Multimodality reporter gene imaging provides valuable, noninvasive information on the fate of engineered cell populations. To complement magnetic resonance imaging (MRI) measures of tumor volume and 2-dimensional reporter-based optical measures of cell viability, reporter-based MRI may offer 3-dimensional information on the distribution of viable cancer cells in deep tissues.
Here, we engineered human and murine triple-negative breast cancer cells with lentivirus encoding tdTomato and firefly luciferase for fluorescence imaging and bioluminescence imaging (BLI). A subset of these cells was additionally engineered with lentivirus encoding organic anion transporting polypeptide 1a1 (Oatp1a1) for MRI. Oatp1a1 operates by transporting gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) into cells, and it concomitantly improves BLI substrate uptake. After orthotopic implantation of engineered cells expressing or not expressing Oatp1a1, longitudinal fluorescence imaging, BLI, and 3-Tesla MRI were performed.
Oatp1a1-expressing tumors displayed significantly increased BLI signals relative to control tumors at all time points (P < 0.05). On MRI, post–Gd-EOB-DTPA T 1-weighted images of Oatp1a1-expressing tumors exhibited significantly increased contrast-to-noise ratios compared with control tumors and precontrast images (P < 0.05). At endpoint, tumors expressing Oatp1a1 displayed intratumoral MR signal heterogeneity not present at earlier time points. Pixel-based analysis of matched in vivo MR and ex vivo fluorescence microscopy images revealed a strong, positive correlation between MR intensity and tdTomato intensity for Oatp1a1-expressing tumors (P < 0.05), but not control tumors.
These results characterize Oatp1a1 as a sensitive, quantitative, positive contrast MRI reporter gene for 3-dimensional assessment of viable cancer cell intratumoral distribution and concomitant BLI enhancement. This multimodality reporter gene system can provide new insights into the influence of viable cancer cell intratumoral distribution on tumor progression and metastasis, as well as improved assessments of anticancer therapies.
From the *Department of Medical Biophysics, University of Western Ontario;
†Medical Imaging Laboratories, Robarts Research Institute, London, Ontario;
‡Department of Medical Sciences, University of Western Ontario, London, Ontario;
§Ontario Institute for Cancer Research, MaRS Centre, Toronto, Ontario; and
∥Lawson Health Research Institute, London, Ontario, Canada.
Received for publication September 18, 2018; and accepted for publication, after revision, November 15, 2018.
Conflicts of interest and sources of funding: The authors declare no potential conflicts of interest. Financial support for this manuscript was provided by Natural Sciences and Engineering Research Council Discovery Grants (J.A.R., RGPIN-2016-05420; T.J.S., RGPIN-2017-06338) and an Ontario Institute for Cancer Research Investigator Award (T.J.S., IA-028). In addition, a Breast Cancer Society of Canada Scholarship was awarded to Nivin Nyström to help support this project.
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Correspondence to: John A. Ronald, PhD, Robarts Research Institute, Schulich School of Medicine and Dentistry, University of Western Ontario, Room 2241A, London, Ontario, Canada N6A 5B7. E-mail: email@example.com.