Synergistic Effect of Binary Mixed-Pluronic Systems on Temperature Dependent Self-assembly Process and Drug Solubility

Synthesis and Optimization of Next-Generation Low-Molecular-Weight Pentablock Copolymer Nanoadjuvants

Polymeric nanomaterials such as Pluronic®-based pentablock copolymers offer important advantages over traditional vaccine adjuvants and have been increasingly investigated in an effort to develop more efficacious vaccines. Previous work with Pluronic® F127-based pentablock copolymers, functionalized with poly(diethyl aminoethyl methacrylate) (PDEAEM) blocks, demonstrated adjuvant capabilities through the antigen presentation and crosslinking of B cell receptors. In this work, we describe the synthesis and optimization of a new family of low-molecular-weight Pluronic®-based pentablock copolymer nanoadjuvants with high biocompatibility and improved adjuvanticity at low doses. We synthesized low-molecular-weight Pluronic® P123-based pentablock copolymers with PDEAEM blocks and investigated the relationship between polymer concentration, micellar size, and zeta potential, and measured the release kinetics of a model antigen, ovalbumin, from these nanomaterials. The Pluronic® P123-based pentablock copolymer nanoadjuvants showed higher biocompatibility than the first-generation Pluronic® F127-based pentablock copolymer nanoadjuvants. We assessed the adjuvant capabilities of the ovalbumin-containing Pluronic® P123-based pentablock copolymer-based nanovaccines in mice, and showed that animals immunized with these nanovaccines elicited high antibody titers, even when used at significantly reduced doses compared to Pluronic® F127-based pentablock copolymers. Collectively, these studies demonstrate the synthesis, self-assembly, biocompatibility, and adjuvant properties of a new family of low-molecular-weight Pluronic® P123-based pentablock copolymer nanomaterials, with the added benefits of more efficient renal clearance, high biocompatibility, and enhanced adjuvanticity at low polymer concentrations.

Glucose-induced self-assembly and phase separation in hydrophilic triblock copolymers and the governing mechanism

Poly(ethylene oxide, EO)-poly(propylene oxide, PO)-poly(ethylene oxide, EO)-based triblock copolymers (BCPs) with 80% hydrophilicity stay molecularly dissolved as Gaussian chains at ambient temperature, even at fairly high concentrations (>5 %w/v). This study presents the plausible micellization behaviour of such very-hydrophilic Pluronics® - F38, F68, F88, F98, and F108 - incited upon the addition of glucose at low concentrations and temperatures. The outcomes obtained from phase behaviour and scattering studies are described. At temperatures near to ambient temperature, these BCPs form micelles with a central core made of a PO block, surrounded by a corona of highly hydrated EO chains. The phase transitions in these hydrophilic Pluronics® in the presence of glucose are demonstrated via the dehydration of the copolymer coil, leading to a decrease in the I₁/I₃ ratio, as determined using fluorescence spectroscopy. The temperature-dependent cloud point (CP) showed a marked decrease with an increase in the PO molecular weight and also in the presence of glucose. The change in solution relative viscosity (η_rel) caused by glucose is due to the enhanced dehydration of the EO block of the BCP amphiphile. Dynamic light scattering (DLS) and small-angle neutron scattering (SANS) investigations suggested that the dimensions of the hydrophobic core increase during the dehydration of the EO-PO blocks upon a temperature increase or after adding varying concentrations of glucose, thereby resulting in a micellar shape transition. It has been observed that added glucose influences the phase behaviour of BCPs in an analogous way to the influence of temperature. Also, plausible interactions between the EO-PO blocks and glucose were suggested based on the evaluated optimized descriptors obtained from a computational simulation approach. In addition, the core-shell blended micelles obtained using these BCPs are successfully utilized for drug (curcumin, Cur) solubilization based on the observed peak intensities from UV-visible spectroscopy. The loading of Cur into glucose-containing and glucose-free hydrophilic Pluronic® micelles shows how the radius of the micellar core (R_c) increases in the presence of glucose, thereby indicating Cur solubility enhancement for the Pluronic® micelles. Various kinetics models were employed, demonstrating a drug release profile that enables this approach to be used as an ideal platform for drug delivery.

Norfloxacin loaded nano-cubosomes for enhanced management of otitis externa: In vitro and in vivo evaluation

The research's goal is to design and formulate nano-structured cubosomes loaded with norfloxacin (NFX)formanagement of otitis externa. In this study, glyceryl monooleate (GMO) as lipid phase, Cremophor EL as surfactant and either Pluronic F108 or Pluronic F127 as stabilizer were the used ingredients. The nano-cubosomal formulation "CUB 1" (its dispersed phase is composed of GMO (95%), Cremophor EL (2.5%) and Pluronic F108 (2.5%)) was the best achieved one. It had small particles size (216.75 ± 2.47 nm), good polydispersity index (0.339 ± 0.012) and acceptable zeta potential (-41.2 ± 2.262 mV). Images obtained after transmission electron microscopy examination ensured nearly cubic shape of formed nanoparticles with excellent dispersibility. Moreover, micrographs of rabbit ear skin specimens examined by confocal laser microscopy ensured good permeation capability of nano-structured cubosomes.In addition, in vivoskin deposition results revealed that higher amount of NFX was deposited in the rabbit ear skin throughout the study period (10 h) compared to drug suspension. Additionally, histopathological results proved that NFX loaded cubosomes can be safely applied topically on ear skin without any signs of inflammation nor skin irritation. Accordingly, these results anticipated the nano-structured cubosomal capabilities as a favorable nano-carrier for dermal NFX delivery to external ear skin for enhancing the management of otitis externa.

Design of Non-Haemolytic Nanoemulsions for Intravenous Administration of Hydrophobic APIs

Among advanced formulation strategies, nanoemulsions are considered useful drug-delivery systems allowing to improve the solubility and the bioavailability of lipophilic drugs. To select safe excipients for nanoemulsion formulation and to discard any haemolytic potential, an in vitro miniaturized test was performed on human whole blood. From haemolysis results obtained on eighteen of the most commonly used excipients, a medium chain triglyceride, a surfactant, and a solubilizer were selected for formulation assays. Based on a design of experiments and a ternary diagram, the feasibility of nanoemulsions was determined. The composition was defined to produce monodisperse nanodroplets with a diameter of either 50 or 120 nm, and their physicochemical properties were optimized to be suitable for intravenous administration. These nanoemulsions, stable over 21 days in storage conditions, were shown to be able to encapsulate with high encapsulation efficiency and high drug loading, up to 16% (w/w), two water practically insoluble drug models: ibuprofen and fenofibrate. Both drugs may be released according to a modulable profile in sink conditions. Such nanoemulsions appear as a very promising and attractive strategy for the efficient early preclinical development of hydrophobic drugs.

Exploring NIR Aza-BODIPY-Based Polarity Sensitive Probes with ON-and-OFF Fluorescence Switching in Pluronic Nanoparticles

Because of their deep penetration capability in tissue, red or near infrared (NIR) fluorophores attract much attention in bio-optical imaging. Among these fluorophores, the ones that respond to the immediate microenvironment (i.e., temperature, polarity, pH, viscosity, hypoxia, etc.) are highly desirable. We studied the response of six NIR aza-BODIPY-based and structurally similar fluorophores to polarity and viscosity for incorporation inside Pluronic nanoparticles as switchable fluorescent probes (SFPs). Based on our results, all of these fluorophores were moderately to strongly sensitive to the polarity of the microenvironment. We concluded that attaching amine groups to the fluorophore is not necessary for having strong polarity sensitive probes. We further studied the response of the fluorophores when embedded inside Pluronic nanoparticles and found that four of them qualified as SFPs. We also found that the switching ratio of the fluorophore-encapsulated Pluronic nanoparticles (I_ON-to-I_OFF) is related to the length of the hydrophobic chain of the Pluronic tri-block copolymers. As such, the highest switching ratio pertained to F-68 with the lowest hydrophobic block poly (propylene oxide) (PPO chain of only 30 units).

Pluronic micelles with suppressing doxorubicin efflux and detoxification for efficiently reversing breast cancer resistance

The antitumor activity of doxorubicin (DOX) is often limited owing to the occurrence of multidrug resistance (MDR) during treatment. Herein, we developed hybrid polymeric micelles, which consisted of pluronic F127 as long-circulating helper in blood, and phenylboronic ester-grafted pluronic P123 (PHE) as efflux and detoxification regulator to efficiently deliver DOX and reverse MDR in vivo. Hybrid F127/PHE micelles exhibited higher stability and drug encapsulation (~80%) than simple F127/P123 micelles due to its lower CMC, and displayed in vitro drug release in a hydrogen peroxide (H₂O₂)-sensitive manner. Besides, DOX-loaded hybrid micelles (F127/PHE-DOX) possessed higher cell-killing ability and induce more apoptotic in MDR-cells than other groups, which was probably because it not only could greatly increase intracellular drug concentration by inhibiting P-gp mediated drug efflux, but also promote reactive oxygen species (ROS) generation by decreasing glutathione (GSH) levels. Besides, in vivo evaluation indicated that F127/PHE-DOX could well accumulate at tumor regions and exhibit the strongest tumor growth inhibition (TGI 87.87%) accompanied with low side effects. As a result, F127/PHE micelles had great potentials as a platform for anticancer drugs delivery and tumor MDR reversal in clinical application.

Erratum: Synergistic Effect of Binary Mixed-Pluronic Systems on Temperature Dependent Self-Assembly Process and Drug Solubility. Polymers 2018, 10, 105

The authors wish to make changes to the above-mentioned published paper [1].[...].