The authors acknowledge funding from the National Institutes of Health R21CA182333.

1. Preparation of Polymeric Aqueous Two Phase System (ATPS)
<ol>
	<li>Weigh 0.5 g of polyethylene glycol (PEG) (MW: 35,000) and add it to 9.5 ml of complete growth medium in a sterile 15 ml conical to prepare 10 ml of 5% (w/v) aqueous PEG phase. 
	Note: Adding half of the medium to the conical first followed by adding the polymer and then the remaining amount of medium minimizes adhesion of the polymer to the conical walls and helps the polymer dissolve faster.</li>
	<li>Weigh 0.128 g of dextran (DEX) (MW: 500,000) and add it to 0.872 ml of complete growth medium in a sterile 1.5 ml microcentrifuge tube to prepare 1 ml of 12.8% (w/v) aqueous DEX phase.</li>
	<li>Vortex both solutions for about 1 min to dissolve the polymers in the medium.</li>
	<li>Keep both solutions in a water bath at 37 &#176;C for 1 hr to ensure dissolution and homogenous mixtures. Keep the caps above the water level to avoid the possibility of contamination of solutions from the bath water.</li>
	<li>Load the PEG phase solution into a sterile, plastic syringe and pass it through a syringe filter of 0.2 &#181;m pore size to remove impurities. 
	Note: Fill the syringe with the PEG solution, place it in the insert of the filter on top of a conical tube and using force, slowly push the solution through the filter. It is normal to experience resistance against movement of the syringe plunger. Minor loss of the polymer solution occurs as some of the solution will remain in the filter, but the polymer concentration will not change.</li>
	<li>Pipette 10 &#181;l of the DEX phase solution and dilute it in 10 &#181;l of medium in a separate tube to result in 6.4% (w/v) DEX phase solution. Aspirate 100 &#181;l of the PEG phase solution and dispense it into a Petri dish.
	<ol>
		<li>Dispense 0.5 &#181;l of the 6.4% (w/v) DEX phase solution into the PEG phase solution. Visually confirm successful ATPS formation by observing a DEX drop under a microscope. The drop boundary should remain visible, indicating presence of two stable, separate aqueous phases.</li>
	</ol>
	</li>
	<li>Store the stock aqueous PEG and DEX phase solutions in 4 &#176;C until use. 
	Note: It is recommended that polymer solutions are prepared fresh prior to each experiment and used within 24 hr of storage.</li>
</ol>
2. Preparation for Printing of Cancer Cell Spheroids
<ol>
	<li>Grow cancer cells of interest (e.g., MDA-MB-157 breast cancer cells) to a 90%-100% confluent monolayer. For MDA-MB-157 cells, use a medium composed of DMEM containing 10% FBS, 1% glutamine, and 1% antibiotic.
	<ol>
		<li>Harvest cells using a cell dissociation buffer (according to manufacturer&#8217;s protocol) and load the suspension into a 15 ml conical. Centrifuge it for 5 min at 173.3 x g, remove supernatant, and resuspend cells in 1 ml of complete growth medium.</li>
	</ol>
	</li>
	<li>Load cells onto a hemocytometer and count them to calculate the required number of cells for a desired spheroid cell density. A confluent monolayer of MDA-MB-157 cells grown in a T75 flask usually gives ~7 x 106 cells. 
	Note: Required cell density for a drop volume to generate a single spheroid will depend on the cell type.22 For example, a density of 1.5 x 104 or larger for MDA-MB-157 cells is recommended per 0.3 &#181;l DEX phase drop to ensure formation of a single spheroid.</li>
	<li>Centrifuge cells for a second time for 5 min at 173.3 x g and resuspend them in an appropriate volume of growth medium to concentrate the suspension to a desired cell density. 
	Note: For example if 7 x 106 cancer cells were harvested, the total volume of cell suspension required to form a spheroid of 1.5 x 104 cell density in a 0.3 &#181;l DEX phase drop will be 140 &#181;l. However due to dilution with the DEX phase solution in the next step, only use 70 &#181;l of cell culture medium to resuspend cells.</li>
	<li>Add to the resulting cell suspension an equal volume of the 12.8% (w/v) aqueous DEX phase solution prepared in 1.2. For the example of 1.5 x 104 cell density spheroid, 70 &#181;l of the DEX phase solution is added to 70 &#181;l of cell suspension.</li>
	<li>Thoroughly mix the cell suspension to ensure uniform distribution of cells and mixing of DEX solution. Pipetting up and down should be done gently to prevent bubble formation.</li>
</ol>
3. Preparation for Printing of Co-cultured Spheroids
<ol>
	<li>Grow cancer cells (e.g., MDA-MB-157 human breast cancer cells) and support cells (e.g., human fibroblasts) to a 90%-100% confluent monolayer. Harvest each cell type using a cell dissociation buffer (according to manufacturer&#8217;s protocol).
	<ol>
		<li>Load each suspension into a 15 ml conical, centrifuge them for 5 min at 173.3 x g, and aspirate supernatant from each conical. Resuspend cells of each conical in 1 ml of complete growth medium. 
		Note: Fluorescent dyes such as Calcein AM (live cell stain) and nuclear dyes (Hoechst) can be used to distinguish the two cell types.</li>
	</ol>
	</li>
	<li>Load each cell type separately onto a hemocytometer and count them to calculate the required number of each cell type for a desired ratio of cancer cells to supporting cells in co-cultured spheroids. Confluent monolayers of MDA-MB-157 cells and fibroblasts grown in T75 flasks usually give ~7 x 106 and ~6 x 106 cells, respectively.</li>
	<li>Add the correct volume from the suspension of supporting cells to cancer cells suspension to give a desired ratio of the number of two cell types. For example, use a ratio of 50 cancer cells to 1 fibroblast cell.</li>
	<li>Centrifuge the conical containing the mixed cell suspension for 5 min at 173.3 x g and resuspend cells in an appropriate volume to result in final density comprising of equal volumes of growth medium and the 12.8% (w/v) aqueous DEX phase solution (prepared in 1.2).</li>
	<li>Gently pipette the resulting cell suspension up and down to ensure homogeneity of the suspension.</li>
</ol>
4. Printing of Tumor Spheroids into a 96-well Plate
<ol>
	<li>One day prior to experiments, coat non-treated, round-bottom 96-well plates with 1% (w/v) Pluronic at 37 &#176;C for 24 hr. This coating prevents cell attachment over the culture period.</li>
	<li>Dispense 50 &#181;l of the filtered 5% (w/v) aqueous PEG phase into each well of a 96-well plate (destination plate).</li>
	<li>Using a pipette, mix the cell suspension (prepared in step 2 or step 3 for mono- and co-culture, respectively) and add 20 &#181;l of the suspension to every other well from one column of a 384-well plate (source plate).</li>
	<li>Turn on the liquid handler and &#8220;home&#8221; the pipetting head to register coordinates. Then compile a previously defined protocol (below in 4.6) to ensure labware and parameters are defined correctly. This &#8220;homing&#8221; step may be different for different liquid handlers. 
	Note: The flow of the protocol, shown step-by-step below in 4.6, will be similar regardless of the robotic liquid handler used; however, the programming interface may look different due to the use of different software.</li>
	<li>Place the source plate, the destination plate, and pipette tip boxes at defined positions on the workstation of the liquid handler as shown in Figure 1.</li>
	<li>Execute the protocol that includes the following steps:
	<ol>
		<li>Load one column of barrels from the pipetting head of the liquid handler with mixing pipette tips (8 tips) from the workstation (Figure 1).</li>
		<li>Mix the cell suspension in wells of the source plate (Figure 1). Select a mixing volume smaller than the cell suspension volume in wells to avoid bubble formation.</li>
		<li>Eject tips into an empty waste tips box (Figure 1).</li>
		<li>Load one column of barrels from the pipetting head with 10 &#181;l dispensing pipette tips (Figure 1).</li>
		<li>Aspirate 0.3 &#181;l of the cell suspension from the source plate (Figure 1) into each pipette tip.</li>
		<li>Dispense the cell suspension into wells of one column of the destination plate (Figure 1). Use a dispense height of 0.5 mm and a dispense flow rate of smaller than 1 &#181;l/sec.</li>
		<li>Repeat steps 4.6.1 through 4.6.6 until the column-by-column printing into the entire destination plate is complete.</li>
	</ol>
	</li>
	<li>Carefully remove the destination plate from the workstation surface and place it in a humid incubator at 37 &#176;C and 5% CO2. Maintain the plate horizontal when carrying it into the incubator to avoid disrupting of DEX phase drops containing cells.</li>
	<li>Incubate the plate for 24 hr to allow aggregation of cells into a spheroid within the DEX phase drop.</li>
</ol>
5. Drug Treatment of Cancer Cell Spheroids
Note that the following protocol is for a 4-day drug treatment and includes a renewal with fresh drug after day 2. It can be modified for other treatment periods.
<ol>
	<li>Visually confirm spheroid formation in 96-well plates after 24 hr. If needed, image wells for measurement of size of spheroids by averaging the smallest and largest diameters of each spheroid.</li>
	<li>Prepare the stock solution of a desired drug by dissolving it in a solvent recommended by the manufacturer at a predetermined solubility concentration. For example, dissolve cisplatin in water at 2 mg/ml. 
	Note: Protect the stock solution of the drug from light if the drug is light-sensitive.</li>
	<li>Using the serial dilution technique, prepare diluted drug concentrations with cell culture medium from the stock solution prepared in the previous step. Each dilution should be made twice the desired concentration. Dilution ratios will vary depending on the starting stock concentration and desired working concentrations.</li>
	<li>Add 50 &#181;l of drug solution prepared in the previous step to each well. This can be done robotically or by manual pipetting. 
	Note: Each drug concentration will be diluted in half to the desired concentration by the 50 &#181;l aqueous PEG phase already in each well.
	<ol>
		<li>Use spheroids from two columns of a 96-well plate (n=16) for each concentration.</li>
		<li>In control wells, add only 50 &#181;l of fresh culture medium to the existing 50 &#181;l of the aqueous PEG phase.</li>
	</ol>
	</li>
	<li>Incubate spheroids with the drug for 48 hr at 37 &#176;C and 5% CO2, protected from light.</li>
	<li>After 48 hr of incubation, prepare fresh dilutions of the drug at desired concentrations and renew drug by adding 50 &#181;l of fresh drug solution to each well. 
	Note: The wells already contain the desired drug concentration from the first drug treatment. Therefore in this renewal phase, each concentration is prepared at the desired concentration since no dilution will occur.</li>
	<li>Incubate spheroids with the drug for another 48 hr at 37 &#176;C and 5% CO2, protected from light.</li>
</ol>
6. Analysis of Cellular Viability in Spheroids
<ol>
	<li>After 48 hr of incubation with renewed drug (i.e., total time of treatment of spheroids with a drug is 4 days), measure the total volume of medium in one well by manual pipetting. 
	Note: Typical volume in one well is ~140 &#181;l (a small decrease occurs due to evaporation).</li>
	<li>Calculate the volume of cell viability reagent (e.g., PrestoBlue) as 10% concentration of the total well volume. Add this volume of cell viability reagent to each well. 
	Note: With an existing media volume of 140 &#181;l in a well, a volume of 15.6 &#181;l is required to give a 10% concentration of the total well. This is calculated by dividing the existing media volume by 9 (140 &#181;l / 9 = 15.6 &#181;l).</li>
	<li>Incubate the plate with the cell viability reagent added to each well for 6 hr at 37 &#176;C, protected from light.</li>
	<li>Place the plate in a micro-plate reader and read the fluorescence signal at 560 nm and 590 nm excitation and emission wavelengths, respectively.</li>
	<li>Calculate the percent viability of cells in spheroids by normalizing the fluorescent signal from treated wells to that of control wells after averaging the values from the same treatment conditions.</li>
</ol>

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S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Human+mammary+fibroblasts+stimulate+invasion+of+breast+cancer+cells+in+a+three-dimensional+culture+and+increase+stroma+development+in+mouse+xenografts.">Human mammary fibroblasts stimulate invasion of breast cancer cells in a three-dimensional culture and increase stroma development in mouse xenografts.</a> BMC Cancer. 10, 444 (2010).</li><li>Ozdemir, B. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Depletion+of+carcinoma-associated+fibroblasts+and+fibrosis+induces+immunosuppression+and+accelerates+pancreas+cancer+with+reduced+survival.">Depletion of carcinoma-associated fibroblasts and fibrosis induces immunosuppression and accelerates pancreas cancer with reduced survival.</a> Cancer Cell. 25, 719-734 (2014).</li><li>Hsiao, A. Y., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+system+for+formation+of+PC-3+prostate+cancer+co-culture+spheroids.">Microfluidic system for formation of PC-3 prostate cancer co-culture spheroids.</a> Biomaterials. 30, 3020-3027 (2009).</li><li>Friedrich, J., Seidel, C., Ebner, R., Kunz-Schughart, L. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spheroid-based+drug+screen:+considerations+and+practical+approach.">Spheroid-based drug screen: considerations and practical approach.</a> Nat. Protoc. 4, 309-324 (2009).</li><li>Weigelt, B., Bissell, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Unraveling+the+microenvironmental+influences+on+the+normal+mammary+gland+and+breast+cancer.">Unraveling the microenvironmental influences on the normal mammary gland and breast cancer.</a> Semin. Cancer Biol. 18, 311-321 (2008).</li><li>Mueller, M. M., Fusenig, N. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Friends+or+foes+-+bipolar+effects+of+the+tumour+stroma+in+cancer.">Friends or foes - bipolar effects of the tumour stroma in cancer.</a> Nature Reviews Cance. 4, 839-849 (2004).</li><li>Bissell, M. J., Radisky, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Putting+tumours+in+context.">Putting tumours in context.</a> Nat. Rev. Cancer. 1, 46-54 (2001).</li></ol>

The authors have nothing to disclose.

Spheroids present a realistic model to better understand tumor physiology and drug efficacy and provide a useful tool for anti-cancer drug discovery. Such applications would greatly benefit from simple spheroid generation and maintenance techniques that only require standard labware, liquid handling tools and screening equipment. The use of an aqueous two-phase system to spontaneously aggregate cancer cells within the drop phase allows efficient production and maintenance of spheroids with robotic liquid handlers, and <e...

Cell-based assays provide an important tool for the development and discovery of new anti-cancer drugs.1,2 Historically, monolayer cultures of cancer cells have been employed to investigate the efficacy of candidate compounds against particular types of cancer cells. The ease of maintenance of monolayer cultures in standard culture plates, the compatibility of standard plates with commercial robotic tools for addition of reagents, and with screening equipment for downstream analysis of cellular responses to chemical compounds are the major benefits that render 2D cultures an attractive tool for drug testing.3 Unfortunately, monolayer cell assays often fail to predict the efficacy of compounds in vivo, making drug development and discovery an extremely costly process.4,5 Despite significant investment and effort by pharmaceutical companies and academic units, only ~1% of anti-cancer drugs in clinical trials were approved by the FDA over the past two decades.6 Disparity between 2D cultures and the complex 3D environment of cancer cells in vivo is a major shortcoming of monolayer culture systems.7 Therefore, screening of candidate compounds against tumor cells in a setting that more closely resembles the 3D tumor environment may expedite development of novel chemotherapy drugs.8
Cancer cell spheroids present a relevant 3D tumor model in vitro.9,10 Spheroids are compact clusters that form through spontaneous or induced assembly of cancer cells on non-adherent surfaces or in suspension using techniques such as spinner flask, liquid overlay, microfabricated micro-well arrays, microfluidics, and hanging drops.11-16 Spheroids mimic key features of solid tumors including geometry and limited transport of oxygen, nutrients, and drug compounds into the central zone; hence, they more closely regenerate drug response of solid tumors compared to monolayer cultures.17-19 Despite this marked benefit, spheroids are not routinely used for screening of chemical compounds against cancer cells. Difficulty of producing uniform sized spheroids in a standard high throughput setting that is compatible with commercially available robotics and screening/imaging tools impedes incorporation of spheroid culture into drug development pipeline. Although custom materials and plates have recently become commercially available to address this need, cost considerations deter their widespread use.
Two major techniques with the capability of producing consistent sized spheroids in high throughput use a new hanging drop platform and microfabricated micro-wells.13,16,20 However, both approaches require special plates and devices that are expensive to fabricate and inconvenient for endpoint users in core research centers and pharmaceutical industries where the most major efforts for the discovery of new anti-cancer drugs are made. Despite some improvements in the stability of cell-containing drops with a recent design of hanging drop plates, only every other hole of the plate is still used during culture to avoid spreading/merging of drops.16 This significantly decreases experimental throughput. Drug addition and renewal is difficult with manual or robotic pipetting and spheroids need to be transferred into a standard plate for biochemical analysis because this plate configuration is not readily compatible with conventional screening equipment such as plate readers.21 Micro-wells fabricated using soft lithography also allow controlled size spheroid production.13,20 However, incompatibility of this platform with standard pipetting tools prevents treating of individual spheroids with different drug compounds/concentrations, exposing all spheroids to a single treatment condition. Thus, this method is not appropriate for high throughput compound screening that requires simultaneous testing of multiple compounds/concentrations.
To overcome these obstacles, a new technique for high throughput production of consistently sized cancer cell spheroids in standard 96-well plates has been developed.22,23 The approach is based on a polymeric aqueous two-phase system (ATPS) with polyethylene glycol (PEG) and dextran (DEX) as phase-forming polymers.24 ATPSs have recently been utilized in a variety of novel cell biological applications to enable cell micropatterning and localized delivery of biological reagents to cells in highly aqueous media.25-32 To form a spheroid, cancer cells are mixed with the aqueous DEX phase and a sub-microliter drop of the resulting suspension is pipetted into a well containing the immersion aqueous PEG phase solution. The drop remains immiscible from the immersion phase and confines cells to facilitate formation of a spheroid. Importantly, the highly aqueous immersion phase provides nutrients to cells of the spheroid and minimizes the well-known problem of media evaporation common to some other assays that causes changes in media osmolality and fluctuations of drug concentrations. This technique enables spheroid production and drug treatment only using commercially-available reagents and pipetting tools in standard 96-well plates. Importantly, analysis of cellular responses of spheroids is performed in the same plate using standard biochemical assays and plate readers. The ease of working with ATPS and adaptability of the approach to robotic liquid handling makes high throughput generation of both mono-culture and co-culture spheroids a straightforward laboratory technique. This new approach will be a major step forward toward integration of cancer cell spheroids into drug development and discovery processes with improved testing throughput and cost-effectiveness (increasing numbers of tested compounds and reduced reagent consumption) and efficiency (reducing hands-on time).
A detailed protocol for robotic production of cancer cell spheroids in 96-well plates using the ATPS approach is described below. In addition, details of drug treatment of resulting spheroids and downstream analysis of cellular responses using a commercial biochemical assay are presented.

<table><tbody><tr><td colspan="4">&lt;strong&gt;Reagents and Consumables&lt;/strong&gt;</td></tr><tr><td>Polyethylene glycol, MW: 35,000</td><td>Sigma-Aldrich</td><td>94646</td><td></td></tr><tr><td>Dextran, MW: 500,000</td><td>Pharmacosmos</td><td>5510 0500 9007</td><td></td></tr><tr><td>Dulbecco&#039;s Modified Eagle Medium (DMEM)</td><td>Sigma-Aldrich</td><td>D6429</td><td></td></tr><tr><td>Fetal Bovine Serum</td><td>Sigma-Aldrich</td><td>12306C</td><td></td></tr><tr><td>Glutamine</td><td>Life Technologies</td><td>35050-061</td><td></td></tr><tr><td>Antibiotic</td><td>Life Technologies</td><td>15240-062</td><td></td></tr><tr><td>Clacein AM</td><td>Life Technologies</td><td>C3100MP</td><td></td></tr><tr><td>Hoechst</td><td>Life Technologies</td><td>33342</td><td></td></tr><tr><td>Cisplatin</td><td>Spectrum Chemicals</td><td>15663-27-1</td><td></td></tr><tr><td>PrestoBlue</td><td>Life Technologies</td><td>A-13261</td><td></td></tr><tr><td>Pluronic F-108</td><td>Sigma Aldrich</td><td>542342</td><td></td></tr><tr><td>Disposable Tips (10 &amp;micro;l)</td><td>Fluotics</td><td>C-P10V11.ST</td><td></td></tr><tr><td>Disposable Tips (70 &amp;micro;l)</td><td>Fluotics</td><td>C-P70V11.ST</td><td></td></tr><tr><td>Round-bottom 96-well plates</td><td>Nunc</td><td>268200</td><td></td></tr><tr><td colspan="4">&lt;strong&gt;Equipment&lt;/strong&gt;</td></tr><tr><td>Liquid Handler</td><td>Agilent Technologies</td><td>SRT Bravo</td><td></td></tr><tr><td>Microplate Reader</td><td>Biotek Instruments</td><td>Synergy H1M</td><td></td></tr></tbody></table>

robotic production of cancer cell spheroids with an aqueous two-phase system for drug testing

Cancer cell spheroids present a relevant in vitro model of avascular tumors for anti-cancer drug testing applications. A detailed protocol for producing both mono-culture and co-culture spheroids in a high throughput 96-well plate format is described in this work. This approach utilizes an aqueous two-phase system to confine cells into a drop of the denser aqueous phase immersed within the second aqueous phase. The drop rests on the well surface and keeps cells in close proximity to form a single spheroid. This technology has been adapted to a robotic liquid handler to produce size-controlled spheroids and expedite the process of spheroid production for compound screening applications. Spheroids treated with a clinically-used drug show reduced cell viability with increase in the drug dose. The use of a standard micro-well plate for spheroid generation makes it straightforward to analyze viability of cancer cells of drug-treated spheroids with a micro-plate reader. This technology is straightforward to implement both robotically and with other liquid handling tools such as manual pipettes.

The workstation of the robotic liquid handler is shown in Figure 1. The pipetting head and all stations used in the robotic printing of spheroids in section 4.6 are labeled. The image shows the use of two different stations for tip boxes (one set of tips for mixing and the second set for aspirating/dispensing of cell suspension&#8211;aqueous DEX phase mixture). The entire setup is housed within a standard biological safety cabinet to maintain sterility. Figure 2 depicts a schematic of th...

Watch this Scientific Journal Video about Robotic Production of Cancer Cell Spheroids with an Aqueous Two-phase System for Drug Testing at JoVE.com

Robotic Production of Cancer Cell Spheroids with an Aqueous Two-phase System for Drug Testing

A protocol for robotic printing of cancer cell spheroids in a high throughput 96-well plate format using an aqueous two-phase system is presented.

Cancer cell spheroids present a relevant in vitro model of avascular tumors for anti-cancer drug testing applications. A detailed protocol for producing ...

robotic-production-cancer-cell-spheroids-with-an-aqueous-two-phase

Research

JoVE Journal

Bioengineering

8.9K Views.  The University of Akron. A protocol for robotic printing of cancer cell spheroids in a high throughput 96-well plate format using an aqueous two-phase system is presented.

Video: Robotic Production of Cancer Cell Spheroids with an Aqueous Two-phase System for Drug Testing

Generation of High-Throughput Three-Dimensional Tumor Spheroids for Drug Screening

Cancer cells have routinely been cultured in two dimensions (2D) on a plastic surface. This technique, however, lacks the true environment a tumor mass is exposed to in vivo. Solid tumors grow not as a sheet attached to plastic, but instead as a collection of clonal cells in a three-dimensional (3D) space interacting with their neighbors, and with distinct spatial properties such as the disruption of normal cellular polarity. These interactions cause 3D-cultured cells to acquire morphological and cellular characteristics which are more relevant to in vivo tumors. Additionally, a tumor mass is in direct contact with other cell types such as stromal and immune cells, as well as the extracellular matrix from all other cell types. The matrix deposited is comprised of macromolecules such as collagen and fibronectin.
In an attempt to increase the translation of research findings in oncology from bench to bedside, many groups have started to investigate the use of 3D model systems in their drug development strategies. These systems are thought to be more physiologically relevant because they attempt to recapitulate the complex and heterogeneous environment of a tumor. These systems, however, can be quite complex, and, although amenable to growth in 96-well formats, and some now even in 384, they offer few choices for large-scale growth and screening. This observed gap has led to the development of the methods described here in detail to culture tumor spheroids in a high-throughput capacity in 1536-well plates. These methods represent a compromise to the highly complex matrix-based systems, which are difficult to screen, and conventional 2D assays. A variety of cancer cell lines harboring different genetic mutations are successfully screened, examining compound efficacy by using a curated library of compounds targeting the Mitogen-Activated Protein Kinase or MAPK pathway. The spheroid culture responses are then compared to the response of cells grown in 2D, and differential activities are reported. These methods provide a unique protocol for testing compound activity in a high-throughput 3D setting.

Across a wide variety of disease indications, more physiologically relevant models are being developed and implemented into drug discovery programs. The new model system described here demonstrates how three-dimensional tumor spheroids can be cultured and screened in a high-throughput 1536-well plate-based system to search for new oncology drugs.

Cancer cells have routinely been cultured in two dimensions (2D) on a plastic surface. This technique, however, lacks the true environment a tumor mass is ...

Cancer Research

Analysis of Cancer Cell Invasion and Anti-metastatic Drug Screening Using Hydrogel Micro-chamber Array (HMCA)-based Plates

Cancer metastasis is known to cause 90% of cancer lethality. Metastasis is a multistage process which initiates with the penetration/invasion of tumor cells into neighboring tissue. Thus, invasion is a crucial step in metastasis, making the invasion process research and development of anti-metastatic drugs, highly significant. To address this demand, there is a need to develop 3D in vitro models which imitate the architecture of solid tumors and their microenvironment most closely to in vivo state on one hand, but at the same time be reproducible, robust and suitable for high yield and high content measurements. Currently, most invasion assays lean on sophisticated microfluidic technologies which are adequate for research but not for high volume drug screening. Other assays using plate-based devices with isolated individual spheroids in each well are material consuming and have low sample size per condition. The goal of the current protocol is to provide a simple and reproducible biomimetic 3D cell-based system for the analysis of invasion capacity in large populations of tumor spheroids. We developed a 3D model for invasion assay based on HMCA imaging plate for the research of tumor invasion and anti-metastatic drug discovery. This device enables the production of numerous uniform spheroids per well (high sample size per condition) surrounded by ECM components, while continuously and simultaneously observing and measuring the spheroids at single-element resolution for medium throughput screening of anti-metastatic drugs. This platform is presented here by the production of HeLa and MCF7 spheroids for exemplifying single cell and collective invasion. We compare the influence of the ECM component hyaluronic acid (HA) on the invasive capacity of collagen surrounding HeLa spheroids. Finally, we introduce Fisetin (invasion inhibitor) to HeLa spheroids and nitric oxide (NO) (invasion activator) to MCF7 spheroids. The results are analyzed by in-house software which enables semi-automatic, simple and fast analysis which facilitates multi-parameter examination.

Analysis of Cancer Cell Invasion and Anti-metastatic Drug Screening Using Hydrogel Micro-chamber Array HMCA-based Plates

A HMCA-based imaging plate is presented for invasion assay performance. This plate facilitates the formation of three-dimensional (3D) tumor spheroids and the measurement of cancer cell invasion into the extracellular matrix (ECM). The invasion assay quantification is achieved by semi-automatic analysis.

Cancer metastasis is known to cause 90% of cancer lethality. Metastasis is a multistage process which initiates with the penetration/invasion of tumor ...

A Spheroid Killing Assay by CAR T Cells

Immunotherapy has become a field of growing interest in the fight against cancer otherwise untreatable. Among all immunotherapeutic methods, chimeric antigen receptor (CAR) redirected T cells obtained the most spectacular results, in particular with pediatric B-acute lymphoblastic leukemia (B-ALL). Classical validation methods of CAR T cells rely on the use of specificity and functionality assays of the CAR T cells against target cells in suspension and in xenograft models. Unfortunately, observations made in vitro are often decoupled from results obtained in vivo and a lot of effort and animals could be spared by adding another step: the use of 3D culture. The production of spheroids out of potential target cells that mimic the 3D structure of the tumor cells when they are engrafted into the animal model represents an ideal alternative. Here, we report an affordable, reliable and easy method to produce spheroids from a transduced colorectal cell line as a validation tool for adoptive cell therapy (exemplified here by CD19 CAR T cells). This method is coupled with an advanced live imaging system that can follow spheroid growth, effector cells cytotoxicity and tumor cell apoptosis.

This protocol is designed to assess immunotherapeutic redirected T-cell (CAR T-cell) cytotoxicity against 3D structured cancerous cells (spheroids) in real time.

Immunotherapy has become a field of growing interest in the fight against cancer otherwise untreatable. Among all immunotherapeutic methods, chimeric ...

Production of Large Numbers of Size-controlled Tumor Spheroids Using Microwell Plates

Tumor spheroids are increasingly recognized as an important in vitro model for the behavior of tumor cells in three dimensions. More physiologically relevant than conventional adherent-sheet cultures, they more accurately recapitulate the complexity and interactions present in real tumors. In order to harness this model to better assess tumor biology, or the efficacy of novel therapeutic agents, it is necessary to be able to generate spheroids reproducibly, in a controlled manner and in significant numbers.
The AggreWell system consists of a high-density array of pyramid-shaped microwells, into which a suspension of single cells is centrifuged. The numbers of cells clustering at the bottom of each microwell, and the number and ratio of distinct cell types involved depend only on the properties of the suspension introduced by the experimenter. Thus, we are able to generate tumor spheroids of arbitrary size and composition without needing to modify the underlying platform technology. The hundreds of microwells per square centimeter of culture surface area in turn ensure that extremely high production levels may be attained via a straightforward, nonlabor-intensive process. We therefore expect that this protocol will be broadly useful to researchers in the tumor spheroid field.

We introduce a protocol for the generation of large numbers (thousands to hundreds of thousands) of uniform size- and composition-controlled tumor spheroids, using commercially available microwell plates.

Tumor spheroids are increasingly recognized as an important in vitro model for the behavior of tumor cells in three dimensions. More physiologically ...

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 ...

Establishing 3-Dimensional Spheroids from Patient-Derived Tumor Samples and Evaluating their Sensitivity to Drugs

Despite remarkable advances in understanding tumor biology, the vast majority of oncology drug candidates entering clinical trials fail, often due to a lack of clinical efficacy. This high failure rate illuminates the inability of the current preclinical models to predict clinical efficacy, mainly due to their inadequacy in reflecting tumor heterogeneity and the tumor microenvironment. These limitations can be addressed with 3-dimensional (3D) culture models (spheroids) established from human tumor samples derived from individual patients. These 3D cultures represent real-world biology better than established cell lines that do not reflect tumor heterogeneity. Furthermore, 3D cultures are better than 2-dimensional (2D) culture models (monolayer structures) since they replicate elements of the tumor environment, such as hypoxia, necrosis, and cell adhesion, and preserve the natural cell shape and growth. In the present study, a method was developed for preparing primary cultures of cancer cells from individual patients that are 3D and grow in multicellular spheroids. The cells can be derived directly from patient tumors or patient-derived xenografts. The method is widely applicable to solid tumors (e.g., colon, breast, and lung) and is also cost-effective, as it can be performed in its entirety in a typical cancer research/cell biology lab without relying on specialized equipment. Herein, a protocol is presented for generating 3D tumor culture models (multicellular spheroids) from primary cancer cells and evaluating their sensitivity to drugs using two complementary approaches: a cell-viability assay (MTT) and microscopic examinations. These multicellular spheroids can be used to assess potential drug candidates, identify potential biomarkers or therapeutic targets, and investigate the mechanisms of response and resistance.

The present protocol describes generating 3D tumor culture models from primary cancer cells and evaluating their sensitivity to drugs using cell-viability assays and microscopic examinations.

Despite remarkable advances in understanding tumor biology, the vast majority of oncology drug candidates entering clinical trials fail, often due to a ...

Generation of 3D Tumor Spheroids for Drug Evaluation Studies

In recent decades, in addition to monolayer-cultured cells, three-dimensional tumor spheroids have been developed as a potentially powerful tool for the evaluation of anticancer drugs. However, the conventional culture methods lack the ability to manipulate the tumor spheroids in a homogeneous manner at the three-dimensional level. To address this limitation, in this paper, we present a convenient and effective method of constructing average-sized tumor spheroids. Additionally, we describe a method of image-based analysis using artificial intelligence-based analysis software that can scan the whole plate and obtain data on three-dimensional spheroids. Several parameters were studied. By using a standard method of tumor spheroid construction and a high-throughput imaging and analysis system, the effectiveness and accuracy of drug tests performed on three-dimensional spheroids can be dramatically increased.

This article demonstrates a standardized method for constructing three-dimensional tumor spheroids. A strategy for spheroid observation and image-based deep-learning analysis using an automated imaging system is also described.

In recent decades, in addition to monolayer-cultured cells, three-dimensional tumor spheroids have been developed as a potentially powerful tool for the ...

Semi-Automated Phenotypic Analysis of Functional 3D Spheroid Cell Cultures

We present a protocol that describes the properties and advantages of using a standalone clinostat incubator for growing, treating, and monitoring 3D cell cultures. The clinostat mimics an environment where cells can assemble as highly reproducible spheroids with low shear forces and active nutrient diffusion. We demonstrate that both cancer and non-cancer hepatocytes (HepG2/C3A and THLE-3 cell lines) require 3 weeks of growth prior to achieving functionalities comparable to liver cells. This protocol highlights the convenience of utilizing incubators for 3D cells with cameras monitoring the cell growth, as snapshots can be taken to count and measure spheroids upon treatment. We describe the comparison of THLE-3 and HepG2/C3A cell lines, showing how non-cancerous cell lines can be grown as well as immortalized cancer cells. We demonstrate and illustrate how proteomics experiments can be conducted from a few spheroids, which can be collected without perturbing cell signaling, i.e., no trypsinization required. We show that proteomics analysis can be used to monitor the typical liver phenotype of respiratory chain metabolism and the production of proteins involved in metal detoxification and describe a semi-automated system to count and measure the spheroid's area. Altogether, the protocol presents a toolbox that comprises a phenotypic characterization via image capture and a proteomics pipeline to experiment on 3D cell culture models.

We present a protocol for growing high-reproducible spheroids and their phenotypic characterization using image capture and proteomics.

We present a protocol that describes the properties and advantages of using a standalone clinostat incubator for growing, treating, and monitoring 3D cell ...

Biochemistry

Multicellular Spheroid Formation for FLIM-Based Metabolic and Hypoxia Analysis

Production and Multi-Parameter Live Cell Fluorescence Lifetime Imaging Microscopy (FLIM) of Multicellular Spheroids

Multicellular tumor spheroids are a popular 3D tissue microaggregate&#160;model for reproducing tumor microenvironment, testing and optimizing drug therapies&#160;and using bio- and nanosensors in a 3D context. Their ease of production, predictable size, growth, and observed nutrient and metabolite gradients are important to recapitulate the 3D niche-like&#160;cell microenvironment. However, spheroid heterogeneity and variability of their production methods can influence overall cell metabolism, viability, and drug response. This makes it difficult to choose the most appropriate&#160;methodology, considering the requirements in size, variability, needs of biofabrication, and use as in vitro 3D tissue models in stem and cancer cell biology. In particular, spheroid production can influence their compatibility with quantitative live microscopies, such as optical metabolic imaging, fluorescence lifetime imaging microscopy (FLIM), monitoring of spheroid&#160;hypoxia with nanosensors, or viability. Here, a number of conventional spheroid formation protocols are presented, highlighting their compatibility with the live widefield, confocal, and two-photon microscopies. The follow-up imaging to analysis&#160;pipeline with multiplexed autofluorescence FLIM and, using various types of cancer and stem cell spheroids, is also presented.

Author Spotlight: Standardizing Spheroid Formation Methods for Metabolic and Oxygenation Analysis Using Fluorescence Lifetime Imaging Microscopy

Here, we describe different multicellular spheroid formation methods to perform follow-up multi-parameter live cell microscopy. Using fluorescence lifetime imaging microscopy (FLIM), cellular autofluorescence, staining dyes, and nanoparticles, the approach for analysis of cell metabolism, hypoxia, and cell death in live three-dimensional (3D) cancer and stem cell-derived spheroids is demonstrated.

Multicellular tumor spheroids are a popular 3D tissue microaggregate&#160;model for reproducing tumor microenvironment, testing and optimizing drug ...

An Efficient and Flexible Cell Aggregation Method for 3D Spheroid Production

Monolayer cell culture does not adequately model the in vivo behavior of tissues, which involves complex cell-cell and cell-matrix interactions. Three-dimensional (3D) cell culture techniques are a recent innovation developed to address the shortcomings of adherent cell culture. While several techniques for generating tissue analogues in vitro have been developed, these methods are frequently complex, expensive to establish, require specialized equipment, and are generally limited by compatibility with only certain cell types. Here, we describe a rapid and flexible protocol for aggregating cells into multicellular 3D spheroids of consistent size that is compatible with growth of a variety of tumor and normal cell lines. We utilize varying concentrations of serum and methyl cellulose (MC) to promote anchorage-independent spheroid generation and prevent the formation of cell monolayers in a highly reproducible manner. Optimal conditions for individual cell lines can be achieved by adjusting MC or serum concentrations in the spheroid formation medium. The 3D spheroids generated can be collected for use in a wide range of applications, including cell signaling or gene expression studies, candidate drug screening, or in the study of cellular processes such as tumor cell invasion and migration. The protocol is also readily adapted to generate clonal spheroids from single cells, and can be adapted to assess anchorage-independent growth and anoikis-resistance. Overall, our protocol provides an easily modifiable method for generating and utilizing 3D cell spheroids in order to recapitulate the 3D microenvironment of tissues and model the in vivo growth of normal and tumor cells.

Here, we describe a rapid and flexible protocol for the formation of 3D cell spheroids through cell aggregation. This is easily adapted to multiple cell types and is suitable for use in a variety of applications including cell migration, invasion, or anoikis assays, and for imaging and quantifying cell-matrix interactions.