Localization of indium-111 in human malignant tumor xenografts and control by chelators

Abstract The kinetics of soluble indium-111 ( 111 In) in human malignant tumor xenografts and cells was investigated in combination with chelators. Firstly, without chelator, the kinetics of 111 In-chloride was investigated in vitro and in vivo using four human malignant neuroblastoma SK-N-MC, pulmonary papillary adenocarcinoma NCI-H441, pulmonary squamous cell carcinoma PC 9, and colon adenocarcinoma LS 180 cells and xenografts. 111 In was incorporated into tumor cells in vitro to a maximum level during a 60-min incubation. A maximum level of radioactivity was demonstrated in vivo in four human malignant tumors xenografted into nude mice at 24 h postinjection of 111 In-chloride. Secondly, the effect of edetate calcium disodium (CaNa 2 EDTA) on radioactivity in 111 In-labeled tumors xenografts and cells was studied in vitro and in vivo. CaNa 2 EDTA significantly reduced 111 In-activity from the labeled tumor xenografts, whereas it had no affect on the radioactivity in the labeled cells. Thirdly, the effect of CaNa 2 EDTA on radioactivity in human malignant tumors xenografted into nude mice injected with 111 In-chloride was investigated. In one group of mice CaNa 2 EDTA administered intraperitoneally at 1, 22, 34, 46, 58, and 70 h after injection of 111 In-chloride (postadministration), the localization of 111 In at the tumors was significantly decreased at 72 h compared with the control in all four tumor types. In the other group of mice, CaNa 2 EDTA administered intraperitoneally at 12 and 1 h before injection of 111 In-chloride and 1, 22, 34, 46, 58, and 70 h postinjection (pre- and postadministration), the radioactivity of tumors was also significantly decreased at 72 h, and the reduction was greater than that with use of postadministration. In a comparative study, CaNa 3 DTPA had a more powerful effect than CaNa 2 EDTA. In conclusion, 111 In-activity in tumors consists of intracellular and extracellular components, and the extracellular 111 In may be cleared by chelators. Pre- and postadministration of CaNa 3 DTPA could remove 111 In-nonspecific localization in tumors when 111 In is released from the radiolabeled agents.