ABSTRACT
@#[Abstract] Objective: To investigate the function and mechanism of ferroptosis in the radiation resistance of colorectal tumor-repopulating cells. Methods: Human colorectal tumor cells HCT116 (defined as Control cells) were cultured in two-dimensional normal conditions, and tumor regenerative cells with high tumorigenicity (defined as TRCs) were cultured and screened in three-dimensional fibrin soft gels by the mechanical force method. Both the control group and TRC group cells were exposed to X-rays with different doses (2, 4, 6, 8 Gy) and MTS and the clone formation assay were used tomeasure the cell viability rate and proliferation ability. After the Control cells and TRCs were treated with ferroptosis inducer (Erastin) and X-rays respectively, they were stained with C11-BODIPY reagent, and the lipid peroxidation level of the cells was observed and determined by confocal microscopy and flow cytometry. qPCR was used to determine the effects of Erastin and X-rays treatments on the expressions of ferroptosis-related genes glutathione peroxidase 4 (GPX4) and acyl-coenzyme A synthetase long-chain family member 4 (ACSL4) in the Control cells and TRCs; WB assay was performed to determine the effects on the expressions of ferroptosis-related proteins GPX4 and ACSL4. Results: Colorectal TRCs with high stemness were cultured and screened out from soft fibrin gels. After irradiation with different doses (2, 4, 6, 8 Gy) of X-rays, the viability rate, the clone sizeand the number of clones in the control group were significantly lower than those in the TRC group (all P<0.05). After the cells in the control group were irradiated with different doses of X-rays (4, 8 Gy) and treated with Erastin, the lipid peroxidation level of the cells in the X-ray treated group was significantly higher than that in the untreated group (P<0.05). The lipid peroxidation level of the cells in the Erastin-treated group was significantly higher than that in the DMSO-treated group (P<0.05). There was no statistical difference among all treatment subgroups in the TRC group (all P>0.05). The mechanism study indicated that compared with those in control cells, GPX4 and ACSL4 in TRCs under ferroptosis-inducing conditions (X-ray radiation and Erastin treatment) presented expressions that contributed more to radiation resistance, i.e., continued upregulation of GPX4 and downregulation of ACSL4 and their expressions were dependent on the doses of Erastin. Conclusion: Colorectal TRCs may resist ferroptosis through a high expression of GPX4 and a low expression of ACSL4, which in turn induces radiation resistance.