Biodistribution properties of (111)Indium-labeled C-functionalized trans-cyclohexyl diethylenetriaminepentaacetic acid humanized 3S193 diabody and F(ab ')(2) constructs in a breast carcinoma xenograft model

The humanized complementarity determining region-grafted anti-le,vis Y (Le( y)) monoclonal antibody [humanized 3S193 (hu3S193)] was developed for targe ting Le(y)-expressing epithelial tumors such as breast, colon, lung, prosta te, and ovarian carcinoma. We are exploring the potential use of smaller mo lecular size, bivalent analogues of hu3S193, because the faster blood clear ance of M-r similar to 54,000 diabody and M-r similar to 110,000 F(ab')(2) molecules may be advantageous in achieving optimal and rapid tumor uptake f or diagnostic and potential therapeutic applications, The single-chain vari able fragment-5 residue linker construct (diabody) was expressed using the bacterial secretion vector pPOW3, and soluble product was purified without refolding processes. The F(ab'), fragment was obtained by pepsin digest of parental hu3S193. To facilitate evaluations, the radiometal In-111 was used to label C-functionalized trans-cyclohexyl diethylenetriaminepentaacetic a cid chelated diabody and F(ab')(2), The immunoreactivity of the radiolabele d constructs was 41.3 and 58.6%, and the K-a was 1.68 x 10(6) M-1 and 5.33 x 10(6) M-1 for the diabody and F(ab')(2), respectively. Radioconjugates we re injected into mice bearing Le(y)-positive MCF-7 tumors, and biodistribut ion properties were determined at various time points after injection. The uptake of radiolabeled diabody in xenografts was maximal at 1 h after injec tion (4.7 +/- 0.6% injected dose/g), whereas the F(ab')(2) peaked at 8 h af ter injection (14.2 +/- 2.4% injected dose/g), The tumor:blood ratio at 4 h for the diabody and F(ab')(2) was 5:1 and 2:1, which increased to 20:1 and 5:1, respectively, at 8 h and increased further to 40:1 and 130:1, respect ively, at 48 h, These results demonstrate that the diabody construct may ha ve applications as a diagnostic imaging reagent, whereas F(ab'), displayed effective tumor targeting and may have potential as a therapeutic molecule in patients with Le(y)-expressing tumors.