Study Of Bio-distribution And Monitoring The Hypoxic Status Of Tumor By ～(18)FMISO In Bearing H22 Hepatocarcinoma Mice

Objective: To evaluate the bio-distribution of ¹⁸FMISO in bearing H22 hepatocarcinoma mice, and to determine whether the accumulation of ¹⁸FMISO in tumors could aid in monitoring the hypoxic status of tumor pre and after radiation therapy.Methods: 1. Animal bio-distribution experiment: 30 tumor- bearing KM mice were injected via the tail veins with ¹⁸FMISO in 0.1ml containing 3.7MBq, and animals were killed at 5min, 30min, 60min, 90min, 120min and 180min after injection. Heart, liver, spleen, stomach, kidney, muscle, small intestine, blood, lung and tumor samples were weighted and counted. The percentage of radioactivity administered dose per gram of tissue (%ID/g) and ratio tumor to non-tumor (T/NT) were used to express the isotope retention.2. ¹⁸FMISO in monitoring the hypoxic status of tumor pre and after radiation therapy: Tumor-bearing KM mice were divided into control group and 1d, 3d and 5d post-irradiation groups. The irradiation groups were exposed to ⁶⁰Co at a single dose of 15Gy.â‘ Chose five tumor-bearing KM mice from the four groups respectively at random, 20 mice in all. Then the 20 mice were injected via the tail veins with ¹⁸FMISO in 0.1ml containing 3.7MBq, and animals were killed at 120min after injection. The tumor and contralateral muscles were excised, weighted and radioactivity was measured. %ID/g and tumor-to- muscle (T/M) ratio were computed to quantitate the tracer uptake. Immunohistochemical analyses of hypoxia-inducible factor-1α(HIF-1α)expression were also performed in excised tumor.â‘¡Chose one tumor-bearing KM mice from the control and the 3d post-irradiation group respectively at random. The mice were injected via the tail veins with ¹⁸FMISO in 0.2ml containing 37MBq. After anesthetized, the mice were fixed in EplusTMAnimal PET. The PET images were performed 120minutes after injection.Results: 1. Results of Animal bio-distribution experiment: The uptakes of liver were the highest, and the uptakes of small intestine were the next. The kidney's uptakes were also high, but were lower than the small intestinal. The uptakes of stomach, blood, lung, heart and muscle were the lowest. Showed that the radio pharmaceutical excreted mostly by liver. The tumor radioactivity presented(3.95±0.19)%ID/g at 30min post-injection(pi), then stepped up gradually. At 90min pi the tumor radioactivity presented peak(4.21±0.32)%ID/g. At 120min pi the tumor radioactivity presented(3.79±0.72)%ID/g. And at 180min pi the tumor radioactivity presented the lowest(2.56±0.48)%ID/g. Analyzed the %ID/g of different time groups besides 5min group, the result showed the %ID/g values were not all equal (F=12.25, P<0.01), then compared each two groups, the result suggested the significant difference between the 30min, 60min, 90min, 120min and 180min pi group (P<0.05); compared the %ID/g of 30min, 60min, 90min and 120min pi respectively, all showed no significant difference (P>0.05).The radio of T/NT continued to increase untilled 180min pi. The radio of T/M presented peak 4.20 at 180min pi, although the %ID/g were decreased. Analyzed the T/M values of different time groups besides 5min group, the result showed the T/M values were not all equal (F=24.25, P<0.01), then compared each two groups, the result suggested that no significant difference between 30min and 60min pi group (P>0.05); compared 60min and 90min pi group, the result showed no significant difference (P>0.05). The T/M values of 120min and 180min pi obviously increased, showed the significant difference between 90min pi group (P<0.05); compared 120min and 180min pi group, the result showed no significant difference (P>0.05).2.Results of the experiment of ¹⁸FMISO in monitoring the hypoxic status of tumor pre and after radiation therapy:â‘ The changes of tracer uptake in different time groups post-irradiation: Compared with the control group, the tumor %ID/g of irradiation groups decreased first and then increased. Among them the tumor %ID/g had decreased at 1d, then the %ID/g decreased markedly at 3d post-irradiation, but at 5d post-irradiation the %ID/g increased to near the control group. Analyzed the %ID/g of different time groups, the result showed the %ID/g values were not all equal (F=8.67, P<0.01), then compared each two groups, the result suggested that no significant difference between the 5d post-irradiation and the control group (P>0.05); the %ID/g of 1d and 3d post-irradiation obviously reduced, showed the significant difference with the control group (P<0.05); compared the %ID/g of 1d, 3d and 5d post-irradiation respectively, all showed the significant difference (P<0.05). The changes of T/M radio were similar to %ID/g.â‘¡Result of immunohistochemistry: There were buff or isabelline particles in the endochylema of HIF-1αexpression positive cell. Percentage of positive cell less than 25% is (+); Percentage of positive cell between 25% and 50% is (++), then more than 50% is (+++). According to this, the control group and the 5d post-irradiation group were (+++), the 1d post-irradiation groups were (++), and the 3d post-irradiation groups were (+). Analyzed the relationship between HIF-1αexpression and %ID/g, T/M values in different time groups respectively, the result showed that there were significant positive correlation between them(r=0.73, 0.82; P<0.01).â‘¢PET imaging : The tumor imaging of the control group were clearly visible, there were obvious radioactivity gathering in the tumor images. There were a few radioactivity defection areas in the center of tumor. The tumor image of 3d group reduced to the most obviously thin, the area of radioactivity defection increased larger in the center of tumor, while strong radioactivity was observed in the border zone. The image presented the typical"concentric circles".Conclusion:â‘ The uptake and retention of ¹⁸FMISO in tumor are higher. But the clearance of the normal tissue is slow. And the T/NT is lower.â‘¡¹⁸FMISO hypoxia imaging not only can show the change of the hypoxic status of tumor pre and after radiation therapy , but also can measure the reoxygenation of the tumor cells after radiation therapy. So ¹⁸FMISO hypoxia imaging is of much more clinical value in detecting the hypoxic degree and monitoring the hypoxic status of tumor for certain tumors.