Shutsung Liao

Growth inhibition and regression of human prostate and breast tumors in athymic mice by tea epigallocatechin gallate

The human prostate cancer cell lines, PC-3 (androgen-insensitive) and LNCaP 104-R (androgen-repressed) were inoculated subcutaneously into nude mice to produce prostate tumors. Intraperitoneal injection of green tea (-)epigallocatechin-3-gallate but not structurally related catechins, such as (-)epicatechin-3-gallate, inhibited the growth and rapidly reduced the size of human prostate tumors in nude mice. (-)Epigallocatechin-3-gallate also rapidly inhibited the growth of tumor growth formed by the human mammary cancer cell line MCF-7 in nude mice. It is possible that there is a relationship between the high consumption of green tea and the low incidence of prostate and breast cancers in some Asian countries.

Structure-activity relationships for inhibition of human 5α-reductases by polyphenols

Abstract The enzyme steroid 5α-reductase (EC 1.3.99.5) catalyzes the NADPH-dependent reduction of the double bond of a variety of 3-oxo-Δ4 steroids including the conversion of testosterone to 5α-dihydrotestosterone. In humans, 5α-reductase activity is critical for certain aspects of male sexual differentiation, and may be involved in the development of benign prostatic hyperplasia, alopecia, hirsutism, and prostate cancer. Certain natural products contain components that are inhibitors of 5α-reductase, such as the green tea catechin (−)-epigallocatechin gallate (EGCG). EGCG shows potent inhibition in cell-free but not in whole-cell assays of 5α-reductase. Replacement of the gallate ester in EGCG with long-chain fatty acids produced potent 5α-reductase inhibitors that were active in both cell-free and whole-cell assay systems. Other flavonoids that were potent inhibitors of the type 1 5α-reductase include myricetin, quercitin, baicalein, and fisetin. Biochanin A, daidzein, genistein, and kaempferol were much better inhibitors of the type 2 than the type 1 isozyme. Several other natural and synthetic polyphenolic compounds were more effective inhibitors of the type 1 than the type 2 isozyme, including alizarin, anthrarobin, gossypol, nordihydroguaiaretic acid, caffeic acid phenethyl ester, and octyl and dodecyl gallates. The presence of a catechol group was characteristic of almost all inhibitors that showed selectivity for the type 1 isozyme of 5α-reductase. Since some of these compounds are consumed as part of the normal diet or in supplements, they have the potential to inhibit 5α-reductase activity, which may be useful for the prevention or treatment of androgen-dependent disorders. However, these compounds also may adversely affect male sexual differentiation.

Green tea: biochemical and biological basis for health benefits.

Publisher Summary Green tea beverages originated many thousands of years ago as a medicinal tonic. The historically long use of many folk remedies does not necessary prove their medical usefulness. However, recent evidence based on modern scientific evaluations of green tea appears to support the possibility that green tea compounds, especially catechins, are medically valuable. The chapter focuses on green tea and green tea catechins rather than on fermented teas or catechin by-products that are produced during fermentation. Theaflavins and thearubigins, a complex mixture of catechin condensation products with a heterogeneous molecular weight distribution, are major fermentation products in black tea, which, like catechins, have antioxidant and antitumorigenic activities. Experimental studies on the physiological effects of some polyphenolic tannins from other plants indicate that they also may be beneficial for decreasing serum lipids, reducing blood pressure, and modulating immune responses and for use as antitumorigenic and antibacterial agents and use in food preservation. The chapter discusses that tea polyphenols are widely used as natural antioxidants for prevention of oxidation of edible oils or discoloring of foods.

Antiproliferative Effect of Liver X Receptor Agonists on LNCaP Human Prostate Cancer Cells

Liver X receptors function as central transcriptional regulators for lipid homeostasis, for which agonists have been developed as potential drugs for treatment of cardiovascular diseases and metabolic syndromes. Because dysregulation of lipid metabolism has been implicated in sex hormone-dependent cancers, we investigated the effect of liver X receptor agonists on prostate and breast cancer cell proliferation. Treatment of human prostate cancer LNCaP cell lines with the synthetic liver X receptor agonist T0901317 decreased the percentage of S-phase cells in a dose-dependent manner and increased the expression of cyclin-dependent kinase inhibitor p27Kip-1 (p27). Knockdown of p27 by RNA interference blocks T0901317-induced growth inhibition, suggesting that p27 expression plays a crucial role in this signaling. Liver X receptor agonists also inhibited the proliferation of other prostate and breast cancer cell lines. The level of liver X receptor α expression correlated directly with sensitivity to growth inhibition by liver X receptor agonists. Retroviral expression of liver X receptor α in human breast cancer MDA-MB435S cells, which express low levels of endogenous liver X receptors and are insensitive to T0901317, sensitized these cells to T0901317. Consistent with our observations in LNCaP cells, T0901317 induces dramatic up-regulation of p27 in liver X receptor α–overexpressing MDA-MB435S cells. Furthermore, oral administration of T0901317 inhibited the growth of LNCaP tumors in athymic nude mice. Based on these results, modulation of the liver X receptor signaling pathway is a new target for controlling tumor cell proliferation; therefore, liver X receptor agonists may have utility as antitumorigenic agents.

Inhibition of Tumor Growth and Progression of LNCaP Prostate Cancer Cells in Athymic Mice by Androgen and Liver X Receptor Agonist

Androgen-dependent human LNCaP 104-S tumor xenografts progressed to androgen-independent relapsed tumors (104-Rrel) in athymic mice after castration. The growth of 104-Rrel tumors was suppressed by testosterone. However, 104-Rrel tumors adapted to androgen and regrew as androgen-stimulated 104-Radp tumors. Androgen receptor expression in tumors and serum prostate-specific antigen increased during progression from 104-S to 104-Rrel but decreased during transition from 104-Rrel to 104-Radp. Expression of genes related to liver X receptor (LXR) signaling changed during progression. LXRalpha, LXRbeta, ATP-binding cassette transporter A1 (ABCA1), and sterol 27-hydroxylase decreased during progression from 104-S to 104-Rrel. These coordinated changes in LXR signaling in mice during progression are consistent with our previous findings that reduction of ABCA1 gene expression stimulates proliferation of LNCaP cells. To test if attenuation of LXR signaling may enhance prostate cancer progression from an androgen-dependent state to an androgen-independent state, castrated mice carrying 104-S tumors were given the synthetic LXR agonist T0901317 by gavage. T0901317 delayed progression from 104-S to 104-Rrel tumors. Based on our in vivo model, androgen is beneficial for the treatment of androgen-independent androgen receptor-rich prostate cancer and modulation of LXR signaling may be a potentially useful therapy for prostate cancer.

Molecular Action of Androgen in the Normal and Neoplastic Prostate

Publisher Summary This chapter discusses the molecular action of androgen in the normal and neoplastic prostate. Androgens are steroid hormones that are required for normal male sexual development and maintenance of the male phenotype. Testosterone is the most abundant circulating androgen in males and secreted principally by the Leydig cells of the testis. The adrenal glands produce a small amount of circulating testosterone either directly or by peripheral conversion of secreted androstenedione or dehydroepiandrosterone. The ovary produces a small amount of testosterone in females. 5α-dihydrotestosterone (5α-DHT) is also produced by the testis, but most of the circulating 5α-DHT is derived from the metabolic conversion of testosterone in target tissues and organs. Antiandrogens can be very effective at inhibiting androgen binding and the activation of the androgen receptor (AR), but they can cause undesirable side effects. Inhibitors of 5α-reductase may have advantages over antiandrogens, because they can selectively suppress 5α-DHT-dependent disorders such as prostate cancer, benign prostatic hypertrophy (BPH), acne, baldness. It is found that amino-terminal truncations in rat AR resulted in loss of activity when the steroid-binding domain was present, but the loss was much less severe when the steroid-binding domain was absent also. The presence of the amino-terminal domain also appears to inhibit the rate of steroid dissociation from the receptor and thereby stabilizes the receptor against degradation.

Selective activation of liver X receptor alpha by 6α-hydroxy bile acids and analogs

We have found that certain natural 6alpha-hydroxylated bile acids are receptor-specific activators of nuclear liver X receptor alpha (LXRalpha) (NR1H3), a nuclear receptor regulating the expression of the cholesterol 7alpha-hydroxylase gene, coding for the rate-limiting enzyme in the major pathway of bile acid synthesis. The LXR homolog, ubiquitous nuclear receptor (UR/LXRbeta) (NR1H2), was also activated by these bile acids, but at higher concentrations than for LXRalpha. Synthetic 6alpha-hydroxylated bile acid analogs were synthesized with LXRalpha-selective agonistic activity, with potential to modulate cholesterol catabolism in hypercholesterolemia.

Auto-oxidized cholesterol sulfates are antagonistic ligands of liver X receptors: implications for the development and treatment of atherosclerosis

Liver X receptors (LXRs) are members of the nuclear receptor superfamily that are involved in regulation of cholesterol transport and metabolism. Expression of cholesterol 7alpha-hydroxylase, cholesteryl ester transfer protein and certain ATP-binding cassette transporters that are responsible for cholesterol efflux from cells is regulated by LXR and its ligands. In this report we show that 5alpha, 6alpha-epoxycholesterol-3-sulfate (ECHS) and 7-ketocholesterol-3-sulfate inhibit transactivation of a reporter gene by LXR. Non-sulfated forms of these compounds, as well as many other steroid sulfates, had no antagonistic activity. Using chimeric receptors, the antagonistic activity of ECHS was dependent on its interaction with the ligand-binding domain of LXR. ECHS disrupts recruitment of the co-activator Grip 1 into a complex with agonist-bound LXR and this may be responsible for the observed antagonistic properties of these compounds. In various cultured cells, these LXR antagonists also promote de novo cholesterol synthesis and apoptosis. 7-Ketocholesterol and 5alpha, 6alpha-epoxycholesterol are present in blood and have been found in atherosclerotic plaques. If sulfated forms of these oxidized sterols are also present, they may have an important role in foam cell formation by inhibiting LXR function. Since LXR agonists can counteract the activity of these antagonists, they may have therapeutic potential against atherosclerosis.

Androgen Causes Growth Suppression and Reversion of Androgen-Independent Prostate Cancer Xenografts to an Androgen-Stimulated Phenotype in Athymic Mice

Most prostate cancer patients develop androgen-independent recurrent prostate tumors a few years after androgen ablation therapy. No therapy, however, has been shown to substantially extend survival in these patients. Previously, we reported that androgen suppresses the growth of androgen-independent LNCaP prostate tumor cells both in vitro and in vivo. In cell culture, androgen receptor (AR)-rich androgen-independent LNCaP 104-R1 cells adapt to growth suppression by androgen and then their growth is androgen stimulated. Because maintaining androgen dependency of prostate tumor cells should prolong the usefulness of androgen ablation therapy, we determined if androgen-independent prostate tumors would revert to an androgen-stimulated phenotype in vivo upon androgen treatment. Growth of the LNCaP 104-R1 tumors was suppressed by androgen, but tumors then adapted to suppression by androgen and growth became androgen stimulated. Tumor AR and prostate-specific antigen mRNA and protein were initially high in 104-R1 tumors but decreased during adaptation. Subsequent removal of androgen decreased the serum prostate-specific antigen level further and stopped the growth of the adapted tumors. Because androgen caused growth suppression and then reversion of androgen-independent tumors to an androgen-stimulated phenotype and because the growth of androgen-stimulated tumors could be restrained by androgen ablation, these results suggest a novel therapy for AR-positive androgen-independent prostate cancer.

A transcriptional activation function of p53 is dispensable for and inhibitory of its apoptotic function

The tumor suppressor p53 is an inducer of cell cycle arrest and programmed cell death (apoptosis). The ability of p53 to induce cell cycle arrest is linked to its ability to induce transcription of genes such as the cyclin-dependent kinase inhibitor p21. However, the dependence of p53-mediated apoptosis on transcriptional activation remains controversial. Ectopic expression of a temperature-sensitive (ts) p53 allele induced expression of p53 target genes and elicited both G1 and G2/M cell cycle arrest upon shift to the permissive temperature. Ectopic expression of the same ts p53 allele with two additional point mutations (Gln22, Ser23) that abolish p53-transcriptional activation did not induce p53 target genes and G1 nor G2/M cell cycle arrest. In HCT116 colon carcinoma cells ectopic expression of wild type p53 does not elicit apoptosis whereas p53 mutant deficient in trans-activation induces apoptosis. The ability of wild type p53 to induce apoptosis is restored in HCT116 cells that are null for p21. However, the trans-activation deficient mutant of p53 is still more potent mediator of apoptosis than wild type p53 in the p21 null cells. Although the ability of Gln22,Ser23 to trans-activate p53 target genes is diminished, it retains the ability to repress Bcl-2 expression. Thus, we conclude that while ectopic expression of wild type p53 can induce both G1 and G2/M arrest, in a p21 dependent manner, without apoptosis, a p53 mutant defective in trans-activation elicits apoptosis without inducing cell cycle arrest. Further, the anti-apoptotic function of p53 is dependent on trans-activation and is linked to cell cycle arrest. The results strongly suggest that the trans-activation deficient mutant is a more potent inducer of apoptosis because it lost its anti-apoptotic function and retains its ability to repress pro-apoptotic genes such as Bcl-2. Taken together, the results imply that employing a trans-activation deficient p53 in gene therapy approaches or the use of drugs that convert mutant p53 to a trans-activation-independent mediator of apoptosis may be much more efficient therapeutic approaches than current approaches that employ wild type p53.