DCE-MRI Detects OATP-expressing Transplanted Cells Using Clinical Doses of Gadolinium Contrast Agent.

Purpose: Hepatic organic anion transporting polypeptides (OATPs) transport off-the-shelf, FDA-approved, hepatospecific Gd-based MRI contrast agents into cells that express the transporters enhancing signal on T1-weighted MRI. Studies have used MRI to identify OATP-overexpressing tumors and metastases transplanted in mice following the delivery of Gd-EOB-DTPA at 27-67-fold higher than clinical doses. With safety and regulatory concerns over Gd-based contrast agents, translating OATPs as an MRI reporter protein to humans for regenerative medicine will require substantially lower doses of agent.

Procedures: We engineered the MyC-CaP mouse tumor cell line to express rat OATP1B2, which influxes both Gd-EOB-DTPA and Gd-BOPTA, resulting in signal enhancement on T1-weighted MRI. We then inoculated mice with rat OATP1B2 and non-expressing cells bilaterally to generate tumors. 3-4 weeks after inoculation, when tumors had formed, in-vivo MRI imaging was performed with delivery of 0.025 mmol/kg or 0.25 mmol/kg of the Gd-based contrast agents. We complemented static T1-weighted MRI and T1-mapping with dynamic contrast enhanced (DCE)-MRI and performed area under the curve (AUC) analysis to discriminate the two tumor types.

Results: While all OATP1B2-expressing tumors were easily visible at the high dose of 0.25 mmol/kg on T1-weighted MRI and easy to distinguish from control tumors, OATP1B2-expressing tumors were hard to identify and distinguish from non-expressing tumors at the lower, clinical dose of 0.025 mmol/kg with standard T1-weighted MRI or T1-mapping. However, AUC analyses of the DCE-MRI curves could identify and distinguish these tumors, needing 30 (Gd-EOB-DTPA) or 45 (Gd-BOPTA) minutes acquisition time.

Conclusions: By performing AUC analyses of DCE-MRI curves following delivery of clinical concentration of MRI contrast agents, OATP1B2-expressing tumors could be identified and distinguished from control tumors, suggesting this imaging approach as a path to substantially reducing the amount of contrast agent needed to use OATPs as a clinically viable reporter protein for imaging regenerative medicine.