INHIBITION OF PROLIFERATION OF T47D HUMAN BREAST-CANCER CELLS - ALTERATIONS IN PROGESTERONE-RECEPTOR AND P53 TUMOR-SUPPRESSOR PROTEIN

We have investigated the influence of three structurally different but functionally related compounds [1, 10 ortho-phenanthroline (phenanthr oline), Rifampicin and aurin tricarboxylic acid (ATA)] on the rate and the extent of proliferation of progesterone-responsive T47D human bre ast cancer cells. These compounds have previously been used in this la boratory and have been shown to modulate properties of nucleic acid bi nding proteins. Because p53 and the progesterone receptor (PR) are bot h DNA binding proteins that appear to regulate proliferation of breast cells, alterations in T47D cell p53 and PR levels were examined to de termine their relevance in cell proliferation. T47D cells were grown i n the absence of phenol red and in the presence of 5% fetal calf serum with or without charcoal stripping in the presence of the inhibitors. The rate of proliferation of cells grown in Rifampicin containing med ium exhibited nearly 70% inhibition. Phenanthroline, a known metal che lator, was an effective inhibitor of proliferation at 3 mM reducing th e cell number by more than 75%. ATA (0.24-2.4 mu g/ml) inhibited the g rowth of the cells by nearly 50%. Analysis of the mechanism of action of these compounds revealed that treatment with these compounds caused specific changes in the molecular composition of T47D cell PR. Wherea s ATA caused increased stability of PR isoforms, Rifampicin induced a upshift in the mobility of PR in SDS gels-a phenomenon associated with hyperphosphorylation of steroid receptors (SRs). Phenanthroline treat ment (> 2 mM) caused a complete down-regulation of PR and the tumor su ppressor protein, p53. The downregulation of p53 paralleled the change s in the molecular composition of PR. We propose that the inhibition o f T47D cell proliferation by phenanthroline, Rifampicin and ATA result s from a number of cellular changes that include regulation of p53 and PR.