Chondroitin Sulfate-Based Self-Assembling Nanoprodrug for Controlled Methotrexate Delivery in Cancer Therapy

In this study, a pH-responsive chondroitin sulfate–methotrexate (MTX) polymeric prodrug was synthesized through Schiff base formation between oxidized chondroitin sulfate and MTX. The resulting amphiphilic conjugate exhibited a conjugation degree of 184 mg MTX per g conjugate and spontaneously self-assembled into stable nanoparticles (CSMXPs) with a mean diameter of 120 ± 10 nm, a polydispersity index of 0.24, and a critical aggregation concentration of 4.7 × 10−4 mg mL−1. Drug release studies demonstrated a marked pH-dependent behavior, with complete MTX release after 24 h at pH 5.0 and a sustained release profile under physiological conditions. The release mechanism followed reversible first-order kinetics and was accelerated by acid-catalyzed hydrolysis of the imine linkage. Biological evaluation revealed enhanced therapeutic selectivity of CSMXPs compared with free MTX. At 36 μM MTX-equivalent concentration, CSMXPs reduced HeLa cell viability to 37%, while maintaining MCF-10A viability above 88%, whereas free MTX decreased viability in both cell lines (51% and 65%, respectively). Fluorescence confocal microscopy confirmed efficient nanoparticle uptake by cancer cells. These findings demonstrate that CSMXPs represent a promising self-assembling nanoprodrug platform for selective and targeted cancer therapy.