pH-responsive nanoparticles for cancer drug delivery

Solid tumors have an acidic extracellular environment and an altered pH gradient across their cell compartments. Nanoparticles responsive to the pH gradients are promising for cancer drug delivery. Such pH-responsive nanoparticles consist of a corona and a core, one or both of which respond to the external pH to change their soluble/insoluble or charge states. Nanoparticles whose coronas become positively charged or become soluble to make their targeting groups available for binding at the tumor extracellular pH have been developed for promoting cellular targeting and internalization. Nanoparticles whose cores become soluble or change their structures to release the carried drugs at the tumor extracellular pH or lysosomal pH have been developed for fast drug release into the extracellular fluid or cytosol. Such pH-responsive nanoparticles have therapeutic advantages over the conventional pH-insensitive counterparts.

Enhanced stability of core-surface cross-linked micelles fabricated from amphiphilic brush copolymers

"Stealth" nanoparticles made from polymer micelles have been widely explored as drug carriers for targeted drug delivery. High stability (i.e., low critical micelle concentration (CMC)) is required for their intravenous applications. Herein, we present a "core-surface cross-linking" concept to greatly enhance nanoparticle's stability: amphiphilic brush copolymers form core-surface cross-linked micelles (nanoparticles) (SCNs). The amphiphilic brush copolymers consisted of hydrophobic poly(epsilon-caprolactone) (PCL) and hydrophilic poly(ethylene glycol) (PEG) or poly(2-(N,N-dimethylamino)ethyl methacrylate) (PDMA) chains were synthesized by macromonomer copolymerization method and used to demonstrate this concept. The resulting SCNs were about 100 times more stable than micelles from corresponding amphiphilic block copolymers. The size and surface properties of the SCNs could be easily tailored by the copolymer's compositions.