Name: detection of lung tumor progression in mice by ultrasound imaging
Uploaded: 2020-02-27T12:30:00
Description: Watch this Scientific Journal Video about Detection of Lung Tumor Progression in Mice by Ultrasound Imaging at JoVE.com

We thank Dr. I. Verma for the lentiviral Ca2Cre-shp53 vector. The work was supported by funds from the Canadian Institutes of Health Research (CIHR MOP 137113) to AEK.

Animal studies were performed in accordance with the Institutional Animal Care and Use Committee (IACUC) of McGill University and procedures were approved by the Animal Welfare Committee of McGill University (animal use protocol # 2009-5754).
1. Generation of CA2Cre-shp53 Lentiviral Titre
NOTE: The following protocol is the same as that described in Xia et al.6, with minor modifications.
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	<li>Preparation of lentivirus (for 15 cm x 10 c...

<ol>
	<li>Eisenstein, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Personalized+medicine:+Special+treatment.">Personalized medicine: Special treatment.</a> Nature. 513, 8 (2014).</li><li>Karachaliou, N., 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=KRAS+mutations+in+lung+cancer.">KRAS mutations in lung cancer.</a> Clinical Lung Cancer. 14 (3), 205-214 (2013).</li><li>Jackson, E. 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We demonstrate a method that can assess lung tumor growth in the Cre-inducible LSL-KRAS G12D mouse model by ultrasound. This method can be used for evaluating the effect of pharmacological inhibitors on lung tumor growth. It can also be used to compare lung tumor growth between mice of different genetic backgrounds. Using this technique does not require specialized computational skills, however, it is important to be systematic in the number of frames used for analysis to allow for proper comparison if the method is used...

As the leading cause of cancer-related deaths worldwide, lung cancer remains refractory to treatments, mainly due to lack of relevant pre-clinical models that can recapitulate the disease in the lab1. Around 25% of lung cancer cases are due to mutations in the KRAS oncogene2. KRAS-driven lung cancer is often associated with poor prognosis and low response to therapy, highlighting the importance of further studies in this disease2.
We optimized a method that allows the relative evaluation of lung tumor growth in real time in KRAS lung cancer-induced immune-competent mice. We use Lox-Stop-Lox KRAS G12D (LSL-KRAS G12D) mice in which the KRAS G12D oncogene can be expressed by Cre lentiviral vectors3,4. These vectors are driven by carbonic anhydrase 2, allowing the viral infection to take place specifically in alveolar epithelial cells5. In addition, to accelerate the initiation and progression of lung tumors, the lentiviral construct also expresses P53 shRNA from an U6/H1 promoter (the lentiviral construct herein will be referred to as Ca2Cre-shp53)6. The biological relevance of this method lies in the natural course of lung tumor development in mice as opposed to xenografts of non-orthotopic tumors in mice. An obstacle using the orthotopic method is monitoring lung tumor growth without sacrificing the mouse. To overcome this limitation, we optimized ultrasound imaging to permit the analysis of lung tumor progression in two-dimensional (2D) mode in this mouse model. Initiating tumors at 7 weeks post-infection are reflected as B-lines in ultrasound images, which can be counted, but will not reflect the exact number of tumors present on the lung. B-lines are characterized by laser-like vertical white lines arising from the pleural line in the lung parenchyma7,8. Large tumors can be visualized after 18 weeks of infection. The relative volume of these tumors is quantified by 2D measurements done on ultrasound.
This method is optimal for researchers investigating the effect of pharmacological drugs on lung tumor growth in the LSL-KRAS G12D mouse model. In addition, lung tumor progression can be compared between mice with different genetic lineages, to examine the importance of the presence or absence of certain genes/proteins on the development of lung tumor volume.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>0.45 &#956;m Acrodisc Syringe Filters</td>
			<td>Pall Corporation</td>
			<td>PN 4614</td>
			<td></td>
		</tr>
		<tr>
			<td>100-mm Cell Cultre Plate</td>
			<td>CELLSTAR</td>
			<td>664 160</td>
			<td></td>
		</tr>
		<tr>
			<td>6-well Cell Culture Plate</td>
			<td>CELLSTAR</td>
			<td>657 160</td>
			<td></td>
		</tr>
		<tr>
			<td>Amicon Ultra - 15 Centrifugal Filter Units</td>
			<td>Merck Millipore Ltd.</td>
			<td>UFC910024</td>
			<td></td>
		</tr>
		<tr>
			<td>BD LSR-Fortessa</td>
			<td>BD Biosciences</td>
			<td>649225B 3024</td>
			<td></td>
		</tr>
		<tr>
			<td>CA2Cre-shp53 lentiviral vector</td>
			<td></td>
			<td></td>
			<td>From Dr. I Verma Laboratory</td>
		</tr>
		<tr>
			<td>DMEM</td>
			<td>Multicell</td>
			<td>319-005-CL</td>
			<td></td>
		</tr>
		<tr>
			<td>FBS</td>
			<td>Multicell</td>
			<td>80450</td>
			<td></td>
		</tr>
		<tr>
			<td>LSL-KRASG12D mouse</td>
			<td>JAX Mice</td>
			<td>8179</td>
			<td></td>
		</tr>
		<tr>
			<td>MX550S; Centre Transmit: 40 MHz</td>
			<td>FUJIFILM VisualSonics</td>
			<td>51070</td>
			<td></td>
		</tr>
		<tr>
			<td>OptiMEM</td>
			<td>gibco</td>
			<td>11058-021</td>
			<td></td>
		</tr>
		<tr>
			<td>Pen/strep</td>
			<td>Multicell</td>
			<td>450-201-EL</td>
			<td></td>
		</tr>
		<tr>
			<td>pMD2.G</td>
			<td>Addgene</td>
			<td>12259</td>
			<td></td>
		</tr>
		<tr>
			<td>PsPAX2</td>
			<td>Addgene</td>
			<td>12260</td>
			<td></td>
		</tr>
		<tr>
			<td>VEVO-3100</td>
			<td>FUJIFILM VisualSonics</td>
			<td>51072-50</td>
			<td></td>
		</tr>
	</tbody>
</table>

detection of lung tumor progression in mice by ultrasound imaging

With ~1.6 million victims per year, lung cancer contributes tremendously to the worldwide burden of cancer. Lung cancer is partly driven by genetic alterations in oncogenes such as the KRAS oncogene, which constitutes ~25% of lung cancer cases. The difficulty in therapeutically targeting KRAS-driven lung cancer partly stems from having poor models that can mimic the progression of the disease in the lab. We describe a method that permits the relative quantification of primary KRAS lung tumors in a Cre-inducible LSL-KRAS G12D mouse model via ultrasound imaging. This method relies on brightness (B)-mode acquisition of the lung parenchyma. Tumors that are initially formed in this model are visualized as B-lines and can be quantified by counting the number of B-lines present in the acquired images. These would represent the relative tumor number formed on the surface of the mouse lung. As the formed tumors develop with time, they are perceived as deep clefts within the lung parenchyma. Since the circumference of the formed tumor is well-defined, calculating the relative tumor volume is achieved by measuring the length and width of the tumor and applying them in the formula used for tumor caliper measurements. Ultrasound imaging is a non-invasive, fast and user-friendly technique that is often used for tumor quantifications in mice. Although artifacts may appear when obtaining ultrasound images, it has been shown that this imaging technique is more advantageous for tumor quantifications in mice compared to other imaging techniques such as computed tomography (CT) imaging and bioluminescence imaging (BLI). Researchers can investigate novel therapeutic targets using this technique by comparing lung tumor initiation and progression between different groups of mice.

After obtaining a lentiviral infectious titer of ~2 x 106 TU/mL (Figure 1), the Ca2Cre-shp53 lentivirus was intratracheally injected when LSL-KRAS G12D mice reached an appropriate age (6&#8722;8 weeks)9. Ultrasound imaging was performed after 7 weeks of infection upon initiation of tumors (Figure 3B). Imaging was done at 7 weeks in order to include the various types of precursor lesions that occur in the LSL-KR...

Watch this Scientific Journal Video about Detection of Lung Tumor Progression in Mice by Ultrasound Imaging at JoVE.com

Detection of Lung Tumor Progression in Mice by Ultrasound Imaging

This protocol describes the steps taken to induce KRAS lung tumors in mice as well as the quantification of formed tumors by ultrasound imaging. Small tumors are visualized in early timepoints as B-lines. At later timepoints, relative tumor volume measurements are achieved by the measurement tool in the ultrasound software.

With ~1.6 million victims per year, lung cancer contributes tremendously to the worldwide burden of cancer. Lung cancer is partly driven by genetic ...

The significance of this protocol lies in the real time detectability of the lung tumors that developed spontaneously in this mouse model, from tumor initiation to tumor progression. The advantage of this technique are that is non-invasive, is require only basic skill and allow us directly monitor the effect of the drug and treatment of interest. Lung tumor progression can also be evaluated in the presence or absence of a gene of interest.Using this analysis, novel treatment strategies can be potentially extended to the clinic. Seven and 18 weeks after lentiviral intubation, turn on the heating pump for the ultrasound gel and the temperature monitor and set up a 33 degrees celsius incubator. Place the 3D motor on the integrated rail system and confirm that the motor and transducer mounting system are secured in place.Connect a 40 hertz frequency transducer to the 3D motor and open a new study in the ultrasound software. In the new study window, enter the study name. In the series name window, enter series name and any other relevant information.After clicking done, select the transducer type. The program will change to B mode. Place a heating lamp in a convenient position above the animal platform and confirm a lack of response to pedal reflex in the anesthetized experimental mouse.Place the mouse on the animal platform into cubitus ventral and apply ointment to the animal's eyes. Secure the limbs firmly to the platform with tape and apply a thin layer of the warmed ultrasound gel to the animal's chest. Use the height control knob to lower the acquisition probe until it touches the surface of the mouse chest and position the probe such that the heart of the mouse is approximately centered.Then use the micro knobs to acquire images of the whole chest from both extremities in the transverse orientation. Ideally gathering 500 frames per mouse. When all of the images have been captured, clean the gel from the chest of the mouse and place the animal into the warming incubator.For 2D analysis of the ultrasound images, open the acquired frames in the ultrasound software and manually scan the frames for tumors. For small initiating tumors, count the number of beelines periodically every 10 frames for the full length of the 500 frames acquired. For 2D measurements of large tumors use the linear tool to measure the width and length of the tumor present, then calculate the volume of the tumors using the formula.Seven weeks after intra tracheal infection, ultrasound imaging is performed to visualize the various types of precursor lesions that occur in the experimental mouse model after the injection. These beeline identified precursor lesions can be counted by the eye and represent small tumors on the surface of the lungs. Scatter plotting of these data allows quantification of the tumors within the experimental mice to allow estimation of the relative tumor number per animal.At 18 weeks post infection, large tumors appear as deep clefts interrupting the plural surface that can be measured within the ultrasound software. The relative tumor volume can then be quantified for statistical analysis. Hematoxylin and eosin staining on lung sections harvested at 20 weeks post infection confirms the formation of large tumors as well as the formation of adenoma and adenocarcinoma.It is important not to confuse the lung tumors, which are dynamic, with false positives, which are static. Since the qualification of the tumor number of the volume is relative in this method, we suggest to use additional methods, such as petri staining. This model allows direct assessment of the effects of genetic aberrations or treatment strategies on lung cancer development in mice.

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