Colorectal cancer (CRC) is one of the most prevalent and deadly cancers of the digestive system, ranking third globally in incidence and second in mortality worldwide (Yang et al., 2023). Its progression is influenced by various factors, including metabolic abnormalities, dietary habits, and chronic inflammation (Wang et al., 2023). Despite advancements in early detection and treatment, CRC survival rates remain low, primarily due to metastasis, which is the leading cause of CRC-related mortality (Ren et al., 2023, Shi et al., 2023). This highlights the critical need to address the complex factors contributing to CRC progression to improve patient outcomes.

5-Fluorouracil (5-FU), a synthetic fluoropyrimidine analogue, works by inhibiting thymidylate synthase (TS) and disrupting DNA synthesis, resulting in S-phase arrest and apoptosis (Qiu et al., 2023). For decades, 5-FU-based chemotherapy has demonstrated efficacy in CRC treatment (Wu et al., 2022). However, both intrinsic and acquired resistance to 5-FU significantly limits its effectiveness, presenting a major challenge in CRC therapy and contributing to poor patient prognosis (Li et al., 2023, Yao et al., 2022, Zhang et al., 2019). Therefore, understanding the molecular mechanisms that influence 5-FU sensitivity is essential to developing more effective therapeutic strategies for CRC.

Autophagy is a vital cellular mechanism that facilitates the breakdown and recycling of damaged organelles, misfolded proteins, and other cellular debris through lysosomal degradation. This process, governed by autophagy-related genes, is integral to maintaining cellular homeostasis and contributes to diverse physiological processes, including development, aging, inflammation, oxidative stress, and immune regulation (Debnath et al., 2023, Klionsky et al., 2021). However, in the context of cancer, autophagy plays a paradoxical role. While it helps normal cells combat genotoxic stress and prevents tumor formation, it can also enable cancer cells to adapt to adverse conditions, such as chemotherapy or radiotherapy, thereby promoting survival and resistance to treatment (Hu et al., 2021, Saha et al., 2018). This dual function of autophagy has positioned it as a key factor in chemotherapy resistance and a potential therapeutic target (Jin et al., 2021, Li et al., 2024). In CRC, the relationship between autophagy and resistance to 5-fluorouracil (5-FU) has been increasingly recognized. Research has demonstrated that silencing NEAT1 in CRC cells reduces the expression of autophagy markers such as Beclin-1, ULK1, and LC3, while simultaneously enhancing the cells’ sensitivity to 5-FU (Liu et al., 2020). This suggests that NEAT1 facilitates chemotherapy resistance by activating autophagy, underscoring the complex nature of autophagy in CRC progression. While autophagy is crucial for maintaining normal cellular integrity, its activation in cancer cells helps them survive therapeutic stress, highlighting its dual role and reinforcing its potential as a target to overcome drug resistance. This study emphasized the importance of autophagy activation in developing 5-FU resistance in CRC cells.

Morin (2,3,4,5,7-pentahydroxy flavone), a flavonoid derived from the Moraceae plant family, is known for its health benefits and therapeutic potential (Shin et al., 2021). Previous studies have demonstrated that Morin can mitigate STZ-induced diabetic retinopathy (Jiang et al., 2020) and inhibit DOX-induced vascular inflammation (Yu et al., 2022). In cancer research, Morin has exhibited anti-tumor effects across various types of cancer, including liver, colorectal, and ovarian cancers (Chen and Zhang, 2019, Xu and Zhang, 2019, Zhao et al., 2023). Beyond its role in inhibiting autophagy, Morin has been shown to modulate multiple signaling pathways involved in tumor progression and chemotherapy resistance, making it a promising adjunctive agent in cancer treatment (Cakmak et al., 2023, Zhao et al., 2024). Morin has been reported to induce apoptosis in cancer cells via both intrinsic and extrinsic pathways, leading to the activation of caspase cascades and mitochondrial dysfunction (Mottaghi and Abbaszadeh, 2021). It promotes the expression of pro-apoptotic proteins such as Bax while downregulating anti-apoptotic molecules like Bcl-2, ultimately driving programmed cell death in CRC and other malignancies (Balaga et al., 2023). This apoptotic effect enhances the efficacy of chemotherapy drugs like 5-FU by sensitizing tumor cells to cytotoxic stress (Lori et al., 2019). In addition to its pro-apoptotic effects, Morin has been found to exert anti-proliferative properties by interfering with cell cycle progression (Nowak et al., 2020). It arrests cancer cells at the G0/G1 phase by downregulating cyclins and cyclin-dependent kinases (CDKs), thereby reducing the proliferation capacity of tumor cells (Maharjan et al., 2025). Moreover, Morin has been shown to modulate oxidative stress by reducing intracellular reactive oxygen species (ROS) levels, which can contribute to enhanced drug resistance (Kim et al., 2010). By restoring redox homeostasis, Morin may improve the response of CRC cells to chemotherapy while limiting oxidative damage to normal tissues.

Recent studies have further highlighted Morin’s role in modulating key molecular pathways involved in tumor progression. Specifically, Morin has been shown to inhibit low molecular weight protein tyrosine phosphatase (LMW-PTP), an enzyme associated with chemotherapy resistance in multiple cancer types. In melanoma cells, LMW-PTP overexpression enhances resistance to traditional chemotherapeutic agents, while Morin-mediated inhibition of LMW-PTP improves the sensitivity of melanoma cells to 5-FU and radiotherapy, significantly enhancing treatment efficacy (Lori et al., 2018). Similarly, in colorectal cancer, Morin has been shown to downregulate LMW-PTP expression in both in vitro and in vivo models, leading to increased apoptosis and reduced tumor growth (Lori et al., 2019). These findings suggest that Morin not only possesses direct anti-cancer properties but also enhances the effectiveness of existing chemotherapy regimens by targeting resistance mechanisms.

Importantly, Morin has shown the ability to modulate autophagy. Studies testified that Morin has an anti-autophagic effect in ifosfamide-induced testicular toxicity in rats (Cakmak et al., 2023) and lung damage (Yesildag et al., 2022). Beyond this, Morin’s ability to suppress tumor-associated autophagy has been linked to overcoming drug resistance in chemoresistant cancers (Singh et al., 2019). By targeting key autophagy-related proteins such as Beclin-1 and LC3, Morin reduces cancer cell survival under chemotherapy-induced stress, thereby enhancing drug efficacy (Singh et al., 2019). Furthermore, studies have indicated that Morin can interact with multiple oncogenic pathways, such as PI3K/AKT/mTOR and MAPK/ERK, which are crucial regulators of both autophagy and cell proliferation (Maharjan et al., 2025, Nie et al., 2019). Through these mechanisms, Morin acts as a multifaceted therapeutic agent capable of potentiating the effects of standard chemotherapy while simultaneously disrupting adaptive resistance mechanisms in CRC. Therefore, morin may have potential as a therapeutic agent for CRC, particularly in cases resistant to conventional treatments.

In this study, we investigate the effects of Morin on 5-FU-resistant CRC (5-FU/CRC) cells, with a focus on its role in inhibiting autophagy. Our research aims to elucidate the molecular mechanisms by which Morin suppresses the progression of 5-FU-resistant CRC, highlighting its potential to overcome autophagy-mediated resistance. By examining how Morin impacts autophagy in CRC, we seek to uncover novel therapeutic strategies that could enhance the effectiveness of CRC treatments and ultimately improve patient outcomes.