Organometallic Phyllosilicate-Gold Nanocomplex: An Effective Oral Delivery System of Methotrexate for Enhanced in vivo Efficacy Against Colorectal Cancer

Purpose: Oral administration, although convenient and preferred for treating colorectal cancer (CRC), faces challenges due to limited CRC-related intestinal positioning and a dense mucus barrier. In the present study, a gold-nanoparticle decorated–organometallic phyllosilicate nanocomposite (AC-Au), with a pH-dependent surface coating, was employed for more effective oral delivery of anticancer drugs to treat CRC. Methods: The organometallic AC-Au was synthesized using the in-situ sol-gel method. Subsequently, methotrexate (MTX) was loaded into AC-Au, and the complex (AC-Au/MTX) was surface-coated with poly (methacrylic acid-co-methyl methacrylate) (1:2), a pH-dependent polymer (E/AC-Au/MTX). The in vitro characteristics of nanoparticles were examined using various analytical methods. In vivo efficacy studies were also conducted using an HCT-116 orthotopic colorectal cancer model. Results: AC-Au emerged as a spherical nanoparticle with a mean size of 26.5 ± 0.43 nm, displaying a positive charge over the pH range of 2–10. Both the uncoated and coated drug–loaded nanocomplexes (AC-Au/MTX and E/AC-Au/MTX) were fabricated with high entrapment efficiency (> 80%). Various analyses, including ultraviolet-visible spectroscopy, X-ray powder diffraction, transmission electron microscopy, and energy dispersive X-ray spectroscopy, confirmed the formation of the nanocomplexes. While AC-Au /MTX achieved rapid and extensive drug release at the pH range of 1.2–7.4, E/AC-Au/MTX exhibited pH-dependent drug release, with approximately 23% at pH 1.2 and 74% at pH 7.4. Relative to free MTX, the AC-Au-based nanocomplex significantly enhanced the cytotoxicity of MTX in HCT-116 cells. Furthermore, orally administered E/AC-Au/MTX significantly improved the anti-tumor activity of MTX in an HCT-116 orthotopic colorectal cancer model, resulting in approximately 60% suppression of tumor mass compared with the positive control. Conclusion: The organometallic AC-Au nanocomplex coated with a pH-dependent polymer has the potential to be an effective colonic drug delivery system of MTX, enhancing in vivo efficacy against colorectal cancer.