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.