Mammary carcinoma: a specific biochemical defect in autonomous tumors

Heterogeneous localization of adenylate and guanylate cyclases in R3230AC rat mammary adenocarcinoma cells

Adenylate and guanylate cyclase activities were demonstrated in R3230AC rat mammary adenocarcinomas by electron microscopic cytochemistry. Adenylate (AC) and guanylate (GC) cyclases were detected on plasma membrane of tumor epithelial cells, but not on fibroblasts and endothelial cells in the perivascular space. Both AC and GC activities were enriched in tumor epithelial cells at the periphery of the tumor lobular parenchyma rather than in cells in central core of the lobular parenchyma. Furthermore, the tumor cell plasma membranes facing the connective tissue stroma were in paucity or devoid of either enzyme activity. These heterogeneous distributions of both AC and GC among tumor epithelia suggest that R3230AC epithelial cells in different parts of the tumor mass may vary significantly in their regulation of cellular physiology.

Evaluation of 5'-nucleotide phosphodiesterase isozyme-V as a predictor for liver metastasis in breast cancer patients

5'-nucleotide phosphodiesterase isozyme-V (5'-NPD-V) was evaluated in 85 biopsy proven breast cancer patients as a potential marker for early liver metastasis. It correctly predicts liver metastasis in 6/7 (85.7%) patients with abnormal radiologic liver scan and 2/2 other patients with palpable liver. Serum glutamic-oxaloacetic transaminase (SGOT), lactic dehydrogenase (LDH), alkaline phosphatase (AP) and total bilirubin (B) were also determined in 79 of these patients as routine liver function tests (LFT). Forty-one out of 79 from this group had all four markers all within normal limits. Yet of the 41 patients, 12 patients were found positive for 5'-NPD-V. Of these 12, one was found to have liver metastasis at surgery and one had abnormal liver scan. Five other patients had liver dysfunction and one had been diagnosed as an alcoholic. Four others had no evidence of either liver problems or liver metastasis, but follow-up data were lacking. This retrospective study, therefore suggests that there is a definite advantage to include the 5'-NPD-V in the liver profile studies for breast cancer patients, although a positive 5'-NPD-V may only indicate liver repair or liver regeneration. Long-term prospective studies of these tests with breast cancer patients should be worthwhile. No relation was found between 5'-NPV-V and axillary lymph node involvement or the estrogen receptor status of the excised tumor. Thus there is no evidence currently that the appearance of the 5'-NPD-V in serum is related to lymph node metastases or hormonal control.

Pregnancy stimulates DNA synthesis in R3230AC mammary adenocarcinoma

The transplantable R3230AC mammary adenocarcinoma was grown in virgin, pregnant and lactating rats and in vivo rates of [3H]-thymidine incorporation into DNA and acid-soluble dTTP were compared between tumor and host mammary glands. The tumor differed from the host gland in that the rates of uptake and phosphorylation of the injected thymidine remained unchanged throughout the lactation cycle, but the dTTP pool increased greatly during pregnancy and declined during lactation. In both tumor and host gland, DNA labeling rates were higher during pregnancy than during lactation. Tumor DNA synthesis rates, in terms of incorporated dTMP, increased markedly during pregnancy and returned to pre-pregnant rates following parturition and during lactation. This pattern was similar to host mammary glands, but the change was of a greater magnitude. The data illustrate the usefulness of growing a transplantable mammary tumor in rats of varying physiological states. This way, similarities and differences between a mammary tumor and the host mammary gland regarding their responses to the hormonal milieu of pregnancy and lactation can be assessed.

[Mechanisms of action of estrogens physiological and pharmacological aspects of hormonal "receptivity". The anti-estrogens (author's transl)]

Receptivity to estrogens may indeed depend on the concentration of the corresponding receptor in the target cells. This concentration varies physiologically, and would possibly explain, at least in part, certain hormonal interactions and receptivity changes during the physiological cycles. The modifications of receptor concentrations could perhaps be of significance in explaining the effects of "priming" and the negative influence of one steroid on another. The simultaneous presence of different receptors for the same hormone or the competition of different hormones for the same receptor offer interesting pharmacological possibilities. It has already been shown that the characteristics of receptors can explain the differences between a natural hormone like estradiol and diethylstilbestrol, the hormone with the most common synthesis. A series of synthetic derivatives (triphenylethylene) seem to offer the possibility of an antagonist effect without pollution by significant estrogenic activity, and the potential therapeutic consequences are immense. Regulatory proteins, the steroid hormone receptors, provide some of the most advanced models for rational physico-chemical and physiological approaches to pharmacological and therapeutical problems.

Current status of estrogen and progesterone receptors in breast cancer

Breast cancer is often hormone responsive, since growth or regression of tumors can often be modulated by appropriate endocrine manipulations. Estrogen and progesterone appear to be major hormones involved in regulation of breast tumor growth. It has been recently argued that a more accurate marker of hormonal responsiveness might result if an end product of an intact estrogen response system were measured instead of the initial hormone binding step. Progesterone receptor (PgR) has been investigated in this regard since it can be readily measured in human breast tumors and there is clear evidence in experimental breast tumor model systems that PgR is under acute estrogen control. PgR is rarely found in ER- metastatic breast tumors but is present in approximately 59% of ER+ metastatic tumors, especially in those tumors with high levels of ER. Preliminary clinical correlation of ER, PgR and response to endocrine therapy is encouraging. The response rate is significantly higher if the tumor contains both ER and PgR than if the tumor contains ER alone.

On the mechanism of hormone action in 7,12 dimethylbenz(a)anthracene-induced mammary tumor. I. Prolactin and progesterone effects on estrogen receptor in vitro

The presence of ER in DMBA-tumors was demonstrated by the use of dextran-charcoal assay, sephadex chromatography, sucrose gradient sedimentation, and organ culture techniques. It was found that tumors have binding sites ranging from 10-13 to 10-15 moles/mg protein, and a dissociation constant of ER 10-9 to 10-10 M. In experiments with tumor explants, prolactin-insulin significantly stimulated ER binding capacity, as compared with control without prolactin. This stimulation was tissue-specific and inhibited by progesterone. Insulin had a synergistic effect on prolactin stimulation of ER. Our results presents a plausible explanation for tumor responses to these hormones in vivo. This interaction of prolactin, estrogen, and progesterone may be a common phenomenon for all estrogen-responsive tissues.

Androgen receptors: relationship to growth response and to intracellular androgen transport in nine variant lines of the Shionogi mouse mammary carcinoma

Aspects of the biological significance of androgen receptors have been studied in nine variant lines of the Shionogi carcinoma, two of which are androgen dependent and seven of which are autonomous. The dependent lines, and two of the seven autonomous lines, contain androgen receptors; this finding demonstrates that the presence of receptors is not an accurate marker of hormonal dependence in vivo. Since the ability to transport androgens into the nucleus, as judged from the relative maximal rates of transport, is virtually restricted to dependent and autonomous lines which possess cytoplasmic receptors, it is clear that such receptors may play a role in regulating the intranuclear concentration of androgens. The absence of cytoplasmic receptors and the comparative lack of perceptible transfer of androgens across the nuclear membrane are features peculiar to the autonomous condition.

Estrogen and estrogen receptors of breast cancer

Human breast cancer can be divided into a group that contains specific receptor sites for estrogen and a group without such specific estrogen-binding sites. The presence of specific estrogen receptors in some tumors indicating hormonal dependency has been shown to be of predictive value for endocrine treatment. This would greatly improve therapeutic planning for patients with breast cancer. Tumor tissue from 52 patients was investigated for content of both cytosol estrogen and estrogen receptor. In addition, the total tumor estrogen was also determined in 14 of these tumors. The results of this investigation show two distinct groups: one group containing both estrogen receptor and estrogen and a second group with no receptor but with measurable amount of estrogen. Tumors with estrogen receptors have higher tissue levels of estrogen than tumors without specific estrogen receptor. Even in the absence of estrogen recptor, however, most tumor tissue examined contained a measurable amount of estrogen.

Prolactin receptors in estrogen receptor-deficient mammary carcinoma

We demonstrate for the first time the presence of specific high-affinity receptors for prolactin in rat mammayy carcinoma. There appear to be no significant differences between normal rat mammary tissue and the transplantable, estrogen receptor-deficient R3230AC tumor with regard to the number of binding sites, the affinity of the receptor for prolactin, or the specificity of binding.

Estrogen receptors in human breast cancer

Specific quantitative techniques have been used to measure the cytoplasmic estradiol-binding protein (EBP) in human mammary carcinoma tissue specimens. Sucrose gradient centrifugation reveals EBP to sediment at 8S and 4S. Variable quantities of non-specific estradiol binding occurs in the 4S region of the sucrose gradient necessitating controls to insure specificity of the estradiol protein interaction. Using dextran-coated charcoal to separate bound from free estradiol Scatchard analysis finds the dissociation constant of the estradiol EBP interaction to be approximately 2.6x10(-10) M, indicative of the very high affinity of the ligand for the EBP. Quantitation of EBP sites in 64 primary and metastatic human breast tumors demonstrates a continuous spectrum of values from 0 to 612 fmol per mg of cytoplasmic protein. Specific 8S binding in the sucrose gradient centrifugation was not detected in specimens containing less than 9.0 fmol EBP per mg cytoplasmic protein. Since data from animal breast tumors and preliminary evidence from human breast tumors indicates an excellent correlation between the presence of abundant tumor EBP and endocrine-induced breast cancer regressions, precise quantitation of EBP in all human primary tumors may prove to be an excellent prognosticator of endocrine therapy in metastatic breast cancer.

Glucocorticoid receptors and the role of glucocorticoids in fetal lung development

The cellular mechanism of glucocorticoid effects upon fetal lung was examined in studies of specific binding activity for corticosteroids. Cytoplasm of fetal rabbit lung contains receptor sites for [(3)H]dexamethasone at a concentration of 0.43 +/- 0.04 pmol/mg of cytosol protein, and the apparent dissociation constant for the binding reaction is 2.7 +/- 0.4 nM. The ability of various steroids to compete with labeled dexamethasone for binding to receptor correlates with their biologic potency. The hormone-receptor complex formed in vitro at 0 degrees binds with high affinity at 20 degrees to isolated lung nuclei. It is estimated that there are 9500 nuclear binding sites and 12,000 cytoplasmic receptor sites per fetal lung cell. During the last 12 days of gestation in a rabbit, the concentration of cytoplasmic receptor in lung is constant and is 2- to 5-times greater than receptor-site concentration in fetal skin, kidney, heart, muscle, gut, liver, brain, thymus, and placenta. These findings demonstrate that the early steps in the mechanism of glucocorticoid action in target tissues are present in lung cells, and suggest that these hormones accelerate fetal lung differentiation and surfactant production in animals by the induction of new protein synthesis mediated by receptor.