Abstract
Lung cancer has the highest mortality rate of any tissue-specific cancer in both men and women. Research continues to investigate novel drugs and therapies to mitigate poor treatment efficacy, but the lack of a good descriptive lung cancer animal model for preclinical drug evaluation remains an obstacle. Here we describe the development of an orthotopic lung cancer animal model which utilizes the human sodium iodide symporter gene (hNIS; SLC5A5) as an imaging reporter gene for the purpose of non-invasive, longitudinal tumor quantification. hNIS is a glycoprotein that naturally transports iodide (I-) into thyroid cells and has the ability to symport the radiotracer 99mTc-pertechnetate (99mTcO4-). A549 lung adenocarcinoma cells were genetically modified with plasmid or lentiviral vectors to express hNIS. Modified cells were implanted into athymic nude mice to develop two tumor models: a subcutaneous and an orthotopic xenograft tumor model. Tumor progression was longitudinally imaged using SPECT/CT and quantified by SPECT voxel analysis. hNIS expression in lung tumors was analyzed by quantitative real-time PCR. Additionally, hematoxylin and eosin staining and visual inspection of pulmonary tumors was performed. We observed that lentiviral transduction provided enhanced and stable hNIS expression in A549 cells. Furthermore, 99mTcO4- uptake and accumulation was observed within lung tumors allowing for imaging and quantification of tumor mass at two-time points. This study illustrates the development of an orthotopic lung cancer model that can be longitudinally imaged throughout the experimental timeline thus avoiding inter-animal variability and leading to a reduction in total animal numbers. Furthermore, our orthotopic lung cancer animal model is clinically relevant and the genetic modification of cells for SPECT/CT imaging can be translated to other tissue-specific tumor animal models.
Highlights
Lung cancer remains the leading cause of cancer deaths among both men and women with a five-year survival rate of 18.7% [1]
The SFFV promoter further resulted in a 2.9-fold stronger mean fluorescence intensity than the phospho-glycerate kinase housekeeping gene (PGK) promoter (S1 Fig), the lentiviral vector cells containing the SFFV promoter to drive human sodium iodide symporter gene (hNIS) expression were used for in vivo studies
The s.c. induction of xenograft tumors is a common method of transplanting tumor cells or material in nude mice allowing researchers to directly measure the effect of drugs on tumor sizes and burden measured using a caliper [33]
Summary
Lung cancer remains the leading cause of cancer deaths among both men and women with a five-year survival rate of 18.7% [1]. Current lung cancer animal models cannot quantify tumor burden longitudinally throughout treatment precisely and requires the sacrifice of animals at several time points throughout treatment. This results in studies with large animal cohorts to quantify tumor burden at multiple time points throughout treatment, leading to variability in tumor sizes because of inter-animal differences. Many of these animal models do not closely resemble the clinical features of the human cancer-type being studied [2,3]. The use of in vivo imaging modalities, like computed tomography and optical imaging, have made it possible to study tumor growth or treatment longitudinally in a single animal; precise tumor imaging has been limited by problems with imaging sensitivity, spatial resolution, and the ability to precisely quantify tumor burden and growth [4]
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