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Updated: Jun 28, 2026
MR Molecular Imaging of Prostate Cancer with a Small Molecular CLT1 Peptide Targeted Contrast Agent
Published on: September 3, 2013
Engineered humanized diabodies for microPET imaging of prostate stem cell antigen-expressing tumors
Jeffrey V Leyton1, Tove Olafsen, Mark A Sherman
1Crump Institute for Molecular Imaging, Department of Molecular and Medical Pharmacology, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095, USA.
Abstract:
We have previously demonstrated preclinical in vivo targeting of prostate stem cell antigen (PSCA) using a humanized anti-PSCA 2B3 monoclonal antibody (mAb). However, humanization resulted in 5-fold loss of apparent affinity relative to the parental mAb (1 nM). In this study, diabodies (scFv dimers of 55 kDa) were generated from 2B3 including variants with different linker lengths as well as back-mutations to original murine residues to improve affinity. Parental 2B3 (p2B3) and back-mutated 2B3 (bm2B3) diabodies (Dbs) with five- or eight-amino acid linkers (p2B3-Db5, p2B3-Db8, bm2B3-Db5 and bm2B3-Db8) were evaluated for binding to PSCA by flow cytometry and affinities were determined by surface plasmon resonance. Back-mutation restored the affinity from 5.4 to 1.9 nM. Stability, evaluated by size exclusion, revealed that diabodies with eight-residue linkers existed as a mixture of dimeric and monomeric species at low concentrations (
