A ratiometric fluorescent probe based on peptide modified MnFe2O4 nanoparticles for matrix metalloproteinase-7 activity detection in vitro and in vivo

Abstract

Abnormal expression of matrix metalloproteinases plays an important role in tumor invasion and metastasis. In this report, a peptide modified MnFe₂O₄ ratiometric fluorescent nanoprobe is developed for noninvasively visualizing the distribution of matrix metalloproteinase-7 (MMP-7) in vitro and in vivo. A fluorescein isothiocyanate (FITC) modified peptide containing the specific motif VPLSLTMG for MMP-7 cleavage was conjugated with MnFe₂O₄ nanoparticles (NPs) to establish a Förster resonance energy transfer (FRET) system for sensing the protease. The rhodamine B (RhB) modified targeting peptide immobilized on the nanoparticle surface was not only used as an internal reference for forming a ratiometric fluorescence system together with the FITC dye, but also used for enhancing the tumor targeting ability. The tumor accumulation amount of the as-developed ratiometric fluorescent probe (termed MnFe₂O₄-pep-dyes) can be measured by T₂-weighted magnetic resonance (T₂-weighted MR) imaging because MnFe₂O₄ NPs display an excellent T₂-weighted MR contrast ability. In the presence of MMP-7, FITC detached from the MnFe₂O₄ surface resulting in the recovery of FITC fluorescence, while no obvious change of the RhB fluorescence was observed. The recovery ratio of FITC to RhB fluorescence intensity is linearly dependent on the MMP-7 concentration within the range of 0.1 to 15 nM in buffer and 5 × 10² to 1 × 10⁴ cells in cell lysates with a limit of detection of 0.1 nM and 436 cells, respectively. MnFe₂O₄-pep-dyes was further applied to spatially observe MMP-7 expression in a tumor-bearing mouse by in vivo fluorescence imaging with external magnetic field assistance for demonstrating its practicability.