5-Fluorouracil loaded copper‑aluminum layered double hydroxides inhibit colorectal cancer cells by inducing oxidative stress, mitochondrial membrane depolarization, apoptosis, and cell cycle arrest.

Colorectal cancer (CRC) is one of the global health issues. Current treatments still present major challenges such as off-target cytotoxicity and the emergence of drug resistance, the development of potent and innovative therapeutics is urgently needed. Here, we synthesized copper‑aluminum (CuAl) layered double hydroxides (LDH) using a hydrothermal method and loaded them with the 5-fluorouracil (5-FU) (CuAl-5FU) to improve their anticancer efficacy. The LDHs were 2D-sheeted and rosette-like in shape. The hydrodynamic diameter of CuAl and CuAl-5FU was 568 and 661 nm, respectively. Zeta potential values of CuAl-5FU ranged from +31.39 to +34.93 mV across pH 3 to 9, indicating good colloidal stability. The drug loading and encapsulation efficiency were 18.19% and 36.37%, respectively. Dose-dependent cytotoxicity was seen in HCT-116 and HT-29 CRC cells. Comparatively, CuAl-5FU LDH exhibited greater anticancer activity compared to LDH alone and free 5-FU drug in both monolayer and tumor spheroid models. Mechanistic studies revealed that CuAl-5FU significantly induced reactive oxygen species (ROS) production, mitochondrial membrane depolarization, and promoted apoptosis by upregulating the pro-apoptotic Bax protein and PARP cleavage in both CRC cells. Transcriptomic analysis and qPCR validation revealed the downregulation of oncogenic MAPK signaling and modulation of key genes related to proliferation (JUN, DUSP1, FOSB, EGR1, and FOS), apoptosis (TP53I3, ZMAT3, GADD45A, BBC3, MDM2, TNFRSF10B, E2F1, and ORC1), and cell cycle arrest (CDKN1A and CDC25A). Notably, we identified altered expression of several chemoresistance-related genes (AVPI1, HROB, DDIAS, PTGES, and LAMA3), suggesting the early emergence of adaptive responses in CRC cells. To validate this observation, CuAl-5FU-resistant HCT-116 G3 and HT-29 G2 cell lines were established and their chemoresistant phenotypes were characterized. Indeed, the chemoresistance-associated genes were upregulated, together with significantly higher IC50 values and clonogenic survival fractions than their respective parental cells. Collectively, these findings suggest that CuAl-5FU improves anticancer activity in CRC cells by modulating multiple genes involved in ROS production, mitochondrial membrane depolarization, apoptosis, and cell cycle regulation. Nevertheless, chemoresistance developed rapidly following repeated treatment, highlighting a potential limitation of this therapeutic approach. Overall, this study provides a new potential strategy for CRC treatment while emphasizing the importance of elucidating the molecular mechanisms underlying acquired chemoresistance. Future studies should also optimize the physicochemical properties of the CuAl-5FU LDH, particularly the large particle size (∼661 nm) by optimizing the hydrothermal synthesis conditions and incorporating surface modifications to further improve the tumor penetration and drug delivery.