Extracellular domain shedding influences specific tumor uptake and organ distribution of the EGFR PET tracer 89Zr-imgatuzumab

Abstract

Preclinical positron emission tomography (PET) imaging revealed a mismatch between in vivo epidermal growth factor receptor (EGFR) expression and EGFR antibody tracer tumor uptake. Shed EGFR ectodomain (sEGFR), which is present in cancer patient sera, can potentially bind tracer and therefore influence tracer kinetics. To optimize EGFR-PET, we examined the influence of sEGFR levels on tracer kinetics and tumor uptake of EGFR monoclonal antibody ⁸⁹Zr-imgatuzumab in varying xenograft models. Human cancer cell lines A431 (EGFR overexpressing, epidermoid), A549 and H441 (both EGFR medium expressing, non-small cell lung cancer) were xenografted in mice. Xenografted mice received 10, 25 or 160 μg ⁸⁹Zr-imgatuzumab, co-injected with equal doses ¹¹¹In-IgG control. MicroPET scans were made 24, 72 and 144 h post injection, followed by biodistribution analysis. sEGFR levels in liver and plasma samples were determined by ELISA. ⁸⁹Zr-imgatuzumab uptake in A431 tumors was highest (29.8 ± 5.4 %ID/g) in the 160 μg dose group. Contrary, highest uptake in A549 and H441 tumors was found at the lowest (10 μg) ⁸⁹Zr-imgatuzumab dose. High ⁸⁹Zr-imgatuzumab liver accumulation was found in A431 xenografted mice, which decreased with antibody dose increments. ⁸⁹Zr-imgatuzumab liver uptake in A549 and H441 xenografted mice was low at all doses. sEGFR levels in liver and plasma of A431 bearing mice were up to 1000-fold higher than levels found in A549, H441 and non-tumor xenografted mice. ⁸⁹Zr-imgatuzumab effectively visualizes EGFR-expressing tumors. High sEGFR levels can redirect ⁸⁹Zr-imgatuzumab to the liver, in which case tumor visualization can be improved by increasing tracer antibody dose.