Utilization of Ultrasound Guided Tissue-directed Cellular Implantation for the Establishment of Biologically Relevant Metastatic Tumor Xenografts

The goal of this method is to establish biologically relevant cancer orthotopic xenografts for preclinical studies. Patient-derived neuroblastoma cells are injected into the murine adrenal gland by ultrasound guidance without open surgery or prolonged recovery. This method can help answer critical questions in cancer biology and in translational research, such as studies of tumor evolution, therapeutic responses in the native microenvironment and metastases.

Such a knowledge would greatly improve the reliability of preclinical studies and facilitate drug discovery. The main advantage of this technique is that it is patient-derived, tissue-directed, efficient, and reliable in producing an orthotopic xenographed model for cancer therapy research. Demonstrating the critical steps in the procedure will be Sahiti Chukkapalli, a senior technician and our lab manager, along with Tina Thomas, a research fellow in our laboratory.

Generate a single, patient-derived cancer cell suspension from tumor tissue using a tumor dissociation kit. Begin by transferring approximately half a gram of tumor tissue to a 100 millimeter cell culture dish containing five milliliters of enzyme supplemented RPMI buffer. Then, use scissors and tissue forceps to mince the tumor into small pieces of two to four millimeters.

Pipette the tumor mixture into a dissociater tube and close the tube. Invert the tube, attach onto the sleeve of a tissue dissociater, and dissociate the tissue using the appropriate program. After dissociating, incubate the tumor cell suspension on a rotating rack at 37 degrees Celsius for one hour.

Triturate the cell suspension every 15 minutes during the incubation. Following the incubation, transfer the cell suspension to a new 50 milliliter conical tube and add 10 milliliters of RPMI. Then, centrifuge the cell suspension at 314g for five minutes.

After the centrifugation, remove the supernatant and suspend the pellet in five milliliters of RPMI. Pass the cell suspension through a 40 micron cell strainer and collect the strained solution into a fresh, 50 milliliter tube. After washing the strainer with five milliliters of RPMI media, centrifuge the cell suspension at 314g for five minutes to collect a pellet.

Count the cells using a hemocytometer. Then, suspend the pellet in RPMI to obtain a final concentration of four times 10 to the five cells per 10 microliter volume. Transfer five microliters of this cell suspension per injection to a fresh tube, and the same volume of basement membrane matrix to make 10 microliters of cell solution for each injection and place it on ice.

Transfer the mouse to the imaging platform with the abdominal side down. Fit and secure the nose cone to maintain isoflurane anesthesia. Begin the implantation procedure using hair removal lotion and a shaver to depilate the back and flank of a properly anesthetized six to eight week old immune-deficient NSG mouse.

Apply optical ointment over the animal's eyes to prevent drying. Then, tape the mouse in place to prevent any inadvertent movement. Next, use ultrasound visualization to identify the murine liver, vena cava, spleen, left kidney, and adjacent left adrenal gland.

Load a chilled Hamilton syringe, fitted with a small bore needle, with 10 microliters of cell solution. Then, under ultrasound guidance, gently inserted a chilled 22-gauge catheter through the skin and back muscle, directly into the left adrenal gland to provide a channel for cellular injection. Remove the needle and leave the catheter in place.

Visualization of the adrenal gland throughout the insertion of the catheter, along with the needle and its trajectory, is imperative to ensure minimal injury to surrounding structures and organs and lower murine morbidity. Then, guide the syringe through the catheter positioned into the center of the adrenal gland. As the syringe is guided through the catheter, it is important to maintain catheter stability and watch the needle advance.

Note that the needle itself extends approximately two millimeters beyond termination of the catheter, its position easily seen on ultrasound. Inject the cells into the targeted adrenal tissue. Leave the needle in place for one to two minutes to allow the basement membrane matrix to set.

After the basement membrane matrix has set, slowly remove the needle, followed by the removal of the catheter. Finally, place the mouse into a recovery cage until it regains sufficient consciousness to maintain sternal recumbency before returning to the home cage. Ultrasound imaging monitors in vivo tumor progression.

This image shows an ultrasound image of the adrenal gland, one week following injection. Here, luminescence imaging of a neuroblastoma injected mouse one week post-injection, shows readings not indicative of tumor engraftment. After two weeks, ultrasound imaging shows tumor engraftment and progression to an area of approximately 40 square millimeters.

Bioluminescence at two weeks post-injection showed radiance measuring 10 to the seventh, which is suggestive of cell uptake and tumor growth correlating with ultrasound findings. Ultrasound imaging eight weeks post-injection showed continued tumor growth with an area measurement of greater than 100 square millimeters. Again, bioluminescence confirmed the ultrasound findings with increased radiance levels of 10 to the nine.

3-D ultrasound imaging of the tumor showed a volume greater than 100 cubic millimeters, the baseline that our laboratory utilizes for initiation of preclinical therapeutic trials. Excised tumor grossly measured greater than one centimeter in size, correlating with ultrasound measurements and luminescence signals. This media provides demonstration of how to successfully establish adrenal orthotopic xenographs with patient-derived neuroblastoma cells, utilizing ultrasound guidance.

Once mastered, this technique can be done in less than 12 minutes per injection if it is performed properly.