Triphenyltin isoselenocyanate: a novel nuclear retinoid X receptor ligand with antiproliferative and cytotoxic properties in cell lines derived from human breast cancer.

Several commercially available triorganotin compounds were previously found to function as agonist ligands for nuclear retinoid X receptor (RXR) molecules. Triphenyltin isoselenocyanate (TPT-NCSe), a novel selenium atom containing a derivative of triorganotin origin, was found to represent a new cognate bioactive ligand for RXRs. TPT-NCSe displayed a concentration- and time-dependent decrease in the cell viability in both human breast carcinoma MCF-7 (estrogen receptor positive) and MDA­MB­231 (triple negative) cell lines. Reactive oxygen species levels generated in response to TPT-NCSe were significantly higher in both carcinoma cell lines treated with TPT-NCSe when compared to mock-treated samples. Treatment with 500 nM TPT-NCSe caused a decrease in SOD1 and increased SOD2 mRNA in MCF-7 cells. The levels of SOD2 mRNA were more increased following the treatment with TPT-NCSe along with 1 µM all-trans retinoic acid (AtRA) in MCF-7 cells. An increased superoxide dismutase SOD1 and SOD2 mRNA levels were also detected in combination treatment of 500 nM TPT-NCSe and 1 µM AtRA in TPT-NCSe-treated MDA-MB-231 cells. The data have also shown that TPT-NCSe induces apoptosis via a caspase cascade triggered by the mitochondrial apoptotic pathway. TPT-NCSe modulates the expression levels of apoptosis­related proteins, Annexin A5, Bcl­2 and BAX family proteins, and finally, it enhances the expression levels of its cognate nuclear receptor subtypes RXRalpha and RXRbeta.

Expression of selected nuclear receptors in human epithelial ovarian cell line Caov3 exposed to bisphenol derivatives.

Objectives. Bisphenol A (BPA) is an indispensable industrial chemical. However, as a proven endocrine disruptor, it may be associated with several health disturbances, including the reproductive functions impairment and cancer. Due to the restriction of BPA usage, many bisphenol derivatives gradually substitute BPA. However, studies have reported adverse biological effects of BPA analogs, but the specific sites of their action remain largely unknown. Nuclear receptors (NRs) appear to play significant roles in various types of cancer. In addition, they are considered relevant targets of bisphenols. In the present study, we investigated the effects of BPA and its analogs bisphenol S (BPS), bisphenol F (BPF), and bisphenol AF (BPAF) on mRNA expression of selected NRs in the human ovarian epithelial cell line Caov3. The NRs examined included retinoic acid receptor α (RARA), retinoid X receptor α (RXRA), peroxisome proliferator activating receptor ß/δ (PPARD), chicken ovalbumin upstream promoter-transcription factor 2 (COUPTFII), and nuclear receptor-related protein 1 (NURR1). Methods. Caov3 cells were treated with the bisphenols at the concentrations of 1 nM, 100 nM, 10 µM and 100 µM. After 24 h and 72 h of incubation, cell viability was determined by the MTS assay, and the selected genes expression was analyzed using RT-qPCR. Results. Bisphenol treatment did not affect Caov3 cell viability, except the significant impairment after exposure to the highest BPAF dose (100 µM). At lower doses, neither bisphenol analog altered the expression of the NRs. However, at the highest concentration (100 µM), BPAF and BPA altered the mRNA levels of PPARD, COUPTFII, and NURR1 in a time- and receptor-specific manner. Conclusions. The effects of bisphenols on the specific NRs in the epithelial ovarian cancer cells were addressed for the first time by the present study. Although generally we did not find that bisphenols may provoke significant alterations in the expression of the selected NRs in Caov3 cells, they may alter mRNA expression of certain NRs at high concentrations.

The effect of all-trans retinoic acid on the mitochondrial function and survival of cardiomyoblasts exposed to local photodamage.

Using H9C2 cardiomyoblasts, we have shown that all-trans retinoic acid (ATRA), the biologically active metabolite of vitamin A, affects mitochondrial dynamics and functions. The low dose (10 nM) ATRA stimulates the expression of nuclear retinoid receptors and induces mechanisms that are protective against severe local damage caused by laser irradiation at the mitochondrial level. These changes include increased density of the mitochondrial network, higher number of mitochondrial junctions, and enhanced mitochondrial velocity. Moreover, the treated cells had lower basal level of reactive oxygen species (ROS) and could maintain mitochondrial potential (ΔΨm ) after photodamage. Cells treated with 10 nM ATRA had significantly better survival rate after photodamage in comparison to control cells. Cells treated with pharmacological concentration of ATRA (1 µM) expressed higher mitochondrial connectivity without increased motility, which did not lead to better survival or decreased ROS level as was in the case of low-dose ATRA. The proteomics analysis showed changes in proteins related to cellular metabolism (glycolysis) and respiration in ATRA-treated cells. The l-lactate assay confirmed the shift to anaerobic glycolysis in cells treated with 1 µm ATRA, whereas the 10 nM ATRA decreased the level of lactate in medium. The increased levels of cytochrome c or peroxiredoxins 5 level and also lower expression of retinoid and rexinoid receptors were observed in cells treated with 1 µM ATRA. The effect of ATRA is concentration-dependent; the increased mitochondrial dynamics and slower metabolism at 10 nM ATRA contributed significantly to the chance of survival of the cells after photodamage whereas the higher concentration of ATRA overrode the protective effect and led to the unfavorable ones.

Chronic propranolol treatment moderately attenuated development of N-methyl-N-nitrosourea-induced mammary carcinoma in female rats.

The sympathetic nervous system participates in the development and progression of several cancer types and this effect is mediated mainly via ß-adrenergic signaling. However, the potential of ß-adrenergic signaling blockade to prevent cancer development after exposure to carcinogens has not been investigated, yet. Therefore, in our study, we determined the effect of the ß-blocker propranolol on the development and progression of mammary cancer induced in female rats by administration of the chemical carcinogen N-methyl-N-nitrosourea (MNU). The propranolol treatment (20 mg/kg body weight) started 12 days after MNU administration and lasted 10 weeks. We found that both saline and propranolol treatment significantly increased gene expression of the catecholamine-synthesizing enzyme tyrosine hydroxylase, indicating that repeated injection of saline or propranolol-induced stress in these two groups. However, compared to the vehicle-treated group, propranolol slightly delayed the development and moderately reduced the incidence of mammary carcinoma in animals. To evaluate the mechanisms mediating the effect of propranolol on the development of MNU-induced cancer, we investigated several parameters of the tumor microenvironment and found that propranolol increased gene expression of Casp3. Our data indicate that propranolol treatment that starts after exposure to carcinogens might represent a new, useful approach for preventing the development of cancer, especially in stressed individuals. However, the potential efficiency of propranolol treatment for preventing cancer development and progression in individuals exposed to carcinogens needs further investigation.

CD44 and vimentin, markers involved with epithelial-mesenchymal transition: A proteomic analysis of sequential proteins extraction of triple-negative breast cancer cells after treatment with all-trans retinoic acid.

This work aimed to provide, in one isolation and separation step, an overview of the content of proteins with different solubility after treatment with all-trans retinoic acid, which is considered to be an important therapeutic agent, predominantly in acute promyelocytic leukemia. Breast, ovarian, bladder, and skin cancers have been demonstrated to be suppressed by retinoic acid, as well. The bottom-up proteomic strategies were applied for the analysis of proteins extracted from triple-negative breast cancer MDA-MB-231 cells utilizing a commercially manufactured kit. The gel electrophoresis followed by MALDI-TOF MS analysis was used for protein determination. By employing PDQuest™ software, we identified several proteins affected by all-trans retinoic acid. Two proteins, vimentin and CD44, which are associated with the epithelial-mesenchymal transition, were selected for a detailed study. We have found that all-trans retinoic acid results in significantly reduced levels of vimentin and CD44 in both the cytoplasmic and membrane fractions. A significant effect was particularly evident in CD44, where protein level in the cytoplasmic fraction was almost completely suppressed.

Down-regulation of vimentin by triorganotin isothiocyanates-nuclear retinoid X receptor agonists: A proteomic approach.

An attempt has been made to delineate the role of natural and synthetic retinoid receptor ligands on vimentin expression in the human triple-negative breast cancer cells. The effects of currently synthesized triorganotin derivatives of the general formula R3SnX (R is butyl or phenyl, X is isothiocyanate), which are considered RXR ligands, were investigated in the human MDA-MB-231 breast cancer cell line. Studies were evaluated in the presence and absence of all-trans retinoic acid (ATRA), a natural RAR ligand. Vimentin represents the major protein associated with epithelial-mesenchymal transition (EMT), an essential process when the primary tumour transforms into a malignant one. mRNA and proteomic data obtained in this study, based on the PDQuest software protein evaluation and further quantification of proteins by iTRAQ analysis, suggest that vimentin was significantly reduced in the combination of RAR ligand and RXR ligand treatment. Both tested triorganotin compounds showed similarly reduced expression of vimentin, but tributyltin isothiocyanate (TBT-ITC) proved to be more effective than triphenyltin isothiocyanate (TPT-ITC). Furthermore, the effect of natural (9cRA) and synthetic RXR ligands, both chloride and isothiocyanate derivatives, on vimentin expression was compared.

Causal associations of autoimmune thyroiditis and papillary thyroid carcinoma: mRNA expression of selected nuclear receptors and other molecular targets.

Potential causal associations of autoimmune thyroiditis (AIT) and papillary thyroid carcinoma (PTC) have been studied previously. The mRNA expression patterns of thyroid hormone receptors (TR), retinoid receptors (RAR), rexinoid receptors (RXR), dihydroxyvitamin D3 receptors (VDR), and progesterone receptors (PR) in PTC tissue of patients without autoimmune thyroiditis (PTC/AIT-) and in PTC tissue of patients with coexisting AIT (PTC/AIT+) have been investigated in order to judge whether the observed changes may take part in the promotion and progression of thyroid cancer. Tumours with or without AIT were classified histologically and the semiquantitative PCR was performed. The results revealed that there was decreased expression of TRα, TRßα, RARα and PR mRNA in PTC/AIT+ tumours when compared with PTC/AIT- tumours. Decreased expression of RARα in PTC/AIT+ was detected when compared with PTC/AIT- patients. A similar effect of AIT was observed with a decrease in RARγ expression in PTC/AIT+ patients. On the other hand, there was an increased expression of VDR in thyroid tumours (PTC/AIT+) when compared with PTC/AIT-. PR mRNA was decreased in the thyroid tumours of PTC/AIT+ patients when compared with PTC/AIT- patients. In addition, there was an increased expression of MKi67 and complement C3 in PTC of PTC/AIT+ when compared with PTC/AIT-. In the PTC/AIT+ group, a decreased level of IGF-1 mRNA was found when compared with the PTC/AIT- group. According to the significant differences of the studied markers in PTC/AIT+ compared with PTC/AIT-, it was indicated that AIT may be a predisposing factor for the development of PTC.

Novel insights into the combined effect of triorganotin compounds and all-trans retinoic acid on expression of selected proteins associated with tumor progression in breast cancer cell line MDA-MB-231: Proteomic approach.

Trialkyltins and triaryltins function as nuclear retinoid X receptors (RXR) agonists due to their affinity to the ligand-binding domain of RXR subtypes and function as transcriptional activators. We present the data on combined effects of all-trans retinoic acid (ATRA), retinoic acid receptor (RAR) ligand and tributyltin chloride or triphenyltin chloride (RXR ligands) on protein pattern in MDA-MB-231 cells. Proteomic strategies based on bottom-up method were applied in this study. The total cell proteins were extracted, separated on 2D SDS-PAGE and their characterization was achieved by MALDI-TOF/TOF MS/MS. By employing PDQuest™ software, we identified more than 30 proteins differently affected by the above compounds. For further studies, we selected specific proteins associated either with metabolic pathway (glyceraldehyde-3-phosphate dehydrogenase) or to cellular processes as apoptosis, regulation of gene transcription or epithelial-mesenchymal transition (annexin 5, nucleoside diphosphate kinase B and vimentin). We have found that treatment of MDA-MB-231 cells with triorganotins reduced the expression of studied proteins. Moreover, the treatment of MDA-MB-231 cells with triorganotin compounds together with ATRA resulted in an additional reduction of annexin 5, vimentin and nucleoside diphosphate kinase B. These results demonstrate that RXR/RAR heterodimer may act under this experimental design as permissive heterodimer allowing activation of RXR by triorganotins.

Evaluation of estrogenic potency of a standardized hops extract on mammary gland biology and on MNU-induced mammary tumor growth in rats.

Supplements with estrogenic activities are intensively investigated as potential alternatives for the treatment of menopausal symptoms. These investigations include studies on their safety regarding potential breast cancer risks. Therefore, the aim of this study was to assess whether or not a standardized hops (Humulus lupulus) extract, containing 0.42% of the estrogenic flavanone, 8-prenylnaringenin, would stimulate growth of methyl-nitrosourea (MNU) induced mammary cancer in ovariectomized (OVX) Sprague-Dawley (SD) rats or would impact on the proliferative activity within the normal mammary gland of Wistar rats. To induce tumorigenesis SD-rats received an intraperitoneal injection of 50mg/kg body weight of MNU on postnatal days PND 50 and 52. 28days later animals were OVX or were SHAM operated (positive control) and randomly allocated and maintained for 140days on either a phytoestrogen-free placebo diet (SHAM and negative control) or on the hops fortified diet. For the investigations in the normal mammary gland young adult Wistar rats were bilaterally OVX and randomly allocated to a control group fed to a phytoestrogen-free diet, or to a diet supplemented either with E2-benzoate or the hops extract. As a major result, the tumor incidence was 15% (3 tumors totally) in OVX controls, whereas it was 85% (39 tumors totally) in SHAM operated positive controls. No tumors were detectable in the hops group. In addition, no estrogenic activity of the hops extract was detectable in uterus and liver of these animals. In investigations on the normal mammary gland, no impact of hops extract on the expression of estrogen dependent proliferation markers or of progesterone receptor became apparent. In conclusion, the lack of growth stimulation of MNU-induced breast cancer in OVX SD-rats and the lack of stimulation proliferative events in the normal mammary gland of OVX Wistar rats by standardized hops extracts provides an important piece of evidence regarding the safety of these extracts in the management of menopausal symptoms.

Effects of natural ligands and synthetic triorganotin compounds of nuclear retinoid X receptors in human MCF-7 breast cancer cell line.

In the present study, we analyzed in vitro effects of natural and synthetic triorganotin ligands of nuclear retinoid X receptors in human MCF-7 breast cancer cells. Our data has shown that all-trans retinoic acid significantly reduced expression of RXRalpha mRNA, Bcl2 and enhanced expression of BAX proteins. Tributyltin bromide markedly decreased mRNA level of RXRalpha and RXRbeta. Significantly reduced levels of both RXRs proteins were observed after treatment with tributyltin chloride (TBT-Cl) but not after treatment with triphenyltin chloride (TPT-Cl) for RXRbeta protein. Both RXRalpha and RXRbeta protein levels decrease was found also by combination ATRA+TBT-Cl/TPT-Cl.

The role of retinoic acid receptors and their cognate ligands in reproduction in a context of triorganotin based endocrine disrupting chemicals.

Retinoic acid (RA), an active form of vitamin A, regulates the embryonic development, male and female reproduction and induces important effects on the cell development, proliferation, and differentiation. These effects are mediated by the retinoid (RAR) and rexinoid nuclear receptors (RXR), which are considered to be a ligand-activated, DNA-binding, trans-acting, and transcription-modulating proteins, involved in a general molecular mechanism responsible for the transcriptional responses in target genes. Organotin compounds are typical environmental contaminants and suspected endocrine disrupting substances. They may affect processes of reproductive system in mammals, predominantly via nuclear receptor signaling pathways. Triorganotins, such as tributyltin chloride (TBTCl) and triphenyltin chloride (TPTCl), are capable to bind to RXR molecules, and thus represent potent agonists of RXR subtypes of nuclear receptors not sharing any structural characteristics with endogenous ligands of nuclear receptors. Th is article summarizes selected effects of biologically active retinoids and rexinoids on both male and female reproduction and also deals with the effects of organotin compounds evoking endocrine disrupting actions in reproduction.

The phytoestrogenic Cyclopia extract, SM6Met, increases median tumor free survival and reduces tumor mass and volume in chemically induced rat mammary gland carcinogenesis.

SM6Met, a phytoestrogenic extract of Cyclopia subternata indigenous to the Western Cape province of South Africa, displays estrogenic attributes with potential for breast cancer chemoprevention. In this study, we report that SM6Met, in the presence of estradiol, induces a significant cell cycle G0/G1 phase arrest similar to the selective estrogen receptor modulator, tamoxifen. Furthermore, as a proof of concept, in the N-Methyl-N-nitrosourea induced rat mammary gland carcinogenesis model, SM6Met increases tumor latency by 7days and median tumor free survival by 42 days, while decreasing palpable tumor frequency by 32%, tumor mass by 40%, and tumor volume by 53%. Therefore, the current study provides proof of concept that SM6Met has definite potential as a chemopreventative agent against the development and progression of breast cancer.

A comparative study of protein patterns of human estrogen receptor positive (MCF-7) and negative (MDA-MB-231) breast cancer cell lines.

In the present study, we analyzed the cell lysates of human tumour cell lines representing two major clinically different types of breast cancer. Our main goal was to show the differences between them on proteomic level. Gel electrophoresis followed by MALDI-TOF MS analysis was used for proteins determination. Exactly 98 proteins were unequivocally identified and 60 of them were expressed differentially between MDA-MB-231 and MCF-7 cell lines. Among the proteins reported here, some well-known breast cancer markers (e.g., annexin A1, annexin A2 and vimentin) were identified in the MDA-MB-231 cell line and thus we were able to distinguish both cell lines sufficiently.

Radioligand binding assay for accurate determination of nuclear retinoid X receptors: A case of triorganotin endocrine disrupting ligands.

Nuclear 9-cis retinoic acid receptors (retinoid X receptors, RXR) are promiscuous dimerization partners for a number of nuclear receptors. In the present study, we established a novel in vitro method for quantitative determination of the nuclear retinoid X receptors in rat liver. One type of high affinity and limited capacity RXR specific binding sites with the Ka value ranging from 1.011 to 1.727×10(9)l/mol and the Bmax value ranging from 0.346 to 0.567pmol/mg, was demonstrated. Maximal 9-cis retinoic acid (9cRA) specific binding to nuclear retinoid X receptors was achieved at 20°C, and the optimal incubation time for the 9cRA-RXR complex formation was 120min. From a number of endocrine disruptors, tributyltins and triphenyltins are known as RXR ligands. Our data confirmed the property of tributyltin chloride or triphenyltin chloride to bind to a high affinity and limited capacity RXR binding sites. Described optimal conditions for ligand binding to RXR molecules enabled us to calculate maximal binding capacity (Bmax) and affinity (Ka) values. This study provides an original RXR radioligand binding assay that can be employed for investigation of novel RXR ligands that comprise both drugs and endocrine disruptors.

Relationship between histology, development and tumorigenesis of mammary gland in female rat.

The mammary gland is a dynamic organ that undergoes structural and functional changes associated with growth, reproduction, and post-menopausal regression. The postnatal transformations of the epithelium and stromal cells of the mammary gland may contribute to its susceptibility to carcinogenesis. The increased cancer incidence in mammary glands of humans and similarly of rodents in association with their development is believed to be partly explained by proliferative activity together with lesser degree of differentiation, but it is not completely understood how the virgin gland retains its higher susceptibility to carcinogenesis. During its developmental cycle, the mammary gland displays many of the properties associated with breast cancer. An early first full-term pregnancy may have a protective effect. Rodent models are useful for investigating potential breast carcinogens. The purpose of this review is to help recognizing histological appearance of the epithelium and the stroma of the normal mammary gland in rats, and throughout its development in relation to tumorigenic potential.

Agonistic effect of selected isoflavones on arylhydrocarbon receptor in a novel AZ-AhR transgenic gene reporter human cell line.

The aryl hydrocarbon receptor (AhR) is a ligand-activated transcription factor that controls the expression of a diverse set of genes. Structurally diverse compounds bind to AhR and act as AhR agonists. Well characterised family of natural AhR ligands are isoflavones, which are compounds found predominantly in soy beans or red clover. In this study we have examined agonistic effect of selected isoflavones (genistein, daidzein, biochanin A, formononetin and equol) on AhR in the novel transgenic gene reporter human cell line AZ-AhR, a stably transfected AhR-responsive cell line allowing rapid and sensitive assessment of AhR transcriptional activity. We demonstrated that biochanin A, formononetin and genistein at concentration 10(-4) mol/l exerted agonistic effects on AhR with fold activation of 309- fold, 108-fold and 27-fold, which is about 84.8%, 29.6% and 7.4%, respectively, of the value attained by 2,3,7,8-tetrachlorodibenzo-p-dioxin. Daidzein and equol did not show any significant effects on AhR.

The relationship between renal cell carcinoma and nuclear retinoid/rexinoid receptors.

BACKGROUND: Renal cell carcinoma (RCC) is a urologic malignancy with a steady rise in incidence and high mortality rate. Between 60 to 70% of patients with renal cell carcinoma can only be cured with surgery but despite advances in early diagnostis, in around 20-30% of cases there is metastasis. For these patients, chemotherapy and radiotherapy are ineffective and hence the prognosis is poor. Retinoids are biologically active compounds of either natural or synthetic origin that are involved in complex physiological and developmental processes in many tissues including cell proliferation and activation of tumour suppression genes. This article reviews the role of retinoids and their cognate nuclear retinoid/rexinoid receptors in relation to renal cell carcinoma. METHODS: A literature search using ScienceDirect and Medline with a focus on the relationship between renal cell carcinoma and nuclear retinoid/rexinoid receptors. RESULTS: Use of retinoids/rexinoids in the treatment of locally advanced and metastatic RCC significantly prolongs median time of tumour progression and overall survival of patients. Combination therapy with other preparations has greater efficacy than treatment with retinoids alone. Patient survival can be predicted on the basis of the expression of different all-trans retinoic acid receptor (RAR) and 9-cis retinoic acid receptor (RXR) subtypes. CONCLUSIONS: Since nuclear retinoid receptors play a crucial role as ligand-activated, DNA binding, trans-acting, transcription-modulating proteins involved in a general molecular mechanism responsible for transcriptional responses in target genes, retinoids might be an alternative approach for the treatment of renal cell carcinoma.

Nuclear receptors - target molecules for isoflavones in cancer chemoprevention.

Breast cancer is the most occurring type of cancer among women. In Slovakia, there are yearly diagnosed about 1900 new cases of this disease. Breast cancer treatment is very expensive, psychic stressful and in some cases ineffective. Therefore, it is essential to search for new and/or alternative methods for breast cancer treatment, since nuclear receptors are considered to be a central goal for maximizing treatment opportunities in breast cancer. Among natural ligands for estrogen receptors (ERα and ERß), which are member of nuclear receptors superfamily, belongs also isoflavones. These natural compounds have similar structure to main female hormon-17ß estradiol. A rich source of isoflavones is soy and its products. Three aglycones form of isoflavones (genistein, daidzein, glycitein) are predominantly found in soybean and red clover. Among other important isoflavones belongs also biochanin A and formononetin.

mRNA expression pattern of retinoic acid and retinoid X nuclear receptor subtypes in human thyroid papillary carcinoma.

Retinoids have shown potential for the inhibition of tumour growth and progression. The objective of this study was to investigate retinoic acid nuclear receptor subtypes RAR/RXR and iodothyronine 5'-deiodinase, type I expression pattern in papillary thyroid tumour tissue of 26 patients in order to compare with those of the non-neoplastic thyroid tissue of the corresponding patients. The expression of selected parameters mRNA was examined by semi-quantitative RT-PCR. Papillary thyroid carcinoma (PTC) expressed RXRγ, when compared to non-neoplastic thyroid tissues of the corresponding patients that were lacking expression of RXRγ or its expression was very low. Moreover, we found significantly increased expression of RARα and RARγ in the overall group of PTC. This increase was detected in cases with positive lymph node metastasis (LNM), but not in cases with negative LNM. RARß was significantly reduced in the subgroup of classic variant (CV). We also detected absence or significantly lower expression of hDIO1 mRNA in tumour tissue when compared to non-neoplastic tissue in both overall PTC cases and in the CV subgroup. However, the significantly decreased levels of hDIO1 mRNA were detected in cases with negative LNM but not in cases with positive LNM when compared to corresponding non-tumour tissue in both overall PTC cases and in the CV subgroup. Differences in RAR and RXR subtype mRNA expression patterns in various PTCs may contribute to the immunochemistry data available, and may thus find exploitation in clinical oncology, particularly in the differential diagnosis of thyroid neoplasms.

MNU-induced mammary gland carcinogenesis: chemopreventive and therapeutic effects of vitamin D and Seocalcitol on selected regulatory vitamin D receptor pathways.

The effects of administration of vitamin D3 and Seocalcitol on MNU-induced carcinogenesis of mammary gland in Sprague-Dawley rats have been investigated. Administration of both substances in a weekly dose of 7 µg/kg caused prolonged latency of mammary gland tumors. The latency of tumors was markedly prolonged for 30-40 days by Seocalcitol. Using PET analysis, reduction in [¹8F]2-fluoro-2-deoxy-d-glucose (FDG) uptake or tumor volume in tumors chemopreventively treated with vitamin D3 were detected in MNU-induced tumors, vitamin D3 reduced expression of 25-hydroxylase (25OHase) (p<0.01) and 24-hydroxylase (24OHase) (p<0.01) and Seocalcitol 24OHase. Positive regulation of 25OHase mRNA level after the treatment with vitamin D3 was observed in liver, while in kidney, vitamin D3 and Seocalcitol induced expression of 24OHase was significant. Our observations indicate a cross talk between respective pathways of VDR, RARs/RXRs, TRs and ERs in carcinogenesis process.