Biomedical subjects

N Bruchovsky

Publications and source records attributed to N Bruchovsky.

At least 55 records · Page 3Linked to original sources

PubMed1993

Relationship between variant forms of estrogen receptor RNA and an apoptosis-related RNA, TRPM-2, with survival in patients with breast cancer.

BACKGROUND: Although smaller variant forms of estrogen receptor (ER) messenger RNA (mRNA) have been detected in breast tumors, neither their prevalence nor their prognostic significance have been evaluated. Similarly, TRPM-2 mRNA, the product of a gene induced principally during the onset of apoptosis, is present in mouse and human breast cancer cell lines, but whether it also occurs in primary breast tumors and is related to disease outcome is unknown. METHODS: The relative expression and transcript size of ER mRNA and TRPM-2 mRNA in 126 primary breast tumors were measured by Northern analysis and compared with tumor grade, hormone receptor status, extent of tumor necrosis, and survival. RESULTS: In ER-positive tumors, 64% of the tumors had only the normal 6.5 kb ER mRNA, an additional 9% had the normal plus smaller ER mRNA, and 2% had variant forms. Only 8% of ER-negative tumors had ER mRNA transcripts. There were significant relationships between the occurrence of ER mRNA and low tumor grade, ER-positive receptor status, and better survival. In contrast, TRPM-2 mRNA was found in only 17% of breast tumors, none of which could be grouped with respect to grade, hormone receptor status, or survival. CONCLUSIONS: The presence of smaller variant forms of ER mRNA either alone or in association with the normal ER transcript is not indicative of an unfavorable prognosis, whereas TRPM-2 mRNA occurs in many primary breast tumors, but has no apparent relationship to survival.

Adult↗

PubMed1993

Luteinizing hormone-releasing hormone agonists in prostate cancer. Elimination of flare reaction by pretreatment with cyproterone acetate and low-dose diethylstilbestrol.

BACKGROUND: In response to the first administration of a luteinizing hormone-releasing hormone (LHRH) agonist, the secretion of pituitary gonadotropin increases sharply and gives rise to a transient surge in the concentration of serum testosterone. This effect reaches a peak 4 to 7 days after the start of therapy and results in the onset of clinical symptoms and signs of tumor flare in 5% to 10% of patients. METHODS: To determine whether the effects of the LHRH-induced flare reaction are preventable, cyproterone acetate (100 mg) and low-dose diethylstilbestrol (0.1 mg) were administered daily for 4 weeks to inhibit the pituitary before the initiation of therapy with a depot LHRH agonist, goserelin acetate (3.6 mg every 4 weeks). Diethylstilbestrol was stopped after 8 weeks to eliminate associated minor toxicity while administration of cyproterone acetate was continued to suppress vasomotor symptoms. Twenty-four men with histologically confirmed prostate cancer were enrolled in the study: 6 with Stage C, 2 with Stage D1, and 16 with Stage D2 disease. RESULTS: Lead-in therapy reduced the concentration of serum testosterone into the castrate range within 1 week, and no significant change was observed in the mean level after administration of goserelin acetate. Neither was there an effect on the initial rate of normalization of serum prostate specific antigen (PSA); normal PSA values were obtained in 50% of patients after 10 weeks and in 70% after 32 weeks. In the subgroup of patients with Stage D2 disease, longer median survival was predicted by a normal serum PSA, either stable or decreasing, after 32 weeks of treatment. The regimen was well tolerated with a low incidence of hot flushes. CONCLUSIONS: These results imply that in the absence of LHRH-induced tumor flare, prognosis is related to the ability of therapy to maintain a PSA nadir in the normal range.

Acid Phosphatase↗

PubMed1993

Effects of intermittent androgen suppression on androgen-dependent tumors. Apoptosis and serum prostate-specific antigen.

BACKGROUND: Since postcastration progression of tumors to an androgen-independent state appears to be linked to the cessation of androgen-induced differentiation of tumorigenic stem cells, the authors hypothesized that the replacement of androgens at the end of a period of apoptotic regression might result in the regeneration of differentiated tumor cells with further apoptotic potential. METHODS AND RESULTS: To determine the effect of intermittent exposure of androgens on the androgen-dependent Shionogi carcinoma, the tumor was transplanted into a succession of male mice, each of which was castrated when the estimated tumor weight became about 3 g. After the tumor had regressed to 30% of the original weight, it was transplanted into the next noncastrated male. This cycle of transplantation and castration-induced apoptosis was repeated successfully four times before growth became androgen-independent during the fifth cycle. In four of Stage C and three of Stage D patients with prostate cancer, androgen withdrawal was initiated with cyproterone acetate (100 mg/d) and diethylstilbestrol (0.1 mg/d) and then maintained with cyproterone acetate in combination with the luteinizing hormone-releasing hormone agonist, goserelin acetate (3.6 mg/month). After 6 or more months of suppression of serum prostate-specific antigen (PSA) into the normal range, treatment was interrupted for 2 to 11 months. After recovery of testicular function, androgen-withdrawal therapy was resumed when serum PSA increased to a level of about 20 micrograms/l. This cycle was repeated sequentially to a total of two to four times over treatment periods of 21 to 47 months with no loss of androgen dependence. CONCLUSIONS: These results demonstrate that intermittent androgen suppression can be used to induce multiple apoptotic regressions of a tumor; they also suggest that the cyclic effects of such treatment on prostate cancer can be followed by the sequential measurement of serum PSA levels.

Adenocarcinoma↗

PubMed1993

Characterization of two cis-acting DNA elements involved in the androgen regulation of the probasin gene.

The location and sequence of androgen responsive elements (AREs) in the 5'-flanking DNA of the androgen-regulated rat probasin (PB) gene were determined. The DNA- and steroid-binding domains of the rat androgen receptor [glutathione-S-transferase (GST)-AR1] and the DNA-binding domain and hinge region alone (GST-AR2) were expressed in Escherichia coli as isopropyl-B-D-thioglactopyranoside-induced fusion proteins with GST and purified using glutathione affinity chromatography. Band shift assays indicated that the AR1 peptide was at least five times more effective than AR2 in binding to PB 5'-flanking DNA (-426 to +28), although both gave qualitatively similar patterns and were displaced by anti-AR antibodies. DNase I footprinting experiments revealed two putative AREs: one between positions -236 and -223 (ARE-1) and the other between -140 and -117 (ARE-2). Hormonal regulation of PB was determined by cotransfecting reporter constructions containing the PB 5'-flanking region (-426 to +28) linked to the bacterial chloramphenicol acetyl transferase (CAT) gene with androgen, glucocorticoid, or progesterone receptor expression vectors into human prostatic carcinoma cells (PC-3). PB-CAT gene expression was more effectively induced by androgens than by glucocorticoids or progestins. Both 5'- and 3'-deletion mapping of the PB 5'-flanking DNA revealed that ARE-1 and ARE-2 were required for androgen regulation. A single base mutation in either ARE resulted in a more than 95% loss of androgen induction of CAT. In comparable transfection experiments, the PB hormone-responsive elements showed a greater induction by androgens than did mouse mammary tumor virus or tyrosine aminotransferase elements. Thus, the preferential androgen regulation of the PB gene involves the participation of two different cis-acting DNA elements that bind AR.

Amino Acid Sequence↗

PubMed1991

Use of cyproterone acetate in prostate cancer.

Cyproterone acetate is a progestational antiandrogen with potent antigonadotropic activity that results in rapid suppression of serum testosterone. Used as a single agent, cyproterone acetate yields a total androgen blockade. It may be combined with low-dose diethylstilbestrol, orchiectomy, or LHRH agonists to improve, in theory, the results of such therapy. In clinical testing, cyproterone acetate has proved equivalent to diethylstilbestrol with markedly less toxicity. It is useful in conjunction with LHRH agonists, either transiently to block the flare phenomenon, or continuously to block peripheral androgen receptors; the necessity for this latter action has not yet been proved. Cyproterone acetate may afford transient objective improvement in patients not responding to other forms of hormone deprivation. Experience in this role is limited. The drug may be used to suppress the hot flushes associated with orchiectomy or LHRH agonist therapy. Cyproterone acetate induces local tumor regression; owing to its reversible effects, it is useful as neoadjuvant or adjuvant androgen withdrawal therapy in patients with lower-stage disease undergoing radical surgery or radiotherapy. Adverse effects are mostly those related to hormone withdrawal, namely, impotence, infertility, and lassitude. Gynecomastia and breast tenderness occur in less than 18% and cardiovascular complications in approximately 10% of treated men.

Androgen Antagonists↗

PubMed1990

Loss of androgen dependence is associated with an increase in tumorigenic stem cells and resistance to cell-death genes.

Complete remissions of the androgen-dependent Shionogi mouse mammary carcinoma are observed after androgen withdrawal but invariably the disease recurs and is refractory to further hormonal manipulations. To determine the proportions of androgen-dependent (AD) and -independent (AI) tumorigenic stem cells in parent and recurrent tumors an in vivo limiting dilution assay was developed. There was a marked enrichment of stem cells in the recurrent tumors (1/200 tumor cells) relative to the parent tumors (1/4000 tumor cells) when assayed in male hosts. By assaying tumor takes in female mice, the proportion of AI stem cells was found to be 1/370,000 tumor cells in the parent vs 1/800 tumor cells in the recurrent carcinoma; a 500-fold increase in AI stem cells resulting from androgen-withdrawal. Unexpectedly, no enrichment of AI stem cells was evident in regressing parent tumors; rather, the proportion of such cells was very small (1/2,200,000 tumor cells). This finding implies that the AI cells which survive androgen withdrawal may result from the ability of small number of initially AD stem cells to adapt to an altered hormonal environment. This adaptive process was further defined in terms of the disappearance of androgen receptors from the nucleus and the expression of androgen-repressed genes including the proto-oncogenes, c-fos and c-myc, and the cell death gene, TRPM-2; all of which are constitutively active in recurrent AI tumor cells. Overall, our results indicate: (1) the tumor mass consists mainly of differentiated cells; (2) stem cells initially are AD but at most the killing effect of androgen-withdrawal will be limited to 2-3 logarithms before compensatory adaptive mechanisms supervene; and (3) progression of stem cells to an AI state, in which they are resistant to the killing effects of cell death genes, might be prevented by the inhibition of androgen-repressed adaptive mechanisms which come into play when androgens are withdrawn.

Androgens↗

PubMed1990

DNA content in prostatic adenocarcinoma. A flow cytometry study of the predictive value of aneuploidy for tumor volume, percentage Gleason grade 4 and 5, and lymph node metastases.

DNA content of prostatic adenocarcinoma was determined by flow cytometry on formalin-fixed, paraffin-embedded tissue from 57 radical prostatectomies. This was done to define the relationship of aneuploidy to prostatic adenocarcinoma grade, volume, and pathologic stage and to examine its utility in candidates for surgical treatment. Aneuploidy was found in 26 (46%) cases. With one exception, all of the aneuploid cases were found in tumors larger than 4 cc. The percentage of aneuploid cases increased with advancing pathologic stage, and it was highest in those cases with lymph node metastases. This percentage was also higher among more poorly differentiated tumors. However, diploid tumors were also found among these groups, and the relationship between aneuploidy versus pathologic stage and grade did not achieve statistical significance. Except for a 91% specificity for tumor volume greater than 4 cc, the sensitivity and specificity of DNA content analysis to predict these groups was low (50% to 72%). It is concluded that aneuploidy is a later event linked to tumor progression, but it is not a requirement for progression to occur. The overlap in aneuploid and diploid tumor behavior precludes the use of DNA content analysis as an independent predictor to direct preoperative treatment of prostatic carcinoma.

Adenocarcinoma↗

PubMed1990

Effects of androgen withdrawal on the stem cell composition of the Shionogi carcinoma.

The parent Shionogi mouse mammary carcinoma is androgen dependent but cells that survive hormone withdrawal progress and give rise to an androgen-independent tumor. To determine whether renewed growth might be attributed to the persistence or partial recovery of an androgenic stimulus, we compared the amount of dihydrotestosterone and nuclear androgen receptor in parent and recurrent tumors. The whole tissue concentration of dihydrotestosterone in the parent tumor before castration was 1.40 +/- 0.46 (SE) as compared with 0.22 +/- 0.10 pmol/mg of DNA in the recurrent tumor. The initial concentration of nuclear androgen receptor in the parent was 0.65 +/- 0.12 pmol/mg of DNA; this was reduced to zero within 24 h after castration. Also in keeping with the androgen independence, no receptor was detected in the nuclear fraction of the recurrent carcinoma. In an attempt to relate malignant potential to nonhormonal factors associated with progression, we compared the proportions of androgen-dependent and -independent tumorigenic (stem) cells in parent and recurrent tumors using an in vivo limiting dilution assay. The difference observed, i.e., one stem cell per 4000 tumor cells in the parent versus one stem cell per 200 tumor cells in the recurrent carcinoma, was consistent with a marked enrichment of stem cells in the latter. The proportion of androgen-independent stem cells was also determined by assaying tumor takes in female hosts. The difference, i.e., one stem cell per 370,000 tumor cells in the parent versus one stem cell per 800 tumor cells in the recurrent carcinoma, demonstrated a striking 500-fold increase in androgen-independent stem cells resulting from androgen withdrawal. Unexpectedly, no enrichment of androgen-independent stem cells was evident in regressing parent tumors; rather, the proportion of such cells was very small, i.e., one androgen-independent stem cell per 2,200,000 regressing parent cells. This finding implies that the androgen-independent state of cells which survive androgen withdrawal may result from the ability of a small number of initially androgen-dependent stem cells to adapt to an altered hormone environment.

Androgens↗

PubMed1989

Primary structure and androgen regulation of a 20-kilodalton protein specific to rat ventral prostate.

Nuclear and cytosolic forms of a 20-kdalton rat ventral prostate protein were purified and partially sequenced from their N-termini. Isolated nuclei were treated with micrococcal nuclease and extracted in 0.6 M NaCl, and proteins were separated by affinity chromatography on Matrex gel green A, ammonium sulfate fractionation, and fast protein liquid chromatography on Superose 12. The 43 amino acid N-terminal sequence of the nuclear 20-kdalton protein was identical with the cytosolic protein except it lacked 7 N-terminal amino acids present in the cytosolic form. The DNA sequence of a full-length complementary DNA clone isolated from a ventral prostate gt11 library extended the N-terminal sequence of the cytosolic form by an additional nine amino acids from the predicted initiation methionine. The cDNA included the nucleotide sequence for the 43 amino acid N-terminal sequence of the purified 20-kdalton protein and predicted molecular weights of 16,686, 17,521, and 18,650, respectively, for the nuclear, cytoplasmic, and nonprocessed proteins. Northern blot analyses of reproductive tract tissue RNAs using the 20-kdalton protein cDNA as probe revealed a single mRNA species of 0.92 kb detectable only in extracts of rat ventral prostate. Expression of the 0.92-kb mRNA was androgen dependent since the mRNA was undetectable in extracts obtained 4 days after castration and was restored 16 h after restimulation with androgen.

Amino Acid Sequence↗

PubMed1989

Prostate. III--A structural feature characteristic of the rat prostate 5 alpha-reductase active site.

To aid in the design of new inhibitors of steroidal 5 alpha-reductase for treatment of prostate cancer, we have studied the topography of the 5 alpha-reductase active site (5 alpha-R) and of the related androgen (RA) and progesterone (RP) receptors in the region complementary to C.6 of progesterone. To this end we have determined the total structures of 17 alpha-acetoxy-6-methylene-4-pregnene-3,20-dione (VII; R = H) and of 17 beta-hydroxy-6,6-ethylene-4-androsten-3-one (VIa) by X-ray crystal structure analysis and, using these data, have developed Newman projections of the 6 alpha-Me, 6 beta-Me, 6-methylene and 6,6-ethylene derivatives of progesterone. From them we have developed a Newman projection of a composite model formed from steroids (V), (VI), (VIIIa) and (VIIIb). This is shown in Fig. 4 and illustrates the relative conformations of these substituents around C.6. From there we proceeded to receptor-binding studies. Our results led to the conclusion that androgen receptor, (RA), takes up preferred but different conformations when bound to testosterone (T) and to 17 beta-hydroxy-5 alpha-androstan-3-one (5 alpha-dihydrotestosterone, DHT), respectively, and that the resulting steroid-receptor complexes bind preferentially to different chromatin acceptor sites. We have therefore used the convention RT and RDHT in place of RA as appropriate. Working on the assumption that binding affinities reflect spatial contours, we have developed comparative silhouettes for the 5 alpha-R, RP and RDHT protein binding sites complementary to C.6 of the steroidal ligand. These data show that the 5 alpha-reductase active site is characterized by a hydrophobic pocket which specifically accommodates a 6-methylenic moiety and partially accommodates a 6 beta-methyl group. RDHT, in contrast, shows much less specificity and largely accommodates all the above substituents. Progesterone receptor differs in failing to accommodate 6,6-ethylene and 6 beta-methyl, with minimal accommodation of 6-methylene. It possesses a hydrophobic pocket skewed towards the alpha-face of the steroid, thereby allowing optimal binding of the 6 alpha-methyl substituent to the receptor. 6-Methylene-4-pregnene-3,20-dione (V) fails to bind significantly to androgen and progesterone receptors thereby supporting the postulate that its antiprostatic activity stems primarily from 5 alpha-reductase inhibition.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗

PubMed1989

Cortisol alters gene expression during involution of the rat ventral prostate.

The ability of high doses of cortisol to retard the involution process in the rat ventral prostate was related to alterations in the pattern of gene expression. Poly(A)+ RNA preparations from the prostates of noncastrated, castrated, and castrated rats injected daily for 7 days with cortisol were compared by Northern blot hybridizations for the relative expression of genes associated with cell differentiation and maintenance (the C1 prostatic steroid binding protein gene and alpha-tubulin), with cell death (TRPM-2, hsp 70, and c-fos), and with hormone regulation (the androgen and glucocorticoid receptors). As anticipated, the concentration of C1 mRNA in the prostate fell to less than 4% of that in the noncastrated controls within 4 days after castration and was nearly undetectable after 7 days. This decline was retarded by cortisol treatment of 7-day castrated animals which sustained the level of C1 transcripts at approximately 50% of control. While the pattern of expression of alpha-tubulin indicated some minor fluctuations, with the highest level occurring 7 days after castration, the prostates of the cortisol-treated group had essentially the same concentration of this mRNA as the noncastrates. Cortisol also modified the expression of genes associated with prostatic cell death. The large increase in prostatic TRPM-2 mRNA, seen 7 days after castration, was reduced by over 80% after treatment with the glucocorticoid. Although not as abundantly expressed as TRPM-2, the castration-induced levels of transcripts for both hsp 70 and the protooncogene c-fos were substantially reduced by cortisol.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Gene expression during the early phases of regression of the androgen-dependent Shionogi mouse mammary carcinoma.

The effects of castration on gene expression were measured in the androgen-dependent Shionogi mouse mammary carcinoma. From 0 to 144 h after castration, polyadenylated RNA from the tumors was analyzed by Northern blotting for the expression of genes associated with cell maintenance (beta-actin and alpha-tubulin), cell growth and differentiation (c-fos and c-myc), and cell stress and death (heat shock 70 and TRPM-2). During the first 48-72 h after castration, the tumor continued to increase its mass but thereafter (72-144 h) began to regress. Throughout, the concentration of polyadenylated RNA recovered and the expression of both beta-actin and alpha-tubulin remained relatively constant, implying that in the surviving cells there are no major decreases in RNA synthesis. By comparison, c-myc exhibited a small increase in relative expression during the entire period examined, whereas c-fos displayed a transient peak at 12 h after castration, suggesting that this gene is acutely sensitive to androgen withdrawal. Heat shock protein 70 displayed a pattern similar to that of c-fos; however, the transient rise in the level of heat shock protein 70 expression could be induced by sham operations alone. The concentration of the transcripts encoding TRPM-2 rose only when tumor regression was most evident (72-144 h after castration). Thus, gene expression in the Shionogi carcinoma following castration can be grouped according to those genes which show little or no response, those which are acutely sensitive, and those which show a late effect and are more closely affiliated with cell death.

Animals↗

PubMed1988

The relationship between inhibition of plasminogen-activator activity and prostatic involution.

The role of plasminogen activators (PAs) as potential mediators of involution of the rat ventral prostate was investigated by using an approach involving the administration in vivo of anti-PA drugs. The prostates of castrated rats, which had been injected daily for 7 days with the anti-PA drugs 6-aminohexanoic acid, tranexamic acid, aprotinin and cortisol, were assayed for PA activity, weight and cell number. In the prostates from the castrated controls, there was a 10-fold increase in the mean PA activity and a 7-fold decrease in cell number relative to that of the non-castrated animals. Although this rise in enzyme activity could be decreased to some extent by all the drugs except aprotinin, only treatment with high doses of tranexamic acid or cortisol had a statistically significant effect. A similar pattern was observed with respect to the relative potency of the drugs in preventing the loss of prostatic weight and cell number after castration. The effects of cortisol were dose-dependent, with complete inhibition of both the rise in PA activity and cell loss occurring at a dose of about 15 mg/day. Since the concentration of the principal intranuclear androgen, dihydrotestosterone, was the same in the prostates from treated and untreated castrated rats, the effects of cortisol are not due to increased retention of this androgen. Rather, the high inverse correlation (r = 0.86) between the cellular concentration of PA activity and the cell population of the prostate implies that PAs are directly associated with prostatic involution and that cortisol, and to a lesser extent tranexamic acid, blocks the involution process through inhibition of PAs.

Aminocaproates↗

PubMed1988

The combination of cyproterone acetate and low dose diethylstilbestrol in the treatment of advanced prostatic carcinoma.

Cyproterone acetate is a steroidal antiandrogen with weak progestational activity that results in the partial suppression of pituitary gonadotropin. We demonstrate that the associated decrease in serum testosterone is more complete and prolonged if cyproterone acetate (200 mg. daily) is combined with a low dose of diethylstilbestrol (0.1 mg. daily). The effectiveness of the combination in the treatment of prostatic carcinoma was investigated in 51 patients with stage D2 malignancy. From an initial concentration of 360 +/- 23 ng. per dl. (mean +/- standard error), serum testosterone decreased to 56 +/- 5 ng. per dl. after 1 week and reached a plateau of approximately 30 ng. per dl. after 2 months. This was accompanied by a decrease in serum prostatic acid phosphatase from a mean starting concentration of 43 +/- 11 ng. per ml. to a low of 3 +/- 1 ng. per ml. at 12 months; the proportion of normal values increased from 10 to 80 per cent. A complete response was observed in 7 patients (13 per cent), partial response in 35 (69 per cent) and stable disease in 8 (16 per cent), yielding an over-all objective response rate of 98 per cent (1980 National Prostatic Cancer Project criteria). The actuarial median time to progression was 17 months and the median survival time was 23.5 months. In 26 patients who subsequently had signs of progressive carcinoma the relapse rate in bone (85 per cent) far exceeded that in nonskeletal sites (23 per cent). The incidence of cardiovascular toxicity was 12 per cent. These results indicate that cyproterone acetate and low dose diethylstilbestrol may be co-administered to achieve a synergistic and potent androgen withdrawal effect in the treatment of advanced prostatic carcinoma.

Acid Phosphatase↗

PubMed1988

Relative effectiveness of alternative androgen withdrawal therapies in initiating regression of rat prostate.

From a large number of potentially effective androgen withdrawal regimens including bilateral orchiectomy, estrogens, antiandrogens and LHRH agonists alone or in combinations, we compared the ability of 12 different treatment options to mimic the acute results of surgical castration on the rat prostate. Agents were administered s.c. in clinical doses to groups of male rats daily for three days. On day 4 the prostatic tissue was removed and analyzed by conventional methods for whole-tissue and nuclear concentrations of dihydrotestosterone, nuclear androgen receptor and cytoplasmic androgen receptor. Castration-like changes were most pronounced with the synergistic combinations of cyproterone acetate + low-dose diethylstilbestrol, and megestrol acetate + low-dose diethylstilbestrol. Comparing the effectiveness of single agents, low-dose diethylstilbestrol was superior to cyproterone acetate, megestrol acetate, flutamide, leuprolide and RU23908. Leuprolide combined with flutamide was superior to leuprolide + cyproterone acetate, leuprolide + cyproterone acetate + low-dose diethylstilbestrol or leuprolide + RU23908 after three days of administration; however, this advantage disappeared when the treatments were extended to seven days. The observations indicate that the most potent androgen withdrawal therapies such as cyproterone acetate + low-dose diethylstilbestrol and megestrol acetate + low-dose diethylstilbestrol at best approximate but do not surpass the early effects of surgical castration. During the same time course, other regimens are characterized by a slower onset of action and a lesser degree of suppression of androgenic mechanisms within the cell.

Anilides↗

PubMed1988

Relationship of androgen receptors to the growth and regression of the prostate.

Since androgen receptors (AR) stimulate growth and block regression of the prostate through direct binding to nuclear sites, androgen withdrawal therapies must effectively eliminate AR from nuclei to bring about regression of prostatic carcinoma. Using this criterion, we compared the effects of surgical castration with those of 12 different androgen-withdrawal regimens on the rat prostate. The most potent treatment in this regard, a combination of cyproterone acetate and low-dose diethylstilbestrol, caused an initial objective response rate of 98% in 51 patients with stage D prostate cancer. Thus, although assays for AR are useful for evaluating new drugs, the high initial response rates to treatment make them irrelevant for routine patient selection. Accordingly, the principal reason for studying AR is to determine the cellular and molecular processes leading to the eventual emergence of androgen-resistant stem cells. At the cellular level, tumor recurrence in the androgen-dependent Shionogi tumor system is characterized by a 30-fold enrichment of stem cells that possess cytoplasmic AR but that lack the ability to retain AR in the nucleus. While at the molecular level definitive results await the purification of AR and their genes, the occurrence of biologically active truncated and chimeric forms of AR, analogous to those that have been synthesized in vitro for other steroid receptors, would predictably yield an androgen-resistant phenotype.

Androgen Antagonists↗

PubMed1988

Kinetic parameters of 5 alpha-reductase activity in stroma and epithelium of normal, hyperplastic, and carcinomatous human prostates.

To study the influence of 5 alpha-reductase on the concentration of dihydrotestosterone in prostatic tissue, we measured the activity of this enzyme in stroma and epithelium from 15 normal, 50 hyperplastic, and 20 carcinomatous prostates. Maximum velocity (Vmax) and Km parameters based on the Lineweaver-Burk and Eadie-Hofstee transformations of the Michaelis-Menten equation were related to the stromal and epithelial concentrations of dihydrotestosterone. On the basis of relative Vmax values, there was 6-15 times more 5 alpha-reductase activity in stroma than in epithelium regardless of the histology of the prostate. Stromal enzyme activity also was unique in having a 2- to 5-fold larger mean Km value and greater resistance to competitive and noncompetitive inhibition. Despite the enrichment of 5 alpha-reductase activity in stroma, the dihydrotestosterone concentrations in the stromal and epithelial fractions were very similar. In addition, similar concentrations were found in the stromal fractions of hyperplastic and carcinomatous tissues, notwithstanding a 4-fold difference in the mean Vmax values. This anomaly occurred in association with a large disparity in mean Km values, i.e. 68.3 +/- 1.6 (+/- SE) nmol/L in hyperplasia vs. 23.0 +/- 2.9 nmol/L in carcinoma. The dissociation between parameters of 5 alpha-reductase activity and tissue dihydrotestosterone concentrations was apparent to some extent in benign prostatic hyperplasia, in which the lowest stromal androgen concentrations were found in prostates with the largest Vmax and Km values; also, a rise in stromal Km was almost invariably associated with a proportional increase in Vmax (correlation coefficient = 0.95). These data strongly suggest that the stromal and epithelial forms of 5 alpha-reductase are separate isoenzymes, and that the excess of 5 alpha-reductase in stroma does not promote accumulation of an abnormal amount of dihydrotestosterone. They also imply that both the augmentation of 5 alpha-reductase activity in hyperplastic stroma and the condition of benign hyperplasia of the prostate are mutual consequences of a primary increase in Km.

Aged↗

PubMed1987

Chemical demonstration of nuclear androgen receptor following affinity chromatography with immobilized ligands.

With increasing purification of the androgen receptor from nuclei of rat ventral prostate, a receptor-like protein could be demonstrated by chemical staining with silver nitrate. After sonication and digestion of nuclei with micrococcal nuclease, the solubilized receptor was applied to a column of Matrex Gel Green A and eluted with a linear gradient of 0-2 M NaCl. Characterized by specific binding of dihydrotestosterone, this form of the receptor was also androgen dependent and yielded an apparent Mr of 33,000 when analyzed by polyacrylamide gel electrophoresis and silver nitrate staining. To facilitate recovery following chromatography, the receptor was precipitated with 0-40% ammonium sulfate. Analysis of the 15-fold enriched fraction by sucrose density-gradient centrifugation confirmed the presence of a 3S androgen-binding protein. About 200 ng of the precipitated protein was applied to a column of dihydrotestosterone-17 beta-succinyl agarose (ligand concentration, 0.25 mumol/ml). The fractions eluted with 50 microM dihydrotestosterone were electrophoresed and stained as before; again, the presence of a 33,000 Mr protein sensitive to castration was demonstrated. Alternatively, when the precipitated protein was fractionated by fast protein liquid chromatography utilizing a Superose 12 HR 10/30 column, the receptor coeluted with nuclear proteins in the 29,000-36,000 Mr range as determined both by retention time and electrophoresis. In combination, the above methods may be used to obtain a receptor protein purified to near homogeneity with a yield of 5-10%. The amount of receptor afforded by the purification sequence is small but nevertheless sufficient for chemical detection. We anticipate that with modification, the procedures may prove suitable for the recovery of nuclear androgen receptor on a preparative scale.

Animals↗