Tumor-targeted micelle-forming block copolymers for overcoming of multidrug resistance

Polyelectrolyte-protein synergism: pH-responsive polyelectrolyte/insulin complexes as versatile carriers for targeted protein and drug delivery

The co-assembly of polyelectrolytes (PE) with proteins offers a promising approach for designing complex structures with customizable morphologies, charge distribution, and stability for targeted cargo delivery. However, the complexity of protein structure limits our ability to predict the properties of the formed nanoparticles, and our goal is to identify the key triggers of the morphological transition in protein/PE complexes and evaluate their ability to encapsulate multivalent ionic drugs. A positively charged PE can assemble with a protein at pH above isoelectric point due to the electrostatic attraction and disassemble at pH below isoelectric point due to the repulsion. The additional hydrophilic block of the polymer should stabilize the particles in solution and enable them to encapsulate a negatively charged drug in the presence of PE excess. We demonstrated that diblock copolymers, poly(ethylene oxide)-block-poly(N,N-dimethylaminoethyl methacrylate) and poly(ethylene oxide)-block-poly(N,N,N-trimethylammonioethyl methacrylate), consisting of a polycation block and a neutral hydrophilic block, reversibly co-assemble with insulin in pH range between 5 and 8. Using small-angle neutron and X-ray scattering (SANS, SAXS), we showed that insulin arrangement within formed particles is controlled by intermolecular electrostatic forces between protein molecules, and can be tuned by varying ionic strength. For the first time, we observed by fluorescence that formed protein/PE complexes with excess of positive charges exhibited potential for encapsulating and controlled release of negatively charged bivalent drugs, protoporphyrin-IX and zinc(II) protoporphyrin-IX, enabling the development of nanocarriers for combination therapies with adjustable charge, stability, internal structure, and size.

Nanodelivery systems: An efficient and target-specific approach for drug-resistant cancers

BACKGROUND

Cancer treatment is still a global health challenge. Nowadays, chemotherapy is widely applied for treating cancer and reducing its burden. However, its application might be in accordance with various adverse effects by exposing the healthy tissues and multidrug resistance (MDR), leading to disease relapse or metastasis. In addition, due to tumor heterogeneity and the varied pharmacokinetic features of prescribed drugs, combination therapy has only shown modestly improved results in MDR malignancies. Nanotechnology has been explored as a potential tool for cancer treatment, due to the efficiency of nanoparticles to function as a vehicle for drug delivery.

METHODS

With this viewpoint, functionalized nanosystems have been investigated as a potential strategy to overcome drug resistance.

RESULTS

This approach aims to improve the efficacy of anticancer medicines while decreasing their associated side effects through a range of mechanisms, such as bypassing drug efflux, controlling drug release, and disrupting metabolism. This review discusses the MDR mechanisms contributing to therapeutic failure, the most cutting-edge approaches used in nanomedicine to create and assess nanocarriers, and designed nanomedicine to counteract MDR with emphasis on recent developments, their potential, and limitations.

CONCLUSIONS

Studies have shown that nanoparticle-mediated drug delivery confers distinct benefits over traditional pharmaceuticals, including improved biocompatibility, stability, permeability, retention effect, and targeting capabilities.

NIR Activated Multimodal Therapeutics Based on Metal-Phenolic Networks-Functionalized Nanoplatform for Combating against Multidrug Resistance and Metastasis

Multidrug resistance (MDR) and metastasis in cancer have become increasingly serious problems since antitumor efficiency is greatly restricted by a single therapeutic modality and the insensitive tumor microenvironment (TME). Herein, metal-phenolic network-functionalized nanoparticles (t-P@TFP NPs) are designed to realize multiple therapeutic modalities and reshape the TME from insensitive to sensitive under multimodal imaging monitoring. After a single irradiation, a near-infrared laser-activated multistage reaction occurs. t-P@TFP NPs trigger the phase transition of perfluoropentane (PFP) to release tannic acid (TA)/ferric ion (Fe³⁺ )-coated paclitaxel (PTX) and cause hyperthermia in the tumor region to efficiently kill cancer cells. Additionally, PTX is released after the disassembly of the TA-Fe³⁺ film by the abundant adenosine triphosphate (ATP) in the malignant tumor, which concurrently inhibits ATP-dependent drug efflux to improve sensitivity to chemotherapeutic agents. Furthermore, hyperthermia-induced immunogenic cell death (ICD) transforms "cold" tumors into "hot" tumors with the assistance of PD-1/PD-L1 blockade to evoke antitumor immunogenicity. This work carefully reveals the mechanisms underlying the abilities of these multifunctional NPs, providing new insights into combating the proliferation and metastasis of multidrug-resistant tumors.

Applications of Nanotechnology-based Approaches to Overcome Multi-drug Resistance in Cancer

Cancer is one of the leading causes of death worldwide. Chemotherapy and radiation therapy are the major treatments used for the management of cancer. Multidrug resistance (MDR) is a major hindrance faced in the treatment of cancer and is also responsible for cancer relapse. To date, several studies have been carried out on strategies to overcome or reverse MDR in cancer. Unfortunately, the MDR reversing agents have been proven to have minimal clinical benefits, and eventually, no improvement has been made in therapeutic efficacy to date. Thus, several investigational studies have also focused on overcoming drug resistance rather than reversing the MDR. In this review, we focus primarily on nanoformulations regarded as a novel approach to overcome or bypass the MDR in cancer. The nanoformulation systems serve as an attractive strategy as these nanosized materials selectively get accumulated in tumor tissues, thereby improving the clinical outcomes of patients suffering from MDR cancer. In the current work, we present an overview of recent trends in the application of various nano-formulations, belonging to different mechanistic classes and functionalization like carbon nanotubes, carbon nanohorns, carbon nanospheres, liposomes, dendrimers, etc., to overcome MDR in cancer. A detailed overview of these techniques will help researchers in exploring the applicability of nanotechnologybased approaches to treat MDR.

NIR Activated Upper Critical Solution Temperature Polymeric Micelles for Trimodal Combinational Cancer Therapy

The balance between drug efficiency and its side effects on normal tissues is still a challenging problem to be solved in current cancer therapies. Among different strategies, cancer therapeutic methods based on nanomedicine delivery systems have received extensive attention due to their unique advantages such as improved circulation and reduced toxicity of drugs in the body. Herein, we constructed dual-responsive polymeric micelles DOX&ALS@MFM based on an upper critical solution temperature (UCST) polymer to simultaneously combine chemotherapy, photothermal therapy (PTT), and photodynamic therapy (PDT). Amphiphilic block copolymer P(AAm-co-AN)-b-PEI-ss-PEG-FA with a critical point of 42 °C was able to self-assemble into polymeric micelles under physiological conditions, which further encapsulated anticancer drug doxorubicin (DOX) and photosensitizer ALS to obtain drug-loaded micelles DOX&ALS@MFM. Micelles aggregated at tumor sites due to folate targeting and an enhanced permeability retention (EPR) effect. After that, the high intracellular concentration of glutathione (GSH) and near-infrared (NIR) light prompted disassembly of the polymer to release DOX and ALS. ALS not only plays a role in PTT but also produces singlet oxygen, therefore killing tumor cells by PDT. Both in vitro and in vivo studies demonstrated the photothermal conversion and reactive oxygen species generation ability of DOX&ALS@MFM micelles, at the same time as the excellent inhibitory effect on tumor growth with NIR light irradiation. Thus, our research substantiated a new strategy for the biomedical application of UCST polymers in the cited triple modal tumor therapy.

Polymer-Based Drug-Free Therapeutics for Anticancer, Anti-Inflammatory, and Antibacterial Treatment

This paper summarizes the area of biomedicinal polymers, which serve as nanomedicines even though they do not contain any anticancer or antiinflammatory drugs. These polymer nanomedicines with unique design are in the literature highlighted as a novel class of therapeutics called "drug-free macromolecular therapeutics." Their therapeutic efficacy is based on the tailored multiple presentations of biologically active vectors, i.e., peptides, oligopeptides, or oligosaccharides. Thus, they enable, for example, to directly induce the apoptosis of malignant cells by the crosslinking of surface slowly internalizing receptors, or to deplete the efficacy of tumor-associated proteins. The precise biorecognition of natural binding motifs by multiple vectors on the polymer construct remains the crucial part in the designing of these drug-free nanomedicines. Here, the rationales, designs, synthetic approaches, and therapeutic potential of drug-free macromolecular therapeutics consisting of various active vectors are described in detail. Recent developments and achievements for namely B-cell lymphoma treatment, Gal-3-positive tumors, inflammative liver injury, and bacterial treatment are reviewed and highlighted. Finally, a possible future prospect within this highly exciting new field of nanomedicine research is presented.

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.

Nanoparticle-Based Drug Delivery in Cancer Therapy and Its Role in Overcoming Drug Resistance

Nanotechnology has been extensively studied and exploited for cancer treatment as nanoparticles can play a significant role as a drug delivery system. Compared to conventional drugs, nanoparticle-based drug delivery has specific advantages, such as improved stability and biocompatibility, enhanced permeability and retention effect, and precise targeting. The application and development of hybrid nanoparticles, which incorporates the combined properties of different nanoparticles, has led this type of drug-carrier system to the next level. In addition, nanoparticle-based drug delivery systems have been shown to play a role in overcoming cancer-related drug resistance. The mechanisms of cancer drug resistance include overexpression of drug efflux transporters, defective apoptotic pathways, and hypoxic environment. Nanoparticles targeting these mechanisms can lead to an improvement in the reversal of multidrug resistance. Furthermore, as more tumor drug resistance mechanisms are revealed, nanoparticles are increasingly being developed to target these mechanisms. Moreover, scientists have recently started to investigate the role of nanoparticles in immunotherapy, which plays a more important role in cancer treatment. In this review, we discuss the roles of nanoparticles and hybrid nanoparticles for drug delivery in chemotherapy, targeted therapy, and immunotherapy and describe the targeting mechanism of nanoparticle-based drug delivery as well as its function on reversing drug resistance.

Nanoparticle-Based Drug Delivery in Cancer Therapy and Its Role in Overcoming Drug Resistance

Nanotechnology has been extensively studied and exploited for cancer treatment as nanoparticles can play a significant role as a drug delivery system. Compared to conventional drugs, nanoparticle-based drug delivery has specific advantages, such as improved stability and biocompatibility, enhanced permeability and retention effect, and precise targeting. The application and development of hybrid nanoparticles, which incorporates the combined properties of different nanoparticles, has led this type of drug-carrier system to the next level. In addition, nanoparticle-based drug delivery systems have been shown to play a role in overcoming cancer-related drug resistance. The mechanisms of cancer drug resistance include overexpression of drug efflux transporters, defective apoptotic pathways, and hypoxic environment. Nanoparticles targeting these mechanisms can lead to an improvement in the reversal of multidrug resistance. Furthermore, as more tumor drug resistance mechanisms are revealed, nanoparticles are increasingly being developed to target these mechanisms. Moreover, scientists have recently started to investigate the role of nanoparticles in immunotherapy, which plays a more important role in cancer treatment. In this review, we discuss the roles of nanoparticles and hybrid nanoparticles for drug delivery in chemotherapy, targeted therapy, and immunotherapy and describe the targeting mechanism of nanoparticle-based drug delivery as well as its function on reversing drug resistance.

Neuroblastoma-targeted nanoparticles and novel nanotechnology-based treatment methods

Neuroblastoma is a complicated pediatric tumor, originating from the neural crest, which is the most prevalent in adrenal glands, but may rarely be seen in some other tissues as well. Studies are focused on developing new strategies through novel chemo- and immuno-therapeutic drug targets. Different types of oncogenes such as MYCN, tumor suppressor genes such as p53, and some structural genes such as vascular endothelial growth factor are considered as targets for neuroblastoma therapy. The individual expression patterns in NB cells make them appropriate for this purpose. The combined effect of nano-drug delivery systems and specific drug targets will result in lower systemic side effects, prolonged therapeutic effects, and improvements in the pharmacokinetic properties of the drugs. Some of these novel drug delivery systems with a focus on liposomes as carriers are also discussed. In this review, genes and protein products that are beneficial as drug targets in the treatment of neuroblastoma have been discussed.

Dual-responsive TPGS crosslinked nanocarriers to overcome multidrug resistance

Efficient delivery of chemotherapeutic agents into tumor cells and reversal of chemoresistance are crucially important to enhance cancer therapy.

Ultrasmall nanostructured drug based pH-sensitive liposome for effective treatment of drug-resistant tumor

Background

Cancer cells always develop ways to resist and evade chemotherapy. To overcome this obstacle, herein, we introduce a programmatic release drug delivery system that imparts avoiding drug efflux and nuclear transport in synchrony via a simple nanostructured drug strategy.

Results

The programmatic liposome-based nanostructured drugs (LNSD) contained two modules: doxorubicin (DOX) loaded into tetrahedral DNA (TD, ~ 10 nm) to form small nanostructured DOX, and the nanostructured DOX was encapsulated into the pH-sensitive liposomes. In the in vitro and in vivo studies, LNSD shows multiple benefits for drug resistance tumor treatment: (1) not only enhanced the cellular DOX uptake, but also maintained DOX concentration in an optimum level in resistant tumor cells via nanostructure induced anti-efflux effect; (2) small nanostructured DOX efficiently entered into cell nuclear via size depended nuclear-transport for enhanced treatment; (3) improved the pharmacokinetics and biodistribution via reducing DOX leakage during circulation.

Conclusions

The system developed in this study has the potential to provide new therapies for drug-resistant tumor.

Micelle-Forming Block Copolymers Tailored for Inhibition of P-gp-Mediated Multidrug Resistance: Structure to Activity Relationship

Multidrug resistance (MDR) is often caused by the overexpression of efflux pumps, such as ABC transporters, in particular, P-glycoprotein (P-gp). Here, we investigate the di- and tri- block amphiphilic polymer systems based on polypropylene glycol (PPO) and copolymers of (N-(2-hydroxypropyl)methacrylamide) (PHPMA) as potential macromolecular inhibitors of P-gp, and concurrently, carriers of drugs, passively targeting solid tumors by the enhanced permeability and retention (EPR) effect. Interestingly, there were significant differences between the effects of di- and tri- block polymer-based micelles, with the former being significantly more thermodynamically stable and showing much higher P-gp inhibition ability. The presence of Boc-protected hydrazide groups or the Boc-deprotection method did not affect the physico-chemical or biological properties of the block copolymers. Moreover, diblock polymer micelles could be loaded with free PPO containing 5–40 wt % of free PPO, which showed increased P-gp inhibition in comparison to the unloaded micelles. Loaded polymer micelles containing more than 20 wt % free PPO showed a significant increase in toxicity; thus, loaded diblock polymer micelles containing 5–15 wt % free PPO are potential candidates for in vitro and in vivo application as potent MDR inhibitors and drug carriers.

Fluorescence Imaging as a Tool in Preclinical Evaluation of Polymer-Based Nano-DDS Systems Intended for Cancer Treatment

Targeted drug delivery using nano-sized carrier systems with targeting functions to malignant and inflammatory tissue and tailored controlled drug release inside targeted tissues or cells has been and is still intensively studied. A detailed understanding of the correlation between the pharmacokinetic properties and structure of the nano-sized carrier is crucial for the successful transition of targeted drug delivery nanomedicines into clinical practice. In preclinical research in particular, fluorescence imaging has become one of the most commonly used powerful imaging tools. Increasing numbers of suitable fluorescent dyes that are excitable in the visible to near-infrared (NIR) wavelengths of the spectrum and the non-invasive nature of the method have significantly expanded the applicability of fluorescence imaging. This chapter summarizes non-invasive fluorescence-based imaging methods and discusses their potential advantages and limitations in the field of drug delivery, especially in anticancer therapy. This chapter focuses on fluorescent imaging from the cellular level up to the highly sophisticated three-dimensional imaging modality at a systemic level. Moreover, we describe the possibility for simultaneous treatment and imaging using fluorescence theranostics and the combination of different imaging techniques, e.g., fluorescence imaging with computed tomography.

Aggregation-induced emission (AIE) fluorophores as imaging tools to trace the biological fate of nano-based drug delivery systems

The vigorous development of nanotechnology has been accompanied by an equally strong interest and research efforts in nano-based drug delivery systems (NDDSs). However, only a few NDDSs have been translated into clinic thus far. One of the important hurdles is the lack of tools to comprehensively and directly trace the biological fate of NDDSs. Recently, aggregation-induced emission (AIE) fluorophores have emerged as attractive bioimaging tools due to flexible controllability, negligible toxicity and superior photostability. Herein, we recapitulate the current advances in the application of AIE fluorophores to monitor NDDSs both in vitro and in vivo. Particularly, we discuss the cellular fates of self-indicating and stimuli-responsive NDDSs with AIE fluorophores. Moreover, we highlight the in vivo application of AIE agents on the long-term tracking of therapeutics and the multi-modal monitoring of diagnostics in NDDSs. Challenges and opportunities in AIE-guided exploration of NDDSs are also discussed in detail.

Targeted Intracellular Delivery of Antibodies: The State of the Art

A dominant area of antibody research is the extension of the use of this mighty experimental and therapeutic tool for the specific detection of molecules for diagnostics, visualization, and activity blocking. Despite the ability to raise antibodies against different proteins, numerous applications of antibodies in basic research fields, clinical practice, and biotechnology are restricted to permeabilized cells or extracellular antigens, such as membrane or secreted proteins. With the exception of small groups of autoantibodies, natural antibodies to intracellular targets cannot be used within living cells. This excludes the scope of a major class of intracellular targets, including some infamous cancer-associated molecules. Some of these targets are still not druggable via small molecules because of large flat contact areas and the absence of deep hydrophobic pockets in which small molecules can insert and perturb their activity. Thus, the development of technologies for the targeted intracellular delivery of antibodies, their fragments, or antibody-like molecules is extremely important. Various strategies for intracellular targeting of antibodies via protein-transduction domains or their mimics, liposomes, polymer vesicles, and viral envelopes, are reviewed in this article. The pitfalls, challenges, and perspectives of these technologies are discussed.

Novel block glycopolymers prepared as delivery nanocarriers for controlled release of bortezomib

To explore block glycopolymers as novel polymeric delivery nanocarriers for anticancer drug bortezomib (BTZ), three types of block glycopolymers, poly(ethylene glycol)-block-poly(gluconamido ethyl methacrylate) (PEG113-b-PGAMA20), poly(ethylene glycol)-block-poly(styrene)-block-poly(gluconamido ethyl methacrylate) (PEG113-b-PS50-b-PGAMA20), and poly(ethylene glycol)-block-poly(2-(diethyl amino) ethyl methacrylate)-block-poly(gluconamido ethyl methacrylate) (PEG113-b-PDEA50-b-PGAMA20), were synthesized via atom transfer radical polymerization (ATRP) using a PEG-based ATRP macroinitiator. Three glycopolymers possess the capacity to load BTZ via pH-induced dynamic covalent bonding and/or hydrophobic interaction with their specific self-assembly behaviors, and PEG113-b-PS50-b-PGAMA20 carrier maintains the sustain release behavior of BTZ due to the stable micellar structure; PEG113-b-PDEA50-b-PGAMA20 carrier realizes the abrupt release at pH 5.5 by collapse of micellar structure, while PEG113-b-PGAMA20 carrier exhibits the fastest release at studied solution pHs. This study would provide a light to develop novel block glycopolymer carrier for the delivery of anticancer drug bearing boronic acid groups. Graphical abstractᅟᅟ.

Theranostic micelles combined with multiple strategies to effectively overcome multidrug resistance

AIM

To develop precise targeting and versatile Fe₃O₄@SiO₂-P123/PTX-ZnPc nanoparticles (FSP-PTX-ZnPc NPs) to reverse paclitaxel (PTX)-induced multidrug resistance in breast cancer.

MATERIALS & METHODS

PTX and zinc (II) phthalocyanine (ZnPc) co-loaded FSP-PTX-ZnPc NPs were designed. The resulting multifunctional NPs were evaluated systematically in vitro and in vivo, and the mechanism of drug-resistance reversal was investigated.

RESULTS

The NPs enhanced drug uptake in MCF-7/PDR cells by increasing drug solubility and impairing P-glycoprotein efflux. Additionally, magnetic targeting and enhanced permeation and retention (EPR) effect enhanced drug accumulation in tumor, facilitating the chemotherapeutic and photodynamic therapy effects. Moreover, FSP-PTX-ZnPc NPs could penetrate the blood-brain barrier, a desirable trait for brain disease therapy.

CONCLUSION

The multifunctional FSP-PTX-ZnPc NPs are an effective tool for overcoming drug resistance in breast cancer.

TPGS-functionalized and ortho ester-crosslinked dextran nanogels for enhanced cytotoxicity on multidrug resistant tumor cells

Herein pH-sensitive nanogels (NG1) and P-glycoprotein-repressive nanogels (NG2) were prepared by copolymerization between an ortho ester crosslinker (OEAM) and tocopheryl polyethylene glycol succinate (TPGS)-free or conjugated dextran. Nanogels with or without TPGS possessed a uniform diameter (∼180 nm) and excellent stability in various physiological environments. Doxorubicin (DOX) was successfully loaded into NG1 and NG2 to give NG1/DOX and NG2/DOX, both of them showed appropriate drug release profiles under mildly acidic conditions (pH 5.0). NG2/DOX possessed higher drug enrichment and lethality than NG1/DOX did on MCF-7/ADR cells. Analysis of corresponding index of efflux activity showed that NG2 could induce depolarization of mitochondrial membrane and interfere with ATP metabolism. NG2/DOX also displayed increased penetration and growth inhibition on MCF-7/ADR multicellular spheroids. These results demonstrated that pH-sensitive TPGS-functionalized nanogels (NG2) as drug carriers had great potential to suppress drug efflux in MCF-7/ADR cells and even overcome MDR on cancer cells.

Selective Cell Penetrating Peptide-Functionalized Polymersomes Mediate Efficient and Targeted Delivery of Methotrexate Disodium to Human Lung Cancer In Vivo

It is a long challenge to develop nanomedicines that simultaneously possess tumor cell selectivity and penetration functions. Here, it is reported that selective cell penetrating peptide (RLWMRWYSPRTRAYGC)-functionalized polymersomes (SCPP-PS) mediate efficient and targeted delivery of methotrexate disodium (MTX) to human lung cancer in vivo. SCPP-PS with an SCPP density of 18.7% is self-crosslinked, has a small size (63-65 nm), and high MTX loading (up to 19.4 wt%), shows selective uptake and fast penetration into A549 lung cancer cells, and efficiently releases MTX intracellularly. Interestingly, MTX-loaded SCPP-PS (MTX-SCPP-PS) displays much lower IC₅₀ than those of MTX-PS and free MTX. Installing SCPP to polymersomes has no detrimental effect to their long blood circulation time but significantly increases drug accumulation in A549 tumor (5.3% injected dose per gram at 8 h post injection). Remarkably, SCPP-PS exhibits deep penetration in to A549 tumors. MTX-SCPP-PS completely inhibits tumor progression and significantly improves survival rates in mice bearing A549 lung tumor xenografts as compared to MTX-PS and free MTX groups (median survival time: 75 vs 45 and 38 d, respectively), without causing noticeable adverse effects. These results highlight that functionalization of nanomedicines with SCPP is a feasible strategy to achieve efficient and targeted tumor therapy.

Cube-shaped theranostic paclitaxel prodrug nanocrystals with surface functionalization of SPC and MPEG-DSPE for imaging and chemotherapy

As one of nanomedicine delivery systems (NDSs), drug nanocrystals exhibited an excellent anticancer effect. Recently, differences of internalization mechanisms and subcellular localization of both drug nanocrystals and small molecular free drug have drawn much attention. In this paper, paclitaxel (PTX) as a model anticancer drug was directly labeled with 4-chloro-7-nitro-1, 2, 3-benzoxadiazole (NBD-Cl) (a drug-fluorophore conjugate Ma et al. (2016) and Wang et al. (2016) [1,2] (PTX-NBD)). PTX-NBD was synthesized by nucleophilic substitution reaction of PTX with NBD-Cl in high yield and characterized by fluorescence, XRD, ESI-MS, and FT-IR analysis. Subsequently, the cube-shaped PTX-NBD nanocrystals were prepared with an antisolvent method followed by surface functionalization of SPC and MPEG-DSPE. The obtained specific shaped PTX-NBD@PC-PEG NCs had a hydrodynamic particle size of ∼50nm, excellent colloidal stability, and a high drug-loading content of ∼64%. Moreover, in comparison with free PTX-NBD and the sphere-shaped PTX-NBD nanocrystals with surface functionalization of SPC and MPEG-DSPE (PTX-NBD@PC-PEG NSs), PTX-NBD@PC-PEG NCs remarkably reduced burst release and improved cellular uptake efficiency and in vitro cancer cell killing ability. In a word, the work highlights the potential of theranostic prodrug nanocrystals based on the drug-fluorophore conjugates for cell imaging and chemotherapy.

Polymeric mixed micelles loaded mitoxantrone for overcoming multidrug resistance in breast cancer via photodynamic therapy

Mitoxantrone (MIT) is an anticancer agent with photosensitive properties that is commonly used in various cancers. Multidrug resistance (MDR) effect has been an obstacle to using MIT for cancer therapy. Photochemical internalization, on account of photodynamic therapy, has been applied to improve the therapeutic effect of cancers with MDR effect. In this study, an MIT-poly(ε-caprolactone)-pluronic F68-poly(ε-caprolactone)/poly(d,l-lactide-co-glycolide)–poly(ethylene glycol)–poly(d,l-lactide-co-glycolide) (MIT-PFP/PPP) mixed micelles system was applied to reverse the effect of MDR in MCF-7/ADR cells via photochemical reaction when exposed to near-infrared light. MIT-PFP/PPP mixed micelles showed effective interaction with near-infrared light at the wavelength of 660 nm and exerted great cytotoxicity in MCF-7/ADR cells with irradiation. Furthermore, MIT-PFP/PPP mixed micelles could improve reactive oxygen species (ROS) levels, decrease P-glycoprotein activity, and increase the cellular uptake of drugs with improved intracellular drug concentrations, which induced cell apoptosis in MCF-7/ADR cells under irradiation, despite MDR effect, as indicated by the increased level of cleaved poly ADP-ribose polymerase. These findings suggested that MIT-PFP/PPP mixed micelles may become a promising strategy to effectively reverse the MDR effect via photodynamic therapy in breast cancer.

Highly cell-penetrating and ultra-pH-responsive nanoplatform for controlled drug release and enhanced tumor therapy

A stimuli-triggered drug release strategy could considerably reduce side effects while improving the bioavailability of chemotherapeutics. Here, we report that a series of ultra-pH-responsive copolymers are highly efficient drug delivery systems for near-infrared (NIR) imaging and controlled drug release. These polymers self-assemble into nano-sized micelles due to their amphipathic structure and deliver hydrophobic drugs (maximum drug loading rate ∼10wt%) into tumor cells via a controlled and pH-triggered modality. By altering the proportion of hydrophilic and hydrophobic chains, the drug loading rate and the in vitro drug release efficiency can be regulated. Moreover, the drug-loaded micelles with optimized compositions exhibited excellent antitumor efficacy in HeLa and MCF-7 cells, while the blank micelles had minimal cytotoxicity. Cellular uptake experiments further indicated that the ultra-pH-responsive micelles could be rapidly internalized in the tumor cells. This study demonstrated the strong potential of the ultra-pH-responsive platform as a universal carrier for the delivery of anticancer drugs to maximize their therapeutic effect.

pH-responsive unimolecular micelle-gold nanoparticles-drug nanohybrid system for cancer theranostics

The development of an in situ formed pH-responsive theranostic nanocomposite for anticancer drug delivery and computed tomography (CT) imaging was reported. β-cyclodextrin-{poly(lactide)-poly(2-(dimethylamino) ethyl methacrylate)-poly[oligo(2-ethyl-2-oxazoline)methacrylate]}₂₁ [β-CD-(PLA-PDMAEMA-PEtOxMA)₂₁] unimolecular micelles served as a template for the in situ formation of gold nanoparticles (GNPs) and the subsequent encapsulation of doxorubicin (DOX). The formation of unimolecular micelles, microstructures and the distributions of GNPs and DOX were investigated through the combination of experiments and dissipative particle dynamics (DPD) simulations. β-CD-(PLA-PDMAEMA-PEtOxMA)₂₁ formed spherical unimolecular micelles in aqueous solution within a certain range of polymer concentrations. GNPs preferentially distributed in the PDMAEMA area. The maximum wavelength (λ_max) and the size of GNPs increased with increasing concentration of HAuCl₄. DOX preferentially distributed in the PDMAEMA mesosphere, but penetrated the inner PLA core with increasing DOX concentration. DOX-loaded micelles with 41-61% entrapment efficiency showed fast release (88% after 102h) under acidic tumor conditions. Both in vitro and in vivo experiments revealed superior anticancer efficacy and effective CT imaging properties for β-CD-(PLA-PDMAEMA-PEtOxMA)₂₁/Au/DOX. We conclude that the reported unimolecular micelles represent a class of versatile smart nanocarriers for theranostic application.

STATEMENT OF SIGNIFICANCE

Developing polymeric nanoplatforms as integrated theranostic vehicles for improving cancer diagnostics and therapy is an emerging field of much importance. This article aims to develop an in situ formed pH-responsive theranostic nanocomposite for anticancer drug delivery and computed tomography (CT) imaging. Specific emphases is on structure-properties relationship. There is a sea of literature on polymeric drug nanocarriers, and a couple of polymer-stabilized gold nanoparticles (GNPs) systems for cancer diagnosis are also known. However, to our knowledge, there has been no report on polymeric unimolecular micelles capable of dual loading of GNPs without external reducing agents and anticancer drugs for cancer diagnosis and treatment. To this end, the target of the current work was to develop an in situ formed nanocarrier, which actively dual wrapped CT contrast agent GNPs and hydrophobic anticancer drug doxorubicin (DOX), achieving high CT imaging and antitumor efficacy under in vitro and in vivo acid tumor condition. Meanwhile, by taking advantage of dissipative particle dynamics (DPD) simulation, we further obtained the formation process and mechanism of unimolecular micelles, and detailed distributions and microstructures of GNPs and DOX on unimolecular micelles. Taken together, our results here provide insight and guidance for the design of more effective nanocarriers for cancer theranostic application.

Intracellular release of PluronicL64 unimers into MCF-7/ADR cells to overcome multidrug resistance by surface-modified PAMAM

Multidrug resistance (MDR) has been a major obstacle to tumor chemotherapy. Pluronic unimers have been reported to be promising copolymers to reverse MDR, and the intracellular delivery of Pluronic unimers is a problem worth thinking. To exert the excellent reversal effect of Pluronic unimers, DOX-loaded G4.0 PAMAM was modified with PluronicL64 via cis-aconitic acid as a pH-sensitive linkage (PCPAMAM/DOX), which could release DOX and Pluronic unimers into cytoplasm. The Pluronic-modified PAMAM (PCPAMAM) exhibited favorable biocompatibility and pH-sensitivity. PCPAMAM/DOX showed a nano-scale size and a sustained in vitro release profile. Compared with a control formulation, PCPAMAM/DOX showed a higher reversal effect on MCF-7/ADR cells and enhanced intracellular drug accumulation. The results of P-gp activity, subcellular distribution of PluronicL64, the ATP level and mitochondrial transmembrane potential all illustrated that free Pluronic unimers could be released by PCPAMAM functioning as reversal agents. In conclusion, PCPAMAM could be a promising vehicle to enhance DOX accumulation by overcoming MDR in MCF-7/ADR cells. This work also provided an effective method to deliver Pluronic unimers into MDR cells.

A comparison study to investigate the effect of the drug-loading site on its delivery efficacy using double hydrophilic block copolymer-based prodrugs

Polymeric delivery vehicles can improve the safety and efficacy of chemotherapy drugs by facilitating preferential tumor delivery. Double hydrophilic block copolymer (DHBC)-based prodrugs are considered as ideal candidates for drug delivery due to the elegant integration of benefits from both structures including polymeric prodrugs' superior protection and minimal premature drug release using covalent links and a DHBC-based "green" self-assembly strategy by a simple stimulus in a pure aqueous phase without the use of any organic solvent. Clearly, the location of drug molecules in the polymeric prodrugs has exerted a significant effect on their therapeutic efficiency. However, there has been no published data so far, to our knowledge, reporting the effect of drug-conjugated sites on its therapeutic efficacy, as well as some basic guidelines that can be followed to direct the future design of polymeric prodrugs. To this end, herein a thermo-sensitive DHBC, poly(N-(2-hydroxypropyl) methacrylamide)-b-poly(N-isopropyl acrylamide) (P(HPMA)-b-P(NIPAAm)), was designed and synthesized by successive reversible addition and fragmentation chain transfer (RAFT) polymerizations, and was chosen as a platform to clarify this issue. An anti-cancer drug, doxorubicin (DOX) was conjugated to the hydrophilic PHPMA block and the temperature-responsive P(NIPAAm) block, respectively, through a pH-liable hydrazone bond to fabricate two different types of polymeric prodrugs with the drug tethered to the micellar hydrophilic PHPMA shell or encapsulated within the hydrophobic P(NIPAAm) core upon temperature elevation above its lower critical solution temperature (LCST). A detailed comparison study was carried out to investigate which structure exhibits better properties and higher therapeutic efficacy in terms of micellar size, stability, cellular uptake, drug loading capacity, drug release behaviors and cell viability. The results showed the self-assembly of both DHBC-based prodrugs into well-dispersed spherical micelles with similar average hydrodynamic diameters (D_h) around 150 nm in phosphate buffer (PBS, pH 7.4) at 37 °C, but a higher drug loading content (DLC), and enhanced pH-mediated drug release, i.e., much accelerated drug release at pH 5.0, while slower at pH 7.4, as well as enhanced cytotoxicity when the drug was conjugated to the hydrophilic shell of the micelles. The guidelines obtained in this study are thus believed to direct the future design and development of polymeric prodrugs for efficient cancer therapy.