Study of biodistribution and imaging for ⁹⁹Tc^m-octreotide in bearing H22 hepatocarcinoma mice

Objective: To evaluate the practicability of ⁹⁹ Tc^m-octreotide as an imaging agent of somatostatin receptor-positive tumors. Methods: Preparation of ⁹⁹ Tc^m-octreotide was that technetium-99m was labeled directly with cold-kit of octreotide. 1 Animal biodistribution experiment: Twenty-five normal and fifteen tumor-bearing mice were injected with ⁹⁹Tc^m-octreotide in 0. 1 ml containing 3. 7 MBq. The biodistribution was performed in routine methods and the percentage of radio-activity administered dose per gram of tissue (% ID/ g) and target to non-target ratios (T/NT) at different interval were calculated. 2 Imaging of tumor-bearing mice: Five tumor-bearing mice were imaged respectively at 1, 2, 3, 4, 6, 24 h pi and calculated target to background ratios(T/B). Results: 1 The normal mice biodistribution indicated that the blood radioactivity presented peak [(3. 20±0. 54) %ID/g] at 30 min pi and ⁹⁹ Tc^m-octreotide were cleared rapidly thereafter. Physiological uptakes of kidney [(13. 62±4. 83) % ID/g] were the highest at 1 h pi and showed the radio pharmaceutical excreted mostly by kidney. The in vivo distribution of bearing-tumor mice was similar to normal mice. The tumor T/NT were higher and reached to (6. 44±0. 20) at 2 h pi. 2 Receptor scintigraphy showed that the imaging of mice outline were clearly seen at 1 h pi. The radioactivity uptake in kidneys and bladder were very highly too. Known tumor sites showed rapid and intense tracer accumulation. The tumor imaging was high quality at 2 h and then gradually unclear from time to time. Up to 24 h, the imaging was blurred; The T/B were 2. 64, 4. 46, 7. 25, 5. 40, 5. 49 and 6. 48 at 1, 2, 3, 4, 6, 24 h respectively. The T/B was raised rapidly from 1 h to 2h and 3h, and the difference was significant between that of 1 h and other times (P<0. 05). After 3 h, the uptake change was not obvious with time. Conclusion: The distribution of ⁹⁹Tc^m-octreotide by one step method labeled in bearing-tumor mice is very quickly, extinction is slower relatively and the ratios of tumor to background are high. The imaging of tumor is best quality 2h pi. These results suggest that ⁹⁹ Tc^m-octreotide is a promising radiopharmaceutical for somatostatin receptor scintigraphy.