Experimental Study On Monitoring The Chemotherapy Response Of Lung Cancer In Mice With ¹⁸F-FLT And ¹⁸F-FDG

Objective:In this study, bio-distribution in human A549 lung cancer-bearing BALB/C nude mice and Micro PET/CT imaging in Lewis lung cancer-bearing C57BL/6 mice with ¹⁸F-FLT and ¹⁸F-FDG were performed, to assess the value of ¹⁸F-FLT in monitoring the response of chemotherapy and the time for monitoring with ¹⁸F-FLT whether earlier than ¹⁸F-FDG or not.Methods and Materials:1 Group: First, 48 tumor-bearing BALB/C nude mice whose tumor growed well and had no remarkable difference were selected, then divided into four groups randomly: a (paclitaxel), b (cisplatin), c (paclitaxel/cisplatin), d (sodium chloride), 12 mice in each group. Second, each group was divided into 1 (1 day) and 2 (2 day) two sub-groups, each sub-group contained 6 mice. Finally, each sub-group was divided into two small groups according to the imaging agent, the T (¹⁸F-FLT) group and the G (¹⁸F-FDG) group, 3 mice in each small group.12 tumor-bearing C57BL/6 mice were randomly divided into 3 groups: a (paclitaxel), b (cisplatin), and c (control), 4 mice in each group. Then each group was divided into 2 sub-groups according to the imaging time: the 1 day group and the 2 day group, 2 mice in each group. Finally, according to the imaging agent, each sub-group was divided into 2 small groups: the T (FLT) group and the G (FDG) group, 1 mouse in each small group.2 Process:â‘ Animal bio-distribution experiment: The mice of group a, b, c and d were injected paclitaxel (0.2mg/ml), cisplatin (0.1mg/ml), paclitaxel (0.2mg/0.5ml) and cisplatin (0.1mg/0.5ml) and sodium chloride (1 ml) respectively via abdominal cavity. In sub-group 1 and 2 of each group, 3 mice were selected randomly, and then administered ¹⁸F-FLT and ¹⁸F-FDG 7.4 MBq (0.2 mCi) /0.2ml respectively via the tail veins. 60 minutes later, killed the mice according to the time of injection, then extracted blood from eyeballs, separated the heart, liver, spleen, lung, kidney, stomach, small intestine, muscle, bone and tumor samples, weighted and counted the radioactive counts. The percentage of radioactivity administered dose per gram of tissue (%ID/g) and the ratio of tumor to non-tumor (T/NT) were calculated to express the isotope retention.â‘¡Imaging of Micro PET/CT: The Lewis lung cancer-bearing mice of group a, b and c were injected paclitaxel (0.3mg/ml), cisplatin (0.1mg/ml) and sodium chloride (1ml) respectively via abdominal cavity. 1 day and 2 days later, 1 mouse of each small group was injected ¹⁸F-FLT and ¹⁸F-FDG 18.5MBq (0.5mCi)/0.2ml respectively via the tail veins, 55 minutes later, 10% chloral hydrate were administered via abdominal cavity according to the weigh of mouse, and then fixed on the bed of Micro PET/CT, imaging was acquisited and the uptake of tumor on each image was analyzed by naked eyes.â‘¢Pathological examination: Tumor samples of each group were fixed into 4% paraformaldehyde, 48 hours later, embed with paraffin wax, resected into 5μm section, then routine HE staining and SP immunohistochemical staining were performed to evaluate the expression of proliferating cell nuclear antigen (PCNA). The linear correlation analysis between the PCNA-LI and the data of bio-distribution (%ID/g), the PCNA-LI and the ration of T/NT were performed.Results:1 Results of the bio-distribution:â‘ Tumor's uptake of ¹⁸F-FLT and ¹⁸F-FDG after treatment: Tumor's uptake of ¹⁸F-FLT was highest in group d [(2.41±0.03)%ID/g], and then group a [1 day: (2.11±0.02)%ID/g; 2 day: (1.73±0.03)%ID/g] and group b [1 day: (1.94±0.06)%ID/g; 2 day: (1.45±0.05)%ID/g], group c was the last [1 day: (1.57±0.06)%ID/g; 2 day: (1.16±0.05)%ID/g]. The statistical analysis showed there was significance of %ID/g between group a and d, b and d, and c and d (p <0.01); the ratio of tumor to non-tumor (lung, T/L; musle, T/M) for ¹⁸F-FLT had the same trend with the %ID/g, also group d was the highest(5.85±0.17,5.22±0.23), and then group a (1 day: 5.00±0.15, 4.66±0.12; 2 day: 4.01±0.17, 4.13±0.11), group b(1 day: 4.75±0.20, 4.03±0.19; 2 day: 3.08±0.04, 3.18±0.08), group c was at the bottom (1 day: 3.86±0.17, 3.38±0.22; 2 day: 2.52±0.19, 2.40±0.09). Tumor's uptake of ¹⁸F-FDG, only group c [(5.87±0.06) %ID/g] had significance compared with group d [(6.35±0.12) %ID/g] 1 day after treatment (p <0.05); but there were significant difference (p <0.05) between group a [(6.18±0.10) %ID/g] and d, b[(6.11±0.04) %ID/g] and d, c[(5.43±0.05) %ID/g] and d 2 day after treatment. The ratio of tumor to non-tumor (lung, T/L; musle, T/M) for ¹⁸F-FDG had the same trend with the %ID/g, group d also was the highest (2.70±0.04, 1.73±0.05), group a (1 day: 2.66±0.02, 1.75±0.06; 2 day: 2.478±0.01, 1.62±0.01) and b (1 day: 2.59±0.01, 1.71±0.04; 2 day: 2.48±0.06, 1.65±0.01) were near to each other, and group c was the last (1 day: 2.47±0.08, 1.58±0.02; 2 day: 2.32±0.14, 1.48±0.02). These data showed that tumor's uptake of ¹⁸F-FLT declined significantly 1 day after treatment by one kind of drug, but there were no significant change of ¹⁸F-FDG, it implied that the time for monitoring the response of one kind of drug was earlier with ¹⁸F-FLT than with ¹⁸F-FDG. But the early response of TP (paclitaxel/cisplatin) could be monitored with both ¹⁸F-FLT and ¹⁸F-FDG.â‘¡The decrease of tumor's uptake of ¹⁸F-FLT and ¹⁸F-FDG in group c 1 day after treatment and all the a, b, c group 2 days after treatment were compared, and showed significant difference (p <0.05). It implied that the change of tumor's uptake of ¹⁸F-FLT was higher than ¹⁸F-FDG after treatment by paclitaxel, cisplatin, and TP. It indirectly showed that ¹⁸F-FLT was better than ¹⁸F-FDG in monitoring response.â‘¢There was significant difference between tumor's uptake of ¹⁸F-FLT and ¹⁸F-FDG in group d (p <0.01), it implied that lung cancer's uptake of ¹⁸F-FLT was lower than that of ¹⁸F-FDG, and this was consistent with the results of other scholars at home and abroad.2 Micro PET/CT imaging:The ¹⁸F-FLT Micro PET/CT imaging of Lewis lung cancer-bearing mice 1 day after treatment showed: There were little nuclide distributed in the chest of mice, but the abdomen very much in group a, b, and c. Tumor's imaging was like a ring, and the center of tumor had no nuclide distributed. Tumor's uptake of ¹⁸F-FLT: group c was the most concentrated of all, group a and group b were less than group c. The CT imaging showed that the shape of tumor was irregular, protruded around, and had no clear boundaries with around tissues and the density was lower in the center of the tumor.2 days after treatment, there were some nuclide ditributed in the chest wall in group a and b, especially the rib showed clear, tumor's periphery uptaked a little nuclide, and was lower than that of group c. Tumor's images were obscure, but the center still had no nuclide distributed. The CT imaging showed that tumor's shape, size and density had no change compared with 1 day.The Micro PET/CT imaging of ¹⁸F-FDG was clear, and tumor's uptake was obvious, but uneven at different part, the center also was nuclide defective. There seemed no difference among group a, b and c.3 Expression of PCNA determinated through immunohistochemistryThe PCNA labeling index in each group was as follows, group d (49.67±1.528) was the highest, and then was group a (1 day: 42.00±1.00; 2 day: 36.67±1.52) and b (1 day: 28.67±1.528; 2 day: 24.00±1.00), group c was the lowest (1 day: 23.33±1.528; 2 day: 20.00±1.00), and there was significant difference in groups after treatment by paclitaxel, cisplatin and TP compared with group d. It implied that these drugs can suppress lung cancer cell's proliferation. There also was significant difference between 1 day and 2 day in the corresponding groups, it showed that the effect of drugs increased with the time.A significant correlation was observed between %ID/g, T/NT for ¹⁸F-FLT and PCNA labeling index (r=0.905, p<0.01; r=0.935, p<0.01; r=0.936, p<0.01) and for ¹⁸F-FDG (r=0.687, p<0.01; r=0.787, p<0.01; r=0.777, p<0.01), and the r value of ¹⁸F-FLT was higher than that of ¹⁸F-FDG.Conclusions: 1 The change of tumor's uptake of ¹⁸F-FLT after treatment by paclitaxel, cisplatin was earlier than ¹⁸F-FDG, it implies that the time for monitoring response with ¹⁸F-FLT is earlier than with ¹⁸F-FDG.2 The decrease of tumor's uptake of ¹⁸F-FLT after treatment by TP was significant higher than that of ¹⁸F-FDG, it suggests that we might monitor the response of TP to lung cancer with ¹⁸F-FLT, and it is better than ¹⁸F-FDG.3 Lung cancer's uptake of ¹⁸F-FLT is lower than that of ¹⁸F-FDG.4 There is significant correlation between tumor's uptake of ¹⁸F-FLT and PCNA labeling index, and it is better than that of ¹⁸F-FDG.