Sustainable pH-responsive casein/hyaluronic acid layered nanoparticles for targeted delivery of metformin to colorectal cancer

Colorectal cancer (CRC) is a major global health concern, ranking as the third most diagnosed and second deadliest cancer worldwide. This study aimed to develop a novel, pH-responsive, colon-targeted oral drug delivery system (OCDDS) for metformin (MET), an antidiabetic agent, which has been repurposed for treating CRC. A hyaluronic acid (HA)-chitosan (CH) polyelectrolyte complex (PEC) core for CD44 receptor targeting in CRC was coated within pH-responsive casein (CA) and pectin (PT) outer layer, forming CA/PT-MET-CH/HA PEC nanoparticles, ensuring drug release primarily in the colon. Response surface methodology (RSM) was employed to optimize the composition of the prepared inner and outer layers of the prepared OCDDS, which were characterized in terms of particle size, entrapment efficiency, zeta potential, and in vitro drug release. The optimized formulation underwent further characterization using transmission electron microscopy (TEM), cytotoxicity and cellular uptake studies on HT-29 CRC cells. The interactions between different excipients were studied via molecular modelling and confirmed by Fourier-transform infrared spectroscopy (FTIR). The optimized formulation, F8, comprised 1 % and 2 % of CH and HA, respectively. The coated CA/PT-MET-CH/HA nanoparticles, designated as CF3, contained 1.5 % CA and 0.5 % PT, and exhibited a particle size of 798.93 +/- 45.38 nm, a high drug entrapment efficiency of 83.26 %, and a controlled drug release profile with maximal release at pH 7.4, simulating the colon environment. The prepared uncoated and coated OCDDS systems exhibited higher cytotoxicity and cellular uptake compared to free metformin, suggesting the successful release of the encapsulated MET-CH/HA PECs from the CA/PT layer. These results highlight the potential of CA/PT-coated OCDDS for targeted colon delivery and treatment of CRC using HA as a targeting ligand.