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Here, we present several simple methods for evaluating viability and death in 3D cancer cell spheroids, which mimic the physico-chemical gradients of in vivo tumors much better than the 2D culture. The spheroid model, therefore, allows evaluation of the cancer drug efficacy with improved translation to in vivo conditions.
Three-dimensional spheroids of cancer cells are important tools for both cancer drug screens and for gaining mechanistic insight into cancer cell biology. The power of this preparation lies in its ability to mimic many aspects of the in vivo conditions of tumors while being fast, cheap, and versatile enough to allow relatively high-throughput screening. The spheroid culture conditions can recapitulate the physico-chemical gradients in a tumor, including the increasing extracellular acidity, increased lactate, and decreasing glucose and oxygen availability, from the spheroid periphery to its core. Also, the mechanical properties and cell-cell interactions of in vivo tumors are in part mimicked by this model. The specific properties and consequently the optimal growth conditions, of 3D spheroids, differ widely between different types of cancer cells. Furthermore, the assessment of cell viability and death in 3D spheroids requires methods that differ in part from those employed for 2D cultures. Here we describe several protocols for preparing 3D spheroids of cancer cells, and for using such cultures to assess cell viability and death in the context of evaluating the efficacy of anticancer drugs.
The use of multicellular spheroid models in cancer biology is several decades old1,2, but has gained substantial momentum in recent years. In large part, this reflects increased awareness of how strongly the phenotype of cancer cells is dependent on their microenvironment and specific growth conditions. The microenvironment in solid tumors is fundamentally different from that in corresponding normal tissues. This includes physico-chemical conditions such as pH, oxygen tension, as well as interstitial pressure, concentration gradients of soluble factors such as nutrients, waste products, and secreted signaling compounds (growth factors, cytokines). Furthermore, it includes the organization of the extracellular matrix (ECM), cell-cell interactions and intercellular signaling, and other aspects of the particular three-dimensional (3D) architecture of the tumor3,4,5,6. The specific microenvironmental conditions in which cancer cells exist, profoundly affect their gene expression profile and functional properties, and it is clear that, compared to that of cells grown in 2D, the phenotype of 3D spheroids much more closely mimics that of in vivo tumors7,8,9,10,11. 2D models, even if they employ hypoxia, acidic pH, and high lactate concentrations to mimic known aspects of the tumor microenvironment, still fail to capture the gradients of physico-chemical parameters arising within tumors, as well as their 3D tumor architecture. On the other hand, animal models are costly, slow, and ethically problematic, and generally, also have shortcomings in their ability to recapitulate human tumor conditions. Consequently, 3D spheroids have been applied as an intermediate complexity model in studies of a wide range of properties of most solid cancers9,11,12,13,14,15,16,17.
A widely employed use of 3D spheroids is in screening assays of anticancer therapy efficacy9,18,19,20. Treatment responses are particularly sensitive to the tumor microenvironment, reflecting both the impact of the tortuosity, restricted diffusion, high interstitial pressure, and acidic environmental pH on drug delivery, and the impact of hypoxia and other aspects of the microenvironment on the cell death response9,17. Because the environment within 3D spheroids inherently develops all of these properties7,8,9,10,11, employing 3D cell cultures can substantially improve the translation of results to in vivo conditions, yet allow efficient and affordable high-throughput screening of the net growth. However, the great majority of studies on the drug response of cancer cells are still carried out under 2D conditions. This likely reflects that, while some assays can relatively easily be implemented for 3D cell cultures, many, such as viability assays, western blotting, and immunofluorescence analysis, are much more conveniently done in 2D than in 3D.
The aim of the present work is to provide easily amenable assays and precise protocols for analyses of the effect of treatment with anti-cancer drugs on cancer cell viability and survival in a 3D tumor mimicking setting. Specifically, we provide and compare three different methods for spheroid formation, followed by methods for qualitative and quantitative analyses of growth, viability and drug response.
1. Generation of Spheroids
2. Drug Treatment of Spheroids
NOTE: Long-term drug treatment can be applied to the spheroids in order to screen for effects of a drug of interest. Before initiating the drug treatment, it is advisable to perform a dose response experiment of the drug(s), in order to find an appropriate dose for the experimental treatment. The doses should be based on the determined IC50/Ki of the drug and range from around 0.2x-10x of this value.
3. Cell Viability Assay for Spheroids
4. Preparing Protein Lysates for Western Blotting from 3D Spheroid Cultures
NOTE: When collecting the spheroids, it is advisable to use a P200 pipette and cut the end of the tip to allow a bigger opening and hence an easier capture of the spheroids without disturbing their structure.
5. Propidium Iodide (PI) Staining of Spheroids
6. Embedding of 3D Spheroids
Spheroid growth assays based on the spheroid formation protocol schematically illustrated in Figure 1A and Figure 1B, were used as a starting point for analysis of the effects of anti-cancer drug treatments in a 3D tumor mimicking setting. The ease with which spheroids are formed is cell line specific, and some cell lines require supplementation with rBM in order to form coherent spheroids22. The concentr...
The use of 3D cancer cell spheroids has proven a valuable and versatile tool not only for anticancer drug screening, but also for gaining mechanistic insight into the regulation of cancer cell death and viability under conditions mimicking those in the tumor microenvironment. This is particularly crucial as the accessibility, cellular uptake, and intracellular effects of chemotherapeutic drugs are profoundly impacted by the physico-chemical conditions in the tumor, including pH, oxygen tension, tortuosity, and physical a...
The authors declare no conflict of interest.
We are grateful to Katrine Franklin Mark and Annette Bartels for excellent technical assistance and to Asbjørn Nøhr-Nielsen for performing the experiments in Figure 1D. This work was funded by the Einar Willumsen Foundation, the Novo Nordisk Foundation, and Fondation Juchum (all to SFP).
Name | Company | Catalog Number | Comments |
2-(4-amidinophenyl)-1H-indole-6-carboxamidine (DAPI) | Invitrogen | # C10595 | For staining nuclei |
5-Fluorouracil (5-FU) | Sigma-Aldrich | #F6627 | Component in chemotherapeutic treatment |
5-(N-ethyl-isopropyl) amiloride (EIPA) | Life Technologies | #E3111 | Inhibitor of NHE1 |
Antibody against PARP and cPARP | Cell signaling | #9542 | Used in western blotting |
Antibody against Ki-67 | Cell signaling | #9449 | Used for IHC |
Antibody against p53 | Cell Signaling | #2524 | Used for IHC |
Antibody against β-actin | Sigma | A5441 | Used in western blotting |
Bactoagar | BD Bioscience | #214010 | Used for agarose gel preparation |
Benchmark protein ladder | Invitrogen | #10747-012 | Used for SDS-PAGE |
Bio-Rad DC Protein Assay kit | Bio-Rad Laboratories | #500-0113, #500-0114, #500-0115 | Used for protein determination from lysates |
Bürker chamber | Marienfeld | 610311 | For cell counting |
BX63 epifluoresence microscope | Olympus | Used for fluorescent imaging | |
CellTiter-Glo 3D Cell Viability Assay | Promega | #G9681 | Used for the cell viability assay |
Cisplatin | Sigma-Aldrich | #P4394 | Component in chemotherapeutic treatment |
Corning Spheroid Microplate, 96 well, Black with clear round bottom, Ultra-low attachment, With lid, Sterile | Corning | #4520 | Used for growing spheroids with luminescence measurements as end point |
Corning 96 well, clear round bottom, Ultra-low attachment microplate, With lid, Sterile | Corning | #7007 | Sufficient for spheroid growth without luminescence measurements as end point |
Criterion TGX Precast Gels | Bio-Rad | 5671025 | Used for SDS-PAGE |
Doxorubicin | Abcam | #120629 | Component in chemotherapeutic treatment |
FLUOStar Optima Microplate reader | BMG Labtech | Used for recording luminescence | |
Formaldehyde | VWR Chemicals | #9713.1000 | Used for cell fixation |
Geltrex LDEV-Free Reduced Growth Factor Basement Membrane Matrix | Gibco | #A1413202 | Keep at 4 °C to prevent solidification. Referred to as rBM in the protocol. |
Heat-inactivated FBS | Sigma | #F9665 | Serum for growth media |
ImageJ | NIH | Scientific Image analysis | |
Medim Uni-safe casette | Medim Histotechnologie | 10-0114 | Used for storage of embedded spheroids |
Mini protease inhibitor cocktail tablets | Roche Diagnostics GmBH | # 11836153001 | Used for lysis buffer preparation |
MZ16 microscope | Leica | Used for light microscopic images | |
NuPAGE LDS 4x Sample Buffer | Invitrogen | #NP0007 | Used for western blotting |
Pierce ECL Western blotting substrate | Thermo scientific | #32106 | Used for western blotting |
Ponceau S | Sigma-Aldrich | #P7170-1L | Used for protein band staining |
Prism 6.0 | Graphpad | Scientific graphing and statistical software | |
Propidium iodide (1mg/ml solution in water) | Invitrogen | P3566 | Light sensitive |
Sterile reservoirs, multichannel | SPL lifesciences | 21002 | Used for seeding cells for spheroid formation |
Superfrost Ultra-Plus Adhesion slide | Menzel-Gläser | #J3800AMNZ | Microscope glass slide used for embedding |
Tamoxifen | Sigma-Aldrich | #T5648 | Used as chemotherapeutic treatment |
Trans-blot Turbo 0.2 µm nitrocellulose membranes | Bio-Rad | #170-4159 | Used for western blotting |
Tris/Glycine/SDS running buffer | Bio-Rad | #161 0732 | Used for SDS-PAGE |
Trypsin-EDTA solution | Sigma | #T4174 | Cell dissociation enzyme |
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