Background The hairpin cell-penetrating peptides （hCPPs） demonstrate an interesting characteristic of conditioned activation by molecules. We hypothesized that hCPPs have the potential to selectively deliver a paramagnetic gadolinium probe into the matrix metalloproteinase 2 （MMP-2） positive human ovary adenocarcinoma cell lines, SKOV-3. Methods hCPPs were synthesized and labeled with 1,4,7,10-tetraazacyclododecane-N,N＇,N＂,N＂＇-tetraacetic acid gadolinium （111） （Gd-DOTA） and fluorescein isothiocyanate （FITC） by f-moc strategy using a standard solid phase peptide synthesis protocol. MMP-2 expression and activity were demonstrated by reverse transcriptase polymerase chain reaction （RT-PCR） and zymography. Internalization and location of hCPPs in SKOV-3 cells were observed by fluorescein imaging and flow cytometery. Selective delivery of Gd-DOTA in SKOV-3 cells was observed by magnetic resonance imaging （MRI） and transmission electron microscopy （TEM）. Results The uptake of hCPPs by SKOV-3 cells depended on the activity of MMP-2. T1WI signals of SKOV-3 cells treated with Gd-DOTA-hCPPs suggested the uptake of Gd-DOTA-hCPPs increased in a time- （r=0.990, P 〈0.01） and concentration-dependent manner （r=0.964, P 〈0.001）, but was inhibited by a MMP-2 inhibitor. Electron-dense particles observed in the cytoplasm and nucleus by transmission electron microscopy proved the intracellular penetration of gadolinium. Conclusions hCPPs can be used as an effective vector for an MRI molecular probe to assess the activity of MMP-2.
