Abstract
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Objectives: Membrane-type serine protease 1 (MT-SP1), also known as matriptase, is upregulated in many cancers including cervical, breast, ovarian and prostate and inhibition of this protease reduces the invasiveness of cancer cells. This work aims to develop a PET agent to investigate imaging of tumors that express this protease using a 18F-labeled scFv, E2, which has picomolar binding affinity for the catalytic domain of MT-SP1.
Methods: E2 was chosen for its selectivity for matriptase from a phage display library of over 2 x 109 members. E2 was nonspecifically labeled by conjugation of N-succinimidyl 4-[18F]fluorobenzoate (FSB) to free amine groups of the molecule. FSB was synthesized as according to the literature (Appl. Rad. Isot. 63, 329-332, 2005) and purified via solid phase extraction. FSB was allowed to react with E2 or a control scFv in borate buffer at pH 8.3 for 45 minutes and purified by size exclusion chromatography. The labeled scFvs were incubated with a human colon cancer cell line, HT-29, and specific binding was assessed.
Results: Labeled E2 was prepared in yields of 1-5% EOB, with specific activity of ~7500 Ci/mmol. A 3-4 fold increase in accumulation was observed with the labeled E2 in in vitro studies with HT-29 cells over a labeled control scFv indicating preserved immunoreactivity.
Conclusions: We have successfully labeled the scFv, E2, with fluorine-18 and demonstrated immunoreactivity of the labeled molecule in vitro. Experiments are underway to determine the validity of this approach in vivo. This work illustrates that [18F]-labeled E2 is a potential marker of matriptase.
Research Support: This work was supported by NIH grants CA90788 (HFV) and CA72006 (CSC) and a NSF graduate research fellowship (MRD).
- Society of Nuclear Medicine, Inc.