Selective inhibition of prostatic tumor 5 alpha-reductase by a 4-methyl-4-azasteroid

The effect of sodium 4-methyl-3-oxo-4-aza-5 alpha-pregnane-20(s)-carboxylate (4-MAPC) on testosterone metabolism was investigated in rat and human prostates in organ culture. The general properties of the test system for androgen metabolism and response to inhibitors were in close agreement with in vivo observations. As an inhibitor of prostatic tumor 5 alpha-reductase, 4-MAPC was equally as effective as 17 beta-N,N-diethylcarbamoyl-4-methyl-4-aza-5 alpha-androstan-3-one, reported to be a potent 5 alpha-reductase inhibitor. Inhibition of 5 alpha-reductase activity by 4-MAPC, but not by 17 beta-N,N-diethylcarbamoyl-4-methyl-4-aza-5 alpha-androstan-3-one, was accompanied by concomitant stimulation of 17 beta-oxidation of testosterone. This differential effect was observed in explants of human prostatic carcinoma and benign prostatic hypertrophy containing a relatively high degree of glandular hyperplasia. It was also seen in explants of dorsolateral rat prostate but not in the ventral prostate. 4-MAPC exhibited low affinity for rat prostatic cytosol 8S androgen receptor. Steroid extraction of purified nuclei from inhibited rat tissues revealed substantial amounts of radioactivity derived from [3H]testosterone cochromatographed with other metabolites in addition to dihydrotestosterone. The endocrine changes produced by this inhibitor of 5 alpha-reductase are reconcilable with the responsiveness of androgen-sensitive malignant prostatic cells to hormonal therapy.     

Dual effects of androgens on mammary gland

Androgens have a dual effect on mammary cells. Indeed, they have an influence on mammary cells proliferation thanks to several possible mechanisms, including their transformation into dihydrotestosterone (5alpha-reductase pathway) or into estradiol (aromatase pathway) or their binding to the androgen receptor (AR) and/or to the estrogen receptor (ER). Androgen signaling, using 5alpha-reductase pathway, enables the control of cell proliferation, mediated by AR. So androgen signaling plays a crucial role in breast homeostasis, negating the proliferative effects of estrogen signaling in the breast. When androgens transform into estrogens (aromatase pathway), they increase cell proliferation and mammary carcinogenesis risk. High levels of androgens and estrogens in the serum are associated with increased incidence of postmenopausal breast cancers. Genetic variations in metabolic genes (CYP11, CYP19) and in the AR gene are both involved in dual effects of androgens. Since mammary cells metabolic enzymes vary with time, aging increases the risk of breast cancer induced by estrogens and androgens. In addition, AR function can be perturbed by low doses of synthetic progestin, acting as endocrine disruptors to negate the protective effects of androgen signaling in the breast. In the future, the determination of AR expression in infiltrative breast cancer specimens and circulating androgens levels could provide additional information about hormonal dependency and prognosis of breast carcinomas.     

Identification and localization of human pancreatic tumor-associated antigens by monoclonal antibodies to RWP-1 and RWP-2 cells

Human pancreatic adenocarcinoma cell lines, RWP-1 and RWP-2 (Dexter, D. L., Matook, G. M., Meitner, P. A., Bogaars, H. A., Jolly, G. A., Turner, M. D., and Calabresi, P. Cancer Res., 42: 2705-2714, 1982), were used as immunogens for the production of monoclonal antibodies to tumor-associated membrane antigens. BALB/c mice were immunized by i.p. injection of viable cells and hybridomas resulting from the fusion of splenocytes to myeloma cell line P3 X 63/Ag8.653 were screened by enzyme-linked immunosorbent assay for antibodies which reacted with both RWP-1 and RWP-2 cells. Hybridomas AR2-20 and AR1-28, both IgG1 antibody-producing cell lines, demonstrated membrane staining by immunofluorescence cytochemistry on three of seven pancreatic tumor cell lines but not on six human tumor cell lines of nonpancreatic origin, or on normal human fibroblasts. The antibodies stained frozen sections of RWP xenografts, propagated s.c. in nude mice, and tumor cells in paraffin sections of seven of seven cases of pancreatic ductal adenocarcinoma, using indirect immunofluorescence and immunoperoxidase histochemistry, but not normal adult or fetal pancreas, or a number of other normal adult tissues. Immunoprecipitation of 125I-labeled RWP-2 cells resulted in a single band with a molecular weight of 190,000 under reducing conditions. Sequential immunoprecipitation demonstrated that both AR2-20 and AR1-28 bind to the same molecule.     

Retardation of prostate tumor progression in the Noble rat by 4-methyl-4-aza-steroidal inhibitors of 5 alpha-reductase

The effect of 4-methyl-4-aza-steroidal inhibitors of 5 alpha-reductase has been evaluated on tumor growth in the Noble rat model of prostatic adenocarcinoma. The growth characteristics of the tumor line 2Pr-121D(1) were consistent with heterogeneity of cell types, composed of androgen-sensitive and androgen-insensitive malignant cells. Both sodium 4-methyl-3-oxo-4-aza-5 alpha-pregnane-20 (s)-carboxylate and 17 beta-N,N-diethylcarbamoyl-4-methyl-4-aza-5 and 17 beta-N,N-diethylcarbamoyl-4-methyl-4-aza-5 alpha-androstan-3-one significantly retarded tumor progression. Each agent increased tumor volume doubling time by approximately 62%. On the basis of their similarities to female rats and male castrate group, in terms of growth rate, tumor doubling time, and histologic characteristics, the treatments with the 4-methyl-4-aza-steroids appeared to produce effects common to both castration and estrogenization (chronic administration of pharmacologic doses of estrogen). The failure of 5 alpha-reductase inhibitors to be active as antiprostatic agents in vivo has hitherto detracted from their use of therapeutic agents. Present studies demonstrate that the 4-methyl-4-aza-steroidal inhibitors of 5 alpha-reductase may represent an alternative to orchiectomy and chronic estrogen therapy for the management of the hormone-dependent phase of prostate cancer.     

Theaflavin-3,3'-digallate and penta-O-galloyl-beta-D-glucose inhibit rat liver microsomal 5alpha-reductase activity and the expression of androgen receptor in LNCaP prostate cancer cells

Androgens play a critical role in regulating the growth, differentiation and survival of epithelial cells in many androgen-responsive organs, such as prostate and skin. The enzyme steroid 5alpha-reductase (EC 1.3.99.5) catalyzes the conversion of testosterone (T) to a more active androgen, dihydrotestosterone (DHT). DHT then binds to androgen receptors (AR) and functions in the nucleus to regulate specific gene expression. Androgens via their cognate receptor may be involved in the development and progression of benign prostate hyperplasia, prostate cancer, hirsutism, male pattern alopecia and acne. The aim of this study was to determine whether theaflavin-3,3'-digallate (TF3) and penta-O-galloyl-beta-D-glucose (5GG) have inhibitory effects on androgen production and action. We found that TF3 and 5GG inhibit rat liver microsomal 5alpha-reductase activity. Furthermore, TF3 and 5GG significantly reduced androgen-responsive LNCaP prostate cancer cell growth, suppressed expression of the AR and lowered androgen-induced prostate-specific antigen secretion and fatty acid synthase protein level. In conclusion, our result suggests that TF3 and 5GG might be useful chemoprevention agents for prostate cancer through suppressing the function of androgen and its receptor.     

Amphiregulin is a potent mitogen in human pancreatic-cancer cells - correlation with patient survival

The epidermal growth factor (EGF) receptor (EGFR) is activated by EGF and other EGF-like growth factors, including amphiregulin (AR). We characterized the localization and mitogenic action of AR in T3M4 and COLO-357 human pancreatic cancer cell lines and determined whether the presence of AR in human pancreatic cancers correlates with patient survival. Both T3M4 and COLO-357 cells were found to be extremely sensitive to AR, one-half maximal stimulation occurring at a concentration of 70 and 50 pM, respectively. The magnitude of the stimulatory effect was greater with AR than with EGF. Both cell lines exhibited AR immunostaining, which was present in a variable manner in the cytoplasm, nucleus and nucleoli. Immunohistochemical analysis of 62 pancreatic cancer tissues revealed the presence of nuclear and/or cytoplasmic AR immunoreactivity in the cancer cells. Cytoplasmic, but not nuclear localization of AR in the pancreatic cancer cells was associated with a statistically significant decrease in the post-operative survival period. The presence of EGFR alone in the cancer cells did not correlate with decreased survival, whereas coexpression of cytoplasmic AR and EGFR was associated with shorter survival. Distant metastases did not always exhibit cytoplasmic AR immunoreactivity. These findings point to the existence of an EGFR: AR autocrine loop in human pancreatic cancer which may contribute to its biological aggressiveness.     

Differential expression of genes related to androgen and estrogen metabolism in hereditary versus sporadic prostate cancer.

The hereditary predisposition to prostate cancer is rare and accounts for <5% of cases. Except for younger age at diagnosis, no phenotypic features have been clearly associated with hereditary prostate cancer. The aim of the study was to analyze the expression of genes related to androgen and estrogen metabolism in both hereditary and sporadic prostate cancers in patients matched for clinicopathologic features. Tissues were obtained from patients included in a national familial prostate cancer registry. From the 120 cases of hereditary forms suggesting autosomal dominant Mendelian inheritance, 21 patients were treated by radical prostatectomy for whom formalin-fixed tissue was available. Twenty-one sporadic cases were then matched according to age, Gleason score, and pathologic stage. Immunohistochemistry was done on tissue microarray using antibodies directed against androgen receptor (AR), estrogen receptor alpha (ERA), estrogen receptor beta, 5alpha-reductase I and II, aromatase, and the proliferation marker Ki67. The percentage of AR-positive cancer cells was higher in hereditary cancer compared with sporadic cases (P < 0.004). In contrast, the mean number of ERA-positive stromal cells was lower in hereditary versus sporadic cancer (P < 0.03). This differential expression of AR and ERA suggests that a specific pattern of hormone receptors is associated with hereditary predisposition to prostate cancer.     

Cryptotanshinone suppresses androgen receptor-mediated growth in androgen dependent and castration resistant prostate cancer cells

Androgen receptor (AR) is the major therapeutic target for the treatment of prostate cancer (PCa). Anti-androgens to reduce or prevent androgens binding to AR are widely used to suppress AR-mediated PCa growth; however, the androgen depletion therapy is only effective for a short period of time. Here we found a natural product/Chinese herbal medicine cryptotanshinone (CTS), with a structure similar to dihydrotestosterone (DHT), can effectively inhibit the DHT-induced AR transactivation and prostate cancer cell growth. Our results indicated that 0.5 μM CTS effectively suppresses the growth of AR-positive PCa cells, but has little effect on AR negative PC-3 cells and non-malignant prostate epithelial cells. Furthermore, our data indicated that CTS could modulate AR transactivation and suppress the DHT-mediated AR target genes (PSA, TMPRSS2, and TMEPA1) expression in both androgen responsive PCa LNCaP cells and castration resistant CWR22rv1 cells. Importantly, CTS selectively inhibits AR without repressing the activities of other nuclear receptors, including ERα, GR, and PR. The mechanistic studies indicate that CTS functions as an AR inhibitor to suppress androgen/AR-mediated cell growth and PSA expression by blocking AR dimerization and the AR-coregulator complex formation. Furthermore, we showed that CTS effectively inhibits CWR22Rv1 cell growth and expressions of AR target genes in the xenograft animal model. The previously un-described mechanisms of CTS may explain how CTS inhibits the growth of PCa cells and help us to establish new therapeutic concepts for the treatment of PCa.     

Molecular mechanisms involved in hormone resistance of prostate cancer

Prostate cancer has an androgen-dependent growth mediated by the androgen receptor (AR). Androgen pathway blockage is the standard therapy for the treatment of prostate cancers at an advanced stage. In spite of an initial sensitivity, prostate cancers become more or less quickly towards androgen-independent. Hormone refractory can be due to amplification of AR gene, AR mutations and the increase in co-activator protein expression or in the 5alpha-reductase activity. These induce an agonist activity with the anti-androgens or others steroid hormones like estrogens on AR and allow AR activation with weak concentrations of androgens. Growth factors and cytokines can induce AR phosphorylation independently of the ligand fixation. In condition of androgenic deprivation, AR remains actively involved in the growth of the cancerous cells prostate. Nevertheless, there are others partial AR-independent pathways as neuroendocrine differentiation. The comprehension of these various mechanisms is the key of the development of more effective therapies on hormono-refractory prostate cancers.     

Mechanism of estrogen enhancement in the growth of androgen-dependent Shionogi carcinoma 115

The mechanism of estrogen enhancement in the growth of androgen-dependent Shionogi carcinoma 115 (SC115) maintained in castrated DS mice by low doses of androgen (10 micrograms of testosterone propionate or 4 micrograms of 5 alpha-dihydrotestosterone/mouse/day) is reported. Although the low androgen treatment slightly but significantly (P less than 0.05) stimulated tumor growth, concomitant estrogen (4 micrograms of 17 beta-estradiol/mouse/day) significantly (P less than 0.01) enhanced the tumor growth. The high growth rate, histological type (medullary carcinoma), androgen dependency, and high androgen receptor content of the tumor grown during estrogen plus low androgen treatment did not differ significantly from those of the original SC115 tumor grown in normal males or in castrated mice treated with high doses of androgen. On the other hand, the treatment with low doses of androgen alone induced the development of slowly growing spindle-shaped cells from the medullary SC115 cells. The spindle-shaped cells containing low levels of androgen receptor were shown to be androgen independent and were also induced from the SC115 cells in nontreated castrated mice. These findings demonstrated that low doses of androgen and estrogen synergize to maintain and increase the growth of SC115 cells, whereas low doses of androgen alone fail to maintain the SC115 cells.     

Quantitation of androgen receptor gene expression in sporadic breast tumors by real-time RT-PCR: evidence that MYC is an AR-regulated gene

Little is known of the function and clinical significance of the androgen receptor (AR) in human breast cancer. Paradoxically, synthetic progestins, such as medroxyprogesterone acetate, are used for second line hormone therapy of breast cancer following tamoxifen failure. A sensitive and accurate assay for AR expression in breast tumors is thus required. Here we have developed and validated a real-time RT-PCR assay to quantify AR gene expression at the mRNA level in a series of 131 patients with unilateral invasive primary breast tumors. AR expression varied widely in tumor tissues (by at least 3 orders of magnitude), being underexpressed in 24/131 (18.3%) and overexpressed in 45/131 (34.4%) relative to normal breast tissues. We observed links (or trends) between AR status and age, menopausal status, Scarff-Bloom-Richardson histopathological grade, lymph node status and estrogen receptor alpha and progesterone receptor status. High AR mRNA levels were negatively linked to MYC gene overexpression (P = 8 x 10(-6)), confirming previous in vitro studies. Our results also suggest a role of the ARA70 gene (which encodes a major AR co-activator) in the AR pathway dysregulation observed in breast cancer. This simple, rapid and semi-automated method will be useful for screening cancer patients for altered AR expression and for predicting the response to androgen therapy in AR-related cancer patients.     

雄激素受体对乳腺癌细胞增殖及相关分子表达作用的研究进展

乳腺癌是激素依赖性肿瘤。除雌激素外,雄激素在乳腺癌的发生发展中也发挥重要作用。雄激素受体（AR）经雄激素作用激活,通过不同方式调控雌激素受体（ER）及芳香化酶的表达,影响人表皮生长因子受体-2（HER-2）、孕激素受体（PR）、E-钙黏蛋白的转录,对乳腺癌细胞的增殖既有抑制也有促进作用。AR还与雌激素受体调节剂（SERMs）他莫昔芬及芳香化酶抑制剂（AIs）的耐药机制有关。深入研究AR调控乳腺癌分子表达的机制有助于将AR作为治疗靶点,提高乳腺癌内分泌治疗的疗效。     

Regulation of androgen receptor activity by tyrosine phosphorylation

The androgen receptor (AR) is essential for the growth of prostate cancer cells. Here, we report that tyrosine phosphorylation of AR is induced by growth factors and elevated in hormone-refractory prostate tumors. Mutation of the major tyrosine phosphorylation site in AR significantly inhibits the growth of prostate cancer cells under androgen-depleted conditions. The Src tyrosine kinase appears to be responsible for phosphorylating AR, and there is a positive correlation of AR tyrosine phosphorylation with Src tyrosine kinase activity in human prostate tumors. Our data collectively suggest that growth factors and their downstream tyrosine kinases, which are elevated during hormone-ablation therapy, can induce tyrosine phosphorylation of AR and such modification may be important for prostate tumor growth under androgen-depleted conditions.     

Enhanced antiproliferative and proapoptotic effects on prostate cancer cells by simultaneously inhibiting androgen receptor and cAMP‐dependent protein kinase A

The androgen‐signaling pathway with the androgen receptor (AR) as its key molecule is widely understood to influence prostate tumor growth significantly even after androgen ablation. Under androgen‐deprived conditions, the AR may be activated inappropriately through interaction with other molecules, including cyclic AMP‐dependent protein kinase A (PKA). In a previous study, we have shown that knocking down the AR significantly inhibits prostate tumor growth. In this study, we show that combined inhibition of the AR and the regulatory subunit I alpha of PKA (RIα) with small interference RNAs significantly increased the growth‐inhibitory and proapoptotic effects of AR knockdown. This treatment strategy was effective in androgen‐sensitive and in androgen ablation‐resistant prostate cancer cells. In addition, we report that downregulating PKA RIα was sufficient to inhibit PKA signaling and interestingly also impaired AR expression and activation. Vice versa, AR knockdown induced a decline in PKA RIα, associated with reduced PKA activity. This mutual influence on expression level was specific, because siRNAs against the AR did not affect expression of PKA RIα in AR negative DU‐145 cells and a siRNA control did not affect protein expression. Another important finding of our study was that depletion of PKA RIα also potentiated the antiproliferative effect of the antiandrogen bicalutamide in androgen‐sensitive LNCaP. We therefore concluded that combined inhibition of PKA RIα and AR may be a promising new therapeutic option for prostate cancer patients and might be superior to solely preventing AR expression.