Naturally Occurring Coumarins Inhibit Human Cytochromes P450 and Block Benzo[a]pyrene and 7,12-Dimethylbenz[a]anthracene DNA Adduct Formation in MCF-7 Cells

Abstract

Naturally occurring coumarins (NOCs) inhibit polycyclic aromatic hydrocarbon-induced skin tumor initiation in mice by blocking cytochrome P450 (P450)-mediated bioactivation of benzo[a]pyrene (B[a]P) and 7,12-dimethylbenz[a]anthracene (DMBA). Bergamottin selectively inhibits tumor initiation by B[a]P, whereas imperatorin and isopimpinellin inhibit tumor initiation with both carcinogens. The goals of the current study were to examine the ability of NOCs to inhibit human P450s in vitro and to establish whether NOCs, which are anticarcinogenic in mice, can block carcinogen bioactivation in cultured human cells. For the initial experiments, incubations containing 5 microM P450, P450 substrate, an NADPH generating system, and NOCs were used to determine the concentrations of each inhibitor that blocked 50% of P450 activity (IC(50)). These results confirmed that NOCs are capable of inhibiting multiple human P450s and that they exhibit selectivity for certain isoforms of human P450s. In subsequent experiments, we examined the effects of bergamottin, imperatorin, and isopimpinellin on DMBA and B[a]P DNA adduct formation in the human breast MCF-7 adenocarcinoma cell line. Coincubation of cells with the three different NOCs significantly inhibited DMBA DNA adduct formation by 29-82% at doses ranging from 2 to 10 microM and significantly inhibited B[a]P DNA adduct formation by 37-80% at doses ranging from 20 to 80 microM. HPLC analysis of the DNA hydrolysates demonstrated that inhibition of DNA adducts corresponded to inhibition of the major B[a]P and DMBA diol-epoxide-derived adducts. Although bergamottin was not effective at blocking DMBA bioactivation in the mouse skin model, it was similar in effectiveness to imperatorin and isopimpinellin in MCF-7 cells. These results demonstrate that NOCs, which are present in citrus fruits and other components of the human diet, are capable of inhibiting carcinogen metabolizing enzymes and blocking bioactivation of both B[a]P and DMBA in MCF-7 cells.

Chemistry and Biological Activity of Natural and Synthetic Prenyloxycoumarins †

“…When applied topically to mouse epidermis BG decreased covalent binding to DNA of benzo [a]pyrene (B [a]P). The effect was dosedependent (a 72% decrease at a concentration of 400 nM) [105,109] and remarkably selective, as it did not occur with 7,12-dimethylbenz [a]anthracene (DMBA). This selectivity might be explained by the finding that BG preferentially inhibited P450 1A1, the enzyme that converts B [a]P to the corresponding 7,8 dihydrodiol, rather than other isoform of CYP that act on DMBA [108].…”

“…BG also prevented B [a]P bioactivation by CYP. At a concentration of 800 nM, BG inhibited skin tumor initiation in vivo [105,109]. Taking into account the effects on CYP exerted by BG, isoimperatorin and isopimpinellin, Di Giovanni and coworkers sketched the following mechanism of cancer prevention by these furanocoumarins (Scheme 4).…”

“…109]. They found that in SENCAR mice orally administered or topically applied imperatorin significantly inhibited cytochrome-mediated B [a]P-DNA adduct formation.…”

Bergamottin, a natural furanocoumarin abundantly present in grapefruit juice, suppresses the invasiveness of human glioma cells via inactivation of Rac1 signaling

“…Bergamottin, a natural furanocoumarin abundantly present in grapefruit juice, has been demonstrated to exhibit anticancer effects in a variety of human cancers, including chronic myelogenous leukemia (11), multiple myeloma (12), skin cancer (13) and breast cancer (14). It has been reported that bergamottin enhances tumor necrosis factor-induced apoptosis in human chronic myelogenous leukemia via inactivation of nuclear factor-κB signaling (11).…”

A Ligand-Based Drug Design. Discovery of 4-Trifluoromethyl-7,8-pyranocoumarin as a Selective Inhibitor of Human Cytochrome P450 1A2

“…1,2 Therefore, selective inhibition of P450 1A2 is a potential molecular target for chemoprevention of environmental arylamine-caused DNA mutations and carcino-genesis. 3 Certain compounds with varying molecular structures have been shown to effectively inhibit P450 1A2, including aryl hydrocarbons, stilbenoids, flavonoids, coumarins, and anthra-quinone, etc. 4–10 However, because of the high degree of similarity between P450 1A2 and P450s 1A1 and 1B1 (sharing 80% and 40% amino acid sequence identity, respectively), most P450 1A2 inhibitors also show some extent of inhibitory activity toward P450s 1A1 and 1B1.…”