Magnetic PEGylated Pt₃Co Nanoparticles As A Novel MR Contrast Agent: In Vivo MR Imaging And Long-term Toxicity Study

Objective To study the feasibility and value of ultra-small superparamagnetic Pt3Conanoparticles as a novel MR T2contrast agent for magnetic response imaging (MRI).Methods①SynthesizePt3Co magnetic nanoparticles, which is then functionalizedby a biocompatible polyethylene glycol (PEG) to acquire high stability in physiologicalsolutions. And then, the stability, characterization and magnetic property of Pt3Co-PEGwere evaluated.②4T1cells, HL7702cells, Sk-br-3cells and293T cells was observedeven after cells were incubated with various concentrations of Pt3Co-PEG. The cellcytotoxicity of Pt3Co-PEG was evaluated by the MTT assay, LDH leakage assay and ROSassay.③Two groups of Female4T1tumor-bearing Balb/C mice intravenously injectedwith the same metal concentration of Pt3Co-PEG and Resovist respectively were imagedunder a3.0T clinical MRI scanner at different time points including2h,6h and24h. Andthe T2signal intensity in the tumor region was measured at these time points.④Twentyfemale healthy Balb/C mice injected with Pt3Co-PEG (five mice per group) and other fivemice without injection were sacrificed at desired time points (1day,7days,30days,60daysp.i.), and major organs were collected for hematoxylin and eosin (HE) staining. In additionto histology examination, serum biochemistry and complete blood panel analysis werecarried out to look for any potential toxicity of our nanoparticlas to the treated mice.Results①The transmission electron microscopy (TEM) and high resolution TEM(HR-TEM) images of the sample in solution indicated the good uniformity of Pt3Conanoparticles, and the size was about6nm; after modified with an amphiphilicC18PMH-PEG, the Pt3Co-PEG nanoparticles exhibited excellent stability in variousphysiological solutions. The hysteresis loop measurement suggested the superparamagneticnature of our Pt3Co-PEG nanoparticles. In the Fourier transform infrared (FT-IR) spectraof Pt3Co and Pt3Co-PEG nanoparticles, the strong IR absorbance bands around3000cm-1from the Pt3Co-PEG sample could be attributed to C-H vibrations in the PEG coating. The r2relaxivity of the Pt3Co-PEG based on the Co concentration was measured to be451.2mM/s, which was2.3-fold higher than that of Resovist.②A series ofin vitrocytotoxicity assay showed no significant cytotoxic response of cells even at highnanoparticle concentrations.③T wo groups of4T1tumor-bearing Balb/c miceintravenously injected with the same metal concentration of Pt3Co-PEG and Resovistrespectively were scanned by a3.0T MR scanner at different time points. The MR imagingof tumor-bearing mice presents much better tumor contrast offered by Pt3Co-PEGnanoparticles in comparison to Resovist; while the T2-weighted MR imaging of twogroups showed similar darkening effects in the liver regions.④T hrough long-term toxicityand in vivo biodistribution study of Pt3Co-PEG nanoparticles, we conclude that althoughPt3Co-PEG nanoparticles show high RES uptake and tend to be retained in the mouse bodyfor a long time, no noticeable toxicity is induced to the treated animals within60days atour tested dose. Hematoxylin and eosin (H&E) stained tissue slices, serum biochemistryand complete blood panel analysis also showed no potential in vivo toxicity of ourPt3Co-PEG nanoparticles to mice,Conclusion Ultra-small superparamagnetic Pt3Co-PEG nanoparticles were stable inphysiological environments and exhibited excellent magnetic property. In vivo MRimaging suggested our Pt3Co-PEG nanoparticles obvious tumor MR contrasts, and theeffect much better than the commercial agent Resovist. In addition, both in vitro and invivo studies uncover no obvious toxicity for Pt3Co-PEG nanoparticles. Therefore, ourPt3Co-PEG magnetic nanoparticles could be used as a novel MRI T2contrast agent fortumor diagnosis.