Enhancing the radiosensitivity of colorectal cancer cells by reducing spermine synthase through promoting autophagy and DNA damage

Background: Colorectal cancer (CRC), the third most prevalent cancer worldwide, poses a significant threat to human health. Resistance to radiotherapy remains a major challenge, reducing treatment efficacy. Recent studies suggest that spermine synthase (SMS) may be a promising target to enhance radiosensitivity in CRC.
Aim: To explore the relationship between SMS expression and radiosensitivity in CRC cells and elucidate the underlying molecular mechanisms.
Methods: SMS expression levels were analyzed in normal colonic epithelial cells and CRC cell lines using western blotting. HCT116 cells were transfected with control or SMS-specific shRNA, as well as control or SMS-overexpressing plasmids (pcDNA3.1-SMS). Cellular viability, colony formation, and apoptosis were assessed using MTT assays, colony formation assays, and GDC-0084 flow cytometry. Radiosensitivity was examined in SMS-knockdown HCT116 cells following 4 Gy radiation, with evaluations of cell viability, colony formation, apoptosis, DNA damage (comet assays), autophagy (immunofluorescence), and expression of mTOR pathway proteins (western blotting).
Results: SMS expression was significantly upregulated in CRC cell lines compared to normal colonic cells. SMS knockdown led to decreased cell viability and colony formation, along with increased apoptosis. Notably, downregulation of SMS enhanced radiosensitivity in HCT116 cells, as evidenced by elevated DNA damage and autophagy levels. Additionally, SMS suppression reduced the expression of key proteins in the mTOR signaling pathway.
Conclusion: SMS knockdown enhances radiosensitivity in CRC cells by inhibiting the mTOR signaling pathway, which promotes autophagy and DNA damage. Targeting SMS may represent a novel strategy to improve radiotherapy outcomes in CRC.