| The concept of "cell apoptosis"is an active process modulated by multiple genes. It distinguishs from cell necrosis and lies in many physiological phenomena and pathological conditions. At present, researchers increasingly attach importance to the roles of it on the tumor basic study and clinical diagnosis. One of the aims of tumor therapy is to induce the apoptosis of tumor cells. At an early stage of apoptosis, phosphatidylserine(PS), a constitutive membrane aminophospholipid normally presents on the membrane's inner surface, is exposed on the outer surface. This change can be detected by the binding of AnnexinⅤ, a human protein, which has a reversible, strictly calcium-dependent, nanomolar affinity for the PS. Due to the non-invasiveness, quantitative and other advantages, radiolabeled AnnexinⅤ in vivo apoptotic imaging, has been greatly developed. This new imaging technology can be suitable for recommending the tumor treatment, inspecting the therapeutic effect, evaluating the patients' prognosis, and playing an important role in the area of developing new anti-tumor drugs. Objectives: we focused on evaluating the effectiveness of cell apoptosis imaging in vivo of tumor response after a single dose of chemotherapy in mice bearing tumor by using 99mTc-HYNIC-AnnexinⅤ. Methods: Hydrazinonicotinamide (HYNIC)-Annexin V was labeled with 99mTc. Seven days after being inoculated with S-180 sarcoma in the right upper limbs, the mice were randomized to receive a single dose of cyclophosphamide(150 mg/kg intraperitoneally ) as experimental groups or to receive the same volume of physiological saline as controls. Firstly, we determined the optimum imaging time after a single dose of chemotherapy. Having been received cyclophosphamide 72 h,48 h,24 h and 8 h later, the mice were injected 99mTc-HYNIC-AnnexinⅤ by tail vein. Imaging results and radioactivity in tissues were obtained 1h after injection of imaging agent. Secondly, we needed to judge if cyclophosphamide could change the blood flow of tumor. 99mTc-DTPA-HSA was used as a marker of tumor blood flow. Thirdly, we tried to investigate the best imaging time postinjection of 99mTc-HYNIC-AnnexinⅤ. According to the optimum chemotherapy time above, the mice were injected 99mTc-HYNIC-AnnexinⅤ. 5 min, 30 min, 1 h, 3 h and 6 h later, imaging results and radioactivity in tissues were obtained too. All data of in vivo biodistribution were analyzed by the statistic software of SPSS 12.0. Results: The radiochemical purity of 99mTc-HYNIC-AnnexinⅤreached 99%. Cyclophosphamide treatment significantly increased the tumor uptake(percentage activity of injected dose per gram of tissue [%ID/g])of 99mTc-HYNIC-AnnexinⅤ. The optimum imaging time after chemotherapy could be considered 72 h(1.87 ± 0.579 %ID/g for treated 72 h mice and 1.18 ± 0.128 %ID/g for controls, P < 0.05). 99mTc-DTPA-HSA uptake was not significantly different in the treated and untreated groups, which indicated the increased accumulation of 99mTc-HYNIC-AnnexinⅤ in the tumor is not attributable to changes in blood flow. It also could be seen that 6 h was the best imaging time after 99mTc-HYNIC-AnnexinⅤ having been injected through tail vein. The imaging agent accumulated in the kidney, lung and liver mainly. It was cleared quickly through blood, the ratio of T/M and T/B were relatively high, which were beneficial to the imaging effect. Conclusions: It is just 72 h after a single dose of cyclophosphamide treatment that the tumor uptake of 99mTc-HYNIC-AnnexinⅤ is significantly increased, which is 58% increase. And the optimum time of the tumor uptake of the imaging agent is 6 h after being injected the imaging agent. The current results suggest the potential utility of cell apoptosis imaging in vivo as a noninvasive means to assess tumor response after a single dose of chemotherapy. It also provides an important basis for further study, however, the more complicated clinical evaluation is required. |
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