Comparative biodistribution analysis across four different ⁸⁹Zr-monoclonal antibody tracers—The first step towards an imaging warehouse

Rationale: Knowledge on monoclonal antibody biodistribution in healthy tissues in humans can support clinical drug development. Molecular imaging with positron emission tomography (PET) can yield information in this setting. However, recent imaging studies have analyzed the behavior of single antibodies only, neglecting comparison across different antibodies. Methods: We compared the distribution of four 89 Zr-labeled antibodies in healthy tissue in a retrospective analysis based on the recently published harmonization protocol for 89 Zr-tracers and our delineation protocol. Results: The biodistribution patterns of 89 Zr-lumretuzumab, 89 Zr-MMOT0530A, 89 Zr-bevacizumab and 89 Zr-trastuzumab on day 4 after tracer injection were largely similar. The highest tracer concentration was seen in healthy liver, spleen, kidney and intestines. About one-third of the injected tracer dose was found in the circulation, up to 15% in the liver and only 4% in the spleen and kidney. Lower tracer concentration was seen in bone marrow, lung, compact bone, muscle, fat and the brain. Despite low tracer accumulation per gram of tissue, large-volume tissues, especially fat, can influence overall distribution: On average, 5-7% of the injected tracer dose accumulated in fat, with a peak of 19% in a patient with morbid obesity.