A QbD optimization of a pH-responsive Eudragit S100–chitosan nanoformulation for the co-delivery of pentoxifylline and simvastatin in colorectal cancer therapy

Abstract

Colorectal cancer (CRC) presents a significant global health challenge, where the efficacy of conventional treatments is often hampered by systemic toxicity, poor bioavailability, and drug resistance. Drug repurposing and nanotechnology offer promising avenues to overcome these limitations. While pH-responsive Eudragit S100–chitosan hybrid systems are established as robust pH-responsive oral delivery carriers, the present study introduces a novel therapeutic strategy by combining these platforms with the co-delivery of the repurposed drugs pentoxifylline (PTX) and simvastatin (SIM) for synergistic CRC therapy. A hybrid nanoparticle system was synthesized using ionic gelation, combining the mucoadhesive properties of chitosan with the pH-dependent release of Eudragit S100. The formulation was optimized using a Quality by Design (QbD) Box–Behnken design to yield nanoparticles with a particle size of 152 ± 5 nm, a zeta potential of +31.2 ± 1.5 mV, and high entrapment efficiency for both drugs (PTX: 85.4 ± 3.1%; SIM: 78.9 ± 2.8%). In vitro release studies in simulated gastrointestinal media demonstrated minimal drug release in acidic conditions (PTX <8.3%; SIM <5.7%) and sustained release at colonic pH (cumulative release: PTX 82.3 ± 3.7%, SIM 78.6 ± 3.2% at 24 h; plateau levels of 89.7% and 85.4% by 48 h), confirming the pH-responsive release behavior of the formulation, with preferential drug liberation at neutral-to-alkaline pH conditions mimicking the colonic environment. These in vitro findings demonstrate pH-triggered release characteristics consistent with a mechanistic rationale for preferential colonic drug exposure; however, in vivo validation is required to confirm whether site-specific delivery to the colon is achieved under physiological conditions. Molecular docking simulations revealed strong binding affinities of simvastatin against key cancer targets EGFR, CA9, and GSK3β (ΔG: −7.5 to −8.7 kcal mol⁻¹), providing a mechanistic rationale for its repurposing. The optimized nanoformulation (NP-PTX/SIM) exhibited significant synergistic anti-proliferative cytotoxic effects against HCT-116 cells (IC₅₀ = 10.21 µg mL⁻¹) compared to free drugs through caspase-3 activation and suppression of proliferative (Ki-67) and angiogenic vascular endothelial growth factor (VEGF) markers confirming its apoptotic effects. By integrating the established Eudragit S100–chitosan carrier with the novel co-delivery of pentoxifylline and simvastatin, coupled with QbD optimization and comprehensive therapeutic evaluation, this work presents a distinct and innovative multi-targeted therapeutic strategy for CRC with improved efficacy and reduced off-target effects.