111Indium labeling of cultured human tumor cells

At least one microCi of 111indium oxine (111InOx) could be incorporated into 10(6) human tumor cells without cytotoxicity as determined by colony assay or by trypan blue staining. 111In bound to prekilled cells was removed preferentially by washings, and prelabeled cells killed with diphtheria toxin released radioactivity much more rapidly than did viable cells. The metal chelator calcium disodium edetate did not facilitate 111In removal from either viable or dead cells. High sensitivity can be obtained for in vitro or in vivo cytotoxicity assays using human cells prelabeled with 111InOx.