Estrogen and progesterone receptors in human breast cancer. Correlation with histologic subtype and degree of differentiation

Microscopic review of 490 consecutive human breast biopsy and mastectomy specimens were correlated with estrogen and progesterone receptor content of the tissue, by subtype and degree of differentiation. Of the 4 grades of differentiation, the less differentiated Grade III and IV tumors showed significantly lower levels of estrogen and progesterone receptors in infiltrating ductal and lobular carcinoma (P less than 0.001). In contrast, patients with medullary carcinoma had the lowest tissue levels of estrogen and progesterone receptors with approximately 80% of the cases with less than 10 fmol/mg protein. Patients with mucinous carcinoma had the highest percentages of positive estrogen and progesterone receptor levels (75% and 87%, respectively). Sixty-three percent of the patients with Grade IV infiltrating ductal carcinoma were younger than 53 years of age (P less than 0.001). Patients younger than 53 years of age with Grade II and III infiltrating ductal carcinoma also had significantly lower levels of estrogen receptors, but not of progesterone receptors, than those patients older than 53 years of age (P less than 0.001). Nineteen of 20 "normal" breast tissue specimens were negative (less than 3 fmol/mg protein) for estrogen and progesterone receptors. About 50% of 17 tissue specimens from benign breast lesions (fibroadenoma, fibrocystic disease, sclerosing adenosis) showed positive estrogen (greater than 10 fmol/mg protein) or progesterone receptor values. In two patients with gynecomastia, no estrogen or progesterone receptors were detectable.     

Progesterone crosstalks with insulin-like growth factor signaling in breast cancer cells via induction of insulin receptor substrate-2

Both progesterone and the insulin-like growth factors (IGFs) are critically involved in mammary gland development and also in breast cancer progression. However, how the progesterone and IGF signaling pathways interact with each other to regulate breast cancer cell growth remains unresolved. In this study, we investigated progesterone regulation of IGF signaling components in breast cancer cells. We found that insulin receptor substrate-2 (IRS-2) levels were markedly induced by progesterone and the synthetic progestin R5020 in MCF-7 and other progesterone receptor (PR) positive breast cancer cell lines, whereas IRS-1 and the IGF-I receptor were not induced. The antiprogestin RU486 blocked the R5020 effect on IRS-2 expression. Ectopic expression of either PR-A or PR-B in C4-12 breast cancer cells (estrogen receptor and PR negative) showed that progestin upregulation of IRS-2 was mediated specifically by PR-B. The IRS-2 induction by R5020 occurred via an increase of IRS-2 mRNA levels. Furthermore, progestin treatment prior to IGF-I stimulation resulted in higher tyrosine-phosphorylated IRS-2 levels, increased binding of IRS-2 to Grb-2 and the PI3K regulatory subunit p85, and correspondingly enhanced ERK and Akt activation, as compared with IGF-I-only conditions. Taken together, our data suggest that IRS-2 may play an important role in crosstalk between progesterone and the IGFs in breast cancer cells.     

Selective loss of AKR1C1 and AKR1C2 in breast cancer and their potential effect on progesterone signaling

Progesterone plays an essential role in breast development and cancer formation. The local metabolism of progesterone may limit its interactions with the progesterone receptor (PR) and thereby act as a prereceptor regulator. Selective loss of AKR1C1, which encodes a 20alpha-hydroxysteroid dehydrogenase [20alpha-HSD (EC 1.1.1.149)], and AKR1C2, which encodes a 3alpha-hydroxysteroid dehydrogenase [3alpha-HSD (EC 1.1.1.52)], was found in 24 paired breast cancer samples as compared with paired normal tissues from the same individuals. In contrast, AKR1C3, which shares 84% sequence identity, and 5alpha-reductase type I (SRD5A1) were minimally affected. Breast cancer cell lines T-47D and MCF-7 also expressed reduced AKR1C1, whereas the breast epithelial cell line MCF-10A expressed AKR1C1 at levels comparable with those of normal breast tissues. Immunohistochemical staining confirmed loss of AKR1C1 expression in breast tumors. AKR1C3 and AKR1C1 were localized on the same myoepithelial and luminal epithelial cell layers. Suppression of ARK1C1 and AKR1C2 by selective small interfering RNAs inhibited production of 20alpha-dihydroprogesterone and was associated with increased progesterone in MCF-10A cells. Suppression of AKR1C1 alone or with AKR1C2 in T-47D cells led to decreased growth in the presence of progesterone. Overexpression of AKR1C1 and, to a lesser extent, AKR1C2 (but not AKR1C3) decreased progesterone-dependent PR activation of a mouse mammary tumor virus promoter in both prostate (PC-3) and breast (T-47D) cancer cell lines. We speculate that loss of AKR1C1 and AKR1C2 in breast cancer results in decreased progesterone catabolism, which, in combination with increased PR expression, may augment progesterone signaling by its nuclear receptors.     

Modulation of Adriamycin Resistance in Human Breast Carcinoma MCF-7 Cells in vitro and in vivo by Medroxyprogesterone Acetate

The combination effect of adriamycin (ADM) and medroxyprogesterone acetate (MPA) was examined in vitro against human breast carcinoma MCF-7 and its ADM-resistant line (MCF-7/ADM). MCF-7 cells, which are positive for estrogen receptors, progesterone receptors and high-affinity MPA-binding activity, were more susceptible to the growth-inhibitory activity of ADM or MPA than MCF-7/ADM cells. A combination effect of ADM and MPA was observed against MCF-7/ADM cells, which are negative for steroid receptors, and furthermore against human nasopharynx carcinoma KB and its ADM-resistant line KB-A1. This combination effect of ADM and MPA against MCF-7/ADM cells was demonstrated to be synergistic by using the median effect plot method. The activity of MPA was almost equivalent to that of chlormadinone acetate or tamoxifen, greater than that of progesterone, and less than that of verapamil. The accumulation of ADM in MCF-7/ADM cells was enhanced by treatment with 10 μ M MPA as well as 10 μ M verapamil. The efflux of accumulated ADM from MCF-7/ADM cells was also partially inhibited by treatment with MPA or verapamil. MPA augmented the growth-inhibitory activity of ADM against MCF-7/ADM tumors inoculated into nude mice, although statistical significance was not observed. It is suggested that the clinical advantage of the combination of MPA with ADM against advanced breast cancers may be partly explained by the modulation of ADM resistance by MPA.     

THE EFFECTS OF ESTRADIOL ON BREAST CANCER CELL LINES

The estradiol effects on breast cancer cell lines including estrogen receptors (ER) positive and negative were studied with flow cytometry analysis, scanning and transmission electron microscopy (SEM and TEM), immunogold and immunofluorescence staining techniques. The results showed that estradiol markedly stimulated the division and proliferation of the ER( ) MCF-7 cells at 10 nM, but had no marked effect on the cell cycle of the ER(-) H466B cells at the same concentration, and that tamo-xifen inhibited the stimulation of estradiol on MCF-7 cells. Estradiol obviously influenced the ultrastruc-ture of MCF-7 cells. Immunocytochemical localization of epidermal growth factor receptor (EGFR) on the MCF-7 cell membrane surface indicated that one of the mechanisms involving the growth of MCF-7 breast cancer cell and the stimulating effect on MCF-7 cells growth by estradiol is autocrine secretion.     

Changes in Radiation Sensitivity and Steroid Receptor Content Induced by Hormonal Agents and Ionizing Radiation in Breast Cancer Cells in Vitro

Possible influences of tamoxifen and estradiol on in vitro radiation sensitivity and cellular receptor content after irradiation and/or tamoxifen treatment were studied in breast cancer cell lines; estrogen receptor (ER) and progesterone receptor (PgR) positive cell lines MCF-7 and MCF-7/TAM^R-1 and the ER and PgR negative cell line MDA-MB-231. The tamoxifen resistant MCF-7/TAM^R-1 cells were more resistant to ionizing radiation than the MCF-7 and MDA-MB-231 cells. Exposure to tamoxifen made the MCF-7 cells more radiation resistant, while estradiol made the MDA-MB-231 cells more radiation sensitive. A radiation dose of 6 Gy reduced the ER content in cytosol in both MCF-7 and MCF-7/TAM^R-1 cells, but brought no alterations to the PgR content. In MCF-7/TAM^R-1 cells tamoxifen exposure significantly increased the ER and reduced the PgR content, an effect not observed in the MCF-7 cells. To conclude, the present study indicates that irradiation and tamoxifen may modify the ER and PgR content in cytosol in breast cancer cells. Hormonal treatment may alter the radiation sensitivity, even in ER negative cells, suggesting that hormonal agents may act both via receptor and non-receptor binding mechanisms.     

T1N0M0乳腺癌的激素受体状况对预后的影响

对４８例Ｔ１Ｎ０Ｍ０乳腺癌患者进行激素受体与预后关系的分析，平均随诊时间为８．５年，全部病例行改良根治术，术后均未进行辅助治疗。雌激素受体或孕酮受体阳性组病例的无复发，生存率明显优于相应之阴性组病例。初步认为Ｔ１Ｎ０Ｍ０浸润性乳腺癌病例的雌激素及／或孕酮受体阴性者应进行术后化疗。     

The relationship between somatostatin, epidermal growth factor, and steroid hormone receptors in breast cancer

The somatostatin (SS) and the epidermal growth factor (EGF) receptor content have been established in 36 primary breast cancers by receptor autoradiography on adjacent tissue sections. Iodine 125 (125I)-EGF was used as radioligand for EGF receptor visualization whereas an iodinated SS-28 analogue or an octapeptide SS analogue were used to measure SS receptors. Six of 36 tumors contained SS receptors, whereas ten of the 36 tumors were shown to contain EGF receptors. None of the tumor samples containing SS receptors were simultaneously EGF receptor positive. In contrast, all SS receptor-positive tumors simultaneously contained steroid receptors. The positive correlation between SS receptors and steroid receptors as well as the negative correlation between SS receptors and EGF receptors therefore suggest that the small percentage of SS receptor-positive breast tumors are a group of differentiated breast tumors with a good prognosis. In these cases, combined hormonetherapy including SS analogs may be of potential interest.     

Response of human lung tumor xenografts to treatment with a somatostatin analogue (Somatuline)

Four human small cell lung carcinomas, NCI-H69, NCI-N417, NCI-H345, LX-1, and a non-small cell lung carcinoma, H-165, implanted s.c. as tumor xenografts in athymic nude mice, were treated with Somatuline (BIM-23014C), an endocrinologically potent octapeptide analogue of somatostatin. All tumors responded, although in varying degrees, with percentage of test/control values ranging from 3 to 88. Somatuline administered as a perilesional infusion effectively inhibited xenograft growth inducing prolonged remissions. When treatment was terminated, some tumors regrew, suggesting antimitogenic activity rather than cytocidal. Absence of observable systemic or local toxicity during prolonged treatment would support this conclusion and suggest the feasibility of long term maintenance therapy with a resultant extended survival.     

Levels of estrogen and progesterone receptor proteins in patients with breast cancer during various phases of the menses

Analysis of estrogen and progesterone receptor proteins was carried out in 75 premenopausal and 79 postmenopausal patients with primary operable breast carcinoma who were treated from January 1983 to December 1984. The frequency of estrogen receptor protein positive/progesterone receptor protein positive (+/+); estrogen receptor protein negative/progesterone receptor protein negative (-/-); estrogen receptor protein negative/progesterone receptor protein positive (-/+); and estrogen receptor protein positive/progesterone receptor protein negative (+/-) was 40.5%, 30.5%, 23%, and 6% in premenopausal patients, respectively, and 52%, 24%, 2.5%, and 21.5% in postmenopausal patients, respectively (p less than 0.001). The mean positive estrogen receptor protein concentration (expressed as femtomoles per milligram of protein +/- SEM) was significantly higher in postmenopausal patients (54 +/- 6) than in premenopausal patients (19 +/- 2) (p less than 0.005). The progesterone receptor protein values did not differ significantly between these two groups. The phase of the menstrual cycle was recorded at the time of surgery in the 75 premenopausal women. Maximum receptor positivity occurred in the secretory phase, however, this difference is not statistically significant, and our data suggest that there are no distributional differences between the phase of menses and positivity of estrogen and progesterone receptor proteins. Future studies which included analyses of circulating sex steroid levels and receptor proteins will provide a better understanding of complex hormonal regulatory mechanisms which exist in patients with breast cancer.     

Application of smoothing methods to evaluate treatment-prognostic factor interactions in breast cancer data

In breast cancer research, investigators often are interested in knowing any pattern of change in efficacy of a hormonal or chemo therapy over a continuum of a prognostic factor such as age or hormonal receptor level. Bonetti and Gelber (1) introduced a graphical method to evaluate treatment-covariate interactions by using the Cox model (2, 3). By combining their concepts and the well-known locally weighted regression smoothing procedure, Fisher, Jeong, Bryant et al. (4) evaluated pattern of average annual recurrence rates as a continuous function of age among breast cancer patients with histologically negative lymph nodes and positive estrogen receptors. In this article, we elaborate on the combined exploratory smoothing technique to evaluate an interaction between treatment effect and hormonal receptor level among breast cancer patients with positive estrogen receptors and positive progesterone receptors. The results reveal that the patients with higher estrogen receptor level tend to benefit more from tamoxifen and the incremental benefit from adding a chemotherapy to tamoxifen tend to be greater for the patients with lower estrogen receptor level. The progesterone level does not affect the size of benefit from tamoxifen, but the benefit from the addition of the chemotherapy is greater for patients with higher progesterone level.     

Destabilization of steroid receptors by heat shock protein 90-binding drugs: a ligand-independent approach to hormonal therapy of breast cancer.

Steroid hormone receptors have become an important target in the management of breast cancers. Despite a good initial response rate, however, most tumors become refractory to current hormonal therapies within a year of starting treatment. To address this problem, we evaluated the effects of agents that bind the molecular chaperone heat shock protein 90 (Hsp90) on estrogen receptor function in breast cancer. Unstimulated estrogen and progesterone receptors exist as multimolecular complexes consisting of the hormone-binding protein itself and several essential molecular chaperones including Hsp90. We found that interaction of the Hsp90-binding drugs geldanamycin and radicicol with the chaperone destabilizes these hormone receptors in a ligand-independent manner, leading to profound and prolonged depletion of their levels in breast cancer cells cultured in vitro. Consistent with these findings, in vivo administration of the geldanamycin derivative 17-allylaminogeldanamycin (17AAG; NSC330507) to estrogen-supplemented, tumor-bearing SCID mice resulted in marked depletion of progesterone receptor levels in both uterus and tumor. Drug administration also delayed the growth of established, hormone-responsive MCF-7 and T47D human tumor xenografts for up to 3 weeks after the initiation of therapy. We conclude that in light of their novel mechanism of anti-hormone action, consideration should be given to examining the activity of 17AAG and other Hsp90-binding agents in patients with refractory breast cancer in future clinical trials, either alone or in combination with conventional hormone antagonists.     

Prevalence of androgen receptors in invasive breast carcinoma and its relation with estrogen receptor,progesterone receptor and Her2/neu expression

Background and aimsAlthough Breast carcinoma had many targeted biomarkers for its treatment, however, it is a heterogeneous disease with different outcomes and need new markers especially for the triple negative group when estrogen receptor, progesterone receptors and Her2/neu are negative. Androgen receptor is a new target with unclear role. The aim of this study was to examine the prevalence of androgen receptors in invasive breast cancer and tries to elucidate its relation to some well recognized clinicopathological and immunohistochemical markers.Materials and methodsOne hundred and fifty cases of invasive breast carcinoma were evaluated for type, grade and stage and studied immunohistochemically for estrogen receptor, progesterone receptor, Her2/neu and androgen expression. Androgen receptor expression was correlated with histopathological factors and the three studied markers separately then the studied cases were classified into three groups according to estrogen, progesterone receptor and Her2/neu expression and correlated with androgen receptor expression.ResultsAndrogen receptor was expressed in 71% of breast cancer cases. Its expression is associated significantly with both the stage and the grade. Also it was significantly associated with estrogen receptor and Her2/neu expression. It was expressed in a significant number of triple negative breast carcinoma, in Her2/neu positive cases and in estrogen negative cases which indicate that androgen receptor could be a new target for the treatment of these groups.ConclusionsAlthough the impact of androgen receptor on breast cancer outcomes had not been clearly established, this result may provide evidence that androgen receptor is a good prognostic and predictive marker.     

Steroid-hormone receptors in nonpalpable and more advanced stages of breast cancer. A contribution to the biology and natural history of carcinoma of the female breast

Tumors of five groups of patients, with (1) nonpalpable primary breast cancer, (2) palpable operable primary breast cancer, (3) loco-regionally advanced primary breast cancer, (4) first and (5) late metastatic breast cancer, were studied in respect to their steroid receptor content. A statistically significant decrease of progesterone receptor positive tumors and of tumors positive for estradiol and progesterone receptors, was found with increasing advance of the disease. A reversed extrapolation of these figures supports the hypothesis that every breast cancer contains steroid receptors and is hormone-dependent from its inception.     

Inhibition of growth of MX-1, MCF-7-MIII and MDA-MB-231 human breast cancer xenografts after administration of a targeted cytotoxic analog of somatostatin, AN-238.

Since somatostatin (sst) receptors are expressed in a high percentage of human breast cancers, we studied the effects of a targeted cytotoxic somatostatin analog (AN-238) formed by linking the highly active doxorubicin (DOX) derivative 2-pyrrolino-DOX (AN-201) to octapeptide RC-121 (D-Phe-Cys-Tyr-D-Trp-Lys-Val-Cys-Thr-NH(2)) in 3 human breast cancer models. The models included estrogen-independent MDA-MB-231 and MX-1 and estrogen-sensitive MCF-7-MIII tumors. Nude mice bearing xenografts of these cancers were injected i.v. with 250 nmol/kg doses of cytotoxic radical AN-201, cytotoxic analog AN-238 or the unconjugated mixture of AN-201 and sst analog RC-121. Significant inhibition of growth of MDA-MB-231, MX-1 and MCF-7-MIII tumors was observed 1 week after injection of a single dose of cytotoxic analog AN-238. The volume of MDA-MB-231 tumors remained significantly decreased 3 weeks after treatment. The volumes and weights of MCF-7-MIII tumors continued to be significantly reduced 60 days after therapy with AN-238. AN-238 also caused complete regression of MX-1 tumors in 5 of 10 animals, which remained tumor-free 60 days after treatment. In contrast, after treatment with cytotoxic radical AN-201, MDA-MB-231 and MCF-7-MIII tumors grew steadily and the regression of MX-1 tumors was only transitory in most animals. Toxicity of AN-201 was much greater than that of AN-238, as measured by animal deaths, loss of body weight and leukopenia. High-affinity sst receptors and mRNA for both sst(2) and sst(5) subtypes were found in all 3 tumor lines. Expression of sst receptors was not significantly affected by treatment with AN-238. Our results indicate that the cytotoxic somatostatin analog AN-238 efficaciously inhibits growth of human breast cancers expressing sst receptor subtypes 2 and 5.     

Steroid Hormone Receptor Positive Breast Cancer Patient-Derived Xenografts

The vast majority of breast cancers are positive for estrogen receptor (ER) and depend on estrogens for growth. These tumors are treated with a variety of ER-targeted endocrine therapies, although eventual resistance remains a major clinical problem. Other steroid hormone receptors such as progesterone receptor (PR) and androgen receptor (AR) are emerging as additional prospective targets in breast cancer. The fundamental mechanism of action of these steroid receptors in gene regulation has been defined mainly by several breast cancer cell lines that were established in the late 1970s. More recently, breast cancer patient-derived xenografts (PDX) have been developed by multiple groups at institutions in several countries. These new models capture the large degree of heterogeneity between patients and within tumors and promise to advance our understanding of steroid hormone receptor positive breast cancer and endocrine resistance. Unfortunately, steroid hormone receptor positive breast cancers are much more difficult than their receptor negative counterparts to establish into sustainable PDX. Herein we discuss the derivation of steroid hormone receptor positive breast cancer PDX, several pitfalls in their genesis, and their utility in preclinical and translational steroid hormone receptor research.     

Association of the 323/A3 surface glycoprotein with tumor characteristics and behavior in human breast cancer

We have earlier described a monoclonal antibody (323/A3) against a Mr 43,000 surface glycoprotein of MCF-7 human breast cancer cells which shows considerable specificity for primary and metastatic breast tumors (Cancer Res., 46: 1306-1317, 1986). Here we report the occurrence of the 323/A3 antigen in a large cohort of primary breast tumors (m = 384) and its interrelationship with several clinically important variables. Frozen, stored tumor tissues were examined by a Western blot procedure, and the level of 323/A3 protein in individual tumors was calculated in arbitrary units based on the integrated Mr 43,000 signal in tumors compared with an MCF-7 internal standard. Thirty-six % (139 of 384) of tumors were found to be positive for 323/A3. Higher frequencies of 323/A3 protein were found in tumors larger than 2 cm (P = 0.03), tumors with infiltrated lymph nodes (P = 0.01), and tumors without estrogen receptor (P = 0.006). No significant relationship was found with patient age, menopausal status, or progesterone receptor status. Of the newer clinical determinants proliferative rate (% S phase), DNA ploidy, and the lysosomal protease cathepsin D, but not the HER-2/neu oncogene protein, were significantly correlated with 323/A3. The presence of 323/A3 protein was also related to increased recurrence (P = 0.003) and mortality (P = 0.036) after primary treatment. As an exposed surface antigen, this glycoprotein might be a useful target in radioimaging and immunotherapy of some human breast tumors, especially those having large size, infiltrated lymph nodes, deficient estrogen receptor, high proliferative rate, abnormal DNA content, and high levels of cathepsin D, all of which are ominous indicators of tumor behavior.     

1,25-dihydroxyvitamin-d-3 and breast-cancer - growth-inhibition by 2 analogs (ro23-4319 and ro23-7553) and detection of receptors in routinely formalin-fixed paraffin-embedded material

In addition to the regulation of calcium absorption and bone mineralization, the active form of vitamin D-3, 1,25-dihydroxyvitamin D-3 (1,25(OH)(2)D-3), has been shown to inhibit the proliferation and induce the differentiation of a wide range of normal and malignant cells via binding to a specific intracellular receptor. In this study, we demonstrated that the growth of estrogen receptor positive (MCF-7 and T47D) and negative (MDA-MB-231 and BT-20) human breast cancer cells was inhibited in a dose-dependent manner by 22-ene-1,25(OH)(2)D-3 (Ro23-4319) and 16-ene-23-yne-1,25(OH)(2)D-3 (Ro23-7553), two noncalcemic analogues of 1,25(OH)(2)D-3. Moreover, we showed that the antitumor effect exerted by the antiestrogen 4-hydroxytamoxifen was enhanced by Ro23-7553 in MCF-7 cells. Taken together, these results provide further evidence for the clinical interest of the noncalcemic analogues of 1,25(OH)(2)D-3 both for patients with estrogen receptor positive and negative breast tumors. These observations combined with the potential pronostic Value of the 1,25(OH)(2)D-3 receptor (VDR) status in breast cancer led us to test an immunohistochemical method performed on 32 routinely formalin-fixed paraffin-embedded breast tumor samples which were until now unusable for VDR detection. We compared this method, involving a pretreatment of the tissue sections in a microwave oven, with the conventional biochemical assay. Our results showed that breast tumors were massively stained (80% to 98% of the tumor cell nuclei) and that the parallelism observed between the staining intensity and the VDR concentration, could be proposed to either select a responsive population of patients or to carry out retrospective studies intended to specify the pronostic interest of VDR in breast cancer. We also demonstrated, as others, that no relationship existed between the presence of VDR and the age of the patients, the presence of estrogen and progesterone receptors and the lymph node involvement.     

Engaged urokinase receptors enhance tumor breast cell migration and invasion by upregulating alpha(v)beta5 vitronectin receptor cell surface expression

We have previously shown that urokinase receptor physically and functionally interacts with alpha(v)beta5 vitronectin receptor, leading to tumor breast cell migration and invasion. Here, the link between these 2 receptors was further investigated by analyzing the expression levels of urokinase receptor and alpha(v)beta5 integrin in 35 human breast carcinomas and 5 benign breast lesions. The occurrence of a positive correlation between urokinase receptor and alpha(v)beta5 protein levels in benign and malignant tumor specimens prompted us to investigate whether engaged urokinase receptors might modulate alpha(v)beta5 expression. Here, we report the receptor-dependent ability of catalytically inactive urokinase to upregulate the alpha(v) and beta5 chains in MDA-MB-231 and MCF-7 breast carcinoma cell lines in a time- and concentration-dependent manner. This effect is dependent on protein kinase C activity and requires new protein synthesis. Accordingly, the availability of assembled alpha(v)beta5 receptors on the cell surface increases upon urokinase treatment, as shown by immunoprecipitation and immunocytochemical analyses. Exposure to urokinase leads to enhanced tumor cell migration and invasion, which is prevented by the "phosphorylation-like" urokinase receptor antagonist His-uPA(138E/303E), the DNA-binding drug mithramycin, the protein kinase C inhibitor calphostin C and anti-alpha(v)beta5 antibodies. Finally, urokinase enables benign breast MCF-10A cells to cross Matrigel in a alpha(v)beta5- and urokinase receptor-dependent manner, indicating that urokinase controls a regulatory circuitry crucial to breast tumor progression.