Role of hypoxia and EGF on expression, activity, localization and phosphorylation of carbonic anhydrase IX in MDA-MB-231 breast cancer cells.

Carbonic anhydrase IX (CAIX) is a zinc metalloenzyme that catalyzes the reversible hydration of CO(2). CAIX is overexpressed in many types of cancer, including breast cancer, but is most frequently absent in corresponding normal tissues. CAIX expression is strongly induced by hypoxia and is significantly associated with tumor grade and poor survival. Herein, we show that hypoxia induces a significant increase in CAIX protein in MDA-MB-231 breast cancer cells. Using a unique mass spectrophotometric assay, we demonstrate that CAIX activity in plasma membranes isolated from MDA-MB-231 is correlated with CAIX content. We also show that CAIX exists predominantly as a dimeric, high-mannose N-linked glycoprotein. While there is some evidence that the dimeric form resides specifically in lipid rafts, our data do not support this hypothesis. EGF, alone, did not affect the distribution of CAIX into lipid rafts. However, acute EGF treatment in the context of hypoxia increased the amount of CAIX in lipid rafts by about 5-fold. EGF did not stimulate tyrosine phosphorylation of CAIX, although EGFR and down-stream signaling pathways were activated by EGF. Interestingly, hypoxia activated Akt independent of EGF action. Together, these data demonstrate that the active form of CAIX in the MDA-MB-231 breast cancer cell line is dimeric but that neither lipid raft localization nor phosphorylation are likely required for its dimerization or activity.

Detecting extracellular carbonic anhydrase activity using membrane inlet mass spectrometry.

Current research into the function of carbonic anhydrases (CAs) in cell physiology emphasizes the role of membrane-bound CAs such as CA IX, which has been identified in malignant tumors and is associated with extracellular acidification as a response to hypoxia. Here we present a mass spectrometric method to determine the extent to which total CA activity is due to extracellular CA in whole cell preparations. The method is based on the biphasic rate of depletion of (18)O from CO(2) measured by membrane inlet mass spectrometry. The slopes of the biphasic depletion are a sensitive measure of the presence of CA inside and outside of the cells. This property is demonstrated here using suspensions of human red cells in which external CA was added to the suspending solution. It is also applied to breast and prostate cancer cells, both of which express exofacial CA IX. Inhibition of external CA is achieved by the use of a membrane impermeant inhibitor that was synthesized for this purpose, p-aminomethylbenzenesulfonamide attached to a polyethylene glycol polymer.

Porphyromonas gingivalis invades human trophoblasts and inhibits proliferation by inducing G1 arrest and apoptosis.

Porphyromonas gingivalis is an oral pathogen that is also associated with serious systemic conditions such as preterm delivery. Here we investigated the interaction between P. gingivalis and a cell line of extravillous trophoblasts (HTR-8) derived from the human placenta. P. gingivalis internalized within HTR-8 cells and inhibited proliferation through induction of arrest in the G1 phase of the cell cycle. G1 arrest was associated with decreased expression of cyclin D and of CDKs 2, 4 and 6. In addition, levels of CDK inhibitors p15, p16, p18 and p21 were increased following P. gingivalis infection. The amount of Rb was diminished by P. gingivalis, and transient overexpression of Rb, with concomitant upregulation of phospho-Rb, relieved P. gingivalis-induced G1 arrest. HTR-8 cells halted in the G1 phase became apoptotic, and apoptosis was accompanied by an increase in the ratio of Bax/Bcl-2 and increased activity of caspases 3, 7 and 9. HTR-8 cells infected with P. gingivalis also exhibited a sustained activation of ERK1/2, and knock-down of ERK1/2 activity with siRNA abrogated both G1 arrest and apoptosis. Thus, P. gingivalis can invade placental trophoblasts and induce G1 arrest and apoptosis through pathways involving ERK1/2 and its downstream effectors, properties that provide a mechanistic basis for pathogenicity in complications of pregnancy.

Antibody-specific detection of CAIX in breast and prostate cancers.

Carbonic anhydrase IX (CAIX) is frequently expressed in human tumors and serves as a marker for hypoxia. Further, CAIX expression is considered a predictor of poor survival in many, but not all, cancer types. Herein, we compare the specificity of two CAIX antibodies: the M75, monoclonal antibody which recognizes an epitope in the N-terminus and a commercially available polyclonal antibody generated against a C-terminal peptide (NB100-417). Western blot analysis of multiple breast cell lines revealed that the polyclonal antibody detected both membrane-bound and soluble proteins. The M75 antibody recognized only the membrane-bound species, which is presumed to be CAIX. These data were confirmed in an aggressive prostate cell line. We further compared these antibodies in prostate tumors by immunohistochemistry. Staining with NB100 was comparable to that of the M75 antibody, but only at high dilution. Otherwise, cytoplasmic staining was also noted. Two-dimensional gel electrophoresis followed by mass spectrometric analysis revealed that the cytoplasmic protein detected by NB100 is beta-tubulin. This cross-reactivity could lead to false-positives for CAIX expression in samples where cytosolic proteins are present.

Expression and activity of carbonic anhydrase IX is associated with metabolic dysfunction in MDA-MB-231 breast cancer cells.

The expression of carbonic anhydrase IX (CAIX), a marker for hypoxic tumors, is correlated with poor prognosis in breast cancer patients. We show herein that the MDA-MB-231 cells, a "triple-negative," basal B line, express exclusively CAIX, while a luminal cell line (T47D) expresses carbonic anhydrase XII (CAXII). CAIX expression in the basal B cells is both density- and hypoxia-dependent and is correlated with carbonic anhydrase activity. Evidence is provided that CAIX contributes to extracellular acidification through studies on pH, lactic acid production, and CAIX inhibition. Together, these studies suggest that CAIX expression and activity is associated with metabolic dysfunction in MDA-MB-231 cells.

Phase II trial of isoflavone in prostate-specific antigen recurrent prostate cancer after previous local therapy.

BACKGROUND: Data exist that demonstrate isoflavones' potent antiproliferative effects on prostate cancer cells. We evaluated the efficacy of isoflavone in patients with PSA recurrent prostate cancer after prior therapy. We postulated that isoflavone therapy would slow the rate of rise of serum PSA. METHODS: Twenty patients with rising PSA after prior local therapy were enrolled in this open-labeled, Phase II, nonrandomized trial (Trial registration # NCT00596895). Patients were treated with soy milk containing 47 mg of isoflavonoid per 8 oz serving three times per day for 12 months. Serum PSA, testosterone, lipids, isoflavone levels (genistein, daidzein, and equol), and quality of life (QOL) were measured at various time points from 0 to 12 months. PSA outcome was evaluated. RESULTS: Within the mixed regression model, it was estimated that PSA had increased 56% per year before study entry and only increased 20% per year for the 12-month study period (p = 0.05). Specifically, the slope of PSA after study entry was significantly lower than that before study entry in 6 patients and the slope of PSA after study entry was significantly higher than before study entry in 2 patients. For the remaining 12 patients, the change in slope was statistically insignificant. Nearly two thirds of the patients were noted to have significant levels of free equol in their serum while on therapy. CONCLUSION: Dietary intervention with isoflavone supplementation may have biologic activity in men with biochemical recurrent prostate cancer as shown by a decline in the slope of PSA. This study may lend support to the literature that nutritional supplements have biologic activity in prostate cancer and therefore, further studies with these agents in randomized clinical trials should be encouraged.

Knock-down of Bcl-2 by antisense oligodeoxynucleotides induces radiosensitization and inhibition of angiogenesis in human PC-3 prostate tumor xenografts.

Expression of the proto-oncogene Bcl-2 is associated with tumor progression. Bcl-2's broad expression in tumors, coupled with its role in resistance to chemotherapy and radiation therapy-induced apoptosis, makes it a rational target for anticancer therapy. Antisense Bcl-2 oligodeoxynucleotide (ODN) reagents have been shown to be effective in reducing Bcl-2 expression in a number of systems. We investigated whether treating human prostate cancer cells with antisense Bcl-2 ODN (G3139, oblimersen sodium, Genasense) before irradiation would render them more susceptible to radiation effects. Two prostate cancer cell lines expressing Bcl-2 at different levels (PC-3-Bcl-2 and PC-3-Neo) were subjected to antisense Bcl-2 ODN, reverse control (CTL), or mock treatment. Antisense Bcl-2 ODN alone produced no cytotoxic effects and was associated with G(1) cell cycle arrest. The combination of antisense Bcl-2 ODN with irradiation sensitized both cell lines to the killing effects of radiation. Both PC-3-Bcl-2 and PC-3-Neo xenografts in mice treated with the combination of antisense Bcl-2 ODN and irradiation were more than three times smaller by volume compared with xenografts in mice treated with reverse CTL alone, antisense Bcl-2 ODN alone, irradiation alone, or reverse CTL plus radiotherapy (P = 0.0001). Specifically, PC-3-Bcl-2 xenograft tumors treated with antisense Bcl-2 ODN and irradiation had increased rates of apoptosis and decreased rates of angiogenesis and proliferation. PC-3-Neo xenograft tumors had decreased proliferation only. This is the first study which shows that therapy directed at Bcl-2 affects tumor vasculature. Together, these findings warrant further study of this novel combination of Bcl-2 reduction and radiation therapy, as well as Bcl-2 reduction and angiogenic therapy.

Combination of PTEN gene therapy and radiation inhibits the growth of human prostate cancer xenografts.

The resistance of prostate cancers to radiation therapy has been linked to abnormalities in overexpression of Bcl-2, an oncogene associated with inhibition of apoptosis. In this study, we evaluated whether the combination of the overexpression of phosphatase and tensin homolog (PTEN), a protein known to inhibit Bcl-2 expression, and radiation therapy would inhibit proliferation of Bcl-2-expressing human prostate cancer cells inoculated into the subcutis of athymic mice. Compared with either treatment alone, the combination of adenoviral vector-expressed PTEN (AdPTEN) and radiation (5 Gy) significantly inhibited xenograft tumor growth. Median tumor size on day 48 was 1030 mm3 in untreated controls, 656 mm3 in mice treated with radiation (5 Gy) alone, 640 mm3 in mice treated with AdPTEN alone, and 253 mm3 in mice treated with the combination (p<0.001). Treatment was well tolerated in all cases. Combination treatment also enhanced apoptosis (p=0.048), inhibited cellular proliferation (p=0.005), and inhibited tumor-induced neovascularity (p=0.030). Interestingly, this treatment increased apoptosis not only in tumor cells but also in tumor-associated endothelial cells. Together, these findings indicate that AdPTEN strongly inhibits the growth of human prostate tumors, especially when combined with radiation therapy, and that this effect is mediated by the induction of apoptosis and by the inhibition of angiogenesis and cellular proliferation.

Gene Expression Patterns Are Altered in Athymic Mice and Metabolic Syndrome Factors Are Reduced in C57BL/6J Mice Fed High-Fat Diets Supplemented with Soy Isoflavones.

Soy isoflavones exert beneficial health effects; however, their potential to ameliorate conditions associated with the metabolic syndrome (MetS) has not been studied in detail. In vitro and in vivo models were used to determine the effect of isoflavones on lipid metabolism, inflammation, and oxidative stress. In nude mice, consumption of Novasoy (NS) increased cholesterol and lipid metabolism gene expression, including Scd-1 (27.7-fold), Cyp4a14 (35.2-fold), and Cyp4a10 (9.5-fold), and reduced anti-inflammatory genes, including Cebpd (16.4-fold). A high-fat (HF) diet containing 0.4% (w/w) NS for 10 weeks significantly reduced percent weight gain (74.6 ± 2.5 vs 68.6 ± 3.5%) and hepatic lipid accumulation (20 ± 1.2 vs 27 ± 1.5%), compared to HF alone (p < 0.05) in C57BL/6J mice. NS also increased lipid oxidation and antioxidant gene expression while decreasing inflammatory cytokines. In vitro analysis in HepG2 cells revealed that genistein dose-dependently decreases oleic acid-induced lipid accumulation. Soy isoflavones may ameliorate symptoms associated with MetS via anti-inflammatory, antioxidant, and hypolipidemic modulation.

Docetaxel and bortezomib downregulate Bcl-2 and sensitize PC-3-Bcl-2 expressing prostate cancer cells to irradiation.

BACKGROUND: Currently, docetaxel is used to treat hormone-refractory metastatic prostate cancer. Docetaxel not only inhibits microtubule formation but can also downregulate expression of Bcl-2, a known antiapoptotic oncogene. Furthermore, the 26S proteasome inhibitor bortezomib can downregulate Bcl-2 expression. Previously, we demonstrated that overexpression of Bcl-2 renders cells resistant to radiation therapy. In this study, we investigated whether treating human prostate cancer cells with docetaxel, bortezomib, or both could modulate Bcl-2 expression and whether such modulation could render Bcl-2-overexpressing cells more susceptible to radiation. METHODS: PC-3-Bcl-2 and PC-3-Neo human prostate cancer cells treated with docetaxel and/or bortezomib in addition to irradiation were analyzed in vitro for proliferation, clonogenic survival, cell cycle phase distribution, and expression of Bcl-2 and Bcl-xL proteins. RESULTS: Docetaxel and bortezomib alone had significant cytotoxic effects. In addition, docetaxel, bortezomib, or radiation resulted in a G2M phase arrest in PC-3-Bcl-2, whereas only docetaxel or radiation did so in PC-3-Neo cells. Both cell lines were more sensitized to radiation's killing effects when treated with the combination of docetaxel and bortezomib than when treated with either agent alone. Furthermore, docetaxel and bortezomib-treated cells exhibited marked changes in the expression of Bcl-2 and Bcl-xL. CONCLUSIONS: This is the first study to demonstrate that docetaxel and bortezomib in combination can effectively sensitize Bcl-2-overexpressing human prostate cancer cells to radiation effects by modulating the expression of key members of the Bcl-2 family. Together, these findings warrant further evaluation of the combination of docetaxel and bortezomib in prostate cancer.

Dichloroacetate (DCA) sensitizes both wild-type and over expressing Bcl-2 prostate cancer cells in vitro to radiation.

BACKGROUND: Bcl-2 protects cells from apoptosis and provides a survival advantage to cells over-expressing this oncogene. In addition, over expression of Bcl-2 renders cell resistant to radiation therapy. Recently, dichloroacetate (DCA) was proven to potentiate the apoptotic machinery by interacting with Bcl-2. In this study, we investigated whether treating human prostate cancer cells with DCA could modulate Bcl-2 expression and if the modulation in Bcl-2 expression could render the Bcl-2 over expressing cells more susceptible to cytotoxicity effects of radiation. METHODS: PC-3-Bcl-2 and PC-3-Neo human prostate cancer cells treated with DCA in addition to irradiation were analyzed in vitro for changes in proliferation, clonogenic survival, apoptosis, cell cycle phase distribution, mitochondrial membrane potential, and expression of Bcl-2, Bcl-xL, Bax, or Bak proteins. RESULTS: DCA alone produced significant cytotoxic effects and was associated with G1 cell cycle arrest. Furthermore, DCA was associated with an increased rate of apoptosis. The combination of DCA with irradiation sensitized both cell lines to radiation's killing effects. Treatment of PC-3-Bcl-2 or PC-3-Neo with DCA and irradiation resulted in marked changes in various members of the Bcl-2 family. In addition, DCA therapy resulted in a significant change in mitochondria membrane potential, thus supporting the notion that DCAs effect is on the mitochondria. CONCLUSIONS: This is the first study to demonstrate DCA can effectively sensitize wild-type and over expressing Bcl-2 human prostate cancer cells to radiation by modulating the expression of key members of the Bcl-2 family. Together, these findings warrant further evaluation of the combination of DCA and irradiation.

Downregulation of BCL-2 induces downregulation of carbonic anhydrase IX, vascular endothelial growth factor, and pAkt and induces radiation sensitization.

OBJECTIVES: Our group previously demonstrated that expression of the oncogene, Bcl-2, was associated with radiation resistance. The aim of the present study was to determine whether Bcl-2 expression in radiation-resistant tumors was associated with expression of carbonic anhydrase IX (CAIX), vascular endothelial growth factor (VEGF), and pAkt and whether downregulation of Bcl-2 could modulate the expression of CAIX, VEGF, and pAkt. METHODS: Two prostate cancer cell lines, PC-3-Bcl-2 and PC-3-Neo, were injected into the subcutaneous flanks of 192 athymic male nude mice; 96 received PC-3 Bcl-2 and 96 PC-3-Neo. The mice were then treated with antisense Bcl-2 oligodeoxynucleotide (ASODN), reverse control ODN, or vehicle only (mock treatment) with or without irradiation (4 Gy). The tumors were monitored for growth (ie, volume) over time, resected at various points, and processed and sectioned for protein analyses. RESULTS: Bcl-2 ASODN treatment was associated with downregulation of Bcl-2, VEGF, pAkt, and CAIX. PC-3-Bcl-2 and PC-3-Neo prostate tumor xenografts in mice treated with the combination of Bcl-2 ASODN and irradiation were significantly (ie, one third) smaller than those in mice treated with reverse control ODN alone, Bcl-2 ASODN alone, irradiation alone, or reverse control ODN plus irradiation (P = 0.0001). An increased tumor response to the combined therapy was associated with decreased expression of Bcl-2, VEGF, and pAkt proteins. CONCLUSIONS: These findings have demonstrated an intimate relationship among CAIX, VEGF, pAkt, and Bcl-2 in prostate tumors. Thus, CAIX might prove effective as a potential marker of tumor radiation resistance. Downregulation of CAIX might lead to radiation sensitization. Consequently, the combination of CAIX reduction and radiotherapy warrants further consideration as a new strategy for therapy.

Increased expression of cyclooxygenase-2 correlates with resistance to radiation in human prostate adenocarcinoma cells.

PURPOSE: Cyclooxygenase-2 functions as a survival factor by protecting cells from apoptosis. We analyzed cyclooxygenase-2 expression in LNCaP-COX-2 and LNCaP-Neo cell lines treated with irradiation. MATERIALS AND METHODS: LNCaP-COX-2 and LNCaP-Neo cells were treated with 0 to 500 microM celecoxib and a dose response curve was generated. A clonogenic assay was performed in which cells were subjected to irradiation (0 to 6 Gy) with or without celecoxib. Cyclooxygenase-2 protein and other relevant proteins were measured by immunohistochemistry Western blot analysis after irradiation and celecoxib treatment. RESULTS: The 2 studied cell lines experienced cytotoxic effects of celecoxib in a dose related manner. Clonogenic assays demonstrated that LNCaP-COX-2 cells were significantly more resistant to radiation therapy than LNCaP-Neo cells. Furthermore, the addition of celecoxib sensitized LNCaP-Neo and LNCaP-COX-2 cells to the cytocidal effects of radiation. Moreover, cyclooxygenase-2 over expression was associated with the over expression of pAkt and carbonic anhydrase. In this cell line irradiation alone was associated with increased expression of cyclooxygenase-2 and carbonic anhydrase. Combination therapy with irradiation and celecoxib down-regulated cyclooxygenase-2, pAKT and carbonic anhydrase. LNCaP-Neo cells expressed carbonic anhydrase and pAkt. Irradiation of these cells increased carbonic anhydrase and pAkt expression. Combination therapy with irradiation and celecoxib down-regulated carbonic anhydrase and pAkt. CONCLUSIONS: Cyclooxygenase-2 expression is also associated with pAkt and carbonic anhydrase expression. Down-regulation of cyclooxygenase-2 by celecoxib is associated with decreased expression of cyclooxygenase-2, pAkt and carbonic anhydrase, and eventual radiation sensitization, which is a phenomenon that may have clinical usefulness.

Soy isoflavones exert differential effects on androgen responsive genes in LNCaP human prostate cancer cells.

The high consumption of soy isoflavones in Asian diets has been correlated to a lower incidence of clinically important cases of prostate cancer. This study characterized the effects of a soy-derived isoflavone concentrate (ISF) on growth and gene expression profiles in the LNCaP, an androgen-sensitive human prostate cancer cell line. ISF caused a dose-dependent decrease in viability (P < 0.05) and DNA synthesis (P < 0.01), as well as an accumulation of cells in G(2)/M, and G(0)/G(1) phases of the cell cycle compared with controls. Using Affymetrix oligonucleotide DNA microarrays (U133A), we determined that ISF upregulated 80 genes and downregulated 33 genes (P < 0.05) involving androgen-regulated genes and pathways controlling cell cycle, metabolism, and intracellular trafficking. Changes in the expression of the genes of interest, identified by microarrays, were validated by Western immunoblot, Northern blot, and luciferase reporter assays. Prostate-specific antigen, homeobox protein NKX3, and cyclin B mRNA were significantly reduced, whereas mRNA was significantly upregulated for p21(CIP1), a major cell cycle inhibitory protein, and fatty acid and cholesterol synthesis pathway genes. ISF also significantly increased cyclin-dependent kinase inhibitor p27(KIP1) and FOXO3A/FKHRL1, a forkhead transcription factor. A differential pattern of androgen-regulated genes was apparent with genes involved in prostate cancer progression being downregulated by ISF, whereas metabolism genes were upregulated. In summary, we found that ISF inhibits the growth of LNCaP cells through the modulation of cell cycle progression and the differential expression of androgen-regulated genes. Thus, ISF treatment serves to identify new therapeutic targets designed to prevent proliferation of malignant prostate cells.

Soy isoflavones alter expression of genes associated with cancer progression, including interleukin-8, in androgen-independent PC-3 human prostate cancer cells.

High consumption of soy isoflavones in Asian diets has been correlated with a lower incidence of clinically important cases of prostate cancer. The chemopreventive properties of these diets may result from an interaction of several types of isoflavones, including genistein and daidzein. The present study investigated the effects of a soy isoflavone concentrate (ISF) on growth and gene expression profiles of PC-3 human prostate cancer cells. Trypan blue exclusion and [3H]-thymidine incorporation assays showed that ISF decreased cell viability and caused a dose-dependent inhibition of DNA synthesis, respectively, with 50% inhibition (IC50) of DNA synthesis at 52 mg/L (P = 0.05). The glucoside conjugates of genistein and daidzein in ISF were converted to bioactive free aglycones in cell culture in association with the inhibition of DNA synthesis. Flow cytometry and Western immunoblot analyses showed that ISF at 200 mg/L caused an accumulation of cells in the G2/M phase of the cell cycle (P < 0.05) and decreased cyclin A by 20% (P < 0.05), respectively. The effect of ISF on the gene expression profile of PC-3 cells was analyzed using Affymetrix oligonucleotide DNA microarrays that interrogate approximately 17,000 human genes. Of the 75 genes altered by ISF, 28 were upregulated and 47 were downregulated (P < 0.05). Further analysis showed that IL-8, matrix metalloproteinase 13, inhibin beta A, follistatin, and fibronectin mRNA levels were significantly reduced, whereas the expression of p21(CIP1), a major cell cycle inhibitory protein, was increased. The effects of ISF on the expression of IL-8 and p21(CIP1) mRNA and protein were validated at high and low ISF concentrations. Our data show that ISF inhibits the growth of PC-3 cells through modulation of cell cycle progression and the expression of genes involved in cell cycle regulation, metastasis, and angiogenesis.

Benzo(a)pyrene, but not 2,3,7,8-tetrachlorodibenzo-p-dioxin, alters cell adhesion proteins in human uterine RL95-2 cells.

This study compared the effects of benzo(a)pyrene (BaP) and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), two aryl hydrocarbon receptor agonists, on cell attachment and adherens junction proteins in RL95-2 human uterine endometrial cells. Exposure to 10 microM BaP significantly decreased cell attachment to Matrigel, whereas 10 nM TCDD had no effect. Immunocytochemistry and Western immunoblot analysis showed that BaP, but not TCDD, produced a marked loss of plasma membrane epidermal growth factor receptor (EGF-R) localized along intercellular boundaries. BaP-treated cells exhibited significant decreases in beta-catenin and cadherin protein levels, while vinculin levels remained unchanged relative to control. In contrast, TCDD treatment had no effect on the levels of beta-catenin, cadherin, or vinculin. Further studies using the fluorescein labeled peptide phalloidin showed the presence of continuous subcortical actin filaments in control cells, whereas BaP-treated cells had subcortical actin aggregates. Thus, in contrast to TCDD, BaP produces a loss of cell attachment involving decreased localization of molecules important for cell-cell interactions in RL95-2 cells.

Mechanisms of the growth inhibitory effects of the isoflavonoid biochanin A on LNCaP cells and xenografts.

BACKGROUND: Isoflavones inhibit the growth of some types of tumor cells, including prostate adenocarcinoma. This study used LNCaP cells and xenografts to investigate the mechanisms of the antiproliferative effects of biochanin A, a major isoflavone present in red clover but not soy-derived products. METHODS: LNCaP cells were exposed to varying doses of biochanin A to evaluate viability, DNA synthesis, and DNA fragmentation (TUNEL) analysis. Regulation of gene expression was determined by using Western immunoblotting and cDNA microarrays. Anti-tumorigenic effects were evaluated by using athymic mice with LNCaP flank tumors. RESULTS: Biochanin A induced a dose-dependent inhibition of proliferation and [(3)H]thymidine incorporation that correlated with increased DNA fragmentation, indicative of apoptosis. Western blot analyses of cell cycle regulatory proteins revealed that biochanin A significantly decreased expression of cyclin B and p21, whereas flow cytometry showed that cells were accumulating in the G(0)/G(1) phase. cDNA microarray analyses identified 29 down-regulated genes with six reduced below assay detection limits. Eleven genes were up-regulated, including 9 that were undetectable in controls. In mice with LNCaP xenografts, biochanin A significantly reduced tumor size and incidence. CONCLUSION: These results indicate that biochanin A inhibits prostate cancer cell growth through induction of cell cycle arrest and apoptosis. Biochanin A-regulated genes suggest multiple pathways of action. Biochanin A inhibits the incidence and growth of LNCaP xenograft tumors in athymic mice.