Abstract 807: Hydrogen sulfide-releasing aspirin modulates xenobiotic metabolizing enzymes in vitro and in vivo

Abstract

Abstract Introduction: Xenobiotic metabolizing enzymes are classified as phase-I (oxidation/reduction) and phase-II (conjugation) enzymes; the balance between the phase-I carcinogen-activating enzymes and the phase-II detoxifying enzymes may be important in determining an individual's risk for cancer. Hydrogen sulfide-releasing aspirin (HS-ASA) is a new compound with significant anti-inflammatory properties. It consists of ASA covalently attached to 5-(4-hydroxyphenyl)-3H-1,2-dithiole-3-thione, which releases hydrogen sulfide. Our initial studies indicate that HS-ASA has chemopreventive properties. In the present study, we evaluated the effect of HS-ASA on xenobiotic metabolizing enzymes both in vitro and vivo. Methods: HS-ASA was synthesized and purified by us with 1H-NMR verification. Cell lines: HT-29 human colon adenocarcinoma and Hepa 1c1c7 mouse liver adenocarcinoma. Cell growth inhibition: MTT. Levels of cytochrome P450 1A1 (CYP 1A1) a phase-1 enzyme and NAD(P)H:quinone oxireductase (NQO), glutathione S-transferase (GST) and UDP-glucuronyltransferase (UGT), phase-II enzymes by immunoblots. Enzyme activity: GST and thioredoxin reductase (Trx). In vivo: Male Wistar rats (N = 4/group) were treated via gavage either with vehicle or with HS-ASA 100 mg/kg/day. Weight of animals in each group was recorded every 3 days. After 21 days, animals were killed and liver microsomes and cytosols were prepared for phase-I and phase-II enzyme evaluation. Results: HS-ASA inhibited the growth of HT-29 and Hepa 1c1c7 cells, with an IC50 of 2.5 ± 0.3 µM and 2.9 ± 0.4 µM, respectively. The IC50 for ASA in both cell lines was >5,000 µM at 24h. The ratio ASA/HS-ASA is >2000 in the HT-29 cells and >1700 in Hepa 1c1c7 cells, suggesting that HS-ASA is at least 1700-2000-fold more potent than traditional ASA. In HT-29 cells, at 0.5xIC50, 1xIC50, and 2xIC50, HS-ASA increased GST activity by 2.5-, 7.2-, and 11-fold; and it inhibited Txr by 36 ± 3%, 67 ± 2% and 79 ± 2% respectively. In HT-29 cells, levels of CYP 1A1 were not significantly affected whereas levels of GST and UGT were increased dose-dependently by HS-ASA. In Hepa 1c1c7 cells, levels of NQO were also significantly increased. In vivo, HS-ASA: 1. had no effect on rat's weight; 2. increased hepatic GST activity by 3.4-fold and NQO by 1.4-fold; 3. immunoblots showed significant increases in GST and NQO protein levels but no changes in CYP 1A1 protein levels. Conclusions: HS-ASA co-induces multiple phase-II metabolizing enzymes and thus may be regarded as a monofunctional inducer. This represents one mechanism by which HS-ASA exhibits chemopreventive properties. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 807. doi:10.1158/1538-7445.AM2011-807