The Effect of Polymerization Method in Stereo-active Block Copolymers on the Stability of Polymeric Micelles and their Drug Release Profile

Variations in the inner core affect the pharmacokinetics of indomethacin-encapsulated polymeric micelles

Hydrophobic ion pairing (HIP) is a drug encapsulation technology that uses electrostatic interactions between a drug and an additive. However, although polymeric micelles can encapsulate hydrophobic drugs in the core, the encapsulated drug often leaks. Therefore, we designed polymeric micelles with HIP functionalized in a hydrophobic inner core using three diblock copolymers comprising polypeptides with different ratios of polar and hydrophobic amino acids and polyethylene glycol (PEG) to encapsulate indomethacin (IND). The three IND-encapsulated HIP micelles showed different area under the curve (AUC) values as an index of blood retention after intravenous injection in mice. Despite having the same PEG shell, IND-PEG-poly(H/F)n showed a 1.56-fold higher AUC than IND-PEG-poly(D/F)n. PEG interface morphologies were evaluated to determine the differences in pharmacokinetic parameters caused by changes in inner core HIP patterns. The micellarized diblock copolymer was desorbed from IND-PEG-poly(D/F)n due to electrostatic repulsion between IND and the diblock copolymer comprising aspartic acid. Our results suggest that changes in the HIP patterns of the micelle inner core affected the PEG interface morphologies, such as PEG density and diblock copolymer desorption from micelles. These phenomena might lead to changes in the interaction of plasma proteins and drug dispositions.

Application of arteether-loaded polyurethane nanomicelles to induce immune response in breast cancer model

To concentrate a potent anticancer drug (Arteether) in tumor microenvironment, we encapsulated it in biodegradable and pH sensitive polyurethane (PU) nanomicelles (NMs). The nanocomplex was characterized by Fourier transform infrared (FTIR), dynamic light scattering (DLS). The loading capacity and release profile in pH of 5.4 and 7.4 were considered. The cytotoxicity effect was evaluated in vitro and in vivo settings. The level of IFN-γ and IL-4 cytokines of mice splenocytes were assessed by enzyme-linked immunosorbent assay (ELISA). The nanocomplex showed negative zeta charge of -26.2 mV, size of 42.30 nm and high loading capacity (92%). Release profile showed a faster rate of drug liberation at pH 5.4 as compared to that of pH 7.4. It indicated significant inhibitory effect on the growth of 4T1 cell line and increased IFN-γ level.

A novel cabazitaxel-loaded polymeric micelle system with superior in vitro stability and long blood circulation time

Cabazitaxel (CTX) is a second-generation semisynthetic taxane that demonstrates antitumor activity superior to docetaxel. However, the low aqueous solubility of CTX has hampered its use as a therapeutic agent. In this work, CTX-loaded N-t-butoxycarbonyl-L-phenylalanine end-capped monomethyl poly (ethylene glycol)-block-poly (D,L-lactide) (mPEG-PLA-Phe(Boc)/CTX) micelles were prepared to improve the solubility of CTX while retaining its superior stability before accessing the tumor site. The mPEG-PLA-Phe(Boc)/CTX micelles showed excellent stability in vitro compared with mPEG-PLA/CTX micelles. When stored at 25 °C, the mPEG-PLA/CTX micelles tended to aggregate within 1 h, whereas the mPEG-PLA-Phe(Boc)/CTX micelles were uniformly transparent even after three weeks. Dilution of mPEG-PLA/CTX micelles widened their size distribution and decreased the encapsulation efficiency, while significant change was not found in mPEG-PLA-Phe(Boc)/CTX micelles, even when diluted 1000-fold. Pharmacokinetic results in Sprague-Dawley rats indicated that, compared with Jevtana(®), intravenous administration of mPEG-PLA-Phe(Boc)/CTX micelles stably retained the CTX in plasma with 26.03-fold larger of the area under the time-concentration curve, 2.13-fold longer of the half-life, and 9.99-fold higher of the maximum concentration. In conclusion, mPEG-PLA-Phe(Boc) micelle may be a potential nanocarrier not only to improve the solubility of CTX but also to prolong the blood circulation time, which results in improved biological activity.

Rational design of block copolymer micelles to control burst drug release at a nanoscale dimension

To circumvent the problem of burst drug release from polymeric micelles, we designed three layered ABC micelles consisting of methoxy poly(ethylene oxide) (PEO) as the shell layer (A block); poly(lactic acid) (PLA) of different stereo-chemistries as the outer core (B block) and poly(α-benzylcarboxylate-ε-caprolactone) (PBCL) or poly(ε-caprolactone) (PCL) as the inner core (C block). The micelles were used to encapsulate a model hydrophobic drug, nimodipine. The effect of PLA (B block) incorporation and stereochemistry on the formation of semi crystalline outer cores in ABC triblock copolymer micelles, micelle stability, drug loading and release was then assessed in comparison to diblock copolymer micelles. The PLA outer core was expected to act as a barrier lowering the rate of drug diffusion out of the micellar carrier owing to a high Flory Huggins interaction parameter between nimodipine and PLA (χ=1.35). Introduction of PLA outer cores in ABC block copolymer micelles reduced the burst release of nimodipine from polymeric micelles without jeopardizing its high encapsulation efficiency. In ABC polymeric micelles with stereo-regular PLA blocks; semi-crystalline outer PLA cores were not formed, which was in contrast to PEO-PLA diblock copolymer micelles. Accordingly, PLA stereo-chemistry had no significant effect on drug release in ABC polymeric micelles. In contrast to diblock copolymers, no sign of stereo-complexation in mixed micelles composed of a 50:50 mixture of PdLA and PlLA containing ABC triblock copolymers was observed. The results showed the capability of properly designed ABC triblock copolymer micelles as reservoirs for drug solubilization and depot release at nanoscale dimensions.

STATEMENT OF SIGNIFICANCE

Polymeric micelles are core-shell nanostructures that are widely used for drug delivery. Their hydrophobic core accommodates poor water soluble drugs and their hydrophilic shell allows the whole structure to be water soluble. A common problem with the use of polymeric micelles is leakage of the incorporated drug from these carriers. Here we have shown that a properly designed three layered (ABC) block copolymer micelle with drug compatible blocks at the inner core and drug incompatible blocks at the outer core can be used to reduce the initial fast rate of drug release while providing high amount of drug encapsulated in the core. Moreover, changes in the chemical structure of the inner core may be used to modify the stability of these systems.