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

Background: Colorectal cancer (CRC), the third most common cancer worldwide, has increasingly detrimental effects on human health. Radiotherapy resistance diminishes treatment efficacy. Studies suggest that spermine synthase (SMS) may serve as a potential target to enhance the radiosensitivity.

Aim: To investigate the association between SMS and radiosensitivity in CRC cells, along with a detailed elucidation of the underlying mechanisms.

Methods: Western blot was adopted to assess SMS expression in normal colonic epithelial cells and CRC cell lines. HCT116 cells were transfected with control/SMS-specific shRNA or control/pcDNA3.1-SMS plasmids. Assessments included cell viability, colony formation, and apoptosis via MTT assays, colony formation assays, and flow cytometry. Radiosensitivity was studied in SMS-specific shRNA-transfected HCT116 cells post-4 Gy radiation, evaluating cell viability, colony formation, apoptosis, DNA damage (comet assays), autophagy (immunofluorescence), and mammalian target of rapamycin (mTOR) pathway protein expression (western blot).

Results: Significant up-regulation of SMS expression levels was observed in the CRC cell lines. Upon down-regulation of SMS expression, cellular viability and colony-forming ability were markedly suppressed, concomitant with a notable increase in apoptotic indices. Furthermore, attenuation of SMS expression significantly augmented the sensitivity of HCT116 cells to radiation therapy, evidenced by a pronounced elevation in levels of cellular DNA damage and autophagy. Importantly, down-regulation of SMS corresponded with a marked reduction in the expression levels of proteins associated with the mTOR signaling pathway.

Conclusion: Knocking down SMS attenuates the mTOR signaling pathway, thereby promoting cellular autophagy and DNA damage to enhance the radiosensitivity of CRC cells.