Long-term Hypoxia Inhibits Sphere Formation on PC-3 and MDA-MB-231 Cell Line Models

Abstract

Background Cancer stem cells (CSCs) represent a relatively small subset of cells within tumors, capable of self-renewal and associated with metastasis and cancer recurrence. While conventional chemotherapy targets actively dividing bulk tumor cells, dormant CSCs remain unaffected and survive. Hypoxia or deprivation of oxygen supply is a common feature of solid tumors, which plays a critical role in metastatic progression and CSC maintenance. However, the cellular responses to hypoxia might be influenced by many factors, including the severity, duration, and other specific characteristics of this stress. Objective In our study, we assessed the impact of long-term hypoxia on the CSCs population in 5 cell lines representing 5 different tumor types. Methods We assessed and characterized the effect of oxygen concentration on CSC population using the sphere formation assay. The protein levels in tumor spheres were examined by western blot analysis. Results Long-term hypoxia inhibited sphere formation by PC-3 and MDA-MB-231 CSCs. Moreover, chronic hypoxic stress suppressed cell proliferation in tumor spheres in all 5 tested cell lines: SNB-19, HCT116, MDA-MB-231, NCI-H460 and PC-3. This effect was accompanied by PCNA downregulation in tumorspheres derived from NCI-H460 and PC-3 cells. Conclusion The prolonged hypoxic conditions impede tumor sphere formation by PC-3 prostate CSCs, primarily through the downregulation of PCNA levels. The specific cellular response to hypoxia depends on the duration and, supposedly, other specific features of this stress.