Estrogen response of MCF-7 cells grown on diverse substrates and in suspension culture: promotion of morphological heterogeneity, modulation of progestin receptor induction; cell-substrate interactions on collagen gels

Breast Cancer MCF-7 Cells Acquire Heterogeneity during Successive Co-Culture with Hematopoietic and Bone Marrow-Derived Mesenchymal Stem/Stromal Cells

During disease progression and bone metastasis, breast tumor cells interact with various types of bystander cells residing in the tumor microenvironment. Such interactions prompt tumor cell heterogeneity. We used successive co-culture as an experimental model to examine cancer-bystander cell interaction. RMCF7-2, a clone of the human breast cancer MCF-7 cells tagged with a red fluorescent protein, was tracked for morphologic, behavioral, and gene expression changes. Co-cultured with various types of hematopoietic cells, RMCF7-2 adopted stable changes to a rounded shape in suspension growth of red fluorescent cells, from which derivative clones displayed marked expressional changes of marker proteins, including reduced E-cadherin and estrogen receptor α, and loss of progesterone receptor. In a successive co-culture with bone marrow-derived mesenchymal stem/stromal cells, the red fluorescent clones in suspension growth changed once more, adopting an attachment growth, but in diversified shapes. Red fluorescent clones recovered from the second-round co-culture were heterogeneous in morphology, but retained the altered marker protein expression while displaying increased proliferation, migration, and xenograft tumor formation. Interaction with bystander cells caused permanent morphologic, growth behavioral, and gene expressional changes under successive co-culture, which is a powerful model for studying cancer cell heterogeneity during breast cancer progression and metastasis.

Development of a Multicellular Three-dimensional Organotypic Model of the Human Intestinal Mucosa Grown Under Microgravity

Because cells growing in a three-dimensional (3-D) environment have the potential to bridge many gaps of cell cultivation in 2-D environments (e.g., flasks or dishes). In fact, it is widely recognized that cells grown in flasks or dishes tend to de-differentiate and lose specialized features of the tissues from which they were derived. Currently, there are mainly two types of 3-D culture systems where the cells are seeded into scaffolds mimicking the native extracellular matrix (ECM): (a) static models and (b) models using bioreactors. The first breakthrough was the static 3-D models. 3-D models using bioreactors such as the rotating-wall-vessel (RWV) bioreactors are a more recent development. The original concept of the RWV bioreactors was developed at NASA's Johnson Space Center in the early 1990s and is believed to overcome the limitations of static models such as the development of hypoxic, necrotic cores. The RWV bioreactors might circumvent this problem by providing fluid dynamics that allow the efficient diffusion of nutrients and oxygen. These bioreactors consist of a rotator base that serves to support and rotate two different formats of culture vessels that differ by their aeration source type: (1) Slow Turning Lateral Vessels (STLVs) with a co-axial oxygenator in the center, or (2) High Aspect Ratio Vessels (HARVs) with oxygenation via a flat, silicone rubber gas transfer membrane. These vessels allow efficient gas transfer while avoiding bubble formation and consequent turbulence. These conditions result in laminar flow and minimal shear force that models reduced gravity (microgravity) inside the culture vessel. Here we describe the development of a multicellular 3-D organotypic model of the human intestinal mucosa composed of an intestinal epithelial cell line and primary human lymphocytes, endothelial cells and fibroblasts cultured under microgravity provided by the RWV bioreactor.

Phenotypic drug profiling in droplet microfluidics for better targeting of drug-resistant tumors

Acquired drug resistance is a key factor in the failure of chemotherapy. Due to intratumoral heterogeneity, cancer cells depict variations in intracellular drug uptake and efflux at the single cell level, which may not be detectable in bulk assays. In this study we present a droplet microfluidics-based approach to assess the dynamics of drug uptake, efflux and cytotoxicity in drug-sensitive and drug-resistant breast cancer cells. An integrated droplet generation and docking microarray was utilized to encapsulate single cells as well as homotypic cell aggregates. Drug-sensitive cells showed greater death in the presence or absence of Doxorubicin (Dox) compared to the drug-resistant cells. We observed heterogeneous Dox uptake in individual drug-sensitive cells while the drug-resistant cells showed uniformly low uptake and retention. Dox-resistant cells were classified into distinct subsets based on their efflux properties. Cells that showed longer retention of extracellular reagents also demonstrated maximal death. We further observed homotypic fusion of both cell types in droplets, which resulted in increased cell survival in the presence of high doses of Dox. Our results establish the applicability of this microfluidic platform for quantitative drug screening in single cells and multicellular interactions.

The favorable impact of PIK3CA mutations on survival: an analysis of 2587 patients with breast cancer

The phosphatidylinositol-3 kinase (PI3K) pathway regulates a number of cellular processes, including cell survival, cell growth, and cell cycle progression. Consequently, this pathway is commonly deregulated in cancer. In particular, mutations in the gene PIK3CA that encodes the p110α catalytic subunit of the PI3K enzymes result in cell proliferation and resistance to apoptosis in vitro and induce breast tumors in transgenic mice. These data underscore the role of this pathway during oncogenesis. Thus, an ongoing, large-scale effort is underway to develop clinically active drugs that target elements of the PI3K pathway. However, conflicting data suggest that gain-of-function PIK3CA mutations may be associated with either a favorable or a poor clinical outcome, compared with the wild-type PIK3CA gene. In the current study, we performed a systematic review of breast cancer clinical studies. Upon evaluation of 2587 breast cancer cases from 12 independent studies, we showed that patients with tumors harboring a PIK3CA mutation have a better clinical outcome than those with a wild-type PIK3CA gene. Importantly, this improved prognosis may pertain only to patients with mutations in the kinase domain of p110α and to postmenopausal women with estrogen receptor-positive breast cancer. We propose three potential explanations for this paradoxical observation. First, PIK3CA mutations may interfere with the metastasis process or may induce senescence, which results in a better outcome for patients with mutated tumors. Secondly, we speculate that PIK3CA mutations may increase early tumor diagnosis by modification of the actin cytoskeleton in tumor cells. Lastly, we propose that PIK3CA mutations may be a favorable predictive factor for response to hormonal therapy, giving a therapeutic advantage to these patients. Ultimately, an improved understanding of the clinical impact of PIK3CA mutations is critical for the development of optimally personalized therapeutics against breast cancer and other solid tumors. This effort will be important to prevent or explain therapeutic failures and select patients who are most likely to respond to new therapies that inhibit the PI3K pathway.

Experimental anti-tumor therapy in 3-D: spheroids--old hat or new challenge?

PURPOSE

To give a state-of-the-art overview on the promise of three-dimensional (3-D) culture systems for anticancer drug development, with particular emphasis on multicellular tumor spheroids (MCTS).

RESULTS AND CONCLUSIONS

Cell-based assays have become an integral component in many stages of routine anti-tumor drug testing. However, they are almost always based on homogenous monolayer or suspension cultures and thus represent a rather artificial cellular environment. 3-D cultures--such as the well established spheroid culture system--better reflect the in vivo behavior of cells in tumor tissues and are increasingly recognized as valuable advanced tools for evaluating the efficacy of therapeutic intervention. The present article summarizes past and current applications and particularly discusses technological challenges, required improvements and recent progress with the use of the spheroid model in experimental therapeutics, as a basis for sophisticated drug/therapy screening. A brief overview is given focusing on the nomenclature of spherical 3-D cultures, their potential to mimic many aspects of the pathophysiological situation in tumors, and currently available protocols for culturing and analysis. A list of spheroid-forming epithelial cancer cell lines of different origin is provided and the recent trend to use spheroids for testing combination treatment strategies is highlighted. Finally, various spheroid co-culture approaches are presented that have been established to study heterologous cell interactions in solid tumors and thereby are able to reflect the cellular tumor environment with increasing accuracy. The intriguing observation that in order to retain certain tumor initiating cell properties, some primary tumor cell populations must be maintained exclusively in 3-D culture is mentioned, adding a new but fascinating challenge for future therapeutic campaigns.

Decreased tyrosine phosphorylation of focal adhesion kinase after estradiol treatment of MCF-7 human breast carcinoma cells

MCF-7 human breast carcinoma cultures grown in the presence of 17-beta estradiol form solid, multicellular nodules, a process that reflects changes in cell-substrate adhesions and loss of growth inhibition. We examined the effects of estradiol on the status of tyrosine phosphorylation in focal adhesion kinase (FAK) and the association of FAK with paxillin using immunoprecipitations and then probing western blots for FAK, phosphotyrosine, and paxillin. Culture of MCF-7 cells for seven days in the presence of 1 nM E2 resulted in decreased tyrosine phosphorylation of FAK compared to controls. The estradiol-induced effect was blocked by 100 nM of the estrogen receptor antagonist 4-hydroxytamoxifen, indicating dephosphorylation of FAK is an estrogen receptor-mediated event. FAK immunoprecipitated from either estradiol or DMSO-treated cells phosphorylated the exogenous substrate poly(Glu,Tyr), suggesting that the potential kinase activity of FAK was not changed by estradiol. Estradiol treatment also resulted in a reduced association between FAK and paxillin. The decreased phosphorylation levels and reduced association between FAK and paxillin may be important steps leading to the loss of stable focal contacts and loss of growth inhibition during MCF-7 nodulation.

Effects of sex- and glucocorticoid steroids on breast cancer cells grown as either multicellular tumor spheroids or monolayers

The effects of estradiol, medroxyprogesterone acetate (MPA) dexamethasone, dihydrotestosterone and the antihormones 4-OH tamoxifen and RU 38486 were studied in two established breast carcinoma cell lines, the estrogen-sensitive ZR-75-1 and the estrogen-independent BT 20 cells applying two different in vitro systems, spheroid and monolayer cell culture in steroid deprived medium. Growth of ZR-75-1 spheroids was dramatically stimulated by the addition of estradiol, an effect which was neutralized by the simultaneous addition of 4-OH tamoxifen. The antiestrogen alone as well as dihydrotestosterone and MPA reduced ZR-75-1 spheroid growth significantly. While growth of BT 20 spheroids was only transiently inhibited by tamoxifen and dihydrotestosterone, a persistent increase in BT 20 spheroid growth was observed under MPA treatment in a concentration of 1 microM. This effect, although statistically significant, was very moderate. With the exception of this finding, growth effects of the different test compounds were similar in both in vitro systems, tumor spheroids and monolayer cell cultures.

17-beta-Estradiol induced alterations of cell-matrix and intercellular adhesions in a human mammary carcinoma cell line

The MCF-7 human mammary carcinoma cell line undergoes morphological differentiation in vitro when treated with 17-beta-estradiol. A prominent feature of this process is the postconfluent development of multicellular, three-dimensional nodules that rise above the surrounding monolayer. Formation of the nodules suggests that changes in cellular adhesion occur during this cellular overgrowth. Therefore changes in the distribution of cell-matrix and cell-cell adhesion plaque proteins were examined with respect to estradiol induction of nodule development. Estradiol treatment of the carcinoma cell line had the following effects: (1) vinculin- and talin-rich cell-matrix adhesion plaques were reduced in overall number and size in confluent and postconfluent cultures. No overt change in distribution or morphology of adhesion plaques was observed in subconfluent cultures. (2) Staining for vinculin was reduced in cell-cell adhesions situated at the apical region of subconfluent, confluent and postconfluent monolayers. Staining for F-actin and plakoglobin was retained at this region in estradiol-induced cells. (3) vinculin was not detected in intercellular adhesions of nodule cells although intense labelling for both F-actin and plakoglobin was observed. In addition, in untreated monolayer cells, both F-actin and plakoglobin were concentrated in a subapical/basolateral location, as a vesicle-like pattern, which corresponded to intercellular spaces observed with phase-contrast microscopy. Treatment with estradiol caused the rearrangement of subapical/basolateral F-actin and plakoglobin staining into a more uniform pattern. The findings of this study show that estradiol induces changes in both cell-matrix and cell-cell adhesions in an estrogen-responsive carcinoma cell line. The gradual loss of vinculin from cell-matrix and cell-cell adherens junctions of the monolayer could be a potential factor in the capacity of these cells to form multilayers or nodules in postconfluent growth. Furthermore, the development of the nodules in response to estradiol may provide a useful system in which to study steroid hormone regulation of adhesion and the cytoskeleton in responsive tumor cells.

Evaluation of the growth rate of MCF-7 breast cancer multicellular spheroids using three mathematical models

Growth data on 60 multicellular spheroids of MCF-7 human breast cancer cells were fitted, on an individual basis, by the Gompertz, Bertalanffy and logistic equations. MCF-7 spheroids, initiated and grown in medium containing oestrogens, exhibited a growth rate that decreased continuously as spheroid size increased. Plots of spheroid volume v. time generated sigmoid curves that showed an early portion with an approximately exponential volume increase; a middle region or retardation phase characterized by a continuously decreasing growth rate; and, finally, a late segment or plateau phase approaching zero growth rate, that permitted an estimate of the maximum spheroid size (Vmax). Growth curves generated by MCF-7 spheroids under different experimental conditions (hormones, drugs and radiation exposures) can be compared after normalization. Linearized forms of the fitted Gompertz curves provided a convenient way to express differences in growth rate.

Optimization of estrogen growth response in MCF-7 cells

The factors involved in estradiol-17 beta induced growth stimulation of MCF-7 human breast cancer cells have been examined. Wild type MCF-7 cells (and clone E3) were shown to undergo slow growth in phenol-red-free medium containing specific calf sera. The E3 clone was used to document a mean 6-day growth stimulation of 3.35-fold (doubling time = 33 +/- 3 h) in cultures supplemented with 10(-11) M estradiol-17 beta. The serum batch utilized in the culture medium is most important in acquiring significant growth stimulation of MCF-7 cells by estradiol-17 beta. Regardless of the absence of phenol-red, only selected sera (2 out of 14 tested) supported minimal growth of MCF-7 cells in the absence of added estradiol 17 beta (doubling time = 55 +/- 11 h). When a calf-serum-supplemented culture failed to display a complete growth response to estradiol-17 beta, it was due to the rapid growth of the cells in the control (minus estradiol-17 beta) flasks. Sera that promoted shorter doubling times for MCF-7 cells cultured in the absence of estradiol-17 beta were rendered less supportive of growth if treated with dextran-coated charcoal or when cultures were supplemented with the estrogen antagonist ICI 164,384 (10(-7) M). Pooled extracts of these sera were shown to contain stimulatory levels of estradiol-17 beta. Dextran-coated charcoal treatment of sera removed or deactivated factors (other than estradiol-17 beta) which were not only required for the growth of MCF-7 cells, but were necessary for estrogen-stimulated growth. Varying the serum-containing medium, buffer, and nutrient mix or the addition of insulin has no effect on the growth response of these cells to estradiol-17 beta. These investigations document the culture conditions required to produce a maximal and consistent proliferative effect of E2 on MCF-7 cells without exposing the serum constituent to damaging chemical or absorbent agents.

MCF-7 breast cancer cells grown as multicellular spheroids in vitro: effect of 17 beta-estradiol

To obtain multicellular spheroids from MCF-7 human breast cancer cells we adhered to the following procedure: (a) limiting the adherence of cell to the substratum; (b) seeding more than the minimum number of cells; (c) guaranteeing the presence of estrogens in the culture medium. Charcoal-dextran (CD)-treated sera seemed to inhibit spheroid formation. A reduction in the concentration of CD-human sera (from 10% to 5%) added to phenol-red-free medium facilitated progress from cellular aggregates to multicellular spheroids. Once the spheroids became initiated, size increased at a rate that showed a good fit to a Gompertzian equation (A = 0.368 +/- 0.067 alpha = 0.065 +/- 0.013, r range = 0.890-0.989). Three different patterns of spheroid morphology and proliferative kinetic were defined: (a) spheroids with diameter less than 200 microns had a constant pattern of heterogeneity in the distribution of 3H-TdR-labelled cells and in the expression of estrogen receptors; (b) spheroids 250 to 700 microns in diameter showed a decrease in the proportion of 3H-TdR-labelled cells accompanying inward progression (50% in the outer shell, less than 10% in a cell layer located at a depth of 150 microns) while, at a depth of 170 microns, of signs of concurrent cellular degeneration and death were apparent; and (c) spheroids with a diameter of greater than 750 microns showed a crust of viable cells uniformly labelled with thymidine without impairment of the proportion of labelled cells when progressing inward from the spheroid crust. The larger the spheroid volume, the lower its growth fraction and the longer its volume doubling time. The hormone-dependence of MCF-7 cells in forming multicellular spheroids represents a unique experimental model for assessing estrogen action on cell organization and proliferation.

Estrogen-stimulation of postconfluent cell accumulation and foci formation of human MCF-7 breast cancer cells

Foci, nodules of cellular overgrowth, that appear after confluence are an in vitro characteristic of malignant transformation. A well-studied in vitro model of estrogen-dependent tumors is the MCF-7 cell line, derived from a pleural metastasis of a human breast adenocarcinoma. We report that cultivation of MCF-7 cells, using routine methods, results in extensive estrogen-stimulated postconfluent cell accumulation characterized by discrete three-dimensional arrays. Side view Nomarski optical sections revealed these to be principally multicellular foci with occasional domes and pseudoacinar vacuoles. This effect on MCF-7 cell growth occurs in media containing fetal bovine serum but not with calf serum or charcoal-dextran-treated fetal bovine serum unless supplemented with estrogens. Foci formation starts 5-6 days after confluence, and the number of foci generated is a function of the concentration of added estrogens. Foci formation is suppressed by the antiestrogens Tamoxifen and LY 156758. Addition of progesterone, testosterone, or dexamethasone had little or no effect, while various estrogens (ethinyl estradiol, diethylstilbestrol, and moxestrol) induced foci development. Clones derived from single cells of the initial MCF-7 population revealed a wide variance in estrogen-induced foci formation, demonstrating heterogeneity of this tumor cell line. The postconfluent cell growth of the estrogen receptor-deficient cell line, MDA-MB-231, contrasted with MCF-7 by developing an extensive multilayer morphology devoid of discrete structures. The tumorigenic potential of the MCF-7 cells used in our experiments was confirmed by their estrogen-dependent growth in immunosuppressed male BDF1 mice. These data suggest an estrogen receptor-based mechanism for the development of multicellular foci during postconfluent growth of MCF-7 cells. After confluence, foci, in contrast to the quiescent surrounding monolayer, retain proliferating cells. Focus formation, therefore, reflects the heterogeneous responsiveness of these cells to estrogens and should provide a model permitting in vitro comparisons between the progenitor cells of multicellular foci and the monolayer population.

Inhibition of postconfluent focus production in cultures of MCF-7 human breast cancer cells by 2,3,7,8-tetrachlorodibenzo-p-dioxin

2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a potent inducer of differentiation and an antiestrogen, is shown to suppress in vitro postconfluent cell accumulation in the estrogen-dependent MCF-7 human breast tumor cell line. This dose-responsive suppression is apparent by 14 days of exposure with an EC50 between 10(-10) and 10(-11) M TCDD, and is characterized by reduced cell density (approximately 60% of controls after 14 days). This was attributed to a reduced formation in TCDD-treated cultures of multicellular foci which are characteristic of cancer cell growth in vitro (less than 1/mm2 compared to control levels of 40/mm2). Preconfluent cell growth and viability of MCF-7 cells is not affected by 10(-9) M TCDD. These results suggest that the principle of TCDD's activity may be useful in the study and possibly the management of estrogen-dependent breast tumors.

Early alterations at the plasma membrane of breast cancer cell lines in response to estradiol and hydroxytamoxifen

The time course of the early stage of estradiol-17 beta (E2) and hydroxytamoxifen (OHTAM) action at the plasma membrane of hormone-responsive MCF-7 and non-responsive MDA-MB-231 (MDA) breast cancer cell lines was investigated using scanning electron microscopy (SEM), electron probe X-ray microanalysis and microelectrophysiology analysis. SEM showed a marked increase in the density and the length of microvilli (MV) on MCF-7 cells treated with 1 nM estradiol for 1 min. This membrane response disappeared at 5 min. No early effect was obtained with OHTAM, but both compounds produced a similar surge of heterogeneous MV at 15 min of treatment. The morphological change induced by E2 subsided at 60 min, whereas that of OHTAM persisted. X-ray microanalysis and computer determination of peak/background ratios permitted the demonstration that these morphological alterations were concomitant with a rise in the intracellular level of potassium. Microelectrophysiology analysis showed a sharp transitory decrease in the membrane potential of MCF-7 cells in response to estradiol. In the estrogen-insensitive MDA cells, the hormone did not modify the membrane potential and K levels decreased at 1 and 5 min before rising again to control levels at minute 15 when MV appeared. With OHTAM, potassium decreased significantly at 60 min of treatment. These initial and transitory changes in surface morphology paralleled by alterations in potassium level may be consistent with the occurrence of estrogen membrane receptors on target cells, a new aspect of steroid hormone action.