Medicine
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Pre-Conditioning the Airways of Mice with Bleomycin Increases the Efficiency of Orthotopic Lung Cancer Cell Engraftment
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Summary June 28th, 2018
We describe a method to significantly enhance orthotopic engraftment of lung cancer cells into the murine lungs by pre-conditioning the airways with injury. This approach may also be applied to study stromal interactions within the lung microenvironment, metastatic dissemination, lung cancer co-morbidities, and to more efficiently generate patient derived xenografts.
Transcript
The overall goal of this procedure is to increase the efficiency of transplanting tumor-initiating lung cancer cells into the airways of mice. This method can help establish new preclinical models in order to answer key questions in cancer biology, including the causes of drug resistance and relationship between fibrosis and lung cancer. The main advantage of this technique is that it increase the transplantation efficiency of tumor-initiating cells into the lungs of a variety of mouse strains.
The implications of this technique extend toward therapy, because it enables us to model a greater variety of human lung cancer subtypes, known to have different clinical responses to treatment. For this protocol, the mice must first be injected with bleomycin. Then, after 14 days, the tumor cells are injected.
The procedure for both injections is very similar and described here. Two hours prior to the injection, thaw the bleomycin stock on ice and dilute it to the working concentration. Keep it on ice.
For a cell bolus, have a cell suspension prepared as described in the text protocol. The procedure time for each mouse is about 10 minutes all together. Be certain to confirm proper anesthesia using a toe pinch, and apply vet ointment to the eyes.
At this time, if the mouse has dark hair, then shave the entire rib area both ventrally and dorsally so it can be imaged correctly. Then, place the mouse on the intubation platform by securing it by its front teeth with it's back against the platform. If a cell bolus is to be injected, resuspend it now with gentle trituration.
Now illuminate the upper-chest region, open the mouth, and gently pull out the tongue using flat forceps. Prepare an IV catheter for the trachea by removing the needle, then position it over the tracheal opening. Next, insert the catheter into the trachea until the top of the catheter is near the front teeth and illuminate the interior of the catheter to confirm its placement.
Then, dispense the 50 microliters of freshly made bleomycin, or cell suspension, directly into the catheter. Wait a few seconds for the entire volume to travel down the catheter. Then, remove the catheter and dispose of it in 10%bleach.
If the mouse is not inhaling the liquid, carefully monitor its breathing and adjust the catheter position. If the mouse stops breathing, immediately remove the catheter and allow the mouse to breath before you reinsert the catheter in. After removing the catheter, continue performing the procedure to have five treated mice, still anesthetized, and ready to image.
For recovery, place the mouse supine on an IACUC approved heating pad in a recovery cage and monitor it until it has fully recovered. Two or three minutes after injecting the cells, inject 100 microliters of luciferin retro-orbitally, using an insulin needle. Alternate the eye used for injection every imaging session.
After waiting at lest two minutes, position up to five mice in an animal bioluminescence imager, in the sternal recumbency position and acquire a dorsal picture using luminescence settings. Under the control panel, adjust the resolution and sensitivity settings, to measure the luminescence of the cells. For most applications, start with three minutes, set the binning to medium, set the f/stop to one, set the field of view to d, and set the subject height to 1.5.
If the injection was successful, a signal is detected in the upper chest area in one lung or both lungs. If cells are clustered at the entrance of the trachea, the injection was unsuccessful. After taking the dorsal image, flip the mice and acquire a ventral image and adjust the setting as needed.
After imaging, proceed with postoperative care as described in the text protocol. Then, repeat this imaging protocol three days post-engraftment and weekly thereafter. To analyze the images, use a bioluminescence analysis software.
First, load all the appropriate images in the series. This section is detailed to one software package. Next, for each mouse, in the first image of the series, create a square region of interest and position it over the upper chest area covering the entire lung region.
Then, using a right click, access the copy all regions of interest function, and use this tool to apply the same regions of interest to each image in the group. Then, within each image, tweak the positions of the squares to cover the upper chest of each mouse. Do this for both the ventral and dorsal views.
Now, in the upper left corner of the image window, select the photons function. Then select the measure option. The data from the regions of interest is then displayed in an output table as total flux.
Analyze this data as needed. When immune compromised, athymic mice were treated with bleomycin. Prior to cell-bolus engraftment, transient fibrosis was observed by day 14 in bleomycin-treated mice, but not vehicle-treated mice.
Next, cells from the established human lung cancer cell line, H2030, were delivered intratracheally into the lungs of these mice. After 35 days, bleomycin-treated mice had a high lung-tumor burden. However, in vehicle treated animals, no tumors were detected.
The lung-tumor burden was confirmed using histology. Lungs pretreated with vehicle had no evidence of tumor nodules, whereas bleomycin pretreated lungs had large tumor nodules. After transplanting a metastatic H2030 BrM 3 cell line, by 39 to 57 days, bioluminescence was too intense for imaging, so metastasis was analyzed in distant organs ex vivo.
Small lesions could be detected in various tissues, suggesting that this method holds promise, to study spontaneously disseminated disease. Once mastered, this technique can be done in 10 minutes per cage of five mice without imaging and 20 minutes per cage when also imaging the mice. While attempting this procedure, it is important to remember to ensure proper insertion of the catheter and to monitor the animal's breathing.
Following this procedure, other methods like pharmacological studies or aminoacetic chemistry of harvested tissue can be performed in order to answer additional questions, like how engrafted tumors respond to drugs or characterizing tumor stromal interactions specific to the lungs. After its development, this technique can be applied to different mouse strains and tumor models, including patient-derived xenografts in a physiologically relevant setting. Don't forgot that working with bleomycin can be extremely hazardous and precautions such as manipulation in a biohazard hood and proper disposal should always be taken while performing this procedure.
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