The Study Of ¹²⁵I-AIBZM Nanoliposomes For Brain Imaging Agents

Many kinds of central nervous system diseases, such as Parkinson's disease, Alzheimer's disease, have great relationship with abnormality of cerebral dopaminergic neurotransmission. For the diagnosis, treatment, prognosis and pathogenesis research of these diseases, it is extremely important to acquire the information of dopamine's changes. Radioactive brain receptor imaging technique can be used to acquire the information of dopamine receptor which can infer the situation of dopamine. (S)-5-125I-N-(1-ethyl-2-pyrrolidinyl)methyl-4-amine-2-methoxy-benzamide(125I-AIBZ M)shows a high affinity with dopaminergic receptor, while it's hardly uptaken in brain due to its low lipophilicity. Therefore, the application of 125I-AIBZM as a brain imaging agent is limited.In this paper, the objective is to improve the brain uptake of 125I-AIBZM with various methods.First, the structure modification was performed, resulting in a new compound 125I-DMAIBZM((S)-5-125I-Iodo-N-(1-ethyl-2-pyrrolidinyl)methyl-4-dimethyl-amine-2-methoxy-benzamide) produced (4-amine of I-AIBZM transformed into 4-dimethyl- amine).Labeling was achieved by Iodogen method, with 74% radiochemical yield. After HPLC purification, radiochemical purity>99% was obtained. The biodistribution in vivo of mice and rats focus on their brain uptake.The mice biodistribution data for 125I-DMAIBZM (striatum/cerebellum>6.5) indicated a good distribution in striatum with high specificity and affinity, while the rats brain biodistribution data proved an improvement on brain uptake comparing with the one reported by another paper.Second, preparation 125I-AIBZM-lactoferrin-nano liposome(125I-AIBZM-Lf-L) was used to pass the brain blood barrier actively. Labeling was performed as the same as 125I-DMAIBZM, with 99% radiochemical yield. Blank liposomes (L) were prepared by film hydration method. After hydration, L was pressed to pass the polycarbonate membrane by high-pressure homogenizer (Micro-extrusion device) to form suitable L (particle size was about 100 nm), with regular shape and uniform distribution of particle size. Reacted with lactoferrin, L can transfer to latofrrin-L(Lf-L).There was little difference between L and Lf-L through high-resolution transmission electron microscopy. Drug-loaded liposomes were prepared by ammonium sulfate gradient method. Labled precursors ABZM were chosen to do the cold experiment before the hot experiment to tell if the compound ABZM could be loaded to the L by ammonium sulfate gradient method. The result was positive, and the encapsulation efficiency of ABZM-L was 20.42%, calculated by the standard curve method. According to the cold experiment, hot experiment was carried out.125I-AIBZM-L,125I-AIBZM-Lf-L were prepared, with their encapsulation efficiency:39.29% and 35.2%. Leak test of drud loaded liposomes indicated 125I-AIBZM-L and 125I-AIBZM-Lf-L were steady in the PBS solution (pH=7.4) at room temperature, while they could quickly release drugs in another PBS solution (pH=4.0).The ratio of Lf-L/Lf was obtained by gel electrophoresis and autoradiography(80.2%).DIR-L and DIR-Lf-L were prepared to perform fluorescence in vivo imaging. The result indicated DIR-Lf-L's brain targeting was obvious. Pharmacokinetic experiments showed that the retention time of 125I-AIBZM-L and 125I-AIBZM-Lf-L in vivo blood circulation was significantly longer compared with 125I-AIBZM, which could help improve brain uptake of 12SI-AIBZM-Lf-L. Finally, the biodistribution experiments of 125I-AIBZM-Lf-L,125I-AIBZM-L,125I-AIBZM were performed. The brain uptake at the same time phase were compared. The brain uptake of 125I-AIBZM-Lf-L was significantly increased and reached its peak at 0.5 h(ID%g 1.61), much higher than 125I-AIBZM-L (0.65),125I-AIBZM (0.09).