Chain-shattering polymeric therapeutics with on-demand drug-release capability

A reactive oxygen species-triggerable theranostic prodrug system

Abnormally elevated levels of reactive oxygen species (ROS) are considered one of the characteristics of tumors and have been extensively employed in the construction of tumor-activated prodrugs. However, ideal ROS-activated molecular triggers that possess high sensitivity and easy functionalization for tailoring specific prodrugs, remain scarce. In this work, we developed a highly reactive oxygen species (hROS, such as •OH, ONOO- and HOCl)-responsive molecular trigger (namely FDROS-4) through the conjunction of methylene blue (MB) and 2, 6-bis (hydroxymethyl) aniline via urea bond, integrating imaging and therapeutic functions. FDROS-4 could be readily modified as multifunctional prodrugs and efficiently activated by hROS, leading to the release of near-infrared emissive MB and parent drugs. By using chlorambucil as a model drug and incorporating varying numbers of galactose as liver-targeting ligands, we designed and synthesized a series of prodrugs named FDROS-6, FDROS-7, and FDROS-8. The optimal prodrug, FDROS-7, could self-assemble into monocomponent nanoparticles, exhibiting enhanced biocompatibility and therapeutic efficacy compared to the parent drug. This hROS-activated molecular trigger holds promise for the development of stimulus-responsive prodrugs in chemotherapy.

Polymeric Nanoparticles for Drug Delivery

The recent emergence of nanomedicine has revolutionized the therapeutic landscape and necessitated the creation of more sophisticated drug delivery systems. Polymeric nanoparticles sit at the forefront of numerous promising drug delivery designs, due to their unmatched control over physiochemical properties such as size, shape, architecture, charge, and surface functionality. Furthermore, polymeric nanoparticles have the ability to navigate various biological barriers to precisely target specific sites within the body, encapsulate a diverse range of therapeutic cargo and efficiently release this cargo in response to internal and external stimuli. However, despite these remarkable advantages, the presence of polymeric nanoparticles in wider clinical application is minimal. This review will provide a comprehensive understanding of polymeric nanoparticles as drug delivery vehicles. The biological barriers affecting drug delivery will be outlined first, followed by a comprehensive description of the various nanoparticle designs and preparation methods, beginning with the polymers on which they are based. The review will meticulously explore the current performance of polymeric nanoparticles against a myriad of diseases including cancer, viral and bacterial infections, before finally evaluating the advantages and crucial challenges that will determine their wider clinical potential in the decades to come.

Structural Determinants of Stimuli-Responsiveness in Amphiphilic Macromolecular Nano-assemblies

Stimuli-responsive nano-assemblies from amphiphilic macromolecules could undergo controlled structural transformations and generate diverse macroscopic phenomenon under stimuli. Due to the controllable responsiveness, they have been applied for broad material and biomedical applications, such as biologics delivery, sensing, imaging, and catalysis. Understanding the mechanisms of the assembly-disassembly processes and structural determinants behind the responsive properties is fundamentally important for designing the next generation of nano-assemblies with programmable responsiveness. In this review, we focus on structural determinants of assemblies from amphiphilic macromolecules and their macromolecular level alterations under stimuli, such as the disruption of hydrophilic-lipophilic balance (HLB), depolymerization, decrosslinking, and changes of molecular packing in assemblies, which eventually lead to a series of macroscopic phenomenon for practical purposes. Applications of stimuli-responsive nano-assemblies in delivery, sensing and imaging were also summarized based on their structural features. We expect this review could provide readers an overview of the structural considerations in the design and applications of nanoassemblies and incentivize more explorations in stimuli-responsive soft matters.

Polyprodrugs for tumor chemotherapy: from molecular structure to drug release performance

Polyprodrugs have been recognized as promising carrier-free drug delivery systems (DDSs) for tumor chemotherapy in recent years, showing distinct superiority in comparison with the conventional polymer prodrugs. In the present work, the structure-property relationship of polyprodrugs was explored from the perspective of molecular structure, by discussing the effects of the conjugations and linkers on their drug content and drug releasing performance, including drug releasing rate and drug releasing selectivity, as well as the anti-tumor performance of the released drugs. Moreover, the future challenges in the design of polyprodrug-based DDSs with high anti-tumor efficacy were also highlighted.

Nucleus-selective self-augmenting cascade nanoassemblies for targeted synergistic photo-chemo therapy of tumors

A nucleus-targeted enzyme prodrug nanocomposite, assembled from β-cyclodextrin-lysine (CL), catalase (CAT), Pt(IV) and chlorin e6 (Ce6), was developed for self-augmenting cascade photo-chemo therapy of tumors. It can effectively transport through the cytoplasm and accumulate in the nucleus, thereby significantly inhibiting tumor growth and lung metastasis.

Self-amplified chain-shattering cinnamaldehyde-based poly(thioacetal) boosts cancer chemo-immunotherapy

The selective activation of stimuli-responsive polymers in the tumor microenvironment is a great concern to achieve intelligent cancer therapy, but most of them show inadequate response due to insufficient endogenous triggering agents. Herein, we rationally designed a reactive oxygen species (ROS)-responsive cinnamaldehyde (CA)-based poly(thioacetal), consisting of ROS-responsive thioacetal (TA) and ROS-generating agent CA, with self-amplified chain-shattering polymer degradation. The mechanism of self-amplified chain-shattering is that endogenous ROS as a triggering agent facilitates chain cleavage of TA with the release of CA, which in turn produces more ROS through mitochondrial dysfunction, resulting in an exponential polymer degradation cascade. The polymer can be further modified with anticancer drug doxorubicin (DOX) for cooperative amplification of oxidative stress and immunogenic cell death (ICD) of tumor cells, thereby boosting the effect of chemo-immunotherapy. The self-amplified chain-shattering polymer designed in this work holds great promise in developing stimuli-responsive polymers for efficient drug delivery. STATEMENT OF SIGNIFICANCE: This study presented an approach to utilize self-amplified chain-shattering cinnamaldehyde-based poly (thioacetal) as a drug delivery system to restrain tumor growth and boost chemo-immunotherapy. The endogenous ROS as a triggering agent initiates the chain cleavage with the release of CA, which in turn produces ROS through mitochondria dysfunction, resulting in an exponential polymer degradation cascade and rapid drug release.

Degradable polyprodrugs: design and therapeutic efficiency

Prodrugs are developed to increase the therapeutic properties of drugs and reduce their side effects. Polyprodrugs emerged as highly efficient prodrugs produced by the polymerization of one or several drug monomers. Polyprodrugs can be gradually degraded to release therapeutic agents. The complete degradation of polyprodrugs is an important factor to guarantee the successful disposal of the drug delivery system from the body. The degradation of polyprodrugs and release rate of the drugs can be controlled by the type of covalent bonds linking the monomer drug units in the polymer structure. Therefore, various types of polyprodrugs have been developed based on polyesters, polyanhydrides, polycarbonates, polyurethanes, polyamides, polyketals, polymetallodrugs, polyphosphazenes, and polyimines. Furthermore, the presence of stimuli-responsive groups, such as redox-responsive linkages (disulfide, boronate ester, metal-complex, and oxalate), pH-responsive linkages (ester, imine, hydrazone, acetal, orthoester, P-O and P-N), light-responsive (metal-complex, o-nitrophenyl groups) and enzyme-responsive linkages (ester, peptides) allow for a selective degradation of the polymer backbone in targeted tumors. We envision that new strategies providing a more efficient synergistic therapy will be developed by combining polyprodrugs with gene delivery segments and targeting moieties.

Chain-Shattering Polymers as Degradable Microdispersive Solid-Phase Extraction Sorbents

A chain-shattering polymer (CSP) has been proposed as a microdispersive solid-phase extraction (μdSPE) sorbent in a proof-of-concept study of degradable materials for analytical purposes. The responsive CSP was synthesized from 1,3,5-tris(bromomethyl)-2-nitrobenzene acting as the self-immolative trigger responsive unit and 2,6-naphthalenedicarboxylic acid as aromatic linker to enhance noncovalent aromatic interactions with the analytes. The CSP was characterized and applied as a μdSPE sorbent of a group of plasticizers, which were selected as model analytes, from different types of environmental water samples (tap, waste, and spring waters). Gas chromatography coupled to mass spectrometry detection was used for analyte determination. Mean recovery values were in the range of 80%–118% with RSD values below 22%. After the extraction, the polymer could be efficiently degraded by UV irradiation or by chemical reduction, recovering the aromatic linker. This work has proved the potential of CSPs as recyclable sorbents, paving the way to more environmentally benign analytical procedures.

Self-boosting stimulus activation of a polyprodrug with cascade amplification for enhanced antitumor efficacy

The use of polyprodrugs, which bind drugs to polymer chains through responsive linkers, is a potential technique for cancer therapy; however, a lack of endogenous triggering factors limits drug activation in tumor tissue. Herein, we rationally created a reactive oxygen species (ROS)-sensitive polyprodrug (TS_CA/DOX) with cascade amplification of triggering agents and drug activation by incorporating both an ROS signal amplifier (TA_CA) and a drug activation amplifier (SIP_DOX) into a delivery system. Endogenous ROS as a triggering mechanism kicked off the initial circulation phase to increase intracellular ROS signals. Subsequently, the enhanced ROS initiated the second degradation step, allowing the polyprodrug SIP_DOX to fracture spontaneously in a domino-like fashion, resulting in self-accelerated drug activation in tumor tissue. Therefore, the polyprodrug created in this study with cascade amplification of drug activation holds great promise for effective cancer treatment.

A multifunctional platinum(IV) and cyanine dye-based polyprodrug for trimodal imaging-guided chemo-phototherapy

Imaging-guided chemo-phototherapy based on a single nanoplatform has a great significance to improve the efficiency of cancer therapy and diagnosis. However, high drug content, no burst release and real-time tracking of nanodrugs are the three main challenges for this kind of multifunctional nanotheranostics. In this work, we developed an innovative theranostic nanoplatform based on a Pt(IV) prodrug and a near-infrared (NIR) photosensitizer. A Pt(IV) prodrug and a cyanine dye (HOCyOH, Cy) were copolymerized and incorporated into the main chain of a polyprodrug (PCPP), which self-assembled into nanoparticles (NPs) with ∼27.61% Cy loading and ∼9.37% Pt loading, respectively. PCPP NPs enabled reduction-triggered backbone cleavage of polyprodrugs and bioactive Pt(II) release; Cy could be activated under 808 nm laser irradiation to produce local hyperthermia and reactive oxygen species (ROS) for phototherapy. Moreover, PCPP NPs with extremely high Cy and Pt heavy metal contents in the backbone of the polyprodrug could directly track the nanodrugs themselves via near-infrared fluorescence (NIRF) imaging, photothermal imaging, and computed tomography (CT) imaging in vitro and in vivo. As revealed by trimodal imaging, PCPP NPs were found to exhibit excellent tumor accumulation and antitumor efficiency after intravenous injection into H22-tumor-bearing mice. The dual-drug backboned polyprodrug nanoplatform exhibited great potential for bioimaging and combined chemo-phototherapy.

Polyprodrug Nanomedicines: An Emerging Paradigm for Cancer Therapy

Nanomedicines have the potential to provide advanced therapeutic strategies in combating tumors. Polymer-prodrug-based nanomedicines are particularly attractive in cancer therapies owing to the maximum drug loading, prolonged blood circulation, and reduced premature leakage and side effects in comparison with conventional nanomaterials. However, the difficulty in precisely tuning the composition and drug loading of polymer-drug conjugates leads to batch-to-batch variations of the prodrugs, thus significantly restricting their clinical translation. Polyprodrug nanomedicines inherit the numerous intrinsic advantages of polymer-drug conjugates and exhibit well-controlled composition and drug loading via direct polymerization of therapeutic monomers, representing a promising nanomedicine for clinical tumor therapies. In this review, recent advances in the development of polyprodrug nanomedicines are summarized for tumor elimination. Various types of polyprodrug nanomedicines and the corresponding properties are first summarized. The unique advantages of polyprodrug nanomedicines and their key roles in various tumor therapies are further highlighted. Finally, current challenges and the perspectives on future research of polyprodrug nanomedicines are discussed.

Recent advances in self-immolative linkers and their applications in polymeric reporting systems

Interest in self-immolative chemistry has grown over the past decade with more research groups harnessing the versatility to control the release of a compound from a larger chemical entity, given...

Construction of Glycogen-Based Nanoparticles Loaded with Resveratrol for the Alleviation of High-Fat Diet-Induced Nonalcoholic Fatty Liver Disease

The purpose of this study was to construct a glycogen (Gly)-based nanoparticle (NP) with liver-targeted and redox response to effectively deliver resveratrol (Res) for improving nonalcoholic fatty liver disease (NAFLD). Herein, Gly was modified using α-lipoic acid (α-LA) and lactobionic acid (Lac) to obtain an amphiphilic polymer (Gly-LA-Lac), which was self-assembled in water and then encapsulated in Res to form Res NPs with excellent stability. As expected, the Res NPs exhibited liver-targeted and redox response release behavior. In vitro cell studies demonstrated that the nanocarrier treatment enhanced the cellular uptake of Res and reduced oxidative stress and inflammatory factor levels. Meanwhile, the in vivo tests proved that the nanocarriers effectively reduced hepatic lipid accumulation and oxidative stress levels via regulating the TLR4/NF-κB signal pathway to improve liver damage in NAFLD mice. In conclusion, this study provides a promising strategy through the construction of Gly-based nanocarriers for the encapsulation of Res to effectively alleviate the process of NAFLD.

Self-Immolative Polymers: An Emerging Class of Degradable Materials with Distinct Disassembly Profiles

Self-immolative polymers are an emerging class of macromolecules with distinct disassembly profiles that set them apart from other general degradable materials. These polymers are programmed to disassemble spontaneously from head to tail, through a domino-like fragmentation, upon response to extremal stimuli. In the time since we first reported this unique type of molecule, several groups around the world have developed new, creative molecular structures that perform analogously to our pioneering polymers. Self-immolative polymers are now widely recognized as an important class of stimuli-responsive materials for a wide range of applications such as signal amplification, biosensing, drug delivery, and materials science. The quinone-methide elimination was shown to be an effective tool to achieve rapid domino-like fragmentation of polymeric molecules. Thus, numerous applications of self-immolative polymers are based on this disassembly chemistry. Although several other fragmentation reactions achieved the function requested for sequential disassembly, we predominantly focused in this Perspective on examples of self-immolative polymers that disassemble through the quinone-methide elimination. Selected examples of self-immolative polymers that disassembled through other chemistries are briefly described. The growing demand for stimuli-responsive degradable materials with novel molecular backbones and enhanced properties guarantees the future interest of the scientific community in this unique class of polymers.

A Water-Soluble Polyacid Polymer Based on Hydrophilic Metal-Organic Frameworks Using Amphoteric Carboxylic Acid Ligands as Linkers for Hydroxycamptothecin Loading and Release In Vitro

The poor water solubility and severe side effects of hydroxycamptothecin (HCPT) limit its clinical application; therefore, it is necessary to synthesize applicable nanodrug carriers with good solubility to expand the applications of HCPT. In this study, a hydrophilic metal-organic framework (MOF) with amphoteric carboxylic acid ligands as linkers was first synthesized and characterized. Then, water-soluble acrylamide and methacrylic acid were applied as monomers to prepare a water-soluble polyacid polymer MOF@P, which had a solubility of 370 μg/mL. The effects of the MOF@P material on the HCPT loading and solubility were investigated. The results showed that the polymer material could improve the HCPT solubility in water. Moreover, the in vitro release study indicated that the MOF@P polymeric composite exhibited a sustained-release effect on HCPT, with a cumulative release rate of 30.18% in 72 h at pH 7.4. Furthermore, the cytotoxicity test demonstrated that the hydrophilic MOF and the MOF@P had low cell toxicities. The results indicate that the prepared MOF@P polymeric complex can be applied for the sustained release of HCPT in clinics.

Dual-Responsive Material Based on Catechol-Modified Self-Immolative Poly(Disulfide) Backbones

Functional materials engineered to degrade upon triggering are in high demand due their potentially lower impact on the environment as well as their use in sensing and in medical applications. Here, stimuli-responsive polymers are prepared by decorating a self-immolative poly(dithiothreitol) backbone with pendant catechol units. The highly functional polymer is fashioned into stimuli-responsive gels, formed through pH-dependent catecholato-metal ion cross-links. The gels degrade in response to specific environmental changes, either by addressing the pH responsive, non-covalent, catecholato-metal complexes, or by addition of a thiol. The latter stimulus triggers end-to-end depolymerization of the entire self-immolative backbone through end-cap replacement via thiol-disufide exchanges. Gel degradation is visualized by release of a dye from the supramolecular gel as it itself is converted into smaller molecules.

Acid-triggered degradable polyprodrug with drug as unique repeating unit for long-acting drug delivery with minimal leakage

Acid-triggered degradable polyprodrug P(DOX-AH) was designed for long-acting drug delivery with minimal leakage and enhanced antitumor efficacy. By facile polymerization of doxorubicin (DOX) and N-(tert-butoxycarbonyl)acryloylhydrazine (Boc-AH), P(DOX-AH) with drug as unique repeating unit was obtained, possessing an ultrahigh drug content. It was stable in the neutral media but could degrade completely into DOX-AH in the acidic media without any other by-product. The cleavage of the hydrazone linkage between the DOX-AH repeating units was revealed by the LC-MS/MS analysis. Furthermore, a slow solubility-controlled drug release performance was achieved in the acidic media because of the low solubility of the released DOX-AH. Even with the slow DOX-AH releasing, the enhanced antitumor efficacy was obtained than free DOX in the in vitro cellular experiments. These features demonstrated the promising potential of the proposed polyprodrug for long-acting drug delivery in future tumor chemotherapy.

Nanoparticulation of Prodrug into Medicines for Cancer Therapy

This article provides a broad spectrum about the nanoprodrug fabrication advances co-driven by prodrug and nanotechnology development to potentiate cancer treatment. The nanoprodrug inherits the features of both prodrug concept and nanomedicine know-how, attempts to solve underexploited challenge in cancer treatment cooperatively. Prodrugs can release bioactive drugs on-demand at specific sites to reduce systemic toxicity, this is done by using the special properties of the tumor microenvironment, such as pH value, glutathione concentration, and specific overexpressed enzymes; or by using exogenous stimulation, such as light, heat, and ultrasound. The nanotechnology, manipulating the matter within nanoscale, has high relevance to certain biological conditions, and has been widely utilized in cancer therapy. Together, the marriage of prodrug strategy which shield the side effects of parent drug and nanotechnology with pinpoint delivery capability has conceived highly camouflaged Trojan horse to maneuver cancerous threats.

Photo- and Acid-Degradable Polyacylhydrazone-Doxorubicin Conjugates

Light-mediated polymer degradation has attracted considerable attention in various applications, including photo-patterning, tissue engineering and photo-triggered drug delivery. In this study, we report the synthesis and characterization of a new, linear, main-chain photo- and acid-degradable copolymer based on acylhydrazone linkages. The polymer was synthesized via a step-growth copolymerization of adipic acid dihydrazide with a bifunctional poly(ethylene glycol) bearing benzaldehyde end-groups, under mild acidic conditions, to afford a hydrophilic PEG-alt-adipic acid (PEG-alt-AA) alternating copolymer. The synthesized polymer was characterized by size exclusion chromatography, proton nuclear magnetic resonance and attenuated total reflection-Fourier transform infrared spectroscopies. The main-chain photo- and acid-induced degradation of the copolymer in dimethylsulfoxide and water, respectively, was verified by UV-vis spectroscopy at light intensities as low as 0.1 mW cm⁻² at λ = 254 nm. Next, a model anticancer drug, doxorubicin (DOX), was chemically linked to the polymer chain end(s) via acylhydrazone bond(s), resulting in amphiphilic PEG-alt-adipic acid-DOX (PEG-alt-AA-DOX) polymer–drug conjugates. The conjugates were self-assembled in water to form spherical nanoparticles, as evidenced by scanning and transmission electron microscopies. The irradiation of the self-assembled PEG-alt-AA-DOX conjugates with UV light and the decrease of the solution pH resulted in the disruption of the assemblies due to the photolysis and acidolysis of the acylhydrazone bonds, and the release of the therapeutic cargo.

Facile one-pot synthesis of amphiphilic acid/hypoxia co-triggered degradable diblock polyprodrug for tumor selective drug delivery

More precise drug release is expected by conjugating the drug structural units in the polyprodrugs with dynamic covalent bonds responding to different stimuli. Here, amphiphilic acid/hypoxia co-triggered degradable diblock polyprodrug was designed via a facile one-pot method with drug content of 78.6% (1.22 mmol/g) and relatively molecular weight of 2.08 × 10⁴, by condensation polymerization of acid-sensitive dimer of doxorubicin (D-DOX_ADH) with 2-iminothiolane, in presence of PEGylated D-DOX_ADH as end capping reagent for the PEGylation. Polyprodrug nanoparticles were easily obtained with mean hydrodynamic diameter of 177.6 ± 8.9 nm via self-assembly, which showed excellent acid/hypoxia co-triggered degradation and drug release performance. The ideal tumor selective cytotoxicity and enhanced antitumor efficacy were revealed with the in vitro cellular experiments. Such features make the proposed amphiphilic acid/hypoxia co-triggered degradable diblock polyprodrug a promising candidate for tumor chemotherapy.

Tuning the physicochemical properties of reticular covalent organic frameworks (COFs) for biomedical applications

Since the first report by Yaghi's group in 2005, research enthusiasm has been increasingly raised to synthesize diverse crystalline porous materials as -B-O-, -C-N-, -C-C-, and -C-O- linkage-based COFs. Recently, the biomedical applications of COFs have become more and more attractive in biomedical applications, including drug delivery, bioimaging, biosensing, antimicrobial, and therapeutic applications, as these materials bear well-defined crystalline porous structures and well-customized functionalities. However, the clinical translation of these research findings is challenging due to the formidable hindrances for in vivo use, such as low biocompatibility, poor selectivity, and long bio-persistence. Some attempts have raised a promising solution towards these obstacles by tailored engineering the functionalities of COFs. To speed up the clinical translations of COFs, a short review of principles and strategies to tune the physicochemical properties of COFs is timely and necessary. In this review, we summarized the biomedical utilities of COFs and discussed the related key physicochemical properties. To improve the performances of COFs in biomedical uses, we propose approaches for the tailored functionalization of COFs, including large-scale manufacture, standardization in nanomedicines, enhancing targeting efficacy, maintaining predesigned functions upon transformations, and manipulation of multifunctional COFs. We expect that this minireview strengthens the fundamental understandings of property-bioactivity relationships of COFs and provides insights for the rational design of their high-order reticular structures.

Aptamer-based ATP-responsive delivery systems for cancer diagnosis and treatment

In recent years, many stimuli-triggered drug delivery platforms have been designed to deliver drugs accurately to specific sites and reduce their side effects, improving "on-demand" therapeutic efficacy. Adenosine-5'-triphosphate (ATP)-responsive drug delivery methods are examples of these systems that use ATP molecules as a trigger for delivery of therapeutic agents. Since intra- and extra-cellular ATP concentrations are significantly different from each other (1-10 mM and <0.4 mM, respectively), the use of ATP can be a practical method for regulating drug release. Aptamers possess unique properties including, ligand-specific response, short sequence (~ 20-80 bases) and easy functionalization. Thus, their combination with ATP-responsive systems results in more accurate drug delivery systems and greater control of drug release. A wide range of nanoparticles, such as polymeric nanogels, liposomes, metallic nanoparticles, protein, or DNA nano-assemblies, have been employed in the fabrication of nanocarriers. In this review, we describe several ATP-responsive drug delivery systems based on the various carriers and discuss the challenges and strengths of each method.

Construction of biodegradable core cross-linked nanoparticles from near infrared dyes encoded in polyprodrug amphiphiles and investigation of their synergistic anticancer activity

Amphiphilic polyprodrugs with reduction-responsive camptothecin prodrug and photothermal converted IR780 dyes was performed via core cross-linking protocol. The nanoparticles could be served as a nanocarrier and presented severe cytotoxicity to HeLa cells.

Synthesis Characterization of Platinum (IV) Complex Curcumin Backboned Polyprodrugs: In Vitro Drug Release Anticancer Activity

The conventional mono-chemotherapy still suffers from unsatisfied potency for cancer therapy due to tumor heterogeneity and the occurrence of drug resistance. Combination chemotherapy based on the nanosized drug delivery systems (nDDSs) has been developed as a promising platform to circumvent the limitations of mono-chemotherapy. In this work, starting from cisplatin and curcumin (Cur), we prepared a dual drug backboned shattering polymeric nDDS for synergistic chemotherapy. By in situ polymerization of the Cur, platinum (IV) complex-based prodrug monomer (DHP), L-lysine diisocyanate (LDI), and then conjugation with a hydrophilic poly (ethylene glycol) monomethyl ether (mPEG) derivative, a backbone-type platinum (IV) and Cur linkage containing mPEG-poly(platinum-co-Cur)-mPEG (PCPt) copolymer was synthesized. Notably, the platinum (IV) (Pt (IV)) and Cur were incorporated into the hydrophobic segment of PCPt with the fixed drugs loading ratio and high drugs loading content. The batch-to-batch variability could be decreased. The resulting prodrug copolymer then self-assembled into nanoparticles (PCPt NPs) with an average diameter around 100 nm, to formulate a synergetic nDDS. Importantly, PCPt NPs could greatly improve the solubility and stability of Cur. In vitro drug release profiles have demonstrated that PCPt NPs were stable in PBS 7.4, rapid burst release was greatly decreased, and the Pt and Cur release could be largely enhanced under reductive conditions due to the complete dissociation of the hydrophobic main chain of PCPt. In vitro cell viability test indicated that PCPt NPs were efficient synergistic chemotherapy units. Moreover, PCPt NPs were synergistic for cisplatin-resistant cell lines A549/DDP cells, and they exhibited excellent reversal ability of tumor resistance to cisplatin. This work provides a promising strategy for the design and synthesis of nDDS for combination chemotherapy.

Targeted Engineering of Medicinal Chemistry for Cancer Therapy: Recent Advances and Perspectives

Severe side effects and poor therapeutic efficacy are the main drawbacks of current anticancer drugs. These problems can be mitigated by targeting, but the targeting efficacy of current drugs is poor and urgently needs improvement. Taking this into consideration, this Review first summarizes the current targeting strategies for cancer therapy in terms of cancer tissue and organelles. Then, we analyse the systematic targeting of anticancer drugs and conclude that a typical journey for a targeted drug administered by intravenous injection is a CTIO cascade of at least four steps. Furthermore, to ensure high overall targeting efficacy, the properties of a targeting drug needed in each step are further analysed, and some guidelines for structure optimization to obtain effective targeting drugs are offered. Finally, some viewpoints highlighting the crucial problems and potential challenges of future research on targeted cancer therapy are presented. This review could actively promote the development of precision medicine against cancer.

Dimerization-induced self-assembly of a redox-responsive prodrug into nanoparticles for improved therapeutic index

Although some formats of nanomedicines are now available for clinical use, the translation of new nanoparticles to the clinic remains a considerable challenge. Here, we describe a simple yet cost-effective strategy that converts a toxic drug, cabazitaxel, into a safe and effective nanomedicine. The strategy involves the ligation of drug molecules via a self-immolating spacer, followed by dimerization-induced self-assembly to assemble stable nanoparticles. Self-assembled cabazitaxel dimers could be further refined by PEGylation with amphiphilic polymers suitable for preclinical studies. This protocol enables the formation of systemically injectable nanoparticles (termed SNPs) with nearly quantitative entrapment efficiencies and exceptionally high drug loading (> 86%). In healthy mice, PEGylated SNPs show a favorable safety profile, with reduced systemic toxicity and negligible immunotoxicity. In two separate mouse xenograft models of cancer, administration of SNPs produces efficient antitumor activity with durable tumor suppression during therapeutic studies. Overall, this methodology opens up a practical and expedient route for the fabrication of clinically useful nanomedicines, transforming a hydrophobic and highly toxic drug into a systemic self-deliverable nanotherapy. STATEMENT OF SIGNIFICANCE: Despite the great progress in cancer nanomedicines, clinical translation of nanomedicines still remains a considerable challenge. In this study, we designed a self-assembling nanoplatform based on cabazitaxel dimer reversibly ligated via a bioactivatable linker. This approach enabled the generation of systemically injectable nanomedicines with quantitative entrapment efficiencies and exceptionally high drug loading (> 86%), which greatly obviates concerns about excipient-associated side effects. Self-assembled dimeric cabazitaxel exhibited a higher safety profile than free cabazitaxel and negligible immunotoxicity in animals. This is a practical and expedient example how the chemical ligation of a hydrophobic and highly toxic anticancer drug can be leveraged to create a self-assembling delivery nanotherapy which preserves inherent pharmacologic efficacy while reduces in vivo systemic and immune toxicity.

In Situ Formation of Polymeric Nanoassemblies Using an Efficient Reversible Click Reaction

Polymer-drug conjugates are promising as strategies for drug delivery, because of their high drug loading capacity and low premature release profile. However, the preparation of these conjugates is often tedious. In this paper, we report an efficient method for polymer-drug conjugates using an ultrafast and reversible click reaction in a post-polymerization functionalization strategy. The reaction is based on the rapid condensation of boronic acid functionalities with salicylhydroxamates. The polymer, bearing the latter functionality, has been designed such that the reaction with boronic acid bearing drugs induces an in situ self-assembly of the conjugates to form well-defined nanostructures. We show that this method is not only applicable for molecules with an intrinsic boronic acid group, but also for the other molecules that can be linked to aryl boronic acids through a self-immolative linker. The linker has been designed to cause traceless release of the attached drug molecules, the efficiency of which has been demonstrated through intracellular delivery.

Base-triggered self-amplifying degradable polyurethanes with the ability to translate local stimulation to continuous long-range degradation

A new type of base-triggered self-amplifying degradable polyurethane is reported that degrades under mild conditions, with the release of increasing amounts of amine product leading to self-amplified degradation. The polymer incorporates a base-sensitive Fmoc-derivative into every repeating unit to enable highly sensitive amine amplified degradation. A sigmoidal degradation curve for the linear polymer was observed consistent with a self-amplifying degradation mechanism. An analogous cross-linked polyurethane gel was prepared and also found to undergo amplified breakdown. In this case, a trace amount of localized base initiates the degradation, which in turn propagates through the material in an amplified manner. The results demonstrate the potential utility of these new generation polyurethanes in enhanced disposability and as stimuli responsive materials.

Synthesis of Acid-Labile Poly(Doxazolidine) as a Polyprodrug with an Ultra-High Drug Content for Self-Delivery of High-Performance Chemotherapeutics

Drug self-delivery systems (DSDSs) have attracted intense attention due to their high drug content. However, their practical application still suffers from their premature drug leakage, slow drug release, and/or low antitumor efficacy of the released small molecular drugs. Here, acid-labile poly(Doxazolidine) (P(Doxaz)) is designed as a polyprodrug for the self-delivery of high antitumor chemotherapeutics (Doxazolidine (Doxaz)), with an ultrahigh Doxaz content of 92.45%. The P(Doxaz) nanoparticles could completely degrade into Doxaz within 10 h in the simulated tumor intracellular microenvironment, with a low drug leakage of 12.9% over 12 h in the normal physiological media. Owing to the ultrahigh drug content, fast acid-triggered degradation and drug release, and high antitumor efficacy of Doxaz, the proposed DSDS possesses an enhanced antiproliferation efficacy compared to the free DOX, demonstrating its potential in future tumor treatments.

Self-immolative polymers in biomedicine

Biomedical use cases for self-immolative polymers.

Acoustically responsive polydopamine nanodroplets: A novel theranostic agent

Ultrasound-induced cavitation has been used as a tool of enhancing extravasation and tissue penetration of anticancer agents in tumours. Initiating cavitation in tissue however, requires high acoustic intensities that are neither safe nor easy to achieve with current clinical systems. The use of cavitation nuclei can however lower the acoustic intensities required to initiate cavitation and the resulting bio-effects in situ. Microbubbles, solid gas-trapping nanoparticles, and phase shift nanodroplets are some examples in a growing list of proposed cavitation nuclei. Besides the ability to lower the cavitation threshold, stability, long circulation times, biocompatibility and biodegradability, are some of the desirable characteristics that a clinically applicable cavitation agent should possess. In this study, we present a novel formulation of ultrasound-triggered phase transition sub-micrometer sized nanodroplets (~400 nm) stabilised with a biocompatible polymer, polydopamine (PDA). PDA offers some important benefits: (1) facile fabrication, as dopamine monomers are directly polymerised on the nanodroplets, (2) high polymer biocompatibility, and (3) ease of functionalisation with other molecules such as drugs or targeting species. We demonstrate that the acoustic intensities required to initiate inertial cavitation can all be achieved with existing clinical ultrasound systems. Cell viability and haemolysis studies show that nanodroplets are biocompatible. Our results demonstrate the great potential of PDA nanodroplets as an acoustically active nanodevice, which is highly valuable for biomedical applications including drug delivery and treatment monitoring.

Tumor-Specific Expansion of Oxidative Stress by Glutathione Depletion and Use of a Fenton Nanoagent for Enhanced Chemodynamic Therapy

Amplifying intracellular oxidative stress effectively destroys cancer cells. In addition, iron-mediated Fenton reaction converts endogenous H₂O₂ to produce hypertoxic hydroxyl radical (^•OH), resulting in irreversible oxidative damage to combat tumor cells. This method is known as chemodynamic therapy (CDT). Overexpressed glutathione (GSH) in tumor cells efficiently scavenges ^•OH, significantly reducing the curative effects of CDT. To overcome this challenge and enhance intracellular oxidative stress, iron oxide nanocarriers loaded with β-lapachone (Lapa) drugs (Fe₃O₄-HSA@Lapa) were constructed and had both Fenton-like agents and GSH depletion properties to amplify intracellular oxidative stress. Release of Lapa selectively increases tumor site-specific generation of H₂O₂ via NAD(P)H: quinone oxidoreductase 1 (NQO1) catalysis. Subsequently, the iron ions released from the ionization of Fe₃O₄ in the acidic environment selectively convert H₂O₂ into highly toxic ^•OH by Fenton reaction, dramatically improving CDT with minimal systemic toxicity due to low NQO1 expression in normal tissues. Meanwhile, released Lapa consumes GSH in the tumor, amplifying oxidative stress and enhancing the efficacy of CDT. Designed Fe₃O₄-HSA@Lapa nanoparticles (NPs) exhibit perfect targeting capability, prolonged blood circulation, and increased tumor accumulation. Furthermore, Fe₃O₄-HSA@Lapa NPs effectively enhance the inhibition of tumor growth and reduce the side effects of anticancer drugs. This work establishes a remarkably enhanced tumor-selective CDT against NQO1-overexpressing tumors by significantly inducing intratumoral oxidative stress with minimal side effects.

Light-Activatable Prodrug and AIEgen Copolymer Nanoparticle for Dual-Drug Monitoring and Combination Therapy

Polyprodrug nanoparticles have been employed recently for safer and more effective cancer treatment. However, it remains a challenge to elucidate how and when the polyprodrug nanoparticles are dissociated and activated to release active drugs in cancer cells. Herein, a visible light-activatable Pt(IV) prodrug and an aggregation-induced emission luminogen (AIEgen) were copolymerized and embedded in the main chain of PtAIECP, and the chemotherapeutic doxorubicin (DOX) was subsequently encapsulated in the nanoparticles self-assembled by PtAIECP (PtAIECP@DOX NP). PtAIECP@DOX NP enabled the monitoring of both the light-activation of Pt(IV) prodrug to active Pt(II) and release of encapsulated DOX intracellularly through the fluorescence "turn-on" in the course of visible-light-induced polymer-main-chain cleavage and self-assembled structure dissociation in vitro and ex vivo. The synergistic anticancer efficacy of the activated Pt(II) drug and DOX in PtAIECP@DOX NP was also investigated in vitro and in vivo. The implementation of polyprodrug and AIE combination strategy empowered dual drug release and monitoring, which could be further used to guide the temporal and spatial control of light irradiation to maximize therapeutic efficiency, and will inspire other combinational bioimaging and therapy strategies.

Facile fabrication of pH-responsive nanoparticles from cellulose derivatives via Schiff base formation for controlled release

A controllable drug delivery system demonstrates a promising tool for diverse biomedical applications. In this work, a group of amphiphilic macromolecules was designed and prepared via Schiff base reactions between 2,3-dialdehyde cellulose (DAC) with oleylamine and amino-containing compounds. Benefiting from the self-assemble process of these amphiphilic macromolecules in the poor solvent, a group of novel pH-responsive nanoparticles (NPs) were facilely fabricated by using nanoprecipitation dropping technique. The high amount of aldehyde groups on DAC chains enabled immobilization of tunable amounts of amine compounds (up to 1.67 mmol/g) in the NPs. Furthermore, the Schiff base bonds in NPs allowed the efficient release of the drug in acidic tumor microenvironment by cleaving the Schiff base linkages. This study demonstrates the formation of a group of novel pH-sensitive and drug-loadable NPs, which provide a simple and efficient drug delivery system for the potential application for cancer treatment.

Polymer-drug conjugate therapeutics: advances, insights and prospects

Polymer-drug conjugates have long been a mainstay of the drug delivery field, with several conjugates successfully translated into clinical practice. The conjugation of therapeutic agents to polymeric carriers, such as polyethylene glycol, offers several advantages, including improved drug solubilization, prolonged circulation, reduced immunogenicity, controlled release and enhanced safety. In this Review, we discuss the rational design, physicochemical characteristics and recent advances in the development of different classes of polymer-drug conjugates, including polymer-protein and polymer-small-molecule drug conjugates, dendrimers, polymer nanoparticles and multifunctional systems. Current obstacles hampering the clinical translation of polymer-drug conjugate therapeutics and future prospects are also presented.

Nanocapsules for Programmed Neurotransmitter Release: Toward Artificial Extracellular Synaptic Vesicles

Nanocapsules present a promising platform for delivering chemicals and biomolecules to a site of action in a living organism. Because the biological action of the encapsulated molecules is blocked until they are released from the nanocapsules, the encapsulation structure enables triggering of the topical and timely action of the molecules at the target site. A similar mechanism seems promising for the spatiotemporal control of signal transduction triggered by the release of signal molecules in neuronal, metabolic, and immune systems. From this perspective, nanocapsules can be regarded as practical tools to apply signal molecules such as neurotransmitters to intervene in signal transduction. However, spatiotemporal control of the payload release from nanocapsules persists as a key technical issue. Stimulus-responsive nanocapsules that release payloads in response to external input of physical stimuli are promising platforms to enable programmed payload release. These programmable nanocapsules encapsulating neurotransmitters are expected to lead to new insights and perspectives related to artificial extracellular synaptic vesicles that might provide an experimental and therapeutic strategy for neuromodulation and nervous system disorders.