systems still face several issues; at present, the simultaneous control of target-selective delivery and release of incorporated drugs remains difficult. To resolve these points, the introduction of stimuli-responsive mechanisms to drug carrier systems is believed to be a promising approach to provide better solutions for future tumor drug targeting strategies. As possible trigger signals, biological acidic pH, light, heating/cooling and ultrasound actively play significant roles in signal-triggering drug release and carrier interaction with target cells. This review article summarizes several molecular designs for stimuli-responsive polymeric micelles in response to variation of pH, light and temperature and discusses their potentials as next-generation tumor drug targeting systems.

Core-Crosslinked Polymeric Micelles: Principles, Preparation, Biomedical Applications and Clinical Translation

Polymeric micelles (PM) are extensively used to improve the delivery of hydrophobic drugs. Many different PM have been designed and evaluated over the years, and some of them have steadily progressed through clinical trials. Increasing evidence suggests, however, that for prolonged circulation times and for efficient EPR-mediated drug targeting to tumors and to sites of inflammation, PM need to be stabilized, to prevent premature disintegration. Core-crosslinking is among the most popular methods to improve the in vivo stability of PM, and a number of core-crosslinked polymeric micelles (CCPM) have demonstrated promising efficacy in animal models. The latter is particularly true for CCPM in which (pro-) drugs are covalently entrapped. This ensures proper drug retention in the micelles during systemic circulation, efficient drug delivery to pathological sites via EPR, and tailorable drug release kinetics at the target site. We here summarize recent advances in the CCPM field, addressing the chemistry involved in preparing them, their in vitro and in vivo performance, potential biomedical applications, and guidelines for efficient clinical translation.

Dual-stimuli sensitive keratin graft PHPMA as physiological trigger responsive drug carriers

Keratin graft PHPMA copolymers were successfully synthesized and can be used as drug carriers with physiological stimuli responsive properties.

Fluorophore labeling of core-crosslinked polymeric micelles for multimodal in vivo and ex vivo optical imaging

AIM

To enable multimodal in vivo and ex vivo optical imaging of the biodistribution and tumor accumulation of core-crosslinked polymeric micelles (CCPMs).

MATERIALS & METHODS

mPEG-b-p(HPMAm-Lac)-based polymeric micelles, core-crosslinked via cystamine and covalently labeled with two different fluorophores (Dy-676/488), were synthesized. The CCPMs were intravenously injected into CT26 tumor-bearing mice.

RESULTS

Upon intravenous injection, the CCPMs accumulated in CT26 tumors reasonably efficiently, with values reaching approximately 4%ID at 24 h. Ex vivo two-photon laser scanning microscopy confirmed efficient extravasation of the image-guided CCPMs out of tumor blood vessels and relatively deep penetration into the tumor interstitium.

CONCLUSION

CCPMs were labeled with multiple fluorophores, and the results obtained exemplify that combining several different in vivo and ex vivo optical imaging techniques is highly useful for analyzing the biodistribution and tumor accumulation of nanomedicines.

“AND” logic gate regulated pH and reduction dual-responsive prodrug nanoparticles for efficient intracellular anticancer drug delivery

A copper ion-based core-cross-linking strategy is used to develop an AND logic gate regulated pH-/reduction-responsive antitumor drug delivery system.

In vitro study of a pH-sensitive multifunctional doxorubicin–gold nanoparticle system: therapeutic effect and surface enhanced Raman scattering

A pH-sensitive multifunctional doxorubicin–gold nanoparticle drug delivery system, which has the potential to detect and treat tumors, was developed.

Efficient reduction and pH co-triggered DOX-loaded magnetic nanogel carrier using disulfide crosslinking

To reduce leakage on the drug-delivery pathway to minimize side effect of reduction or pH sensitive drug delivery systems, we designed a glutathione (GSH)/pH co-triggered magnetic nanogel drug delivery system for doxorubicin (DOX) based on the GSH concentration and pH difference between intracellular and extracellular environments. The introduction of superparamagnetic iron oxide nanoparticles (SPION) was intended for magnetic targeting. The magnetic DOX-loaded nanogel was then prepared by the oxidation of thiolated alginate with thiolated SPION in the presence of DOX. The nanogel size can be readily regulated in a range of 120-320 nm upon preparation conditions, with a negative surface charge of around -40 mV. Saturation magnetization was estimated at 27.4 emu/g Fe by VSM. In vitro release was conducted in simulated cancerous environment conditions such as a high GSH concentration and mild acidity. As a result, the nanogel expressed, upon dual stimuli of pH 5/10 mM GSH, significantly higher accumulative release than upon single stimulus of pH 5 without GSH or pH 7.4/10 mM GSH. In vitro cytotoxicity against HeLa cells clearly illustrated that the nanogel could effectively inhibit cell growth, and the IC50 was figured out to be 2.3 μg/mL of the nanogel, while the nanogel exclusive of DOX was nontoxic. Confocal laser scanning microscopy observation, combined with the result of Prussian blue staining, indicated that DOX was efficiently internalized into HeLa cells through endocytosis, released into the cytoplasm, and then principally entered the nuclei. The quantitative examination of the iron content revealed an exponential increase in the cellular uptake and an exponential decrease in the uptake efficiency with the fed nanogel. This drug-loaded nanogel could be a promising drug carrier for effective tumor-targeted chemotherapy.

Reduction-responsive polymeric micelles and vesicles for triggered intracellular drug release

SIGNIFICANCE

The therapeutic effects of current micellar and vesicular drug formulations are restricted by slow and inefficient drug release at the pathological site. The development of smart polymeric nanocarriers that release drugs upon arriving at the target site has received a tremendous amount of attention for cancer therapy.

RECENT ADVANCES

Taking advantage of a high reducing potential in the tumor tissues and in particular inside the tumor cells, various reduction-sensitive polymeric micelles and vesicles have been designed and explored for triggered anticancer drug release. These reduction-responsive nanosystems have demonstrated several unique features, such as good stability under physiological conditions, fast response to intracellular reducing environment, triggering drug release right in the cytosol and cell nucleus, and significantly improved antitumor activity, compared to traditional reduction-insensitive counterparts.

CRITICAL ISSUES

Although reduction-sensitive micelles and polymersomes have accomplished rapid intracellular drug release and enhanced in vitro antitumor effect, their fate inside the cells including the mechanism, site, and rate of reduction reaction remains unclear. Moreover, the systemic fate and performance of reduction-sensitive polymeric drug formulations have to be investigated.

FUTURE DIRECTIONS

Biophysical studies should be carried out to gain insight into the degradation and drug release behaviors of reduction-responsive nanocarriers inside the tumor cells. Furthermore, novel ligand-decorated reduction-sensitive nanoparticulate drug formulations should be designed and explored for targeted cancer therapy in vivo.