A chimeric anti-CEA antibody with heavy interchain disulfide bonds deleted: Molecular characterization and biodistributions in normal and tumor bearing mice

We have deleted the interchain disulfide bonds in a chimeric anti-CEA antib ody (chT84.66) by mutating two cysteines in the heavy chain to glycine resi dues. The resulting antibody Delta SSchT84.66 was expressed in high yield i n a bioreactor and purified to homogeneity in a single step on an anti-idio typic antibody affinity column. The molecular size of the antibody was 150 kDa as judged by gel filtration, SDS gel electrophoresis under non-reducing conditions, and MALDITOF/MS. The 150 kDa antibody had nearly identical kin etic (k(on) = 1.53 x 10(6) M-1 s(-1),.k(off) = 1.14 x 10(-5) s(-1)) and aff inity constants (K-aff = 1.34 x 10 M-1) compared to the parent murine (K-af f = 1.25 x 10(11) M-1) and chimeric (K-aff =1.16 x 10(11) M-1) antibodies w hen tested on biosensor chips. When Delta SSchT84.66 was conjugated to the isothiocynato derivative of DTPA, radiolabeled with In-111, and injected in to either noimnl ol nude mice bearing tumor xenografts, it gave nearly iden tical biodistributions to chT84.66. Delta SSchT84.66 and chT84.66 antibodie s gave a maximum tumor uptake of 48 and 74 %ID/g, and tumor to blood ratios of 5.3 and 6.2 at 48 h, respectively. We conclude that Delta SSchT84.66 ir reversibly associates into H2L2 dimers after concentration, that the dimers are stable under both the in vitro and in vivo conditions used in this stu dy, and the properties of the antibody are virtually indistinguishable from the parent chT84.66 antibody.