Stimuli-Responsive Nano-Architecture Drug-Delivery Systems to Solid Tumor Micromilieu: Past, Present, and Future Perspectives

Multitasking polyamine/ferrioxalate nano-sized assemblies: thermo-, photo-, and redox-responsive soft materials made easy

Responsive nanomaterials have emerged as key components in materials sciences. Herein, we report the one-step preparation of multi-stimuli responsive polyamine-salt aggregates (PSA) by ionically crosslinking polyethylenimine with potassium ferrioxalate (FeOx). The unique properties of FeOx enables a novel class of soft nanomaterial that disassembles by exposure to light, reducing environments and temperature.

Dual and multi-targeted nanoparticles for site-specific brain drug delivery

In recent years, nanomedicines have emerged as a promising method for central nervous system drug delivery, enabling the drugs to overcome the blood-brain barrier and accumulate preferentially in the brain. Despite the current success of brain-targeted nanomedicines, limitations still exist in terms of the targeting specificity. Based on the molecular mechanism, the exact cell populations and subcellular organelles where the injury occurs and the drugs take effect have been increasingly accepted as a more specific target for the next generation of nanomedicines. Dual and multi-targeted nanoparticles integrate different targeting functionalities and have provided a paradigm for precisely delivering the drug to the pathological site inside the brain. The targeting process often involves the sequential or synchronized navigation of the targeting moieties, which allows highly controlled drug delivery compared to conventional targeting strategies. Herein, we focus on the up-to-date design of pathological site-specific nanoparticles for brain drug delivery, highlighting the dual and multi-targeting strategies that were employed and their impact on improving targeting specificity and therapeutic effects. Furthermore, the background discussion of the basic properties of a brain-targeted nanoparticle and the common lesion features classified by neurological pathology are systematically summarized.

ZnO capped flower-like porous carbon-Fe3O4 composite as carrier for bi-triggered drug delivery

In this work, ZnO capped flower-like porous carbon-Fe₃O₄ composite (FPCS-Fe₃O₄-ZnO) was constructed as a carrier for pH and microwave bi-triggered drug delivery. In the composite, the FPCS achieves high-efficiency drug loading, the Fe₃O₄ acts as magnetic targeting agent and microwave absorption enhancer, and the ZnO nanoparticle as a sealing agent in response to pH stimulation. The carrier exhibited a flower-mesoporous sphere of 270 nm, a specific surface area of 101 m²/g, a saturation magnetization of 14.08 emu/g, as well as good microwave thermal conversion properties (The temperature was raised from 25 °C to 60 °C only 24 s). Simultaneously, the carrier achieved an efficient drug loading with a drug loading rate of 99.1%. During the drug release experiments, obvious pH-dependent release behavior was observed, the drug release rate at 12 h was 8.2%, 19.0%, and 56.3% at pH 7.4, 5.0 and 3.0 respectively. Moreover the drug release rate increased from 8.2% to 39.9% after microwave stimulation at pH 7.4. In addition, cytotoxicity tests indicate that the carrier has good biocompatibility. Thus, this multifunctional pH and microwave bi-triggered carrier was expected to be further applied to drug delivery system(DDS).

Thirty Years of Cancer Nanomedicine: Success, Frustration, and Hope

Starting with the enhanced permeability and retention (EPR) effect discovery, nanomedicine has gained a crucial role in cancer treatment. The advances in the field have led to the approval of nanodrugs with improved safety profile and still inspire the ongoing investigations. However, several restrictions, such as high manufacturing costs, technical challenges, and effectiveness below expectations, raised skeptical opinions within the scientific community about the clinical relevance of nanomedicine. In this review, we aim to give an overall vision of the current hurdles encountered by nanotherapeutics along with their design, development, and translation, and we offer a prospective view on possible strategies to overcome such limitations.

A bottlebrush-architectured dextran polyprodrug as an acidity-responsive vector for enhanced chemotherapy efficiency

Compared to normal tissues, unique conditions in the tumor microenvironment, such as a lower pH, can induce accurate release of a drug into specific lesions. This strategy provides an efficient approach to overcome the issues of unexpected drug leakage and poor circulation stability, thereby reducing the side effects and enhancing the effect of cancer treatment. In this study, we designed a class of acid activatable supramolecular nano-prodrugs (DOM@DOX) with a bottlebrush architecture based on the dextran (DEX) polysaccharide, which connects with a hydrophilic polyethylene glycol chain by atom transfer radical polymerization and further conjugates with an anticancer drug doxorubicin (DOX) at the backbone of the copolymer via an acidity-responsive hydrazine bond. Furthermore, the DOM@DOX prodrug has a high drug loading up to 48 wt% for DOX, and the prodrug can maintain a stable nano-sized spherical shape in aqueous solution by a self-assembly strategy. In an acidic environment inside tumor cells, the hydrazine bond of the prodrug breaks, leading to the release of DOX from parental micelles. Owing to the small size of the carrier, the prodrug exhibits good intratumoral permeability, good circulation stability and significant tumor suppression efficiency in tumor-bearing mouse models, which is beneficial for the development of new generation nanomedicine for enhanced chemotherapy.

Theoretical Study of the Optimal Design of a UV-Controllable Smart Surface Decorated by a Hybrid Azobenzene-Containing Polymer Layer

Although grafting polymers onto surfaces is widely suggested for designing smart systems, optimizing the performance of such systems is not simple. In this article, we investigate an azo-polymer-based smart surface using the single-chain-in-mean-field theory. Through the numerical simulations, we study the adhesion/erasion transition of the system and show that the performance of the smart surface can be characterized by the difference between the effective nanoparticle-surface interactions in the UV-on and UV-off states. Further exploring the optimization of the smart surface, we find that the distribution function of the receptor can have typical bimodal characteristics, which is crucial for optimizing the position of the azo-bond along the azo-polymer, f. Moreover, the presence of the homopolymer is also essential for the optimal performance of the smart surface, and we build a reference map for the good combinations of f and the homopolymer design f_homo.

Doxorubicin-doxorubicin conjugate prodrug as drug self-delivery system for intracellular pH-triggered slow release

Drug content and releasing rate are the main determining factors for the drug delivery systems (DDSs). Here, doxorubicin dimer (D-DOXcar) was synthesized as drug-drug conjugate prodrug with high drug content of 86%, via an acid-triggered hydrolysable carbamate linker. The prodrug nanoparticles (D-DOXcar-NP) with different diameters were prepared as drug self-delivery system (DSDS) for intracellular pH-triggered slow release. They showed size- and concentration-dependent pH-triggered slow DOX release. For the D-DOXcar-sNP with smaller diameter, the cumulative release ratio reached 25.6% at pH 5.0 within 60 h. The MTT results demonstrated that the proposed DSDS showed similar tumor inhibition regardless of carboxylesterases, and an enhanced anti-tumor efficacy on the HepG2 cells in comparison with the free DOX.

Tumor self-responsive upconversion nanomedicines for theranostic applications

To date, malignant tumors continue to be the most lethal disease, causing more than 8.2 million deaths worldwide each year. In recent years, nanostructures based on rare-earth upconversion luminescent nanoparticles have shown significant advantages in the integration of multimodal imaging and therapy. Compared with normal tissues, the tumor microenvironment (TME) exhibits unique characteristics including high interstitial fluid pressure, abnormal blood vessels, a hypoxic and slightly acidic environment, and high levels of glutathione (GSH) and hydrogen peroxide (H2O2). According to these characteristics, increasing attention in the antitumor field has been given to designing nanomedicines with specific responses to the TME based on rare-earth upconversion nanoparticles (UCNPs) and to achieving efficient tumor diagnosis and treatment under the premise of reducing side effects. Nevertheless, a review that systematically summarizes TME-responsive upconversion nanomedicines (UCNMs) for realizing tumor self-enhanced theranostics has not been published to date. In this review, we summarize the recent progress made in UCNP-based nanotherapeutics by highlighting the increasingly developing trend of TME-responsive UCNMs. The general characteristics of the TME are introduced in detail and their utilization in designing TME-responsive UCNMs is systematically discussed. Based on NIR light-excited optical imaging, we discuss the superiority of UCNMs when applied in tumor theranostics with an emphasis on how to use them to realize TME-mediated multimodal imaging-guided therapy.

Fabrication Of Dual pH/redox-Responsive Lipid-Polymer Hybrid Nanoparticles For Anticancer Drug Delivery And Controlled Release

BACKGROUND

The development of biocompatible nanocarriers that can efficiently encapsulate and deliver anticancer drug to the tumor site and provide controlled release of cargos in response to the specific cues for cancer therapy is of great significance.

METHODS

In this work, dual pH/redox-responsive fabrication of hybrid lipid-polymer nanoparticles (LPNPs) self-assembled from amphiphilic polymer poly(ethylene glycol) methyl ether-grafted disulfide-poly(β-amino esters) (PBAE-ss-mPEG) and PEGylated lipid were prepared and used as drug delivery carriers. The optimization of PEGylated lipid modification was confirmed by analysis of particle size, polydispersity index (PDI), cellular uptake, serum stability, and drug loading capacity. The pK b value of LPNPs was determined as 6.55, indicating the pH-sensitivity. The critical micelle concentration (CMC) values and zeta-potential of LPNPs at different pH values were investigated to confirm its pH-sensitivity. The morphology of LPNPs before and after incubation with reducing agent was imaged to study the redox-responsibility.

RESULTS

The in vitro results showed that the drug had controlled release from LPNPs triggered by low pH and high concentration of reducing agent. Furthermore, the cytotoxicity of LPNPs was very low, and the doxorubicin (DOX)-loaded LPNPs could efficiently induce the death of tumor cells in comparison to free DOX.

CONCLUSION

All results demonstrated that the fabricated LPNPs could be potential anticancer drug delivery carriers with a pH/redox-triggered drug release profile, and PEGylated lipid modification might be a useful method to fabricate the drug delivery platform.

Dynamic Hybrid Colloidosomes via Electrostatic Interactions for pH-Balanced Low Premature Leakage and Ultrafast Cargo Release

A trade-off between minimized premature leakage and rapid cargo release on demand is an intractable obstacle faced by smart delivery systems that restrains them from lab to market. To address this dilemma, dynamic hybrid colloidosomes relying on strong yet reversible electrostatic interactions are developed, simply through one-pot cooperative self-assembly of silica nanoparticles and fluorescent carbon dots at the interface of emulsion droplets. Specifically, pH-driven charge reversal of zwitterionic carbon dots leads to immediate electrostatic conversion between the two building blocks from attraction to repulsion. This makes robust locking and instantaneous breakdown of the colloidosomes subtly balanced, thus enabling low off-state leakage (10.5% over 7 days) while ultrafast on-state release (>90% within 5 min) upon an acidic stimulus. We envision that such biocompatible, traceable, and smart colloidosomes will offer unique opportunities for broad applications as on-demand release is desired.

Engineered Polymeric Materials for Biological Applications: Overcoming Challenges of the Bio-Nano Interface

Nanomedicine has generated significant interest as an alternative to conventional cancertherapy due to the ability for nanoparticles to tune cargo release. However, while nanoparticletechnology has promised significant benefit, there are still limited examples of nanoparticles inclinical practice. The low translational success of nanoparticle research is due to the series ofbiological roadblocks that nanoparticles must migrate to be effective, including blood and plasmainteractions, clearance, extravasation, and tumor penetration, through to cellular targeting,internalization, and endosomal escape. It is important to consider these roadblocks holistically inorder to design more effective delivery systems. This perspective will discuss how nanoparticlescan be designed to migrate each of these biological challenges and thus improve nanoparticledelivery systems in the future. In this review, we have limited the literature discussed to studiesinvestigating the impact of polymer nanoparticle structure or composition on therapeutic deliveryand associated advancements. The focus of this review is to highlight the impact of nanoparticlecharacteristics on the interaction with different biological barriers. More specific studies/reviewshave been referenced where possible.

A stage-specific cancer chemotherapy strategy through flexible combination of reduction-activated charge-conversional core-shell nanoparticles

Precision medicine has increased the demand for stage-specific cancer chemotherapy. Drugs with different properties are needed for different stages of tumor development, which is, inducing rapid destruction in the early stage and facilitating deep penetration in the advanced stage. Herein, we report a novel reduction-activated charge-conversional core-shell nanoparticle (CS NP) formula based on ring-closing metathesis of the thiamine disulfide system (TDS) to deliver the chemotherapeutic agent-gambogic acid (GA). Methods: The shell consisted of hyaluronic acid-all-trans retinoid acid with a disulfide bond as the linker (HA-SS-ATRA). The core was selected from poly (γ-glutamic acid) with different grafting rates of the functional group (Fx%) of TDS. GA/CF100%S NPs, with the strongest reduction-responsive drug release, and GA/CF60%S NPs with the strongest penetration have been finally screened. On this basis, a stage-specific administration strategy against a two-stage hepatocellular carcinoma was proposed. Results: The developed CS NPs have been confirmed as inducing reduction-activated charge conversion from about -25 to +30 mV with up to 95% drug release within 48 h. The administration strategy, GA/CF100%S NPs for the early-stage tumor, and sequential administration of GA/CF60%S NPs followed by GA/CF100%S NPs for the advanced-stage tumor, achieved excellent tumor inhibition rates of 93.86±2.94% and 90.76±6.43%, respectively. Conclusions: Our CS NPs provide a novel platform for charge conversion activated by reduction. The stage-specific administration strategy showed great promise for cancer therapy.

All-In-One "Schizophrenic" Self-Assembly of Orthogonally Tuned Thermoresponsive Diblock Copolymers

Smart, fully orthogonal switching was realized in a highly biocompatible diblock copolymer system with variable trigger-induced aqueous self-assembly. The polymers are composed of nonionic and zwitterionic blocks featuring lower and upper critical solution temperatures (LCSTs and UCSTs). In the system investigated, diblock copolymers from poly( N-isopropyl methacrylamide) (PNIPMAM) and a poly(sulfobetaine methacrylamide), systematic variation of the molar mass of the latter block allowed for shifting the UCST of the latter above the LCST of the PNIPMAM block in a salt-free condition. Thus, successive thermal switching results in "schizophrenic" micellization, in which the roles of the hydrophobic core block and the hydrophilic shell block are interchanged depending on the temperature. Furthermore, by virtue of the strong electrolyte-sensitivity of the zwitterionic polysulfobetaine block, we succeeded to shift its UCST below the LCST of the PNIPMAM block by adding small amounts of an electrolyte, thus inverting the pathway of switching. This superimposed orthogonal switching by electrolyte addition enabled us to control the switching scenarios between the two types of micelles (i) via an insoluble state, if the LCST-type cloud point is below the UCST-type cloud point, which is the case at low salt concentrations or (ii) via a molecularly dissolved state, if the LCST-type cloud point is above the UCST-type cloud point, which is the case at high salt concentrations. Systematic variation of the block lengths allowed for verifying the anticipated behavior and identifying the molecular architecture needed. The versatile and tunable self-assembly offers manifold opportunities, for example, for smart emulsifiers or for sophisticated carrier systems.

Cascade-amplification of therapeutic efficacy: An emerging opportunity in cancer treatment

Increasing research evidence reveals that cancer is complex disease involving many biological factors, processes and systems, which may severely limit the actual efficacy of conventional monotonic anticancer approaches. To overcome these obstacles in cancer treatment, a new strategy has been proposed by combining multiple synergistic therapeutic modalities accessing different but inherently related targets and acting sequentially. A major benefit of this strategy is that the multi-target mechanism could result in a cascade-amplification effect leading to enhanced anticancer activity. In this review, we provide a critical discussion on the application of cascade-amplification strategy in the treatment of various cancer indications, focusing on the rational combination of therapeutic agents and their mechanisms of action. A concise yet comprehensive analysis on the potential therapeutic benefit of this strategy was also included. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease.

A journey through the emergence of nanomedicines with poly(alkylcyanoacrylate) based nanoparticles

Starting in the late 1970s, the pioneering work of Patrick Couvreur gave birth to the first biodegradable nanoparticles composed of a biodegradable synthetic polymer. These nanoparticles, made of poly(alkylcyanoacrylate) (PACA), were the first synthetic polymer-based nanoparticulate drug carriers undergoing a phase III clinical trial so far. Analyzing the journey from the birth of PACA nanoparticles to their clinical evaluation, this paper highlights their remarkable adaptability to bypass various drug delivery challenges found on the way. At present, PACA nanoparticles include a wide range of nanoparticles that can associate drugs of different chemical nature and can be administered in vivo by different routes. The most recent technologies giving the nanoparticles customised functions could also be implemented on this family of nanoparticles. Through different examples, this paper discusses the seminal role of the PACA nanoparticles' family in the development of nanomedicines.

Concepts of nanoparticle cellular uptake, intracellular trafficking, and kinetics in nanomedicine

Nanoparticle-based therapeutics and diagnostics are commonly referred to as nanomedicine and may significantly impact the future of healthcare. However, the clinical translation of these technologies is challenging. One of these challenges is the efficient delivery of nanoparticles to specific cell populations and subcellular targets in the body to elicit desired biological and therapeutic responses. It is critical for researchers to understand the fundamental concepts of how nanoparticles interact with biological systems to predict and control in vivo nanoparticle transport for improved clinical benefit. In this overview article, we review and discuss cellular internalization pathways, summarize the field`s understanding of how nanoparticle physicochemical properties affect cellular interactions, and explore and discuss intracellular nanoparticle trafficking and kinetics. Our overview may provide a valuable resource for researchers and may inspire new studies to expand our current understanding of nanotechnology-biology interactions at cellular and subcellular levels with the goal to improve clinical translation of nanomedicines.

Rational Design of Cancer Nanomedicine for Simultaneous Stealth Surface and Enhanced Cellular Uptake

Owing to the complex and still not fully understood physiological environment, the development of traditional nanosized drug delivery systems is very challenging for precision cancer therapy. It is very difficult to control the in vivo distribution of nanoparticles after intravenous injection. The ideal drug nanocarriers should not only have stealth surface for prolonged circulation time but also possess enhanced cellular internalization in tumor sites. Unfortunately, the stealth surface and enhanced cellular uptake seem contradictory to each other. How to integrate the two opposite aspects into one system is a very herculean but meaningful task. As an alternative drug delivery strategy, chameleon-like drug delivery systems were developed to achieve long circulation time while maintaining enhanced cancer cell uptake. Such drug nanocarriers can "turn off" their internalization ability during circulation. However, the enhanced cellular uptake can be readily activated upon arriving at tumor tissues. In this way, stealth surface and enhanced uptake are of dialectical unity in drug delivery. In this review, we focus on the surface engineering of drug nanocarriers to obtain simultaneous stealth surfaces in circulation and enhanced uptake in tumors. The current strategies and ongoing developments, including programmed tumor-targeting strategies and some specific zwitterionic surfaces, will be discussed in detail.

Lipoic acid-derived cross-linked liposomes for reduction-responsive delivery of anticancer drug

Liposomes have emerged as a fascinating nanocarriers for the delivery of cancer therapeutics. However, their efficacy for cancer therapy is reduced partially because of the serum-instability and incomplete drug release. In this study, a novel disulfide cross-linked liposomes (CLs) assembled from dimeric lipoic acid-derived glycerophosphorylcholine (di-LA-PC) conjugate was developed. The conjugate was synthesized by a facial esterification of lipoic acid (LA) and glycerophosphorylcholine (GPC) and characterized by MS, ¹H NMR and ¹³C NMR. Featuring the enhanced serum-stability and intracellular drug release determined by in vitro stability and GSH-responsive behavior, CLs prepared with dried thin film technique following 10 % dithiothreitol (DTT) cross-linking can attain effective delivery of anticancer candidates. Notably, CLs stably encapsulated doxorubicin (Dox) in their vesicular structures and showed a remarkable thiol-sensitive release of payload upon cellular uptake by cancer cells, compared to that of uncross-linked liposomes (uCLs) or Doxil-like liposome (DLLs). The cell viability and apoptosis of Dox-loaded CLs worked the pronounced cytotoxic effects to MCF-7 cells with an IC₅₀ value of 10.8 μg Dox equiv./mL comparable to free Dox and 2.8-fold higher than DLLs. More importantly, it is demonstrated that the nanoscale characteristics of Dox-loaded CLs could prevent the proliferation of adriamycin-resistant MCF-7/ADR cell line, highlighting their potential in reversal of drug resistance. Furthermore, the preliminary in vivo test (n = 3) showed that disulfide cross-linked liposomal formulation of Dox (Dox-CLs) improved the therapeutic efficacy compared to free Dox and DLLs in a human breast carcinoma xenograft mouse model. Therefore, the current thiol-responsive cross-linked liposome may provide a robust drug delivery platform for cancer therapy.

Self-assembly and self-delivery nanodrug of bortezomib: a simple approach to achieve the trade-off between functionality and druggability

A pH-responsive self-delivery nanosystem with high drug loading and outstanding stability was constructed via a simple method to deliver bortezomib.