Rational Construction of a Mitochondrial Targeting, Fluorescent Self-Reporting Drug-Delivery Platform for Combined Enhancement of Endogenous ROS Responsiveness.

To maximize the utilization and response to the high oxidative stress environment of tumor sites while avoiding the dilemma of enhancing reactive oxygen species (ROS) response in a single way, mitochondrial targeting combined with fluorescent self-reporting polymeric nanocarriers (1K-TPP and 2K-TPP) with grafted structures were synthesized via a chemoenzymatic method in a high yield to simultaneously enhance the drug delivery of endogenous ROS responses. 1K-TPP and 2K-TPP loaded doxorubicin (DOX) at a high content over 12% and formed homogeneous spherical micelles. In vitro, both of them showed promising high sensitivity (detection limit below 200 nM H2O2), fast response, and ratiometric fluorescent self-reporting properties (fluorescent enhancement more than 200 times) to ROS and excellent stability under physiological conditions, while achieving a rapid release of the DOX in response to 1 mM H2O2. Cell co-localization experiments exhibited that they had favorable mitochondrial targeting, and mitochondrial isolation experiments also confirmed that the TPP-modified 1K-TPP selectively accumulated nearly three times in mitochondria than that in total cells. The internalization of 1K-TPP and 2K-TPP into cancer cells was greatly improved by nearly 200% compared to that of unmodified control (1K-OH and 2K-OH) and also explored a unique energy-dependent endocytosis. Furthermore, stimulation of endogenous ROS enhanced the green fluorescence intensity (up to 51.4%) of the linked probe so as to destroy the internal structure of the nanocarriers, achieving self-reporting of the drug's intracellular release and tracking of the intracellular location of nanocarriers. The cytotoxicity of DOX-loaded 1K-TPP and 2K-TPP in tumor cells with a higher ROS content showed statistical superiority to that of 1K-OH and 2K-OH, benefiting from the extremely good endogenous ROS response sensitivity leading to the differential selective release of drugs. These results demonstrate the potential of 1K-TPP and 2K-TPP, especially for 1K-TPP, as mitochondria-targeted, fluorescent self-reporting nanocarriers for combined enhancement of endogenous ROS responsiveness.

Preparation of fluorophore-tagged polymeric drug delivery vehicles with multiple biological stimuli-triggered drug release.

In the field of drug delivery, the controlled release of drugs is continuously one of the highly prioritized research domains. Stimuli-responsive polymers are being investigated as drug delivery vehicles that modulate pharmaceutical effect via tumor specific mechanisms. In this work, a biocompatible graft copolymer (denoted as PSNC-g-mPEG/TPE) was constructed, which comprised a triple-responsive polycarbonate backbone coupled with fluorescent TPE and hydrophilic methoxypoly(ethylene glycol) (mPEG) segments. This multifunctional amphiphilic copolymer was able to self-assemble in aqueous solutions and acted as a drug delivery vehicle that releases cargo in response to multiple biological stimuli (ROS, pH and enzymes). And the results of confocal laser scanning microscopy (CLSM) suggested that these micelles could be rapidly internalized by cells and achieve more effective drug release in cancer cells. Furthermore, the cytotoxicity assays proved the safety of this material. It is anticipated that this strategy has enormous potential in constructing novel anticancer therapeutics.

Hierarchical Targeted Delivery of Lonidamine and Camptothecin Based on the Ultra-Rapid pH/GSH Response Nanoparticles for Synergistic Chemotherapy.

A facile strategy to construct dual-drug delivery nanoparticles (TL-CPT NPs), which possessed higher loading content of CPT and TPP-LND. Notably, TL-CPT NPs showed promising ultrarapid pH/GSH response to release more than 86% of loaded TPP-LND or 93% of loaded CPT in just 2 h. The results showed that the nanoparticles hierarchically delivered CPT and TPP-LND to targeted different organelles without mutual influence benefiting the ultrarapid pH/GSH response to drug release, and further significantly and synergistically induced cell apoptosis and improved chemotherapeutic efficiency in cancer cells.

GSH/pH dual-responsive biodegradable camptothecin polymeric prodrugs combined with doxorubicin for synergistic anticancer efficiency.

Dual stimuli-responsive camptothecin polymeric prodrugs (CPT Prodrugs) with grafted structures were designed via chemoenzymatic methods and combined with doxorubicin (DOX) for synergistic drug delivery to improve anticancer efficiency. The CPT Prodrugs loaded DOX with a high efficiency through the cooperative contribution of several interaction forces. The produced amphiphilic polymeric prodrugs loaded with DOX, referred to as DOX@CPT Prodrugs, formed homogeneous spherical micelles of appropriate sizes (sub-50 nm). The DOX@CPT Prodrug micelles showed excellent stability in release experiments under in vitro physiological conditions and maintained over 80% drug loading after 4 weeks when stored at 4 °C. Under weakly acidic pH and reduced glutathione (GSH) conditions, the DOX@CPT Prodrugs with high disulfide and tertiary amine content achieved synergistic release of the two loaded drugs and biodegraded into low-molecular-weight compounds. The cell experiments confirmed that the internalization of DOX@CPT Prodrugs into cancer cells was greatly improved by nearly 30% compared with that of free drugs. Furthermore, the synergistic drug delivery system exhibited superior anticancer efficiency with highly improved cell selectivity ratios (up to 127.0%) and greatly enhanced synergistic effects (up to 23.9%) benefiting from good long-term stability, better internalization by cells and sensitive pH and GSH dual-responsivity. In addition, the DOX@CPT Prodrugs with suitable sizes and good water solubility also exhibited a greater penetrability in the case of simulating solid tumors than the free drugs. These results demonstrate the potential of DOX@CPT Prodrugs as biodegradable, dual-responsive combination therapy nanocarriers for synergistic anticancer treatment.

Enzymatic synthesis of selenium-containing amphiphilic aliphatic polycarbonate as an oxidation-responsive drug delivery vehicle.

Although functional aliphatic polycarbonates (APCs) have attracted prominent research interest as stimuli-responsive biomaterials, the majority of functional APCs are fabricated by detrimental organometallic catalysts or organo-catalysts. Herein, a facile synthetic strategy based on enzymatic polymerization was developed to construct a selenium-containing amphiphilic aliphatic polycarbonate (mPEG-b-CMP45). Specifically, the selenium in its backbone framework underwent a hydrophobic-hydrophilic transition upon exposure to the abnormal ROS level of the tumor, thus providing a promising platform for ROS-triggered drug release. This amphiphilic mPEG-b-CMP45 efficiently encapsulated doxorubicin (DOX) via self-assembly in aqueous solution and showed an excellent ability to regulate the release of DOX in response to H2O2 at biologically relevant concentrations (100 µM). These DOX-loaded nanoparticles could easily be internalized into U87 cells and possess the inherent antitumor properties of DOX, while they exhibited much lower cytotoxicity in normal cells HL-7702. Moreover, in many cases, the introduction of selenium caused high cytotoxicity of the materials, but the cytotoxicity results in HL-7702 cells demonstrated the good biocompatibility of mPEG-b-CMP45. These collective data suggested the potential use of mPEG-b-CMP45 as a biocompatible and smart drug delivery vehicle.

Synthesis of high drug loading, reactive oxygen species and esterase dual-responsive polymeric micelles for drug delivery.

Stimulus-responsive, controlled-release systems are of great importance in medical science and have drawn significant research attention, leading to the development of many stimulus-responsive materials over the past few decades. However, these materials are mainly designed to respond to external stimuli and ignore the key problem of the amount of drug loading. In this study, exploiting the synergistic effect of boronic esters and N-isopropylacrylamide (NIPAM) pendant, we present a copolymer as an ROS and esterase dual-stimulus responsive drug delivery system that has a drug loading of up to 6.99 wt% and an entrapment efficiency of 76.9%. This copolymer can successfully self-assemble into polymer micelles in water with a narrow distribution. Additionally, the measured CMC hinted at the good stability of the polymeric micelles in water solution, ensuing long circulation time in the body. This strategy for increasing the drug loading on the basis of stimulus response opens up a new avenue for the development of drug delivery systems.

Trackable Water-Soluble Prodrug Micelles Capable of Rapid Mitochondrial-Targeting and Alkaline pH-Responsive Drug Release for Highly Improved Anticancer Efficacy.

A trackable water-soluble prodrug conjugate possessing high contents of chlorambucil (Cb) and triphenylphosphonium cation (TPP) was designed and developed after TPP modification on the "branch" of amphipathic prodrugs based on convenient synthesis of heterobifunctional clickable poly(ethylene glycol) (PEG). The aqueous self-assembly of fluorescent polymeric micelles along precise composition can be easily prepared after directly dissolved (DD) in aqueous solution, and exhibit superior cytotoxicity to cancer cells along with highly improved selectivity and sensitivity because of their rapid mitochondrial-targeting and alkaline pH-responsive drug release capabilities. Notably, efficient codelivery of doxorubicin (DOX) for synergistic targeted drug delivery and cancer therapy was achieved.

Chemoenzymatic synthesis of dual-responsive graft copolymers for drug delivery: long-term stability, high loading and cell selectivity.

A series of amphiphilic graft copolymers, poly(N-propargyldiethanolamine 4,4'-dithiodibutyionate)-graft-monomethoxy poly(ethylene glycol) (PPD-g-mPEG), were designed via a chemoenzymatic method for pH and reduced glutathione (GSH) dual-responsive drug delivery. The effects of percent grafting and molecular weights of mPEG on critical micelle concentration (CMC) values, size of micelles, drug loading and dual-response were tested. The graft copolymers could easily form homogeneous spherical micelles with appropriate sizes and zeta-potentials. The micelles of PPD-g-mPEG copolymers loaded doxorubicin (DOX) in high efficiency, and showed excellent stability under physiological conditions and synergetic dual-response to weakly acidic pH and GSH. In vitro experiments confirmed that the DOX-loaded micelles could be internalized into cancer cells efficiently and release DOX over time. Furthermore, cell cytotoxicity assays indicated that the graft copolymers were non-cytotoxic to both cancerous and normal cells while the DOX-loaded micelles greatly improved the selectivity ratios between HeLa cells and HL-7702 cells. DOX-loaded micelles also avoided hemolysis of red blood cells (RBCs) effectively compared with commercialized doxorubicin hydrochloride. All these demonstrated the potential of PPD-g-mPEG as a model to create more functional dual-responsive nanocarriers for controlled drug delivery.