Use of a Peptide Derived from Foot-and-Mouth Disease Virus for the Noninvasive Imaging of Human Cancer: Generation and Evaluation of 4-[18F]Fluorobenzoyl A20FMDV2 for In vivo Imaging of Integrin αvβ6 Expression with Positron Emission Tomography

Abstract

Expression of the epithelial-specific integrin A v B 6 is low or undetectable in most adult tissues but may be increased during wound healing and inflammation and is up-regulated dramatically by many different carcinomas, making A v B 6 a promising target for the in vivo detection of cancer using noninvasive imaging. In addition, A v B 6 is recognized as promoting invasion and correlates with aggressive behavior of human cancers and thus agents that recognize A v B 6 specifically in vivo will be an essential tool for the future management of A v B 6 -positive cancers. Recently, we identified the peptide NAVPNLRGDLQV-LAQKVART (A20FMDV2), derived from foot-and-mouth disease virus, as a potent inhibitor of A v B 6 . Using flow cytometry and ELISA, we show that this peptide is highly selective, inhibiting A v B 6 -ligand binding with a IC 50 of 3 nmol/L, an activity 1,000-fold more selective for A v B 6 than for other RGDdirected integrins (A v B 3 , A v B 5 , and A 5 B 1 ). A20FMDV2 was radiolabeled on solid-phase using 4-[18 F]fluorobenzoic acid, injected into mice bearing both A v B 6 -negative and A v B 6 -positive (DX3puro/DX3puroB6 cell lines) xenografts and imaged using a small animal positron emission tomography (PET) scanner. Rapid uptake (<30 min) and selective retention (>5 h) of radioactivity in the A v B 6 -positive versus the A v B 6 -negative tumor, together with fast renal elimination of nonspecifically bound activity, resulted in specific imaging of the A v B 6 -positive neoplasm. These data suggest that PET imaging of A v B 6 -positive tumors is feasible and will provide an important new tool for early detection and improved management of many types of cancers. [Cancer Res 2007;67(16):7833-40]

High-throughput in vivo screening of targeted molecular imaging agents

“…The 42 peptides identified from the libraries, as well as A20FMDV2 (which served as the ''gold standard''), were radiolabeled with [ 18 F]FBA and evaluated in vivo using microPET over the span of 11 consecutive days. A20FMDV2 is a peptide comprised of 20 aa and was chosen as the gold standard because of its well-defined binding to the ␣ v ␤ 6 integrin in vivo in the same mouse model (26). A complete list of peptides evaluated, as well as their IC 50 s, is listed in Table S1.…”

“…The specific activity of the purified peptides, as determined by HPLC, was found to be Ͼ1 Ci/ mol. Each individual peptide was simultaneously injected via tail-vein catheter into 2 animals bearing paired tumors (␣ v ␤ 6 positive and ␣ v ␤ 6 negative) (26), and microPET images were acquired. Scanning 4 pairs of mice a day at 5 timepoints yielded 40 scans per day (in 2 instances we were unable to obtain a final scan at 180 min; on one day only 3 pairs of mice were scanned).…”

“…Solid-phase radiolabeling has been shown to be an efficient and reliable method for the incorporation of the fluorine-18-bearing prosthetic group 4-[ 18 F]fluorobenzoic acid ([ 18 F]FBA) into resin-bound peptides yielding the desired radiolabeled peptide in quantities sufficient for in vivo imaging (25,26). Although the ␣ v ␤ 6 integrin was chosen as the model target for this HTS study, this approach can be applied to the identification of molecular imaging agents that target any cell surface receptor.…”

“…Although the ␣ v ␤ 6 integrin was chosen as the model target for this HTS study, this approach can be applied to the identification of molecular imaging agents that target any cell surface receptor. The ␣ v ␤ 6 integrin is an interesting target because although its expression is generally low or undetectable in normal epithelium, upregulation of this integrin has been linked with multiple types of cancer and was recently identified as a prognostic indicator for such diseases (26)(27)(28)(29)(30). Herein we report the combination of OBOC chemistry and solid-phase radiolabeling for the implementation of a high-throughput in vivo methodology for the identification of previously uncharacterized fluorine-18 radiolabeled molecular imaging agents for the ␣ v ␤ 6 integrin.…”

Preclinical SPECT/CT Imaging of αvβ6 Integrins for Molecular Stratification of Idiopathic Pulmonary Fibrosis

“…Therefore, we developed a strategy for detecting the avb6 integrin in vivo using an imaging technique with a peptide derived from the VP1 coat protein of the foot-and-mouth disease virus. The A20FMDV2 peptide shows highly selective avb6 ligand binding activity and is 1,000-fold more selective for avb6 than for other arginine-glycine-aspartate (RGD)-binding integrins (a v b 3 , avb5, and a5b1) (29). avb6-expressing human pancreatic (30) and breast (31) cancer cells have been imaged by PET or SPECT scanning in murine models using radiolabeled A20FMDV2; however, there are no reports measuring endogenous avb6 levels in vivo.…”