Predicting the physiological relevance of in vitro cancer preventive activities of phytochemicals

67-kDa Laminin Receptor-Mediated Cellular Sensing System of Green Tea Polyphenol EGCG and Functional Food Pairing

The body is equipped with a “food factor-sensing system” that senses food factors, such as polyphenols, sulfur-containing compounds, and vitamins, taken into the body, and plays an essential role in manifesting their physiological effects. For example, (–)-epigallocatechin-3-O-gallate (EGCG), the representative catechin in green tea (Camellia sinensi L.), exerts various effects, including anti-cancer, anti-inflammatory, and anti-allergic effects, when sensed by the cell surficial protein 67-kDa laminin receptor (67LR). Here, we focus on three representative effects of EGCG and provide their specific signaling mechanisms, the 67LR-mediated EGCG-sensing systems. Various components present in foods, such as eriodictyol, hesperetin, sulfide, vitamin A, and fatty acids, have been found to act on the food factor-sensing system and affect the functionality of other foods/food factors, such as green tea extract, EGCG, or its O-methylated derivative at different experimental levels, i.e., in vitro, animal models, and/or clinical trials. These phenomena are observed by increasing or decreasing the activity or expression of EGCG-sensing-related molecules. Such functional interaction between food factors is called “functional food pairing”. In this review, we introduce examples of functional food pairings using EGCG.

Indole glucosinolates exhibit anti-inflammatory effects on Ehrlich ascites carcinoma cells through modulation of inflammatory markers and miRNAs

BACKGROUND

Nuclear factor-κB (NF-κB) has been identified as the major link between inflammation and cancer. Natural agents that inhibit this pathway are essential in attenuating inflammation induced by cancer or chemotherapeutic drugs. High intake of Brassicaceae vegetables has been determined to modulate essential pathways related to chronic diseases. In this study, we investigated the anti-proliferative and anti-inflammatory effects of the indole glucosinolates; indole-3-carbinol (I3C) and its metabolite 3,3-diindolylmethane (DIM) on the inflammatory biomarkers and miRNAs controlling the NF-κB pathway.

METHODS AND RESULTS

In our study, we inoculated Ehrlich ascites carcinoma (EAC) cells in female albino mice, which increased their packed cell volume and induced a significant increase in the levels of several cytokines and inflammatory biomarkers (NF-κB IL-6, IL-1b, TNF-α, and NO). A significant elevation in inflammatory-medicated miRNAs (miR-31 and miR-21) was also noted. Treatment with 5-fluorouracil (5-FU) significantly reduced packed cell volume and viable cell count. However, it was accompanied by a significant increase in the levels of inflammatory markers and expression of miR-31 and miR-21. Nevertheless, although treatment with indoles (I3C and DIM) significantly reduced the packed cell volume and viable cell count, their prominent effect was the marked reduction of all inflammatory biomarkers compared to both the EAC untreated group and the EAC group treated with 5-FU. Moreover, the anti-inflammatory effect of I3C or DIM was accompanied by a significant decrease in the expression of miR-31 and miR-21.

CONCLUSION

Our findings have; therefore, revealed that I3C and DIM have strong anti-inflammatory effects, implying that their use as a co-treatment with chemotherapeutic drugs can effectively improve the anti-tumor effect of chemotherapeutic drugs.

Role of chemopreventive phytochemicals in NRF2-mediated redox homeostasis in humans

While functioning as a second messenger in the intracellular signaling, ROS can cause oxidative stress when produced in excess or not neutralized/eliminated properly. Excessive ROS production is implicated in multi-stage carcinogenesis. Our body is equipped with a defense system to cope with constant oxidative stress caused by the external insults, including redox-cycling chemicals, radiation, and microbial infection as well as endogenously generated ROS. The transcription factor, nuclear transcription factor erythroid 2-related factor 2 (NRF2) is a master switch in the cellular antioxidant signaling and plays a vital role in adaptive survival response to ROS-induced oxidative stress. Although NRF2 is transiently activated when cellular redox balance is challenged, this can be overwhelmed by massive oxidative stress. Therefore, it is necessary to maintain the NRF2-mediated antioxidant defense capacity at an optimal level. This review summarizes the natural NRF2 inducers/activators, especially those present in the plant-based diet, in relation to their cancer chemopreventive potential in humans. The molecular mechanisms underlying their stabilization or activation of NRF2 are also discussed.

Epigallocatechin-3-gallate stimulates StAR expression and progesterone production in human granulosa cells through the 67-kDa laminin receptor-mediated CREB signaling pathway

Epigallocatechin-3-gallate (EGCG) is the most abundant and biologically active catechins extracted from green tea. The health benefits of EGCG have been extendedly studied. Ovarian steroidogenesis plays a pivotal role in maintaining normal reproductive function. Granulosa cells in the ovary are essential for steroid hormone production. To date, the effect of EGCG on steroidogenesis in human granulosa cells remains unclear. In the present study, we examine the physiological concentrations of EGCG on steroidogenesis in a steroidogenic human granulosa-like tumor cell line, KGN. Our results demonstrate that treatment with EGCG upregulates steroidogenic acute regulatory protein (StAR) expression and increases progesterone (P4) production. EGCG does not affect the expression levels of other steroidogenesis-related enzymes, such as P450 side-chain cleavage enzyme, 3β-hydroxysteroid dehydrogenase, and aromatase. In addition, we identify the expression of 67-kDa laminin receptor (67LR) in KGN cells. Moreover, EGCG-induced StAR expression and P4 production require the 67LR-mediated activation of the PKA-CREB signaling pathway. These results provide a better understanding of the function of EGCG on ovarian steroidogenesis, which may lead to the development of alternative therapeutic approaches for reproductive disorders.

Association between Oral Cancer and Diet: An Update

Oral cancer, included within head and neck cancer, is the sixth most common malignant neoplasm in the world. The main etiological factors are tobacco and alcohol, although currently, diet is considered an important determinant for its development. Several dietary nutrients have specific mechanisms of action, contributing to both protection against cancer and increasing the risk for development, growth, and spread. Foods such as fruits, vegetables, curcumin, and green tea can reduce the risk of oral cancer, while the so-called pro-inflammatory diet, rich in red meat and fried foods, can enhance the risk of occurrence. Dietary factors with a protective effect show different mechanisms that complement and overlap with antioxidant, anti-inflammatory, anti-angiogenic, and anti-proliferative effects. The main limitation of in vivo studies is the complexity of isolating the effects related to each one of the nutrients and the relationship with other possible etiological mechanisms. On the contrary, in vitro studies allow determining the specific mechanisms of action of some of the dietary compounds. In conclusion, and despite research limitations, the beneficial effects of a diet rich in vegetables and fruits are attributed to different micronutrients that are also found in fish and animal products. These compounds show antioxidant, anti-inflammatory, anti-angiogenic, and anti-proliferative properties that have a preventive role in the development of oral and other types of cancer.

Green Tea Polyphenol-Sensitive Calcium Signaling in Immune T Cell Function

Polyphenol compounds found in green tea have a great therapeutic potential to influence multiple human diseases including malignancy and inflammation. In this mini review, we describe effects of green tea and the most important component EGCG in malignancy and inflammation. We focus on cellular mechanisms involved in the modification of T cell function by green tea polyphenol EGCG. The case is made that EGCG downregulates calcium channel activity by influencing miRNAs regulating expression of the channel at the post-transcriptional level.

The Power of Phytochemicals Combination in Cancer Chemoprevention

Conventional therapies for cancer treatment have posed many challenges, including toxicity, multidrug resistance and economic expenses. In contrast, complementary alternative medicine (CAM), employing phytochemicals have recently received increased attention owing to their capability to modulate a myriad of molecular mechanisms with a less toxic effect. Increasing evidence from preclinical and clinical studies suggest that phytochemicals can favorably modulate several signaling pathways involved in cancer development and progression. Combinations of phytochemicals promote cell death, inhibit cell proliferation and invasion, sensitize cancerous cells, and boost the immune system, thus making them striking alternatives in cancer therapy. We previously investigated the effect of six phytochemicals (Indol-3-Carbinol, Resveratrol, C-phycocyanin, Isoflavone, Curcumin and Quercetin), at their bioavailable levels on breast cancer cell lines and were compared to primary cell lines over a period of 6 days. This study showed the compounds had a synergestic effect in inhibiting cell proliferation, reducing cellular migration and invasion, inducing both cell cycle arrest and apoptosis. Despite the vast number of basic science and preclinical cancer studies involving phytochemicals, the number of CAM clinical trials in cancer treatment still remains nascent. In this review, we summarize findings from preclinical and clinical studies, including our work involving use of phytochemicals, individually as well as in combination and further discuss the potential of these phytochemicals to pave way to integrate CAM in primary health care.

Combination of xanthohumol and phenethyl isothiocyanate inhibits NF-κB and activates Nrf2 in pancreatic cancer cells

Phytochemicals such as phenethyl isothiocyanate (PEITC), indole-3-carbinol (I3C), xanthohumol (XAN), and resveratrol (RES) have been shown to target signaling pathways that are involved in the proliferation and survival of different pancreatic cancer (PC) cell lines. While the activity of these compounds alone was extensively studied, their combinations were never assessed. Thus, the aim of this study was to evaluate and compare the effect of PEITC, I3C, XAN, and RES and their combinations on the expression and activation of NF-κB and Nrf2 in human PC cell line PANC-1. The combination of XAN and PEITC was more efficient than the single compounds in reducing the binding of NF-κB p65 subunits to DNA by 47-60% and expression of p65 gene by 28-48%. The combination of XAN and PEITC also enhanced the activation and expression of Nrf2 and subsequently the expression of GSTP, NQO1, and SOD genes which are controlled by this transcription factor. Modulation of the activity of NF-κB and Nrf2 by the combination of XAN and PEITC was found to lead to reduced proliferation of PANC-1 cells. These results suggest that the combination of XAN and PEITC might be considered as a novel strategy for the prophylaxis and/or treatment of PC.

Effect of Indole-3-Carbinol on Dimyristoylphosphatidylcholine Multilamellar Vesicles

This study reports the interaction of indole-3-carbinol (I3C), which is a chemopreventive reagent, with an artificial model membrane {(dimyristoylphosphatidylcholine (DMPC) multilamellar vesicles (MLVs)}, using the intrinsic fluorescence properties of I3C, extrinsic fluorescence properties of Nile Red (NR), differential scanning calorimetry (DSC), dynamic light scattering (DLS), and confocal microscopy. The intrinsic fluorescence of I3C helps to provide information about its location, partitioning ability, and sensitivity toward the phase-transition temperature of liposomes, confirmed by cetylpyridinium chloride (CPC) quenching study, partition coefficient values {(4.60 ± 0.1) × 10⁵ (solid gel phase) and (7.29 ± 0.1) × 10⁵ M^-1 (liquid crystalline phase)} and temperature-dependent emission behavior of I3C. I3C perturbs the DMPC MLVs above 15 mol %, as observed using the fluorescence properties of NR, DSC, and DLS data. This perturbation occurs as a consequence of interfacial hydration of the DMPC MLVs, which was clearly indicated by the fluorescence properties (emission intensity, fluorescence lifetime, and nonextensive distribution analysis) of NR.

Targeting antioxidant enzymes as a radiosensitizing strategy

Radiotherapy represents a major anti-cancer modality and effectively kills cancer cells through generation of reactive oxygen species (ROS). However, cancer cells are commonly characterized by increased activity of ROS-scavenging enzymes in adaptation to intrinsic oxidative stress, leading to radioresistance. Abrogation of this defense network by pharmacological ROS insults therefore is shown to improve radioresponse in preclinical models; some of them are then tested in clinical trials. In this review, we address (1) the importance of ROS in radioresponse, (2) the main systems regulating redox homeostasis with a special focus on their prognostic effect and predictive role in radiotherapy, and (3) the potential radiosensitizers acting through inhibition of antioxidant enzymes.

Detection of Plasma Curcuminoids from Dietary Intake of Turmeric-Containing Food in Human Volunteers

SCOPE

Curcumin (from turmeric), has been extensively investigated for potential beneficial properties in numerous diseases. Most work has focused on supra-dietary concentrations/doses that would necessitate curcumin supplementation. However, much evidence instigating curcumin research is underpinned by epidemiological data based on low dietary intake via turmeric consumption.

METHODS AND RESULTS

Here, a novel, highly sensitive liquid chromatography-electrospray ionization-mass spectrometry (LC-ESI-MS/MS) method for detection of curcuminoids is described. Assay sensitivity is demonstrated in a pilot pharmacokinetic volunteer study following ingestion of foodstuffs containing a standardized mass of turmeric, representative of daily consumption by certain South Asian populations. Free parent curcumin was detectable in plasma from one individual, reaching maximal plasma concentrations (C_max ) of 3.2 nm. Curcumin conjugates were detected in all volunteers; C_max for curcumin glucuronide is 47.6 ± 28.5 nm 30 min post-food, while C_max for demethoxycurcumin glucuronide and curcumin sulfate is ≈2 nm. Curcumin and its major metabolites persist in plasma for at least 8 h.

CONCLUSION

Despite poor absorption and rapid conjugation, dietary intake of standard culinary turmeric within complex food matrices furnished human plasma with detectable levels of curcuminoids. Whether sustained low systemic concentrations of these non-nutritive, biologically active, dietary components may have pharmacological activity for human health benefit, warrants further research.

Chitosan-based polymer hybrids for thermo-responsive nanogel delivery of curcumin

The purpose of this study is to design and develop thermoresponsive nano-sized hydrogel particles from a natural polymer, chitosan, as smart material platforms for curcumin delivery. Chitosan was used as the backbone material to be grafted with poly-(N-isopropylacrylamide) (pNIPAM) using an EDC/NHS coupling reaction. The conjugated products were characterized by ¹H NMR and TGA. Chitosan-grafted pNIPAM (CS-g-pN) nanogels were prepared by a sonication method. The loading of curcumin into the CS-g-pN nanogels was achieved using an incubation method. Size, morphology of nanogels, amounts of curcumin loaded to the nanogels and cellular uptake were investigated by DLS, TEM, fluorescent spectroscopy and confocal microscopy techniques, respectively. A CellTiter-Blue^® cell viability assay was performed in NIH-3T3 and HeLa cells to assess the safety while MTT assay was carried out in MDA-231, Caco-2, HepG2, and HT-29 cells for determining cytotoxic effects. Results showed that CS-g-pN with 3-60% degree of modification were simply assembled into spherical nanogel particles with submicron sizes, in which curcumin was encapsulated. The thermoresponsive behavior of each CS-g-pN nanogel formulation differed due to the grafted pNIPAM length and density. The CS-g-pN nanogel formulations were non-toxic towards NIH-3T3 and HeLa cells. Each curcumin-loaded CS-g-pN nanogel formulation could be up taken into NIH-3T3 cell lines and showed the dose-dependent cytotoxicity against tested cell lines. Successful development of this curcumin-loaded nanogel will lead to advanced materials that can be functionalized and optimized for targeted therapy and controlled delivery of small molecules and/or biomolecules for biomedical applications.

Epigallocatechin-3-gallate (EGCG) up-regulates miR-15b expression thus attenuating store operated calcium entry (SOCE) into murine CD4+ T cells and human leukaemic T cell lymphoblasts

CD4⁺ T cells are key elements in immune responses and inflammation. Activation of T cell receptors in CD4⁺ T cells triggers cytosolic Ca²⁺ release with subsequent store operated Ca²⁺ entry (SOCE), which is accomplished by the pore forming Ca²⁺ release activated Ca²⁺ (CRAC) channel Orai1 and its regulator stromal cell-interaction molecule 2 (STIM2). Green tea polyphenol epigallocatechin-3-gallate (EGCG) acts as a potent anti-inflammatory and anti-oxidant agent for various types of cells including immune cells. However, how post-transcriptional gene regulators such as miRNAs are involved in the regulation of Ca²⁺ influx into murine CD4⁺ T cells and human Jurkat T cells through EGCG is not defined. EGCG treatment of murine CD4⁺ T cells significantly down-regulated the expression of STIM2 and Orai1 both at mRNA and protein levels. Furthermore, EGCG significantly decreased SOCE in both murine and human T cells. EGCG treatment increased miRNA-15b (miR-15b) abundance in both murine and human T cells. Bioinformatics analysis reveals that miR-15b, which has a STIM2 binding site, is involved in the down-regulation of SOCE. Overexpression of miR-15b significantly decreased the mRNA and protein expression of STIM2 and Orai1 in murine T cells. Treatment of Jurkat T cells with 10 μM EGCG further decreased mTOR and PTEN protein levels. EGCG decreased mitochondrial membrane potential (MMP) in both human and murine T cells. In conclusion, the observations suggest that EGCG inhibits the Ca²⁺ entry into murine and human T cells, an effect accomplished at least in part by up-regulation of miR-15b.

Dose-Dependent Responses of I3C and DIM on T-Cell Activation in the Human T Lymphocyte Jurkat Cell Line

Indole-3-carbinol (I3C) and its dimer diindolylmethane (DIM) are bioactive metabolites of a glucosinolate, glucobrassicin, found in cruciferous vegetables. Both I3C and DIM have been reported to possess pro-apoptotic, anti-proliferative and anti-carcinogenic properties via modulation of immune pathways. However, results from these studies remain inconclusive since they lack thorough evaluation of these bioactives’ physiological versus pharmacological effects. In the present study, we investigated I3C and DIM’s dose-dependent effects on cytokines production in human T lymphocytes Jurkat cell line (Clone E6-1). The results showed that I3C and DIM pretreatment, at higher concentrations of 50 and 10 μM, respectively, significantly increased PMA/ionomycin-induced interleukin-2 (IL-2), interleukin-8 (IL-8) and tumor necrosis factor-α (TNF-α) production, measured by real time polymerase chain reaction (RT-PCR) and enzyme linked immunosorbent assay (ELISA). As a plausible mechanism underlying such pronounced cytokine release, we found robust increase in downstream nuclear factor κB (NF-κB) and nuclear factor of activated T-cells 1 (NFAT1) signaling with I3C pretreatment, whereas DIM pretreatment only significantly induced NF-κB activation, but not NFAT1. We hypothesize that I3C/DIM pretreatment primes the T cells to become hyperresponsive upon PMA/ionomycin stimulation which in turn differentially induces two major downstream Ca²⁺-dependent inflammatory pathways, NF-κB and NFAT1. Our data show novel insights into the mechanisms underlying induction of pro-inflammatory cytokine release by pharmacological concentrations of I3C and DIM, an effect negligible under physiological conditions.

Sulforaphane and Other Nutrigenomic Nrf2 Activators: Can the Clinician's Expectation Be Matched by the Reality?

The recognition that food-derived nonnutrient molecules can modulate gene expression to influence intracellular molecular mechanisms has seen the emergence of the fields of nutrigenomics and nutrigenetics. The aim of this review is to describe the properties of nutrigenomic activators of transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2), comparing the potential for sulforaphane and other phytochemicals to demonstrate clinical efficacy as complementary medicines. Broccoli-derived sulforaphane emerges as a phytochemical with this capability, with oral doses capable of favourably modifying genes associated with chemoprevention. Compared with widely used phytochemical-based supplements like curcumin, silymarin, and resveratrol, sulforaphane more potently activates Nrf2 to induce the expression of a battery of cytoprotective genes. By virtue of its lipophilic nature and low molecular weight, sulforaphane displays significantly higher bioavailability than the polyphenol-based dietary supplements that also activate Nrf2. Nrf2 activation induces cytoprotective genes such as those playing key roles in cellular defense mechanisms including redox status and detoxification. Both its high bioavailability and significant Nrf2 inducer capacity contribute to the therapeutic potential of sulforaphane-yielding supplements.

ERK signaling mediates long-term low concentration 3,3'-diindolylmethane inhibited nasopharyngeal carcinoma growth and metastasis: An in vitro and in vivo study

It is well known that crucifers have antitumor effects and 3,3'-diindolylmethane (DIM) is one of the major bioactive components, and the associated molecular mechanisms in a short-term high-dose manner are widely discussed. However, the antitumor effects of DIM in a long-term low-dose manner in nasopharyngeal carcinoma (NPC) has not been reported yet, as to the potential mechanisms in the human body. In the present study, NPC cells were induced by 20 µmol/l DIM for over a month, and the proliferation, apoptosis, migration and in vivo metastasis were investigated. The results showed that DIM significantly reduced the proliferation and migration; however, changes in apoptosis were not observed. In vivo study showed the metastasis was significantly reduced. Compared to the short-term high-dose manner, incomplete similar qualities were observed; next we explored the possible signal pathway revolved, the ERK signaling showed similar changes, while the PI3K/Akt, NF-κB, P38, JNK pathways were significantly altered in the short-term high-dose manner (our previous study) showed no obvious change, indicating the ERK signaling may be the main effector of DIM.

Epigenetic-based combinatorial resveratrol and pterostilbene alters DNA damage response by affecting SIRT1 and DNMT enzyme expression, including SIRT1-dependent γ-H2AX and telomerase regulation in triple-negative breast cancer

Background

Nutrition is believed to be a primary contributor in regulating gene expression by affecting epigenetic pathways such as DNA methylation and histone modification. Resveratrol and pterostilbene are phytoalexins produced by plants as part of their defense system. These two bioactive compounds when used alone have been shown to alter genetic and epigenetic profiles of tumor cells, but the concentrations employed in various studies often far exceed physiologically achievable doses. Triple-negative breast cancer (TNBC) is an often fatal condition that may be prevented or treated through novel dietary-based approaches.

Methods

HCC1806 and MDA-MB-157 breast cancer cells were used as TNBC cell lines in this study. MCF10A cells were used as control breast epithelial cells to determine the safety of this dietary regimen. CompuSyn software was used to determine the combination index (CI) for drug combinations.

Results

Combinatorial resveratrol and pterostilbene administered at close to physiologically relevant doses resulted in synergistic (CI <1) growth inhibition of TNBCs. SIRT1, a type III histone deacetylase (HDAC), was down-regulated in response to this combinatorial treatment. We further explored the effects of this novel combinatorial approach on DNA damage response by monitoring γ-H2AX and telomerase expression. With combination of these two compounds there was a significant decrease in these two proteins which might further resulted in significant growth inhibition, apoptosis and cell cycle arrest in HCC1806 and MDA-MB-157 breast cancer cells, while there was no significant effect on cellular viability, colony forming potential, morphology or apoptosis in control MCF10A breast epithelial cells. SIRT1 knockdown reproduced the effects of combinatorial resveratrol and pterostilbene-induced SIRT1 down-regulation through inhibition of both telomerase activity and γ-H2AX expression in HCC1806 breast cancer cells. As a part of the repair mechanisms and role of SIRT1 in recruiting DNMTs, the effects of this combination treatment was also explored on DNA methyltransferases (DNMTs) expression. Interestingly, the compounds resulted in a significant down-regulation of DNMT enzymes with no significant effects on DNMT enzyme expression in MCF10A control cells.

Conclusion

Collectively, these results provide new insights into the epigenetic mechanisms of a novel combinatorial nutrient control strategy that exhibits synergy and may contribute to future recalcitrant TNBC prevention and/or therapy.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1693-z) contains supplementary material, which is available to authorized users.

Phytochemical regulation of the tumor suppressive microRNA, miR-34a, by p53-dependent and independent responses in human breast cancer cells

The tumor suppressive microRNA miR-34a is transcriptionally regulated by p53 and shown to inhibit breast cancer cell proliferation as well as being a marker of increased disease free survival. Indole-3-carbinol (I3C) derived from cruciferous vegetables, artemisinin, extracted from the sweet wormwood plant, and artesunate, a semi-synthetic derivative of artemisinin, are phytochemicals with anti-tumorigenic properties however, little is known about the role of microRNAs in their mechanism of action. Human breast cancer cells expressing wild-type (MCF-7) or mutant p53 (T47D) were treated with a concentration range and time course of each phytochemical under conditions of cell cycle arrest as detected by flow cytometry to examine the potential connection between miR-34a expression and their anti-proliferative responses. Real-time PCR and western blot analysis of extracted RNA and total protein revealed artemsinin and artesunate increased miR-34a expression in a dose-dependent manner correlating with down-regulation of the miR-34a target gene, CDK4. I3C stimulation of miR-34a expression required functional p53, whereas, both artemisinin and artesunate up-regulated miR-34a expression regardless of p53 mutational status or in the presence of dominant negative p53. Phytochemical treatments inhibited the luciferase activity of a construct containing the wild-type 3'UTR of CDK4, but not those with a mutated miR-34a binding site, whereas, transfection of miR-34a inhibitors ablated the phytochemical mediated down-regulation of CDK4 and induction of cell cycle arrest. Our results suggest that miR-34a is an essential component of the anti-proliferative activities of I3C, artemisinin, and artesunate and demonstrate that both wild-type p53 dependent and independent pathways are responsible for miR-34a induction.

A possible role of aryl hydrocarbon receptor in spontaneous preterm birth

Preterm birth (PTB) is defined as birth before 37 weeks of gestation and is a leading cause of neonatal mortality and morbidity. To date, the etiology of spontaneous PTB (sPTB) remains unclear; however, intrauterine bacterial infection-induced inflammation is considered to be one of the major triggers. Aryl hydrocarbon receptor (AhR) is a ligand-dependent transcription factor. Upon activation, AhR signaling mediates many biological processes. AhR is abundantly expressed in human placentas, primarily in trophoblasts, and several fetal organs and tissues. The activation of AhR signaling can modulate inflammatory responses via promoting production of pro-inflammatory cytokines by the placenta and fetal membranes. These cytokines could enhance expression and/or activity of cyclooxygenase-2 (COX2) in human trophoblasts and amniotic epithelia, which in turn stimulate synthesis and release of prostaglandins (PGs; e.g., PGE2 and PGF2α). Given the discovery of a number of natural and endogenous AhR ligands in human, we hypothesize that in a subset of patients with high AhR expression in placentas and fetal membranes, repeated exposure to these AhR ligands hyperactivates AhR, inducing hyperactivation of the cytokines/COX2/PGs pathway, resulting in myometrial contractions, ultimately leading to sPTB. We further hypothesize that hyperactivation of this AhR pathway can induce sPTB either directly or in synergy with the bacterial infection. Proof of this hypothesis may provide a novel mechanism underlying sPTB.

Cell death pathway induced by resveratrol-bovine serum albumin nanoparticles in a human ovarian cell line

Resveratrol-bovine serum albumin nanoparticles (RES-BSANP) exhibit chemotherapeutic properties, which trigger apoptosis. The aim of the present study was to investigate the caspase-independent cell death pathway induced by RES-BSANP in human ovarian cancer SKOV3 cells and to analyze its mechanism. Morphological changes were observed by apoptotic body/cell nucleus DNA staining using inverted and fluorescence microscopy. The cell death pathway was determined by phosphatidylserine translocation. Western blot analysis was conducted to detect the activation of apoptosis-inducing factor (AIF), cytochrome c (Cyto c) and B-cell lymphoma 2-associated X protein (Bax). Apoptotic body and nuclear condensation and fragmentation were observed simultaneously following treatment with RES-BSANP. RES-BSANP induced apoptosis in a dose-dependent manner in the human ovarian cancer SKOV3 cells. The translocation of AIF from the mitochondria to the cytoplasm occurred earlier than that of Cyto c. In addition, Bax binding to the mitochondria was required for the release of AIF and Cyto c from the mitochondria. The AIF apoptosis pathway may present an alternative caspase-dependent apoptosis pathway in human ovarian cell death induced by RES-BSANP. Elucidation of this pathway may be critical for the treatment of cancer using high doses of RES-BSANP.

Enhancing the delivery of resveratrol in humans: if low bioavailability is the problem, what is the solution?

Resveratrol has emerged as a leading candidate for improving healthspan through potentially slowing the aging process and preventing chronic diseases. The poor bioavailability of resveratrol in humans has been a major concern for translating basic science findings into clinical utility. Although a number of positive findings have emerged from human clinical trials, there remain many conflicting results, which may partially be attributed to the dosing protocols used. A number of theoretical solutions have been developed to improve the bioavailability of resveratrol, including consumption with various foods, micronized powders, combining it with additional phytochemicals, controlled release devices, and nanotechnological formulations. While laboratory models indicate these approaches all have potential to improve bioavailability of resveratrol and optimize its clinical utility, there is surprisingly very little data regarding the bioavailability of resveratrol in humans. If bioavailability is indeed a limitation in the clinical utility of resveratrol, there is a need to further explore methods to optimize bioavailability in humans. This review summarizes the current bioavailability data, focusing on data from humans, and provides suggested directions for future research in this realm.

Zyflamend, a polyherbal mixture, down regulates class I and class II histone deacetylases and increases p21 levels in castrate-resistant prostate cancer cells

BACKGROUND

Zyflamend, a mixture containing extracts of ten herbs, has shown promise in a variety of preclinical cancer models, including prostate cancer. The current experiments were designed to investigate the effects of Zyflamend on the expression of class I and II histone deacetylases, a family of enzymes known to be over expressed in a variety of cancers.

METHODS

CWR22Rv1 cells, a castrate-resistant prostate cancer cell line, were treated with Zyflamend and the expression of class I and II histone deacetylases, along with their downstream target the tumor suppressor gene p21, was investigated. Involvement of p21 was confirmed with siRNA knockdown and over expression experiments.

RESULTS

Zyflamend down-regulated the expression of all class I and II histone deacetylases where Chinese goldthread and baikal skullcap (two of its components) appear to be primarily responsible for these results. In addition, Zyflamend up regulated the histone acetyl transferase complex CBP/p300, potentially contributing to the increase in histone 3 acetylation. Expression of the tumor suppressor gene p21, a known downstream target of histone deacetylases and CBP/p300, was increased by Zyflamend treatment and the effect on p21 was, in part, mediated through Erk1/2. Knockdown of p21 with siRNA technology attenuated Zyflamend-induced growth inhibition. Over expression of p21 inhibited cell growth and concomitant treatment with Zyflamend enhanced this effect.

CONCLUSIONS

Our results suggest that the extracts of this polyherbal combination increase histone 3 acetylation, inhibit the expression of class I and class II histone deacetylases, increase the activation of CBP/p300 and inhibit cell proliferation, in part, by up regulating p21 expression.

Effects of physiological levels of the green tea extract epigallocatechin-3-gallate on breast cancer cells

Physiological concentrations of the green tea extract epigallocatechin-3-gallate (EGCG) caused growth inhibition in estrogen receptor α (ERα)-positive MCF7 cells that was associated with down-regulation of the ERα and reduced insulin-like growth factor binding protein-2 abundance and increased protein abundance of the tumor suppressor genes p53/p21. In contrast to MCF7 cells that have wt p53, EGCG alone did not change cell proliferation or death significantly in another ERα-positive cell line T47D that possesses mutant p53. EGCG increased ERα protein levels and as a consequence, the cells responded significantly better to an ERα antagonist tamoxifen (TAM) in the presence of EGCG. EGCG significantly increased cell death in an ERα-negative cell line, MDA-MB-231 that also possesses mutant p53. EGCG significantly increased the ERα and insulin-like growth factor-I receptor levels and thereby enhanced the sensitivities of the cells to TAM and a blocking antibody targeting the insulin-like growth factor-1 receptor (αIR3). In contrast to MCF7, T47D and MDA-MB-231 breast cancer cells that exhibited significant changes in key molecules involved in breast growth and survival upon treatment with physiological levels of EGCG, the growth, survival, and levels of these proteins in non-malignant breast epithelial cells, MCF10A cells, were not affected.

Replicated, replicable and relevant-target engagement and pharmacological experimentation in the 21st century

A pharmacological experiment is typically conducted to: i) test or expand a hypothesis regarding the potential role of a target in the mechanism(s) underlying a disease state using an existing drug or tool compound in normal and/or diseased tissue or animals; or ii) characterize and optimize a new chemical entity (NCE) targeted to modulate a specific disease-associated target to restore homeostasis as a potential drug candidate. Hypothesis testing necessitates an intellectually rigorous, null hypothesis approach that is distinct from a high throughput fishing expedition in search of a hypothesis. In conducting an experiment, the protocol should be transparently defined along with its powering, design, appropriate statistical analysis and consideration of the anticipated outcome (s) before it is initiated. Compound-target interactions often involve the direct study of phenotype(s) unique to the target at the cell, tissue or animal/human level. However, in vivo studies are often compromised by a lack of sufficient information on the compound pharmacokinetics necessary to ensure target engagement and also by the context-free analysis of ubiquitous cellular signaling pathways downstream from the target. The use of single tool compounds/drugs at one concentration in engineered cell lines frequently results in reductionistic data that have no physiologically relevance. This overview, focused on trends in the peer-reviewed literature, discusses the execution and reporting of experiments and the criteria recommended for the physiologically-relevant assessment of target engagement to identify viable new drug targets and facilitate the advancement of translational studies.

Mitogenesis of vascular smooth muscle cell stimulated by platelet-derived growth factor-bb is inhibited by blocking of intracellular signaling by epigallocatechin-3-O-gallate

Epigallocatechin gallate (EGCG) is known to exhibit antioxidant, antiproliferative, and antithrombogenic effects and reduce the risk of cardiovascular diseases. Key events in the development of cardiovascular disease are hypertrophy and hyperplasia according to vascular smooth muscle cell proliferation. In this study, we investigated whether EGCG can interfere with PDGF-bb stimulated proliferation, cell cycle distribution, and the gelatinolytic activity of MMP and signal transduction pathways on RAOSMC when it was treated in two different ways-cotreatment with PDGF-bb and pretreatment of EGCG before addition of PDGF-bb. Both cotreated and pretreated EGCG significantly inhibited PDGF-bb induced proliferation, cell cycle progression of the G0/G1 phase, and the gelatinolytic activity of MMP-2/9 on RAOSMC. Also, EGCG blocked PDGF receptor-β (PDGFR-β) phosphorylation on PDGF-bb stimulated RAOSMC under pretreatment with cells as well as cotreatment with PDGF-bb. The downstream signal transduction pathways of PDGFR-β, including p42/44 MAPK, p38 MAPK, and Akt phosphorylation, were also inhibited by EGCG in a pattern similar to PDGFR-β phosphorylation. These findings suggest that EGCG can inhibit PDGF-bb stimulated mitogenesis by indirectly and directly interrupting PDGF-bb signals and blocking the signaling pathway via PDGFR-β phosphorylation. Furthermore, EGCG may be used for treatment and prevention of cardiovascular disease through blocking of PDGF-bb signaling.

Translational paradigms in pharmacology and drug discovery

The translational sciences represent the core element in enabling and utilizing the output from the biomedical sciences and to improving drug discovery metrics by reducing the attrition rate as compounds move from preclinical research to clinical proof of concept. Key to understanding the basis of disease causality and to developing therapeutics is an ability to accurately diagnose the disease and to identify and develop safe and effective therapeutics for its treatment. The former requires validated biomarkers and the latter, qualified targets. Progress has been hampered by semantic issues, specifically those that define the end product, and by scientific issues that include data reliability, an overt reductionistic cultural focus and a lack of hierarchically integrated data gathering and systematic analysis. A necessary framework for these activities is represented by the discipline of pharmacology, efforts and training in which require recognition and revitalization.

3,3'-Diindolylmethane inhibits lipopolysaccharide-induced microglial hyperactivation and attenuates brain inflammation

Recent studies have revealed that microglial hyperactivation and neuroinflammation are implicated in development and progression of neurodegenerative diseases. In this study, we examined the beneficial effects of 3,3'-diindolylmethane (DIM) and indole-3-carbinol (I3C), dietary components found in cruciferous vegetables, on brain inflammation. DIM, a major metabolite of I3C, suppressed lipopolysaccharide (LPS)-induced expression of inducible nitric oxide synthase and cyclooxygenase-2 in BV-2 microglia, but I3C did not. DIM, but not I3C, attenuated DNA-binding activity of nuclear factor-κB (NF-κB) and phosphorylation of inhibitor of κB, suggesting that DIM might inhibit microglial hyperactivation by attenuating inflammatory transcription factor NF-κB. In addition, DIM, but not I3C, protected primary cortical neurons from inflammatory toxicity induced by the conditioned media from LPS-stimulated BV-2 microglia, indicating that DIM might attenuate microglial hyperactivation-mediated neuronal death. In an in vivo model of neuroinflammation, DIM suppressed LPS-induced brain inflammation in mouse hippocampus, as determined by the number of Iba-1-positive cells and the mRNA expression of F4/80. Taken together, these results suggest that DIM may have beneficial potential against brain inflammation and neurodegenerative diseases through the negative regulation of the NF-κB signal pathway in microglia.

3,3'-diindolylmethane rapidly and selectively inhibits hepatocyte growth factor/c-Met signaling in breast cancer cells

3,3'-Diindolylmethane (DIM), an indole derivative from vegetables of the Brassica genus, has antiproliferative activity in breast cancer cells. Part of this activity is thought to be due to DIM inhibition of Akt signaling, but an upstream mechanism of DIM-induced Akt inhibition has not been described. The goals of this study were to investigate the kinetics of inhibition of Akt by physiologically relevant concentrations of DIM and to identify an upstream factor that mediates this effect. Here we report that DIM (5-25 μM) inhibited Akt activation from 30 min to 24h in tumorigenic MDA-MB-231 cells but did not inhibit Akt activation in non-tumorigenic preneoplastic MCF10AT cells. DIM inhibited hepatocyte growth factor (HGF)-induced Akt activation by up to 46%, cell migration by 66% and cell proliferation by up to 54%, but did not inhibit induction of Akt by epidermal growth factor or insulin-like growth factor-1. DIM decreased phosphorylation of the HGF receptor, c-Met, at tyrosines 1234 and 1235, indicating decreased activation of the receptor. This decrease was reversed by pretreatment with inhibitors of p38 or calcineurin. Our results demonstrate the important role of HGF and c-Met in DIM's anti-proliferative effect on breast cancer cells and suggest that DIM could have preventive or clinical value as an inhibitor of c-Met signaling.

Polyisoprenylated methylated protein methyl esterase is both sensitive to curcumin and overexpressed in colorectal cancer: implications for chemoprevention and treatment

Inhibition of PMPMEase, a key enzyme in the polyisoprenylation pathway, induces cancer cell death. In this study, purified PMPMEase was inhibited by the chemopreventive agent, curcumin, with a K(i) of 0.3 μM (IC50 = 12.4 μM). Preincubation of PMPMEase with 1 mM curcumin followed by gel-filtration chromatography resulted in recovery of the enzyme activity, indicative of reversible inhibition. Kinetics analysis with N-para-nitrobenzoyl-S-trans,trans-farnesylcysteine methyl ester substrate yielded K M values of 23.6 ± 2.7 and 85.3 ± 15.3 μM in the absence or presence of 20 μM curcumin, respectively. Treatment of colorectal cancer (Caco2) cells with curcumin resulted in concentration-dependent cell death with an EC50 of 22.0 μg/mL. PMPMEase activity in the curcumin-treated cell lysate followed a similar concentration-dependent profile with IC50 of 22.6 μg/mL. In colorectal cancer tissue microarray studies, PMPMEase immunoreactivity was significantly higher in 88.6% of cases compared to normal colon tissues (P < 0.0001). The mean scores ± SEM were 91.7 ± 11.4 (normal), 75.0 ± 14.4 (normal adjacent), 294.8 ± 7.8 (adenocarcinoma), and 310.0 ± 22.6 (mucinous adenocarcinoma), respectively. PMPMEase overexpression in colorectal cancer and cancer cell death stemming from its inhibition is an indication of its possible role in cancer progression and a target for chemopreventive agents.

Prolonged biologically active colonic tissue levels of curcumin achieved after oral administration--a clinical pilot study including assessment of patient acceptability

Curcumin, the main constituent of turmeric, is suspected to possess cancer chemopreventive properties. Pharmacokinetic and pharmacodynamic parameters have been reported, but few data exist describing whether methodologies are suitably robust for curcuminoid detection in colonic biopsy specimens. Information on the acceptability of prolonged administration of daily curcumin is not available. This is of vital importance to implement chemoprevention strategies. This study aimed to quantify levels of curcuminoids in colorectal mucosa of patients undergoing colorectal endoscopy or surgical resection and to obtain information on the acceptability and compliance with daily curcumin. Curcumin C3 complex (2.35 g) was administered to patients once daily for 14 days before endoscopic biopsy or colonic resection. Safety and tolerance were monitored. Analysis of curcuminoids in plasma, urine, and colonic mucosa was conducted by ultraperformance liquid chromatography (UPLC)-UV with characterization by liquid chromatography/tandem mass spectrometry (LC/MS-MS). Twenty-four of 26 patients commencing curcumin completed the course. Six patients reported mild gastrointestinal adverse events. Curcuminoids were detectable in nine of 24 plasma samples, 24 of 24 urine samples, and in the colonic mucosa of all 23 biopsied participants. Mean tissue levels were 48.4 μg/g (127.8 nmol/g) of parent curcuminoids. The major conjugate, curcumin glucuronide, was detectable in 29 of 35 biopsies. High levels of topical curcumin persisted in the mucosa for up to 40 hours postadministration. Sixteen participants (67%) stated that they would take curcumin long-term should it be of proven benefit. In summary, pharmacologically active levels of curcumin were recovered from colonic mucosa. The regimen used here seems safe, and patients support its use in long-term trials.

Resveratrol: French paradox revisited

Resveratrol is a polyphenol that plays a potentially important role in many disorders and has been studied in different diseases. The research on this chemical started through the “French paradox,” which describes improved cardiovascular outcomes despite a high-fat diet in French people. Since then, resveratrol has been broadly studied and shown to have antioxidant, anti-inflammatory, anti-proliferative, and anti-angiogenic effects, with those on oxidative stress possibly being most important and underlying some of the others, but many signaling pathways are among the molecular targets of resveratrol. In concert they may be beneficial in many disorders, particularly in diseases where oxidative stress plays an important role. The main focus of this review will be the pathways affected by resveratrol. Based on these mechanistic considerations, the involvement of resveratrol especially in cardiovascular diseases, cancer, neurodegenerative diseases, and possibly in longevity will be is addressed.

Polyphenols sensitization potentiates susceptibility of MCF-7 and MDA MB-231 cells to Centchroman

Polyphenols as “sensitizers” together with cytotoxic drugs as “inducers” cooperate to trigger apoptosis in various cancer cells. Hence, their combination having similar mode of mechanism may be a novel approach to enhance the efficacy of inducers. Additionally, this will also enable to achieve the physiological concentrations facilitating significant increase in the activity at concentrations which the compound can individually provide. Here we propose that polyphenols (Resveratrol (RES) and Curcumin (CUR)) pre-treatment may sensitize MCF-7/MDA MB-231 (Human Breast Cancer Cells, HBCCs) to Centchroman (CC, antineoplastic agent). 6 h pre-treated cells with 10 µM RES/CUR and 100 µM RES/30 µM CUR doses, followed by 10 µM CC for 18 h were investigated for Ser-167 ER-phosphorylation, cell cycle arrest, redox homeostasis, stress activated protein kinase (SAPKs: JNK and p38 MAPK) pathways and downstream apoptosis effectors. Low dose RES/CUR enhances the CC action through ROS mediated JNK/p38 as well as mitochondrial pathway in MCF-7 cells. However, RES/CUR sensitization enhanced apoptosis in p53 mutant MDA MB-231 cells without/with involvement of ROS mediated JNK/p38 adjunct to Caspase-9. Contrarily, through high dose sensitization in CC treated cells, the parameters remained unaltered as in polyphenols alone. We conclude that differential sensitization of HBCCs with low dose polyphenol augments apoptotic efficacy of CC. This may offer a novel approach to achieve enhanced action of CC with concomitant reduction of side effects enabling improved management of hormone-dependent breast cancer.

Epigenetic diet: impact on the epigenome and cancer

A number of bioactive dietary components are of particular interest in the field of epigenetics. Many of these compounds display anticancer properties and may play a role in cancer prevention. Numerous studies suggest that a number of nutritional compounds have epigenetic targets in cancer cells. Importantly, emerging evidence strongly suggests that consumption of dietary agents can alter normal epigenetic states as well as reverse abnormal gene activation or silencing. Epigenetic modifications induced by bioactive dietary compounds are thought to be beneficial. Substantial evidence is mounting proclaiming that commonly consumed bioactive dietary factors act to modify the epigenome and may be incorporated into an 'epigenetic diet'. Bioactive nutritional components of an epigenetic diet may be incorporated into one's regular dietary regimen and used therapeutically for medicinal or chemopreventive purposes. This article will primarily focus on dietary factors that have been demonstrated to influence the epigenome and that may be used in conjunction with other cancer prevention and chemotherapeutic therapies.

Curcumin differentially regulates endoplasmic reticulum stress through transcriptional corepressor SMILE (small heterodimer partner-interacting leucine zipper protein)-mediated inhibition of CREBH (cAMP responsive element-binding protein H)

Curcumin (diferuloylmethane), a major active component of turmeric (Curcuma longa), is a natural polyphenolic compound. Herein the effect of curcumin on endoplasmic reticulum (ER) stress responsive gene expression was investigated. We report that curcumin induces transcriptional corepressor small heterodimer partner-interacting leucine zipper protein (SMILE) gene expression through liver kinase B1 (LKB1)/adenosine monophosphate-activated kinase (AMPK) signaling pathway and represses ER stress-responsive gene transcription in an ER-bound transcription factor specific manner. cAMP responsive element-binding protein H (CREBH) and activating transcription factor 6 (ATF6) are both ER-bound bZIP family transcription factors that are activated upon ER stress. Of interest, we observed that both curcumin treatment and SMILE overexpression only represses CREBH-mediated transactivation of the target gene but not ATF6-mediated transactivation. Knockdown of endogenous SMILE significantly releases the inhibitory effect of curcumin on CREBH transactivation. Intrinsic repressive activity of SMILE is observed in the Gal4 fusion system, and the intrinsic repressive domain is mapped to the C terminus of SMILE spanning amino acid residues 203-269, corresponding to the basic region leucine zipper (bZIP) domain. In vivo interaction assay revealed that through its bZIP domain, SMILE interacts with CREBH and inhibits its transcriptional activity. Interestingly, we observed that SMILE does not interact with ATF6. Furthermore, competition between SMILE and the coactivator peroxisome proliferator-activated receptor α (PGC-1α) on CREBH transactivation has been demonstrated in vitro and in vivo. Finally, chromatin immunoprecipitation assays revealed that curcumin decreases the binding of PGC-1α and CREBH on target gene promoter in a SMILE-dependent manner. Overall, for the first time we suggest a novel phenomenon that the curcumin/LKB1/AMPK/SMILE/PGC1α pathway differentially regulates ER stress-mediated gene transcription.

Dietary ligands of the aryl hydrocarbon receptor induce anti-inflammatory and immunoregulatory effects on murine dendritic cells

Activation of the aryl hydrocarbon receptor (AhR) in immune cells, such as dendritic cells (DCs), can lead to suppressed immune responses. Although AhR activation is most recognized for mediating the effects of its prototypical ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), many compounds existing in dietary sources can also bind the AhR. Because the immunomodulatory effects of indole-3-carbinol (I3C) and indirubin-3'-oxime (IO) have yet to be investigated in DCs, we evaluated the potential immunomodulatory effects of these compounds on murine DCs. We hypothesized that I3C and IO suppress immune and inflammatory responses in DCs. We found that both I3C and IO decreased the expression of CD11c, CD40, and CD54 while they increased expression of MHC2 and CD80. Following lipopolysaccharide (LPS)-activation, I3C and IO suppressed the production of pro-inflammatory mediators including tumor necrosis factor-α, interleukin (IL)-1β, IL-6, IL-12, and nitric oxide but increased IL-10 levels. These effects of I3C and IO were partially mediated by the AhR. Additionally, immunoregulatory genes, such as ALDH1A, IDO and TGFB, were upregulated following treatment with I3C or IO. Both I3C and IO decreased basal levels of nuclear factor-kappa B p65, but only I3C suppressed the LPS-induced activity of RelB. Finally, when cultured with naïve T cells, bone marrow-derived dendritic cells treated with the dietary AhR ligands increased the frequency of Foxp3+ Tregs in an antigen-specific manner. Taken together, these results indicate that I3C and IO exhibit immunosuppressive and anti-inflammatory effects on DCs. Because I3C and IO are significantly less toxic than TCDD, these natural products may ultimately become useful therapeutics for the treatment of autoimmune and inflammatory diseases.

Chemopreventive effect of dietary polyphenols in colorectal cancer cell lines

Colorectal cancer (CRC) is the second most fatal and the third most diagnosed type of cancer worldwide. Despite having multifactorial causes, most CRC cases are mainly determined by dietary factors. In recent years, a large number of studies have attributed a protective effect to polyphenols and foods containing these compounds (fruits and vegetables) against CRC. Indeed, polyphenols have been reported to interfere with cancer initiation, promotion, and progression, acting as chemopreventive agents. The aim of this review is to summarize the main chemopreventive properties of some polyphenols (quercetin, rutin, myricetin, chrysin, epigallocatechin-3-gallate, epicatechin, catechin, resveratrol, and xanthohumol) against CRC, observed in cell culture models. From the data reviewed in this article, it can be concluded that these compounds inhibit cell growth, by inducing cell cycle arrest and/or apoptosis; inhibit proliferation, angiogenesis, and/or metastasis; and exhibit anti-inflammatory and/or antioxidant effects. In turn, these effects involve multiple molecular and biochemical mechanisms of action, which are still not completely characterized. Thus, caution is mandatory when attempting to extrapolate the observations obtained in CRC cell line studies to humans.