This work was supported by the National Institutes of Health (NIMHD-G12MD007581) through the RCMI-Center for Environmental Health at Jackson State University and the U.S. Department of Defense, Idea Award 11-1-0205.

NOTE: This protocol is described in McArdle et al.11. A timeline is provided in Figure 1.
1. Preparation of the culture plate
<ol>
	<li>Wash the 35-mm culture dish containing a 10-mm glass-bottom well with 1 mL of 1 M hydrochloric acid (HCl) for 15 min to lower the hydrophobicity of the glass-bottom.</li>
	<li>Wash the culture plate twice with 1 mL of phosphate buffer saline (PBS) to get rid of all the HCl.</li>
	<li>Wash the culture plate twice with 1 mL of 70% ethanol.</li>
	<li>Rinse the culture plate with 1 mL of the cell specific culture medium (here, use &#945;-MEM supplemented with 10% heat inactivated FBS and 1% non-essential amino acids). 
	Note: The treated culture plate containing the culture medium can be stored in the CO2 incubator with a humidifier at 37 &#176;C until the next day.</li>
	<li>Grow the cells (MSCs and MCF-7 co-culture) in the treated glass-bottom well of the 35-mm culture dish to 100% confluency. Co-culture 35,000 MSC cells and 75,000 of MCF7 cells for 24 h.</li>
</ol>
2. Preparation of the collagen gel
<ol>
	<li>Store the micropipette tips used for pipetting the collagen gel in the freezer to prevent the polymerization of the collagen upon contact. 
	Note: This is the most critical step.</li>
	<li>Determine a volume of rat tail collagen I to be used based on the concentration of the collagen stock. Prepare 100 &#181;L of collagen gel for this assay. 
	Note: High concentration of rat tail collagen I stock works better. Determine the volume of 10x Dulbecco&#39;s Modified Eagle&#39;s Medium to be used to dilute the collagen accordingly.</li>
	<li>Combine on ice rat tail collagen I (3.8 &#181;g/mL stock), 10x Dulbecco&#39;s Modified Eagle&#39;s Medium and 1x cell culture medium supplemented with 2% fetal bovine serum and the appropriate chemoattractant to a final concentration of collagen of 2.4 mg/mL.</li>
	<li>Add to the mixture 4.5% of sodium bicarbonate solution to neutralize the collagen gel. 
	Note: The volume of sodium bicarbonate solution added may vary based on the exact pH of the other reagents. It is best to test the mixture with pH strips to ensure neutral solution, or use a pH indicator in the culture medium.</li>
	<li>Lay 80 &#181;L of the collagen mixture over the cells within the glass-bottom well of the culture dish.</li>
	<li>Allow the collagen gel to polymerize for 30 min in a CO2 incubator with a humidifier at 37 &#176;C.</li>
	<li>Cover the collagen gel with 2 mL of cell medium with reduced serum (2%) and incubate the cells at 37 &#176;C in a CO2 incubator with a humidifier for 24, 48, or 72 h. 
	Caution: The plate should be handled with care to prevent the collagen gel from detaching from the glass bottom.</li>
</ol>
3. Example of preparation of collagen gel using a rat tail collagen stock of 3.8 &#181;g /mL
<ol>
	<li>On ice, combine 114.5 &#181;L of rat tail collagen, 16.6 &#181;L of 10x DMEM, and 33.1 &#181;L of culture medium containing the chemoattractant.</li>
	<li>Neutralize the collagen mixture with 14.0 &#181;L of sodium bicarbonate.</li>
	<li>Continue as in step 2.5.</li>
</ol>
4. Imaging of the cells
<ol>
	<li>Gently remove the media from the dish.</li>
	<li>Gently rinse the gel with 1 mL of PBS.</li>
	<li>Fix the cells with 1 mL of 4% paraformaldehyde for 15 min.</li>
	<li>Wash the cells twice with 1 mL of PBS.</li>
	<li>Stain the cells with DAPI solution (100 ng/mL) for 20 min at room temperature.</li>
	<li>Image the cells using a confocal microscope at different locations and taking 400 &#181;m z-stack images of each location in 16 &#181;m steps. The microscope used has a disk scanning unit that enables confocal imaging using a white light, arc excitation source. Use a 20X lens utilized with numerical aperture of 0.75.</li>
	<li>Reconstitute images .
	<ol>
		<li>Open images for a given gel (approximately 25 images) and create an image stack by clicking image &#8594; stacks &#8594;&#160;images to stack. The first image corresponded to the bottom of the gel (z = 0 &#181;m), the second image corresponded to the first step in the z direction (z = 16 &#181;m), the third image corresponded to the second step in the z direction (z = 32 &#181;m). Assess each nucleus at each image depth and designate the depth at which the nucleus was in sharpest focus as the invasion depth for that particular cell.</li>
	</ol>
	</li>
</ol>

<ol>
	<li>Friedl, P., Brocker, E. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+biology+of+cell+locomotion+within+three-dimensional+extracellular+matric.">The biology of cell locomotion within three-dimensional extracellular matric.</a> Cell Mol Life Sci. 57, 41-64 (2000).</li><li>Bissell, M. J., Rizki, A., Mian, I. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tissue+architecture:+the+ultimate+regulator+of+breast+epithelial+function.">Tissue architecture: the ultimate regulator of breast epithelial function.</a> Curr Opin Cell Biol. 15, 753-762 (2003).</li><li>Friedl, P., Wolf, K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tumour-cell+invasion+and+migration:+diversity+and+escape+mechanisms.">Tumour-cell invasion and migration: diversity and escape mechanisms.</a> Nat Rev Cancer. 3, 362-374 (2003).</li><li>Yarrow, J. C., Perlman, Z. E., Westwood, N. J., Mitchison, T. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+high-throughput+cell+migration+assay+using+scratch+wound+healing,+a+comparison+of+image-based+readout+methods.">A high-throughput cell migration assay using scratch wound healing, a comparison of image-based readout methods.</a> BMC Biotechnol. 4, 21 (2004).</li><li>Wolf, K., 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=Compensation+mechanism+in+tumor+cell+migration:+mesenchymal-amoeboid+transition+after+blocking+of+pericellular+proteolysis.">Compensation mechanism in tumor cell migration: mesenchymal-amoeboid transition after blocking of pericellular proteolysis.</a> J Cell Biol. 160, 267-277 (2003).</li><li>Sahai, E., Marshall, C. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Differing+modes+of+tumour+cell+invasion+have+distinct+requirements+for+Rho/ROCK+signalling+and+extracellular+proteolysis.">Differing modes of tumour cell invasion have distinct requirements for Rho/ROCK signalling and extracellular proteolysis.</a> Nat Cell Biol. 5, 711-719 (2003).</li><li>Kam, Y., Guess, C., Estrada, L., Weidow, B., Quaranta, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+novel+circular+invasion+assay+mimics+in+vivo+invasive+behavior+of+cancer+cell+lines+and+distinguishes+single-cell+motility+in+vitro.">A novel circular invasion assay mimics in vivo invasive behavior of cancer cell lines and distinguishes single-cell motility in vitro.</a> BMC Cancer. 8, 198 (2008).</li><li>Staton, C. A., Reed, M. W., Brown, N. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+critical+analysis+of+current+in+vitro+and+in+vivo+angiogenesis+assays.">A critical analysis of current in vitro and in vivo angiogenesis assays.</a> Int J Exp Pathol. 90, 195-221 (2009).</li><li>Poujade, M., 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=Collective+migration+of+an+epithelial+monolayer+in+response+to+a+model+wound.">Collective migration of an epithelial monolayer in response to a model wound.</a> Proc Natl Acad Sci USA. 104, 15988-15993 (2007).</li><li>Noubissi, F. K., Harkness, T., Alexander, C. M., Ogle, B. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Apoptosis-induced+cancer+cell+fusion:+a+mechanism+of+breast+cancer+metastasis.">Apoptosis-induced cancer cell fusion: a mechanism of breast cancer metastasis.</a> FASEB J. 29, 4036-4045 (2015).</li><li>McArdle, T. J., Ogle, B. M., Noubissi, F. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=An+In+Vitro+Inverted+Vertical+Invasion+Assay+to+Avoid+Manipulation+of+Rare+or+Sensitive+Cell+Types.">An In Vitro Inverted Vertical Invasion Assay to Avoid Manipulation of Rare or Sensitive Cell Types.</a> J Cancer. 7, 2333-2340 (2016).</li><li>Noubissi, F. K., Ogle, B. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cancer+Cell+Fusion:+Mechanisms+Slowly+Unravel.">Cancer Cell Fusion: Mechanisms Slowly Unravel.</a> Int J Mol Sci. 17, (2016).</li><li>Meyvantsson, I., Beebe, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+culture+models+in+microfluidic+systems.">Cell culture models in microfluidic systems.</a> Annu Rev Anal Chem. 1, 423-449 (2008).</li><li>Hooper, S., Marshall, J. F., Sahai, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tumor+cell+migration+in+three+dimensions.">Tumor cell migration in three dimensions.</a> Methods In Enzymol. 406, 625-643 (2006).</li><li>Yang, C., Tibbitt, M. W., Basta, L., Anseth, K. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mechanical+memory+and+dosing+influence+stem+cell+fate.">Mechanical memory and dosing influence stem cell fate.</a> Nat Materials. 13, 645-652 (2014).</li></ol>

The authors have declared that no competing interest exists.

Here, we describe a simple inverted vertical invasion assay which is convenient for a variety of cell types including cells that are rare and/or dependent on their microenvironment. In this 3D invasion assay, cells remain in their original microenvironment and are covered by the collagen gel containing a chemoattractant. The cells then migrate and invade in the collagen. In this assay, the cells can be stained and easily monitored within the gel. The simplicity and reproducibility of this assay makes it a convenient tool for studying cancer cell migration and invasion in a 3D system. However, strong chemoattractants seem to be required to break the cell affinity to the bottom of the culture dish.
We optimized the inverted vertical invasion assay in the 35-mm culture dish. This culture dish has a 10-mm glass-bottom well which is well fitted for imaging. One limitation of this culture dish is the considerable amount of collagen gel required to perform an assay. Finding smaller culture dishes with a design compatible with imaging would be more economical. The gel layer appropriate for the 35-mm dish design is very delicate due to its strength and can easily detach from the bottom of the plate if not handled carefully. A different cell culture design might improve the stability of the collagen gel layer but the compatibility between the collagen gel strength and cell viability should be optimized.
Despite these limitations, the inverted vertical invasion assay presents many advantages compared to other 3D invasion assay formats. The main benefit is that cells remain in their original culture environment, which is not the case in the Boyden chamber assay. This protocol preserves the cell microenvironment that is advantageous for cells stringently controlled by their microenvironment such as stem cells15. This assay also prevents cell damage or cell loss especially for cells that are delicate or rare10,11. In addition, with this assay, the cell morphology and associated kinetics could be assessed within the gel, which is not possible with the Boyden chamber assay. Moreover, the non-physiologic polycarbonate or polypropylene filter of the Boyden chamber assay system is not used in the inverted vertical invasion assay. The inverted vertical invasion assay is a static design, it does not mimic the in vivo dynamic environment that the microfluidic invasion assay design offers but it provides a simpler, less challenging and cost-effective 3D environment to quantify migration and invasion of a variety of cell types in a preserved and controlled microenvironment.
The inverted vertical invasion assay has many potential applications in pathophysiological studies. This approach could serve as an in vitro platform to study cell motility during embryonic development, wound healing, and/or inflammatory responses3. Cell interaction with the ECM and other cell types during migration and invasion could also be investigated using this protocol. This assay could also represent a useful tool for initial drug screening of anti-metastatic drugs. A model system of organ-specific cancer metastasis could be developed using the inverted vertical invasion assay as well.
The inverted vertical invasion assay was developed to circumvent the challenge that the displacement of some cells from their original microenvironment presents in the Boyden chamber assay system. This assay is easy, reliable, and reproducible; it is flexible and can be used to quantify the invasive potential of a wide variety of cell types including sensitive and rare cell types. This assay can be applied to detect the migratory activity associated with matrix degradation and can also be adapted to study the selective degrading activity on different matrix substrates.

Cell motility is a normal developmental and physiological process of cells. However, changes in the pattern and the ability of cells to migrate and invade are associated with pathological conditions including inflammatory diseases and cancer metastasis1,2,3. Metastasis is arguably the most poorly understood aspect in cancer. To metastasize, cancer cells must degrade the extra cellular matrix (ECM), invade the local tissue and intravasate. Once in circulation, the cancer cells will disseminate to the distant site, extravasate and form secondary tumors. Therefore, the ability of cells to degrade the ECM, to migrate, and to invade is related to their metastatic potential. Different approaches have been developed to analyze and quantify the migration and invasion capabilities of cells. The most used approaches include the wound healing assay, time-lapse microscopy, and the Boyden chamber assay. The wound healing assay4 and time lapse microscopy are simple and convenient assays that would give preliminary insight into cell migration. However, both are 2D assays that do not reflect the 3D environment in which cells exist in vivo. Studies have shown that cells respond differently to a 3D environment compared to a 2D one5,6. Moreover, wound healing assays are difficult to reproduce and to yield quantitative results7,8,9. The Cell Exclusion Zone assay, which is a 3D modification of the wound healing assay, is a more physiologically relevant assay but it is not suitable for cells low in number such as hybrid cells resulting from cell fusion events10,11.
The Boyden chamber assay is a 3-dimensional assay that provides relevant microenvironments for cellular studies. However, it requires cells to be removed from their original microenvironment and to be deposited into the upper chamber of the Boyden assay system to migrate and invade downwards toward the chemoattractant containing medium. This 3D approach is not appropriate in analyzing the migration and invasion capability of cells vulnerable to their microenvironment and/or limited in number10,11,12. A newer approach to analyze cell migration and invasion is the microfluidic gradient chamber assay13. Although suitable and reliable in migration and invasion studies, this assay is more expensive and could be technically challenging for a typical laboratory. We describe here a simple inverted vertical invasion assay that is compatible with many cell types including cells sensitive to their microenvironment and/or restricted in number. This assay was adapted from the protocol proposed by Hooper et al.14. In this assay, the cells remain in their original microenvironment and their migration and invasion is monitored as they move upwards in the collagen gel containing a chemoattractant11. This assay is reproducible and has been optimized and validated in the 35-mm culture dish. It could be adapted to different assay conditions including different cell culture sizes, different matrices or strength of adhesion, and different chemoattractants. This assay could serve as an in vitro platform for initial screening in the drug discovery process.

<table border="0" cellpadding="0" cellspacing="0" style="width:880px;" width="880">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:228px;">MatTek P35G-1.5-10C</td>
			<td style="width:269px;">MatTek Corporation, Ashland, MA</td>
			<td style="width:151px;">P35G-1.5-10-C</td>
			<td style="width:232px;">mattek glass bottom dishes</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Rat tail collagen I</td>
			<td>Corning, Corning, NY, USA</td>
			<td align="right">354236</td>
			<td>Collagen gel</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Hydrochloric acid</td>
			<td>Sigma-Aldrich, St. Louis, MO 63178 USA</td>
			<td>H1758</td>
			<td>HCl</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Phosphate buffered saline</td>
			<td>Thermo Fisher Scientific Inc., Whaltham, MA, USA</td>
			<td align="right">10010023</td>
			<td>PBS</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">10X Dulbecco&#39;s Modified Eagle&#39;s Medium</td>
			<td>Sigma-Aldrich, St. Louis, MO 63178 USA</td>
			<td>D2429</td>
			<td>10X DMEM</td>
		</tr>
		<tr height="24">
			<td height="24" style="height:24px;">Sodium bicarbonate</td>
			<td>Sigma-Aldrich, St. Louis, MO 63178 USA</td>
			<td>S5761</td>
			<td>NaHCO3</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Confocal Fluorescent microscope</td>
			<td>Olympus America, Center Valley, PA, USA</td>
			<td>Olympus IX81</td>
			<td>Confocal&#160; microscope</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Defined Fetal Bovine Serum</td>
			<td>GE Healthcare Life Sciences HyClone Laboratories, Utah, USA</td>
			<td>SH30070.03</td>
			<td>FBS</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Ti:Sapphire multi-photon laser scanning microscope</td>
			<td>Prarie Technologies, Sioux Falls, SD, USA</td>
			<td>40x NA 0.8 objective</td>
			<td>MPLSM</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Imaris software</td>
			<td>Bitplane Inc. Zurich, CH</td>
			<td>Imaris 7.5.2</td>
			<td>Imaris software</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">DAPI</td>
			<td style="width:269px;">Sigma-Aldrich, St. Louis, MO 63178, USA</td>
			<td>D9542</td>
			<td>DAPI</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Paraformaldehyde</td>
			<td>Thermo Fisher Scientific Inc., Whaltham, MA, USA</td>
			<td align="right">50980487</td>
			<td>PFA</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">&#945;-minimum essential medium</td>
			<td>Sigma-Aldrich, St. Louis, MO 63178, USA</td>
			<td>M0894</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">MDA-MB-231</td>
			<td>ATCC; Manassas, VA, USA</td>
			<td>HBT-22</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">MSC</td>
			<td>Trivedi and Hematti, 2007</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">20X lens UPLAPO</td>
			<td>Olympus America, Center Valley, PA, USA</td>
			<td>36-064</td>
			<td>Olympus UPLSAPO 20X Objective</td>
		</tr>
	</tbody>
</table>

moving upwards: a simple and flexible in vitro three-dimensional invasion assay protocol

Although 3D invasion assays have been developed, the challenge remains to study cells without affecting the integrity of their microenvironment. Traditional 3D assays such as the Boyden Chamber require that cells are displaced from the original culture location and moved to a new environment. Not only does this disrupt the cellular processes that are intrinsic to the microenvironment, but it often results in a loss of cells. These problems are especially challenging when dealing with cells that are either rare, or extremely sensitive to their microenvironment. Here, we describe the development of a 3D invasion assay that avoids both concerns. In this assay, cells are plated within a small well and an ECM matrix containing a chemoattractant is laid atop the cells. This requires no cell displacement, and allows the cells to invade upwards into the matrix. In this assay, cell invasion as well as cell morphology can be assessed within the collagen gel. Using this assay, we characterize the invasive capacity of rare and sensitive cells; the hybrid cells resulting from fusion between breast cancer cells MCF7 and mesenchymal/multipotent stem/stroma cells (MSCs).

We have used a 35-mm culture dish with a glass bottom and rat tail collagen I to develop and optimize an in vitro 3D invasion assay protocol. Using this assay, we showed that breast cancer cells MCF7 and MSC cells could invade into the collagen gel to an average distance of 0.04 &#177; 1.8 &#181;m, and 41.3 &#177; 76.0 &#181;m respectively after 48 h when IGF1 (18.6 ng/mL) was used as chemoattractant (Figure 2). More importantly, we showed that fusion products from MSC and MCF7 cells, which are rare cells, could invade into the collagen gel as well. Their average distance of invasion in 48 h was 10.7 &#177; 12.4 &#181;m when IGF I at 18.6 ng/mL was used as chemoattractant (Figure 2). The difference in the invasion capability between MCF7 and MSCs was statistically significant (P &#60;0.01)11. The difference between the invasion capability of the fusion products and the one of MCF7 or MCSs was not statistically significant. However, this assay consistently showed that the cancer cell fusion products had a greater migratory and invasive capability than the parental cancer cells, MCF7.
Cells remained healthy throughout the experiments as shown by their morphology and quantity 48 h post gel polymerization (Figure 3a). With the inverted vertical invasion assay design, the kinetics of cell migration and invasion can be analyzed (Figure 3b, 4) and cell morphology can be assessed (Figure 4).
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/56568/56568fig1.jpg" /> 
Figure 1: Timeline of the inverted vertical invasion assay design &#160;<a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56568/56568fig1large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/56568/56568fig2.jpg" /> 
Figure 2: Invasion capability of cancer cell fusion products. The invasion capacity of cancer cell fusion products could be determined using the inverted vertical invasion assay. The numbers represent the average invasion capacity of four independent fusion products from three separate co-cultures and their parental cell lines analyzed from eight different fields within each assay. This experiment was performed in triplicate. ANOVA with Tukey&#39;s HSD post hoc test. **P &#60;0.01. Error bars represent standard deviation (SD). This figure has been adapted from 11. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56568/56568fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/56568/56568fig3.jpg" /> 
Figure 3: Cell viability and Z series of the inverted vertical invasion assay. 
a) 20X bright field images showing the morphology of cells under the collagen gel after two days. From left to right MCF7 and MSC co-culture, MCF7, and MSC; b) representation of z series showing two locations (i and ii) within a dish from the bottom to the top. Successive images are 16 &#181;m apart. 3.8% FBS was used as a chemoattractant. Green circles on both panels indicate invading cells; note, out of focus at the bottom of the gel and in focus in the top gel, invading into the gel. Red circles on both panels indicate cells remaining at the bottom layer of the z series (non-invading cells). Scale bar (a): 15 &#181;m; Scale bar (b): 10 &#181;m. This figure has been adapted from 11.&#160;<a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56568/56568fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/56568/56568fig4.jpg" /> 
Figure 4: Cell morphology in the inverted vertical invasion assay. Morphology of MSCs in the collagen gel at one location from the bottom (Z = 0 &#181;m) to the Z = 20 &#181;m. 3.8% FBS was used as a chemoattractant. The long arrow indicates the appendage of an MSC invading into the gel. The arrowhead indicates an MSC, which is aligned along the bottom of the gel, and not invading. The blue shows the nuclear DAPI stain while the red shows the phalloidin stained actin filaments.This figure has been adapted from 11. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/56568/56568fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Moving Upwards: A Simple and Flexible In Vitro Three-dimensional Invasion Assay Protocol at JoVE.com

Moving Upwards: A Simple and Flexible In Vitro Three-dimensional Invasion Assay Protocol

This protocol describes an inverted vertical invasion assay that could be used to quantify the migration and invasion capabilities of cells in a three-dimensional setting while preserving the cell microenvironment. This assay is suitable for rare and/or sensitive cells.

Moving Upwards: A Simple and Flexible In Vitro Three-dimensional Invasion Assay Protocol

Although 3D invasion assays have been developed, the challenge remains to study cells without affecting the integrity of their microenvironment. ...

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Nanyang Technological University

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Cancer Research

6.0K Views.  University of Minnesota - Twin Cities. This protocol describes an inverted vertical invasion assay that could be used to quantify the migration and invasion capabilities of cells in a three-dimensional setting while preserving the cell microenvironment. This assay is suitable for rare and/or sensitive cells.

Video: Moving Upwards: A Simple and Flexible In Vitro Three-dimensional Invasion Assay Protocol

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 ...

Real Time Detection of In Vitro Tumor Cell Apoptosis Induced by CD8+ T Cells to Study Immune Suppressive Functions of Tumor-infiltrating Myeloid Cells

Potentiation of the tumor-killing ability of CD8+ T cells in tumors, along with their efficient tumor infiltration, is a key element of successful immunotherapies. Several studies have indicated that tumor infiltrating myeloid cells (e.g., myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs)) suppress cytotoxicity of CD8+ T cells in the tumor microenvironment, and that targeting these regulatory myeloid cells can improve immunotherapies. Here, we present an in vitro assay system to evaluate immune suppressive effects of monocytic-MDSCs and TAMs on the tumor-killing ability of CD8+ T cells. To this end, we first cultured na&#239;ve splenic CD8+ T cells with anti-CD3/CD28 activating antibodies in the presence or absence of suppressor cells, and then co-cultured the pre-activated T cells with target cancer cells in the presence of a fluorogenic caspase-3 substrate. Fluorescence from the substrate in cancer cells was detected by real-time fluorescence microscopy as an indicator of T-cell induced tumor cell apoptosis. In this assay, we can successfully detect the increase of tumor cell apoptosis by CD8+ T cells and its suppression by pre-culture with TAMs or MDSCs. This functional assay is useful for investigating CD8+ T cell suppression mechanisms by regulatory myeloid cells and identifying druggable targets to overcome it via high throughput screening.

Real Time Detection of In Vitro Tumor Cell Apoptosis Induced by CD8+ T Cells to Study Immune Suppressive Functions of Tumor-infiltrating Myeloid Cells

We describe here a protocol to investigate cytotoxicity of pre-activated CD8+ T cells against cancer cells by detecting apoptotic cancer cells via real-time microscopy. This protocol can investigate mechanisms behind myeloid cell-induced T cell suppression and evaluate compounds aimed at replenishing T cells via blockade of immune suppressive myeloid cells.

Potentiation of the tumor-killing ability of CD8+ T cells in tumors, along with their efficient tumor infiltration, is a key element of successful ...

A Simple Migration/Invasion Workflow Using an Automated Live-cell Imager

Cancer cell mobility is crucial for the initiation of metastasis. Therefore, investigation of the cell movement and invasive capacity is of great significance. Migration assays provide basic insight of cell movement at a 2D level, whereas invasion assays are more physiologically relevant, mimicking in vivo cancer cell dislodgment from the original site and invading through the extracellular matrix. The current protocol provides a single workflow for migration and invasion assays. Together with the integrated automated microscopic camera for real-time HD images and built-in analysis module, it gives researchers a time-efficient, simple and reproducible experimental option. This protocol also includes substitutions for the consumables and alternative analysis methods for users to choose from.

The current protocol describes an integrated method investigating cancer cell migration and invasion on a single platform in real-time, providing an easily reproducible and time-efficient option to study cell mobility and morphology.

Cancer cell mobility is crucial for the initiation of metastasis. Therefore, investigation of the cell movement and invasive capacity is of great ...

Three-Dimensional Bone Extracellular Matrix Model for Osteosarcoma

Osteosarcoma (OS) is the most common and a highly aggressive primary bone tumor. It is characterized with anatomic and histologic variations along with diagnostic or prognostic difficulties. OS comprises genotypically and phenotypically heterogeneous cancer cells. Bone microenvironment elements are proved to account for tumor heterogeneity and disease progression. Bone extracellular matrix (BEM) retains the microstructural matrices and biochemical components of native extracellular matrix. This tissue-specific niche provides a favorable and long-term scaffold for OS cell seeding and proliferation. This article provides a protocol for the preparation of BEM model and its further experimental application. OS cells can grow and differentiate into multiple phenotypes consistent with the histopathological complexity of OS clinical specimens. The model also allows visualization of diverse morphologies and their association with genetic alterations and underlying regulatory mechanisms. As homologous to human OS, this BEM-OS model can be developed and applied to the pathology and clinical research of OS.

The bone extracellular matrix (BEM) model for osteosarcoma (OS) is well established and shown here. It can be used as a suitable scaffold for mimicking primary tumor growth in vitro and providing an ideal model for studying the histologic and cytogenic heterogeneity of OS.

Osteosarcoma (OS) is the most common and a highly aggressive primary bone tumor. It is characterized with anatomic and histologic variations along with ...

Fully Human Tumor-based Matrix in Three-dimensional Spheroid Invasion Assay

Two-dimensional cell culture-based assays are commonly used in in vitro cancer research. However, they lack several basic elements that form the tumor microenvironment. To obtain more reliable in vitro results, several three-dimensional (3D) cell culture assays have been introduced. These assays allow cancer cells to interact with the extracellular matrix. This interaction affects cell behavior, such as proliferation and invasion, as well as cell morphology. Additionally, this interaction could induce or suppress the expression of several pro- and anti-tumorigenic molecules. Spheroid invasion assay was developed to provide a suitable 3D in vitro method to study cancer cell invasion. Currently, animal-derived matrices, such as mouse sarcoma-derived matrix (MSDM) and rat tail type I collagen, are mainly used in the spheroid invasion assays. Taking into consideration the differences between the human tumor microenvironment and animal-derived matrices, a human myoma-derived matrix (HMDM) was developed from benign uterus leiomyoma tissue. It has been shown that HMDM induces migration and invasion of carcinoma cells better than MSDM. This protocol provided a simple, reproducible, and reliable 3D human tumor-based spheroid invasion assay using the HMDM/fibrin matrix. It also includes detailed instructions on imaging and analysis. The spheroids grow in a U-shaped ultra-low attachment plate within the HMDM/fibrin matrix and invade through it. The invasion is daily imaged, measured, and analyzed using ilastik and Fiji ImageJ software. The assay platform was demonstrated using human laryngeal primary and metastatic squamous cell carcinoma cell lines. However, the protocol is suitable also for other solid cancer cell lines.

Tumor microenvironment is an essential part of cancer growth and invasion. To mimic carcinoma progression, a biologically relevant human matrix is needed. This protocol introduces an improvement for the in vitro three-dimensional spheroid invasion assay by applying a human leiomyoma-based matrix. The protocol also introduces a computer-based cell invasion analysis.

Two-dimensional cell culture-based assays are commonly used in in vitro cancer research. However, they lack several basic elements that form the tumor ...

In Vitro Assay to Study Tumor-macrophage Interaction

Tumor associated macrophages (TAMs) account for a large percentage of cells in the tumor mass for different types of cancers. Glioblastoma (GBM), a malignant brain tumor with no cure, has up to a half the tumor mass TAMs. TAMs can be pro-tumoral or anti-tumoral, depending on the activation of specific genes in the cells. Genetic mutations in the tumors, through regulating cytokine expression, can affect recruitment of TAMs to the tumor microenvironment. Here, we describe a quantitative cell-based assay to assess macrophage recruitment by the conditioned medium from the tumor cells. This assay uses the human macrophage cell line MV-4-11 to study macrophage attraction by the conditioned medium from glioblastoma, allowing for high reproducibility and low variability. Data generated with this assay can contribute to a better understanding of the interaction between the tumor and the tumor microenvironment. Similar assay can be used to assess interaction between the tumor cells and other immune cells, including T cells and natural killer (NK) cells.

This article represents a useful in vitro assay to evaluate the capability of conditioned medium from tumor cells to attract macrophages.

Tumor associated macrophages (TAMs) account for a large percentage of cells in the tumor mass for different types of cancers. Glioblastoma (GBM), a ...

A 3D Spheroid Model as a More Physiological System for Cancer-Associated Fibroblasts Differentiation and Invasion In Vitro Studies

Defining the ideal model for an in vitro study is essential, mainly if studying physiological processes such as differentiation of cells. In the tumor stroma, host fibroblasts are stimulated by cancer cells to differentiate. Thus, they acquire a phenotype that contributes to the tumor microenvironment and supports tumor progression. By using the spheroid model, we have set up such a 3D in vitro model system, in which we analyzed the role of laminin-332 and its receptor integrin &#945;3&#946;1 in this differentiation process. This spheroid model system not only reproduces the tumor microenvironment conditions in a more accurate way, but also is a very versatile model since it allows different downstream studies, such as immunofluorescent staining of both intra- and extracellular markers, as well as deposited extracellular matrix proteins. Moreover, transcriptional analyses by qPCR, flow cytometry and cellular invasion can be studied with this model. Here, we describe a protocol of a spheroid model to assess the role of CAFs&#39; integrin &#945;3&#946;1 and its ectopically deposited ligand, laminin-332, in differentiation and in supporting the invasion of pancreatic cancer cells.

The goal of this protocol is to establish a 3D in vitro model to study the differentiation of cancer-associated fibroblasts (CAFs) in a tumor bulk-like environment, which can be addressed in different analysis systems, such as immunofluorescence, transcriptional analysis and life cell imaging.

Defining the ideal model for an in vitro study is essential, mainly if studying physiological processes such as differentiation of cells. In the tumor ...

Establishment and Analysis of Three-Dimensional (3D) Organoids Derived from Patient Prostate Cancer Bone Metastasis Specimens and their Xenografts

Three-dimensional (3D) culture of organoids from tumor specimens of human patients and patient-derived xenograft (PDX) models of prostate cancer, referred to as patient-derived organoids (PDO), are an invaluable resource for studying the mechanism of tumorigenesis and metastasis of prostate cancer. Their main advantage is that they maintain the distinctive genomic and functional heterogeneity of the original tissue compared to conventional cell lines that do not. Furthermore, 3D cultures of PDO can be used to predict the effects of drug treatment on individual patients and are a step towards personalized medicine. Despite these advantages, few groups routinely use this method in part because of the extensive optimization of PDO culture conditions that may be required for different patient samples. We previously demonstrated that our prostate cancer bone metastasis PDX model, PCSD1, recapitulated the resistance of the donor patient&rsquo;s bone metastasis to anti-androgen therapy. We used PCSD1 3D organoids to characterize further the mechanisms of anti-androgen resistance. Following an overview of currently published studies of PDX and PDO models, we describe a step-by-step protocol for 3D culture of PDO using domed or floating basement membrane (e.g., Matrigel) spheres in optimized culture conditions. In vivo stitch imaging and cell processing for histology are also described. This protocol can be further optimized for other applications including western blot, co-culture, etc. and can be used to explore characteristics of 3D cultured PDO pertaining to drug resistance, tumorigenesis, metastasis and therapeutics.

Establishment and Analysis of Three-Dimensional 3D Organoids Derived from Patient Prostate Cancer Bone Metastasis Specimens and their Xenografts

Three-dimensional cultures of patient BMPC specimens and xenografts of bone metastatic prostate cancer maintain the functional heterogeneity of their original tumors resulting in cysts, spheroids and complex, tumor-like organoids. This manuscript provides an optimization strategy and protocol for 3D culture of heterogeneous patient derived samples and their analysis using IFC.

Three-dimensional (3D) culture of organoids from tumor specimens of human patients and patient-derived xenograft (PDX) models of prostate cancer, referred ...

A Three-dimensional Model of Spheroids to Study Colon Cancer Stem Cells

Colorectal cancers are characterized by heterogeneity and a hierarchical organization comprising a population of cancer stem cells (CSCs) responsible for tumor development, maintenance, and resistance to drugs. A better understanding of CSC properties for their specific targeting is, therefore, a pre-requisite for effective therapy. However, there is a paucity of suitable preclinical models for in-depth investigations. Although in vitro two-dimensional (2D) cancer cell lines provide valuable insights into tumor biology, they do not replicate the phenotypic and genetic tumor heterogeneity. In contrast, three-dimensional (3D) models address and reproduce near-physiological cancer complexity and cell heterogeneity. The aim of this work was to design a robust and reproducible 3D culture system to study CSC biology. The present methodology describes the development and optimization of conditions to generate 3D spheroids, which are homogenous in size, from Caco2 colon adenocarcinoma cells, a model that can be used for long-term culture. Importantly, within the spheroids, the cells which were organized around lumen-like structures, were characterized by differential cell proliferation patterns and by the presence of CSCs expressing a panel of markers. These results provide the first proof-of-concept for the appropriateness of this 3D approach to study cell heterogeneity and CSC biology, including the response to chemotherapy.

This protocol presents a novel, robust, and reproducible culture system to generate and grow three-dimensional spheroids from Caco2 colon adenocarcinoma cells. The results provide the first proof-of-concept for the appropriateness of this approach to study cancer stem cell biology, including the response to chemotherapy.

Colorectal cancers are characterized by heterogeneity and a hierarchical organization comprising a population of cancer stem cells (CSCs) responsible for ...

Three-Dimensional In Vitro Biomimetic Model of Neuroblastoma Using Collagen-Based Scaffolds

Neuroblastoma is the most common extracranial solid tumor in children, accounting for 15% of overall pediatric cancer deaths. The native tumor tissue is a complex three-dimensional (3D) microenvironment involving layers of cancerous and non-cancerous cells surrounded by an extracellular matrix (ECM). The ECM provides physical and biological support and contributes to disease progression, patient prognosis, and therapeutic response.
This paper describes a protocol for assembling a 3D scaffold-based system to mimic the neuroblastoma microenvironment using neuroblastoma cell lines and collagen-based scaffolds. The scaffolds are supplemented with either nanohydroxyapatite (nHA) or glycosaminoglycans (GAGs), naturally found at high concentrations in the bone and bone marrow, the most common metastatic sites of neuroblastoma. The 3D porous structure of these scaffolds allows neuroblastoma cell attachment, proliferation and migration, and the formation of cell clusters. In this 3D matrix, the cell response to therapeutics is more reflective of the in vivo situation.
The scaffold-based culture system can maintain higher cell densities than conventional two-dimensional (2D) cell culture. Therefore, optimization protocols for initial seeding cell numbers are dependent on the desired experimental timeframes. The model is monitored by assessing cell growth via DNA quantification, cell viability via metabolic assays, and cell distribution within the scaffolds via histological staining.
This model&#39;s applications include the assessment of gene and protein expression profiles as well as cytotoxicity testing using conventional drugs and miRNAs. The 3D culture system allows for the precise manipulation of cell and ECM components, creating an environment more physiologically similar to native tumor tissue. Therefore, this 3D in vitro model will advance the understanding of the disease pathogenesis and improve the correlation between results obtained in vitro, in vivo in&#160;animal models, and human subjects.

Three-Dimensional In Vitro Biomimetic Model of Neuroblastoma Using Collagen-Based Scaffolds

This paper lists the steps required to seed neuroblastoma cell lines on previously described three-dimensional collagen-based scaffolds, maintain cell growth for a predetermined timeframe, and retrieve scaffolds for several cell growth and cell behavior analyses and downstream applications, adaptable to satisfy a range of experimental aims.

Neuroblastoma is the most common extracranial solid tumor in children, accounting for 15% of overall pediatric cancer deaths. The native tumor tissue is a ...