Comparison of the Accuracy of FMT/CT and PET/MRI for the Assessment of Antibody Biodistribution in Squamous Cell Carcinoma Xenografts

Abstract

Non-invasive imaging technologies are increasingly used in preclinical drug research for the pharmacokinetic analysis of therapeutic compounds in living animals over time. The different preclinical imaging modalities available differ intrinsically in their detection principle and thus might exhibit limitations for a specific application. Here, we systematically investigated the performance of advanced fluorescence mediated tomography/micro-computed tomography (FMT/CT) in comparison to positron emission tomography/magnetic resonance imaging (PET/MRI) for quantitative analysis of the biodistribution of different antibody formats and in dependence of the required imaging label in a squamous cell carcinoma xenograft model. Methods: Different formats of an anti-EGFR antibody (mAb, F(ab’)2 and Fab) were labeled with Alexa750 or [⁶⁴Cu]NODAGA and injected intravenously into separate cohorts of nude mice bearing subcutaneous A-431 tumors. Two and 24 h after injection, mice were measured by FMT/CT and PET/MRI. Probe accumulation was quantitatively assessed in organs and tumors. In vivo data were compared between modalities and correlated with ex vivo fluorescence, gamma counting and ECLIA analysis. Results: Both imaging methods faithfully monitored the biodistribution and elimination routes of the compounds and organs’ accumulation measured by FMT/CT and PET/MRI correlated significantly with ex vivo measurements. In addition, the accumulation in kidney, muscle and tumor tissue correlated between FMT/CT and PET/MRI. However, the pharmacokinetic of the Alexa750-labeled antibody formats showed shorter blood half-life times and higher liver uptake than the radio-labeled counterparts. Conclusion: FMT/CT imaging allows quantifying the biodistribution of antibodies in nude mice and provides an alternative to classical PET analysis in preclinical drug research. However, even for large molecules, such as mAb, Alexa750-labeling can change pharmacokinetics and trigger liver uptake.