Differential effects of fluoranthene and benzo[a]pyrene in MCF-7 cells

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental contaminants, which are suspected carcinogens and may affect the reproductive system as potential endocrine disruptors. Therefore, we tested fluoranthene (FL) and benzo[a]pyrene (BaP) on human breast cancer cell line (MCF-7 cells) to determine possible toxic effects. The cells were incubated in the presence of medium, medium containing 0.1% dimethylsulfoxide (DMSO) as vehicle, or in the presence of FL (10, 50, and 100 microg/ml), BaP (10, 50, and 100 microg/ml), 17beta-estradiol (E2; 5 microg/ml and 500 ng/ml), or tamoxifen (Tx; 5 microg/ml and 500 ng/ml). After 24 h, FL (100 microg/ml), BaP (100 microg/ml), or Tx (5 microg/ml) killed significant numbers of cells. After 72 h, FL (50 and 100 microg/ml), BaP (100 microg/ml), E2 (5 microg/ml), or Tx (5 microg/ml and 500 ng/ml) decreased MCF-7 cell viability significantly as demonstrated by the MTT assay. Measurement of DNA synthesis was conducted using 3H-thymidine incorporation into MCF-7 cell DNA for 72 h. After 72 h, BaP (10, 50, and 100 microg/ml) and Tx (5 microg/ml and 500 ng/ml) significantly decreased DNA synthesis in MCF-7 cells. FL did not significantly alter 3H-thymidine incorporation into the cells. While higher concentration of E2 (5 microg/ml) decreased 3H-thymidine incorporation, the lower concentration of E2 (500 ng/ml) increased cell proliferation. Apoptotic response was tested by in situ fluorescence staining of cells incubated for 72 h in media containing 0.1% DMSO, or vehicle containing FL (10 microg/ml), BaP (10 microg/ml), E2 (500 ng/ml), or Tx (500 ng/ml). Microscopic examination demonstrated presence of apoptosis with BaP (10 microg/ml) and Tx (500 ng/ml), but not with FL (10 microg/ml) and E2 (500 ng/ml). The cell cycle analysis using flow cytometry demonstrated that E2 (500 ng/ml) did not significantly change the progression of MCF-7 cells after 72 h of incubation. However, FL (10 microg/ml) only suppressed G2/M phase. Tx (500 ng/ml) blocked G0/G1, S, and G2/M phases, and BaP (10 microg/ml) suppressed the G0/G1 phase. These data suggest that BaP on MCF-7 cells is growth inhibitory and apoptotic, whereas the toxic effects of FL are not exerted through apoptosis.