We would like to thank Dr. Arnulfo Mendoza who provided training in the PuMA technique. Additionally, we would like to acknowledge Drs. Chand Khanna, Susan Garfield (NCI/NIH), and Sam Aparicio (BC Cancer Agency) for providing use of their microscopes during the course of this study. This research was supported (in part) by the Intramural Research Program of the National Institutes of Health, Center for Cancer Research, Pediatric Oncology Branch. M.M.L. was supported by the National Institutes of Health Intramural Visiting Fellow Program (award 15335), and is currently supported by a Joan Parker Fellowship in Metastasis Research. P.H.S. is supported by British Columbia Cancer Foundation.

All animal protocols from which imaging data were obtained were performed with approval of the Animal Care and Use Committee of the National Cancer Institute, National Institutes of Health. All animal protocols discussed and portrayed in the article video have been approved by the University of British Columbia Animal Care Committee.
1. Preparation of tumor cells for injection and materials for the PuMA model
NOTE: The amount of solutions and cells will be enough for ...

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The authors have nothing to disclose.

The following technical article describes some practical aspects of the PuMA model in studying lung colonization in OS. Some critical steps in the protocol where researchers should take extra care include the following:
a) Cannulation of the trachea. The trachea can be easily damaged while dissecting the surrounding muscle and connective tissue. In addition, the needle of the catheter can easily be pushed through the trachea. Pay close attention to how the bevel of the needle enters the trache...

Improved outcomes for pediatric patients with metastatic osteosarcoma (OS) still remains a critical unmet clinical need 1. This underscores the importance of developing new molecularly-targeted therapies. Conventional chemotherapeutics that target tumor cell proliferation have not proven to be effective in treating metastatic disease, and thus novel strategies must target the metastatic process itself 2. The current article discusses the practical aspects of a relatively new type of ex vivo lung metastasis model, the pulmonary metastasis assay (PuMA) developed by Mendoza and colleagues3, which provides a useful tool in discovering new molecular drivers in lung metastasis progression in OS 4,5. Before proceeding, however, it would be prudent to briefly touch upon several current models of metastasis, and how the PuMA model offers several advantages over conventional in vitro assays.
Most experimental models used to study metastasis comprise of in vitro and in vivo systems that recapitulate either a specific step or several steps of the metastatic cascade. These steps include: 1) tumor cells migrating away from the primary tumor, 2) intravasation into nearby vessels (blood or lymphatic) and transit within circulation, 3) arrest at the secondary site, 4) extravasation and survival at the secondary site, 5) formation of micrometastases, and 6) growth into vascularized metastases (Figure 1). In vitro models of metastasis can include 2-dimensional (2D) migration and 3-dimensional (3D) Matrigel invasion assays which are reviewed in detail elsewhere 6. For in vivo models, the two commonly used model systems include: 1) the spontaneous metastasis model is where a tumor cells are orthotopically injected into a specific tissue type to form a local tumor which spontaneously sheds metastatic cells to distant sites; 2) the experimental metastasis model is where tumor cells are injected into the blood vessel upstream of the target organ. For example, a tail vein injection of tumor cells results in the development lung metastases5,7,8. Other experimental metastasis models include injection of tumor cells into the spleen or mesenteric vein which results in the development of liver metastases9,10. Practical considerations of these in vivo models are discussed in detail by Welch 11. Another in vivo model used to study metastasis in pediatric sarcomas is the renal kidney subcapsular tumor implantation model which results in local tumor formation and spontaneous metastasis to the lungs 12,13. A more technically demanding technique such as intravital videomicroscopy can directly visualize, in real-time, interactions between metastatic cancer cells and the microvasculature of a metastatic site (ie. lung or liver) as described by MacDonald14 and Entenberg15, or cancer cell extravasation in the chorioallantoic membrane as described by Kim 16.
The PuMA model is an ex vivo, lung tissue explant, closed culture system where the growth of fluorescent tumor cells can be longitudinally observed via fluorescence microscopy over a period of a month (see Figure 2A). This model recapitulates the initial stages of lung colonization (steps 3 to 5) in the metastatic cascade. Some major advantages of the PuMA model over conventional in vitro models are: 1) it provides an opportunity to longitudinally measure metastatic cancer cell growth in a 3D microenvironment that retains many features of the lung microenvironment in vivo 3; 2) PuMA allows the researcher to assess whether the knockdown of a candidate gene or drug treatment has anti-metastatic activity in the context of a 3D lung microenvironment; 3) the PuMA model is flexible with many types of fluorescence microscopy platforms (Figure 2B) such as widefield fluorescence microscopy or laser-scanning confocal microscopy, examples of each are shown in Figure 2C &#38; D, respectively. This article will discuss how to use the PuMA model to obtain longitudinal imaging data on the metastatic growth of enhanced green fluorescent protein (eGFP)-expressing, human high and low metastatic osteosarcoma cells (MNNG and HOS cells, respectively) using low-magnification widefield fluorescence. Examples of imaging a fluorescent dye which labels the lung parenchyma, and a red-fluorescent protein genetic reporter which labels mitochondria in OS cells in the PuMA model using confocal laser-scanning microscopy are also discussed.

<table>
	<tbody>
		<tr>
			<td>Table 2</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Cell culture reagents for A-media, B-media, and complete media</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>MNNG-HOS</td>
			<td>ATCC</td>
			<td>CRL-1547</td>
			<td>highly metastatic OS cell line</td>
		</tr>
		<tr>
			<td>HOS</td>
			<td>ATCC</td>
			<td>CRL-1543</td>
			<td>poorly metastatic OS cell line</td>
		</tr>
		<tr>
			<td>MG63.3</td>
			<td>Amy LeBlanc Laboratory (NCI)</td>
			<td>N/A</td>
			<td>highly metastatic OS cell line</td>
		</tr>
		<tr>
			<td>MG63</td>
			<td>ATCC</td>
			<td>CRL-1427</td>
			<td>poorly metastatic OS cell line</td>
		</tr>
		<tr>
			<td>10X M199 media</td>
			<td>Thermofisher</td>
			<td>11825015</td>
			<td>Base media for A-media and B-media</td>
		</tr>
		<tr>
			<td>Distilled Water (sterilized)</td>
			<td>Thermofisher</td>
			<td>15230-147</td>
			<td>Component of A-media &#38; B-media</td>
		</tr>
		<tr>
			<td>7.5% sodium bicarbonate solution</td>
			<td>Thermofisher</td>
			<td>25080094</td>
			<td>Component of A-media &#38; B-media</td>
		</tr>
		<tr>
			<td>Hydrocortizone</td>
			<td>Sigma-Alrich</td>
			<td>H6909</td>
			<td>Component of A-media &#38; B-media</td>
		</tr>
		<tr>
			<td>Retinol acetate-water soluable</td>
			<td>Sigma-Alrich</td>
			<td>R0635-5MG</td>
			<td>Component of A-media &#38; B-media</td>
		</tr>
		<tr>
			<td>Penicillin/Streptomycin 10X concentrated (10000 U/ml) solution</td>
			<td>Thermofisher</td>
			<td>15140122</td>
			<td>Component of A-media &#38; B-media, complete media.</td>
		</tr>
		<tr>
			<td>Bovine insulin solution (10mg/ml)</td>
			<td>Sigma-Alrich</td>
			<td>I0516-5ML</td>
			<td>Component of A-media &#38; B-media</td>
		</tr>
		<tr>
			<td>DMEM, high glucose</td>
			<td>Thermofisher</td>
			<td>11965092</td>
			<td>Base media of Complete Media</td>
		</tr>
		<tr>
			<td>L-Glutamine (200 mM)</td>
			<td>Thermofisher</td>
			<td>25030081</td>
			<td>Component of Complete Media</td>
		</tr>
		<tr>
			<td>Fetal Bovine Serum</td>
			<td>Thermofisher</td>
			<td>16000044</td>
			<td>Component of Complete Media</td>
		</tr>
		<tr>
			<td>Dulbecco&#8217;s Phosphate Buffered Saline</td>
			<td>Thermofisher</td>
			<td>14190144</td>
			<td>Used in cell culture.</td>
		</tr>
		<tr>
			<td>Hank&#8217;s Buffered Salts Solution, no calcium, no magnesium, no phenol red</td>
			<td>Thermofisher</td>
			<td>14175095</td>
			<td>Used to resuspend cell pellet prior to injection</td>
		</tr>
		<tr>
			<td>Trypsin-EDTA (0.25%), phenol red</td>
			<td>Thermofisher</td>
			<td>25200114</td>
			<td>Used in cell culture.</td>
		</tr>
		<tr>
			<td>DAR4M</td>
			<td>Enzo</td>
			<td>ALX-620-069-M001</td>
			<td>Used to label lung parenchyma.</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Table 3</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Materials for PuMA</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Zeiss 710 Confocal LSM</td>
			<td>Zeiss</td>
			<td>N/A</td>
			<td>Upright LSM confocal microscope</td>
		</tr>
		<tr>
			<td>Zeiss 780 Confocal LSM</td>
			<td>Zeiss</td>
			<td>N/A</td>
			<td>Inverted LSM confocal microscope</td>
		</tr>
		<tr>
			<td>SCID mice</td>
			<td>Charles River</td>
			<td>N/A</td>
			<td>NOD.CB17-Prkdcscid/NcrCrl, female, age 6-8 weeks</td>
		</tr>
		<tr>
			<td>GelFoam</td>
			<td>Harvard Apparatus</td>
			<td>59-9863</td>
			<td>Used as a support for lung tissue sections.</td>
		</tr>
		<tr>
			<td>SeaPlaque Agarose</td>
			<td>Lonza</td>
			<td>50100</td>
			<td>Used during insufflation of the lung.</td>
		</tr>
		<tr>
			<td>1 ml syringe with 27 gauge needle</td>
			<td>Fisherscientific</td>
			<td>14-826-87</td>
			<td>Used for tail vein injection.</td>
		</tr>
		<tr>
			<td>10 ml syringe</td>
			<td>BD</td>
			<td>309604</td>
			<td>Used for insufflation of the lung.</td>
		</tr>
		<tr>
			<td>20 gauge catheter</td>
			<td>Terumo</td>
			<td>SR-OX2032CA</td>
			<td>Used during insufflation of the lung.</td>
		</tr>
		<tr>
			<td>Abbott IV extension set (30&#34;, Sterile)</td>
			<td>Medisca</td>
			<td>8342</td>
			<td>Used during insufflation of the lung.</td>
		</tr>
		<tr>
			<td>Alcohol swabs</td>
			<td>BD</td>
			<td>326895</td>
			<td>For wiping tail vein before injection</td>
		</tr>
		<tr>
			<td>Sterile surgical gloves</td>
			<td>Fisherscientific</td>
			<td>Varies with size</td>
			<td>Asceptic handing of mouse lungs</td>
		</tr>
		<tr>
			<td>30 cm ruler</td>
			<td>Staples</td>
			<td></td>
			<td>Used for insufflation of the lung.</td>
		</tr>
		<tr>
			<td>Support stand for ruler</td>
			<td>Pipette.com</td>
			<td>HS29022A</td>
			<td>Used for insufflation of the lung.</td>
		</tr>
		<tr>
			<td>35 mm glass-bottomed culture dish</td>
			<td>Ibidi</td>
			<td>81158</td>
			<td>Used during imaging of lung slices</td>
		</tr>
		<tr>
			<td>Absorbent Underpads with Waterproof Moisture Barrier</td>
			<td>VWR</td>
			<td>56617-014</td>
			<td>Used to line the sterile work area in the biological hood.</td>
		</tr>
		<tr>
			<td>Catgut Plain Absorbable Suture</td>
			<td>Braun</td>
			<td>N/A</td>
			<td>Used to tie off cannulated trachea.</td>
		</tr>
		<tr>
			<td>Name</td>
			<td>Company</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr>
			<td>Table 4</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Surgical instruments for PuMA</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Micro Dissecting Scissors 3.5&#34; Straight Sharp/Sharp</td>
			<td>Roboz</td>
			<td>RS-5910</td>
			<td>For cutting lung sections</td>
		</tr>
		<tr>
			<td>4&#8221; (10 cm) Long Serrated Straight Extra Delicate 0.5mm Tip</td>
			<td>Roboz</td>
			<td>RS-5132</td>
			<td>For manipulating/holding lung sections.</td>
		</tr>
		<tr>
			<td>4&#8221; (10 cm) Long Serrated Slight Curve 0.8mm Tip</td>
			<td>Roboz</td>
			<td>RS5135</td>
			<td>For manipulating/holding lung sections.</td>
		</tr>
		<tr>
			<td>Thumb Dressing Forceps; Serrated; Delicate; 4.5&#34; Length; 1.3 mm Tip Width</td>
			<td>Roboz</td>
			<td>RS-8120</td>
			<td>For general dissection.</td>
		</tr>
		<tr>
			<td>Thumb Dressing Forceps 4.5&#34; Serrated 2.2 mm Tip Width</td>
			<td>Roboz</td>
			<td>RS-8100</td>
			<td>For general dissection.</td>
		</tr>
		<tr>
			<td>Extra Fine Micro Dissecting Scissors 3.5&#34; Straight Sharp/Sharp, 20mm blade</td>
			<td>Roboz</td>
			<td>RS-5880</td>
			<td>For general dissection.</td>
		</tr>
		<tr>
			<td>Knapp Scissors; Straight; Sharp-Blunt; 27mm Blade Length; 4&#34; Overall Length</td>
			<td>Roboz</td>
			<td>RS-5960</td>
			<td>For general dissection.</td>
		</tr>
	</tbody>
</table>

practical considerations in studying metastatic lung colonization in osteosarcoma using the pulmonary metastasis assay

The pulmonary metastasis assay (PuMA) is an ex vivo lung explant and closed cell culture system that permits researchers to study the biology of lung colonization in osteosarcoma (OS) by fluorescence microscopy. This article provides a detailed description of the protocol, and discusses examples of obtaining image data on metastatic growth using widefield or confocal fluorescence microscopy platforms. The flexibility of the PuMA model permits researchers to study not only the growth of OS cells in the lung microenvironment, but also to assess the effects of anti-metastatic therapeutics over time. Confocal microscopy allows for unprecedented, high-resolution imaging of OS cell interactions with the lung parenchyma. Moreover, when the PuMA model is combined with fluorescent dyes or fluorescent protein genetic reporters, researchers can study the lung microenvironment, cellular and subcellular structures, gene function, and promoter activity in metastatic OS cells. The PuMA model provides a new tool for osteosarcoma researchers to discover new metastasis biology and assess the activity of novel anti-metastatic, targeted therapies.

Low-magnification widefield fluorescence microscopy
For widefield fluorescence microscopy of PuMA lung slices, representative images and quantification data are shown in Figure 2C, and Figure 4A and B. The metastatic propensities for high and low metastatic cell lines are visually apparent over progressive time points. MNNG cel...

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Practical Considerations in Studying Metastatic Lung Colonization in Osteosarcoma Using the Pulmonary Metastasis Assay

The goal of this article is to provide a detailed description of the protocol for the pulmonary metastasis assay (PuMA). This model permits researchers to study metastatic osteosarcoma (OS) cell growth in lung tissue using a widefield fluorescence or confocal laser-scanning microscope.

The pulmonary metastasis assay (PuMA) is an ex vivo lung explant and closed cell culture system that permits researchers to study the biology of lung ...

The overall goal of this pulmonary metastasis assay is to directly visualize and study the growth of metastatic osteosarcoma cells in viable lung tissue. This method can help answer really key questions in the osteosarcoma metastasis field. Such as, how metastatic osteosarcoma cells adapt, survive, and proliferate in the lung micro environment.The main advantage of this technique is that it permits a direct visualization of metastatic osteosarcoma cell growth in a relevant three dimensional micro environment. Generally, individuals new to this method will struggle, because of the technically challenging steps of cannulating the trachea and insufflating the lung. The tail vein injection of tumor cells and mouse euthanasia are done according to standard institutional guidelines.After five minutes, place the euthanized mouse in dorsal recumbency on a sterile pad in a laminar flow hood, and use small, sterile scissors to carefully dissect out the sternum, past the thoracic inlet on both sides of the trachea, without puncturing the lungs. Dissecting all of the muscle and connective tissue surrounding the trachea is essential for a successful cannulation. Next, use a 20 gauge IV catheter to carefully cannulate the trachea and use a sterile catgut suture to loosely secure the catheter and the trachea.Attach an IV extension set from the catheter to the 10 milliliter syringe of a gravity profusion apparatus and pour 37 degrees celsius liquid agarose mixed with A medium solution into the syringe. Fill the lungs with the agarose solution until they are fully insufflated. Then remove the cannula and firmly tie off the suture to prevent leakage of the agarose solution.It is important to keep the lung intact during the insufflation. A proper insufflation with agarose and subsequent cooling of the pluck, will maintain the lung in an expanded state. Harvest the pluck, trachea, heart, and lung, taking care not to puncture or damage the surface of the lung.Place the tissues in 30 milliliters of pre-chilled PBS supplemented with antibiotics, and allow the agarose to solidify. Place the pluck on ice for 20 minutes. After 20 minutes, use fine scissors and tweezers to cut the lung into 3 x 1.5 millimeter pieces, and place the slices into individual wells of a 6 well plate containing 2 x 2 centimeter gelatin sponges pre-soaked in B medium.On the day of imaging, carefully transfer the lung slices from the 6 well plate, into a sterile 35 millimeter glass bottom round dish in columns according to their experimental group. Next, on a wide field fluorescence microscope, select the 2.5x objective and set the imaging parameters to provide the best contrast between the fluorescent tumor cells and the non fluorescing background tissue in the control tissue sample group. Image all of the samples using the same parameters as for the control tissues.If the software isn't scale calibrated, image a micrometer using the same objective as the lung tissue in order to obtain a scale reference, and save all of the images as tif files. When all of the images have been obtained, to analyze the images in ImageJ, open the first file. Use the polygon selection tool to outline the entire lung slice to determine the area of the total lung slice.Select process and subtract background. Set the rolling ball radius to a starting value of 50 pixels. This value will be dependent on the degree of background fluorescence and should be optimized for each data set.Make sure to uncheck the light background. Select image and type, 8-bit, then image and properties, enter pixels. Under unit of length, enter 1 for the pixel width, pixel height, and voxel depth.Then, check global to apply these parameters to all of the subsequent images. Next, select image, then adjust, then threshold. Highlight default and black and white, and use the slider to threshold the image so that the majority of the tumor cells are accurately highlighted.Click apply one time to turn the lung black and the fluorescent lesions white. Then, click apply a second time to invert the image so that all of the fluorescent structures turn black. To quantify the number and shape of the lesions, select analyze and set measurements, and check area.Uncheck all of the other boxes. Then, select analyze particles and in the size field use the area of the smallest lesion determined to be a single cell by ImageJ, to set the range of shapes that the program will enumerate. Use an image from day zero vehicle group to choose the smallest area that is considered to be a single tumor cell.When the lower limit has been set, click okay. A results window will pop up containing all of the enumerated shapes and area measurements. Then, copy and paste the data from the results window into a spreadsheet, and use the sum mathematical function to add all of the areas of the metastatic lesions for that particular lung slice.The metastatic propensities for high and low metastatic cell lines are visually apparent over progressive time points. More specifically, these microscopy images show how highly metastatic cells are able to colonize the lung more efficiently than low metastatic cell lines. Image analysis, quantification, and statistical analysis of the image data confirms that highly metastatic tumor cells can efficiently colonize the lung tissue.Whereas low metastatic cells cannot grow at all. High magnification confocal fluorescence microscopy allows visualization of the lung parenchyma cells in great spatial detail compared to EGFP expressing tumor cells. As well as facilitates the analysis of subcellular structures, such as these mitochondria.Depending on the number of mice used, this technique can be completed in four hours if it is performed properly. While attempting this procedure it is important to remember to work with clean, sterile surgical equipment. After it's development, the technique paved the way for researchers in the field of cancer research to explore metastasis progression in the lungs of mice.Following this procedure, other methods like in vitro cell culture assays and western blotting can be performed to answer additional questions about the effects of gene knockdown or drug treatment on cancer cells. After watching this video, you should have a good understanding of how to perform a pulmonary metastasis assay. Don't forget that working with human cancer cells can be extremely hazardous, and that precautions such as working in a bio level safety two laboratory, should always be taken while performing this procedure.

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10.0K vistas.  National Institutes of Health. The overall goal of this pulmonary metastasis assay is to directly visualize and study the growth of metastatic osteosarcoma cells in viable lung tissue. This method can help answer really key questions in the osteosarcoma metastasis field. Such as, how metastatic osteosarcoma cells adapt, survive, and proliferate in the lung micro environment.The main advantage of this technique is that it permits a direct visualization of metastatic osteosarcoma cell growth in a relevant three dimens...