Cell Cycle Status Influences Resistance to Apoptosis Induced by Oxidative Stress in Human Breast Cancer Cells, Which Is Accompanied by Modulation of Autophagy.

Cancer cells are characterised by uncontrolled cell proliferation; however, some of them can temporarily arrest their cell cycle at the G0 or G1 phase, which could contribute to tumour heterogeneity and drug resistance. The cell cycle status plays a critical role in chemosensitivity; however, the influence of G0- and G1-arrest has not been elucidated. To study the cell cycle arrest-mediated resistance, we used MCF-7 cells and generated three populations of cells: (1) cells arrested in the G0-like phase, (2) cells that resumed the cell cycle after the G0-like phase and (3) cells arrested in early G1 with a history of G0-like arrest. We observed that both the G0-like- and the G1-arrested cells acquired resistance to apoptosis induced by oxidative stress, accompanied by a decreased intracellular reactive oxygen species and DNA damage. This effect was associated with increased autophagy, likely facilitating their survival at DNA damage insult. The cell cycle reinitiation restored a sensitivity to oxidative stress typical for cells with a non-modulated cell cycle, with a concomitant decrease in autophagy. Our results support the need for further research on the resistance of G0- and G1-arrested cancer cells to DNA-damaging agents and present autophagy as a candidate for targeting in anticancer treatment.