| CXCR4is a transmembrane recptor that functions in cancer cell survival, proliferation, invasion and metastasis. Since it is extensively involved in oncological events, it has been considered an ideal target for cancer imaging and chemotherapies. Many CXCR4antagonists have been developed for drug delivering, and in recent years, targeted PET imaging. There has also been some attempts introducing them to MRI contrast agents. In our study, a novel CXCR4binding peptide (Pep12) was introduced for targeted MRI. Immuno-fluorescence experiments and flow cytometry showed that pep12had great binding affinity to tumor cells expressing CXCR4, which is comparable to CXCR4monoclonal antibodies. After that, ultrasmall paramagnetic iron oxide nanoparticle (USPIO-Np) was synthesized and conjugated to Pep12, yielding a CXCR4targeted MR contrast agent. Pep12-USPIO was water soluble, and formed stable aqueous colloid in water/PBS solution. The hydro diameter was80.5nm. MTS tests proved its low toxicity to cells. Pullulan stain showed pep12-USPIO could bind to tumor cells in a concentration dependent way, while UPSIO alone could not. Human lung cancer cell (A549), pancreatic cancer cell (PANC-1) and breast cancer cell (MCF-7), each with different level of CXCR4expression, were incubated with Pep12-USPIO, and underwent MR scan. A significant T2/T2*signal dropdown was observed in Pepl2-USPIO incubated cell suspension, while USPIO incubated cell suspension only had slight T2/T2*signal change. More excitingly, the value of T2/T2*change has positive correlation to the expression level of CXCR4in those tumor cells. In a word, a peptide based MR contrast agent was developed for CXCR4targeted imaging, it could specificly bind to CXCR4expressing cells and produce MR signal change. The value of T2/T2*change might be used for the prediction of CXCR4expression and somehow, tumor metastasis potential. Further studies of this CXCR4targeted probe will be carried out in mice xenograft models, to see its pharmacokinetics, biological toxicity and ability to detect tumor metastasis potential in vivo. |
