Human Epidermal Growth Factor Receptor 3-Specific Tumor Uptake and Biodistribution of Zr-MSB0010853 Visualized by Real-Time and Noninvasive PET Imaging.

The human epidermal growth factor receptor 3 (HER3) is an interesting target for antitumor therapy. For optimal HER3 signaling inhibition, a biparatopic Nanobody construct (MSB0010853) was developed that binds 2 different HER3 epitopes. In addition, MSB0010853 contains a third HER3 epitope that binds albumin to extend its circulation time. MSB0010853 is cross-reactive with HER3 and albumin of mouse origin. We aimed to gain insight into MSB0010853 biodistribution and tumor uptake by radiolabeling the Nanobody construct with Zr. MSB0010853 was radiolabeled with Zr. Dose- and time-dependent tumor uptake was studied in nude BALB/c mice bearing a subcutaneous HER3 overexpressing H441 non-small cell lung cancer xenograft. Dose-dependent biodistribution of Zr-MSB0010853 was assessed ex vivo at 24 h after intravenous injection. Protein doses of 5, 10, 25, 100, and 1,000 μg were used. Time-dependent biodistribution of MSB0010853 was analyzed ex vivo at 3, 6, 24, and 96 h after intravenous administration of 25 μg of Zr-MSB0010853. PET imaging and biodistribution were performed 24 h after administration of 25 μg of Zr-MSB0010853 to mice bearing human H441, FaDu (high HER3 expression), or Calu-1 (no HER3 expression) tumor xenografts. Radiolabeling of MSB0010853 with Zr was performed with a radiochemical purity of greater than 95%. Ex vivo biodistribution showed protein dose- and time-dependent distribution of Zr-MSB0010853 in all organs. Uptake of Zr-MSB0010853 in H441 tumors was only time-dependent. Tumor could be visualized up to at least 96 h after injection. The highest mean SUV of 0.6 ± 0.2 was observed at 24 h after injection of 25 μg of Zr-MSB0010853. Zr-MSB0010853 tumor uptake correlated with HER3 expression and was highest in H441 (6.2 ± 1.1 percentage injected dose per gram [%ID/g]) and lowest in Calu-1 (2.3 ± 0.3 %ID/g) xenografts. Zr-MSB0010853 organ distribution and tumor uptake in mice are time-dependent, and tumor uptake correlates with HER3 expression. In contrast to tumor uptake except for kidney uptake, organ distribution of Zr-MSB0010853 is protein dose-dependent for the tested doses. Zr-MSB0010853 PET imaging gives insight into the in vivo behavior of MSB0010853.