RAFT synthesis of amphiphilic (A-ran-B)-b-C diblock copolymers with tunable pH-sensitivity

Separated Micelles Formation of pH-Responsive Random and Block Copolymers Containing Phosphorylcholine Groups

The self-assembly of pH-responsive random and block copolymers composed of 2-(N,N-diisopropylamino)ethyl methacrylate and 2-methacryloyloxyethyl phosphorylcholine was investigated in aqueous media. Their pH-responsive behaviors were investigated in aqueous media by dynamic light scattering (DLS) and fluorescence measurements using a pyrene hydrophobic fluorescence probe. In an acidic environment, these copolymers existed as single polymer chains that did not interact with each other. In contrast, upon increasing the pH of the solution above the critical value of ~8, separated micelles were formed in the mixture, which was indicated by bimodal distribution in DLS results with radius of 4.5 and 10.4 nm, corresponding to the random and block copolymer micelles, respectively. Fluorescence resonance energy transfer efficiencies were near to zero in the mixture of the donor labeled block and acceptor labeled random copolymers under both acidic and basic pH. These results demonstrated the coexistence of two distinct micelles.

TME-Responsive Polyprodrug Micelles for Multistage Delivery of Doxorubicin with Improved Cancer Therapeutic Efficacy in Rodents

It is of great significance to develop multifunctional biomaterials to effectively deliver anticancer drug to tumor cells for cancer therapy. Here, inspired by the specific tumor microenvironment (TME) cues, a unique multistage pH/redox-responsive polyprodrug composed of amphiphilic pH-sensitive diblock copolymer poly(ethylene glycol) methyl ether-b-poly(β-amino esters) conjugated with doxorubicin (DOX) via redox-sensitive disulfide bonds (mPEG-b-PAE-ss-DOX) is designed and developed. This polyprodrug can self-assemble into micelles (DOX-ss@PMs) at low concentration with high serum stability, indicating that DOX-ss@PMs have prolonged circulation time. The dual pH/redox-responsiveness of the multistage platform is thoroughly evaluated. In vitro results demonstrate that DOX-ss@PMs can highly accumulate at tumor site, followed by responding to the acidity for disassembly and effectively penetrating into the tumor cells. DOX is released from the platform due to the cleavage of disulfide bonds induced by high glutathione (GSH) concentration, thereby inducing the apoptosis of tumor cells. In vivo studies further reveal that multistage DOX-ss@PMs can more efficiently inhibit the growth of tumors and improve the survival of tumor-bearing mice in comparison to the free drug and control. These results imply that multistage delivery system might be a potential and effective strategy for drug delivery and DOX-ss@PMs could be a promising nanomedicine for cancer chemotherapy.

pH-Responsive Nanoparticles Targeted to Lungs for Improved Therapy of Acute Lung Inflammation/Injury

Dysregulated vascular inflammation is the underlying cause of acute lung inflammation/injury (ALI). Bacterial infections and trauma cause ALI that may rapidly lead to acute respiratory distress syndrome (ARDS). There are no pharmacological therapies available to patients with ALI/ARDS, partially as drugs cannot specifically target the lungs. Herein, we developed a stimuli-responsive nanoparticle (NP) to target inflammatory lungs for ALI therapies. The NP is composed of a sharp acid-sensitive segment poly(β-amino esters) as a core for drug loading and controlled release and a polyethylene glycol-biotin on the particle surface available for bioconjugation, enabling lung targeting and extended circulation. The studies on dissipative particle dynamics simulation and characteristics of NPs suggest that anti-ICAM-1 antibodies can be coated to the particle surface and this coating is required to enhance lung targeting of NPs. A model drug of anti-inflammatory agent TPCA-1 is encapsulated in NPs with a high drug-loading content at 24% (w/w). In the mouse ALI model, our TPCA-1-loaded NPs coated with anti-ICAM-1 can target inflamed lungs after intravenous injection, followed by drug release triggered by the acid environment, thus mitigating lung inflammation and injury. Our studies reveal the rational design of nanotherapeutics for improved therapy of ALI, which may be applied to treating a wide range of vascular inflammation.

RAFT-mediated polymerisation of dialkylaminoethyl methacrylates in tert-butanol

Dialkylaminoethyl methacrylates were polymerised by RAFT in tert-butanol to make macro-chain transfer agents for subsequent grafting onto various substrates.

Dissipative particle dynamics studies of doxorubicin-loaded micelles assembled from four-arm star triblock polymers 4AS-PCL-b-PDEAEMA-b-PPEGMA and their pH-release mechanism

Dissipative particle dynamics (DPD) simulation was applied to investigate the microstructures of the micelles self-assembled from pH-sensitive four-arm star triblock poly(ε-caprolactone)-b-poly(2-(diethylamino)ethyl methacrylate)-b-poly(poly(ethylene glycol) methyl ether methacrylate) (4AS-PCL-b-PDEAEMA-b-PPEGMA). In the optimized system, the micelles have a core-mesosphere-shell three-layer structure. The drug-loading process and its distribution at different formulations in the micelles were studied. The results show that DOX molecules distributed in the core and the interface between the core and the mesosphere, suggesting the potential encapsulation capacity of DOX molecules. More drugs were loaded in the micelles with the increase in DOX, and the size of micelles became larger. However, some openings start to generate on the PEG shell when the DOX reaches a certain concentration. By changing the pH values of the system, different morphologies of the micelles were acquired after the pH-sensitive blocks PDEAEMA were protonated, the mechanism of which was also analyzed through correlating functions. The results indicated that the sudden increase in solubility parameter of the pH-sensitive blocks and the swelling of the micelles were the key factors on the change of morphologies. Furthermore, with the decrease in pH value, the number and size of the cracks on the surface of the micelles were larger, which may have a direct effect on the drug release. In conclusion, 4AS-PCL-b-PDEAEMA-b-PPEGMA has great promising applications in delivering hydrophobic anticancer drugs for improved cancer therapy.

Stimulus-sensitive polymeric nanoparticles and their applications as drug and gene carriers

Polymeric nanoparticles are promising candidates as drug and gene carriers. Among polymeric nanoparticles, those that are responsive to internal or external stimuli are of greater interest because they allow more efficient delivery of therapeutics to pathological regions. Stimulus-sensitive polymeric nanoparticles have been fabricated based on numerous nanostructures, including micelles, vesicles, crosslinked nanoparticles, and hybrid nanoparticles. The changes in chemical or physical properties of polymeric nanoparticles that occur in response to single, dual, or multiple stimuli endow these nanoparticles with the ability to retain cargoes during circulation, target the pathological region, and release their cargoes after cell internalization. This Review focuses on the most recent developments in the preparation of stimulus-sensitive polymeric nanoparticles and their applications in drug and gene delivery.

Development of pH sensitive 2-(diisopropylamino)ethyl methacrylate based nanoparticles for photodynamic therapy

Photodynamic therapy is an effective treatment for tumors that involves the administration of light-activated photosensitizers. However, most photosensitizers are insoluble and non-specific. To target the acid environment of tumor sites, we synthesized three poly(ethylene glycol) methacrylate-co-2-(diisopropylamino)ethyl methacrylate (PEGMA-co-DPA) copolymers capable of self-assembly to form pH sensitive nanoparticles in an aqueous environment, as a means of encapsulating the water-insoluble photosensitizer, meso-tetra(hydroxyphenyl)chlorin (m-THPC). The critical aggregation pH of the PEGMA-co-DPA polymers was 5.8-6.6 and the critical aggregation concentration was 0.0045-0.0089 wt% at pH 7.4. Using solvent evaporation, m-THPC loaded nanoparticles were prepared with a high drug encapsulation efficiency (approximately 89%). Dynamic light scattering and transmission electron microscopy revealed the spherical shape and 132 nm diameter of the nanoparticles. The in vitro release rate of m-THPC at pH 5.0 was faster than at pH 7.0 (58% versus 10% m-THPC released within 48 h, respectively). The in vitro photodynamic therapy efficiency was tested with the HT-29 cell line. m-THPC loaded PEGMA-co-DPA nanoparticles exhibited obvious phototoxicity in HT-29 colon cancer cells after light irradiation. The results indicate that these pH sensitive nanoparticles are potential carriers for tumor targeting and photodynamic therapy.