High-throughput in vivo screening of targeted molecular imaging agents

Abstract

The rapid development and translation of targeted molecular imaging agents from bench to bedside is currently a slow process, with a clear bottleneck between the discovery of new compounds and the development of an appropriate molecular imaging agent. The ability to identify promising new molecular imaging agents, as well as failures, much earlier in the development process using high-throughput screening techniques could save significant time and money. This work combines the advantages of combinatorial chemistry, sitespecific solid-phase radiolabeling, and in vivo imaging for the rapid screening of molecular imaging agents. A one-bead-one-compound library was prepared and evaluated in vitro, leading to the identification of 42 promising lead peptides. Over 11 consecutive days, these peptides, along with a control peptide, were successfully radiolabeled with 4-[ 18 F]fluorobenzoic acid and evaluated in vivo using microPET. Four peptides were radiolabeled per day, followed by simultaneous injection of each individual peptide into 2 animals. As a result, 4 promising new molecular imaging agents were identified that otherwise would not have been selected based solely on in vitro data. This study is the first example of the practical application of a high-throughput screening approach using microPET imaging of [ 18 F]-labeled peptides for the rapid in vivo identification of potential new molecular imaging agents.high-throughput screening ͉ in vivo imaging ͉ microPET ͉ radiolabeled peptides ͉ positron emission tomography C ombinatorial chemistry (1, 2) and phage display (3) techniques have become essential tools for the production of large compound libraries, which can be rapidly produced for the discovery of new drugs. Designing and implementing high-throughput screening (HTS) approaches to identify lead compounds that show affinity for a biological target from these large libraries, wherein millions of new compounds may exist, is often accomplished through in vitro screening. In general, the 2 approaches by which this can be accomplished are either solution-phase screening techniques (4-11), generally used by drug discovery programs, or solid-phase screening, which has garnered interest for the evaluation of libraries prepared using combinatorial chemistry.Though there are many reports outlining high-throughput approaches for in vitro screening, few exist where the sole purpose is to develop high-throughput in vivo methodologies for the identification of new molecular imaging agents. While the feasibility of using magnetic resonance imaging (MRI) for high-throughput applications has been explored with both the development of scanner technology and the scanning of multiple animals in parallel (12)(13)(14)(15)(16)(17)(18)(19)(20), positron emission tomography (PET) has received very little attention for high-throughput applications. This is likely the result of the unique set of problems that arise when considering using the latter imaging modality. The half-lives of the radioactive isotopes commonly used for PET ar...

Positively Charged Residues at the Five-Fold Symmetry Axis of Cell Culture-Adapted Foot-and-Mouth Disease Virus Permit Novel Receptor Interactions

“…Structural analyses of FMDV and FMDV-derived peptides have shown that the integrin-binding loop consists of a short region of a ␤-strand followed by the RGD, which is in turn is followed by a helical structure (16,(18)(19)(20)(21)(22). Typically, native ligands for ␣v␤6 have leucine (L) or methionine (M) at the RGD ϩ1 site and leucine or isoleucine (I) at the RGD ϩ4 site (16,23,24). FMDV may be highly adapted to use ␣v␤6 as a receptor, as it has a similar conserved sequence (L, M, or arginine at the RGD ϩ1 site and L or I at the RGD ϩ4 site) following the RGD.…”

Emerging Role of ImmunoPET in Receptor Targeted Cancer Therapy

“…In this strategy, the selected amino group is unprotected and the otherwise protected peptide is labeled site-specifically on solid phase then cleaved from the resin and deprotected and purified. The solid phase radiolabeling approach is very robust and a wide variety of 18 F-labeled peptides could be obtained with minimal optimization of the radiolabeling procedure [22]. Because the solid phase approach is time consuming and the overall yield is generally inversely proportional to the size of the peptide faster and more efficient methods for 18 F-fluorination of peptides have been sought.…”

Diagnosis and therapy are walking together on radiopeptides’ avenue

“…An effective answer to this request can be found through the in vivo screening tests of targeted molecular imaging agents. For example, Gagnon et al [3] demonstrated the feasibility of a high-throughput in vivo screening approach using animal imaging for 18 F peptides.…”