Ultrasound Guided Injection of Tumor Cells into Mice

DATE: DECEMBER 2018
University of Nebraska Medical Center | Cancer Research
Caroline Stead, Graduate Student

Small animal models are an invaluable tool in cancer research. They allow researchers to follow trends in living tissue and observe interactions in an environment that closely models humans. Xenograft models are made by injecting tumor pieces or cells into the animal’s flank, subcutaneously, or directly into the organ of interest, orthotopically. In translational research, orthotopic models allow better understanding of drug treatment efficacies and facilitate longitudinal studies because the cells are in a more natural environment. Current orthotopic injection methods require surgically opening the abdomen of an animal to see the organ of interest. Cells or drug treatments maintained on ice are quickly injected using a short, disposable syringe. Finally, the animal is sutured closed and observed during the recovery process. Trauma from this surgery causes inflammation, immune activation, and prolongs recovery time. In this process, cells are at risk of recoil through the injection canal and leakage, causing tumor growth outside of the intended organ. Similarly, drugs leak can induce unintended reactions in proximal organs. All of these factors can obscure the animal’s response to tumor cells or treatment and therefore our ability to accurately interpret data obtained from small animal models of human disease.

There are, however, a handful of studies showing the value of ultrasound guided injection of tumor cells into mice as accurate models of human disease (Huynh et al., 2011, PLoS One, 6(5): e20330; Van Noord et al., 2017, In Vivo, 31(5): 779–791). This technique is less invasive, allows for a shorter recovery time and, a potentially faster turnaround time for studies. The Hamilton Threaded Plunger Syringe and a variety of custom Hamilton needles will be the lynch pin for developing this novel technique in the Hollingsworth laboratory and eventual training of additional students and laboratories at the University of Nebraska Medical Center (UNMC). This unique syringe will reduce the need for open surgeries by assisting students in the development of ultrasound guided injection techniques. With the aid of Dr. Heather Jensen Smith, students will test two-inch, 26, 28, and 30 gauge, type 4 needles with 45˚ beveled tips. They will use the 3100 Vevo Ultrasound and Photoacoustic Imaging system to optimize cell and drug delivery. For injections, the Hamilton Threaded Plunger Syringe will be mounted on a micromanipulator. A custom two-inch Hamilton needle is necessary to clear the mount and reach various parts of the animal. Students will learn to how to use ultrasound guided imaging to locate their organ of interest and inject cells or drug treatments at controlled rates. The unique photoacoustic module will give students the opportunity to utilize contrast dyes in evaluating cell and drug delivery rates, retention in different organs, and recoil rate. This module will also help students test role of solution viscosity in reducing cell and drug loss following injection. The increased control afforded by Hamilton threaded syringes will allow for more precise delivery of multiple test solutions.

Teaching students how to apply the less-invasive USGS cell and drug delivery technique to any number of studies using animal models of disease exemplifies our larger teaching philosophy; problem-based learning courses that encourage student innovation. Students in our lab, and the Eppley Cancer Institute at UNMC, have a penchant for innovation. One student has already created a 3D printed window that can be used to observe changes in the tumor microenvironment when fluorescently-labeled pancreatic tumor cells are injected into the pancreas and subsequently tracked over time. Another has developed a multiplexed antibody labeling technique to characterize immune cell infiltration, cellular interactions, and modifications to the tumor microenvironment in patient-derived samples.

Utilizing threaded plunger syringes while testing a variety of needles and suspension vehicles custom-tailored to individual target organs will encourage the development of innovative cancer models within our laboratory and the Eppley Cancer Institute. This technique will provide the entire institution with new models that require less recovery time and inflict less trauma on small animals. Given that the current technique requires at least five laboratory members several hours to implant cancer cells in the mice, this technique will also save time in the lab. Finally, this innovation will ideally profile sufficient data and supplies to encourage and support a transition from abdominal surgery-based to US-based techniques in the program. It will afford multiple teaching opportunities for students, faculty, and staff. Indeed, anticipation of this new ultrasound-guided technique is already encouraging students to develop ways to use this technique for other projects. For example, one student plans to use ultrasound guided injection for delivery of chemotherapeutic drugs directly into tumors. This would allow him to reduce overall toxicity with drugs that are more potent by reducing systemic toxicities that can occur using current treatment regimens.

Every minute counts in the fight against cancer. One of the educational goals of this lab is to encourage innovation to improve lab techniques which reduces ‘bench side to bedside’ times for our translational research. This grant would provide syringes and needles for the development of a novel technique. It will be a catalyst in the lab, the program, and the fight against cancer.