E. von Angerer

Effect of growth factors on estrogen receptor mediated gene expression

The proliferation of mammary carcinoma cells can be stimulated by estrogens and various growth factors such as EGF and IGF-I. Steroid hormones and growth factors are understood to exert their effects via different receptors and signal transduction pathways. Recently, it has been shown that growth factors can utilize the unliganded estrogen receptor (ER) as a transcription factor. This study was aimed at identifying the growth factors that can act via the estrogen receptor, and finding new estrogen antagonists that block this activity. Originally, a transcription assay was used in which HeLa cells had been transiently co-transfected with the expression vector for the human ER and a reporter plasmid EREwtc luc. EGF and, to a lesser extent, insulin stimulated the expression of the reporter gene in the absence of estradiol (E2), whereas IGF-I was inactive. The stimulatory effect of E2 and insulin was suppressed when the ER was blocked by the pure antiestrogen ICI 182,780. In ER-positive MCF-7 cells, transfected transiently with the reporter plasmid, EGF had no stimulatory effect on luciferase expression. IGF-I stimulated the transcription to about 50% of the E2 value. Similar activity was found for insulin. The effect of both growth factors was only partly reversed by the addition of a pure antiestrogen. The combination of E2 and IGF-I or insulin led to a synergistic activation of transcription. Because transiently transfected cells do not allow one to study the influence of chromatin structure on gene expression, an MCF-7 subline (MCF-7/2a) was established, in which the reporter construct had been integrated in the genome. IGF-I stimulated luciferase expression in these cells, but showed no overadditive effect with E2. The effects of both agents were completely suppressed by the pure antiestrogen ICI 182,780. These data suggest the existence of an ER-independent mechanism for the activation of the reporter gene in transiently transfected cells, but not in stable transfectants.

Antitumour activity of coumarin and 7-hydroxycoumarin against 7, 12-dimethylbenz[a]anthracene-induced rat mammary carcinomas

Female SD rats with established 7, 12-dimethylbenz [a]anthracene(DMBA)-induced mammary tumours were treated with coumarin (20 mg/kg body weight; six times per week) or its metabolite 7-hydroxycoumarin (20 mg/kg) for 4 weeks. The anti-oestrogen tamoxifen (8.8 mg/kg) served as the reference drug. The inhibitory effect of coumarin was similar to that of tamoxifen [mean change of tumour area: 428% (coumarin) compared to 528% (tamoxifen); control 822%]. The strongest inhibition was observed with 7-hydroxycoumarin (248%); the difference compared to the control was significant (P<0.01). Neither coumarin nor 7-hydroxycoumarin reduced the number of tumours appearing during treatment as tamoxifen did. However, the size of the tumours treated with coumarin or its metabolite was generally much smaller than those in the tamoxifen group or in the control group. From the data obtained it appears that coumarin and 7-hydroxycoumarin inhibit the growth of tumours that have reached a certain size but do not prevent the formation of tumours after exposure to the carcinogen.

Evaluation of the antitumour activity of coumarin in prostate cancer models

Responses to coumarin have been reported for patients suffering from malignant melanoma, metastatic renal carcinoma and, recently, advanced prostate cancer. These data together with some experimental evidence for antiprostatic effect prompted us to study the activity of coumarin in various prostate tumour models and evaluate the endocrine properties of this drug. In rats no antiandrogenic activity was found. The growth of Noble Nb-R prostate tumours of the rat was strongly inhibited by coumarin (40 mg/kg; administered three times per week), whereas the hormonally more sensitive Dunning R3327-G rat prostate carcinoma did not respond to coumarin (40 mg) even when the drug was administered daily. Coumarin was also shown to posses antimetastatic activity in a Dunning R3327-MatLu tumour model. In this model small pieces of the hormone-independent tumour were implanted into the ear of the animal and later resected to mimic the clinical situation where primary tumours have been removed. The number of lung metastases was reduced significantly by 40%–50% following the administration of coumarin (40 mg daily).

Entwicklung neuer Antiöstrogene vom Typ des 3,3′-Dihydroxy-α,β-diäthylstilbens und ihre Prüfung am DMBA-induzierten, hormonabhängigen Mammacarcinom der SD-Ratte

SummaryThe displacement of the phenolic OH-group of diethylstilbestrol into the 3,3′-position (trans-3,3′-dihydroxy-α,β-diethylstilbene compd. III) leads to a strong decrease of the estrogenic effect under conservation of the receptor affinity. In vitro, III inhibits the estradiol-receptor-interaction competitively and, in vivo, antagonises the uterotropic effect of estrone in the mouse. In tests with the DMBA-induced, hormone-dependent mammary carcinoma of the rat a dose-dependent strong decrease of tumor size and yield is achieved under the influence of III, due to the antiestrogenic, properties of III. The replacement of the α,β-bound ethyl groups in III by other alkyl chains leads to no further increase of the antiestrogenic and antitumor activity.ZusammenfassungDie Verlagerung der phenolischen OH-Gruppen des Diäthylstilböstrols in die 3,3′-position (trans-3,3′-Dihydroxy-α,β-diäthylstilben, Verb. Nr. III) führt unter Erhaltung der Rezeptoraffinität zu einer starken Abnhme der östrogenen Wirkung. III hemmt in vitro die östradiol-Rezeptor-Wechselbeziehung kompetitiv und antagonisiert in vivo bei der Maus die uterotrope Wirkung des Östrons. In Versuchen am DMBA-induzierten, hormonabhängigen Mammacarcinom der Ratte kommt es, unter III-Einwirkung dosisabhägig zu einer starken Abnahme von Tumorgröße und-zahl, die durch die antiöstrogenen Eigenschaften von III bedingt, ist. Der Austausch der α,β-ständigen Äthylreste in III durch andere Alkylketten führt zu keiner weiteren, Steigerung der antiöstrogenen und tumorhemmenden, Wirkung.

Antiproliferative activity of casodex (ICI 176.334) in hormone-dependent tumours

The nonsteroidal antiandrogen casodex has been described as a peripherally selective drug for the treatment of prostatic cancer. In this study we determined its activity in various models of hormone-dependent malignancies including those of the prostate and the breast. Analysis of endocrine effects in rats after 15 days of treatment revealed a strong reduction of the weights of prostates and seminal vesicles and a significant rise of testosterone serum levels as a result of the interference with central feedback mechanisms. The growth of androgen-sensitive human LNCaP/FGC prostate cancer cells was strongly inhibited by casodex. Unlike hydroxyflutamide, casodex was also active in hormone-depleted medium. The inhibitory effect was overcome by addition of testosterone propionate, which indicates an androgen-receptor-mediated mode of action. In rats bearing Dunning R3327-G prostate carcinomas casodex exerted a strong antitumour effect at the beginning of therapy. However, after 4 weeks of treatment tumours resumed growth whereas diethylstilboestrol-treated tumours remained static. In MXT-M3.2 mouse mammary tumours with significant quantities of androgen receptors casodex was also effective in inhibiting tumour growth. After 6 weeks of treatment, tumour weights were reduced by 69% whereas uterine weights were significantly increased, possibly because of a progestin-like activity of the drug. Casodex is very active in various models of hormone-dependent carcinomas. However, the limited duration of action in prostatic tumours and the incomplete growth inhibition in mammary tumours suggest that it should be used only combination with other endocrine therapies.

A rapid luciferase transfection assay for transcription activation effects and stability control of estrogenic drugs in cell cultures

A rapid assay system for measuring the potential of estrogenic drugs is introduced. Luciferase induction could be measured in estrogen-receptor-positive human MCF-7 breast cancer cells, which had been transfected with a novel luciferase reporter plasmid ERE luc. The minimal requirement was 1 h exposure to the inducing drug and 3.5 h of incubation after removal of the drug. The assay system was used to measure the stability of the drug diaqua-[1,2-bis (2,6-dichloro-4-hydroxyphenyl) ethylenediamine] platinum(II) sulfate, containing an estrogenic ligand and reactive platinum. Luciferase activity was observed only when the drug was in the culture medium and cells for short times, whereas the estrogenic ligand alone remained active. It is assumed that binding of the platinum moiety to macromolecular constituents of the culture or cells renders the drug inaccessible for binding to the estrogen receptor.

2-Phenylindoles with sulfur containing side chains. Estrogen receptor affinity, antiestrogenic potency, and antitumor activity

The 2-phenylindole system has been identified as a suitable structure for the design of non-steroidal pure estrogen antagonists [E. von Angerer et al., J. Steroid Biochem. Molec. Biol. 49 (1994) 51-62]. Derivatives with an amide function in the side chain antagonized the stimulatory effect of estrogens both in vitro and in vivo, and showed no agonistic activity when given alone. The findings of other groups who studied steroidal antiestrogens prompted us to replace the amide function by sulfide, sulfoxide, sulfone, sulfonamide and related groups. The compounds with polar sulfur functions retained the high binding affinity for the calf uterine estrogen receptor (RBA: 1-5% of estradiol; ICI 182,780; 6.2%). The estrogenic effect was quantified in a transcription assay using HeLa cells cotransfected with the expression vector HEG0 for the human estrogen receptor and a reporter plasmid that harbored a Vit. A2 ERE and the luciferase gene driven by a thymidine kinase promotor. Pentylsulfide, -sulfinyl, and -sulfonyl groups, linked to the indole nitrogen by a decamethylene spacer, were devoid of any transcriptional activity. These results were confirmed in the mouse uterine weight test. The sulfone (ZK 164,015) completely abolished the effect of a standard dose of estrone at a daily dose of 7 mg/kg. This compound strongly inhibited the growth of hormone-sensitive human MCF-7 breast cancer cells with an IC50-value close to 1 nM. Similar activity was found for the steroidal sulfoxide ICI 182,780. We were also able to demonstrate significant antineoplastic activity in vivo for some of these new 2-phenylindole derivatives.

3,4-Bis(3′-hydroxyphenyl)hexane — A new mammary tumor-inhibiting compound

SummaryThe syntheses of the hexestrol derivatives 3,4-bis-(3′-hydroxyphenyl)hexane (4a), 3,4-bis(4′-fluoro-3′-hydroxyphenyl)hexane (4b), 3,4-bis(3′, 4′dihydroxyphenyl)hexane (4c), and 3,4-bis(3′,4′-diacetoxyphenyl)hexane (4d) are described. All compounds showed a marked, competitive inhibition of the estradiol receptor interaction (Ka4c>Ka4a>Ka4d>Ka4b). Evaluated in the mouse uterine weight test compounds 4c and 4d almost reached the estrone effect, whereas 4a and 4b did not produce full uterotrophic response. Compounds 4a-d antagonized the estrone stimulated uterine growth of the immature mouse. Compound 4a (NSC-297170) exhibited a specific, dose-related growth inhibition of the estrogen responsive MCF-7 human breast tumor cell line. Tested on the 9,10-dimethyl-1,2-benzanthracene-induced hormonedependent mammary adenocarcinoma of the Sprague-Dawley rat all compounds showed marked inhibition of tumor growth. As in all experiments compounds 4a and 4b, which is resistant to hydroxylation in 4′position exhibited an identical pattern of action, which is different from that shown by compound 4c, the effect of compound 4a cannot be explained by its possible catechol metabolite 4c.

Effect of zindoxifene on experimental prostatic tumours of the rat

SummaryThe anti-oestrogen zindoxifene was originally developed as a drug for the treatment of hormone-dependent mammary carcinomas. Experiments with rats bearing androgen-dependent prostatic tumours revealed antineoplastic activity of zindoxifene on these tumours also. Therefore, the inhibitory effect of this drug was studied in various prostatic tumour models in comparison to the anti-oestrogen tamoxifen and to castration. The growth of the hormone-dependent Dunning R3327 H tumour was strongly inhibited by zindoxifene (4 mg/kg), which was more effective than tamoxifen (43%T/C vs 87%T/C, the ratios of tumour weights in control and drugtreated rats). Zindoxifene was able to delay the relapse of these tumours by 7 weeks in comparison to castration. The experiments with Noble Nb-R prostatic tumours showed that administration of zindoxifene (5 mg) is superior to castration (5%T/C vs 52%T/C). The growth of tumours in castrated rats was completely inhibited by administration of zindoxifene. Therefore a peripheral mode of action has to be assumed.

1-Benzyl-2-phenylindole- and 1,2-diphenylindole-based antiestrogens. Estimation of agonist and antagonist activities in transfection assays.

In the 2-phenylindole system, the side chain at the nitrogen atom dominates the endocrine profile both in respect to the reduction of estrogenic action and the increase of antiestrogenic potency. In previous papers we reported on 2-phenylindoles with aliphatic side chains and various functional groups [Biberger, C. and von Angerer, E., J. Steroid Biochem. Molec. Biol., 1996, 58, 31-43 and references therein]. In this study, we incorporated one or two phenyl rings into the side chain in order to lower the flexibility of the side chain. The sulfone group which was used as a polar function was linked to various positions of a benzyl or a phenyl group attached to the indole moiety. The relative binding affinities (RBA) ranged from 1.5 to 8.4% of estradiol. Agonist and antagonist activities were estimated in transfection assays using transiently transfected HeLa cells (cotransfected with the HEG0 vector) and stably transfected MCF-7/2a human breast cancer cells. The reporter plasmid contained the ERE from the Vitellogenin 2A gene, a viral tk promotor and the luciferase gene. Many of the new derivatives showed no or only very low estrogenic activity except for the compound 4e which contained two benzyl elements in the side chain. The antiestrogenic potency was very variable when concentrations 100-fold higher than that of estradiol were applied. The compound with the para-substituted benzyl fragment (4b) proved to be a pure antagonist in the transfection assays. It antagonized the effect of estradiol (10 nM) with an IC50 value of 10(-7) M. It also inhibited strongly the growth of estrogen-sensitive human MCF-7 mammary carcinoma cells (IC50, 3 nM). Its activity was comparable to the one of the corresponding aliphatic 2-phenylindole derivative ZK 164.015. The data from the transcription and proliferation assays suggest that a phenyl ring can be incorporated into the side chain of pure antiestrogens without reducing their potency, provided the aromatic ring is para-substituted and a methylene group between the indole nitrogen and the phenyl group can act as hinge.