Anomalous origin of the anterior choroidal artery.

SUMMARY: We describe a very rare case of anomalous origin of the anterior choroidal artery. In our case the anterior choroidal artery arises from the internal carotid artery proximal to the posterior communicating artery.

Adaptive hypersensitivity to estrogen: mechanisms and clinical relevance to aromatase inhibitor therapy in breast cancer treatment.

Breast tumors in women can adapt to endocrine deprivation therapy by developing hypersensitivity to estradiol. For this reason, aromatase inhibitors can be effective in women relapsing after treatment with tamoxifen or following oophorectomy. To understand the mechanisms responsible, we examined estrogenic stimulation of cell proliferation in a model system and provided in vitro and in vivo evidence that long-term estradiol deprivation (LTED) causes "adaptive hypersensitivity". The primary mechanisms responsible involve up-regulation of ER alpha as well as the MAP kinase, PI-3 kinase, and mTOR growth factor pathways. ER alpha is 4-10-fold up-regulated and co-opts a classical growth factor pathway using Shc, Grb2, and Sos. This induces rapid non-genomic effects which are enhanced in LTED cells. Estradiol binds to cell membrane associated ER alpha, physically associates with the adaptor protein Shc, and induces its phosphorylation. In turn, Shc binds Grb2 and Sos which result in the rapid activation of MAP kinase. These non-genomic effects of estradiol produce biologic effects as evidenced by Elk activation and by morphologic changes in cell membranes. Additional effects include activation of PI-3 kinase and mTOR pathways through estradiol induced binding of ER alpha to the IGF-1 and EGF receptors. Further proof of the non-genomic effects of estradiol involved use of "designer" cells which selectively express ER alpha in nucleus, cytosol, and cell membrane. We have used a new downstream inhibitor of these pathways, farnesyl-thio-salicylic acid (FTS), to block proliferation in hypersensitive cells as a model for a potentially effective strategy for treatment of patients.

Adaptive hypersensitivity to estrogen: mechanism for superiority of aromatase inhibitors over selective estrogen receptor modulators for breast cancer treatment and prevention.

Clinical observations suggest that human breast tumors can adapt to endocrine therapy by developing hypersensitivity to estradiol (E(2)). To understand the mechanisms responsible, we examined estrogenic stimulation of cell proliferation in a model system and provided in vitro and in vivo evidence that long-term E(2) deprivation (LTED) causes "adaptive hypersensitivity". The enhanced responses to E(2) do not involve mechanisms acting at the level of transcription of estrogen-regulated genes. We found no evidence of hypersensitivity when examining the effects of E(2) on regulation of c-myc, pS2, progesterone receptor, several estrogen receptor (ER) reporter genes, or c-myb in hypersensitive cells. Estrogen deprivation of breast cells long-term does up-regulate both the MAP kinase and phosphatidyl-inositol 3-kinase pathways. As a potential explanation for up-regulation of these signaling pathways, we found that ERalpha is 4- to 10-fold up-regulated and co-opts a classic growth factor pathway using Shc, Grb-2 and Sos. This induces rapid non-genomic effects which are enhanced in LTED cells. E(2) binds to cell membrane-associated ERalpha, physically associates with the adapter protein SHC, and induces its phosphorylation. In turn, Shc binds Grb-2 and Sos, which results in the rapid activation of MAP kinase. These non-genomic effects of E(2) produce biological effects as evidenced by Elk activation and by morphological changes in cell membranes. Further proof of the non-genomic effects of E(2) involved use of cells which selectively expressed ERalpha in the nucleus, cytosol and cell membrane. We created these COS-1 "designer cells" by transfecting ERalpha lacking a nuclear localization signal and containing a membrane localizing signal. The concept of "adaptive hypersensitivity" and the mechanisms responsible for this phenomenon have important clinical implications. Adaptive hypersensitivity would explain the superiority of aromatase inhibitors over the selective ER modulators (SERMs) for treatment of breast cancer. The development of highly potent third-generation aromatase inhibitors allows reduction of breast tissue E2 to very low levels and circumvents the enhanced sensitivity of these cells to the proliferative effects of E(2). Clinical trials in the adjuvant, neoadjuvant and advanced disease settings demonstrate the greater clinical efficacy of the aromatase inhibitors over the SERMs. More recent observations indicate that the aromatase inhibitors are superior for the prevention of breast cancer as well. These observations may be explained by the hypothesis that estrogens induce breast cancer both by stimulating cell proliferation and by their metabolism to genotoxic products. The SERMs block ER-mediated proliferation only, whereas the aromatase inhibitors exert dual effects on proliferation and genotoxic metabolite formation.

Adaptive mechanisms induced by long-term estrogen deprivation in breast cancer cells.

Clinical observations suggest that human breast tumors can adapt in response to endocrine therapy by developing hypersensitivity to estradiol. To understand the mechanisms responsible, we examined estrogenic stimulation of cell proliferation in a model system and provided evidence that long-term deprivation of estradiol causes adaptive hypersensitivity. The enhanced responses to estradiol do not involve mechanisms acting at the level of transcription of estrogen regulated genes. We found no evidence of hypersensitivity when examining the effects of estradiol on regulation of c-myc, pS2, progesterone receptor, several ER reporter genes or c-myb in hypersensitive cells. On the other hand, deprivation of breast cells long term was found to up-regulate a separate pathway whereby the estrogen receptor co-opts a classical growth factor pathway and induces rapid non-genomic effects. Through this pathway, estradiol caused rapid activation of mitogen-activated protein (MAP) kinase. In exploring the mechanisms mediating this event, we found that estradiol binds to cell membrane associated estrogen receptors and causes phosphorylation of Shc, an adaptor protein usually involved in growth factor signaling pathways. ERalpha was found to complex with Shc under these conditions. In turn, Shc bound Grb-2 and Sos which resulted in the activation of MAP kinase. The pure antiestrogen, ICI 182,780, blocked several steps in the rapidly responding ER alpha, Shc, MAP kinase pathway. These non-genomic effects of estradiol produced biologic effects by activating Elk and by inducing morphologic changes in cell membranes. Using confocal microscopy, we demonstrated that estradiol caused a rapid alteration in membrane ruffling, the formation of pseudopodia and translocation of ER alpha to regions contiguous with the cell membrane. These morphologic effects could be blocked with a pure anti-estrogen. We conclude that long-term estradiol deprived cells utilize both genomic (transcriptional) and rapid, non-genomic estradiol induced pathways. We postulate that synergy between these two pathways acting at the level of the cell cycle is responsible for adaptive hypersensitivity.

[Clinical experience of intra-arterial chemotherapy for liver metastases of breast cancer patients].

The aim of this study was to evaluate retrospectively the effect of intra-arterial chemotherapy for liver metastases of breast cancer patients. Eleven patients treated between August 1991 and July 1997 at Keio University Hospital, Tokyo, Japan, were the subjects for this study. The duration of disease-free periods after the operation ranged from 9 to 78 months (median 27 months). The site of the recurrence was the liver alone in 6 cases, and the liver and lung in 1 case, bone in 1 case, lymph nodes in 2 cases, and a local region, in 1 case. The main drugs were adriamycin (ADM) and 5-fluorouracil (5-FU), administered in a single injection or continuously via an indwelling catheter in the hepatic artery. This method had a 36% response rate, including PR in 4 cases, NC in 3 cases and PD in 4 cases. The survival duration was 1 to 19 months (median 14 months) following this treatment, and 3 to 49 months (median 17 months) after the recognition of the recurrence. The only side effects of Grade 3 or 4 were leucocytopenia or granulocytopenia and nausea. These results suggest that intra-arterial chemotherapy for liver metastases of breast cancer patients may be an effective method for the control of liver metastases with minor side effects. However, further study may be necessary to establish methods to manage the indwelling catheter and to control patients with multiple metastases of the other organs, to improve the prognosis for recurrent breast cancer patients.

[Current status of adjuvant endocrine therapy for hormone responsive breast cancer].

Three important meetings on adjuvant hormone therapy for breast cancer were held recently: the 5th EBCTCG Meeting, NIH Consensus Meeting, 7th International Conference on Adjuvant Therapy of Primary Breast Cancer. The conclusions of these meetings are: 1. adjuvant hormone therapy should be indicated only for patients with estrogen/progesterone receptor positive cancer, 2. five years of tamoxifen is the standard care at present, 3. ovarian ablation by any means has been proved effective in premenopausal patients and LH-RH agonist should be given at least two years, and 4. aromatase inhibitors should not be used in clinical practice, because several prospective randomized trials are ongoing at present. The patients treated with LH-RH agonist combined with tamoxifen showed better relapse-free survival compared with LH-RH agonist alone in the INT-0101 trial. This was an important trial because combined hormone therapy had not been proven more effective than individual hormone therapy previously. Combined hormone therapy including LH-RH agonist may be considered in premenopausal patients. There is a growing consensus that chemotherapy is effective through the ovarian suppression. In this sense, hormonal therapy should be considered first for hormone responsive patients. On the contrary, standard chemotherapy has shifted from CMF combination to an anthracycline containing regimen. Chemoendocrine therapy may be considered in high risk patients.

Adaptive hypersensitivity to estradiol: potential mechanism for secondary hormonal responses in breast cancer patients.

Women with hormone dependent breast cancer initially respond to hormone deprivation therapy with tamoxifen or oophorectomy for 12-18 months but later relapse. Upon secondary therapy with aromatase inhibitors, patients often experience further tumor regression. The mechanisms responsible for secondary responses are unknown. We postulated that hormone deprivation induces hypersensitivity to estradiol. Evidence of this phenomenon was provided in a model system involving MCF-7 cells grown in vitro and in xenografts. To determine if the ER transcriptional process is involved in hypersensitivity, we examined the effect of estradiol on ER reporter activity, PgR, PS2, and c-myc as markers and found no alterations in hypersensitive cells. Next, we examined whether MAP kinase may be upregulated in the hypersensitive cells as a reflection of increased growth factor secretion or action. Basal MAP kinase activity was increased both in vitro and in vivo in hypersensitive cells. Proof of principle studies indicated that an increase in MAP kinase activity induced by TGFalpha administration caused a two- to three-fold shift to the left in estradiol dose response curves in wild type cells. Blockade of MAP kinase with PD98059 returned the shifted curve back to baseline. These data suggested that MAP kinase overexpression could induce hypersensitivity. To determine why MAP kinase was increased, we excluded constitutive receptor activity and growth factor secretion by the demonstration that the pure anti-estrogen, ICI 182780, could inhibit MAP kinase activation. We also excluded hypersensitivity to estradiol induced growth factor secretion, and thus MAP kinase activation, since estradiol stimulated MAP kinase at 24, 48, and 72 h at the same concentrations in hypersensitive as in wild type cells. Surprisingly, a series of experiments suggested that MAP kinase increased in hypersensitive cells as a result of estrogen activation via a non-genomic pathway. We examined the classical signal pathway in which SHC is phosphorylated and binds to SOS and GRB-2 to activate Ras, Raf, and MAP kinase. With 5-20 min of exposure, estradiol caused binding of SHC to the estrogen receptor, phosphorylation of SHC, binding of GRB-2 to SOS, and activation of MAP kinase. All of these affects could be blocked by ICI 182780. Taken together, these observations suggest that the cell membrane ER pathway may be responsible for upregulation of MAP kinase and hypersensitivity in cells adapted to estradiol deprivation.

Sentinel lymph node biopsy using tin colloid RI and blue dye method.

Axillary dissection has been considered essential for breast cancer staging because nodal metastasis is the most powerful predictive factor for recurrence. On the other hand, morbidity, such as lymphedema and shoulder dysfunction, may occur. Sentinel node biopsy is a good way to avoid unnecessary axillary dissection. We used tin colloid as a carrier of Tc99m tracer together with the blue dye method. The detection rate of the sentinel node was 27 cases out of 29 (90%) for the blue dye method, 10 cases out of 19 (53%) for the RI method, and 27 out of 33 (82%) for the combined method. The detection rate of the RI method was improved after adding the subcutaneous injection over the tumor from 45% before adding the subcutaneous injection to 82% after adding it. The false negative rate was 11% for the blue dye method, 0% for the RI method, and 10% for the combined method. This yields a sensitivity of 89% for the blue dye method, 100% for the RI method, and 90% for the combined method. Specificity was 100% for all three methods. Accuracy was 96% for the blue dye method, 100% for the RI method, and 96% for the combined method. There were two false negative cases. The average number of sentinel lymph nodes was 2.12 for the dye method, 1.66 for the RI method, and 1.95 for the combined method. There were three of 49 cases with identified parasternal lymph nodes by RI imaging. Lymphatic mapping using tin colloid may be useful for detecting sentinel nodes.

[Chemo/endocrine therapy for breast cancer patients].

Standard adjuvant chemo/endocrine therapy for breast cancer patient is based upon St. Gallen's consensus 1998. Recent development in the field of adjuvant chemo/endocrine therapy is an usage of LH-RH analogue with tamoxifen for premenopausal hormone receptor positive women, and also an emerging role of taxans. Orally given 5-FU derivatives may work in adjuvant settings. The third generation aromatase inhibitors have established their role in second line hormone therapy for the advanced or recurrent breast cancer patients. High dose chemotherapy should not be used in outside clinical trials.

[MRI of ductal carcinoma in situ of the breast: patterns of findings and evaluation of disease extent].

Ten cases of ductal carcinoma in situ (DCIS) or DCIS with microinvasion were reviewed in order to evaluate the characteristic findings of DCIS and to evaluate the extent of disease on MRI. A 1.5Tesla Signa or Horizon (GE Medical Systems) unit was used with a dedicated receive-only breast coil. The pulse sequence based on RARE was used with the fat suppression technique. After examining both breasts with a large FOV (30 cm), the affected breast alone was examined with a smaller FOV (18 cm) and larger matrix (512 x 384) with and without Gd-enhancement. DCIS showed several types of findings on MRI: linear, spotty enhancement; gathering of linear enhancement; enhanced area or mass without distortion of the surrounding tissue; and well-circumscribed mass mimicking intraductal papilloma. Compared with typical findings of invasive carcinoma, DCIS tended to be enhanced slowly. After performing MR examination in addition to mammography and ultrasonography, a more accurate diagnosis of disease extent was possible in 6 of 10 patients. MRI was useful in providing more precise information on the disease extent of DCIS, and it is considered useful in planning the type of surgery. Further study using larger series and precise pathological correlations are necessary.

Estradiol hypersensitivity and mitogen-activated protein kinase expression in long-term estrogen deprived human breast cancer cells in vivo.

Women with breast cancer who have responded to initial hormonal therapy frequently experience additional remissions upon further endocrine manipulation. We postulate that hypersensitivity to estradiol (E2) may serve as a mechanistic explanation for these secondary responses. We previously provided evidence of hypersensitivity using an in vitro breast cancer model system and demonstrated the role of mitogen-activated protein kinase (MAP kinase) in the process of adaptation to long-term estradiol deprivation. In the present study, we wished to demonstrate that hypersensitivity to E2 could occur under more complex in vivo conditions and that MAP kinase activation is enhanced under these circumstances. We used an MCF-7 breast cancer model system involving long-term estradiol deprived (LTED) cells to produce xenografts in nude mice and an E2 clamp method to precisely control sex steroid levels. The E2 clamp was designed to maintain plasma E2 at a series of doubling doses from 1.25 pg/ml to 20.0 pg/ml in oophorectomized nude mice. As evidence of the validity of the clamp method, a uterine weight bioassay revealed an excellent, linear dose-response relationship between the predicted level of plasma E2 and stimulation of uterine weight. As evidence of hypersensitivity, we found that LTED xenograft tumors grew to a greater extent than wild-type in response to E2 concentrations of 1.25 pg/ml (P = 0.003) and 2.5 pg/ml (P = 0.0002). At the 10.0 and 20.0 pg/ml plasma concentrations, the LTED tumors were stimulated to a lesser extent than the wild-type. This pattern of increased growth at lower concentrations and reduced growth vs. the wild-type at higher concentrations mimics closely the pattern seen for LTED cells in vitro. All LTED cell tumors exhibited enhanced activation of MAP kinase ranging from 18 to 25%, and E2 did not increase this further. In contrast, E2 caused a linear increase in the percentage of activated MAP kinase positive cells (P < 0.0001) in wild-type tumors from basal levels of 2.66% to maximal levels of 6.40%. These observations suggest a dynamic interplay whereby activation of MAP kinase renders cells more sensitive to the proliferative effects of E2. The precise mechanisms for this interplay are unknown but, when further understood, could potentially provide insight into approaches to prevent the evolution of tumors to a hormone insensitive state.

Determinants of tissue estradiol levels and biologic responsiveness in breast tumors.

Estradiol stimulates the growth of breast tumor cells in both pre- and post menopausal women. Following the menopause, the levels of estradiol in breast tumor tissues are similar to those from tumors obtained prior to cessation of ovarian function, even though plasma estrogen levels are 10-50 fold lower in post- than in premenopausal women. These observations suggested the possibility of enhanced estradiol uptake from plasma or in situ synthesis in post-menopausal women. We systematically studied these possibilities in a series of model systems. Initially we demonstrated a very high affinity estradiol binding site in tissues from castrated rats. Enhanced uptake occurred under conditions of low plasma estrogen levels when compared to animals with higher estradiol levels. In situ synthesis also occurred both through the sulfatase and aromatase pathways. In further studies, we compared uptake from plasma with in situ synthesis via aromatase in a nude mouse model. Under the conditions utilized, in situ synthesis resulted in much higher tissue estradiol levels and tumor growth rates than did uptake from plasma. During these studies we demonstrated that tumors deprived of estradiol developed mechanisms rendering them more sensitive to estrogen. This involved the ability of cells to adapt to estradiol deprivation to allow them to be responsive to four log lower amounts of estrogen than when studied under wild type conditions. In addition, cells adapted by increasing their level of aromatase and thus developing the capability to become more sensitive to estrogen precursors. Taken together, these studies demonstrate that breast cancer tissue is highly plastic and can adapt to conditions of estrogen deprivation via a variety of mechanisms.

Estrogen receptor expression and function in long-term estrogen-deprived human breast cancer cells.

Hormone-dependent breast cancer responds to primary therapies that block estrogen production or action, but tumor regrowth often occurs 12-18 months later. Additional hormonal treatments that further reduce estrogen synthesis or more effectively block its action cause additional remissions, but the mechanisms responsible for these secondary responses are not well understood. As a working hypothesis, we postulated that primary hormonal therapy induces adaptive changes, resulting in enhanced estrogen receptor (ER) expression and target gene activation and, further, that secondary treatment modalities interfere with these receptor-mediated transcriptional pathways. To test this hypothesis, we used an MCF-7 breast cancer model system involving deprivation of estradiol in culture for a prolonged period. These long-term estradiol-deprived (LTED) cells adapt by acquiring the ability to regrow in the absence of added estradiol. The experimental paradigm involved the comparison of wild-type cells with LTED cells. As endpoints, we directly assessed ER expression at the messenger RNA-, protein-, and ligand-binding levels and ER functionality by quantitating reporter gene activation and expression of endogenous estrogen target gene messenger RNA, as well as ER coactivator levels. Our data demonstrated an adaptive increase in ER expression and in basal ER functionality, as assessed by read-out of three different transfected reporters in LTED, as opposed to wild-type MCF-7 cells. Increased reporter gene read-out was dramatically inhibited by the pure antiestrogen ICI 182,780. As verification that endogenous (as well as transfected) estrogen target genes had enhanced transcription, we found that the basal levels of c-myb and c-myc message were substantially increased in LTED cells and could be inhibited by antiestrogen. Interestingly, the levels of c-myb and c-myc message in the LTED cells seemed to be increased out of proportion to the degree of ER reporter gene activation and were similar to those in wild-type cells maximally stimulated with estradiol. In addition, not all estrogen-responsive genes were activated, because transforming growth factor-alpha message level was not increased in LTED cells. Up-regulation of the steroid receptor coactivator SRC-1 did not seem to mediate the process of enhanced ER-induced transcription. Considering these observations together, we suggest that long-term estradiol deprivation causes adaptive processes that not only involve up-regulation of the ER but also influence the specificity and magnitude of activation of estrogen-responsive genes.

[Anticancer drug intraperitoneal chemotherapy using T-type reservoir sheet for unresectable gastric cancer].

T-type reservoir sheets (anti-adhesion sheets developed to prevent adhesions + reservoir) were intraperitoneally implanted in 16 patients with unresectable gastric cancer and postoperatively used to suction off ascitic fluid, to prevent cancerous adhesions of the intestines, and to intraperitoneally infuse anticancer drugs with a view to improving QOL and prolonging survival time. The results showed that whereas all of the patients had been class V according to intraoperative cytodiagnosis, postoperatively they were all class I-II and their ascites had either completely or temporarily resolved. Performance status (PS) improved in 14 patients (87.5%), and 14 patients (87.5%) were discharged. According to the Cancer Body Cavity Efficacy Rating Criteria (Japan Society for Cancer Therapy), CR was achieved in 10 cases, PR in 3 cases, NR in 3 cases, and the mean home care rate was 45.4%. Mean survival time to date, February 1997, is 7.8 months, two patients are alive, and the longest survival time has been 22 months. This method facilitates suctioning of ascitic fluid. It prevents irregular adhesions of the intestine, and protects against the development of ileus. It enables repeated intraperitoneal administration of high concentrations of anticancer drugs, uniformly, extensively, safely and easily. It facilitates intraperitoneal cytodiagnosis, ascitic fluid sampling, and monitoring of the efficacy of anticancer agents. The special features of this method are the high percentage of patients residing at home and the ability to administer intraperitoneal infusions of anticancer agents continually and repeatedly on an outpatient basis.

Mechanism for maintenance of high breast tumor estradiol concentrations in the absence of ovarian function: role of very high affinity tissue uptake.

Breast tumors from postmenopausal women contain levels of estradiol similar to those in premenopausal patients even though serum estradiol levels fall by an order of magnitude upon cessation of ovarian function. The present study sought to examine enhanced uptake from plasma as one potential mechanism for maintenance of high tissue estradiol levels in postmenopausal patients. Accordingly, we used osmotic minipumps to continuously infuse estradiol (E2) at rates producing serum concentrations ranging from pre- to postmenopausal levels for two weeks to oophorectomized Sprague-Dawley rats bearing nitrosomethylurea-induced mammary tumors. We then measured E2 concentrations in various tissues and sera and reasoned that tissue affinities for estradiol could be directly calculated from in vivo measurements by adapting Scatchard analysis to steroid infusion data. Using this method, we demonstrated a very high affinity estradiol binding component with a Kd two orders of magnitude higher (i.e., 0.35 x 10(-12) M) than determined with standard in vitro techniques. A second estradiol binding component with the expected Kd of 1 x 10(-10) M was also present. Estradiol bound to both classes of binding sites could be 98% displaced with diethylstilbestrol within a 6-hr period. In vivo steroid binding off-times calculated from log-linear slopes averaged approximately 60 min. These data demonstrated that the actual E2 binding affinity in target tissues in vivo, especially at low estrogen concentrations, is much higher than usually estimated from standard, in vitro estrogen receptor assays. These observations provide one mechanism to explain why estradiol concentrations remain high in breast cancer tissue from postmenopausal women and consequently can stimulate tumor proliferation.

Evidence of in situ estrogen synthesis in nitrosomethylurea-induced rat mammary tumors via the enzyme estrone sulfatase.

A variety of indirect evidence suggests that mammary tumors can synthesize free estrogens in situ via the sulfatase enzyme. The present study utilized an isotopic kinetic technique to provide direct confirmation of local tumor synthesis. Animals bearing nitrosomethylurea (NMU)-induced rat mammary tumors were infused with 14C-estrone as well as 3H-estrone sulfate and plasma:tissue gradients for each steroid measured. Liver, serving as a control tissue, uniformly synthesized free estrone from estrone sulfate with local synthesis in this organ providing an average of 78 +/- 1.0% of the estrone in this tissue. In rat mammary tumors, five out of seven synthesized estrone locally with individual values ranging from 19 to 50% synthesized in tissue. These data indicate that liver uniformly converts estrone sulfate to free estrone, whereas the majority, but not all, breast tumors synthesize estrogen locally via this pathway.

Estrogen deprivation causes estradiol hypersensitivity in human breast cancer cells.

Genetic and environmental factors can modulate the level of sensitivity to various hormones, including estrogens. Enhanced sensitivity to estradiol (E2) has been demonstrated in several biological conditions, such as in sheep during the nonbreeding season, in untreated patients with Turner's syndrome, and in the prepubertal state in normal girls. We postulated that secondary responses to hormonal therapy in patients with breast cancer could also result from enhanced E2 sensitivity, developing as an adaptive mechanism to E2 deprivation. The present study used the MCF-7 human breast cancer cell line as a model system to test the concept that enhanced sensitivity to E2 may occur as a result of adaptation to low E2 levels. After depriving MCF-7 cells of estrogens in tissue culture medium for periods of 1-6 months, we established conditions under which replication could be stimulated maximally by 10(-14)-10(-15) mol/L E2. In contrast, wild-type cells not exposed to estrogen deprivation required 10(-10) mol/L E2 to grow at the same rate. Further, the concentration of the antiestrogen, ICI 164384, needed to inhibit growth by 50% in estrogen-deprived cells was much lower than that required in wild-type cells (i.e. 10(-15) vs. 10(-9) mol/L). Nude mice implanted with these estrogen-deprived cells demonstrated an earlier appearance of palpable tumors in response to E2 than animals bearing wild-type cells. Reexposure to 10(-10)-10(-9) mol/L E2, either in vivo or in vitro, returned these cells to the level of estrogen sensitivity observed in wild-type cells. Taken together, these observations suggest that breast cancer cells can adapt to low levels of estrogens by enhancing their sensitivity to E2.

Aromatase inhibitor development for treatment of breast cancer.

Inhibition of estrogen production provides effective therapy for patients with hormone-dependent breast cancer. The source of estrogens in premenopausal women is predominantly the ovary, but after the menopause, estradiol is synthesized in peripheral tissues through the aromatization of androgens to estrogens. Uptake from plasma is the primary mechanism for maintenance of estradiol concentrations in breast cancer tissue in premenopausal women, whereas several steps may be operant in postmenopausal women. These include enzymatic synthesis of estradiol via sulfatase, aromatase, and 17 beta-hydroxysteroid dehydrogenase in the tumor itself. Aromatization of androgens secreted by the adrenal to estrogens in peripheral tissues and transport to the tumor via circulation in the plasma provides another means of maintaining breast tumor estradiol levels in postmenopausal women. These various sources contribute to the high tissue estrogen levels measured in breast tumor tissue. To effectively suppress tissue concentrations of estrogens and circulating estradiol in postmenopausal patients, various aromatase inhibitors have been developed recently. These include steroidal inhibitors such as 4-hydroxy-androstenedione as well as non-steroidal compounds with imidazole and triazole structures. The most potent of these, CGS 20267, is reported to suppress levels of active estrogens (i.e., estrone, estrone sulfatase, and estradiol) by more than 95%. This compound can suppress both serum and 24-hr urine estrogens to a greater extent than produced by the second generation inhibitor, CGS 16949A. CGS 20267 is highly specific since it does not affect cortisol and aldosterone serum levels during ACTH stimulation tests nor sodium and potassium balance in 24-hr urine samples.(ABSTRACT TRUNCATED AT 250 WORDS)