Protective effect of metformin in CD1 mice placed on a high carbohydrate-high fat diet

A high carbohydrate-high fat (HC-HF) diet-associated with hyperinsulinemia has been previously reported to induce accelerated growth of prostate cancer in a xenograft model. High energy supply and insulin/insulin growth factor-1 axis are two of the mechanisms proposed. We hypothesize that metformin may have a protective effect against prostate cancer progression by affecting metabolisms associated with high energy intake. In the present study, animals were randomized into five groups, receiving a HC-HF diet with 50, 100, or 250mg/kg body weight (mg/kg) metformin in drinking water, a standard diet or HC-HF diet alone. Animals on the HC-HF diet developed obesity and insulin resistance. They had significantly higher body weight, fasting blood glucose at an upper level of normal range, higher insulin secretion and utilization, and fatty degeneration of the liver. Metformin at the doses employed significantly reduced food and water consumption; however, only a dose of 250mg/kg showed a significant reduction in body weight gain and suppression of gluconeogenesis as well remarkably reduced insulin secretion. There was no observed metformin-related hepato-toxicity in any of the groups. In summary, metformin at various doses exhibits protective effects on the metabolic disorder caused by the HC-HF diet with the most effective protection at a dose of 250mg/kg. These effects may explain its translational role relating to its anti-neoplastic potential.

Abstract 5724: Capsaicin and lycopene in combination reduce proliferation and induce apoptosis in prostate cancer cells via TRPV6 mediated phenomenon

Introduction and Hypothesis: Prostate cancer (PCa) is the most common internal malignancy and the second most frequent cause of cancer death in Canadian men. Capsaicin recently investigated for its anti-cancer properties, is the active compound found in chilli peppers. Well-established as a pain reliever, capsaicin acts mainly on the transient receptor potential vanilloid (TRPV)-1 and TRPV6 receptor. The TRPV1 receptor is a non-selective cation channel that induces an inflow of cations Ca2+ and Na+ when activated. Similarly, activation of the TRPV6 receptor facilitates Ca2+ entry across the plasma membrane. Both TRPV1 and TRPV6 receptors are expressed in PCa tissue. Our present study aims to investigate the chemopreventive effect of capsaicin in combination with lycopene, an antioxidant found in tomatoes. We have found that PCa cells treated with capsaicin and lycopene alone and combined, cause a significant reduction in proliferation and an induction of apoptosis. Mechanistic studies examining this relationship have not been well defined. We hypothesize that capsaicin and lycopene in combination reduce proliferation and induce apoptosis via the TRPV6 and TRPV1 receptor in PCa cells in vitro.

Materials and Methods: Two human PCa cell lines (LNCaP (AR+) and PC3 (AR-)) were analyzed. Cells were treated with capsaicin alone, or in combination with lycopene. Cells were incubated for up to 24 hours and proliferation assessed using MTS assay. Alterations in TRPV6, TRPV1, PSA, cell-regulatory molecules, and apoptotic markers were assessed by Western blot analysis.

Results: There was a significant (P< 0.05) decrease in the proliferation of LNCaP and PC3 cells treated with capsaicin alone and in combination with lycopene (p< 0.001). Western blot analysis revealed a reduction (2-fold change) in PSA expression in LNCaP cells when treated with capsaicin alone. Interestingly this treatment resulted in the up-regulation in cell cycle marker p27 as well as cleaved PARP, in a time-dependent manner, demonstrating that the cells are undergoing cell cycle arrest and apoptosis. Further, we established that there is an up-regulation (3-fold change) of TRPV6 expression and an increase in TRPV1 expression with the treatment of capsaicin and lycopene alone and in combination. A plausible mechanism of action for this combination of capsaicin and lycopene is currently being investigated.

Conclusions: We have shown for the first time that the TRPV6 receptor may play an important role in capsaicin and lycopene mediated cell-cycle arrest and apoptosis in human PCa cells. These studies may eventually help identify patients likely to benefit from the use of capsaicin in combination with lycopene. Ultimately these strategies may have a more meaningful impact on PCa morbidity and mortality than other therapeutic strategies currently in use.

Funding: CIHR grant to VV.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5724.

Abstract 1799: Utilizing metformin to enhance the efficacy of androgen deprivation therapy in the treatment of prostate cancer

The incidence of prostate cancer varies dramatically by geographic location, with developed countries exhibiting significantly higher levels of disease. Some attribute this to the ‘Westernized lifestyle’ of high energy diets coupled with lack of physical activity and consequent obesity. Rising obesity levels have been mirrored by increased diagnoses of non-insulin dependent diabetes (NIDDM). Whilst evidence for a causal association between obesity or NIDDM, and prostate cancer is mixed, clear evidence exists that obese prostate cancer sufferers have higher levels of prostate cancer-specific mortality. This may be due to obesity or diabetes-induced hyperinsulinemia, causing upregulated pro-proliferative insulin/insulin-like growth factor signaling. Our group has previously reported the association between diet-induced hyperinsulinemia and enhanced prostate cancer tumor growth in a murine xenograft model.

Prostate cancer treatment varies depending on the stage/grade of the presenting disease. However, androgen ablation therapy remains the treatment of choice for advanced disease. Metformin (an oral biguanide used to treat NIDDM) has been shown to possess anti-neoplastic properties in vitro and in vivo. Studies have also shown that metformin treated diabetics experience less cancer diagnoses and/or prostate cancer-specific mortality. We assessed the potential additive benefit of androgen ablation therapy (bicalutamide) in combination with metformin.

Using MTT and clonogenic assays we assessed the effect of bicalutamide and/or metformin on cell proliferation rates in LNCaP, PC3, DU145 and PC3AR2 prostate cancer cell lines.

Exposing the cell lines to micromolar concentrations of bicalutamide or millimolar concentrations of metformin resulted in significant dose-dependent reductions in cellular proliferation (p<0.0001). Combined treatment with bicalutamide and metformin caused a further 10-fold reduction in cell proliferation. This effect was pronounced in cell lines expressing functional androgen receptors.

Combining bicalutamide and metformin significantly reduces prostate cancer cell proliferation rates, further than monotherapy alone. These preliminary results are being further evaluated to determine whether this positive interaction is additive or synergistic. We are also assessing the combination regimen in vivo using a murine xenograft model and are performing mechanistic studies to determine how bicalutamide and metformin interact.

This combination regimen may potentially improve prostate-cancer specific survival via the direct anti-neoplastic properties described above. In addition, although not investigated here, metformin, within the combination treatment regimen may improve overall survival rates by reducing the risk of anti-androgen induced metabolic syndrome, and its consequent cardiovascular related mortality.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1799.

A combination of micronutrients is beneficial in reducing the incidence of prostate cancer and increasing survival in the Lady transgenic model

We have previously shown that administration of a combination of micronutrients (selenium, vitamin E, and lycopene) inhibits prostate cancer (PCa) development in the Lady transgenic model. In the present study, we examine timing of initiation of micronutrients, and the effect of micronutrient combinations, on PCa development in Lady transgenic model. Transgenic males were randomized to either a control diet; control diet supplemented with human equivalent doses of vitamin E, selenium, and lycopene (E+S+L); or control diet supplemented with vitamin E and selenium (E+S). In separate experiments, the combination of E+S+L was initiated at varying time points (4, 8, 20, and 36 weeks of age). A combination of E+S+L resulted in a significant reduction in PCa and liver metastasis when intervention was commenced within 8 weeks of age (P < 0.0001). Immunohistochemical analysis revealed a strong correlation between disease-free state with up-regulation of the prognostic marker p27(Kip1) (P < 0.0001) and decreased expression of proliferating cell nuclear antigen and significantly increased apoptotic index (P < 0.0001). On the contrary, a combination of E+S was not effectual in preventing PCa, with a high proportion (84.6%) of animals developing PCa and a small proportion (11.5%) developing high-grade PIN. Early commencement of micronutrients (E+S+L) is beneficial in reducing PCa. Lycopene is an essential component of the combination and effective (when used with E+S) for PCa prevention. These observations provide support for their chemopreventive effect and some clues about their mechanism of action. These key findings will be complementary to the outcome from the Selenium and Vitamin E Chemoprevention Trial.

The impact of diet and micronutrient supplements on the expression of neuroendocrine markers in murine Lady transgenic prostate

BACKGROUND

Neuroendocrine (NE) differentiation (NED) in prostate cancer (PCa) is associated with morbidity and death; however, the underlying cause(s) promoting NED in PCa have yet to be determined. In this study, we examined the effect of both diet and micronutrient supplementation on the expression of NE markers using the Lady (12T-10) transgenic model of PCa. Lady (12T-10) transgenic animals develop advanced adenocarcinoma with NE characteristics that exhibits metastases in approximately 80% of cases. In this model a high fat diet has been shown to increase the severity of disease, while the use of micronutrients can inhibit this progression.

METHODS

In this study we used immunohistochemical analysis to determine expression of the NE markers: chromogranin A (CgA), neuron-specific enolase (NSE), bombesin, parathyroid hormone-related peptide (PTHrP), neurotensin and serotonin in prostates of PCa-bearing Lady (12T-10) mice.

RESULTS

High fat diet was correlated with significantly elevated expression of CgA and serotonin in prostate tissue of Lady (12T-10) mice. Addition of micronutrients to the control and high fat diet reproducibly elevated PTHrP and bombesin expression and suppressed NSE expression, while prostate tissue from the control diet supplemented with micronutrients exhibited significantly lower numbers of calcitonin- and neurotensin-positive cells.

CONCLUSIONS

These results highlight the importance of dietary control in management of disease and identify differential changes in NE marker expression, which may be diagnostically viable in monitoring the impact of therapies on disease status.

Association of diet-induced hyperinsulinemia with accelerated growth of prostate cancer (LNCaP) xenografts

BACKGROUND

Prior research suggested that energy balance and fat intake influence prostate cancer progression, but the influence of dietary carbohydrate on prostate cancer progression has not been well characterized. We hypothesized that hyperinsulinemia resulting from high intake of refined carbohydrates would lead to more rapid growth of tumors in the murine LNCaP xenograft model of prostate cancer.

METHODS

Athymic mice were injected subcutaneously with LNCaP human prostate cancer cells and, when tumors were palpable, were randomly assigned (n = 20 per group) to high carbohydrate-high fat or low carbohydrate-high fat diets. Body weight and tumor volume were measured weekly. After 9 weeks, serum levels of insulin and insulin-like growth factor 1 (IGF-1) were measured by enzyme immunoassay. AKT activation and the levels of the insulin receptor in tumor cells were determined by immunoblotting. The in vitro growth response of LNCaP cells to serum from mice in the two treatment groups was measured based on tetrazolium compound reduction. All statistical tests were two-sided.

RESULTS

After 9 weeks on the experimental diets, mice on the high carbohydrate-high fat diet were heavier (mean body weight of mice on the high carbohydrate-high fat diet = 34 g versus 29.1 g on the low carbohydrate-high fat diet, difference = 4.9 g, 95% CI = 3.8 to 6.0 g; P = .003), experienced increased tumor growth (mean tumor volume in mice on high carbohydrate-high fat diet = 1695 versus 980 mm3 on low carbohydrate-high fat diet, difference = 715 mm3, 95% CI = 608 to 822 mm3; P<.001), and experienced a statistically significant increase in serum insulin and IGF-1 levels. Tumors from mice on the high carbohydrate-high fat diet had higher levels of activated AKT and modestly higher insulin receptor levels than tumors from mice on the low carbohydrate-high fat diet. Serum from mice on the high carbohydrate-high fat diet was more mitogenic for LNCaP cells in vitro than serum from mice fed the low carbohydrate-high fat diet.

CONCLUSION

A diet high in refined carbohydrates is associated with increased tumor growth and with activation of signaling pathways distal to the insulin receptor in a murine model of prostate cancer.

A genome-wide association screen identifies regions on chromosomes 1q25 and 7p21 as risk loci for sporadic prostate cancer

We conducted a genome-wide association study of 3090 sporadic prostate cancer patients and controls using the Affymetrix 10 000 SNP GeneChip. Initial screening of 40 prostate cancer cases and 40 non-cancer controls revealed 237 SNPs to be associated with prostate cancer (P<0.05). Among these SNPs, 33 were selected for further association analysis of 2069 men who had undergone a cancer-screening prostate biopsy. Results identified five loci as being significantly associated with increased prostate cancer risk in this larger sample (rs 1930293, OR=1.7, P=0.03; rs 717809-2p12, OR=1.3, P=0.03; rs 494770-4q34, OR=1.3, P=0.01; rs 2348763-7p21, OR=1.5, P=0.01; rs 1552895-9p22, OR=1.5, P=0.002). To validate these association data, 61 additional HapMap tagSNPs spanning the latter five loci were genotyped in this subject cohort and an additional 1021 men (total subject number=3090). This analysis revealed tag SNP rs 4568789 (chromosome 1q25) and tag SNP rs 13225697 (chromosome 7p21) to be significantly associated with prostate cancer (P-values 0.009 and 0.008, respectively). Haplotype analysis revealed significant associations of prostate cancer with two allele risk haplotypes on both chromosome 1q25 (adjusted OR of 2.7 for prostate cancer, P=0.0003) and chromosome 7p21 (adjusted OR of 1.3, P=0.0004). As linkage data have identified a putative prostate cancer gene on chromosome 1q25 (HPC1), and microarray data have revealed the ETV1 oncogene to be overexpressed in prostate cancer tissue, it appears that chromosome 1q25 and 7p21 may be sites of gene variants conferring risk for sporadic and inherited forms of prostate cancer.

Expression of TMPRSS2:ERG gene fusion in prostate cancer cells is an important prognostic factor for cancer progression

The prostate-specific gene, TMPRSS2, is fused with the transcription factor gene, ERG in a high proportion of prostate cancers. However, the clinical significance of TMPRSS2:ERG gene fusion among prostate cancer patients is unknown. We assayed for the presence of the TMPRSS2:ERG gene fusion product among 26 patients who underwent surgery for clinically localized prostate cancer using RT-PCR and direct DNA sequencing, and evaluated its prognostic significance. All 26 patients had cancers of the same histologic grade (Gleason score 7). The fusion protein was present within prostate cancer tumor cells in eleven patients (42.3%). Nine patients experienced biochemical disease relapse (elevated PSA) after a mean follow-up of 12 months (range 1 to 48 months). Patients with the fusion protein had a significantly higher rate of recurrence (5-year recurrence rate 79.5%) compared to patients who lacked the fusion protein (five-year recurrence rate 37.5%, p = 0.009). The adjusted hazard ratio for disease relapse for patients with the fusion protein was 7.1 (95% C.I.: 1.1-45, p = 0.03) compared to patients without the fusion protein. In multivariate analysis, the presence of gene fusion was the single most important prognostic factor. Our study indicates that the expression of TMPRSS2:ERG fusion gene among prostate cancer patients treated with surgery is a strong prognostic factor for disease relapse, and may have important clinical implications.

Variants of the hK2 protein gene (KLK2) are associated with serum hK2 levels and predict the presence of prostate cancer at biopsy

PURPOSE

Increased levels of serum human kallikrein-2 (hK2) and an hK2 gene (KLK2) variant are positively associated for prostate cancer, but the relationships between them remain unclear. We examined five variants of the KLK2 gene to further define its relevance to prostate cancer susceptibility and hK2 levels.

EXPERIMENTAL DESIGN

We genotyped 645 men with biopsy-proven prostate cancer (cases) and 606 males with biopsies negative for prostate cancer (controls) for five additional single nucleotide polymorphisms (SNP) across the KLK2 gene and also tested for serum hK2 levels. These SNPs were identified from sequencing the KLK2 gene among 20 patients with aggressive prostate cancer. Odds ratios (OR) for prostate cancer detection and haplotype analysis were done.

RESULTS

Among the SNPs studied, the A allele of the KLK2-SNP1 (G>A, rs2664155) and the T allele of the KLK2-SNP5 (C>T, rs198977) polymorphisms showed positive associations with prostate cancer, adjusted ORs for KLK2-SNP1 AG and AA genotypes being 1.4 [95% confidence interval (95% CI), 1.2-1.8; P=0.002] and for KLK2-SNP5 TT or CT genotypes being 1.3 (95% CI, 1.1-1.6; P=0.05). Haplotype analyses also revealed a significant association between prostate cancer and the haplotype containing both risk alleles (ACCTT), OR being 5.1 (95% CI, 1.6-6.5; P=0.005). Analysis of serum hK2 revealed hK2 levels to be significantly increased in association with KLK2-SNP1 AA and AG risk genotypes compared with the GG genotype (P=0.001) and also in association with the ACCTT risk haplotype compared with the most common non-risk haplotype (P=0.05).

CONCLUSIONS

These findings suggest a role for the KLK2 gene in prostate cancer susceptibility and imply that this role may be realized at least in part by the induction of increases in hK2 production.

Novel antiproliferative flavonoids induce cell cycle arrest in human prostate cancer cell lines

Epidemiologic studies have demonstrated an inverse association between flavonoid intake and prostate cancer (PCa) risk. The East Asian diet is very high in flavonoids and, correspondingly, men in China and Japan have the lowest incidence of PCa worldwide. There are thousands of different naturally occurring and synthetic flavonoids. However, only a few have been studied in PCa. Our aim was to identify novel flavonoids with antiproliferative effect in PCa cell lines, as well as determine their effects on cell cycle. We have screened a representative subgroup of 26 flavonoids for antiproliferative effect on the human PCa (LNCaP and PC3), breast cancer (MCF-7), and normal prostate stromal cell lines (PrSC). Using a fluorescence-based cell proliferation assay (Cyquant), we have identified five flavonoids, including the novel compounds 2,2'-dihydroxychalcone and fisetin, with antiproliferative and cell cycle arresting properties in human PCa in vitro. Most of the flavonoids tested exerted antiproliferative effect at lower doses in the PCa cell lines compared to the non-PCa cells. Flow cytometry was used as a means to determine the effects on cell cycle. PC3 cells were arrested in G2/M phase by flavonoids. LNCaP cells demonstrated different cell cycle profiles. Further studies are warranted to determine the molecular mechanism of action of 2,2'-DHC and fisetin in PCa, and to establish their effectiveness in vivo.

Synergistic effect of vitamin E and selenium in human prostate cancer cell lines

Vitamin E and selenium are the two most popular dietary supplements used to prevent prostate cancer. The hypothesis that these antioxidants reduce prostate risk is being tested in the selenium and vitamin E chemoprevention trial (SELECT). We hypothesize that selenium potentiates vitamin E-induced inhibition of prostate cancer cell growth in vitro. Prostate cancer cell populations growing asynchronously were treated with a combination of vitamin E and selenium and processed for flow cytometric analysis. Prostate cancer cells treated with a combination of the antioxidants revealed that selenium potentiates vitamin E-induced inhibition of LNCaP cells in vitro. This was demonstrated by a reduction in the percentage of cells in the S phase. This crucial finding confirms our previous observations that antioxidant molecules act via distinct mechanistic pathways. These independent biological effects can be exploited in order to augment the anticancer properties of individual agents. These data also validate the two factorial design of the SELECT trial, permitting pairwise comparisons between agents in combination and alone.

Antioxidants block prostate cancer in lady transgenic mice

The development of chemopreventive agents against prostate cancer would benefit from conclusive evidence of their efficacy in animal models that emulate human disease. To date there has been little in vivo evidence supporting their preventive capabilities. The 12T-10 Lady transgenic model spontaneously develops localized prostatic adenocarcinoma and neuroendocrine cancer followed by metastases, recapitulating the natural history of human prostate cancer in many respects. Using male Lady version of the transgenic adenocarcinoma of the mouse prostate mice, we show that administration of antioxidants (vitamin E, selenium, and lycopene) in the diet dramatically inhibits prostate cancer development and increases the disease free survival. Treatment of animals with the antioxidants resulted in a 4-fold reduction in the incidence of prostate cancer compared with the untreated animals. Prostate cancer developed in 73.68% (14 of 19) and 100% (19 of 19) of the animals from the standard and high fat diet, respectively. In contrast, only 10.53% (2 of 19) and 15.79% (3 of 19; P < 0.0001) of the animals in the standard and high fat diets supplemented with antioxidants developed tumors. The micronutrients were well tolerated with no evidence of antioxidant-related toxicity. Histopathological analysis confirmed absence of cancer in the additive treated groups. Immunohistochemistry demonstrated a strong correlation between disease-free state and increased levels of the prognostic marker p27(Kip1) and a marked decrease in proliferating cell nuclear antigen expression. These observations provide support for the chemopreventive effect of these micronutrients and some clues as to their mechanism of action.

Dietary Fat and Prostate Cancer

PURPOSE

Data from histopathological and migratory studies suggest that 1 or more late stage environmental promoters are involved in the development of clinical carcinoma of the prostate. Laboratory investigations and variously designed epidemiological studies in man have suggested that dietary fat may be one of these candidate tumor promoters but other studies have questioned this association. The biologically plausible associations that have been hypothesized include total energy consumption, altered androgen metabolism, oxidative stress, specific fatty acid consumption and pesticide intake. We provide a critical appraisal of the existing evidence for an association between dietary fat consumption and prostate cancer, and review the biologically plausible relationships.

MATERIALS AND METHODS

All 33 published case-control and cohort studies that examined the relationship between prostate cancer and dietary fat or specific fatty food types were critically appraised. Eight studies suggested a statistically significant association, and many studies noted significant associations for specific types of fatty foods (eg milk or meat) and prostate cancer.

RESULTS

In light of the inherent biases in the methodology of studying dietary fat intake and carcinoma of the prostate, we conclude that the evidence is consistent.

CONCLUSIONS

Corroborative studies in humans are required to better define this relationship. Prospective studies of dietary intervention should be encouraged.

Modulation of cell proliferation and cell cycle regulators by vitamin E in human prostate carcinoma cell lines

PURPOSE

Vitamin E has been identified as a candidate agent for the prevention of prostate cancer. We hypothesize that the mechanism for this effect is in part a result of cell cycle inhibition rather than only due to a reduction in reactive oxygen species. We tested whether vitamin E induces cell cycle arrest in prostate carcinoma, mediated by alterations in cell cycle regulatory proteins, including cyclin E, cdk2 and p27.

MATERIALS AND METHODS

Cells were incubated with and without vitamin E (alpha-tocopherol succinate, 20 microg./ml.), fixed and stained with propidium iodide for flow cytometry analysis. In parallel experiments total protein was extracted, immunoprecipitated with cyclin E antibody and analyzed by Western blot for the expression of cell cycle markers.

RESULTS

Flow cytometry analysis revealed a dramatic reduction in the S phase percent of LNCaP and PC3 cells in response to vitamin E (69% and 95%, respectively). It was accompanied by over expression of p27 (3-fold increase) with vitamin E treatment.

CONCLUSIONS

This study demonstrates that at physiological concentrations vitamin E induced profound cell cycle arrest mediated by up-regulation of p27. This observation provides a theoretical basis for the putative chemopreventive effect of vitamin E.

Modulation of cell proliferation and cell cycle regulators by vitamin E in human prostate carcinoma cell lines

PURPOSE

Vitamin E has been identified as a candidate agent for the prevention of prostate cancer. We hypothesize that the mechanism for this effect is in part a result of cell cycle inhibition rather than only due to a reduction in reactive oxygen species. We tested whether vitamin E induces cell cycle arrest in prostate carcinoma, mediated by alterations in cell cycle regulatory proteins, including cyclin E, cdk2 and p27.

MATERIALS AND METHODS

Cells were incubated with and without vitamin E (alpha-tocopherol succinate, 20 microg./ml.), fixed and stained with propidium iodide for flow cytometry analysis. In parallel experiments total protein was extracted, immunoprecipitated with cyclin E antibody and analyzed by Western blot for the expression of cell cycle markers.

RESULTS

Flow cytometry analysis revealed a dramatic reduction in the S phase percent of LNCaP and PC3 cells in response to vitamin E (69% and 95%, respectively). It was accompanied by over expression of p27 (3-fold increase) with vitamin E treatment.

CONCLUSIONS

This study demonstrates that at physiological concentrations vitamin E induced profound cell cycle arrest mediated by up-regulation of p27. This observation provides a theoretical basis for the putative chemopreventive effect of vitamin E.

Selenium modulation of cell proliferation and cell cycle biomarkers in human prostate carcinoma cell lines

Prostate cancer (PCA) is the most common histological malignancy and the second leading cause of cancer deaths among North American men. There has been considerable interest in the chemopreventative properties of selenium. In this study, we assessed whether selenium inhibits cell growth and associated cell cycle regulatory proteins. Human PCA cells (LNCaP, PC3, PC3-AR2, and PC3-M) were incubated with and without selenium (Seleno-DL-methionine, 150 microM) for 24, 48, and 72 h. Cells were fixed and stained with propidium iodide for flow cytometry analysis. In parallel experiments, total protein was extracted, immunoprecipitated with cyclin E antibody, and analyzed by Western blot for the expression of cell cycle markers. Treatment with selenium caused G1 arrest and an 80% reduction in the S phase of LNCaP with no effect on PC3. However, PC3 cells transfected with the androgen receptor (PC3-AR2) exhibited a G2/M arrest and a marked reduction (57%) in the S phase during cell cycle progression. In the analysis of cell cycle regulatory molecules, selenium-treated cells demonstrated a significant induction of cyclin-dependent kinase inhibitors Cip1/p21 and Kip1/p27. These data suggest that selenium possesses strong antiproliferative properties in regard to human PCA. This effect appears to be dependent on the presence of a functioning androgen receptor. This provides a theoretical basis for Phase III studies of selenium in PCA prevention.

Salivary mesenchyme cells that induce mammary epithelial hyperplasia up-regulate EGF receptors in primary cultures of mammary epithelium within collagen gels

Salivary mesenchyme is a potent stimulator of mammary epithelial hyperplasia and carcinogen-induced tumor formation in vivo. We have utilized a three-dimensional collagen gel culture system, which mimics the in vivo growth environment, to identify growth stimulatory molecules produced by salivary mesenchyme cells. In this report we describe the development and characteristics of salivary mesenchyme cell lines, and we present further evidence that these cells produce growth factor(s) which could account for the effect by interacting with epidermal growth factor (EGF) receptors on primary mouse mammary epithelial cells isolated from midpregnant mice. Using a receptor assay with isolated cell membranes, we characterized [125I]-EGF binding to mammary epithelial cells cultured within collagen gels. Scatchard analysis revealed one class of high affinity EGF receptors with a Kd ranging from 8.3 x 10(-11) M on day one to 5.1 x 10(-11) M on day 10 of the culture period. Addition of 10 ng/ml purified EGF to the culture medium progressively up-regulated the expression of EGF receptors during a 10-day culture period. Scatchard analysis showed that the increase in specific [125I]-EGF binding was due predominantly to an increase in EGF receptor number. We also demonstrated that conditioned medium collected from salivary mesenchyme cells competed effectively for EGF receptor sites on mammary epithelial cells, and chronic exposure to conditioned medium up-regulated EGF receptor expression. Thus, EGF-related growth factor(s) released by salivary mesenchyme cells may induce hyperplasia of adjacent mammary epithelium in vivo, both by directly activating EGF receptors, and by provoking long term up-regulation of EGF receptors.

A transforming growth factor related to epidermal growth factor is expressed by fetal mouse salivary mesenchyme cells in culture

Fetal mouse salivary mesenchyme cells secrete a protein with an apparent MW of 15 Kd that is immunologically related to epidermal growth factor (EGF). Conditioned medium collected from these cells in culture stimulates the growth of primary mouse mammary epithelial cells cultured within collagen gels, competes for binding to EGF receptor sites on these mammary epithelial cells and stimulates the anchorage-independent growth of normal rat kidney fibroblast cells within soft agarose. Prior immunoprecipitation of salivary mesenchyme cell conditioned medium with anti-EGF antibodies effectively removes or attenuates all of these effects confirming that an EGF-like factor is involved in these responses.