Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Spheroids”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 235 records · Page 13Linked to original sources
PubMed1983

Response of multicell spheroids to 1-MHz ultrasonic irradiation: cavitation-related damage.

The response of EMT6/Ro single cells and multicell spheroids (150-800 microns diameter) to 1-MHz ultrasonic irradiation was determined for intensities of 0-5 W/cm2 for 1-5 min. Damage was assessed by evaluating both lysis and survival of individual spheroid cells, growth of whole spheroids, and the physical integrity of whole spheroids by histological and scanning electron microscopic techniques. The surviving fraction of spheroid cells was higher than that of single cells, and several of the intensity-duration combinations showed a statistically significant correlation between resistance to ultrasound and increased spheroid size. This resistance with size was also found in spheroid growth experiments. Histological sections showed that both peripheral and internal damage occur. The relationship of spheroid damage to studies of effects on tissues and possible therapeutic use of nonthermal ultrasound are discussed.

Animals↗
PubMed1980

Selective dissociation and characterization of cells from different regions of multicell tumor spheroids.

A technique has been developed which takes advantage of the spherical symmetry of EMT6/Ro multicellular tumor spheroids to isolate subpopulations of cells originating from various locations in the spheroid structure. The method involves gently exposing spheroids to a dilute trypsin solution at 18 to 20 degrees in specially designed dishes on a rotary shaker. Under these conditions, cells are released only from the outer spheroid surface; successive trypsin treatments dissociate cells from increasing depths in the spheroid. Measurements of the spheroid diameter and rate of cell dissociation demonstrated the reproducibility of the technique. Observations of histological sections showed that trypsin was active only over a small distance into the spheroid. Characterization of the cells isolated indicated that cell volume, membrane integrity, and clonogenic capacity all decreased for cells located in inner spheroid regions. Autoradiography and DNA content analysis by flow cytometry established that outer region cells were actively proliferating while inner region cells were in a nonproliferative state. There was a significant number of cells arrested with S- and G2-phase DNA contents as well as a large number arrested with a G1 DNA content, similar to recent findings for nonproliferating cells in tumors.

Animals↗
PubMed1999

Three-dimensional spheroid cultures of human prostate cancer cell lines.

BACKGROUND: Many of the available human prostate cancer (PC) cell lines have lost androgen sensitivity and no longer secrete prostate-specific proteins after serial culturing in cell monolayers. Three-dimensional spheroid cultures have been found to better mimic the in vivo phenotypes of several nonprostatic cell lines. METHODS: We analyzed seven PC cell lines to determine if spheroid culturing results in greater sensitivity to androgens and 1alpha,25(OH)(2) vitamin D(3) (1,25(OH)(2) D(3)) with regards to their growth, differentiation, and apoptotic potential. RESULTS: Only PC-3 cells showed greater sensitivity to the growth-inhibitory effects of 1, 25(OH)(2) D(3), while ALVA-31 showed a diminished response. The regulation of prostate-specific antigen and prostate-specific acid phosphatase remained unchanged. However, these studies provided several unique findings not observed in cell monolayers. First, three basic spheroid morphologies were observed with varying degrees of intercellular adhesions. Secondly, the cell lines that formed the tightest spheroids consistently grew at the slowest rates, regardless of their growth rate in monolayers. Lastly, 1,25(OH)(2) D(3) treatment of ALVA-31 and PPC-1 spheroids greatly reduced intercellular adhesions, and rendered ALVA-31 spheroids resistant to apoptotic induction by Fas ligand expressed via a recombinant adenoviral construct. CONCLUSIONS: Our results suggest that spheroid cultures of human PC cells may provide unique insights regarding cell adhesion and apoptotic potential that are diminished or absent in monolayer cultures.

Androgens↗
PubMed2003

Mixed-ligand modification of polyamidoamine dendrimers to develop an effective scaffold for maintenance of hepatocyte spheroids.

Compared with a monolayer culture, hepatocyte spheroids are known to maintain liver function for long periods. We found that hepatocytes formed spheroids when cultured on polyamidoamine dendrimers modified with fructose. Because galactose is a ligand for the asialoglycoprotein receptor on the hepatocyte cytoplasmic membrane, it was chosen as another ligand for modification in order to maintain adhesion of spheroids for long periods. Simultaneous modification of dendrimers with fructose and galactose had a marked effect on the time length of spheroid adhesion. Suppression of apoptosis and necrosis was observed in hepatocyte spheroids cultured on a dendrimer modified with fructose and galactose (F/G dendrimer). Moreover, the hepatocyte spheroids cultured on the F/G dendrimer had higher activities of liver-specific functions, such as urea synthesis and albumin gene expression, than did those cultured on single-ligand-modified dendrimers. The expression of heat shock protein (HSP) genes was examined to evaluate the stress response of cells to scaffolds. The hepatocytes cultured on the F/G dendrimer had very low expression levels of both HSP60 and HSP70 mRNAs. Thus immobilization of mixed-ligand-modified dendrimers could generate a suitable surface for hepatocyte spheroid formation. These dendrimers could be a powerful tool for generating custom-made scaffolds for cells other than hepatocytes by selecting the ligands suitable for each cell type.

Animals↗
PubMed1999

A mouse fibroblast line cycles between monolayer and spheroid forms, regulates Met and HGF expression, and releases an attachment and growth-promoting substance.

A subline of mesoderm-derived mouse NIH3T3 fibroblasts was selected for its ability to proliferate in serum-free media. This cell line (SFDH) grows as a monolayer at low density and spontaneously forms dense, multicellular spheroids at high density. Spheroid formation can also be induced by the addition of dexamethasone, polybrene, or heparin. Spheroids eventually detach from the substrate, but will reattach and re-form monolayers when transferred to fresh culture vessels and media, repeating the cycle again upon reaching high density. Thin section analysis of spheroids shows morphologically-distinct regions of cells, including an attenuated outer surface and a cuboidal interior with occasional lumen-like areas. Over time in culture, spheroids express increasing levels of met, the Met ligand-SF/HGF and cytokeratin, an epithelial marker, in comparison to monolayers. Both monolayer and spheroid-derived cells are rapidly tumorigenic in nude mice. Media conditioned by SFDH cells contain factors that stimulate growth and attachment of a variety of tumorigenic and non-tumorigenic cell lines, inducing cells to divide in serum-free media for up to 14 days when plated on tissue culture-treated and nontreated plastic surfaces pre-coated with SFDH conditional media. The growth-stimulating activity fractionates as a single peak over a sepharose column in the presence of 6 m urea, and sediments as a high molecular weight complex. Growth-stimulating activity can be neutralized by several antisera specific for hepatocyte growth factor, and the same sera recognize a novel approximately 37 kD protein in active supernatants. The cyclic, continuous nature of alternating monolayer and spheroid forms makes this cell line appropriate for studying changing gene expression patterns in progressive cell-cell/cell-matrix interactions.

3T3 Cells↗
PubMed2003

Enhancement of effects of irradiation by gemcitabine in a glioblastoma cell line and cell line spheroids.

BACKGROUND AND PURPOSE: To determine the cytotoxicity of, and radioenhancement by, gemcitabine on a glioma cell line grown as a monolayer and as spheroid cultures. MATERIAL AND METHODS: We used a human glioma cell line, Gli-6, which originated from a biopsy specimen of a patient with a glioblastoma multiforme. Spheroids of Gli-6 were prepared by seeding a single cell suspension on agarose-coated Petri dishes. Clonogenic and growth delay assays were used to determine radio-chemosensitivity of monolayer cultures. The growth delay assay was used to determine that of Gli-6 spheroid cultures. RESULTS: Spheroid cultures were found to be more resistant to irradiation with/or without gemcitabine than monolayer cultures. Whereas gemcitabine significantly enhances the radiation effect of exponentially growing Gli-6 monolayer cultures at minimal cytotoxic concentrations (10 nM, 24 h), no enhancement was seen in confluent monolayer cultures and in large spheroids at the same concentration. In small spheroids no enhancement was observed at a low-dose gemcitabine (10 nM for 24 h), but an enhancement was observed at higher concentrations (100 nM for 24 h). CONCLUSION: Gemcitabine can lead to enhancement of the effects of X-irradiation in both monolayer as spheroid glioblastoma cultures. The lack of enhancement in confluent monolayer cultures supports the view that cell cycle distribution of cells is important in radiosensitisation by gemcitabine

Antimetabolites, Antineoplastic↗
PubMed2006

Dynamic analysis of hepatoma spheroid formation: roles of E-cadherin and beta1-integrin.

A spheroid is an in vitro multicellular aggregate that provides a microenvironment resembling that of normal tissue in vivo. Although cell adhesion molecules such as integrins and cadherins have been implicated in participating in the process of spheroid formation, little is known about the timing of their action. In this study, we have employed an image-based quantitative method to investigate the compactness of cell aggregates during hepatoma spheroid formation in a dynamic fashion. By modulating beta1-integrin and E-cadherin activity with specific blocking antibodies, ion chelators, and RGD-sequence-containing peptides, we show that these cell adhesion molecules mediate the formation of spheroids through the establishment of complex cell-cell and cell-extracellular matrix (ECM) interactions. The dynamics of spheroid formation can be separated into three stages. In the first stage, ECM fibers act as a long-chain linker for the attachment of dispersed single-cells to form loose aggregations through the binding of integrins. This is followed by a delay period in which cell aggregates pause in compaction, presumably because of the accumulation of sufficient amounts of E-cadherins. In the third stage, strong homophilic interaction of E-cadherins is a major factor for the morphological transition from loose cell aggregates to compact spheroids. These findings thus provide comprehensive information on the molecular mechanisms and dynamics of hepatoma spheroid formation.

Cadherins↗
PubMed1996

On the relation between size of necrosis and diameter of tumor spheroids.

PURPOSE: In many previous experimental studies on multicellular tumor spheroids, the spheroid diameter at which central necrosis develops has been determined to be twice the thickness of the viable cell rim measured at a later stage of spheroid growth. This procedure tacitly assumes that there is a linear relation between the diameter of necrosis and that of the whole spheroid over the entire range of emergence and growth of necrosis. However, some experimental investigations have demonstrated that necroses do not grow gradually with spheroid diameter, but show a rapid initial increase, once a few cells have died. The present article offers an explanation for this phenomenon, which is derived from basic diffusion theory. METHODS AND MATERIALS: A theoretical relation between sizes of spheroids and of their central necroses is developed, which is based on the assumption that formation of necrosis is caused by depletion of substrates or accumulation of metabolic waste products. In a second part, the theoretical model is fitted to experimental data from the literature, and oxygen consumption rate as a function of spheroid size is determined. RESULTS: It turns out that the model closely mimics the experimentally observed behavior described above. These experimental results, therefore, do not furnish any evidence for assuming other hypotheses of necrosis formation. Resulting O2 consumption rates are well in the range of previously published data. In all cases, approximations to the measured data are better than the corresponding linear squares fits. CONCLUSION: At least in some tumor cell lines, depletion of substrates or accumulation of waste products can explain formation of necrosis without the assumption of any additional mechanisms. Moreover, the model presented in this article offers an alternative way of determining the turnover rate of a substrate or metabolic waste product provided that depletion/accumulation of this substance represents the cause for necrosis development.

Least-Squares Analysis↗
PubMed2005

Reactive oxygen species-linked regulation of the multidrug resistance transporter P-glycoprotein in Nox-1 overexpressing prostate tumor spheroids.

Expression of the multidrug resistance (MDR) transporter P-glycoprotein (P-gp) has been demonstrated to be regulated by hypoxia-inducible factor-1alpha (HIF-1alpha) and inhibited by intracellular reactive oxygen species (ROS). Herein, P-gp and HIF-1alpha expression were investigated in multicellular prostate tumor spheroids overexpressing the ROS-generating enzyme Nox-1 in comparison to the mother cell line DU-145. In Nox-1-overexpressing tumor spheroids (DU-145Nox1) generation of ROS as well as expression of Nox-1 was significantly increased as compared to DU-145 tumor spheroids. ROS generation was significantly inhibited in the presence of the NADPH-oxidase antagonists diphenylen-iodonium chloride (DPI) and 4-(2-aminoethyl)benzenesulfonyl fluoride (AEBSF). Albeit growth kinetic of DU-145Nox1 tumor spheroids was decreased as compared to DU-145 spheroids, elevated expression of Ki-67 was observed indicating increased cell cycle activity. In DU-145Nox1 tumor spheroids, expression of HIF-1alpha as well as P-gp was significantly decreased as compared to DU-145 spheroids, which resulted in an increased retention of the anticancer agent doxorubicin. Pretreatment with the free radical scavengers vitamin E and vitamin C increased the expression of P-gp as well as HIF-1alpha in Nox-1-overexpressing cells, whereas no effect of free radical scavengers was observed on mdr-1 mRNA expression. In summary, the data of the present study demonstrate that the development of P-gp-mediated MDR is abolished under conditions of elevated ROS levels, suggesting that the MDR phenotype can be circumvented by modest increase of intracellular ROS generation.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1995

Volume estimation of multicellular colon carcinoma spheroids using Cavalieri's principle.

Multicellular tumour-spheroids are regarded as suitable models for cancer research, similar to avascular tumour parts. As a size parameter of the spheroids, usually their maximum diameter is used, estimated on a section presumed to be equatorial or near equatorial. Estimation of the volume of spheroids is of interest for the detection of subtle changes in different kinds of investigations. Since spheroids are often not truly spherical, and because model-based methods for volume determination may be biased, Cavalieri's principle, rediscovered recently for stereology, was used to determine the volume of the spheroids. Here we report the results of the volume estimation of colon carcinoma spheroids, together with an outline of the basic stereological principle and formulas used. The spheroids investigated had a volume between 1.4 and 92.3 mm3 (mean 33.9). The volume fraction of necrotic to viable tissue cells was between 0.6:1 and 2.2:1. The coefficient of error (CE) was remarkably low with 3.7% for the volumes. Both inter- and intraobserver-variability were extremely low with correlation coefficients (r2) of 99%. Thus, the high precision of the stereological method, combined with a low workload, make it ideally suitable for routine volume estimation.

Carcinoma↗
PubMed2001

Radiation response and cure rate of human colon adenocarcinoma spheroids of different size: the significance of hypoxia on tumor control modelling.

PURPOSE: To evaluate the adequacy of a Poisson tumor control probability (tcp) model and the impact of hypoxia on tumor cure. METHODS AND MATERIALS: A human colon adenocarcinoma cell line, WiDr, was grown as multicellular spheroids of different diameters. Measurements were made of cell survival and spheroid cure following 300-kV X-ray external beam irradiation in air and nitrogen. Cell survival data were fitted using a two-compartment and an oxygen diffusion model. Spheroid cure data were fitted using the tcp model. RESULTS: Hypoxia was seen only for spheroids greater than 500 microm in diameter. For small spheroids tcp estimates of radiosensitivity and clonogenic number showed excellent agreement with experimentally derived values. For large spheroids, although tcp estimates of radiosensitivity were comparable with measurements, estimates of the clonogenic number were considerably lower than the experimental count. Reoxygenation of large spheroids before irradiation resulted in the tcp estimates of the number of clonogenic cells agreeing with measured values. CONCLUSIONS: When hypoxia was absent, the tcp model accurately predicted cure from measured radiosensitivity and clonogen number. When hypoxia was present, the number of cells capable of regrowth in situ was considerably lower than the number of clonogenic cells that initially survived irradiation. As this counteracted the decreased radiosensitivity, hypoxia was less important for cure than predicted from cell survival assays. This finding suggests that chronic hypoxia may not limit directly the success of radiation therapy.

Adenocarcinoma↗
PubMed2002

Long-term enhancement of cytochrome P450 2B1/2 expression in rat hepatocyte spheroids through adenovirus-mediated gene transfer.

Tissue-like structures of cells organized in vitro have a great potential for a number of clinical and biomedical applications. Cell functions may be modulated with gene delivery, improving the characteristics of these structures. Hepatocytes that self-assemble into spheroids can be transduced through adenovirus-mediated gene transfer. An adenoviral vector (AdGFP) was employed to deliver a gene encoding for green fluorescent protein (GFP) in rat hepatocyte spheroids. GFP fluorescence was detected for at least one month. Furthermore, the rat cytochrome P450 2B1 gene (CYP2B1) was transferred through infection with a recombinant adenovirus (AdCYP2B1) in hepatocyte spheroids cultured in suspension. The CYP2B1/2 mRNA and apoprotein levels were continuously higher for over 23 days compared to phenobarbital-induced and control cultures. P450-catalyzed pentoxyresorufin-O-dealkylation activity was also high in the AdCYP2B1-infected spheroids. In these spheroid cultures, albumin and urea levels were similar to those in uninfected spheroid cultures, indicating that expression of the CYP2B1 transgene did not impair these liver-specific functions. Hepatocyte spheroids transduced by recombinant adenoviral vectors can be efficiently used for drug metabolism studies, in implantation, and in bioartificial liver devices.

Adenoviridae↗
PubMed2006

Macrophages promote angiogenesis in human breast tumour spheroids in vivo.

An in vivo model has been established to study the role of macrophages in the initiation of angiogenesis by human breast tumour spheroids in vivo. The extent of the angiogenic response induced by T47D spheroids implanted into the dorsal skinfold chamber in nude mice was measured in vivo and compared to that induced by spheroids infiltrated with human macrophages prior to implantation. Our results indicate that the presence of macrophages in spheroids resulted in at least a three-fold upregulation in the release of vascular endothelial growth factor (VEGF) in vitro when compared with spheroids composed only of tumour cells. The angiogenic response measured around the spheroids, 3 days after in vivo implantation, was significantly greater in the spheroids infiltrated with macrophages. The number of vessels increased (macrophages vs no macrophages 34+/-1.9 vs 26+/-2.5, P<0.01), were shorter in length (macrophages vs no macrophages 116+/-4.92 vs 136+/-6.52, P<0.008) with an increased number of junctions (macrophages vs no macrophages 14+/-0.93 vs 11+/-1.25, P<0.025) all parameters indicative of new vessel formation. This is the first study to demonstrate a role for macrophages in the initiation of tumour angiogenesis in vivo.

Animals↗
PubMed2000

Expression of poly(ADP-ribose) polymerase and distribution of poly(ADP-ribosyl)ation in glioblastoma and in a glioma multicellular tumour spheroid model.

Development of necrosis is a characteristic feature of glioblastoma but its pathogenesis remains poorly understood. The process of poly(ADP-ribosyl)ation in response to DNA damage is mediated by poly(ADP-ribose) polymerase (PARP) and results in NAD+ depletion. The consequent ATP and energy depletion may result in cell necrosis. Therefore PARP activation is a potential candidate for a regulatory role in the pathogenesis of necrosis in glioblastoma. This study investigated whether there might be a relationship between both PARP expression and poly(ADP-ribosyl)ation, and necrosis in glioblastoma. The pattern of expression of PARP and of poly(ADP-ribose) groups in an archival series of glioblastoma was examined using immunohistochemistry. These parameters were also studied in multicellular tumour spheroids, derived from human glioma cell lines in which central necrosis develops with increasing spheroid diameter. Poly(ADP-ribose) groups were expressed in peri-necrotic tumour cells in glioblastoma. In the spheroid model poly(ADP-ribosyl)ation was seen centrally in pre-necrotic and necrotic cells with increasing spheroid diameter. PARP was widely expressed in viable tumour cells in the glioblastoma sections. In the spheroids, PARP expression, which was initially diffuse, became confined to the outer proliferative zone with increasing diameter. The pattern of expression of poly(ADP-ribose) groups in the spheroids and in glioblastoma raises the possibility that poly(ADP-ribosyl)ation may play a role in the development of necrosis in glioma. The high basal PARP expression in both glioblastoma and the spheroids suggests that this enzyme may have additional roles in glioma cell biology.

Adult↗
PubMed2000

Monocytes secrete interleukin-6 when co-cultured in vitro with benign or malignant autologous fragment spheroids from squamous cell carcinoma patients.

Biopsies from tumour and benign mucosa were removed from patients with head and neck squamous-cell carcinoma (HNSCC), chopped into cubes and transferred to a nonadhesive culture system where in vitro fragment (F)-spheroids were established. The F-spheroids stabilized within 14 days of culture in vitro with epithelial cells and fibroblasts on the surface. F-spheroids were co-cultured with freshly isolated autologous monocytes. The monocytes of 10 of 11 patients secreted interleukin (IL)-6 at a level similar to that of the average monocyte endotoxin-stimulated response. Secreted IL-1beta or tumour necrosis factor-alpha (TNF-alpha) levels greater than 0.1 times the endotoxin-stimulated secretion were determined in one and two of the 11 co-culture experiments, respectively. This different monocyte response to F-spheroids compared with endotoxin stimulation was also present at the mRNA expression level. HNSCC monocytes secreted no IL-6 after co-culture with autologous fibroblasts. When monocytes and F-spheroids were cultured separated by a semipermeable membrane, the IL-6 supernatant level was only approximately 25% of that observed during co-culture with direct contact. F-spheroids secreted only trace amounts of IL-6. In conclusion, monocytes of HNSCC patients generally secrete IL-6, but not IL-1beta or TNF-alpha, after stimulation with epithelial-associated components of F-spheroids upon direct contact and in part by a soluble substance.

Aged↗
PubMed2001

Human autologous monocytes and monocyte-derived macrophages in co-culture with carcinoma F-spheroids secrete IL-6 by a non-CD14-dependent pathway.

The secretion of interleukin (IL)-1 beta, IL-6 and tumour necrosis factor (TNF)-alpha were compared when freshly isolated autologous monocytes or monocytederived macrophages (MDMs) were co-cultured in vitro with autologous fragment (F)-spheroids established from a series of head and neck squamous cell carcinoma (HNSCC) patients. F-spheroids were generated from the malignant tumour (M-spheroids) or from benign mucosa (B-spheroids) from which the tumour originated control. If monocytes maturated towards MDMs before co-culture, the IL-6 secretion declined dependent on the extent of the MDM maturation by both M- and B-spheroid stimulation. When MDMs maturated in continuous co-culture, a steady-state secretion of IL-6 continued for several days but diminished when the culture medium was changed every 24 h. No co-culture-induced IL-1 beta or TNF-alpha was determined. Both the cytokine secretion and the mRNA gene expression revealed a different monocyte/MDM activation when co-culture and lipopolysaccharide (LPS)-stimulation were compared. Addition of anti-CD14 (10 microg/ml) decreased monocyte LPS-stimulated, but increased monocyte co-culture stimulated IL-6 secretion. In conclusion, M- and B-spheroids similarly stimulated monocytes and to a lesser extent MDMs. MDMs that maturated with F-spheroids present, retained responsiveness at the monocyte level. Co-culture-induced monocyte stimulation, as measured by IL-6 secretion, was not dependent on activation via the CD14 molecule.

Carcinoma, Squamous Cell↗
PubMedDate not supplied

Ultrastructural and functional investigations of adult hepatocyte spheroids during in vitro cultivation.

Cultivation of primary adult hepatocytes creates a challenge because of their loss of hepatocellular functions if prevented from attaining polarized cell-cell and cell-matrix interactions. Thus, when hepatocytes are seeded in nonadhesive porous alginate scaffolds, they form 100-microm-diameter spheroids with enhanced cell-cell interactions. Using transmission electron microcopy (TEM), histology, and functional studies, we investigated the state of hepatocyte spheroids during in vitro cultivation. TEM of day 3 spheroids revealed multiple cell layers, with tight junctions between adjacent cells and microvillus-lined channels that resembled bile canaliculi, both structurally and functionally. When copper ions were added to the external medium, the spheroidal hepatocytes performed endocytosis and eventually secreted the heavy metal ions into the bile lumens. From day 8 on, however, there was a rapid decline in cell viability. Histology and TEM analysis of day 13 spheroids revealed a necrotic center, with one viable cell layer on the outskirts. The absence of DNA laddering and negative results in TUNEL assay indicated that apoptosis is not the main process leading to cell death. Cell necrosis may be a result of accumulated bile secretions in the compacted spheroids. Collectively, our results suggest that spheroids derived from adult hepatocytes may have limited utility in long-term applications.

Animals↗
PubMedDate not supplied

Immunohistochemical analysis of differentiation in static and mixed prostate cancer spheroids.

Neoplastic multicellular spheroids are in vitro models of solid tumors employed in drug testing and basic research. This study compares differentiation in static and mixed prostate cancer spheroids. Staining intensity of prostate specific antigen (PSA) was down-regulated upon mixing, from 0.21 +/- 0.03 to 0.13 +/- 0.03 in LNCaP multicellular spheroids, and from 0.13 +/- 0.04 to 0.03 +/- 0.02 in DU 145 multicellular spheroids. This was accompanied by 65% increase in the expression of cytokeratins 8 and 18 in DU 145 spheroids. PSA expression extended 60 micro m within static spheroids and was disrupted in mixed culture. Diminished PSA expression and spatial organization suggests a more aggressive cancer. Higher cytokeratin expression could result from either differentiation towards a luminal phenotype or activation of the Ras pathway during dedifferentiation. Thus, the existing paradigm of differentiation established for normal tissue does not apply for our neoplastic spheroids. Cell dedifferentiation is attributed to improved interstitial transport and synthesis of extracellular matrix.

Animals↗