The present study addresses the synthesis and characterization of new chitosan Schiff bases, Cs-IS-1 and Cs-IS-2, that possess 2-(2,3-dioxoindolin-1-yl)-N-phenylacetamide derivatives to meet the urgent demand for new antibacterial agents with improved biocompatibility. The synthesized compounds demonstrated notable antibacterial activity against Gram-positive (Bacillus subtilis, Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa, Escherichia coli) bacteria. Specifically, inhibition zones of 17.8 ± 2.5 mm (Cs-IS-1) and 16.7 ± 1.3 mm (Cs-IS-2) were observed against B. subtilis. Furthermore, toxicity studies on multiple human cell lines showed that Cs-IS-2 could hinder the proliferation of breast and skin cancer cells, with IC50 values of 44 and 48 μg/mL, respectively. It also displayed good safety against human skin fibroblasts (HSF cells). Mechanistic investigations revealed that Cs-IS-2 triggered a significant S-phase arrest in MCF-7 cells, while also inhibiting CDK2 activity (IC50 = 11.98 μg/mL). This suggests that blocking the cell cycle was a substantial factor in its ability to inhibit cell growth. Moreover, Cs-IS-1 and Cs-IS-2 exhibited improved antioxidant properties, with DPPH scavenging abilities of 52.72 % and 57.41 % at 1 mg/mL, respectively, surpassing that of chitosan (43.86 %). In silico studies employing molecular docking were conducted to elucidate the mechanism of action, revealing that the antibacterial and anticancer capabilities of these compounds are attributed to their binding patterns in the grooves of druggable proteins, specifically DNA gyrase (PDB: 4URO) and CDK2 (PDB: 3IG7). In silico ADMET analysis further confirmed the increased drug-likeness of Cs-IS-2, revealing higher membrane permeability, metabolic stability, and target tissue distribution.
