Real-Time In Vivo Imaging For Sensitive Detection Of Primary And Metastatic Disease In A Human Breast-To-Lung Orthotopic Model

Abstract Orthotopic mouse models of human disease are absolutely essential for validating therapeutic targets and assessing efficacy of emerging therapies. Early detection of in vivo tumor growth is a critical benchmark in humanized mouse models, for it reveals tumor take at a time of reasonable tumor burden. To develop an optimal mouse model of human metastatic breast cancer, we utilized TMD231 breast cancer cells (derived from MDA-MB-231) that have a high propensity to metastasize to the lung. TMD231 tumor take and improved kinetics of tumor growth and metastatic foci formation appeared more consistently and at a faster rate in NOD.Cg-Prkdcscid Il2rgtm1Wjl/SzJ (NSG) versus NOD/SCID mice. For in vivo detection of small tumor burden at study initiation and metastatic lesions over time, TMD231 breast cancer cells were transduced with lentiviral vectors that express either mCherry or E2-Crimson fluorescent proteins (FPs). Flow cytometric analysis indicated transduction efficiencies for the lentiviral vectors expressing mCherry and E2-Crimson in the TMD231 cells was >99% and >80%, respectively. TMD231 cells expressing either the mCherry or E2-Crimson FPs were implanted into NSG mice and were imaged weekly using the Optix MX3 (ART Technologies, Montreal, Canada) to assess to what degree fluorescently tagged cells could be longitudinally and non-invasively visualized at primary and secondary sites within the NSG mice. While photon emission from TMD231 tumors expressing mCherry could be detected, levels were low and did not correlate with tumor growth overtime. In contrast, high levels of photon emission were detected using TMD231-E2-Crimson cells. Non-palpable tumors expressing the E2-Crimson FP could be detected in NSG mice as early as 7 days post-implant into the mammary fat pad. Additionally, metastatic foci in the lung were detected via optical imaging as early as 2-3 weeks post-implant. Following imaging analysis, TMD231-E2-Crimson tumor size correlated to increased fluorescent intensity, tumor depth, and fluorescent concentration longitudinally. In vitro imaging analysis of TMD231-E2-Crimson cells confirmed the in vivo imaging results showing a linear relationship between cell number and fluorescent intensity. The discrepancy in the in vivo detection of mCherry versus E2-Crimson proteins is most likely due to the greater brightness of E2-Crimson, as well as the closer alignment of the excitation/emission spectra of E2-Crimson with the laser/filter set of the Optix MX3 imaging system. To confirm optical imaging results, H&E staining indicated the presence of numerous foci in the lungs post-mortem. The optimized orthotopic model described here is being used to investigate mechanisms of metastasis as well as novel therapeutic strategies in metastatic breast cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1409. doi:1538-7445.AM2012-1409