INHIBITION OF ABERRANT PROLIFERATION AND INDUCTION OF APOPTOSIS IN PRENEOPLASTIC HUMAN MAMMARY EPITHELIAL-CELLS BY NATURAL PHYTOCHEMICALS

Aberrant proliferation and modulated apoptosis leading to impaired cel lular homeostasis represent crucial early events in the multi-step car cinogenic process. Regulation of these perturbed biomarkers may predic t efficacious prevention of cancer development. present experiments on non-cancerous human mammary epithelial 184-B5 cells were designed to examine whether i) exposure to suspect environmental human carcinogen Benzo (alpha) pyrene (BP) alters the status of cell proliferation and apoptosis and ii) BP-induced alterations are modulated in response to select natural phytochemicals that inhibit rodent mammary tumorigenesi s. Flow cytometric analysis, cellular immunoreactivity to proliferatio n specific and apoptosis specific gene products and anchorage-dependen t colony formation represented quantitative endpoints. Cruciferous glu cosinolate indole-3-carbinol (I3C), tea polyphenol (-) epigallo catech in gallate (EGCC) and soy isoflavone genistein (GEN) represented the c hemopreventive test compounds. A single 24 h exposure to 39 mu M BP re sulted in a 50% decrease (P=0.02) in the ratio of quiescent (Q=G(0)) t o proliferative (P=S + M) population in part due to increase in aberra ntly proliferative cells. The BP-initiated cells also exhibited an 87. 8% inhibition (P=0.0001) in confluency-associated apoptosis and a conc omitant decrease in cellular immunoreactivity to wild-type p53. Simult aneous treatment of cultures with BP + I3C, BP + EGCG and BP + GEN res ulted in a 1.8- to 3.4-fold increase (P<0.01) in Q/P ratio and 1.8- to 6.9-fold increase (P=0.001) in sub G(0) (apoptotic) population. The i nduction of apoptosis was accompanied by enhanced p53 immunoreactivity (P<0.01). In long-term (21 day) experiments, BP treatment induced a 1 45.3% increase (P=0.001) in anchorage-dependent colony formation. This aberrant proliferation was inhibited by 44.2% to 65.3% (P=0.01) in th e presence of the three phytochemicals. Thus, BP-induced aberrant prol iferation is inhibited by the natural phytochemicals in part due to re gulation of cell cycle progression and induction of p53 dependent apop tosis.