Synthesis And Bioimaging Application Of Ultrasmall Magnetic Ferrite Nanoparticles-based PET/MR Dual-modal Imaging Probe

Early diagnosis of tumor is of great significance to the effective treatment and prognosis of patients.The single-modal imaging diagnosis cannot perform the high-sensitivity and high-resolution visualization simultaneously,while multi-modality can combine the advantages of different modality and become the key to improve the diagnostic accuracy.Nowadays,Ultra-small ferrite magnetic nanoparticles（UMFNPs）have been serving as a popular platform material for multi-modal diagnostic agents due to their unique magnetic properties,adjustable size,T₁ relaxation enhancement and facile modification.Herein,We designed an UMFNPs based PET/MR dual-modal imaging probe via the surface modification of nuclear imaging metal ion ⁶⁸Ga,and systematic studied its radiochemical yield,radiochemical stability,MRI performance,PET/MR dual-modal diagnostic application,pharmacokinetics and safety in vivo and in vitro.Additionally,ultra-small magnesium-doped ferrite with higher T₁ relaxation were investigated.The detailed results are as follows:（1）Construction and characterization of active-targeted dual modal imaging probe ⁶⁸Ga-NOTA-UMFNPs-Glu.The UMFNPs were fabricated via dynamic simultaneous thermal decomposition,then,we used the glutamate urea analogue（Glu-urea-Lys,Glu）,which can specifically target the prostate-specific membrane antigen on the surface of prostate cancer cells and the macrocyclic chelating agent NOTA coupled on the surface of the nanoparticles to construct active-targeted precursor NOTA-UMFNPs-Glu.The results show that as-prepared UMFNPs has an average hydrated diameter of about 3.1 nm and saturation magnetization value of 22.2emu/g with a hydrodynamic diameter of 13.4 nm.At last,a dual-modal imaging probe ⁶⁸Ga-NOTA-UMFNPs-Glu was prepared by chelating radioactive ⁶⁸Ga,which has a higher r₁relaxation of 8.18 m M^-1 s^-1.The radiochemical yield of the labeled product is 97%,and after placed in PBS and 10%FBS solution for 4 h,the radiochemical yield of is still above 90%,showing good stability in vitro.（2）Performance valuation of probe ⁶⁸Ga-NOTA-UMFNPs-Glu for the targeting efficiency,pharmacokinetics,safety and dual-modal imaging performance in mice.The active targeted probe can be effectively swallowed by LNCa P cells,showing good prostate cancer cell targeting effect,cell viability remains above 80%at the probe concentration of 100μg/m L.The results of in vivo experiments presented that the blood half-life of our probe is 41.7 min,which mainly distributes in the liver with no obvious damage to the main organs of mice.The PET/MR dual-modal imaging of prostate cancer demonstrated that the ⁶⁸Ga-NOTA-UMFNPs-Glu nanoprobe with a tumor radioactive uptake rate of 1.8%ID/g increased T₁ signal of MRI by 22.8%,indicating that our nanoprobe directly target to tumor site with an effective accumulation for enhancement of the contrast between tumor tissues and normal tissues,holding new promise for the accurate diagnosis of clinical prostate cancer.（3）Construction of ultra-small magnesium-doped ferrite nanoparticles with higher T₁relaxation efficiency.Different amount magnesium were doped into ultra-small ferrite nanoparticles.The results showed the r₁ value of ultra-small magnesium-doped ferrite nanoparticles increased firstly and then decreased with the increase of magnesium-doping content（0.025,0.05,0.1,0.2,0.5 mol）,when doping ratio x=0.05,the r₁ value reached the highest,12.8 m M^-1s^-1.This trend is basically consistent with the change of its saturation magnetization value（M_s）that may be due to the influence between the outer sphere model and the T₁ relaxation process,resulting in a remarkable improvement of T₁ contrast performance.（4）Evaluation of ultra-small magnesium-doped ferrite nanoparticles pharmacokinetics,safety and MRI contrast performance in mice.The ultra-small magnesium-doped ferrite nanoparticles(Mg_0.05-γFe₂O₃)with the highest T₁ relaxation efficiency as a model system for evaluation.The results showed that its blood half-life was 1.57 h,and the renal clearance rate reached 24.71%after 2 days.,the liver clearance rate reached 74.69%after 7 days,and the probe had no damage on liver,kidney function and other major organs,showing good blood compatibility and histocompatibility.The MR imaging of breast cancer showed that the our contrast agent can effectively enhance the T₁ signal at the tumor site and significantly improve the contrast between the tumor and the normal tissues.