Effect of castration and 17 beta-estradiol pulse on cell proliferation in the uterus and the MXT mouse mammary tumor

The effects of a single 17 beta-estradiol (E2) injection on cell proliferation were studied in 3 groups of 30 mice transplanted with the MXT ovary-dependent mammary tumor. In group A, all animals were castrated prior to tumor implantation; groups B and C had intact ovaries at the time of transplantation, but group B was left intact throughout the experiment, while group C underwent castration 4 weeks later. On day 40 in groups B and C and on day 80 in group A, in which tumor development was significantly delayed, the same procedure for testing the effects of E2 was applied: Ten controls received 0.1 ml saline ip and were killed on the next day; 4 lots of 5 mice received 0.25 micrograms E2 ip and were killed one by one at 12-hour intervals. Exactly 1 hour prior to sacrifice, each animal received 25 microCi [methyl-3H]thymidine ip. Histologic sections of tumors and uteri were processed for autoradiography, and nuclear thymidine (dThd) labeling indices (LI) were determined. All tumors of group A grafted under unfavorable hormonal conditions were poorly differentiated, and E2 injection induced no appreciable changes in their dThd LI. Tumors B and C were well-differentiated adenocarcinomas, in which E2 induced significant modifications of cell proliferation. In group B, complex changes in dThd LI occurred in tumors as well as in uteri, probably due to interferences with the ovarian hormonal production. In group C, E2 produced a marked rise in dThd LI in tumors, lasting from the 12th to the 36th hour after its injection. Stimulation was maximum at the 24th hour, representing a 2.8-fold increase over mean basal dThd LI. It is concluded that the presence of an intact ovarian function at the time of transplantation is critical for maintaining the properties of hormone dependence in MXT tumors. In mice castrated after tumor implantation, a single E2 injection induces a marked and partially synchronous proliferation of neoplastic cells. The hypothesis that such hormonal manipulation might amplify the killing effect of cell cycle- or phase-specific cytotoxic drugs could be adequately tested with this model.

Tritiated actinomycin-D staining method: a valuable tool to study oestrogen receptor-induced modifications of transcriptional activity in normal and neoplastic cells

Exposure at 4 degrees C of purified cell nuclei from uterus and hormone-sensitive mammary cancer to their own cytosol preincubated with oestradiol produced a significant increase in their ability to bind [3H] actinomycin D (3H-AMD). This increase did not occur under conditions preventing the transfer of the oestrogen-receptor into the cell nucleus, nor in cancer cell nuclei devoid of oestrogen-receptors. Uterine cytosol preincubated with the strong antioestrogen 4-hydroxytamoxifen did not modify the 3H-AMD binding capacity of the uterine nuclei but significantly suppressed the increase induced by oestradiol. Moreover, ultrastructural study of tumour nuclei revealed that the oestradiol receptor-induced increase was associated with a marked chromatin dispersion. These results strongly suggest that the 3H-AMD staining method is a valuable tool for the assessment of oestrogen receptor-induced modifications of transcriptional activity in normal and pathological tissue as well.

Histological staining by tritiated actinomycin D: a useful tool to study neoplastic cell heterogeneity and estrogen sensitivity of mammary tumors

The MXT mouse transplantable mammary cancer is characterized by significant amounts of steroid hormone receptors. Moreover this model, as other solid tumors, contains diverse subpopulations of neoplastic cells. In the present study we have examined this pattern as well as the influence of exogenous physiologic doses of estradiol on tumor cell subpopulations. Their identification was undertaken at the morphological level employing incubation of tritiated actinomycin D with fixed material followed by autoradiography. This semiquantitative cytochemical method has proved itself to be a useful tool in order to assess the cellular heterogeneity of carcinoma cells.

Synthesis and evaluation of novel N-substituted N'-(3-hydroxy-17-oxoestra-1,3,5(10)-trien-2- and -4-yl)thiourea derivatives for binding to the estrogen receptor and cytotoxic activity on MCF-7 cells

A novel series of estrone derivatives having a free 3-phenolic group with the 2- or 4-position substituted with a thiourea function was synthesized. None of the products showed significant binding to the estrogen receptor, and the cytotoxic activity on MCF-7 cells for VII and X was weak.

[Relation between estrogen and progesterone receptors and response to hormone therapy]

In mammary cancers, and more especially at the stage of generalization, the detection of estrogen receptors plays a prominent role in the choice of treatment. Recent studies indicate that nearly half of cancers containing receptors are responsive to various hormone treatments while only a minority of cancers not containing receptors are responsive to the same treatments. The present review emphasizes the benefits of a quantitative dosage of these receptors compared to their simple detection. It also evaluates the predictive value of progesterone receptors as an additional test for hormonodependence. Finally, it analyses the part played by receptors dosage in the current therapeutic strategy as well as in the development of new clinical protocols.

Guide-lines in the design of new antiestrogens and cytotoxic-linked estrogens for the treatment of breast cancer

Antiestrogens (Tamoxifen) are used for the treatment of breast cancer. However these compounds are also weak estrogens that may stimulate tumor growth. Cytotoxic-linked estrogens (Estradiol Mustard, Estracyt) are devoid of major therapeutic activity. This led to search for new antiestrogens devoid of estrogenicity and for active cytotoxic-estrogens. Hydroxylation of C-4 of triphenylethylene antiestrogens (tamoxifen, CI 628 and U 23,469) largely increases their binding affinity for the estrogen receptor (ER). Hydroxylation also increases the in vitro antitumor activity of the drugs as shown by their higher ability to inhibit the growth of the ER-positive cell line MCF-7. Triphenylethylene antiestrogens contain an aminoethoxy side chain which appears essential for their physiological activity. Removal of the chain of tamoxifen suppresses its antiestrogenicity and antitumor activity. The grafting of side chains on a weak estrogen of the gem-diphenylethylene category produces "symmetrical" antiestrogens devoid of estrogenic activity. This observation raises the question of the role played by the third phenyl ring of the triphenylethylenes since the trans-isomers of the latter display antiestrogenicity and the cis-isomers estrogenicity. Comparison of the binding affinity for ER and antitumor activity of di- and triphenylethylene antiestrogens suggests that this third phenyl ring increases the interaction with ER of the 4-phenolic group of the drugs and/or their aminoethoxy side chain. An analogue of this chain is without any biological activity suggesting that the di-(tri)pheny-lalkene structure is required for promoting the interaction of the chain with ER. New chemical structures yielding antiestrogens with antitumor activity are also reviewed. New cytotoxic estrogens designed for producing lethal damage of DNA show a low binding affinity for ER. Moreover, there is no evidence suggesting specific antitumor activity. Such activity may be more easily obtained with estrogens bearing reagents for proteins rather than DNA. The biological properties of a 2-mesylate derivative of estrone irreversibly interacting with ER supports the concept. On MCF-7 cells, the drug displays a strong antitumor activity which can only be suppressed by high, equimolar, concentrations of estradiol. It is devoid of cytotoxic activity on the ER-negative cell line Evsa-T suggesting that ER is involved in its action.

Effect of an homo-aza-steroidal ester on estrogen receptor

A new modified steroid esterified with the cytotoxic moiety, p-[N,N-bis(2-chloroethyl)amino]phenyl-acetic acid, has been synthesized and tested for interaction with estrogen receptor and cytotoxic activity on the MCF-7 cell line.

[Histofluorescence localization of cellular sites binding steroid hormones in human breast cancers]

Cytochemical steroids binding activity of human mammary cancer cells is demonstrated in cryostat frozen sections using hydrophilic fluorescent steroid hormone ligands. The cytochemical results indicate that mammary carcinomas are composed of heterogeneous populations of positive and negative cancer cells in varying proportions. A comparison with biochemical data was made. There exists no correlation between the results obtained with the histochemical and the biochemical techniques. The specificity of this new tool of investigation is discussed.

Cytotoxic estrogens in hormone receptive tumors

A high proportion of human mammary cancers contain a measurable amount of estrogen receptors. The presence of estrogen receptors correlates well with the response of patients to endocrine therapy, but not with their response to chemotherapy. However, receptor-mediated chemotherapy should result in more selective and efficient treatment of receptor-positive tumors. Several agents containing an estrogenic and a cytotoxic moiety have been synthesized in the past. It is not surprising that the affinity of these compounds for the estradiol receptor is very low, since most of them were synthesized before our knowledge of hormone receptor mechanisms. An international workshop on cytotoxic estrogens was held on September 27-28, 1979, in Diepenbeek, Belgium, to celebrate the opening of the Dr. L. Willems-Instituut. The purpose of the workshop was to determine the structural requirements for binding to the estrogen receptor and to obtain a consensus on screening techniques for selecting potential drugs of this type.

Clinical significance of the quantitative assessment of estrogen receptors in advanced breast cancer

The predictive value of the estrogen receptor (ER) assay with regard to the response to hormonal treatment was analyzed in women with advanced breast carcinoma. The significance of ten clinical variables of putative prognostic value was also investigated. A total of 49 courses of endocrine therapy were available for study. The respective merits of using the receptor information as a qualitative or a quantitative variable were compared. Linear logistic regression analysis showed that the quantitative information was significantly related to the therapeutic response (P < 0.0001) and proved to be superior to the qualitative information. Compared with the clinical variables tested with the logistic model, receptor concentration was by far the most important single predictor of response. Nevertheless, introduction of two of these clinical variables (i.e., age and menopausal status) into the model in addition to receptor concentration improved its predictive value. Presented in graphic form, the improved model provides a simple means to estimate the probability that a given patient will respond to endocrine therapy. Successive ER assays were available in a series of patients who had received no systemic treatment. In ER+ cases, there was a significant correlation between receptor concentrations in the consecutive assays. There was no influence of the time interval between tissue samplings. Data were also consistent in ER- patients. These results give support to the practice of routine receptor determination in the primary tumor at the time of mastectomy. It is concluded that the distinction between hormone-responsive and hormone-resistant tumors appears artificial. The therapeutic implications of a continuous gradient of hormone-dependency among breast cancers are discussed.

Oestrogen-induced protein in rat mammary tumour and uterus

Biology Unit, Institute of Interdisciplinary Research, Free University of Brussels, 115 B Waterloo, 1000-Brussels, Belgium and *Service de Médecine et Laboratoire d'Investigation Clinique, Institut J. Bordet, 1000-Brussels, Belgium

(Received 19 April 1977)

We wish to report evidence for the early induction by oestradiol-17β of a protein in mammary tumours induced in Sprague–Dawley rats by 7,12-dimethylbenz(a)anthracene (DMBA). The protein appears to be analogous to the oestrogen-induced protein first discovered in the rat uterus by Notides & Gorski (1966) and widely known as 'induced protein' (IP). Induction of IP by oestradiol-17β has been demonstrated in rodents in several tissues of the female genital tract that are targets for oestrogens (Katzman, Larson & Podratz, 1971; Katzenellenbogen & Leake, 1974; Dupont-Mairesse & Galand, 1975) and correlated with the rate of nuclear accumulation of oestrogen receptors (Katzenellenbogen & Gorski, 1972; Katzenellenbogen, 1975). Therefore, the search for induction of IP in DMBA-induced mammary tumours containing oestrogen

Significance of quantitative assessment of estrogen receptors for endocrine therapy in advanced breast cancer

The predictive significance of quantitative assessment of estrogen receptors in tumor tissue was analyzed in women with advanced breast carcinoma. Receptor concentration was measured by the 3H-estradiol binding capacity of the cytosol fraction of biopsies taken before initiation of the treatment. The E. O. R. T. C. criteria for the assessment of the patients' response were used. In a total of 34 assessments, 25 biopsies contained receptors; the remaining ones were negative. Objective remission to various endocrine therapies was recorded in only eight of the receptor-positive patients. Responses occurred along the whole scale of receptor concentrations with an apparent crowding in the region of the higher values. Linear logistic regression analysis revealed that among 12 variables of known prognostic value, receptor concentration was the most significant in relation to therapeutic response. Other significant variables were bone involvement and age. Computations yielded formulas that are presented in graph form and provide an estimate of the probability of a given patient to respond to endocrine treatments. On the other hand, the results suggest that all patients are possibly hormone dependent, although to variable degrees. The latter concept has very definite therapeutic implications.

Affinity of estradiol mustard for estrogen receptors and its enzymatic degradation in uterine and breast cancer cytosols

Estradiol mustard (EM) is the 3,17beta-diester of estradiol-17beta (E2) with the nitrogen mustard derivative chlorphenacyl. The ability of EM to bind to cytoplasmic estrogen receptors was tested by inhibition of the binding of 3H-E2 to rat uterine cytosol at 18 degrees C and 30 degrees C. At both temperatures an inhibition curve was observed in the presence of a large excess of drug, suggesting that the latter has a very weak binding affinity (100,000 times lower than E2). Incubation of uterine cytosol with increasing amounts of 3H-E2 in the presence and absence of an excess of EM indicated that the drug interacted with the receptors at the same sites as E2 (competitive inhibition). Preincubation of uterine cytosol at 18 degrees C with EM induced a progressive reduction of 3H-E2 binding capacity. This reduction also occurred, although to a lesser extent, when long-term incubation of the cytosol with EM was performed in the presence of labelled E2 from the start. The process was faster at 18 degrees C than at 4 degrees C and did not occur with EM preincubated in homogenization buffer. Exchange assays by 3H-E2 of uterine receptors preincubated with labelled E2 and excess EM indicated that the drug-induced inhibition of binding capacity was reversible and produced no apparent alteration of the receptors. Furthermore, the rate of exchange was similar to that observed with receptors previously filled with unlabelled E2. In 9 "receptor-positive" cytosols from human breast cancers, time-course study of the binding of 3H-E2 in the presence of excess of EM yielded similar results as those obtained with rat uterine cytosol. These results show that EM has a very low binding affinity for the extrogen receptors and that it is metabolized into one or several compounds of higher binding affinity. They suggest that EM is probably not significantly concentrated by the estrogen target tissues such as mammary cancers. Therefore, the drug is unlikely to be very valuable in the treatment of breast cancer through a specific mechanism involving concentration by the estrogen receptors.

Estradiol-dependent collagenolytic enzyme activity in long-term organ culture of human breast cancer

An organ culture method suitable for the maintenance of viable human breast cancer for at least 14 days has been described. This method was applied to a total of 94 breast cancer specimens. It allowed good survival of "soft" tumors of various histological types, with loose connective stroma even in hormone-free medium. In contrast, "scirrhous" cancers showed poor survival in hormone-free medium; viable cells were maintained only at the very periphery of the explants. Supplementation of the medium with insulin (10 mug/ml), ovine prolactin (5 mug/ml), and hydrocortisone (1 mug/ml) in various combinations seemed to induce enlargement of viable cancer cells and moderate loosening of the stroma in some cases. However, it did not improve the survival of central tumor cords in scirrhous explants. Further supplementation of the medium with 17 beta-estradiol (minimum effective dose, 0.1 to 10 ng/ml), although it did not affect soft tumors, markedly improved survival of the cancer cells of scirrhous tumors throughout the whole explants, with evidence of collagen digestion around the neoplastic cells. This was observed in 18 of 20 scirrhous cancers subjected to this treatment. Estradiol need not be present during the whole culture period; the results at 14 days were identical in explants treated with estradiol for the first 7 days only or for the entire period. Addition of purified collagenase during the first 24 or 48 hr of culture resulted in complete dissolution of the collage. After such treatment, culture under the usual conditions resulted in excellent survival of the explants without improvement from hormone supplementation; thus, while estradiol was necessary when collagen was present, it was not longer required after collagen digestion. It can be concluded that breast cancer cells in organ culture are only slightly, or not at all, hormone dependent for survival, provided that they are not restrained by a dense collagen barrier. The estrogen-induced changes allowing survival inside the scirrhous explants strongly suggest the presence of an estrogen-dependent collagenolytic enzyme system in the collagen-rich breast cancers. This system could represent an important component of the hormone dependency of human breast cancer growth.

Oestrogen receptors in breast cancer: a changing concept

Oestrogen receptors were found in 156 (73%) out of 214 primary breast cancers and in 98 (58%) out of 168 metastatic deposits. These proportions reached 82% and 70% respectively in the second half of the study. Receptors were not found in samples of normal breast tissue but small amounts were present in tissue from some hyperplastic lesions and in male gynaecomastia. Receptor concentrations in the malignant samples were evenly distributed over a wide range of values, suggesting that even "negative" tumours might contain trace amounts undetectable by the method used. Each tumour was characterized by a given level of receptor concentration. In most cases the amounts found in the invaded axillary nodes and their corresponding primary tumours were the same. We suggest that quantitative rather than qualitative assessment should provide an appropriate criterion for studies of biochemical and clinical correlations.