Hypoxia, Mn-SOD and H2O2 regulate p53 reactivation and PRIMA-1 toxicity irrespective of p53 status in human breast cancer cells

Hypoxia is part of the tumor microenvironment favoring cancer resistance to chemotherapy mediated by mutations in the tumor suppressor p53 gene (TP53), or by conformational wt TP53 dysfunction. Since it is important to suppress tumor adaptation to hypoxia, irrespective of p53 status, we compared the efficacy of nutlin-3 which prevents MDM2-wt p53 interactions and PRIMA-1 which promotes mutant p53 reactivation and induction of massive apoptosis, under normoxia and hypoxia, against (a) SKBR3 breast carcinoma harboring a mutant p53R175H and over-expressing erbB2; and (b) genetically matched breast cancer ERα positive MCF-7 cells harboring either wt p53 or mutant p53 R175H. Under normoxia, PRIMA-1 was active against breast cancer cells harboring mutant p53. However, hypoxia further increased the susceptibility of mutant p53 breast cancer SKBR3 cells to lower PRIMA-1 levels, possibly through oxidative stress since this was counteracted by N-acetylcysteine. When using MCF-7 cells over-expressing mutant p53, PRIMA-1 synergized with exogenous peroxidase to increase apoptosis concomitantly with induction of PUMA and Mn-SOD, under normoxia. Wt p53 MCF-7 cells responded to hypoxia by increasing superoxide dismutase and their reactivity with the PAb240 antibody, known to recognize conformationally-inactive p53. This correlated with sensitization of wt p53 MCF-7 cells to PRIMA-1 but not to nutlin-3. PRIMA-1 toxicity against normoxic wt p53 MCF-7 cells was also decreased by Mn-SOD over-expression or when added with the glutathione antagonist, buthionine sulfoximine. This report shows for the first time that hypoxia increases PRIMA-1 toxicity in human breast cancer cells, partly by modulating p53 conformation and by inducing superoxide turnover. Our results suggest that PRIMA-1 may help to prevent hypoxia-mediated tumor chemoresistance.