Peter D. Feil

Aromatase activity in primary and metastatic human breast cancer

Aromatase activity was measured in 104 primary and 24 metastatic breast cancer patients. The assay employed quantitates the production of 3H water release from 1β‐[3H] androstenedione after aromatization. Of 104 human primary breast tumors studied, 64 contained measurable aromatase activity, ranging from 5–70.5 pmol estrone formed/g protein/hour. In primary breast cancers there was no difference in levels of aromatase activity when analyzed by menstrual status or age by decade. Aromatase activity was similar in small and large primary tumors. The median aromatase activity of primary breast tumors (8.6 pmol/g/h) was similar to that found in metastatic breast cancer deposits (12.0 pmol/g/h). Aromatase activity did not correlate with either estrogen (ER) or progesterone (PR) receptor concentration in the tissues assayed. In this regard there were 33 ER− PR− tumor biopsies. Twelve of these 33 tumors contained aromatase activity greater than 10 pmol/g/hour. Cancer 59:779‐782, 1987.

The in vivo regulation of the progesterone "receptor" in guinea pig uterus: dependence on estrogen and progesterone.

Abstract An assay for quantifying the high affinity progesterone binding protein in guinea pig uterine cytosol was developed using Florisil to separate bound and free steroid. The activity of the progesterone binding protein increased between 4–12 hours following estrogen administration and by 4 days of treatment was 10-fold higher than castrate controls. When estrogen administration was discontinued the progesterone binding activity declined slowly with a half-life of 3 days. By contrast, progesterone treatment caused a rapid decline of binding activity within 3 hours. These studies suggest that the antagonistic actions of estrogen and progesterone determine the quantity of available progesterone binding sites in guinea pig uterine cytosol.

Enzymatic Control of Estrogen Production in Human Breast Cancer: Relative Significance of Aromatase versus Sulfatase Pathways

One-third of the cases of breast cancer in postmenopausal women are hormone-dependent and the lesions regress upon treatment with antiestrogens or inhibition of estrogen biosynthesis. In these patients, estrogens are synthesized in extraglandular tissues from adrenal precursors and re-enter plasma to produce estrone levels of 52 +/- 6.5 pg/ml (mean +/- SEM) and estradiol concentrations of 13.1 +/- 0.7 pg/ml. However, the fact that the levels of estrogen in breast tumor tissue are an order of magnitude higher than plasma levels suggested the possibility of in situ estrogen production. To address this possibility, we measured several enzymes involved in estradiol biosynthesis in human tumors. Forty-eight of 61 tumors contained aromatase (estrogen synthetase) activity ranging from 5-80 pg/gm protein per hour. By comparison, the levels of estrone sulfatase were 10(6) higher, ranging from 0.8-125 micrograms/gm protein per hour. Because the sulfatase enzyme was of lower affinity (i.e., Km = 27 microM) than that of aromatase (i.e., 0.027 microM), the amount of estrogen formed under conditions of similar substrate concentrations was compared and found to be 10-fold higher via the sulfatase enzyme. In 41 additional tumors, the 17 beta-hydroxysteroid dehydrogenase enzyme, catalyzing the conversion of estrone to estradiol, was uniformly present. To test the biologic relevance of the estrone sulfate to estrone to estradiol pathway, estrogen-dependent nitrosomethylurea rat mammary tumors were grown in soft agar in the presence of estrone sulfate. Concentrations of estrone sulfate of 10(-6) microM significantly (p less than 0.01) stimulated colony formation in this system in which 75.5-98.6% of estrone sulfate was converted to estrone and 0.2 to 6% to estradiol. These data support the hypothesis that mammary carcinomas can synthesize estradiol in situ from circulating estrogen precursor and that local conversion is biologically important. On the basis of comparative data, the estrone sulfate to estrone to estradiol pathway is quantitatively more important than that involving androstenedione to estrone to estradiol.

Estrone sulfate: A potential source of estradiol in human breast cancer tissues

SummaryLocal formation of estradiol in human breast tumors could provide a more important source of estrogen than is delivered from plasma. Prior studies have suggested that estrone is primarily synthesized from estrone sulfate. The enzyme 17β-hydroxysteroid dehydrogenase (HSD) would be required to convert estrone to estradiol.This study characterized HSD in 1000 × g supernatants from human breast tumors. Estradiol synthesis was linearly related to tissue concentration or time over the range studied. Cofactor requirements varied with estrone concentration. High and low affinity sites were found in 50% of tissues studied, while the remainder contained only low affinity sites. Screen assays showed measurable activity in all 42 samples tested. This activity ranged from 0.73−>100 nmol estrone synthesized/g protein/hr, with a median activity of 5.9 nmol/g/hr.We evaluated the biological relevance of the sulfatase-HSD pathway by testing the ability of estrone sulfate to stimulate colony formation in soft agar cultures of nitrosomethylurea-induced rat mammary tumors. The maximally effective concentration ranged from 10−7 to 10−4 M. Significant stimulation of colony formation was observed in 7 of 8 experiments. The estrone sulfate stimulation pattern was similar to that previously observed with estradiol. Of the3H-estrone sulfate added to the dishes, 20–98% was recovered as estrone and 0.2–6% as estradiol. These studies suggest that the requisite enzymes are present in human breast tumors for conversion of estrone sulfate to estradiol, and that this pathway may be biologically significant.

Marked heterogeneity of aromatase activity in human malignant melanoma tissue

The prognosis from human malignant melanoma varies according to sex and to multiple histologic, biologic and cell kinetic parameters. Thus melanomas exhibit a major degree of heterogeneity in their biologic properties and further characterization of their biochemical heterogeneity should yield important information. The present study sought to demonstrate the activity of a biochemical marker of estrogen synthesis, the aromatase enzyme, in melanoma tissue and to determine its range of activity. Initially, we validated a highly sensitive radiometric assay for aromatase by comparing it with a direct product isolation method. We detected production of 417 pmol/g protein/h of estrone and 37.3 pmol/g protein/h of estradiol by direct product isolation in a human melanoma and 398 pmol estrone/g protein/h by the radiometric assay. The activity present was blocked by similar amounts of the aromatase inhibitor, aminoglutethimide, as were necessary to block placental, breast cancer, and rat brain aromatase activity. We then assayed aromatase radiometrically in 19 human melanomas and found measurable activity ranging from 9 to 398 pmol estrone/g protein/h in 15 tissues. No relationship with the patients age or sex was demonstrated. The activity exceeded by 2-fold that previously detected in 49/61 human breast cancers. This study identified a marker enzyme in melanoma tissue which varied by 40-fold among human tumors. Correlation of aromatase activity with prognosis and response to various types of therapy is now necessary to establish the biologic relevance of this finding.

FACTORS THAT INFLUENCE STEROID INDUCTION OF ENDOMETRIAL GLYCOGENESIS IN ORGAN CULTURE

Studies of progesterone action on chick oviduct have suggested that hormonestimulated differentiation is mediated via steroid receptor interaction with the genome.’ The mechanism of action of progesterone on the mammalian uterus, however, is less well understood, due in part to its broad spectrum of activities. Progesterone can stimulate uterine growth,2 inhibit c~n t r ac t ion , ’~~ potentiateS or inhibit actions of e s t r ~ g e n , ~ , ~ and increase specific uterine proteins, such as blastokinin.*s9 In addition, progestins promote the formation of a secretory endometrium, an event required for ovum implantation and pregnancy.1°-12 One of the features of the latter steroid-mediated response is the accumulation of endometrial g1yc0gen.I~ The specificity of this effect suggested that it might be used to study the action of progesterone on the uterus. Experiments with fragments of human endometrium indicated that progesterone-induced glycogenesis can be studied in vitro. 14*15 There are several reasons, however, that make the use of human material inconvenient. First, the tissue supply is unpredictable. Second, the hormonal milieu of the tissue donors is variable, which alters both the endogenous glycogen levels and the amount of glycogen that endometrial explants will accumulate in culture. For studies on the mechanism of hormone-stimulated glycogenesis, it was important, therefore, to find an animal that could provide uniform endometrial fragments for in vitro experiments. The present study defines some of the factors that influence this response in guinea pig uterus. The results indicate that this in vitro system will provide both insight into the mechanism of steroid action and a simple bioassay of progestational activity.

Involvement of polyamines in the progestin-induced stimulation of endometrial glycogen synthesis during organ culture.

Abstract Addition of progesterone to an organ culture of endometrial fragments increased glycogen levels 2–3 fold. Concomitant with this increase in glycogen was an increase in S-adenosyl-L-methionine decarboxylase activity and the conversion of putrescine into spermidine. When an inhibitor of S-adenosyl-L-methionine decarboxylase, methylglyoxyl bis(guanylhydrazone), was added to the culture with progesterone, glycogen synthesis was blocked. Inhibition of glycogen synthesis was reversed by the addition of spermidine, suggesting that spermidine synthesis may be necessary for the progestin-induced accumulation of endometrial glycogen.

Effect of photoaffinity labeling on rabbit uterine progesterone receptor

Photoaffinity labeling with [17 alpha-methyl-3H]promegestone ([ 3H]R5020) is an effective technique for the covalent labeling of the progesterone receptor (PR), which allows monitoring of the steroid receptor complex under denaturing conditions. The present study was initiated to evaluate whether photolabeled PR could be used also as a marker for PR under nondenaturing conditions. Accordingly, the effect of irradiation on each component of the reaction was evaluated separately. When [3H]R5020 alone was irradiated, there was a rapid (less than 5 min), light dependent destruction of [3H]R5020, as evident from increased formation of a more polar tritiated product on TLC and a concomitant decrease in the ability of the irradiated preparation to bind to PR. When rabbit uterine PR was irradiated in the absence of steroid, a gradual decrease in the binding capacity was observed, reaching 70% of the nonirradiated control in 10 min. The optimal irradiation time for covalent [3H]R5020-PR complex formation was determined by irradiation for up to 5 min, and separation of the products by sodium dodecylsulfate (SDS)-polyacrylamide gel electrophoresis. Specific labeling of proteins of Mr 116,000 and 85,000 was observed, with the rate of labeling of the two being similar, and reaching a plateau by 4 min of irradiation. The photolabeling efficiency ranged from 2 to 12%. Sucrose gradient ultracentrifugation of photolabeled PR revealed that both the irradiated sample and the nonirradiated control sedimented to the same position. Subsequent SDS-polyacrylamide gel electrophoresis of the sucrose gradient peak from the photolabeled sample showed the presence of both labeled proteins of Mr 116,000 and 85,000. In addition, photolabeled rabbit uterine PR (Mr 116,000 and 85,000) could be immunoprecipitated with a guinea pig antiserum raised against rabbit uterine PR. Analysis of the photoaffinity labeling procedure in our system revealed that the photodestruction of [3H]R5020 was very rapid. However, maximal labeling with [3H]R5020 was obtainable with minimal photodestruction of PR which suggests that photolabeled receptor can be used as a marker for PR under nondenaturing conditions.

17β-hydroxysteroid dehydrogenase in human breast cancer: Analysis of kinetic and clinical parameters

In this study, we assessed the rate of estradiol degradation via the 17 beta-hydroxysteroid dehydrogenase (HSD) enzyme in breast tumors from postmenopausal women. We initially studied the effects of time, level of enzyme activity, amount of tissue assayed, and substrate concentration on the linearity of conversion of estradiol to estrone in breast tumor homogenates. The reaction was demonstrated to be linear when less than 15% conversion of estradiol to estrone occurred over 30 min with homogenates produced from 2.5 mg of tissue. Detailed kinetic experiments demonstrated the presence of two classes of enzyme activity, one with high affinity and the other with low affinity. In 83% of the tumors examined, the high affinity form was present and had a median Km of 0.62 microM and Vmax of 82 nmol/g protein/h. In 29 tumors, HSD activity could be precisely quantified and correlated with clinical parameters. No statistically significant correlation of enzyme activity with estrogen receptor (r2 = 0.06) or progesterone receptor (r2 = 0.006) or with patient age could be detected (r2 = 0.001). In 12 additional tumors, activity exceeded 15% conversion of estradiol to estrone at 30 min and precise quantitation was not possible. The average content of progesterone receptor was similar for these 12 tumors as for the 19 with lower HSD activity. However, estrogen receptor content and patient age were lower in the group with high HSD activity. The finding of a high affinity form of HSD in this study provides support for the biological importance of this enzyme in breast cancer tissues.

Concomitant existence of carcinoma and secretory endometrium.

Abstract Two cases of endometrial adenocarcinoma concurrent with secretory endometrium are described. The theory that the side effects of continuous estrogenic exposure can be averted by periodic interruption with progestins is also discussed.