Chitosan (CS) is a semi-synthetic bio-based polysaccharide with promising biological and antitumor properties. However, its possible underlying anticancer mechanisms and molecular interactions have remained largely unknown. Herein, we have shown that CS exerts an inhibitory effect on the proliferation of MDA-MB-231, MCF-7 and T47D breast cancer cells in a dose and time-dependent manner while being non-toxic to fibroblast L929 normal cells. Exposure of MDA-MB-231 cells to CS led to depolarization of the mitochondrial membrane, increase in ROS, DNA oxidation, and S phase cell cycle arrest. Furthermore, EB/AO staining, Annexin–PI staining, TUNEL assay, and altered expression of caspase 3 in MDA-MB-231 cells all indicated that cancer cells progressively became apoptotic upon CS exposure. S phase arrest in MDA-MB-231 cells suggests possible CS–DNA interaction. UV-visible spectroscopy confirmed CS interaction with DNA, and competitive displacement fluorescence assay revealed a binding constant of 7.6 × 105 M−1 for CS. In addition, its binding modes with DNA were established by CD analysis. These results clearly indicate that along with being a safe biopolymer to normal cells, CS can be considered as an effectual anticancer agent.
