Curcumin-Loaded Ligand-Conjugated Chitosan Nanoparticles: A Comparative Study of Folic Acid, Phenylalanine, and Butyric Acid Conjugates for Colorectal Cancer

Colorectal cancer therapy requires drug delivery systems that improve treatment efficacy and minimize systemic toxicity. In this study, chitosan-based nanoparticles were fabricated and functionalized with folic acid (FA), phenylalanine (PA), and butyric acid (BA) to enhance the delivery of curcumin to Caco-2 cancer cells. The nanoparticles were prepared using an ionic gelation method, and their physicochemical properties, cellular uptake efficiency, and cytotoxicity—including safety evaluation against normal HIEC-6 cells—were investigated. Results showed that ligand conjugation significantly influenced the physicochemical properties of the nanoparticles. CRFANP (FA-modified) exhibited the largest particle size (263.5 nm) due to its rigid aromatic structure, while CRPANP (PA-modified) showed an intermediate size (138.0 nm) and the lowest surface charge (15.59 mV). In contrast, CRBANP (BA-modified) presented the smallest particle size (128.2 nm) and the highest positive surface charge (23.27 mV). These distinct physicochemical properties directly influenced their cellular interactions; CRBANP and CRFANP showed higher uptake than CRPANP, with CRBANP yielding the maximum accumulation of curcumin in Caco-2 (21.92 nM/mg protein) and HT-29 cells (22.09 nM/mg protein). Correlating with the uptake data, cytotoxicity assays revealed that CRBANP was the most potent formulation, exhibiting the lowest IC50 of 1.30 µM in Caco-2 cells, which was significantly lower than that of CRFANP (3.49 µM) and CRPANP (7.40 µM), while demonstrating high selectivity against Caco-2 cells with an SI of 46.5 and no apparent toxicity toward normal HIEC-6 cells. This enhanced efficacy is attributed to the synergistic action of butyric acid as a histone deacetylase inhibitor (HDACi), which complements curcumin’s anticancer activity. These findings indicate that integrating butyric acid into chitosan nanoparticles provides an effective and selective strategy for targeted colorectal cancer therapy.