Characterization Of Polymeric Micelles Research Articles

Thioether-Based Polymeric Micelles with Fine-Tuned Oxidation Sensitivities for Chemotherapeutic Drug Delivery.

Oxidation-sensitive drug delivery systems (DDSs) have attracted attention due to the potential to improve efficacy and safety of chemotherapeutics. These systems are designed to release the payload in response to oxidative stress conditions, which are associated with many types of cancer. Despite extensive research on the development of oxidation-sensitive DDS, the lack of selectivity toward cancer cells over healthy cells remains a challenge. Here, we report the design and characterization of polymeric micelles containing thioether groups with varying oxidation sensitivities within the micellar core, which become hydrophilic upon thioether oxidation, leading to destabilization of the micellar structure. We first used the thioether model compounds, 3-methylthiopropylamide (TPAM), thiomorpholine amide (TMAM), and 4-(methylthio)benzylamide (TPhAM) to investigate the effect of the chemical structures of the thioethers on the oxidation by hydrogen peroxide (H2O2). TPAM shows the fastest oxidation, followed by TMAM and TPhAM, showing that the oxidation reaction of thioethers can be modulated by changing the substituent groups bound to the sulfur atom. We next prepared micelles containing these different thioether groups within the core (TP, TM, and TPh micelles). The micelles containing the thioether groups with a higher oxidation sensitivity were destabilized by H2O2 at a lower concentration. Micelle destabilization was also tested in human liver cancer (HepG2) cells and human umbilical vein endothelial cells (HUVECs). The TP micelles having the highest oxidation sensitivity were destabilized in both HepG2 cells and HUVECs, while the TPh micelles, which showed the lowest reactivity toward H2O2, were stable in these cell lines. The TM micelles possessing a moderate oxidation sensitivity were destabilized in HepG2 cells but were stable in HUVECs. Furthermore, the micelles were loaded with doxorubicin (Dox) to evaluate their potential in drug delivery applications. Among the micelles, the TM micelles loaded with Dox showed the enhanced relative toxicity in HepG2 cells over HUVECs. Therefore, our approach to fine-tune the oxidation sensitivity of the micelles has potential for improving therapeutic efficacy and safety of drugs in cancer treatment.

Nanoscopic micelle delivery improves the photophysical properties and efficacy of photodynamic therapy of protoporphyrin IX

Nanodelivery systems have shown considerable promise in increasing the solubility and delivery efficiency of hydrophobic photosensitizers for photodynamic therapy (PDT) applications. In this study, we report the preparation and characterization of polymeric micelles that incorporate protoporphyrin IX (PpIX), a potent photosensitizer, using non-covalent encapsulation and covalent conjugation methods. Depending on the incorporation method and PpIX loading percentage, PpIX existed as a monomer, dimer or aggregate in the micelle core. The PpIX state directly affected the fluorescence intensity and 1O 2 generation efficiency of the resulting micelles in aqueous solution. Micelles with lower PpIX loading density (e.g. 0.2%) showed brighter fluorescence and higher 1O 2 yield than those with higher PpIX loading density (e.g. 4%) in solution. However, PDT efficacy in H2009 lung cancer cells showed an opposite trend. In particular, 4% PpIX-conjugated micelles demonstrated the largest PDT therapeutic window, as indicated by the highest phototoxicity and relatively low dark toxicity. Results from this study contribute to the fundamental understanding of nanoscopic structure–property relationships of micelle-delivered PpIX and establish a viable micelle formulation (i.e. 4% PpIX-conjugated micelles) for in vivo evaluation of antitumor efficacy.

Preparation and Characterization of Polymeric Micelles from Poly( D, L-lactide) and Methoxypolyethylene Glycol Block Copolymers as Potential Drug Carriers

Amphiphilic diblock copolymers composed of methoxy polyethylene glycol (MePEG) and poly( D, L-lactide) (PDLLA) were prepared for the preparation of polymeric micelles. The use of MePEG-PDLLA as drug carriers has been reported in the open literature, but there are only few data on the application of a series of MePEG-PDLLA copolymers with different lengths in the medical field. The shape of the polymeric micelles is also important in drug delivery. Studies on in vitro drug release profiles require a good sink condition. The critical micelle concentration of a series of MePEG-PDLLA has a significant role in drug release. To estimate their feasibility as a drug carrier, polymeric micelles made of MePEG-PDLLA block copolymer were prepared by the oil in water (O/W) emulsion method. From dynamic light scattering (DLS) measurements, the size of the micelle formed was less than 200 nm. The critical micelle concentration of polymeric micelles with various compositions was determined using pyrene as a fluorescence probe. The critical micelle concentration decreased with increasing number of hydrophobic segments. MePEG-PDLLA micelles have a considerably low critical micelle concentration (0.4–0.5 μg/mL), which is apparently an advantage in utilizing these micelles as drug carriers. The morphology of the polymeric micelles was observed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The micelles were found to be nearly spherical. The yield of the polymeric micelles obtained from the O/W method is as high as 85%.