99mTc-YIGSR as a Receptor Tracer in Imaging the Ehrlich Ascites Tumor-bearing Mice as Compared with 99mTc-MIBI

The validity of 99mTc-YIGSR,a novel receptor radio-tracer,in imaging the Ehrlich ascites tumor was evaluated.YIGSR,a pentapeptide of laminin,was labeled with 99mTc by using a bifunc-tional chelator S-Acetly-NH3-MAG3.The MIBI was labeled with 99mTc by following the kit instruc-tion.The mice of tumor group were intravenously injected 1-2 mCi of 99mTc-YIGSR or 99mTc-MIBI via caudal vein,immobilized and imaged under a Gamma camera.The same procedure was per-formed in mice of blockade group,in which the unlabeled YIGSR was previously injected to block the receptor-recognition sites,and inflammation group serving as control.The reverse-phase Sep-Pak C18 chromatogram was found to have an essentially complete conjugation between YIGSR and S-Acetly-NH3-MAG3.The conjugated YIGSR could be radio-labeled successfully with 99mTc at room temperature and neutral pH,with a radio-labeling yield of 62%.Without the chelator S-Acetly-NH3-MAG3,the YIGSR was labeled with 99mTc at an efficiency of 4%.The imagological study revealed obvious tumor accumulation of 99mTc-YIGSR 15 min after the injection,and the up-take peaked after 3 h with a tumor-to-muscle ratio(T/M) of 11.36.The radio-tracer was slowly cleared up and resulted in a T/M of 3.01 at the 8th h after the injection.As for blocked group,the tu-mor uptake of radiotracer was significantly lower,with the highest T/M being 4.61 after 3 h and 0.89 after 8 h.The T/M was 3.72 at the 3rd h and 1.29 at the 8th h after the 99mTc-YIGSR injection in the inflammatory group.The T/M was significantly higher in tumor group than in inflammatory group or control group(P<0.001).In the 99mTc-MIBI group,the T/M was 1.40 at the 3rd h and 0.55 at the 8th h after the injection,which showed a significant difference as compared with 99mTc-YIGSR(P<0.001).It is concluded that YIGSR can be successfully radiolabelled by using S-Acetly-NH3-MAG3.99mTc-YIGSR has many advantages in tumor imaging,such as quick and clear visualization,high sensitivity and specificity,and satisfactory target/non-target ratio(N/NT).It promises to be tumor ra-dio-tracer.