Abstract
BackgroundThe motif RXDLXXL-based nanoprobes allow specific imaging of integrin αvβ6, a protein overexpressed during tumorigenesis and tumor progression of various tumors. We applied a novel RXDLXXL-coupled cyclic arginine-glycine-aspartate (RGD) nonapeptide conjugated with ultrasmall superparamagnetic iron oxide nanoparticles (referred to as cFK-9-USPIO) for the application of integrin αvβ6-targeted magnetic resonance (MR) molecular imaging for breast cancer.MethodsA novel MR-targeted nanoprobe, cFK-9-USPIO, was synthesized by conjugating integrin αvβ6-targeted peptide cFK-9 to N-amino (−NH2)-modified USPIO nanoparticles via a dehydration esterification reaction. Integrin αvβ6-positive mouse breast cancer (4 T1) and integrin αvβ6 negative human embryonic kidney 293 (HEK293) cell lines were incubated with cFK-9-AbFlour 647 (blocking group) or cFK-9-USPIO (experimental group), and subsequently imaged using laser scanning confocal microscopy (LSCM) and 3.0 Tesla magnetic resonance imaging (MRI) system. The affinity of cFK-9 targeting αvβ6 was analyzed by calculating the mean fluorescent intensity in cells, and the nanoparticle targeting effect was measured by the reduction of T2 values in an in vitro MRI. The in vivo MRI capability of cFK-9-USPIO was investigated in 4 T1 xenograft mouse models. Binding of the targeted nanoparticles to αvβ6-positive 4 T1 tumors was determined by ex vivo histopathology.ResultsIn vitro laser scanning confocal microscopy (LSCM) imaging showed that the difference in fluorescence intensity between the targeting and blocking groups of 4 T1 cells was significantly greater than that in HEK293 cells (P < 0.05). The in vitro MRI demonstrated a more remarkable T2 reduction in 4 T1 cells than in HEK293 cells (P < 0.001). The in vivo MRI of 4 T1 xenograft tumor-bearing nude mice showed significant T2 reduction in tumors compared to controls. Prussian blue staining further confirmed that αvβ6 integrin-targeted nanoparticles were specifically accumulated in 4 T1 tumors and notably fewer nanoparticles were detected in 4 T1 tumors of mice injected with control USPIO and HEK293 tumors of mice administered cFK-9-USPIO.ConclusionsIntegrin αvβ6-targeted nanoparticles have great potential for use in the detection of αvβ6-overexpressed breast cancer with MR molecular imaging.
Highlights
The motif RXDLXXL-based nanoprobes allow specific imaging of integrin αvβ6, a protein overexpressed during tumorigenesis and tumor progression of various tumors
The core size of Cyclo [FRGDLAFp(NMe)K] (cFK-9)-Ultrasmall superparamagnetic iron oxide (USPIO) and USPIO determined by Transmission electron microscope (TEM) was 5.54 ± 1.01 nm and 5.52 ± 0.81 nm, respectively
By comparing the T2-weighted images of tumor-bearing mice at 3.0 T before and after injection with targeted cFK-9-USPIO nanoparticles, we found that T2 signal intensity gradually reduced in 4 T1 tumors after cFK-9-USPIO circulation for 8 h, and the reduced T2 signal effect remained in the tumor area after 24 h
Summary
The motif RXDLXXL-based nanoprobes allow specific imaging of integrin αvβ, a protein overexpressed during tumorigenesis and tumor progression of various tumors. A novel sub-nanomolar αvβ6-specific ligand, the nonapeptide cyclo [FRGDLAFp(NMe)K] (referred to as cFK-9) was identified, which is characterized by the RXDLXXL motif sequence [18]. It has high αvβ binding affinity (IC50 = 0.26 nM), remarkable selectivity against other integrins (αvβ: IC50 = 632 nM; α5β1: IC50 = 73 nM; αvβ and αIIbβ, IC50 > 1000 nM), and is very stable in human plasma [18]. Nuclear medicine imaging has a relatively low spatial resolution, which may not be conducive to the precise localization of the target lesion Another limitation is the exposure to ionizing radiation
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