A Step-by-Step Multiple Stimuli-Responsive Nanoplatform for Enhancing Combined Chemo-Photodynamic Therapy

Glutathione Triggered Cascade Degradation of an Amphiphilic Poly(disulfide)-Drug Conjugate and Targeted Release

A bioreducible poly(disulfide)-derived amphiphilic block copolymer-drug conjugate (loading content 31%) was synthesized by post-polymerization modification. It shows redox-responsive polymersome assembly in water with aggregation induced emission property arising from the appended Camptothecin (CPT) drug. Glutathione (GSH), a tripeptide overexpressed in cancer cells, triggers a cascade reaction resulting in simultaneous degradation of the polymer backbone (consisting of disulfide linkage) and the release of the pendant drug. The cascade reaction involves GSH trigger cleavage of the backbone disulfide bond producing free thiol followed by its intrachain nucleophilic attack to the adjacent carbonate group that links the appended drug molecule. The polymeric pro-drug exhibits killing efficiency to a cancer cell with remarkably low IC₅₀ value of 3.1 μg/mL (based on the CPT concentration) while it shows negligible toxicity to a normal cell up to polymer concentration 300 μg/mL.

Oxygen Production of Modified Core-Shell CuO@ZrO2 Nanocomposites by Microwave Radiation to Alleviate Cancer Hypoxia for Enhanced Chemo-Microwave Thermal Therapy

There are acknowledged risks of metastasis of cancer cells and obstructing cancer treatment from hypoxia. In this work, we design a multifunctional nanocomposite for treating hypoxia based on the oxygen release capability of CuO triggered by microwave (MW). Core-shell CuO@ZrO₂ nanocomposites are prepared by confining CuO nanoparticles within the cavities of mesoporous ZrO₂ hollow nanospheres. 1-Butyl-3-methylimidazolium hexafluorophosphate (IL) is loaded to the CuO@ZrO₂ nanocomposites for improving microwave thermal therapy (MWTT). 1-Tetradecanol (PCM) is introduced to regulate the release of chemotherapeutic drugs of doxorubicin (DOX). Thus, the IL-DOX-PCM-CuO@ZrO₂ multifunctional (IDPC@Zr) nanocomposites are obtained. Finally, IDPC@Zr nanocomposites are modified by monomethoxy polyethylene glycol sulfhydryl (mPEG-SH, 5 kDa) (IDPC@Zr-PEG nanocomposites). IDPC@Zr-PEG nanocomposites can produce oxygen in the tumor microenvironment during the course of tumor treatment, thereby alleviating the hypoxic state and improving the therapeutic effect. In vivo antitumor experiments demonstrate a very high tumor inhibition rate of 92.14%. In addition, computed tomography (CT) imaging contrast of the nanocomposites can be enhanced due to the high atomic number of Zr. Therefore, IDPC@Zr-PEG nanocomposites can be applied for monitoring the tumor-treatment process in real time. This combined therapy offers many opportunities, such as the production of oxygen from CuO nanoparticles by MW to alleviate hypoxia, the enhancement of combined treatment of MWTT and chemotherapy, and the potential application of CT imaging to visualize the treatment process, which therefore provides a promising method for the clinical treatment of tumors in the future.

Enhancing the Accumulation of Polymer Micelles by Selectively Dilating Tumor Blood Vessels with NO for Highly Effective Cancer Treatment

The accumulation of nanoparticles in tumors by the enhanced permeability and retention (EPR) effect is effective and well known. However, how to maximize accumulation is still a bottleneck in the development of nanomedicine. Herein, a tumor vascular-targeted hybrid polymeric micelle, which has a great capacity to selectively augment the EPR effect of nanoparticles by dilating tumor blood vessels via the activity of nitric oxide (NO), is presented. Under neutral conditions, the micelle is stable, with a long blood circulation half-life due to the carboxylated poly(ethylene glycol) (PEG) layer; in mildly acidic tumor tissues, the micelle can selectively target the tumor blood vessels by the exposed cyclic Arg-Gly-Asp peptide (cRGD) peptides, which is realized with a pH-dependent hydrolysis of the monomethoxy PEG layer. Simultaneously, exposed copper ions catalyze the decomposition of endogenous NO donors, which generates NO in situ, leading to vasodilation and increased tumor vascular permeability. As a result, the accumulation of nanoparticles is significantly enhanced, and a high accumulation of doxorubicin in tumors is achieved at 48 h after injection. This high dose of therapeutic agent produces a large inhibition of tumor growth (94%) in cancer treatment, and shows no general toxicity, with 100% of the mice surviving the treatment regimen.

A high therapeutic efficacy of polymeric prodrug nano-assembly for a combination of photodynamic therapy and chemotherapy

Combination of photodynamic therapy and chemotherapy has been emerging as a new strategy for cancer treatment. Conventional photosensitizer tends to aggregate in aqueous media, which causes fluorescence quenching, reduces reactive oxygen species (ROS) production, and limits its clinical application to photodynamic therapy. Traditional nanoparticle drug delivery system for chemotherapy also has its disadvantages, such as low drug loading content, drug leakage, and off-target toxicity for normal tissues. Here, we developed a reduction-sensitive co-delivery micelles TB@PMP for combinational therapy, which composed of entrapping a red aggregation-induced emission fluorogen (AIEgen) for photodynamic therapy and PMP that contains a reduction-sensitive paclitaxel polymeric prodrug for chemotherapy. AIEgen photosensitizer illustrates a much improved photostability and ROS production efficiency in aggregate state and PMP loads a high dose of paclitaxel and carries a smart stimuli-triggered drug release property. This co-delivery system provides a better option that replaces AIEgen photosensitizer for cancer diagnosis and therapy.

Xiaoqing Yi et al. report a co-drug delivery micelle system that demonstrates a high therapeutic efficacy for cancer. This system shows a much improved drug load, photostability, and production of reactive oxygen species, compared to traditional photosensitizer-loaded nanoparticles.

Recent Advances in Targeted Tumor Chemotherapy Based on Smart Nanomedicines

Efficacy and safety of chemotherapeutic drugs constitute two major criteria in tumor chemotherapy. Nanomedicines with tumor-targeted properties hold great promise for improving the efficacy and safety. To design targeted nanomedicines, the pathological characteristics of tumors are extensively and deeply excavated. Here, the rationale, principles, and advantages of exploiting these pathological characteristics to develop targeted nanoplatforms for tumor chemotherapy are discussed. Homotypic targeting with the ability of self-recognition to source tumors is reviewed individually. In the meanwhile, the limitations and perspective of these targeted nanomedicines are also discussed.

PEGylated Multistimuli-Responsive Dendritic Prodrug-Based Nanoscale System for Enhanced Anticancer Activity

A PEGylated multistimuli-responsive dendritic copolymer-doxorubicin (DOX) prodrug-based nanoscale system was developed as a delivery model for hydrophobic drugs. In this system, PEGylation did not only prolong circulation of the nanoscale system in the body (average half-life of 14.6 h, four times longer than that of the free drug), but also allowed the system to aggregate into nanoparticles (NPs) because of interactions between hydrophilic (polyethylene glycol) and hydrophobic (dendritic prodrug) moieties for better uptake through endocytosis (around 150 nm of particle size with a neutrally charged surface for the PEGylated dendritic prodrug with 12.1 wt % of DOX). The dendritic structure was built by bridging poly[ N-(2-hydroxypropyl)methacrylamide] segments with enzyme-responsive GFLG (Gly-Phe-Leu-Gly tetrapeptide) linkers. DOX was released by hydrolyzing the hydrazone bond between DOX and the copolymer framework in the acidic endosomes/lysosomes. In vitro studies on DOX released from the NPs induced mitochondrial dysfunction during apoptosis. By imaging the main organs and tumor tissues from mice treated with the NPs, boosted accumulation of this nanoscale medicine was found in tumor tissues, leading to a decrease in toxicity and side effects to normal tissues and enhancement in drug tolerance. In the 4T1 breast cancer model, these NPs exhibited a superior antitumor efficacy confirmed by inhibiting angiogenesis, proliferation of tumor tissues, and inducing procedural apoptosis of tumor cells. The highest tumor growth inhibition value mediated by the NPs was up to 86.5%. Therefore, this PEGylated multistimuli-responsive dendritic copolymer-DOX prodrug-based nanoscale system may be further explored as an alternative to traditional chemotherapy for breast cancer treatment.

Preparation of Reduction-Responsive Camptothecin Nanocapsules by Combining Nanoprecipitation and In Situ Polymerization for Anticancer Therapy

Stimuli-responsive systems for controlled drug release have been extensively explored in recent years. In this work, we developed a reduction-responsive camptothecin (CPT) nanocapsule (CPT-NC) by combining nanoprecipitation and in situ polymerization using a polymerized surface ligand and a disulfide bond-containing crosslinker. Dissolution rate studies proved that the CPT-NCs have robust drug-release profiles in the presence of glutathione (GSH) owing to the division of the disulfide bond crosslinker which triggers the collapse of the polymer layer. Furthermore, the in vitro investigations demonstrated that the CPT-NCs exhibited a high-cellular uptake efficiency and cytotoxicity for cancer cells of squamous cell carcinoma (SCC-15). Our approach thus presents an effective intracellular drug delivery strategy for anticancer therapy.

PDT‐Driven Highly Efficient Intracellular Delivery and Controlled Release of CO in Combination with Sufficient Singlet Oxygen Production for Synergistic Anticancer Therapy

The precise delivery and controllable release of carbon monoxide (CO) to tumor tissues is an emerging anticancer therapy because CO in a high dose can be detrimental to cell survival and tumor growth. However, CO gas therapy is limited by the gaseous nature of CO that hinders its enrichment and controllable release to tumor tissues. Here, a novel photodynamic therapy (PDT)‐driven CO controllable release system (CORM@G3DSP‐Ce6) that integrates the photosensitizer chlorin e6 (Ce6) and H2O2‐sensitive CO releasing molecule CORM‐401 into peptide dendrimer‐based nanogels (G3DSP) is described. Upon excitation with near‐infrared light, Ce6‐mediated photochemical effect not only promotes the efficient cellular internalization of CORM@G3DSP‐Ce6, but also triggers the rapid intracellular CO release from CORM‐401 by depleting the H2O2 produced during PDT. Importantly, the PDT‐driven CO release does not impair the generation capability of singlet oxygen (1O2). As a result, accompanied with the simultaneous generation of large amounts of 1O2 and CO in cells, the combination of PDT and CO gas therapy offers significant synergistic anticancer effects and superior therapeutic safety both in vitro and in vivo.

Metal-Organic Framework-Based Nanoplatform for Intracellular Environment-Responsive Endo/Lysosomal Escape and Enhanced Cancer Therapy

Nowadays, efficient endo/lysosomal escape and the subsequent release of drugs into the cytosol are the major obstacles for nanoplatform-based cancer therapy. Herein, we first report a metal-organic framework-based nanoplatform (doxorubicin@ZIF-8@AS1411) for intracellular environment-responsive endo/lysosomal escape and enhanced cancer therapy. In our system, the nanoplatform was first targeted toward the cancer cells. Then, it was entrapped in endo/lysosomes, where pH-responsive decomposition occurred and abundant Zn ions were released. The released Zn ions could induce an influx of counterions, promote reactive singlet oxygen (ROS) generation to rupture the endo/lysosomal membrane, and accelerate the release of anticancer drugs in the cytosol. Finally, the released drugs and the generation of ROS could synergistically enhance cancer therapy. With excellent biocompatibility, effective endo/lysosomal escape, and enhanced therapeutic effect, the novel drug delivery systems are supposed to become a promising anticancer agent for cancer therapy and bring more opportunities for biomedical application.

Three-in-One Self-Assembled Nanocarrier for Dual-Drug Delivery, Two-Photon Imaging, and Chemo-Photodynamic Synergistic Therapy

We herein present a three-in-one nanoplatform (named Fu/LD@RuCD) for dual-drug delivery, two-photon imaging, and chemo-photodynamic synergistic therapy, enabled by simple self-assembly between adamantine-functionalized ruthenium complexes ([Ru(phen-ad)₃](PF₆)₂, Ru) and natural cyclodextrin (β-CD) monomers. By host-guest chemistry, nanocarrier RuCD 70-90 nm in diameter is fabricated through a very simple mixing step in water at room temperature, in which the octahedral configuration of Ru complex provides a rigid skeleton and the hydrogen bonding of secondary hydroxyl groups formed between two adjacent β-CD monomers displays a bridging role allowing for three-dimensional architectures. The dual-drug-loaded nanoparticle Fu/LD@RuCD (Fu: 5-fluorouracil; LD: lonidamine) effectively penetrates into cancer cells in 8 h and selectively accumulates in lysosomes, in which dual-drug release is promoted by the mildly acidic environment. Under visible light irradiation, nanocarrier RuCD exhibits excellent photodynamic therapy capability by producing sufficient reactive oxygen species and damaging lysosomes, accordingly 5-fluorouracil and lonidamine can escape from lysosomes and reach their sites of action, resulting in mitochondria dysfunction and cancer cell apoptosis. Simultaneously, the excellent photophysical properties of the nanocarrier enable the facile track of drug delivery under one-photon and two-photon excitation. Moreover, in vivo anticancer investigations show that Fu/LD@RuCD can effectively inhibit the tumor growth without systemic side effects by chemo-photodynamic synergistic therapy, and the therapeutic effect is better than the free anticancer drugs and the sole therapeutic modality.

Lactobionic/Folate Dual-Targeted Amphiphilic Maltodextrin-Based Micelles for Targeted Codelivery of Sulfasalazine and Resveratrol to Hepatocellular Carcinoma

In this study, promising approaches of dual-targeted micelles and drug-polymer conjugation were combined to enable injection of poorly soluble anticancer drugs together with site-specific drug release. Ursodeoxycholic acid (UDCA) as a hepatoprotective agent was grafted to maltodextrin (MD) via carbodiimide coupling to develop amphiphilic maltodextrin-ursodeoxycholic acid (MDCA)-based micelles. Sulfasalazine (SSZ), as a novel anticancer agent, was conjugated via a tumor-cleavable ester bond to MD backbone to obtain tumor-specific release, whereas resveratrol (RSV) was physically entrapped within the hydrophobic micellar core. For maximal tumor-targeting, both folic acid (FA) and lactobionic acid (LA) were coupled to the surface of micelles to obtain dual-targeted micelles. The decrease of critical micelle concentration (CMC) from 0.012 to 0.006 mg/mL declares the significance of a dual hydrophobicized core of micelles by both UDCA and SSZ. The dual-targeted micelles showed a great hemocompatibility, as well as enhanced cytotoxicity and internalization into HepG-2 liver cancer cells via binding to overexpressed folate and asialoglycoprotein receptors. In vivo, the micelles demonstrated superior antitumor effects revealed as reduction in the liver/body weight ratio, inhibition of angiogenesis, and enhanced apoptosis. Overall, combined strategies of dual active targeted micelles with bioresponsive drug conjugation could be utilized as a promising approach for tumor-targeted drug delivery.

Plasma membrane-anchorable photosensitizing nanomicelles for lipid raft-responsive and light-controllable intracellular drug delivery

The past decade has witnessed a growing number of nanoparticulate drug delivery systems for cancer treatment. However, insufficient cellular uptake by cancer cells and the undesirable endo/lysosomal entrapment of internalized therapeutic drugs remain the "Achilles heel" of many developed nanoagents. Here, we develop a novel lipid raft-responsive and light-controllable polymeric drug for efficient cytosolic delivery of photosensitizers. Conjugating a photosensitizer protoporphyrin IX (PpIX) to a polyethylene glycol-cholesterol polymer affords the amphiphilic drug (denoted as Chol-PEG-PpIX) that forms micelles in aqueous solutions. The Chol-PEG-PpIX with two hydrophobic units (cholesterol and PpIX) showed robust binding to plasma membranes and enabled significant cellular uptake via two pathways: (1) cholesterol moiety triggered the lipid raft-mediated endocytosis of Chol-PEG-PpIX with minimized endo/lysosomal trafficking after internalization; (2) the membrane-bound PpIX acted as a light-controlled trigger and can augment the permeability of plasma membranes upon laser irradiation, allowing the rapid influx of extracellular Chol-PEG-PpIX within 5 min. For systemic drug delivery, Chol-PEG-PpIX was anchored on the surface of liposomes via in situ membrane modification, which substantially avoided nonspecific binding of Chol-PEG-PpIX to red blood cells during circulation. Besides, the Chol-PEG-PpIX-anchored liposomes exhibited enhanced in vivo fluorescence, reduced liver uptake, prolonged tumor retention, and effective tumor ablation by photodynamic therapy. This work illustrates a new strategy for direct and efficient cytosolic delivery of photosensitizers, which may hold great promise in cancer therapy.

Tumor-targeted and nitric oxide-generated nanogels of keratin and hyaluronan for enhanced cancer therapy

The development of safe and effective nano-drug delivery systems to deliver anticancer drugs to targeted cells and organs is crucial to enhance the therapeutic efficacy and overcome unwanted side effects of chemotherapy. Herein, we prepared CD44-targeted dual-stimuli responsive human hair keratin and hyaluronic acid nanogels (KHA-NGs) through a simple crosslinking method. KHA-NGs, which consisted of spheres 50 nm in diameter, were used as carriers to load the anticancer drug doxorubicin hydrochloride (DOX). The drug release, cellular uptake, cytotoxicity, and targeting ability of DOX-loaded KHA-NGs (DOX@KHA-NGs) were assessed in vitro and the anticancer effects were further evaluated in vivo. The DOX@KHA-NGs had a super-high drug loading capacity (54.1%, w/w) and were stable under physiological conditions (10 μM glutathione (GSH)), with the drug being rapidly released under a tumor cell microenvironment of trypsin and 10 mM GSH. Cellular uptake and in vitro cytotoxicity results indicated that DOX@KHA-NGs specifically targeted cancer cells and effectively inhibited their growth. Furthermore, KHA-NGs were capable of improving intracellular nitric oxide levels, which sensitizes the cells and enhances the anticancer efficacy of chemotherapeutic drugs. In vivo experiments showed that DOX@KHA-NGs had a better anti-tumor effect and lower side effects compared to free DOX. These results suggest that the bio-responsive KHA-NGs have potential applications for targeted cancer therapy.

Photoresponsive Drug/Gene Delivery Systems

Light as an external stimulus can be precisely manipulated in terms of irradiation time, site, wavelength, and density. As such, photoresponsive drug/gene delivery systems have been increasingly pursued and utilized for the spatiotemporal control of drug/gene delivery to enhance their therapeutic efficacy and safety. In this review, we summarized the recent research progress on photoresponsive drug/gene delivery, and two major categories of delivery systems were discussed. The first category is the direct responsive systems that experience photoreactions on the vehicle or drug themselves, and different materials as well as chemical structures responsive to UV, visible, and NIR light are summarized. The second category is the indirect responsive systems that require a light-generated mediator signal, such as heat, ROS, hypoxia, and gas molecules, to cascadingly trigger the structural transformation. The future outlook and challenges are also discussed at the end.

Light-Activated ROS-Responsive Nanoplatform Codelivering Apatinib and Doxorubicin for Enhanced Chemo-Photodynamic Therapy of Multidrug-Resistant Tumors

Clinical chemotherapy confronts a challenge resulting from cancer-related multidrug resistance (MDR), which can directly lead to treatment failure. To address it, an innovative approach is proposed to construct a light-activated reactive oxygen species (ROS)-responsive nanoplatform based on a protoporphyrin (PpIX)-conjugated and dual chemotherapeutics-loaded polymer micelle. This system combines chemotherapy and photodynamic therapy (PDT) to defeat the MDR of tumors. Such an intelligent nanocarrier can prolong the circulation time in blood because of the negative polysaccharide component of chondroitin sulfate, and subsequently being selectively internalized by MCF-7/ADR cells [doxorubicin (DOX)-resistant]. When exposed to 635 nm red light, this nanoplatform generates sufficient ROS through the photoconversion of PpIX, further triggering the disassociation of the micelles to release the dual cargoes. Afterward, the released apatinib, serving as a reversal inhibitor of MDR, can recover the chemosensitivity of DOX by competitively inhibiting the P-glycoprotein drug pump in drug-resistant tumor cells, and the excessive ROS has a strong capacity to exert its PDT effect to act on the mitochondria or the nuclei, ultimately causing cell apoptosis. As expected, this intelligent nanosystem successfully reverses tumor MDR via the synergism between apatinib-enhanced DOX sensitivity and ROS-mediated PDT performance.

A triple modality BSA-coated dendritic nanoplatform for NIR imaging, enhanced tumor penetration and anticancer therapy

Functional theranostic systems for drug delivery capable of concurrent near-infrared (NIR) fluorescence imaging, active tumor targeting and anticancer therapies are desired for concise cancer diagnosis and treatment. Dendrimers with controllable size and surface functionalities are good candidates for such platforms. However, integration of active targeting ligands and imaging agents separately on the surface or encapsulation of the imaging agents in the inner core of the dendrimers will result in a more complex composition or reduced drug loading efficiency. Herein, we reported a PAMAM-based theranostic system, with a simple integrin-specific imaging ligand prepared from two motifs. One motif is a NIR carbocyanine fluorescent dye (Cyp) for precise in vivo monitoring of the system and identification of tumor or cancer cells, and the other is a novel tumor-penetrating cyclic peptide (CRGDKGPDC, abbreviated iRGD). BSA was non-covalently bonded with Cyp to reduce NIR agent fluorescence-quenching aggregates and enhance imaging signals. The chemotherapy effect of these dendritic systems was achieved by encapsulating paclitaxel into the hydrophobic interior of the dendrimers. In vitro and in vivo targeting and penetrating studies revealed that a significantly high amount of the dendritic systems was endocytosed by HepG2 cells and enhanced accumulation and penetration at tumor sites. Our safety evaluation showed that masking of cationic-end groups of PAMAM to neutral or anionic groups has resulted in decreased or even zero-toxicity. The preliminary antitumor efficacy of the dendritic system was evaluated. In vitro and in vivo studies confirmed that paclitaxel-encapsulated functionalized PAMAM can efficiently kill HepG2 cancer cells. In conclusion, our functionalized theranostic dendritic system could be a promising nanocarrier to effectively deliver drugs to deep tumor regions for anticancer therapy.

The impact of light irradiation timing on the efficacy of nanoformula-based photo/chemo combination therapy

Photo/chemo combination therapy has been demonstrated to be a generally more powerful strategy for treating cancers than a single treatment modality. However, it is unknown whether the timing of light irradiation has any impact on therapeutic efficacy. We designed a carrier-free and self-monitoring nanodrug to monitor the entire dual-drug release profile and determined the impact of photodynamic therapy (PDT) at different time points. The designed nanodrug consists of the chemotherapeutic doxorubicin (DOX) and the photosensitizer pheophorbide A (PhA). The drugs form a fluorescence resonance energy transfer (FRET) pair (DOX transferring energy to PhA) when present at a precise ratio in the combination nanodrug. Due to the FRET effect, the DOX-PhA nanoparticles (NPs) show PhA fluorescence in a normal pH environment (such as cytoplasm). However, the FRET effect is lost when the NPs are disassembled in an acidic environment (such as lysosomes), and the DOX fluorescence is recovered. By real-time fluorescence variation monitoring, we determined the key time points when the drugs reached various subcellular locations, which helped us to determine the PDT-triggering time points and investigate the impact on the therapeutic effect in the combination therapy. Furthermore, the PDT was triggered at these established time points both in vitro and in vivo, which revealed that the best PDT-triggering time point in the combination therapy was achieved after nuclear entry of DOX. The study suggests that the optimization of combination therapy, not only photo/chemo but also chemo/chemo combination therapy, may require not only a controlled drug ratio but also a controlled drug release profile and target arrival time.

Multistage Targeting Strategy Using Magnetic Composite Nanoparticles for Synergism of Photothermal Therapy and Chemotherapy

Mitochondrial-targeting therapy is an emerging strategy for enhanced cancer treatment. In the present study, a multistage targeting strategy using doxorubicin-loaded magnetic composite nanoparticles is developed for enhanced efficacy of photothermal and chemical therapy. The nanoparticles with a core-shell-SS-shell architecture are composed of a core of Fe₃ O₄ colloidal nanocrystal clusters, an inner shell of polydopamine (PDA) functionalized with triphenylphosphonium (TPP), and an outer shell of methoxy poly(ethylene glycol) linked to the PDA by disulfide bonds. The magnetic core can increase the accumulation of nanoparticles at the tumor site for the first stage of tumor tissue targeting. After the nanoparticles enter the tumor cells, the second stage of mitochondrial targeting is realized as the mPEG shell is detached from the nanoparticles by redox responsiveness to expose the TPP. Using near-infrared light irradiation at the tumor site, a photothermal effect is generated from the PDA photosensitizer, leading to a dramatic decrease in mitochondrial membrane potential. Simultaneously, the loaded doxorubicin can rapidly enter the mitochondria and subsequently damage the mitochondrial DNA, resulting in cell apoptosis. Thus, the synergism of photothermal therapy and chemotherapy targeting the mitochondria significantly enhances the cancer treatment.

A Magnetofluorescent Carbon Dot Assembly as an Acidic H2 O2 -Driven Oxygenerator to Regulate Tumor Hypoxia for Simultaneous Bimodal Imaging and Enhanced Photodynamic Therapy

Recent studies indicate that carbon dots (CDs) can efficiently generate singlet oxygen (¹ O₂ ) for photodynamic therapy (PDT) of cancer. However, the hypoxic tumor microenvironment and rapid consumption of oxygen in the PDT process will severely limit therapeutic effects of CDs due to the oxygen-dependent PDT. Thus, it is becoming particularly important to develop a novel CD as an in situ tumor oxygenerator for overcoming hypoxia and substantially enhancing the PDT efficacy. Herein, for the first time, magnetofluorescent Mn-CDs are successfully prepared using manganese(II) phthalocyanine as a precursor. After cooperative self-assembly with DSPE-PEG, the obtained Mn-CD assembly can be applied as a smart contrast agent for both near-infrared fluorescence (FL) (maximum peak at 745 nm) and T₁ -weighted magnetic resonance (MR) (relaxivity value of 6.97 mM^-1 s^-1 ) imaging. More interestingly, the Mn-CD assembly can not only effectively produce ¹ O₂ (quantum yield of 0.40) but also highly catalyze H₂ O₂ to generate oxygen. These collective properties of the Mn-CD assembly enable it to be utilized as an acidic H₂ O₂ -driven oxygenerator to increase the oxygen concentration in hypoxic solid tumors for simultaneous bimodal FL/MR imaging and enhanced PDT. This work explores a new biomedical use of CDs and provides a versatile carbon nanomaterial candidate for multifunctional nanotheranostic applications.

A biomimetic and pH-sensitive polymeric micelle as carrier for paclitaxel delivery

As nano-scale drug delivery systems, smart micelles that are sensitive to specific biological environment and allowed for target site-triggered drug release by reversible stabilization of micelle structure are attractive. In this work, a biocompatible and pH-sensitive copolymer is synthesized through bridging poly (2-methacryloyloxyethyl phosphorylcholine) (PMPC) block and poly (D, L-lactide) (PLA) block by a benzoyl imine linkage (Blink). Biomimetic micelles with excellent biocompatibility based on such PLA-Blink-PMPC copolymer are prepared as carriers for paclitaxel (PTX) delivery. Due to the rapid breakage of the benzoyl imine linkage under acidic condition, the micelle structure is disrupted with accelerated PTX release. Such pH-sensitive triggered drug release behavior in synchronization with acidic conditions at tumor site is helpful for improving the utilization of drug and facilitating antitumor efficacy. These micelles can be used as promising drug delivery systems due to their biocompatible and smart properties.

Self-assembled organic nanorods for dual chemo-photodynamic therapies

Photodynamic therapy (PDT) and chemotherapy have been extensively developed as effective approaches against cancer. Herein, we constructed organic nanorods by rational co-assembly of photosensitizer, di-iodinated borondipyrromethene (BDP-I2), and chemical anticancer drug, paclitaxel (PTX). The physico- and photochemical properties of the obtained nanorods were carefully investigated. BDP-I2 was selected for its high singlet oxygen (1O2) quantum yields. And the corresponding 1O2 generation ability and photodynamic effect were evaluated both in vitro and in vivo. The accelerated endosomal escape of the nanorods induced by the photodynamic effect enhanced the chemotherapeutic efficacy of PTX. We believe that this synergetic nanomedicine represents a new development for antitumor chemophotodynamic therapy.

One-Step Synthesis of Targeted Acid-Labile Polysaccharide Prodrug for Efficiently Intracellular Drug Delivery

The therapeutic potential of the active targeting and acid-sensitive polysaccharide prodrug was investigated. The active targeting of polysaccharide prodrug was based on the specific interaction between cyclo(Arg-Gly-Asp-d-Phe-Lys) peptide (c(RGDfK)) and its receptor α_vβ₃ integrin overexpressed on the membrane of tumor cells. The cRGD-modified doxorubicin-conjugated hydroxyethyl starch (HES=DOX/cRGD) was synthesized via a one-step Schiff base reaction between oxidized HES, and DOX and c(RGDfK) that achieved an acid-accelerated drug release profile. The targeted polysaccharide prodrug self-assembled into micelle in aqueous environment with a moderate hydrodynamic diameter of 77.1 nm. All data in vitro indicated enhanced cell uptake and elevated cytotoxicity of HES=DOX/cRGD toward human malignant melanoma A375 cells compared with HES=DOX and DOX. Moreover, the smart prodrug also exhibited upregulated accumulation in the tumor, improved antitumor efficacy, and reduced systemic cytotoxicity in vivo. The cRGD-decorated acid-sensitive polysaccharide prodrug was advantageous in both antitumor efficacy and systemic security, showing great prospect in clinical application.

Induction of mitochondrial apoptosis for cancer therapy via dual-targeted cascade-responsive multifunctional micelles

A dual-targeted cascade-responsive multifunctional micelle is fabricated, which can carry the therapeutic agent into the mitochondrion to induce mitochondrial apoptosis.

Cancer-targeted reactive oxygen species-degradable polymer nanoparticles for near infrared light-induced drug release

Nanocarriers can be translocated to the peripheral region of tumor tissues through the well-known enhanced permeability and retention effects.

Hierarchical nanocomposites of graphene oxide and PEGylated protoporphyrin as carriers to load doxorubicin hydrochloride for trimodal synergistic therapy

We report a supramolecular hierarchical nanocomposite for combination photodynamic, photothermal, and chemotherapy.

Dual controlled delivery of squalenoyl-gemcitabine and paclitaxel using thermo-responsive polymeric micelles for pancreatic cancer

A thermoresponsive block copolymer has been developed with the capability to co-carry two drug molecules and to augment their cytotoxic properties via direct cell membrane interaction with cancer cells.

Light-activatable dual-source ROS-responsive prodrug nanoplatform for synergistic chemo-photodynamic therapy

In the context of prodrug nanomedicines for cancer therapy, one of the great challenges is the slow and variable release of the parent drug in tumors.

A reactive oxygen species–responsive prodrug micelle with efficient cellular uptake and excellent bioavailability

Stimuli-responsive polymeric drug delivery systems are of great interest in anticancer research. Here, a reactive oxygen species (ROS)–responsive prodrug was prepared by thioketal linkage of poly(ethylene glycol) (PEG) and the anticancer drug doxorubicin (DOX).

NIR-I-to-NIR-II fluorescent nanomaterials for biomedical imaging and cancer therapy

This review discusses the recent development of nanomaterials with NIR-I-to-NIR-II fluorescence and their applications in biomedical imaging and cancer therapy.

A Small Molecule Nanodrug by Self-Assembly of Dual Anticancer Drugs and Photosensitizer for Synergistic near-Infrared Cancer Theranostics

Phototherapy including photodynamic therapy (PDT) and photothermal therapy (PTT) has attracted great attention. However, applications of some photosensitizers remain an obstacle by their poor photostability. To enhance the treatment efficiency of photosensitizers and tumor theranostic effect, herein, we reported a novel carrier-free, theranostic nanodrug by self-assembly of small molecule dual anticancer drugs and photosensitizer for tumor targeting. The developed carrier-free small molecule nanodrug delivery system was formed by hydrophobic ursolic acid, paclitaxel, and amphipathic indocyanine green (ICG) associated with electrostatic, π-π stacking, and hydrophobic interactions exhibiting water stability. The self-assembling of ICG on the dual anticancer nanodrug significantly enhanced water solubility of hydrophobic anticancer drugs and ICG photostability contributing to long-term near-infrared (NIR) fluorescence imaging and effective chemophototherapy of tumor. The in vivo NIR fluorescence imaging showed that the theranostic nanodrug could be targeted to the tumor site via a potential enhanced permeability and retention effect proving the efficient accumulation of nanoparticles in the tumor site. Dramatically, chemophototherapy of tumor-bearing mice in vivo almost completely suppressed tumor growth and no tumor recurrence was observed. Encouraged by its carrier-free, prominent imaging and effective therapy, the small molecule nanodrug via self-assembly will provide a promising strategy for synergistic cancer theranostics.

Cancer-mitochondria-targeted photodynamic therapy with supramolecular assembly of HA and a water soluble NIR cyanine dye

Mitochondria-targeted cancer therapies have proven to be more effective than other similar non-targeting techniques, especially in photodynamic therapy (PDT). Indocyanine dye derivatives, particularly IR-780, are widely known for their PDT utility. However, poor water solubility, dark toxicity, and photobleaching are limiting factors for these dyes, which otherwise show promise based on their good absorption in the near-infrared (NIR) region and mitochondria targeting ability. Herein, we introduce an indocyanine derivative (IR-Pyr) that is highly water soluble, exhibiting higher mitochondrial targetability and better photostability than IR-780. Furthermore, electrostatic interactions between the positively charged IR-Pyr and negatively charged hyaluronic acid (HA) were utilized to construct a micellar aggregate that is selective towards cancer cells. The cancer mitochondria-targeted strategy confirms high PDT efficacy as proved by in vitro and in vivo experiments.

Acid-Activatable Theranostic Unimolecular Micelles Composed of Amphiphilic Star-like Polymeric Prodrug with High Drug Loading for Enhanced Cancer Therapy

Stimuli-responsive nanomedicine with theranostic functionalities with reduced side-effects has attracted growing attention, although there are some major obstacles to overcome before clinical applications. Herein, we present an acid-activatable theranostic unimolecular micelles based on amphiphilic star-like polymeric prodrug to systematically address typical existing issues. This smart polymeric prodrug has a preferable size of about 35 nm and strong micellar stability in aqueous solution, which is beneficial to long-term blood circulation and efficient extravasation from tumoral vessels. Remarkably, the polymeric prodrug has a high drug loading rate up to 53.1 wt%, which induces considerably higher cytotoxicity against tumor cells (HeLa cells and MCF-7 cells) than normal cells (HUVEC cells) suggesting a spontaneous tumor-specific targeting capability. Moreover, the polymeric prodrug can serve as a fluorescent nanoprobe activated by the acidic microenvironment in tumor cells, which can be used as a promising platform for tumor diagnosis. The superior antitumor effect in this in vitro study demonstrates the potential of this prodrug as a promising platform for drug delivery and cancer therapy.

Tumor Neovasculature-Targeted APRPG-PEG-PDLLA/MPEG-PDLLA Mixed Micelle Loading Combretastatin A-4 for Breast Cancer Therapy

Breast cancer has been the first killer among women. In this study, combretastatin A-4 (CA-4) loaded 5-amino acid peptide Ala-Pro-Arg-Pro-Gly (APRPG) modified PEG-PDLLA mixed micelles was developed to target tumor neovasculature for breast cancer therapy. CA-4 is an effective vascular disrupting agent. The APRPG-modified PEG-PDLLA polymer was successfully synthesized and thin-film hydration method was used to prepare APRPG-PEG-PDLLA/MPEG-PDLLA mixed micelles. Drug loading capacity (DL), encapsulation efficiency (EE), and the optimized ratio of APRPG-PEG-PDLLA: MPEG-PDLLA for efficient drug loading was investigated. The particle size, zeta potential, morphology, and the crystallographic study were carried out to characterize the micelles. In vitro release study revealed a sustained release of CA-4 from the mixed micelles while compared to free CA-4. Moreover, the cytotoxicity data of blank and drug loaded mixed micelles suggested that the APRPG-PEG-PDLLA/MPEG-PDLLA mixed micelles were safe drug carriers and the encapsulated CA-4 remained potent antitumor effect. The cellular uptake study and the in vivo imaging and biodistribution study demonstrated that the APRPG peptide modified mixed micelles has the higher cellular uptake efficiency and could significantly facilitate the accumulation at tumor site. Furthermore, the micelles were slowly extravasated from blood vessels and inhibited embryonic angiogenesis in the transgenic zebrafish model. Consequently, the CA-4 loaded APRPG-PEG-PDLLA/MPEG-PDLLA mixed micelles group demonstrated a significant inhibition of tumor growth in 4T1 breast cancer model. In short, the CA-4 loaded APRPG-PEG-PDLLA/MPEG-PDLLA mixed micelles might have great potential for breast cancer therapy.

Reduction-Responsive Polypeptide Micelles for Intracellular Delivery of Antineoplastic Agent

Reduction-responsive methoxy poly(ethylene glycol)-block-poly(S-tert-butylmercapto-L-cysteine) copolymers (i.e., mPEG₁₁₃-b-PBMLC₄ and mPEG₁₁₃-b-PBMLC₉) were facilely synthesized through primary amino-initiated ring-opening polymerization (ROP) of disulfide-containing N-carboxyanhydride monomer. The reduction-responsive block copolymers were then investigated for intracellular delivery of antitumor drug after forming smart micelles in vitro and in vivo. The micelles were denoted as P4M and P9M, respectively. Doxorubicin (DOX) was selected as a model chemotherapeutic agent, which was loaded into micelles via hydrophobic interaction. The drug loading efficiency (DLE) were detected to be 55.4 and 61.7 wt % for P4M and P9M, respectively. The loaded micelles, referred as P4M/DOX and P9M/DOX, exhibited spherical morphologies with hydrodynamic radii of 92.3 ± 2.3 and 80.2 ± 2.8 nm, respectively. Compared to P4M/DOX, P9M/DOX with a smaller size exhibited upregulated cell endocytosis and higher cytotoxicity to human breast cancer MCF-7 cells. Furthermore, the loading micelles, especially P9M/DOX, demonstrated improved antitumor efficacy toward an MCF-7 breast tumor-bearing BALB/c nude mouse model compared with free doxorubicin hydrochloride (DOX·HCl). This was also confirmed by the histopathological and immunohistochemical results. The above results demonstrated that the facially prepared smart polypeptide micelles exhibited a potent prospect in intracellular drug delivery in vitro and in vivo.

Light-switchable systems for remotely controlled drug delivery

Light-switchable systems have recently received attention as a new mode of remotely controlled drug delivery. In the past, a multitude of nanomedicine studies have sought to enhance the specificity of drug delivery to target sites by focusing on receptors overexpressed on malignant cells or environmental features of diseases sites. Despite these immense efforts, however, there are few clinically available nanomedicines. We need a paradigm shift in drug delivery. One strategy that may overcome the limitations of pathophysiology-based drug delivery is the use of remotely controlled delivery technology. Unlike pathophysiology-based active drug targeting strategies, light-switchable systems are not affected by the heterogeneity of cells, tissue types, and/or microenvironments. Instead, they are triggered by remote light (i.e., near-infrared) stimuli, which are absorbed by photoresponsive molecules or three-dimensional nanostructures. The sequential conversion of light to heat or reactive oxygen species can activate drug release and allow it to be spatio-temporally controlled. Light-switchable systems have been used to activate endosomal drug escape, modulate the release of chemical and biological drugs, and alter nanoparticle structures to control the release rates of drugs. This review will address the limitations of pathophysiology-based drug delivery systems, the current status of light-based remote-switch systems, and future directions in the application of light-switchable systems for remotely controlled drug delivery.

Cellular uptake of pH/reduction responsive phosphorylcholine micelles

We study the relationship between the PDEA content and internalization/intracellular drug release of pH responsive phosphorylcholine micelles as drug carriers.

Dual redox-responsive PEG–PPS–cRGD self-crosslinked nanocapsules for targeted chemotherapy of squamous cell carcinoma

A multifunctional branched copolymer, PEG–PPS–cRGD, was designed for developing dual redox-responsive self-crosslinked nanocapsules for targeted chemotherapy of squamous cell carcinoma.