Prostate cancer chemoprevention by green tea: in vitro and in vivo inhibition of testosterone-mediated induction of ornithine decarboxylase.

Recently, we have shown that ornithine decarboxylase (ODC), a rate-controlling enzyme in the polyamine biosynthetic pathway, is overexpressed in prostate cancer (PCA) and prostatic fluid in humans (R. R. Mohan et al., Clin. Cancer Res., 5: 143-147, 1999). ODC is also characterized as an androgen-responsive gene, and the androgenic stimulation regulates the development and growth of both normal and tumorigenic prostate cells. Thus, chemopreventive approaches aimed toward the modulation of ODC could be effective against PCA. Green tea polyphenols (GTPs) possess strong chemopreventive properties against a variety of animal tumor models and in some human epidemiological studies. At least two epidemiological studies have suggested that people who consume tea regularly may have a decreased risk of PCA. In this study, we investigated the effect of GTPs against testosterone-mediated induction of ODC in human prostate carcinoma cells, LNCaP as an in vitro model, and in Cpb:WU rats and C57BL/6 mice as in vivo models. Treatment of LNCaP cells with testosterone resulted in induction of ODC activity in a dose-dependent manner. Pretreatment of the cells with GTPs resulted in a significant inhibition of testosterone-caused induction of ODC activity in a dose-dependent manner. Similar effects of GTPs were observed in anchorage-independent growth assay of LNCaP cells where pretreatment of the cells with GTP was found to result in dose-dependent inhibition of colony formation. Testosterone treatment of the cells resulted in a significant increase in the level of ODC mRNA, and this increase was almost completely abolished by prior treatment of the cells with GTPs. The administration of testosterone (10 mg/kg body weight, i.p.) to sham-operated and castrated Cpb:WU rats resulted in 2- and 38-fold increases in ODC activity, respectively, in the ventral prostate. Oral feeding of 0.2% GTPs in drinking water for 7 days before testosterone administration resulted in 20 and 54% decreases in testosterone-caused induction of ODC activity in sham-operated and castrated rats, respectively. Similar results were obtained with C57BL/6 mice, where testosterone treatment at similar dosage resulted in a 2-fold increase in ODC activity in the ventral prostate and prior oral feeding with 0.2% GTPs resulted in 40% inhibition in this induction.

A flavonoid antioxidant, silymarin, affords exceptionally high protection against tumor promotion in the SENCAR mouse skin tumorigenesis model.

In cancer chemoprevention studies, the identification of better antitumor-promoting agents is highly desired because they may have a wider applicability against the development of clinical cancers. Both epidemiological and animal studies have suggested that microchemicals present in the diet and several herbs and plants with diversified pharmacological properties are useful agents for the prevention of a wide variety of human cancers. Silymarin, a flavonoid isolated from milk thistle, is used clinically in Europe and Asia as an antihepatotoxic agent, largely due to its strong antioxidant activity. Because most antioxidants afford protection against tumor promotion, in this study, we assessed the protective effect of silymarin on tumor promotion in the SENCAR mouse skin tumorigenesis model. Application of silymarin prior to each 12-O-tetradecanoylphorbol 13-acetate (TPA) application resulted in a highly significant protection against tumor promotion in 7,12-dimethylbenz(a)anthracene-initiated mouse skin. The protective effect of silymarin was evident in terms of reduction in tumor incidence (25, 40, and 75% protection, P < 0.001, X2 test), tumor multiplicity (76, 84, and 97% protection, P < 0.001, Wilcoxon rank sum test), and tumor volume (76, 94, and 96% protection, P < 0.001, Student's t test) at the doses of 3, 6, and 12 mg per application, respectively. To dissect out the stage specificity of silymarin against tumor promotion, we next assessed its effect against both stage I and stage II of tumor promotion. Application of silymarin prior to that of TPA in stage I or mezerein in stage II tumor promotion in dimethylbenz(a)anthracene-initiated SENCAR mouse skin resulted in an exceptionally high protective effect during stage I tumor promotion, showing 74% protection against tumor incidence (P < 0.001, X2 test), 92% protection against tumor multiplicity (P < 0.001, Wilcoxon rank sum test), and 96% protection against tumor volume (P < 0.001, Student's t test). With regard to stage II tumor promotion, silymarin showed 26, 63, and 54% protection in tumor incidence, multiplicity, and volume, respectively. Similar effect of silymarin to that in anti-stage I studies, were also observed when applied during both stage I and stage II protocols. In other studies, silymarin significantly inhibited: (a) TPA-induced skin edema, epidermal hyperplasia, and proliferating cell nuclear antigen-positive cells; (b) DNA synthesis; and (c) epidermal lipid peroxidation, the early markers of TPA-caused changes that are associated with tumor promotion. Taken together, these results suggest that silymarin possesses exceptionally high protective effects against tumor promotion, primarily targeted against stage I tumors, and that the mechanism of such effects may involve inhibition of promoter-induced edema, hyperplasia, proliferation index, and oxidant state.

Protection against induction of mouse skin papillomas with low and high risk of conversion to malignancy by green tea polyphenols.

We earlier showed that a polyphenolic fraction isolated from green tea (GTP) affords protection against tumor promotion and tumor progression in SENCAR mouse skin. The present study was designed to further evaluate the protective effect of GTP against the induction and subsequent progression of papillomas to squamous cell carcinomas (SCCs) in experimental protocols where papillomas were developed with a low or high probability of their malignant conversion. Topical application of GTP (6 mg/animal) 30 min prior to that of 12-O-tetradecanoylphorbol-13-acetate (TPA) either once a week for 5 weeks (high risk TPA protocol) or once a week for 20 weeks (low risk TPA protocol) or mezerein (MEZ) twice a week for 20 weeks (high risk MEZ protocol) in 7,12-dimethylbenz[a]anthracene (DMBA)-initiated mouse skin resulted in significant protection against skin tumor promotion in terms of tumor incidence (32-60%), multiplicity (49-63%) and tumor volume/mouse (73-90%) at the termination of the experiment at 20 weeks. In three separate malignant progression experiments when papilloma yield in DMBA-initiated and TPA or MEZ promoted low and high risk protocols was stabilized at 20 weeks, animals were divided into two subgroups. These animals were either topically treated twice weekly with acetone (0.2 ml/animal, spontaneous malignant conversion group) or with GTP (6 mg/animal in 0.2 ml acetone) for an additional period of 31 weeks. During these treatment regimens, all suspected carcinomas were recorded and each one was verified histopathologically either at the time when tumor-bearing mouse died/moribund or at the termination of the experiment at 51 weeks. GTP resulted in significant protection against the malignant conversion of papillomas to SCC in all the protocols employed. At the termination of the experiment at 51 weeks, these protective effects were evident in terms of mice with carcinomas (35-41%), carcinomas per mouse (47-55%) and percent malignant conversion of papillomas to carcinomas (47-58%). The kinetics of malignant conversion suggest that a subset of papillomas formed in the early phase of tumor promotion in all the protocols had a higher probability of malignant conversion into SCCs because all the positive control groups (acetone treated) produced nearly the same number of carcinomas (33-38 in a group of 20 animals) at the end of the progression period. In the GTP-treated group of animals the number of carcinomas formed was less (14-20 in a group of 20 animals), which shows the ability of GTP to protect against the malignant conversion of papillomas of higher probability of malignant conversion to SCCs. The results of this study suggest that irrespective of the risk involved, GTP may be highly useful in affording protection against skin cancer risk.

Novel anti-carcinogenic activity of an organosulfide from garlic: inhibition of H-RAS oncogene transformed tumor growth in vivo by diallyl disulfide is associated with inhibition of p21H-ras processing.

In this study, we report a novel anticarcinogenic activity of an organosulfur compound from garlic, diallyl disulfide (DADS). DADS treatment significantly inhibited the growth of H-ras oncogene transformed tumors in nude mice. As compared to controls, the appearance of tumors was also delayed markedly by oral administration of DADS. The inhibition of tumor growth by DADS treatment correlated with the inhibition of p21H-ras membrane association in the tumor tissue. The levels of membrane associated p21H-ras were markedly lower in the tumor tissues of DADS treated mice as compared to controls. An opposite trend, however, was evident for cytosolic p21H-ras. Furthermore, DADS treatment resulted in a significant inhibition of hepatic as well as tumoral 3-hydroxy-3-methylglutaryl coenzyme A reductase activity. These results indicate that DADS suppresses the growth of H-ras oncogene transformed tumors in nude mice by inhibiting the membrane association of tumoral p21H-ras.