Drug-Resistant Stem Cells: Novel Approach for Colon Cancer Therapy

BACKGROUND

Next to breast cancer, advanced stage metastatic colon cancer represents a major cause for mortality in women. Germline or somatic mutations in tumor suppressor genes or in DNA mismatch repair genes represent risk factors for genetic predisposition of colon cancer that are also detectable in sporadic colon cancer. Conventional chemotherapy for colon cancer includes combination of 5-fluoro-uracil with oxaliplatin and irinotecan or targeted therapy with non-steroid anti-inflammatory drugs and selective cyclooxygenase-2 inhibitors. Major limitations of these therapeutic interventions are associated with systemic toxicity, acquired tumor resistance and the emergence of drug resistant stem cells that favor initiation, progression and metastasis of therapy-resistant disease. These limitations emphasize an unmet need to identify tumor stem cell selective testable alternatives. Drug-resistant stem cell models facilitate the identification of new testable alternatives from natural phytochemicals and herbal formulations. The goal of this review is to provide an overview relevant to the current status of conventional/targeted therapy, the role of cancer stem cells and the status of testable alternatives for therapy-resistant colon cancer. Experimental models: Hyper-proliferative and tumorigenic cell lines from genetically predisposed colonic tissues of female mice represent experimental models. Chemotherapeutic agents select drug-resistant phenotypes that exhibit upregulated expressions of cellular and molecular stem cell markers. Mechanistically distinct natural phytochemicals effectively inhibit stem cell growth and downregulate the expressions of stem cell markers.

CONCLUSIONS

The present review discusses the status of colon cancer therapy and inherent limitations, cancer stem cell biology, potential lead compounds and their advantages over chemotherapy. The present experimental approaches will facilitate the identification of pharmacological and naturally-occurring agents as lead compounds for stem cell targeted therapy of colon cancer.

Anti-proliferative and pro-apoptotic effects of Dipsacus asperoides in a cellular model for triple-negative breast cancer

Background: Triple negative breast cancer (TNBC) lacks expressions of estrogen receptor-α (ER-α), progesterone receptor (PR) and amplified human epidermal growth factor receptor-2 (HER-2). Current treatment for TNBC includes anthracyclin, taxol and cisplatin-based conventional chemotherapy and survival pathway PARP, PI3K, AKT and mTOR selective targeted therapy. These treatments exhibit dose-limiting systemic toxicity and presence of drug resistant cancer stem cells, which highlight the need for identification of efficacious testable alternatives that are not toxic to non-tumorigenic cells. Dipsacus asperoides (DA) is a Chinese nutritional herb and its root represents a common ingredient in Chinese herbal formulations used in women for estrogen related health issues, osteoporosis and breast diseases. This study aims to investigate the growth inhibitory effects of DA, and to detect mechanisms for its efficacy. Methods: Human mammary carcinoma derived triple negative MDA-MB-231 cell line represented the TNBC model. Non-fractionated aqueous extract from DA represented the test agent. Anchorage dependent growth, anchorage independent (AI) colony formation and cell cycle progression quantified growth inhibition. Western blot-based analysis for inhibition of RAS, PI3K and AKT and RB signaling identified mechanistic leads. Results: Treatment with DA induced a dose dependent cytostatic growth arrest (IC50:15 µg/ml; IC90: 30 µg/ml), reduced AI growth and inhibited cell cycle progression via G2/M arrest. DA affected the RAS, PI3K, AKT and RB signaling pathways, and functioned as a natural inhibitor of cyclin dependent kinase 4/6. Cellular apoptosis paralleled increase in pro-apoptotic Caspase 3/7 activity.   Conclusion: These results demonstrate that DA inhibited growth, affected cell cycle progression, induced apoptosis and inhibited cancer cell survival pathways. This study validates a mechanism-based approach to identifying testable substitutes for secondary prevention/therapy of TNBC.

Isolation and Characterization of Chemo-Resistant Stem Cells from a Mouse Model of Hereditary Non-Polyposis Colon Cancer

Rationale

Loss of function mutations in DNA mismatch repair genes is the primary genetic defects in high-risk hereditary non-polyposis colon cancer (HNPCC). Cytotoxic chemotherapy and anti-inflammatory drugs are potential treatment options. These treatment options lead to systemic toxicity, acquired tumor resistance and the emergence of drug-resistant stem cells. A colonic epithelial cell culture model expressing the relevant genetic defects in chemo-resistant stem cells provides a relevant experimental system for HNPCC.

Objective

To develop a colonic epithelial cell culture system from a mouse model for HNPCC and to isolate and characterize drug-resistant stem cells.

Experimental Models and Biomarkers

The Mlh₁^[-/-]/Apc ^[-/-] Mlh₁/1638N COL-Cl₁ cells is a mouse model for HNPCC, and the 5-fluoro-uracil resistant (5-FU-R) phenotype represents a model for the drug-resistant stem cells. Tumor spheroid formation, and the expression of CD44, CD133 and c-Myc represent stem cell markers.

Results

The HNPCC model exhibits aneuploidy, hyper-proliferation, accelerated cell cycle progression and downregulated cellular apoptosis. Long-term exposure to 5-FU selects for the drug-resistant phenotype. These resistant cells exhibit increased formation of tumor spheroids and upregulated expression of cancer stem cell markers CD44, CD133 and c-Myc.

Conclusion

In the present study, a stem cell model for HNPCC was validated and offered a novel experimental approach to test stem cell-targeted alternatives to drug-resistant therapy.

Stem cell models for genetically predisposed colon cancer

Negative growth regulatory tumor suppressor genes and positive growth regulatory oncogenes serve important roles in initiation/progression of colon cancer. Germline mutation in the adenomatous polyposis coli (APC) tumor suppressor gene represents a primary genetic defect for familial adenomatous polyposis (FAP) syndrome, a predisposing factor for clinical colon cancer. Somatic mutations in the APC gene are common in sporadic colon cancer. Preclinical and clinical efficacy is documented for targeted therapy with non-steroidal anti-inflammatory drugs, selective cyclo-oxygenase-2 inhibitors for prostaglandin biosynthesis and selective inhibitor of ornithine decarboxylase for polyamine biosynthesis. However, these therapeutic options lead to systemic toxicity, acquired tumor resistance and emergence of therapy resistant cancer stem cells. By contrast, non-toxic natural products are unlikely to exhibit drug resistance and may represent testable alternatives for therapy resistant colon cancer. Tumorigenic Apc [-/-] colonic epithelial cell lines derived from preclinical FAP models provide novel cellular models for drug resistant cancer stem cells. Apc [-/-] Sulindac resistant (SUL-R) cells exhibit upregulated expression levels of cancer stem cell markers. Natural products, such as naturally occurring vitamin A derivative all-trans retinoic acid (ATRA) and the anti-cancer agent from Turmeric root curcumin (CUR), represent testable alternatives. Relative to the non-tumorigenic Apc [+/+] C57 COL colonic epithelial cells, the tumorigenic Apc [-/-] 1638N COL and Apc [-/-] 850 ^MIN COL cells exhibit aneuploid cell hyper-proliferation and upregulated expression of Apc target genes β-catenin, cyclin D1, c-myc and COX-2. The SUL-R phenotypes exhibit enhanced tumor spheroid formation and upregulated expression levels of stem cell markers CD44, CD133 and c-Myc. Treatment of the SUL-R stem cells with ATRA and CUR inhibits tumor spheroid formation and reduces the expression of stem cell markers. Stem cell models developed for FAP syndrome provide a novel experimental approach to identify mechanistic leads for efficacious natural products as testable alternatives for therapy-resistant, genetically predisposed colon cancer.

Growth inhibitory efficacy and anti-aromatase activity of Tabebuia avellanedae in a model for post-menopausal Luminal A breast cancer

Aromatase inhibitors (AIs) represent a treatment option for post-menopausal estrogen receptor-positive (ER⁺) breast cancer as monotherapy, or in combination with cyclin-dependent kinase 4/6 or mTOR inhibitors. Long-term treatment with these agents leads to dose-limiting toxicity and drug resistance. Natural substances provide testable alternatives to current therapy. Tabebuia avellanedae (TA) tree is indigenous to the Amazon rainforest. The inner bark of TA represents a medicinal dietary supplement known as Taheebo. Non-fractionated aqueous extract from TA is an effective growth inhibitor in the Luminal A and triple negative breast cancer models. The quinone derivative naphthofurandione (NFD) is a major bioactive agent in TA. The present study examined the efficacy of finely ground powder from the inner bark of TA, available under the name of Taheebo-NFD-Marugoto (TNM). The ER⁺ MCF-7 cells stably transfected with the aromatase gene MCF-7^AROM represented a model for aromatase-expressing post-menopausal breast cancer. Anchorage-independent colony formation, cell cycle progression, pro-apoptotic caspase 3/7 activity, apoptosis-specific gene expression, aromatase activity and select estradiol (E₂) target gene expression represented the mechanistic end points. Treatment of MCF-7^AROM cells with TNM induced a dose-dependent reduction in E₂-promoted anchorage-independent colony number. Mechanistic assays on TNM-treated MCF-7^AROM cells demonstrated that TNM at a concentration of 10 µg (NFD content: 2 ng), induced S-phase arrest, increased pro-apoptotic caspase 3/7 activity, increased pro-apoptotic BAX and decreased anti-apoptotic BCL-2 gene expression, and inhibited aromatase activity. Additionally, TNM treatment downregulated ESR-1 (gene for ER-α), aromatase and progesterone gene expression and reduced mRNA levels of E₂ target genes pS2, GRB2 and cyclin D1. Inhibition of aromatase activity, based on the NFD content of TNM was superior to the clinical AIs Letrozole and Exemestane. These data demonstrated the potential efficacy of TNM as a nutritional alternative for current therapy of aromatase positive, post-menopausal breast cancer.

Anti-proliferative and pro-apoptotic effects of rosemary and constituent terpenoids in a model for the HER-2-enriched molecular subtype of clinical breast cancer

Neoadjuvant treatment options for human epidermal growth factor receptor-2 (HER-2)-enriched and luminal B molecular subtypes of clinical breast cancer include HER-2-targeted therapy with chemotherapy or anti-hormonal therapy. These treatment options result in systemic toxicity and acquired tumor resistance. Minimally toxic naturally occurring phytochemicals may represent testable alternatives to conventional therapy. HER-2-overexpressing tumorigenic human mammary epithelial 184-B5/HER cells represent a model for the HER-2-enriched breast cancer subtype. Non-fractionated rosemary extract (RME) and constituent phenolic terpenoids ursolic acid (UA), carnosol (CSOL) and carnosic acid (CA) represented the test agents. Anchorage-independent (AI) proliferation, cell cycle progression, cellular apoptosis and expression of cell cycle-regulatory and apoptosis-specific proteins represented the mechanistic end point biomarkers. Relative to the parental non-tumorigenic 184-B5 cells, tumorigenic 184-B5/HER cells exhibited decreased population doubling, increased saturation density, accelerated cell cycle progression and downregulated cellular apoptosis, confirming the loss of homeostatic control of proliferation. Treatment with the test agents resulted in a dose-dependent decrease in AI colony number, indicating a decrease in cancer risk. Mechanistically, RME and UA inhibited G₁-S phase transition resulting in an increased G₁:S+G₂/M ratio and decreased cyclin D1 expression. The pro-apoptotic effect of RME and UA was indicated by increased sub-G₀ (apoptotic) cell population, and relevant reciprocal modulation, as demonstrated by decreased anti-apoptotic B-cell lymphoma-2 (Bcl-2) and increased pro-apoptotic Bcl-2-associated X protein expression. In contrast, treatment with CA and CSOL resulted in cytostatic G₂/M arrest and an increase in cyclin B1 expression; thus, naturally-occurring rosemary and its constitutive terpenoids re-establish homeostatic control of proliferation and decrease cancer risk via distinct mechanisms. These data validate an experimental approach to prioritize efficacious natural compounds as testable alternatives for conventional chemo-endocrine and HER-2-targeted therapies in HER-2-enriched breast cancer.

Anti-inflammatory drug resistance selects putative cancer stem cells in a cellular model for genetically predisposed colon cancer

Mutations in the adenomatous polyposis coli (Apc) tumor suppressor gene represent the primary genetic defect in colon carcinogenesis. Apc^+/- mouse models exhibit pre-invasive small intestinal adenomas. Cell culture models exhibiting Apc defects in the colon and quantifiable cancer risk provide a novel clinically relevant approach. The tumor-derived Apc^-/- colonic epithelial cell line 1638N COL-Pr₁ represented the experimental model. The anti-inflammatory drugs sulindac (SUL) and celecoxib (CLX) represented the test compounds. Compared with non-tumorigenic Apc^+/+ C57COL cells, the Apc^+/- 1638N COL cells and Apc^-/- 1638N COL-Pr₁ cells exhibited progressive loss of homeostatic growth control. Compared with Apc^+/- cells, Apc^-/- cells displayed increased expression of biomarkers specific for hyper-proliferation. Treatment of Apc^-/- cells with SUL and CLX resulted in inhibition of anchorage-independent colony formation in vitro, which is indicative of reduced cancer risk in vivo. Mechanistically, SUL and CLX suppressed the expression of the Apc target genes β-catenin, cyclin D1, c-Myc and cyclooxygenase-2. Long-term treatment with high concentrations of SUL and CLX led to the selection of hyper-proliferative drug-resistant phenotypes. The Apc^-/- SUL-resistant phenotype displayed spheroid formation and enhanced the expression of the stem cell-specific molecular markers CD44, CD133 and c-Myc. These data demonstrated the growth-inhibitory efficacy of SUL and CLX and indicated that drug resistance leads to the selection of a putative cancer stem cell phenotype. The study outcome validates a stem cell-targeted mechanistic approach to identify testable alternative leads for chemotherapy-resistant colon cancer.

Growth inhibitory efficacy of natural products in a model for triple negative molecular subtype of clinical breast cancer

Global gene expression profiling identifies predictive and prognostic biomarkers and rationalizes breast cancer subtype-targeted treatment. The Anthracyclin/Taxol and survival pathway specific small molecular inhibitors, constitute current treatment options. These options are associated with acquired tumor resistance and emergence of drug-resistant cancer stem cells. Dietary supplements and constitutive bioactive phytochemicals with relatively low systemic toxicity may provide testable alternatives for current therapy. Human breast epithelial cell lines 184-B5 (non-tumorigenic triple negative cell type) and MDA-MB-231 (breast carcinoma derived triple negative cell type) were used as the experimental models. Putative cancer chemo-preventive natural products and their constitutive bioactive agents represented the test agents. Anchorage independent growth, cell cycle progression and cell apoptosis quantified the treatment efficacy. Compared to the 184-B5 cells, the MDA-MB-231 cells exhibited anchorage-independent growth indicative of persistent cancer risk. Additionally, the MDA-MB-231 cells exhibited hyper-proliferation, accelerated cell cycle progression and inhibited apoptosis indicative of loss of homeostatic growth control. The test agents inhibited anchorage-independent growth via cytostatic and pro-apoptotic effects. The triple negative carcinoma-derived Doxorubicin-resistant phenotype exhibited cancer stem cell markers, including tumor spheroid formation and expression of CD44, NANOG and c-Myc. These data identify clinically relevant mechanistic leads for the efficacy of natural products in the aggressive therapy-resistant breast cancer subtype and suggests a testable approach for cancer stem cell-targeted therapy.

Inhibitory effects of Chinese nutritional herbs in isogenic breast carcinoma cells with modulated estrogen receptor function

In estrogen receptor (ER)+ MCF-7 cells, ER represents a ligand-activated transcription factor, and 17β-estradiol (E2) represents its physiological ligand. Maintenance of the human breast carcinoma-derived MCF-7 cells with 0.7% serum selected a proliferative sub-population of E2-responsive cells with transiently non-functional ER due to limited availability of E2. Culture of MCF-7 cells in the presence of either 0.7% serum, <1 nM E2 or 0.7% serum + 20 nM E2 selected isogenic cells with either non-functional ER (ER-NF) or functional ER (ER-F) phenotype. The two phenotypes responded to the growth-promoting effects of E2 and to the growth-inhibitory effects of the selective ER modulator tamoxifen, indicating retention of E2 responsiveness. Comparative dose-response experiments with Chinese nutritional herbs on ER-NF and ER-F cells identified the inhibitory concentration (IC)50 values for these herbs, while the IC50 ratios for the ER-NF:ER-F phenotypes facilitated their rank ordering in terms of efficacy. Out of the 11 efficacious herbs tested, five herbs exhibited ER-F > ER-NF inhibitory activity, four exhibited ER-F = ER-NF inhibitory activity and two exhibited ER-NF > ER-F inhibitory activity. Extracts from representative herbs, Lycium barbarum bark, Epimedium grandiflorum and Cornus officinalis, from each of the three groups inhibited anchorage-independent growth, induced G₁ or G2/M arrest and/or apoptosis, and generated anti-proliferative E₂ metabolites. The differential growth inhibition in ER-NF and ER-F phenotypes, together with the mechanistic efficacy of representative herbs, identified potential leads for their efficacy on ER⁺ and/or ER- breast cancer.

Comparative efficacy of extracts from Lycium barbarum bark and fruit on estrogen receptor positive human mammary carcinoma MCF-7 cells

Chemo-endocrine therapy for estrogen receptor positive (ER(+)) breast cancer exhibits acquired tumor resistance. Herbal medicines provide integrative support for breast cancer patients. Present study compared the efficacy of aqueous extracts from Lycium barbarum bark (LBB) and Lycium barbarum fruit (LBF) on ER(+) MCF-7 cells. Cellular growth and 17ß-estradiol (E2) metabolism quantified the efficacy. MCF-7 cells maintained in serum depleted medium+ E2 exhibited increased anchorage-dependent and anchorage-independent growth. LBB exhibited greater potency than LBF (95% reduction in IC50). LBB produced a 6.8-fold increase, 40% decrease, and a 3.7-fold increase in 2-hydroxyestrone (2-OHE1), 16α-hydroxyestrone (16α-OHE1), and estriol (E3) formation. The corresponding values for LBF were 3.9, 33, and 10.5. LBB produced a16.3-fold and a twofold increase in 2-OHE1:16α-OHE1 and E3:16α-OHE1 ratios, whereas LBF produced a sixfold and a 2.9-fold increase. The efficacy of LBB is due to increased 2-OHE1 formation, whereas that of LBF is due to accelerated conversion of 16α-OHE1 to E3. Specific growth inhibitory profiles of LBB and LBF may be due to their distinct chemical composition and their complementary actions on E2 metabolism. This study validates a mechanistic approach to identify efficacious herbal extracts for clinical ER(+) breast cancer.

Abstract P4-09-05: Preventive efficacy of the Chinese nutritional herb epimedium grandiflorum in a preclinical cell culture model for luminal A molecular subtype of breast cancer

Background: The Luminal A molecular sub-type of clinical breast cancer expresses estrogen receptor (ER) and progesterone receptor (PR), but lacks the expression of HER-2 oncogene. This cancer sub-type responds to endocrine therapy involving the use of selective estrogen receptor modulators or inhibitors of estrogen biosynthesis. Conventional therapeutic options are frequently associated with acquired tumor resistance and systemic toxicity, and therefore, emphasize a need for identification of promising new non-toxic agents for secondary prevention. Nutritional substances that do not incur long-term toxicity represent ideal candidates. Nutritional herbs have been used in traditional Chinese medicine for a variety of health related issues, including prevention of breast cancer.

Methods: The present study utilized the human mammary carcinoma derived ER+/PR+/HER-2- MCF-7 cells as a model for the Luminal A breast cancer to examine the preventive efficacy of non-fractionated aqueous extract from Epimedium grandiflorum (EG), a popular Chinese nutritional herb. Anchorage dependent growth, cell cycle progression, cellular metabolism of 17b-estradiol (E2), and anchorage independent colony formation represented the quantitative end point biomarkers for preventive efficacy.

Results: Maintenance of MCF-7 cells in a chemically defined serum depleted culture medium (serum 0.7%, E2&lt;1 nM) retained their cellular growth promoting response to the physiologically relevant concentration range of 1 nM to 20 nM E2, exhibiting a 10.3% to a 91.9% increase in the viable cell number, respectively. A 7 day treatment of MCF-7 cells with EG resulted in a dose dependent inhibition of E2 promoted growth (EG IC50: 0.49%). At its maximum cytostatic concentration, EG inhibited cell cycle progression via G1 arrest, resulting in a 1.6 fold increase in the G1:S+G2/M ratio, and modulated the cellular metabolism of E2 in favor of formation of anti-proliferative metabolites 2-hydroxyestrone (2-OHE1) and estriol (E3), exhibiting a 5.1 and a 7.6 fold increase, respectively. In addition, EG produced a favorable 3.9 fold increase in the

2-OHE1: 16α-OHE1 ratio, an endocrine biomarker of breast cancer risk. A 21 day treatment of MCF-7 cells with EG produced a dose dependent inhibition in anchorage independent growth (EG IC50: 0.49%; IC90: 1.03%).

Conclusions: These data demonstrate the growth inhibitory effects of EG and identify clinically relevant mechanistic leads for its preventive efficacy. The present approach promises to facilitate identification of new efficacious herbs for the secondary prevention of the Luminal A subtype of clinical breast cancer.

Citation Information: Cancer Res 2013;73(24 Suppl): Abstract nr P4-09-05.

Epithelial cell culture models for the prevention and therapy of clinical breast cancer (Review)

Clinical breast cancer progresses via a multi-step carcinogenic process wherein genetic, molecular, endocrine and dietary factors play significant roles in the pathogenesis, prevention and therapy of the disease. Preclinical cell culture models, expressing clinically relevant genetic and endocrine defects and exhibiting quantifiable cancer risk, may provide facile, clinically translatable approaches to identify molecular targets and susceptible mechanistic pathways for the efficacy of novel interventional approaches. This review summarizes laboratory investigations focused on i) developing murine and human mammary tissue-derived cell culture models; ii) optimizing mechanism-based quantitative endpoint biomarker assays specific for carcinogenic risk and preventive/therapeutic efficacy; and iii) providing quantifiable proof-of-principle evidence for validation of the present cell culture approaches, capable of prioritizing efficacious lead compounds for subsequent in vivo animal studies and clinical trials for the prevention/therapy of breast cancer. Epithelial cell culture models are developed and characterized where the carcinogenic process is initiated by the targeted expression of clinically relevant oncogenes. The cell culture systems from mouse mammary tissue are in vitro approaches that complement the Ras and Myc transgenic mouse models. The human mammary tissue-derived systems are in vitro models for chemoendocrine, therapy-resistant, clinical, pre-invasive ER(-)/PR(-)/HER-2(+) comedo ductal carcinoma in situ, ER(+)/PR(+) chemoendocrine therapy-responsive breast cancer and ER(-)/PR(-)/HER-2(-) triple-negative chemoendocrine, therapy-resistant breast cancer. The oncogene-initiated phenotypes exhibit loss of homeostatic growth control, downregulation of cell apoptosis and gain of carcinogenic risk in vitro, as well as transplantable tumor development in vivo. Numerous mechanistically distinct, synthetic pharmacological agents, as well as naturally occurring dietary compounds, re-establish homeostatic growth control via cell cycle arrest and/or induction of cell apoptosis, downregulate oncogene-mediated cell signaling pathways, modulate the expression of numerous cell cycle regulatory and apoptosis-specific proteins and reduce carcinogenic risk in pre-neoplastic and carcinoma-derived cell culture models. These data validate the present cell culture approaches as novel, mechanism-based screens to evaluate and prioritize promising lead compounds for the prevention/therapy of clinical breast cancer.

Adipocyte-derived factor as a modulator of oxidative estrogen metabolism: implications for obesity and estrogen-dependent breast cancer

The role of body fat as a risk factor for breast cancer has been well established. A decrease in the urinary 2/16α-hydroxyestrone ratio has also been shown to be a risk marker for breast cancer. These two observations are connected by the fact that obese women have decreased levels of 2-hydroxyestrone. To test the hypothesis that fat depots secrete factors that inhibit 2-hydroxylation, the effect of substances released into the media from adipocytes incubated in Krebs-Ringer buffer, on estrogen metabolism by MCF-7 cells in minimum essential medium eagle (MEM) plus adipocyte-conditioned media (ACM) was studied. The 1:1 ACM-MEM culture system resulted in a substantial and highly significant decrease in 2-hydroxylation of estradiol. This inhibition was partially reversed by the addition of indole-3-carbinol, a potent inducer of 2-hydroxylation of estradiol. Centrifugal sizing showed that the active 2-hydroxylation inhibitor in the medium had a molecular weight of about 30 kDa. These results suggest a mechanism for the decrease in 2-hydroxylation of estradiol that is observed in obese women and the increase in 2-hydroxylation observed in women with depleted fat depots.

Preclinical in vitro models from genetically engineered mice for breast and colon cancer (Review)

Genetically engineered mice with targeted alterations in clinically relevant oncogenes, tumor suppressor genes or DNA mismatch repair genes provide unique predictive animal models for human carcinogenesis, and cancer prevention/therapy. However, some of the genetically engineered mouse models lack target organ specificity for colon carcinogenesis. We have established, characterized and validated stable epithelial cell lines from 'normal' and 'genetically' predisposed target organs that offer innovative and mechanistic approaches, complementing in vivo studies on existing animal models for clinical breast and colon cancer. Epithelial cell lines with up- regulated Ras or myc oncogene, mutated Apc tumor suppressor gene and Mlh1 DNA mismatch repair gene provide facile experimental systems for organ site carcinogenesis and cancer prevention. Altered expression of cancer specific biomarkers and their modulation by several synthetic pharmacological agents such as retinoids, selective estrogen receptor modulators, non-steroidal anti-inflammatory drugs and specific enzyme inhibitors have been reported from our laboratory. Oncogene expressing MMEC-Ras and MMEC-myc mammary epithelial cells, Apc mutant 850Min COL and 1638N COL, and DNA mismatch repair/Apc mutant Mlh1/1638N COL colon epithelial cells exhibit aberrant cell cycle progression, down-regulated apoptosis and enhanced carcinogenic risk in vitro and tumor formation in vivo. We have reported that relative to the parental 'normal' non-neoplastic cells, genetically 'altered' pre-neoplastic cells exhibit enhanced sensitivity for growth arrest by multiple mechanistically distinct pharmacological agents. Comparative experiments on isogenic 'normal' and genetically 'altered' target cell lines facilitate cancer selective efficacy and identification of susceptible mechanistic pathways. Treatment of these genetically 'altered' pre-neoplastic cells with low dose combination of mechanistically distinct pharmacological agents as well as naturally occurring phytochemicals induce cytostatic growth arrest, alter cell cycle progression and reduce carcinogenic risk. The availability of validated technology for model development, and for mechanism based biomarker assays now establishes a novel platform to rapidly test carcinogenicity and preventive/therapeutic efficacy of novel pharmacological agents as well as naturally occurring phytochemicals. Thus, these data permit rational prioritization of efficacious lead compounds for preclinical testing and future clinical trials for prevention/therapy of breast and colon cancer.

Growth inhibition of estrogen receptor positive human breast cancer cells by Taheebo from the inner bark of Tabebuia avellandae tree

Selective estrogen receptor (ER) modulators are used as a therapy for ER+ clinical breast cancer, but they exhibit adverse effects. Herbal medicines may provide an alternative or complementary approach. Taheebo, extracted from the inner bark of the Tabebuia avellandae tree found in the Brazilian Amazon, exhibits selective anti-proliferative effects in carcinoma cell lines. The present study identifies the mechanistic leads for the inhibitory effects of Taheebo. Human breast carcinoma derived ER+MCF-7 cells were used as the model. Aqueous extract of Taheebo was the test compound. Cell cycle analysis, clonogenic assay, and global gene expression profiles were the quantitative parameters. Taheebo treatment resulted in a dose/time-dependent growth inhibition (S phase arrest, reduced clonogeneticity) and initiation of apoptosis (chromatin condensation). A 6-h treatment with 1.5 mg/ml Taheebo modulated the gene expression of G2 specific cyclin B1 (-2.0-fold); S phase specific PCNA (-2.0-fold) and OKL38 (+11.0-fold); apoptosis specific GADD-45 family (+1.9-5.4-fold), Caspases (+1.6-1.7-fold), BCL-2 family (-1.5-2.5-fold), estrogen responsive ESR1 (-1.5-fold), and xeno-biotic metabolism specific CYP 1A1 (+19.8 fold) and CYP 1B1 (+7.9-fold). The anti-proliferative effects of Taheebo correlate with down-regulated cell cycle regulatory and estrogen responsive genes, and up-regulated apoptosis specific and xeno-biotic metabolism specific genes. These data validate a rapid mechanistic approach to prioritize efficacious herbal medicines, thereby complementing the existing endocrine therapy for breast cancer.

Novel cell culture model for prevention of carcinogenic risk in familial adenomatous polyposis syndrome

Clinical familial adenomatous polyposis (FAP) syndrome represents a high risk pre-invasive precursor for colon cancer, and is characterized by germ line mutation in the adenomatous polyposis coli (APC) tumor suppressor gene. Cellular models with relevant genetic and biological characteristics should provide important mechanistic leads for predisposition and preventive intervention. Cloned colon epithelial cell line from the Apc850 Min/+ mouse represented a model for FAP. Cell cycle progression, cellular apoptosis and anchorage-independent growth represented the biomarkers for carcinogenic risk. The Apc mutant 850Min COL-Cl1 cells exhibited decreased G0/G1:S+G2/M ratio, increased S+G2/M:subG0 ratio, and increased anchorage-independent colony formation, indicating loss of homeostatic growth control and gain of anchorage-independent growth. Growth of these cells in serum-depleted medium was promoted by mitogenic insulin and epidermal growth factor, and inhibited by anti-mitogenic transforming growth factor-beta1 and dexamethasone. Treatment with low dose combinations of synthetic enzyme inhibitor difluoro methylornithine (DFMO), synthetic non-steroidal anti-inflammatory drug sulindac (SUL), and naturally occurring epigallocatechin gallate (EGCG), and eicosapen-taenoic acid (EPA) produced cytostatic growth arrest and inhibited anchorage-independent colony formation. These data identify a novel cell culture model and validate a mechanism-based approach to prioritize combinations of effective chemopreventive compounds for prevention/therapy of colon cancer.

Cell culture model for colon cancer prevention and therapy: an alternative approach to animal experimentation

Mouse models for colon cancer that harbor a germ line mutation in the tumor suppressor gene Adenomatous polyposis coli (Apc) exhibit a primary genetic defect that predisposes to a high incidence of adenomatous polyps in the small intestine rather than in the colon. Colon cell culture models expressing quantifiable markers for carcinogenic risk may represent an alternative approach to reduce, refine or replace long-term animal experimentation. The newly developed colon epithelial cell lines 1638N COL-Cl(1) (clonal derivative of the parental Apc mutant cell line 1638N COL) and 1638N COL-Pr(1) (tumor derivative of the clone), established from an Apc1638N [+/-] mutant mouse, exhibit aberrant cell cycle progression, downregulated apoptosis, enhanced carcinogenic risk and tumor formation, indicating that aberrantly proliferative preneoplastic1638N COL-Cl(1) cells exhibit a quantifiable risk for carcinogenesis. Treatment of these preneoplastic Apc mutant cells with a combination of celecoxib and 5-fluorouracil at clinically achievable low concentrations produced a 2.1 fold to 5.5 fold higher efficacy for cytostatic growth arrest and a 40.2% to 52.4% higher efficacy for inhibition of carcinogenic risk, relative to that obtained by these agents used individually. Thus, a low dose combination of mechanistically distinct agents resulted in enhanced efficacy. These data validate a novel cell culture model and a rapid mechanism-based approach to prioritize efficacious drug combinations for animal studies and clinical trials on cancer prevention and, thereby, support the 3R concept by refining and/or reducing the use of animals in biomedical research relevant to prevention/therapy of colon cancer.

Combinatorial prevention of carcinogenic risk in a model for familial colon cancer

Germ line mutations in the tumor suppressor adenomatous polyposis coli (APC) gene, predispose for the clinical familial adenomatous polyposis (FAP) syndrome, a high risk precursor for early onset colon cancer. Similar mutations in the murine homolog of the APC gene, however, produce adenomas predominantly in the small intestine, rather than in the colon. The objectives of the present study were: i) to develop a preclinical cell culture model for human FAP syndrome and ii) to validate this model as a rapid mechanism-based approach for evaluation of the preventive efficacy of combinations of synthetic pharmacological agents or naturally-occurring phytochemicals, for the risk of colon carcinogenesis. The clonally selected 850Min COL-Cl1 cell line derived from histologically normal colon of ApcMin/+ mouse exhibited aberrant proliferation (64.7% decrease in population doubling time, 820% increase in saturation density, and 81.4% decrease in spontaneous apoptosis), relative to that observed in the colon epithelial cell line C57 COL established from Apc [+/+] C57BL/6J mouse. In addition, unlike the Apc [+/+] C57 COL cells, the Apc mutant cells exhibited enhanced risk for spontaneous carcinogenic transformation as evidenced by 100% increase in anchorage-independent colony formation (C57 COL: 0/12; 850Min COL-Cl1: 12/12, mean colony number 23.6+/-2.7). Treatment of Apc mutant cells with low dose combination of select mechanistically distinct synthetic chemopreventive agents such as celecoxib (CLX) + difluoro methylornithine (DFMO), or naturally-occurring epigallocatechin gallate (EGCG) + curcumin (CUR) produced 160-400% and 220-430% decrease in the viable cell number respectively, relative to these agents used independently. Furthermore, relative to independent agents, CLX+DFMO and EGCG+CUR combinations produced 31.5-82.1% and 45.9-105.4% greater reduction in the number of anchorage-independent colonies. Thus, aberrant proliferation and increased risk for carcinogenesis in the Apc mutant cells, and their susceptibility to low dose combinations of mechanistically distinct chemopreventive agents validate a rapid approach to prioritize efficacious combinations for long-term animal studies and future clinical trials on prevention of colon cancer.

Efficacy of chemopreventive agents for growth inhibition of Apc [+/-] 1638NCOL colonic epithelial cells

Germline mutations of the Apc tumor suppressor gene result in increased risk for gastrointestinal carcinogenesis. The Apc1638N [+/-] mouse exhibits accelerated gastrointestinal carcinogenesis that is modifiable by select pharmacological and dietary agents. Experiments in the present study were conducted on a subculturable epithelial 1638NCOL cell line established from histologically normal colon of Apc1638N [+/-] mouse to examine the effects of selected chemopreventive agents that differ in their mechanism of action. Extent of growth arrest, number of cell population doublings, cell cycle progression and aneuploid G0/G1: S + G2/M ratio represented the quantitative endpoints for the susceptibility and efficacy of chemopreventive agents. Treatment of exponentially growing 1638NCOL cells with maximum cytostatic dose of 9cisRA, DFMO or SUL (100 microM) produced a 60-70% growth arrest, that with TAM and AMF (10 microM) produced a 20-40% growth arrest, while that with OLT (100 microM) produced a 25% growth arrest. This response was associated with corresponding decrease in the number of cell population doubling. 9cisRA, SUL or AMF increased the aneuploid G0/G1: S + G2/M ratio by inducing G1 checkpoint arrest, while DFMO, TAM and OLT decreased the ratio by inducing G2 checkpoint arrest. Thus, cell cycle phase-dependent susceptibility of the Apc [+/-] 1638NCOL cell line to mechanistically distinct chemopreventive agents validates a novel colon epithelial cell culture model for mechanistic, preventive or therapeutic studies on Apc regulated colon carcinogenesis.

Chemopreventive agents inhibit aberrant proliferation of the aneuploid phenotype in a colon epithelial cell line established from Apc 1638N [+/-] mouse

Loss of function of the adenomatous polyposis coli (APC) tumor suppressor gene predisposes for familial adenomatous polyposis (FAP) syndrome. The Apc gene knockout mice exhibit accelerated intestinal carcinogensis modifiable by diverse pharmacological agents. Present experiments utilized the Apc[+/-] 1638N COL colon epithelial cell line (origin: histologically normal colon) as the model. Retinoid receptor modulator 9-cis-retinoic acid (9-cis-RA), ornithine decarboxylase inhibitor difluoromethyl ornithine (DFMO), and nonselective cyclooxygenase inhibitor sulindac (SUL) represented the chemopreventive test compounds. Population doubling, cell cycle progression, and anchorage-independent growth provided mechanistic end points for chemopreventive efficacy. Treatment of 1638N COL cells with 9-cis-RA, DFMO and SUL produced a dose-dependent cytostatic growth arrest by decreasing the number of population doublings and altering aneuploid G0/G1:S+G2/M ratio. The clonally expanded 1638N-Cl1 cells selected for anchorage-independent growth exhibited decreased anchorage-independent colony formation in response to treatment with the three test compounds. Susceptibility of preneoplastic 1638N COL cells to mechanistically distinct chemopreventive agents validates a unique epithelial cell culture model for FAP syndrome, and facilitates investigations on Apc regulated colon carcinogenesis and cancer prevention.

Resveratrol inhibits cyclooxygenase-2 transcription in human mammary epithelial cells

A large body of evidence suggests that inhibiting cyclooxygenase-2 (COX-2), the inducible form of COX, will be an important strategy for preventing cancer. In this study, we investigated whether resveratrol, a chemopreventive agent found in grapes, could suppress phorbol ester (PMA)-mediated induction of COX-2 in human mammary and oral epithelial cells. Treatment of cells with PMA induced COX-2 mRNA, COX-2 protein, and prostaglandin synthesis. These effects were inhibited by resveratrol. Nuclear runoffs revealed increased rates of COX-2 transcription after treatment with PMA, an effect that was inhibited by resveratrol. Resveratrol inhibited PMA-mediated activation of protein kinase C and the induction of COX-2 promoter activity by c-Jun. Phorbol ester-mediated induction of AP-1 activity was blocked by resveratrol. These data are likely to be important for understanding the anticancer and anti-inflammatory properties of resveratrol.

Resveratrol inhibits cyclooxygenase-2 transcription and activity in phorbol ester-treated human mammary epithelial cells

We determined whether resveratrol, a phenolic antioxidant found in grapes and other food products, inhibited phorbol ester (PMA)-mediated induction of COX-2 in human mammary and oral epithelial cells. Treatment of cells with PMA induces COX-2 and causes a marked increase in the production of prostaglandin E2. These effects were inhibited by resveratrol. Resveratrol suppressed PMA-mediated increases in COX-2 mRNA and protein. Nuclear run-offs revealed increased rates of COX-2 transcription after treatment with PMA, an effect that was inhibited by resveratrol. PMA caused about a 6-fold increase in COX-2 promoter activity, which was suppressed by resveratrol. Transient transfections utilizing COX-2 promoter deletion constructs and COX-2 promoter constructs, in which specific enhancer elements were mutagenized, indicated that the effects of PMA and resveratrol were mediated via a cyclic AMP response element. Resveratrol inhibited PMA-mediated activation of protein kinase C. Overexpressing protein kinase C-alpha, ERK1, and c-Jun led to 4.7-, 5.1-, and 4-fold increases in COX-2 promoter activity, respectively. These effects also were inhibited by resveratrol. Resveratrol blocked PMA-dependent activation of AP-1-mediated gene expression. In addition to the above effects on gene expression, we found that resveratrol also directly inhibited the activity of COX-2. These data are likely to be important for understanding the anti-cancer and anti-inflammatory properties of resveratrol.

Transcription of cyclooxygenase-2 is enhanced in transformed mammary epithelial cells

Cancers form more prostaglandins than the normal tissues from which they arise. Cyclooxygenase-2 (prostaglandin H synthase-2, PGHS-2, EC 1.14.99.1), an enzyme that catalyzes the formation of prostaglandins from arachidonic acid, is inducible in epithelial cells. We investigated whether transformation of mammary cells was associated with up-regulation of Cox-2 as a basis for increased production of prostaglandin E2 (PGE2) by these cells. This hypothesis was tested in two pairs of mammary cell lines between which the mode of transformation (viral versus oncogene) differed. Virally transformed RIII/Pr1 cells, which are highly tumorigenic in mice, produced markedly increased amounts of PGE2 compared to virally initiated RIII/MG cells, a weakly tumorigenic strain. Cox-2 mRNA and protein were increased concomitantly in RIII/Pr1 cells. Similarly, Ras-induced transformation of C57/MG cells resulted in increased levels of Cox-2 mRNA and protein and increased production of PGE2. Nuclear run-offs revealed increased rates of Cox-2 transcription in the virally transformed and oncogene-transformed cell lines. Transient transfection experiments demonstrated that the oncogenes src and ras up-regulated Cox-2 promoter activity. Src-mediated up-regulation of Cox-2 promoter activity was suppressed by dominant negative ras. Our data indicate that cellular transformation is associated with enhanced transcription of Cox-2 and increased production of PGE2.

Mammary ductal epithelial cell hyperproliferation and hyperplasia induced by a nutritional stress diet containing four components of a western-style diet

We have studied effects of several nutrients on the proliferation of mammary ductal epithelial cells in C57BL/6J virgin female mice, using morphometry and [3H]dT in vivo labeling. A nutritional stress diet was given based on the AIN-76A semi-synthetic diet modified to contain four significant risk factors of a Western-style diet: high fat and phosphate and decreased calcium and vitamin D. The numbers of large, intermediate and terminal ducts and proliferating epithelial cells in mammary glands were assayed in control and stress diet groups. An increased number of mammary ducts and increased number of proliferating cells were found at the level of the small terminal ducts, a cancer-prone region in the mammary gland in the stress diet group compared to the control group after 20 weeks of diet administration. Thus, mammary terminal ductal hyperproliferation, expansion in the size of the proliferative epithelial cell compartment and excessive duplication of mammary ductal epithelial cells were found after this Western-style diet containing decreased dietary calcium and vitamin D. These changes are similar to those developing in colonic epithelium of mice maintained on the same diets and during chemically induced colonic carcinogenesis.

Expression of biomarkers for transformation in 7,12-dimethylbenz[a]anthracene-treated mammary epithelial-cells

The ability of the mammary procarcinogen 7,12-dimethylbenz(a)anthracene (DMBA) to induce the expression of selected molecular and cellular biomarkers for preneoplastic transformation is examined in a newly developed, immortalized but nontumorigenic mammary epithelial cell line C57/MG. This cell line is established from the mammary tissues of virgin female C57BL/6J strain of mouse. The biomarkers examined included: DMBA-DNA adduct formation and DNA repair (molecular markers), and anchorage-dependent and anchorage-independent growth (cellular markers). Log phase cultures of C57/MG cells were treated for 24 h with 2, 20, and 200 ng/ml of DMBA, and were assayed for DNA adduct formation by the P-32-postlabeling, for DNA repair by the hydroxyurea (HU)-insensitive H-3-thymidine uptake, and for anchorage-dependent and anchorage-independent growth by colony forming efficiency in adherent and non-adherent conditions, respectively. A DMBA dose-dependent increase was detected in DNA adduct formation ranging from 6 adducts/10(9) nucleotides at 2 ng/ml to >1600 adducts/10(9) nucleotides at 200 ng/ml DMBA concentration and in induction of DNA repair synthesis ranging from 10 to 251%. The colony forming efficiency in adherent and non-adherent conditions, exhibited progressive increase up to the dose of 200 ng/ml of DMBA. These results indicate that C57/MG cells are capable of metabolizing the procarcinogen DMBA to generate DNA adducts which may, in part, be responsible for the aberrant proliferation. These molecular and cellular biomarkers that are expressed prior to tumorigenesis may thus constitute useful endpoints for preneoplastic transformation.