Biodistribution and plasma survival in mice of anti-melanoma monoclonal antibody cross-linked to OKT3.

Anti-melanoma monoclonal antibody XMMME-001 was cross-linked to anti-CD3 monoclonal antibody OKT3 with succinimidyl 3(2-pyridyldithio)propionate (SPDP), and 2-iminothiolane. The dimer heteroconjugate was purified by HPLC gel filtration, labeled with 131I, and 10 micrograms was injected into each of 24 BALB/c mice. The dimeric heteroconjugate's blood survival in sequentially bled mice (n = 3) and its biodistribution in organs of sacrificed mice (n = 21) were studied. In plasma, the heteroconjugate showed an alpha phase with a half-life of 4 h, and a beta phase with a half-life of about 18 h. Electrophoretic analysis of labeled heteroconjugate in plasma showed that the half-life of disulfide bonds linking the monoclonal antibodies was approximately 7-8 h. Radioactive heteroconjugate accumulated primarily in the liver; significant uptake was also seen in white blood cells and spleen. Very little radioactivity accumulated in kidney, lung, or colon. As a comparison, SPDP-derivatized anti-melanoma antibody was studied by the same methods. It showed an average alpha-phase half-life of 12.5 h; its maximum accumulation in liver or white blood cells was less than 30% of that of the heteroconjugate. Very low levels accumulated in other tissues. The results imply that the shorter half-life in plasma of the heteroconjugate is primarily determined by clearance due to its larger size and conformation, not the lability of cross-linking disulfide bonds.