Edgar S. Diaz-Cruz

Translational studies on aromatase, cyclooxygenases, and enzyme inhibitors in breast cancer☆

Aromatase expression and enzyme activity in breast cancer patients is greater in or near the tumor tissue compared with the normal breast tissue. Regulation of aromatase expression in human tissues is quite complex, involving alternative promoter sites that provide tissue-specific control. Previous studies in our laboratories suggested a strong association between aromatase (CYP19) gene expression and the expression of cyclooxygenase (COX) genes. Our hypothesis is that higher levels of COX expression result in higher levels of prostaglandin E2 (PGE2), which in turn increases CYP19 expression through increases in intracellular cyclic AMP levels. This biochemical mechanism may explain the beneficial effects of non-steroidal anti-inflammatory drugs (NSAIDs) on reducing the risks of breast cancer. The effects of NSAIDs (ibuprofen, piroxicam, and indomethacin), a COX-1 selective inhibitor (SC-560), and COX-2 selective inhibitors (celecoxib, niflumic acid, nimesulide, NS-398, and SC-58125) on aromatase activity and CYP19 expression were investigated in breast cancer cell culture systems. Dose-dependent decreases in aromatase activity were observed following treatment with an NSAID or COX inhibitor, with the most effective agents being COX selective inhibitors. Real time PCR analysis of aromatase gene expression showed a significant decrease in mRNA levels in treated cells when compared to vehicle control. These results suggest that the effect of COX inhibitors on aromatase occurs at the transcriptional level. To further probe these interactions, short interfering RNAs (siRNA) were designed against either human CYP19 mRNA or human COX-2 mRNA. Treatment of breast cancer cells with aromatase siRNAs suppressed CYP19 mRNA and aromatase enzyme activity. Finally, treatment with COX-2 siRNAs downregulated the expression of COX-2 mRNA; furthermore, the siCOX-2-mediated suppression of COX-2 also resulted in suppression of aromatase mRNA. In summary, pharmacological regulation of aromatase and cyclooxygenases can act locally in an autocrine fashion to decrease the biosynthesis of estrogen and may provide additional therapy options for patients with hormone-dependent breast cancer.

Evaluation of synthetic isoflavones on cell proliferation, estrogen receptor binding affinity, and apoptosis in human breast cancer cells

Natural isoflavones have demonstrated numerous pharmacological activities in breast cancer cells, including antiproliferative activities and binding affinities for estrogen receptors (ERs). Chemical modifications on the isoflavone ring system have been prepared and explored for the development of new therapeutics for hormone-dependent breast cancer. The antiproliferative actions of the synthesized isoflavones on MCF-7 and MDA-MB-231 breast cancer cells were examined, as well as cytotoxicity, interaction with estrogen receptors, and proapoptotic activity. The compounds were screened in the absence and in the presence of estradiol to evaluate whether or not estradiol could rescue cell proliferation on MCF-7 cells. Several compounds were able to inhibit cell proliferation in a dose-dependent manner, and compounds containing the bulky 7-phenylmethoxy substituent resulted in cell toxicity not only in MCF-7 cells but also in MDA-MB-231 cells. Selected synthetic isoflavones were able to bind to estrogen receptor with low affinity. Apoptotic pathways were also activated by these compounds in breast cancer cells. The majority of the compounds can bind to both ERs with low affinity, and their effects on hormone-independent breast cancer cells suggest that their ability to inhibit cell growth in breast cancer cells is not exclusively mediated by ERs. Thus, the synthetic trisubstituted isoflavones act on multiple signaling pathways leading to activation of mechanisms of cell-death and ultimately affecting breast cancer cell survival.

Aromatase and COX in breast cancer: Enzyme inhibitors and beyond ☆

Aromatase expression and enzyme activity in breast cancer patients is greater in or near the tumor tissue compared with the normal breast tissue. Complex regulation of aromatase expression in human tissues involves alternative promoter sites that provide tissue-specific control. Previous studies in our laboratories suggested a strong association between aromatase (CYP19) gene expression and the expression of cyclooxygenase (COX) genes. Additionally, nonsteroidal anti-inflammatory drugs (NSAIDs) and COX selective inhibitors can suppress CYP19 gene expression and decrease aromatase activity. Our current hypothesis is that pharmacological regulation of aromatase and/or cyclooxygenases can act locally to decrease the biosynthesis of estrogen and may provide additional therapy options for patients with hormone-dependent breast cancer. Two pharmacological approaches are being developed, one involving mRNA silencing by selective short interfering RNAs (siRNA) molecules and the second utilizing small molecule drug design. In the first approach, short interfering RNAs were designed against either human aromatase mRNA or human COX-2 mRNA. Treatment of breast cancer cells with siAROMs completely masked the aromatase enzyme activity. Treatment with COX-2 siRNAs decreased the expression of COX-2 mRNA; furthermore, the siCOX-2-mediated decrease also resulted in suppression of CYP19 mRNA. The small molecule drug design approach focuses on the synthesis and biological evaluation of a novel series of sulfonanilide analogs derived from the COX-2 selective inhibitors. The compounds suppress aromatase enzyme activity in SK-BR-3 breast cancer cells in a dose and time-dependent manner, and structure activity analysis does not find a correlation between aromatase suppression and COX inhibition. Real-time PCR analysis demonstrates that the sulfonanilide analogs decrease aromatase gene transcription in breast cells. Thus, these results suggest that the siRNAs and novel sulfonanilides targeting aromatase expression may be valuable tools for selective regulation of aromatase in breast cancer.

Interrelationships between cyclooxygenases and aromatase: unraveling the relevance of cyclooxygenase inhibitors in breast cancer.

Breast cancer is the most common cancer among women, and ranks second among cancer deaths in women. Approximately 60% of all breast cancer patients have hormone-dependent breast cancer, which contains estrogen receptors and requires estrogen for tumor growth. Estradiol is biosynthesized from androgens by the cytochrome P450 enzyme complex called aromatase. Aromatase is found in several tissues in the body and aromatase (CYP19) gene expression is regulated in a tissue-specific manner via use of alternative promoters. Aromatase transcript expression and activity in breast tumor tissue is greater than that in the normal breast tissue, and prostaglandins can increase CYP19 expression and aromatase activity in breast cancer cells. Cyclooxygenase (COX) is a key enzyme in the production of prostaglandins. Studies have shown higher levels of COX-2 isoform in breast cancer tissue when compared to normal breast tissue, and this is accompanied by high concentrations of prostaglandin E(2) (PGE(2)). Previous studies suggest a strong association between CYP19 gene expression and the expression of COX genes. While studies have shown that nonsteroidal anti-inflammatory drugs (NSAIDs) have beneficial effects on breast cancer, the mechanism by which this occurs is still unclear. Studies have shown that COX inhibitors decrease aromatase activity in breast cancer cells and this effect starts at the transcriptional level. Real time PCR data shows that this molecular mechanism involves promoters I.4 and II, the promoters involved in the development of breast cancer. High levels of COX-2 expression result in higher levels of prostaglandin E(2) (PGE(2)), which in turn increases CYP19 expression through increases in intracellular cyclic AMP levels and activation of promoter II. Thus, PGE(2) produced via COX may act locally in paracrine and autocrine fashion to increase the biosynthesis of estrogen by aromatase in hormone-dependent breast cancer development.

Deregulated Estrogen Receptor α and p53 Heterozygosity Collaborate in the Development of Mammary Hyperplasia

Both increased estrogen receptor alpha (ER(alpha)) expression and germline disruption of one p53 allele increase breast cancer risk in women. Genetically engineered mouse models of deregulated ER(alpha) expression and p53 haploinsufficiency were used to investigate similarities and differences of each genetic lesion alone and in combination on mammary preneoplasia development. Each genetic lesion independently and in combination led to development of age-dependent preneoplasia, but the highest prevalence was found in compound mice with increased ER(alpha) expression coupled with p53 heterozygosity. All genetic lesions were associated with extracellular signal-regulated kinase 1/2 activation; however, only p53 heterozygous and compound mice showed increased levels of phosphorylated AKT and decreased p27 expression. The highest levels of cell proliferation were found in compound mice, but increased levels were also found with either increased ER(alpha) expression or p53 heterozygosity. Mice with increased ER(alpha) expression showed predicted higher levels of nuclear-localized ER(alpha), but this was attenuated in compound mice in association with a relative increase in Src phosphorylation. Parity protection was limited to p53 heterozygous mice and not found in mice with increased ER(alpha) alone. In summary, increased and deregulated ER(alpha) collaborates with p53 heterozygosity in increasing the risk of mammary preneoplasia development.

Suppression of Aromatase in Human Breast Cells by A Cyclooxygenase-2 Inhibitor and Its Analog Involves Multiple Mechanisms Independent of Cyclooxygenase-2 Inhibition

Previous studies have demonstrated that cyclooxygenase-2 (COX-2) inhibitor NS-398 decrease aromatase activity at the transcript level in breast cancer cells. However, N-Methyl NS-398, which does not have COX-2 inhibitory activity but has very similar structure to NS-398, decreases aromatase activity and transcription in MCF-7 and MDA-MB-231 breast cells to the same extent as NS-398. This suggests that NS-398 decrease aromatase expression in breast cancer cells via other mechanism(s). Further investigations find that both compounds only decrease aromatase activity stimulated by forskolin/phorbol ester at the transcript level in both breast cancer cell lines and in breast stromal cells from patients. They do not affect aromatase expression and activity stimulated by dexamethasone. Both compounds also suppress MCF-7 cell proliferation stimulated by testosterone. Aromatase inhibition studies using placental microsomes demonstrate that the compounds show only weak direct aromatase inhibition. These results suggest that NS-398 and its N-methyl analog suppress aromatase expression and activity with multiple mechanisms.

The CDK4/6 inhibitor PD0332991 reverses epithelial dysplasia associated with abnormal activation of the Cyclin-CDK-Rb pathway

Loss of normal growth control is a hallmark of cancer progression. Therefore, understanding the early mechanisms of normal growth regulation and the changes that occur during preneoplasia may provide insights of both diagnostic and therapeutic importance. Models of dysplasia that help elucidate the mechanisms responsible for disease progression are useful in highlighting potential targets for prevention. An important strategy in cancer prevention treatment programs is to reduce hyperplasia and dysplasia. This study identified abnormal upregulation of cell cycle–related proteins cyclin D1, cyclin-dependent kinase (CDK)4, CDK6, and phosphorylated retinoblastoma protein (pRb) as mechanisms responsible for maintenance of hyperplasia and dysplasia following downregulation of the initiating viral oncoprotein Simian virus 40 (SV40) T antigen. Significantly, p53 was not required for successful reversal of hyperplasia and dysplasia. Ligand-induced activation of retinoid X receptor and PPARγ agonists attenuated cyclin D1 and CDK6 but not CDK4 or phosphorylated pRb upregulation with limited reversal of hyperplasia and dysplasia. PD0332991, an orally available CDK4/6 inhibitor, was able to prevent upregulation of cyclin D1 and CDK6 as well as CDK4 and phosphorylated pRb and this correlated with a more profound reversal of hyperplasia and dysplasia. In summary, the study distinguished CDK4 and phosphorylated pRb as targets for chemoprevention regimens targeting reversal of hyperplasia and dysplasia. Cancer Prev Res; 5(6); 810–21. ©2012 AACR.

Association of Over-Expressed Estrogen Receptor Alpha with Development of Tamoxifen Resistant Hyperplasia and Adenocarcinomas in Genetically Engineered Mice.

Background Estrogen receptor alpha (ERα) and cyclin D1 are frequently co-expressed in human breast cancer. Some, but not all, studies link tamoxifen resistance to co-expression of cyclin D1 and ERα. In mice over-expression of either cyclin D1 or ERα in mammary epithelial cells is sufficient to induce mammary hyperplasia. Cyclin D1 over-expression in mice leads to mammary adenocarcinoma associated with activated estrogen signaling pathways. ERα over-expression in mice leads to mammary hyperplasia and cancer. Significantly, disease development in these mice is abrogated by loss of cyclin D1. Methods Genetically engineered mouse models were used to determine whether or not ERα over-expression demonstrated cooperativity with cyclin D1 over-expression in cancer development, reaction to the chemical carcinogen DMBA, or tamoxifen response. Results Adding ERα over-expression to cyclin D1 over-expression increased the prevalence of hyperplasia but not cancer. Single dose DMBA exposure did not increase cancer prevalence in any of the genotypes although cyclin D1 over-expressing mice demonstrated a significant increase in hyperplasia. Tamoxifen treatment was initiated at both young and older ages to test for genotype-specific differences in response. Although normal ductal structures regressed in all genotypes at both younger and older ages, tamoxifen did not significantly reduce the prevalence of either hyperplasia or cancer in any of the genotypes. All of the cancers that developed were hormone receptor positive, including those that developed on tamoxifen, and all showed expression of nuclear-localized cyclin D1. In summary, development of tamoxifen resistant hyperplasia and cancer was associated with expression of ERα and cyclin D1. Conclusion These preclinical models will be useful to test strategies for overcoming tamoxifen resistance, perhaps by simultaneously targeting cell cycle regulatory pathways associated with cyclin D1.

Abstract B70: A conditional aromatase over-expressing in the mammary gland transgenic mouse as a potential model in cancer prevention research

Abstracts: Frontiers in Cancer Prevention Research 2008 B70 Background Breast cancer develops as genetic changes accumulate in the ductal epithelium giving rise to precursor lesions such as atypical ductal hyperplasias, which may progress to ductal carcinoma in situ (DCIS) and eventually invasive breast cancer. This progress is promoted by estrogens. Estrogens are biosynthesized from androgens by the aromatase enzyme. Estrogen is required for the proliferation and morphogenesis of the normal mammary gland; however, studies suggest that estrogen and its metabolites may have mutagenic and carcinogenic potential in the mammary gland. Therefore, it is highly valuable to have mouse models with increased local estrogen production to use to develop optimal therapeutic and chemopreventive strategies to treat these lesions. Purpose The purpose of this work is to develop a conditional transgenic mouse model that would provide an in vivo method of controlling the spatial and temporal regulation of aromatase expression. Methodology The transgenic mouse model was developed by using two transgenes. One transgene is composed of the mouse mammary tumor virus-long terminal repeat (MMTV-LTR) linked to sequences encoding the tetracycline responsive reverse transactivator (rtTA). The other transgene has a tetracycline responsive promoter (tet-op) linked to sequences encoding the human aromatase (MMTV-rtTA/tet-op-Arom). Mammary glands were collected at 4 months of age for morphological, histological, and gene expression studies in both MMTV-rtTA/tet-op-Arom and wild-type mice. Results RT-PCR analysis of aromatase mRNA shows that the gene is conditionally expressed in the mammary gland as compared to control mice. The mammary glands were evaluated for morphological changes using confocal microscopy, whole-mount and hematoxylin and eosin staining. Preliminary data at 4 months of age shows that overexpressing aromatase in the mammary gland leads to developmental abnormalities, abnormal ductal growth and increased ductal density. Gene expression studies will be performed to evaluate additional markers of proliferation, survival, and differentiation. This model is being cross-bred to our conditional overexpression of estrogen receptor α (ERα) in the mammary gland (CERM) model. CERM mice are an established tool for investigation of mechanisms involved in progression and regression of ERα-induced mammary hyperplasia and DCIS. Conclusion The novel CERM/tet-op-aromatase mouse model (CERM/Arom) is being developed to model more closely the human breast with expression of both ERα and aromatase in mammary tissue. This model can be utilized to evaluate agents to prevent carcinogenesis in the presence of aromatase over-expression in the mammary gland at specific times during development. This research is supported by the Susan G. Komen for the Cure Postodoctoral Fellowship Award KG080359 and the NIH National Cancer Institute Grant R01CA112176. Citation Information: Cancer Prev Res 2008;1(7 Suppl):B70.