PP blocks cell cycle progression and modulates cell cycle
regulatory proteins.
We next asked if PP mediated growth
suppression was due to its cell cycle intervention. To determine the
effect of PP on the cell cycle alteration, all cell lines were evaluated
by propidium iodide flow cytometry at 24 hrs. After PP treatment,
MCF-7 cells showed 1.61 fold (10%–16.18%) whereas MDA-MB-
468 revealed 2.52 fold (14.28%–35.94%) increase in G2 phase.
Likewise MDA-MB-231 and MDA-MB-453 cells showed 1.76 fold
(18.44%–32.58%) and 1.69 fold (19.99%–33.92%) increases in the
S phase, respectively as compared to their individual controls
(Figure 2A & 2B). Cell cycle checkpoints are important control
mechanisms that ensure the proper execution of cell cycle events.
Levels of cell cycle–regulated proteins were inhibited in all breast
cancer cells. We found a dose-dependent decrease in the levels of
CDK1, CDK2, cyclin B1 and cyclin E and increase in the p21
proteins. All these proteins are strongly associated with cell cycle
arrest at G2/M and S phase (Figure 2C).