Vol. 30, Issue 3, 262-269, March 2002

Induction of CYP1A1 and CYP1B1 in T-47D Human Breast Cancer Cells by Benzo[a]pyrene Is Diminished by Arsenite

David C. Spink, Barbara H. Katz, Mirza M. Hussain, Barbara C. Spink, Susan J. Wu, Ning Liu, Ronald Pause, and Laurence S. Kaminsky

Laboratory of Human Toxicology and Molecular Epidemiology, Wadsworth Center, New York State Department of Health, Albany, New York

Polycyclic aromatic hydrocarbons (PAHs) and metals are often environmental cocontaminants, yet there have been relatively few studies of combined effects of PAHs and metals on cytochrome P450 (P450)-catalyzed metabolism. We examined the effects of NaAsO₂ in combination with benzo[a]pyrene (BAP) on CYP1A1 and CYP1B1 in T-47D human breast cancer cells by using estrogen metabolism as a probe of their activities. Exposure to BAP caused elevated rates of the 2- and 4-hydroxylation pathways of estrogen metabolism, indicating induction of both CYP1A1, an estradiol 2-hydroxylase, and CYP1B1, an estradiol 4-hydroxylase. BAP-induced metabolism peaked 9 to 16 h after exposure and returned to near-basal levels by 48 h. Concentration-response studies showed maximal induction of the 2- and 4-hydroxylation pathways at 3 µM BAP; higher levels caused reduced rates of metabolism due to inhibition of CYP1A1 and CYP1B1. NaAsO₂ caused pronounced decreases in the induction of CYP1A1 and CYP1B1 by 3 µM BAP because cotreatment with 10 µM NaAsO₂ inhibited the rates of the 2- and 4-hydroxylation pathways by 86 and 92%, respectively. Western immunoblots showed diminished levels of BAP-induced CYP1A1 by coexposure to NaAsO₂. The levels of the CYP1A1 and CYP1B1 mRNAs induced by BAP were not significantly affected by coexposure to NaAsO₂; however, heme oxygenase 1 mRNA levels were markedly induced by coexposure to BAP and NaAsO₂. These results indicate a post-transcriptional inhibitory effect of arsenite on the expression of CYP1A1 and CYP1B1 in T-47D cells, possibly resulting from reduced heme availability.