Detection and quantification of enzymatically active prostate-specific antigenin vivo

Abstract

Abstract. Assays for blood levels of prostate-specific antigen (PSA), performed in prostate cancer detection, measure mostly inactive/complexed PSA and do not provide information regarding enzymatically active PSA, which is biologically more relevant. Thus, we designed and synthesized an enzymatically cleavable peptide sequence labeled with near-infrared (NIR) fluorophores (ex/em 740∕770 nm) and coupled it to a pharmacokinetic modifier designed to improve its plasma kinetics. In its native state, the agent, PSA750 FAST™ (PSA750), is optically quenched (>95%) and only becomes fluorescent upon cleavage by active PSA, yielding a significant increase in signal. This activation is highly selective for PSA relative to a large panel of disease-relevant enzymes. Active PSA was detected in tumor frozen sections using PSA750 and this activity was abolished in the presence of the inhibitor, alpha-1 anti-chymotrypsin. In vivo imaging of tumor-bearing mice using fluorescence molecular tomography demonstrated a significantly higher fluorescent signal in PSA þ LNCaP tumors as compared to PSA − prostate cancer 3 tumors (13.0 AE 3.7 versus 2.8 AE 0.8 pmol, p ¼ 0.023). Ex vivo imaging of tumor sections confirms PSA750-derived NIR signal localization in nonvascular tissue. This is the first report that demonstrates the feasibility and effectiveness of noninvasive, real time, fluorescence molecular imaging of PSA enzymatic activity in prostate cancer. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

Optical imaging probes in oncology

“…In this scenario, a specific probe for the active form of PSA has been developed and it is commercially available (Perkin Elmer): PSA 750 FAST [146] Fluorescent Imaging Agent. This is an optically silent probe in which the fluorescent signal appears only after the occurrence of an enzymatic cleavage by active PSA.…”

Fluorescence Molecular Tomography Reconstruction of Small Targets Using Stacked Auto-Encoder Neural Networks

“…Fluorescence molecular tomography (FMT) has attracted widespread interest due to its non-invasive property and sensitivity in applications such as drug discovery [1], cancer detection [2], and gene expression visualization [3], among others. However, FMT reconstruction is highly illconditioned because of the lack of sufficient external measurements required for complex images [4]- [6].…”