| Objective:We aimed to synthesis the novel targeting probes 131I-PAMAM(G5.0)-SR,131I-PAMAM(G5.0)-GP and 131I-PAMAM(G5.0)-SR/GP as experimental groups,and evaluate their targetability on the model of medullary thyroid carcinoma(MTC).Methods:1.The target peptides SR,GP and SR/GP were purified and analyzed by high performance liquid chromatography(HPLC),and then covalently linked with the modified PAMAM(G5.0)to synthesize PAMAM(G5.0)-SR,PAMAM(G5.0)-GP and PAMAM(G5.0)-SR/GP.2.Analysis of PAMAM(G5.0)and PAMAM(G5.0)-peptides[PAMAM(G5.0)-SR,PAMAM(G5.0)-GP,PAMAM(G5.0)-SR/GP]by HPLC.3.The diameter and zeta potential of PAMAM(G5.0)and PAMAM(G5.0)-peptides were detected by dynamic light scattering(DLS).4.Detection of the spatial structure of PAM AM(G5.0)by high resolution field emission scanning electron microscopy(SEM)5.The modified PAMAM(G5.0),PAMAM(G5.0)-SR,PAMAM(G5.0)-GP and PAMAM(G5.0)-SR/GP were labeled with radioisotope 131I by chloramine T method.the radiolabeled yields,radiochemistry purity and stability were determined by thin layer chromatography(TLC)respectively.6.Tumor pathology and immunohistochemistry indicated that the thyroid medullary carcinoma tumor models were development successfully.Serum calcitonin(CT)and carcinoembryonic antigen(CEA)increased to varying degrees.7.SPECT/CT imaging was performed in negative control group(Na131I),positive control group[PAMAM(G.0)]and experimental groups[PAMAM(G5.0)-SR,PAMAM(G5.0)-GP and PAMAM(G5.0)-SR/GP]at 4?8?12?24 and 48 h after the probes were administered model mice peritoneal cavity respectively,and the target/non-target(T/NT)ratio of tumor was detected.8.Three mice were randomly sacrificed in all groups after SPECT/CT imaging at 8,12 and 24 h respectively.We calculated the percentage injection dose per gram(%ID/g)with the tumor and important organs such as thyroid,lung,bone,liver,blood et al.9.Every group was in triplicates.Repetitive measurement and analysis of variance was used to compare the T/NT of different times in all groups.Least-Significant Difference(LSD)test was used to compare in two groups.One-way analysis of variance was used to compare the%ID/g at 24 h and T/NT of different time in same group.Pearson distribution was used to analysis the correlation of T/NT and%ID/g.P<0.05 was considered statistically significant.Results:1.The purity of purified targeting peptides was 99%.The results of HPLC showed that the main peak of PAMAM(G5.0)-peptides appeared earlier than PAMAM(G5.0).The main peak of PAMAM(G5.0)-SR/GP is the earliest than others.It appeared at about 13-14 min.2.The diameter of PAMAM(G5.0)and PAMAM(G5.0)-peptide were 4.47 nm and 5.7 nm respectively.And the Zeta potential of PAMAM(G5.0)and PAMAM(G5.0)-peptide were+37.95 mV and+20.02 mV respectively.3.Scanning electron microscopy of PAMAM(G5.0)indicated that it has high surface density and empty inner spaces provide a flexible option.4.The radiolabeling rates of the four types of 131I probes were above 75%.The radiochemistry purities of purified probes were more than 90%,and it was still over 85%after 48h incubation at room temperature.5.Pathological and immunohistochemical indicated that the establishment of MTC model was successful.And the calcitonin(CT)and carcinoembryonic antigen(CEA)were Increased.6.All T/NT of experimental groups were higher than control groups.After Repetitive measurement and analysis of variance,the 5 probes had the main effects between groups(F value:4.776,P value:0.012)and time main effects(F value:8.63,P value:0.001),but had no the interaction effects(F value:1.55,P value:0.18).Compared with the positive and negative control groups,the T/NT ratios significantly increased in 131I-PAMAM(G5.0)-GP group at 4 h post-injection(t value:3.165 and 5.893,all P<0.05).Compared with the negative control group,the T/NT ratios significantly increased in 131I-PAMAM(G5.0)-SR group at 4,8 and 24 h(t value:4.169,7.123 and 4.032,all P<0.05).The T/NT ratio in 131I-PAMAM(G5.0)-SR group was higher than that in 131I-PAMAM(G5.0)-SR/GP groups at 24 h post-injection(t value:2.871,P<0.05).The peak value of tumor T/NT and ID%/g were at 4 h in thegroups of 131I-PAMAM(G5.0)-GP and 131I-PAMAM(G5.0)-SR/GP,and at 8 h in 131I-PAMAM(G5.0)and 131I-PAMAM(G5.0)-SR.The T/NT value decreased 57%from 4 h to 12 h in 131I-PAMAM(G5.0)-GP.Compared with 4 h,the T/NT ratios significantly decreased at 24,48 h post-injection(t value:-4.15?-4.033,all P<0.05).And Compared with 8 h,it decreased at 48 h post-injection(t value:5.893,P<0.05).7.The difference of%ID/g at 24 h post-injection was significant(F value:14.4,P<0.05)in all groups.Compared with the negative control groups,the%ID/g significantly increased in 131I-PAMAM(G5.0)-SR and 131I PAMAM(G5.0)-GP(t value:3.360 and 3.364,all P<0.05).8.There was a positive correlation between T/NT and tumor%ID/g of each group of probes at 24 h after injection,and the correlation of the experimental group was statistically significant(r=0.775,0.999,0.985,respectively,P<0.05).Conclusions:1.The methods of peptides SR and GP synthesized were simple.And peptides SR and GP had high purity.PAMAM(G5.0)and PAMAM(G5.0)-peptide had good physicochemical properties.2.The radioactive nano-targeting systems 131I-PAMAM(G5.0)and 131I-PAMAM(G5.0)-peptides synthesized in this study were stable.And the synthesis method is simple and fast.3.SR and GP peptides enhance the targetability of 131I-PAMAM(G5.0)on MTC cell and neovascularization respectively.4.131I-PAMAM(G5.0)-GP probe may be superior for MTC molecular imaging diagnoses because of its rapider ingestion and excretion than other probes in model mice.5.131I-PAMAM(G5.0)-SR probe may provide a new precision method for MTC treatment and the following up because of its better targetability and longer residence time than other probes in model mice. |
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