Glycogen-based hybrid copolymers as a biodegradable construction materials for drug delivery purposes

Background: Despite continuous evolvement in cancer therapy there are still severe problems with side effects coming from insufficient selectivity of treatment for cancer tissue compared to healthy tissues, which is also a problem of cancer diagnostics. Conjugates with polymer carriers bring significant improvements for such purposes, we introduce completely new biodegradable polymer carrier platform based on body's own polysaccharide glycogen.

Materials and Methods: We used glycogen-graft-poly(2-alkyl-2-oxazolines) with various types of fluorescent dyes. Dansyl, FITC and Dyomics 615 were chosen as a fluorescent dyes for our polymer glycogen based carrier. Various techniques of in vitro and in vivo testing were applied to test potential of this platform, namely confocal microscopy for localization of modified glycogen, flow cytometry for assessment of endocytosis of polymer, MTT assay and measurement of in vivo fluorescence in CD1-Nude mice. We used HepG2 cell line for all in vitro tests. Type of degradation was addressed with colocalization studies using our polymer combined with fluorescent dye for lysosomes. Flow cytometry studies were performed in triplicates, using three types of inhibitors (cytochalasin D inhibits both type of endocytosis, hypertonic sucrose inhibits clathrin-mediated endocytosis and methyl-β-cyklodextrin inhibits caveolae-mediated endocytosis). Three types of modified glycogen (glycogen-FITC, glycogen-graft-poly(2-alkyl-2-oxazoline)-FITC and glycogen-GdDOTA-Dyomics 615) were tested to confirm their non-cytotoxic effect. At last but not least in vivo fluorescence was measured to determine time of biodistribution and confirm non-immunogenicity. Three female CD1-Nude mice were used.

Results: Results from confocal microscopy reveal that glycogen-based nanocarriers are present in the cytoplasm but not in the nucleus or in lysosomes, thus they are most probably degraded by physiological pathway for glycogen intracellular degradation. Drug delivery systems based on glycogen are not cytotoxic to the HepG2 cells, actually they provide additional energy source to the cancer cells. In vivo testing confirmed biodegradability of the system. The conjugates are also not significantly entrapped into the reticuloendothelial system.

Conclusions: We can conclude that this promising polymer carrier platform possess beneficial characteristics as biodegradability, biocompatibility or possibility to various synthetic modifications and can be used prospectively for diagnostic and therapy purposes.

The authors thank for financial support to the Ministry of Health of the Czech Republic, grant #15–25781A.

No conflict of interest.