Acid pH-activated glycol chitosan/fullerene nanogels for efficient tumor therapy

Glycol chitosan (GC) grafted with 2,3-dimethylmaleic acid (DMA) and fullerene (C60) conjugates (GC-g-DMA-g-C60) were developed for use in a photosensitizer prodrug. GC-g-DMA-g-C60 was prepared via the simple two-step chemical grafting reactions of (i) DMA to free amine groups of GC and (ii) hydroxyl groups of GC-g-DMA to ππ carbon bonds of C60. This conjugate was self-assembled to form polysaccharidic nanogels consisting of a hydrophilic block (GC and DMA) and a hydrophobic block (C60). Here, GC-g-DMA-g-C60 nanogels also formed multi-nanogel aggregates due to the electrostatic interaction between the pendant carboxylic acid group (due to the DMA) and residual free amine group of GC at pH 7.4. Interestingly, the nanogel aggregates can be disintegrated at pH 5.0 due to the reduction of electrostatic interaction resulting from the cleavage of the DMA blocks at pH 5.0. Upon 670 nm light illumination, photo-responsive properties of the nanogel aggregates allowed different singlet oxygen generation according to the pH condition: the reduced singlet oxygen generation (due to increased photo-interference effect between C60 molecules close-packed in nanogel aggregates) at pH 7.4, but the elevated singlet oxygen generation (due to the disintegration of nanogel aggregates) at pH 5.0. GC-g-DMA-g-C60 nanogel aggregates responds to pH 5.0 (∼endosomal pH) can be a good candidate for endosomal pH targeting and in vivo photodynamic therapy in various malignant tumor cells.