Effect of albumin fusion on the biodistribution of interleukin-2

We investigated and compared the biodistribution of Albuleukin, a human serum albumin (HSA)-interleukin-2 (IL-2) fusion protein, with those of IL-2 and HSA. The objective was to determine whether Albuleukin distributes differently to normal organs and lymphoid tissues than IL-2 by virtue of its genetic fusion with HSA. The chelating agent 2-( p-isothiocyanato-benzyl)-cyclohexyl-diethylenetriaminepentaacetic acid (CHX-A(II) was selected for radiolabeling with (111)In, and conjugation with CHX-A(II) did not alter bioactivities of IL-2 and Albuleukin on proliferation of CTLL-2 cells. The radiolabeled proteins were injected intravenously into mice, uptake in organs was measured, and whole-body autoradiography was performed. Striking differences in the biodistribution of IL-2 and Albuleukin were noted. (111)In-IL-2 cleared from blood rapidly, with less than 1% ID/g (percentage of injected dose per gram of tissue) at 20 min after injection. At this time, the kidneys showed more than 120% ID/g uptake, and these high levels persisted through 6 h. (111)In-Albuleukin, by contrast, showed significantly longer circulation (14% ID/g at 6 h), lower kidney uptake (