Prevention of mouse colon and lung tumors and modulation of mRNA expression of genes by isoliquiritigenin.

B109

Licorice, the dried roots and stolons (or rhizomes) of Glycyrrhiza glabra L. (Fabaceae; "Glycyrrhiza Radix"), and other varieties of this species are used commercially as an herbal medicine. Flavonoids comprise about 1-1.5% of licorice root, that include isoliquiritigenin (4,2N,4N-trihydroxychalcone) and its' major glycosidic form, isoliquiritin. Isoliquiritigenin is a potent antioxidant with anti-inflammatory activity that has been reported to prevent aberrant crypt foci in rats. We therefore evaluated isoliquiritigenin for the ability to prevent colon as well as lung tumors in mice. For greater efficiency and to minimize costs of preclinical studies for efficacy of chemopreventive agents, we evaluate agents for prevention of cancer in both organs using a "Combined Mouse Colon and Lung Cancer Chemoprevention Model". In addition, we also determined in the colon and lung tumors the ability of isoliquiritigenin to increase mRNA expression of down-regulated tumor suppressor genes, as a preliminary screen for the ability to modulate genes that are hypermethylated. Female Swiss-Webster mice received 10 mg/kg of 1, 2-dimethylhydrazine (DMH) twice a week for eight weeks. Seven days after the last dose of DMH, the mice were administered in their diet 50, 100 or 300 mg/kg isoliquiritigenin or 100 mg/kg piroxicam, as a positive control. The mice continued to receive the two agents until they were sacrificed 36 weeks after the first dose of DMH. Both isoliquiritigenin (300 mg/kg dose) and piroxicam prevented colon and lung tumors. The ability of isoliquiritigenin to prevent lung tumors is being confirmed in a second study. Female Swiss-Webster mice were administered 16 mg/kg vinyl carbamate once a week for two weeks to induce lung tumors. Six weeks after the last dose of carcinogen the mice started to receive 0.3, 1.0 and 3.0 gm/kg of isoliquiritigenin in their diet. The mRNA expression of the transcription factor, CCAAT enhancer binding protein alpha (C/EBPα) gene was decreased in colon tumors, but increased in lung tumors induced by DMH. The increased expression of the C/EBPα gene in lung tumors may have resulted from Type-2 epithelial cells being the origin of the lung tumors, which normally have high expression of the gene. Both piroxicam and isoliquiritigenin increased C/EBPα expression in colon tumors. The mRNA expression of the tissue inhibitor of metalloproteinase 3 (TIMP3) gene was decreased in colon and lung tumors and was increased in both organs by piroxicam and isoliquiritigenin. It is possible that the decreased expression of the two genes in tumors resulted from hypermethylation, so that isoliquiritigenin and piroxicam could have increased their expression by preventing the hypermethylation. The ability of isoliquiritigenin to prevent colon and lung tumors and to modulate mRNA expression of genes indicates that this botanical warrants further evaluation as a chemopreventive agent for both organs.