This work was supported by grant R15CA169978 from the National Institutes of Health. Additional funding came from Villanova University.

All experiments and methods were performed as authorized by Villanova University Institutional Animal Care and Use Committee (IACUC).
1. Gene Expression in Cultured Mouse Mammary Tumor Cells
<ol>
	<li>First, prepare the cell lines to be tested.</li>
	<li>Use a breeding colony of BALB/cV mice. These mice carry the BALB/cV strain of mouse mammary tumor virus, transmitted to pups in milk6,7. Fifty percent of breeding females develop mammary tumors by 10 months of age.
	<ol>
		<li>To establish a tumor cell line, sacrifice a tumor-bearing dam using an IACUC-approved protocol. Soak the abdominal skin in 70% EtOH and remove the tumor under sterile conditions in a laminar flow hood. Tumors are subcutaneous, so take care to avoid puncturing the peritoneum.</li>
		<li>Place tumor fragments from non-necrotic areas in a petri dish with a small amount of sterile Hanks Balanced Saline Solution (HBSS) and mince very finely with a sterile razor blade.</li>
		<li>Transfer the dispersed cell clumps to a T25 cell culture flask containing 5 mL Dulbecco&#39;s Modified Eagle Medium or DMEM (4.5 g/L glucose, phenol red, and L-glutamine) supplemented with 50% Fetal Bovine Serum or FBS and 1% antibiotic/antimycotic solution. Grow cells in treated cell culture flasks in an incubator with 5% CO2 and 100% humidity at 37 &#176;C.</li>
		<li>Wash off non-adherent cells after 24-48 h and replace the DMEM with 50% FBS and 1% antibiotic/antimycotic solution. Return the cells to the incubator.</li>
		<li>Replace liquid culture media every 3 days.</li>
		<li>Split or passage the cells when they are 90% confluent. Remove culture media and wash adherent cells with HBSS (without calcium or magnesium). Incubate cells with 0.25% Trypsin-EDTA solution for 1-5 min at 37 &#176;C until cells are rounded and detached. Dilute cells 1:10 in fresh culture media and add to a new flask. A T-25 cell culture flask requires 5-8 mL culture media, 5 mL of HBSS to wash, and 1 mL of trypsin-EDTA to passage. Return the flask to the incubator.</li>
		<li>Reduce the FBS concentration to 40% after the first passage, then 30% after the second passage, then 20% after the third passage, and finally 10% for all subsequent passages. The process of establishing growth in standard DMEM medium with 10% FBS requires four passages and 2 - 8 months.</li>
	</ol>
	</li>
	<li>Once the cell line(s) are established, alter the expression of suspected oncogenes by transfection of shRNA targeting mRNA or CRISPR for non-essential genes.
	<ol>
		<li>Establish antibiotic-resistant stable cell lines with individual clones that are verified by western blot and/or RT-qPCR for consistent results, however, transient transfections can work as well since the assay only requires 22 h. Control cell lines with non-specific target sequences are also required.</li>
	</ol>
	</li>
</ol>
2. In Vitro Invasion Assay
<ol>
	<li>Grow adherent mouse mammary tumor cells in a T25 flask until 70-90% confluent for Day 1 of the experiment. 
	NOTE: Other cell lines or experimental conditions may require different cell culture media. For example, if hormone-responsive breast cancer cells are being tested, charcoal-filtered serum may be needed to remove compounds that activate estrogen or other hormone receptors.</li>
	<li>Prepare the Boyden chamber inserts by warming them to room temperature (from -20 &#176;C storage) for about 20 min in a cell culture hood. Avoid freeze-thaw cycles for unused inserts. Use three inserts (replicates) to generate statistically valid data for each cell line for each experiment.
	<ol>
		<li>Add pre-warmed 37 &#176;C serum-free DMEM media to the well and then the insert. For inserts designed for 24-well dishes, add 500 &#181;L of serum-free DMEM to the well and then 500 &#181;L of serum-free DMEM to the insert so the porous membrane and gel are hydrated on both sides. 
		NOTE: For larger inserts designed for a 6-well dish, use 2 mL of serum-free DMEM on both sides.</li>
	</ol>
	</li>
	<li>Place the dish with inserts into a 37 &#176;C cell culture incubator with 5% CO2 and 100% humidity for at least 2 h to thoroughly hydrate and acclimate.</li>
	<li>Prepare cells by removing the growth media and rinsing the cells with 5 mL HBSS.
	<ol>
		<li>Remove the HBSS and add 1 mL 0.25% trypsin-EDTA solution for 1 - 5 min at 37 &#176;C or until cells appear rounded or show signs of detachment from the flask.</li>
		<li>Gently tap the flask to detach all the cells. Resuspend the cells in 5 mL of DMEM + 10% FBS and transfer to a sterile 15 mL centrifuge tube.</li>
		<li>Centrifuge the cells at 1,000 x g for 5 min to gently pellet the cells. Remove the media and replace with 5 mL serum-free DMEM to resuspend the cells.</li>
		<li>Repeat the centrifugation and suspension in serum-free media twice more for a total of 3 washes.</li>
		<li>Thoroughly resuspend the cells in the final 5 mL of serum-free DMEM and ensure there are no clumps of cells.</li>
	</ol>
	</li>
	<li>Determine the cell concentration using a hemocytometer. Count only viable cells. Dilute the cell suspension to 5 x 104 cells/mL in 5 mL of serum-free DMEM. 
	NOTE: This concentration yields 2,500 cells per insert in a 24-well dish. This number of cells is enough for aggressive cancer cells with high rates of migration and invasion. Less aggressive cell lines may require more cells, up to 10,000 cells per insert for observable invading cells. If reduced cell invasion is expected, consider maximizing invading cells by increasing cell number. If increased cell invasion is expected, begin with fewer cells.</li>
	<li>Remove the cell culture dish from the incubator and gently aspirate the media from the insert. Lift the insert and aspirate the media from the well. Working quickly, add the chemoattractant to the lower chamber. For a 24-well dish, add 750 &#181;L of DMEM with 5% FBS.
	<ol>
		<li>Place the insert in the well and add the cells to the insert. For a 24-well dish, use 500 &#181;L of cell suspension. For a 6-well dish insert, use 2.5 mL of chemoattract and 2 mL of cells. Ensure that no bubbles of air are present on either side of the membrane.</li>
		<li>Return the dish to the cell culture incubator for 22 h.</li>
	</ol>
	</li>
	<li>After 22 h, fix and stain the cells. Prepare a solution of 1% paraformaldehyde in 1x phosphate buffered saline (PBS) for fixation.
	<ol>
		<li>In a clean 24-well cell culture dish, add 1 mL of fixative to individual wells so there is one well for each insert.</li>
		<li>Prepare the staining solution (freshly made) of 0.1% crystal violet (w/v) in a solution of PBS with 10% ethanol (v/v). Similarly, add 1 mL of staining solution to a clean well in a 24-well culture dish for each insert.</li>
		<li>Remove each insert one at a time with forceps and place a sterile cotton swab inside the insert and swab the upper side of the membrane to remove unmigrated cells.</li>
		<li>Repeat with a second cotton swab. The membrane is rather strong, so gentle pressure while swabbing does not compromise the integrity of the membrane.</li>
		<li>Remove any remaining media from the inside of the insert and add 750 &#181;L of PBS to wash away detached cells.</li>
		<li>Remove the PBS and repeat the wash. Place the insert into a well containing fixative to fix the migrated cells on the underside of the membrane. Repeat for all inserts.</li>
		<li>Fix the inserts for 15 min at room temperature.</li>
		<li>Following fixation remove the insert. Wash the insert again with 750 &#181;L PBS.</li>
		<li>Place the insert into the well with the staining solution to stain all migrated and fixed cells. Stain the cells for 15 min at room temperature. 
		NOTE: For 6-well dish inserts, use 2 mL of fixative solution, 2 mL staining solution, and 2 mL of PBS wash.</li>
	</ol>
	</li>
	<li>Use a beaker with distilled water to destain the inserts. Remove the inserts and dip into the distilled water until the water running off the insert is clear.
	<ol>
		<li>Remove any excess water droplets and place the inserts onto a filter paper sidewise to air dry (usually overnight).</li>
	</ol>
	</li>
	<li>Prepare the membrane for imaging by labeling a clean glass microscope slide for each insert and place a small drop of microscope immersion oil in the center of the slide.
	<ol>
		<li>Detach the membrane from the insert using a scalpel to cut around the perimeter of the membrane on the inside of the plastic insert.</li>
		<li>Remove the membrane using forceps and place on the top of the oil drop on the slide to hold it in place. 
		NOTE: The membranes are very thin and very light, so they can easily be lost by gentle air flow.</li>
	</ol>
	</li>
</ol>
3. Imaging and Analysis
<ol>
	<li>Since the porous membranes are clear and staining cells with crystal violet give them contrast, use a compound light microscope to view the cells. Use a camera and/or software to quantify for many samples but is not necessary. View cells at 5x, 10x, or 20x magnification. For quantification, use multiple, non-overlapping images at 10x magnification. Alternatively, count all migrated cells on the membrane at 10x magnification.</li>
	<li>Determine the total number of invading cells or cells per area for all samples. For each experiment, perform each condition in the assay with three replicate inserts and repeat multiple times for statistically useful results.</li>
	<li>When comparing different cell lines with different growth rates and migration rates, do a parallel experiment to compare cells that invade through a protein matrix and compare to a Boyden Chamber assembly without protein matrix (migrated cells only). Calculate percent invasion for each cell line (Number of invaded cells/number of migrated cells x 100%). 
	NOTE: This approach can help compare invasion rate to migration rates. If comparing different conditions applied to the same cell line, calculating invasion alone is more relevant calculations. The outer edge of the membrane sometimes has a higher number of cells than the central areas and is, therefore, less accurate. If this occurs, exclude those cells from the quantification and ensure that all cells are removed by a cotton swab in a repeat experiment.</li>
</ol>

<ol>
	<li>He, X., Lee, B., Jiang, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell-ECM+Interactions+in+Tumor+Invasion.">Cell-ECM Interactions in Tumor Invasion.</a> Advances in Experimental Medicine and Biology. 936, 73-91 (2016).</li><li>Albini, A., 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=A+rapid+in+vitro+assay+for+quantitating+the+invasive+potential+of+tumor+cells.">A rapid in vitro assay for quantitating the invasive potential of tumor cells.</a> Cancer Research. 47 (12), 3239-3245 (1987).</li><li>Simon, N., Noel, A., Foidart, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+in+vitro+reconstituted+basement+membrane+assay+to+assess+the+invasiveness+of+tumor+cells.">Evaluation of in vitro reconstituted basement membrane assay to assess the invasiveness of tumor cells.</a> Invasion and Metastasis. 12 (3-4), 156-167 (1992).</li><li>Benton, G., Arnaoutova, I., George, J., Kleinman, H. K., Koblinski, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Matrigel:+from+discovery+and+ECM+mimicry+to+assays+and+models+for+cancer+research.">Matrigel: from discovery and ECM mimicry to assays and models for cancer research.</a> Advanced Drug Delivery Reviews. 79-80, 3-18 (2014).</li><li>Kleinman, H. K., Martin, G. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Matrigel:+basement+membrane+matrix+with+biological+activity.">Matrigel: basement membrane matrix with biological activity.</a> Seminars in Cancer Biology. 15 (5), 378-386 (2005).</li><li>Kang, J. J., Schwegel, T., Knepper, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sequence+similarity+between+the+long+terminal+repeat+coding+regions+of+mammary-tumorigenic+BALB/cV+and+renal-tumorigenic+C3H-K+strains+of+mouse+mammary+tumor+virus.">Sequence similarity between the long terminal repeat coding regions of mammary-tumorigenic BALB/cV and renal-tumorigenic C3H-K strains of mouse mammary tumor virus.</a> Virology. 196 (1), 303-308 (1993).</li><li>Slagle, B. L., Lanford, R. E., Medina, D., Butel, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Expression+of+mammary+tumor+virus+proteins+in+preneoplastic+outgrowth+lines+and+mammary+tumors+of+BALB/cV+mice.">Expression of mammary tumor virus proteins in preneoplastic outgrowth lines and mammary tumors of BALB/cV mice.</a> Cancer Research. 44 (5), 2155-2162 (1984).</li><li>Schmidt, J. A., 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=Regulation+of+the+oncogenic+phenotype+by+the+nuclear+body+protein+ZC3H8.">Regulation of the oncogenic phenotype by the nuclear body protein ZC3H8.</a> BMC Cancer. 18 (1), 759 (2018).</li><li>Neophytou, C., Boutsikos, P., Papageorgis, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+Mechanisms+and+Emerging+Therapeutic+Targets+of+Triple-Negative+Breast+Cancer+Metastasis.">Molecular Mechanisms and Emerging Therapeutic Targets of Triple-Negative Breast Cancer Metastasis.</a> Frontiers in Oncology. 8, 31 (2018).</li><li>Al-Alwan, 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=Fascin+is+a+key+regulator+of+breast+cancer+invasion+that+acts+via+the+modification+of+metastasis-associated+molecules.">Fascin is a key regulator of breast cancer invasion that acts via the modification of metastasis-associated molecules.</a> PloS One. 6 (11), e27339 (2011).</li><li>Wang, M. J., Zhang, H., Li, J., Zhao, H. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=microRNA-98+inhibits+the+proliferation,+invasion,+migration+and+promotes+apoptosis+of+breast+cancer+cells+by+binding+to+HMGA2.">microRNA-98 inhibits the proliferation, invasion, migration and promotes apoptosis of breast cancer cells by binding to HMGA2.</a> Bioscience Reports. 38 (5), (2018).</li><li>Zheng, Y. F., Luo, J., Gan, G. 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The authors have nothing to disclose.

The in vitro invasion assay is an inexpensive, rapid, quantitative, and straightforward method for studying the factors promoting cancer cell invasion. Breast cancer is the most commonly diagnosed cancer among women. Of the three major subtypes of breast cancer, triple negative, (or ER-, PR-, HER2/neu-), is the most aggressive, most likely to metastasize, and most deadly9. Therefore, understanding the genes and expression that result in metastasis can help find new therapeutic targets and...

The in vitro invasion assay can be a useful tool when measuring a cell&#39;s ability to migrate through a protein-coated membrane, analogous to the first steps in metastasis. A key feature of malignant cancer cells is their ability to migrate through and invade nearby tissues. Cancer that has spread or metastasized poses more treatment challenges and has lower rates of long-term survival, while localized tumors are easier to treat and have higher rates of long-term survival. In order to metastasize, cancer cells must leave the primary tumor and migrate into the circulatory or lymphatic system, a process which requires passing through the extracellular matrix and basement membrane1. In the process called the epithelial mesenchymal transition (EMT), the tumor cells must break cell-cell contacts, migrate directionally, and invade nearby blood or lymph vessels. The initial steps of this metastasis cascade are of great interest since these steps are what can make cancer deadlier. The genetic and epigenetic factors involved in the early steps of metastasis are the focus of a great amount of research, but accurate and reliable experimental tools are needed to test these early steps both in vivo and in vitro.
Tools to measure changes in cell migration such as wound healing (scratch) assays or growth in 3D environments such as soft agar assays can partially address the need for experimental methods of measuring early steps of metastasis, but an assay to measure invasion is more challenging since the process occurs in the body within a complex tumor microenvironment. For the purposes of screening drugs or gene alterations to determine important factors in invasion and metastasis, a system that can be used in vitro with cultured cells and mimic the challenges faced by metastatic cells in vivo is the invasion assay2,3. Breast cancer is the most commonly diagnosed type of cancer in women and the second leading cause of cancer death in women, so understanding the genes responsible for breast cancer cell invasion and metastasis is critically important for public health. Moreover, mouse cells are a useful model system for studying breast cancer and its progression.
The in vitro invasion assay is based on the Boyden Chamber assembly where two chambers of growth media are separated by a porous membrane3. To mimic the tumor microenvironment, a protein-rich gel is also included to separate cells in one chamber from a chemoattractant in the other and act as a basement membrane barrier. In order to migrate towards the chemoattractant, cells must first pass through the protein-rich barrier then pass through the porous membrane - a process analogous to how metastatic cells migrate through stroma. The protein-rich gel can be altered based on the needs of the experiment, but usually consists of collagen, or basement membrane extract (e.g., Matrigel)4. It is a complex mixture of proteins, proteoglycans and growth factors, but mostly consists of laminins and collagen IV 4,5. Cells must then pass through a porous membrane typically made of polycarbonate, polyester, or polytetrafluoroethylene (PTFE). Membranes may be purchased commercially with or without a protein gel (typically collagens), or the gel may be purchased separately and added. The pore size can be adjusted based on the cell size. While pore sizes are available from 0.4 - 8.0 &#181;m, only pores from 3.0 - 8.0 &#181;m are large enough for cell migration. The invasion assay has been used to determine the effectiveness of inhibitors on the ability of cells to migrate and invade. While lacking the exact tumor microenvironment that is present in vivo, the in vitro invasion assay is beneficial at screening many conditions in a short time while minimizing the need for animal models. The goal of these experiments is to compare gene expression of suspected oncogenes and determine the effects on cancer cell behavior and disease aggressiveness using the in vitro invasion assay and other tests. Overall, the invasion assay provides consistent, quantitative, and rapid results for determining metastatic potential while also being a relatively inexpensive, straightforward, and adaptable method.

<table><tbody><tr><td>24-well plates</td><td>Corning</td><td>353504</td><td></td></tr><tr><td>Antibiotic-Antimycotic (100x)</td><td>ThermoFisher</td><td>15240062</td><td></td></tr><tr><td>BALB/c mice</td><td></td><td></td><td></td></tr><tr><td>Cell Culture Incubator</td><td></td><td></td><td></td></tr><tr><td>Cell Culture Treated Flasks</td><td></td><td></td><td></td></tr><tr><td>Clinical cenrifuge</td><td></td><td></td><td></td></tr><tr><td>Cotton swab</td><td>Puritan</td><td>25-806</td><td></td></tr><tr><td>Crystal Violet</td><td>Sigma Aldrich</td><td>C0775</td><td></td></tr><tr><td>Distilled water</td><td></td><td></td><td></td></tr><tr><td>DMEM</td><td>ThermoFisher</td><td>10566-016</td><td>high glucose, GlutaMAX</td></tr><tr><td>Ethanol</td><td></td><td></td><td></td></tr><tr><td>FBS</td><td>Sigma Aldrich</td><td>F2442-500ML</td><td></td></tr><tr><td>Forcepts</td><td></td><td></td><td></td></tr><tr><td>Glass Slide</td><td>VWR</td><td>16004-422</td><td></td></tr><tr><td>HBSS</td><td>ThermoFisher</td><td>14025076</td><td>no calcium, no magnesium</td></tr><tr><td>Hemocytometer</td><td></td><td></td><td></td></tr><tr><td>Imersion oil</td><td></td><td></td><td></td></tr><tr><td>Invasion Chambers (24-well)</td><td>Corning</td><td>354480</td><td>Cat. #354481 for 6-well</td></tr><tr><td>Light Microscope</td><td></td><td></td><td></td></tr><tr><td>Lipofectamine Transfection Reagent</td><td></td><td></td><td></td></tr><tr><td>Paraformaldehyde</td><td>Sigma Aldrich</td><td>P6148</td><td></td></tr><tr><td>PBS</td><td></td><td></td><td></td></tr><tr><td>Scalpel, disposable</td><td></td><td></td><td>#11</td></tr><tr><td>shRNA</td><td></td><td></td><td></td></tr><tr><td>Sterile Transfer pipet</td><td></td><td></td><td></td></tr><tr><td>Trypsin-EDTA</td><td>ThermoFisher</td><td>25200056</td><td></td></tr></tbody></table>

the use of mouse mammary tumor cells in an in vitro invasion assay as a measure of oncogenic cell behavior

The in vitro invasion assay uses a protein-rich matrix in a Boyden chamber to measure the ability of cultured cells to pass through the matrix and a porous membrane in a process analogous to the initial steps of cancer cell metastasis. The tested cells can be altered for the gene expression or treated with inhibitors to test for changes in the invasion potential. This experiment tests the aggressive phenotype of the mouse mammary tumor cells to discover and characterize the potential oncogenes that promote cell invasion. This technique, however, can be versatile and adapted to many different applications. The experiment itself can be done in one day and the results are acquired by light microscopy in less than a day. The results include counts of the number of invading cells for comparison and analysis. The in vitro invasion assay is a rapid, inexpensive, and clear-cut method for determining cell behavior in a culture that can be used as an initial assessment before more involved in vivo assays.

This method of in vitro invasion through a protein matrix was used to assess the aggressive phenotypes and oncogenic cell behaviors of mouse mammary tumor cells with altered expression of the zinc finger protein ZC3H88. In conjunction with other approaches that also examine cell migration and growth in 3D environments, it was found that higher levels of expression of Zc3h8 in tumor cell lines, or by promoter-mediated expression from a plasmid, resulted in rapid rat...

Watch this Scientific Journal Video about The Use of Mouse Mammary Tumor Cells in an In Vitro Invasion Assay as a Measure of Oncogenic Cell Behavior at JoVE.com

The Use of Mouse Mammary Tumor Cells in an In Vitro Invasion Assay as a Measure of Oncogenic Cell Behavior

The in vitro cell invasion assay is used to measure the potential of cancer metastasis by quantifying the cellular potential for invasion and migration using cell culture inserts containing protein matrix. Cells are challenged to migrate through the protein matrix and a porous membrane, towards a chemoattractant, and then quantified by light microscopy.

The in vitro invasion assay uses a protein-rich matrix in a Boyden chamber to measure the ability of cultured cells to pass through the matrix and a ...

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Research

JoVE Journal

Genetics

5.1K Views.  Villanova University. The in vitro cell invasion assay is used to measure the potential of cancer metastasis by quantifying the cellular potential for invasion and migration using cell culture inserts containing protein matrix. Cells are challenged to migrate through the protein matrix and a porous membrane, towards a chemoattractant, and then quantified by light microscopy.

Video: The Use of Mouse Mammary Tumor Cells in an In Vitro Invasion Assay as a Measure of Oncogenic Cell Behavior

Spheroid Assay to Measure TGF-&#946;-induced Invasion

TGF-&beta; has opposing roles in breast cancer progression by acting as a tumor suppressor in the initial phase, but stimulating invasion and metastasis at later stage1,2. Moreover, TGF-&beta; is frequently overexpressed in breast cancer and its expression correlates with poor prognosis and metastasis 3,4. The mechanisms by which TGF-&beta; induces invasion are not well understood.
TGF-&beta; elicits its cellular responses via TGF-&beta; type II (T&beta;RII) and type I (T&beta;RI) receptors. Upon TGF-&beta;-induced heteromeric complex formation, T&beta;RII phosphorylates the T&beta;RI. The activated T&beta;RI initiates its intracellular canonical signaling pathway by phosphorylating receptor Smads (R-Smads), i.e. Smad2 and Smad3. These activated R-Smads form heteromeric complexes with Smad4, which accumulate in the nucleus and regulate the transcription of target genes5. In addition to the previously described Smad pathway, receptor activation results in activation of several other non-Smad signaling pathways, for example Mitogen Activated Protein Kinase (MAPK) pathways6.
To study the role of TGF-&beta; in different stages of breast cancer, we made use of the MCF10A cell system. This system consists of spontaneously immortalized MCF10A1 (M1) breast epithelial cells7, the H-RAS transformed M1-derivative MCF10AneoT (M2), which produces premalignant lesions in mice8, and the M2-derivative MCF10CA1a (M4), which was established from M2 xenografts and forms high grade carcinomas with the ability to metastasize to the lung9. This MCF10A series offers the possibility to study the responses of cells with different grades of malignancy that are not biased by a different genetic background.
For the analysis of TGF-&beta;-induced invasion, we generated homotypic MCF10A spheroid cell cultures embedded in a 3D collagen matrix in vitro (Fig 1). Such models closely resemble human tumors in vivo by establishing a gradient of oxygen and nutrients, resulting in active and invasive cells on the outside and quiescent or even necrotic cells in the inside of the spheroid10. Spheroid based assays have also been shown to better recapitulate drug resistance than monolayer cultures11. This MCF10 3D model system allowed us to investigate the impact of TGF-&beta; signaling on the invasive properties of breast cells in different stages of malignancy.

An assay to quantitatively measure Transforming Growth Factor (TGF)-&#x03B2;-induced invasion in 3-dimensional collagen gels is described. This assay takes advantage of the MCF10A series of cell lines, which represent different stages of breast cancer development. This method can be adopted to be used with other cell lines and might be used to investigate other potential activators or inhibitors of invasion.

TGF-&beta; has opposing roles in breast cancer progression by acting as a tumor suppressor in the initial phase, but stimulating invasion and metastasis ...

Medicine

Orthotopic Injection of Breast Cancer Cells into the Mice Mammary Fat Pad

A proper animal model is crucial for a better understanding of diseases. Animal models established by different methods (subcutaneous injections, xenografts, genetic manipulation, chemical reagents induction, etc.) have various pathological characters and play important roles in investigating certain aspects of diseases. Although no single model can totally mimic the whole human disease progression, orthotopic organs disease models with a proper stromal environment play an irreplaceable role in understanding diseases and screening for potential drugs. In this article, we describe how to implant breast cancer cells into the mammary fat pad in a simple, less invasive, and easy-to-handle way, and follow the metastasis to distant organs. With the proper features of primary tumor growth, breast and nipple pathological changes, and a high occurrence of other organs&#39; metastasis, this model maximumly mimics human breast cancer progression. Primary tumor growth in situ, long-distant metastasis, and the tumor microenvironment of breast cancer can be investigated by using this model.

Here, we present a protocol to implant breast cancer cells into the mammary fat pad in a simple, less invasive, and easy-to-handle way, and this mouse orthotopic breast cancer model with a proper mammary fat pad environment can be used to investigate various aspects of cancer.

A proper animal model is crucial for a better understanding of diseases. Animal models established by different methods (subcutaneous injections, ...

Cancer Research

Orthotopic Transplantation of Breast Tumors as Preclinical Models for Breast Cancer

Preclinical models that faithfully recapitulate tumor heterogeneity and therapeutic response are critical for translational breast cancer research. Immortalized cell lines are easy to grow and genetically modify to study molecular mechanisms, yet the selective pressure from cell culture often leads to genetic and epigenetic alterations over time. Patient-derived xenograft (PDX) models faithfully recapitulate the heterogeneity and drug response of human breast tumors. PDX models exhibit a relatively short latency after orthotopic transplantation that facilitates the investigation of breast tumor biology and drug response. The transplantable genetically engineered mouse models allow the study of breast tumor immunity. The current protocol describes the method to orthotopically transplant breast tumor fragments into the mammary fat pad followed by drug treatments. These preclinical models provide valuable approaches to investigate breast tumor biology, drug response, biomarker discovery and mechanisms of drug resistance.

Patient-derived xenograft (PDX) models and transplantable genetically engineered mouse models faithfully recapitulate human disease and are preferred models for basic and translational breast cancer research. Here, a method is described to orthotopically transplant breast tumor fragments into the mammary fat pad to study tumor biology and evaluate drug response.

Preclinical models that faithfully recapitulate tumor heterogeneity and therapeutic response are critical for translational breast cancer research. ...

In Vitro Evaluation of Oncogenic Transformation in Human Mammary Epithelial Cells

Tumorigenesis is a multi-step process in which cells acquire capabilities&#160;that allow their growth, survival, and dissemination under hostile conditions. Different tests seek to identify and quantify these hallmarks of cancerous cells; however, they often focus on a single aspect of cellular transformation and, in fact, multiple tests are required for their proper characterization. The purpose of this work is to provide researchers with a set of tools to assess cellular transformation in vitro from a broad perspective, thereby making it possible to draw sound conclusions.
A sustained proliferative signaling activation is the major feature of tumoral tissues and can be easily monitored under in vitro conditions by calculating the number of population doublings achieved over time. Besides, the growth of cells in 3D cultures allows their interaction with surrounding cells, resembling what occurs in vivo. This enables the evaluation of cellular aggregation and, together with immunofluorescent labeling of distinctive cellular markers, to obtain information on another relevant feature of tumoral transformation: the loss of proper organization. Another remarkable characteristic of transformed cells is their capacity to grow without attachment to other cells and to the extracellular matrix, which can be evaluated with the anchorage assay.
Detailed experimental procedures to evaluate cell growth rate, to perform immunofluorescent labeling of cell lineage markers in 3D cultures, and to test anchorage-independent cell growth in soft agar are provided. These methodologies are optimized for Breast Primary Epithelial Cells (BPEC) due to its relevance in breast cancer; however, procedures can be applied to other cell types after some adjustments.

This protocol provides experimental in vitro tools to evaluate the transformation of human mammary cells. Detailed steps to follow-up cell proliferation rate, anchorage-independent growth capacity, and distribution of cell lineages in 3D cultures with basement membrane matrix are described.

Tumorigenesis is a multi-step process in which cells acquire capabilities&#160;that allow their growth, survival, and dissemination under hostile ...

Initiation of Metastatic Breast Carcinoma by Targeting of the Ductal Epithelium with Adenovirus-Cre: A Novel Transgenic Mouse Model of Breast Cancer

Breast cancer is a heterogeneous disease involving complex cellular interactions between the developing tumor and immune system, eventually resulting in exponential tumor growth and metastasis to distal tissues and the collapse of anti-tumor immunity. Many useful animal models exist to study breast cancer, but none completely recapitulate the disease progression that occurs in humans. In order to gain a better understanding of the cellular interactions that result in the formation of latent metastasis and decreased survival, we have generated an inducible transgenic mouse model of YFP-expressing ductal carcinoma that develops after sexual maturity in immune-competent mice and is driven by consistent, endocrine-independent oncogene expression. Activation of YFP, ablation of p53, and expression of an oncogenic form of K-ras was achieved by the delivery of an adenovirus expressing Cre-recombinase into the mammary duct of sexually mature, virgin female mice. Tumors begin to appear 6 weeks after the initiation of oncogenic events. After tumors become apparent, they progress slowly for approximately two weeks before they begin to grow exponentially. After 7-8 weeks post-adenovirus injection, vasculature is observed connecting the tumor mass to distal lymph nodes, with eventual lymphovascular invasion of YFP+ tumor cells to the distal axillary lymph nodes. Infiltrating leukocyte populations are similar to those found in human breast carcinomas, including the presence of &#945;&#946; and &#947;&#948; T cells, macrophages and MDSCs. This unique model will facilitate the study of cellular and immunological mechanisms involved in latent metastasis and dormancy in addition to being useful for designing novel immunotherapeutic interventions to treat invasive breast cancer.

Activation of latent mutations with adenovirus-Cre into the mammary ductal system results in a clinically relevant metastatic breast cancer. Incorporation of a YFP promoter allows tracking of distal metastatic tumor cells. This model is useful to study latent metastasis, anti-tumor immunity, and for designing novel immunotherapies to treat breast cancer.

Breast cancer is a heterogeneous disease involving complex cellular interactions between the developing tumor and immune system, eventually resulting in ...

In Vivo Imaging to Measure Spontaneous Lung Metastasis of Orthotopically-injected Breast Tumor Cells

Metastasis remains the primary cause of cancer-related death. The succession of events that characterize the metastatic cascade presents multiple opportunities for therapeutic intervention, and the ability to accurately model them in mice is critical to evaluate their effects. Here, a step-by-step protocol is presented for the establishment of orthotopic primary breast tumors and the subsequent monitoring of the establishment and growth of metastatic lesions in the lung using in vivo bioluminescence imaging. This methodology allows for the evaluation of treatment or its biological effects along the entire range of metastatic development, from primary tumor escape to outgrowth in the lungs. Breast orthotopic tumors are generated in mice via injection of a luciferase-labeled cell suspension in the 4th mammary gland. Tumors are allowed to grow and disseminate for a specific amount of time and are then surgically resected. Upon resection, spontaneous lung metastasis is detected, and the growth over time is monitored using in vivo bioluminescence imaging. At the desired experimental endpoint, lung tissue can be collected for downstream analysis. The treatment of established, clinically evident metastasis is critical to improve outcomes for stage IV cancer patients, and it can be evaluated through tail vein models of experimental lung metastasis. However, metastatic dissemination occurs early in breast cancer, and many patients have latent, subclinical disseminated disease after surgery. Utilization of spontaneous models such as this one provides the opportunity to study the whole spectrum of the disease, especially the systemic effects driven by treatment of the primary tumor such as pre-metastatic niche priming, and evaluate treatments on dormant and subclinical disease after surgery.

In Vivo Imaging to Measure Spontaneous Lung Metastasis of Orthotopically-injected Breast Tumor Cells

The manuscript describes a methodology for the establishment as well as longitudinal growth monitoring of spontaneous lung metastasis from orthotopically-injected breast tumors, amenable to intervention at all stages of the metastatic cascade.

Metastasis remains the primary cause of cancer-related death. The succession of events that characterize the metastatic cascade presents multiple ...

Quantification of Breast Cancer Cell Invasiveness Using a Three-dimensional (3D) Model

It is now well known that the cellular and tissue microenvironment are critical regulators influencing tumor initiation and progression. Moreover, the extracellular matrix (ECM) has been demonstrated to be a critical regulator of cell behavior in culture and homeostasis in vivo. The current approach of culturing cells on two-dimensional (2D), plastic surfaces results in the disturbance and loss of complex interactions between cells and their microenvironment. Through the use of three-dimensional (3D) culture assays, the conditions for cell-microenvironment interaction are established resembling the in vivo microenvironment. This article provides a detailed methodology to grow breast cancer cells in a 3D basement membrane protein matrix, exemplifying the potential of 3D culture in the assessment of cell invasion into the surrounding environment. In addition, we discuss how these 3D assays have the potential to examine the loss of signaling molecules that regulate epithelial morphology by immunostaining procedures. These studies aid to identify important mechanistic details into the processes regulating invasion, required for the spread of breast cancer.

Quantification of Breast Cancer Cell Invasiveness Using a Three-dimensional 3D Model

This article provides detailed methodologies for the use of three-dimensional (3D) assays to quantify breast cancer cell invasion. Specifically, we discuss the procedures required to set up such assays, quantification, and data analysis, as well as methods to examine the loss of membrane integrity that occurs when cells invade.

It is now well known that the cellular and tissue microenvironment are critical regulators influencing tumor initiation and progression. Moreover, the ...

In Vivo Gene Delivery into Mouse Mammary Epithelial Cells Through Mammary Intraductal Injection

Mouse mammary glands comprise ductal trees, which are lined by epithelial cells and have one opening at the tip of each nipple. The epithelial cells play a major role in mammary gland function and are the origin of most mammary tumors. Introducing genes of interest into mouse mammary epithelial cells is a critical step in evaluating gene function in epithelial cells and generating mouse mammary tumor models. This goal can be accomplished through the intraductal injection of a viral vector carrying the genes of interest into the mouse mammary ductal tree. The injected virus subsequently infects mammary epithelial cells, bringing in the genes of interest. The viral vector can be lentiviral, retroviral, adenoviral, or adenovirus-associated viral (AAV). This study demonstrates how a gene of interest is delivered into mammary epithelial cells through mouse mammary intraductal injection of a viral vector. A lentivirus carrying GFP is used to show stable expression of a delivered gene, and a retrovirus carrying Erbb2 (HER2/Neu) is used to demonstrate oncogene-induced atypical hyperplastic lesions and mammary tumors.

In Vivo Gene Delivery into Mouse Mammary Epithelial Cells Through Mammary Intraductal Injection

The present protocol describes intraductal injection of viral vectors via the teat to deliver genes of interest into the mammary epithelial cells.

Mouse mammary glands comprise ductal trees, which are lined by epithelial cells and have one opening at the tip of each nipple. The epithelial cells play ...

Orthotopic Injection of Breast Cancer Cells into the Mammary Fat Pad of Mice to Study Tumor Growth.

Breast cancer growth can be studied in mice using a plethora of models. Genetic manipulation of breast cancer cells may provide insights into the functions of proteins involved in oncogenic progression or help to discover new tumor suppressors. In addition, injecting cancer cells into mice with different genotypes might provide a better understanding of the importance of the stromal compartment. Many models may be useful to investigate certain aspects of disease progression but do not recapitulate the entire cancerous process. In contrast, breast cancer cells engraftment to the mammary fat pad of mice better recapitulates the location of the disease and presence of the proper stromal compartment and therefore better mimics human cancerous disease. In this article, we describe how to implant breast cancer cells into mice orthotopically and explain how to collect tissues to analyse the tumor milieu and metastasis to distant organs. Using this model, many aspects (growth, angiogenesis, and metastasis) of cancer can be investigated simply by providing a proper environment for tumor cells to grow.

Cancer is a complex disease that is influenced by the tissue surrounding the tumor as well as local pro- and anti-inflammatory mediators. Therefore, orthotropic injection models, rather than subcutaneous models may be useful to study cancer progression in a manner that better mimics human pathology.

Breast cancer growth can be studied in mice using a plethora of models. Genetic manipulation of breast cancer cells may provide insights into the ...

Three-Dimensional (3D) Tumor Spheroid Invasion Assay

Invasion of surrounding normal tissues is generally considered to be a key hallmark of malignant (as opposed to benign) tumors. For some cancers in particular (e.g., brain tumors such as glioblastoma multiforme and squamous cell carcinoma of the head and neck &#8211; SCCHN) it is a cause of severe morbidity and can be life-threatening even in the absence of distant metastases. In addition, cancers which have relapsed following treatment unfortunately often present with a more aggressive phenotype. Therefore, there is an opportunity to target the process of invasion to provide novel therapies that could be complementary to standard anti-proliferative agents. Until now, this strategy has been hampered by the lack of robust, reproducible assays suitable for a detailed analysis of invasion and for drug screening. Here we provide a simple micro-plate method (based on uniform, self-assembling 3D tumor spheroids) which has great potential for such studies. We exemplify the assay platform using a human glioblastoma cell line and also an SCCHN model where the development of resistance against targeted epidermal growth factor receptor (EGFR) inhibitors is associated with enhanced matrix-invasive potential. We also provide two alternative methods of semi-automated quantification: one using an imaging cytometer and a second which simply requires standard microscopy and image capture with digital image analysis.

Three-Dimensional 3D Tumor Spheroid Invasion Assay

Invasion of surrounding normal tissues is a defining characteristic of malignant tumors. We provide here a simple, semi-automated micro-plate assay of invasion into a natural 3D biomatrix that has been exemplified with a number of models of advanced human cancers.

Invasion of surrounding normal tissues is generally considered to be a key hallmark of malignant (as opposed to benign) tumors. For some cancers in ...

The Use of Mouse Mammary Tumor Cells in an In Vitro Invasion Assay as a Measure of Oncogenic Cell Behavior

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Spheroid Assay to Measure TGF-β-induced Invasion

Orthotopic Injection of Breast Cancer Cells into the Mice Mammary Fat Pad

Orthotopic Transplantation of Breast Tumors as Preclinical Models for Breast Cancer

In Vitro Evaluation of Oncogenic Transformation in Human Mammary Epithelial Cells

Initiation of Metastatic Breast Carcinoma by Targeting of the Ductal Epithelium with Adenovirus-Cre: A Novel Transgenic Mouse Model of Breast Cancer

In Vivo Imaging to Measure Spontaneous Lung Metastasis of Orthotopically-injected Breast Tumor Cells

Quantification of Breast Cancer Cell Invasiveness Using a Three-dimensional (3D) Model

In Vivo Gene Delivery into Mouse Mammary Epithelial Cells Through Mammary Intraductal Injection

Orthotopic Injection of Breast Cancer Cells into the Mammary Fat Pad of Mice to Study Tumor Growth.

Three-Dimensional (3D) Tumor Spheroid Invasion Assay