This study was supported by a grant from the Baden-W&#252;rttemberg Stiftung (Adult Stem Cells Program II) awarded to C.L. We thank Dr. Martina Konantz for critical input and review of the manuscript. We thank Emmanuel Traunecker and Toni Krebs from the DBM FACS Facility (University Hospital Basel) for assistance with FACS sorting.

1. Generation of OVCAR-3 Human ovarian Carcinoma Cells Stably Transduced with Lentiviruses Containing the SOX2 Regulatory Region Reporter Construct
<ol>
	<li>Generate lentiviral particles by transfecting the HEK 293T-packaging cell line with a reporter construct recognizing a SOX2 regulatory region as described10,21. 
	NOTE: The reporter construct further contains a destabilization domain of the ProteoTuner Shield System ahead of the tdTomato fluorescence protein. Shield1 binds to the destabilization domain thereby preventing the proteasome to degrade the fluorescence protein22.</li>
	<li>Transduce OVCAR-3 cells with lentiviral particles over a time period of 24 hr. Afterwards, remove the viral supernatant and wash the cells with phosphate buffered saline (PBS) and cultured in complete medium (RPMI supplemented with 10% FBS, 100 U/ml penicillin, 100 &#956;g/ml streptomycin).</li>
	<li>48 hr later, 10 &#956;g/ml puromycin were added to the cultures and maintained for 5 days to allow selection of properly transduced cells.</li>
</ol>
2. Preparation of Cell Sorting and Plating
<ol>
	<li>Add Shield1 at 1:1,000 dilution 24 hr prior to cell sorting. Use stably transduced OVCAR-3 cells without Shield1 treatment as negative controls (Figure 1). Aspirate media from flask, wash cells with 1x PBS and trypsinize cells with 0.05% Trypsin-EDTA for 3 min.</li>
	<li>Stop trypsin by using complete medium (see above), count cell numbers, centrifuge cells at 300 x g at RT (15 - 25 &#176;C) for 5 min.</li>
	<li>Decant supernatant and resuspend cells carefully in 0.5 - 1 ml sterile PBS.</li>
	<li>Use 40 &#181;m cell strainer cap filter to obtain single-cell suspension.</li>
	<li>Adjust cell count to 5 million cells per ml.</li>
	<li>Prepare ultra low-attachment 96-well plates with 100 &#956;l spheres medium (MEGM supplemented with growth factors, cytokines, and supplements, B-27, heparine-sodium; or DMEM/F12 supplemented with growth factors, cytokines, and supplements, B-27, heparine-sodium with or without addition of 1% methylcellulose, see also Table 1). Optionally add antibiotics to the medium at a concentration of 100 U/ml penicillin and 100 &#956;g/ml streptomycin to minimize the risk of possible contamination.</li>
	<li>Sort RFP+ and RFP- cells into prepared 96-well plates from above, 1 cell per well (single cell-based spheres assay) and 100 cells per well (multi cell-based spheres assay), respectively. Perform sort on commercially available cell sorter (see Materials) using single cell mode, Sort setup: 100 &#956; nozzle, sheath pressure 20 psi, and yield mask 0, purity mask 32, phase mask 16.</li>
	<li>Assess plating efficiency by microscopically scoring wells containing cells (for the single cell-based assay) and by counting cell numbers in individual wells (for the multi cell-based assay; Figure 2).</li>
	<li>Incubate cells under standard conditions in spheres medium (for composition see step 2.6) at 37 &#176;C and 5% CO2. Supplement daily bFGF (20 ng/ml) and EGF (20 ng/ml).</li>
	<li>After one week, count numbers of emerging tumor spheres using a standard microscope with 4X or 10X magnification and a fluorescence microscope to detect fluorescence signal from the integrated reporter system. Count spheres with a diameter exceeding 100 &#956;m as &#8220;large&#8221; spheres, and spheres with a diameter 50 - 100 &#956;m as &#8220;small&#8221; spheres (Figure 3). Be sure that you count real spheres and not cell clusters. 
	NOTE: In single cell-based assays sphere formation is easier to score microscopically after 10 (versus 7) days of culture.</li>
	<li>Calculate the proportion of sphere-forming cells in RFP+ and respectively RFP- cells in single cell-based assays (one 96-well plate for each individual experiment) or multi cell-based spheres assays (one well for each individual experiment) as presented by Shaw et al.16 
	NOTE: Proportion of sphere forming cells (%) = (number of spheres) / (number of seeded cells) x 100</li>
</ol>
3. Serial Passaging of Spheres
<ol>
	<li>Place the content of each well in an appropriate sterile tube and centrifuge at 300 x g for 10 min at RT. For multi cell-based spheres assays, collect together the spheres from one well. Wash the well 3 - 5 times with PBS and centrifuge 2 min longer. For single cell-based spheres assays, collect individual spheres. Due to the low numbers of cells, use 1.5 ml tubes for centrifugation and washing steps.</li>
	<li>Remove supernatant and resuspend pellet in 200 &#181;l of 0.05% Trypsin-EDTA.</li>
	<li>In order to achieve optimal cell separation, incubate the cell suspension at 37 &#176;C for 5 min in a soft shaker. Optimize trypsinization time for your cell line to lower cell death rate: if no large spheres is visible triturate gently using a 100 &#956;l pipette tip. In case large spheres are still present, incubate with trypsin another 3 min and then proceed to the trituration step. In case of single cell-based assays make sure to optimize the time for optimal cell yield of living cells during the trypsinization step.</li>
	<li>To inactivate the trypsin, add 500 &#181;l complete medium and centrifuge at 300 x g for 10 min, in the case of single cell assays, centrifuge for additional 2 min.</li>
	<li>Remove supernatant and resuspend cells carefully in spheres medium.</li>
	<li>Use a 40 &#181;m cell strainer cap filter to obtain a single-cell suspension.</li>
	<li>In the case of using RFP+ and RFP- cells in multi cell-bassed assays, assess the percentage of fluorescent cells in each well after resuspension via flow cytometer analysis.</li>
	<li>For serial replating assays of single cells, seed 1 cell per well into a new ultra low-attachment 96-well plate prepared as detailed above. From one individual sphere, seed approximately 20 individual wells. For replating assays of multi cell-based primary spheres, seed cells obtained from one well of primary spheres into a new 96-well plate and count the cell numbers next day by microscopy.</li>
	<li>Assess the proportion of sphere-forming cells in secondary spheres assays using the formula described in step 2.11.</li>
</ol>
4. Result Analysis
<ol>
	<li>Analyze results from experiments performed in independent triplicates and use two-sided Student&#8217;s t-Test to analyze normally distributed values and otherwise Mann-Whitney-Tests for statistical analysis.</li>
</ol>

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The authors have nothing to disclose.

Spheres cultures are a widely used method to assay cancer stem cell potential and enrich for stem-like cells in a wide range of human tumor cells15,25,26. Under these culture conditions, cancer cells that lack self-renewal ability are expected to differentiate and eventually undergo cell death. Although they may initially form cell clusters or even tumor spheres especially in primary assays, they are not able to sustain sphere-forming ability upon serial replating due to lack of self-renewing properties. Spher...

There is increasing evidence that ovarian carcinomas are comprised of heterogeneous mixtures of cells and harbor so-called &#8220;cancer stem cells&#8221; (CSCs) responsible for disease initiation, maintenance and relapse after conventional cytotoxic therapies1-3. Therefore, the development of molecular strategies targeting ovarian CSCs is an important goal and promises to improve the therapy of ovarian cancer patients.
A pre-requisite for the understanding of the molecular features of CSCs is their reliable isolation from the non-CSCs. However, identification of ovarian CSCs appears challenging. While CD133 expression and aldehyde dehydrogenase (ALDH) activity4,5 have been reported to mark ovarian CSCs, some data indicate that these markers are unstable6. Consistently, in ovarian cancer, other than for example in breast carcinoma7, expression of ALDH1 associates with favorable outcome8 and expression of the proposed stem cell marker CD44 variant has no prognostic value9. More recently, we have shown that expression of the embryonic stem cell protein SOX2 confers stemness to ovarian carcinoma cells10 and high SOX2 expression associates with clinically aggressive ovarian and breast carcinomas11,12. Therefore, in this report we use a lentiviral reporter construct containing a red fluorescence protein (RFP) whose expression is controlled by a SOX2 regulatory region, as a method to isolate putative ovarian CSCs.
By definition, CSCs can both self-renew and differentiate, giving rise to all tumor cell types. Putative CSC populations need to be analyzed in functional assays performed in vivo. For obvious reasons, in human cells such functional tests are confined to xenograft assays, comprising mostly transplantation of human tumor cells into immuno-compromised mice10,13.
An alternative in vitro method was offered by Brent Reynolds and Sam Weiss who firstly reported the so-called neurosphere assay as a surrogate assay evaluating stem potential in neural cells14. Dontu and colleagues later confirmed the use of this assay for evaluation of stem cell potential in breast cells15,16. Here, human mammary cells were plated in different numbers in serum-free medium supplemented with epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), B-27 and heparin and cultured under non-adherent conditions for seven to ten days before sphere formation was scored by microscopy. Following this protocol with some adjustments in cell numbers, growth medium and supplements, several groups have explored in vitro stem cell potential from several cancer types such as breast17, brain18, pancreas19 and colon20 tumors. In ovarian carcinoma, we have recently reported feasibility of the spheres assay and compared its results to those collected in in vivo murine xenograft models10. We found that overexpression of the stem cell protein SOX2 enhanced both in vitro sphere formation as well as in vivo tumorigenicity of human ovarian carcinoma cells10. However, the frequency of sphere-initiating cells was higher than the frequency of tumor-initiating cells measured in vivo10 suggesting that either the sphere assay may lead to false positive results due to technical reasons or, alternatively, the in vivo assay may be inefficient and result in false negative results.
In this report, we analyze multi cell-based ovarian spheres assays in more detail, review the different protocols available in the literature and compare them to a single cell-based assay. We show that the single cell-based assay provides more accurate and reproducible results than multi cell-based assays, which can be highly influenced by the density of plated cells unless methylcellulose is added to the cultures to immobilize cells. However, also in single cell-based assays, in vitro sphere-initiating potential is observed at higher frequency than in vivo tumor-initiating potential.

<table><tbody><tr><td>Low-attachment plate</td><td>Corning</td><td>3474</td><td></td></tr><tr><td>MEGM</td><td>Lonza</td><td>CC-3151</td><td></td></tr><tr><td>Insulin</td><td>Lonza</td><td>CC-4136</td><td>SingleQuots&amp;trade; Kit</td></tr><tr><td>Hydrocortisone</td><td>Lonza</td><td>CC-4136</td><td>SingleQuots&amp;trade; Kit</td></tr><tr><td>EGF</td><td>Lonza</td><td>CC-4136</td><td>SingleQuots&amp;trade; Kit</td></tr><tr><td>EGF</td><td>Sigma</td><td>E9644</td><td>end concentration: 20 ng/ml</td></tr><tr><td>FGF</td><td>PeproTech</td><td>100-18B</td><td>end concentration: 20 ng/ml</td></tr><tr><td>B-27</td><td>Invitrogen/ Gibco</td><td>17504-044</td><td>end concentration: 1X</td></tr><tr><td>Heparin-Natrium-25000 IE</td><td>Ratiopharm</td><td>N68542.02</td><td>dilution 1:1,000</td></tr><tr><td>Pen/Strep</td><td>Gibco</td><td>15140-122</td><td></td></tr><tr><td>FCS</td><td>Gibco</td><td>10500-064</td><td></td></tr><tr><td>RPMI 1640</td><td>Gibco</td><td>21875-034</td><td></td></tr><tr><td>Trypsin-EDTA</td><td>Gibco</td><td>25300-054</td><td></td></tr><tr><td>Dulbecco&amp;rsquo;s PBS (1X)</td><td>Gibco</td><td>14190-094</td><td></td></tr><tr><td>Shield1</td><td>Clontech</td><td>632189</td><td>dilution 1:1,000</td></tr><tr><td>DMEM/F12</td><td>Gibco</td><td>21041-025</td><td></td></tr><tr><td>DMEM/F12 (powder)</td><td>Gibco</td><td>42400-010</td><td></td></tr><tr><td>Methyl cellulose</td><td>Sigma</td><td>M0387</td><td></td></tr><tr><td>Puromycin dihydrochloride</td><td>Applichem</td><td>A2856</td><td></td></tr><tr><td>Cell sorter</td><td>BD</td><td></td><td>Aria III cell sorter</td></tr><tr><td>FACS analyser</td><td>BD</td><td></td><td>Accuri c6 flow cytometer</td></tr><tr><td>Microscope</td><td>Olympus</td><td></td><td>IX50 Osiris</td></tr></tbody></table>

evaluation of stem cell properties in human ovarian carcinoma cells using multi and single cell-based spheres assays

Years of research indicates that ovarian cancers harbor a heterogeneous mixture of cells including a subpopulation of so-called &#8220;cancer stem cells&#8221; (CSCs) responsible for tumor initiation, maintenance and relapse following conventional chemotherapies. Identification of ovarian CSCs is therefore an important goal. A commonly used method to assess CSC potential in vitro is the spheres assay in which cells are plated under non-adherent culture conditions in serum-free medium supplemented with growth factors and sphere formation is scored after a few days. Here, we review currently available protocols for human ovarian cancer spheres assays and perform a side-by-side analysis between commonly used multi cell-based assays and a more accurate system based on single cell plating. Our results indicate that both multi cell-based as well as single cell-based spheres assays can be used to investigate sphere formation in vitro. The more laborious and expensive single cell-based assays are more suitable for functional assessment of individual cells and lead to overall more accurate results while multi cell-based assays can be strongly influenced by the density of plated cells and require titration experiments upfront. Methylcellulose supplementation to multi cell-based assays can be effectively used to reduce mechanical artifacts.

In conventional spheres assays, nearly 40% of RFP+ OVCAR-3 cells vs. 20% of RFP- cells gave rise to an individual tumor sphere in the primary spheres assay (Figure 4A). Moreover, spheres formed by RFP+ cells were larger in size than those formed by RFP- cells.
When plated in single cell-based assays, RFP+ cells also formed more spheres than RFP- cells, confirming the results above. However, there was a tendency towards generation of fewer spheres per plated in the single versu...

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Evaluation of Stem Cell Properties in Human Ovarian Carcinoma Cells Using Multi and Single Cell-based Spheres Assays

In vitro spheres assays are commonly used to identify cancer stem cells. Here we compare single with multi cell-based spheres assays. The more laborious single cell-based assays or methylcellulose supplementation give more accurate results while multi cell-based assays performed in liquid medium can be highly influenced by cell density.

Years of research indicates that ovarian cancers harbor a heterogeneous mixture of cells including a subpopulation of so-called &#8220;cancer stem ...

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Research

JoVE Journal

Medicine

9.5K Views.  University Hospital Basel. In vitro spheres assays are commonly used to identify cancer stem cells. Here we compare single with multi cell-based spheres assays. The more laborious single cell-based assays or methylcellulose supplementation give more accurate results while multi cell-based assays performed in liquid medium can be highly influenced by cell density.

Video: Evaluation of Stem Cell Properties in Human Ovarian Carcinoma Cells Using Multi and Single Cell-based Spheres Assays

Establishment of Cancer Stem Cell Cultures from Human Conventional Osteosarcoma

The current improvements in therapy against osteosarcoma (OS) have prolonged the lives of cancer patients, but the survival rate of five years remains poor when metastasis has occurred. The Cancer Stem Cell (CSC) theory holds that there is a subset of tumor cells within the tumor that have stem-like characteristics, including the capacity to maintain the tumor and to resist multidrug chemotherapy. Therefore, a better understanding of OS biology and pathogenesis is needed in order to advance the development of targeted therapies to eradicate this particular subset and to reduce morbidity and mortality among patients. Isolating CSCs, establishing cell cultures of CSCs, and studying their biology are important steps to improving our understanding of OS biology and pathogenesis. The establishment of human-derived OS-CSCs from biopsies of OS has been made possible using several methods, including the capacity to create 3-dimensional stem cell cultures under nonadherent conditions. Under these conditions, CSCs are able to create spherical floating colonies formed by daughter stem cells; these colonies are termed &#34;cellular spheres&#34;. Here, we describe a method to establish CSC cultures from primary cell cultures of conventional OS obtained from OS biopsies. We clearly describe the several passages required to isolate and characterize CSCs.

The presence of cancer stem cells (CSCs) in bone sarcomas has recently been linked to their pathogenesis. In this article, we present the isolation of CSCs from primary cell cultures obtained from human biopsies of conventional osteosarcoma (OS) using the ability of CSCs to grow under nonadherent conditions.

The current improvements in therapy against osteosarcoma (OS) have prolonged the lives of cancer patients, but the survival rate of five years remains ...

Cancer Research

In vitro Mesothelial Clearance Assay that Models the Early Steps of Ovarian Cancer Metastasis

Ovarian cancer is the fifth leading cause of cancer related deaths in the United States1. Despite a positive initial response to therapies, 70 to 90 percent of women with ovarian cancer develop new metastases, and the recurrence is often fatal2. It is, therefore, necessary to understand how secondary metastases arise in order to develop better treatments for intermediate and late stage ovarian cancer. Ovarian cancer metastasis occurs when malignant cells detach from the primary tumor site and disseminate throughout the peritoneal cavity. The disseminated cells can form multicellular clusters, or spheroids, that will either remain unattached, or implant onto organs within the peritoneal cavity3 (Figure 1, Movie 1). 
All of the organs within the peritoneal cavity are lined with a single, continuous, layer of mesothelial cells4-6 (Figure 2). However, mesothelial cells are absent from underneath peritoneal tumor masses, as revealed by electron micrograph studies of excised human tumor tissue sections3,5-7 (Figure 2). This suggests that mesothelial cells are excluded from underneath the tumor mass by an unknown process. 
Previous in vitro experiments demonstrated that primary ovarian cancer cells attach more efficiently to extracellular matrix than to mesothelial cells8, and more recent studies showed that primary peritoneal mesothelial cells actually provide a barrier to ovarian cancer cell adhesion and invasion (as compared to adhesion and invasion on substrates that were not covered with mesothelial cells)9,10. This would suggest that mesothelial cells act as a barrier against ovarian cancer metastasis. The cellular and molecular mechanisms by which ovarian cancer cells breach this barrier, and exclude the mesothelium have, until recently, remained unknown. 
Here we describe the methodology for an in vitro assay that models the interaction between ovarian cancer cell spheroids and mesothelial cells in vivo (Figure 3, Movie 2). Our protocol was adapted from previously described methods for analyzing ovarian tumor cell interactions with mesothelial monolayers8-16, and was first described in a report showing that ovarian tumor cells utilize an integrin &#x2013;dependent activation of myosin and traction force to promote the exclusion of the mesothelial cells from under a tumor spheroid17. This model takes advantage of time-lapse fluorescence microscopy to monitor the two cell populations in real time, providing spatial and temporal information on the interaction. The ovarian cancer cells express red fluorescent protein (RFP) while the mesothelial cells express green fluorescent protein (GFP). RFP-expressing ovarian cancer cell spheroids attach to the GFP-expressing mesothelial monolayer. The spheroids spread, invade, and force the mesothelial cells aside creating a hole in the monolayer. This hole is visualized as the negative space (black) in the GFP image. The area of the hole can then be measured to quantitatively analyze differences in clearance activity between control and experimental populations of ovarian cancer and/ or mesothelial cells. This assay requires only a small number of ovarian cancer cells (100 cells per spheroid X 20-30 spheroids per condition), so it is feasible to perform this assay using precious primary tumor cell samples. Furthermore, this assay can be easily adapted for high throughput screening.

In vitro Mesothelial Clearance Assay that Models the Early Steps of Ovarian Cancer Metastasis

The mesothelial clearance assay described here takes advantage of fluorescently labeled cells and time-lapse video microscopy to visualize and quantitatively measure the interactions of ovarian cancer multicellular spheroids and mesothelial cell monolayers. This assay models the early steps of ovarian cancer metastasis.

Ovarian cancer is the fifth leading cause of cancer related deaths in the United States1. Despite a positive initial response to therapies, 70 to 90 ...

Heterotypic Three-dimensional In Vitro Modeling of Stromal-Epithelial Interactions During Ovarian Cancer Initiation and Progression

Epithelial ovarian cancers (EOCs) are the leading cause of death from gynecological malignancy in Western societies. Despite advances in surgical treatments and improved platinum-based chemotherapies, there has been little improvement in EOC survival rates for more than four decades 1,2. Whilst stage I tumors have 5-year survival rates &gt;85%, survival rates for stage III/IV disease are &lt;40%. Thus, the high rates of mortality for EOC could be significantly decreased if tumors were detected at earlier, more treatable, stages 3-5. At present, the molecular genetic and biological basis of early stage disease development is poorly understood. More specifically, little is known about the role of the microenvironment during tumor initiation; but known risk factors for EOCs (e.g. age and parity) suggest that the microenvironment plays a key role in the early genesis of EOCs. We therefore developed three-dimensional heterotypic models of both the normal ovary and of early stage ovarian cancers. For the normal ovary, we co-cultured normal ovarian surface epithelial (IOSE) and normal stromal fibroblast (INOF)&nbsp;cells, immortalized by retrovrial transduction of the catalytic subunit of human telomerase holoenzyme (hTERT) to extend the lifespan of these cells in culture. To model the earliest stages of ovarian epithelial cell transformation, overexpression of the CMYC oncogene in IOSE cells, again co-cultured with INOF cells. These heterotypic models were used to investigate the effects of aging and senescence on the transformation and invasion of epithelial cells. Here we describe the methodological steps in development of these three-dimensional model; these methodologies aren't specific to the development of normal ovary and ovarian cancer tissues, and could be used to study other tissue types where stromal and epithelial cell interactions are a fundamental aspect of the tissue maintenance and disease development.

Heterotypic Three-dimensional In Vitro Modeling of Stromal-Epithelial Interactions During Ovarian Cancer Initiation and Progression

We describe methodologies for establishing in vitro heterotypic three-dimensional models comprising ovarian fibroblasts and normal ovarian surface or ovarian cancer epithelial cells. We discuss the use of these models to study stromal-epithelial interactions that occur during ovarian cancer development.

Epithelial ovarian cancers (EOCs) are the leading cause of death from gynecological malignancy in Western societies. Despite advances in surgical ...

Physiologic Patient Derived 3D Spheroids for Anti-neoplastic Drug Screening to Target Cancer Stem Cells

In this protocol, we outline the procedure for generation of tumor spheroids within 384-well hanging droplets to allow for high-throughput screening of anti-cancer therapeutics in a physiologically representative microenvironment. We outline the formation of patient derived cancer stem cell spheroids, as well as, the manipulation of these spheroids for thorough analysis following drug treatment. Specifically, we describe collection of spheroid morphology, proliferation, viability, drug toxicity, cell phenotype and cell localization data. This protocol focuses heavily on analysis techniques that are easily implemented using the 384-well hanging drop platform, making it ideal for high throughput drug screening. While we emphasize the importance of this model in ovarian cancer studies and cancer stem cell research, the 384-well platform is amenable to research of other cancer types and disease models, extending the utility of the platform to many fields. By improving the speed of personalized drug screening and the quality of screening results through easily implemented physiologically representative 3D cultures, this platform is predicted to aid in the development of new therapeutics and patient-specific treatment strategies, and thus have wide-reaching clinical impact.

This protocol describes generation of patient-derived spheroids, and downstream analysis including quantification of proliferation, cytotoxicity testing, flow cytometry, immunofluorescence staining and confocal imaging, in order to assess drug candidates&#8217; potential as anti-neoplastic therapeutics. This protocol supports precision medicine with identification of specific drugs for each patient and stage of disease.

In this protocol, we outline the procedure for generation of tumor spheroids within 384-well hanging droplets to allow for high-throughput screening of ...

Obtaining Cancer Stem Cell Spheres from Gynecological and Breast Cancer Tumors

Cancer stem cells (CSC) are a small population with self-renewal and plasticity which are responsible for tumorigenesis, resistance to treatment and recurrent disease. This population can be identified by surface markers, enzymatic activity and a functional profile. These approaches per se are limited, due to phenotypic heterogeneity and CSC plasticity. Here, we update the sphere-forming protocol to obtain CSC spheres from breast and gynecological cancers, assessing functional properties, CSC markers and protein expression. The spheres are obtained with single-cell seeding at low density in suspension culture, using a semi-solid methylcellulose medium to avoid migration and aggregates. This profitable protocol can be used in cancer cell lines but also in primary tumors. The tridimensional non-adherent suspension culture thought to mimic the tumor microenvironment, particularly the CSC-niche, is supplemented with epidermal growth factor and basic fibroblast growth factor to ensure CSC signaling. Aiming for robust identification of CSC, we propose a complementary approach, combining functional and phenotypic evaluation. Sphere-forming capacity, self-renewal and sphere projection area establish CSC functional properties. Additionally, characterization comprises flow cytometry evaluation of the markers, represented by CD44+/CD24- and CD133, and Western blot, considering ALDH. The presented protocol was also optimized for primary tumor samples, following a sample digestion procedure, useful for translational research.

The aim of this methodology is to identify cancer stem cells (CSC) in cancer cell lines and primary human tumor samples with the sphere-forming protocol, in a robust manner, using functional assays and phenotypic characterization with flow cytometry and Western blot.

Cancer stem cells (CSC) are a small population with self-renewal and plasticity which are responsible for tumorigenesis, resistance to treatment and ...

Isolation and Expansion of Human Glioblastoma Multiforme Tumor Cells Using the Neurosphere Assay

Stem-like cells have been isolated in tumors such as breast, lung, colon, prostate and brain. A critical issue in all these tumors, especially in glioblastoma mutliforme (GBM), is to identify and isolate tumor initiating cell population(s) to investigate their role in tumor formation, progression, and recurrence. Understanding tumor initiating cell populations will provide clues to finding effective therapeutic approaches for these tumors. The neurosphere assay (NSA) due to its simplicity and reproducibility has been used as the method of choice for isolation and propagation of many of this tumor cells. This protocol demonstrates the neurosphere culture method to isolate and expand stem-like cells in surgically resected human GBM tumor tissue. The procedures include an initial chemical digestion and mechanical dissociation of tumor tissue, and subsequently plating the resulting single cell suspension in NSA culture. After 7-10 days, primary neurospheres of 150-200 &mu;m in diameter can be observed and are ready for further passaging and expansion.

This video protocol demonstrates the isolation and expansion of stem like cells from surgically resected human glioblastoma mutliforme (GBM) tumor tissue using the neurosphere assay culture method.

Stem-like cells have been isolated in tumors such as breast, lung, colon, prostate and brain. A critical issue in all these tumors, especially in ...

Neuroscience

Assessment of Ovarian Cancer Spheroid Attachment and Invasion of Mesothelial Cells in Real Time

Ovarian cancers metastasize by shedding into the peritoneal fluid and dispersing to distal sites within the peritoneum. Monolayer cultures do not accurately model the behaviors of cancer cells within a nonadherent environment, as cancer cells inherently aggregate into multicellular structures which contribute to the metastatic process by attaching to and invading the peritoneal lining to form secondary tumors. To model this important stage of ovarian cancer metastasis, multicellular aggregates, or spheroids, can be generated from established ovarian cancer cell lines maintained under nonadherent conditions. To mimic the peritoneal microenvironment encountered by tumor cells in vivo, a spheroid-mesothelial co-culture model was established in which preformed spheroids are plated on top of a human mesothelial cell monolayer, formed over an extracellular matrix barrier. Methods were then developed using a real-time cell analyzer to conduct quantitative real time measurements of the invasive capacity of different ovarian cancer cell lines grown as spheroids. This approach allows for the continuous measurement of invasion over long periods of time, which has several advantages over traditional endpoint assays and more laborious real time microscopy image analyses. In short, this method enables a rapid, determination of factors which regulate the interactions between ovarian cancer spheroid cells invading through mesothelial and matrix barriers over time.

Ovarian cancer cell invasion into the mesothelial lining of the peritoneum is a dynamic process over time. Utilizing a real time analyzer, the invasive capacity of ovarian cancer cells in a spheroid-mesothelial cell co-culture model can be quantified over prolonged time periods, providing insights into factors regulating the metastatic process.

Ovarian cancers metastasize by shedding into the peritoneal fluid and dispersing to distal sites within the peritoneum. Monolayer cultures do not ...

Enrichment for Chemoresistant Ovarian Cancer Stem Cells from Human Cell Lines

Cancer stem cells (CSCs) are defined as a subset of slow cycling and undifferentiated cells that divide asymmetrically to generate highly proliferative, invasive, and chemoresistant tumor cells. Therefore, CSCs are an attractive population of cells to target therapeutically. CSCs are predicted to contribute to a number of types of malignancies including those in the blood, brain, lung, gastrointestinal tract, prostate, and ovary. Isolating and enriching a tumor cell population for CSCs will enable researchers to study the properties, genetics, and therapeutic response of CSCs. We generated a protocol that reproducibly enriches for ovarian cancer CSCs from ovarian cancer cell lines (SKOV3 and OVCA429). Cell lines are treated with 20 &#181;M cisplatin for 3 days. Surviving cells are isolated and cultured in a serum-free stem cell media containing cytokines and growth factors. We demonstrate an enrichment of these purified CSCs by analyzing the isolated cells for known stem cell markers Oct4, Nanog, and Prom1 (CD133) and cell surface expression of CD177 and CD133. The CSCs exhibit increased chemoresistance. This method for isolation of CSCs is a useful tool for studying the role of CSCs in chemoresistance and tumor relapse.

Cancer stem cells (CSCs) are&#160;implicated in tumor relapse due to chemoresistance. We have optimized a protocol for selection and expansion of CSCs from ovarian cancer cell lines. By treating cells with the chemotherapeutic cisplatin and culturing&#160;in a stem cell promoting media we enrich for non-adherent CSC cultures.

Cancer stem cells (CSCs) are defined as a subset of slow cycling and undifferentiated cells that divide asymmetrically to generate highly proliferative, ...

Mammosphere Formation Assay from Human Breast Cancer Tissues and Cell Lines

Similar to healthy tissues, many blood and solid malignancies are now thought to be organised hierarchically, with a subset of stem-like cancer cells that self-renew while giving rise to more differentiated progeny. Understanding and targeting these cancer stem cells in breast cancer, which may possess enhanced chemo- and radio-resistance compared to the non-stem tumor bulk, has become an important research area. Markers including CD44, CD24, and ALDH activity can be assessed using fluorescence activated cell sorting (FACS) to prospectively isolate cells that display enhanced tumorigenicity when implanted into immunocompromised mice: the mammosphere assay has also become widely used for its ability to retrospectively identify sphere-forming cells that develop from single stem cell-like clones. Here we outline approaches for the appropriate culturing of mammospheres from cell lines or primary patient samples, their passaging, and calculations to estimate sphere forming efficiency (SFE). First we discuss key considerations and pitfalls in the appropriate planning and interpretation of mammosphere experiments.

Floating mammosphere assays can investigate the subset of stem-like breast cancer cells that survive in suspension conditions and show enhanced tumorigenesis when implanted into mice. This protocol provides a convenient in vitro measure of sphere-forming ability, a proxy for in vivo tumorigenesis, while facilitating analysis of the stem-associated transcriptional landscape.

Similar to healthy tissues, many blood and solid malignancies are now thought to be organised hierarchically, with a subset of stem-like cancer cells that ...

Studying Pancreatic Cancer Stem Cell Characteristics for Developing New Treatment Strategies

Pancreatic ductal adenocarcinoma (PDAC) contains a subset of exclusively tumorigenic cancer stem cells (CSCs) which have been shown to drive tumor initiation, metastasis and resistance to radio- and chemotherapy. Here we describe a specific methodology for culturing primary human pancreatic CSCs as tumor spheres in anchorage-independent conditions. Cells are grown in serum-free, non-adherent conditions in order to enrich for CSCs while their more differentiated progenies do not survive and proliferate during the initial phase following seeding of single cells. This assay can be used to estimate the percentage of CSCs present in a population of tumor cells. Both size (which can range from 35 to 250 micrometers) and number of tumor spheres formed represents CSC activity harbored in either bulk populations of cultured cancer cells or freshly harvested and digested tumors 1,2. Using this assay, we recently found that metformin selectively ablates pancreatic CSCs; a finding that was subsequently further corroborated by demonstrating diminished expression of pluripotency-associated genes/surface markers and reduced in vivo tumorigenicity of metformin-treated cells. As the final step for preclinical development we treated mice bearing established tumors with metformin and found significantly prolonged survival. Clinical studies testing the use of metformin in patients with PDAC are currently underway (e.g., NCT01210911, NCT01167738, and NCT01488552). Mechanistically, we found that metformin induces a fatal energy crisis in CSCs by enhancing reactive oxygen species (ROS) production and reducing mitochondrial transmembrane potential. In contrast, non-CSCs were not eliminated by metformin treatment, but rather underwent reversible cell cycle arrest. Therefore, our study serves as a successful example for the potential of in vitro sphere formation as a screening tool to identify compounds that potentially target CSCs, but this technique will require further in vitro and in vivo validation to eliminate false discoveries.

Pancreatic cancer stem cells (CSCs) can be expanded in vitro using the anchorage-independent sphere culture technique, which represents a powerful tool to study CSC biology and can serve as the first step to develop novel CSC-targeting therapies. Here the methodology for expanding, analyzing and targeting of pancreatic CSCs is provided.

Evaluation of Stem Cell Properties in Human Ovarian Carcinoma Cells Using Multi and Single Cell-based Spheres Assays

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