M. K. Penny1, K. J. Basham2, S. Chukkapalli3, Y. Yu3, M. J. Hoenerhoff4, G. D. Hammer2,5, E. A. Newman3 1University Of Michigan,Doctoral Program In Cancer Biology,Ann Arbor, MI, USA 2University Of Michigan,Department Of Internal Medicine, Division Of Metabolism, Endocrinology And Diabetes,Ann Arbor, MI, USA 3University Of Michigan,Department Of Surgery, C.S. Mott Children’s And Women’s Hospital, Mott Solid Tumor Oncology Program,Ann Arbor, MI, USA 4University Of Michigan,Unit For Laboratory Animal Medicine,Ann Arbor, MI, USA 5University Of Michigan,Endocrine Oncology Program, Rogel Cancer Center,Ann Arbor, MI, USA
Introduction: Adrenocortical carcinoma (ACC) is a rare and often aggressive cancer, with a 5-year survival rate of 15% for those diagnosed with advanced disease. Improved models of this disease are needed for predictive preclinical testing in vivo. Subcutaneous, renal subcapsular, and splenic xenograft models of ACC do not mimic the endogenous tumor microenvironment and require injection of high cell quantity (≥ 2.5×106) for efficient tumor engraftment. The development of orthotopic ACC xenograft models has been significantly limited by the complexity and morbidity of open surgery. In this study, we introduce a novel model of orthotopic ACC xenografts utilizing ultrasound-guided percutaneous implantation directly into the adrenal gland tissue, using as few as 200,000 cells.
Methods: NCI-H295R and Y1 cells tagged with luciferase were percutaneously implanted into the adrenal of six to twelve-week old immunocompromised (NSG) mice. Mice were injected with 200,000 cells or 1,000,000 cells. Mice were monitored weekly by ultrasound and bioluminescent imaging and were euthanized and grossly dissected when tumors reached endpoint as defined by 150mm3 detected by ultrasound or 1011photons/sec/cm2/sr detected by bioluminescent imaging. The liver, lung, spleen, kidney, adrenal, and lymph nodes were examined histologically.
Results: At endpoint, 89% of mice injected with 200,000 Y1 cells, 80% of mice injected with 200,000 NCI-H295R cells, and 75% of mice injected with 1,000,000 NCI-H295R cells had locally-invasive primary tumor in the adrenal and periadrenal space. Y1 metastases were found in the liver and lung. Average time to endpoint was 5.2 weeks, 8.9 weeks, and 9.6 weeks respectively. Bioluminescent photon flux and maximum radiance were not linearly correlated with tumor size in vivo.
Conclusion: Minimally invasive orthotopic xenografts of ACC cells in NSG mice are an efficient and reliable method of developing biologically relevant tumors. Successful tumor growth and spontaneous metastasis following injection of as few as 200,000 cells per adrenal demonstrates the advantage of modeling of the tumor microenvironment, as compared to subcutaneous and more recently published renal and splenic xenograft models, as well as orthotopic xenografts by open surgery. This model is an important improvement over standard ACC models for preclinical testing of new therapeutics and investigation of tumor biology.