The antitumor potency of progesterone antagonists is due to their differentiation potential

CDB-4124, a progesterone receptor modulator, inhibits mammary carcinogenesis by suppressing cell proliferation and inducing apoptosis

CDB-4124 (Proellex or telapristone acetate) is a modulator of progesterone receptor (PR) signaling, which is currently employed in preclinical studies for prevention and treatment of breast cancer and has been used in clinical studies for treatment of uterine fibroids and endometriosis. Here we provide evidence for its action on steroid hormone-signaling, cell cycle-regulated genes and in vivo on mammary carcinogenesis. When CDB-4124 is given to rats at 200 mg/kg for 24 months, it prevents the development of spontaneous mammary hyperplastic and premalignant lesions. Also, CDB-4124 given as subcutaneous pellets at two different doses suppressed, dose dependently, N-methyl-N-nitrosourea (MNU)-induced mammary carcinogenesis. The high dose (30 mg, over 84 days) increased tumor latency from 66 ± 24 days to 87 ± 20 days (P < 0.02), decreased incidence from 85% to 35% (P < 0.001), and reduced multiplicity from 3.0 to 1.1 tumors/animal (P < 0.001). Tumor burden decreased from 2.6 g/animal to 0.26 g/animal (P < 0.01). CDB-4124 inhibited cell proliferation and induced apoptosis in MNU-induced mammary tumors, which correlated with a decreased proportion of PR(+) tumor cells and with decreased serum progesterone. CDB-4124 did not affect serum estradiol. In a mechanistic study employing T47D cells we found that CDB-4124 suppressed G(1)/G(0)-S transition by inhibiting CDK2 and CDK4 expressions, which correlated with inhibition of estrogen receptor (ER) expression. Taken together, these data indicate that CDB-4124 can suppress the development of precancerous lesions and carcinogen-induced ER(+) mammary tumors in rats, and may have implications for prevention and treatment of human breast cancer.

Potentiation of the antitumor effect of tamoxifen by combination with the antiprogestin onapristone

The present study was undertaken to investigate the antitumor effect of a combination of the antiestrogen tamoxifen (TAM) and either the antiprogestin onapristone (ON) or the progestogen megestrol acetate (MEG) in experimental mammary tumor models. Rats bearing DMBA- or NMU-induced mammary tumors were treated with ON or MEG either alone or in combination with TAM for four weeks. In the DMBA-tumor model, treatment with ON or TAM alone caused tumor remissions, whereas the combination of ON and TAM was almost as effective as ovariectomy (100% remission) and led to a remission of 86-100%. The combination of TAM and ON was distinctly more effective than that of TAM and MEG. A similar potentiation of the antitumor effect of TAM and ON was observed in the NMU-tumor model. In DMBA-tumors, the concentration of progesterone receptors was found to increase after treatment for three days with TAM and ON. In hosts bearing DMBA-tumors, treatment with the combination of TAM and ON caused a reduction in ovarian and uterine weights. In the same animals, the basal level of progesterone was decreased in spite of a slight increase in the LH level. These findings suggest that the high antitumor effect of the combination of TAM and ON compared to the corresponding monotherapies can be related not only to the interaction of antihormones and receptors, but also to the up-regulation of PR and to a decrease in progesterone production. These data clearly suggest the sense of a combination of TAM with an antiprogestin in breast cancer treatment.

Steroid hormone receptors as targets for the therapy of breast and prostate cancer--recent advances, mechanisms of resistance, and new approaches

Surgical ovariectomy and orchiectomy, first proposed over a century ago, are effective in breast and prostate cancer therapy, respectively. Later, the discovery of steroid hormones and their nuclear receptors led to the concept that inhibition of steroid receptor function by an antagonist prevents tumour growth. While the first anti-hormones, cyproteroneacetate (CPA) and tamoxifen were found accidentally, deeper understanding of nuclear receptors as transcription factors enabled more rational, structure-activity based drug discovery. Results from a drug-finding program on pure anti-estrogens will be reported. These new steroidal anti-estrogens are highly active, pure ER-antagonists that lead to an efficient degradation of the estrogen receptor alpha (ERalpha) protein without any agonistic activity. Data obtained in preclinical tumour models in mice and rats showed a high potency in growth inhibition of ERalpha-positive breast cancer. In parallel, by comparing three independently generated anti-estrogen-resistant breast cancer cell lines, it was our intention to gain insight into the mechanisms of endocrine resistance which will allow to define new approaches for the treatment of endocrine-resistant breast cancer. Candidate proteins potentially involved in mechanisms of anti-estrogen-resistant growth of breast cancer cell lines were analyzed. ERalpha and progesterone receptor (PR) expressions were lost on the protein level in all three anti-estrogen-resistant cell lines, whereas binding of epidermal growth factor (EGF) and protein expression of epidermal growth factor receptor (EGFR) were increased. Loss of ERalpha expression may be linked to the acquisition of anti-estrogen resistance and enhanced expression of the EGFR and of members of the S100 family of Ca2+-binding proteins may contribute to the outgrowth of resistant cells. Furthermore, we describe the pharmacological development of a novel, highly potent progesterone receptor antagonist. In rat mammary tumour models, treatment with the PR antagonist completely suppressed the growth of established tumours and prevented the development of breast tumours. Advanced prostate cancer is effectively treated by androgen ablation. However, this therapy becomes inefficient although the androgen receptor (AR) is still functionally expressed. One novel strategy for the treatment of advanced prostate cancer could be the selective inhibition of AR protein expression by anti-sense oligonucleotides or small interfering RNA (siRNA) molecules. Down-regulation of the human AR caused significant inhibition of LNCaP prostate cancer growth in vivo. Taken together, many promising alternatives for endocrine therapy of breast and prostate cancer are arising.

Apoptotic cell death of renal tubules in experimental severe acute pancreatitis

BACKGROUND

Recently renal cell apoptosis has been reported in various disorders that result in renal failure. Thus we hypothesized that renal cell injury resulting from apoptosis is involved in renal failure with severe acute pancreatitis.

METHODS

Renal cell apoptosis in kidneys harvested from rats with necrotizing pancreatitis was evaluated by in situ nick-end labeling. Ascitic fluid that had been collected 6 hours after development of pancreatitis was injected into the peritoneal cavities of healthy rats, and renal apoptosis was also evaluated. The apoptosis-inducing activity of the ascitic fluid was estimated in vitro with use of isolated rat renal tubules and the normal rat kidney cell line NRK52E by nuclear staining, cell cycle analysis, and DNA electrophoresis.

RESULTS

Apoptosis was detected by in situ nick-end labeling on the renal tubules 6 hours after induction of pancreatitis in vivo. Similar tubular apoptosis was detected in the rats that had intraperitoneal injection of the ascitic fluid. In in vitro analyses the ascitic fluid induced nuclear and DNA fragmentation on the isolated renal tubules and promoted apoptosis on NRK52E cells in a time-dependent manner.

CONCLUSIONS

Apoptotic cell death of renal tubules occurs in severe acute pancreatitis within several hours and is possibly involved in the mechanism of renal failure through undefined substance(s) in the ascitic fluid associated with pancreatitis.

Involvement of peritoneal macrophage in the induction of cytotoxicity due to apoptosis in ascitic fluid associated with severe acute pancreatitis

The aim of this study was to assess the significance of peritoneal macrophage in inducing cytotoxicity in ascitic fluid associated with severe acute pancreatitis. The involvement of peritoneal macrophage was examined experimentally in rats by macrophage depletion with peritoneal lavage prior to the development of pancreatitis. More than 94% of the cellular components collected from peritoneal cavities by the lavage are macrophages. Although the ascitic fluid collected from the rats with necrotizing pancreatitis showed cytocidal effects via apoptosis on Madin-Darby canine kidney cells in a dose- and time-dependent manner, cytotoxicity or apoptosis-inducing activity almost disappeared from the ascitic fluid by the preceding peritoneal lavage. The ascitic fluid did not show significant differences by the lavage in osmolarity and in concentrations of albumin, bilirubin, amylase, and lipase. Although a slight reduction of tumor necrosis factor-alpha was noted with the lavage, tumor necrosis factor-alpha failed to induce apoptotic cell death in the cells, and the neutralization by antibody ameliorated neither cell death nor apoptosis. We conclude that peritoneal macrophages secrete apoptosis-inducing factor(s) into pancreatitis-associated ascitic fluid, other than tumor necrosis factor-alpha.

The biology of breast cancer

This article focuses on the major hormones and growth factors for which a critical role in normal mammary growth has been clearly defined. Certainly other hormonal systems and growth factors could also affect breast cancer initiation and progression, but their exact contribution to normal and/or malignant breast cell growth is poorly delineated. Examples of such factors include somatostatin, mammostatin, mammary-derived growth inhibitor (MDGI), mammary-derived growth factor-1 (MDGF-1), inhibins, activins, androgens, glucocorticoids, vitamin D, thyroid hormones, ecosinoids, and oxytocin. Clearly, the hormonal regulation of breast cancer cell growth and survival is multifaceted and very complex. In particular, the effects of estrogens and anti-estrogens on breast cells may depend on their interaction with a wide variety of other pathways. In addition, these interactions may vary among individual breast tumors depending on other genetic changes in the tumor cells that have not been discussed here, such as oncogene activation and loss of tumor suppressors. A more detailed understanding of how cells circumvent a dependency on these pathways is greatly needed in order to identify new biological targets and to design novel therapies for breast cancers that are resistant to anti-estrogen therapy. Such agents could be used alone or in combination with anti-estrogens to improve response to a second course of hormonal therapy.

The effect of onapristone, a progesterone antagonist, on the growth of human gastrointestinal cancer xenografts

Onapristone is a progesterone antagonist which inhibits the growth of mammary tumours in mice. The effect of Onapristone and concomitant oestrogen (E2) supplements on the growth of five human gastrointestinal cancer xenografts was examined. E2 stimulated RD19 (gastric tumour) tumour growth in female mice and tumours grew less well when also treated with Onapristone (P < 0.05). Onapristone had no effect on male mice bearing RD19 tumours or mice of either sex bearing MKN45G (gastric) tumours. PAN-1 (pancreatic) tumours were significantly stimulated by E2 (by 64% of control, P = 0.02) and Onapristone treatment inhibited E2 stimulated growth (52% reduction of E2 control, P > 0.05). C146 (colorectal) tumour growth was not stimulated by E2 nor inhibited by Onapristone. E2 stimulated formation of AP5LV (colorectal) tumour nodules (in lungs) (mean 38-52, P = 0.001). Onapristone significantly reduced the number of nodules (mean 32, P < 0.05) only in female mice not given E2. Xenografts of some GI tumour cell lines grow at different rates in male and female mice. E2 may cause additional growth stimulation and E2 stimulated growth can be reversed by Onapristone to basal levels.

Induction of apoptotic cell death by pancreatitis-associated ascitic fluid in Madin-Darby canine kidney cells

We investigated the cytotoxicity on Madin-Darby canine kidney (MDCK) cells of pancreatitis-associated ascitic fluid (PAAF) collected from rats with experimental necrotizing pancreatitis. PAAF reduced viability of MDCK cells in a time- and dose-dependent manner. We detected DNA fragmentation on the PAAF-treated MDCK cells, indicating that the cytocidal action of PAAF is via apoptosis. From the results obtained, we conclude that PAAF contains factor(s) inducing apoptosis on MDCK cells, and we assume that apoptotic cell death is involved in the mechanism of organ failure in acute pancreatitis.

Antiprogestins inhibit growth and stimulate differentiation in the normal mammary gland

Antiprogestins possess a potent antitumor activity in hormone-dependent experimental breast cancer models. Though the underlying mechanism is not clear, induction of functional differentiation seems to be a major event. This study attempts to test directly for antiproliferative and differentiation promoting activities of antiprogestins on the normal mammary gland. To this end, whole organ cultures of mammary glands from estradiol/progesterone-primed virgin mice maintained in a serum-free medium with aldosteron, prolactin, insulin, and hydrocortisone were exposed to the antiprogestin ZK114043. A 4-day treatment of organ cultures led to a strong inhibition of epithelial DNA synthesis. In parallel, ZK114043 caused alveolar cells to acquire a more differentiated phenotype distinguished by secretory active alveoli composed of single cell layers with increased fat droplet accumulation and enhanced expression of the milk proteins beta-casein and whey acidic protein (WAP). Particularly strong effects were found on the expression of mammary-derived growth inhibitor (MDGI). Both half-maximal inhibition of epithelial DNA synthesis and stimulation of MDGI mRNA expression were found at about 5 ng/ml of ZK114043. Presence in the medium of 5 micrograms/ml hydrocortisone rendered antiglucocorticoid effects of ZK114043 highly unlikely. Furthermore, prevention of action of ZK114043 by the progesterone agonist R5020 and ZK114043 stimulated expression of beta-casein and MDGI mRNA in cultured glands of 10-week-old unprimed virgin mice suggest a progesterone receptor-mediated mechanism of antiprogestin action. Two other antiprogestins, Mifepristone and Onapristone, likewise stimulated MDGI expression. The data provide direct evidence that antiprogestins act like a differentiation factor in the normal mammary gland.

Enhancement of the antitumor efficacy of the antiprogestin, onapristone, by combination with the antiestrogen, ICI 164384

So far, no combination of endocrine treatments has been routinely used in the therapy of breast Cancer. It was, therefore, our interest to determine whether the combination of the antiprogestin, onapristone (ON), and the pure antiestrogen, ICI 164384 (ICI) might provide a more effective therapy than either monotherapy in experimental mammary tumors containing both estrogen and progesterone receptors. In the MXT-mammary tumor of the mouse, ON (5 mg/kg) administered for 3 weeks exerted an ovariectomy-like antitumor effect (56% inhibition), whereas ICI (30 mg/kg) was weakly effective (28% inhibition). The combination of ON and ICI was, however, distinctly more effective than the monotherapies or ovariectomy, causing 78% inhibition. A similar potentiation of antitumor effect by the combination was manifested in the dimethylbenzanthracene-induced mammary tumor of the rat when ON (5 mg/kg) and ICI (30 mg/kg) were administered once daily for 4 weeks (s.c.). The remission rates of tumors found after treatment with ICI, ON, the combination and ovariectomy (complete and partial remission) were 15%, 46%, 71% and 100% respectively. In the animals bearing DMBA-induced tumors, treatment with ON alone significantly increased the serum levels of luteinizing hormone and prolactin, but caused only a slight increase in the peripheral levels of estradiol and progesterone. ON had no appreciable effect on the uterine and ovarian weights. ICI reduced the uterine weight and the serum progesterone level. In the combination with ON, ICI reversed the effect of ON on the progesterone level without influencing the luteinizing hormone and prolactin levels. These findings suggest that the augmentation of antitumor effectiveness by the combination of two antihormones can be ascribed not only to their effects at estrogen- and progesterone-receptor-binding sites, but also to the decrease in the peripheral level of progesterone. Thus, an appropriate combination of antiprogestin and pure antiestrogen may be useful in the management of breast cancer.

Stromal expression of tenascin is inversely correlated to epithelial differentiation of hormone dependent tissues

We were previously investigating the expression of the extracellular matrix glycoprotein tenascin in normal and malignant endometrial tissues of humans and rodents. These studies suggested that the expression of tenascin was induced by proliferating epithelia (normal and particularly malignant) and was downregulated with their differentiation. The aim of this study was to investigate the hormone dependency of tenascin expression in (a) the transplantable EnDA endometrial tumor model with or without estrogen deprivation (ovariectomy) of the animals, (b) DMBA-induced rat mammary tumors with or without a hormonal treatment of the animals [ovariectomy, antiestrogen (tamoxifen) or antiprogestin (ZK 98299) treatment] and (c) in the rat prostate of untreated or androgen deprived animals (orchiectomy, flutamide-, casodex- or cyproterone acetate (CPA)-treatment). 1. Estrogen withdrawal by ovariectomy did not affect tenascin expression in transplantable EnDA endometrial adenocarcinoma, meaning the entire extracellular space of the stromal mesenchyme was decorated by tenascin immunoreactivity. 2. In untreated DMBA-induced rat mammary tumors almost the entire extracellular space of the stroma was stained by tenascin immunoreactivity. Ovariectomy and antiestrogen treatment did not affect tenascin expression. In contrast, antiprogestin treatment induced terminal differentiation of mammary tumor cells and in parallel downregulated tenascin expression. 3. In the normal rat prostate no tenascin was detectable by immunocytochemistry. However, following androgen deprivation we found tenascin expression in the stroma of the prostate. The most prominent expression was observable after CPA-treatment, possibly due to its progestagenic potency. In conclusion, the hormones and antihormones tested show no direct effect on the stromal expression of tenascin. However, proliferative activity and a low degree of differentiation of the epithelium induces tenascin expression, whereas epithelial differentiation apparently shuts down tenascin expression. Preliminary in vitro studies suggest that paracrine acting growth factors trigger the hormonal regulation of tenascin expression.

Mitotic activity, apoptosis and TRPM-2 mRNA expression in DMBA-induced rat mammary carcinoma treated with anti-estrogen toremifene

Anti-estrogen toremifene inhibits growth of the 7,12-dimethylbenz(a)anthracene(DMBA)-induced rat mammary carcinoma. The changes in proliferation and cell death were studied in detail. Proliferation was measured by counting mitotic figures in histologic sections, expressed by volume-corrected mitotic index (M/V INDEX). Respective volume corrected apoptotic index (A/V INDEX) was measured by counting apoptotic nuclei in the same sections. The presence of apoptotic cells was confirmed by transmission electron microscopy. In the untreated tumors, both mitosis and apoptosis were frequent. In the toremifene-treated tumors, the mean M/V INDEX was about half of the mean M/V INDEX in the untreated control tumors. The mean A/V INDEX in the toremifene-treated tumors was about 3/4 of the mean A/V INDEX in the controls. In toremifene-treated tumors, A/V INDEX was strongly correlated with TRPM-2-gene expression, which was also enhanced when compared with the controls. TRPM-2 gene has been associated with programmed cell death induced by hormonal ablation in prostate- and breast-cancer cells. No such correlation was seen in control tumors. These findings suggest that, in the DMBA-tumor model, toremifene affects the cell turnover by inhibiting mitotic activity and modifying abundant spontaneous apoptosis. In this model, the inhibition of tumor growth results mostly from reduction of mitotic activity.