Inhibitory effects of lemon grass (Cymbopogon citratus Stapf) on formation of azoxymethane-induced DNA adducts and aberrant crypt foci in the rat colon

The 80%-ethanol extract of lemon grass (Cymbopogon citratus Stapf), a medicinal plant in Thailand, has been reported to be antimutagenic against various known mutagens in the Salmonella mutation assay. To investigate chemoprevention in an animal carcinogenesis model, we examined inhibitory effects of the lemon grass extract on the formation of azoxymethane (AOM)-induced DNA adducts and aberrant crypt foci (ACF) in the rat colon. One week after the start of the treatment with lemon grass extract at doses of 0.5 or 5 g/kg body wt by gavage, F344 rats received two s.c. injections of 15 mg of AOM per kg body weight at 1 week apart. For DNA adduct analysis of the colon and liver, the rats were killed 12 h after the second AOM injection. The DNA from the liver and colon were used for O6-methylguanine and N7-methylguanine analysis. For ACF analysis in the initiation stage, AOM-injected rats were continuously treated with lemon grass extract and were killed 3 weeks after the second AOM injection. For analysis in the promotion stage the treatment with the lemon grass extract (0.5 g/kg) started 2 weeks after the second AOM injection and continued for 12 weeks until the animals were killed. Lemon grass treatment significantly inhibited DNA adduct formation in both the colonic mucosa and the muscular layer but not in the liver. In addition, lemon grass extract treatment significantly inhibited ACF formation in both the initiation stage and the promotion stage. Especially in the promotion stage, lemon grass treatment inhibited the formation of larger ACF (with four or more crypts per focus), which was predictive of tumor incidence. Furthermore, lemon grass extract inhibited fecal beta-glucuronidase competitively and had antioxidant activity. These results suggest that the lemon grass extract inhibits the release of activated aglycon, methylazoxymethanol, from a glucuronide conjugate in the colon, and decreases the DNA adducts and ACF formation in the rat colon.      

MDM2 RNA binding is blocked by novel monoclonal antibody h-MDM2-F4-14

Amplification of MDM2 has been described in a variety of human cancers. Prognostic studies have revealed that abnormal MDM2 expression correlates with poor prognosis. Many of the consequences of mdm2/p53 interactions have been investigated, and mdm2-p53 dependent events characterized. In contrast, understanding of mdm2-p53 independent activities is comparatively in it's infancy amongst these the ability of mdm2 to bind RNA. However, although the significance of this activity has been the subject of some speculation, the precise role and impact of this function upon cell replication or apoptosis has yet to be fully defined. These studies have been obstructed by a lack of specific reagents able to interfere with this reaction. As a prelude to further exploring the significance of mdm2 RNA binding we report the inhibition of mdm2 RNA binding activity by newly produced MDM2 monoclonal antibodies anti-h-mdm2 F4-14 and F2-2. A variety of MDM2 specific antibodies have been produced and applied in research without complete knowledge of their reactivity profiles, but in the face of the growing number of mdm2 RNA isoforms, the results of such studies can be difficult to interpret. Each of the RNA binding inhibitory antibodies produced in this study was found to be reactive with full length MDM2 protein expressed in tumor cell lysates, transfected NIH3T3 cell lysates and via eukaryotic cell free rabbit reticulocyte in vitro translation. Antibody F4-14, the most potently inhibitory antibody, reacts strongly with the full length MDM2 together with protein isoforms A, B, C and D. In contrast, antibody F2-2 reacts only with full-length MDM2 protein. The ability of h-mdm2-F4-14 and to a lesser extent F2-2 to inhibit RNA binding presents the possibility of modulating human mdm2s ability to bind RNA, compromise this function and present opportunities to investigate in more detail the biological significance of this activity.