Abstract C126: Plant isolate dibenzyl trisulfide potently inhibits cytochrome P450 1 enzyme activity and the growth of breast cancer cells derived from African American patients

Triple-negative breast cancer (TNBC), characterized by tumors that lack expression of the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2), carries a poor prognosis. African American women develop TNBC at disproportionately higher rates than women of other ethnic groups. Dibenzyl trisulfide (DTS), found expressed in the Jamaican plant Petiveria alliacea, has been shown to inhibit the growth of several cancer types. However, little is known about whether this plant isolate displays anticancer activity in TNBC cells from African American patients or modulates cytochrome P450 1 (CYP1) enzyme activity. This work, as part of an ongoing ethnopharmacology-based bioactivity screening, was designed to fill this deficit. African American TNBC (AA-TNBC) cells HCC1806 and MDA-MB-468 were treated with varying concentrations of DTS for 48 h and cell viability was assessed using the Alamar Blue assay. DTS potently inhibited the growth of HCC1806 and MDA-MB-468 cells, producing IC50 values of 10.6 ± 1.2μM and 10.3 ± 2.0μM, respectively. Additionally, we discovered that DTS induced apoptosis in these cells. Furthermore, we investigated the ability DTS to impact the activities of the CYP1 family of enzymes, which are known to convert procarcinogens to carcinogens. The IC50 values obtained for CYPs 1A1, 1A2 and 1B1 were 1.68 ± 0.3μM, 1.9 ± 0.2μM and 1.29 ± 0.3μM, respectively. These data indicate DTS exhibits potent inhibition of the activities of these enzymes. In particular, DTS was able to bind to CYP1A2 in accordance with irreversible kinetics. In addition, DTS reduced CYP1 mRNA expression in both cell lines. Our findings provide a rationale for in vivo evaluations of DTS as a potential candidate for chemoprevention and for treating AA-TNBC patients.

Citation Format: Jonathan V. Wooten, Shaniece Wauchope, Nicole Mavingire, Petreena Campbell, JéAnn Watson, Maxine Gossell-Williams, Rupika Delgoda, Eileen Brantley. Plant isolate dibenzyl trisulfide potently inhibits cytochrome P450 1 enzyme activity and the growth of breast cancer cells derived from African American patients [abstract]. In: Proceedings of the Eleventh AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2018 Nov 2-5; New Orleans, LA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl):Abstract nr C126.

Abstract 16: 3,3'-diindolylmethane induces cytoglobin expression and synergizes with poly ADP ribose polymerase inhibitor PJ34 to inhibit triple negative breast cancer cell growth

Triple negative breast cancer (TNBC), characterized by tumors that lack expression of the estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2), carries a poor prognosis. While recently approved poly ADP ribose polymerase (PARP) inhibitor olaparib shows favorable activity in patients with TNBC harboring tumors deficient in DNA repair enzyme BRCA1, patients with TNBC possessing BRCA1-proficient tumors are largely unresponsive to olaparib. Emerging evidence suggests that small molecules that activate aryl hydrocarbon receptor (AhR) signaling have the capacity to confer anticancer actions. 3,3′-diindolylmethane (DIM), an AhR ligand, is the major metabolite of indole-3-carbinol (I3C) found in cruciferous vegetables such as broccoli. Patients often consume natural product-derived AhR ligands while undergoing chemotherapy. It is therefore crucial to enhance our understanding of nutraceutical-pharmaceutical interactions. We previously demonstrated the ability of synthetic AhR ligands to induce the expression of putative tumor suppressor cytoglobin (CYGB) and inhibit Akt signaling in breast cancer cells. Since PARP inhibitor PJ34 has been shown to synergize with Akt inhibitors we hypothesize that DIM induces CYGB expression and synergizes with PJ34 to inhibit TNBC cell growth. Using the Alamar Blue assay, we found that DIM substantially enhanced the sensitivity of TNBC BRCA1 proficient cells to PJ34, though knockdown of CYGB did not significantly influence the responsiveness of cells to DIM. Chromatin immunoprecipitation followed by next-generation sequencing data revealed that DIM promoted the binding of AhR to the CYGB promoter in breast cancer cells. Finally, DIM induced CYGB gene expression in TNBC cells as determined by quantitative PCR. Taken together, our data suggest that DIM upregulates CYGB in TNBC cells and synergizes with PJ34 to confer anticancer actions in TNBC. Our data provide a rationale for incorporating the use of natural product-derived AhR ligands as a strategy to enhance PARP inhibitor efficacy in patients with TNBC that have BRCA1-proficient tumors.

Citation Format: Jonathan V. Wooten, Nicole Mavingire, Leah Rowland, Jason Matthews, Eileen Brantley. 3,3'-diindolylmethane induces cytoglobin expression and synergizes with poly ADP ribose polymerase inhibitor PJ34 to inhibit triple negative breast cancer cell growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 16.

Putative tumor suppressor cytoglobin promotes aryl hydrocarbon receptor ligand-mediated triple negative breast cancer cell death

Nearly 40 000 women die annually from breast cancer in the United States. Clinically available targeted breast cancer therapy is largely ineffective in triple negative breast cancer (TNBC), characterized by tumors that lack expression of the estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (Her2). TNBC is associated with a poor prognosis. Previous reports show that aryl hydrocarbon receptor (AhR) partial agonist 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole (5F 203) selectively inhibits the growth of breast cancer cells, including those of the TNBC subtype. We previously demonstrated that 5F 203 induced the expression of putative tumor suppressor gene cytoglobin (CYGB) in breast cancer cells. In the current study, we determined that 5F 203 induces apoptosis and caspase-3 activation in MDA-MB-468 TNBC cells and in T47D ER+ PR + Her2 - breast cancer cells. We also show that caspases and CYGB promote 5F 203-mediated apoptosis in MDA-MB-468 cells. 5F 203 induced lysosomal membrane permeabilization (LMP) and cathepsin B release in MDA-MB-468 and T47D cells. In addition, silencing CYGB attenuated the ability of 5F 203 to induce caspase-3/-7 activation, proapoptotic gene expression, LMP, and cathepsin B release in MDA-MB-468 cells. Moreover, 5F 203 induced CYGB protein expression, proapoptotic protein expression, and caspase-3 cleavage in MDA-MB-468 cells and in MDA-MB-468 xenograft tumors grown orthotopically in athymic mice. These data provide a basis for the development of AhR ligands with the potential to restore CYGB expression as a novel strategy to treat TNBC.

AhR ligand aminoflavone suppresses α6-integrin-Src-Akt signaling to attenuate tamoxifen resistance in breast cancer cells

More than 40% of patients with luminal breast cancer treated with endocrine therapy agent tamoxifen demonstrate resistance. Emerging evidence suggests tumor initiating cells (TICs) and aberrant activation of Src and Akt signaling drive tamoxifen resistance and relapse. We previously demonstrated that aryl hydrocarbon receptor ligand aminoflavone (AF) inhibits the expression of TIC gene α6-integrin and disrupts mammospheres derived from tamoxifen-sensitive breast cancer cells. In the current study, we hypothesize that tamoxifen-resistant (TamR) cells exhibit higher levels of α6-integrin than tamoxifen-sensitive cells and that AF inhibits the growth of TamR cells by suppressing α6-integrin-Src-Akt signaling. In support of our hypothesis, TamR cells and associated mammospheres were found to exhibit elevated α6-integrin expression compared with their tamoxifen-sensitive counterparts. Furthermore, tumor sections from patients who relapsed on tamoxifen showed enhanced α6-integrin expression. Gene expression profiling from the TCGA database further revealed that basal-like breast cancer samples, known to be largely unresponsive to tamoxifen, demonstrated higher α6-integrin levels than luminal breast cancer samples. Importantly, AF reduced TamR cell viability and disrupted TamR mammospheres while concomitantly reducing α6-integrin messenger RNA and protein levels. In addition, AF and small interfering RNA against α6-integrin blocked tamoxifen-stimulated proliferation of TamR MCF-7 cells and further sensitized these cells to tamoxifen. Moreover, AF reduced Src and Akt signaling activation in TamR MCF-7 cells. Our findings suggest elevated α6-integrin expression is associated with tamoxifen resistance and AF suppresses α6-integrin-Src-Akt signaling activation to confer activity against TamR breast cancer.

Household exposures to drinking water disinfection by-products: whole blood trihalomethane levels

Exposure to drinking water disinfection by-products (DBPs), such as trihalomethanes (THMs), has been associated with bladder and colorectal cancer in humans. Exposure to DBPs has typically been determined by examining historical water treatment records and reconstructing study participants' water consumption histories. However, other exposure routes, such as dermal absorption and inhalation, may be important components of an individual's total exposure to drinking water DBPs. In this study, we examined individuals' exposure to THMs through drinking, showering, or bathing in tap water. Thirty-one adult volunteers showered with tap water for 10 min (n = 11), bathed for 10 min in a bathtub filled with tap water (n = 10), or drank 1 l of tap water during a 10 min time period (n = 10). Participants provided three 10 ml blood samples: one sample immediately before the exposure; one sample 10 min after the exposure ended; and one sample 30 min (for shower and tub exposure) or 1 h ( for ingestion) after the exposure ended. A sample of the water (from the tap, from the bath, or from the shower) was collected for each participant. We analyzed water samples and whole blood for THMs (bromoform, bromodichloromethane, dibromochloromethane, and chloroform) using a purge-and-trap/gas chromatography/mass spectrometry method with detection limits in the parts-per-quadrillion range. The highest levels of THMs were found in the blood samples from people who took 10 min showers, whereas the lowest levels were found in the blood samples from people who drank 1 l of water in 10 min. The results from this study indicate that household activities such as bathing and showering are important routes for human exposure to THMs.

The use of solid-phase microextraction in conjunction with a benchtop quadrupole mass spectrometer for the analysis of volatile organic compounds in human blood at the low parts-per-trillion level

The analysis of volatile organic compounds (VOCs) in whole human blood at the low parts-per-trillion level has until recently required the use of a high-resolution mass spectrometer to obtain the specificity and detection limits required for epidemiological studies of VOC exposure in the general public. Because of the expense and expertise required to operate and maintain a high-resolution instrument, the applicability of this method has been limited. These limitations are overcome in a new method using automated headspace solid-phase microextraction (SPME) in conjunction with a gas chromatograph and a benchtop quadrupole mass spectrometer. A combination of SPME and multiple single-ion monitoring minimizes the interferences and chemical noise associated with whole blood samples. This method permits the analysis of 10 VOCs in human blood while simplifying the sample preparation and reducing the possible exposure of the analyst to blood aerosols. Twelve samples can be run successively in a fully automated mode, thus eliminating the need for operator attention. Detection limits are below 50 ppt (pg/mL) for a majority of the VOCs tested with a 5-mL sample.

Measurement of volatile organic compounds in human blood

Volatile organic compounds (VOCs) are an important public health problem throughout the developed world. Many important questions remain to be addressed in assessing exposure to these compounds. Because they are ubiquitous and highly volatile, special techniques must be applied in the analytical determination of VOCs. The analytical methodology chosen to measure toxicants in biological materials must be well validated and carefully carried out; poor quality assurance can lead to invalid results that can have a direct bearing on treating exposed persons. The pharmacokinetics of VOCs show that most of the internal dose of these compounds is quickly eliminated, but there is a fraction that is only slowly removed, and these compounds may bioaccumulate. VOCs are found in the general population at the high parts-per-trillion range, but some people with much higher levels have apparently been exposed to VOC sources away from the workplace. Smoking is the most significant confounder to internal dose levels of VOCs and must be considered when evaluating suspected cases of exposure.

Measurement of methyl tert-butyl ether and tert-butyl alcohol in human blood by purge-and-trap gas chromatography-mass spectrometry using an isotope-dilution method

We developed an isotope-dilution method for measuring methyl tert-butyl ether (MTBE) and tert-butyl alcohol (TBA) in whole human blood using a purge-and-trap gas chromatographic-mass spectrometric method. The labeled analogues for MTBE and TBA were [2H12]methyl tert-butyl ether and [2H9]-tert-butyl alcohol, respectively. Volatiles were removed from the blood by direct helium purging of the liquid; were trapped on a Tenax trap; and were desorbed, cryofocused, and chromatographed on a DB-624 capillary column that was connected directly to the ion source of a mass spectrometer. Detection was by mass analysis using a double-focusing magnetic-sector mass spectrometer operating in the full-scan mode at the medium mass resolution of 3000. For the isotope-dilution method, the minimum detection limits in blood (5-10 mL) are 0.01 microgram/L for MTBE and 0.06 microgram/L for TBA. The isotope-dilution method proved to be a big improvement in recovery, reproducibility, and sensitivity over our previous analytical method, which used the labeled ketone, [4-2H3]-2-butanone, as the internal standard for both MTBE and TBA. The isotope-dilution method has sufficient sensitivity for monitoring blood levels of MTBE and TBA in populations exposed to oxygenated fuels containing MTBE.

Blood concentrations of volatile organic compounds in a nonoccupationally exposed US population and in groups with suspected exposure

Exposure to certain volatile organic compounds (VOCs) commonly occurs in industrialized countries. We developed a method for measuring 32 VOCs in 10 mL of whole blood at low concentration. We used this method to determine the internal dose of these compounds in 600 or more people in the US who participated in the Third National Health and Nutrition Examination Survey. From our study results, we established a reference range for these VOCs in the general population of the US. We found detectable concentrations of 1,1,1-trichloroethane, 1,4-dichlorobenzene, 2-butanone, acetone, benzene, chloroform, ethylbenzene, m,p-xylene, styrene, tetrachloroethane, and toluene in most of the blood samples of nonoccupationally exposed persons. The accuracy of VOC evaluations depends on the ability of investigators to make sensitive and reproducible measurements of low concentrations of VOCs and to eliminate all sources of interference and contamination.

Blood concentrations of volatile organic compounds in a nonoccupationally exposed US population and in groups with suspected exposure

Exposure to certain volatile organic compounds (VOCs) commonly occurs in industrialized countries. We developed a method for measuring 32 VOCs in 10 mL of whole blood at low concentration. We used this method to determine the internal dose of these compounds in 600 or more people in the US who participated in the Third National Health and Nutrition Examination Survey. From our study results, we established a reference range for these VOCs in the general population of the US. We found detectable concentrations of 1,1,1-trichloroethane, 1,4-dichlorobenzene, 2-butanone, acetone, benzene, chloroform, ethylbenzene, m,p-xylene, styrene, tetrachloroethane, and toluene in most of the blood samples of nonoccupationally exposed persons. The accuracy of VOC evaluations depends on the ability of investigators to make sensitive and reproducible measurements of low concentrations of VOCs and to eliminate all sources of interference and contamination.