Large Molecule Therapeutics Anti-MET ImmunoPET for Non–Small Cell LungCancer Using Novel Fully Human Antibody Fragments

MET, the receptor of hepatocyte growth factor, plays important roles in tumorigenesis anddrug resistance in numerous cancers, including non–small cell lung cancer (NSCLC). As increasing numbers of MET inhibitors are being developed for clinical applications, antibody fragment–based immunopositron emission tomogra-phy (immunoPET) has the potential to rapidly quantify in vivo MET expression levels for drug response evaluation and patient stratification for these targeted therapies. Here, fully human single-chain variable fragments (scFvs) isolated from aphage display librarywere reformatted into bivalent cys-diabodies (scFv-cys dimers) with affinities toMET ranging from 0.7 to 5.1 nmol/L. The candidatewith the highest affinity, H2,was radiolabeledwith 89Zr for immunoPET studies targetingNSCLC xenografts: lowMET-expressingHcc827 and the gefitinib-resistant Hcc827-GR6 with 4-fold MET overexpression. ImmunoPET at as early as 4 hours after injection produced high-contrast images, and ex vivo biodistribution analysis at 20 hours after injection showed about 2-fold difference in tracer uptake levels between the parental and resistant tumors (P < 0.01). Further immunoPET studies using a larger fragment, the H2 minibody (scFv-CH3 dimer), produced similar results at later time points. Two of the antibody clones (H2 and H5) showed in vitro growth inhibitory effects on MET-dependent gefitinib-resistant cell lines, whereas no effects were observed on resistant lines lacking MET activation. In conclusion, these fully human antibody fragments inhibit MET-dependent cancer cells and enable rapid immunoPET imaging to assessMET expression levels, showing potential for both therapeutic and diagnostic applications. Mol Cancer Ther; 13(11); 2607–17. 2014 AACR