Induction of mammary tumors in rat by intraperitoneal injection of NMU: histopathology and estral cycle influence

The attenuation effect of low piperine Piper nigrum extract on doxorubicin-induced toxicity of blood chemical and immunological properties in mammary tumour rats

CONTEXT

Many natural extracts have been shown to minimize the toxicity of doxorubicin (Dox). Low piperine Piper nigrum L. (Piperaceae) extract (PFPE) is a natural extract containing many types of antioxidants that may reduce Dox toxicities.

OBJECTIVE

To evaluate the effect of PFPE in attenuating the side effects of Dox.

MATERIALS AND METHODS

Tumour-bearing Sprague Dawley rats were divided into five groups including normal, vehicle, 100 mg/kg BW of PFPE plus 2 mg/kg BW of Dox (P100 + Dox), 100 mg/kg BW of PFPE plus 2 mg/kg BW of Dox (P200 + Dox) and Dox. Rats were treated with Dox and/or PFPE three times/week for 4 weeks. Tumour burden, blood parameters, weight of internal organs and immunological data were investigated.

RESULTS

The addition of 200 mg/kg PFPE significantly restored the levels of AST from 174.60 ± 45.67 U/L in the Dox group near to normal levels at 109.80 ± 4.99 U/L. The combination of PFPE and Dox also decreased the levels of CXCL7, TIMP-1, sICAM-1 and l-selectin about 1.4-1.6-fold compared to Dox group. Feeding rats with 200 mg/kg BW of PFPE combination with Dox slightly increased Th1 from 161.67 ± 14.28 cells in Dox group to 200.75 ± 5.8 cells meanwhile suppressed Treg from 3088 ± 78 cells in Dox to 2561 ± 71 cells.

DISCUSSION AND CONCLUSIONS

This study showed that PFPE ameliorated Dox toxicity in many aspects indicating the role of antioxidant and other substances in the extract on toxicity attenuation. This suggested the using of PFPE may be valuable for Dox treated patients.

Insights into Immune Escape During Tumor Evolution and Response to Immunotherapy Using a Rat Model of Breast Cancer

Animal models are critical for the preclinical validation of cancer immunotherapies. Unfortunately, mouse breast cancer models do not faithfully reproduce the molecular subtypes and immune environment of the human disease. In particular, there are no good murine models of estrogen receptor-positive (ER+) breast cancer, the predominant subtype in patients. Here, we show that Nitroso-N-methylurea-induced mammary tumors in outbred Sprague-Dawley rats recapitulate the heterogeneity for mutational profiles, ER expression, and immune evasive mechanisms observed in human breast cancer. We demonstrate the utility of this model for preclinical studies by dissecting mechanisms of response to immunotherapy using combination TGFBR inhibition and PD-L1 blockade. Short-term treatment of early-stage tumors induced durable responses. Gene expression profiling and spatial mapping classified tumors as inflammatory and noninflammatory, and identified IFNγ, T-cell receptor (TCR), and B-cell receptor (BCR) signaling, CD74/MHC II, and epithelium-interacting CD8+ T cells as markers of response, whereas the complement system, M2 macrophage phenotype, and translation in mitochondria were associated with resistance. We found that the expression of CD74 correlated with leukocyte fraction and TCR diversity in human breast cancer. We identified a subset of rat ER+ tumors marked by expression of antigen-processing genes that had an active immune environment and responded to treatment. A gene signature characteristic of these tumors predicted disease-free survival in patients with ER+ Luminal A breast cancer and overall survival in patients with metastatic breast cancer receiving anti-PD-L1 therapy. We demonstrate the usefulness of this preclinical model for immunotherapy and suggest examination to expand immunotherapy to a subset of patients with ER+ disease. See related Spotlight by Roussos Torres, p. 672.

Microemulsion for Prolonged Release of Fenretinide in the Mammary Tissue and Prevention of Breast Cancer Development

The need of pharmacological strategies to preclude breast cancer development motivated us to develop a non-aqueous microemulsion (ME) capable of forming a depot after administration in the mammary tissue and uptake of interstitial fluids for prolonged release of the retinoid fenretinide. The selected ME was composed of phosphatidylcholine/tricaprylin/propylene glycol (45:5:50, w/w/w) and presented a droplet diameter of 175.3 ± 8.9 nm. Upon water uptake, the ME transformed successively into a lamellar phase, gel, and a lamellar phase-containing emulsion in vitro as the water content increased and released 30% of fenretinide in vitro after 9 days. Consistent with the slow release, the ME formed a depot in cell cultures and increased fenretinide IC₅₀ values by 68.3- and 13.2-fold in MCF-7 and T-47D cells compared to a solution, respectively. At non-cytotoxic concentrations, the ME reduced T-47D cell migration by 75.9% and spheroid growth, resulting in ∼30% smaller structures. The depot formed in vivo prolonged a fluorochrome release for 30 days without producing any sings of local irritation. In a preclinical model of chemically induced carcinogenesis, ME administration every 3 weeks for 3 months significantly reduced (4.7-fold) the incidence of breast tumors and increased type II collagen expression, which might contribute to limit spreading. These promising results support the potential ME applicability as a preventive therapy of breast cancer.

Effect of multiple doses of N-methyl-N-nitrosourea, an end product of methylguanidine (found in processed food), on the fertility of female Swiss albino mice

Methylguanidine, an originator of carcinogenic methylnitrosourea, has been found in many animal meats and processed stored food often in high concentration. The present study was designed to understand the multiple dose effect of N-methyl-N-nitrosourea (MNU), an end product of methylguanidine, in Swiss albino mice fertility as well as cancer induction. Accordingly, a total of five experimental groups of animal (female Swiss albino mice) were taken, considering group-I as vehicle control and group-II-V as treatment groups (whereas group-II-Vwere treated with single to quadruple doses of 50 mg/kg of MNU respectively in a three weeks interval). After accomplishment of MNU injection, each female mice was mated with male mice to check the fertility efficiency. The results of the study indicated that, mice treated with highest number of MNU doses were 42.85% less efficient in getting pregnant than the control mice. There were noted changes in body weight, food and water intake upon MNU-exposure compared to control group. A significant increase in cumulative weight of vital female organs like uterus and ovary were also observed in mice injected with quadruple doses of MNU (50 mg/kg) compared to control mice. The findings of the study suggest the direct effect of MNU in pregnancy, without any cancer incidence in the vital female organs of Swiss albino mice.

Vascular Endothelial Growth Factor Mediates the Sprouted Axonogenesis of Breast Cancer in Rat

Nerve infiltration into the tumor is a common feature of the tumor microenvironment. The mechanisms of axonogenesis in breast cancer remain unclear. We hypothesized that vascular endothelial growth factor (VEGF), as well as nerve growth factor (NGF), is involved in the axonogenesis of breast cancer. A N-methyl-N-nitrosourea (MNU)-induced rat model of breast cancer was used to explore the presence of axonogenesis in breast tumor and the involvement of VEGF, as well as NGF, in the axonogenesis of breast tumor. Nerve infiltration into the tumor was found in MNU-induced rat model of breast cancer including the sensory and sympathetic nerve fibers. Nerve density was increased following the growth of tumor. The sensory neurons innervating the thoracic and abdominal mammary tumors peaked at T5 to T6 and L1 to L2 dorsal root ganglions, respectively. Either VEGF receptor inhibitor or antibody against VEGF receptor 2, as well as NGF receptor inhibitor, apparently decreased both the nerve density and vascular density of breast tumor. The reduced nerve density was correlated with the decreased vascular density induced by these treatments. In cultured dorsal root ganglion neurons, phosphatidylinositol 3 (PI3K)/Akt, extracellular signal-regulated protein kinase (ERK), and p38 inhibitors significantly attenuated VEGF-induced neurite elongation. These findings provide direct evidence that VEGF, as well as NGF, may control the axonogenesis of breast cancer.

Moderate Beer Consumption Modifies Tumoral Growth Parameters and Pyrrolidone Carboxypeptidase Type-I and Type-II Specific Activities in the Hypothalamus-Pituitary-Mammary Gland Axis in an Animal Model of Breast Cancer

AIMS

To determine the effect of moderate alcoholic and nonalcoholic beer consumption on tumoral growth parameters, the histopathology, pyrrolidone carboxypeptidase type I (Pcp I), and type II (Pcp II) specific activities in the hypothalamus-pituitary-mammary gland axis, and the circulating levels of estradiol (E₂) and progesterone (P₄) in rats with N-methyl-N-nitrosourea (NMU) induced mammary tumors.

MATERIAL AND METHODS

Food and drink intake, weight gain and tumor growth parameters were collected. The malignant phenotype of the tumor was performed using the Scarff-Bloom-Richardson grading method. Pcp specific activities were fluorometrically analyzed using pyroglutamyl-β-naphthylamide as substrate. Circulating steroid hormones were determined.

RESULTS

Differences were found in tumoral parameters, depending on the drink. Animals that were given alcohol-containing beer (A/C) beer to drink showed the lowest values of hypothalamic Pcp I, in association with the lowest levels of circulating E₂. The significant decrease in Pcp I activity in all NMU-treated groups suggest a clear role of the Pcp I in the tumoral process, and A/C beer interferes with it.

DISCUSSION

Moderate consumption of alcoholic beer would have beneficial effects against mammary tumors through the modification of the endocrine status mediated by GnRH due to changes on Pcp I and II activities at different levels.

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.

The Effectiveness of Raloxifene-Loaded Liposomes and Cochleates in Breast Cancer Therapy

Liposome (spherical vesicles) and cochleate (multilayer crystalline, spiral structure) formulations containing raloxifene have been developed having dimethyl-β-cyclodextrin (DM-β-CD) or sodium taurocholate (NaTC). Raloxifene was approved initially for the treatment of osteoporosis but it is also effective on breast tissue and endometrial cells. Raloxifene inhibits matrix metalloproteinase-2 (MMP-2) enzyme, which is known to be responsible for tumor invasion and the initiation of angiogenesis during the tumor growth. Therefore, raloxifene was selected as a model drug. A series of raloxifene-loaded liposome and cochleate formulations were prepared. In vitro release studies and in vivo tests were performed. Breast cancer cell lines (MCF-7) were also used to find the most effective formulation. Highest antitumor activity was observed, and MMP-2 enzyme was also found to be inhibited with raloxifene-loaded cochleates containing DM-β-CD. These developed formulations can be helpful for further treatment alternatives and new strategies for cancer therapy.

Forkhead Box Transcription Factor (FOXO3a) mediates the cytotoxic effect of vernodalin in vitro and inhibits the breast tumor growth in vivo

Background

Natural compounds have been demonstrated to lower breast cancer risk and sensitize tumor cells to anticancer therapies. Recently, we demonstrated that vernodalin (the active constituent of the medicinal herb Centratherum anthelminticum seeds) induces apoptosis in breast cancer cell-lines. The aim of this work was to gain an insight into the underlying anticancer mechanism of vernodalin using in vitro and in vivo model.

Methods

Vernodalin was isolated through the bioassay guided fractionation from the seeds. The protein expression of p-Akt, PI3K, FOXO3a, Bim, p27kip1, cyclinD1, and cyclinE was examined by the Western blot analysis. Immunoprecipitation assays were performed to analyse Akt kinase activity. Small interfering RNA (siRNA) was used to study the role of FOXO3a upregulation and their targets during vernodalin treatment. Immunofluorescence, subcellular localisation of FOXO3a by Western blot was performed to analyse FOXO3a localisation in nucleus of breast cancer cells. Immunohistochemical analysis of PCNA, Ki67, p27kip1, FOXO3a and p-FOXO3a in the LA7-induced mammary gland tumor model was performed.

Results

Our results showed that vernodalin regulates cancer cell apoptosis through activation of FOXO transcription factors and its downstream targets (Bim, p27Kip1, p21Waf1/cip1, cyclin D1, cyclin E) as examined by Western blots. Furthermore, we showed that FOXO3a/PI3K-Akt played a significant role in vernodalin induced apoptosis in breast cancer cells. Immunoprecipitation assays showed Akt kinase activity was downregulated. Immunofluorescence, subcellular fractionation and Western blot showed FOXO3a accumulation in the nucleus of breast cancer cells after vernodalin treatment. Silencing of FOXO3a protected breast cancer cells against vernodalin induced apoptosis. The anti-tumor action of vernodalin was further confirmed by examining cell proliferative markers, PCNA and Ki67 in the LA7-induced mammary gland tumor model. We also corroborated our findings in vivo by showing upregulation of p27Kip1, FOXO3a and decrease in the p-FOXO3a level in vernodalin-treated breast tumor tissue.

Conclusions

Our results suggest that PI3K-Akt/FOXOa pathway is a critical mediator of vernodalin-induced cytotoxicity and this compound could be further developed as a potential chemopreventive or chemotherapeutic agent for breast cancer therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-015-0266-y) contains supplementary material, which is available to authorized users.

N-Methyl-N-nitrosourea as a mammary carcinogenic agent

The administration of chemical carcinogens is one of the most commonly used methods to induce tumors in several organs in laboratory animals in order to study oncologic diseases of humans. The carcinogen agent N-methyl-N-nitrosourea (MNU) is the oldest member of the nitroso compounds that has the ability to alkylate DNA. MNU is classified as a complete, potent, and direct alkylating compound. Depending on the animals' species and strain, dose, route, and age at the administration, MNU may induce tumors' development in several organs. The aim of this manuscript was to review MNU as a carcinogenic agent, taking into account that this carcinogen agent has been frequently used in experimental protocols to study the carcinogenesis in several tissues, namely breast, ovary, uterus, prostate, liver, spleen, kidney, stomach, small intestine, colon, hematopoietic system, lung, skin, retina, and urinary bladder. In this paper, we also reviewed the experimental conditions to the chemical induction of tumors in different organs with this carcinogen agent, with a special emphasis in the mammary carcinogenesis.

Anti-Tumor Action, Clinical Biochemistry Profile and Phytochemical Constituents of a Pharmacologically Active Fraction of S. crispus in NMU-Induced Rat Mammary Tumour Model

Cancer patients seek alternative remedies such as traditional medicinal plants for safe and effective treatment and help overcome the side effects of conventional therapy. Current knowledge indicates that extracts of Strobilanthes crispus of the Acanthaceae family exhibit potent anticancer properties in vitro and are non-toxic in vivo. S. crispus was also reported to be protective against chemical hepatocarcinogenesis. We previously showed that a bioactive fraction of S. crispus leaves also synergized with tamoxifen to cause apoptosis of human breast cancer cell lines without damaging non-malignant epithelial cells. The present study aimed to evaluate the antitumor effect of S. crispus dichloromethane fraction (F3) using N-methyl-N-Nitrosourea (NMU)-induced rat mammary tumor model. Tumor regression was observed in 75% of the rats following 8-week oral administration of F3 with no secondary tumour formation and no signs of anemia or infection. However, no improvement in the liver and renal function profiles was observed. Major constituents of F3 were identified as lutein, 13¹-hydroxy-13²-oxo-pheophytin a, campesterol, stigmasterol, β-sitosterol, pheophytin a and 13²-hydroxy-pheophytin a. These compounds however, may not significantly contribute to the antitumor effect of F3.

Determinants of DHA incorporation into tumor tissue during dietary DHA supplementation

Docosahexaenoic acid (DHA), upon incorporation into tumor tissue, has the potential to sensitize tumors to the effects of chemotherapy or radiation therapy. Although DHA has usually been supplied to tumor tissue in the diet, appropriate dietary conditions required to obtain optimal tumor levels have not been established. Hence, we studied mammary tumor tissue responses in rats fed various durations and doses of DHA. Rats fed a palm oil enriched diet (diet 0) were switched to diets providing either 0.8 g DHA/day (diet 1) or 1.5 g DHA/day (diet 2). Tumor tissue fatty acid composition was analysed at baseline (diet 0), at weeks 1, 4 and 9 during diet 1 and at week 4 during diet 2. Dietary DHA supplementation differentially increased DHA within phospholipids (PL) and triacylglycerol (TAG) fractions in tumors. DHA level equilibrated between 2 and 4 weeks in PL while DHA increase was more progressive in TAG and did not reach a steady state. A higher dose of DHA further increased DHA content in tumor PL and TAG (P = 0.018 and P < 0.001, respectively). DHA concentration in plasma PL was positively correlated with DHA in tumor PL (r = 0.72; P = 0.0003) and TAG (r = 0.64; P = 0.003). We conclude that dietary DHA supplementation enhances tumor content of DHA in a time- and dose-dependent manner, and that the DHA level in plasma PL could be used as a proxy for tumor DHA. These findings have implications for dietary DHA supplementations in cancer patients.

Hypothalamus-pituitary-thyroid axis disruption in rats with breast cancer is related to an altered endogenous oxytocin/insulin-regulated aminopeptidase (IRAP) system

Associations of breast cancer with diseases of the thyroid have been repeatedly reported, but the mechanism underlying this association remains to be elucidated. It has been reported that oxytocin (OXT) attenuates the thyroid-stimulating hormone (TSH) release in response to thyrotrophin-releasing hormone (TRH) and decreased plasma levels of TSH as well as the thyroid hormones by an effect mediated by the central nervous system. Oxytocinase (IRAP) is the regulatory proteolytic enzyme reported to hydrolyze OXT. Changes in IRAP activity have been reported in both human breast cancer and N-methyl-nitrosourea (NMU)-induced rat mammary tumours. Here, we measure IRAP activity fluorometrically using cystyl-β-naphthylamide as the substrate, in the hypothalamus-pituitary-thyroid axis together with the circulating levels of OXT, and its relationship with circulating levels of TSH and free thyroxine (fT4), as markers of thyroid function in control rats and rats with breast cancer induced by NMU. We found decreased thyroid function in rats with breast cancer induced by NMU, supported by the existence of lower serum circulating levels of both TSH and fT4 than their corresponding controls. Concomitantly, we found a decrease of hypothalamic IRAP activity and an increase in circulating levels of OXT. We propose that breast cancer increases OXT pituitary release by decreasing its hypothalamic catabolism through IRAP activity, probably due to the alteration of the estrogenic endocrine status. Thus, high circulating levels of OXT decreased TSH release from the pituitary, and therefore, of thyroid hormones from the thyroid, supporting the association between breast cancer and thyroid function disruption.

Enhancing chemotherapeutic drug inhibition on tumor growth by ultrasound: an in vivo experiment

An in vivo study on enhancing epirubicin hydrochloride (EPI) inhibition on tumor growth by ultrasound (US) was reported. Five-week-old male nude mice were used and HL-60 cells were s.c. (subcutaneous injection) inoculated in axilla of these mice. Six groups were designed and five consecutive treatments were applied to investigate the inhibition on tumor growth and body weight growth. US applied locally to the tumor resulted in a substantially increased drug uptake in tumor cells. The inhibition on tumor growth depended on the position of drug injection and phospholipid-based microbubble (PMB) application. Tumor growth rate under group 1 (PMB+US) was similar to that of blank control. The order of the inhibition on tumor volume growth was: group 4 (s.c. EPI+PMB+US) > group 5 intraperitoneal (i.p. EPI+PMB+US) > group 2 (i.p. EPI) > group 3 (s.c. EPI+US) > group 1 (PMB+US). Similar conclusion was obtained from experimental measurements of tumor weight change. The order of animal survival status for EPI administration groups was: group 4 > group 5 > group 2 > group 3. Chemotherapeutic drug inhibition on tumor growth could be enhanced by local US combined with PMB, which might provide a potential application for US-mediated chemotherapy.

Renin-angiotensin system-regulating aminopeptidase activities are modified in the pineal gland of rats with breast cancer induced by N-methyl-nitrosourea

OBJECTIVE

Pineal function has been considered particularly as a neuroendocrine modulator in hormone responsive tumors, like the hormone-dependent mammary tumors. The complexity of the gland function, moreover, is denoted by the presence of a local renin-angiotensin-system (RAS) that regulates melatonin biosynthesis. Classically, angiotensin II (Ang II) has been considered as the effector peptide of the RAS, but Ang II is not the only active peptide. Several of its degradation products, including angiotensin III (Ang III) and angiotensin IV (Ang IV) also possess biological functions. These peptides are formed via the activity of several aminopeptidases. Our aim is to know their role in the regulation of pineal RAS and breast cancer.

DESIGN

Aminopeptidase N (APN), aminopeptidase B (APB) and aminopeptidase A (aspartyl- and glutamyl-aminopeptidase, APA) activities are measured in the pineal gland of rats with breast cancer induced by N-methyl nitrosourea (NMU).

METHODS

Aminopeptidase activities were measured fluorimetrically using their corresponding aminoacyl-beta-naphthylamides as substrates.

RESULTS

Specific APN and APB activities in pineal gland of controls and NMU-treated rats were not modified. Aspartyl aminopeptidase activity significantly decreased in NMU-treated rats when compared with control group. On the contrary, glutamyl aminopeptidase activity did not show significant differences between groups.

CONCLUSIONS

We propose that the local RAS in pineal gland is modified in rats with breast cancer induced by NMU through the inhibition of AspAP activity, which may lead to increased levels of Ang II. Ang II could be responsible of the overproduction of melatonin, supporting a mechanism to restrain the promotion and/or progression of breast cancer.

Specific enkephalin-degrading aminopeptidase activity in the HPT and HPO axes of rats with breast cancer induced by N-methyl nitrosourea

State and function of breast depend on an endocrinological balance, the upsetting of which can be a factor favorable to the development of cancer. Enkephalins (ENK) have been considered as a particular form of adaptation to defense to the organism against neoplastic processes. However, ENK may modify the endocrine functions of glands such as the ovary or the thyroid through the hypothalamus-pituitary axis, acting direct or indirectly as endocrine, paracrine or autocrine stimulatory growth factors. The present work analyses enkephalin-degrading tyrosyl aminopeptidase (EDA) activity in the hypothalamus-pituitary-thyroid (HPT) and hypothalamus-pituitary-ovary (HPO) axes in a rat model of breast cancer induced by N-methyl-nitrosourea (NMU) to state the relationship between ENK levels modification through EDA activity at different neuroendocrine levels and breast cancer. Results obtained show a decrease in EDA activity in hypothalamus, anterior and posterior pituitary, thyroid and ovary, suggesting increased levels of ENK in all these locations. These ENK may induce breast cancer cell growth and progression not only at breast level, but also acting at several neuroendocrine levels such as the HPT and HPO axes, inducing an unbalance of several other hormones, which could also facilitate the progression of cancer as an undesirable concomitant effect.

Food and Botanical Groupings and Risk of Breast Cancer: A Case-Control Study in Shanghai, China

Breast cancer incidence rates more than double in Chinese women as they migrate from China to Hong Kong to the United States, suggesting that environmental factors contribute to the international variation in breast cancer incidence. Several dietary factors, which differ between the United States and the Chinese population, including intake of soy, meat, and fruits and vegetables, have been suggested to affect breast cancer risk. This report describes results from a case-control study of diet and risk of breast cancer nested in a randomized trial of breast self exam in Shanghai, China. Participating breast cancer cases (n = 378) and frequency age-matched controls (n = 1,070) completed a comprehensive food frequency questionnaire and a risk factor questionnaire. After adjustment for age, total energy intake, and total years of breast-feeding, women in the highest quartile of fruit and vegetable intake (≥3.8 servings/d) were significantly less likely to have breast cancer (odds ratio, 0.48; 95% confidence interval, 0.29-0.78) as compared with women in the lowest quartile of intake (≤2.3 servings/d). Egg consumption was also significantly inversely associated with risk of breast cancer (odds ratio for ≥6.0 eggs/wk versus ≤2.0 eggs/wk is 0.56; 95% confidence interval, 0.35-0.91). There was no difference in soy consumption between cases and controls. None of the associations with a single botanical family explained the strong inverse relationship between fruits and vegetables and breast cancer risk. These results provide additional evidence in support of the important role of fruits and vegetables in breast cancer prevention.

Serum oxytocinase activity is related to tumor growth parameters in N-methyl nitrosourea induced rat breast cancer

Oxytocinase has been reported to hydrolyse the peptide hormone oxytocin (OT). We have previously described changes in oxytocinase activity in human breast cancer, where a highly significant increase occurred in tumoral tissue. In the present work, we analysed oxytocinase activity in serum of rats with breast cancer induced by N-methyl-nitrosourea (NMU). We also correlated these data with the number and size of tumors and the body weight of the animals to evaluate the putative value of this activity as a biological marker of the disease. Our results confirm the involvement of OT in carcinogenesis and suggest a mayor role for oxytocinase activity in the development of breast cancer.

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.

Estrous cycle regulation of mammary epithelial cell proliferation, differentiation, and death in the Sprague-Dawley rat: a model for investigating the role of estrous cycling in mammary carcinogenesis

The Sprague-Dawley rat is highly regarded for studies designed to investigate the effects of endocrine modulation on mammary carcinogenesis. In this study, we further evaluate the validity of the Sprague-Dawley rat model for the study of human breast cancer by evaluating the effects of normal 4-day estrous cycling on mammary epithelial cell proliferation, differentiation, and apoptotic death. Trends in mammary gland development with stage of 4-day estrous cycle were evident. Mammary glands isolated from follicular and early luteal stages had predominantly ductal histoarchitecture, whereas glands isolated from mid-late luteal were predominantly lobuloalveolar. Quantitation of BrdU incorporation revealed that epithelial cell proliferation was eight-fold higher in metestrus and diestrus-1 than in proestrus. Expression of beta-casein and whey acidic protein (WAP)4 mRNA was also highly dependent on stage of estrous, with detection restricted to midcycle. Apoptotic cell death of mammary epithelium was found to be suppressed during the peak in cell proliferation. TRPM-2/ clusterin mRNA was elevated when apoptosis was low and milk protein mRNA levels were high, consistent with putative roles for TRPM-2/clusterin in inhibiting cell death in regressing tissues and inducing mammary epithelial cell differentiation. Cell proliferation, differentiation, and death occurred only in a subset of epithelial cells per estrous cycle, and these cells appeared randomly distributed throughout multiple ductules and alveoli. These observations suggest that cellular response(s) to ovarian hormone-dependent signals is asynchronous. Cumulatively, these observations demonstrate that rat mammary epithelial cell proliferation, differentiation, and death are under the control of cycling ovarian hormones, similarly to the human mammary epithelium during the menstrual cycle.

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.

Somatic mutation in the mammary gland: influence of time and estrus

A critical factor in the quantitation of mutation induction in vivo is the time interval between treatment and sampling. In order to study mutagenesis in the mammary epithelium, the cell type in which breast cancer arises, we have measured the manifestation time, the minimum time required for the maximum mutant frequency to be achieved, in this tissue. The F1 LacZ transgenic mice (Muta MousexSWR) were treated with N-ethyl-N-nitrosourea (ENU) at 50 mg/kg for five consecutive days and then sampled at 1, 2, 4, 6, 9, or 12 weeks after the last treatment. The LacZ- mutant frequency reached a maximum at 4 weeks post-treatment and did not vary significantly thereafter. Dlb-1- mutations in the small intestine reached a maximum at 2 weeks after treatment and did not vary significantly thereafter. Since the stage of estrus cycle during carcinogen exposure influences the mammary tumor incidence and latency, it was expected that it would also affect mutation induction. To test this, F1 LacZ mice in the estrus or di-estrus stage were treated with an acute dose of 250 mg/kg ENU and sampled 10-13 weeks post-treatment. No statistical difference between the two groups was found, indicating that the effect of estrus on carcinogenesis is not due to variation in the sensitivity of the stage of the mammary gland to mutation.

Interactive effects of psychosocial stressors and gender on mouse mammary tumor growth

We have previously demonstrated that social housing condition significantly affects the growth rate of the androgen-responsive Shionogi mouse mammary carcinoma (AR SC115) in male mice. The present study examined the effects of social housing condition and acute daily exposure to a novel environment on the growth rate of an androgen-independent variant of the AR SC115 carcinoma, designated SC115V, in male and female mice. Immediately following tumor cell injection, male and female mice that were reared as individuals (I) or in groups (G) of the same sex were rehoused either from individual to same-sex groups (IG) or from group to individual (GI), or remained in their group housing condition (GG). Approximately half the mice in each housing condition were subjected to acute daily exposure to novel environments (novelty stress), a treatment shown previously to increase the significant difference in tumor growth rates between male mice in the IG and GI housing conditions. The remaining mice were left undisturbed (no novelty stress). In the presence of acute daily novelty stress, the growth rate of the SC115V tumor was significantly increased in GI compared to IG males. However, no significant differences in SC115V tumor growth rates among nonstressed GI, IG, or GG males were observed. For females, in contrast to males, acute daily novelty stress significantly decreased tumor growth in GI compared to IG mice, whereas under nonstressed conditions, tumor growth rate was significantly increased in GI compared to IG females. Neither housing condition nor novelty stress altered estrous cyclicity, nor did the stage of the estrous cycle at the time of tumor cell injection influence tumor growth rates. These findings suggest that social housing condition and novelty stress may interact to produce differential effects on the growth rate of the SC115V tumor in male and female mice.

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.

Radiochemical and radiopharmacological properties of pirocarbotrat and other labeled charcoal dispersions: comparative studies in rats with NMU-induced mammary tumors

The purpose of this work is to study the physicochemical properties of Pirocarbotrat to explain its radiopharmacological behavior. We also studied a mixture of charcoal plus chromic [32P]phosphate and charcoal plus sodium [32P]orthophosphate only for comparative purposes. The results show that the mean diameter of the Pirocarbotrat particles was 2.5 microm with an homogeneous distribution, while the other products show an heterogeneous distribution of the particle sizes, with a mean size diameter between 0.5 and 0.9 microm. Hydrolysis studies with a solution of 0.1 N HCl and with sulfochromic mixture revealed that in Pirocarbotrat the 32P is strongly bound to the charcoal particles. Bioelimination studies of Pirocarbotrat show that the total eliminated activity was 12.70 +/- 3.90%, with a higher amount in urine (8.30 +/- 1.80%) than in feces (4.40 +/- 3.50%). When biodistribution studies of Pirocarbotrat were carried out, we found that the 84.50 +/- 2.60% of the activity remained in the tumor with almost null irradiation of the other organs under study. When therapeutic action was evaluated, we observed that the percentage of tumor regression was 78.3% for the tumors injected with Pirocarbotrat. The other dispersions under study showed different behaviors with high activity percentages distributed throughout the organism. These studies demonstrate that Pirocarbotrat has the best radiopharmacological properties to ensure irradiation of the tumor with the least concomitant irradiation of surroundings or other organs or tissues.

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.

Pirocarbotrat: a new radiopharmaceutical for the treatment of solid tumors--comparative studies in N-nitrosomethylurea-induced rat mammary tumors

To evaluate the effectiveness of a single intratumoral dose of Pirocarbotrat, a gelatin-protected charcoal suspension labeled with chromic [32P]pyrophosphate, studies of bioelimination, biodistribution and therapeutic action were carried out in rats, and the results obtained were compared with those of other 32P dispersions. We found that 78.3% of the treated tumors reduced size after 32 days of treatment. At that time, the total eliminated activity was 12.70 +/- 3.90% distributed in urine (8.30 +/- 1.80%) and feces (4.40 +/- 3.50%). Biodistribution studies demonstrate that 84.50 +/- 2.60% of the injected activity remained in the tumor, with no significant concentration in the rest of the organism. We conclude that Pirocarbotrat can be used as a safe agent for brachytherapy of solid tumors with beta particles.

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.

A cytochrome P4502E1 genetic polymorphism and tobacco smoking in breast cancer

Known breast-cancer risk factors account for only part of the variability in breast-cancer incidence. Tobacco smoke is not commonly considered a breast carcinogen, but many of its constituents, such as N-nitrosamines, are carcinogenic in laboratory animal studies. Herein, we assessed a cytochrome P4502E1 (CYP2E1) genetic polymorphism (a Dral restriction enzyme site in intron 6) as a risk factor for breast cancer in both premenopausal and postmenopausal women. Because N-nitrosamines are metabolically activated by CYP2E1, the risk among women smokers was investigated. Caucasian women were enrolled in a case-control study of breast cancer between 1986 and 1991. A subset of the women (219 premenopausal and 387 postmenopausal women) consented to phlebotomy. The allelic frequencies for the premenopausal women (D allele = 0.91 and C allele = 0.09) and postmenopausal women (D allele = 0.93 and C allele = 0.07) were similar to those previously reported. There was no statistically significant association between the CYP2E1 polymorphism and breast-cancer risk for premenopausal or postmenopausal women (adjusted odds ratio (OR) = 1.04, 95% confidence interval (CI) = 0.48, 2.24, and OR = 1.01, 95% CI = 0.55, 1.84, respectively). When the women were categorized as nonsmokers versus smokers (those who smoked more than one cigarette per week for more than 1 yr), premenopausal women with one or two C alleles who had a history of smoking were found to be at increased risk (unadjusted OR = 7.00, 95% CI = 0.75, 14.53, and adjusted OR = 11.09, 95% CI = 1.51, 81.41), although the number of study subjects with those genotypes was small. The small number of study subjects with a C allele precluded meaningful classification by level of smoking, but categorizing the smokers into two groups (above and below the median) also suggested an increased risk. Premenopausal women with the DD genotype and postmenopausal women with any genotype were not at increased risk. Breast-cancer risk was not related to the CYP2E1 genotype in either premenopausal nonsmokers or smokers (adjusted OR = 0.66, 95% CI = 0.20, 2.17, and OR = 2.13, 95% CI = 0.60, 7.59, respectively) or postmenopausal nonsmokers or smokers (OR = 0.90, 95% CI = 0.34, 2.35, and OR = 1.02, 95% CI = 0.46, 2.23, respectively), although the difference in the ORs for premenopausal nonsmokers and smokers suggests an increased risk for smokers. While there are limitations to this study, particularly related to the small number of subjects with the DC and CC genotypes, the study suggests that some women may be susceptible to tobacco smoke because of a CYP2E1 polymorphism. However, these results are preliminary and must be replicated.

Use of colloids of chromic [32P] phosphate in treatment of solid tumors

In order to evaluate the effectiveness of an intratumorally single dose of chromic [32P] phosphate for the treatment of solid tumors, studies of bioelimination, biodistribution, and therapeutic action were carried out. Only for comparative purposes were similar studies undertaken using a solution of sodium [32P] orthophosphate-gelatin. Results show that when sodium [32P] orthophosphate-gelatin was intratumorally injected, the percentage of total elimination, after 32 days of treatment, was equal to 85.90 +/- 8.70%, with a higher percentage in urine (64.50 +/- 13.70%) than in feces (21.40 +/- 4.50%). In biodistribution studies, the greater percentage was found in bone (15.54 +/- 2.21%), whereas only 2.51 +/- 0.39% remained in the tumor. When chromic [32P] phosphate was intratumorally injected, we found that the total elimination was equal to 51.70 +/- 6.90%, with a higher amount in feces (32.70 +/- 4.80%) than in urine (19.00 +/- 3.60%). Biodistribution studies demonstrated that 28.93 +/- 1.30% was still in the tumor and 19.01 +/- 1.30% of the injected activity was found in the liver. On the other hand, when therapeutic action was evaluated, no tumoral regression was observed. These results demonstrate that the colloid of chromic [32P] phosphate cannot be used in the treatment of solid tumors as it mobilizes from the injection point, delivering a high dose to the entire organism.

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

Mammary adenocarcinomas induces in female Sprague-Dawley rats by three intraperitoneal injections of N-nitroso-N-methylurea were studied in order to characterize their estrogen (ER), progesterone (PgR), prolactin (PRLR) and epidermal growth factor (EGFR) receptors. All samples evaluated showed the presence of ER and PgR in the cytosol fraction and PRLR amd EGFR in the membrane fraction. Q (fmol/mg) and K(d) (nM) values were as follows: ER, 56 +/- 11 and 0.5 +/- 0.1; PgR, 109 +/- 25 and 2.2 +/- 0.5 and PRLR, 335 +/- 75 and 0.5 +/- 0.2, respectively. In all tumors studied, two specific sites were found for EGFR, one with Q(1) = 22 +/- 9 and K(d1) = 0.6 +/- 0.3, and the other with Q(2) = 125 +/- 33 and K(d2) = 2.1 +/- 0.5. Receptor content was found to be independent of tumor histopathological variety. Displacement index (DI) with estradiol and tamoxifen of [I(3)H]E2-ER binding showed great heterogeneity, with values ranging from 0.01 to1.54. No correlation between ER content and DI values was found. Antiestrogenic binding sites were not found in the microsomal fraction of ten mammary tumors examined. Proliferation of this experimental mammary tumor may be regulated by a complex interaction of steroid and polypeptide hormones, as well as growth factors.

Effect of tamoxifen on intraperitoneal N-nitroso-N-methylurea induced tumors

The effect of tamoxifen (TAM) was evaluated on a mammary tumor model induced in Sprague-Dawley rats by intraperitoneal administration of three N-nitroso-N-methylurea (NMU) doses. Animals received TAM (1 mg/kg per day) from 10 days before the first NMU dose up to 140 days later. Thereafter, treatment was discontinued and the observation period was extended 60 days longer. Mean overall latency period, tumor number per rat and tumor incidence were recorded. Significant differences between treated and control batches were observed in tumor number per rat (1.8 +/- 1.1 versus 5.2 +/- 1.6; P < 0.05) and in tumor incidence (50% versus 100%; P < 0.05), respectively. No significant difference in latency period between both batches was recorded. All lesions induced in the control batch were malignant, whereas only 45% of those induced in TAM-treated animals were malignant and the remaining 55% were preneoplastic. At 60 days after treatment discontinuance, tumor incidence increased to 90% and also tumor number per rat increased to 4.6 +/- 1.5. TAM effect was also evaluated in rats with NMU-induced tumors by treatment with 1 mg/kg per day during 60 days starting when tumors reached a 1.5-cm diameter. Regression to less than 80% of initial size in 49% of the tumors was observed, while in ovariectomized rats, 33% of tumors regressed. Estrogen receptor content, ER (fmol/mg protein) and Kd (nM) in control tumors were: 56 +/- 10 and 0.5 +/- 0.1. In tumors of TAM-treated animals, ER was less than 5 fmol/mg protein. Findings demonstrate that TAM significantly decreased the appearance of tumors induced in rats by i.p. injection of NMU and when TAM treatment was initiated after tumor induction, some tumors failed to respond to hormonal manipulation. Differential tumor growth response after TAM or oophorectomy in each tumor indicates that in the same rat it is possible to distinguish hormone-dependent and hormone-autonomous tumor populations. Hormonal regulation of tumor growth can be under intrinsic control, regardless of the hormonal status of the whole organism.

H1 and H2 histamine receptors in N-nitroso-N-methylurea (NMU)-induced carcinomas with atypical coupling to signal transducers

Two specific binding sites for histamine were characterized in the cell membrane of N-nitroso-N-methylurea (NMU)-induced tumors. The first one, with higher affinity (Kd = 4 +/- 2 nM), was further identified as an H2 type, while the lower affinity one (35 +/- 10 nM) corresponded to an H1 receptor. Histamine concentrations up to 50 nM, as well as H2 agonists, significantly enhanced the phosphoinositide turnover by acting through higher affinity H2 receptors. On the other hand, histamine at concentrations over 50 nM and H1 agonists produced a 100% increase in cAMP levels in a response specifically blocked by mepyramine. These H1 and H2 histamine receptors that exhibit different linkages to second messenger systems may prove to be a characteristic of cells with a high proliferating capacity, such as undifferentiated or transformed cells.

Histamine receptors in an experimental mammary carcinoma

An experimental mammary carcinoma was induced in Sprague-Dawley rats by the ip administration of N-nitroso-N-methylurea (NMU) in three doses of 50 mg/kg. In order to study the expression of histamine receptors in these experimental tumors, the presence of specific binding sites for histamine was studied. Using [3H]-histamine as a radioligand, two specific binding sites were characterized on the cell membrane. The first site, of high affinity, Kd = 4 +/- 2 nM, was further characterized as an H2 type using [3H]-cimetidine and [3H]-tiotidine as radioligands and by displacement experiments with different histamine agonists and antagonists. The second one of low affinity, Kd = 35 +/- 14 nM, needs further characterization. The determination of cAMP levels showed that histamine and the H2 agonist dimaprit, produced a significant decrease in the nucleotide concentration 6 minutes after stimulation, in a response that was specifically abolished by H2 antagonists. Based on these results, we conclude that neoplastic cells from NMU induced tumors express H2 histamine membrane receptors which are coupled to a transductional pathway different from cAMP production, which may be involved in the regulation of tumor growth.