Cellular alterations associated with therapy-induced senescence

A large amount of apparently senescent tumor cells are observed after chemo/radio therapy, as indicated by ß-Gal staining in HeLa and MCF7 long-term cultures. 
The observation of ß-Gal positive cells indicates the coexistence of sub-populations of cells with possible different behaviors in terms of resistance to therapeutic agents. 
In both camptothecin-treated and irradiated MCF7 cells, together with enlarged and flattened cells, were observed numerous cell-in-cell structures, known to produce polynucleation. Are these cells escaping from therapy-induced senescence, thus promoting post-therapy cell repopulation? We do not yet know the fates of internalizing cells; however similar cell structures are also found in many different tumors.  
  • All HeLa and MCF7 treated-cells are positive to ß-Gal staining (B, C; E, F).
  • HeLa treated-cells are flattened and may be mononucleated (H) or polynucleated (I); MCF7 treated-cells show cell-in-cell subpopulations (L).
  • HeLa treated-cells are positive for LC3B autophagy marker (N, O); MCF7 treated-cells are slightly positive for LC3B (Q), especially cell-in-cell subpopulations (R).
  • All HeLa and MCF7 show an increased number of gamma-H2AX foci after treatment (T, U; W, X).