Anti-MET ImmunoPET for Non–Small Cell Lung Cancer Using Novel Fully Human Antibody Fragments

Abstract

MET, the receptor of hepatocyte growth factor, plays important roles in tumorigenesis and drug resistance in numerous cancers including non-small cell lung cancer. As increasing numbers of MET inhibitors are being developed for clinical applications, antibody fragment based immuno-positron emission tomography (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 a phage display library were re-formatted into bivalent cys-diabodies (scFv-cys dimers) with affinities to MET ranging from 0.7 nM to 5.1 nM. The candidate with the highest affinity, H2, was radiolabeled with 89Zr for immunoPET studies targeting non-small cell lung cancer xenografts: low MET expressing Hcc827 and the gefitinib-resistant Hcc827-GR6 with 4-fold MET over-expression. ImmunoPET at as early as 4 hours post injection produced high contrast images, and ex vivo biodistribution analysis at 20 hours post 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, while 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 assess MET expression levels, showing potential for both therapeutic and diagnostic applications.

In vivo imaging with antibodies and engineered fragments

“…Antibody-directed imaging might also provide a method for assessing the development of resistance to therapy. Li et al recently used engineered minibodies and diabodies derived from a phage display anti-MET antibody to image elevated MET in non-small cell lung cancer xenografts from cell lines resistant to EGFR-targeted therapy via overexpression of MET (Figure 6) (Li et al, 2014). …”

“…PET imaging MET using a 89 Zr-DFO-labeled MET-specific human minibody clearly visualized the overexpression of MET in the gefitinib-resistant tumors. (Knowles et al, 2014a; Li et al, 2014)…”

c-Met PET Imaging Detects Early-Stage Locoregional Recurrence of Basal-Like Breast Cancer

“…Similarly, Li et al explored the use of c-Met-targeting scFv-cys dimers in non-small cell lung cancer xenografts. Despite showing very high affinity for c-Met, good-contrast immune-PET imaging was achieved only at 20 h after injection (30).…”

Nanoparticles and radiotracers: advances toward radionanomedicine

“…54 4-[ 18 F]fluorobenzyl-2-bromoacetamide ([ 18 F]FBBA) was used for radiolabeling precursor polymers, which were subsequently integrated into a polymeric NP using nanoprecipitation. 55 If longer in vivo time points are desired, 64 Cu (t 1/2 = 12.7 h) easily allows for imaging out to 48 h. Recently, direct incorporation of a porphyrin into the polar head group of a lipid produced a novel chelating lipid that also self assembled. The authors showed that 64 Cu could be incorporated into the porphysomes with high serum stability to 48 h. PET imaging of untargeted porphysomes in vivo was able to resolve margins of an orthotopic PC3 prostate cancer tumor in mice.…”