Nanogels comprising reduction-cleavable polymers for glutathione-induced intracellular curcumin delivery

Stimuli-Responsive Polymeric Nanocarriers for Drug Delivery, Imaging, and Theragnosis

In the past few decades, polymeric nanocarriers have been recognized as promising tools and have gained attention from researchers for their potential to efficiently deliver bioactive compounds, including drugs, proteins, genes, nucleic acids, etc., in pharmaceutical and biomedical applications. Remarkably, these polymeric nanocarriers could be further modified as stimuli-responsive systems based on the mechanism of triggered release, i.e., response to a specific stimulus, either endogenous (pH, enzymes, temperature, redox values, hypoxia, glucose levels) or exogenous (light, magnetism, ultrasound, electrical pulses) for the effective biodistribution and controlled release of drugs or genes at specific sites. Various nanoparticles (NPs) have been functionalized and used as templates for imaging systems in the form of metallic NPs, dendrimers, polymeric NPs, quantum dots, and liposomes. The use of polymeric nanocarriers for imaging and to deliver active compounds has attracted considerable interest in various cancer therapy fields. So-called smart nanopolymer systems are built to respond to certain stimuli such as temperature, pH, light intensity and wavelength, and electrical, magnetic and ultrasonic fields. Many imaging techniques have been explored including optical imaging, magnetic resonance imaging (MRI), nuclear imaging, ultrasound, photoacoustic imaging (PAI), single photon emission computed tomography (SPECT), and positron emission tomography (PET). This review reports on the most recent developments in imaging methods by analyzing examples of smart nanopolymers that can be imaged using one or more imaging techniques. Unique features, including nontoxicity, water solubility, biocompatibility, and the presence of multiple functional groups, designate polymeric nanocues as attractive nanomedicine candidates. In this context, we summarize various classes of multifunctional, polymeric, nano-sized formulations such as liposomes, micelles, nanogels, and dendrimers.

Exogenous vitamin C triggered structural changes of redox-activated dual core-crosslinked biodegradable nanogels for boosting the antitumor efficiency

Premature leakage of drugs during blood circulation and slow drug release at the tumor site are two major challenges that nanocarriers have to overcome to achieve successful cancer therapy. Herein, a dual core-crosslinked, redox-sensitive polymeric nanogel (sDL) was constructed by the self-assembly of two star-shaped amphiphilic copolymers (4sP(EG-b-LLA)-N₃, 4sP(EG-b-DLA)-N₃) in the presence of a redox-sensitive crosslinker (d-ss-Bu), where hydrophilic polyethylene glycol (PEG) was used as the shell and the functional hydrophobic poly(l-lactide) (PLLA) and poly(d-lactide) (PDLA) were used as the dual crosslinked core via stereocomplex formation and chemical interactions. The dual core-crosslinked structure of the nanogels allowed for almost 2-fold enhanced doxorubicin (DOX)-loading capacity, favorable structural stability to restrict the premature leakage of therapeutic drug and smaller particle size to accelerate the internalization efficiency compared to non-crosslinked nanocarriers. Furthermore, exogenous vitamin C (Vc) can trigger the breakage of redox-sensitive bonds to accelerate drug release from nanogels for improved in vitro antitumor efficacy. Notably, in vivo near-infrared imaging showed that the highly stable DOX-loaded sDL efficiently aggregated at the tumor site. Sequential administration of DOX-loaded sDL and Vc exhibited the highest tumor inhibition effect without associated systemic toxicity compared to the corresponding single injection of Vc or DOX-loaded sDL control groups for in vivo studies, indicating that exogenous administration of Vc can synergistically impact the release of DOX from sDL. Therefore, the developed nanogels proved to be promising smart carriers for achieving precise tunable-stability in response to relevant environments and the combination of Vc to activate reduction-sensitive drug delivery is a promising approach to maximize the therapeutic efficacy.

Smart Nanoformulation Based on Stimuli-Responsive Nanogels and Curcumin: Promising Therapy against Colon Cancer

Curcumin (CUR) has gained much attention for its widely reported anticancer effect; however, its clinical use is restricted due to its low water solubility and, consequently, its poor bioavailability. Here, we report on the use of a nanoformulation of CUR with cationic nanogels for colon cancer therapy. Cationic stimuli-sensitive nanogels were prepared using a scale-up polymerization methodology based on surfactant-free emulsion polymerization of N,N'-diethylaminoethyl methacrylate (DEAEM) and poly(ethyleneglycol) methacrylate (PEGMA). The obtained nanogels showed a homogeneous size distribution (from 51 to 162 nm, polydispersity index (PDI) < 0.138) and exhibited a spherical form and core-shell morphology as confirmed by dynamic light scattering and electron microscopy, respectively. Nanogels were responsive to and degradable by variations of pH, temperature, or the redox environment, depending on the cross-linker used in the synthesis. Nanogels cross-linked with bis(acryloyl)cystamine incubated in a buffer (pH 7.4) containing 3 mM glutathione degraded in 60 min, while nanogels cross-linked with a divinylacetal cross-linker degraded in 10 min (pH ≤ 6). Nanoformulations of nanogels with CUR were stable as tested up to 30 days at physiological conditions. In vitro studies of the human colon cancer cell line (HCT-116) showed a synergistic effect of CUR and the degradable nanogels. Further, in vivo acute cytotoxicity tests of empty nanogels in mice demonstrate their potential as CUR nanocarriers for colon-anticancer therapies.

Degradable nanohydrogel with high doxorubicin loadings exhibiting controlled drug release and decreased toxicity against healthy cells

A new nanogel/drug carrier of 100-150 nm size, based on poly(N-isopropylacrylamide-co-sodium acrylate) and degradable crosslinker (cystine derivative), was synthesized. Using the electrostatic interactions between the carboxylic groups in the polymer network and the protonated amine groups of doxorubicin it was possible to load the drug into the carrier to a very high level of 28-30% relative to the dry mass of the polymer. The presence of the -S-S- groups made the polymer network susceptible to degradation by glutathione. The size of the nanoparticles was small enough to enable them to easily penetrate the cells. The MTT assay indicated that compared to free doxorubicin the nanogel particles loaded with doxorubicin were more cytotoxic against the MCF-7 and A2780 cancer cells, while they were 150 times less toxic against the MCF-10A healthy cells. The new carrier nanoparticles appeared also to be useful for prolonged drug delivery.

Ring opening polymerization of α-amino acids: advances in synthesis, architecture and applications of polypeptides and their hybrids

This review provides a comprehensive overview of the latest advances in the synthesis, architectural design and biomedical applications of polypeptides and their hybrids.