Receptors characterization of intraperitoneally N-nitroso-N-methylurea-induced mammary tumors in rats

Effects of the pesticide chlorpyrifos on breast cancer disease. Implication of epigenetic mechanisms

Chlorpyrifos (CPF) is an organophosphorus pesticide used for agricultural pest control all over the world. We have previously demonstrated that environmental concentrations of this pesticide alter mammary gland histological structure and hormonal balance in rats chronically exposed. In this work, we analyzed the effects of CPF on mammary tumors development. Our results demonstrated that CPF increases tumor incidence and reduces latency of NMU-induced mammary tumors. Although no changes were observed in tumor growth rate, we found a reduced steroid hormone receptor expression in the tumors of animals exposed to the pesticide. Moreover, we analyzed the role of epigenetic mechanisms in CPF effects. Our results indicated that CPF alters HDAC1 mRNA expression in mammary gland, although no changes were observed in DNA methylation. In summary, we demonstrate that the exposure to CPF promotes mammary tumors development with a reduced steroid receptors expression. It has also been found that CPF affects HDAC1 mRNA levels in mammary tissue pointing that CPF may act as a breast cancer risk factor.

Glibenclamide inhibits cell growth by inducing G0/G1 arrest in the human breast cancer cell line MDA-MB-231

BACKGROUND

Glibenclamide (Gli) binds to the sulphonylurea receptor (SUR) that is a regulatory subunit of ATP-sensitive potassium channels (KATP channels). Binding of Gli to SUR produces the closure of KATP channels and the inhibition of their activity. This drug is widely used for treatment of type 2-diabetes and it has been signaled as antiproliferative in several tumor cell lines. In previous experiments we demonstrated the antitumoral effect of Gli in mammary tumors induced in rats. The aim of the present work was to investigate the effect of Gli on MDA-MB-231 breast cancer cell proliferation and to examine the possible pathways involved in this action.

RESULTS

The mRNA expression of the different subunits that compose the KATP channels was evaluated in MDA-MB-231 cells by reverse transcriptase-polymerase chain reaction. Results showed the expression of mRNA for both pore-forming isoforms Kir6.1 and Kir6.2 and for the regulatory isoform SUR2B in this cell line. Gli inhibited cell proliferation assessed by a clonogenic method in a dose dependent manner, with an increment in the population doubling time. The KATP channel opener minoxidil increased clonogenic proliferation, effect that was counteracted by Gli. When cell cycle analysis was performed by flow cytometry, Gli induced a significant cell-cycle arrest in G0/G1 phase, together with an up-regulation of p27 levels and a diminution in cyclin E expression, both evaluated by immunoblot. However, neither differentiation evaluated by neutral lipid accumulation nor apoptosis assessed by different methodologies were detected. The cytostatic, non toxic effect on cell proliferation was confirmed by removal of the drug.Combination treatment of Gli with tamoxifen or doxorubicin showed an increment in the antiproliferative effect only for doxorubicin.

CONCLUSIONS

Our data clearly demonstrated a cytostatic effect of Gli in MDA-MB-231 cells that may be mediated through KATP channels, associated to the inhibition of the G1-S phase progression. In addition, an interesting observation about the effect of the combination of Gli with doxorubicin leads to future research for a potential novel role for Gli as an adjuvant in breast cancer treatment.

Hexachlorobenzene is a tumor co-carcinogen and induces alterations in insulin-growth factors signaling pathway in the rat mammary gland

Hexachlorobenzene (HCB) is a widespread environmental pollutant. Controversy still exists about the breast carcinogenic properties of organochlorines in humans. The ligands, receptors, and related signaling proteins of the insulin growth factor family are involved in the regulation of breast-cancer cell growth. The aims of this study were to determine: (1) whether HCB is co-carcinogenic in a medium term assay of N-nitroso N-methylurea (NMU)-induced mammary tumors in rats; (2) the effect of HCB on insulin receptor (IR), insulin-like growth factor-I receptor (IGF-IR) and insulin receptor substrate-1 (IRS-1) levels and on IRS-1 phosphorylation; (3) microsomal and cytosolic Protein Tyrosine Kinase (PTK) activities in mammary glands and NMU-induced tumors. Sprague Dawley rats were injected with 50 mg/kg body weight of NMU at 50, 80, and 110 days old. HCB (100 mg/kg body weight) was administered three times a week from 65 to 110 days of age. Rats were separated in four groups: control, NMU, HCB, and NMU-HCB. HCB alone did not induce tumor development. Parameters of tumor development were increased in NMU-HCB compared to NMU rats. A higher cellular undifferentiation was observed in NMU-HCB tumors. IR, IGF-IR, and IRS-1 levels were higher in HCB than in controls. Conversely IGF-IR levels decreased in NMU-HCB vs. NMU group. The IRS-1 phosphorylation increased in HCB rats; however, it decreased in NMU-HCB vs. NMU. HCB decreased microsomal PTK activity in tumors. This study showed for the first time that HCB is a co-carcinogenic agent in NMU-induced mammary tumors in rats. Our results suggest that the IR and/or IGF-IR signaling pathway may be involved in the mechanism of action of HCB.

Gene expression profiling of NMU-induced rat mammary tumors: cross species comparison with human breast cancer

Breast cancer is a complex genetic disease characterized by the accumulation of multiple molecular alterations. The NMU breast cancer model induced in the rat is used for the study of mammary carcinogenesis because it closely mimics human breast disease. To assess the validity of this model from a more global molecular perspective, and also to devise a general technique to compare animal profiles with human microarray studies, we have characterized 25 NMU-induced mammary tumors and 11 normal glands using a combination of immunohistochemical and microarray analyses. The rat mammary carcinomas were classified as non-invasive, ER-positive ductal carcinomas with a composition of differentiated epithelial and myoepithelial cell lineages. Gene expression profiles generated using rat Affymetrix arrays containing 15,866 genes demonstrated that the rat mammary tumors are homogeneous and that H-ras mutations did not confer a unique molecular signature. We compared the resulting rat profiles with those obtained from a human dataset by merging the raw microarray data, using an approach that involves a combination of cross-species and cross-platform analysis. Using this novel strategy, we demonstrate the ability of 2305 rat orthologs to recapitulate the classification of human tumors derived from human Affymetrix arrays. The gene expression profiles of the NMU-induced primary tumors were most similar to ER-positive, low to intermediate grade breast cancer. Our technique provides a means to correlate gene expression data from animal models of cancer to human cancer and disease states.

Estrogen receptor profiles: changes in mouse and rat mammary tumors by treatment with selective estrogen receptor modifiers

OBJECTIVE

The aim of this work was to analyze the effect of estradiol (E(2)), medroxyprogesterone and the two selective estrogen receptor modulators (SERMs) (tamoxifen (Tam) and raloxifene (Ral)) on the estrogen receptor (ER) conformers profile performed by size exclusion HPLC in relation to hormone dependence of mammary tumors.

MATERIALS AND METHODS

Two types of mammary tumors were studied: tumors transplanted in BALB/c mice that are medroxyprogesterone acetate (MPA)-dependent for growth, and tumors induced in Sprague-Dawley rats by intraperitoneal injection of N-nitroso-N-methylurea (NMU). Tumors from mice treated with MPA, E(2), Tam or Ral and NMU-treated rats were analyzed and compared to that of control.

RESULTS

The tumor conformer profiles were as follows: control and MPA-treated mice showed only one peak (oligomeric form); E(2)-treated mice also showed only one peak (dimer); Tam-treated mice showed one peak corresponding to a possible proteolytic fragment, and Ral-treated mice showed two peaks (oligomeric and a possible proteolytic fragment). On the other hand, NMU-induced mammary tumors from rats showed three peaks (oligomeric, monomeric and proteolytic).

CONCLUSION

Our findings may indicate that SERMs affect the aggregation state of ER and thereby its ability to modulate genomic transcription mechanisms related to growth rate.

Suppression of mammary gland tumorigenesis in diabetic rats

The aim of this study was to compare mammary gland tumorigenesis in diabetic and non-diabetic rats. Streptozotocin and N-nitroso-N-methylurea were used to induce diabetes and mammary tumors, respectively. A suppression of mammary carcinogenesis in diabetic rats was shown by a longer latency period, a lower number of tumors per animal and a smaller final tumor volume. An 84% of the lesions developed in diabetic animals were benign tumors. Eighty day-old diabetic rats had significantly lower plasma levels of total-IGF-I and insulin versus non-diabetic rats. We postulate that the decrease in the total IGF-I and insulin levels during the promotion phase of carcinogenesis in this model plays an important role in retarding the tumor development in diabetic animals and in favoring the development of benign mammary lesions.

Antitumoral activity of a new series of 5,6-dihydrobenzo(a)carbazoles

The overlapping of three-dimensional structures of 5,6-dihydrobenzo(a)carbazole (DHBC) derivatives over the structure of 4-hydroxytamoxifen (4-OH-TAM), by means of the MDL CHEMLAB 11.0 computational program, shows a reasonable structural and spatial resemblance. This finding raised the hypothesis of their possible antitumoral activity, similar to that of tamoxifen (TAM). A number of DHBCs with an alkyl chain and a second basic nitrogen as substituent were synthesized in our laboratory and their possible antitumoral activity was tested by means of: 1) competitive radioligand assays to determine relative drug affinity for the estrogen receptor (ER); 2) in vivo studies, giving the synthetic drugs subcutaneously (1 mg kg-1 day-1) to Sprague-Dawley rats with N-nitroso-N-methylurea (NMU)-induced mammary tumors; and 3) in vitro cell proliferation experiments employing the soft agar clonogenic technique. Besides, studies on toxicity and histopathological analyses of organs and tumors from treated animals were performed. Results obtained showed that: 1) relative binding affinities (RBA) for the ER were similar to that of TAM; 2) some structures showed significant antitumoral activity and induced tumoral regression similar to TAM; and 3) these compounds had in vitro inhibitory effect on cell proliferation. Even though all the compounds of the series of synthesized DHBCs showed affinity for the ER similar to TAM, the results of in vivo experiments confirmed the crucial role of hydroxyl groups in the molecule and of the interatomic distance between them, similar to that of estradiol, as well as the necessary presence of the aminoalkyl chain on the annular N atom. However, the effect of alkyl chain enlargement in the nitrogen substituent on the biological activity of those drugs is as yet unclear.

Histamine as an autocrine growth factor: an unusual role for a widespread mediator

The involvement of histamine in cancer growth represents an old controversy and direct experimental evidence proving this hypothesis is not still available. In this paper we review the most relevant mechanisms referring to the role of histamine receptors, histidine decarboxylase and histamine release in the onset of an autocrine loop, that enables histamine to act as an autocrine growth factor. We postulate that this autocrine loop, that has been studied in an experimental mammary carcinoma model induced in rats, may be present in different human neoplasias. Therefore, the better understanding of this novel regulatory pathway that is controlled by histamine may contribute to identifying new therapeutic targets.

An overview of Argentine contributions to diabetes research in the decade of the 1990s

Argentina has a longstanding tradition of diabetes research, beginning with the seminal work of Prof. Bernardo A. Houssay, who was awarded the first Nobel Prize in Medical Sciences for his studies on the relationship between diabetes and pituitary function. Prof. Luis F. Leloir, who was also awarded the Nobel Prize for his work in carbohydrate metabolism, also inspired younger generations of biologists to work in the field of diabetes research. The aim of this paper is to provide a review of the contributions of Argentine researchers during the 1990s. This manuscript includes only reports of Argentine researchers working on diabetes in local laboratories and quoted in Medline. Thus, important contributions not reported in journals included in Medline or produced by Argentine researchers working abroad may have been omitted. The material consists of a brief description of clinical research (epidemiology and costs, metabolic control, associated risk factors, immunological aspects, and other clinical studies) and basic research (animal model with spontaneous diabetes, islet morphology and function in normal and pathological conditions, insulin action, metabolic disorders related to diabetes, and some miscellaneous effects related to drug-induced diabetes). Altogether, a broad idea of the continuous contribution of our national research to the international field of diabetes is provided, as well as a list of Argentine researchers and research centers devoted to the study of diabetes.

An experimental model of diabetes and cancer in rats

The aim of this study was to develop an experimental model for the study of cancer associated with diabetes. For diabetes induction, Sprague-Dawley rats were given streptozotocin (STZ, 90 mg/kg body weight (BW), by intraperitoneal injection on the second day of life. For mammary tumour induction, rats were injected with 50 mg/kg BW of N-nitroso-N-methylurea (NMU) at 50, 80 and 110 days old. The neoplastic process and the effect of tamoxifen treatment was examined in non-diabetic and diabetic rats. The latency period, NMU-induced tumour incidence and the number of tumours per rat in diabetic rats versus controls were 117 +/- 7 days versus 79 +/- 9 days (P < 0.001); 93% versus 95% (NS); and 5.2 +/- 1.6 versus 2.7 +/- 0.5 (P < 0.02). A more benign histological pattern for tumours in diabetic animals was observed. Mammary tumours in diabetic rats grew more slowly than in controls. Tamoxifen (1 mg/kg/day) treated diabetic rats showed tumour regression in 67% of NMU-induced mammary tumours versus 53% in controls (NS). Our results show that tumour progression seems to be affected by diabetes in this experimental model. We suggest this is the result of changes to insulin-like growth factors and their receptors, which occur in diabetics, and our future research will examine this hypothesis.

Epidermal growth factor in NMU-induced mammary tumors in rats

In this work we analyze the hypothesis that tumors induced by i.p. N-nitroso-N-methylurea injection express EGF-like peptides and EGF receptors which could be involved in the response to hormone manipulation. EGF receptors (EGFR) were determined in the purified membrane fraction of tumors from control and ovariectomized (OVX) animals and no significant differences were found in either maximal binding capacities (Q) or dissociation constants (Kd) between them. Neither did we observe differences between tumors that regressed (HR) or continued growing (HU) after ovariectomy. In order to test the ability of EGFR to trigger a biological response we measured the production of second messengers inositol triphosphates (IP3) and cAMP levels; we found that EGF increases IP3 production in a dose-dependent way, while cAMP levels were not affected. In addition, EGF was able to induce in vitro cell proliferation in a concentration-dependent manner when tested in primary cultures of tumor cells by the clonogenic soft agar technique. EGF/TGF-alpha activity was determined by a radioreceptor assay in tumor cytosols from control and OVX rats. Results showed a trend to lower values in tumors from OVX rats, but no differences between HR and HU tumors. A positive correlation was found between EGF/TGF-alpha activity and progesterone receptor maximal binding capacity. When we tested the action of estradiol and EGF added together to primary cultures of tumor cells we found an additive effect on cell proliferation. The study of steady state mRNA levels showed that E2 increases PgR and c-myc mRNA levels in HR but not in HU tumors. In conclusion, the autocrine loop EGFR-EGF/TGF-alpha present in all tumors is hormonally regulated, possibly by Pg, but is not related to the tumor response to ovariectomy.

Hormone dependence of mammary tumors induced in rats by intraperitoneal NMU injection

The purpose of this work was to determine the hormone dependence of mammary tumors induced in Sprague-Dawley rats by three intraperitoneal injections of N-nitroso-N-methylurea at 50, 80, and 110 days of age. Two experimental designs were carried out: (a) Ten days before the first NMU injection, 130 rats were divided into 13 batches and randomly assigned to the following treatments: control, ovariectomy (OVX), tamoxifen (TAM), bromocriptine (BROM), haloperidol (HAL), estradiol (E2), progesterone (Pg), OVX + BROM, TAM + BROM, OVX + HAL, TAM + HAL, OVX + TAM, and E2 + BROM. After 150 days of treatment the following growth parameters were determined: latency period (LP), mean tumor number per rat (n/t), and tumor incidence (TI). LP was significantly increased (p < 0.05) only by Pg and TAM + BROM. The n/t was significantly decreased (p < 0.05) by all treatments except HAL. TI was significantly reduced by OVX, TAM, BROM, and their combinations, (b) Rats bearing ip-NMU-induced mammary tumors were divided into 7 batches and assigned to the following treatments: control, OVX, TAM, BROM, HAL, OVX + BROM, and TAM + BROM. Tumor growth was assessed up to 60 days of treatment; only OVX, TAM and their combination with BROM were able to produce tumor regression. These results support the essential role of E2 and prolactin in the promotion stage of carcinogenesis. However, for established tumors, growth becomes more independent from hormone influence, in particular from prolactin deprivation. We conclude that this model seems suitable for studying the mechanisms underlying the evasion of hormonal control of tumor growth.