Mechanisms of the actions of aromatase inhibitors 4-hydroxyandrostenedione, fadrozole, and aminoglutethimide on aromatase in JEG-3 cell culture

Selective inhibition of estrogen production with aromatase inhibitors has been found to be an effective strategy for breast cancer treatment. Most studies have focused on inhibitor screening and in vitro kinetic analysis of aromatase inhibition using placental microsomes. In order to determine the effects of different inhibitors on aromatase in the whole cell, we have utilized the human choriocarcinoma cell line, JEG-3 in culture to compare and study three classes of aromatase inhibitors, 4-hydroxyandrostenedione, fadrozole (CGS 16949A), and aminoglutethimide. Fadrozole is the most potent competitive inhibitor and aminoglutethimide is the least potent among the three. However, stimulation of aromatase activity was found to occur when JEG-3 cells were preincubated with aminoglutethimide. In contrast, 4-OHA and fadrozole caused sustained inhibition of aromatase activity in both JEG-3 cells and placental microsomes, which was not reversed even after the removal of the inhibitors. 4-OHA bound irreversibly to the active site of aromatase and caused inactivation of the enzyme which followed pseudo-first order kinetics. However, 4-OHA appears to be metabolized rapidly in JEG-3 cells. Sustained inhibition of aromatase induced by fadrozole occurs by a different mechanism. Although fadrozole bound tightly to aromatase at a site distinct from the steroid binding site, the inhibition of aromatase activity by fadrozole does not involve a reactive process. None of the inhibitors stimulated aromatase mRNA synthesis in JEG-3 cells during 8 h treatment. The stimulation of aromatase activity by AG appeared to be due to stabilization of aromatase protein. According to these results, 4-OHA and fadrozole would be expected to be more beneficial in the treatment of breast cancer patients than AG. The increase in aromatase activity by AG may counteract its therapeutic effect and might be partially responsible for relapse of breast cancer patients from this treatment.

[P53 expression and clinical significance in oral squamous cell carcinoma]

P53 protein expression was investigated in oral squamous cell carcinomas and oral premalignant lesions by monoclonal antibody Do-1 and immunohistochemistry technique. 4 of 12 (33.3%) samples of severe epithelial dysplasia and 25 of 44 (56.8%) samples of squamous cell carcinoma expressed P53 protein while all the normal mucosa, mild and moderate epithelial dysplasia were negative. The P53 expression in carcinomas was associated with differentiation, lymph node metastasis and tumour stage. This result indicated that P53 genic mutation might be an early event in oral mucosa carcinogenesis and related to oral tumor progression. Detection of P53 protein probably has clinical significance in identifying the premalignant lesions of oral mucosa and predicting the prognosis of oral carcinomas.

Estrogen production via the aromatase enzyme in breast carcinoma: which cell type is responsible?

Studies of breast tumor homogenates from women with breast cancer have demonstrated the synthesis of estrogens in situ through the enzyme aromatase. The present series of investigations sought to determine which cell type within the tumor is responsible for local estrogen biosynthesis, and whether or not the amount produced is biologically important. Accordingly, we utilized an indirect immunohistochemical scoring method (H-score) to determine the relative amount of enzyme present in tumor epithelial and stromal cells. This revealed a value of 13 for tumor stromal cells and 4.8 for the epithelial component. Contributing to this difference is the fact that a greater percentage of cells in the tumor were stromal (45%) than epithelial (37%). To obtain direct evidence that tumor stromal cells could synthesize estrogens, we isolated and grew these cells in tissue culture. Stromal cells originating from within the tumor could be stimulated by known enhancers of transcription to produce nearly as much aromatase as is found in placental microsomes. Stromal cells isolated from benign tissue distal to the tumor exhibited properties similar to those of the tumor stroma. Epithelial cells, in contrast, did not respond to these enhancers and had low levels of aromatase basally. To obtain proof of the principle that local estrogen synthesis can be biologically meaningful, we measured tumor tissue estradiol levels and growth rates in aromatase-transfected MCF-7 cells implanted into nude mice. Local synthesis resulted in tumor levels ranging from 300 to 800 pg/g and growth rates substantially higher than in non-aromatase-containing tumors. These data suggest that tumor stromal cells contribute the major portion of estrogen synthesized in tumors, and that this local synthesis can increase tumor estradiol levels and growth rates.

Aromatase inhibitors: rationale for use following antiestrogen therapy

One third of breast cancers are hormone dependent and regress on blockade of estrogen biosynthesis or receptor-mediated action. Several hormonal approaches are available to accomplish these goals, including use of the antiestrogen tamoxifen and administration of inhibitors of aromatase, the rate-limiting enzyme for estrogen biosynthesis in postmenopausal women. Empirical observations demonstrate that women who respond to an initial hormonal therapy may experience secondary or tertiary tumor regressions when given additional endocrine-based therapies. The mechanistic basis for sequential responses to hormonal therapies is incompletely understood at the present time. In this report, we synthesize information from multiple sources to raise a hypothesis that could explain secondary hormonal responses in patients with breast cancer. The hypothesis postulates that tumor cells adapt to a deprivation in estrogenic stimulation by developing hypersensitivity to the residual levels of estrogen present. The process of hypersensitivity could result either from an absolute lowering of estrogen levels as induced by surgical oophorectomy or from interference of the estrogen response pathway by antiestrogens. This hypothesis, if correct, would explain why women respond to aromatase inhibitors secondarily after experiencing tumor regression following oophorectomy or tamoxifen therapy. This report summarizes studies documenting the development of enhanced estradiol sensitivity in cells grown in culture. This process is dynamic and reproducible on serial estrogen deprivation and re-exposure. We postulate that enhanced sensitivity to precursors of estradiol could also be induced by estrogen deprivation. With this adaptive mechanism, tumors would synthesize greater amounts of estrogen locally in the tumor after a period of estrogen deprivation. Enhancement of the amount or activity of the enzyme aromatase is one possible means of tumor adaptation. As a tool to evaluate this possibility, a new nude mouse model for postmenopausal breast cancer has been developed. In this model, the major source of tumor estrogen is that locally produced through conversion of androstenedione to estrone through the aromatase pathway. Studies using this model demonstrate higher antitumor potency of aromatase inhibitors than tamoxifen and have implications regarding combination therapy with both aromatase inhibitors and antiestrogens. This model will serve as a basis for future studies of the potential regulation of intratumoral aromatase.

Expression of aromatase protein and messenger ribonucleic acid in tumor epithelial cells and evidence of functional significance of locally produced estrogen in human breast cancers

The expression of aromatase by breast cancer cells and the role of locally produced estrogen in the stimulation of tumor growth has been controversial. The present study was performed to determine the site of aromatization in human breast cancers, using both immunocytochemistry and in situ hybridization. The functional significance of locally produced estrogens on growth of the tumor was addressed by measuring aromatase activity and a marker of proliferation (PCNA score). In addition, histocultures of some tumors were carried out to investigate whether testosterone aromatization could stimulate tumor proliferation. Of the 19 tumors investigated, 10 (52.6%) showed significant immunoreactivity to antiaromatase antibody in the cytoplasm of tumor epithelial cells and in surrounding stromal cells. The presence of aromatase mRNA detected by ISH was also located in tumor epithelial cells and stromal cell, and the pattern of expression was the same as with immunocytochemistry. In the ten tumors that showed immunoreaction to aromatase, the average aromatase activity measured in cryosections was 286.5 +/- 18.6 (SE) fmol estrogen/mg protein.h, whereas in nine tumors with weak aromatase immunoreaction, the enzyme activity was 154.7 +/- 19.3 (SE) fmol estrogen/mg protein-h (P < 0.05). The mean PCNA score was 33.8 +/- 5.1 (SE)% in strongly stained tumors and 20.8 +/- 2.0 (SE)% in weakly stained tumors (P < 0.05). Aromatase activity level and PCNA score were significantly correlated. In histoculture of four tumors, estradiol increased the incorporation of [3H]-thymidine into DNA. In two of these tumors, aromatase activity was high and [3H]-thymidine incorporation into DNA was also stimulated by testosterone. In the other two tumors that had low aromatase activity, no such stimulation occurred with testosterone. The results indicate that aromatase is expressed mainly in tumor epithelial cells and that sufficient amounts of estrogen are synthesized by the tumor to produce a proliferative response. It is concluded that estrogen synthesis by cancer cells could play a important role in promoting growth in a significant proportion of breast tumors.

Development of an avian model for restenosis

Recurrence of atherosclerotic plaque growth after interventional therapy, restenosis, is a significant clinical problem occurring in 20%-50% of cases. We have developed a new avian model for the investigation of restenosis after arterial injury in cholesterol fed White Leghorn roosters. Atherosclerotic plaque growth 1-30 weeks after angioplasty balloon mediated endothelial injury in the abdominal aorta was studied in 37 roosters. Roosters were maintained on either normal poultry diet or high cholesterol diet. Twelve cholesterol fed roosters were also fed a hormone supplemented diet in order to modify plaque morphology. The procedural success rate was high. Angiographic stenoses (mean 36% with maximum of 74%) were detectable in cholesterol fed roosters after balloon angioplasty with associated histological evidence of plaque growth (P < 0.017). Cholesterol feeding enhanced fatty plaque growth; hormone manipulation increased calcific and ulcerated plaque but with high associated morbidity. Three interventional devices were subsequently examined in 32 roosters (16 laser angioplasty, 7 atherectomy, and 9 stent implant). Plaque development was again assessed by contrast angiography and histological analysis. We conclude that balloon mediated arterial injury in cholesterol fed roosters produces early proliferative and late, complex atherosclerotic lesions providing an inexpensive model for plaque development after intimal injury.

The human breast cell DNA synthesome: its purification from tumor tissue and cell culture

In this report, we describe for the first time the isolation and purification of a multiprotein complex for DNA replication from MDA MB-468 human breast cancer cells. This complex, which we designate the DNA synthesome, fully supports the in vitro replication of simian virus 40 (SV40) origin-containing DNA in the presence of the viral large T-antigen. Since the SV40 virus utilizes the host's cellular proteins for its own DNA replication, our results indicate that the DNA synthesome may play a role not only in viral DNA synthesis but in human breast cell DNA replication as well. Our studies demonstrate that the following DNA replication proteins constitute the DNA synthesome: DNA polymerase alpha, DNA primase, DNA polymerase delta, proliferating cell nuclear antigen, replication protein A, replication factor C, DNA topoisomerases I, II, and DNA polymerase epsilon. In addition, we successfully isolated the DNA synthesome from human breast tumor tissue as well as from xenografts from nude mice injected with the human breast cancer cell line MCF-7. The DNA synthesome purified from the breast cancer tissues fully supports SV40 DNA replication in vitro. Furthermore, our results obtained from a novel forward mutagenesis assay suggest that the DNA synthesome isolated from a nonmalignant breast cell line mediates SV40 DNA replication by an error-resistant mechanism. In contrast, the DNA synthesome derived from malignant breast cells and tissue exhibited a lower fidelity for DNA synthesis in vitro. Overall, our data support the role of the DNA synthesome as mediating breast cell DNA replication in vitro and in vivo.

Effect of aromatase inhibitors on growth of mammary tumors in a nude mouse model

The effects of aromatase inhibitors 4-hydroxyandrostenedione (4-OHA), CGS 16949A, and CGS 20267, and of the antiestrogen tamoxifen (TAM), were studied on the growth of human breast carcinoma in a nude mouse model. To simulate the postmenopausal breast cancer patient, tumors were formed from inoculates of MCF-7 cells transfected with the human aromatase gene to provide a source of non-ovarian estrogen in ovariectomized mice. Tumor growth was significantly inhibited by all treatments (P < 0.05). Greater reduction in growth occurred in mice treated with TAM combined with aromatase inhibitors than with TAM alone. Tumor progesterone receptor concentrations were unaltered by TAM treatment but were reduced by aromatase inhibitors. Progesterone receptor concentrations correlated with tumor growth. The greatest reduction occurred in tumors of CGS 20267-treated mice in which no progesterone receptors were detected. In the ovariectomized mice used in these studies, uterine weight was maintained by estrogen produced from the tumor. Uterine weight was reduced by aromatase inhibitors but not by TAM treatment. However, there was a significant increase in uterine weight in mice treated with the combination of TAM and 4-OHA. Thus, the agonist effect of TAM was evident when estrogen synthesis was inhibited. The results indicate that aromatase inhibitors have potent effects on mammary tumor growth but lack the estrogenic effects on the uterus observed with TAM. There appeared to be no significant benefit in combining TAM with 4-OHA over 4-OHA treatment alone.

Human testicular aromatase: immunocytochemical and biochemical studies

The location of the aromatase enzyme in the testes of human subjects ages 3 months to 72 yr was determined immunocytochemically using a monoclonal antibody specific to human aromatase. In addition, an assay was developed to measure aromatase activity in suspensions of cryosections in order to validate the presence and to quantitate the activity of aromatase in the sections. In mature testes, aromatase immunostain was always associated with Leydig cells and was absent from Sertoli cells. Aromatase activity ranged from 0.014-0.55 pmol estrogen per mg/h and was significantly correlated with the immunostain intensity (P < 0.02). Thus, the aromatase activity provided a semiquantitative estimate of the immunoreaction. Activity and immunostain intensity of aromatase did not correlate with increasing age. Rather, the highest levels were measured in four of six testes of men ages 18-20 yr, three of whom also had the strongest immunostain for aromatase. The Leydig cell clusters of these subjects were larger and more prominent than those in the other specimens. A low level of aromatase activity but no immunostain was detected in prepubertal testes. Aromatase was not detected by either method in normal tissue from the testis of a patient with testicular cancer.

A new nude mouse model for postmenopausal breast cancer using MCF-7 cells transfected with the human aromatase gene

MCF-7 cells transfected with human placental aromatase gene (MCF-7Ca cells) or cells transfected with plasmid vector only (MCF-7Cc cells) were inoculated into nude mice with Matrigel. Tumors formed from both MCF-7Ca and MCF-7Cc cells grew faster in intact mice than in ovariectomized mice, suggesting that the tumors maintained their responsiveness to estrogen stimulation and that their growth was supported by ovarian estrogen. Injections of androstenedione (0.1 mg/mouse/day) to provide the substrate for aromatization to ovariectomized mice bearing MCF-7Ca tumors accelerated their growth but did not affect growth of MCF-7Cc tumors. This result indicates that local production of estrogen by intratumoral aromatase was sufficient to stimulate tumor growth. When ovariectomized mice with MCF-7Ca tumors supplemented with androstenedione were treated with aromatase inhibitors 4-hydroxyandrostenedione (1 mg/mouse/day, s.c.) or CGS 16949A (0.5 mg/mouse/day, s.c.), or with the antiestrogen tamoxifen (10 micrograms/mouse/day, s.c.), tumor growth was significantly inhibited. Tumor aromatase activity measured at the end of treatment was also inhibited by 4-hydroxyandrostenedione when the mice were sacrificed 4 h after the last injection. The tumors of this mouse model are dependent for their growth on estrogens from an endogenous nonovarian source. Thus, it simulates the situation in the postmenopausal breast cancer patient and could be used to evaluate the effect of aromatase inhibitors and antiestrogens.

Detection of aromatase and keratinocyte growth factor expression in breast tumors using reverse transcription-polymerase chain reaction

It has been proposed that local production of estrogen may contribute to breast tumor growth, in part by regulating growth factor production. In view of this, we studied the expression of mRNAs for aromatase cytochrome P-450, the enzyme which catalyzes estrogen synthesis, and keratinocyte growth factor (KGF), a heparin-binding growth factor specific for epithelial cells, in breast tumors. In order to detect mRNAs of low-abundance, reverse transcription-polymerase chain reaction (RT-PCR) was used. RNA from breast tumors and normal breast tissue was reverse transcribed and then amplified using oligonucleotide primers for human aromatase or KGF. Twelve of 15 breast tumor samples yielded variable amounts of aromatase PCR product, but consistently strong KGF PCR signals. Of the three aromatase mRNA-negative samples, two gave weak KGF signals while one was negative for KGF. Both aromatase and KGF transcripts were also detected in all five normal breast tissue samples examined. These results indicate that a high proportion of breast tumors have the potential to produce aromatase and KGF, both of which could play important roles in their growth. The results also suggest that RT-PCR can be used to evaluate local expression of growth mediators in tumors.

MCF-7 human breast carcinomas in nude mice as a model for evaluating aromatase inhibitors

While hormone-dependent, mammary tumors induced with carcinogens (DMBA or NMU) in intact rats have been used extensively for studying aromatase inhibitors, there is currently no suitable model to investigate their effects in human breast cancers in vivo. While hormone responsive tumors can be formed in the athymic mouse using human breast carcinoma MCF-7 cells, due to the low ovarian estrogen production, tumor growth is induced with estradiol supplementation. Thus, this model is unsuitable for studies of aromatase inhibitors. We have induced tumors without the need for estrogen supplementation by co-inoculating MCF-7 cells with Matrigel, a basement membrane preparation, into intact athymic mice. In one experiment, 45 days after inoculation, mice were assigned to the control group or 4-hydroxyandrostenedione (4-OHA) (1 mg/day s.c.) treatment for 52 days. Tumor volumes in the control mice increased 672%, whereas tumor volumes in the treated mice did not change significantly (178.9 +/- 16.2 to 336.6 +/- 120 mm3). In the second experiment, 55 days after inoculation, groups of mice were treated with the antiestrogen, tamoxifen (5 micrograms/day s.c.) or vehicle (controls). Tumor volumes in the control mice increased 325% in 58 days, whereas there was no significant change in tumor volume in the tamoxifen treated group (338.8 +/- 55.3 to 330.6 +/- 84.9 mm3). The results suggest that (1) the tumors resulting from MCF-7 cells co-inoculated with Matrigel are estrogen-dependent and (2) tamoxifen and 4-OHA were effective in suppressing growth of these tumors. The results suggest that this model should be useful for evaluating the effects of aromatase inhibitors and for comparing breast cancer treatments.

Laser-induced fluorescence emission: I. The spectroscopic identification of fibrotic endocardium and myocardium

Laser-induced fluorescence has been developed as a guidance system for laser angioplasty. Laser ablation has been used for resection of arrhythmogenic ventricular scar. We have investigated the use of laser-induced fluorescence for the detection of fibrotic and ischemic changes in endocardium and myocardium. Fluorescence emission spectra from human necropsy specimens were correlated with histologic examination. Normalized fluorescence intensity detected from both the endocardial and the myocardial surfaces of the fibrotic ventricular specimens was significantly higher than that of corresponding normal specimens at 440 to 475 nm. Fibrotic endocardium could be identified by a fluorescence emission intensity ratio less than 1.5 for wavelength ratio 375/450nm. Acutely infarcted endocardium was recognizable by a ratio of 1.5 to 2.0. The specificity and sensitivity of detection of scarred endocardium was 70 and 100%, respectively. Fibrotic myocardium was also consistently identified by fluorescence spectroscopy.

CONCLUSION

Fluorescence emission spectroscopy can differentiate normal and fibrotic endocardium and myocardium, in vitro. This technique may be useful for guidance during laser ablation of arrhythmogenic ventricular scar.

[Acute toxicity testing (LD50) of Chinese mineral drugs]

Acute toxicity and LD50 of 62 mineral drugs were determined by ig, ip or iv in mice, in order to provide some guidelines for safety in clinical use, as well as for pharmacological and toxicological studies. In the present investigation, the difference in the acute toxicity and LD50 between raw drugs and medicines prepared by roasting is explained.