Mechanistic Role of Cytochrome P450 (CYP) 1 Enzymes in Polycyclic Aromatic Hydrocarbon (PAH)‐Mediated Carcinogenesis

Abstract

Lung cancer is the leading cause of cancer‐related deaths in the United States. Polycyclic aromatic hydrocarbons (PAHs) are a group of chemicals that increase the risk of lung cancer in humans. PAHs induce phase I and II metabolism enzymes through aryl hydrocarbon receptor (AhR)‐ dependent and independent pathways. Cytochrome P450 (CYPs) enzymes are among these phase I enzymes and promote detoxification of PAHs. However, CYP1A1, 1A2, and 1B1, which belong to the CYP1A1 family of enzymes, are also involved in the bioactivation of PAHs, leading to the formation of reactive intermediates that can form mutagenic DNA adducts. In this study, we hypothesized that mice lacking all the genes of the Cyp1 family will be resistant to PAH‐mediated pulmonary carcinogenesis. To test this hypothesis, A/J (WT) and Cyp1a1/1a2/1b1‐triple knockout (Cyp1‐3ko) mice were exposed to 3‐methylcholanthrene (MC; 100 μmol/kg), benzo(a)pyrene (BP; 200 μmol/kg), or corn oil (vehicle) via a single intraperitoneal injection. Liver and lung tissues were harvested at 1, 8, and 15 days post PAH exposure for our short‐term studies. Mice in our tumor study were harvested 36 weeks post PAH exposure for tumor incidence and multiplicity analysis. We found that MC caused significant induction of hepatic CYP1A1/1A2 gene expression in WT but not CYP1‐3KO mice at each time point. MC treatment caused formation of DNA adducts in liver and lung for up to 15 days post MC treatment in both genotypes. However, compared to WT animals, Cyp1‐3ko mice had significantly reduced hepatic DNA adducts on day 15 and up to 95% less pulmonary DNA adducts at 1, 8 and 15 days post MC treatment. In addition to the DNA adduct inhibition, Cyp1‐3ko mice formed 93% less pulmonary tumors compared to their MC treated WT counterparts. The significant reduction in DNA adducts and pulmonary tumors in Cyp1‐3ko mice provide strong evidence of the mechanistic role these enzymes play in PAH‐mediated carcinogenesis. Future studies on the specific role of each of the enzymes of the CYP1A family will be important for the identification of specific targets that could be used in the prevention and/or treatment of lung carcinogenesis in humans exposed to PAHs and other environmental carcinogens.Support or Funding Information1R01ES029382‐01This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.